US20080156773A1

US20080156773A1 - End point detection method applying resonance phenomenon, end point detection apparatus, chemical mechanical polishing apparatus on which the detection apparatus is loaded, and semiconductor device fabricated by the chemical mechanical polishing apparatus

Info

Publication number: US20080156773A1
Application number: US11/904,374
Authority: US
Inventors: Keita Kitade; Osamu Matsushita; Takashi Fujita; Toshiyuki Yokoyama
Original assignee: Tokyo Seimitsu Co Ltd
Current assignee: Tokyo Seimitsu Co Ltd
Priority date: 2006-12-27
Filing date: 2007-09-27
Publication date: 2008-07-03
Also published as: JP2008166449A; KR20080061248A; TW200827667A

Abstract

To provide an end point detection method applying a resonance phenomenon, an end point detection apparatus, and a chemical mechanical polishing apparatus on which the detection apparatus is loaded for monitoring variation in the thickness of an electrically conductive film in real time, reliably detecting a polishing end point of the electrically conductive film at high accuracy, without generating noise, low power consumption, and capable of reducing the cost.

In order to achieve above described objects, the present invention provides an end point detection method applying a resonance phenomenon in which a polishing end point is detected when the electrically conductive film is polished and removed to an appropriate thickness, wherein a sensor 37 composed of an oscillation circuit of the Colpitts type or the like having a planar inductor and a concentrated constant capacitor is used, and the variation in the thickness of the electrically conductive film is monitored in real time from the variation in the oscillation frequency of the sensor 37 caused along with the variation in the thickness of the electrically conductive film opposed to the planar inductor.

Description

FIELD OF THE INVENTION

The present invention relates to an end point detection method applying a resonance phenomenon, an end point detection apparatus, a chemical mechanical polishing apparatus on which the detection apparatus is loaded, and a semiconductor device fabricated by the chemical mechanical polishing apparatus, and particularly relates to an end point detection method applying the resonance phenomenon capable of reliably detecting a polishing end point of an electrically conductive film at high accuracy in chemical mechanical polishing processing (CMP), an end point detection apparatus, a chemical mechanical polishing apparatus on which the detection apparatus is loaded, and a semiconductor device fabricated by the chemical mechanical polishing apparatus.

BACKGROUND OF THE INVENTION

As a conventional art related to an end point detection method applying the resonance phenomenon, an end point detection apparatus, and a chemical mechanical polishing apparatus on which the detection apparatus is loaded, for example, a method of monitoring the variation in the film thickness on site. This conventional art is a method for monitoring the thickness variation of an electrically conductive film in a method of removing the electrically conductive film from a base main body (semiconductor wafer) by chemical mechanical polishing. A sensor including a series or parallel resonance circuit of an inductor composed of a coil wound around ferrite toroid and a capacitor is disposed in the vicinity of the electrically conductive film. The sweep output from a high-frequency excitation signal source is applied to the sensor via an impedance means for operation point setting, thereby generating an alternating electromagnetic field and inducing an eddy current in the electrically conductive film. The frequency shift related to a sensor resonance peak caused by the thickness variation of the electrically conductive film is monitored. As a result, the thickness variation of the electrically conductive film is detected (for example, see Patent Document 1).
Also, as another conventional art related to the end point detection method applying the resonance phenomenon, the end point detection apparatus, and the chemical mechanical polishing apparatus on which the detection apparatus is loaded, for example, a following eddy current sensor is known. This conventional art is provided with a sensor coil (eddy current sensor) disposed in the vicinity of an electrically conductive film or a substrate on which an electrically conductive film is formed, an AC signal source which supplies an AC signal of a constant frequency to the sensor coil and forms an eddy current in the electrically conductive film, and a detection circuit which measures a reactance component and a resistance component including the electrically conductive film. The sensor coil has an oscillation coil which connects to the signal source, a detection coil disposed in the side of the electrically conductive film of the coil, and a balance coil disposed in the opposite side of the oscillation coil in the side of the electrically conductive film. The detection coil and the balance coil are connected so that they have reverse phases. A synthetic impedance from the resistance component and the reactance component detected by the detection circuit is output, and the variation in the thickness of the electrically conductive film is detected from the variation of the impedance as approximately linear relation in a wide range. (for example, see Patent Document 2).
Furthermore, as another conventional art related to the end point detection method applying the resonance phenomenon, the end point detection apparatus, and the chemical mechanical polishing apparatus on which the detection apparatus is loaded, for example, a following IC for distance measurement is known. This conventional art is provided with an oscillator built in a package and a planar inductor which is connected to the oscillator and specifies the oscillation frequency of the oscillator. When an electrically conductive substance approaches the package surface of the IC, the oscillation frequency of the oscillator is changed by the planar inductor. The approach distance of the electrically conductive substance can be detected by detecting the oscillation frequency. In order to shorten the measurement time, a high frequency current is caused to flow through the planar inductor, and electrostatic induction generated on the surface is effectively utilized. Use thereof includes, for example, control of an arm in position measurement of the robot arm and pressure detection performed by storing it in a position detector (for example, see Patent Document 3).
Patent Document 1 Japanese Patent Publication No. 2878178 (2nd page, FIG. 1, FIG. 2).
Patent Document 2 Japanese Patent Publication No. 3587822 (3rd page, FIGS. 1 to 11).
Patent Document 3 Japanese Patent Publication NO. 3352619 (2nd to 4th pages, FIG. 18).
There is a known process in which an oxide film formed on a semiconductor wafer is subjected to lithography and etching, thereby forming a groove pattern corresponding to a wiring pattern, an electrically conductive film composed of Cu or the like for filling the groove pattern is formed thereon, and the wiring pattern is formed by removing the unnecessary portion of the electrically conductive film by chemical mechanical polishing. In formation of the wiring pattern, it is very important to reliably detect the polishing end point at which the electrically conductive film is removed to an appropriate thickness to stop the processing. When polishing of the electrically conductive film is excessive, the resistance of wiring increases, and insulation failure is caused when polishing is insufficient.
On the other hand, in the conventional art according to Patent Document 1 or the like, in which the thickness of the electrically conductive film is monitored by utilizing the eddy current, a strong magnetic flux for causing the eddy current is required to be generated, and the shape of the inductor is three dimensional. Therefore, in incorporation of the eddy current sensor to a polishing apparatus or the like, generally there are following problems. The current that flows through the coil is increased, the power consumption is increased, and the size of a power supply device is also increased. The magnetic flux leaks to the periphery, and noise is readily generated. A step of winding a conductor wire like a coil is required, and the cost is increased.
The conventional art according to Patent Document 3 comprising the IC for distance measurement comprises the oscillator and the planar inductor which is connected to the oscillator and specifies the oscillation frequency of the oscillator. However, it is used in, for example, control of the arm in position measurement of the robot arm and pressure detection by storing it in a position detector as uses thereof.
In the case of the conventional eddy current sensor, the variation of the oscillation frequency with respect to the variation of the film thickness is monotonous, and there is no extreme value (peak) which is extremely useful in determination of an end point; therefore, reliability of end point determination is low. (see Japanese Patent Application 2003-021501)
Therefore, technical problems to be solved for monitoring the variation of the film thickness of the electrically conductive film in real time to reliably detect the polishing end point of the electrically conductive film at high accuracy and reducing the cost without generating noise at low power consumption are generated; and it is an object of the present invention to solve the problems.

SUMMARY OF THE INVENTION

The present invention has been accomplished for achieving the above object, and the invention according to claim 1 provides an end point detection method applying a resonance phenomenon in which an electrically conductive film is polished and a polishing end point at which an appropriate thickness of the film is removed is detected, wherein a sensor composed of an oscillation circuit of a Colpitts type or the like having a planar inductor and a concentrated constant capacitor is used, and variation in the thickness of the electrically conductive film is monitored in real time from variation in an oscillation frequency of the sensor caused along with the variation in the thickness of the electrically conductive film opposed to the planar inductor.
According to this configuration, when the planar inductor is caused to face the electrically conductive film, the following phenomena are considered to occur. First of all, electrostatic induction is caused in the side of the electrically conductive film by the phase distribution that the planar inductor has, and the planar inductor and the electrically conductive film undergoes electrostatic coupling via the distributed capacitance. In the region in which the film thickness resistance of the electrically conductive film cannot be ignored, an equivalent circuit in which the distributed capacitance and the film thickness resistance of the electrically conductive film are added to the inductance of the planar inductor and the concentrated constant capacitance of the capacitor can be considered as a parallel oscillation circuit. In an expressed equation of the resonance frequency of the parallel resonance circuit, the film thickness resistance value is related in the form of a time constant which is a product with the distributed capacitance. Therefore, the sensor comprising the oscillation circuit having the planar inductor and the concentrated constant capacitor oscillates at a resonance frequency corresponding to the variation of the film thickness resistance value of the electrically conductive film via the electrostatic coupling, and increase in the oscillation frequency is caused along with increase in the film thickness resistance value.
Secondly, the planar inductor generates a varying primary magnetic field. The planar inductor causes electrostatic induction in the side of the electrically conductive film by the phase difference on the planar inductor, and the planar inductor undergoes electrostatic coupling with the electrically conductive film via the distributed capacitance. The induced current generated in the surface portion of the electrically conductive film upon the electrostatic induction generates a secondary magnetic field in the direction that cancels out the primary magnetic field. The secondary magnetic field acts in the direction that reduces the inductance. Herein, in the region in which the thickness of the electrically conductive film is thin so that the skin effect cannot be ignored, it is considered that the thinner the film thickness, the more the generation amount of the induced current generated in the electrically conductive film is reduced, and the secondary magnetic field is attenuated at the same time. Therefore, reduction in the thickness of the electrically conductive film leads to reduction in the reduction component of the inductance, and the inductance of the sensor circuit system is equivalently increased as a result, thereby reducing the oscillation frequency.
Thirdly, the planar inductance generates a primary magnetic field that is varied along with time. The primary magnetic field that is varied along with time generates induced current in the electrically conductive film. The induced current in the electrically conductive film generates a secondary magnetic field that cancels out the primary magnetic field generated by the planar inductor, and electromagnetic coupling is caused between the planar inductor and the electrically conductive film. The secondary magnetic field generated by the induced current acts in the direction that reduces the inductance. herein, in the region in which the thickness of the electrically conductive film is thin so that the skin effect cannot be ignored, it is considered that the thinner the film thickness, the more the generation amount of the induced current generated in the electrically conductive film is reduced, and the secondary magnetic field is also attenuated at the same time. Therefore, reduction in the thickness of the electrically conductive film leads to reduction in the reduction component of the inductance, and the inductance of the sensor circuit system is equivalently increased as a result, thereby reducing the oscillation frequency.
The sensor composed of the oscillation circuit having the planar inductor and the concentrated constant capacitor oscillates at a resonance frequency corresponding to the overlapped variations of: the variation in the film thickness resistance value of the electrically conductive film via the first electrostatic coupling, the variation in the inductance of the sensor circuit system caused by the secondary magnetic field generated as a result of the second electrostatic coupling, and the variation in the inductance of the sensor circuit system caused by the secondary magnetic field generated as a result of the third electromagnetic coupling. The variation in the thickness of the electrically conductive film is monitored in real time according to the variation in the oscillation frequency, and a polishing end point at which the electrically conductive film is polished and removed to an appropriate thickness is detected.
The invention according to claim 2 provides the end point detection method applying the resonance phenomenon, wherein the sensor uses digital output using a counter as a transmission method of the oscillation frequency.
According to this configuration, the oscillation frequency output of the sensor is digitally transmitted; therefore, influence of noise and attenuation of output is reduced. Moreover, the film thickness data can be readily managed.
The invention according to claim 3 provides the end point detection method applying the resonance frequency, wherein an oscillation frequency band of the sensor is 30 MHz.
According to this configuration, the high frequency of 30 MHz or more is used as the oscillation frequency band of the sensor; therefore, for example, electrostatic coupling between the planar inductor and the electrically conductive film via the distributed capacitance and the electromagnetic coupling between the planar inductor and the electrically conductive film is appropriately generated. As a result, the variation in the film thickness resistance value of the electrically conductive film via the electrostatic coupling and the variation in the inductance of the sensor circuit system caused by the secondary magnetic field generated as a result of the electrostatic coupling is appropriately generated. Then, an oscillation signal at a resonance frequency corresponding to the variation in which these variations are overlapped can be obtained. The oscillation frequency band of the sensor is the high frequency band; therefore, high-speed measurement can be performed, and variation in the thickness of the electrically conductive film is reliably monitored in real time.
The invention according to claim 4 provides the end point detection method applying the resonance phenomenon, wherein the concentrated constant capacitor in the sensor has a variable capacitance, and the sensor can select an oscillation frequency band.
According to this configuration, when the film type of the electrically conductive film is different, the thickness of the electrically conductive film at which the oscillation frequency reaches a peak is different due to the difference of the conductivity. When the concentrated constant capacitor has a variable capacitance, the oscillation frequency band can be selected, and the film thickness at which it reaches the peak can be controlled. Therefore, corresponding to the film types having different conductivities, polishing can be reliably stopped before a next layer is exposed after the peak of the oscillation frequency is detected.
The invention according to claim 5 provides the end point detection method applying the resonance phenomenon, wherein the electrically conductive film is formed of Cu, W, Ta, Cr, Al, Ti, or TiN and a pattern of a film type including them.
According to this configuration, the end point detection method in which the variation in the thickness of the electrically conductive film is monitored in real time is applied when metal films which are normally used in multi-layer mutual structures or the like on a semiconductor wafer are subjected to polishing and removal.
The invention described in claim 6 provides the end point detection method applying the resonance phenomenon, wherein the electrically conductive film is removed by chemical mechanical polishing.
According to this configuration, the end point detection method in which the variation in the thickness of the electrically conductive film is monitored in real time is applied when chemical mechanical polishing in which the electrically conductive film is pressed against a polishing pad with a controlled pressure under the presence of the slurry having chemical reactivity corresponding to the film type and is appropriately rotated so as to polish and remove the electrically conductive film is performed.
The invention according to claim 7 provides the end point detection method applying the resonance phenomenon, wherein one or more the sensor is embedded in an upper surface portion of a platen constituting a chemical mechanical polishing apparatus.
According to this configuration, the sensor is embedded in the upper surface portion of the platen; therefore, the variation in the thickness of the electrically conductive film can be monitored in real time during operation of the chemical mechanical polishing apparatus. Moreover, according to this configuration, the sensor performs scanning in the diameter direction of the electrically conductive film, and the information of the in-plane film thickness distribution in the diameter direction of the electrically conductive film can be acquired. Moreover, the number of the sensor(s) to be embedded is one or more; therefore, more detailed distribution information in the film thickness variation in the film plane can be obtained.
The invention according to claim 8 provides the end point detection method applying the resonance phenomenon, wherein one or more said sensor is embedded in a polishing head constituting the chemical mechanical polishing apparatus.
According to this configuration, the sensor is embedded in the polishing head; therefore, the variation in the thickness of the electrically conductive film can be monitored in real time during operation of the chemical mechanical polishing apparatus. The number of the embedded sensor(s) is one or more; therefore, the distribution information of the film thickness variation in the film plane can be obtained in a manner similar to that described above.
The invention according to claim 9 provides the end point detection method applying the resonance phenomenon, wherein the variation in the oscillation frequency of the sensor caused along with the variation in the thickness of the electrically conductive film is not monotonous increase or decrease but has a peak, and the polishing end point is detected based on the peak.
According to this configuration, the value of the oscillation frequency obtained when the polishing state of the electrically conductive film is monitored by using the sensor composed of the oscillation circuit having the planar inductor is oscillated at a resonance frequency corresponding to the overlapped variations of: the variation in the film thickness resistance value of the electrically conductive film via the first electrostatic coupling, the variation in the inductance caused by the second magnetic field generated as a result of the second electrostatic coupling, and the variation in the inductance caused by the secondary magnetic field generated as a result of the third electromagnetic coupling. Then, with respect to the variation in the film thickness resistance value of the electrically conductive film via the electrostatic coupling, increase in the oscillation frequency is caused along with increase in the film thickness resistance value. Also, with respect to both the variation in the inductance of the sensor circuit system caused by the secondary magnetic field generated as a result of the electrostatic coupling and the variation in the inductance of the sensor circuit system caused by the secondary magnetic field generated as a result of electromagnetic coupling, the oscillation frequency is reduced along with reduction in the thickness of the electrically conductive film. The value of the oscillation frequency corresponding to the variation, in which various variations are overlapped, is increased along with progress of the polishing, reaches a peak in the vicinity of the polishing end point, and then drops. Detection of the polishing end point is performed based on the peak of the oscillation frequency.
The invention according to claim 10 provides the polishing end point applying the resonance phenomenon, wherein the variation in the oscillation frequency of the sensor caused along with the variation in the thickness of the electrically conductive film is not monotonous increase or decrease but has a peak, and the polishing is stopped by using either a point at which the peak is detected or a point at which a predetermined amount of polishing is performed after the peak is detected as a polishing end point depending on the film type of the electrically conductive film.
According to this configuration, the peak of the oscillation frequency appears as a rapid form or a gentle form depending on the difference in the film type of the electrically conductive film. Therefore, the point at which a peak is detected is immediately set as a polishing end point for the film type for which the peak appears in a rapid form, and a point at which a predetermined amount of polishing is performed after the point the peak is detected can be set as a polishing end point for the film type for which the peak appears in a gentle form; as a result, the polishing end points appropriate for the electrically conductive films having different film types.
The invention according claim 11 provides the end point detection method applying the resonance phenomenon, wherein the fact that an oscillation frequency peak value generated at the point when polishing reaches the thickness of the electrically conductive film is constant, a threshold value is set based on the oscillation frequency peak value in accordance with the film type, and the polishing is stopped at a polishing end point when the oscillation frequency reaches the threshold value before the peak or after the peak.
According to this configuration, the oscillation frequency peak value generated when the electrically conductive film reaches a certain thickness is always constant with respect to the distance between the inductor and the electrically conductive film and the selected oscillation frequency band. Excessive polishing and insufficiency in the polishing amount can be prevented by setting a threshold value based on the stable peak value and setting the point at which the oscillation frequency reaches the threshold value before or after the peak as a polishing end point.
The invention according to claim 12 provides the end point detection method applying the resonance phenomenon, wherein the electrically conductive film is formed on a surface of a wafer, and the planar inductor is in the vicinity of either the electrically conductive film of the wafer surface portion or the back surface of the wafer.
According to this configuration, when the sensor is embedded in the upper surface portion of the platen constituting the chemical mechanical polishing apparatus, the planar inductor is configured to be opposed to the electrically conductive film without the intermediation of the wafer. When the sensor is embedded in the polishing head, the planar inductor is configured to be opposed to the electrically conductive film via the wafer. Even when the planar inductor and the electrically conductive film are in either one of the opposing configurations, the variation in the thickness of the electrically conductive film is monitored in real time, and a polishing end point at which the electrically conductive film is polished and removed to an appropriate thickness is detected.
The invention according to claim 13 provides an end point detection apparatus applying the resonance phenomenon characterized by executing the end point detection method applying the resonance phenomenon according to claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, wherein the apparatus having a sensor composed of an oscillation circuit of a Colpitts type or the like having a planar inductor and a concentrated constant capacitor.
According to this configuration, the end point detection apparatus having the sensor composed of the oscillation circuit of, for example, the Colpitts type or the like having the planar inductor and the concentrated constant capacitor can carry out oscillation at a resonance frequency corresponding to the overlapped variations of: the variation in the film thickness resistance value of the electrically conductive film via the electrostatic coupling, the variation in the inductance of the sensor circuit system caused by the secondary magnetic field generated as a result of the electrostatic coupling, and the variation in the inductance of the sensor circuit system caused by the secondary magnetic field generated as a result of the electromagnetic coupling. From the variation in the oscillation frequency, the variation in the thickness of the electrically conductive film is monitored in real time, and the polishing end point at which the electrically conductive film is polished and removed to an appropriate thickness is detected.
The invention according to claim 14 provides a chemical mechanical polishing apparatus loaded the end point detection apparatus applying the resonance phenomenon according to claim 13.
According to this configuration, the end point detection apparatus having the sensor composed of the oscillation circuit of, for example, the Colpitts type or the like having the planar inductor and the concentrated constant capacitor is loaded so that the apparatus is embedded in either the upper surface portion of the platen in the chemical mechanical polishing apparatus or in the polishing head, the variation in the thickness of the electrically conductive film is monitored in real time, and the polishing end point at which the electrically conductive film is polished and removed to an appropriate thickness is detected.
The invention according to claim 15 provides a semiconductor device fabricated by the chemical mechanical polishing apparatus according to claim 14.
According to this configuration, the end point detection apparatus having the sensor composed of the oscillation circuit of, for example, the Colpitts type or the like having the planar inductor and the concentrated constant capacitor is loaded so that the apparatus is embedded in either the upper surface portion of the platen in the chemical mechanical polishing apparatus or in the polishing head, the variation in the thickness of the electrically conductive film is monitored in real time, and the polishing endpoint at which the electrically conductive film is polished and removed to an appropriate thickness is detected; thus, a high-performance semiconductor device can be fabricated.
In the invention according to claim 1, a sensor composed of an oscillation circuit of a Colpitts type or the like having a planar inductor and a concentrated constant capacitor is used, and variation in the thickness of the electrically conductive film is monitored in real time from variation in an oscillation frequency of the sensor caused along with the variation in the thickness of the electrically conductive film opposed to the planar inductor. Therefore, when the sensor oscillates at a resonance frequency corresponding to the overlapped variations of: the variation in the film thickness resistance value of the electrically conductive film via the electrostatic coupling between the planar inductor and the electrically conductive film, the variation in the inductance of the sensor circuit system caused by the secondary magnetic field generated as a result of the electromagnetic coupling, and the variation in the inductance of the sensor circuit system caused by the secondary magnetic field generated as a result of electromagnetic coupling, there is an advantage that, based on the variation in the oscillation frequency, the polishing end point at which the electrically conductive film is polished and removed to an appropriate thickness can be reliably detected at high accuracy.
In the invention according to claim 2, the transmission method of the oscillation frequency of the sensor is digital output using the counter; therefore, there are advantages that influence of noise and attenuation of the oscillation frequency output is prevented, and the polishing end point at which the electrically conductive film is polished and removed to an appropriate thickness can be reliably detected.
In the invention according to claim 3, the oscillation frequency band of the sensor is a high frequency band of 30 MHz or more; therefore, for example, electrostatic coupling between the planar inductor and the electrically conductive film via the distributed capacitance and the electromagnetic coupling between the planar inductor and the electrically conductive film can be appropriately generated. Moreover, there is an advantage that high-speed measurement can be performed, and the variation in the thickness of the electrically conductive film can be monitored in real time.
In the invention according to claim 4, the concentrated constant capacitor in the sensor has a variable capacitance, and the sensor can select an oscillation frequency band; therefore, there is an advantage that polishing end point at which the electrically conductive film is polished and removed to an appropriate thickness can be reliably detected for the electrically conductive films having different film types since the electric conductivity is different when the film type of the electrically conductive films are different, and therefore the oscillation frequency band corresponding to the film thickness at which the variation by which the polishing end point can be obtained is generally different.
In the invention according to claim 5, the electrically conductive film is formed of Cu, W, Ta, Cr, Al, Ti, or TiN and a pattern of a film type including them; therefore, there is an advantage that, upon polishing and removal of the metal films which are normally used in multi-layer mutual structures or the like on semiconductor wafers, the sensor composed of the oscillation circuit of, for example, the Colpitts type or the like having the planar inductor and the concentrated constant capacitor can reliably detect the polishing end point, at which an appropriate thickness thereof is polished and removed, by monitoring the variation in the thickness of the metal films based on the variation in the oscillation frequency.
In the invention according to claim 6, the electrically conductive film is removed by chemical mechanical polishing; therefore, the end point detection method of monitoring the variation in the thickness of the electrically conductive film in real time is applied when chemical mechanical polishing, in which the electrically conductive film is pressed against a polishing pad with a controlled pressure and appropriately rotated under the presence of slurry having chemical reactivity corresponding to the film type thereof so as to polish and remove the film, is performed, and there is an advantage that the polishing end point at which the electrically conductive film is polished and removed to an appropriate thickness can be reliably detected.
In the invention according to claim 7, one or more the sensor is embedded in an upper surface portion of a platen constituting a chemical mechanical polishing apparatus; therefore, as a result of embedding the sensor(s) in the upper surface portion of the platen, the film thickness variation of the electrically conductive film to be polished and removed can be monitored in real time during operation of the chemical mechanical polishing apparatus. Moreover, according to this configuration, the sensor performs scanning in the diameter direction of the electrically conductive film, and there is an advantage that the in-plane film thickness distribution information of the electrically conductive film in the diameter direction can be obtained at the same time.
Furthermore, as a result of embedding one or more sensors, there is an advantage that more detailed distribution information of the film thickness variation in the film plane can be obtained.
In the invention according to claim 8, one or more the sensor is embedded in a polishing head constituting the chemical mechanical polishing apparatus; therefore, as a result of embedding the sensor(s) in the polishing head, the variation in the thickness of the electrically conductive film which is polished and removed during operation of the chemical mechanical polishing apparatus can be monitored in real time. Moreover, since one or more sensor(s) is embedded, there is an advantage that the distribution information of the film thickness variation in the film plane can be obtained at the same time as well as the case described above.
In the invention according to claim 9, the variation in the oscillation frequency of the sensor caused along with the variation in the thickness of the electrically conductive film is not monotonous increase or decrease but has a peak, and the polishing end point is detected based on the peak; therefore, the value of the oscillation frequency which is obtained when the polishing state of the electrically conductive film is monitored by using the sensor composed of the oscillation circuit having the planar inductor is oscillated at a resonance frequency corresponding to the overlapped variation of: the variation in the film thickness resistance value of the electrically conductive film via the electromagnetic coupling between the planar inductor and the electrically conductive film, the variation in the inductance of the sensor circuit system caused by the secondary magnetic field generated as a result of electrostatic coupling, and the variation in the inductance of the sensor circuit system caused by the secondary magnetic field generated as a result of electromagnetic coupling. Then, with respect to the variation in the film thickness resistance value of the electrically conductive film via the electrostatic coupling, increase in the oscillation frequency is caused along with increase in the film thickness resistance value. With respect to both the variations of the variation in the inductance of the sensor circuit system caused by the secondary magnetic field caused as a result of the electrostatic coupling and the variation in the inductance of the sensor circuit system caused by the secondary magnetic field generated as a result of electromagnetic coupling, the oscillation frequency is reduced in both cases along with reduction in the thickness of the electrically conductive film. The value of the oscillation frequency corresponding to variation in which such variations are overlapped is increased along with the progress of polishing and reaches a peak in the vicinity of the polishing end point. Therefore, there is an advantage that the polishing end point, at which it is removed to an appropriate thickness by polishing, can be reliably detected a significantly high accuracy based on the peak of the oscillation frequency compared with the case in which the variation is monotonous.
In the invention according to claim 10, the variation in the oscillation frequency of the sensor caused along with the variation in the thickness of the electrically conductive film is not monotonous increase or decrease but has a peak, and the polishing is stopped by using either a point at which the peak is detected or a point at which a predetermined amount of polishing is performed after the peak is detected as a polishing end point depending on the film type of the electrically conductive film; therefore, there is an advantage that appropriate polishing end points can be appropriately obtained respectively for the electrically conductive films having different film types since the peaks of the oscillation frequencies from the sensor appears as a rapid form or a gentle form depending on the film type of the electrically conductive film.
In the invention according to claim 11, the variation in the oscillation frequency of the sensor caused along with the variation in the thickness of the electrically conductive film is not monotonous increase or decrease but has a peak, and the film thickness at which the peak appears is constant; therefore, a threshold value is set based on the peak, and the point at which the oscillation frequency reaches the threshold value before or after the peak is set as a polishing end point; thus, there is an advantage that excessive polishing or insufficiency in the polishing amount can be prevented.
In the invention according to claim 12, the electrically conductive film is formed on a surface of a wafer, and the planar inductor is in the vicinity of either the electrically conductive film of the wafer surface portion or the back surface of the wafer; therefore, in both the case in which the planar inductor is opposed to the electrically conductive film without the intermediation of the wafer and the case in which the planar inductor is opposed to the electrically conductive film via the wafer, the variation in the thickness of the electrically conductive film can be monitored in real time, and the polishing end point at which the electrically conductive film is polished and removed to an appropriate thickness can be detected. Therefore, there is an advantage that the sensor can be embedded in either the upper surface portion of the platen constituting the chemical mechanical polishing apparatus or in the polishing head.
The invention according to claim 13 is an end point detection apparatus which executes the end point detection method applying the resonance phenomenon according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, wherein the apparatus has a sensor composed of an oscillation circuit of a Colpitts type or the like having a planar inductor and a concentrated constant capacitor; therefore, the end point detection apparatus can monitor the variation in the thickness of the electrically conductive film in real time based on the variation in the oscillation frequency from the sensor and can reliably detect the polishing end point, at which the electrically conductive film is polished and removed to an appropriate thickness, at high accuracy. Moreover, the planar inductor which is a main constituent element causes almost no generation of noise and power consumption, and the price thereof is comparatively low; therefore, there is an advantage that the cost can be reduced.
The invention according to claim 14 is a chemical mechanical polishing apparatus on which the end point detection apparatus applying the resonance phenomenon according to claim 13 is loaded; therefore, when the end point detection apparatus having the sensor composed of the oscillation circuit of, for example, the Colpitts type or the like having the planar inductor and the concentrated constant capacitor is loaded so that the apparatus is embedded in the upper surface portion of the platen in the chemical mechanical polishing apparatus or in the polishing head, the variation in the thickness of the electrically conductive film, which is to be polished and removed, can be reliably monitored in real time, and there is an advantage that the polishing end point, at which the electrically conductive film is removed and polished to an appropriate thickness, can be detected at high accuracy.
The invention according to claim 15 is a semiconductor device fabricated in the chemical mechanical polishing apparatus according to claim 14; therefore, the end point detection apparatus having the sensor composed of an oscillation circuit of, for example, the Colpitts type or the like having the planar inductor and the concentrated constant capacitor is loaded in the manner that it is embedded in either the upper surface portion of the platen in the chemical mechanical polishing apparatus or in the polishing head, monitors the variation in the thickness of the electrically conductive film in real time, and can detect the polishing end point, at which the electrically conductive film is polished and removed to an appropriate thickness, at high accuracy. Therefore, there is an advantage that a high-performance semiconductor device can be fabricated.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings show an end point detection method applying a resonance phenomenon, an end point detection apparatus, and a chemical mechanical polishing apparatus on which the detection apparatus is loaded according to the embodiment of the present invention.

FIG. 1 is a perspective view of the chemical mechanical polishing apparatus in which the end point detection apparatus applying the resonance phenomenon is incorporated.

FIG. 2 is an enlarged vertical cross sectional view of a polishing head in the chemical mechanical polishing apparatus of FIG. 1.

FIG. 3 are drawings for explaining the state in which a sensor is incorporated in a platen in the end point detection apparatus, wherein 3A is a partially transparent schematic side view, and 3B is a schematic plan view.

FIG. 4 is a schematic side view which is shown in a partially transparent manner for explaining the state in which the sensor in the end point detection apparatus is incorporated in the polishing head.

FIG. 5 are drawings showing a basic configuration example of the sensor, wherein 5A is a configuration example, and 5B is an equivalent circuit thereof.

FIG. 6A is a configuration diagram for explaining the variation action of the film thickness resistance value of the electrically conductive film via electrostatic coupling in the sensor of FIG. 5, 6B is an equivalent circuit thereof, and 6C shows simulation results thereof.

FIGS. 7A and 7B are configuration diagrams for explaining the variation action of the inductance caused by a secondary magnetic field generated in electrostatic coupling of the sensor in FIG. 5.

FIGS. 8A and 8B are configuration diagrams for explaining the variation action of the inductance caused by a secondary magnetic field generated by electromagnetic coupling in the sensor of FIG. 5.

FIG. 9 is a block diagram showing a specific configuration example of the sensor.

FIGS. 10A and 10B are diagrams schematically showing wafer cross sections having electrically conductive films, wherein 10A is a wafer having a Cu film, and 10B is a wafer having a tungsten film.

FIG. 11 are characteristic diagrams showing variation examples of the resonance frequencies with respect to the thickness of the electrically conductive film by the sensor, wherein 11A is the case in which the electrically conductive film is Cu, and 11B is the case in which the electrically conductive film is tungsten.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This is an end point detection method in which an electrically conductive film is polished and a polishing end point at which an appropriate thickness thereof is removed is detected in order to achieve objects of monitoring the variation in the thickness of the electrically conductive film in real time so as to reliably detect the polishing end point of the electrically conductive film at high accuracy, eliminating generation of noise, achieving low power consumption, and reducing the cost. The method is realized by using a sensor composed of an oscillation circuit of the Colpitts type or the like having a planar inductor and a concentrated constant capacitor, monitoring the variation in the thickness of the electrically conductive film in real time from the variation in the oscillation frequency of the sensor caused along with the variation in the thickness of the electrically conductive film opposed to the planar inductor, and detecting the polishing end point based on the peak that is generated in the variation of the oscillation frequency of the sensor.
Hereinafter, a preferable embodiment of the present invention will be described in detail with reference to drawings. FIG. 1 is a perspective view of a chemical mechanical polishing apparatus into which an end point detection apparatus applying a resonance phenomenon; FIG. 2 is a an enlarged vertical cross sectional view of a polishing head; FIG. 3 are drawings for explaining the state in which a sensor in the end point detection apparatus is incorporated in a platen, wherein 3A is a partially-transparent schematic side view and 3B is a schematic plan view; and FIG. 4 is a partially transparent schematic side view for explaining the state in which the sensor in the end point detection apparatus is incorporated in the polishing head.
First of all, a configuration of the chemical mechanical polishing apparatus will be described among an end point detection method applying a resonance phenomenon, the end point detection apparatus, and the configuration of the chemical mechanical polishing apparatus, in which the apparatus is incorporated, according to the present embodiment. In FIG. 1, the chemical mechanical polishing apparatus 1 is mainly composed of the platen 2 and the polishing head 3. The platen 2 is formed into a disk-like shape, a rotating shaft 4 is coupled to the center of the lower surface thereof, and it is rotated in the direction of an arrow A when a motor 5 is driven. A polishing pad 6 is attached to the upper surface of the platen 2, and slurry which is a mixture of an abrasive agent and a chemical agent is provided onto the polishing pad 6 from a nozzle which is not shown.
As shown in FIG. 2, the polishing head 3 is mainly composed of a head main body 7, a carrier 8, a retainer ring 9, a retainer ring pressing means 10, an elastic sheet 11, a carrier pressing means 16, and a control means of, for example, air.
The head main body 7 is formed into a disk-like shape, and a rotating shaft 12 (see FIG. 1) is coupled to the center of the upper surface thereof. The head main body 7 is rotatably attached to the rotating shaft 12 and rotated in the direction of an arrow B in FIG. 1 when it is driven by a motor, which is not shown.
The carrier 8 is formed into a disk-like shape and disposed at the center of the head main body 7. A dry plate 13 is provided between a center portion of the upper surface of the carrier 8 and a lower portion of the center portion of the head main body 7, and rotation is transmitted thereto from the head main body 7 via pins 14, 14.
An actuation transformer main body 15 a is fixed between a lower center portion of the dry plate 13 and an upper center portion of the carrier 8, a core 15 b of an actuation transformer 15 is fixed at an upper center portion of the carrier 8, and the transformer is coupled to a control unit, which is not shown, and outputs a polishing state signal of an electrically conductive film composed of Cu or the like formed on a wafer W (lower side in FIG. 2) to the control unit.
A carrier pressing member 16 a is provided on an upper-surface peripheral portion of the carrier 8, and pressing force is transmitted to the carrier 8 from a carrier pressing means 16 via the carrier pressing member 16 a.
Air blowout openings 19 for injecting air to the elastic sheet 11 from an air float line 17 are provided in the lower surface of the carrier 8. The air float line 17 is connected to an air supply pump 21, which is an air supply source, via an air filter 20 and an automatic opening/closing valve V1. Blowout of air from the air blowout openings 19 is executed by switching of the automatic opening/closing valve V1.
In the lower surface of the carrier 8, holes 22 for vacuuming and jetting out DIW (pure water) or air in accordance with needs are formed. Suction of the air is executed by driving a vacuum pump 23. An automatic opening/closing valve V2 is provided on a vacuum line 24, and vacuum and supply of DIW is executed via the vacuum line 24 by switching the automatic opening/closing valve V2.
Air feeding from the air float line 17 and vacuum actuation and feeding of DIW or the like from the vacuum line 24 is executed by command signals from the control unit.
The carrier pressing means 16 is disposed at the periphery of a center portion of the lower surface of the head main body 7; and, when pressing force is applied to the carrier pressing member 16 a, the means transmits the pressing force to the carrier 8 coupled thereto. The carrier pressing means 16 is preferably composed of an air bag 25 made of a rubber sheet that expands/contracts upon intake/discharge of air. An air supply mechanism, which is not shown, for supplying air is coupled to the air bag 25.
The retainer ring 9 is formed into a ring-like shape and disposed at the outer periphery of the carrier 8. The retainer ring 9 is attached to a retainer ring holder 27 provided on the polishing head 3, and the elastic sheet 11 is stretched over the inner periphery portion thereof.
The elastic sheet 11 is formed into a circular shape, and the plurality of holes 22 are perforated therein. A periphery portion of the elastic sheet 11 is sandwiched between the retainer ring 9 and the retainer ring holder 27 so that the sheet is stretched over the inside of the retainer ring 9.
Below the carrier 8 over which the elastic sheet 11 is stretched, an air chamber 29 is formed between the carrier 8 and the elastic sheet 11. The wafer W on which the electrically conductive film is formed is pressed against the carrier 8 via the air chamber 29. The retainer ring holder 27 is attached to an attachment member 30, which is formed into a ring-like shape, via a snap ring 31. A retainer ring pressing member 10 a is coupled to the attachment member 30. The pressing force from the retainer ring pressing means 10 is transmitted to the retainer ring 9 via the retainer ring pressing member 10 a.
The retainer ring pressing means 10 is disposed at an outer peripheral portion of the lower surface of the head main body 7; and, when pressing force is applied to the retainer ring pressing member 10 a, the retainer ring 9 coupled thereto is pressed against the polishing pad 6. The retainer ring pressing means is also preferred to be composed of an air bag 16 b made of a rubber sheet as well as the carrier pressing means 16. An air supply mechanism, which is not shown, for supplying air is coupled to the air bag 16 b.
As shown in FIGS. 3A and 3B and FIG. 4, a sensor 37, which will be described later, for detecting the polishing end point of the electrically conductive film is incorporated in an upper portion of the platen 2 in the chemical mechanical polishing apparatus 1 or the part of the carrier 8 of the polishing head 3. When the sensor 37 is incorporated in the platen 2 side, a detection signal or the like of the polishing end point from the sensor 37 is output to outside via a slip ring 32.
When the sensor is loaded on the upper portion of the platen 2 in the chemical mechanical polishing apparatus 1, the sensor 37 performs scanning in the diameter direction within the plane of the wafer W, and the information of the in-plane film thickness distribution in the diameter direction of the electrically conductive film can be acquired. Note that, two or more sensors 37 may be incorporated in the upper portion of the platen 2 or the part of the carrier 8 of the polishing head 3. When two or more sensors 37 are incorporated, and film thickness information is collected in a time-oriented manner, the distribution information, for example, the film thickness variation in the plane of the wafer W can be obtained from the sensor 37 in front side in rotate direction.
FIG. 5 show a basic configuration view of the sensor, wherein 5A is a configuration example, and 5B shows an equivalent circuit thereof. The basic sensor 33 is mainly composed of an oscillation circuit 36 comprising a planar inductor 34 and a concentrated constant capacitor 35. The shape of the planar inductor 34 may be round-shaped or square-shaped spiral or the like other than the meander shape shown in FIG. 5A.
The oscillation circuit 36 is, for example, a Colpitts-type oscillation circuit, wherein the oscillation frequency band f thereof is determined by the inductance L of the planar inductor 34 and the capacitance C₀of the concentrated constant capacitor 35 as shown in the below expression (1).
$\begin{matrix} f = \frac{1}{2 π \sqrt{L C_{0}}} & (1) \end{matrix}$
When the planar inductance 34 is caused to approach the electrically conductive film 28 so that they are parallel to each other with a distance therebetween of about 10 mm or less, following three phenomena of (a) variation in the film thickness resistance value of the electrically conductive film via electrostatic coupling, (b) variation in the inductance due to a secondary magnetic field generated by electrostatic coupling, and (c) variation in the inductance due to a secondary magnetic field generated by electromagnetic coupling occur. These three phenomena (a), (b), and (c) will be sequentially described with reference to drawings.
(a) Variation in the film thickness resistance value of the electrically conductive film via electrostatic coupling. This phenomenon will be described with reference to FIG. 6. When the planar inductor 34 is caused to approach the electrically conductive film 28 in parallel, electrostatic induction is caused in the side of the electrically conductive film 28 by the phase distribution that the planar inductor 34 has, and the planar inductor 34 undergoes electrostatic coupling with the electrically conductive film 28 via a distributed capacitance Cm′.
When the film thickness of the electrically conductive film 28 is sufficiently thick, the electrically conductive film 28 can be considered as a conductor having almost no resistance; however, in the region having an extremely thin thickness, the film thickness resistance R thereof cannot be ignored. The equivalent circuit of FIG. 6A of this case can be illustrated like FIG. 6B, and it can be considered as a parallel resonance circuit to which the distributed capacitance Cm′ and the film thickness resistance R of the electrically conductive film 28 are added to the inductance L of the planar inductor 34 and the capacitance C₀of the concentrated constant capacitor 35.
When the admittance Y is obtained for the equivalent circuit of FIG. 6B, it can be described as the expression (2).
$\begin{matrix} Y = \frac{ω^{2} {Cm}^{′2} R}{1 + {(ω C m^{'} R)}^{2}} + j {\frac{ω {Cm}^{'}}{1 + {(ω {Cm}^{'} R)}^{2}} + ω C_{0} - \frac{1}{ω L}} & (2) \end{matrix}$
Therefore, the susceptance B thereof will be that shown in the expression (3).
$\begin{matrix} B = \frac{ω {Cm}^{'}}{1 + {(ω {Cm}^{'} R)}^{2}} + ω C_{0} - \frac{1}{ω L} & (3) \end{matrix}$
The resonance frequency of the parallel resonance circuit is the value of ω (=2πf) when the susceptance component B=0 at the admittance Y of the equivalent circuit. According to the expression (3), the film thickness resistance R is related to the resonance conditions in the form of a time constant (Cm′·R) which is a product thereof and the distributed capacitance Cm′. Therefore, the oscillation frequency of the 33 is affected by the film thickness resistance R via the distributed capacitance Cm′. The obtained results of the relation between the film thickness and the resonance frequency in the case in which the equivalent circuit of FIG. 6B is subjected to a simulator and the film thickness resistance R is changed from 0 to ∞ (film thickness: thick to thin) are shown in FIG. 6C. According to FIG. 6B, it can be understood that reduction in the film thickness of the electrically conductive film 28, in other words, increase in the film thickness resistance R can cause increase in the oscillation frequency. Also, the results of the simulation show that a peak of the resonance frequency can be formed in the region in which the film thickness resistance R is significantly large.
(b) Change in the inductance caused by a secondary magnetic field generated by electrostatic coupling. This phenomenon will be described with reference to FIG. 7. The planar inductor 34 generates a primary varying magnetic field M₁. The planar inductor 34 causes electrostatic induction in the side of the electrically conductive film 28 by the phase difference on the planar inductor 34, and the planar inductor 34 undergoes electrostatic coupling with the electrically conductive film 28 via the distributed capacitance Cm′.
The induced current I₁generated in the surface portion of the electrically conductive film 28 upon the electrostatic induction generates a secondary magnetic field M₂in the direction cancelling out the primary magnetic field M₁. The secondary magnetic field M₂acts in the direction that reduces the inductance. Therefore, when the reduced amount of the inductance is Lm, the oscillation frequency can be expressed as the expression (4).
$\begin{matrix} f = \frac{1}{2 π \sqrt{(L - Lm) C_{0}}} & (4) \end{matrix}$
Herein, in the region in which the thickness of the electrically conductive film 28 is thin so that the skin effects cannot be ignored, it is conceived that the thinner the film thickness, the less the generation amount of the induced current I₁generated in the electrically conductive film 28, and the secondary magnetic field M2 is attenuated at the same time. Therefore, reduction in the film thickness of the electrically conductive film 28 leads to reduction in the reduction amount Lm of the inductance. As a result, the inductance of the sensor circuit system is equivalently increased, and the oscillation frequency of the sensor 33 is reduced.
(c) Variation in the inductance caused by the secondary magnetic field generated by electromagnetic coupling. This phenomenon will be described with reference to FIG. 8. The planar inductor 34 generates a primary magnetic field M₁which is varied along with time. The primary magnetic field M₁which is varied along with time generates an induced current Ii in the electrically conductive film 28. The induced current Ii in the electrically conductive film 28 generates a secondary magnetic field M₃in the direction that cancels out the primary magnetic field M₁generated by the planar inductor 34, and electromagnetic coupling is caused between the planar inductor 34 and the electrically conductive film 28.
The secondary magnetic field M₃generated by the induced current Ii acts in the direction that reduces the inductance. Therefore, when the reduction amount of the inductance is Lm, the oscillation frequency can be expressed in the same manner as the above described expression (4).
In the region in which the thickness of the electrically conductive film 28 is thin so that skin effects cannot be ignored, it is conceived that the less the film thickness, the more the generation amount of the induced current Ii generated in the conductive film 28 is reduced, and the secondary magnetic field M₃is attenuated at the same time. Therefore, reduction in the thickness of the electrically conductive film 28 leads to reduction in the reduction amount Lm of the inductance. As a result, the inductance of the sensor circuit system is equivalently increased, and the oscillation frequency of the planar-inductor-loaded electrostatic-coupling-type sensor 33 is reduced.
When the above described three phenomena (a), (b), and (c) are taken into consideration, the value of the oscillation frequency of the planar-inductor-mounted electrostatic-coupling-type sensor 33 with respect to the film thickness of the electrically conductive film 28 is no longer uniformly varied. In the present embodiment, a suitable signal is extracted in end point detection by actively using the three phenomena.
FIGS. 11A and 11B show the relation between the film thickness and the resonance frequency of the case in which Cu and W wafers are actually polished. According to FIGS. 11A and 11B, the resonance frequencies are increased in the course of removing the film after polishing initiation, and these increasing regions correspond to the phenomenon of (a). Then, the resonance frequencies reach peaks, and the resonance frequencies are reduced and settled to constant values when the film is removed. The reducing regions correspond to the phenomena of (a), (b), and (c).
In this course, the above described variation characteristics of the resonance frequencies are obtained not only when the three variations of (a), (b), and (c) are overlapped but also when the variation of (a) is overlapped with at least either one of the variations of (b) and (c) among (a) the variation in the film thickness resistance value of the electrically conductive film via electrostatic coupling, (b) the variation in the inductance caused by the secondary magnetic field generated by electrostatic coupling, and (c) the variation in the inductance caused by the secondary magnetic field generated by electromagnetic coupling. Also, according to the simulation results of FIG. 6C, the above described variation characteristic of the resonance frequency can be also obtained when merely the phenomenon of (a) is utilized. In this process, when a substance such as ferrite having high magnetic permeability and a high resistance or a substance having a high dielectric constant is interposed between the planar inductor and the electrically conductive film, phenomena can be selectively combined, and the variation characteristics of the resonance frequencies can be controlled.
FIG. 9 shows a specific configuration example of the sensor. A planar inductor 38 in the sensor 37 of the configuration example is formed into a meander shape by using an electrically conductive substance such as Cu on a substrate 38 a composed of an insulating substance. An oscillation circuit 39 is an oscillation circuit of, for example, the Colpitts type in which the oscillation frequency band f thereof is determined by the inductance of the planar inductor 38 and the capacitance of a concentrated constant capacitor 40, wherein the oscillation frequency band f is set at a high frequency band of 30 to 1000 MHz or more.
The capacitance of the concentrated constant capacitor 40 constituting the oscillation circuit 39 is variable, and the sensor 37 can select the frequency band within the range of the oscillation frequency band f in accordance with the film type of the electrically conductive film to be polished and removed. When the film type of the electrically conductive film is different, because of the difference of the electrical conductivity thereof, the oscillation frequency band corresponding to the size of the film thickness that generates the variation by which a polishing end point can be detected is generally different. Therefore, when the capacitance of the concentrated constant capacitor 40 is variable in this manner, polishing end points can be reliably detected when the electrically conductive films having different film types are polished and removed to an appropriate thickness.
When the oscillation frequency band f of the sensor 37 is a high frequency band, for example, electrostatic coupling between the planar inductor 38 and the electrically conductive film via the distributed capacitance and electromagnetic coupling between the planar inductor 38 and the electrically conductive film is appropriately caused.
As a result, the above described variations of (a) the variation in the film thickness resistance value of the electrically conductive film via electrostatic coupling, (b) the variation in the inductance caused by the secondary magnetic field generate by electrostatic coupling, and (c) the variation in the inductance caused by the secondary magnetic field generated by electromagnetic coupling are appropriately generated. The sensor 37 oscillates at a resonance frequency corresponding to the variation in which the above described variations are overlapped, and the variation characteristics of the resonance frequency shown in FIG. 11A is obtained with respect to the variation of the thickness of the electrically conductive film.
Furthermore, when the oscillation frequency band f of the sensor 37 is the high frequency band, high-speed measurement can be performed, and the variation in the thickness of the electrically conductive film can be reliably monitored in real time.
The sensor 37 of FIG. 9 has, in addition to the planar inductor 38 and the capacitor 40, an amplifier 41 composed of an operational amplifier or the like, a feedback network 42 composed of a resistance or the like, and a frequency counter 43. A resonance frequency signal serving as a detection signal or the like of a polishing end point is digitally output from the frequency counter 43. When the detection signal output of the sensor 37 is digitally transmitted, influence of noise and attenuation of the output can be prevented. Moreover, management of film thickness data becomes easy.
Next, polishing working and an end point detection method of the chemical mechanical polishing apparatus into which the end point detection apparatus using the sensor configured in the above described manner is incorporated will be described. In the present end point detection method, the case in which the sensor 37 is incorporated in the upper portion of the platen 2 as shown in FIG. 3A will be described.
First of all, the polishing head 3 is placed on the wafer W, which is on standby at a predetermined position and has the unpolished electrically conductive film 28, by a transporting mechanism which is not shown. Then, the vacuum line 24 of the polishing head 3 is actuated, and the air chamber 29 on the lower surface of the elastic sheet 11 is vacuumed via a vacuum opening 19 a and the holes 22 (vacuum holes), thereby sucking and retaining the wafer W of which electrically conductive film 28 is unpolished. Then, the transporting mechanism transports the polishing head 3 sucking and retaining the wafer W of which electrically conductive film 28 is unpolished to a position above the platen 2 and places the wafer W on the platen 2 so that the electrically conductive film 28 is faced to and in contact with the polishing pad 6.
When the polishing operation of the electrically conductive film 28 of the upper portion of the wafer W is finished, the vacuum line 24 again sucks and retains the wafer W by the polishing head 3 by actuating the vacuum line 24, and it used also when the wafer is transported to a washing apparatus which is not shown.
Then, actuation of the vacuum line 24 is cancelled, and air is supplied to the air bag 25 from a pump, which is not shown, thereby expanding the air bag 25. At the same time, air is supplied to the air chamber 29 from the air blowout openings 19 provided in the carrier 8. As a result, the internal pressure of the air chamber 29 is increased.
By the expansion of the air bag 25, the electrically conductive film 28 of the upper portion of the wafer W and the retainer ring 9 are pressed against the polishing pad 6 by a predetermined pressure. In this state, the platen 2 is rotated in the direction of the arrow A of FIG. 1, the polishing head 3 is simultaneously rotated in the direction of the arrow B of FIG. 1, and slurry is supplied from a nozzle, which is not shown, onto the rotating polishing pad 6, thereby polishing the electrically conductive film 28 of the upper portion of the wafer W.
Then, with respect to the electrically conductive film 28 of the upper portion of the wafer W during polishing, variation of the film thickness along with progress of polishing is monitored, and a polishing endpoint is detected by the sensor 37. The cases in which monitoring of the film thickness variation of the electrically conductive film 28 is performed for a wafer Wa having a Cu film shown in FIG. 10A and a wafer Wb having a tungsten (W) film shown in FIG. 10B will be described with reference to variation characteristics of the resonance frequencies with respect to the film thicknesses of the electrically conductive films of FIG. 11A and FIG. 11B.
In the wafer Wa having the Cu film, Th—SiO₂(thermally-oxidized film), a TaN film, and a Ta film are sequentially laminated on a Si semiconductor wafer substrate, and an electrically conductive film 28 a composed of the Cu film, which is to be polished and removed, is formed on the Ta film. In the wafer Wb having the tungsten (W) film, a conductive film 28 b composed of the tungsten (W) film, which is to be polished and removed, is formed on a Si semiconductor wafer substrate via a TiN film.
The sensor 37 incorporated in the platen 2 oscillates with respect to the variation of the thickness of the electrically conductive film 28 along with progress of polishing at a resonance frequency corresponding to the overlapped variation of the above described three variations: (a) the variation in the film thickness resistance value of the electrically conductive film 28 via electrostatic coupling, (b) the variation in the inductance caused by the secondary magnetic field generated by electrostatic coupling, and (c) the variation in the inductance caused by the second magnetic field generated by electromagnetic coupling.
Then, when the electrically conductive film 28 to be polished and removed is the Cu film, as shown in FIG. 11A, the less the film thickness, the more the film thickness resistance value of the electrically conductive film 28 is gradually increased, and the resonance frequency can be gradually increased along with that. When polishing progresses to the point that the electrically conductive film 28 is removed, the film thickness resistance value of the electrically conductive film 28 is increased, and the resonance frequency is rapidly increased, reaches a peak P at the point when a certain film thickness is achieved, and rapidly drops. When the peak P that is the clear variation in the resonance frequency is monitored, the polishing endpoint when an appropriate thickness is removed by polishing is detected.
Also, when the electrically conductive film 28 to be polished and removed is the tungsten (W) film, as shown in FIG. 11B, the more the film thickness is reduced, the more the film thickness resistance value of the electrically conductive film 28 is gradually increased, and the resonance frequency is gently increased along with that. When polishing progresses to the point that the electrically conductive film 28 is removed, the film thickness resistance value of the electrically conductive film 28 is increased, and the resonance frequency reaches a peak P and then gently decreases. With respect to the tungsten (W) film in which the peak P appears in a gentle form as described above, the point when a predetermined amount of polishing is performed after the peak P is detected is considered as a polishing end point at which an appropriate thickness is removed by polishing.
In the above described end point detection method, the cases in which the electrically conductive films 28 to be polished and removed are the Cu film and the tungsten (W) film are described. However, the end point detection method of the present embodiment can be also applied to the cases in which other metal films such as a Ta film, a Cr film, an Al film, a Ti film, a TiN film or the like, which are normally used in multi-layer mutual structures or the like other than the Cu film and the tungsten (W) film, are to be polished and removed.
An in-plane film thickness distribution feedback system which performs feedback with respect to polishing parameters such as a polishing pressure or a zone pressure according to the polished shape of the electrically conductive film 28 obtained by using the sensor 37 can be built.
A real time in-plane film thickness distribution control system in which the polishing state of the electrically conductive film 28 can be monitored in real time by using the electrically coupling-type sensor 37, and, according to the wafer in-plane distribution of the film thickness obtained during the process, the polishing parameters such as the polishing pressure or the zone pressure is controlled in real time can be built.
An automatic interval system which controls dress, head washing in real time by monitoring the polishing state of the electrically conductive film 28 in real time by using the sensor 37 and detecting the polishing rate or the polishing shape can be built.
Semiconductor devices exhibiting extremely good performance can be fabricated by the end point detection apparatus in which at least any one system of the in-plane film thickness distribution feedback system, the real time in-plane film thickness distribution control system, and the automatic interval system is loaded.
As described above, in the end point detection method, the end point detection apparatus, and the chemical mechanical polishing apparatus in which the detection apparatus is loaded, the sensor 37 oscillates at a resonance frequency corresponding to the overlapped variations of: (a) the variation in the film thickness resistance value of the electrically conductive film 28 via electrostatic coupling, (b) the variation in the inductance caused by the secondary magnetic field generated as a result of electrostatic coupling, and (c) the variation in the inductance caused by the secondary magnetic field generated as a result of electromagnetic coupling. The value of the oscillation frequency is increased along with progress of polishing and reaches a peak in the vicinity of a polishing end point. Therefore, the polishing end point at which an appropriate thickness is removed by polishing can be reliably detected at high accuracy based on the peak of the resonance frequency.
The peak of the oscillation frequency from the sensor 37 appears as a rapid form or a gentle form depending on the difference of the film type of the electrically conductive film 28. Therefore, corresponding to the film type of the electrically conductive film 28, either the point when the peak is detected or the point when a predetermined amount of polishing is performed after the peak is detected is considered as a polishing end point. As a result, appropriate polishing end points can be appropriately obtained respectively for the electrically conductive films 28 having different film types, and polishing can be finished in the state in which a desired film thickness is remaining or the state in which the film is completely removed.
When a threshold value is set based on the peak of the oscillation frequency from the sensor 37, and the point before the peak or the point at which the oscillation frequency reaches the threshold value after the peak is set as a polishing end point, excessive polishing or insufficient polishing can be prevented, and polishing can be finished in the state in which a desired film thickness is remaining.
Furthermore, a method in which a start point is determined based on the point from which the oscillation frequency from the sensor 37 increases from a certain value can be employed, or an end point can be determined based on the point at which the value reaches a certain value after reduction.
When the region in which the polishing rate is the highest is selected from the in-plane film thickness distribution which can be acquired from the sensor 37 is selected, and an end point is determined merely by the region, the situation that the wafer is partially polished to a lower layer can be avoided.
The transmission method of the oscillation frequency of the sensor 37 employs digital output using the frequency counter 43. As a result, influence of noise and attenuation of oscillation frequency output can be prevented, and a polishing end point can be reliably detected.
The oscillation frequency bond of the sensor 37 is 30 MHz or more. As a result, for example, electrostatic coupling between the planar inductor 38 and the electrically conductive film 28 via the distributed capacitance and electromagnetic coupling between the planar inductor 38 and the electrically conductive film 28 can be appropriately generated. Also, high-speed measurement can be performed, and variation in the thickness of the electrically conductive film 28 can be reliably monitored in real time.
The capacitance of the concentrated constant capacitor 35 constituting the sensor 37 is variable. As a result, polishing end points can be reliably detected for the electrically conductive films 28 having different film types.
In polishing and removal of metal films of, for example, Cu, tungsten (W), Ta, Cr, Al, Ti, and TiN which are normally used in multi-layer mutual structures or the like on semiconductor wafers, the variation in the thickness of the metal films can be monitored in real time, and polishing end points can be reliably detected.
The planar inductor 38 which is a main constituent element of the sensor 37 has almost no generation of noise and electric power consumption, and the cost thereof is comparatively low; therefore, cost can be reduced.
Note that, in the present invention, it goes without saying that various modifications can be made without departing from the spirit of the present invention, and the present invention pertains to the modifications.

Claims

1. An end point detection method applying a resonance phenomenon in which an electrically conductive film is polished and a polishing end point at which an appropriate thickness of the film is removed is detected, wherein

a sensor composed of an oscillation circuit of a Colpitts type or the like having a planar inductor and a concentrated constant capacitor is used, and variation in the thickness of the electrically conductive film is monitored in real time from variation in an oscillation frequency of the sensor caused along with the variation in the thickness of the electrically conductive film opposed to the planar inductor.

2. The end point detection method applying the resonance phenomenon according to claim 1, wherein the sensor uses digital output using a counter as a transmission method of the oscillation frequency.

3. The end point detection method applying the resonance frequency according to claim 1 or 2, wherein an oscillation frequency band of the sensor is 30 MHz.

4. The end point detection method applying the resonance phenomenon according to claim 1, 2, or 3, wherein the concentrated constant capacitor in the sensor has a variable capacitance, and the sensor can select an oscillation frequency band.

5. The end point detection method applying the resonance phenomenon according to 1, 2, 3, or 4, wherein the electrically conductive film is formed of Cu, W, Ta, Cr, Al, Ti, or TiN and a pattern of a film type including them.

6. The end point detection method applying the resonance phenomenon according to claim 1, 2, 3, 4, or 5, wherein the electrically conductive film is removed by chemical mechanical polishing.

7. The end point detection method applying the resonance phenomenon according to claim 1, 2, 3, 4, 5, or 6, wherein one or more the sensor is embedded in an upper surface portion of a platen constituting a chemical mechanical polishing apparatus.

8. The end point detection method applying the resonance phenomenon according to claim 1, 2, 3, 4, 5, or 6, wherein one or more the sensor is embedded in a polishing head constituting the chemical mechanical polishing apparatus.

9. The end point detection method applying the resonance phenomenon according to claim 1, 2, 3, 4, 5, 6, 7, or 8, wherein the variation in the oscillation frequency of the sensor caused along with the variation in the thickness of the electrically conductive film is not monotonous increase or decrease but has a peak, and the polishing end point is detected based on the peak.

10. The polishing end point applying the resonance phenomenon according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, wherein the variation in the oscillation frequency of the sensor caused along with the variation in the thickness of the electrically conductive film is not monotonous increase or decrease but has a peak, and the polishing is stopped by using either a point at which the peak is detected or a point at which a predetermined amount of polishing is performed after the peak is detected as a polishing end point depending on the film type of the electrically conductive film.

11. The end point detection method applying the resonance phenomenon according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, wherein the fact that an oscillation frequency peak value generated at the point when polishing reaches the thickness of the electrically conductive film is constant, a threshold value is set based on the oscillation frequency peak value in accordance with the film type, and the polishing is stopped at a polishing end point when the oscillation frequency reaches the threshold value before the peak or after the peak.

12. The end point detection method applying the resonance frequency according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11, wherein the electrically conductive film is formed on a surface of a wafer, and the planar inductor is in the vicinity of either the electrically conductive film of the wafer surface portion or the back surface of the wafer.

13. An end point detection apparatus utilizing a resonance phenomenon, wherein the apparatus executes the end point detection method applying the resonance phenomenon described in claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, the apparatus having a sensor composed of an oscillation circuit of a Colpitts type or the like having a planar inductor and a concentrated constant capacitor.

14. A chemical mechanical polishing apparatus, wherein the end point detection apparatus applying the resonance phenomenon according to claim 13 is loaded.

15. A semiconductor device fabricated by the chemical mechanical polishing apparatus according to claim 14.