US20060189257A1

US20060189257A1 - Systems and methods for wafer polishing

Info

Publication number: US20060189257A1
Application number: US11/158,450
Authority: US
Inventors: Robert Donis
Original assignee: LSI Logic Corp
Current assignee: LSI Corp; Bell Semiconductor LLC
Priority date: 2005-02-22
Filing date: 2005-06-21
Publication date: 2006-08-24

Abstract

An electromagnetic polish head (100) comprises at least one electromagnet. An embodiment may also include the addition of a slurry component or components that can be affected by an electromagnetic field. During polishing or planarization, a field or fields may be generated by the polish head (100) to affect the polishing of a wafer by attracting or repelling the slurry to a portion or portions of the substrate.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation-in-part of, and claims priority to, co-pending and commonly-assigned U.S. patent application Ser. No. 11/063,384, filed Feb. 22, 2005, entitled “Systems and Methods for Wafer Polishing,” which is incorporated in its entirety herein by reference.

BACKGROUND

A. Technical Field
The present invention relates generally to the field of semiconductor wafer fabrication, and more particularly, to chemical mechanical planarization or polishing (CMP) of wafers.
B. Background of the Invention
The manufacturing of semiconductor devices, including integrated circuits, microchips, or chips, often involves multiple processes. For example, a semiconductor device may comprise a substrate on which a number of films of various chemical compositions are layered. During manufacturing, a layer's thickness or uniformity may need to be within a set limit for the final device to function properly. Thus, at one or more times during the manufacturing of a semiconductor device, the wafer under development may need to be planarized. One method for planarizing substrates utilized in semiconductor manufacturing is called chemical mechanical polishing or planarization. Chemical mechanical polishing or planarization (CMP) is a polishing process that uses a combination of mechanical removal and chemical etching to planarize a wafer's surface.
A typical CMP apparatus comprises a polish head (also referred to as a carrier head) and a polishing pad. The polish head is a tool fixture that holds a wafer during the CMP process. Typically, the wafer is held in place, in an inverted position, against the polish head through vacuum pressure. A polishing pad faces the wafer when the wafer is positioned on the polish head. During a CMP process, the polish head presses the wafer against the polishing pad. Depending on the particular CMP apparatus configuration, both the polishing pad and the polish head may rotate to create the mechanical polishing. Typically, a chemical etching solution is continuously pumped onto the polishing pad during the CMP process.
The chemical etching solution, also referred to as the “slurry,” is normally a mixture of an abrasive or abrasives and other chemicals. For example, a slurry may contain silica or alumina particles dispersed and suspended in an acidic or a basic etching solution, depending on the application.
CMP processes are normally used to planarize silicon wafers at both post-ingot wafer slicing and at various levels of the chip development. For example, once the bare silicon wafer is cut from the silicon ingot, its surface is usually rough and uneven. Generally, there are strict tolerances as to the planarity of the wafer before it can be used to produce yielding chips. To achieve an acceptable level of planarity, CMP is typically employed to planarize the wafer.
Also, during the production of an integrated circuit, it is typically very desirable that the wafer's surface be planar throughout each process. However, due to the nature of certain processes, a non-planar surface may be produced. This non-planar surface may lead to various problems in production, which generally leads to a reduced yield of functional chips. For example, due to uneven topography of the wafer, possibly resulting from prior deposition cycles or other manufacturing processes, reactants may grow uneven layers onto the surface of the wafer. Once again, CMP is often used to reduce the wafer's altitude variations so that subsequent process steps can be performed.
Although the use of CMP processing during the manufacturing of semiconductor manufacturing helps increase yield, the CMP process has limits. Currently, the CMP process may not be able to planarize sufficiently a wafer that possesses too great a disparity in wafer surface altitude. Furthermore, current CMP process may introduce defects into wafers by over-polishing or under-polishing certain areas. These problems may lead-to decreased yields of semiconductor products.

SUMMARY OF THE INVENTION

In general, exemplary embodiments of the invention are concerned with an electromagnetic polish head comprising at least one electromagnet. An embodiment may also include employing a slurry component or components that can be affected by an electromagnetic field, such as, for example, a polarized or polarizable slurry component or components. In one embodiment, during polishing or planarization, a field or fields may be generated by the polish head to affect the polishing of a wafer by attracting or repelling the slurry component or components to a portion or portions of the substrate. In an embodiment, the field or fields generated by an electromagnetic polish head may be varied during the polishing process. An embodiment of the present invention may include a contoller, computer system, or processing unit to monitor and/or control the fields generated by the electromagnetic polish head.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will be made to embodiments of the invention, examples of which may be illustrated in the accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
FIG. 1 illustrates a partial profile of a chemical mechanical polishing apparatus, including an embodiment of an electromagnetic polish head and slurry.
FIG. 2 is a top view of the embodiment of the electromagnetic polish head depicted in FIG. 1.
FIG. 3 is a top view of an alternate embodiment of an electromagnetic polish head.
FIG. 4 is a top view of an alternate embodiment of an electromagnetic polish head.
FIG. 5 is a top view of an alternate embodiment of an electromagnetic polish head.
FIG. 6 is a block diagram of an alternate embodiment of an electromagnetic polish head system.
FIG. 7 is a flow chart illustrating an embodiment of a method for utilizing an electromagnetic polish head and slurry to control the polishing or planarization of a substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, for purposes of explanation, specific details are set forth in order to provide an understanding of the invention. It will be apparent, however, to one skilled in the art that the invention can be practiced without these details. Furthermore, one skilled in the art will recognize that embodiments of the present invention, described below, may be performed in a variety of ways and using a variety of means, including software, hardware, firmware, or a combination thereof. Accordingly, the embodiments described below are illustrative of specific embodiments of the invention and are meant to avoid obscuring the invention.
Reference in the specification to “one embodiment,” “a preferred embodiment,” or “an embodiment” means that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment,” “in an embodiment,” or the like in various places in the specification are not necessarily all referring to the same embodiment.
FIG. 1 is a cross-sectional view of part of a chemical mechanical polishing apparatus 150 with an embodiment of an electromagnetic polishing head 100A holding a wafer substrate 102. According to the present invention, electromagnetic polishing head 100A comprises a carrier head 106 for holding substrate 102 during polishing and also possesses one or more zones 101 capable of inducing an electromagnetic field. In the embodiment depicted in FIG. 1, polishing head 100A possess five zones, 101A-101E, which are each capable of generating electromagnetic fields.
In FIG. 1, slurry 103 contains the chemicals for a CMP process and is introduced onto a polishing pad 104. Slurry 103 may also contain one or more polarized or polarizable chemicals capable of being affected by an electromagnetic field. In an embodiment, slurry 103 may contain one or more ferromagnetic components, such as, for example, iron, nickel, cobalt, or other such components know in the art. A component shall be understood to include an element in any form including ions and chemicals containing ion or non-ionic forms. For example, an iron component may include iron molecules, iron ions (Fe²⁺ or Fe³⁺), iron compounds wherein iron or iron ions are constituents, or any combination thereof. In an embodiment, slurry 103 may contain one or more paramagnetic components. As depicted in FIG. 1, slurry 103 has a general concentration over the surface of the polishing pad 104 and wafer 102. As further illustrated, a higher concentration 105 of the slurry exists under zone 101C. The higher concentration under zone 101C is a result of an electromagnetic field being generated in zone 101C. Accordingly, electromagnetic polish head 100A has the ability to affect the distribution of the slurry 103 in contact with wafer 102.
Because slurry component or components may be drawn to or repelled from a region, the present invention provides greater control over a CMP process. The present invention may provide for more or less polishing on portions of a wafer by attracting or repelling slurry to a particular portion of a wafer, depending upon the polarizations of the slurry and the electromagnetic field or fields. By controlling the polishing rates at different locations on the wafer, the present invention may be employed to create a desired profile on a wafer. Furthermore, wafers that previously may have possessed surface variations too severe for a CMP process to correct may, through application of the present invention, be planarized. Accordingly, greater outputs in yield may be achieved.
FIG. 2 depicts the top view of the electromagnetic polish head 100A illustrated in FIG. 1. Electromagnetic polish head 100A comprises a plurality of distinct zones or regions. In the embodiment depicted in FIG. 2, polish head 100A is comprised of five concentric zones 101A-101E. Each zone 101A-E may be electrically isolated and thus may be capable of generating its own electromagnetic field. It should be noted that the present invention is not limited to concentric zones as depicted in FIGS. 1 and 2. Any of a number of patterns of electromagnets or electromagnetic zone configurations may be utilized in polish head 100.
For example, FIG. 3 depicts an alternate embodiment of an electromagnetic polish head. Polish head 100B possesses a plurality of parallel or substantially parallel zones 301A-301 n. Each of zones 301A-301 n may possess one or more electromagnets capable of generating a magnetic field. In the embodiment depicted in FIG. 3, polish head 100B may be configured with a number of zones varying from 1 to n.
FIG. 4 depicts an alternative embodiment of an electromagnetic polish head. Polish head 100C possesses a plurality of radial or pie-shaped zones 401A-401H. Each of zones 401A-401H may possess one or more electromagnets capable of generating a magnetic field. In the embodiment depicted in FIG. 4, polish head 100C may be configured with a number of zones varying from 1 to n.
FIG. 5 depicts yet another embodiment of an electromagnetic polish head. Polish head 100D possesses a plurality of small zones 501A-501 n. Each of zones 501A-501 n may possess one or more electromagnets capable of generating an electromagnetic field. In the embodiment depicted in FIG. 5, polish head 100D may be configured with a number of zones varying from 1 to n. The small zones 501A-501 n increase the ability to direct slurry chemicals to smaller regions on a wafer. It should be understood with this embodiment, as with each of the embodiments, that the different zones of polish head 100 may be the same size or may be different sizes.
FIG. 6 depicts a block diagram of an embodiment of a system comprising an electromagnetic polish head 100 and a controller 604. As depicted in FIG. 6, electromagnetic polish head 100 is functionally connected via connection 602 to a controller 604. One skilled in the art will recognize that controller 604 may be any of a number of devices or combination of devices known for controlling electromagnets, controlling voltages, or controlling current flows. Furthermore, controller 604 may be implemented in hardware, software, firmware, or any combination thereof.
In one embodiment, electromagnetic polish head 100 may be electrically coupled to an alternating current or a direct current for energizing an electromagnetic field or zones. In an embodiment, controller 604 may comprise a processor or computer system that controls the magnitude, polarity, and rate of change of one or both of the magnitude or polarity of the electromagnetic fields generated by the different zones of polish head 100.
One skilled in the art will recognize that a number of open loop and closed loop feedback systems may be employed as part of the present invention to provide information to controller 604. In an embodiment, a processor may receive profile information to determine the desired electromagnetic field strength and polarity needed to produce the desired wafer profile. A desired slurry/electromagnetic profile may be determined and applied during the CMP process in a number of ways. For example, sample wafers may be inspected to determine the profile resulting from the manufacturing process. In an alternate embodiment, the desired profile may be determined given the known wafer geographies and/or previous manufacturing processes. In another embodiment, the wafer, itself, may be examined to determine its specific profile. In yet another embodiment, the polish head motor current may be used to provide closed-loop feedback. The layers of a wafer with their varying material property also vary in the amount of energy required to polish them. As the polish head passes from one layer to a different layer, changes in the motor current can be detected. In one embodiment, reflectance/transmittance methods may be used to profile a wafer's surface. A polish pad may be equipped with one or more areas through which light may be transmitted to detect a wafer's surface during a polishing process. It should be noted that no particular feedback system or configuration is critical to the practice of the present invention.
One skilled in the art will recognize that the electromagnetic fields generated by the electromagnets need not be held constant during the entire CMP process. Rather, the fields may be changed during the process to adjust the rates of polishing during the CMP process. It should also be noted that although each zone is capable of generating an electromagnetic field of different magnitude and polarity than the other zones, two or more zones may be set to generate electromagnetic fields of the same magnitude and polarity. One skilled in the art will recognize factors to consider regarding changes to the electromagnetic field include, but may not be limited to, the strength of polarity of slurry component, the size of polish head, the polish head pressure on the substrate, the rate at which the polish head rotates, and the slurry flow rate.
FIG. 7 depicts a flow chart illustrating an embodiment of a method according to the present invention. A wafer or substrate is placed 710 onto an embodiment of an electromagnetic polish head 100. Electromagnetic polish head 100 may possess one or more electromagnets for generating electromagnetic fields. A slurry 103 with at least one component that is affected by an electromagnetic field is applied 720 between the polishing pad 104 and the substrate 102. At least one electromagnetic field may be generated 730 in at least one zone in the polish head 100 to attract or repel the slurry 103 to a portion of the substrate 102. Due to the attraction or repulsion of the slurry by the electromagnetic polish head 100, slurry 130 may mechanically and/or chemically polish more or less of a portion of the wafer.
In an embodiment, two or more electromagnetic fields may be generated. It should be noted that these fields may be generated at the same time or at different times during the CMP process. In another embodiment, one or more of the field's magnitude, polarity, or magnitude and polarity may be varied or adjusted 740 during the CMP process. Accordingly, the CMP process may be adjusted to customize the distribution of the slurry to match the changing wafer profile.
The above description is included to illustrate embodiments of the present invention and is not meant to limit the scope of the invention. The scope of the invention is to be limited only by the following claims. From the above discussion, many variations will be apparent to one skilled in the art that would yet be encompassed by the scope of the present invention.

Claims

1. A polish head for polishing a substrate comprising:

a carrier head for holding the substrate during polishing; and

an electromagnet within the carrier head for affecting a slurry's distribution across at least a portion of the substrate's surface during polishing with a Polish pad.

2. The polish head of claim 1 wherein an electromagnetic field generated by the electromagnet affects the rate of polishing on at least a portion of the substrate by attracting said slurry to said portion of the substrate.

3. The polish head of claim 1 wherein an electromagnetic field generated by the electromagnet affects the rate of polishing on at least a portion of the substrate by repelling said slurry from said portion of the substrate.

4. The polish head of claim 1 wherein an electromagnetic field generated by the electromagnet is varied during polishing.

5. The polish head of claim 1 further comprising at least one additional electromagnet.

6. The polish head of claim 5 wherein electromagnetic fields generated by the electromagnets affect the rate of polishing on at least a portion of the substrate by attracting said slurry to said portion of the substrate.

7. The polish head of claim 5 wherein at least one of the electromagnets generates an electromagnetic field that is varied during polishing.

8. The polish head of claim 5 wherein the carrier head rotates during polishing.

9. A method for affecting the polishing rate on at least a portion of a substrate comprising:

using a slurry with at least one component capable of being affected by a electromagnetic field;

placing the substrate on a polish head comprising an electromagnet;

using the electromagnet to generate an electromagnetic field to affect the slurry's distribution across at least a portion of the substrate's surface while polishing with a polish pad.

10. The method of claim 9 further comprising a step of using a feedback system to determine an adjustment to the electromagnetic field.

11. The method of claim 10 wherein the feedback system is an open-loop feedback system.

12. The method of claim 11 wherein the step of using the open-loop feedback system comprises obtaining a substrate profile.

13. The method of claim 12 wherein the substrate profile is determined from measuring the profile of a sample substrate.

14. The method of claim 10 wherein the feedback system is a closed-loop feedback system.

15. The method of claim 14 wherein the step of using the closed-loop feedback system comprises obtaining a substrate profile using reflectance/transmittance measurements.

16. The method of claim 14 wherein the step of using the closed-loop feedback system comprises using the polish head's motor current to determine the adjustment to the electromagnetic field.

17. The method of claim 9 wherein the slurry comprises at least one iron, nickel, or cobalt component.

18. The method of claim 9 further comprising the step of generating at least two electromagnetic fields.

19. A slurry for use with a polish head and polish pad for polishing a substrate, said polish head comprising a carrier head for holding the substrate during polishing and an electromagnet within the carrier head that generates an electromagnetic field, the slurry comprising at least one polarizeable component that is affected by the electromagnetic field generated by the electromagnet wherein the slurry's distribution across at least a portion of a substrate's surface may be affected to be non-uniform during polishing.

20. The slurry of claim 19 wherein the polarizeable component is selected from a group comprising a ferromagnetic component, a paramagnetic component and both ferromagnetic and paramagnetic components.