WO1996020498A1

WO1996020498A1 - Oxide film, formation method thereof, and semiconductor device

Info

Publication number: WO1996020498A1
Application number: PCT/JP1995/002730
Authority: WO
Inventors: Tadahiro Ohmi
Original assignee: Tadahiro Ohmi
Priority date: 1994-12-27
Filing date: 1995-12-27
Publication date: 1996-07-04
Also published as: JP3669728B2; JPH08181137A

Abstract

A method of forming an oxide film having high dielectric strength on a clean silicon wafer surface free from organic contamination. This method is applicable to manufacture of a semiconductor device having high integration density and high performance. The formation method comprises the steps of supplying ozonized ultrahigh-purity water to a rotating substrate so as to remove organic matters from the substrate, bringing the oxide film generated in the preceding step into contact with hydrofluoric acid to separate it, and bringing the substrate into contact with ozonized ultrahigh-purity water to form an oxide film.

Description

Description Oxide film and method for forming the same, and semiconductor device

The present invention relates to an oxide film, a method for forming the same, and a semiconductor device. More particularly, the present invention relates to a method for removing an organic impurity attached to a semiconductor substrate or the like and forming an oxide film having excellent characteristics such as extremely high withstand voltage. Background art

The background art will be described using a silicon wafer as an example of a base.

Cleaning of silicon wafers in the semiconductor manufacturing process is one of the most important steps in the semiconductor production process. That is, a large number of various impurities are attached to a silicon wafer, and removal of these impurities is indispensable for manufacturing a device having stable characteristics with a high yield. In particular, as semiconductor devices become more highly integrated and have higher performance, the devices are becoming finer and the wafer size is becoming larger.

As a method for removing these impurities, there are various chemical solutions and washing.

The inventor of the present invention has conducted a series of studies on the relationship between the cleaning method and the device manufactured thereafter, and in the course of conducting a series of studies, it has been impossible to completely remove organic impurities on the substrate by the conventional cleaning method. We saw that it had a large effect on the dielectric strength of the oxide film. For example currently commonly used for the removal of organic _{_{impurities, H 2 S 0 4 + H}} 9 0. + Ultra pure water cleaning, NH ₄ OH + H _n 0 ₂ + Ultra pure water cleaning, HC 1 + H ₂ 〇 ₂ + Ultra pure water cleaning, etc. It has been found that a cleaning method that can completely remove organic substances is necessary for formation.

On the other hand, in the conventional cleaning method, a separate cleaning device or cleaning tank is used for each chemical solution, and the silicon wafer is immersed in the cleaning tank in which each chemical solution and ultrapure water are stored sequentially. Inevitably, the residual chemical solution is brought into the wafer in the process, and there is a problem that the chemical solution in the cleaning tank is cross-contaminated. In addition, transporting between cleaning tanks transports them into the atmosphere, which results in organic contamination from the air and formation of natural oxide films. Furthermore, since the contaminated chemical solution is used more than once and a plurality of silicon wafers are washed at the same time, there is a problem that impurities released from one silicon wafer adhere to other silicon wafers.

Furthermore, since these chemicals are used in a large amount, there is a problem of waste liquid treatment and the like, and because of high temperature treatment, operability is poor and a load on a clean room is increased.

The present invention solves the above problems, and provides an oxide film having excellent performance such as withstand voltage on a clean silicon wafer surface free from organic contamination, and a method for forming the oxide film. It is intended to provide a device. Disclosure of the invention

The method for forming an oxide film according to the present invention comprises the steps of: removing an organic substance attached to a substrate by supplying ultrapure water containing ozone to the substrate while rotating the substrate in an inert gas atmosphere; An oxide film removing step of contacting the oxide film generated in the organic substance removing step with hydrofluoric acid to remove the oxide film, and then contacting the ozone-containing ultrapure water to form an oxide film. , At least.

In the oxide film forming step, it is preferable to supply the ultrapure water containing ozone while rotating the substrate.

The concentration of ozone in the ultrapure water is preferably 2 ppm to 10 ppm, and the concentration of organic impurities in the inert gas is preferably 1 ppm or less.

The rotation speed of the substrate is preferably set to 100 to 300 rpm, and the supply amount of the ozone-containing ultrapure water is preferably set to 100 to 500 cc Zmin. No.

The oxide film of the present invention is an oxide film formed on the surface of a substrate in a liquid phase. The interface between the substrate and the oxide film and the organic matter in the oxide film have a number of CH ₂ groups of _{2 in} terms of arachidic acid. X 10 ¹⁴ cm— ² or less.

The semiconductor device of the present invention has an oxide film formed by a thermal oxidation method or an ion-assisted oxidation method after forming an oxide film by the above-described oxide film forming method. I do. Action

Hereinafter, the operation of the present invention will be described together with embodiments.

The method of forming an oxide film according to the present invention is performed in an inert gas atmosphere, and includes at least a step of washing and removing organic impurities with ozone-added ultrapure water, a step of removing an oxide film with HF + ultrapure water, and an oxidation with ozone-added ultrapure water. A film forming step.

That is, in the organic impurity removing step, the ozone-added ultrapure water is supplied to the substrate surface while rotating the substrate, and the organic matter on the surface is oxidized by the ozone-added ultrapure water. At this time, an oxide film is simultaneously formed on the substrate surface. Then rinse with ultrapure water (or ultrapure water with ozone added) to wash away impurities.

In the oxide film stripping process, the oxide film formed on the surface

(Approximately 0.1% to 1%), peel off, rinse with ultrapure water and wash away chemicals and impurities.

In the oxide film forming step, an oxide film is formed by bringing a clean substrate surface from which organic impurities have been removed into contact with ozone-added ultrapure water. The thickness of this oxide film is preferably from 0.3 to 1.0 nm.

In the oxide film removing step and the oxide film forming step, the substrate may be immersed in each chemical solution, but it is preferable to perform the treatment by supplying the chemical solution while rotating the substrate. As a result, the substrate is always in contact with a fresh chemical solution, and the processing proceeds uniformly within the surface of the substrate, so that an oxide film having higher insulating properties can be formed. It is preferable that the rotation speed of the substrate is controlled to an optimum rotation speed for each step.

Finally, the substrate is spun dry to complete the process. So far, all steps are preferably performed continuously in a single vessel.

The factors affecting the quality of the oxide film will be described below individually.

(Inert gas atmosphere)

In the present invention, it is preferable to keep the inert gas flowing downflow in the closed vessel. By using an inert gas atmosphere, it is possible to prevent the substrate surface from being exposed to impurity components, and to prevent adhesion of organic substances and formation of a natural oxide film. If a natural oxide film is formed after the oxide film stripping step, the oxide film formed by the ozone-added ultrapure water and the subsequent heat treatment becomes non-uniform, so that the insulating properties deteriorate. In addition, when a natural oxide film is formed, minute roughness of the surface increases, and the quality of the oxide film formed by ozone-added ultrapure water and subsequent heat treatment is degraded. Therefore, it is desirable to minimize the formation of a natural oxide film.

In the formation of a natural oxide film, the presence of water alone does not cause the formation of a natural oxide film due to the presence of oxygen alone, and both water and oxygen are generated in parallel. Therefore, if the atmosphere is an inert gas atmosphere, formation of a natural oxide film can be prevented. From this viewpoint, the content of oxygen in the inert gas is preferably 1 O ppb or less, more preferably 10 ppb or less, and most preferably 1 ppb or less. Further, the amount of organic impurities in the gas is preferably 1 ppb or less, more preferably 1 O ppt or less, and most preferably 1 ppt or less. Nitrogen gas is preferred as such an inert gas.

Further, it is preferable to introduce a gas so that the pressure in the closed vessel becomes higher than the external pressure. When the pressure in the closed tank is made higher than that of the outside, it is possible to prevent the air from leaking into the closed tank, and it is possible to more effectively prevent the adhesion of organic substances and the formation of a natural oxide film.

The introduction of the inert gas into the closed tank is preferably performed in a downflow manner. In the case of the down flow, the product detached from the surface falls down along the flow of the gas, so that re-adhesion to the substrate can be prevented, so that cleaning with higher cleanliness can be performed.

The inert gas preferably has a flow rate that does not disturb the chemical solution layer formed on the surface of the substrate.

(Ultra pure water containing ozone)

When used in the organic matter removal step, the concentration of ozone in the ozone-added ultrapure water is preferably 2 ppm to 10 ppm. If it is less than 2 ppm, the oxidation of organic substances may be insufficient.If it exceeds 1 O ppm, the thickness of the oxide film formed on the substrate surface will be too thick, and it will take time to remove it and increase the surface roughness. This is because in some cases, When used in the oxide film forming step, the concentration of ozone in the ozone-added ultrapure water is preferably 2 ppm to 1 O ppm. Within this range, an oxide film with a high withstand voltage can be obtained, and the maximum injected charge Q _BD increases even in the TDDB characteristics of the oxide film under constant current stress.

The ozone-added ultrapure water can be obtained by, for example, electrolyzing ultrapure water. In order to minimize the decrease in concentration due to the decomposition of ozone, it is preferable to manufacture it near the use point.

(Supply of chemical solution such as ultrapure water containing ozone and substrate rotation)

In the present invention, the supply of a chemical solution or ultrapure water is not discontinuous in order to supply a chemical solution or the like while rotating the substrate, and to efficiently and uniformly remove organic substances, remove an oxide film, and form an oxide film. It is preferable to perform the operation continuously as a fluid. In other words, it is important to supply the chemical solution or ultrapure water continuously, not absolutely, in a state where it comes out of the water tap.

The reason for this is not clear, but for example, in the case of organic matter removal, the following may be considered. That is, when the chemical solution is supplied to the surface of the base by continuous supply of the chemical solution, the chemical solution spreads in the radial direction due to centrifugal force and covers the surface, and reacts with the surface contamination source to form a reaction. Generate things. The reaction product is immediately removed from the surface together with the drug solution by centrifugal force, exposing a new surface. On the other hand, since the chemical is supplied continuously, the freshly exposed substrate surface reacts with the fresh chemical. As described above, it is considered that the cleaning can be performed with excellent cleanliness because the new surface is constantly in contact with the new chemical solution. On the other hand, in the case of injection supply, the chemical is supplied in the form of a spray, so that the surface of the substrate is not evenly covered. Therefore, it is presumed that high cleanliness and cleaning cannot be achieved.

As a nozzle for producing the above continuous flow, it is preferable to use a straight pipe type having a uniform inner diameter up to the liquid outlet. And it is preferable to arrange so that the surface of the liquid outlet is horizontal to the substrate. If such a nozzle is used, the chemical solution or ultrapure water flowing out of the outlet will fall directly below the outlet as a continuous fluid, and the drop point will be the center of rotation of the substrate, The dropped chemical solution spreads uniformly in the plane due to centrifugal force, so it is possible to perform uniform cleaning in the plane. In other words, the outlet is restricted In such a case, the chemical solution discharged from the liquid discharge surface becomes a mist and cannot supply a continuous fluid. In addition, when the liquid discharge surface is not horizontal, the amount of the chemical liquid differs from the liquid discharge port, or the chemical liquid does not drop directly below the liquid discharge port, so that it is impossible to supply the liquid uniformly over the surface.

In addition, it is preferable that the supply position of the chemical solution be the center of rotation of the substrate from the viewpoint of further improving in-plane uniformity.

In the present invention, a plurality of chemical solution washing steps may be appropriately performed in addition to the above steps. In this case, since the transfer can be performed in the same tank, it is possible to prevent the adhesion of organic substances, the formation of a natural oxide film, the adhesion of particles, and the like by contact with the air during the transfer of the substrate. In the present invention, the number of rotations of the substrate is an important factor for the degree of cleanliness and the uniformity of the oxide film, and is preferably 100 to 300 rpm, and preferably 250 to 300 rpm. More preferably, it is set to pm.

If it is less than 100 rpm, if the amount of the chemical solution is small, the entire surface cannot be covered with the chemical solution, which may result in the generation of a dry portion, which may lead to a decrease in cleaning, peeling and oxide film formation efficiency. In addition, when the amount of the chemical is large, the chemical may overflow from the surface with a feeling of overflow before spreading due to centrifugal force. Therefore, it is difficult to control the supply amount of the chemical solution to an optimum amount below l O O rpm.

If it exceeds 3 000 rpm, a part of the chemical liquid becomes mist-like, and this mist-like chemical collides with the inner wall of the tank and re-adheres to the surface of the substrate, contaminating the surface that has been thoroughly cleaned. Sometimes.

The supply amount of the chemical is preferably from 100 m1 / min to 500 m1Zmin, more preferably from 300 ml / min to 500 ml / min. Since the treatment itself is completed in a short time, the amount of chemical used even at a large flow rate is greatly reduced compared to the conventional method.

(Immersion process)

In the present invention, it is preferable to perform water spraying at a rotation speed of the substrate of 100 to 400 rpm before performing the chemical treatment. Although the supply amount of ultrapure water varies depending on the surface area of the substrate, in the case of a wafer having a diameter of 3 inches to 8 inches, 2.5 to 10 cc of ultrapure water is applied to the surface of the substrate. Preferably it is supplied.

In other words, pure water cannot be completely covered on the surface if it is less than 2.5 cc, and if it exceeds 10 cc, only a part of ultrapure water flows and one If a channel is formed and the chemical solution is subsequently supplied, the chemical solution will flow preferentially through the flow channel and uniform cleaning will not be possible.

On the other hand, if the rotation speed is less than 100 rpm, it may not be possible to cover the entire surface with water. That is, a drying part may be partially generated. On the other hand, if the rotation speed exceeds 400 rpm, a part of the water striking layer formed on the surface may be destroyed. May be confused.

(Backside cleaning)

It is preferable to supply the chemical solution to the front surface of the substrate and to spray and supply the chemical solution to the back surface. This is because the chemical solution may flow around from the surface of the substrate, and the cleaning of the back surface may be uneven.

(Inner wall cleaning)

In the case of rotary cleaning, the chemical solution is scattered from the surface by centrifugal force, and the scattered chemical solution adheres to the inner wall of the cleaning tank, and the chemical solution attached to the inner wall may separate from the inner wall and re-attach to the substrate surface. Therefore, during the chemical solution cleaning step and the ultrapure water cleaning step, it is preferable to always wash the inner wall surface of the tank with ultrapure water and to wash out the adhered chemical liquid from the inner wall surface in order to perform highly clean cleaning. As a result, secondary contamination of the substrate by the contaminated chemical solution is prevented, and a clean substrate surface is obtained. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view of an apparatus suitable for forming an oxide film according to the present invention.

FIG. 2 is a graph showing the residual amount of organic impurities after washing.

FIG. 3 is a graph showing the effect of removing the surfactant.

FIG. 4 is a graph showing the change in the amount of organic impurities attached when left in a clean room.

(Explanation of code)

1 Closed tank body,

2 lids,

3 A nozzle rack that bundles multiple chemical supply nozzles, 4 Backside cleaning nozzle,

5 rotating wafer holder,

6 rotating motor,

7 Inert gas inlet,

8 Waste liquid outlet,

9 Silicon wafer. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, examples of the present invention will be described.

(Example 1)

FIG. 1 shows an oxide film forming apparatus used in this example. In FIG. 1, 1 is a closed tank body, 2 is a lid, 3 is a nozzle rack in which a plurality of chemical solution supply nozzles are bundled, 4 is a back surface cleaning nozzle, 5 is a rotating wafer holder, 6 is a rotating motor, and 7 is a non-rotating motor. The active gas inlet, 8 is a waste liquid outlet, and 9 is a silicon wafer.

Nitrogen gas (purity: 99.99999%) is introduced from the inert gas inlet 7 in FIG. 1, a 6-inch silicon wafer 15 is set on the wafer holder 4, and the lid 2 is closed. 2.5 to 10 cc ultrapure water was supplied from the first nozzle of the nozzle rack 3 to the surface of the nozzle, and rotated at 300 rpm to uniformly wet the surface of the nozzle. This improves wettability and smoothes other processes.

Subsequently, at a substrate rotation speed of 3000 rpm, ozone-added ultrapure water (2 ppm) was supplied from the second nozzle at 300 cc / min for 3 minutes to oxidize organic substances on the surface. After the formation of ozone, the ozone of the second nozzle was stopped, rinsed with ultrapure water, and ozone-added ultrapure water and impurities were washed and flown.

Next, at a substrate rotation speed of 3000 rpm, a 0.5% aqueous solution of hydrofluoric acid was supplied from the third nozzle at 300 cc Zmin for 2 minutes to remove the oxide film on the surface, and then from the first nozzle. Ultrapure water was supplied, and the chemicals and impurities were washed and flushed.

Next, at a substrate rotation speed of 3000 rpm, ozone-added ultrapure water was supplied from the second nozzle at 500 cc / min for 3 minutes to form an oxide film of 0.6 nm on the wafer surface. 6/20498

9

Finally, the wafer was dried by spinning at 3000 rpm.

During these steps, the same chemical solution as for the front surface cleaning was constantly supplied from the back surface cleaning nozzle 3 toward the back surface, and the back surface was also cleaned at the same time.

First, in order to compare the organic substance removing effect of the cleaning method of the present invention and the conventional cleaning method, after performing organic substance removal cleaning by various methods, the oxide film was peeled off with a 0.5% hydrofluoric acid aqueous solution. At this stage, the amount of organic substances adhering to the silicon surface was measured. The cleaning method was as follows: (1) Batch cleaning by immersion using ammonia-hydrogen peroxide ultrapure water (0.05: 1: 5) at 80-90 ° C; (2) 80-90. Batch cleaning by immersion using C hydrochloric acid hydrogen peroxide / ultra pure water (1: 1: 6), (3) Batch cleaning by immersion using hydrogen peroxide (30%) at 80-90 ° C, (4) Batch cleaning by immersion using sulfuric acid and hydrogen peroxide (4: 1) at 80 to 90 ° C, (5) Batch cleaning by immersion using ultrapure water with ozone (2 ppm), (6) Washing by spinning of this example was performed.

Figure 2 shows the ATR spectrum of the substrate surface after cleaning the silicon wafer by the above-mentioned cleaning method. Incidentally, the scale of the vertical axis in FIG. 2, the film Langmuir-Buroje' preparative method Arakijin cadmium or scan Teariruamin, band intensity on a monomolecular film on a silicon wafer obtained by forming various areas, CH ₂ stretching vibration And a calibration curve for the amount of adhesion was created, and the amount of organic impurities attached was determined from this. As is evident from Fig. 2, the organic substance removal effect of ozone-added ultrapure water has a superior cleaning effect compared to other chemicals, and the effect is further improved by spin cleaning, and the organic matter is completely removed. It can be seen that it can be removed. This indicates that ozone is excellent at removing organic matter, and that spin cleaning is performed in a clean nitrogen atmosphere, a fresh liquid is always supplied, and high-speed rotation of the wafer is required. It is considered that the removal effect is improved by centrifugal force and high-speed liquid flow.

Next, a similar test was performed on a wafer intentionally contaminated by attaching three kinds of surfactants to the wafer. The results are shown in Figure 3. In FIG. 3, each of the ATRs was immersed in an aqueous solution of (a) a cationic, (b) anionic, and (c) a nonionic surfactant, and washed with each method. It is a spectrum. The numbers (4) to (6) in the figure correspond to the numbers of the cleaning method in FIG. As shown in FIG. 3, it can be seen that the cleaning of this example has an excellent effect even on organic impurities such as a surfactant.

Then, after forming an oxide film of 0.5 to 0.7 nm using the above ozone-added ultrapure water and a conventional chemical solution (chemical solutions corresponding to (1) to (5) in Fig. 2), an oxidation furnace at 1000 ° C was used. Then, an oxide film was grown to 4.8 to 5.3 nm. Thereafter, to prepare a MOS Daiodo provided 1 x 10- ⁴ A 1 electrode cm ^2, was boss measure the respective withstand voltage. Table 1 shows the results. Incidentally, the average dielectric strength of Table 1, the voltage value in which a current flows 1 X 10- ⁴ A, 100 pieces of MOS Daio 10 Ah shows the average value of the _de-0

(table 1)

1 Oxide film formation method 1 (1) (2) (3) (4) (5) (6)

1 Average dielectric strength 1 11.3 10.4 12.0 12.2 12.5 14.8

1 (MV / cm) As shown in Table 1, it can be seen that the gate oxide film (6) of this example has an extremely high withstand voltage. Also, from the relationship with FIG. 2, it can be seen that the influence of the residual organic impurities on the wafer greatly affects the deterioration of the withstand voltage of the gate oxide film formed after the contamination.

Also, from the measurement of the TDDB characteristics under a constant stress current, it was found that the maximum injected charge Q _BD was the largest for the gate oxide film (6) of the present example.

(Example 2)

In this example, an oxide film was formed in a liquid in the same manner as in Example 1, and then the oxide film was formed at a low substrate temperature of 450 ° C in a plasma of a mixed gas of Ar and oxygen gas (300: 8). A gate oxide film (7 nm) was grown by an argon ion-assisted oxidation method for growing a GaN film, and a MOS diode was fabricated in the same manner as in Example 1. A bias was applied so that the energy of 7 Lugon ions was 9 eV. A conventional MOS diode was fabricated in the same manner. Table 2 shows the breakdown voltage of the gate oxide film of the fabricated MOS diode. The numbers of the chemicals correspond to those in Table 1, and for reference, the oxide film formed directly by the ion assist acid method without forming an oxide film in the solution is shown as (Reference Example).

(Table 2)

1

1 Oxide film formation method 1 (4) (5) (6) 1 Reference example 1

1

1 Average dielectric strength 1 6. 3 1 8. 1 10. 5 1 4. 9 1

1 (MY / cm)

1 As is evident from Table 2, the gate oxide film of this example has a high withstand voltage, despite the growth of the oxide film at a low temperature, and greatly improves the reliability of the ultra-thin oxide film. You. That is, according to the present invention, a low-temperature process of a semiconductor device can be realized.

Also, by comparison with the reference example, it is found that the breakdown voltage of the gate oxide film is improved by more than twice by forming the oxide film in the solution before the ion assisted oxidation. In the above example, after the oxide film was formed in the liquid, the wafer was set in the ion-assisted oxidizing apparatus by being transported through the N ₂ gas seal. This is to prevent organic impurities from adhering to the surface again by transporting in the air, as organic substances adhere to the surface just by leaving the wafer in the clean room as shown in Fig. 4. . Industrial applicability

According to the present invention, for example, the characteristics of an oxide film of a silicon wafer can be significantly improved, and an oxide film with high characteristics can be formed even in a low-temperature process, so that higher performance and higher performance can be achieved. An integrated semiconductor device can be realized. In addition, since it is not necessary to use sulfuric acid, hydrochloric acid, etc., it is easy to treat waste liquid, etc., and since the process is performed in a completely closed system, the danger of field workers can be reduced.

Claims

The scope of the claims

1. An organic substance removing step of removing organic substances attached to a substrate by supplying ultrapure water containing ozone to the substrate while rotating the substrate in an inert gas atmosphere; and an oxide film formed in the organic substance removing step. And an oxide film forming step of forming an oxide film by contacting with ultrapure water containing ozone thereafter. An oxide film forming method.

2. The oxide film forming method according to claim 1, wherein in the oxide film forming step, ultrapure water containing ozone is supplied while rotating the substrate.

3. The oxide film forming method according to claim 1, wherein the ozone concentration in the ultrapure water is 2 ppm to 10 ppm.

4. The method for forming an oxide film according to claim 1, wherein the number of rotations of the substrate is 100 to 3000 rpm.

5. The method for forming an oxide film according to claim 1, wherein the supply amount of the ultrapure water containing ozone is 100 to 500 ccZmin.

6. The method according to claim 1, wherein the concentration of organic impurities in the inert gas is 1 ppb or less.

7. The method for forming an oxide film according to claim 1, wherein the inert gas is caused to flow in a down flow from above the substrate.

8. The oxide film forming method according to claim 1, wherein the thickness of the oxide film formed in the oxide film forming step is 0.3 to 1. O nm. .

A 9. oxide film formed on the substrate surface in a liquid phase, organic matter amount of the surface及beauty oxide film between said substrate and the oxide film, number 2 X 1 CH ₂ group in Arakijin acid force Domiumu terms 0 ¹⁴ cm—An oxide film characterized by being ² or less.

10. A semiconductor having an oxide film formed by a thermal oxidation method or an ion-assisted oxidation method after forming an oxide film by the oxide film forming method according to any one of claims 1 to 8. apparatus.

11. The semiconductor device according to claim 10, wherein a substrate temperature in the ion-assisted oxidation method is 400 to 450 ° C.

12. The semiconductor device according to claim 10, wherein the grown oxide film has a thickness of 3 to 1 Onm.