JPH0878375A - Silicon carbide-made jig cleaning method - Google Patents

Abstract

PURPOSE: To provide a method of cleaning silicon carbide-made jigs used for making semiconductors. CONSTITUTION: Silicon carbide-made jigs having high-purity silicon carbide surface coats for making semiconductors (e.g. high temp. jigs, boats, susceptors etc. for chemical vapor deposition apparatus) are dipped in a hydrochlorate nitrate water soln. or nitrate hydrofluoride water soln. of 10vol.% or more for 30min or more. An ultrasonic wave applied at the same time will be more effective. This melts metal grains deposited on the surface of the jigs away from it, without damaging the silicon carbide coats whereby pin holes of the coats can be avoided and the repeat number of the reuse of the jigs can be greatly increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning a jig made of silicon carbide used in manufacturing a semiconductor.

[0002]

2. Description of the Related Art In a semiconductor manufacturing process, for example,
High temperature jigs such as vapor phase growth equipment, boats that are heating tables,
The susceptor is used in a high temperature and highly corrosive atmosphere. These jigs are made of graphite or the like as a base material, and their surfaces are coated with high-purity silicon carbide (SiC) so that the products are not contaminated by impurities from the base material.

The situation of using such a jig will be described by taking a susceptor as an example.

In the manufacture of semiconductor devices, there is a step of forming a thin film on the surface of a wafer by supplying a reactive gas onto a wafer placed in a container which is shielded from the outside by using a vapor phase growth apparatus. FIG. 1 is a schematic vertical sectional view of an example of such a vapor phase growth apparatus. The vapor phase growth apparatus 30 is isolated from the outside by a quartz chamber 31 and a chamber base 32, and a substantially cylindrical support stand 33 is rotatably arranged in the center of the chamber. The susceptor 20 is attached to the upper surface of the support table 33, and a plurality of wafer accommodating portions 21 are provided on the upper surface of the susceptor 20 and a wafer 27 is placed thereon.

An opening 22 is formed at the center of the susceptor 20, and a nozzle 34 is connected to the upper part of the support base 33 through the opening 22. Nozzle 34 has multiple nozzle holes
34a is provided, and the source gas introduced into the hollow portion 33a of the support table 33 is supplied from the nozzle holes 34a substantially parallel to the surface of the wafer 27. A source gas discharge port 35 is attached to the chamber base 32. Further, below the susceptor 20, a heater 36 for inductively heating the susceptor 20 to about 1000 ° C. is arranged.

2A and 2B are enlarged views of the susceptor 20. FIG. 2A is a plan view and FIG. 2B is a sectional view taken along line XX of FIG. Base 23
Is made of an isotropic graphite material, and has, for example, a disk shape with a diameter of about 700 mm and a thickness of about 20 mm, an opening 22 is provided at the center thereof, and a rounded portion 23a is provided on the periphery of the opening 22 and the base 23. Are formed. On the upper surface 24 of the base 23, there are provided a plurality of circular counterbore-shaped wafer accommodating portions 21 each having a diameter slightly larger than the diameter of the wafer 27 and having a depth substantially equal to the thickness of the wafer 27.

Further, a base upper surface 24 including the wafer accommodating portion 21
The lower surface 25 of the base and the lower surface 25 of the base are the wafer 27 and the vapor phase growth apparatus due to release of impurities in the base 23 when forming a thin film on the wafer 27.
Silicon carbide coatings 26a, 26b to prevent contamination within 30
Is completely coated with. Note that the silicon carbide coating
26a and 26b are formed to have the same thickness of about 200 μm or less by the CVD method or the like.

The above vapor phase growth apparatus is used to epitaxially grow a Si thin film on, for example, a Si wafer. When the characteristics of the object to be treated (Si wafer in this case) deteriorate due to repeated use of the susceptor. was there. In this process, after the processed Si wafer is collected, in order to remove Si generated in a portion of the susceptor 20 other than the wafer accommodating portion 21, an etching process of exposing the susceptor 20 to a hydrochloric acid (HCl) atmosphere at 1000 to 1200 ° C. is performed. However, the repetition of such etching treatment causes defects called pinholes in the silicon carbide film, and impurities from the base material contaminate the wafer and the inside of the vapor phase growth apparatus, leading to deterioration of the wafer characteristics. It is thought to be due to.

Therefore, the use of the jig (susceptor) must be stopped when a certain number of pinholes are generated in the silicon carbide coating, which reduces the number of times the jig is used and the production due to the replacement of the jig. Lower efficiency and higher costs have been issues.

In order to solve this problem, some proposals have hitherto been made. For example, in Japanese Patent Laid-Open No. 61-268029, the cause of cracks and pinholes on the SiC (silicon carbide) coating surface is due to the coefficient of thermal expansion of the substrate.
Assuming that the SiC coating layer has a large coefficient of thermal expansion and is caused by fatigue of SiC due to repeated thermal stress, a jig that eliminates the difference in coefficient of thermal expansion between the film and the substrate by adjusting the Si / C ratio in SiC It is disclosed.

Further, in JP-A-60-96590, it is stated that the deterioration of the characteristics of the processed wafer is caused by the contamination by impurities diffused from the substrate through the SiC (silicon carbide) coating layer. There is disclosed a technique for suppressing the diffusion of impurities and preventing the performance deterioration of a wafer by defining the amount of grain boundaries of SiC and the form thereof.

However, when the above-mentioned proposed jig is used, even if it is effective at first, pinholes are generated with repeated use, and once pinholes are generated, no matter how diffusion of impurities is suppressed, contamination will occur. Can't be prevented.

[0013]

SUMMARY OF THE INVENTION The present invention solves the above problems and can effectively prevent the generation of pinholes in a silicon carbide coating, increasing the number of times a jig is used to improve production efficiency. The object of the present invention is to provide a jig made of silicon carbide capable of reducing the cost, and more specifically, to provide a jig cleaning method which meets such an object.

[0014]

Means for Solving the Problems While carrying out various investigations to solve the above-mentioned problems, the present inventors found that trace amounts of Mo and W adhered to the pinholes generated in the susceptor that was used less frequently. I found it.

In addition, other metal elements (Cr, Ni, Co and
When the erosion effect of these metal elements including Fe) on the silicon carbide coating film during the etching treatment under the above-mentioned high temperature HCl atmosphere was examined, all of the above metal elements have the effect of promoting the erosion. In the case of Mo and W, it acts so as to cause pitting corrosion at the adhesion position of metal particles, and in the case of Ni, Co and Fe, it erodes the entire area including the adhesion part of metal particles. It turned out that Cr and Cr have both erosive effects.

As a result of elemental analysis of the eroded portion, it was confirmed that Mo and W attached to the surface of the jig tend to remain in that portion. This is considered to be due to the high resistance to hydrochloric acid (HCl) of Mo and W. Therefore, it remains on the surface of the jig despite repeated etching,
It is presumed that this is the main cause of pitting corrosion of the silicon carbide coating due to a catalytic action and the like, thereby generating pinholes in the silicon carbide coating.

Since the silicon carbide coating of the susceptor is usually formed by the CVD method or the like, the impurity concentration is on the order of ppm or less, and the above metal elements are not detected. Further, there is little possibility that these metal particles will adhere during the coating of the silicon carbide coating. Therefore, the metal element that causes the pinhole is metal particles (for example, suspended particles in the atmosphere) attached on the jig after the silicon carbide coating is formed, and the abnormal corrosion caused by the metal particles progresses. Is considered to be the cause of pinholes.

Therefore, the present inventor does not generate pinholes if the metal particles attached to the silicon carbide coating are removed,
Based on the idea that it is possible to extend the life of the silicon carbide jig, various investigations were carried out on the method of removing the adhered metal particles, and as a result, it was possible to sufficiently remove it by a simple operation of dipping in a specific acid. It was confirmed.

The gist of the present invention is that "a jig for manufacturing a semiconductor having a high-purity silicon carbide coating on the surface of each is 10% by volume.
The above method for cleaning a jig made of silicon carbide is characterized in that it is immersed in the aqueous nitric acid chloride solution or the aqueous nitric acid solution for 30 minutes or more.

Here, the nitric acid-hydrochloric acid aqueous solution is an aqueous solution obtained by mixing nitric acid and hydrochloric acid, and the hydrofluoric nitric acid aqueous solution is an aqueous solution obtained by mixing hydrofluoric acid and nitric acid. As will be described later, it is not always necessary to mix nitric acid and hydrochloric acid or hydrofluoric acid and nitric acid in equal amounts.

[0021]

The method of removing the metal particles adhered to the silicon carbide coating can be roughly classified into two methods: a method of treating in a gas phase (gas etching) and a method of cleaning in a liquid phase. Of these, the gas etching is described above.
A typical method is an etching process in which it is exposed to a hydrochloric acid (HCl) atmosphere at a high temperature.
Etc. have a high corrosion resistance by themselves, and are considered to have a catalytic action against the erosion of the silicon carbide coating, and it is impossible to remove only the metal particles without damaging the silicon carbide coating. there were.

Therefore, regarding the cleaning method in the liquid phase, first, pure water is used as a cleaning liquid, and the cleaning water is sprayed on the object to be cleaned in a shower for 1 hour to perform cleaning, and an ultrasonic cleaning apparatus is used. A method of cleaning an object to be cleaned for 1 hour while applying ultrasonic waves was examined. The item to be cleaned is
A graphite film is coated with a SiC film and SUS316 is coated on the surface.
Particles (average particle size 200 μm) are attached.

As a result, no matter whether the above method or the above method was used, residual metal particles were observed on the surface after washing, and an erosion test was carried out in which the particles were kept in a hydrochloric acid (HCl) atmosphere at 1100 ° C. for 1 hour. After a while, a pinhole occurred.
Moreover, the addition of a surfactant to the cleaning solution did not change the above results. This is a few μ on the surface of the silicon carbide coating.
It is considered that there are irregularities of m to several tens of μm, and once metal particles adhere to such a surface, it is difficult to completely remove them by only physical cleaning.

On the other hand, when an acid is used as a cleaning liquid, a cleaning effect is obtained, and particularly when an aqueous solution of nitric acid hydrochloric acid or an aqueous solution of hydrofluoric nitric acid is used and the object to be cleaned is immersed therein, a remarkable effect is recognized.

By using such a mixed acid, only the metal particles attached to the surface can be removed and washed. The surface is not physically washed, but the acid is attached. It is considered that this is due to the cleaning effect based on the chemical reaction in which the metal particles themselves are subjected to the etching action. The silicon carbide coating is highly resistant to these mixed acids and is not easily damaged.

The mixing ratio of each acid constituting the mixed acid is not particularly limited, and any mixture of nitric acid and hydrochloric acid, or hydrofluoric acid and nitric acid may be used, but in order to sufficiently bring out the effect. Is 1: 1 to 1: 5 nitric acid: hydrochloric acid in a nitric acid hydrochloric acid aqueous solution, and 1: 1 to 1: 3 hydrofluoric acid: nitric acid in a hydrofluoric nitric acid aqueous solution (both in volume ratio). Preferably.

When a nitric acid / hydrochloric acid aqueous solution is used, its concentration is
If it is less than 10% by volume (hereinafter simply referred to as “%”), a sufficient effect cannot be obtained, so the amount is made 10% or more. The upper limit of the concentration is not particularly defined, but if it is excessively high, the life of the silicon carbide coating is shortened, so it is preferable to set it to about 70%.

The temperature of the nitric acid / hydrochloric acid aqueous solution is preferably 70 ° C. or lower in order to prevent damage to the silicon carbide film.

The reason why the immersion time in the nitric acid / hydrochloric acid aqueous solution is 30 minutes or more is that metal particles may remain if the time is shorter than this. If ultrasonic vibration is applied at the same time during the immersion treatment, the immersion time can be shortened by about 20%.

When an aqueous solution of hydrofluoric nitric acid is used, its concentration is 10% or more, as in the case of the aqueous solution of nitric acid and hydrochloric acid. Ten%
If it is less than the above, the cleaning effect is not sufficient. Although the upper limit of the concentration is not particularly specified, for the same reason as in the case of the above nitric acid hydrochloric acid aqueous solution,
It is preferably about 50%.

The temperature of the aqueous solution of hydrofluoric nitric acid is 50 ° C. or lower for the same reason as in the case of the aqueous solution of nitric acid chloride.

Also, the immersion time is set to 30 minutes or more as in the case of the nitric acid / hydrochloric acid aqueous solution. If it is less than 30 minutes, the cleaning may be insufficient. The immersion time can be shortened by applying ultrasonic vibration at the same time as in the case of the nitric acid / hydrochloric acid aqueous solution.

[0033]

Example 1 A high-purity graphite material having a size of 100 mm × 100 mm and a thickness of 5 mm and a silicon carbide coating film having a thickness of 150 μm formed on the surface thereof by a CVD method was used as a test piece, and SUS316 having an average particle diameter of 200 μm was used.
The particles were dispersed in alcohol and added dropwise to the surface of the test piece, and the metal particles were attached to the surface of the test piece by the method of evaporating the alcohol.

When this test piece was immersed in a 50% nitric acid hydrochloric acid aqueous solution (30 ° C.) for 30 minutes and the surface was analyzed by IPC-MASS, no metal element was detected.

In the vapor phase growth apparatus, Si was deposited on the surface of the test piece after the above immersion treatment, and then HCl at 1100 ° C.
The operation (process) of etching in the atmosphere was repeated 500 times, but no pinhole was generated.

[0036]

Example 2 A test piece on which a silicon carbide coating was formed was used in the same manner as in Example 1, and the surface of the test piece had an average particle size of 200 μm.
Particles of SUS316 were attached.

This test piece was ultrasonically washed in a 30% nitric acid hydrochloric acid aqueous solution (30 ° C.) for 40 minutes, and surface analysis was performed by IPC-MASS, but no metal element was detected.

As in the case of Example 1, deposition of Si and etching treatment were repeated 500 times on the surface of the test piece, but no pinhole was found.

[0039]

[Comparative Example 1] A test piece having a silicon carbide coating formed thereon was used in the same manner as in Example 1, and the surface of the test piece had an average particle size of 200 μm.
Particles of SUS316 were attached. The surface purity was analyzed by IPC-MASS. Fe, Ni, Cr and Mo were found to be 20
ng / cm ² , 5 ng / cm ² , 5 ng / cm ² and 1 ng / cm ² .

When the deposition of Si and the etching treatment were repeated 50 times on the surface of the test piece, a black spot-like discolored portion was generated on the surface of the SiC film. As a result of examining this portion by microscopic observation, pinholes were generated.

[0041]

[Comparative Example 2] A test piece having a silicon carbide coating formed thereon was used in the same manner as in Example 1, and the surface of the test piece had an average particle size of 200 μm.
Particles of SUS316 were attached.

Pure water was sprayed onto this test piece in the form of a shower to wash for 1 hour, and the surface was analyzed for purity by IPC-MASS. Fe, Ni, Cr and Mo were each 10 ng / cm 2.
^2, 3ng / cm ^2, it was 3 ng / cm ² and 1 ng / cm ^2.

When Si deposition and etching treatment were repeated 50 times on the surface of the test piece, black spot-like discolored portions were generated on the surface of the SiC film as in Comparative Example 1, and microscopic observation results were obtained. , A pinhole was generated.

[0044]

According to the method of the present invention, the metal particles attached to the surface of the jig made of silicon carbide can be dissolved and removed without damaging the silicon carbide coating. As a result, it is possible to prevent the occurrence of pinholes, significantly increase the number of times the jig is used, improve the production efficiency, and reduce the cost.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of an example of a vapor phase growth apparatus.

FIG. 2 is an enlarged view of a susceptor attached to a vapor phase growth apparatus, (a) is a plan view, and (b) is a sectional view taken along line XX of (a).

[Explanation of symbols]

20: susceptor, 21: wafer accommodating portion, 22: opening, 23: base, 24: base upper surface, 25: base lower surface, 26: silicon carbide coating,
27: Wafer, 30: Vapor growth apparatus, 31: Chamber, 32: Chamber base, 33: Support, 34: Nozzle, 35: Raw material gas discharge port, 36: Heater

Claims (1)

[Claims] 1. A silicon carbide curing treatment characterized in that a semiconductor manufacturing jig having a high-purity silicon carbide coating film on its surface is immersed in an aqueous nitric acid chloride solution or a nitric acid fluoride solution of 10% by volume or more for 30 minutes or more, respectively. How to wash ingredients.