JPS6096590A - Tool for heat treatment - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to heat treatment jigs that require high purity, such as crucibles and susceptors used in semiconductor manufacturing.

These heat treatment jigs are capable of rapid heating, rapid cooling, and high-temperature HeI! from room temperature to 1200℃. Gas etching.

The atmosphere required for cleaning impurities deposited on the surface with nitrofluoric acid must have sufficient needle scale and other characteristics.
Another important characteristic is that heat treatment jigs come into contact with products such as high-purity silicon wafers, so they are required not to contaminate the products.

As a material that satisfies the above-mentioned characteristics, SiC-coated lead-covered graphite materials in which the surface of a graphite base material is coated with high-purity SiC't have been used. In other words, SiC is chemical.

Made of thermally stable material, and SiC on the graphite base material surface.
This is to prevent contamination with impurities from the graphite base material by coating the graphite. However, with repeated use of conventional heat treatment jigs in which SiC is coated on a graphite base material, impurities from the graphite base material often contaminate the product and adversely affect the characteristics of the semiconductor. was.

In order to prevent this impurity contamination, a method was taken to make the SiC coating layer on the graphite substrate surface thicker than the conventional one, but this only slightly extended the life of the heat treatment jig, and the silicon It was not possible to prevent contamination of products such as wafers.

The object of the present invention is to solve the above-mentioned drawbacks and to provide a heat treatment jig that can be used repeatedly.

A detailed investigation into the mechanism of contamination of products by these impurities revealed that impurities penetrate the SiC coating layer by diffusing through the chemically active grain boundaries of SiC crystals (detected by chemical treatments such as etching). I decided to go. It has been found that a thicker SiC coating layer in which grain boundaries are present essentially allows impurity elements to pass through by diffusion. Furthermore, from graphite base material to SiC
The time it takes for impurities to pass through the surface of the coating layer is related to the length of the grain boundaries through which the impurities diffuse, and the amount of impurities passing through is related to the amount of grain boundaries. The results of a detailed investigation of the SiC coating layer of heat treatment jigs, which can cause contamination of products due to repeated use.

After mirror-lapping the SiC coating surface, the particles observed by melt etching with NaOH at 700°C for 30 minutes were small, and the ratio of the diffraction peak value of the X-ray diffraction pattern due to α rays to that of Cu on the 8iC coating surface was small. 1(200)/1(
111)=0.03, 1(220)/1(111)=0
．． It was 10. This tight SiC coating layer has large grains observed under a microscope, but small grains constituted by relatively chemically active grain boundaries that appear by NaOH melt etching, and a small SiC crystal grain size measured by X-ray diffraction. It was found that the grain boundaries were oriented in a specific direction.

The present inventors have demonstrated that by regulating the amount and morphology of grain boundaries in coated SiC, it is possible to suppress the amount of impurities in the graphite base material passing through the SiC coating layer due to diffusion to an extent that does not affect the performance of the product. I found out.

The present invention provides a heat treatment jig in which the surface of a graphite base material is coated with SiC, in which SiC particles having a size of lQIMn or more after alkali melt etching on the SiC surface occupy an area ratio of 50 or more, and (200”) plane and (222) plane in X-ray diffraction of the 8iC surface
Ratio of diffraction peak value to (111) plane IC200
)/1 (111) and I (222)/I (111
) is 0.05 to 0.35 and 0.4 to 1.2, respectively.

In the present invention, the size of the SIC particles is determined by mirror-lapping the SiC layer on the surface of the carbon substrate, for example, at 700°C for 30°C.
This is the size of grains constituted by grain boundaries when observed by melt etching with NaOH. Further, the diffraction peak value in X-ray diffraction is a value measured at α for Cu, and an example of the measurement conditions is shown in Table 1.

Table 1 In the present invention, the particle size of the 8iC graphite layer.

When the area ratio and the ratio of diffraction peak values in X-ray diffraction deviate from the above ranges, the grain boundaries in the cross section of the SiC coating layer have developed in a columnar shape from the graphite base material toward the surface, so impurities in the graphite base material diffuses through the grain boundaries and S
A large amount of iC coating layer exposed to the surface contaminates products such as silicone phenol which are in contact with the heat treatment jig, resulting in a decrease in performance. Within the above range, SiC
The grain boundaries of the crystals do not develop into columnar shapes and are intertwined with each other, and there are extremely few grain boundaries that reach directly from the graphite base material to the surface of the layer, so the amount of diffusion of impurities can be kept to a low level, and the heat treatment jig can be repeatedly used. Can withstand use.

In order to coat a graphite substrate with SiC having the characteristics of the present invention, SiC is precipitated by causing a gas phase reaction of the raw material gas under diffusion controlled conditions at a temperature of 1300° C. or higher, for example. The raw material gas is CHsSi containing Si and C in one molecule.
Either a one-component system such as Cls or a two-component system such as 8iC1a and CC1a containing only Si and only C may be used. In order to realize the diffusion-limiting condition, the raw material gas concentration must be 2 used as a carrier gas, for example Ih gas 11! 5 x l □-”mol! in terms of Si element!
It is preferable that it is below.

Further, the temperature is preferably 1300° C. or higher so that the area ratio of particles observed by etching of 10 μm or more is 50% or more. Note that indirect heating from the outside is more preferable than direct heating such as high-frequency induction heating for heating the graphite base material, but this is not particularly limited.

Examples of the present invention will be described below.

Graphite base material processed into the shape of Example (apparent specific gravity 1.76.
Average thermal expansion coefficient from 400 to 1000℃ 4, s x l
o-'/℃) to 1300℃ in a high-frequency induction heating reactor.
and heated in two rows at 1500°C. The raw material gas still introduced into the reactor is CH@5ices, and its concentration is HJ gas 1! for 5X10-”mop, 1
x 10-"moI!, 1 x 10-4mo/. The flow rate of H2 gas was 2017 minutes.

By combining the above conditions, the thickness of the SiC coating layer is approximately 1
The particle size and its area ratio and the first
As shown in the jg2 table, six types were manufactured in which the ratio of the diffraction peak values of XIIIN diffraction under the measurement conditions shown in the table was within the above range. As a comparative example, Suzoshikasu Isodo I X 1 (1”)
1ooJ, temperature 1200℃ + 7) conditions, in the same reaction furnace as in the example, and 1i1 gas flow rate, SiCt-hot lead substrate was coated, and those outside the above range were coated as shown in Table 2.
1 (I made a similar one.

After mirror-lapping the 9 surfaces of Example A20 sample and Comparative Example A2 sample in Table 2, 700℃ 30 at pJBQH
Photographs of the structure of the melt-etched material are shown in FIG. 1 (Example) and FIG. 2 (Comparative Example). As is clear from the figure, the SiC particle diameter of the example is much larger than that of the comparative example.

Using the heat treatment jig obtained in Examples and Comparative Examples, a 201 m process of forming a 100 μm silicon epitaxial layer on a silicon wafer was carried out. Table 2 shows the results of measuring the resistance of the 20th expansion of the epitaxial layer and calculating the impurity concentration.

As is clear from Table 2, the heat treatment jig coated with SiC of the present invention is less susceptible to contamination by impurities than the conventional jig, and is sufficiently durable for repeated use. In contrast, in the conventional wafer, a large amount of impurities in the graphite base material permeated the SiC recoating layer due to repeated use, resulting in contamination to the extent that the performance of the 7 Mekong wafer was adversely affected.

The heat treatment jig of the present invention has remarkable effects such as preventing contamination of the graphite base material by impurities on the products used and being able to withstand repeated use.

[Brief explanation of the drawing]

FIG. 1 is a photograph of the structure of the surface of the heat treatment jig in Example. FIG. 2 is a photograph of the structure of the surface of a heat treatment jig in a comparative example.

Claims (1)

[Claims] 1. In a heat treatment jig in which the surface of a graphite base material is coated with SiC, the size of SiC particles after alkali melt etching on the SiC surface accounts for 50% or more in terms of area ratio, and the SiC (11) of (200) plane and (222) plane in surface X-ray diffraction
1) Ratio of diffraction peak value to plane 1(200)/I(1
11) and a heat treatment jig in which I(222)/I(111) is 0605 to 0.35 and 0.4 to 1.2, respectively.