JPH08236467A - Method for heat-treating semiconductor substrate - Google Patents

Abstract

PURPOSE: To improve the characteristics and manufacturing yield of a semicon ductor element by remarkably reducing heavy metal contamination which occurs in the course of a semiconductor substrate manufacturing method in which high-temperature heat treatment is performed on various kinds of semiconductor substrates. CONSTITUTION: A quartz reaction tube used for the heat treatment of a semiconductor substrate is constructed in a two-layer structure composed of synthetic quartz containing an OH group at a concentration of >=120ppm on the internal surface side and natural crystalline quartz or fused quartz containing an OH group at a concentration of <=80ppm so that the reaction tube can have durability at a high temperature and the contamination of the semiconductor substrate can be reduced after heat treatment. Therefore, the heavy metal contamination of the substrate with iron, etc., can be remarkably reduced when the substrate is heat-treated in an atmosphere containing a hydrogen gas having an etching ability at a temperature between 900 deg.C and l,300 deg.C, especially, >=1,100 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a heat treatment method for a semiconductor substrate such as silicon, and uses a two-layer structure quartz reaction tube having an outer surface made of natural crystalline quartz or fused quartz and an inner surface made of synthetic quartz. The present invention relates to a heat treatment method for a semiconductor substrate, in which heavy metal contamination that occurs in various manufacturing methods in which high-temperature heat treatment is performed can be significantly reduced, and the characteristics and manufacturing yield of semiconductor elements are improved.

[0002]

2. Description of the Related Art As a silicon wafer heat treatment, there are various high temperature heat treatment methods such as DZ treatment (denued dead zone) for reducing crystal defects near the wafer surface and wale diffusion in a device process. In recent years, a method of improving the breakdown voltage of an oxide film by heat-treating a silicon wafer in an atmosphere containing hydrogen gas has been disclosed in Japanese Patent Laid-Open No.
It is known from 0-231365, JP-A-61-19345, and the like.

All of these heat treatments require 900 ° C. or higher, and the reaction tube for heat treatment is a natural crystalline quartz or SiC reaction tube. However, the SiC reaction tube is clearly inferior to the natural crystalline quartz in terms of purity, and most heat treatment reaction tubes currently use natural crystalline quartz.

On the other hand, high temperature heat treatment in an atmosphere containing hydrogen gas causes the following problems. That is, the hydrogen gas etches the inner surface of the quartz reaction tube due to the reducing action, and impurities such as Fe and C contained in the quartz material itself are etched.
It is known to contaminate silicon wafers during heat treatment with heavy metals such as u and Ni.

[0005]

Recently, high integration of semiconductor devices, that is, miniaturization of patterns has been remarkable, and accordingly, required specifications for semiconductor silicon / wafer quality have become more severe. Considering the further reduction of heavy metal contamination, the conventionally used quartz reaction tube is not sufficient. Therefore, in order to solve the above problems, it is conceivable to use synthetic quartz having a higher purity than the conventional natural crystalline quartz reaction tube.

That is, it is known that synthetic quartz has a heavy metal concentration (iron, copper, etc.) lower than that of natural crystalline quartz by about one digit. However, the synthetic quartz material has a high OH group concentration and
Under the condition of 0 ° C to 1300 ° C, the viscosity is much lower than that of oxyhydrogen fused quartz and the like, the deflection of the reaction tube becomes remarkable, and it is difficult to use high temperature heat treatment. Also, synthetic quartz material OH
Although it is possible to reduce the OH group concentration by dehydrating the group, the reaction tube made of synthetic quartz material in its entirety becomes very expensive, and it is impossible to use it in industrial production.

On the other hand, in Japanese Utility Model Publication No. 62-14722, an inner tube having an OH group of 80 ppm or less and an OH group of 120 p are disclosed.
A two-layer quartz reaction tube having an outer tube of pm or more has been proposed. There is no problem with respect to external contamination of the heater, liner tube, etc. because the OH group concentration of the outer surface quartz is 120 ppm or more, but during heat treatment in a hydrogen gas atmosphere, the inner surface quartz is etched and the purity of the quartz The problem arises.

Further, a two-layer structure reaction tube having a structure in which synthetic quartz from the hydrolysis of silicon alkoxide is attached to the inner surface lining of a natural crystalline quartz reaction tube has been proposed (JP-A-4-21587). . However, since the OH group concentration in synthetic quartz is limited to 100 ppm or less, the ability to capture (suppress diffusion) external contamination of heaters, liner tubes, etc. by the OH group is low, and there is a possibility of causing in-furnace contamination. is there.

In order to solve such a problem, therefore, there has been proposed a two-layer structure reaction tube using synthetic quartz glass whose OH group is limited to 1000 to 2000 ppm on the inner surface and high-purity quartz glass on the outer surface. However, since the inner surface synthetic quartz has a high OH group concentration, it is necessary to increase the thickness of the outer surface quartz in order to suppress the deformation of the reaction tube only in the outer surface natural crystalline quartz portion during the high temperature heat treatment (1200 ° C or higher). There is a problem that the response of the cooling rate deteriorates.

In view of these circumstances, it is extremely difficult to reduce heavy metal contamination in the conventionally used reaction tube in view of suppression of reaction tube deformation at high temperature, and when reducing heavy metal contamination, reaction tube thermal deformation occurs. There was a problem that could not be ignored. INDUSTRIAL APPLICABILITY The present invention suppresses reaction tube deformation that occurs in various semiconductor substrate manufacturing methods that are subjected to high-temperature heat treatment, makes it possible to significantly reduce heavy metal contamination, and improves semiconductor element characteristics and manufacturing yield. The purpose is to provide a method.

[0011]

According to the present invention, a semiconductor substrate is placed in a quartz reaction tube having an inner surface made of synthetic quartz and an outer surface made of natural crystalline quartz or fused quartz.
A heat treatment method for a semiconductor substrate is characterized in that the heat treatment is carried out at a temperature of ° C.

Further, according to the present invention, in the above constitution, the heat treatment method for the semiconductor substrate is such that the heat treatment atmosphere is an atmosphere containing hydrogen gas, the OH group concentration in the synthetic quartz material on the inner surface is 120 ppm or more, and the natural crystalline quartz on the outer surface. OH in the material
A heat treatment method for a semiconductor substrate having a base concentration of 80 ppm or less; and a heat treatment method for a semiconductor substrate having a two-layer structure in which the thickness of the quartz on the outer surface side of the quartz reaction tube is 1 mm or more and the thickness of the quartz on the inner surface side is 0.2 mm or more. We also propose.

In the present invention, the OH group concentration in the synthetic quartz material on the inner surface is set to 120 ppm or more because it is confirmed that the structure such as the heater outside the reaction tube is prevented from being contaminated. The reason why the OH group concentration in the crystalline quartz or fused quartz material is set to 80 ppm or less is that the viscosity does not decrease even at high temperatures and it can withstand high temperature heat treatment, and the heavy metal contamination of the wafer during heat treatment is reduced as much as possible. Further, in order to suppress the deformation of the reaction tube even at a high temperature, especially at a heat treatment at 1200 ° C. or higher, the above OH group concentrations on the inner and outer surfaces must be simultaneously satisfied. The OH group concentration in the natural crystalline quartz material on the outer surface is preferably 40 ppm or less in consideration of long-term stability of suppressing reaction tube deformation.

In the present invention, the thickness of the natural crystalline quartz, the oxyhydrogen flame fused quartz or the electrofused quartz on the outer surface side of the quartz reaction tube is set so as to reduce the deflection of the reaction tube at high temperature as much as possible. At least 1 mm or more is required. The form of the quartz reaction tube can be any known form such as a vertical cylinder type, a dome type, and a horizontal tube type, and if the structure of the synthetic quartz on the outer surface side and the inner surface side as the main constituent can be adopted, the structure etc. The structure of can also be adopted.

In the present invention, the method for producing the reaction tube is not particularly limited and can be appropriately selected. For example, the reaction chamber of the quartz reaction tube made of oxyhydrogen flame fused quartz or electrofused quartz is formed. The synthetic quartz lining can be formed by depositing a synthetic quartz material to a required thickness on the entire inner surface by a vapor deposition method such as chemical vapor deposition, sputtering or plasma sputtering.

[0016] The temperature dependence of the diffusion constant of Fe ions in the quartz material is Corrosin Science, 21,
49 ('81). However, the upper limit temperature is 1
Although it is up to 000 ° C., the diffusion constant at 1200 ° C. is estimated to be 1 × 10 ⁻¹² cm ² / sec.
When heat-treated at 1200 ° C for 100 hours, the diffusion length of Fe is 6
μm. Therefore, the thickness of the synthetic quartz on the inner surface side is Fe
From the viewpoint of preventing contamination, it is effective if it is at least 10 μm.

In the present invention, the reason why the thickness of the synthetic quartz on the inner surface side in industrial production is set to 0.2 mm (200 μm) or more is that dilute hydrofluoric acid is usually used for cleaning the reaction tube. It was determined in consideration of etching with hydrofluoric acid. The etching rate of hydrofluoric acid with respect to the quartz material is generally about 0.25 μm / min at 5% hydrofluoric acid,
0.6 μm / min with 25% hydrofluoric acid, 1.8 with 45% hydrofluoric acid
μm / min, and when the time for immersing the quartz reaction tube in dilute hydrofluoric acid at one cleaning is about 10 minutes, it is removed by etching by about 18 μm in 45% hydrofluoric acid, and if the thickness is at least 200 μm, It will be able to withstand about 10 washes.

The purity of synthetic quartz is iron <0.1 pp.
m, copper <0.01 ppm, aluminum <0.1 ppm
The degree of purity of natural crystalline quartz, oxyhydrogen flame fused quartz or electro fused quartz on the outer surface is iron <2 ppm, copper <0.1
A commercially available product level of about ppm and aluminum <30 ppm may be used.

[0019]

According to the present invention, a quartz reaction tube for heat-treating a semiconductor substrate has a two-layer structure of synthetic quartz on the inner surface and natural crystalline quartz or oxyhydrogen fused quartz or electrofused quartz on the outer surface, and has durability at high temperature. In addition, the contamination of the semiconductor substrate after the heat treatment can be reduced. By using high-purity synthetic quartz on the inner surface of the quartz reaction tube,
Heat treatment at 0 ° C to 1300 ° C, particularly 1100 ° C or higher,
At the time of heat treatment in an atmosphere containing hydrogen gas having etching ability and at the time of heat treatment with a non-oxidizing gas (Ar gas etc.),
Contamination of heavy metals such as iron can be greatly prevented.

The heat treatment according to the present invention is particularly effective when epitaxially forming a film on a semiconductor substrate. For example, it is known that the higher the growth temperature, the smaller the pattern shift and the pattern distortion.
The higher the growth temperature, the more the heavy metal contamination is activated.
Normally, the processing temperature cannot be raised. However, in the heat treatment of the present invention, heavy metal contamination is small even at a temperature of 1200 ° C. or higher, the above growth temperature can be set high, and pattern shift and pattern distortion can be reduced.

[0021]

EXAMPLE As a sample, a silicon substrate grown by the Czochralski method was mirror-polished and heat-treated at 1200 ° C. for 1 hour in a 100% hydrogen atmosphere in an electric fused silica reaction tube. For the substrate after the heat treatment, impurities on the substrate surface were collected with an HF aqueous solution, and the surface iron concentration was measured with an ICP-MS apparatus.

Using the same sample as above, synthetic quartz with an OH group concentration of 120 ppm on the inner surface and 75 ppm with an OH group concentration on the outer surface
In a natural crystalline quartz reaction tube of 100% hydrogen atmosphere,
Heat treatment was performed at 1200 ° C. for 1 hour. The substrate surface impurities were measured by the same method as described above. FIG. 1 shows the measurement results of the iron concentration of the conventional method and the method of the present invention, which are about 1% as compared with the conventional method.
It can be seen that the pollution is reduced by an order of magnitude. Also, 70
The temperature was raised from 0 ° C. to 1200 ° C., the heat treatment was performed at 1200 ° C. for 1 hour, and then the temperature lowering cycle up to 700 ° C. was performed 100 times.
No distortion of the quartz reaction tube occurred.

[0023]

The present invention provides a high temperature heat treatment of a semiconductor substrate,
During heat treatment at 900 ° C. to 1300 ° C., particularly in a hydrogen gas-containing atmosphere having etching ability, it is possible to reduce heavy metal contamination on the surface of the substrate after heat treatment, improve device characteristics obtained, and increase manufacturing yield in the process. Can be obtained. Further, in the heat treatment of the present invention, heavy metal contamination is small even at a temperature of 1200 ° C. or higher,
It is possible to set a high growth temperature for epitaxial film formation and reduce pattern shift and pattern distortion.

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[Procedure amendment]

[Submission date] June 30, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Added

[Correction content]

[Brief description of drawings]

FIG. 1 is a graph showing measurement results of iron concentration on a substrate surface after a conventional heat treatment method and a heat treatment method of the present invention.

Claims (4)

[Claims] 1. A heat treatment method for a semiconductor substrate, comprising heat-treating the semiconductor substrate at 900 ° C. to 1300 ° C. in a quartz reaction tube having an inner surface made of synthetic quartz and an outer surface made of natural crystalline quartz or fused quartz. 2. The heat treatment method for a semiconductor substrate according to claim 1, wherein the heat treatment atmosphere is an atmosphere containing hydrogen gas. 3. The concentration of OH groups in the synthetic quartz material of the inner surface is 1
The heat treatment method for a semiconductor substrate according to claim 1, wherein the concentration of OH groups in the natural crystalline quartz material on the outer surface is 20 ppm or more and 80 ppm or less. 4. The thickness of the quartz on the outer surface side of the quartz reaction tube is 1 mm.
The method for heat treating a semiconductor substrate according to claim 1, wherein the inner surface side quartz has a two-layer structure having a thickness of 0.2 mm or more.