JP2522830B2 - Quartz glass material for semiconductor heat treatment and manufacturing method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a quartz glass material useful for forming a furnace core tube for heat treatment of a semiconductor wafer, and particularly to a silica glass material such as sodium in a heat treatment step in a heating furnace. TECHNICAL FIELD The present invention relates to a quartz glass material for semiconductor heat treatment which can highly suppress contamination by metal impurities, and an effective manufacturing method thereof.

[Conventional technology]

Conventionally, furnace tubes and wafer jigs used for heat treatment of semiconductor wafers are required to have heat resistance that does not deform in a high temperature range of 1000 to 1300 ° C., for example. Further, as the degree of integration of semiconductors has been improved, a slight amount of metal, particularly alkali metals, in the heat treatment step has become a serious problem. Contamination in the heat treatment process of semiconductor wafers is due to those metals contained in quartz glass containers and other jigs and metals released from the furnace wall and diffused through the quartz glass containers. Attention has been paid to sodium, which has a high speed.

It is known that the diffusion rate of sodium impurities in quartz glass is very small in water-containing synthetic quartz glass having an OH concentration of 1000 ppm or more, and is large when the OH concentration is small. Such hydrous synthetic quartz glass is generally
Since there are very few metal impurities in the material, it is desirable as a core tube for semiconductor heat treatment as far as metal contamination resistance is concerned, but it is inferior in heat resistance and it deforms significantly in heat treatment above 1000 ° C, so it is practically used as a heat treatment member Cannot be used. Further, if attention is paid to the heat resistance under heat treatment conditions, natural quartz glass is preferable, but it cannot be adopted from the viewpoint of contamination resistance due to the large content of various metal impurities.

[Problems to be Solved by the Invention]

Therefore, a technical object of the present invention is to provide a high-purity quartz glass material having excellent heat resistance at a heat treatment temperature of a semiconductor wafer and containing metal components reduced as much as possible. Another object of the present invention is to provide a quartz glass member capable of highly suppressing the permeation and diffusion of metal impurities from the furnace.

[Means for solving the problem]

As a result of many trials and studies on synthetic quartz glass materials that overcome the above problems, the present inventors prefer glass materials that do not substantially contain OH and metal impurities, and that contain chlorine in a specific range. It has heat resistance and effectively reduces the diffusion rate of sodium diffused from the furnace,
It has been found to be extremely effective in stain resistance.

That is, the present invention, the content of OH is 10ppm or less, substantially does not contain metal impurities, and the content of chlorine is 500 ~.
Quartz glass material for semiconductor heat treatment adjusted in the range of 4,000 ppm, and an effective method for producing such material, that is, deposition of soot-like silica produced by hydrolysis of silicon halogen in oxygen / hydrogen flame A method for producing a quartz glass material for semiconductor heat treatment is provided, in which the obtained porous quartz glass member is heat treated in an atmosphere containing a chlorinating agent.

The quartz glass material for semiconductor heat treatment of the present invention is a novel material in that the synthetic quartz glass substantially free of OH and metal impurities in the glass contains chlorine in an amount capable of reducing the diffusion rate of sodium. There is a feature as.

If the OH content in the quartz glass material of the present invention exceeds 10 ppm, the heat resistance for heat treatment of semiconductors will be insufficient, and the silica glass will be easily deformed, which is not industrially practical. Preferably,
It is 2 ppm or less. Further, in the present invention, substantially free of metal impurities means that the amount of contamination of the semiconductor wafer during the heat treatment is substantially negligible, and particularly,
It is important that sodium having a large diffusion coefficient is 0.2 ppm or less.

Further, the amount of chlorine contained in the glass material of the present invention,
If it is less than 500 ppm, the effect of reducing the diffusion rate of sodium is insufficient, and if it exceeds 4,000 ppm, the heat resistance sharply decreases, and therefore it cannot be used. The preferred chlorine content is in the range of 800 to 2,500 ppm.

Such a quartz glass material is a synthetic quartz glass material effectively provided by heat-treating a porous quartz glass member obtained by a soot method conventionally known as a method for manufacturing an optical fiber in a chlorinating agent atmosphere, and a halogen It can be easily obtained by depositing soot-like silica produced by hydrolyzing silicon oxide in an oxygen / hydrogen flame and heat-treating the obtained porous quartz glass material in an atmosphere containing a chlorinating agent. The porous synthetic quartz glass material formed in this way is
It is required that the purity is as high as possible, and therefore, the raw material silicon tetrachloride used in the soot method is one that is highly purified by a generally known purification means such as distillation.

As the chlorinating agent used for introducing heat treatment of chlorine, chlorine gas and thionyl chloride are typically used, and these may be used alone or in combination. Also,
The chlorinating agent is usually introduced into the atmosphere in the furnace at a concentration in the range of 3 to 100% by volume, and the concentration is adjusted mainly by an inert gas. Moreover, in order to efficiently perform chlorination, a temperature of about 700 to 900 ° C. is generally adopted. The chlorination treatment time depends on the type of the chlorinating agent and its atmospheric concentration and the treatment temperature, and in connection with the desired chlorine content, a person skilled in the art can easily determine it by a simple experiment. it can.

The glass material of the present invention thus obtained is a transparent glass which is easily heated by heating to a temperature at which the porous glass soot is melted under an inert gas atmosphere, for example, 1,300 to 1,500 ° C. or higher. And is provided as a glass member suitable for semiconductor heat treatment.

This clarification can be carried out following the above chlorination step by further raising the temperature of the furnace in the atmosphere as it is, but in this case, since chlorination progresses with transparent vitrification, The chlorination time will be somewhat reduced.

[Work]

INDUSTRIAL APPLICABILITY The quartz glass material for semiconductor heat treatment of the present invention has high heat resistance, can effectively suppress the contamination of semiconductors with metals, especially the contamination with sodium having a high diffusion rate, and is suitable for repeated use. A member having high practicality is provided.

〔Example〕

Next, the present invention will be described in more detail with reference to specific examples. The OH concentration of the sample in the specific examples is measured by the infrared spectrophotometric method, and the chlorine concentration is measured by the turbidimetric method of silver chloride.

Example 1 High-purity silicon tetrachloride was introduced into a loose oxygen / hydrogen flame and flame-hydrolyzed, soot-like silica fine particles were deposited in layers to obtain a porous quartz glass base material.

About 700 g of the porous synthetic quartz glass base material thus formed was heated to a temperature of 800 ° C. in a furnace in a mixed gas atmosphere with a chlorine: helium mixing ratio of 10:90 by volume. Chlorination was performed by heating for an hour.

The chlorine content of the obtained chlorinated glass material is about 850 ppm
The OH concentration was 0.1 ppm or less.

This chlorinated glass material (base material) was heated and melted at a temperature of 1,500 ° C. or higher in a furnace in an atmosphere of helium alone containing no chlorinating agent to obtain a transparent glass member.

Example 2 A chlorinated quartz glass material was produced in the same manner as in Example 1, except that the chlorination treatment in the furnace at a temperature of 800 ° C. was performed for 6 hours instead of 2 hours.

The chlorine content of the obtained chlorinated glass material is about 2,400 p
At pm, the OH concentration was below 0.1 ppm.

The obtained chlorinated glass base material was heated and melted at a temperature of 1,500 ° C. or higher in a furnace in a helium gas atmosphere to obtain a transparent glass member.

Comparative Example 1 About 700 g of a porous synthetic quartz glass base material prepared in the same manner as in Example 1 was heated for 2 hours at a temperature of 800 ° C. in a furnace in a mixed gas atmosphere of chlorine: helium = 5: 95 volume ratio. Processed.

The chlorine content of the obtained chlorinated glass material was about 35.
It was 0 ppm, and the OH concentration was 0.1 ppm or less.

This chlorinated glass base material was heated and melted at a temperature of 1,500 ° C. or higher in a furnace in a helium gas atmosphere to obtain a transparent glass member.

Comparative Example 2 In Example 1, the same chlorinated glass base material as that obtained by performing the chlorination treatment for 2 hours in the furnace was heated to 1,500 ° C. or higher in the furnace temperature in that state. Then, simultaneously with the progress of chlorination, it was heated and melted to form a transparent synthetic quartz glass member.

The chlorine content of the obtained chlorinated transparent quartz glass member,
At about 4,800 ppm, the OH concentration was 0.1 ppm or less.

Example 3 With respect to the above samples, the heat resistance required for heat treatment of semiconductor wafers and the prevention of diffusion of metal impurities were measured and evaluated by the following methods.

Heat resistance: The viscosity η of each sample at 1,200 ° C is measured by the Beam Bending method.

The logarithm of viscosity η: Logη is preferably 12.7 or more.

Diffusion preventive property: After dropping a 1% sodium nitrate aqueous solution onto a sample cut into a flat plate, the sample was heated to a temperature of 1,150 ° C for 2 hours and then rapidly cooled to obtain a diffusion profile of LMA (L
ASER MICRO ANALYSYS) analysis, and from the profile, the sodium diffusion coefficient (D Na
cm ² / sec) is calculated.

It is desirable that this value be as small as possible, and from a practical standpoint, it can be evaluated extremely high if it is on the order of 10 ^-9 .

 The measurement results of each sample are shown in Table 1.

For comparison, those of commercially available water-containing synthetic quartz glass SUPRASIL-1 (manufactured by Heraeus; reference sample 1) and natural quartz glass Heralux (reference sample 2) are also shown.

In addition, Table 2 shows the content of metal impurities in each sample measured by the atomic absorption method together with the OH concentration and the chlorine concentration. However, Examples 1 and 2 and Comparative Examples 1 and 2
The sample was substantially the same as that of Example 1 with a slight variation due to the difference in chlorine content, and the measured value for Example 1 was shown as a representative. All numbers are in ppm.

From the above, the quartz glass material of the present invention has sufficient heat resistance for semiconductor heat treatment, contains very few metal impurities, and has a small sodium diffusion coefficient at 1,150 ° C., and is contaminated by metals and the like in the wafer heat treatment step. Clearly understand that can be highly prevented.

[Effects of the Invention] The quartz glass material of the present invention, when used as a glass member for semiconductor heat treatment, is less likely to be deformed in the high temperature heat treatment step, and in particular, contamination of the wafer by diffusion of impurities such as alkali metal is effectively It has a high industrial value because it is prevented from being suppressed.

Claims (2)

(57) [Claims] 1. A quartz glass material for semiconductor heat treatment, which has an OH content of 10 ppm or less, contains substantially no metal impurities, and has a chlorine content adjusted to a range of 500 to 4,000 ppm. 2. A method of depositing soot-like silica produced by hydrolyzing a silicon halide in an oxygen / hydrogen flame, and heat-treating the obtained porous quartz glass member in an atmosphere containing a chlorinating agent. The method for manufacturing a quartz glass material for semiconductor heat treatment according to claim 1, which is characterized in that.