JP3110639B2 - Quartz glass for silicon semiconductor element heat treatment jig - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a quartz glass for a heat treatment jig for a silicon semiconductor device, and particularly to a jig for a heat treatment such as a wafer boat, a furnace tube, a wafer support and a chamber of a single wafer type heat treatment furnace. Related to quartz glass.

[0002]

2. Description of the Related Art Conventionally, quartz glass has been used as a jig for heat treatment of silicon semiconductor devices because it has a higher purity than other refractory materials and can be fused by welding. . However, in recent years, an increase in the degree of integration of semiconductor elements and the emergence of elements that extremely dislike impurities, such as flash memories, have required high-purity jigs. The development of glass is eager. However, it is difficult to reduce the iron element content to 10 ppb or less in quartz glass manufactured by melting natural quartz. Therefore, synthetic silica glass of extremely high purity, in which the total amount of metal impurities is less than 0.1 ppm, particularly, the iron element content is 1 ppb or less, has been industrially manufactured. , The heat resistance was inferior because of containing a large amount of To improve this, synthetic quartz glass containing no aluminum element and doped with an aluminum element is also manufactured, but it is expensive and not at a stage where it can be used industrially advantageously.

[0003]

In view of the current situation,
As a result of intensive studies, the present inventors have come to the conclusion that quartz glass having excellent heat resistance is optimally produced by an electrofusion method. However, when further research was conducted on this quartz glass, the quartz glass obtained by electro-melting natural quartz powder, which has been conventionally used as a quartz glass for semiconductor element heat treatment jigs, in a hydrogen gas atmosphere was found to be a semiconductor poison. It was found that certain iron elements contaminate silicon wafers.

On the other hand, it has been found that quartz glass produced by a vacuum melting method or an oxyhydrogen flame method is unlikely to contaminate a wafer. That is, quartz glass manufactured by the vacuum melting method or the oxyhydrogen flame method has a small degree of reducing the diffusion length of minority carriers in the adjacent silicon wafer. This was confirmed by the quartz glass evaluation method described in German Patent No. 4234715.

[0005] Quartz glass produced by the electric melting method has Le
As noted by E., there are three forms of hydrogen (R.
W. Lee Phys. Chem. Glasses
Vol. 5 No. 2 (1964) p35-43). In other words, in quartz glass obtained by electromelting natural quartz powder in a hydrogen gas atmosphere, stable OH groups and metastable OH groups are present, although the amount differs depending on the manufacturing conditions, in addition to solid solution hydrogen molecules,
Metastable OH groups are removed by vacuum treatment at 1000 ° C. to 1100 ° C., but stable OH groups cannot be removed by vacuum treatment at any temperature. It has also been reported that metastable OH groups are introduced again when heated in a hydrogen gas atmosphere or a steam atmosphere.

The present inventors have paid attention to the relationship between the decrease in the diffusion length of minority carriers in an adjacent wafer and the state of the hydrogen element in quartz glass. First, the quartz glass manufactured by the oxyhydrogen flame method was measured for the amount of OH groups that increased by heating in a hydrogen gas atmosphere or a steam atmosphere by the method of Lee and the amount of OH groups that were released by vacuum heating. It was found that all of the 130 to 200 ppm OH groups used were stable OH groups, no metastable OH groups were introduced by heating in a hydrogen gas atmosphere or a steam atmosphere, and no residual metastable OH groups were present. Therefore, the present inventors have presumed that the metastable OH group is related to the diffusion length of minority carriers.

If the presence of the metastable OH group itself is harmful, the quartz glass obtained by electromelting natural quartz powder in a hydrogen gas atmosphere is vacuum-heated, for example, at 1000 ° C. for 5 hours to produce the metastable OH group. In the case of quartz glass containing only stable OH groups except for, the diffusion length of minority carriers should not decrease. However, the results of the experiment show that metastable OH
It was stated that even if the base was removed by vacuum heat treatment, this kind of quartz glass did not improve the harm to the diffusion length. On the other hand, when the quartz glass produced by melting natural quartz powder in a vacuum was examined, it contained only stable OH groups of 30 ppm or less, and metastable OH groups could not be introduced by any hydrogen gas treatment or steam treatment. Was. Then, no decrease in the diffusion length of minority carriers in the adjacent wafer was observed.

[0008] These results imply the following.
Although the iron element in the quartz glass is eventually transferred to the wafer and the diffusion length is degraded, metastable OH is contained in the quartz glass.
If the group is charged or has a structure that is easily charged, the iron element in the quartz glass is easily released. Therefore, it can be said that, in the case of quartz glass in which metastable OH groups are not introduced, the diffusion length of minority carriers is not reduced, that is, the silicon wafer is not contaminated by iron. The present invention has been completed based on these findings. Ie

According to the present invention, the viscosity at 1200.degree.
^An object of the present invention is to provide a quartz glass for a heat treatment jig of a silicon semiconductor element which has a heat resistance of ^12.9 dPa · s or more and does not cause any harm to a silicon wafer.

[0010]

The present invention for achieving the above object has a viscosity at 1200 ° C. of 10 ^12.9 dPa · s or more, a metastable OH group content of 20 ppm or less , and a metastable O
H group is not reintroduced and the iron element content is 0.8p
pm or less .

The quartz glass of the present invention has high heat resistance,
At 1200 ° C, which is a standard for industrially advantageous use, 1
× 10 ^12.9 dPa · s or more and metastable OH group content is 2
Quartz glass which is as low as 0 ppm or less and does not cause re-introduction of metastable OH groups. When a jig for heat treatment of a semiconductor element is formed using this quartz glass, the diffusion length of minority carriers in a silicon wafer does not decrease and the wafer does not become contaminated. Therefore, it can be used as a material for a heat treatment jig of a large, high-quality silicon wafer. In particular, it can be advantageously used as a quartz glass material for a single-wafer heat treatment jig.

The viscosity at 1200 ° C. is 10 ^12.9 d.
The condition for heat resistance of not less than Pa · s is that the quartz glass contains an aluminum element in a range of 5 to 25 ppm and that the quartz glass produced by the electrofusion method has a small OH group content. Can be. In addition, in order to reduce the diffusion length of minority carriers in a silicon wafer and prevent contamination by semiconductor poisons, the quartz glass must have an iron element content of 0.8 ppm or less and a metastable OH group must be regenerated. It is essential that there is no introduction.
Even if the quartz glass has no metastable OH group re-introduced, if the iron element content in the quartz glass exceeds 0.8 ppm, contamination of the silicon wafer occurs.

As a method for measuring the diffusion length of minority carriers in the silicon wafer, a measuring method described in German Patent No. 4234715, which can be simply and accurately measured, is preferable. The measurement method described in the publication is a measurement method that utilizes a phenomenon in which, when quartz glass is placed in contact with or close to a silicon wafer and heated, the diffusion length of minority carriers in the wafer changes. It is considered that the change of the diffusion length is caused by the iron element in the quartz glass being transferred to the wafer as a result, but the metastable OH group is charged in the quartz glass or the metastable OH group is It is considered that when the structure has a structure that can be introduced, the iron element in the quartz glass is easily released. For example, metastable OH groups can be introduced around reduced iron, specifically, divalent iron, and whether or not metastable OH groups are introduced is a measure of complex defects containing the iron, If iron is present in the above-mentioned state, it is easy to transfer to the wafer, and it is temporarily established that the diffusion length of minority carriers is reduced, but details are not clear.

The term "metastable OH group" as used herein means an OH group which is released when quartz glass is heated in a vacuum, and the term "re-introduction of metastable OH group" refers to 1% of 850 ° C. for 100 hours.
This refers to the introduction of metastable OH groups when heated in a steam-containing atmosphere.

The quartz glass of the present invention is obtained by purifying natural quartz or natural quartz as a halide described in US Pat. No. 4,983,370 or the like to remove impurities. 5-25pp
m, a natural crystal having an iron element content of 0.8 ppm or less is heated and melted by an electric heating means under vacuum, specifically, under a reduced pressure of 1.3 × 10 ^{-2 to} 1.3 × 10 ³ Pa. It is manufactured by vitrification. In the manufacturing method, for example, a method for manufacturing a quartz glass tube is disclosed in JP-A-49-90710.
Japanese Patent Application Laid-Open No. 56-169 discloses a method for manufacturing a hollow ingot as disclosed in Japanese Patent Application Laid-Open
137 can advantageously be used. Further, as a forming means of the obtained quartz glass, a melt drawing method as described in Japanese Utility Model Publication No. 55-35297 can be adopted.

As described above, the quartz glass of the present invention is advantageously used not only as a material for a jig for heat treatment of a large silicon wafer, particularly as a material for a single-wafer heat treatment jig.
It is also suitably used for ordinary integrated circuit manufacturing.

[0017]

EXAMPLE Using a crystal powder obtained by purifying natural quartz powder and purifying iron and aluminum elements to the contents shown in Table 1,
Quartz glass A, which is electromelted in a hydrogen atmosphere and directly drawn from a tube,
A quartz glass B heated and melted by an electric heating means under vacuum and a quartz glass C produced by an oxyhydrogen flame method were produced, respectively. When the viscosity at 1200 ° C., the aluminum element content and the iron element content of these quartz glasses were measured, the aluminum element content and the iron element content did not change, and the viscosity at 1200 ° C. was as shown in Table 1. Met.

[0018]

[Table 1]

Each of the above quartz glasses was modified as shown in Table 2, and the obtained quartz glass was subjected to the following measurements. Table 2 shows the results.

Measurement method:-The amount of metastable OH groups released; the amount of OH groups reduced by heating in a vacuum at 1000 ° C for 50 hours.-The amount of metastable OH groups received: atmosphere containing about 2% water vapor at 850 ° C. The amount of OH groups increased by heating for 100 hours in water. The total amount of OH groups; the value of the total amount measured by infrared spectroscopy immediately after the treatment shown in the reforming conditions. The amount of molecularly dissolved hydrogen; Raman scattering method The degree of harm to the wafer; the measuring method described in German Patent No. 4234715.

[0021]

[Table 2]

As is clear from Tables 1 and 2, the quartz glass of the present invention does not release or accept metastable OH groups, has a small decrease in the minority carrier diffusion length of the wafer, and has a low
High heat resistance of 1 × 10 ^12.9 dPa · s or more at 0 ° C.

On the other hand, quartz glass A which emits and accepts metastable OH groups has high heat resistance as shown in Table 1, but has a large decrease in the diffusion length of minority carriers of the wafer and causes contamination of the silicon wafer. . Further, the quartz glass C manufactured by the oxyhydrogen flame method without the release or acceptance of metastable OH groups has a small decrease in the diffusion length of minority carriers in the wafer, but has poor heat resistance and is not suitable for a high-temperature process and is thin. This material is insufficient for a single-wafer type heat treatment jig in which a member supports a heavy large wafer.

[0024]

The quartz glass of the present invention has high heat resistance and is less affected by iron as a semiconductor poison, and is suitable as a material for a semiconductor heat treatment jig such as a large, high-quality silicon wafer.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C03C 3/06 C03B 20/00 JICST file (JOIS)

Claims (2)

(57) [Claims] A viscosity at 1200 ° C. of 10 ^12.9 dPa
S or more, metastable OH group content is 20 ppm or less ,
Re-introduction of stable OH groups does not occur and iron content
A quartz glass for a silicon semiconductor element heat treatment jig, wherein the quartz glass is 0.8 ppm or less . 2. An aluminum element content of 5 to 25 ppm.
The quartz glass for a heat treatment jig of a silicon semiconductor device according to claim 1, wherein: