JP2777858B2 - Silica glass tube for heat treatment of semiconductor and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silica glass tube for heat treatment of semiconductors, and more particularly to a silica glass tube obtained by electromelting which can be started up in a short time baking, and a method for producing the same.

[0002]

2. Description of the Related Art Machines, devices, containers, and the like used in semiconductor manufacturing are required to have high heat resistance and high chemical purity. These components must not react with the wafer under any conditions or give any element, even traces, to the wafer. Conventionally, silica glass has been used as a material that meets such demands. Silica glass includes silica glass obtained by melting crystalline quartz by an electric melting method and vitrifying (hereinafter referred to as electrofused silica glass), and silica glass obtained by fusing and crystallizing crystalline quartz by an oxyhydrogen flame method (hereinafter referred to as oxyhydrogen flame). Fused silica glass), and synthetic silica glass obtained by vitrifying silica produced by a sol-gel method or a soot method. However, the oxyhydrogen flame fused silica glass has a large amount of OH.
Since it contains a group, it has a disadvantage that it is crushed or deformed when used for a long time at a high temperature. Further, the synthetic silica glass has a disadvantage that the viscosity is lower than that of the silica glass obtained from the crystalline quartz powder, and bubbles are generated by chlorine and hydrogen chloride mixed during the production, resulting in a poor appearance. For this reason, conventionally, electrofused silica glass has been exclusively used as a jig for semiconductor industry, particularly as a jig material used in a process in which a heat treatment temperature is 1100 ° C. or higher.

However, a new evaluation method has recently been developed,
When the effect of silica glass on the wafer was examined by this evaluation method, it was found that the electrofused silica glass product caused the deterioration of the wafer despite its high purity.
To investigate the cause, an electrofused silica glass tube and an oxyhydrogen flame fused silica glass tube were set in an electric furnace, baked for the same time, and then oxidized.
Then, in the case of the oxyhydrogen flame-fused silica glass tube, a wafer having a lifetime longer than the standard value could be obtained, but in the case of the electrofused silica glass, only a wafer having a small standard value region was obtained. Was. As a cause of the reduction in the lifetime, the incorporation of metal impurity elements into the oxide film of the wafer can be considered.
It is considered that the electrofused silica glass itself exists in the oxyhydrogen flame fused silica glass product since the life time degradation is small. However, since the oxyhydrogen flame fused silica glass product is deformed by a high temperature process of 1100 ° C. or higher and has a short service life, improvement of the electrofused silica glass product has been desired.

[0004]

SUMMARY OF THE INVENTION The present inventors have been studying the shortening of the baking time of the above-mentioned electrofused silica glass tube. Turned out to affect. Therefore, the present inventors first examined the reduction of the iron element content in the entire silica glass bulk, but it was difficult to implement in practice due to contamination during the production and processing of the silica glass tube. Was. After further research, the inner surface was 100
An electrofused silica glass tube having a content of iron element of 100 ppb or less and a content of copper element of 50 ppb or less in a layer up to μm has a baking time similar to that of an oxyhydrogen flame fused silica glass tube, and has a wafer baking time. We found that the lifetime was over the standard value. Therefore, the silica glass layer having a low content of the iron element and the copper element was laminated on the inside of the electro-fused silica glass tube to solve the above problem.
It is technically advanced and costly, which is not a preferable means. The present inventors have conducted further studies in consideration of the above problems, and as a result, it has been found that a layer having a low content of iron and copper elements can be formed by subjecting the electrofused silica glass tube to an atmospheric heat treatment under specific conditions. discovered. The present invention has been completed based on these findings.

[0005] That is, an object of the present invention is to provide a novel electro-fused silica glass tube which can be set up by baking in a short time.

Another object of the present invention is to provide an electro-fused silica glass furnace core tube for wafer heat treatment with high productivity.

Another object of the present invention is to provide a novel method for forming a layer having a low content of iron and copper elements inside an electrofused silica glass tube.

[0008]

Means for Solving the Problems The present invention for achieving the above object is to provide a silica glass tube obtained by electromelting a crystalline quartz powder, wherein the iron element content in the layer from the inner surface to at least 100 μm is 100 ppb or less. Wherein the copper content is 50 ppb or less.

Further, the present invention is characterized in that a layer having a small content of iron element and copper element is formed by subjecting an electrofused silica glass tube to an atmospheric heat treatment under specific conditions.

[0010] In the above description, "crystalline quartz powder" means glass raw material powder obtained by pulverizing and refining natural crystalline silicon dioxide such as quartz. The particle size of this crystalline quartz powder is 1
When the particle size is 10 μm or less, the quartz powder is too fine and bubbles are generated. On the other hand, when the particle size is 1000 μm or more, purification is difficult, and impurities are likely to be mixed.

[0011] In the above description, "blank" means that the furnace core tube is set in an electric furnace, and no wafer is inserted.
Heating means removing contamination inside the furnace core tube and dust inside the electric furnace.

Further, in the above, "atmosphere heat treatment"
This means that the electrofused silica glass tube is heat-treated in an oxygen atmosphere, a nitrogen atmosphere, or a chlorine and hydrogen chloride atmosphere.

In the above electrofused silica glass tube, the iron element content of the layer from the inner surface to 100 μm is 100 pp.
b or less, if the copper content is 50 ppb or less, it is possible to obtain a wafer having a specified value or more in the same baking time as the oxyhydrogen flame fused silica glass furnace core tube, but more preferably the thickness of the layer is 100 μm It is preferably at least 1 mm. 50
There is no effect below μm. On the other hand, it is technically difficult to form a layer having a thickness of 1 mm or more.

In order to make the iron element content of the layer at least 100 μm from the inner layer surface of the electro-fused silica glass tube at 100 ppb or less and the copper element content at 50 ppb or less, the electro-fused silica glass tube is kept in the atmosphere for at least 1 hour. Heat treatment may be performed. If the heating is performed for a long time, the thickness of the layer containing less iron element and copper element can be increased, but the cost becomes high and the economy is lacking.

The above-mentioned atmosphere heat treatment temperature is 900 to 130.
A range of 0 ° C. is preferred. When the treatment temperature is 900 ° C. or less, it takes a long time to remove the iron element and the copper element, which is not economical.
If the temperature is higher than 1300 ° C., the glass tube itself is undesirably deformed.

In the silica glass layers other than the layers having a low iron content and a low copper content, the iron element content is 100 pp.
Although it may be more than b, it is preferably 200 ppb or less. The content of the copper element may be 50 ppb or more, but is preferably 100 ppb or less.

Hereinafter, the present invention will be described in detail with reference to Examples.

(Method of Measuring Life Time) The life time in the wafer surface is measured by map using LIFE TECH-88R manufactured by Semitex.

(Measurement method of iron element and copper element content) The inner surface of silica glass is dissolved with hydrofluoric acid vapor, and after condensing this vapor, the hydrofluoric acid solution is measured with an atomic absorption spectrophotometer. I do. In addition, about the thickness of the melt | dissolved silica glass, the thickness of the silica glass after melt | dissolution was measured, the difference with before melt | dissolution was calculated, and the thickness was confirmed.

[0020]

【Example】

[0021]

Table 1 shows the measured lifetime of the obtained wafer.

[0023]

[Table 1]

[0024]

As shown in the above Table 1, the electrofused silica glass tube of the present invention can achieve almost the same standardized lifetime with the same baking time as the oxyhydrogen fused silica glass tube. Moreover, the viscosity of the silica glass is almost the same as that of the untreated electrofused silica glass. Thus, the silica glass tube of the present invention is an excellent silica glass tube for heat treatment of semiconductors performed at a high heat treatment temperature of 1100 ° C.

On the other hand, the oxyhydrogen-fused silica glass furnace core tube can certainly provide a wafer having an excellent life time despite containing a large amount of iron element. The replacement time must be less than half that of the furnace core tube of the present invention, and is a silica glass tube unsuitable for semiconductor heat treatment.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C03B 20/00 C03C 3/06 H01L 21/22 H01L 21/324

Claims (2)

(57) [Claims] 1. A layer of at least 100 μm from the inner surface of a silica glass tube obtained by electromelting crystalline quartz powder has an iron element content of 100 ppb or less and a copper element content of 50 pb or less.
A silica glass tube for heat-treating a semiconductor, which has a pb or less. 2. A method for producing a silica glass tube for semiconductor heat treatment, comprising subjecting a silica glass tube obtained by electromelting crystalline quartz powder to heat treatment at 900 to 1300 ° C. for at least one hour.