JPH0656600A - Composite quartz glass tube for heat treatment of semiconductor - Google Patents

Abstract

PURPOSE:To obtain a furnace core tube with which the rising time is short by forming a glass tube of an outside layer of glass formed by electromelting of crystalline quartz powder and an inside layer of glass formed by melting crystalline quartz powder with combustion flames. CONSTITUTION:This composite quartz glass tube for heat treatment of semiconductors is constituted by forming the outside layer of the quartz glass obtd. by electromelting of the crystalline quartz powder and the inside layer of the quartz glass obtd. by melting the crystalline quartz powder with the combustion flames. The content of heavy metal impurities, such as iron, chromium, nickel and copper, in the quartz glass on the inner side is required to be <=100ppb. These impurities diffuse into a wafer and the life time of the wafer is drastically shortened if the content is above this range. The wafer having the good life time is obtd. simply by executing no-load firing once. The furnace core tube is high in industrial utilization value, for example, the rising time is shortened, the recycling of a washing liquid is possible, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite quartz glass tube for semiconductor heat treatment, and more particularly to a quartz glass furnace core tube having a short startup time.

[0002]

2. Description of the Related Art Machines, devices, containers, pipes and the like used for semiconductor manufacturing are required to have heat resistance and chemical purity. Further, these members should not react with the wafer under any conditions or give any element to the semiconductor, even if it is a trace. Quartz glass has been conventionally used as a material that meets such requirements. Quartz glass includes quartz glass obtained by melting crystalline quartz by an electric melting method and vitrifying, quartz glass fused by an oxyhydrogen flame method, etc., and synthetic quartz glass manufactured by a sol-gel method or a soot method. . However, the quartz glass obtained by melting by the oxyhydrogen flame method or the like has a drawback in that the quartz glass contains OH groups and is crushed or deformed when used at high temperature for a long time. Further, synthetic quartz glass has a drawback that it has a lower viscosity than quartz glass obtained from crystalline quartz powder and that bubbles are generated due to chlorine and hydrogen chloride mixed in during production, resulting in poor appearance. Therefore, conventionally, quartz glass (hereinafter referred to as electro-fused silica glass) obtained by electro-melting has been used as a jig for the semiconductor industry, especially as a jig material used in a process at a heat treatment temperature of 1100 ° C. or higher. .

However, this fused silica glass has a property that impurities are likely to adhere to the fused silica glass, and the adsorbed impurities are released during heating and have a drawback that the semiconductor is hindered. Therefore, the electric fused silica glass tube needs to be air-baked to remove the impurities, but the removal requires air baking for several weeks to one month. And
During that time, it had a drawback that the heat treatment of the wafer had to be stopped.

In order to solve these drawbacks, there have been proposed composite pipes as disclosed in JP-A-3-170340 and JP-A-3-3323. However, it has been found that when heat treatment of a wafer is performed using this composite furnace core tube, the legs of the wafer boat and the inner layer of the furnace core tube adhere to each other, which causes a problem in taking out. The inventors of the present invention have been pursuing the cause thereof and found that the inner layer synthetic quartz glass forming the furnace core tube becomes sticky when heated at a high temperature of 1100 ° C. or higher for a long time. Furthermore, as a result of continued intensive research, the occurrence of the tackiness was found to occur in quartz glass obtained by melting crystalline quartz powder (crystal powder) with a combustion flame of hydrogen or propane (hereinafter referred to as flame fused silica glass). I discovered that it would not happen. Further, it has been discovered that the flame fused silica glass has less adhesion of heavy metal impurities such as iron, chromium, nickel, and copper as compared with the fused silica glass.

By the way, as described above, the furnace core tube for a wafer is air-baked before its use, and the inside of the furnace core tube is contaminated,
It is necessary to remove dust and the like in the electric furnace, but it has been found that forming the furnace core tube only with the flame fused silica glass causes defects such as crushing and deformation during air baking. Therefore, when this flame fused quartz glass was placed inside and the electric fused quartz glass was placed outside, the crushing and deformation did not occur, and moreover the impurities preferentially adhered to the outer fused silica glass layer, It was discovered that redeposition on the internal surface can be prevented.

[0006]

The present invention has been completed based on the above findings, and an object of the present invention is to provide a furnace core tube having a short startup time.

Another object of the present invention is to provide a furnace core tube in which the lifetime of the wafer is less deteriorated.

[0008]

In order to achieve the above object, the present invention comprises forming an outer layer of quartz glass obtained by electromelting crystalline quartz powder and flame melting the crystalline quartz powder. The present invention relates to a composite quartz glass tube for semiconductor heat treatment, characterized in that an inner layer is formed from the obtained quartz glass.

The above composite quartz glass tube for semiconductor heat treatment is
The quartz glass tube obtained by flame-melting the crystalline quartz powder is made inside, the quartz glass tube obtained by electric melting is made concentric with the outside and kept horizontal, and the inner layer tube is maintained in a pressurized state,
This can be manufactured by a method in which the external heating zone is moved from one end to the other end while rotating the same about the common axis at the same speed to integrate the two tubes (see Japanese Patent Laid-Open No. 170340/1993).

In the above, "crystalline quartz powder" means a glass raw material obtained by crushing and refining natural crystalline silicon dioxide such as quartz. The grain size of this crystalline quartz powder is 10 to 1
000 μm, more preferably 50 to 500 μm,
If the particle size is 10 μm or less, the quartz powder is too fine and bubbles are generated. Further, if the particle size is 1000 μm or more, purification is difficult,
Mixing of impurities easily occurs.

Further, in the above, "air-baking" means setting the furnace core tube in an electric furnace and heating it without inserting a wafer to remove contamination inside the furnace core tube and dust in the electric furnace. Say.

The cleanliness of the furnace core tube is measured by placing the silicon wafer in a furnace after baking and subjecting it to heat treatment for a predetermined time to measure the lifetime of the wafer and the thickness of the oxide film on the surface of the silicon wafer. If the lifetime of the wafer is abnormally short or if the thickness of the oxide film on the wafer surface is abnormally thick, it is necessary to perform baking again because the cleanliness is not sufficient. This is repeated many times until the lifetime of the wafer and the thickness of the oxide film on the surface of the wafer are within the standard.

Heavy metal impurities such as iron, chromium, nickel, and copper are contained in the quartz glass layer on the inner side of the composite tube.
The content needs to be 0 ppb or less, preferably 50 ppb or less. Above this, the impurities diffuse into the wafer, significantly reducing the lifetime of the wafer.

Further, in order to prevent the generation of bubbles in the vitrified quartz glass, the content of chlorine and hydrogen chloride is set to 50.
It should be below 0 ppm, preferably below 100 ppm.

By the way, a hydrogen fluoride solution is used as a cleaning solution for semiconductor jigs, and this solution has the property that the concentration of impurities gradually increases during use. Therefore, until now, a new prescription liquid was required each time it was used. In the composite quartz glass tube of the present invention, the outer layer is made of electrofused quartz glass to facilitate the adsorption of impurities, so that the hydrogen fluoride solution can be reused.

The present invention will be described in more detail below with reference to examples.

(Measurement method of lifetime) A method of measuring the lifetime on the wafer surface by a map using LIFE TECH-88R manufactured by Semitex.

[0018]

[Sample example]

(Sample 1) A quartz glass tube obtained by electrically melting crystalline quartz powder.

(Sample 2) A quartz glass tube obtained by melting crystalline quartz powder with oxyhydrogen.

(Sample 3) A synthetic quartz glass tube obtained by flame hydrolysis of silicon tetrachloride and dehydration treatment with chlorine (chlorine content of about 1000 ppm).

[0021]

EXAMPLE A composite quartz glass tube was obtained with sample 1 on the outside and sample 2 on the inside based on the production method described in JP-A-3-170340. This composite quartz glass tube was set in an electric furnace and baked at 1100 ° C. for 5 hours, then a boat on which a P-type wafer was placed was loaded into the composite quartz glass tube and heated at 1000 ° C. for 5 hours. The lifetime of the wafer was measured.

As comparative examples, the quartz glass tube of the sample 1 (comparative example 1), the quartz glass tube of the sample 2 (comparative example 2), and the sample 1 on the outer side and the sample 3 on the inner side were subjected to flame fusion. The wafer was heat-treated using the composite quartz glass tube (Comparative Example 3) obtained as described above. The results are shown in Table 1.

In the table, the inside means the inside of the tube, and the outside means the outside of the tube. Electric means fused silica glass, oxyhydrogen means oxyhydrogen flame fused quartz glass, and synthetic means synthetic quartz glass. Means

[0024]

[Table 1] In the above table, the standard value of the wafer lifetime is 1
When it is set to 00 μsec, the composite quartz glass tube of the present invention satisfies the standard value from the first baking. On the other hand, the pipe of Comparative Example 1 corresponds to the standard value from the fifth time, and the baking time becomes long.

The tube of Comparative Example 2 satisfies the standard value from the first time, but the value is much lower than that of the composite quartz glass tube of the present invention.

Further, in the composite pipe of Comparative Example 3, many bubbles were generated when the pipe was composited, and the appearance was poor, and after the heat treatment, the feet of the boat adhered to the inner layer.

[0027]

As described in the above embodiment, the composite quartz glass tube of the present invention can obtain a wafer having a good life time by only one firing. Thus, the composite quartz glass furnace core tube of the present invention can shorten the start-up time,
In addition, the cleaning liquid can be reused, which has a high industrial utility value.

Claims (3)

[Claims] 1. An outer layer is formed of quartz glass obtained by electrically melting crystalline quartz powder, and an inner layer is formed of quartz glass obtained by melting crystalline quartz powder by a combustion flame. Composite quartz glass tube for semiconductor heat treatment. 2. The composite quartz glass tube for semiconductor heat treatment according to claim 1, wherein the combustion flame is an oxyhydrogen flame. 3. The composite quartz glass tube for semiconductor heat treatment according to claim 1, wherein the content of heavy metal impurities in the quartz glass layer forming the inner layer is 100 ppb or less.