JP3294356B2 - Quartz glass furnace core tube for semiconductor wafer processing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quartz glass furnace core tube for treating semiconductor wafers, and more particularly, to a semiconductor wafer having a predetermined amount of OH group content in an inner layer to prevent contamination of a semiconductor wafer to be treated. And a quartz glass furnace core tube for processing.

[0002]

2. Description of the Related Art Quartz glass has excellent heat resistance, thermal shock resistance, chemical resistance, and high mechanical strength, and is used as a member for various applications. Conventionally, many quartz glass materials have been used as materials or members in semiconductor manufacturing processes. For example, there are a crucible for pulling a silicon (Si) single crystal, a furnace core tube for a diffusion furnace, and the like. In a semiconductor manufacturing process, impurity contamination is a serious problem, and quartz glass has been used frequently because it has the same constituent components as silica (SiO ₂ ) constituting a semiconductor wafer, and can prevent contamination. However, in recent years, integrated circuits used in various fields have rapidly advanced in the direction of high integration, and the specifications of semiconductor wafers for the substrates are strict, and wafers with higher purity are required.

[0003] For this reason, various proposals have conventionally been made regarding the control of contaminants generated from various members used in the manufacturing process. For example, Japanese Patent Publication No. 54-5404 discloses that a multilayer quartz glass body used for a diffusion tube or the like has an outer layer thickness of 1 mm inside an outer layer covering an inner layer of a synthetic quartz glass tube.
It is proposed to provide a dividing layer having a thickness of 0 to 90% and to include OH ions and the like in the dividing layer to prevent diffusion of impurities such as Na in the inner layer quartz glass to the outer surface and scattering to the outside. Have been. The above method shows the introduction of an OH group as a member for preventing diffusion and scattering of impurities, and as a specific introduction method, the incorporation of an OH group generated at the time of melting quartz particles by an oxyhydrogen burner is described. But 1000
Introducing OH groups of not less than ppm by this method is not industrially practical. Further, when the content of the OH group increases, the viscosity of the quartz glass decreases, and the high-temperature strength decreases.
Therefore, in order to ensure high-temperature strength as a furnace core tube, it is necessary to increase the thickness of each of the outer layers including the inner layer and the divided layers, and increasing the overall thickness increases the material cost and increases the furnace cost. The thermal efficiency of the core tube is deteriorated, and the thermal response at the time of temperature rise and cooling is also reduced.

In order to solve the above-mentioned drawbacks, a quartz glass member has been developed as a member which can be provided for a furnace core tube used at a high temperature in a diffusion step of a semiconductor manufacturing process, in which an OH group content is suppressed as much as possible. For example, Japanese Patent Application Laid-Open No.
No. 587 discloses a semiconductor in which a main body is formed of high-viscosity natural crystalline quartz, and a lining layer of synthetic amorphous silica obtained from a hydrolysis product of silicon alkoxide is integrally formed on one outer surface thereof. A quartz glass member for manufacturing has been proposed.

[0005]

The quartz glass member for semiconductor production proposed above does not deform at high temperatures,
Since the lining layer is made of high-purity synthetic amorphous silica, it does not contaminate silicon wafers even when used in semiconductor manufacturing process members such as furnace furnace tubes for diffusion furnaces, and is useful as a quartz glass member for semiconductor manufacturing. It is. However, the above-mentioned quartz glass member is designed to increase the viscosity in order to ensure high-temperature strength, and the content of the OH group acting as a diffusion blocking member for metal impurities such as Na is suppressed to 100 ppm or less. Although it can be obtained, it may be difficult to sufficiently prevent impurity contamination of the silicon wafer to be processed.

The present invention has been made in view of the above-mentioned circumstances, and while suppressing the diffusion of metal impurities in quartz glass while maintaining the required high-temperature strength, contamination of the silicon wafer to be processed can be sufficiently prevented, and the durability is improved. An object of the present invention is to provide a quartz glass furnace core tube that is excellent in heat treatment of a semiconductor wafer stably and efficiently over a long period of time. The inventors have conducted various studies on the OH group content and the wall thickness of the quartz glass forming the innermost layer of the multilayer furnace core tube constituting the inner wall of the tube in which the object to be treated is arranged for the above purpose. Thus, the present invention has been completed.

[0007]

According to the present invention, there is provided a quartz glass furnace core tube for processing a semiconductor wafer, comprising at least two layers, wherein the innermost layer has a total wall thickness of 5 to 35 mm.
% And an OH group content of 1000 to 20%
A quartz glass furnace core tube for processing a semiconductor wafer is provided, wherein the quartz glass core tube is formed of synthetic quartz glass of 00 ppm, and an outer layer formed outside the innermost layer is formed of high-purity quartz glass. .

[0008]

According to the present invention, the OH group content of the synthetic quartz glass constituting the inner wall layer in the tube in which the silicon wafer to be processed is placed, that is, the innermost layer having the predetermined thickness, is set to 1000. By setting the content to 2,000 ppm, it is possible to prevent the diffusion of contaminants, maintain a predetermined viscosity, and maintain high-temperature strength.

Hereinafter, the present invention will be described in detail. The quartz glass furnace core tube for processing a semiconductor wafer according to the present invention is used in a so-called thermal oxidation / diffusion furnace in a wafer processing step, in which a wafer placed on a quartz boat is placed and installed on the outer peripheral portion. A tube that processes the wafer by heating it with an electric furnace and passing oxygen gas etc., conventionally, usually formed into a cylindrical body such as a cylinder, and high-purity quartz to prevent wafer contamination. Glass or a multilayer structure as described above is employed. The furnace core tube of the present invention has a cylindrical shape and a cylindrical portion is formed of quartz glass having a multi-layer structure, similarly to the related art. The length and thickness of the cylindrical portion are not particularly limited, and can be appropriately selected according to the use conditions of the furnace core tube. Usually, the thickness is preferably 3 to 6 mm. The length can be set arbitrarily according to the installation location and the amount of processing.

[0010] The multilayer structure constituting the cylindrical portion is composed of at least two layers, an innermost layer and an outer layer outside the innermost layer. Each thickness ratio of the innermost layer and the outer layer is about 1/20 to 1/2,
The innermost layer preferably has a thickness of 5 to 35%, more preferably 15 to 25%, of the total thickness of the furnace core tube. If the thickness of the innermost layer is less than 5% of the total thickness of the cylindrical portion, the following effect of suppressing the diffusion of impurities in the innermost layer cannot be obtained. The viscosity of the furnace core tube decreases due to the composition of the quartz glass, and the high-temperature strength of the furnace core tube decreases, which is not preferable.

In the above-mentioned multilayer structure of the furnace core tube section of the present invention, the outer layer excluding the innermost layer constitutes the base of the furnace core tube, and mainly has a high temperature strength and a high viscosity. It is formed of pure quartz glass. As the high-purity quartz glass, it is possible to use a high-purity quartz glass obtained by melting a generally known high-purity silica raw material to form a quartz ingot, and further purifying by passing a direct current at about 1100 ° C. or more. . Preferably, natural crystalline quartz glass and quartz glass having a composition similar to that can be used. When the outer layer is a multilayer, each layer may be made of high-purity quartz glass having the same composition or high-purity quartz glass having a different composition.

Further, the innermost layer constitutes the inner wall of the furnace core tube and can be formed by lamination inside the outer layer. The innermost layer is formed of synthetic quartz glass, and the OH group contained in the synthetic glass is 1000 to 200
It is within the range of 0 ppm. OH group content is 1000p
When it is less than pm, the effect of suppressing impurity metals such as Na diffusing in the quartz glass of the outer layer and / or the innermost layer decreases. On the other hand, if it is more than 2000 ppm, the innermost layer is apt to devitrify, which is not preferable. The occurrence of devitrification in the furnace core tube causes unevenness in heat during processing because the thermal conductivity of the devitrified part is different from that of other quartz glass parts, and uniform processing cannot be performed. The high-purity synthetic quartz glass constituting the innermost layer of the furnace core tube of the present invention can be produced by a usual quartz glass forming method, for example, silicon tetrachloride (SiCl ₄ ), hydrogen (H ₂ ) and oxygen Using (O ₂ ) as a raw material, a quartz glass precursor layer is formed inside the outer layer of the furnace core tube by a CVD (chemical vapor deposition) method, and thereafter, using nitrogen or helium gas as a carrier gas, water vapor (H ₂ O) Can be formed by flowing the mixture so as to come into contact with the quartz glass precursor layer on which water vapor (H ₂ O) is heated and vitrified at about 800 to 1200 ° C. Further, in the furnace core tube of the present invention, it is more preferable that the OH group contained in the inner layer is formed so as to have a form in which the OH group is inclined from the outer layer side toward the inner side. By forming in such a form, the internal layer can have higher high-temperature strength and higher metal impurity diffusion prevention effect. A furnace core tube having a form such as a charcoal base can be obtained by, for example, heating the inside of the furnace core tube after the above-mentioned steam (H ₂ O) heat treatment.

The quartz glass furnace core tube for processing a semiconductor wafer of the present invention is manufactured and obtained by forming a predetermined innermost layer inside a base constituting an outer layer of high-purity quartz glass as described above. By arranging a heater or the like on the outer peripheral surface of the furnace core tube and appropriately arranging a silicon wafer in the tube, it is possible to perform heating and diffusion treatment while eliminating contamination of metal impurities such as Na. It is also conceivable to form a synthetic quartz glass layer having a predetermined OH group content outside the outer layer, install a heater inside the tube, and heat and diffuse the silicon wafer outside the furnace core tube. External synthetic quartz glass having a predetermined OH group content is easily devitrified due to contact or adhesion of impurities or the like, and external coating is not preferable.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on embodiments. However, the present invention is not limited by the following examples. Examples 1-2 and Comparative Examples 1-2 Al: 8 ppm, Fe: 0.4 ppm, N as impurities
a: 0.8 ppm, K: 0.8 ppm, Cu: 0.02
ppm, B: a quartz ingot obtained by melting a high-purity silica raw material powder containing 0.3 ppm at 100 ° C.
Purification was performed by applying a current of 0 V DC for 120 minutes. The impurity content of the obtained high-purity quartz glass ingot is Al:
8 ppm, Fe: 0.4 ppm, Na: 0.1 ppm,
K: 0.1 ppm, Cu: 0.01 ppm, B: 0.0
At 3 ppm, the OH group was 300 ppm. Using the high-purity quartz ingot obtained above, an outer diameter of 207 mmφ,
Four high-purity quartz glass cylinders having an inner diameter of 200 mmφ and a wall thickness of 1,400 mm and a thickness of 3.5 mm were produced. The produced cylindrical body was placed in an electric furnace, heated to about 700 ° C. and heated, and then, SiCl ₄ 20 g / min.
₂ 200 l / min, 30 at 100 l / min O ₂
Then, the quartz glass precursor layer having a thickness of 1.0 mm was formed inside the cylindrical body.

Next, steam (H ₂ O) is passed through the furnace at a rate of 20 liters / minute using nitrogen gas as a carrier gas.
The quartz glass precursor layer formed as described above was vitrified in a water vapor (H ₂ O) atmosphere. In this case, the ratio of steam to nitrogen gas is changed in a range of 1/1 to 1/5 so that the OH group content in the vitrified synthetic quartz glass layer becomes 500 ppm, 1000 ppm, 2000 ppm, and 2500 ppm. Controlled. The OH group content of the synthetic quartz glass of the formed inner layer was determined by FTIR
(Fourier transform infrared spectrometer) and measured from an infrared absorption band of 2.73 μm. The impurities in the synthetic quartz glass of the inner layer were as follows: Al: 0.1 ppm, Fe: 0.05 pp
m, Na: 0.05 ppm, K: 0.05 ppm, C
u: <0.01 ppm, B: <0.01 ppm. A furnace core tube was manufactured using each of the obtained multilayer quartz glass cylinders, and the silicon wafer was heated from room temperature under an argon (Ar) atmosphere in the manufactured furnace core tube using a normal heating device. After heating at about 1100 ° C. for 30 minutes and then cooling to room temperature, two heat treatment cycles were performed.
Repeated 00 times. The impurity amount of the silicon wafer after each heat treatment cycle was measured. OH group content in the inner layer is 500 ppm (Comparative Example 1), 1000 ppm (Example 1), 2000 ppm (Example 2), and 2500 p
FIG. 1 shows the measurement results of each furnace core tube in pm (Comparative Example 2) as the relationship between the number of heat treatment cycles and the amount of impurities. OH group content of the inner layer of Comparative Example 2 was 2500 ppm
As for the furnace core tube, devitrification occurred frequently after 150 heat treatment cycles, and further heat treatment was stopped.

Comparative Example 3 A high-purity quartz glass cylinder was manufactured using a high-purity quartz ingot in the same manner as in Example 1 except that the thickness was 4.5 mm. Using the single-layer high-purity quartz glass cylindrical body as it was, a furnace core tube was produced, and the heat treatment cycle of the silicon wafer was repeated as in Example 1, and the increase in impurities in the silicon wafer was measured in the same manner. The results are also shown in FIG. Also, as a result of observation by FTIR, the OH groups contained in the inner layers of the furnace core tubes of Examples 1 and 2 and Comparative Examples 1 and 2 are distributed in such a manner as to decrease inclining from the outer layer side to the inner direction. On the other hand, it was almost uniformly distributed in the single layer of high purity quartz glass of the furnace core tube of Comparative Example 3.

Examples 3-5 and Comparative Examples 4-5 Four high-purity quartz glass cylinders were produced in the same manner as in Example 1. Place the produced cylinder in an electric furnace,
The temperature was increased to about 700 ° C., and then SiCl ₄ 2 was introduced into the furnace.
0~80g / min, H ₂ 60~240 liters / min, O ₂
It is circulated at a rate of 30 to 120 liters / minute and flows inside the cylindrical body at 0.2 mm (Comparative Example 4), 0.5 mm (Example 3), 1.0 mm (Example 4), 1.5 mm (Example 4). Example 5) A quartz glass precursor was formed to a thickness of 2 mm (Comparative Example 5). The total thickness of these quartz glass precursors was 4.5 mm. Next, a multilayer quartz glass cylinder was prepared in the same manner as in Example 1 except that the ratio of water vapor (H ₂ O) to nitrogen gas was set to 1/2 so that the content of OH groups in the inner layer was 1500 ppm. Produced. A furnace core tube was manufactured using each of the obtained multilayer quartz glass cylinders, and a heat treatment cycle of the silicon wafer was performed using each of the manufactured furnace core tubes in the same manner as in Example 1 to increase impurities in the silicon wafer. The amount was measured.
FIG. 2 similarly shows the results as a relationship between the number of heat treatment cycles and the amount of impurities. The thickness of the inner layer of Comparative Example 5 is 2
The heating process was stopped because the furnace core tube of mm was significantly deformed after 100 heating cycles.

Comparative Example 6 SiCl ₄ was used in the same manner as in Example 1 using a cylindrical forming die.
The mixture was circulated at 20 g / min, 200 liters / minute of H _{2, and} 100 liters / minute of O ₂ for 30 minutes, and then steam (H ₂ O) and nitrogen gas were passed in the same manner as in Example 3 to obtain an OH group content. Was 1500 ppm to obtain a cylindrical body of a single layer of synthetic quartz glass constituting the inner layer in Example 3. A furnace core tube was manufactured using the obtained cylindrical body, and a heat treatment cycle of a silicon wafer was performed in the same manner as in Example 1 using the manufactured furnace core tube. Continuing was difficult.

From the above Examples and Comparative Examples, it was found that the outer layer was made of high-purity quartz glass, and the OH formed therein was formed with a predetermined thickness.
It is clear that a quartz glass furnace core tube having an inner layer of synthetic quartz glass having a base content in the range of 1000 to 2000 ppm does not deform even when repeatedly used at a high temperature of the heat treatment of the silicon wafer. Further, it can be seen that the contamination of the silicon wafer to be processed is extremely small.

[0020]

Industrial Applicability The quartz glass furnace core tube for processing semiconductor wafers of the present invention retains high-temperature strength, does not deform even when repeatedly used for high-temperature heat treatment, and contains Na in the furnace core tube.
It is possible to suppress the diffusion of metal impurities such as that described above, thereby preventing contamination of the semiconductor wafer to be processed. Furthermore, the semiconductor wafer can be repeatedly used without contaminating the semiconductor wafer for a long period of time, and has excellent durability, high reliability, and is extremely useful industrially.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the number of heat treatment cycles of a semiconductor wafer and the amount of impurities, showing the influence of the OH group content in the inner layer of the furnace core tube according to the embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the number of heat treatment cycles of a semiconductor wafer and the amount of impurities showing the influence of the thickness of the inner layer of the furnace core tube of the embodiment of the present invention.

Continuing from the front page (72) Inventor Tatsuya Rouki 30 Development Center of Toshiba Ceramics Co., Ltd., Hadano-shi, Kanagawa Prefecture (72) Inventor Nobuyuki Ueshima 30 Development Center of Toshiba Ceramics Co., Ltd., Hadano-shi, Kanagawa Prefecture (56) Reference Reference JP-A-62-268129 (JP, A) JP-A-62-14722 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/22 C03C 1/00-14 / 00 H01L 21/324

Claims (1)

(57) [Claims] 1. A quartz glass furnace core tube for processing a semiconductor wafer, comprising at least two layers, an innermost layer having a thickness of 5 to 35% of the total thickness of the furnace core tube and containing an OH group. A quartz glass core tube for processing semiconductor wafers, wherein the quartz glass core tube is made of synthetic quartz glass having an amount of 1000 to 2000 ppm, and an outer layer formed outside the innermost layer is made of high-purity quartz glass. .