JPH11204446A - Quartz glass furnace tube for semiconductor heat treatment furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase number of treatment objects that can be treated in one treatment, by constituting a tubular compact using an anisotropic carbon material such that ratio of thermal conductivity in the cylindrically longitudinal direction to the thermal conductivity in the direction of thickness of the compact is a specified ratio or higher, and thus enabling soaking of a furnace tube and extension of an effective thermal radiation range in the longitudinal direction. SOLUTION: A tubular compact 3 inserted between an inner tube 1 and an outer tube 2 which are made of quartz glass is constituted by using an anisotropic carbon material. As the anisotropic carbon material, a material having a graphite crystal structure such as graphite is preferred. Such an anisotropic carbon material is molded into a cylindrical tubular compact in which the a- and b-axis layer planes of its crystal are in parallel to the tube surface while the c-axis direction is matched toward the direction of thickness. In the compact in which the graphite crystal layer plane is thus oriented in parallel to the tubular surface, the thermal conductivity in the cylindrically longitudinal direction is approximately 100 W/m.K or higher and the anisotropic ratio of the thermal conductivity in the cylindrically longitudinal direction to that in the direction of thickness is approximately 30/1 or higher.

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 use in a semiconductor heat treatment furnace, for example, for a diffusion furnace.
More specifically, a quartz glass furnace core tube for a semiconductor heat treatment furnace having a multilayer structure in which a layer made of a specific carbon material having anisotropy is sandwiched between an inner tube and an outer tube made of quartz glass, The effective processing area of the object to be processed, such as wafers, is wide, and the soaking radiation in the furnace, especially in the longitudinal direction of the furnace core tube, is excellent, so that the emission of wafer contaminants from the furnace core tube is avoided. The present invention relates to a quartz glass furnace core tube for a semiconductor heat treatment furnace.

[0002]

2. Description of the Related Art In order to manufacture semiconductors used for various applications such as computers, heat treatment of, for example, wafers is required during the manufacturing process. Tubes are used. This heat treatment apparatus (diffusion furnace) usually includes, for example, as shown in FIG.
It has a structure in which, for example, a coil-shaped heating element 5 is disposed outside a furnace core tube 4 that accommodates a heat-treated object 7 such as a wafer placed on a susceptor 6 therein. The radiated heat rays penetrate the furnace tube wall and reach the object to be treated inside,
This is heat-treated. In order to avoid impurities being diffused from the tube itself and contaminating an object to be treated such as a wafer, the furnace core tube is generally made of quartz glass having the highest purity among ceramics. You.

[0003]

Generally, in a semiconductor heat treatment furnace used for industrial-scale production, an object to be processed such as a wafer is held in a furnace core tube by a susceptor in a longitudinal direction of the furnace core tube. A plurality of sheets are placed at equal intervals and processed at once. Therefore, from the viewpoint of improving productivity, it is preferable to increase the longitudinal effective length of the furnace core tube as much as possible so that as many wafers and the like as possible can be processed at once.
Quartz glass furnace core tubes are transparent, and in the past, semiconductor heat treatment furnaces employ a method in which radiant heat from a heating element, which is a heat source, is applied directly to a workpiece such as a wafer from the tube wall of the transparent furnace core tube. However, since quartz glass has a very low thermal conductivity, heat transfer is not rapid, and local temperature unevenness is likely to occur. In particular, it is extremely difficult to maintain a uniform temperature throughout the furnace core tube in the longitudinal direction. Met. For this reason, the length of the effective treatment area in the longitudinal direction of the furnace core tube is considerably shorter than the entire length thereof, which has conventionally been an obstacle from the viewpoint of improving productivity and reducing manufacturing costs. Therefore, it has been strongly desired to equalize the temperature of the furnace core tube, in particular, to extend the effective heat radiation area in the longitudinal direction as much as possible and to increase the number of objects to be treated at one time.

[0004] The inventors of the present invention aimed at improving the productivity in the above heat treatment step and further reducing the semiconductor manufacturing cost by using a furnace core capable of uniformly heating almost the entire area of a furnace core tube even if the tube length is long. As a result of diligent studies to develop a tube, the furnace core tube wall was constructed in a multi-layer structure in which a layer made of a specific carbon material having anisotropy was sandwiched between the inner and outer tubes made of quartz glass. As a result, the present inventors found that this problem of soaking the furnace core tube was solved, and completed the present invention.

[0005] Therefore, an object of the present invention is to provide a furnace core tube having a long effective processing area even in a longitudinally long furnace core tube, and excellent heat radiation uniformity in a furnace, particularly excellent heat radiation uniformity in the longitudinal direction of a furnace tube.
It is an object of the present invention to provide a quartz glass furnace core tube for a semiconductor heat treatment furnace in which emission of wafer contaminants from the furnace core tube is avoided.

[0006]

According to the present invention, a quartz glass for a semiconductor heat treatment furnace having a multilayer structure in which a tubular molded body made of a carbon material is sandwiched between an inner tube and an outer tube made of quartz glass. In the furnace core tube, the carbon material constituting the tubular molded body has anisotropy, and the ratio of the thermal conductivity in the direction of the cylindrical longitudinal surface to the thickness direction of the molded body is 30/1 or more. A quartz glass furnace core tube for a semiconductor heat treatment furnace is provided.

A quartz glass furnace core tube for a semiconductor heat treatment furnace according to the present invention has a furnace tube wall made of a double quartz glass layer,
It is a remarkable feature that a specific anisotropic carbon material layer is inserted between the layers. Typical examples of carbon having anisotropy include graphite (graphite). Graphite (graphite) has a so-called graphite-type crystal structure in which a condensed six-membered ring layer of carbon atoms spreads in a plane, and this layer surface has a layer structure in which the layers are stacked in layers. Adjacent layers of the graphite crystal structure are connected by a weak van der Waals force. Due to this graphite layer structure, graphite has strong anisotropy in physical properties. For example, in the case of graphite having a complete graphite crystal structure, the value in the direction parallel to the layer surface (base surface) is about 2000 W / MK, the value in the direction perpendicular to the layer surface is about 10 W / mK, indicating a remarkable anisotropy.

According to the present invention, a carbon material exhibiting anisotropy such as graphite is arranged such that its crystal layer planes (a and b axis planes) are substantially parallel along the cylindrical surface, and an axis perpendicular to the layer plane. Crystal orientation is performed such that the (c-axis) direction is oriented in the thickness direction, and a cylindrical shape is formed in this orientation state, and the cylindrical molded body formed in the oriented crystal state is formed into an inner tube and an outer tube made of quartz glass. After that, the end portion of the quartz glass tube is sealed to obtain a quartz glass furnace core tube having a multilayer structure. Therefore, the double-layered quartz glass furnace core tube of the present invention in which the molded body made of the anisotropic carbon material is sealed has a very high thermal conductivity in the plane direction (the longitudinal direction of the cylindrical ring), and includes the longitudinal direction. It is easy to transfer heat to the entire cylindrical surface. This makes it possible to achieve uniform heating over almost the entire area of the furnace core tube (expansion of the effective processing area), as shown in FIG. 2, and to increase the number of wafers that can be processed at one time. Cost reduction has become possible.

Further, when the carbon material is disposed inside the furnace core tube outside the quartz glass tube, it is considered that particles are generated from the carbon material and adhere to the wafer, which adversely affects the yield rate of the wafer. On the other hand, in the present invention, since the anisotropic carbon material is sealed in the double quartz glass tube, impurities from the carbon material generated at the time of heating are trapped in the tube wall and the impurities are trapped in the tube wall. Has the advantage of completely preventing the diffusion of silicon and the resulting contamination of the wafer.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a quartz glass furnace core tube for a semiconductor heat treatment furnace according to the present invention, an anisotropic material which is a constituent material of a tubular molded product inserted between an inner tube and an outer tube made of quartz glass. The conductive carbon material is not particularly limited as long as it has relatively good thermal conductivity as a whole, has high anisotropy in thermal conductivity, and can be formed into a cylindrical tubular molded body. Although not a thing, the carbonaceous molded body is sealed in quartz glass, and receives radiant heat irradiated from outside of the tube as a furnace core tube wall.
Since it is exposed to a high temperature exceeding 000 ° C., it is preferable that the material does not deteriorate, deform, or soften even at a high temperature and does not emit impurities such as volatile substances and gases.

In view of the above, in the present invention, it is preferable to use a carbon material having a graphite crystal structure such as graphite as a molding material, and among the carbon materials having a graphite crystal structure, the plane spacing between the layers is preferable. Those having a thickness between layers in the c-axis direction (Lc) of 800 angstroms or more are particularly preferable from the viewpoint of heat conduction anisotropy. In the present invention, an anisotropic carbon material such as a carbon material having a graphite-type crystal structure is used as a cylinder in which the a- and b-axis layers of the crystal are parallel to the tube surface and the c-axis direction is aligned in the thickness direction. It is formed into a tubular shaped body. Thus, the molded article of the present invention in which the graphite crystal layer surface is oriented parallel to the tubular surface,
Thermal conductivity in the plane direction (longitudinal direction of the cylindrical ring) is 100 W / m
K or more, the anisotropic ratio of the thermal conductivity in the plane direction and the thickness direction is 30 /
It becomes 1 or more.

In the present invention, as a particularly preferable anisotropic carbon material molded product, expanded graphite is used among carbon materials, and a cylindrical tube is manufactured from a product obtained by molding this expanded graphite into a sheet shape, or a granular tube is produced. Also, there can be mentioned those in which an expanded graphite material such as a powder is directly formed into a tubular body. Since the C axis of the graphite crystal is aligned in the thickness direction of this molded body, the thermal conductivity in this direction is relatively low, while the surface direction (longitudinal direction of the cylindrical ring)
Has a remarkably high thermal conductivity because the a and b-axis layers of the graphite crystal are oriented in parallel along the cylindrical surface, and exhibits high heat transfer anisotropy. Moreover, its gas permeability in the thickness direction is
Since expanded graphite has almost no open pores, it has a characteristic that it is significantly lower than other carbon materials, and thus has a characteristic of significantly reducing dust generation and gas emission. This expanded graphite can be easily obtained as a commercial product as a granular or powdery molding material or as a sheet-like molded product.

An example of the physical properties of the commercially available expanded graphite sheet is as follows. Bulk density: 1.3 g / cm ³ Specific heat capacity: 0.6865 J / gK 21 ° C. Thermal diffusivity: thickness direction 0.0319 to 0.0391 cm ² / s In-plane direction 0.919 to 1.030 cm ² / s Heat conduction Ratio: thickness direction 2.3 to 2.6 W / m · K In-plane direction 62 to 71 W / m · K

In order to obtain the tubular molded article of the present invention, for example,
From such a material for commercial molding, press-forming and CIP molding are used to temporarily form a crystal-oriented sheet having a predetermined thickness, or a commercially available sheet having a predetermined thickness and a predetermined property is prepared, and a needle or the like is inserted into the sheet. A large number of small through holes are formed at a predetermined pitch using the sheet, and the sheet is wound around a cylindrical mandrel or the like, and the wound ends are joined to produce a tubular molded body, or a tubular molded body is directly molded from the material. To make. The thickness of the sheet or tubular molded body slightly varies depending on the size of the furnace core tube, use conditions, and the like. However, the anisotropic carbon material generally has a thermal conductivity of 2 in the thickness direction, that is, the c-crystal axis direction.
It is not advisable to form a very thick layer because it is not so high as about 4 W / m · K, and the minimum thickness at which uniform heating is achieved as a furnace core tube wall, usually about 1 to 5 mm Is set to

Preferably, the sheet or the compact is purified by a method such as a high-temperature heat treatment in a vacuum or a heat treatment in a halogen gas, so that the sheet or the compact is occluded in the anisotropic carbon material of the compact. The gas, volatile components, metal impurities in the material, and other contaminants are removed, and the molded body thus purified has an in-plane thermal conductivity of 100 W / m · K or more. It is further improved.

To manufacture the quartz glass furnace core tube for a semiconductor heat treatment furnace of the present invention, for example, first, an outer tube and an inner tube made of quartz glass are prepared, and the inner tube is inserted into the outer tube to burn an oxyhydrogen burner or the like. One end of the tube is sealed, and a tubular molded body made of the anisotropic carbon material is inserted into a gap between the double pipes. To obtain a quartz glass double furnace core tube. That is, as shown in FIG. 1, the quartz glass double furnace core tube includes a cylindrical anisotropic carbon material molded body 3 between a quartz glass inner tube 1 and a quartz glass outer tube 2. The furnace core tube of the present invention thus manufactured is mounted in, for example, a furnace of a thermal diffusion furnace as shown in FIG. 3 and used for heat treatment of a wafer or the like. Hereinafter, the quartz glass furnace core tube of the present invention will be described in more detail with reference to examples, and the performance evaluation results will be shown as a graph in FIG.

[0017]

EXAMPLES Example 1 Expanded graphite (Chuo Kasei Co., Ltd., 99
60 grade) was formed into a sheet to obtain a sheet having a thickness of 0.4 mm. Examination of this orientation by measurement with a powder X-ray diffractometer confirmed that the a and b crystal axes were oriented in the plane direction and the c crystal axis was oriented in the thickness direction. The sheet-shaped expanded graphite was pierced with through holes at a pitch of 2.5 mm with a needle having a diameter of 0.4 mm, and then the sheet was wound around a cylindrical metal mandrill while applying a tension of about 10 kg / cm ² .

The reason why a large number of through-holes are provided in the sheet-like expanded graphite is that if the same is formed in the next step without providing the through-holes, air easily accumulates between the sheets, and expansion occurs in the carbonization and purification steps. This is because the gas generated from the graphite is not sufficiently released, and as a result, the strength of the cylindrical body is reduced, and fine swelling of about φ1 mm is generated on the surface. In this study, it has been confirmed that the most effective method for forming through-holes without the above-mentioned problems is to form the through-holes at a pitch of 1 mm or more and a pitch of 5 mm or less. In addition, it has been confirmed that the diameter of the above-mentioned through-hole is φ3 mm at the upper limit when considering the thermal conductivity in the longitudinal direction of the furnace core tube for a semiconductor heat treatment furnace, and in particular, the uniformity in the furnace core tube. I have.

At the time of winding, in order to bond the sheets, a solution in which a phenol resin was diluted with a methanol solvent and the viscosity was adjusted to 200 to 400 poise was applied to the outer surface of the wound sheet using a brush.

Next, the sheet wound around the mandrel was covered with a cylindrical rubber mold having a thickness of 1 mm, and was molded under a pressure of 1 ton / cm ^{2 by} a hydrostatic press. The obtained molded body was heated in a vacuum at a heating rate of 100 ° C./hr, and heat-treated at 2000 ° C. to carbonize the phenol resin. Thereafter, heat treatment was performed in a halogen gas to remove metal impurities, thereby obtaining a cylindrical tubular anisotropic carbon material molded body having an outer diameter of 100 mm, an inner diameter of 90 mm, and a length of 500 mm.

Separately, outer diameter 110 mm, inner diameter 100 mm,
Quartz glass tube for outside with a length of 1000mm and outer diameter 90m
An inner quartz glass tube having an inner diameter of 80 mm, an inner diameter of 80 mm and a length of 1000 mm was prepared, the inner glass tube was inserted into the outer glass tube, and one end was sealed with an oxyhydrogen burner. The anisotropic carbon material compact was inserted into the gap between the double tubes, and the other end was sealed while reducing the pressure with a vacuum pump, and the anisotropic carbon material as shown in the sectional layer structure diagram in FIG. A quartz glass furnace core tube with an internal multilayer structure was obtained. A ceramic heating element is wound in a coil shape around the center of the furnace core tube in the longitudinal direction at a length of 500 mm, heated to 1000 ° C., a thermocouple is inserted into the reduced pressure furnace core tube, and the thermocouple is moved for 20 mm. Each time, the temperature distribution in the furnace core tube was measured. The measurement result is shown in FIG. 2 as a furnace temperature distribution diagram.

Comparative Example 1 Outer diameter 110 mm, inner diameter 100
A quartz glass tube (outer tube) with a length of 1000 mm and a length of 1000 mm and a quartz glass tube (outer tube) with an outer diameter of 90 mm, an inner diameter of 80 mm, and a length of 1000 mm are prepared. One end was sealed. Then, while reducing the pressure with a vacuum pump, the other end was sealed to produce a quartz glass double furnace core tube having a vacuum inside. A ceramic heating element was provided on this furnace core tube as in Example 1, and the temperature distribution inside the furnace was measured as in Example 1. FIG. 2 shows the measurement results.

As is apparent from FIG. 2, the furnace core tube of the present invention having a multi-layer structure in which the anisotropic carbon material is present has a more effective treatment area than the furnace core tube of Comparative Example 1 made of only quartz glass. Has a length of about 1.5 times as long as that of the conventional product having the same shape, and it has been recognized that the number of processed objects at one time is greatly improved.

[0024]

As described above, the quartz glass furnace core tube for a semiconductor heat treatment furnace according to the present invention has a multilayer structure in which a specific anisotropic carbon material layer is inserted between layers of a double quartz glass layer. Since it consists of a tube wall, it has excellent soaking radiation in the furnace, especially in the longitudinal direction of the furnace core tube. Can be greatly improved. Of course, since the anisotropic carbon material layer is sealed in the quartz glass layer, the emission of contaminants from the furnace core tube to the wafer is also avoided, so that it can be used very suitably as a furnace core tube for a semiconductor heat treatment furnace.

[Brief description of the drawings]

FIG. 1 is a diagram showing a sectional structure of a wall surface of a quartz glass furnace core tube of the present invention.

FIG. 2 is a diagram comparing the furnace temperature distribution measurement values of each furnace core tube of Example 1 and Comparative Example 1, with the vertical axis representing the furnace temperature and the horizontal axis representing the furnace temperature. The distance from the center is shown. The right side of the horizontal axis indicates the upward direction of the furnace, and the left side indicates the downward direction of the furnace.

FIG. 3 is a schematic cross-sectional view for explaining a configuration of a semiconductor heat treatment apparatus (diffusion furnace).

[Description of Signs] 1 quartz glass inner tube 2 quartz glass outer tube 3 cylindrical anisotropic carbon material molded product 4 furnace core tube 5 heating element 6 susceptor 7 workpiece (wafer)

Claims (4)

[Claims] 1. A quartz glass furnace core tube for a semiconductor heat treatment furnace having a multilayer structure in which a tubular molded body made of a carbon material is sandwiched between an inner tube and an outer tube made of quartz glass. The carbon material constituting the body has anisotropy, and the ratio of the thermal conductivity in the cylindrical longitudinal direction and the thermal conductivity in the thickness direction of the formed body is 30 /
A quartz glass furnace core tube for a semiconductor heat treatment furnace, which is at least one. 2. An anisotropic carbon material constituting said tubular molded body has a graphite type crystal structure, and a, b of said graphite type crystal.
The cylindrical layer has a thermal conductivity of 100 W / m · K or more, wherein the axial layer surface is parallel to the tube surface of the molded body, and the c-axis direction is aligned in the thickness direction. 1
4. A quartz glass furnace core tube for a semiconductor heat treatment furnace described in 1. 3. The heat treatment of a semiconductor according to claim 2, wherein the interlayer thickness (Lc) in the c-axis direction of the graphite type crystal structure in the anisotropic carbon material is 800 Å or more. Quartz glass furnace core tube for furnace. 4. A quartz glass furnace core tube for a semiconductor heat treatment furnace according to claim 1, wherein the anisotropic carbon material constituting said tubular molded body is expanded graphite. .