JPH0694380B2 - Silica thermal insulation 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 heat insulating and heat insulating material for silica, for example, a heat insulating cylinder for mounting a wafer supporting boat for heat treating a silicon wafer in a furnace core tube or a large furnace structure. TECHNICAL FIELD The present invention relates to a silica heat-insulating heat insulator, which is required to have heat resistance strength, heat insulation properties, and high temperature pollution resistance, and a manufacturing method thereof.

[0002]

2. Description of the Related Art For example, in a vertical heat treatment apparatus used in the semiconductor industry, a boat in which a large number of wafers are loaded in parallel is placed on a heat insulating cylinder, and 400 ° C. to 1200 ° C. in a furnace core tube.
Various heat treatments such as oxidation, diffusion, vapor phase growth or annealing are performed on the surface area of the semiconductor wafer by heating to a high temperature range of ° C and flowing a specific reactive gas or inert gas. The heat-retaining cylinder as a heat-retaining heat insulator used in the treatment has heat resistance to withstand extremely high temperatures as described above, and a sealing O-ring or other seal portion arranged at the lower open end of the furnace core tube. Thermal insulation that does not transfer heat, heat retention that keeps the temperature inside the furnace uniform, and chemical stability that is not affected by the reaction gas are required.

As a heat insulation material meeting these requirements,
A quartz glass cylindrical container having high heat resistance, high purity and excellent chemical stability was filled with a quartz glass fiber wool as a heat insulating material and the container was vacuum-sealed. However, it is extremely difficult to fabricate a vacuum vessel made of quartz glass, and it is extremely difficult to fabricate it because it causes an internal breakdown due to external pressure or cracking during the fabrication and causes an explosion.

In addition, such a glass-wool-filled depressurized heat insulating cylinder has a low strength because the inside is a cavity in a depressurized state. -Since there were frequent accidents such as thermal deformation and breakage of the heat insulation cylinder itself due to lack of physical strength to withstand the heavy load of the hubot, significant improvement in mechanical strength at high temperature was required.

Further, in repeated use of heat treatment, the reaction gas treated product adhering to the surface of the heat insulating cylinder is used to control the reaction gas.
Since unreacted reaction gas is regenerated and dust is generated due to unwanted scattering of deposits, it is necessary to frequently perform etching cleaning with an acid to remove deposits. Due to this etching, pinholes are generated on the surface of the heat insulating cylinder, so that the etching chemical enters the inside of the heat insulating cylinder in a depressurized state, and there are many accidents where the chemical is vaporized and explodes in the subsequent heat treatment step, which is a serious problem. ing.

In view of such circumstances, the inventors of the present invention have made a quartz glass heat-insulating cylinder in which a plurality of divided small cylinders are combined to enhance the strength, and the small cylinder is a plastic body having a large number of minute spaces and the same. We have found a method of reinforcement by constructing a transparent glass film surrounding the
7020). Although this reinforcing method certainly improves the strength, it is industrially disadvantageous to manufacture a large number of divided small cylinders, and it is extremely difficult to form a glass coating layer of sufficient thickness to surround the plastic body. It is difficult, and the glass coating is damaged during use, exposing the plastic body.

On the other hand, in a vertical furnace used for heat treatment in the semiconductor industry or in a reaction diffusion treatment furnace for doping a specific element into a processed material, unspecified impurities from the furnace material are removed during the processing. In order to avoid invasion, high heat insulation and heat resistant materials such as bricks and heater holders, which are used as furnace wall materials and furnace structural materials, are required to have high purity and structural strength.

Conventionally, as these heat insulation materials, sintered porous bricks or boards mainly composed of alumina, zirconia or silicon carbide have been used, but these are metal oxides themselves and are impurities. Is contained in a large amount, and dust is generated and passes from the porous portion, so that it is unsuitable for the treatment satisfying the various requirements as described above and cannot be practically used.

Further, the heat insulating heat insulating material generally used for the furnace material has an excellent temperature followability and a high heat insulating property for the temperature rise and temperature decrease in the furnace to be used, from the viewpoint of saving the heating energy and improving the efficiency of the heat treatment process. However, in order to improve temperature followability and heat insulation, it is necessary to reduce the density of the heat insulating heat insulating material and reduce the heat conduction area and heat capacity. In the body, if the density is reduced, the strength becomes insufficient, and in a large furnace, the heat capacity is large and it takes time to raise and lower the temperature, and moreover, a large amount of energy is required for the lowering of the temperature, which is inefficient and difficult to adopt. .

[0010]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to have both excellent strength as a structural material, an ability to block impurity dust, and a chemical stability that does not diffuse impurities by itself.
Another object of the present invention is to provide a member having a small density, excellent heat retention, and excellent heat insulation and good operability. In addition, other technical issues
An object of the present invention is to provide a method for industrially producing such a heat insulating material in an advantageous and effective manner.

[0011]

Means for Solving the Problems The inventors of the present invention have conducted various manufacturing researches on the above-mentioned problems and found a heat insulating heat insulator and a manufacturing method thereof which are extremely advantageous in practical use. That is, the gist of the present invention is a silica heat insulating heat insulating material and an effective manufacturing method thereof which satisfy the requirements described in the claims.

The silica heat insulating and heat insulating material according to the present invention, in particular, has a high-purity silica glass plate-shaped sintered body and a high-purity silica glass plate-shaped sintered material on the entire surface of the high-purity silica glass porous material having an apparent density range of 0.1 to 1.6 g / cm ^3. The technical feature lies in the structure in which the hard silica glass plate is integrally formed. Further, the porous body is preferably 70% or less open pore rate, in other words,
It has a three-dimensional strength that contains 30% or more closed cells based on all pores, and is used as a furnace structural material with heat-resistant shape stability that can withstand a high temperature of 1700 ° C, for example. Is very desirable.

When the apparent density of the porous body is less than 0.1 g / cm ³ , it is related to the content ratio of communicating cells, but it is usually
It is not preferable because the mechanical strength and heat-resistant shape stability required for the furnace structural material are insufficient, and when it exceeds 1.6 g / cm ³ , the heat insulating and heat insulating property is deteriorated. The preferable density of the porous body is
It is in the range of 0.2 to 1.0 g / cm ³ .

Further, it is desirable that the metal impurities contained in the silica glass constituting the porous silica material be as small as possible in the heat treatment of semiconductors and the like, but in the heat treatment of semiconductors and the like, the metal impurities are When the content of Al exceeds 100 ppm, the adverse effect of contamination on the wafer cannot be substantially avoided. Therefore, it is important that the total amount of impurity metals is 100 ppm or less.

The heat insulating heat insulating material is usually repeatedly heated and cooled. Under such conditions, the metal impurities contained in the glass act as crystal nuclei to promote crystallization of the porous body and the hard silica glass body enclosing the porous body, and the formed crystallized vitreous portion is not Cracks due to the difference in expansion and contraction due to temperature changes with the crystallized vitreous part will reduce the strength of the glass body, and as a result, the life of the heat insulation material will be shortened. Those that do not contain impurities are desirable.

As such an impurity metal, for example,
Representative examples include cerium, sodium, potassium, aluminum, calcium, nickel and iron. All of these metals are disadvantageous because they accelerate the crystallization of the glass. In particular, the fast-moving alkali metals in silica glass have a remarkable crystallization effect on silica glass, so their content is as small as possible. Is desirable.

The silica glass constituting the silica porous body has a lower heat resistant temperature as the amount of OH groups contained therein increases. For example, silica glass with an OH group content of more than 300 ppm does not provide shape stability in the operating temperature range of 1000 ° C or higher, and in particular, it is easily thermally deformed due to the weight of the load or its own weight, so the operating temperature is extremely limited. Therefore, it cannot be used as a high temperature furnace material. Therefore, in order to use it as a high temperature heat insulation furnace material, OH contained in silica glass is used.
It is practically important that the content of the group is 300 ppm or less. A desirable content is 200 ppm or less.

Further, it is preferable that the content of communicating cells in the porous silica material is small, and if the mechanical strength of the silica thermal insulation body to be formed is taken into consideration, the content rate of the communicating pores in the total pore volume thereof is considered. That is, it is desirable that the open pore ratio is 70% or less. This open pore ratio is, for example, the open density of the open pores calculated by measuring the apparent density of the member and the density of the silica glass itself constituting the member and increasing the weight obtained by immersing the original porous member in a liquid. Easily calculated from the volume.

The plate-like silica glass sintered body and the hard silica glass plate-like body used for the heat insulating and heat insulating material of the present invention include reinforcing the porous body and fine fragments generated from the surface of the porous body and dust from exposed pores. It is a coating shell layer for preventing pollution in the furnace for preventing the scattering of the, and high-purity silica glass is used like the porous body. The thickness of the plate-like shell of silica glass is not preferably too thin or too thick in consideration of temperature followability, and for example, about 1 to 10 mm is preferably adopted. Further, the coated shell layer is preferably a plate-shaped sintered body in consideration of industrially desired performance.

Next, a method for manufacturing the silica heat insulating and heat insulating material of the present invention will be described. The silica glass porous body used for producing the heat insulating body of the present invention can be produced by various commonly known methods for producing silica glass foam.
For example, a silica glass porous body containing many closed cells can be easily prepared by impregnating a silica porous body with a substance that gasifies under the melting temperature condition of glass or by mixing with silica powder and heating and melting the glass. Can be obtained. In that case, if the metal impurity content is 100 ppm or less and the OH group content is
A silica glass material of 300 ppm or less is used, and a foaming gasifying substance that does not introduce metal impurities is used.

Further, it is important that the porous body according to the present invention has sufficient strength as a heat insulating body at a high temperature, and in this connection, the apparent density of silica glass foaming is 0.1 to 1.6 g / It is important to control so as to be in the range of cm ³ and the open cells of the porous body be 70% or less. Such control can be carried out by selecting the foaming conditions, usually the type of gasifying substance, its content, their mixed dispersion state and heating temperature condition. The selection conditions can be easily determined by those skilled in the art by simple experiments.
The method for producing a quartz glass foam described in JP-A 1-308846 can be used.

The silica glass porous body formed in this manner usually has a porous structure depending on the purpose of use or the purpose of use.
With a diamond grindstone or glass blade, for example, it is processed into various desired shapes such as a cube, a rectangular parallelepiped, a cylinder, and the like.
In a heat-resistant mold container made of carbon, a hard silica glass plate-like body and / or a plate-like silica glass sintered body is melt-integrated on the entire surface of the porous body, and these plate bodies are used as a covering shell body. It is formed into a heat insulation body.

In melting and integrating the hard silica glass plate and / or the plate silica glass sintered body into the porous body, high-purity silica glass powder is put in a heat-resistant mold container for molding. By embedding the silica porous body of the desired shape in the powder in the middle part and heating it to a temperature in the range of 1400 to 1800 ° C., a plate-shaped silica glass sintered on the entire surface of the porous body. The body can be formed into a monolithic coated shell.

The silica glass powder used for forming such a plate-shaped silica glass sintered body is prepared by crushing synthetic quartz glass produced by a sol-gel method or a vapor phase synthesis method, and a desired plate-shaped firing is performed. Those having an appropriate particle size range are selected and used according to the formation of the aggregate. The particle size of the powder is not particularly limited, but, for example, a powder pulverized and adjusted to about 50 to 500 μm is preferably used in practice.

Further, a hard silica glass plate is brought into contact with the peripheral side surface, the upper and lower surfaces or the whole surface of the porous body and placed in the heat resistant molding container, at that time, the porous body and the inner surface of the heat resistant molding container. At least a silica glass powder layer is interposed in the portion that directly contacts with, and the glass shell body integrated with the surface of the porous body is formed by heating within a range of 1400 to 1800 ° C in a furnace. . At that time, silica glass powder can be applied to the joint surface between the hard silica glass plate and the porous body to be used as a fusion agent.

Next, the production of the silica heat insulating and heat insulating material of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view in an electric furnace showing an example of a state in which a hard silica glass plate-like sintered body coating layer is formed on the surface of a porous silica glass body. FIG. 2 is a partially cutaway perspective view of an example of a heat retaining cylinder of the cylindrical heat retaining heat insulator according to the present invention. In addition, FIG.
FIG. 6 is a partially cutaway perspective view of an example of a rectangular parallelepiped heat retaining tube.

In FIG. 1, an appropriate amount of silica powder 2 is spread in a bottomed cylindrical heat-resistant molding container mold 1 made of carbon, and a columnar porous body 3 is placed on the silica powder 2 to form a porous structure. Silica powder 4 is filled in the gap between the peripheral side surface of the body and the inner peripheral wall of the container mold 1, and the same silica powder is spread over the silica powder portion and the upper surface of the porous body. Then, a disc-shaped dropping lid 5 made of carbon and having a diameter slightly smaller than the inner diameter of the heat-resistant cylindrical container mold 1 is inserted and placed on the inside of the container mold 1 on the container.

Next, this is placed on the table 6 in the electric furnace,
The heater 7 heats the inside of the furnace to a temperature in the range of 1400 to 1800 ° C. Although slightly different depending on the temperature, the silica powder covering the entire surface of the porous body is sintered after 1 to 2 hours to form a coated shell plate body integrated with the porous body. In this sintering integration process, for example, a spacer (not shown) for horizontally supporting the dropping lid 5 may be attached to an appropriate place in the heat-resistant container mold so that the dropping lid 5 is lowered and held horizontally. It is practical.

In the silica heat insulation heat insulator shown in FIG. 2, a hard silica glass disk 12 is fused and integrated on the upper surface of a cylindrical porous body 11, and a small disk-shaped waferbot or the like is formed on the upper surface thereof. The mount table 13 is formed concentrically and integrally, and a hard silica glass disk 14 is similarly fused and integrated under the porous body 11 and the porous body The tubular outer peripheral curved surface has a structure in which a hard silica glass sintered plate body 15 is fused and integrated. Such a heat insulation body, in particular,
It can be suitably used for a heat insulating cylinder of a semiconductor heat treatment furnace.

The heat insulating and heat insulating body of FIG. 3 is of a brick shape in which a hard silica glass sintered shell body 17 is fused and integrated on all surfaces of the rectangular porous body 16 above, below, left and right, and front and rear, Since the constituent material is a heat insulator made of high-purity hard glass, it is a highly heat-resistant and heat-retaining furnace material that is particularly desirable as a furnace wall of a furnace for heat treatment of semiconductors, etc. where contamination with impurity metals at high temperatures poses a problem. .

[0031]

According to the method of the present invention, a lightweight and high-purity heat-retaining heat insulator can be provided easily and inexpensively. Further, the obtained heat insulator has excellent heat-resistant shape stability and mechanical support strength at high temperatures, and therefore has wide applicability as a heat insulating cylinder and other various heat insulating heat insulating members.

[0032]

【Example】

Example 1 Silica powder containing about 200 ppm of OH groups and having a particle size of 50 μm or less was filled in a cylindrical mold having an inner diameter of about 250 mm to give about 140
It was heated to a temperature of 0 ° C. for about 60 minutes to produce a cylindrical sintered body. Next, this sintered body is subjected to about 80
Ammonia was carried out by heating to a temperature of 0 ° C. and reacting for about 30 minutes. Next, after removing the ammonia gas in the atmosphere,
The silica was melted by heating at a temperature of 1600 ° C. for 5 hours under reduced pressure, and free gas was generated from the inside to produce a porous body by the foaming. This is cut to a diameter of 200 mm and a height of 2
A cylindrical porous body of 00 mm was prepared.

The apparent density of this porous body is 0.4 g / cm ^3.
The ratio of the contained communicating bubbles to all the bubbles was about 50%. Moreover, as a result of analyzing the metal impurities contained therein by the atomic absorption photometry, the amounts of sodium, potassium, lithium, calcium, iron, aluminum, cerium and nickel as metal components are all less than 0.5 ppm. Met.

Two transparent quartz glass disks each having a diameter of 200 mm and a thickness of 8 mm were respectively brought into contact with the upper and lower circular surfaces of the obtained cylindrical porous body to make a smooth surface having an outer diameter of 260 mm and a thickness of mm. A cylinder is placed upright in the center of the carbon disk, and on the outside, a carbon cylinder with an inner diameter of 250 mm, a thickness of 5 mm and a height of 280 mm is installed so that it can be stored inside. The silica glass obtained by the sol-gel method was crushed from above to obtain a synthetic silica powder having a particle size adjusted to 600 μm or less.
It was filled up to a height of 230 mm from the surface of the Bonn disc.

Next, a disk-shaped carbon dropping lid having a diameter of 248 mm and a thickness of 30 mm was placed on the silica glass powder filled in this carbon cylindrical container mold, and the whole was placed in an electric furnace. Then, after depressurizing the inside of the furnace to about 0.1 torr, it is heated at 1700 ° C. for 55 minutes to be fused and integrated while being compressed by the weight of the carbon dropping lid, and at the same time, the silica glass powder is baked on the peripheral side surface. I made it united.

After cooling, the integrated product was taken out from the carbon cylinder type and the outer surface was ground with a cup type diamond grindstone to form a cylindrical glass outer peripheral curved surface with a silica glass sintered body layer having a thickness of 8 mm, and upper and lower circular shapes. A silica thermal insulation body having a diameter of 216 mm and a height of 210 mm having a transparent silica glass plate layer having a thickness of about 7 mm on the surface was obtained.

With respect to the obtained heat-insulating heat insulator, heating-cooling repeated test was conducted, and the rate of temperature increase, rate of temperature decrease and compression strength were tested. Repeated heating-cooling test: Heat insulation 2 in a furnace at 1200 ℃
After holding for a period of time, the sample was allowed to cool to room temperature, put in the furnace again, and heated to perform a repeated heating test. No signs of cracking or crystallization were observed even if the heating and rolling time at 1200 ° C exceeded 2000 hours.

Compressive strength test: 1 kg / min of heat insulation
/ It was subjected to compressive strength tests to increase the pressure at a rate of cm ^2, and not broken even at the pressure of about 120 kg / cm ^2. On the other hand, the same shape as this heat insulation body (diameter 216m
The same compressive strength test was performed on a porous body similar to the porous body contained in the heat insulating and heat insulating body, and as a result, partial destruction was caused at about 10 kg / cm ² . By this test, it was confirmed that the heat insulating and heat insulating material of the present invention has a breaking strength about 12 times or more higher than that of the porous material having the same shape.

Temperature increase-temperature decrease test: internal volume of 80 liters and
Using the heat insulating and heat insulating material of the present invention having the same shape as the furnace opening alumina brick of a cylindrical electric furnace having a heating capacity of 30 kVA as a furnace material, the time during which the temperature in the electric furnace rises to 1200 ° C. and the power is turned off. The time for the temperature to cool to room temperature was investigated.
Whereas the heat insulating heat insulator of the present invention required 2 hours to raise the temperature and 3 hours to lower the temperature, in the case of using the alumina brick used as a normal electric furnace structural material, the temperature rise took 3 hours. , It took 5 hours to cool down. As a result, it was found that the electric power consumption of the electric furnace and the processing cycle were significantly improved.

[0040]

INDUSTRIAL APPLICABILITY The heat insulating and heat insulating material according to the method of the present invention has excellent heat insulating and heat insulating properties and compressive strength, and is extremely stable against repeated temperature changes, and can withstand long-term use. high.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of the inside of an electric furnace for explaining an example of a state in which a silica heat insulating heat insulator of the present invention is manufactured.

FIG. 2 is a partially cutaway perspective view of a heat retaining cylinder of an example of a cylindrical heat retaining heat insulator according to the present invention.

FIG. 3 is a partially cutaway perspective view of an example of a rectangular parallelepiped heat insulating heat insulator according to the present invention.

[Explanation of symbols]

1 Heat-Resistant Molding Container Type 11 Cylindrical Porous Body 2,4 Silica Powder 12 Upper Hard Silica Glass Disc 3 Cylindrical Porous Body 13 Placement Holder 5 Disc Dropper 14 Lower Hard Silica Glass Disc 6 units 15 Hard silica glass sintered plate body 7 Heater 16 Rectangular porous body 17 Hard silica glass sintered shell body

Claims (5)

[Claims] 1. A metal impurity content of 100 ppm or less, OH content
Apparent density composed of silica glass whose base is 300 ppm or less
A silica heat-insulating heat insulator comprising a plate-like silica glass sintered body and / or a hard silica glass plate-like body integrally formed on the entire surface of a porous silica body of 0.1 to 1.6 g / cm ³ . 2. The silica heat insulating / insulating body according to claim 1, wherein the silica glass porous body has an open pore ratio of 70% or less. 3. Silica glass powder is placed in a heat-resistant molding container mold, and the powder has an apparent density of 0.1 to 1.6 g / cm ³ and contains metal impurities of 100 ppm or less. O
H group is embedded in a silica porous body of 300ppm or less, or put into the heat-resistant molding container mold by abutting a hard silica glass plate on the peripheral side surface and / or upper and lower surfaces of the porous body, At this time, at least the silica glass powder is filled in the portion where the porous body and the inner surface of the heat resistant molding container are in direct contact with each other, and 1400
The method for producing a silica heat insulating heat insulator according to claim 1, wherein the heat insulation is carried out at a temperature in the range of 1800 ° C. 4. Silica glass powder is obtained by a sol-gel method or a gas phase synthesis method, containing metal impurities of 100 ppm or less,
4. The method according to claim 3, wherein the glass is prepared by crushing glass having an OH group content of 300 ppm or less. 5. The manufacturing method according to claim 3, wherein the heat integration of the silica porous body and the silica glass powder is performed under a reduced pressure atmosphere condition.