JP2768624B2 - Heat-resistant siliceous foam 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-resistant siliceous foam, and more particularly to a lightweight, heat-resistant siliceous foam useful for the semiconductor heat treatment industry for wafers and the like, and an effective method for producing the same. About.

[0002]

2. Description of the Related Art Silica is a relatively lightweight, high-purity ceramic material having excellent heat resistance, and its foam is used, for example, as a heat insulating material or a heat insulating material in a heat treatment furnace for semiconductor wafers. I have. These silica foams are prepared by heating silica powder in an atmosphere containing ammonia gas to introduce ammonia groups to the surface of the silica, putting the silica powder chemically bonded with ammonia into a desired mold, A foaming method of heating and melting at a high temperature to simultaneously fuse the powder and decompose and release the ammonia group is generally adopted. In this method, for example, a porous silica base material (soot body) obtained by a soot method or an aggregate obtained by solidifying fine quartz glass powder with a resin such as polyvinyl alcohol is generally used. Can be

However, high-purity silica foam is, for example,
Deformation starts at a temperature of around 1300 ° C.
Use for a long time is inconvenient.
Manufactured silica foam is no exception;
The scope and target of their use is generally limited.
In addition, as semiconductor wafers have become larger in diameter,
Lighter with higher heat-resistant temperature and mechanical strength as heat insulator
Foam materials are required, e.g.
Viscosity at 1280 ° C by the bending method is 10
^11.7 Or more, preferably 10^11.9 Materials with the above heat resistance
Fees have come to be demanded in practice. But like that
Despite high industrial demands, high heat resistance as described above
Lightweight silica foams are still industrially advantageous
Not provided.

[0004]

It is an object of the present invention to provide a siliceous foam having higher heat resistance. Another object is to provide a method for effectively producing a siliceous foam having improved mechanical strength and heat resistance, which can be used industrially as a furnace heat insulating material for heat treatment of large semiconductor wafers. It is in.

[0005]

Means for Solving the Problems The present inventors have focused on silica as a highly heat-resistant material for silica-based foams that have overcome the above-mentioned problems, and have carried out a number of trial production experiments on added materials. We have developed a very practical silica-based foam that solves the problems. That is, the present invention relates to a siliceous foam containing a ceramic component in a range of 5 to 100 parts by weight based on 100 parts by weight of the silica, and the foamed material is used as the siliceous constituent component. Summary of the invention is a heat-resistant siliceous foam containing 0.02 to 0.5% by weight of chemically bonded nitrogen atoms.

[0006] The present invention also provides a silica powder having 100 parts by weight,
A ceramic powder selected from the group consisting of alumina, zirconia, titania, boron oxide and silicon carbide
Silica mixed powder containing in a range of 100 parts by weight,
700 to 1200 ° C in an ammonia atmosphere of 1 to 100% by volume
The present invention provides a method for producing a heat-resistant siliceous foam in which the powder is melted and foamed by reacting it with ammonia under the heating conditions described above, and then heating it at a temperature of 1400 to 1800 ° C. in a predetermined mold.

[0007] The present invention is characterized in that a foamed material is a mixture of high-purity silica and the above ceramic component, and the heat resistance of the foam is improved and the mechanical properties of the foam are improved by such a material structure. This has the advantage that the target strength can be improved and a further lightweight foam member can be provided.

In the siliceous material constituting the siliceous foam of the present invention, the ceramic component materials used in combination with silica include alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ),
Titania (TiO ₂ ), boron oxide (B ₂ O ₃ ), and silicon carbide (SiC), and these oxides can be used alone or in combination of two or more kinds and mixed with silica. . The amount used is in the range of 5 to 100 parts by weight based on 100 parts by weight of silica. If the addition amount is less than 5 parts by weight, the effect of improving the heat deformation resistance particularly at high temperatures is insufficient, and if it exceeds 100 parts by weight, not only the desired properties inherent to silica are impaired, but also the desired shape of the foam is reduced. It is not preferable because it becomes difficult to form it on the body.

In the method for producing a heat-resistant siliceous foam according to the present invention, both the raw material silica and the ceramic component are used in the form of fine powder, which are mixed into a uniform composition at a desired weight ratio. You. This uniformly mixed powder is placed in a furnace, and an ammonia gas, for example, an atmosphere for ammonia treatment adjusted to an appropriate desired concentration with an inert gas such as nitrogen gas is flowed into the furnace while the furnace is being used. The temperature is raised to 700 to 1200 ° C. to amminate the siliceous powder. Since this ammoniaation varies depending on the concentration of ammonia, the heating temperature and the reaction time, the factors can be appropriately selected to control the degree of ammoniaation.

For example, when the concentration of ammonia gas in the atmosphere is 1 to 100% by volume, when the temperature is 700 to 900 ° C.,
Ammonia chemically combines with the siliceous component in a reaction time of about 0.5 to 8 hours, and when the temperature is 900 to 1200 ° C, ammonia reacts with the siliceous component in a reaction time of about 0.5 to 2 hours. Chemically bond. The reaction concentration is selected in proportion to the desired foaming degree of the foam to be obtained. A foam having a nitrogen atom content of 0.02 to 0.5% by weight remaining in the foam after foaming provides an excellent heat-resistant foam, but the amount of nitrogen can be easily adjusted empirically according to the amount of bound ammonia. Can be controlled.

Then, the ammoniated siliceous powder is placed in a predetermined mold, heated to a temperature of 1400 to 1800 ° C., and the powder is melted and foamed to obtain a desired silica foam. In this foaming treatment, the bound ammonia is released and gasified as much as possible, but it is desirable that the closed cells on the surface are not ruptured. In addition, it is important that the siliceous foam of the present invention has an appropriate strength in relation to its use or application conditions.
It is formed to an apparent specific gravity of 形成 2 g / ml.

The siliceous foam of the present invention is extremely useful as a refractory material or a heat insulating material for general furnaces, and a suitable bulk density can be freely selected depending on each use, application conditions, size and shape. You. On the other hand, since the siliceous foam of the present invention is excellent in high-temperature heat resistance and lightweight, it is used as a furnace material by laminating with a conventional refractory, for example, a fire-resistant and heat-insulating laminated furnace wall aiming at weight reduction. Particularly useful as a material. The thickness of each layer of the structure in which the silica foam and the refractory are laminated and integrated depends on the type of furnace to be built,
Determined in consideration of the purpose and use conditions.

[0013]

The silica-based foam of the present invention is lightweight, has excellent operability even in a large-sized molded product, is useful as a refractory material, and is used for heat treatment of semiconductors such as silicon. It has excellent utility as a safe and long-life furnace refractory insulation material that does not contaminate them.

[0014]

Now, the present invention will be described in further detail with reference to specific examples. Example 1 Silicon tetrachloride was introduced into an oxyhydrogen flame, and fine silica particles produced by flame hydrolysis were collected by a filter. As the collected silica, fine silica particles having a particle size of 2 to 20 μm as a main component were obtained. 1000 g of the silica fine particles were suspended in 2 liters of pure water to form a slurry.
In this slurry, a chemical grade alumina powder 100 was added.
g (10 parts by weight for 100 parts by weight of silica fine particles),
After stirring, the mixture was dried overnight in an oven at 60 ° C. to obtain a hard lump silica cake.

The silica cake was pulverized in an alumina pot and sieved to obtain a silica-alumina mixed powder having a particle size of 200 to 700 μm. This was immersed in 12N concentrated hydrochloric acid at room temperature, washed well with water and dried. This silica
The alumina mixed powder was placed in a rotary kiln, and heated to a temperature of 800 ° C. for 5 hours in an atmosphere of a mixed gas of an equal volume of ammonia gas and nitrogen gas to perform an ammonia conversion treatment. next,
The silica-alumina mixed powder that had been subjected to the ammonia treatment was transferred to a graphite mold, and this was heated in a vacuum furnace at a temperature of 1650 ° C. for 2 hours to foam.

[0016] The foam molded article taken out of the cooled furnace
Is a virtually closed-cell foam with an apparent specific gravity of 0.56
Met. Further, nitrogen present in the obtained foamed molded article
Content determined by combustion method to be 0.3% by weight
Was. Also, the amount of alkali metal in the foam is determined by atomic absorption method.
As a result of measurement, Na: 15 ppm, K: 18 ppm and Li: 13 ppm
there were. Further, by the beam bending method,
The viscosity η after density correction measured at temperature is 10^11.9 Po
It was. For comparison, mixed alumina powder
Using the same silica fine particles alone as the raw material,
A pure siliceous foam was produced. Nitrogen contained in the foam
The density is 0.3% by weight and the apparent specific gravity is 0.6.
The later viscosity η is 10^11.3 Poise. Compare this viscosity
As can be seen, the foams of the present invention have significantly improved
It can be seen that it has excellent heat resistance.

Example 2 1000 g of silica fine particles prepared in the same manner as in Example 1 were mixed with pure water 2
The slurry was suspended in a liter. 100 g of alumina powder (silica 1) obtained by hydrolyzing and drying aluminum chloride of a semiconductor grade is added to this slurry.
100 parts by weight), mix well, then add 60 parts by weight.
Drying overnight in an oven at ℃ ° C. yielded a hard, lumpy silica cake. The silica cake was pulverized in a quartz pot and sieved to obtain a silica-alumina mixed powder having a particle size of 200 to 700 μm. This was washed with 12N concentrated hydrochloric acid at room temperature, washed with water and dried. The silica / alumina mixed powder was heated in a rotary kiln at a temperature of 800 ° C. for 5 hours in a mixed gas atmosphere of ammonia / nitrogen gas at 50:50 for an ammonia treatment. The treated silica / alumina mixed powder is transferred into a graphite mold, which is then heated at 1650 ° C in a vacuum furnace.
At a temperature of 2 hours for foaming treatment.

After cooling the furnace, a substantially closed cell type apparent
A foam molded article having a specific gravity of 0.43 was obtained. Nitrogen content of the obtained foam
When the weight was measured by the combustion method, it was 0.3% by weight.
Was. Also, the amount of alkali metal in the foam was measured by the atomic absorption method.
As a result, Na was 2 ppm, K was 1 ppm, and Li was 0.8 p.
pm. Further, the temperature of 1280 ° C. was determined by the beam bending method.
When the viscosity was measured at temperature, the viscosity after density correction was
η is 10^12.5 Poise.

Example 3 1000 g of silica fine particles prepared in the same manner as in Example 1 were mixed with pure water 2
A slurry was made by suspending in a liter. 100g of zirconia powder of chemical grade (silica)
(100 parts by weight), stirred, and dried in an oven at 60 ° C. overnight to obtain a hard lump silica cake. This silica cake was pulverized in an alumina pot and then sieved to obtain a silica-zirconia mixed powder having a particle size of 200 to 700 μm. This was washed with 12N concentrated hydrochloric acid at room temperature, washed with water and dried. The washed and dried silica / zirconia mixed powder is heated to 800 ° C. in a 50:50 mixed gas atmosphere in a rotary kiln by mixing ammonia gas and nitrogen gas.
Ammonia treatment was performed by heating for an hour. The ammonia-treated silica-zirconia mixed powder was transferred into a graphite mold, and heated at 1650 ° C. for 2 hours in a vacuum furnace to perform a foaming treatment.

The foam removed from the furnace is substantially independent
Foam consisting solely of air bubbles with an apparent specific gravity of 0.45
Was. The amount of nitrogen contained in the obtained foam is determined by the combustion method.
0.3% by weight, and beam bending
The viscosity was measured at 1280 ° C by the method
The viscosity η after density correction is 10^12.3 Poise.

Comparative Example 1 1000 g of silica fine particles prepared in the same manner as in Example 1 were mixed with pure water 2
Put in a liter, stir well and suspend to make a slurry.
Was prepared. This slurry has a chemical grade of zirconia
30 g of powder (3 parts by weight for 100 parts by weight of silica)
After mixing well and homogenizing, in an oven at 60 ° C
And dried overnight to produce a hard, massive silica cake.
The silica cake was operated in the same manner as in Example 2 to produce a foam.
Built. The resulting foam is a substantially closed cell foam
The apparent specific gravity was 0.45. Of the resulting foam
The nitrogen content was 0.3% by weight as measured by the combustion method,
Measure viscosity at 1280 ° C by beam bending method
The viscosity η after density correction is 10^11.4 Poise
That the zirconia mixing effect is not satisfactory.
I understood.

Comparative Example 2 500 g of silica fine particles prepared in the same manner as in Example 1 were mixed with pure water 2
The slurry was suspended in a liter and stirred well to prepare a slurry. The slurry is coated with chemical grade zirconia powder.
After introducing 750 g (150 parts by weight with respect to 100 parts by weight of silica), the mixture was stirred and dried overnight in an oven at 60 ° C. to obtain a hard bulky silica cake. This silica cake was operated in the same manner as in Example 2 to produce a foam, but a uniform foam could not be obtained. As described above, when other ceramic materials are mixed and used in equal amounts or more with respect to the silica component, it is substantially difficult to produce a siliceous foam having a desired shape.

[0023]

Industrial Applicability The ceramic-containing heat-resistant siliceous foam of the present invention has remarkably improved high heat resistance as compared with pure silica foam, and is extremely advantageous in the field of heat treatment of semiconductors such as silicon. In addition to being used, it is provided as a foam with further improved operability. Further, the siliceous foam of the present invention is useful as a safe refractory heat insulating material for furnaces without fear of contamination, and has extremely wide industrial applicability.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-345636 (JP, A) JP-A-7-17731 (JP, A) JP-A-4-59632 (JP, A) 59633 (JP, A) JP-A-5-306142 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C03C 11/00 C03B 19/08 C03C 14/00

Claims (3)

(57) [Claims] 1. A siliceous foam containing silica in an amount of 5 to 100 parts by weight of a ceramic per 100 parts by weight of the silica, wherein the foam is chemically added to those siliceous components. A heat-resistant siliceous foam containing 0.02-0.5% by weight of bound nitrogen atoms. 2. The heat-resistant siliceous foam according to claim 1, wherein the foam has an apparent specific gravity of 0.2 to 2 g / ml. 3. A siliceous mixed powder containing 100 parts by weight of silica powder and 5 to 100 parts by weight of a ceramic powder selected from the group consisting of alumina, zirconia, titania, boron oxide and silicon carbide. Is reacted with ammonia under a temperature condition of 700 to 1200 ° C. in an atmosphere of 1 to 100% by volume of ammonia, and then put into a predetermined mold and heated to a temperature of 1400 to 1800 ° C. to powder. A method for producing a heat-resistant siliceous foam, characterized by melting and foaming.