JP3145518B2 - Surface high-purity ceramics and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-purity surface ceramic and a method for producing the same, and more particularly to a method for reducing the content of impurities such as alkali metal oxides, which are a source of contamination in a semiconductor production process, in the outer surface area thereof. The present invention relates to a high-purity surface ceramic suitable for a member for a semiconductor manufacturing apparatus and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a ceramic material used for a member for a semiconductor manufacturing apparatus is mainly quartz glass or silicon carbide. In the semiconductor manufacturing process, prevention of contamination by a trace amount of components in the atmosphere is an important issue, and any quartz glass or silicon carbide formed from the same element as silicon constituting the wafer, even if in contact, The reason is that the vaporized gas from these members is also the same kind of element, so that the silicon wafer is not contaminated. However, various problems have been raised with respect to members made of the above quartz glass and silicon carbide, even in the semiconductor manufacturing process that is rapidly progressing. For example, in an etching process, a CVD film forming process, and an ashing process for removing a resist in a recent semiconductor manufacturing process, a fluorine-based gas or plasma is often used. In this case, it has been pointed out that quartz glass and silicon carbide members are significantly corroded by fluorine-based gas. This is because silicon such as quartz glass or silicon carbide reacts with a fluorine-based gas to form a silicon-fluorine compound, and the silicon-fluorine compound has a high vapor pressure and is vaporized and diffused at room temperature.

As described above, in a semiconductor manufacturing apparatus, there has been a demand for the development of an alternative inorganic material other than quartz glass and silicon carbide.
The necessity has increased, and various studies have been made on improvement / improvement and high purification of inorganic materials. Among the conventional inorganic materials,
It has been revealed that common inorganic oxide ceramics other than quartz glass and silicon carbide, such as alumina, zirconia, and rare earth oxides, have relatively high corrosion resistance to fluorine-based gases. For example, alumina reacts with a fluorine-based gas to produce stable aluminum fluoride (A1F ₃ ). It is presumed that the compound A1F ₃ has a low vapor pressure at 700 ° C. or lower and functions as a protective layer on the alumina surface exposed to fluorine gas to prevent corrosion of alumina ceramics.

[0004]

However, conventional inorganic oxide ceramics are mainly deviated in heat resistance and mechanical properties, and their mechanical strength, electrical insulation, heat resistance,
There are few cases where the characteristics such as chemical resistance are used as a structural member, and there are few examples of confirming, controlling, and using the contained impurities. It is not an exaggeration to say that there are few, except for a few examples, such as alumina ceramics for use and permeable alumina ceramics for high pressure sodium lamp arc tubes. In addition, in any case, there is nothing that is considered from the viewpoint of high purity at the semiconductor level, such as a problem of contamination due to scattering of impurities contained in inorganic oxide ceramics such as alkali and alkaline earth. Therefore, at present, the necessary and sufficient conditions for a material used for a semiconductor manufacturing apparatus and not contaminating a silicon wafer have not yet been clarified. The present invention, in the current state of the invention, in addition to the conventional properties such as mechanical strength and heat resistance, even when used as a member for semiconductor manufacturing equipment, without forming a contamination source, impurities contained in the inorganic oxide ceramics An object of the present invention is to provide an inorganic oxide ceramic that does not emit or emit and a method for producing the same.

[0005]

According to the present invention, an inorganic oxide ceramic is provided.
The impurity concentration in the outer surface region whose depth from the surface is in the range of several tens μm to several mm is magnesia and silica.
Several ppm to several tens ppm, except for impurities in the internal region
Content is several tens ppm except for magnesia and silica
To several hundred ppm, wherein the impurity concentration in the outer surface region is lower than the impurity concentration in the inner region.

[0006] Furthermore, after molding using the raw material powder of inorganic oxide ceramics, the obtained molded body is calcined, and the firing temperature is maintained in an atmosphere of hydrogen gas or under vacuum while maintaining an open pore state.
There is provided a method for producing a high-purity surface ceramic, which is characterized by baking after heat treatment at a lower temperature .

[0007]

The inorganic oxide ceramics of the present invention are constructed as described above, and the purity of the surface area of the ceramics is higher than that of the inside thereof. Even when the ceramics are used at a predetermined high temperature, they do not emit impurities. There is no contamination of the silicon wafer as a member for the apparatus. Further, the present invention heats the formed body before sintering the formed inorganic oxide body by sintering, while maintaining the open pore state in which the pores between the inorganic oxide particles constituting the formed body are communicated with each other. By doing
Impurities contained in the surface area of the molded body can be evaporated and scattered, and furthermore, sintering is performed by sintering after heat treatment to form a closed pore state between inorganic oxide particles, so that impurities remaining inside are not diffused to the surface area. . Therefore, a sintered body, that is, an inorganic oxide ceramic can be obtained in a state where the impurity concentration in the outer surface region is lower than that in the inside.

Hereinafter, the present invention will be described in detail. The inorganic oxide ceramics in the present invention is basically a known inorganic oxide raw material powder such as conventional alumina, if necessary, a binder, a molding aid, the preparation of a molding powder by mixing additives such as a firing aid, An inorganic oxide ceramic which is a sintered body that can be obtained by applying a conventional ceramic manufacturing method including each step of forming, forming body processing, calcining, firing, firing body processing, and the like. The distribution is adjusted and controlled in a predetermined manner. That is, the impurities are adjusted to be diluted in the outer surface area of the ceramics and to be contained at a high concentration in the inner area, and to be distributed with a concentration gradient decreasing from the inside toward the outer surface. It is a controlled inorganic oxide ceramic. In this case, the impurity content of the outer surface region and the concentration gradient between the inner region and the inner region are not particularly limited. For example, the purpose and the mode of use of the semiconductor manufacturing apparatus and the like, the type of the inorganic oxide ceramic raw material,
It can be appropriately selected in consideration of the type of impurities contained in the raw material powder and the impurities that can be mixed in the ceramics manufacturing process. Usually, the impurity concentration in the outer surface region is several ppm to several tens ppm except for magnesia, and several tens ppm to several hundred ppm in the inner region except for magnesia.

In the present invention, the outer surface area for reducing the impurity concentration differs depending on the use mode as a member and its thickness, and cannot be unconditionally determined. In general, however, inorganic oxide ceramics, that is, inorganic oxide ceramics, Means a region having a depth in the range of about several tens μm to several mm from the surface of the sintered product. For example, in a semiconductor manufacturing process, apart from a diffusion furnace member used at about 1200 ° C., an etching apparatus or a CV
What is necessary is just to set so that it may not be scattered outside at a temperature of about 400 to 500 ° C. in the D apparatus, the diffusion of impurities existing inside the ceramics can be substantially ignored, and only the simple surface needs to be considered. . On the other hand, when the ceramic is greatly worn by contact with a chemically active substance such as plasma, or when the movement of impurities is promoted by an electric field or the like,
In addition, under conditions where acceleration is applied by direct contact with the silicon wafer, if wear due to mutual rubbing is also a problem, it is not enough to consider only the simple diffusion rate of impurities on the simple surface only. In addition, it is necessary to set the outer surface area range deep, and to more strictly control the impurity concentration.

In the present invention, the impurities contained in the inorganic oxide ceramics are mainly derived from the ceramic raw material powder, and are mixed in from the additives or equipment in the ceramics manufacturing process. Although there are various types, usually, alkali metal oxides such as sodium oxide (Na ₂ O) and potassium oxide (K ₂ O), magnesia (Mg
O), alkaline earth metal oxides such as calcia (CaO), iron group metal oxides such as ferric oxide (Fe ₂ O ₃ ),
Silica (SiO ₂ ) and the like. Although the amount of impurities in the ceramic outer surface region of the present invention indicates the total amount of the above-mentioned various impurities, SiO ₂ is not a contaminant to the semiconductor wafer and need not be included in the reduction target. Among the above impurities, in particular, alkali metal oxides have a high vapor pressure and are easily scattered, and become a source of contamination in a semiconductor manufacturing process.
It is preferable to reduce the content of the ceramic outer surface area as much as possible.

Further, MgO is added to ceramic raw material powder as an agent for suppressing abnormal growth of crystal particles during sintering of ceramics. According to the present inventors, the amount of alkali metal contained in ceramics is reduced to a predetermined amount. Since it has been confirmed that the amount of addition can be reduced by controlling the amount of impurities, the amount of impurities can be reduced as a whole by controlling the alkali metal, and the amount of impurities in the ceramic outer surface region can be reduced. Good.

Next, regarding the production method of the present invention, alumina ceramics will be representatively described among the inorganic oxide ceramics of the present invention. As described above, alumina ceramics are conventionally produced mainly from the steps of preparation, molding, molding, firing, and firing of alumina-based raw material powder, and the alumina-based raw material powder is sintered in the firing step to obtain particles. It is formed as growth and densification progress. According to the inventors, the impurities in the ceramic are substantially uniform as a whole up to the compact of the raw material powder, but a concentration gradient occurs during the firing step, and furthermore, depending on the firing method and the firing conditions, the impurities are removed. It was found that the concentration distribution state was different. For example, when firing in a gas combustion furnace, contamination is observed on the surface of the obtained alumina ceramics. When the cause of this contamination was examined, it was confirmed that it was rust powder blown from the inner wall of the pipe blown from the burner, or an oxide of an alkali metal, an alkaline earth metal, or the like that was evaporated and scattered from the firing jig material. In the case of firing in a hydrogen atmosphere furnace or a vacuum furnace, purification of the surface of the obtained alumina ceramics was observed. This is because, in firing under a hydrogen atmosphere, impurities such as impurities such as alkali metals are reduced to low oxides or simple alkali metals, and are easily vaporized at a high vapor pressure, or easily vaporized under reduced pressure. It is estimated that evaporation from the ceramic surface is promoted.

The above findings have been confirmed for the first time by the present inventors, and the method for producing a high-purity surface ceramic according to the present invention has been completed based on these findings. In other words, in order to purify the ceramic outer surface area, the raw material powder must be of high purity, but the sintering jig in the sintering process must be strictly checked, and the sintering conditions must be selected to determine the impurity concentration. The distribution can be changed, and in particular, firing under a hydrogen atmosphere or under vacuum has been found to be extremely effective. Therefore, the heat treatment of the present invention is preferably performed in a hydrogen atmosphere, preferably while flowing hydrogen gas, or under vacuum. The flow of hydrogen gas or a vacuum state exists in the fired ceramic surface area and reduces impurities or impurities that are easily vaporized under reduced pressure.
Desirable because it is immediately removed from the surface.

In the present invention, the temperature of the heat treatment is lower than the sintering temperature of ordinary inorganic oxide ceramics. In order to scatter and remove impurities on the surface area, the temperature is set as high as possible to increase the vapor pressure of the impurities. This is preferable because impurities can be scattered from the fired ceramic surface area in a short time. For example, in the case of alumina ceramics, usually about 1100 to 1450 ° C., preferably 125 ° C.
Heat treatment can be performed at 0 to 1400 ° C. for about 1 to 3 hours. Furthermore, the heat treatment of the present invention is performed at a temperature lower than the firing temperature, as high as possible as described above, and at a temperature capable of maintaining an open pore state in which pores between particles constituting the molded body communicate. To do. As described above, in the firing step of ceramics, the molded body is usually densified from an open pore state to an independent closed pore state.
On the other hand, the movement of impurities vaporized in the molded body simply moves through the continuous air holes in the open pore state, and diffuses and moves in the molded body in the closed pore state to reach the outer surface area, respectively.
Then, it scatters outside. Therefore, in the heat treatment in a closed pore state, the evaporation rate of impurities is remarkably reduced, and impurities cannot be sufficiently diffused from the outer surface area. Therefore, ceramics having a high-purity surface area in which a predetermined impurity content is reduced are included. Can not get.

Further, in the calcined body in the open pore state of the thick molded body, the impurities evaporated inside the thickness pass through the narrow and long pore space to reach the outer surface, and are scattered and released into the heat treatment atmosphere. Will be. That is, the driving force for moving the impurities in the preliminarily fired ceramic body space during the heat treatment is the impurity concentration gradient in the space, and the inside of the thick molded body where the concentration gradient hardly occurs is hard to be purified. However, as long as impurities can be purified in a predetermined region on the outer surface of the molded body as described above,
In addition, impurities remaining inside after sintering are less likely to move to the outer surface area in the closed pore state, so that no inconvenience is caused. Normally, maintaining the open pore state where impurities easily evaporate to a high temperature at which the vapor pressure becomes high, and eventually proceeding to densification to a true density sintered body by sintering are contradictory, increasing the molding density Then, the densification proceeds, but it becomes a closed pore state at a lower temperature. In this case, it may be held for a long time before the closed pore state is established, and the evaporation amount of the impurities may be increased over a long time. However, it is not practically useful industrially.

As described above, the conditions of the heat treatment under a hydrogen atmosphere or a vacuum in the present invention are such that the type of ceramic raw material inorganic oxide and the content thereof may be such that the open pore state can be maintained and the temperature is as high as possible. Optimum conditions are appropriately selected according to the type and amount of impurities to be performed, the sintering activity of the ceramic raw material, the particle size distribution of the ceramic raw material powder, the shape of the formed body, the formed density, the heating schedule, the atmospheric purity, and the like. In the heat treatment under vacuum, impurities released from the inorganic oxide raw material powder compact generally proceed straight, and if there is an obstacle, so-called sputtering is performed. In vacuum, the condition of the flow rate of hydrogen in a hydrogen atmosphere is not relevant, but the existence state and the filling state of the molded body in the furnace are problematic.

The semi-fired body that has been subjected to the heat treatment as described above is finally fired and sintered, densely and crystallized to obtain the desired surface-high-purity ceramic. The firing conditions can be performed under ordinary known conditions, for example,
The maximum temperature is about 1800 ° C for alumina ceramics
And fired for about 2 hours. Holding for a long time at the highest temperature in this firing step is also effective for removing impurities. However, holding for a long time at the maximum firing temperature also promotes the crystal growth of ceramics, so it is necessary to limit the temperature in consideration of the crystal grain size. In the present invention,
High purity is required because the ceramic surface purified by processing after firing may be contaminated again with impurities, or an internal region containing impurities at a relatively high concentration may appear on the surface by grinding or the like. It is desirable that the shape of the outer surface of the formed member be approximated to the shape of the product before firing as much as possible, and that the deformation of firing and the variation in firing shrinkage between lots be reduced.

[0018]

The present invention will be described below in detail based on examples and comparative examples. However, the present invention is not limited by the following examples. Examples 1-3 each impurity content _{Na 2 O: 10ppm, K 2} O: 30
ppm, SiO ₂ : 40 ppm, Fe ₂ O ₃ : 8 pp
m, CaO: 2 ppm, total impurity amount 90 ppm, specific surface area 25 m ² / g, 10 m ² / g and 5 m
² / g of 3 kinds of alumina raw material powder, magnesia conversion 1
A mixed powder for molding was prepared by adding 00 ppm of magnesium nitrate. To 100 parts by weight of the obtained mixed powder, 150 parts by weight of pure water and 2 parts by weight of an acrylic high-purity binder were added and mixed to form a slurry, which was granulated by a spray drier. Using the obtained granulated powder, 1 ton / cm
Eight pieces each of 65 mm square block-shaped compacts were prepared for each raw material under the pressure of ² , and calcined at 1000 ° C. for 2 hours to burn off the binder.

Two pieces of each calcined body corresponding to each of the raw material powders were heat-treated in a hydrogen atmosphere at a temperature raised from 1200 ° C. to 1500 ° C. every 100 ° C. for 2 hours. . One sample of each of the obtained heat-treated samples under the same conditions was sampled one by one, and the specific surface area was measured by using the BET method to determine whether the pores were open pores or closed pores. The results are shown in Table 1. Each of the remaining samples was fired at 1750 ° C. for another 2 hours in a hydrogen atmosphere.
The obtained fired body was subjected to chemical analysis using IPC emission spectroscopy and atomic absorption spectroscopy for the composition in a region from the outer surface to about 2 mm, and the content of each impurity was measured. The results are shown in Table 1.

[0020]

[Table 1]

From the above results, it can be understood that impurities in alumina ceramics can be diverged and removed by performing a heat treatment in a hydrogen atmosphere in a temperature range in which open pores are maintained.
It can be seen that the properties of the alumina raw material powder are also related to these optimum conditions. In the above embodiment, the amount of MgO added as an abnormal particle growth inhibitor is relatively large, and it seems that there is not much difference in the total amount of impurities. However, alkali metal elements and iron which affect the dielectric loss factor and the transmittance are considered. It is clear that the effect of removing such as is large.

Further, the thick block fired body obtained by heat treatment at 1300 ° C. obtained in Example 1 was cut with a diamond cutter, and the impurity concentration in the center portion and the surface portion was measured in the same manner. Fe, Na, K, Ca, Si and M
g of each impurity was high at the center and low at the surface. In particular, the tendency is remarkable for Na and K,
The concentrations of Na and K in the surface portion were 1/3 or less of those in the central portion, and a decrease in the concentration of other impurity atomic components by 10 to 20% was confirmed.

Next, each of the block-shaped sintered bodies obtained in Example 1 was placed in a quartz glass crucible purified by a hydrogen chloride gas purge at 1200 ° C. for 2 hours, and Na, K, Fe was placed on the crucible. , Ca and Mg contents (×
10 ¹⁰ atoms / cm ² ) were set at ² , 1, 1, 1 and 1, respectively, at 1000 ° C.
For 2 hours. After heating and cooling, the content of each impurity in each silicon wafer was analyzed and obtained. The result is
The results are shown in Table 2.

[0024]

[Table 2]

From the above results, it is clear that the surface of the fired alumina ceramics obtained by performing the heat treatment in a hydrogen atmosphere in an open pore state is purified. That is, the contamination of the silicon wafer heated together with the ceramics is due to impurities released from the ceramics, and the contamination by the ceramics heat-treated in the open pore state is extremely small.
It can be seen that the digits are also reduced. This is more remarkable than the difference between the chemical analysis values of the surface region impurities, and it can be inferred that the purification of the ceramic surface is progressing microscopically.

Comparative Examples 1 to 7 To the alumina raw material powder used in Example 1, 500 ppm of magnesium nitrate in terms of magnesia was added. To 100 parts by weight of this mixture, 150 parts by weight of pure water and 2 parts by weight of an acrylic high-purity binder were added and mixed to form a slurry, which was granulated by a spray drier. Using the obtained granulated powder, a pressure of 1 ton / cm @ 2 and a thickness of 1.35 mm
Were used to form three 65 mm square plate-like bodies. Each of the obtained molded bodies was calcined at 1,000 ° C. for 2 hours in the air to evaporate the binder. In the same manner as described above, the granulated powder was pressed at a pressure of 1 ton / cm @ 2 to form a 65 mm square block-shaped compact.
Individual pieces were formed and calcined similarly to burn out the binder.

Two of the thin calcined bodies obtained above were heated at 1850 ° C. for 2 hours in a hydrogen atmosphere and vacuum, respectively, to obtain a 1 mm thick square 50 mm square body ( Comparative Examples 1 and 2). Further, the other one of the sheet-like calcined bodies manufactured in the same manner was fired in air at 1700 ° C. for 2 hours to obtain a comparative sample (Comparative Example 3). On the other hand, each of the block molded bodies having the above-mentioned thickness was subjected to 5 minutes at 1750 ° C and 1800 ° C, respectively.
Firing was performed in a hydrogen atmosphere and vacuum for a time to obtain fired bodies of 50 mm square block bodies (Comparative Examples 4 to 7). Each of the above fired bodies was subjected to chemical analysis in the same manner as in Example 1, and the content of each impurity was measured. The results are shown in Table 3. In addition, the plate-like fired body was analyzed for its entire composition,
The composition of the central portion of the block fired body was analyzed.

[0028]

[Table 3]

From the results of the above Examples and Comparative Examples, it can be seen that the content of impurities is significantly reduced by heating at a higher temperature in a hydrogen atmosphere or vacuum than in air. A thin plate can reduce impurities only by firing in a hydrogen atmosphere or vacuum without heat treatment. On the other hand, in the case of a thick ceramic molded body such as a block body, it can be seen that the impurity concentration in the ceramic surface region is significantly reduced by the high-temperature heat treatment in the open pore state. In addition, the impurity content of the ceramic surface region obtained by the heat treatment in the closed pore state of the thick ceramic molded body is substantially the same as the impurity content of the central portion of the ceramic obtained by simply firing in a hydrogen atmosphere or vacuum. You can see that they are the same.

Example 4 and Comparative Example 8 100 parts by weight of synthetic mullite raw material powder having an average particle size of 0.5 μm, 20 parts by weight of pure water, and 10 parts by weight of an acrylic binder were kneaded using an alumina roll, and kneaded in a clay state. Things. This clay-like kneaded material was extruded to a thickness of 1 mm and a width of 10 mm.
It was extruded from a 0 mm die and dried to produce a thin plate-shaped molded body. After cutting out the produced plate-like molded body into a predetermined shape, it was heated and pressed to form a shape having a flow path at the center of the thickness. Thereafter, the binder was calcined by calcination in air at 1000 ° C. for 2 hours. The obtained calcined body is 13
Heat treatment was performed at 00 ° C, 1500 ° C, and 1600 ° C, respectively. From each of the heat treatment conditions, heat treatment materials for observing the pore state were extracted, and then, furthermore, 18 hours in air.
It was fired at 00 ° C. for 2 hours to produce a fired mullite ceramic (Example 4). At the same time, the calcined body without the vacuum heat treatment was similarly calcined to produce a calcined body for comparison (Comparative Example 8).

Each of the mullite ceramics produced as described above was processed into a predetermined vacuum chuck shape for carrying a silicon wafer using a diamond grinder. Thereafter, it was washed, dried, and subjected to a silicon wafer transfer treatment test. For each vacuum chuck, each silicon wafer was repeatedly used and transported 100 times, and then the contamination degree of each wafer was analyzed and measured in the same manner as in Example 1. Table 4 shows the results.

[0032]

[Table 4]

From the above results, it is clear that the wafer transfer vacuum chuck made of mullite ceramic obtained by heat-treating the calcined body in a vacuum has little silicon wafer contamination. In particular, it is understood that contamination of the mullite ceramic obtained by the high-temperature heat treatment in the open pore state by the vacuum chuck is extremely small.

[0034]

According to the present invention, the outer surface area of the finally obtained inorganic oxide ceramics is obtained by subjecting the calcined form to heat treatment under a hydrogen atmosphere or vacuum at a predetermined temperature which maintains an open pore state. It has become possible to supply high-purity surface ceramics that meet the conditions for use as members for semiconductor manufacturing equipment.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Haruji Harada, Inuma, Togane, Chiba Pref. 1573-8 Inside Togane Plant, Toshiba Ceramics Co., Ltd. 1573-8 Toshiba Ceramics Co., Ltd. Togane Plant (72) Inventor Kazuto Ando Kazuma Onuma, Togane-shi, Chiba Pref. 1573-8 Toshiba Ceramics Co., Ltd. Togane Plant (56) References (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C04B 35/10 C04B 35/64

Claims (4)

(57) [Claims] 1. A inorganic oxide ceramics, inorganic
The depth from the surface of the oxide ceramic is several tens μm to several
mm in the range of impurity content level in the outer surface area Ma
Several ppm to several tens ppm, excluding gnesia and silica,
The impurity concentration in the internal region is
A 10ppm~ number 100ppm number except mosquitoes, impurity content level in the outer surface region is impure in inner zone
Surface high-purity ceramics characterized in that the concentration is lower than the content concentration of substances . 2. The high-purity surface ceramic according to claim 1, wherein said inorganic oxide ceramic is an alumina ceramic. 3. A molded using an inorganic oxide ceramic material powder, and the obtained molded body calcined, in or under a vacuum atmosphere of hydrogen gas than the firing temperature while maintaining the open pores state
A method for producing high-purity surface ceramics, which comprises performing heat treatment at a low temperature and then firing. 4. The method according to claim 3, wherein the inorganic oxide ceramic is an alumina ceramic.