JPH0611664B2 - ▲ High ▼ Alumina sintered compact - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a novel high-purity alumina sintered body.

In recent years, the development of ceramic materials has been remarkable, and in particular, alumina sintered bodies have excellent physical properties in terms of electrical insulation, thermal conductivity, chemical stability, mechanical strength, etc. It is used for various substrates such as IC and LSI substrates, hybrid IC substrates, and resistance substrates.

When using an alumina sintered body as such a substrate material,
Along with the miniaturization of various elements such as an arrangement formed on a substrate, a resistor, a coil, and a semiconductor, improvement in surface smoothness of an alumina substrate has been strongly demanded.

(Prior Art) Conventionally, an alumina substrate was prepared by adding a small amount of magnesium oxide as a sintering aid to an alumina raw material, and then mixing it with an appropriate binder, dispersant, plasticizer, solvent, etc., and using a doctor blade method or an extrusion method. It is manufactured by a method in which a film is formed by a method such as cutting the film into a desired size and sintering. The surface roughness of such an alumina substrate is generally 0.1 μm or more in terms of center line average roughness.

Recently, for the purpose of improving the surface smoothness of the alumina substrate,
In addition to magnesium oxide, which is a sintering aid, chromium oxide,
Tantalum oxide or the like is added. In particular, when chromium oxide is added, an alumina substrate having an extremely smooth surface with a center line average roughness of 0.05 μ is obtained.

Also, JP-A-59-156690-JP-A-59-156
In 962, the surface smoothness is improved by using an alumina raw material containing impurities of more than 0.01% by weight and further controlling the particle size and shape of the raw alumina powder.

(Problems to be Solved by the Invention) When forming various elements such as wirings, resistors, coils, and semiconductors on an alumina substrate, first, a metal, semiconductor, or the like is formed on the alumina substrate by vacuum deposition, sputtering, MBE, or the like. A general method is to form a fine pattern by forming a thin film such as an insulator and subjecting it to photo-etching. In recent years, along with high-density integration of electronic materials, further miniaturization of such fine patterns has been required, and in order to realize this, it is strongly desired to improve the surface smoothness of the alumina substrate. Furthermore, if the surface smoothness is improved, the adhesion strength, long-term stability, and
It is known that variations in various physical property values, reliability, etc. are also improved, and from this point of view, improvement of the surface smoothness of the alumina substrate is indispensable.

However, the surface smoothness of an alumina substrate that is usually made is 0.1 μm or more in terms of center line average roughness, and with such surface smoothness, various types of wiring, resistors, coils, semiconductors, etc. are formed on the substrate. It is no longer possible to deal with the miniaturization of devices.

On the other hand, the method of adding impurities for improving the surface smoothness of the alumina substrate has been quite successful. However, on the other hand, the added impurities cause a problem that the physical properties of the thin film formed on the substrate are deteriorated.

Generally, when sintering alumina, a small amount of magnesium oxide is added in order to sinter the alumina at a high density. This magnesium oxide exists at the interface of the particles forming the alumina sintered body, that is, at the grain boundary during the sintering of the alumina, and suppresses the abnormal grain growth of the alumina sintered body particles, so that the high density sintering of the alumina is achieved. If possible, do it. Therefore, on the surface of the alumina sintered body after sintering, magnesium oxide does not exist on the entire surface of the alumina sintered body,
It exists only in very limited luck, specifically in the grain boundary part exposed on the surface. Moreover, magnesium oxide near the surface easily evaporates at the sintering temperature of alumina, and the magnesium oxide on the surface of the alumina sintered body can be neglected in practical use, and it can be considered practically that the vicinity of the surface is made of pure alumina.

On the other hand, many additives for improving the surface smoothness are solid-dissolved in alumina, and thus are exposed on the entire surface. For example, chromium oxide is solid-dissolved in alumina and distributed throughout the alumina particles, and therefore,
The result is that it is present on the entire substrate surface. Furthermore, it is believed that chromium oxide inhibits the evaporation of magnesium oxide from the alumina surface.When chromium oxide is added, a small amount of magnesium oxide can be found at the grain boundaries exposed on the surface of the alumina sintered body. It is still present, and it is considered that the amount of magnesium oxide scattered on the surface of the alumina sintered body is larger than that in the case where chromium oxide is not added. That is, adding chromium oxide to improve the surface smoothness of the surface of the alumina substrate, chromium oxide,
This results in the presence of two types of impurities of magnesium oxide, and these impurities cause a serious problem of deteriorating the physical properties of the thin film formed on the substrate.

Also, JP-A-59-156690-JP-A-59-156
In 962, the surface smoothness is improved by using an alumina raw material containing impurities of more than 0.01% by weight and further controlling the particle size and shape of the raw material alumina powder. It is considered that the impurities contained therein considerably contribute to the improvement of the surface smoothness of the alumina sintered body. For example, in JP-A-59-156960, an alumina powder having an average particle size of 0.2 to 0.8 μ and a purity of 99.9% is used as a raw material, and this is formed into a sheet and cut into an appropriate size. By sintering in air at 1550 ° C. for 2 hours, an alumina sintered body having a center line average roughness of 0.01 to 0.05 μ and a smooth surface is produced. Particularly, when the average particle diameters are 0.3 μ and 0.4 μ, the center line average roughness reaches 0.01 μ. However, an alumina sintered body with an extremely smooth surface with a center line average roughness of 0.01μ is
Production is not possible when a known high-purity alumina powder having a purity of 99.99% or more is used as a raw material and sintered by the method of JP-A-59-156960. Known purity 99.99
%, The surface roughness that can be achieved by a usual method using high-purity alumina powder of not less than 100% is a center line average roughness of 0.05 μ. In the alumina sintered body whose surface smoothness is improved by utilizing the effect of impurities in this way, since impurities are solid-solved in the alumina sintered body particles during sintering,
The alumina sintered body is exposed on the entire surface and causes a problem that the physical properties of the thin film formed on the substrate are deteriorated.

(Means for Solving the Problems) The inventors of the present invention have conducted intensive studies to improve the surface smoothness of a high-purity alumina sintered body containing no impurities other than magnesium oxide, and as a result, the alumina sintered body has been obtained. It was found that a high-purity alumina sintered body having an excellent surface smoothness can be obtained by sintering the powder having a small particle size and high density, and thus completed the present invention.

While the conventional method attempts to improve the surface smoothness by using impurities, the method of the present inventors is based on a completely different idea. It improves the surface smoothness of the alumina sintered body while maintaining high purity.
This is completely original and epoch-making in that it achieves this without adding impurities.

Generally, the surface of a high-purity alumina sintered body that is sintered at high density has a structure in which alumina particles are spread, and the alumina particles form convex portions and the grain boundary portions form concave portions. Is dependent on the size of the alumina particles, and the smaller the alumina particles, the smaller the surface irregularities. The present inventors have paid attention to this point, have found that a high-purity alumina sintered body having a smooth surface can be obtained if it can be sintered at a high density while keeping the grain size small, and completed the present invention.

That is, according to the present invention, the size of the particles constituting the sintered body is 3 μm or less, the average particle diameter is 1 to 3 μm, the density of the sintered body is 3.85 g / cm ³ or more, and the surface of the sintered body is Of the center line average roughness is 0.05 to 0.020μ, the amount of magnesium oxide contained in the sintered body is 0.07 to 0.15% by weight, and the total amount of impurities other than magnesium oxide is 0.01% by weight. % Or less, the present invention provides a high-purity alumina sintered body.

In the high-purity alumina sintered body of the present invention, the average particle size of the particles forming the same is in the range of 1 to 3 µ.

In the present invention, the average particle size of the sintered body is obtained by observation with a scanning electron microscope. That is, an electron micrograph of the surface of the sintered body is taken, a straight line of the stomach is drawn on this photograph, the length of this straight line is L, and the number of grain boundaries crossing the straight line is n, the straight line division The length l is calculated by the following formula, Furthermore, the average of the division length of the straight line is calculated by the following formula, Further, this is multiplied by 1.5 to obtain the average particle diameter d.

d = 1.5 × However, m is the total number of measurement points of l.

In the above calculation, n is preferably 5 or more, and it is preferable to take a photograph at an appropriate magnification so that n is 5 or more in one photograph. The number of measurement points for l is 1 to 1 for each photograph.
5 and m are preferably 50 or more.

The surface of the alumina sintered body of the present invention has a structure in which alumina particles are spread, and the alumina particles are slightly raised to form a convex portion, and the grain boundary portion is depressed to form a concave portion. The degree of grain boundary depression depends on the size of the alumina particles, and the smaller the alumina particles, the smaller the grain boundary depressions, and therefore the smoother the surface of the alumina sintered body. That is, in order to improve the surface smoothness of the alumina sintered body, the size of the alumina particles constituting the sintered body must be reduced. However, it is impossible to make the alumina particles infinitely small. This is determined by the size of the particles of the alumina raw material powder that is the starting material. Normally, the average particle diameter of the alumina raw material powder is 0.1 μm or more. In order to sinter, the particle size of the alumina particles constituting the sintered body must be 1 μm or more. Also, if you increase the particle size of the alumina particles,
Since the surface smoothness of the sintered body is deteriorated, the particle size naturally has an upper limit. In the case of the present invention, the size of the alumina particles constituting the sintered body is 3 μm or less.

The density of the high-purity alumina sintered body of the present invention is preferably 3.85 g / cm ³ or more, more preferably 3.90.
g / cm ³ or more.

The density of the high-purity alumina sintered body may be obtained by dividing the weight by the volume, and the measurement may be performed by the commonly known dimensional method or Archimedes method.

The density of the high-purity alumina sintered body of the present invention is preferably 3.85 g / cm ³ or more, which corresponds to about 96.5% of the theoretical density of aluminum of 3.99 g / cm ^3. If the density is lower than this, holes will exist in the grain boundary portion of the surface of the high-purity alumina sintered body in an amount that cannot be ignored practically. Holes on the surface of the sintered body may cause poor adhesion between the thin film and the sintered body or defects in the thin film itself when a thin film is formed on the surface. The above problem occurs. However, when the density of the high-purity alumina sintered body is 3.85 g / cm ³ or more, the number of holes on the surface of the sintered body is small, and there is no practical problem. Further, it is more preferably 3.90 g / cm ³ or more, but in this case, the holes on the surface of the sintered body are almost eliminated, which is the most preferable in practical use.

The surface smoothness of the high-purity alumina sintered body of the present invention has a center line average roughness of 0.05 to 0.020 in a baked state.
μ, and preferably 0.045 to 0.025 μ.

The term "baked state" as used in the present invention means a state in which the material is taken out of the firing furnace after being sintered and is not subjected to post-treatments such as grinding, polishing and cutting.

The center line average roughness referred to in the present invention is defined by JIS B0601, and in the present invention, the measurement length l is 2.5 mm,
The cutoff value λ _c is 0.08 mm, and the stylus used for the measurement has a radius of curvature of the tip of 2 μ. The center line average roughness can be measured by, for example, a universal surface shape measuring instrument SE-3H with a surface information processing function manufactured by Kosaka Laboratory Ltd.

When using a high-purity alumina sintered body as a substrate, it is desirable that the substrate surface be as smooth as possible in order to form a fine pattern on the alumina substrate. This is because if the surface of the alumina substrate is not smooth, it will be difficult to apply the photoresist uniformly and evenly.
This is because defocusing occurs at the time of exposure and it becomes impossible to write fine patterns. That is, if the surface of the alumina substrate is rough, when the photoresist is applied, the roughness is reflected on the resist surface, and a flat resist surface cannot be obtained. Therefore, the surface of the alumina substrate should be as smooth as possible.

The surface roughness of the alumina substrate of the present invention is 0.05 μ or less in terms of center line average roughness, more preferably 0.045.
It is less than or equal to μ. If the center line average roughness is 0.05 μm or less, out-of-focus of the fine pattern is small and it is not a problem in practical use. Thus, it is desirable that the surface of the alumina substrate be as smooth as possible. However, as described above, as long as the alumina raw material powder having an average particle diameter of 0.1 μ or more is used for high-density sintering, the size of the alumina particles constituting the sintered body must be 1 μ or more. I don't get. Therefore, the surface smoothness has a limit. When making the density of the sintered body as high as practically unproblematic, the limit of the surface smoothness is 0.020μ,
When it is 0.025 μm or more, the sintered body has a higher density, which is most preferable in practical use.

In the present invention, the amount of magnesium oxide contained in the sintered body is 0.
It is from 07 to 0.15% by weight.

When magnesium oxide is added during the sintering of alumina, magnesium oxide exists in the grain boundaries of the alumina sintered body and suppresses abnormal grain growth of the alumina sintered body particles, enabling high density sintering of alumina. . If magnesium oxide is added so that the amount of magnesium oxide contained in the sintered body is 0.07% by weight or more, the alumina sintered body can be sintered to almost the theoretical density. Even if magnesium oxide is added in this way, magnesium oxide in the vicinity of the surface of the alumina sintered body will evaporate to some extent during the sintering of alumina. Therefore, if the added amount is small, there will be no practical problem. However, when the amount of magnesium oxide added increases, the amount of evaporation cannot keep up and the amount of magnesium oxide remaining at the grain boundaries near the surface increases, which is a practical problem. Therefore, the amount of magnesium oxide contained in the sintered body is 0.1
It is necessary to add magnesium oxide so as to be 5% by weight or less, and if it is added in this way, almost pure alumina is present near the surface.

The high-purity alumina sintered body of the present invention has a total amount of impurities other than magnesium oxide of 0.01% by weight or less.

Impurities other than magnesium oxide can be ignored if they are in very small amounts, but if they are in large amounts, these impurities will form a solid solution in the alumina sintered body particles, and accordingly, they will be present on the entire surface of the sintered body. Therefore, when the alumina sintered body is used for the substrate, the physical properties of the thin film formed on the substrate are deteriorated. The upper limit of the total amount of such impurities is 0.01 weight,
Below this, there will be no practical problem.

The high-purity alumina sintered body of the present invention is obtained by using high-purity alumina powder via amorphous aluminum hydroxide as a raw material, and subjecting this to powder preparation, film formation, and firing under conditions and methods suitable for this powder. Can be manufactured.

Alumina powder is industrially obtained by neutralizing sodium aluminate with an acid to produce aluminum hydroxide and firing it, but the alumina powder thus obtained usually contains impurities. However, only low purity products can be obtained. However, the present inventors have found that Japanese Patent Application No. 59-248083.
And, by simultaneously using Japanese Patent Application No. 59-249787, it has succeeded in obtaining a high-purity alumina powder by improving the sodium aluminate method. The aluminum hydroxide obtained from the sodium aluminate method usually has a dibsite structure, but the present inventors have found that Japanese Patent Application No. 59-24
By using 8083, high-purity aluminum hydroxide having an amorphous structure can be produced.
This high-purity aluminum hydroxide was calcined using -249787, and succeeded in producing a high-purity alumina powder having a small average particle size, good dispersibility, and excellent sinterability.

The present inventors have found that a high-purity alumina powder obtained by using Japanese Patent Application No. 59-248083 and Japanese Patent Application No. 59-249787 at the same time is a fine powder and has excellent dispersibility and sinterability. Focusing on the fact that it is possible to sinter at a relatively low temperature and with high density even if it is pure, and to sinter to a density close to the theoretical density, and adjust, film-form and sinter under conditions and methods suitable for this powder. As a result, the present invention has been completed.

The high-purity alumina sintered body of the present invention is disclosed in Japanese Patent Application No. 59-248.
No. 083 and Japanese Patent Application No. 59-249787 are used at the same time to produce a high-purity alumina powder, which can be manufactured by the following procedure.

First, high-purity alumina powder is mixed with a sintering aid, a binder, a plasticizer, a solvent, a dispersant, and the like.

As a sintering aid, magnesium oxide powder, or a magnesium salt such as magnesium oxide by heat treatment, for example, magnesium carbonate, magnesium nitrate,
Magnesium sulfate, magnesium acetate, etc. are used.

As the binder, for example, cellulose-based polymer, acrylic-based polymer, vinyl alcohol-based polymer, polyethylene, polystyrene, isocyanate, etc. are used.

As the plasticizer, phthalic acid esters, phosphoric acid esters, fatty acid esters, glycol derivatives, triacetylene, paraffin chloride, castor oil and the like are used.

As the solvent, alcohols, cellosolves, ketones, amides, esters, ethers, hydrocarbons,
It may be used by selecting from chlorinated hydrocarbons, aromatics, water and the like.

Further, as the dispersant, a commercially available synthetic surfactant may be selected and used from nonionic, anionic and cationic types.

Of these additives, the amount of the binder, plasticizer, solvent, and dispersant added is all important in order to maintain good dispersion of the alumina powder and obtain a high-density film-molded product. The amount of binder added is important. That is, the amount of the binder to be added should be such that when the alumina powder is packed at the highest density, it fills the gaps between the powders. The gap increases,
A high-density film-molded product cannot be obtained, and if the amount is too small, partial agglomeration of powder particles occurs, good dispersion cannot be obtained, and the density of the film-molded product becomes low. When the high-purity alumina powder of the present invention is used as a raw material, an appropriate amount of the binder is alumina powder 1 when the specific gravity of the binder is 1.0.
As a result of examination, it was clarified that 6 to 15 parts by weight is suitable for 100 parts by weight.

As a mixing method, a usual method such as a ball mill, a vibration mill, and stirring may be used, but an appropriate dispersion time must be selected depending on the method.

If necessary, the obtained mixture is defoamed and then formed into a film by a usual method such as a doctor blade method or an extrusion method.
The obtained film molded body is dried and then cut into an appropriate size,
Calcination is performed in air at 400 to 1000 ° C. to remove organic substances contained in the film. Further, this is sintered in hydrogen or vacuum at 1400 to 1650 ° C. to obtain a high-purity alumina sintered body. In this sintering step, when alumina powder containing more than 0.01% by weight of impurities is used as a raw material, a sintered body having a smooth surface can be obtained even if it is sintered in air. 156960 to JP-A-59-156962. However, since the alumina raw material powder of the present invention has a high purity, when sintered in air, many pores are contained in the sintered body, and when these pores are present on the surface of the sintered body, Become a hole. Therefore, it is not preferable to sinter the high-purity alumina sintered body of the present invention in air, and it has to be sintered in hydrogen, in vacuum, or in oxygen. That is, a high-purity alumina sintered body with few pores can be obtained only after sintering in hydrogen, vacuum, or oxygen.

Since the alumina raw material used in the present invention is a fine powder and has a uniform powder particle size and has excellent dispersibility and excellent filling property, it is possible to obtain a uniform and high-density film molded product in which there are no aggregates or bubbles. Therefore, it is possible to sinter at a relatively low temperature and a high density.

The surface-smooth high-purity alumina sintered body of the present invention can be achieved only by using such an excellent alumina raw material powder and further performing powder adjustment, film formation, and firing under conditions and methods suitable for this raw material powder. .

(Effects of the Invention) The high-purity alumina sintered body of the present invention has an extremely smooth surface, so that a fine pattern can be formed on the surface of the sintered body, and further various elements are formed on this substrate. In this case, variations between the lots of various elements and long-term stability are improved. Further, since the high-purity alumina sintered body of the present invention has an extremely small amount of impurities, the contamination of various elements by the substrate is small, and the stability of various elements is also greatly improved in this respect.

Further, since the high-purity alumina sintered body of the present invention has high density and high purity, it has excellent properties inherent to alumina in electrical insulation, thermal conductivity, chemical stability, mechanical strength, and the like. It has been successfully pulled out. Therefore, it is possible to use the conventional alumina substrate, which was difficult. For example, it is a thin substrate, a high frequency substrate, a high heat dissipation substrate, a translucent alumina plate, or the like.

(Example) Example 1 100 g of high-purity alumina raw material powder (purity 99.99%) obtained by firing high-purity amorphous aluminum hydroxide
To 0.1g magnesia, 36g methyl ethyl ketone,
9 g of n-butyl alcohol, 14 of dibutyl phthalate
g and span 851 g were mixed in a ball mill for 24 hours, 10 g of polyvinyl butyral was added, and the mixture was further mixed for 24 hours to form a film by a doctor blade method. The obtained film was dried at 100 ° C. for 96 hours, and after sintering, cut into 2 inch squares. This in the air in an electric furnace,
After baking at 1000 ° C. for 1 hour, further in hydrogen, 147
It was baked at 0 ° C. for 30 minutes.

As a result of observing the obtained high-purity alumina sintered body with a scanning electron microscope, the average particle size was 1.4 μm. Moreover, the weight of the thin plate was weighed, and the vertical and horizontal directions and the thickness were each measured with a caliper and a micrometer to calculate the volume, and the density was calculated using these values, which was 3.87 g / cm ³ . .
This was 97% of the theoretical density, and it was found to have a very high density despite sintering at relatively low temperatures. Further, the average roughness of the center line was measured and found to be 0.024μ, and the surface was extremely smooth.

Further, when the obtained sintered body was chemically analyzed, magnesium oxide contained in the sintered body was 0.1% by weight,
Impurities other than magnesium oxide are Na ₂ O 50ppm, SiO ₂
8 ppm, Fe ₂ O ₃ 8 ppm, and other impurities could not be detected. The total amount of impurities other than magnesium oxide is 66.
It was found to be ppm, ie 0.007% by weight.

Example 2 The same high purity alumina raw material powder used in Example 1 as high purity alumina raw material powder (purity 9
0.99%) 100 g, magnesia 0.08 g, butylbenzyl phthalate 3 g, methyl ethyl ketone 30
g, 1,1,1-trichloroethane 65 g, span 20
1 g was mixed by a ball mill for 48 hours, 15 g of polymethylmethacrylate was added thereto, further mixed by a ball mill for 72 hours, and a film was formed by a doctor blade method. This was calcinated by the same procedure as in Example 1, and further calcined in hydrogen at 1550 ° C. for 1 hour.

As a result of observing the obtained high-purity alumina sintered body with a scanning electron microscope, the average particle size was 2.1 μm. Also, the density was measured and found to be 3.91 g / cm ³ , which was 98% of the theoretical density, and it was found that the density was extremely high. Furthermore, the center line average roughness of the surface of the sintered body was measured and found to be 0.038μ, indicating that the surface was extremely smooth.

Further, when the obtained sintered body was chemically analyzed, magnesium oxide contained in the sintered body was 0.08% by weight, impurities other than magnesium oxide were Na ₂ O 48 ppm, S
iO ₂ 11 ppm and Fe ₂ O ₃ 10 ppm, and the total amount of impurities other than magnesium oxide is 69 ppm, that is, 0.0
It was 07% by weight.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Kageyasu, Kageyasu 1-3-1, Yokou, Kawasaki-ku, Kawasaki-shi, Kanagawa Asahi Kasei Kogyo Co., Ltd. (56) Reference JP-A 59-156960 Sho 60-16861 (JP, A) Japanese Patent Sho 53-120 (JP, B2)

Claims (3)

[Claims] 1. The size of particles constituting the sintered body is 3 μm or less, the average particle size is 1 to 3 μm, and the density of the sintered body is 3.
85 g / cm ³ or more, the smoothness of the surface of the sintered body is 0.05 to 0.020 μ in the center line average roughness, and the amount of magnesium oxide contained in the sintered body is 0.07 to 0.15 wt%, A high-purity alumina sintered body characterized in that the total amount of impurities other than magnesium oxide is 0.01% by weight or less. 2. The high-purity alumina sintered body according to claim 1, wherein the density of the sintered body is 3.90 g / cm ³ or more. 3. The high-purity alumina sintered body according to claim 1 or 2, wherein the smoothness of the surface of the sintered body is 0.045 to 0.025 µ in terms of center line average roughness.