JP4223043B2 - Black AlN ceramics - Google Patents

Description

  The present invention relates to a high-purity and black-colored AlN-based ceramic used for a member for a semiconductor manufacturing apparatus, a member for an industrial machine, a heat-resistant and corrosion-resistant member, and the like.

AlN ceramics are used as LSI heat dissipation substrates and various wear-resistant / mechanical structural members because of their excellent thermal conductivity and moderate mechanical properties. In recent years, their application to LSI manufacturing equipment members has been studied. .
Since AlN is difficult to sinter, 1 to 5 weights of yttrium compound typified by Y ₂ O ₃ or calcium compound typified by CaO and Ca ₂ C is usually used as a sintering aid during sintering. It is usual to produce by adding%.

The color tone of the sintered AlN ceramics varies depending on the impurities in the raw material powder used and the type and amount of the sintering aid to be added. Especially when a high-purity AlN raw material with few transition metal impurities is used, it is white. Alternatively, it often exhibits an ivory color (gray) and has translucency.
In addition, yttrium compounds, calcium compounds, and the like are used during the production of AlN ceramics. These compounds react with AlN during sintering, and the product forms a second phase in the grain boundary of the AlN ceramics after sintering. Remain in focus. For example, when an yttrium compound is used, it is known that YAG (Al ₅ Y ₃ O ₁₂ ) or the like is generated at grain boundaries or triple points of AlN ceramics.

These second phases are not necessarily uniformly and finely dispersed in the sintered body, and since AlN is white and translucent, especially when the shape of the ceramic is large, color unevenness, spots, etc. Detected as a defect.
As one method for suppressing the occurrence of defects such as color unevenness, spots, etc., a method that does not use a sintering aid such as an yttrium compound or a calcium compound can be considered. It is difficult to obtain a sintered body having a density. Therefore, it is desired to cause AlN ceramics to develop a black color and suppress the occurrence of defects such as color unevenness and spots. In addition, when AlN ceramics are used as a light-receiving and heating medium by infrared heating or the like, blackening is desired from the viewpoint of infrared absorption efficiency.

  In general, as a method of coloring ceramics including AlN, a method of adding transition metals such as titanium, cobalt, zinc, iron, nickel, etc. or a compound thereof is known, and a transition metal element of about 100 ppm or more is added. As a result, the AlN ceramic is blackened. However, the transition metal element has the most adverse effect on the device in the LSI manufacturing process, and blackening due to the addition of the transition metal element hinders application of AlN ceramics to members for semiconductor manufacturing apparatuses.

  Patent Document 1 discloses an AlN ceramic sintered body in which Er (erbium) is added to aluminum nitride in an amount of 5% by weight or more in terms of metal to suppress generation of spots and color unevenness, but Er (erbium) is disclosed. Lanthanoid elements such as lanthanoid elements, actinoid elements, and other heavy metals, alkali metals, and alkaline earth metals above the periodic table silicon element (atomic number 14) are basically harmful to LSI devices as well as transition metal elements. This obstructs application of AlN ceramics to a member for a semiconductor manufacturing apparatus.

On the other hand, aluminum compound ceramics such as Al ₂ O ₃ , AlN, and AlON have excellent corrosion resistance by forming stable aluminum halide on the surface against halogen gas such as chlorine gas and fluorine gas. Are known. However, in a normal AlN-based ceramic containing an yttrium compound or a calcium compound, even if AlN is excellent in corrosion resistance, the reaction product present as the second phase is inferior in corrosion resistance, so that the ceramic cannot maintain good corrosion resistance. There is.

  In addition, AlN ceramics are extremely brittle among ceramics, as low in fracture toughness as silicon carbide (SiC). For this reason, when grinding AlN ceramic sintered body, chipping and other defects are likely to occur, and it is necessary to pay attention to the processing conditions. Furthermore, when using AlN ceramics as a member, mechanical impact and thermal impact are reduced. Care must be taken to do so. In order to improve the reliability and production efficiency of AlN ceramics, it is strongly desired to improve the mechanical properties of AlN, particularly the fracture toughness.

Patent Document 2 discloses a wear-resistant material containing 80 to 98% by weight of AlN having an average particle size of 8 μm or less and 2 to 20% by weight of AlON having an average particle size of 5 μm or less. In the present specification, the wear resistant material is manufactured by adding AlON raw material powder having an average particle size of 0.5 to 1 μm to AlN raw material powder and sintering at 1650 to 2000 ° C. However, the AlON raw material powder is extremely expensive and it is difficult to obtain a high-purity raw material with few impurities, and AlON itself is also difficult to sinter, so no sintering aid is added. In this case, it is difficult to obtain a dense sintered body, and therefore it is difficult to improve the mechanical properties, particularly fracture toughness, of the AlN ceramics. Moreover, although there is no description regarding the color tone of the sintered body in this publication, even if white AlON is added to AlN, the sintered body does not develop a black color, thus suppressing the occurrence of defects such as color unevenness. I can't do it.
Japanese Patent Laid-Open No. 6-116039 JP 61-117162 A

As described above, since conventional AlN ceramics use an yttrium compound or a calcium compound as a sintering aid, they contain elements other than aluminum, resulting in a decrease in purity as well as white or gray translucency and uneven color. Defects such as these are likely to occur, and corrosion resistance is also likely to deteriorate. There is also a problem that the mechanical properties, particularly the fracture toughness, are poor.
An object of the present invention is to solve these problems and to provide a black AlN ceramic having high purity and excellent corrosion resistance and mechanical properties.

The present inventors have obtained a dense sintered body by adding aluminum oxide to hardly sinterable AlN, and the sintered body is black by generating an AlON phase having lattice defects during the sintering. It was newly discovered that the problem of color unevenness of AlN was solved and the mechanical properties of the sintered body were improved by dispersion strengthening of AlN particles and AlON particles.
The requirement of the present invention is that 1 to 30% by weight of aluminum oxide is added, a mixed powder consisting essentially of aluminum nitride is formed and sintered, and the reaction between aluminum oxide and aluminum nitride is performed during sintering. The density characterized by containing an AlON phase having a lattice defect that occurs is 90% or more of the theoretical value, and is a black AlN-based ceramics substantially composed of two phases of AlN and AlON.

  The black AlN ceramics of the present invention have an alkali metal, alkaline earth metal, metal element number 19 and subsequent elements of the periodic table, and compounds of these metal elements, all of 30 ppm or less, and substantially 2 of AlN and AlON. It is a high-purity sintered body consisting of phases. Since heavy metal elements, alkali metal elements, and alkaline earth metal elements above the silicon element (atomic number 14) of the periodic table are harmful to LSI devices and hinder the application of AlN ceramics semiconductor manufacturing equipment members, Its content should be as low as possible. Moreover, since these non-aluminum elements as impurities are inferior in corrosion resistance to halogen-containing gases such as chlorine gas and fluorine gas, their content must be as low as possible from the viewpoint of the corrosion resistance of AlN ceramics. The contents of these impurity metal elements are each preferably 30 ppm or less and the total amount is preferably 100 ppm or less. The AlN ceramics according to the present invention have high purity such that the content of these impurity metal elements is 30 ppm or less and the total amount is 100 ppm or less, so that they are excellent in applicability to members for semiconductor manufacturing equipment and have excellent corrosion resistance. is there.

  In addition, in the black AlN ceramics of the present invention, yttrium compounds, calcium compounds, and the like that have been conventionally used as sintering aids during the production of AlN ceramics are not added. These yttrium compounds and calcium compounds react with AlN during sintering and the product remains as a second phase in the sintered AlN ceramics, causing defects such as color unevenness, spots and the like. Since it is an earth metal and a heavy metal element from the element periodic table No. 19 or later, applicability to members for semiconductor manufacturing equipment is hindered and corrosion resistance is deteriorated.

In the black AlN ceramic of the present invention, aluminum oxide (alumina) to be added functions as a sintering aid instead of the conventional yttrium compound and calcium compound. Although AlN is a non-oxide ceramic and hardly sinters, alumina is easily sinterable. Therefore, a high-density sintered body can be easily obtained by adding aluminum oxide to AlN.
In addition, by adding aluminum oxide to AlN, AlON (aluminum oxynitride) is generated by the reaction between aluminum oxide and AlN during sintering, but since AlON is a non-stoichiometric compound, lattice defects are present in the crystal. Easy to generate. The lattice defect generated in the AlON crystal becomes the color center, causes the ceramic to develop a black color, and the lattice defect is relatively stable up to a high temperature. On the other hand, when AlON is directly added to AlN, such lattice defects are not generated, and therefore, the AlN ceramic does not develop black color. Thus, although the AlN ceramic of the present invention exhibits a black color, since it does not contain a sintering aid such as an yttrium compound or a calcium compound, the occurrence of defects such as color unevenness, spots, etc. is completely suppressed, and aluminum Since the impurity metal elements other than the element are extremely low, they are excellent in applicability to members for semiconductor manufacturing equipment and exhibit extremely good corrosion resistance. Furthermore, even when AlN ceramics are used as a light-receiving and heating medium by infrared heating or the like, the black AlN ceramics of the present invention have a high infrared absorptivity and exhibit excellent characteristics.

In the present invention, it is difficult to quantitatively express the blackness of the sintered body. For example, in the L ^* a ^* b ^* display (CIELAB display system) defined by JIS Z8729, the lightness index: L ^{* The} value is in the range of 0 to 50, and the saturation: C ^* (= (a ^* ) ² + (b ^* ) ² ) ^1/2 ) is in the range of 0 to 10, more preferably lightness Index: L ^* value is preferably in the range of 0-40. Alternatively, the reflectance of light on the surface of the sintered body in the visible light wavelength region of 400 to 800 nm is preferably 20% or less, and more preferably 15% or less.

  The black AlN ceramic sintered body of the present invention has a microstructure consisting of an AlON phase generated by a reaction between aluminum oxide and AlN and a balance of two phases of AlN, and each particle has a fine structure dispersed with each other. For this reason, the crack propagation from the fracture source is deflected by the so-called particle dispersion effect, and the mechanical properties, particularly fracture toughness and fracture strength are improved.

  As in the present invention, 1 to 30% by weight of aluminum oxide is added, and a mixed powder consisting essentially of aluminum nitride is formed and sintered, and the reaction between aluminum oxide and aluminum nitride occurs during sintering. By containing an AlON phase having a lattice defect that occurs, an AlN-based ceramic exhibiting high purity and black color can be obtained. This high-purity black AlN-based ceramic solves the problems such as color unevenness, low corrosion resistance, low mechanical properties, etc. that conventional AlN-based ceramics have.

Hereinafter, the contents of the present invention will be described in detail.
As the AlN powder to be used, fine particles having an average particle size of 10 μm or less, preferably an average particle size of 1 μm or less (submicron), an alkali metal, an alkaline earth metal, a metal element of element periodic table No. 19 or later, In addition, the content of the compounds of these metal elements is 30 ppm or less, and the total amount of impurity metal elements other than aluminum is 100 ppm or less, which is chemically high purity.

The aluminum oxide powder added to the AlN powder is usually α-type alumina (Al ₂ O ₃ ), but other types of crystals such as β-type, γ-type, θ-type, and κ-type may be used, or during heating. Aluminum hydroxide (Al (OH) ₃ ), AlOOH, or the like that generates α-type alumina may be used. The particle diameter of the aluminum oxide powder is preferably 10 μm or less, which is usually excellent in sinterability, and more preferably 1 μm or less (submicron). In addition, the aluminum oxide powder has an alkali metal, alkaline earth metal, metal element No. 19 or later in the periodic table, and compounds of these metal elements, all of which are 30 ppm or less, and contains impurity metal elements other than aluminum. The total amount is 100 ppm or less and high purity.

  The amount of aluminum oxide added to AlN is 1 to 30% by weight. The AlN raw material usually has an oxide layer of about 0.2% by weight on the surface layer of the powder, but since this oxide layer exists non-uniformly, in order to uniformly blacken the sintered body, aluminum oxide Addition is necessary. If the amount of aluminum oxide to be added is less than 1% by weight, AlN and aluminum oxide are not evenly dispersed during powder mixing, and blackening due to the generation of lattice defects is somewhat insufficient, resulting in partial color unevenness. In some cases, the effect of particle dispersion of AlN and AlON is hardly seen, and the improvement in fracture toughness cannot be expected so much. If the amount of aluminum oxide exceeds 30% by weight, the produced AlON phase becomes excessive, which is disadvantageous in that sintering inhibition occurs.

  By adding aluminum oxide to AlN and containing an AlON phase having lattice defects generated by the reaction of both during sintering, AlN ceramics exhibiting black color and excellent mechanical properties can be produced. Quantitative measurement of lattice defects in a sintered body is usually extremely difficult. For example, the presence or absence of lattice defects is confirmed by analysis using ESR (Electron Spin Resonance).

  As the sintering method of the black AlN ceramic of the present invention, known sintering methods such as atmospheric pressure sintering method, hot press sintering method, gas pressure sintering method, hot isostatic pressing (HIP) sintering method, etc. Any of these can be used, but in order to obtain a dense sintered body having excellent mechanical properties, it is advantageous to use a pressure sintering method. The pressure sintering temperature is preferably 1600 to 1900 ° C. If the temperature is lower than 1600 ° C., the black AlN ceramics are not sufficiently densified, and the characteristics of the obtained sintered body are also inferior. When the firing temperature is higher than 1900 ° C., the growth of AlN or AlON particles becomes remarkable and the characteristics are deteriorated. Therefore, the upper limit is preferably 1900 ° C. The atmosphere during firing is preferably an inert gas atmosphere, particularly an inert atmosphere containing nitrogen gas that is advantageous for firing nitrides. The pressure for pressure sintering is usually 10 MPa or higher, preferably 20 MPa or higher, and the firing time is preferably 1 hour or longer so that the sintering is sufficiently completed.

Since AlON produced by the reaction between AlN and aluminum oxide is a non-stoichiometric compound, it is not easy to accurately determine the theoretical density of the composite ceramic as in the present invention. For example, Al ₂ O ₃ .AlN (specific gravity: 3.837) When the crystal phase is the main product, the theoretical value can be calculated according to the composite rule. If the relative density of the sintered body is not at least 90% of the theoretical value, the above-mentioned preferable characteristics are impaired, which is not desirable.
Hereinafter, although it demonstrates more concretely using an Example, this invention is not limited to the range of an Example.

(Examples 1-6)
The average particle size is 0.2 μm, the content of alkali metals, alkaline earth metals, metal elements on and after the 19th element of the periodic table, and compounds of these metal elements are all 20 ppm or less, and the total amount of these impurities is 50 ppm or less. In the high-purity AlN powder of Table 1, in the weight ratios shown in Examples 1 to 7 in Table 1, the average particle diameter is 0.2 μm, the alkali metal, the alkaline earth metal, the metal elements from the element periodic table No. 19 and the metal After adding high-purity alumina powder in which the content of elemental compounds is all 20 ppm or less and the total amount of these impurities is 100 ppm or less and mixing well using a ball mill, the mixed powder is filled into a φ100 mm graphite die. Hot press sintering was performed at a pressure of 40 MPa in a nitrogen gas stream for 2 hours at a temperature of 1750 ° C.

The sintered body was sequentially ground with a # 140, # 400, and # 1000 diamond grindstone, and then one side was lapped, and the sintered body was inspected for color tone and color unevenness / spots. The color tone was also quantitatively measured with a L ^* a ^* b ^* display (CIELAB display system) using a color difference colorimeter. The sintered body was processed into a 3 × 4 × 38 mm test piece in accordance with JIS R1601, the density was measured by the Archimedes method, and then a three-point bending test was performed at room temperature. The relative density of the sintered body, the generated AlON _Al 2 _O 3 · AlN (specific gravity: 3.837) was calculated as. Moreover, about the toughness of the sintered compact, the fracture magnetic value KIC was measured by SEPB method based on JISR1608.

As a result of analysis by X-ray diffraction, only the peaks of AlN and AlON (Al ₂ O ₃ · AlN) were detected from all the samples of Examples 1 to 6, and the sintered body was substantially two phases of AlN and AlON. It was found to consist of Table 1 shows the relative density (shown as a percentage of the theoretical value) of the sintered body for each composition of Examples 1 to 6, three-point bending strength, fracture toughness value, and color tone (color and L ^* a ^* b ^*). Value), presence / absence of color unevenness / spots, and content of AlON phase calculated from (100) peak of AlN and (400) peak of AlON in X-ray diffraction.
Also, in Table 1, as Comparative Examples 1 and 2, the characteristics of the sintered body of simple AlN not added with alumina and the sintered body added excessively with 40% by weight of alumina are the same as in Examples 1 to 6. Are comparing.

From Examples 1 to 6 and Comparative Example 1, it is clear that by adding alumina to AlN to produce an AlON phase, the sintered body becomes black and the occurrence of color unevenness and spots can be suppressed. Further, by dispersing the AlON phase in AlN, it is possible to improve mechanical properties such as fracture toughness and bending strength.
Further, from Examples 1 to 6 and Comparative Example 2, it is clear that when alumina is added excessively, the density of the sintered body is lowered, and therefore the mechanical properties are deteriorated.

(Examples 7 to 11)
The same high-purity AlN powder and high-purity alumina powder as used in Examples 1 to 6 were weighed into an AlN-1 wt% alumina composition and mixed thoroughly using a ball mill. The die was filled, and hot press sintering was performed at a temperature of 1600 to 1900 ° C. for 2 hours in a nitrogen gas stream at a pressure of 40 MPa. About the obtained sintered compact, various characteristics were evaluated similarly to Examples 1-6. Table 2 shows the relative density, three-point bending strength, and fracture toughness value of each of the sintered bodies of Examples 7 to 11.
From Examples 7-11 it is clear that 1600-1900 ° C. is the proper firing temperature.

(Example 12)
The sintered body of Example 2 (AlN-2 wt% alumina composition, fired at 1750 ° C.) and, as a comparison, added 2 wt% yttria as a sintering aid instead of alumina and sintered by hot press firing at 1750 ° C. The corrosion resistance of the body (Comparative Example 3) was evaluated.
According to the analysis using ESR (Electron Spin Resonance), the peak corresponding to the occurrence of lattice defects was detected very strongly from the sintered body of Example 2, whereas the very weak peak was detected from the sintered body of Comparative Example 3. As a result, only a large number of lattice defects were confirmed in the sintered body of the present invention.

Next, an experiment in which the sintered bodies of Example 2 and Comparative Example 3 were cut to 30 × 30 × 10 mm and lapped on one side was used as a sample and immersed in a 10% HF aqueous solution for 50 hours, and 5% fluorine was included. An experiment was conducted in which argon was heated to 500 ° C. in an argon gas and allowed to stand for 50 hours.
In the sintered body of Example 2, there was no weight reduction and no change in the sample surface after the corrosion resistance evaluation experiment, whereas the sintered body of Comparative Example 3 was 2 to 3% in both corrosion conditions. The weight loss was measured and the sample surface was blowing white powder.

Claims (4)

  AlON having 1-30% by weight of aluminum oxide added, and forming and sintering a mixed powder consisting essentially of aluminum nitride, and having lattice defects caused by the reaction between aluminum oxide and aluminum nitride during sintering A black AlN-based ceramic comprising a phase, substantially composed of two phases of AlN and AlON, and exhibiting a black color with a density of 90% or more of a theoretical value.   The content of alkali metal, alkaline earth metal, metal element No. 19 and subsequent elements in the periodic table, and compounds of these metal elements is all 30 ppm or less, and consists of two phases of substantially AlN and AlON. High purity black AlN ceramics. The blackness of the sintered body is in the range of lightness index: L ^* value of 0-50 and saturation: C ^* value of 0-10 in L ^* a ^* b ^* display (CIELAB display system). The black AlN ceramic according to claim 1 or 2, characterized in that   The black AlN-based ceramics according to any one of claims 1 to 3, wherein a reflectance of light on the surface of the sintered body in a wavelength region of 400 to 800 nm is 20% or less.