JP2000313670A - Silicon nitride sintered compact and sputtering target made of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon nitride sintered compact excellent in electric discharge machining property, being a substantia compacta greatly effective in the cleaning and working efficiency of a sputter target and enabling the occurrence of thermal cracking in sputtering to be reduced. SOLUTION: This silicon nitride sintered compact is added with Mg and/or Y in a total amount of 0.3-40 mol% in terms of MgO and/or Y2O3, respectively and 50-90 mol% nitride of group IV a elements and has a heat conductivity of >=40 W/(m.K) at ordinary temperature, a three-point bending strength of >=600 Mpa at ordinary temperature, an electric resistivity of <=1×10-2 Ω.cm and a relative density of >=96% when a true density is made to be 100%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride sintered body that can be widely used as a sputter target or a member for a structural component such as a member for general machinery, a member for molten metal, a member for a heat engine, and the like.

[0002]

2. Description of the Related Art Since silicon nitride sintered bodies are excellent in strength and toughness, application to machine parts is progressing. On the other hand, it is also applied to a material for electronic parts such as a sputter target used for forming a protective film such as a thermal head.

[0003] As a conventional sputter target made of a silicon nitride sintered body, there is one disclosed in, for example, Japanese Patent Application Laid-Open No. 3-248661. Generally, it is desirable that the sputter target be dense. The main reason is that cleaning is easier and impurities such as dust are easier to remove than those having pores inside the target. Further, since the atmosphere in the apparatus can be made high vacuum in a short time after being attached to the sputtering apparatus, work efficiency is improved.

[0004] However, if the sputter target made of a silicon nitride sintered body is made dense, there is a problem that the target is liable to crack due to heat input during sputtering. According to the above publication, it is described that when the density of the target exceeds 95% of the theoretical density, thermal stress cracking easily occurs due to a difference in thermal expansion between the target and a backing plate to which the target is attached.

[0005]

The sputter target generates heat when particles collide with the sputter surface. In order to prevent overheating due to this heat, a copper backing plate attached to the back surface of a sputter target is usually water-cooled. A thermal stress is generated in the sputter target along with the generation and cooling of the heat, and when the thermal stress increases, the sputter target may be broken.

Many factors are involved in the generation of cracks, such as the amount of heating during sputtering, the relative density of the sputter target, the difference in the coefficient of thermal expansion between the sputter target and the backing plate, the type of gas in the sputter atmosphere, and the pressure. . Conventionally, it is a fact that the conditions under which cracks are unlikely to occur are set while performing trials for individual cases in consideration of these factors.

As described above, in a sputter target made of a silicon nitride sintered body, it is known that making the material relatively porous is effective in preventing cracks. The present inventors investigated the effects of thermal conductivity, strength and relative density on thermal stress cracking in a sputter target made of a silicon nitride sintered body. As a result, the thermal conductivity at room temperature was 4
If the three-point bending strength is at least 0 W / (m · K) and at least 600 MPa, it will be understood that thermal stress cracking does not occur even with a tightly-bound material.

Accordingly, the present inventors have developed a silicon nitride sintered body that can significantly reduce the occurrence of thermal stress cracking during sputtering in a dense sputter target which is highly effective in cleaning and working efficiency of the sputter target. Japanese Patent Application No. 10-159806 has been proposed. The silicon nitride sintered body according to Japanese Patent Application No. 10-159806 discloses a method of converting magnesium (Mg) or yttrium (Y) into magnesium oxide (MgO) or yttrium oxide (Y
_In terms of ₂ O ₃ ), the total amount is 0.3 to 40 mol%, and the thermal conductivity at room temperature is 40 W / (m · K) or more.
The three-point bending strength at room temperature is 600 MPa or more, and the relative density when the true density is 100% is 96% or more.

However, this silicon nitride sintered body has a problem that it is not easy to machine due to its high hardness and high toughness. Therefore, the present invention not only improves the machinability but also has a great effect in terms of cleaning and working efficiency of the sputter target when used for a sputter target, for example, and can significantly reduce the occurrence of thermal stress cracking during sputtering. An object is to provide a silicon sintered body.

[0010]

The present inventors have conducted intensive studies and as a result, have found that a group IVa nitride (Ti
(N, ZrN, HfN), the present inventors have found that a silicon nitride sintered body can be easily processed by electric discharge machining, and have reached the present invention. That is, the silicon nitride sintered body according to the present invention is obtained by converting magnesium (Mg) or yttrium (Y) to magnesium oxide (MgO) or yttrium oxide (Y ₂
O ₃ ), the total amount is 0.3 to 40 mol%, IV
A nitride of group a is added in an amount of 50 to 90 mol%, and a raw material consisting of unavoidable impurities and silicon nitride is sintered, and the thermal conductivity of the sintered body at room temperature is 40 W / (m · K) or more and at room temperature. The three-point bending strength is 600 MPa or more, the electric resistivity is 1 × 10 ⁻² Ω · cm or less, and the true density is 100
% Is 96% or more.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A silicon nitride sintered body according to the present invention will be described. (A) Raw Material (1) Magnesium (Mg) or Yttrium (Y) Magnesium (Mg) or Yttrium (Y) is used as a sintering aid and is effective for dense sintering of silicon nitride raw material powder. These elements are composed of a silicon nitride crystal (Si ₃ N ₄₎ which is a first microstructure component constituting a silicon nitride sintered body.
Crystal), the silicon nitride crystal,
Consequently, the thermal conductivity of the silicon nitride sintered body can be kept at a high level.

If the total amount of magnesium or yttrium in terms of magnesium oxide or yttrium oxide is less than 0.3 mol%, the effect of densification during sintering becomes insufficient, and a relative density of 96% or more cannot be obtained. However, if it exceeds 40 mol%, the amount of the grain boundary phase having a low thermal conductivity, which is the second microstructure component of the silicon nitride sintered body, becomes excessive, and the thermal conductivity of the sputter target becomes 40 W /
(M · K). Therefore, these oxides are preferably contained in a total amount of 0.3 to 40 mol%.

The amount of yttrium oxide added is 0.1 mol
If the amount is less than 1%, the microstructure becomes coarse and the strength is reduced. Therefore, it is more preferable that the amount is not less than 0.1 mol%.

(2) Group IVa Nitride Group IVa nitride is added as a conductive compound to impart conductivity to silicon nitride. If the added amount of these conductive compounds is lower than 50 mol%, mutual contact between the conductive compounds is insufficient and no conductivity is generated. If more than 90 mol% is added, the sinterability decreases, and the porosity of the sintered body increases rapidly, that is, the relative density decreases. A more preferred addition amount of the group IVa nitride is 60 to 80 mol%.

The group IVa nitrides are Ti, Zr, Hf
Of nitride. Since it is known that the oxidation resistance of Zr and Hf nitrides at low temperatures is low, TiN, which is a nitride of Ti, is suitable particularly when used at high temperatures.

TiN is hard to melt and has high hardness, has a low resistivity of the order of 10 ⁻⁵ Ω · cm, and has a positive temperature coefficient of resistance. The TiN powder is uniformly dispersed in silicon nitride, and fine particles are preferably as fine as possible in order to improve the conductivity. Depending on the particle diameter of the silicon nitride powder, the average particle diameter is preferably 5 μm or less. is there.

The group IVa nitride has a higher coefficient of thermal expansion than silicon nitride, and has an effect of increasing the coefficient of thermal expansion of a silicon nitride sintered body when added to silicon nitride. When the silicon nitride sintered body is used in combination with another member such as a copper backing plate having a high coefficient of thermal expansion, such as when used as a target, the coefficient of thermal expansion of the silicon nitride sintered body is increased. I can do it. Therefore, cracking due to the thermal stress described above is less likely to occur.

(3) Remainder The remainder consists essentially of unavoidable impurities and silicon nitride. (4) Aluminum (Al) Al has a function of lowering the thermal conductivity by forming a solid solution in the silicon nitride crystal, and aluminum (Al) is made 0.1 mol% or less in terms of aluminum oxide (Al ₂ O ₃ ). .

(5) Production Method The method for producing the silicon nitride sintered body of the present invention is not particularly limited, and processes such as molding, sintering, and machining used in ordinary production of silicon nitride can be applied. In addition, a known method may be applied to a method of attaching to a backing plate.

(B) Characteristics of the sintered body at normal temperature (1) Thermal conductivity of the sintered body at normal temperature The thermal conductivity of the sintered body at normal temperature is 40 W / (m · K) or more. Thermal conductivity at room temperature is 40W / (mK)
If it is less than 1, the temperature gradient inside the sputter target is large, and the sputter target is easily broken. More preferable thermal conductivity is 60 W / (m · K) or more. Usually, the thermal conductivity of a silicon nitride sintered body at room temperature is about 35 W / (m · K), and the thermal conductivity of TiN at room temperature is 29 W / (m · K).
/ (M · K).

(2) Three-point bending strength at room temperature The three-point bending strength at room temperature is 600 MPa or more.
If the three-point bending strength at room temperature is less than 600 MPa,
This is because cracks due to thermal stress are likely to occur.

(3) Electric resistivity The electric resistivity is set to 1 × 10 ⁻² Ω · cm or less. If the electric resistivity is larger than 1 × 10 ⁻² Ω · cm, electric discharge machining cannot be performed.

(4) Relative Density When the true density is 100%, the relative density is 96% or more. When the relative density is less than 96%, pores existing in the sputter target tend to be connected. These communication holes serve as a reservoir for fine dust and grind fluid components generated during grinding of the sputter target. For this reason, even if the sputter target is immersed in water or an organic solvent after the grinding process and subjected to ultrasonic cleaning, dust and impurity components remaining inside the pores cannot be completely removed. If sputtering is performed in a state where dust and impurity components cannot be completely removed, impurities are released to the atmosphere, and it becomes difficult to form a high-quality film with high purity.

Further, when the sputter target is attached to the sputter apparatus and the inside of the apparatus is evacuated, if communication holes exist in the sputter target, it is difficult to increase the degree of vacuum, or it takes a long time. Or cause malfunctions.

Since the relative density of the sputter target using the silicon nitride sintered body of the present invention is not less than 96%, there is almost no communication hole, so that contamination by dust and impurity components and troubles in evacuation occur. Absent.

The sputter target made of the silicon nitride sintered body of the present invention is suitable for forming a wear-resistant coating used for a thermal head of a thermal transfer printer.

[0027] The film obtained by sputtering has inherently high thermal conductivity characteristics and a sufficiently high sputter rate. Therefore, the film formed by the sputter target of the present invention has high thermal conductivity characteristics. High heat density can be achieved. In addition, the wear-resistant coating for a thermal head formed by the sputter target of the present invention has not only good wear resistance due to the characteristics of silicon nitride but also high thermal conductivity, so that thermal resistance can be reduced, so that printing speed can be reduced. Can be enhanced.

It has been described that the silicon nitride sintered body of the present invention has high resistance to thermal stress cracking generated during sputtering as a sputter target. This is because the silicon nitride sintered body itself of the present invention is resistant to thermal stress. It has high resistance to heat, and can be widely used as a material having high thermal shock resistance other than the sputter target.

As a member for an electronic component, it can be applied to a heat sink member for various heating elements, etc. by utilizing the characteristics of high heat conduction and high strength.

As a member for a structural part, the present invention can be applied to a heater tube, a stalk, a die-cast sleeve, a rotary impeller for stirring a molten metal, a ladle, a thermocouple protection tube, etc. used in the field of molten metal such as aluminum and zinc. In addition, sink rolls, support rolls, bearings, used in continuous plating lines for molten metals such as aluminum and zinc
By applying to a shaft or the like, a member that is hard to be broken by rapid heating or cooling can be obtained. In addition, in the field of steel or non-ferrous processing, if it is used for rolling rolls, squeeze rolls, guide rollers, drawing dies, etc., it has good thermal diffusivity at the time of contact with the workpiece, thus reducing wear and reducing thermal stress cracking. Is less likely to occur. In addition, it can be applied to various heat exchanger parts and heat engine parts.

Further, since the silicon nitride sintered body according to the present invention can be processed into a complicated shape by electric discharge machining, it can be used as a mold used for molding a resin, a light alloy or the like. In this case, since the silicon nitride sintered body according to the present invention has a high thermal conductivity, a large amount of heat is removed from the molten resin or the light alloy injected into the mold, which is smaller than that of the conventional mold material. In addition, solidification of resin and light alloy is quickened, and production efficiency is improved.

[0032]

EXAMPLES (Example 1) Table 1 shows the compositions of the present invention and comparative examples used in Example 1. Average particle size of 0.
2 μm magnesium oxide (MgO) powder or yttrium oxide (Y ₂ O ₃ ) powder with an average particle size of 0.3 μm, titanium nitride (TiN) with an average particle size of 1 μm as a conductive compound
Was added to a silicon nitride (Si ₃ N ₄ ) powder having an average particle diameter of 0.5 μm to prepare a raw material powder. The raw material powder was pulverized and mixed by a ball mill in ethanol. Then, after vacuum drying, the mixture was granulated through a sieve, filled in a graphite mold, and subjected to hot press sintering at 1700 ° C., 2 atmospheres and a nitrogen gas atmosphere for 3 hours.

From the obtained silicon nitride sintered body, a diameter of 102
A sputter target having a size of 8 mm x 8 mm was produced by grinding or the like. The same sintered body has a diameter of 10 mm x
Specimen for thermal conductivity and density measurement of thickness 3mm, length 3
A three-point bending test specimen having a size of 4 mm × width 4 mm × length 40 mm was collected. In addition, a test piece for measuring electrical resistivity having a length of 5 mm, a width of 5 mm, and a length of 70 mm was collected.

The thermal conductivity was measured at room temperature by a laser flash method. The density was determined from the results of dimensional measurement and weight measurement using a micrometer. The three-point bending strength was measured by performing a three-point bending test at room temperature.

The electrical resistivity was calculated by applying a predetermined voltage to both ends of the test piece and measuring the current at this time. In addition, the presence or absence of a communication hole was examined from the presence or absence of a change in buoyancy when the test piece for density measurement was immersed in water. That is, when the buoyancy decreases over time, it is possible to determine that there is water intrusion and the presence of the communication hole.

In order to evaluate the resistance of the silicon nitride sintered body sputter target to thermal stress cracking during sputtering,
The target was bonded to a copper backing plate using a low-melting alloy, attached to a high-frequency magnetron type sputtering device, and output 2K in an argon (Ar) atmosphere.
W was sputtered at an output of 3 KW at which a larger thermal stress occurs. Then, the presence or absence of cracks was examined by observing the sputter target after sputtering.

As comparative examples, silicon nitride sintered bodies having different thermal conductivity, three-point bending strength and relative density were similarly evaluated. Table 2 shows the results of evaluation tests performed on Examples and Comparative Examples of the present invention. In Table 2, the symbol “○” indicates no water intrusion, the symbol “x” indicates the presence of water, and the symbol “○” indicates no cracking after sputtering.

[0038]

[0039]Table 2  Thermal conductivity Bending strength Electric resistivity Relative density Flooding Crack  (W / m / K) (MPa) × 10^-2(Ωcm) (%) 2KW 3KW Inventive Example 1 55 620 0.91 96 ○ ○ ○ Inventive Example 2 50 850 0.34 98 ○ ○ ○ Inventive Example 3 45 900 0.77 98 ○ ○ ○ Inventive Example 4 45 750 0.62 97 ○ ○ ○ Inventive Example 5 65 1100 0.41 99 ○ ○ ○ Inventive Example 6 75 1050 0.77 99 ○ ○ ○ Inventive Example 7 65 1060 0.82 99 ○ ○ ○ Inventive Example 8 75 850 0.25 99 ○ ○ × Comparative Example 1 19 330 2.00 75 × ○ ○ Comparative Example 2 45 570 1.00 94 × ○ × Comparative Example 3 34 750 0.92 99 ○ × × Comparative Example 4 28 680 0.81 99 ○ × ×

In each of Examples 1 to 8 of the present invention, the thermal conductivity of the sintered body at room temperature is 40 W / (m · K) or more, the three-point bending strength at room temperature is 600 MPa or more, and the electrical resistivity is 1 × 10 ^−. Good characteristics of ² Ω · cm or less were obtained. In addition, the relative density was 96% or more when the true density was set to 100%. In the case of the sputter with an output of 2 KW, none of Examples 1 to 8 of the present invention was good without cracking. With an output of 3 KW, the invention example 8 cracked, but the cracks did not occur at an output of 2 KW, so that it can be used sufficiently. In Comparative Examples 1 to 4, any one or more of the thermal conductivity, bending strength, and relative density did not satisfy the range of the present invention, and caused a problem of water immersion or cracking.

Example 2 Table 3 shows examples of the present invention used in Example 2. Magnesium oxide (MgO) powder having an average particle diameter of 0.2 μm or yttrium oxide (Y ₂ O ₃ ) powder having an average particle diameter of 0.3 μm as a sintering aid, and titanium nitride (TiN) having an average particle diameter of 2 μm as a conductive compound Or average particle size 2
μm zirconium nitride (ZrN) with an average particle size of 0.5
A raw material powder was prepared by adding to a μm silicon nitride (Si ₃ N ₄ ) powder. By performing the subsequent treatment and evaluation in the same manner as in Example 1, the silicon nitride sintered bodies having different conductive compounds and the amounts of the conductive compounds were evaluated. Table 4 shows the evaluation results.

[0042]

[0043]Table 4  Thermal conductivity Bending strength Electric resistivity Relative density Flooding Crack  (W / m / K) (MPa) × 10^-2(Ωcm) (%) 2KW 3KW Invention Example 11 65 1050 0.77 99 ○ ○ ○ Invention Example 12 44 770 0.05 99 ○ ○ ○ Invention Example 13 59 990 0.42 99 ○ ○ ○ Invention Example 14 42 650 0.06 99 ○ ○ ○

In Examples 11 to 14 of the present invention, the thermal conductivity was 40 W / (m · K) or more, and the three-point bending strength was 620 M.
At least Pa, the electrical resistivity was at most 1 × 10 ^-2 Ω · cm, and the relative density was at least 96%.

Example 3 Table 5 shows examples of the present invention used in Example 3. Magnesium oxide (MgO) powder having an average particle diameter of 0.2 μm or yttrium oxide (Y ₂ O ₃ ) powder having an average particle diameter of 0.3 μm as a sintering aid, and titanium nitride (TiN) having an average particle diameter of 1 μm as a conductive compound Was added to a silicon nitride (Si ₃ N ₄ ) powder having an average particle diameter of 0.5 μm to prepare a raw material powder. The subsequent treatment and evaluation were performed in the same manner as in Example 1 to evaluate silicon nitride sintered bodies having different amounts of the conductive compound added. Table 6 shows the evaluation results.

[0046]

[0047]Table 6  Thermal conductivity Bending strength Electric resistivity Relative density Flooding Crack  (W / m / K) (MPa) × 10^-2(Ωcm) (%) 2KW 3KW Inventive Example 21 75 1040 0.76 99 ○ ○ ○ Inventive Example 22 66 900 0.53 99 ○ ○ ○ Inventive Example 23 57 860 0.12 99 ○ ○ ○ Inventive Example 24 48 740 0.05 98 ○ ○ ○ Invention Example 25 40 640 0.04 97 ○ ○ × Comparative Example 21 35 450 0.07 80 × × ×

In Examples 21 to 25 of the present invention, the thermal conductivity was 40 W / (m · K) or more, and the three-point bending strength was 620 M.
At least Pa, the electrical resistivity was at most 1 × 10 ^-2 Ω · cm, and the relative density was at least 96%. In Comparative Example 21, the amount of TiN added was 95.
mol%, the relative density after sintering was as low as 80%, so that there was inundation and cracking occurred.

[0049]

According to the present invention, a silicon nitride sintered body having a high thermal conductivity, a high strength and a high density which can be subjected to electric discharge machining can be obtained. In addition, a silicon nitride sputter target can be provided.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G001 BA06 BA09 BA32 BA37 BA38 BA71 BB06 BB09 BB32 BB37 BB38 BB71 BC13 BC42 BD03 BD14 BD22 BD36 4K029 BA58 BA60 BC10 BD04 CA05 DC05 DC09 DC39

Claims (5)

[Claims] 1. Magnesium (Mg) or yttrium
(Y) in magnesium oxide (MgO) or yttrium oxide (Y ₂ O ₃₎ in terms of its total amount 0.3~40mol
%, The nitride of the IVa group is added at 50 to 90 mol%, and the thermal conductivity of the sintered body at room temperature is 40 W / (m · K).
As described above, the three-point bending strength at room temperature is 600 MPa or more,
Electric resistivity is 1 × 10 ^-2 Ωcm or less, true density is 10
A silicon nitride sintered body characterized in that the relative density when it is 0% is 96% or more. 2. The silicon nitride sintered body according to claim 1, wherein yttrium oxide is added in an amount of 0.1 mol% or more together with magnesium oxide. 3. Aluminum (Al) is converted to aluminum oxide
The silicon nitride sintered body according to claim 1, wherein the content is 0.1 mol% or less in terms of (Al ₂ O ₃ ). 4. TiN of the group IVa nitride is 50%.
The silicon nitride sintered body according to any one of claims 1 to 3, wherein about 90 mol% is added. 5. A sputter target comprising the silicon nitride sintered body according to any one of claims 1 to 4.