JP2001019557A - Silicon nitride sintered compact, its production and substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silicon nitride sintered compact having high thermal conductivity and excellent mechanical characteristics. SOLUTION: This silicon nitride sintered compact comprises a silicon nitride particle having <=1,500 ppm total content of oxygen, Al, Ca and Fe and >=2 μm minor axis diameter. In this method for producing the silicon nitride sintered compact by adding one or more kinds of oxides of yttrium and/or lanthanoid group elements to silicon nitride powder to give raw material powder, molding the powder and then sintering the molding product, silicon nitride powder having <=300 ppm Al, <=1 wt.% oxygen and <=70% α ratio is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor substrate,
A silicon nitride sintered body that has high thermal conductivity and excellent mechanical properties such as strength and fracture toughness, and can be used as a material for various structural parts and electric parts used in a wide range of fields such as automobiles and machines. It relates to a manufacturing method.

[0002]

2. Description of the Related Art Sintered silicon nitride (also referred to as silicon nitride ceramics) is a chemically stable material and has excellent mechanical properties. It is. In addition, it is used as an electrical insulating material by utilizing high insulating properties.

[0003] However, silicon nitride is a substance having a strong covalent bond and has excellent high-temperature characteristics, but is a substance which is difficult to be sintered. For this reason, silicon nitride ceramics
An oxide such as ₂ O ₃ is added as a sintering aid to enhance the sinterability and make the material denser. These sintering aids and SiO ₂ contained in the raw material silicon nitride form a grain boundary phase of the silicon nitride ceramics, which affects mechanical and thermal properties.

[0004] Conventional silicon nitride ceramics are obtained by adding a sintering aid to silicon nitride powder, molding the resultant, and firing the obtained molded body at a high temperature of 1600 to 2200 ° C for a predetermined time. Is ground to a desired shape.

On the other hand, a substrate for a semiconductor circuit is required to have high thermal conductivity because of being required to have excellent heat dissipation characteristics in addition to electric insulation.

In recent years, in order to apply circuit boards to automobiles or high-speed electric railways, as circuit boards have become smaller and semiconductor elements have been highly integrated, the heat radiation characteristics of insulating materials in these circuit boards have been further improved. Has been desired. As such a material, silicon carbide (SiC) added with BeO, aluminum nitride (AlN), and the like have been developed. However, although SiC and AlN have high thermal conductivity, they have low mechanical properties such as strength and fracture toughness, and thus have problems in heat cycle characteristics, handling strength, and the like.

That is, SiC, BeO, and AlN, which are known as conventional electrically insulating and high heat conductive ceramics, have a high thermal conductivity of 100 W / mK or more and are excellent in heat radiation characteristics, but have strength, fracture toughness, etc. When used as a circuit board or the like, when the semiconductor element is fixed by screwing in the mounting process, the ceramic substrate may be damaged such as cracking or repeated operation of the semiconductor element. Due to the thermal cycle, cracks are likely to occur in the ceramic substrate near the joint with the metal circuit layer, and there is a problem that the heat resistant cycle characteristics and reliability are low.

[0008] Silicon nitride sintered body is a material that has been applied to structural materials because of its excellent mechanical properties such as strength and fracture toughness. However, since its thermal conductivity is lower than that of SiC or AlN, Application to electrical insulating substrates that require high heat dissipation characteristics has not been sufficiently advanced. In a sintered body to which Y ₂ O ₃ and Al ₂ O ₃ , which are general sintering aids, are added, the thermal conductivity is about 20 W / mK, and the thermal conductivity of AlN or SiC is 100 to
The thermal conductivity was very low as compared to 270 W / mK.

Since silicon nitride is an electrically insulating material, heat transfer near room temperature mainly occurs by phonons. Since phonons are scattered by disorder of the crystal lattice such as vacancies, transitions, and point defects, grain boundary phases, pores, etc., the thermal conductivity of silicon nitride also depends on the crystallinity of silicon nitride particles and the sintering aid. It is affected by the type and density of the sintered body. The theoretical predicted value of silicon nitride is estimated to be about 280 W / mK from its crystal structure, but it is difficult to actually synthesize a single crystal of silicon nitride and apply it to practical use. Manufactured as a body.

The sintering of silicon nitride proceeds while the silicon nitride particles dissolve and precipitate in a liquid phase composed of a sintering aid and a SiO ₂ component contained in the silicon nitride powder. The individual silicon nitride particles in the compact are considered to be close to a single crystal, and relatively high thermal conductivity is expected. However, in an actual silicon nitride sintered body, the influence of the above-mentioned crystallographic purity on the grain boundary phase and the inside of the silicon nitride particles is larger. At present, only about 20% of the thermal conductivity is obtained.

Regarding the high thermal conductivity of the silicon nitride sintered body,
In the "Journal of the Ceramic Society of Japan," the January issue, pp. 56-62, 1989, without the use of a sintering aid, including Al, Y ₂ O ₃
It is described that a sintered body having a thermal conductivity of 70 W / mK can be obtained by adding only HIP (hot isostatic pressure) and sintering.

Further, as described in JP-A-4-175268 and JP-A-4-219371,
Reduce the Al and oxygen contents in the sintered body, Ti, Zr,
There is known a method of obtaining a sintered body having a thermal conductivity of 40 W / mK or more by adding a metal such as Hf and, in some cases, adding Y ₂ O ₃ as a sintering aid.

[0013] Furthermore, in the "Journal of the Ceramic Society of Japan", January 1996, pp. 49-53, a small amount of Y ₂ O ₃ and Nd ₂ O ₃ was used as a sintering aid, and the temperature was as high as 2200 ° C. By performing HIP sintering at a temperature for 4 hours, a silicon nitride sintered body having a thermal conductivity of 122 W / mK is obtained.

Although conventional silicon nitride ceramics have excellent mechanical properties such as strength and fracture toughness, the thermal conductivity is still lower than that of SiC, AlN, and BeO ceramics as described above, and is sufficiently practical for practical use. Not even,
In order to obtain a material having high thermal conductivity, a special sintering method such as HIP sintering must be used at a high temperature using a high-purity silicon nitride raw material powder having a small amount of impurities such as Al.
The resulting sintered body is very expensive, and is not practically used for electronic materials such as circuit boards for semiconductors.

[0015]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and without impairing high heat conductivity and excellent mechanical properties such as strength and fracture toughness.
It is an object of the present invention to provide an inexpensive silicon nitride sintered body that is excellent in heat dissipation characteristics and reliability and is suitable as a material for automobile parts such as semiconductor circuit boards and valves.

[0016]

In order to achieve the above object, the present inventor has set forth the powder characteristics of the raw material powder for obtaining the silicon nitride sintered body, the composition and amount of the sintering aid, and the sintering aid. As a result of intensive studies on the bonding conditions and the like, when silicon nitride particles having a predetermined size or more in the obtained silicon nitride sintered body satisfy a specific composition, without impairing excellent mechanical properties such as strength and fracture toughness. In addition, the present invention has been completed by obtaining a silicon nitride sintered body having higher thermal conductivity than the conventional one.

That is, the present invention relates to a method for producing a silicon nitride sintered body in which a raw material powder obtained by adding one or more oxides of yttria and / or lanthanoid group elements to silicon nitride powder is molded and then sintered. A silicon nitride powder containing 300 ppm or less of Al and 1% by weight of oxygen, and having an alpha conversion of 70% or less is used, and oxygen, Al, Ca, and silicon nitride particles having a minor axis diameter of 2 μm or more are used. A method for producing a silicon nitride sintered body, comprising sintering silicon nitride particles while growing them so that the total content of Fe is 1500 ppm or less.

According to the present invention, the α-rate of the silicon nitride powder is set to X%,
When the ratio of silicon nitride particles having a particle diameter of 2.5 times or more the cumulative average diameter in the silicon nitride powder in the silicon nitride powder is Y volume%, 0 ≦ X ≦ 70, Y ≧ 0, and Y ≧
The method for producing a silicon nitride sintered body described above, having a particle size distribution satisfying -0.05X + 1.

The present invention is characterized in that the sintering operation is maintained at a temperature in the range of 1800 to 2000 ° C. for 8 hours or more in a nitrogen pressurized atmosphere of 9.8 MPa or less. Is the way.

The present invention also relates to oxygen, Al, Ca, Fe
Is a silicon nitride sintered body characterized by having silicon nitride particles having a total content of less than 1500 ppm and a minor axis diameter of 2 μm or more.

The present invention is characterized in that said silicon nitride particles having a minor axis diameter of 2 μm or more account for 10 to 65 area% of the entire silicon nitride sintered body. Body.

The present invention is characterized in that said silicon nitride particles having a minor axis diameter of 2 μm or more account for 10 to 65 area% of the entire silicon nitride sintered body. Body.

According to the present invention, the silicon nitride particles having a short axis diameter of 2 μm or more are 10 to 35 area% with respect to the entire silicon nitride sintered body, and the area of the silicon nitride particles having a short axis diameter of 2 μm or more. The silicon nitride sintered body described above, having an average diameter of 17.5 μm or less.

The present invention has a thermal conductivity of 100 to 160 W /
mK.

According to the present invention, 82 to 91.5% by weight of silicon nitride, 8 to 15% by weight of the total of yttrium and / or lanthanoid group elements in terms of oxide, and 0 to 8 of the total of hafnium and zirconium in terms of oxide. The silicon nitride sintered body described above, which is contained in an amount of 3% by weight.

According to the present invention, the grain boundary phase constituting the silicon nitride sintered body is an M phase (Re ₂ Si ₃ O ₃ N ₄ ) or a J phase (Re ₄ Si ₂
O ₇ N ₄ ), and the sum of the main peak intensities in the X-ray diffraction of the M phase and the J phase is 0 with respect to the peak intensity of the (200) plane of β-type silicon nitride in the silicon nitride sintered body. .01
And 0.2 to 0.2.

In addition, the present invention is a silicon nitride circuit board characterized by using the above silicon nitride sintered body.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Silicon nitride ceramics have a microstructure in which columnar β-type silicon nitride particles are intricately intertwined, and this structure greatly contributes to mechanical properties such as strength and fracture toughness. Moreover, the pores in the sintered body act as defects and affect the strength characteristics. In silicon nitride ceramics, optimizing the structure of the sintered body including these defects can provide a sintered body that has high thermal conductivity and excellent mechanical properties such as strength and fracture toughness. Important for.

The thickness of the interface between the two particles when the silicon nitride particles in the silicon nitride sintered body are in contact with each other is about 1 nm, which is about 1/3 or less of the phonon mean free path at room temperature. The ratio contributing to the thermal conductivity of the sintered body is
It is considered that the inside of the silicon nitride particles is larger than the grain boundary phase. Therefore, in order to increase the thermal conductivity of the silicon nitride sintered body, it is considered important to increase the crystallographic purity of the silicon nitride particles.

Based on the above presumption, the present inventors conducted experiments using various raw material silicon nitride powders and sintering aids to increase the crystallographic purity of the silicon nitride particles in the silicon nitride sintered body. As a result of the study, using a specific silicon nitride raw material powder,
By adopting the specific sintering conditions, oxygen and specific metal impurities are discharged from the silicon nitride particles, that is, a purification action of the silicon nitride particles occurs, and as a result, it has been developed to have a minor axis diameter of 2 μm or more. It has been found that silicon nitride particles, in which silicon nitride particles are grown and which are highly purified, have significantly improved thermal conductivity without impairing the conventional excellent mechanical properties. Thus, the present invention has been accomplished.

That is, the present invention relates to a method for manufacturing a silicon nitride sintered body in which a raw material powder obtained by adding at least one oxide of yttrium and / or a lanthanoid group element to a silicon nitride powder is molded and then sintered. A silicon nitride powder containing 300 ppm or less of Al and 1% by weight of oxygen, and having an alpha conversion of 70% or less is used, and oxygen, Al, Ca, and silicon nitride particles having a minor axis diameter of 2 μm or more are used. A method for producing a silicon nitride sintered body, comprising sintering silicon nitride particles while growing them so that the total content of Fe is 1500 ppm or less.

As the sintering aid for silicon nitride, various oxides and the like are used, and conventionally known sintering aids obtained by using a sintering aid which forms a solid solution with silicon nitride exemplified by Al ₂ O ₃ are used. In the silicon nitride sintered body, since a portion where the sintering aid such as alumina is dissolved in the silicon nitride particles is present as a point defect, phonon scattering occurs near room temperature and the thermal conductivity is reduced. . On the other hand, in the present invention, one of yttrium and / or a lanthanoid group element which does not form a solid solution with silicon nitride is used.
More than one kind of oxide is employed as a sintering aid. Among the yttrium and lanthanoid group elements, elements having a small ionic radius such as Yb, Er, Dy, and Ho are preferable.

For example, the sintering aid of the present invention and the amount of the sintering additive may be represented by the following formula:
The total amount of yttrium and / or lanthanoid group elements is 8 to 15% by weight in terms of oxides, and if necessary, the total of hafnium and zirconium is 0 to 3% by weight in terms of oxides.
Added. Since the oxides of yttrium and / or lanthanoid elements and the oxides of hafnium and zirconium do not form a solid solution with silicon nitride, when used as a sintering aid, the resulting silicon nitride sintered body has a high thermal conductivity. This is because it contributes to the development of

If the total amount of yttrium and / or lanthanoid group elements is less than 8% by weight in terms of oxides, the total amount of the liquid phase will not be small, so that grain growth may be excessive and the strength may be reduced. In particular, when the content is 6% by weight or less, insufficient sintering of the obtained sintered body is likely to occur. On the other hand, if the addition amount is 15% by weight or more, the amount of the grain boundary phase becomes too large, and the influence of phonon scattering in the grain boundary phase cannot be ignored compared to the phonon scattering in silicon nitride grains, resulting in a decrease in thermal conductivity. There are cases.

On the other hand, the addition of hafnium and / or zirconium serves to promote grain growth and the purifying effect.
Although not necessarily added, addition of 0.5% by weight to 3% by weight of hafnium and / or zirconium facilitates the growth and purification effect of silicon nitride particles during sintering, and the object of the present invention is easily achieved. That is, if the total amount of the addition of the oxides of hafnium and zirconium is less than 0.5% by weight, the contribution to the grain growth is small, and it may be difficult to recognize a further effect on the purification action of the silicon nitride particles. On the other hand, when the added amount exceeds 3% by weight in terms of oxide, the amount of the grain boundary phase becomes too large and the effect of phonon scattering in the grain boundary phase cannot be ignored compared to phonon scattering in silicon nitride grains. In some cases, the thermal conductivity may be reduced.

Next, the reason for using silicon nitride powder containing 300 ppm or less of Al and 1% by weight of oxygen and having an α conversion of 70% or less in the present invention will be described.

First, among the metal impurities contained in the raw material powder, Al is dissolved in the silicon nitride particles without being discharged to the grain boundaries during the dissolution-reprecipitation process during sintering. This is because it is present as it is, and the thermal conductivity of the resulting silicon nitride sintered body is reduced.

The effect of the amount of Al in the raw material silicon nitride powder on the thermal conductivity of the obtained silicon nitride sintered body, according to the results of studies by the present inventors, shows that every 100 ppm of Al increases silicon nitride firing. Since the thermal conductivity of the consolidated body is reduced by about 3 W / mK, in order to develop a high thermal conductivity of, for example, 100 W / mK or more with the aim of a circuit board for mounting a semiconductor, A in the raw material powder is required.
l content must be 150 ppm or less.
In order to exhibit a high thermal conductivity of 0 W / mK or more, it is preferable to suppress the Al content to 100 ppm or less.

The oxygen contained in the silicon nitride powder is
In the sintering process, it is usually present as SiO ₂ and constitutes a liquid phase at the time of sintering. Regarding its abundance and its effect on the properties of the obtained silicon nitride sintered body, based on the results of the study by the present inventors, If the amount of oxygen in the raw material powder is too small, pores remain without densification, the thermal conductivity decreases, and the Al
Driving force to discharge metal impurities and oxygen other than to the grain boundary is reduced, and the purification action in the silicon nitride grains is hindered.On the other hand, if too much, a large amount of oxygen forms a solid solution in the silicon nitride particles during liquid phase formation. It has been found that the thermal conductivity is lowered and that the SiO ₂ concentration in the liquid phase is increased to suppress the grain growth. For these reasons, in order to obtain a sintered body without any problem in actual production, the content needs to be 1.0% by weight or less.
It is preferably at least 0.5% by weight.

With respect to the α-rate of the silicon nitride raw material powder, α
If the conversion rate is 70% or more, the densification may be hindered, and in this case, pores remain in the sintered body and the thermal conductivity decreases. In order to produce a silicon nitride sintered body having a high thermal conductivity of 100 W / mK or more in order to be suitable for use as a circuit board for mounting a semiconductor, a relative density of 98 to 10 is required.
0% is required. Therefore, in order to obtain such a sintered body density that almost reaches the theoretical density, it is necessary to reduce the α-rate of the silicon nitride raw material powder to 70% or less.

A silicon nitride raw material having an α conversion of 70% or more is sintered together with a sintering aid system containing at least one oxide of yttrium and / or a lanthanoid element which does not form a solid solution with silicon nitride. In this case, densification can be made relatively easily by adding 1% by weight or more of SiO ₂ as an auxiliary agent. However, in this case, the concentration of SiO ₂ in the liquid phase increases and the thermal conductivity decreases as described above. Therefore, it is difficult to obtain a high thermal conductivity of 100 W / mK or more.

The sintered body of the present invention can be obtained by molding and sintering a mixed powder containing the silicon nitride powder and one or more oxides of yttrium and / or lanthanoid group elements. As the molding method at this time, any conventionally known molding method, for example, any of a press molding method, an extrusion molding method, an injection molding method, a cast molding method and the like can be adopted. The sintering method may be any method as long as the object of the present invention can be achieved.However, the pressure sintering method under a nitrogen atmosphere described below does not require expensive equipment and is stable. Thus, a large amount of silicon nitride sintered body can be supplied, which is preferable.

As described later, the sintering atmosphere must be performed under nitrogen pressure in the temperature range selected in the present invention in order to suppress the decomposition of silicon nitride. The upper limit pressure of nitrogen pressurization is 9.8 MPa or less in view of the thermal conductivity and mechanical properties such as strength and fracture toughness of the silicon nitride sintered body, and is preferably 1 MPa or less. No equipment is required, and the cost of the obtained sintered body can be reduced.

In the pressure sintering method under a nitrogen atmosphere, a compact obtained from the raw material powder is heated in a nitrogen pressure atmosphere of 9.8 MPa or less at a temperature of 1800 to 2000 ° C., and sintered. The silicon nitride particles in the body are grown to a minor axis diameter of 2 μm or more, and oxygen, A
Purification may be performed until the total amount of l, Ca, and Fe becomes 1500 ppm or less, but usually, the temperature may be maintained in the temperature range for 8 hours or more. The upper limit of the holding time is not limited from the viewpoint of purification and growth of the silicon nitride particles, but there are also problems such as a decrease in productivity and, in some cases, a decrease in strength due to excessive growth of the silicon nitride particles. In some cases, it is preferable to maintain the temperature for up to about 72 hours.

In the above temperature range, insufficient sintering occurs at a sintering temperature lower than 1800 ° C., and at a temperature higher than 2,000 ° C., mechanical properties such as the strength of a sintered body obtained by excessively growing grains deteriorate. May be. A preferred temperature range is 1850-1950 ° C.

Further, based on the results of an experimental study conducted by the present inventors on the silicon nitride powder, the α-rate of the silicon nitride powder was set to X
% In the raw material powder having a particle diameter 2.5 times the cumulative average diameter of the silicon nitride powder,
It is preferable to have a particle size distribution satisfying ≦ X ≦ 70, Y ≧ 0, and Y ≧ −0.05X + 1 since a silicon nitride sintered body having a thermal conductivity of 100 W / mK or more can be obtained.

The relationship between X and Y was found by the present inventors as a result of an experimental study. In order to achieve a thermal conductivity suitable for a use such as a semiconductor circuit board,
X and Y need to satisfy a specific relationship, and FIG. 1 shows the above relationship using the thermal conductivity as a parameter.

That is, the α ratio of the silicon nitride powder was X%, and the ratio of silicon nitride particles having a particle diameter of 2.5 times or more the cumulative average diameter of the silicon nitride powder in the silicon nitride powder was Y volume%. In this case, in order to obtain a high thermal conductivity of 100 W / mK or more, 0 ≦ X ≦ 70, Y ≧ 0, and Y ≧ −0.05.
It is necessary to satisfy X + 1, and in order to obtain a high thermal conductivity of 115 W / mK or more, 0 ≦ X ≦ 70, Y ≧ 0, and Y
It is preferable to satisfy ≧ −0.05X + 2.5, and to obtain a high thermal conductivity of 130 W / mK or more, 0 ≦
It is preferable that X ≦ 70, Y ≧ 0, and Y ≧ −0.05X + 4.5 are satisfied.

The particle size distribution of the silicon nitride raw material powder used in the present invention can be measured by a laser scattering method according to JISR1629.

The microstructure of the silicon nitride sintered body of the present invention obtained by the above method can be classified into coarse particles having a minor axis diameter of 2 μm or more, fine particles having a minor axis diameter of less than 2 μm, and a grain boundary phase. it can. The fine particles having a minor axis diameter of less than 2 μm contain a large amount of metal impurities and oxygen in the silicon nitride raw material powder because the above-described purification action is not sufficiently performed, and the grain boundaries are contained in the silicon nitride sintered body. It is considered to be a part that scatters phonons together with the phase and lowers the thermal conductivity.

On the other hand, the coarse particles having a minor axis diameter of 2 μm or more are purifying impurities along with the grain growth. Therefore, the nitrides having a higher purity than the fine particles having a minor axis diameter of less than 2 μm and the grain boundary phase are obtained. Silicon particles are present, and the presence thereof keeps the thermal conductivity of the silicon nitride sintered body high. In order for the silicon nitride sintered body to exhibit a high thermal conductivity of 100 W / mK or more, the total content of oxygen, Al, Ca, and Fe in the coarse particles is 1500 ppm or less.

Regarding the method of measuring the amount of impurities in the silicon nitride sintered body, the silicon nitride sintered body was crushed in an agate mortar,
Perform 60 mesh sieving, Journal of
the American Ceramic Soci
After dissolving the grain boundary phase by the method described in ety Transactions of July 1994, pp. 1857-1862, the particles are classified into fine particles and coarse particles with a minor axis diameter of 2 μm as a boundary by wet classification or centrifugal classification. Regarding the oxygen analysis of the extracted silicon nitride particles, an O / N simultaneous analyzer (TC-4 manufactured by LECO) was used.
36), and other metal impurities may be quantified by ICP analysis.

In the silicon nitride sintered body of the present invention, as described above, oxygen, Al, C
It is characterized by having silicon nitride particles having a minor axis diameter of 2 μm or more in which the total content of a and Fe is within 1500 ppm. If the total amount of the impurities is more than 1500 ppm, it is difficult to exhibit a high thermal conductivity of 100 W / mK or more, which limits the use when used for a circuit board for mounting semiconductors. In order to exhibit a high thermal conductivity of 130 W / mK or more, the total amount of the impurities is preferably 1000 ppm or less.

In the silicon nitride sintered body of the present invention, it is preferable that the silicon nitride particles having the minor axis diameter of 2 μm or more accounts for 10 area% or more and 65 area% or less based on the entire silicon nitride sintered body. As described above, silicon nitride discharges impurities in silicon nitride grains to the grain boundaries as the grains grow, so that some degree of grain growth is required. If the silicon nitride particles having a minor axis diameter of 2 μm or more are less than 10 area% with respect to the entire silicon nitride sintered body, the intragranular purification action is insufficient and sufficient high thermal conductivity may not be obtained. In addition, silicon nitride particles having a minor axis diameter of 2 μm or more account for 65 area% of the entire silicon nitride sintered body.
When the particles are present, the grown particles may collide with each other three-dimensionally, causing a defect in the collision part, causing a decrease in the thermal conductivity. This can be a problem.

With respect to the evaluation of the microstructure of the silicon nitride sintered body, the silicon nitride sintered body was ground and further mirror-polished with diamond abrasive grains, and then subjected to RF plasma etching in CF ₄ gas containing 8% oxygen. Then, the obtained sample may be observed at a magnification of 350 times using a scanning microscope (SEM). Furthermore, regarding quantitative evaluation of microstructure,
Using the obtained SEM photograph, the silicon nitride particles and the grain boundaries are binarized by an image analyzer to obtain an area where only the silicon nitride particles exist, and to observe the total area of 1000 or more particles having a minor axis diameter of 2 μm or more. Is calculated as area%. For the area average diameter of the short axis diameter of 2 μm or more,
The particle diameter corresponding to 50% of the particle diameter area is defined as the area average diameter.

The mechanical properties of the silicon nitride sintered body of the present invention are as follows:
With a three-point bending strength of 450 MPa or more, a fracture toughness value of 6 M
Pa · m ^1/2 or more. These values are sufficient for use not only as a circuit board but also as a heat dissipation board or an engine component, and can be used for applications requiring high reliability.

In addition, as a microstructure of the silicon nitride sintered body used in the present invention, the silicon nitride particles having a minor axis diameter of 2 μm or more are 10 to 35 area% with respect to the whole silicon nitride sintered body, In addition, it is preferable that the area average diameter of silicon nitride particles having a short axis diameter of 2 μm or more is 17.5 μm or less. In this case, as described above, even when used as a heat radiating board or an engine component, it has more excellent mechanical properties, and can be used for applications requiring extremely high reliability.

The silicon nitride sintered body used in the present invention has a thermal conductivity of 100 to 160 W / mK. If the thermal conductivity is less than 100 W / mK, sufficient heat radiation characteristics cannot be obtained as a heat radiation substrate, and its use is limited. Further, if a high thermal conductivity of 160 W / mK or more is to be developed in a silicon nitride sintered body, AlN or Si
This is because the mechanical strength may be lower than that of C.

In the silicon nitride sintered body of the present invention, the M phase (Re ₂ S
i ₃ O ₃ N ₄ ) or J phase (Re ₄ Si ₂ O ₇ N ₄ ),
The sum of the main peak intensities (IGB) in the X-ray diffraction of the M phase and the J phase is 0.01 to less than the peak intensity ISN of the (200) plane of β-type silicon nitride in the silicon nitride sintered body.
0.2. The identification of the crystal phase can be measured by an X-ray diffractometer after grinding the sintered body and keeping the sintered body.

The thermal conductivity of a silicon nitride sintered body is caused by phonon scattering due to crystal defects and grain boundary phases in silicon nitride particles. Therefore, crystallization of the grain boundary phase is useful for further increasing the thermal conductivity. Regarding the type of the grain boundary crystal phase of the silicon nitride sintered body of the present invention, the silicon nitride sintered body contains at least an M phase (Re ₂ Si ₃ O ₃ N ₄ ) or a J phase (Re ₄ Si ₂ O ₇ N ₄ ). . In the grain growth of silicon nitride, the rare earth oxide, silicon nitride and silica unavoidably present in silicon nitride added as an auxiliary as in the present invention form a liquid phase and precipitate on relatively large silicon nitride particles. In the early stage of grain growth, the silica concentration in the liquid phase is sufficiently high, and the Re ₂ SiO
₅ phase, H phase (Re ₁₀ Si ₇ O ₂₃ N ₄ ), K phase (ReSi
₂ N) to form a relatively silica-rich liquid phase, such as.

At this stage, a large amount of oxygen derived from silica is dissolved in the silicon nitride particles from the liquid phase at this stage. However, oxygen and the like are introduced from the silicon nitride particles into the liquid phase during repeated dissolution-reprecipitation. It has been confirmed by the present inventors that so-called purifying action occurs. This purifying action includes metal impurities other than Al and oxygen as metal impurities. Of these, oxygen is discharged to the grain boundaries, becomes silica in the liquid phase, and is further discharged as silicon monoxide in the gas phase. You. For this reason, as the silicon nitride particles grow, the concentration of silica in the liquid phase becomes lower, and the silicon nitride particles become very easily purified. When this state is exhibited, the grain boundary phase composition is the J phase (Re ₄ Si ₂ O ₇ N ₄ ), and when the silica concentration further decreases, finally the M phase (Re ₂ Si ₃ O ₃ N ₄₎ ). That is, each of these grain boundary phase compositions contributes to high thermal conductivity of silicon nitride.

As described above, the silicon nitride sintered body of the present invention is characterized in that the grain boundary phase is crystallized to a specific value or more.
₂ Si ₃ O ₃ N ₄ ) or J phase (Re ₄ Si ₂ O ₇ N ₄ ), and the sum of the main peak intensities (IGB) in the X-ray diffraction of the M phase and the J phase is determined by the silicon nitride sintering. The peak intensity of (200) plane of β-type silicon nitride in the body is 0.0
It is preferably from 1 to 0.2. When the ratio of IGB / ISN is less than 0.01, crystallization of the grain boundary phase is insufficient,
In some cases, sufficient thermal conductivity cannot be obtained. On the other hand, IGB
If the ratio of / ISN exceeds 0.2, the amount of the grain boundary phase becomes too large, and the thermal conductivity may be reduced.

The silicon nitride sintered body of the present invention has high thermal conductivity,
It can be used for a circuit board or the like that requires electrical insulation and mechanical properties. For example, in a circuit board for a power module or the like, high heat transfer performance and high mechanical properties are required in addition to electric insulation, which is conventionally required for a circuit board.

The silicon nitride circuit board of the present invention has excellent mechanical properties such as strength and fracture toughness of the silicon nitride sintered body used for the board. Has high reliability. Further, since silicon nitride itself has a high insulation resistance, it is suitable for a circuit board used under severe use conditions. Furthermore, a silicon nitride circuit board using the silicon nitride sintered body of the present invention is a circuit that not only has excellent mechanical properties but also requires a high thermal conductivity as compared with an alumina circuit board which is a general ceramic circuit board. Suitable for substrate applications.

As a method for obtaining a circuit board from the silicon nitride sintered body of the present invention, a plate-shaped silicon nitride sintered body or a silicon nitride sintered body processed into a plate shape by grinding or the like is used to obtain a metal substrate such as copper. It can be manufactured by forming a circuit by a technique such as etching after bonding with a plate.

With respect to the joining method of the silicon nitride sintered body and the metal plate, for example, the silicon nitride sintered body and the metal plate are heated in an inert gas or a vacuum atmosphere, and the silicon nitride sintered body and the metal plate are joined together. A direct joining method (direct joining method) or a brazing material made by mixing or alloying an active metal such as Ti or Zr with a low melting point alloy such as Ag or Cu between the silicon nitride sintered body and the metal plate. It can be manufactured using a method (active metal method) in which heat and pressure are applied in an inert gas or vacuum atmosphere with intervening.

[0067]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[Examples 1 to 25, Comparative Examples 1 to 12] Table 1
As shown in Table 2, sintering aids were added to the silicon nitride raw material powders A to N having different powder characteristics shown in Table 2, and methanol was further added, followed by mixing for 1 hour by a wet ball mill. Next, after filtering and drying these slurries to obtain raw material powders,
After molding with a molding pressure of 20 MPa, CIP molding with a molding pressure of 200 MPa, 5 mm × 30 mm × 50 mm
Was obtained. The obtained molded body was made of boron nitride (B
N), and sintered in an electric furnace of a carbon heater at a nitrogen gas pressure, a firing temperature and a firing time shown in Table 3 to produce a sintered body. The densities of the various sintered bodies obtained by the above operation were measured by Archimedes' method, and the results were shown in Table 4,
The results are shown in Table 5.

[0069]

[Table 1]

The particle size distribution of the silicon nitride powder in the present invention is measured by a laser scattering method in accordance with JIS R1629, and the raw material of the silicon nitride particles having a particle diameter of 2.5 times or more of the cumulative average diameter of the silicon nitride powder. The ratio in the powder was calculated as volume%.

[0071]

[Table 2]

[0072]

[Table 3]

[0073]

[Table 4]

[0074]

[Table 5]

Next, the obtained various sintered bodies were ground by a diamond wheel of # 200 to obtain a 20 mm × 20 m
It was processed into a shape of mx 3 mm. Examples 1, 5, 14-1
9 and Comparative Examples 5 to 7 and 10 to 12, the crystal phases were identified by X-ray diffraction using these processed bodies. The results of X-ray diffraction are shown in Table 5 above.

With respect to the notation of the crystal phase in Table 3, M indicates M phase, J indicates J phase, R1S indicates monosilicate, and R2S indicates disilicate.

Next, the sintered body was ground, and a 10 mmφ × 3 mm specimen for measuring thermal conductivity and JIS R1
A strength test specimen according to 601 was prepared, and the thermal conductivity at room temperature and the three-point bending strength at room temperature were examined. The thermal conductivity was determined by measuring the thermal diffusivity and the specific heat capacity by a laser flash method (based on JIS R1611) and determining the thermal conductivity by the product of the sintered body density, the thermal diffusivity, and the specific heat capacity. In addition, the strength test specimen is mirror-polished with diamond abrasive grains, and is subjected to JIS R160
The fracture toughness was evaluated by the IF method according to No. 7.

Further, after the mirror-polished sintered body was etched at a power of RF 80 W for 8 minutes in a CF ₄ gas atmosphere containing 8% oxygen, the microstructure of the sintered body was observed by SEM at a magnification of 350 times. Performed at magnification. Next, using these SEM photographs, a quantitative evaluation of the structure of the sintered body was performed by an image analyzer. Regarding the quantitative evaluation of microstructure,
Using the obtained SEM photograph, the image analysis apparatus binarizes the silicon nitride particles and the grain boundaries, obtains the area where only the silicon nitride particles exist, and calculates the total area of 1000 or more particles having a minor axis diameter of 2 μm or more with respect to the total observed area. The abundance ratio was calculated as area%, called the coarse particle ratio. Further, as for the area average diameter of the short axis diameter of 2 μm or more, the particle diameter corresponding to 50% of the particle diameter was defined as the area average diameter.

The method for measuring the amount of impurities in the silicon nitride sintered body was as follows: after the silicon nitride sintered body was crushed in an agate mortar,
Perform 60 mesh sieving, Journal of
the American Ceramic Soci
After dissolving the grain boundary phase by a known method described in ety Transactions, July 1994, pp. 1857-1862, the particles were classified into fine particles and coarse particles with a short axis diameter of 2 μm as a boundary by wet classification. Regarding the oxygen analysis of the silicon nitride particles obtained by the above operation, an O / N simultaneous analyzer (TC-43 manufactured by LECO) was used.
6), and for other metal impurities, the contents of Al, Ca, and Fe as metal impurities were quantified by ICP analysis, and together with the results of the oxygen content analysis, ( The total amount of oxygen + Al + Ca + Fe) impurities was calculated.

Next, the silicon nitride sintered body was formed into a flat plate of 40 mm × 80 mm × 0.6 mm by grinding. An active metal-containing brazing material (Ag
-Cu-Ti: 80-15-5) was screen-printed at a thickness of 30 [mu] m, equipped with circuitry 0.15mm thick copper plate and the back surface of the 0.3mm thick side copper plate, 10 ^-3 Torr stand vacuum Heating was performed at 850 ° C. for 30 minutes in an atmosphere. Thereafter, the mixture was cooled to obtain a composite.

The copper plate having a thickness of 0.3 mm was polished on the composite, a resist for patterning was printed, and after curing by heat, it was immersed and etched in an aqueous ferric chloride solution to form a desired pattern. Further, in order to remove the bonding material remaining between the circuits, the copper plate portion was immersed in an aqueous solution of ammonium ammonium fluoride, and then washed with water to produce a circuit board having a pattern formed thereon.

Holding the circuit board in a constant temperature bath at -50.degree. C. and 150.degree. C. for 30 minutes each is performed up to 3000 cycles, and cracks occur at the portions where the copper circuits are joined. The number of cycles up to was examined.

The following is clear from the comparison between the above Examples and Comparative Examples. That is, silicon nitride powder containing one or more oxides of yttrium and / or a lanthanoid element as a sintering aid, containing 300 ppm or less of Al and 1% by weight of oxygen, and having an alpha conversion of 70% or less. Using oxygen of silicon nitride particles having a short axis diameter of 2 μm or more,
Silicon nitride particles are grown and sintered so that the total content of Al, Ca, and Fe is 1500 ppm or less, and a silicon nitride sintered body having a high thermal conductivity of 100 W / mK or more has been obtained. In particular, Al in silicon nitride raw material powder
A substance having a high thermal conductivity of 130 W / mK or more is used in combination with a lanthanoid group element oxide having a small ionic radius such as ytterbium, erbium, or dyspromium, using a substance having a content of 150 ppm or less and as in Examples 1 to 3. A silicon nitride sintered body has been obtained.

The silicon nitride sintered body exhibiting a high thermal conductivity of 100 W / mK or more has coarse particles having a minor axis diameter of 2 μm or more, and oxygen, Al, Ca, F in the silicon nitride particles.
The total content of e is 1500 ppm or less.

Further, FIG. 1 can be obtained from Examples 1 and 20 to 25. As shown in FIG. 1, when the α ratio is X% and the ratio in the raw material powder having a particle diameter 2.5 times the cumulative average diameter of the silicon nitride powder is Y volume%, the desired thermal conductivity is A relational expression between X and Y is obtained as a parameter, and in order to obtain a high thermal conductivity of 100 W / mK or more,
0 ≦ X ≦ 70, Y ≧ 0, and Y ≧ −0.05X + 1. To obtain a high thermal conductivity of 115 W / mK or more, 0
≤X≤70, Y≥0, and Y≥-0.05X + 2.5
In order to further obtain a high thermal conductivity of 130 W / mK or more, 0 ≦ X ≦ 70, Y ≧ 0, and Y ≧ −0.05X +
It is only necessary to satisfy 4.5.

As shown in Table 2, when the silicon nitride raw material powder having an α conversion ratio of 97.5% was combined with the auxiliary system of the present invention as in Comparative Example 2, the powder was not sufficiently densified. 100W / m
High thermal conductivity of K or higher cannot be obtained. Further, as in Comparative Example 3, even if a large amount of silica was added to this raw material powder so as to densify it, oxygen, Al, Ca,
The total content of Fe becomes 1500 ppm or more, and a high thermal conductivity of 100 W / mK or more cannot be obtained.

In the case of the silicon nitride raw material powder having a large Al content as in Comparative Examples 4, 5 and 6, since Al remains in the silicon nitride particles as impurities, coarse particles having a minor axis diameter of 2 μm or more were removed. Oxygen, A in the silicon nitride particles
The total content of l, Ca, and Fe becomes 1500 ppm or more, and a high thermal conductivity of 100 W / mK or more cannot be obtained.

In the silicon nitride raw material powder having a high oxygen content as in Comparative Examples 10 and 11, oxygen is not sufficiently purified as an impurity even if the raw material powder having a small amount of Al in the silicon nitride particles is used. Therefore, even if there are coarse particles having a minor axis diameter of 2 μm or more, oxygen, Al, C
a, the total content of Fe becomes 1500 ppm or more, and a high thermal conductivity of 100 W / mK or more cannot be obtained.

Further, Comparative Examples 5 to 7 and Comparative Examples 11 and 1
As shown in 2, when the silicon nitride powder used has a large Al content or a large oxygen content, the area ratio of silicon nitride particles having a minor axis diameter of 2 μm or more is less than 10 area%, Insufficient purifying action due to silicon grain growth is 100 W / m
High thermal conductivity of K or higher has not been achieved.

Among the silicon nitride sintered bodies exhibiting a high thermal conductivity of 100 W / mK or more in the examples, the short axis diameter is 2 μm.
The silicon nitride particles having an area average diameter of 17.5 μm or less had a room-temperature bending strength of 450 M as shown in Table 2.
It shows high strength of Pa or more, and -50 using the circuit board.
In a heat cycle test carried out while holding each in a thermostat at 30 ° C. and 150 ° C. for 30 minutes, no cracks were observed even at 3000 cycles.
Note that there is a correlation between the room temperature bending strength of the silicon nitride sintered body and the result of the heat cycle test, and the room temperature bending strength is 350 MPa.
The cracks occurred in less than 2,000 cycles in all of the samples having a or less.

82 to 91.5% by weight of silicon nitride, 8 to 15% by weight of the sum of at least one element of yttrium and / or lanthanoid group element in terms of oxide, and 0 to 15% by weight of hafnium and zirconium in terms of oxide. As shown in Table 2, the silicon nitride sintered body containing 0.5 to 3% by weight exhibits a high thermal conductivity of 100 W / mK or more.

As shown in Table 2, the grain boundary phase of the silicon nitride sintered body exhibiting a high thermal conductivity of 100 W / mK or more is M
Phase (Re ₂ Si ₃ O ₃ N) or J phase (Re ₄ Si ₂ O ₇ N ₄ )
And the sum of the main peak intensities in the X-ray diffraction of the M phase and the J phase is 0.01 to 0. 2
It is.

[0093]

According to the silicon nitride sintered body of the present invention, the solid solution of impurities into silicon nitride particles is suppressed as much as possible, and the purity, microstructure, composition and amount of grain boundary phase in silicon nitride particles are controlled. It has excellent mechanical properties such as strength and fracture toughness, and has a high thermal conductivity of 100 W / mK or more. It is used as a material for various structural components in a wide range of fields, including semiconductor substrates, automobiles and high-speed electric railways. Can be used.

According to the method for producing a silicon nitride sintered body of the present invention, the silicon nitride sintered body can be stably provided in a large amount, which is industrially useful.

Since the silicon nitride circuit board of the present invention has high thermal conductivity and excellent mechanical properties, it is suitable for use in transportation equipment and the like requiring reliability and a circuit board for a power module. .

[Brief description of the drawings]

FIG. 1 is a graph showing a coefficient of thermal conductivity of a silicon nitride sintered body as a parameter, and an α ratio (X%) of a silicon nitride powder and a silicon nitride having a particle diameter of 2.5 times or more of a cumulative average diameter in the silicon nitride powder. FIG. 6 is a diagram showing a relationship that should be satisfied with the ratio of particles in silicon nitride powder (Y volume%).

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Suzuya Yamada 3-5-1 Asahicho, Machida-shi, Tokyo F-term in Central Research Laboratory, Denka Kagaku Kogyo Co., Ltd. 4G001 BA08 BA09 BA10 BA12 BA14 BA32 BA71 BA73 BB08 BB09 BB10 BB12 BB14 BB32 BB71 BC12 BC13 BC48 BC52 BC54 BC55 BD03 BD13 BD14 BD16 BD23 BE01 BE22 BE26

Claims (10)

[Claims] 1. A method for producing a silicon nitride sintered body, comprising sintering a raw material powder obtained by adding one or more oxides of yttrium and / or lanthanoid group elements to silicon nitride powder, followed by sintering. A silicon nitride powder containing not more than 300 ppm and not more than 1% by weight of oxygen and having an alpha conversion of not more than 70%, and oxygen of silicon nitride particles having a short axis diameter of not less than 2 μm;
A method for producing a silicon nitride sintered body, comprising sintering silicon nitride particles while growing them so that the total content of Al, Ca, and Fe is 1500 ppm or less. 2. The method according to claim 1, wherein the α-formation ratio of the silicon nitride powder is X%, and the ratio of silicon nitride particles having a particle diameter of at least 2.5 times the cumulative average diameter in the silicon nitride powder is Y volume%. 0 ≦ X ≦ 70, Y ≧ 0, and Y ≧ −0.05
2. The method for producing a silicon nitride sintered body according to claim 1, having a particle size distribution satisfying X + 1. 3. The silicon nitride according to claim 1, wherein the sintering operation is maintained in a nitrogen pressurized atmosphere of 9.8 MPa or less at a temperature of 1800 to 2000 ° C. for 8 hours or more. A method for manufacturing a sintered body. 4. A silicon nitride sintered body comprising silicon nitride particles having a total content of oxygen, Al, Ca and Fe of 1500 ppm or less and a minor axis diameter of 2 μm or more. 5. The silicon nitride sintered body according to claim 4, wherein the silicon nitride particles having a minor axis diameter of 2 μm or more account for 10 to 65 area% of the entire silicon nitride sintered body. body. 6. A silicon nitride particle having a short axis diameter of 2 μm or more accounts for 10 to 35 area% of the entire silicon nitride sintered body, and a silicon nitride particle having a short axis diameter of 2 μm or more has an area average diameter of 2 μm or more. The silicon nitride sintered body according to claim 4, wherein the thickness is 17.5 μm or less. 7. The silicon nitride sintered body according to claim 4, wherein the thermal conductivity is 100 to 160 W / mK. 8. 82 to 91.5% by weight of silicon nitride, 8 to 15% by weight of the sum of at least one element of yttrium and / or lanthanoid group element in terms of oxide, and the sum of hafnium and zirconium in terms of oxide. 8. The silicon nitride sintered body according to claim 7, wherein the content is 0 to 3% by weight. 9. A grain boundary phase constituting a silicon nitride sintered body contains an M phase (Re ₂ Si ₃ O ₃ N ₄ ) or a J phase (Re ₄ Si ₂ O ₇ N ₄ ), and the M phase And the sum of the main peak intensities in the X-ray diffraction of the J-phase and the β-type silicon nitride in the silicon nitride sintered body is 0.01 to 0.2 with respect to the peak intensity of the (200) plane. The silicon nitride sintered body according to claim 7 or 8, wherein 10. A silicon nitride circuit board comprising the silicon nitride sintered body according to claim 4, claim 5, claim 6, claim 7, claim 8, or claim 9.