JP5142889B2 - Silicon nitride sintered body, manufacturing method thereof, circuit board, and power semiconductor module - Google Patents

Description

The present invention relates to a silicon nitride sintered body, a method for manufacturing the same, a circuit board, and a power semiconductor module. In particular, there is a large amount of Al in at least one kind of crystal particles of β-Si ₃ N ₄ and β-sialon. The present invention relates to a silicon nitride sintered body in which an Al multi-region portion is formed, a manufacturing method thereof, a circuit board, and a power semiconductor module.

  Conventionally, high-strength, high-toughness silicon nitride-based sintered bodies have been used for automobile engine members, heat-resistant structural members, cutting tools, and other industrial members (see, for example, Patent Document 1).

This Patent Document 1 discloses a silicon nitride sintered body composed of at least one kind of crystal particles and a grain boundary phase among β-Si ₃ N ₄ and β-sialon, It is described that 60 vol% is composed of crystal grains having an Al multi-region part in which Al abundance is higher than the other parts of the crystal grains.

Since this silicon nitride sintered body has β sialon nuclei in crystal grains, an internal stress is generated in the crystal grains, and crystal grains having β sialon nuclei grow, so that the aspect ratio is It is described that the strength and toughness of the sintered body can be improved by increasing the size.
JP-A-2-263764

  In recent years, silicon nitride-based sintered bodies have been used for a wide variety of applications, and depending on the application, high thermal conductivity is required. For example, it is known to use a silicon nitride-based sintered body for an insulating circuit board used for a so-called power semiconductor module for mounting a semiconductor that operates at high power. It is necessary to dissipate the heat generated by diffusing.

  For example, in an insulated circuit board, as described above, heat dissipation (high thermal conductivity), thinning, and high strength and toughness are required, but the silicon nitride sintered body disclosed in Patent Document 1 is used as a circuit. When used as a substrate, high strength and toughness can be achieved and thinning can be achieved, but the thermal conductivity of the circuit board is low, and the heat generated from the power semiconductor cannot be sufficiently dissipated. There was a problem.

That is, in the silicon nitride-based sintered body of Patent Document 1, since β sialon nuclei are present in crystal grains, internal stress is generated in the crystal grains, and crystal grains having β-sialon nuclei grow, Although the aspect ratio is increased, the strength and toughness of the sintered body can be improved. However, in Patent Document 1, a fine β-sialon powder having a BET specific surface area of 10 or 5 m ² / g is 5 to 5 times the total amount of raw materials. 20% by mass is added, so that a large amount of β-sialon is completely melted or the surface is melted at the time of firing to make β-sialon nuclei smaller, and a large amount of Al is dispersed and dissolved in crystal grains. There has been a problem that the thermal conductivity of the silicon nitride-based sintered body is lowered and heat dissipation is reduced.

  An object of the present invention is to provide a silicon nitride-based sintered body that can be increased in strength and toughness, and that can improve heat dissipation, a manufacturing method thereof, a circuit board, and a power semiconductor module. .

The silicon nitride-based sintered body of the present invention is a silicon nitride-based sintered body comprising at least one kind of crystal grains of β-Si ₃ N ₄ and β-sialon and a grain boundary phase, In addition, the Al multi-region portion having a larger amount of Al than the other portion of the crystal particles, and the Al multi-region portion is covered with a coating layer containing a rare earth element , the Al multi-region portion and the It said crystal grains having a coating layer, characterized that you present 8-26% by area in any cross-section of the sintered body.

  In such a silicon nitride-based sintered body, since the crystal grain has an Al multi-region portion covered with a coating layer containing a rare earth element, the crystal particle has another crystal having no Al multi-region portion. Grows larger than the grains, increases the aspect ratio, and has an Al multi-region, so that the compressive stress inside the crystal grains increases, which suppresses crack growth and increases the strength and toughness of the sintered body. Can be improved. Furthermore, since the Al multi-region part is covered with a coating layer containing rare earth elements, the amount of Al dispersed from the Al multi-region part into the crystal grains and the amount of solid solution are small, and the heat of the silicon nitride-based sintered body is low. Conductivity can be improved.

  The circuit board of the present invention is characterized in that a conductor layer is formed on the silicon nitride sintered body. In such a circuit board, since the strength and toughness of the silicon nitride sintered body can be improved, the circuit board can be thinned, and the thermal conductivity of the silicon nitride sintered body can be improved. Heat dissipation can be improved. Thereby, for example, the heat generated from the power semiconductor can be sufficiently diffused and dissipated from the circuit board.

  The power semiconductor module of the present invention is obtained by mounting a power semiconductor on the circuit board. In such a power semiconductor module, the heat generated from the power semiconductor can be sufficiently diffused and dissipated from the circuit board.

  In the silicon nitride based sintered body of the present invention, since the crystal grain has an Al multi-region portion covered with a coating layer containing a rare earth element, the crystal particle has another crystal having no Al multi-region portion. Grows larger than the grains, increases the aspect ratio, and has an Al multi-region, so that the compressive stress inside the crystal grains increases, which suppresses crack growth and increases the strength and toughness of the sintered body. Can be improved. Furthermore, since the Al multi-region part is covered with a coating layer containing rare earth elements, the amount of Al dispersed from the Al multi-region part into the crystal grains and the amount of solid solution are small, and the heat of the silicon nitride-based sintered body is low. Conductivity can be improved.

  In the circuit board of the present invention, since the strength and toughness of the silicon nitride sintered body can be improved, the circuit board can be thinned and the thermal conductivity of the silicon nitride sintered body can be improved. Heat dissipation can be improved.

  In the power semiconductor module of the present invention, the heat generated from the power semiconductor can be sufficiently diffused and dissipated from the circuit board.

  The circuit board of the present invention is formed by forming a conductor layer (including a metal circuit) on a mother substrate made of a silicon nitride sintered body, and at least on the upper surface or the lower surface of the mother substrate, and further on both upper and lower surfaces. And a power semiconductor is mounted on the conductor layer.

The mother substrate made of the silicon nitride sintered body is composed of at least one crystal grain 1 and grain boundary phase 3 among β-Si ₃ N ₄ and β-sialon as shown in FIGS. A silicon nitride sintered body having an Al multi-region portion 5 having a larger amount of Al in the crystal particles 1 than in other portions 4 of the crystal particles 1 (hereinafter also simply referred to as other portions). Then, there is a coating layer 6 containing a rare earth element covering the Al multi-region portion 5, and the crystal particles having the Al multi-region portion and the coating layer have an area ratio of 8 to 8 in an arbitrary cross section of the sintered body. There are 26% .

  The average diameter of the Al multi-region portion 5 is 2 μm or more, and containing Al in an amount of 0.053 mass% or more in the total amount of the sintered body is desirable from the viewpoint of improving strength and toughness, and particularly 0.185 mass. % Or more is desirable.

  The coating layer 6 may contain Al in addition to the rare earth element. This rare earth element, Al, is considered to exist as an oxide. It is considered that Al in the coating layer 6 has diffused Al in the Al multi-region portion 5.

  The rare earth element present in the coating layer 6 is preferably at least one of Y, Gd, Dy, Ho, Er, and Yb. In particular, Y, Er, Dy are preferable because silicon nitride particles are easy to grow. Is desirable.

  The rare earth element present in the coating layer 6 may be an element different from the rare earth element between crystal grains described later (which constitutes a part of the grain boundary phase), but it is easy to manufacture and the number of rare earth elements is small. From the viewpoint of reducing costs, it is desirable that the rare earth element present in the coating layer 6 is a rare earth element of the same type as the rare earth element constituting the grain boundary phase between crystal grains.

In the present invention, a solution in which Al is dispersed and dissolved in β-Si ₃ N ₄ is called β-sialon. The sialon is represented by the general formula Si _6-z Al _z O _z N _8-z , but the crystal grain 1 has the Al multi-region portion 5 having a larger Al abundance than the other portions 4, When the crystal particle 1 is β-sialon, the Z value in the general formula of the Al multi-region portion is at least twice as large as the Z value of the other portion 4, that is, has a region where the Al content is more than twice. Point to. The Al multi-region portion 5 is shown by a one-dot chain line in FIG. 2, but is actually defined by the Al content. The reflected electron image or secondary electron image obtained by a scanning electron microscope and wavelength dispersion type microanalyzer analysis. It can be confirmed that the Al multi-region portion 5 is obtained by comparing the above.

Further, in the crystal particle 1 made of β-Si ₃ N ₄ , having the Al multi-region portion 5 having a larger amount of Al than the other portion 4 of the crystal particle 1 means that β is not dissolved in Al. This means that there are Al multi-region portions 5 made of β-Si ₃ N ₄ in which Al is dispersed and dissolved in crystal grains 1 made of —Si ₃ N ₄ .

The size of the Al multi-region portion 5 is equal to or slightly smaller than the particle size of the added β-sialon powder. In the present invention, the crystal particle 1 has the Al multi-region portion 5, and the coating layer 6 containing a rare earth element exists between the other portion 4 and the Al-rich region portion 5. And the aspect ratio of the crystal grains 1 is increased, and the strength and toughness can be improved. Furthermore, the amount of Al dispersed and dissolved in the crystal particles 1 from the Al large area can be reduced, and the thermal conductivity can be improved.

The β-Si ₃ N ₄ and β-sialon crystal particles 1 having the Al multi-region portion 5 have an aspect ratio of 3 to 8 on average and the minor axis length of the crystal particles 1 of 3 to 15 μm on average.

In the present invention, crystal grains 1 having the Al multi-region portion 5, that exist 8-26% by area in any cross-section of the sintered body. Thereby, while being able to raise the intensity | strength and toughness of a sintered compact, the crystal particle 1 which has Al multi-region part 5 can be made to exist moderately, and the heat dissipation of a sintered compact can be made high.

Further, the silicon nitride sintered body of the present invention is contained in the raw material, or you mixed from step N a, K, Fe, Ca , Ba, and mixed with inevitable impurities, such as Mn and B, These inevitable impurities are preferably 0.5% by mass or less in the total amount of the sintered body. Thereby, the fall of the thermal diffusivity of a sintered compact can be suppressed, and the thermal conductivity of a sintered compact can be improved as a result.

Furthermore, it is desirable that the sintered body contains rare earth elements in an amount of 1 to 20% by mass in terms of oxides in terms of improving sinterability, toughness, and improving thermal conductivity. As described above, since silicon nitride is difficult to sinter, it is desirable to add a sintering aid, and generally known rare earth element oxides such as Y ₂ O ₃ , Gd ₂ O _{3 are used.} , Dy ₂ O ₃ , Ho ₂ O ₃ , Er ₂ O _3, and Yb ₂ O ₃ , at least one of them, particularly Y ₂ O ₃ , Er ₂ O ₃ , Dy ₂ O ₃ is added in an amount of 1 to 20% by mass. contains.

Here, the oxide equivalent amount of the rare earth element is set to 1 to 20% by mass in the total amount of the sintered body. If the amount is less than 1% by mass, the function as the sintering aid is insufficient, and exceeds 20% by mass. This is because the amorphous phase having a low thermal conductivity and the crystalline phase having a low thermal conductivity increase in the sintered body and the thermal conductivity of the sintered body tends to decrease. The oxide equivalent amount of the rare earth element is desirably 2 to 17% by mass in the total amount of the sintered body from the viewpoint of improving the sinterability and the thermal diffusivity. The grain boundary phase forming powder (sometimes referred to as a sintering aid) is preferably Er ₂ O ₃ or SiO ₂ .

Of β-Si ₃ N ₄ and β-sialon, at least one kind of crystal particles 1 is desirably contained in an amount of 80 to 91.5 mass% in the total amount of the sintered body.

  The circuit board manufacturing method of the present invention is manufactured by forming a conductor layer on a mother board made of a silicon nitride sintered body. The mother substrate is prepared by mixing rare earth element oxide powder and β-sialon powder, calcining at 700 to 900 ° C., and adding and mixing the obtained calcined powder and grain boundary phase forming powder to silicon nitride powder. After forming this into a predetermined shape, it can be produced by firing at 1750 to 1980 ° C.

As the grain boundary phase forming powder, SiO ₂ or the like can be contained in addition to the rare earth element oxide.

  By mixing rare earth element oxide powder and β-sialon powder and calcining at 700 to 900 ° C., a large amount of rare earth element oxide powder is adhered to the surface of Al-containing β-sialon powder. A layer of oxide powder can be formed.

  Then, the β-sialon powder covered with the rare earth element oxide powder layer is added and mixed together with the grain boundary phase forming powder and the silicon nitride powder, followed by firing, whereby the molten silicon nitride nucleates the β-sialon powder. As a result, the coating layer 6 hardly disperses and dissolves Al in the entire crystal particle 1 and forms a structure in which the β-sialon is covered with the coating layer 6 containing a rare earth element. Thus, a silicon nitride sintered body composed of such crystal grains 1 and grain boundary phases 3 can be produced.

  That is, when the silicon nitride powder is dissolved and the β-sialon powder is precipitated as a nucleus, the rare earth element oxide is dissolved and covers the periphery of the β-sialon, but the surface of the β-sialon powder is coated with the rare earth element. Since it is covered with the coating layer 6 to be contained, the coating layer 6 suppresses the dispersion of Al of β-sialon and suppresses the solid solution of Al in the crystal particles 1. Usually, since silicon nitride is dissolved and precipitated with β-sialon as a nucleus, Al is slightly dissolved in the crystal particles 1.

Silicon nitride powder, oxygen 2.0 mass% or less, N a as an impurity cations, K, Fe, Ca, Ba, 0.5 wt% or less in total of Mn and B, 90 and α-phase type silicon nitride It is desirable to use a powder containing at least mass% and having an average particle size of 1 μm or less.

As the β-sialon powder, a powder represented by the general formula Si _6-z Al _z O _z N _8-z (0 <z ≦ 4) can be used. It is desirable to use a β-sialon powder having a BET specific surface area of 2 m ² / g or less because crystal grains 1 having a large aspect ratio can be formed and strength and toughness are improved. In particular, it is desirable to use a BET specific surface area of 1 m ² / g or less.

  Further, β-sialon powder is desirably added and mixed in an amount of 0.139% by mass or more, particularly 0.416% by mass or more, based on the total amount of raw materials.

  Adding β-sialon powder in an amount of 0.139% by mass or more, preferably 0.416% by mass or more in the total solid content means that silicon nitride powder, the rare earth element oxide powder constituting the coating layer 6, and formation of grain boundary phase It means that 0.139% by mass or more, desirably 0.416% by mass or more of the total amount (total solid content) of the powder and β-sialon powder is β-sialon powder.

As the mother board of the circuit board of the present invention, a thermal conductivity of 99 W · m / K or more, particularly 115 W · m / K or more can be obtained. A strength of 810 MPa or more, particularly 895 MPa or more is obtained. Further, with respect to toughness, 7.5 MPa · m ^1/2 or more, particularly 7.9 MPa · m ^1/2 or more is obtained.

  Furthermore, since the mother substrate of the present invention has high thermal conductivity and high strength and toughness, a thin substrate with a high heat dissipation property that is comparable to aluminum nitride can be obtained by reducing the thickness. On the other hand, in order to increase the strength, even when the thickness is 0.5 mm or more, the thermal conductivity is high, so that it can be used as a circuit board.

  The power semiconductor module of the present invention is configured by connecting a power semiconductor to a conductor layer of a mother board and mounting the power semiconductor on the circuit board. In such a power semiconductor module, the heat generated from the power semiconductor can be sufficiently diffused and dissipated from the circuit board.

As starting materials, silicon nitride α phase containing 95% by mass of silicon nitride α phase, 1% by mass of oxygen, silicon nitride powder having an average particle size of 0.5 μm, and β-sialon having a BET specific surface area of 0.70 to 10.2 m ² / g As powder (z = 0.5-4) and rare earth element oxide powder, Y ₂ O ₃ powder having an average particle diameter of 1.0 μm, Er ₂ O ₃ powder having an average particle diameter of 1 μm, and Yb _{2 having} an average particle diameter of 1 μm. An O ₃ powder, a Gd ₂ O ₃ powder having an average particle diameter of 1 μm, and a Ho ₂ O ₃ powder having an average particle diameter of 1 μm were prepared as SiO ₂ powder having an average particle diameter of 1.3 μm as part of the grain boundary phase forming powder. In addition, the quantity in Table 1 shows the ratio in the total solid content.

First, β-sialon and the rare earth element oxide powder of the coating layer material are weighed so as to have the composition ratio shown in Table 1, mixed, calcined at 800 ° C., and obtained calcined powder, A grain boundary phase forming powder having a composition ratio of 1 was added to and mixed with the silicon nitride powder. Isopropyl alcohol as a solvent and balls made of a silicon nitride sintered body as media were added and mixed for 72 hours in a vibration mill. Thereafter, the slurry is dried by isopropyl alcohol to form a mixed powder, and this mixed powder is die-pressed at a pressure of 0.5 ton / cm ² , and then subjected to an isostatic pressure at a pressure of 3 ton / cm ^{2 to} obtain a molded product. Obtained.

Next, in a pot made of a silicon nitride sintered body, silicon nitride powder and SiO ₂ powder are added, and the material is filled. After the molded body is embedded in the material, the pressure is 0.9 MPa. A sintered body as a sample was obtained by firing at a temperature of 1950 ° C. in a nitrogen gas atmosphere.

  Sample No. No. 18, without pre-calcining β-sialon and rare earth element oxide powder, silicon nitride powder, grain boundary phase forming powder and β-sialon powder were added at once, and molded in the same manner as described above. It is a calcined sample.

  For the sample thus obtained, the Al content was determined by fluorescent X-ray analysis (calibration curve method). The sintered crystal grains are finely processed with a focused ion beam (FIB) apparatus to a submicron thickness, and the Al multi-region portion and the coating layer are confirmed with a wavelength dispersive X-ray microanalyzer (EPMA). 2.

  In addition, using the scanning electron microscope analysis reflection electron image (composition difference image) of any five cross sections of the sintered body, the area ratio of the crystal particles having the Al multi-region portion is obtained by an image analyzer, and these are averaged. The area ratio of the crystal grains having the Al multi-region portion is shown in Table 1.

In addition, for each sample, the thermal diffusivity and specific heat were measured and measured by a laser flash method (Au deposition was performed on both sides of the sample, both sides were blackened, and the ruby laser pulse light was uniformly irradiated at 25 ° C.). The thermal conductivity was calculated by multiplying the thermal diffusivity, the specific heat, and the density determined by the Archimedes method. The fracture toughness is determined according to JIS standard R1607-1995, and the three-point bending strength is JIS
It calculated | required by S1601-1995. These results are listed in the table. Sample No. 1 is a comparative example.

According to these tables, sample Nos. Within the scope of the present invention. It can be seen that Nos. 2 to 17 have the characteristics that the thermal conductivity is 99 W / m · K or more, the three-point bending strength is 810 MPa or more, and the toughness is 7.5 MPa · m ^1/2 or more. On the other hand, without pre-calcining β-sialon and rare earth element oxide powder, sample No. 1 in which silicon nitride powder, sintering aid and β-sialon powder were added at once. No. 18 had no coating layer containing a rare earth element, and the thermal conductivity was as low as 84 W / m · K.

It is a scanning electron microscope analysis reflection electron image (composition difference image) photograph of a sintered compact. It is a schematic diagram of a sintered compact.

Explanation of symbols

1: Crystal grain 3: Grain boundary phase 4: Other part of crystal grain other than Al region (other part)
5: Al multi-region part 6: Coating layer

Claims (3)

A silicon nitride-based sintered body comprising at least one kind of crystal particles of β-Si ₃ N ₄ and β-sialon and a grain boundary phase, and in the crystal particles, more than other portions of the crystal particles The Al multi-region portion having a large amount of Al, and the Al multi-region portion is covered with a coating layer containing a rare earth element, and the crystal particles having the Al multi-region portion and the coating layer are sintered. area ratio in the 8-26% presence to silicon nitride sintered body, characterized in Rukoto in any cross-section of the body. A circuit board comprising a conductive layer formed on the silicon nitride sintered body according to claim 1 . A power semiconductor module comprising a power semiconductor mounted on the circuit board according to claim 2 .