JP-7857389-B2 - Silicon nitride sintered body, insulating circuit board, and semiconductor device.

Inventors

• 松本 理
• 高橋 光隆

Assignees

• 株式会社MARUWA

Dates

Publication Date

20260512

Application Date

20241220

Claims (3)

1. A silicon nitride sintered body comprising a substrate having mutually orthogonal RD and TD directions in a plane perpendicular to the ND direction in the substrate thickness direction, wherein the RD direction is defined as the rolling direction of the green sheet of the silicon nitride sintered body, The bending strength σx in the RD direction and the bending strength σy in the TD direction perpendicular to the RD direction are each 600 MPa or more, and the ratio of the difference between the bending strength σx and the bending strength σy (|σy - σx|/σx) to the bending strength σx is 10% or less. The ratio of the difference between the thermal conductivity λz in the substrate thickness direction and the thermal conductivity λx in the RD direction (|λz - λx|/λx) to the thermal conductivity λx in the RD direction is 6% or less. A silicon nitride sintered body characterized in that the intensity ratio I(002)/I(200) of the integrated intensity I(002) of the X-ray diffraction peak corresponding to the Miller index (002) plane in the ND direction, obtained by X-ray diffraction, and the integrated intensity I(200) of the X-ray diffraction peak corresponding to the Miller index (200) plane is 0.05 to 0.2 .
2. An insulating circuit board comprising the silicon nitride sintered body described in claim 1, and a metal plate bonded to the surface of the silicon nitride sintered body.
3. A semiconductor device comprising an insulating circuit board as described in claim 2, and a semiconductor element mounted on a metal plate of the insulating circuit board.

Description

This invention relates to silicon nitride sintered bodies, insulating circuit boards, and semiconductor devices. In recent years, with the increasing density and power output of electronic devices and semiconductor devices, the heat density of power modules has also increased. Rising temperatures in power modules can cause malfunctions in components and cracking of the insulating circuit board. Therefore, ceramic substrates such as alumina and aluminum nitride, which have relatively high thermal conductivity, have been used for insulating circuit boards. However, alumina and aluminum nitride have the drawback of low mechanical strength. Consequently, thick copper, which experiences strong thermal stress, cannot be directly bonded to the ceramic substrate, limiting the structure of power modules. Specifically, the need to solder heat sinks (metal plates) made of copper or aluminum to the insulating circuit board leads to larger power modules, which is a problem. Therefore, silicon nitride ( Si₃N₄ ) is attracting attention as an insulating circuit board material. Because silicon nitride sintered bodies have higher strength and fracture toughness compared to alumina and aluminum nitride sintered bodies, it becomes possible to directly bond thick copper to the insulating circuit board, contributing to the miniaturization of modules. Therefore, development is underway to improve both the mechanical strength and thermal conductivity of silicon nitride sintered bodies. For example, Patent Document 1 discloses a method for manufacturing a silicon nitride sintered substrate with improved mechanical properties and thermal conductivity. In this manufacturing method, silicon nitride powder with an Al content of 0.1% by weight or less is mixed with a sintering aid of one or more elements selected from Mg, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, and Yb in an amount of 1% to 15% by weight, molded, and then fired at a temperature of 1700°C to 2300°C under a nitrogen gas pressure of 1 atmosphere to 500 atmospheres. The silicon nitride sintered substrate obtained by this manufacturing method is composed of 85% to 99% by weight of β-type silicon nitride grains and the remainder being a grain boundary phase of oxides or oxynitrides. Furthermore, the grain boundary phase contains 0.5% to 10% by weight of one or more metallic elements selected from Mg, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, and Yb. The Al atom content in the grain boundary phase is 1% by weight or less, the porosity is 5% or less, and the microstructure of the sintered body contains 10% to 60% by volume of β-type silicon nitride grains with a short axis diameter of 5 μm or more. In other words, it is known that to obtain a highly thermally conductive silicon nitride sintered substrate, rare earth compounds or magnesium oxide are added as sintering aids, and the thermal conductivity and mechanical strength can be improved by adjusting their mixing ratio and amount. Japanese Patent Application Publication No. 9-30866 This figure shows band contrast images obtained by the EBSD method for silicon nitride sintered bodies of Example 1, Example 2, Comparative Example 1, and Comparative Example 3.{10 -10} pole figures obtained by the EBSD method for silicon nitride sintered bodies of Example 1, Example 2, Comparative Example 1, and Comparative Example 3.Crystal orientation distribution diagrams at φ2 = 0° obtained by the EBSD method for silicon nitride sintered bodies of Example 1, Example 2, Comparative Example 1, and Comparative Example 3.Figure 3 shows the density profiles of the silicon nitride sintered bodies of Example 1, Example 2, Comparative Example 1, and Comparative Example 3 in the range of φ2 = 0°, Φ = 0°, and φ1 = 0 to 60° in the crystal orientation distribution.Figure 3 shows the density profiles of the silicon nitride sintered bodies of Example 1, Example 2, Comparative Example 1, and Comparative Example 3 in the range of φ2 = 0°, Φ = 90°, and φ1 = 0 to 180°, based on the crystal orientation distribution.SEM image (magnification 5000) of pulverized β-type silicon nitride sintered powder in the manufacturing process of the silicon nitride sintered body of the present invention.A schematic diagram showing a semiconductor device of one embodiment of the present invention. One embodiment of silicon nitride sintered body has a substrate shape of a predetermined thickness and can be used as an electronic component mounting substrate for mounting electronic components, mainly by brazing (brazing or soldering) a metal plate such as a copper plate to the substrate surface. The substrate thickness is preferably 0.1 to 1.0 mm. Here, in the silicon nitride sintered body substrate, the substrate thickness direction is defined as the ND or Z direction (normal direction to the substrate surface), the molding (or rolling) direction within the plane perpendicular to the ND direction (substrate surface) is defined as the RD or X direction, and the d