Silicon nitride substrate, a manufacturing method of the silicon nitride substrate, a silicon nitride wiring board using the silicon nitride substrate, and semiconductor module
View Patent ↗In the silicon nitride substrate concerning an embodiment of the invention, degree of in-plane orientation fa of β type silicon nitride is 0.4-0.8. Here, degree of in-plane orientation fa can be determined by the rate of the diffracted X-ray intensity in each lattice plane orientation in β type silicon nitride. As a result of research by the inventors, it turned out that both high fracture toughness and high thermal conductivity are acquired, when degree of in-plane orientation fa was 0.4-0.8. Along the thickness direction, both the fracture toughness of 6.0 MPa·m 1/2 or higher and the thermal conductivity of 90 W/m·K or higher can be attained.
1. A silicon nitride substrate containing β type silicon nitride particles, magnesium (Mg) doped with 0.03˜7.0 mol % of MgO, lutetium (Lu) doped with 0.15˜1.00 mol % of Lu 2 O 3 , one element selected from Rare Earth (RE) elements excluding Lu and including Y doped with 0.13˜0.90 mol % of oxide of said one-element,
wherein degree of in-plane orientation fa, which is a ratio of orientation along in-plane direction perpendicular to thickness direction of said silicon nitride substrate, is 0.4˜0.8,
wherein fracture toughness along thickness direction of said silicon nitride substrate expressed as A, is A≧6.0 Mpa·m 1/2 , and fracture toughness along in-plane direction of said silicon nitride substrate expressed as B, is B≧3.0 Mpa·m 1/2 , and 1.488≦A/B≦1.7143,
wherein thermal conductivity along said thickness direction is higher than 105 W/m·K,
wherein said degree of in-plane orientation fa is expressed as formula (1),
fa =( P−P 0 )/(1− P 0 ) (1)
wherein P is expressed as formula (2), and P means a ratio of sum of diffracted X-ray intensities by (110), (200), (210), (310), and (320) planes of β type silicon nitride in said silicon nitride substrate, and
wherein P 0 is expressed as formula (3), and P 0 means a ratio of sum of diffracted X-ray intensities by (110), (200), (210), (310), and (320) planes of β type silicon nitride in said silicon nitride particles,
P =( I (110) +I (200) +I (210) +I (310) +I (320) )/(I (110) +I (200) +I (101) +I (210) +I (201) +I (310) +I (320) +I (002) ) (2)
P O =(I′ (110) +I′ (200) +I′ (210) +I′ (310) +I′ (320) )/I′ (110) +I′ (200) +I′ (101) +I′ (210)+I′ (201)+I′ (310)+I′ (320)+I′ (002) ) (3).
2. A silicon nitride wiring board comprising:
the silicon nitride substrate according to claim 1 ;
a metal circuit plate bonded on one face of said silicon nitride substrate; and
a metal heat sink bonded on another face of said silicon nitride substrate.
3. A semiconductor module comprising:
the silicon nitride wiring board according to claim 2 ; and
a semiconductor device mounted on said silicon nitride wiring board.
4. A manufacturing method of a silicon nitride substrate, comprising the steps of:
mixing α type silicon nitride powder with oxygen concentration of 2.0 mass % or less, 5˜10 mass % of β type silicon nitride powder with β fraction of 30˜100% and with oxygen concentration of 0.5 mass % or less and with mean particle diameter of 0.2˜10 μm and with mean aspect ratio of 10 or less, 0.4˜1.1 mol % of Lu 2 O 3 powder, 1.7˜7.0 mol % of MgO, and 0.4˜1.4 mol % of oxide of doped elements comprising at least one element selected from rare earth elements excluding Lu and including Y;
making a forming body from the mixed powder; and
sintering said forming body at temperature of 1900˜1950° C. in pressurized nitrogen atmosphere at pressure of 0.5˜1.0 MPa for 5˜30 hours.