Patent ID: 7915533

Claim:
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).