Method for producing nitride semiconductor crystal, and nitride semiconductor wafer and nitride semiconductor device

Claim 1

A method for producing a nitride semiconductor crystal comprising steps (a), (b) and (c), which steps follow in sequence as follows: a step (a) for forming fine crystal particles made of a nitride semiconductor on a substrate; a step (b) for forming a nitride semiconductor island structure comprising substantially polygonal pyramids and thus having a plurality of facets inclined relative to a surface of said substrate using said fine crystal particles as nuclei; and a step (c) for causing said nitride semiconductor island structure to grow in a direction parallel with a surface of said substrate to merge a plurality of said nitride semiconductor island structures with each other, thereby forming a nitride semiconductor crystal layer having a flat surface; said steps (a)-(c) being continuously conducted in the same growing apparatus, wherein the conditions of growing said nitride semiconductor crystal are different in said steps (a)-(c), and wherein at least one of a temperature, an atmosphere pressure, a speed and an atmosphere composition for crystal growth is different among said steps (a)-(c), wherein said substrate has a surface roughness of 5 μm or less by TTV (total thickness variation) and wherein said step (a) comprises a step for forming a nitride semiconductor crystal buffer layer on said substrate at a lower temperature Tg 1 than a crystal-growing temperature in said step (b) Tg 2 and said step (c) Tg 3 , and a step for heat-treating said nitride semiconductor crystal buffer layer at a higher temperature than its crystal-growing temperature Tg 1 to form said fine crystal particles, whereby step (a) thus comprises two separate steps at two separate temperatures such that a temperature Tg 1 , at which said nitride semiconductor crystal buffer layer is formed, is 400 to 800° C. and the heat-treating temperature of said nitride semiconductor crystal buffer layer is 800 to 1200° C. and wherein the crystal-growing temperature is 800 to 1050° C. for Tg 2 in said step (b) and 1060 to 1200° C. for Tg 3 in said step (c).

Claim 2

A method for producing a nitride semiconductor crystal comprising steps (a), (b) and (c), which steps follow in sequence as follows: a step (a) for forming fine crystal particles made of a nitride semiconductor on a substrate; a step (b) for forming a nitride semiconductor island structure comprising substantially polygonal pyramids and thus having a plurality of facets inclined relative to a surface of said substrate using said fine crystal particles as nuclei; and a step (c) for causing said nitride semiconductor island structure to grow in a direction parallel with a surface of said substrate to merge a plurality of said nitride semiconductor island structures with each other, thereby forming a nitride semiconductor crystal layer having a flat surface; said steps (a)-(c) being continuously conducted in the same growing apparatus, wherein the conditions of growing said nitride semiconductor crystal are different in said steps (a)-(c), and wherein at least one of a temperature, an atmosphere pressure, a speed and an atmosphere composition for crystal growth is different among said steps (a)-(c), wherein said substrate has a surface roughness of 5 μm or less by TTV (total thickness variation) and wherein said step (a) comprises a step for forming a nitride semiconductor crystal buffer layer on said substrate at a lower temperature Tg 1 than a crystal-growing temperature in said step (b) Tg 2 and said step (c) Tg 3 , and a step for heat-treating said nitride semiconductor crystal buffer layer at a higher temperature than its crystal-growing temperature Tg 1 to form said fine crystal particles, whereby step (a) thus comprises two separate steps at two separate temperatures such that a temperature Tg 1 , at which said nitride semiconductor crystal buffer layer is formed, is 400 to 800° C. and the heat-treating temperature of said nitride semiconductor crystal buffer layer is 800 to 1200° C. and wherein the crystal-growing temperature is 800 to 1050° C. for Tg 2 in said step (b) and 1060 to 1200° C. for Tg 3 in said step (c).