Nitride semiconductor growth substrate and manufacturing method of the same, nitride semiconductor epitaxial substrate and nitride semiconductor element

A manufacturing method of a nitride semiconductor growth substrate, comprising:

• forming a convex portion on a principal surface comprising a C-plane of a sapphire substrate by photolithography or dry etching such that the convex portion has a cone or pyramid shape or a truncated cone or pyramid shape, is disposed to form a lattice pattern in a top view thereof, and comprises a side surface inclined at an angle of less than 90 degrees relative to the principal surface, wherein the convex portion has a height of 0.5 to 3 μm from the principal surface, a distance between adjacent ones of the convex portion is 1 to 6 μm, and the side surface of the convex portion has a surface roughness (RMS) of not more than 10 nm;
• and
• annealing the sapphire substrate in an atmosphere including oxygen so as to planarize the side surface of the convex portion such that a surface roughness (RMS) of the side surface is not more than 10 nm.