Method of manufacturing nitride substrate for semiconductors
In an independent GaN film manufactured by creating a GaN layer on a base heterosubstrate using vapor-phase deposition and then removing the base substrate, owing to layer-base discrepancy in thermal expansion coefficient and lattice constant, bow will be a large ±40 μm to ±100 μm. Since with that bow device fabrication by photolithography is challenging, reducing the bow to +30 μm to −20 μm is the goal. The surface deflected concavely is ground to impart to it a damaged layer that has a stretching effect, making the surface become convex. The damaged layer on the surface having become convex is removed by etching, which curtails the bow. Alternatively, the convex surface on the side opposite the surface having become convex is ground to generate a damaged layer. With the concave surface having become convex due to the damaged layer, suitably etching off the damaged layer curtails the bow.
1. A method of manufacturing a nitride semiconductor substrate of minimal bow, the method comprising:
a nitride-semiconductor deposition step of vapor-phase depositing nitride semiconductor crystal onto a base heterosubstrate;
a nitride-semiconductor substrate preparation step of removing the base heterosubstrate from the nitride semiconductor crystal grown in said deposition step to thereby obtain a freestanding as-grown nitride semiconductor substrate of from 20 mm to 50 mm diameter, the as-grown substrate thereby intrinsically having a bow of ±40 μm to ±100 μm;
a bow-reduction step of carrying out, on at least either the front side or the back side of the freestanding as-grown nitride semiconductor substrate, at least grinding and etching operations so as to create a bow-reducing damage layer, in which the crystalline structure of the nitride-semiconductor crystal is transformed, on at least either the front side or the back side of the nitride-semiconductor substrate, and so as to remove the damage layer from at least either the front side or the back side of the nitride-semiconductor substrate to an extent such as to minimize the intrinsic bow in the nitride-semiconductor substrate to be within a range of from 30 μm to −20 μm.
2. A nitride semiconductor substrate manufacturing method as set forth in claim 1 , wherein in said bow-reduction step the at least grinding and etching operations are carried out so as to produce a nitride-semiconductor substrate of from 20 μm to −10 μm bow.
3. A nitride semiconductor substrate manufacturing method as set forth in claim 1 , wherein in said bow-reduction step the at least grinding and etching operations are carried out so as to produce a nitride-semiconductor substrate of from 10 μm to −5 μm bow.
4. A nitride semiconductor substrate manufacturing method as set forth in claim 1 , wherein in said bow-reduction step the etching operation is either dry etching or wet etching.