1. Technical Field
The present invention relates to methods of manufacturing Group III nitride crystal in which the occurrence of cracking has been reduced.
2. Description of the Related Art
Group III nitride crystal, which is ideally suited to various semiconductor devices including optoelectronic and electronic devices, is finding large-scale utilization. In the manufacture of such III-nitride crystal, various evaporation-deposition techniques—including hydride vapor-phase epitaxy (HVPE), metalorganic chemical vapor deposition (MOCVD), and sublimation—and various liquid-phase deposition techniques—including growth from solution and flux methods—are employed.
Therein, in order to obtain low-dislocation-density III-nitride crystal in bulk, the epitaxial growth, by an abovementioned technique, onto the principal face of a III-nitride substrate of III-nitride crystal whose constituent-atom type and ratios (that is, chemical composition) are the same as that of the III-nitride substrate, and either the slicing off the III-nitride crystal portion or the removal of the III-nitride substrate by grinding or polishing it away to yield a III-nitride crystal are carried out. (Cf., for example, Int'l./Japanese-Nat'l. App. Pub. No. WO99/23693 [Patent Document 1].)
If, however, the dopant type and concentration of III-nitride crystal grown onto the principal face of a III-nitride substrate are different from—even though the constituent-atom type and ratios are the same as—those of the III-nitride substrate, during post-crystal-growth mechanical processing when the III-nitride crystal portion is sliced off or the III-nitride substrate is removed by grinding or polishing it away, the III-nitride crystal is liable to become cracked. This is believed to be due to strain arising between the III-nitride substrate and the III-nitride crystal, owing to the thermal expansion coefficient and lattice constant in III-nitride substrate and in III-nitride crystal being different.
Furthermore, liquid-phase etching employing a strong acid such as phosphoric acid, or a strong base such as KOH, is ill-suited to III-nitride crystal, inasmuch as the etching speed is slow and the process selectivity is poor.