Control of initial bow of sapphire substrates for III-nitride epitaxy by internally focused laser processing

Processing by a laser beam focused within the substrate is used to control the initial bowing of sapphire substrates for III-nitride epitaxy. The process modifies the sapphire crystallinity at and near the focal area from single crystal to an amorphous phase. As volume expansion occurs inside the sapphire, strain is generated and, consequently, changes in the bowing. By controlling the focal depth and process pitch, we demonstrate a ∼250 μm pre-bowed sapphire substrate while only ±15 μm of bowing control is possible with a regular wafering process. We also demonstrate epitaxial growth of III-nitride on the pre-bowed sapphire substrates by metal organic chemical vapor deposition (MOCVD), which suggests an enlargement for the process window for III-nitride epitaxy on sapphire substrate. It is also shown that the pre-bowing by laser treatment functions to improve the crystal quality of grown III-nitride films.

► New approach to control the initial bow of sapphire substrate was developed. ► Laser processing focused within the substrate was used for bowing control. ► Controllable bowing range of substrate is widened from ±15 to ±250 μm. ► Pre-bowed substrate successfully enlarged the MOCVD process window. ► Accommodation of substrate bowing to any targeted values became possible for the MOCVD process.