Optimization of chemical mechanical polishing of (010) β-Ga2O3

Smooth (< 0.5 nm rms) and subsurface damage-free (010) beta-Ga2O3 was achieved with low-pressure chemical mechanical polishing. An applied pressure of 1 kPa along with colloidal silica and poromeric polyurethane polishing pads rotating at 30 rpm was found to be the optimal polishing parameters for (010) beta-Ga2O3. Using higher pressures typically employed in the current literature induced subsurface damage in the substrates. Diffuse scatter intensity of triple-axis x-ray rocking curves was used to determine the presence of subsurface lattice damage, which was quantified by measuring peak widths below the half maximum (i.e., FWXM where X < 0.5). The initially rough surfaces of (010) beta-Ga2O3 substrates due to wafer slicing and grinding were lapped and polished. A 5 mu m Al2O3 slurry followed by a 0.3 mu m Al2O3 slurry was used as the primary lap material removal step. The material removal rates were & SIM;20 and & SIM;9 mu m/h, respectively. Then, chemical mechanical polishing was performed using colloidal alumina followed by colloidal silica. The removal rates were & SIM;1.3 and & SIM;0.4 mu m/h, respectively. Only colloidal silica showed the complete removal of subsurface damage. The final (020) beta-Ga2O3 rocking curve FWHM was & SIM;13 & DPRIME; and FW(0.001)M was & SIM;120 & DPRIME;, which matches the widths of commercially available pristine (010) beta-Ga2O3. A final cleaning step using dilute bleach and dilute citric acid to remove residual silica slurry particles from the surface was demonstrated. Published under an exclusive license by AIP Publishing.