【Substrate Papers】Chemical-mechanical polishing improvements and subsurface damage elimination for Cz grown (010) β-Ga₂O₃ substrates

      Researchers from the Pennsylvania State University have published a dissertation titled "Chemical-mechanical polishing improvements and subsurface damage elimination for Cz grown (010) β-Ga₂O₃ substrates" in Materials Science in Semiconductor Processing.

Abstract

      An “Optimized Low pH Chemical-Mechanical Polishing (CMP) Process” was developed for manufacturing epi-ready 50 mm (010) gallium oxide (β-Ga₂O₃) substrates from Czochralski (Cz) grown boules. Using a “Pre-Epi Surface Evaluation” method, high-resolution x-ray diffraction (HRXRD), and microscopy, the baseline CMP steps previously reported for (010) β-Ga₂O₃ substrates were observed to induce significant subsurface damage (SSD). With careful selection of the polishing pad, slurry, and pressure to balance the chemical and mechanical components of the CMP process, SSD is effectively eliminated. In particular, reducing the colloidal silica slurry pH to ∼4 on a poromeric pad enables the use of higher pressures up to 3.0 psi (20.68 kPa) while maintaining a balanced CMP process. From a manufacturing perspective, this reduces cycle time by increasing the material removal rate (MRR) and helps to improve flatness and uniformity for large-area substrates. This CMP process was implemented for sets of full 50 mm Fe-doped (010) β-Ga₂O₃ substrates. These improvements resulted in an increased MRR with corresponding 1.5-2x reductions in average surface roughness (Sa/Sq) and x-ray rocking curve (XRRC) (020) full-width at half-maximum (FWHM) values. Elimination of virtually all SSD was also observed while achieving the lowest average surface roughness values (Sq ∼0.1 nm) reported for epi-ready β-Ga₂O₃ substrates to date.

DOI：

https://doi.org/10.1016/j.mssp.2025.109341