Effect of process parameters on oxidation-enhanced removal mechanisms of GaN in photoelectrochemical mechanical polishing

YW Sun and YQ Wu and S Gao and Y Zhao and RK Kang and ZG Dong, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, 302, 110583 (2025).

DOI: 10.1016/j.ijmecsci.2025.110583

The strong chemical stability of gallium nitride (GaN) makes it difficult to form an oxide film during chemical mechanical polishing, resulting in very low polishing efficiency. Photoelectrochemical mechanical polishing (PECMP) is currently the most efficient method for polishing single-crystal GaN wafers. The material removal process in PECMP relies on the formation of an oxide film on the wafer surface through a photoelectrochemical oxidation reaction. However, the underlying removal mechanisms of this oxide film under various mechanical parameters remain largely unexplored. In this study, molecular dynamics simulations were used to investigate the removal process of GaN modified with an oxide film under varying abrasive particle radii, polishing pressures, and polishing speeds. The polishing force, stress distribution, temperature, phase transition, and atomicscale removal were thoroughly analyzed, with the simulation results validated through PECMP experiments. The results indicate that increasing abrasive particle radius and polishing pressure significantly elevate both von Mises and hydrostatic stresses, while having a less pronounced effect on temperature rise. Consequently, the dominant material removal mechanism shifts from being primarily stress-driven to being governed by a combination of mechanical stress and phase transition. Although increased polishing speed has a limited impact on stress levels, it significantly raises the number of abrasive passes and polishing temperature, thereby enhancing the material removal rate. Moreover, the phase transition from hexagonal to cubic structure promotes the formation of stacking faults. Excessively large abrasive radii and high pressures lead to the formation of a subsurface damaged layer with a thickness of tens of nanometers. This study enhances the fundamental understanding of the removal mechanism in PECMP and provides a scientific foundation for optimizing polishing parameters to improve removal efficiency while minimizing surface/subsurface damage.

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