【Substrate Papers】Processing of gallium oxide crystals using liquid-immersion wire-cut electrical discharge machining

      Researchers from the Nanjing University of Aeronautics and Astronautics have published a dissertation titled " Processing of gallium oxide crystals using liquid-immersion wire-cut electrical discharge machining " in Materials Science in Semiconductor Processing.

Abstract

      To address the issues of cracking and cleavage commonly encountered during conventional mechanical processing of gallium oxide (Ga₂O₃) crystals using several methods, such as outer circle cutting and diamond wire sawing, this study proposed a liquid-immersion wire-cut electrical discharge machining (WEDM) technique. This study also revealed that the segregation phenomena during the growth of Ga₂O₃ crystals resulted in non-uniform resistivity within the crystal, leading to the failure of traditional spray-type electro-discharge wire-cutting techniques. To overcome this limitation, the feasibility of the liquid-immersion WEDM technique was proposed, and an experimental platform was established. Resistivity measurements of the cut surfaces of Ga₂O₃ in kerosene immersion revealed a reduction of approximately 99.2 % in the resistivity difference. This result shows that the formation of carbon films during processing can effectively compensate for the intrinsic non-uniform resistivity. An equivalent circuit model for liquid-immersion WEDM of Ga₂O₃ crystals in kerosene was developed. Thermodynamic and kinetic analyses were conducted on hydrocarbon decomposition reactions in kerosene at discharge temperatures. The results confirmed that decomposition reactions could occur during the discharge process. A truncation experiment for Ga₂O₃ ingots was conducted, and a method using single-crystal silicon for electrical assistance in the processing of 1-inch wafers was proposed. The experimental results showed that liquid-immersion WEDM of Ga₂O₃ crystals in kerosene effectively suppressed cracking and cleavage, achieving a processing accuracy within 50 μm and successfully producing a 1-inch circular Ga₂O₃ wafer, with the machining accuracy improved by approximately 66.6 % compared to diamond wire cutting.

DOI：

https://doi.org/10.1016/j.mssp.2024.109049