Observation and modulation of gas film and plasma behavior in electrolytic plasma hybrid etching of semiconductor material 4H–SiC

Micromachining or nanostructuring of SiC single-crystal is attempted by an electrolytic plasma hybrid etching (EPHE) method. Aiming to enhance the process precision and consistency, this study focuses on investigating the phenomena of bubble and plasma occurrence in EPHE with varying pulse conditions. It is found that a higher voltage results in more significant plasma and current and consequently a more evident etching of SiC. EPHE involves oxide layer formation on the SiC surface by plasma or thermal oxidation, which is easily broken under higher voltages and fluid hydrodynamic flow. Increasing the pulse frequency reduces the formed gas/plasma layer thickness, leading to an improved machining resolution. The plasma cannot be induced when the pulse duty ratio is reduced below a critical value due to the rapid dissipation of gaseous bubbles. However, excessive pulse duty ratio causes difficulty in renewing electrolytes, which induces anomalies like sparks. A compact plasma envelope with a minimum thickness is achieved with optimized pulse conditions, which enables micro-drilling of a Φ312 μm microhole with a small machining gap of 6 μm by EPHE using a Φ300 μm microrod electrode. The results demonstrate the feasibility of EPHE for micro-nano scale fabrication of SiC for related applications such as sensors and MEMS.