cryogenic etch

Cryogenic etching performs plasma etching at very low temperatures (typically -100°C to -140°C) to achieve superior anisotropy, selectivity, and sidewall smoothness compared to room temperature processes. Low temperature increases the sticking coefficient of etch byproducts and passivating species on sidewalls, enhancing sidewall protection and anisotropy. Cryogenic silicon etching using SF₆/O₂ chemistry achieves smooth, vertical sidewalls without the scalloping characteristic of the Bosch process. The low temperature also reduces chemical etching component, making the process more ion-driven and directional. Cryogenic etching provides excellent mask selectivity, enabling high aspect ratio features with thin photoresist masks. Applications include MEMS, photonics, and advanced semiconductor devices requiring smooth sidewalls. Challenges include wafer cooling system complexity, condensation management, and longer process times due to reduced chemical etch rates. Temperature control is critical—variations affect passivation stability and etch characteristics.