bosch process

The Bosch process is a deep reactive ion etching technique that alternates between etch and passivation steps to create high aspect ratio features with vertical sidewalls in silicon. Each cycle deposits a fluorocarbon passivation layer on all surfaces, then anisotropic SF₆ plasma etching removes passivation from horizontal surfaces and etches silicon vertically. The sidewall passivation remains intact, preventing lateral etching. Cycles repeat hundreds of times, each removing 0.1-1μm of silicon. The alternating process creates characteristic scalloped sidewalls with period matching the cycle time. Bosch processing enables aspect ratios exceeding 30:1 for MEMS devices, through-silicon vias, and deep trench capacitors. Process parameters including cycle time, gas flows, and RF power control etch rate, profile angle, and sidewall roughness. Faster cycling reduces scallop amplitude but may decrease etch rate. The Bosch process revolutionized MEMS fabrication by enabling deep, high-aspect-ratio structures impossible with conventional RIE.