Vapor phase metal-assisted chemical etching of silicon

This work introduces and explores vapor phase metal-assisted chemical etching (VP-MaCE) of silicon as a method to bypass some of the challenges found in traditional liquid phase metal-assisted chemical etching (LP-MaCE). Average etch rates for Ag, Au, and Pd/Au catalysts are established at 31, 70, and 96 nm/min respectively, and the relationship between etch rate and substrate temperature is examined experimentally. Just as with LP-MaCE, 3D catalyst motion is maintained and three-dimensional structures are fabricated with nanoparticle- and lithography-patterned catalysts. VP-MaCE produces less microporous silicon compared with LP-MaCE and the diffusion/reduction distance of Ag⁺ ions is significantly reduced. This process sacrifices etch rate for increased etch uniformity and lower stiction for applications in micro-electromechanical systems (MEMS) processing. To overcome non-uniformity and microporous silicon generation seen in traditional liquid-phase metal-assisted chemical etching, vapor-phase metal-assisted chemical etching (VP-MaCE) is used instead. The etch rate is evaluated as a function of catalyst, time, and substrate temperature.