16. Additive Processes Physical Vapor Deposition (PVD) 1. Evaporation Deposition is achieved by evaporation or sublimation of heated metal onto substrate. 2. Sputtering Sputtering is achieved by accelerated inert ion by DC drive in plasma through potential gradient to bombard metallic target. Then the targeting material is sputtered away and deposited onto substrate placed on anode.
20. Subtractive Processes Reaction Mechanism Produce reactive species in gas-phase Reactive species diffuse to the solid Adsorption, and diffuse over the surface Reaction Desorption Diffusion Dry Etching Plasma Etching
21. Subtractive Processes Dry Etching Deep Reactive Ion Etching (DRIE) A very high-aspect-ratio silicon etch method DRIE Etched Pillars
22. Subtractive Processes Wet Etching Isotropic Wet Etching Isotropic etchants etch in all directions at nearly the same rate. Commonly use chemical for Silicon is HNA (HF/HNO 3 /Acetic Acid) This results in a finite amount of undercutting
23. Subtractive Processes Wet Etching Anisotropic Wet Etching Anisotropic etchants etch much faster in one direction than in another. Etchants are generally Alkali Hydroxides (KOH, NaOH, CeOH Reaction : Silicon (s) + Water + Hydroxide Ions -> Silicates + Hydrogen