Encroachment and line of sight blocking in micro-cavity sealing

This paper investigates the sealing of micro-cavities with line-of-sight blocking (LOSB) barriers. This is a novel concept that mitigates sealant encroachment into the cavity of a sealed MEMS device. The cap layer over the sacrificial layer forms walls around the entry hole that impedes the diffusion of sealant particles and ensures released devices whose operation is unaffected. LPCVD PSG and PECVD SiO₂ and Si₃N₄ have been used as sealant material and relation between etch-hole size and encroachment for cavity thickness ranging in between 1-2 μm have been tested. LOSB walls are highly effective in confining the sealant particles for larger holes and specially Si₃N₄.