Formation of selective thick porous silicon layers for insulating Si substrate

The performance of Si RF circuits can be improved by insulating Si substrate with high resistance layers. Using thick porous silicon layers can reduce the high frequency loss in Si substrate. Selective thick layers of porous silicon formation on N + substrate is researched. Porous silicon layers of different thickness and porosities are obtained using anodization method via controlling the hydrofluoric acid concentration, current density and time. The cracking of porous silicon was effectively decreased. The maximal thickness of porous silicon layers is 72μm. The formation velocity and surface morphology are measured.