EXTREMELY HIGH SELECTIVE ETCHING OF POROUS SI FOR SINGLE ETCH-STOP BOND-AND-ETCH-BACK SILICON-ON-INSULATOR

The etching characteristics of porous Si in comparison with bulk Si have been investigated for the ultra thin film (UTF) single etch-stop bond-and-etch-back silicon-on-insulator (BESOI). It is found out that porous Si can be selectively etched exclusively by a mixture of HF, H2O2 and H2O due to the structure-sensitive mechanism, that is, inner reaction by capillary-induced penetration of the etchant into the pores followed by collapsing the Si columns. This extremely high etching selectivity reaches as large as 10(5), which results in excellent SOI layer thickness variation of less than 7% across 5-inch SOI wafers with sub-mu m and sub-100-nm thicknesses.