DAMAGE-FREE SELECTIVE ETCHING OF SI NATIVE OXIDES USING NH3 NF3 AND SF6/H2O DOWN-FLOW ETCHING/

Damage-free selective etching of Si native oxides against Si has been achieved by NH3/NF3 and SF6/H2O down-flow etching. In the NH3/NF3 etch ing, the wafer was covered with a film, and after its removal by heati ng above 100-degrees-C, only SiO2 Was found to be etched with an extre mely high selectivity with respect to Si. Selective etching of Si oxid es has also been obtained for SF6/H2O microwave discharge. In this cas e, a film of liquid solution containing HF and H2SOx is considered to form on the wafer surface. The selective etching of SiO2 takes place b y the dissolved HF just as in the wet etching by an HF solution. The m echanisms of these selective reactions are discussed in detail based o n the covalency of Si and SiO2 bondings.