HIGHLY SELECTIVE CHEMICAL ETCHING OF SI VS SI1-XGEX USING NH4OH SOLUTION

Highly selective chemical etching of Si vs. epitaxial Si1-xGex in NH4O H solution has been investigated. It was found the selectivity was bet ter than 80:1 even for a Si0.9Ge0.1 in 10 weight percent (w/o) NH4OH a t 75 degrees C. As the fraction x of Ge was increased, higher selectiv ity was obtained due to the decrease of the etch rate of the Si1-xGex. The achievement of the excellent selectivity in a Si/Si1-xGex/Si hete rostructure was clearly demonstrated by scanning electron microscopy. Surfaces of etched Si1-xGex samples were analyzed using x-ray photoele ctron spectroscopy. The high etch selectivity obtained in NH4OH is ess entially due to a passivation-film effect at the Si1-xGex surface.