Highly Selective Chemical Etching of Si vs. Si1 − x Ge x Using NH 4 OH Solution

Highly selective chemical etching of Si vs. epitaxial Si, 1-x Ge x in NH 4 OH solution has been investigated. It was found the selectivity was better than 80:1 even for a Si 0.9 Ge 0.1 in 10 weight percent (w/o) NH 4 OH at 75°C. As the fraction x of Ge was increased, higher selectivity was obtained due to the decrease of the etch rate of the Si 1-x Ge x . The achievement of the excellent selectivity in a Si/Si 1-x Ge x /Si heterostructure was clearly demonstrated by scanning electron microscopy. Surfaces of etched Si 1-x Ge x samples were analyzed using x-ray photoelectron spectroscopy. The high etch selectivity obtained in NH 4 OH is essentially due to a passivation-film effect at the Si 1-x Ge x surface.