Often metal depositions on semiconductor surfaces are hampered by interfacial reactions between the metal and the semiconductor surface, which led to the formation of impure metal layers. Therefore, we have investigated several ways in which to passivate the semiconductor surface prior to metal deposition to prevent metal/semiconductor interfacial reactions. Two different types of passivation layers were explored. One method involved the use of sulfur as a passivating agent and the second method used cycloaddition chemistry to make a thin organic layer on the semiconductor surface (the latter is discussed in an earlier section).
The use of H2S as a passivating agent was explored.
H2S is a simple sulfur—containing molecule that
decomposed to yield hydrogen gas and deposited sulfur onto the
germanium surface. The surface reactions of H2S were
investigated by ultraviolet photoelectron spectroscopy, Auger
electron spectroscopy, and temperature programmed desorption.
Room temperature exposure of H2S to Ge(100) resulted
in dissociative adsorption which could be followed easily by
ultraviolet photoelectron spectroscopy. Warming the H2S
exposed surface resulted in some molecular desorption and further
decomposition of the adsorbed species. At saturation, 0.25 ML (ML
= monolayer and is defined as one H2S molecule per
surface Ge atom) of H2S decomposes generating 0.5 ML
of atomic hydrogen. Above the hydrogen desorption temperature
some etching of the germanium surface was observed by sulfur. The
etch product, GeS, was observed in temperature programmed
desorption experiments. Exposure of H2S to the Ge
surface at elevated temperatures led to higher sulfur coverages.
A sulfur coverage of 0.5 ML can be deposited at the higher
exposure temperatures. Sulfur layers prepared from H2S
decomposition proved to be an effective barrier to prevent
interfacial reactions.