Infrared dielectric functions of hydrogenated amorphous silicon thin films determined by spectroscopic ellipsometry

Amorphous hydrogenated silicon (a-Si:H) thin films have found use in photovoltaic, transistor, and microbolometer applications. Routine optical metrology of a-Si:H is generally performed in the visible range but is not directly sensitive to hydrogen bonding. Infrared spectroscopic ellipsometry (IR-SE) allows a direct measurement of the relative absorption strength of various hydrogen-related modes, giving some insight into the hydrogen content and relative disorder of films. IR-SE is used here to develop a parameterization of ε=ε₁+iε₂ for several thin (<; 300 nm) hydrogenated amorphous germanium (a-Ge:H) and a-Si:H films deposited onto silicon nitride or titanium-coated crystalline silicon substrates.