OBSERVATION OF A LEAKY-WAVE GUIDE RESONANCE MODE IN POLYCRYSTALLINE SILICON STRUCTURES USING INFRARED SPECTROSCOPIC ELLIPSOMETRY

Optical constants of polycrystalline silicon, used as the gate electro de material in semiconductor technology, have been analyzed by infrare d spectroscopic ellipsometry. In the optical refractive indices n, k o f the polycrystalline silicon material, we observed an unexpected abso rption resonance at 1280 cm(-1). The same effect is seen with differen t layer thicknesses and different polycrystalline texture. The absorpt ion peak is not seen with an additional capping silicon oxide layer on top of the stack. This effect does not arise from an intrinsic absorp tion of the polysilicon but rather because of a longitudinal mode exci tation present in the underlying silicon oxide layer. In the oxide inf rared reststrahlen band, the incident electromagnetic radiation is tot ally reflected at the polysilicon/oxide interface. Further evidence fo r the mechanism is obtained from observation of a polysilicon/nitride/ silicon sample. (C) 1998 American Institute of Physics. [S0003-6951(98 )01042-0].