PHYSICAL-PROPERTIES OF SEMIINSULATING POLYCRYSTALLINE SILICON .3. INFRARED DIAGNOSIS OF THE POLYCRYSTALLINE-SI C-SI INTERFACE

In order to investigate the interface between polycrystalline-silicon (poly-Si) and crystalline silicon (c-Si), which is of crucial importan ce for the passivation of high-voltage devices, an infrared diagnostic method has been developed which is based on a modified attenuated tot al reflection configuration. This interface is shown to consist of sil icon oxides (mainly SiO2) in the monolayer range with a thickness of 7 +/- 2 angstrom. The interpretation of the experimental results is bas ed on a direct comparison of the infrared reflectivity spectrum of the interface to be studied with that of a reference sample containing a 100-angstrom thick SiO2 interface layer, as well as on extensive compu ter calculations. Such calculations have been performed for a three-la yer system as well as for a simplified system consisting of a single a bsorbing layer sandwiched between two transparent half-spaces. The lat ter system can be solved analytically and provides detailed insight in to the physics of the interaction of light with the vibrational excita tions of the interface layer. The existence and properties of such a s ilicon oxide interface layer are compatible with our secondary ion mas s spectrometry experiments (oxygen segregation at the interface) and i ts thickness is in excellent agreement with the thickness of the amorp hous interface layer observed by transmission electron microscopy.