Thin Film Evaluation Techniques for the ESFI SOS Technology

Abstract

The transistor parameters of the ESFI\circledRSOS field-effect transistors strongly depend on the properties of the thin epitaxial silicon film on the sapphire substrate: thickness (<0.8 µm), crystal quality, doping concentration and profile, interface states and lateral homogeneity. The crystal quality is measured by means of the optical absorption (E=2.0 to 2.7 eV) obtained by the reflectance interference method similar to the film thickness evaluation. An appropriately defined optical absorption factor characterizes the crystal quality very well and was gauged by other more direct methods like ion backscattering and electron diffraction. The quality of the film is good near the silicon surface (similar to that of bulk silicon), but rather poor near the silicon/substrate interface due to heteroepitaxial growth, as it is observed by step-by-step etching and measuring the correlated absorption constant. The method of controlled depletion was improved by computer evaluation and was used as a tool to study the doping and mobility profiles with FET's after the process.

Optimization of the Deposition Conditions for Epitaxial Silicon Films on Czochralski Sapphire in the Silane‐Hydrogen System

“…The absorption factor FA agrees well with other methods, e.g., electron diffraction and ion backscattering measurements. In addition, FA is in good correlation with transistor parameters, as for example the channel mobility (20,21). Therefore, FA was used in this present work as a tool to define the epitaxial film quality.…”