Theory and measurement of quantization effects on SiSiO 2 interface trap modeling

Abstract

In highly doped n-channel small geometry devices, the conduction band is quantized into discrete energy levels when the channel is inverted. In addition, the carriers are localized spatially, and the centroid of charge is a finite distance away from the SiSiO 2 interface. Thus, an electron in a filled interface trap will emit to the first allowed energy level, known as the ground state, which resides 50 meV above the surface conduction band energy level for doping densities of 10 17 atoms/cm 3. Bulk potential bias will change the degree of quantization and must be included in a modified theory to correctly extract the emission times and capture cross section values for interface traps. We extend the Shockley-Read-Hall (SRH) theory to include two-dimensional surface quantization effects and formulate the statistics to account for localization of conduction band charge in both space and energy. The interface trap emission characteristics may be obtained with an electrical measurement, called the tri-level charge pumping technique, which offers a convenient method to study emission from interface traps to quantized conduction band states. Measurement techniques of quasi-static C- V, high frequency C- V, drain current, and charge pumping are used to characterize the interface. Tri-level charge pumping measurements on large (100 × 10 μm), highly doped MOSFETs provide experimental evidence of two-dimensional effects, and extracted electron capture cross sections are found to be an order of magnitude larger than values from classical theory.