Effects of stress on metal-oxide-semiconductor structures

Abstract

Metal-oxide-semiconductor (MOS) structures contain built-in stress fields. Such fields could be related to surface-state density, interface charge, and may influence migration, collection, and precipitation of impurities as well as modify the properties of the oxide layer and cause shifts in the band structures of the metal and semiconductor. Consequently these fields may be an important factor in the reliability problems of MOS devices; unfortunately, previous studies have produced results and conclusions which are quite varied. To be able to appraise these various possible effects, shifts in the C-V characteristics of a device due to band structure modifications resulting from stress, which have been suggested to be large, and oxide layer modifications resulting from stress are explored analytically. It is concluded that these contributions to any shift of the C-V characteristics, even for stresses of the order of 1010 dyn/cm2, must be small. These results then permit the effects of stress on generation recombination, surface states, interface structure, and ion drift to be explored experimentally and appraised. The experimental work produced no evidence for stress-induced changes for stresses up to 109 dyn/cm2 even though, for the loading configurations used, these externally imposed stresses substantially changed the built-in field across the interfaces.