The interaction of stoichiometry, mechanical stress, and interface trap density in LPCVD Si-rich SiN x;Si structures

Abstract

Mechanical and electrical properties were correlated in LPCVD SiN x ;Si structures through the characterization of six wafers patterned with MNS capacitors whose insulator films were deposited rich in Si under various processing conditions. The samples were measured for mechanical stress at the SiSiN x interface with X-ray diffraction. The deposited SiN x films were measured for stoichiometry by Rutherford backscattering spectroscopy. Low-temperature C- V measurements were used for the first time to estimate SiSiN x interface trap densities in the capacitors. The interface trap densities were confirmed with the aid of a model based on a numerical analysis of the capacitor small-signal response. The measurement results indicate that an increase in the Si/N ratio in the insulating films was accompanied by a decrease in the film tensile stress. Those SiN x films made sufficiently rich in Si were successfully deposited under compressive stress. Furthermore, a decrease in the magnitude of the stress was accompanied by a decrease in interface trap densities, suggesting that interfacial mechanical stress may be influential in the formation of SiSiN x interface traps. Interface trap densities were lowest in those structures whose insulating films were deposited under compression.