Radiation-Induced Hole Trapping and Interface State Characteristics of Al-Gate and Poly-Si Gate MOS Capacitors

Using the techniques of thermally stimulated current and high-frequency C-V measurements, the device processing dependence of radiation-induced hole traps and interface states in MOS capacitors has been investigated. It was found that the fabrication of poly-Si gates caused all investigated gate oxides to resemble those grown by pyrogenic techniques. The role of postoxidation annealing (POA) in hole trap formation and interface state generation was investigated. The measurements imply that POA causes a "weakening" of bonds in SiO2 which can become hole traps, and, in the presence of OH, lead to the annihilation of certain types of hole traps while generating new types of hole traps and interface states. Possible models and interface state distributions are discussed. Midgap voltage shifts were found not to be generally valid measures of hole trapping in these MOS devices.