Hisayuki Kato

A new portrayal of electron and hole traps in amorphous silicon nitride

Trap centers in amorphous silicon nitride (a‐SiNx) have been considered to be amphoteric. We found two signals of Si3 3/4 Si0 and N3 3/4 Si0 (Si dangling bonds with an unpaired electron) by an electron‐spin‐resonance method, and estimated the hole trap density to be larger than the electron trap density by about one decade, using the nonvolatile memory devices. As a result, we propose a new portrayal in which electron/hole traps are at the interface between Si clusters and a‐SiNx bulk, and hole traps are at nitrogen vacancies in a‐SiNx bulk.

Effect of grain size on degradation of Pt/PLZT/Pt capacitor

Abstract The effect of grain size on electric properties has been investigated. Various (111) oriented PLZT films were prepared using the RF magnetron sputtering method on Pt/Ti/SiO2/Si substrates. Grain size and surface roughness were observed by AFM. The results showed that; 1) surface roughness depends on average grain size and 2) decreasing grain size decreases process degradation and fatigue. The grain boundary was thought to be responsible for process damage, such as reduction by hydrogen, at electrode interface tops. Electric field strength at grain boundaries also increased with increases in surface roughness.

AC Photovoltaic Measurement of Charge Density Uniformity in Silicon Nitride Film Deposited on Si Wafer

Charge density uniformities in an as-deposited silicon nitride film are evaluated using an ac photovoltaic method. The experimental results for photovoltages as a function of the thickness of a silicon nitride film showed that the net charge in silicon nitride is positive, and a negative charge is located near the interface between the silicon nitride and the ultrathin oxide on the silicon substrate. The photovoltages also greatly varied when the gas flow ratio of NH3 to SiH2Cl2 is changed from 5 to 50 while keeping the thickness constant. The ac photovoltaic measurement revealed a charge density inhomogeneity of 8-nm-thick silicon nitride films, which is attributed to local variations of the gas flow ratio.