Gate Oxide Integrity for Polysilicon Thin-film Transistors: A Comparative Study for ELC, MILC, and SPC Crystallized Active Polysilicon Layer

Abstract

In this paper, we present the results of Plasma Enhanced Chemical Vapor Deposition gate oxide (SiO₂) integrity on ELC (excimer laser crystallized), MILC (metal induced lateral crystallized) and SPC (solid phase crystallized) polysilicon films. We observed that gate oxide strength of poly Si TFT strongly depends on the crystallization method for the active silicon layer. In the case of ELC films, asperities on the silicon surface reduce the SiO₂ breakdown field significantly. The metallic contaminants in MILC films are responsible for a deleterious impact on gate oxide integrity. Among the three cases, the SiO₂ breakdown field was the highest for the SPC silicon films. The breakdown fields at the 50% failure points in Weibull plots for the ELC, MILC and SPC cases were 5.1MV/cm, 6.2MV/cm, 8.1MV/cm, respectively. We conclude that the roughness and metallic contamination of the poly Si films are the main factors that cause enhanced breakdown of SiO₂ films.