Electrical Degradation and Recovery of Low-Temperature Polycrystalline Silicon Thin-Film Transistors in Polycrystalline Silicon Plasma Process

The plasma-process-induced damage (PPID) of low-temperature polycrystalline silicon (poly-Si) thin-film transistors (TFTs) during the etching of the poly-Si film was investigated in this paper. The results reveal the relationship between the device degradation and the PPID during TFT liquid-crystal-display fabrication. This degradation is caused in part by the damage at the edge of the poly-Si film in plasma exposure. The trapped-state densities N_trap are measured to clarify the relationship between instability and plasma etching damages. The plasma-process condition substantially affects the PPID of the poly-Si etching process. The main mechanism is the generation of charge trapping states at the poly-Si grain boundary in the damaged edge of the TFT channel active region. The electrical recovery from the plasma damage is also studied with various postetching treatments. Hydrogen-base plasma treatment and laser anneal process are revealed to improve the device characteristics due to reduction of charge trapping states.