Very-Low Surface Roughness in Laser Crystallized Polycrystalline Silicon

ABSTRACTExcimer laser (ECL) crystallization of silicon films on low temperature substrates is one of the most promising technique for large-area polycrystalline silicon films. Crystallization techniques using pulsed-ECL were extensively studied. They are characterized by films with high structural and electrical properties but low uniformity. In this way, the technology using single shot ECL with very large excimer laser (VEL) may be very promising. It was used for the crystallization of amorphous undoped films deposited by PECVD or by LPCVD The LPCVD technique is the most commonly used deposition technique of silicon. It presents numerous advantages and the hydrogen content in the films, known to constitute a drawback in the crystallization process leading to an increased surface roughness, is negligible (∼1 at.%). However, even with these low hydrogen content LPCVD films, high surface roughness is observed after the laser crystallization. Hence surface roughness appears as one of the major problems to be solved in the high performance TFT's realization from laser crystallized films.In this work, the reduction of the surface roughness, determined from Atomic Force Microscopy observations, is presented. This reduction originated from the use of a surface oxidation and an etch treatment to remove the oxide. The mean height of the roughness is then reduced by about 50%.Using these low surface roughness polycrystalline films, TFT's are then realized.