Importance of first layer thickness on TFT characteristics using a-Si:H deposited by 2-step process

Abstract

In order to increase the throughput during thin film transistor-liquid crystal display manufacture, we investigated a 2-step deposition process for hydrogenated amorphous silicon. The first hydrogenated amorphous silicon layer of an inverted staggered type thin film transistor was deposited at a lower deposition rate to improve the interface with the gate insulator layer and the second hydrogenated amorphous silicon layer was deposited at a higher rate to improve the throughput. It was found that the mobility values of thin film transistors increased with increasing first layer thickness and reached a saturation value after a certain first layer thickness. When the first hydrogenated amorphous silicon layer quality was improved by decreasing its deposition rate, a thicker first layer hydrogenated amorphous silicon was needed to reach a mobility saturation.