Effect Of PECVD Hierarchy Structure On The Mobility Of Hydrogenated Amorphous Silicon

The semiconductor integrated circuit industry has rapidly developed since the invention of the semiconductor transistor in the year of1947.Now,the hydrogenated amorphous silicon thin film transistor (a-Si:H TFT) becomes the mainstream of Si-TFT technology. A-Si film can be prepared by Plasma Enhanced Chemical Vapor Deposition (PECVD) at the low temperature of350℃. It is very suitable for large scale production because of the mature technology, high yield, low production costs and high homogeneity. However, there are still many shortcomings in the performance of a-Si:H TFT device in which the most important is the low field-effect mobility(nearly0.3cm2/V.s).In this paper,we investigate the working principle of the a-Si:H TFT and the growth mechanism of the film layers in large-scale industrial production conditions. We prepare the source and drain electrode and a gate electrode metal film by DC magnetron sputter, and the gate insulating layer (G-SiNx), an active layer (a-Si), ohmic contact layer (N+a-Si) by PECVD method. After4times of photolithographic, we picture the transfer characteristic curve and calculate the field-effect mobility of the a-Si:H TFT device by the method of three-electrode using manual probe measuring device. We also measure the roughness of the G-SiNx layers surface at different growth rates by atomic force microscopy, and use the scanning electron microscope to observe the cross section of a-Si:H TFT.We separately investigate how the G-SiNx layer, amorphous silicon layer of high growth speed(AH), amorphous silicon layer of low speed (AL),and the N+layer influence the field effect mobility of a-Si:H TFT device. Then we use multi-factor experiments to combine different factors for sample preparation and measure the impacting intensity of the field effect mobility by each factor. We conclude that the thickness and stratification condition of G-SiNx layer and the N+layer are the main factors affecting the a-Si:H TFT field effect mobility.The amorphous silicon Thin Film Transistor (a-Si TFT) were fabricated with the new stracture, in which the ohmic contact layer (N+layer) and the nitrid silicon insulating layer for grid (G-SiNx) were stratified. The various factors which impact the electron mobility of a-Si TFT are studied using orthogonal test. With the increasing of the number of N+layer,the electronic mobility was also rising. Besides, G-SiNx should be stratified into rapid deposition film (GH) and a low-speed film (GL).The thickness of GL should be increased, with the thickness of GH reduced accordingly to achieve the electron mobility gradually increasing. Finally, based on the experimental results with the orthogonal combination experiments, the a-Si TFT mobility stably reached0.66cm2/V.s, much higher than the traditional volume production data (0.29cm2/V.s)...