Improvement Of Pecvd-SiNx For Tft Gate Insulator By Controlling Ion Bomberdment Energy

Abstract

ABSTRACTIt has been revealed that ion energy and ion flux density play an essentially critical role in SiNx deposition process of PECVD in TFT-LCD production. Ion energy and ion flux density bombarding onto substrate surface are known to be extracted from waveform of RF applied to an electrode. Using this method, authors investigated film quality of SiNx formed in the conventional parallel plate PECVD equipment. When N2+H2 or N2+Ar is employed as a carrier gas in source gas(SiH4+NH3), authors have defined normalized ion flux density as ion flux density divided by deposited SiNx molecule which must be increased to obtain high quality SiNx film while ion energy is suppressed at low level as not giving damages on the film surface. This technique has made it possible to securely form SiNx film (2500 Å) featuring dielectric breakdown field intensity of 8.5MV/cm at 250°C on a glass substrate with Cr gate interconnects of 1000 Å having vertical step structure. One of the important factors to improve film quality of SiNx deposited in PECVD is to increase ion flux density while keeping ion energy low enough to protect growing surface against any damages. Using this technique inverse-staggered TFT-array featuring field effect mobility of 0.96 •/V·s has been demonstrated which gate insulator SiNx, non-doped a-Si:H and a- Si:H(n+) were formed continuously at the same substrate temperature of 2500°C.