REACTIVE ION ETCHING OF PECVD N+ A-SI-H - PLASMA DAMAGE TO PECVD SILICON-NITRIDE FILM AND APPLICATION TO THIN-FILM TRANSISTOR PREPARATION

Process parameters that affect the reactive ion etching of PECVD n+ a-Si:H film have been studied. The n+ a-Si:H etching mechanism is similar to that of a-Si:H etching, e.g., both plasma phase chemistry and ion bombardment are contributing factors. The high chlorine-containing plasma etches the film faster than the low chlorine-containing plasma. The n+ a-Si:H to a-Si:H etch rate ratio is around 1.7 in either CF3Cl or CF2Cl2 plasma, independent of the pressure and the power when the power is higher than 500 W. A high etch ratio of n+ a-Si:H to silicon nitride (e.g., between 3 and 30) has been obtained with these two gases. Plasma phase chemistry affects the etch rate ratio more than the ion bombardment does. The silicon nitride surface damage has been measured to be less than 60 angstrom by the Auger profile method. The EPR intensity of the plasma etched silicon nitride film increases with the increase of the etch time and power, but decreases with the increase of pressure. The film damage does not introduce current leakage through the silicon nitride layer, nor does it deteriorate the TFT characteristics.