Theoretical Consideration on Stepper Shot-Block Perception

Abstract

A large-area high-resolution TFT-LCD is fabricated using a step-aligner, because it's screen size exceeds the photo-mask size A shot-block boundary is sometimes perceived and deteriorates picture quality. The purpose of this paper is to investigate the shot-block perceptibility and the influences to TFT-LCD pixel design, theoretically. A new model with a level-shift voltage induced by a TFT parasitic capacitance has been introduced and an estimation of the currently available step-aligners, which have a maximum pattern-discontinuity of 1.2-1.5μm, showed that they would cause the shot-block images. A generalized design rule related to the shot-block image has been introduced. Using this rule, the aperture ratio of high-resolution TFT-LCDs were estimated and the results showed that the aperture ratio would decrease, as the number of gate lines increased. Possible methods to improve this phenomenon have been summarized.