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Analysis and improvement of the color anomaly in a‐Si TFT channel with new 4‐mask process

In new 4‐mask manufacturing process of the thin film transistor (TFT) liquid crystal display (LCD), the copper in the channel would be damaged by plasma gas, which would cause a negative impact on the subsequent processes, and lead to abnormal channel color. This paper investigates the formation mechanism of the abnormal channel color. In the 1st dry etching, the photo resist (PR) reactes with Cl2, and produced some residual after the 2nd wet etching, which is hard to etch or wash. As a result, the content of SiOx on the surface where there is no residue is higher than the place where the residue exists in O2 plasma process, hence leading to the differences of the silicon etching rate and forming the line‐shape pits at the edge of the channel. Therefore, TFTs under optical microscope show abnormal channel color. Through removing Cl2 or skipping the plasma treatment before 2nd dry etching we could modify this issue.