Study On Improvement Of Four Mask Photolithography Process In TFT-LCD

With the development of information display technology,flat panel display has spread throughout our work and life.The manufacturing process of a TFT-LCD(Thin Film Transistor Liquid Crystal Display)is mainly to manufacture an electronic circuit on a glass substrate,and the photolithography process is a key technology for determining a pattern.The photolithography apparatus is a bottleneck device in the entire manufacturing process in the manufacture of TFT-LCD,which is expensive to manufacture.After several decades of development,the TFT-LCD manufacturing process has been continuously optimized.It has evolved from the first seven mask photolithography processes to the current four mask photolithography process,greatly increasing manufacturing capacity and reducing production costs.At the same time,as the size of the glass increases,the requirements for photolithography process conditions become more and more strict.This paper is mainly based on the G8.5 production line.It has studied and optimized the conditions of four mask photolithography processes in detail,which is of great significance for improving the quality,stability and excellent rate of products.The photolithography process mainly includes three main manufacturing processes of coating,exposure and development.Coating is to uniformly coat the photoresist on the glass substrate,and the exposure is to photochemically react the photoresist on the glass substrate,and the development is to neutralize the developer with the photochemical reaction,leaving Unexposed areas of the photoresist,the final definition of the pattern.In this paper,four mask photolithography process conditions and their optimization will be studied from three aspects of coating,exposure and development.The specific research contents and results are as follows:(1)The research and analysis of TFT four mask photolithography process show that the management of residual film thickness in TFT channel is of great significance to the characteristics of TFT;if the thickness of the residual film is too thick,the source and drain metals are short-circuited,and the thickness of the residual film is too thin,which may cause the active layer to be missing.(2)Through the research and analysis of the exposure process technology,the key process factors of each process of the four mask photolithography processes are clarified,and the theoretical basis for the subsequent four mask photolithography process analysis,optimization and improvement is made.(3)The control method of film thickness and uniformity in the coating process was studied.The results show that the slit coating process can be optimized by adjusting the slit width and the photoresist discharge rate,and get the quantitative relationship between the adjustment amount and the film thickness change.(4)The effect of exposure process on residual film thickness and uniformity was studied.The results show that exposure and focus have an important influence on residual film thickness control.It was found that the exposure amount was linear with the residual film thickness,and the exposure amount was increased by 1mj,and the residual film thickness was lowered by about 200 ?.It is found that the focal position offset has a quadratic curve function with the residual film thickness,and the focus position can be optimized by improving the curvature of the mask,the optical tube temperature management,and the flatness adjustment of the plate stage.(5)The effect of development process on the thickness and uniformity of the residual film was studied.The results show that the development time and the solubility of the photoresist in the developer and the carbonate ion solubility are linear with the residual film thickness,and the shortening of the development time can be improved residual film thickness uniformity.(6)The difference between the design of single slit mask(SSM)and halftone(HTM)mask in four mask photolithography processes,and the process difficulty of the two were studied,and design optimization suggestions are proposed for the mask version.