真空干燥参数对TFT栅极光刻性能的影响

Effect of Vacuum Drying Parameters on Gate Photolithography Performance of TFT

摘要:

液晶显示器薄膜晶体管(TFT)的栅极需经光刻工艺制得。在光刻工艺中,除曝光与显影环节外,光刻胶显影后的关键尺寸(DICD)和锥角(Taper)还受到真空干燥参数的影响。为此,文章以干燥制程的慢抽时间、保压时间和底压为自变量,DICD和Taper为因变量,采用全因子实验,研究了真空干燥制程对光刻胶DICD和Taper的影响。结果表明:慢抽时间和底压产生的影响较小,保压时间则是关键参数:随着保压时间增加,DICD增加、Taper降低。这是因为随着保压时间增加,光刻胶中的溶剂挥发总量增加,光刻胶更致密,显影速度下降,导致DICD增加；同时,光刻胶顶部溶剂挥发量增加,顶部感光剂浓度增加,导致顶部侧向显影程度增加,最终造成光刻胶Taper下降。此外,建立了DICD和Taper与保压时间的回归方程,可以预测光刻效果,或者由预期的光刻效果反推出所需的保压时间。此工作可为薄膜晶体管光刻产线的参数优化和产品良率提升提供参考。

Abstract:

The gate of thin film transistor (TFT) in liquid crystal display is fabricated by photolithography process. It is found that in addition to the exposure and development process, the development inspection critical dimension (DICD) and the profile angle (Taper) are also affected by the vacuum drying parameters. In this paper, the influence of vacuum drying process on DICD and Taper of photoresist (PR) was studied by a full factor experiment, in which the slow pumping time, holding time and bottom pressure were taken as independent variables and DICD and Taper were set as the dependent variables. The results show that:in the vacuum drying process, slow pumping time and bottom pressure has little effect on DICD and Taper, and holding time is the key parameter. With the increase of holding time, DICD increases but Taper decreases. This can be explained as follows:with the increase of holding time, the total amount of solvent volatilization in the PR increases, the PR becomes denser, then the development speed decreases, so the DICD enlarges; meanwhile the amount of solvent volatilization at the top of the PR increases, and the concentration of photosensitizer at the top increases, resulting in the increase of lateral development at the top, and finally the Taper reduces. Furthermore, the regression equation of the DICD and Taper with the holding time was established, through which the DICD and Taper could be predicted or the required holding time corresponding to the expected lithography effect could be deduced. This work provides a reference for the parameter optimization and product yield improvement of TFT lithography production line.