Proximity Exposure Graphics Copy Of Computer-aided Analysis And Process Optimization

Proximity lithography is a mature technology of optical exposure which used long time. But during actual process of mass production, many factors will affect the graphic quality of exposure resulting in graphic distortion. Such as light source, the gap between silicon and mask, uniformity of photo-resist on the wafer surface and other factors for example process control.First of all, the contact / proximity optical parts of Canon PLA-501 were introduced, analyzed theoretically. The distribution of light intensity on the silicon surface was calculated. Then, the setting of gap setting parts was described step by step in detail. Last, the error of gap setting was estimated by the probability theory.The pattern quality of proximity lithography about Canon PLA-501 was analyzed, also the deviation factor in graphic replication. With a lot of experiments, the experimental data of the lithography line-width was obtained in various factors. For example, the gap between wafer and mask was wider, the line-width after lithography was bigger; uneven distribution of light intensity would affect the uniformity of line-width, the uniformity thickness photo-resists on wafer also relate to line-width.Some conclusions were obtained by the analysis and experiment about pattern distortion for proximity lithography mode. The most important element is the gap between silicon and mask, so we must ensure the uniformity and repeatability of the gap for excellent lithography line-width. We made improvement in the key components of gap setting --- parallel calibration gear and vacuum clutch, flat calibration mode also. Secondly, there were four lithography sets that exposure intensity had poor uniformity. A little adjustment was done on their optical paths, therefore uniformity capability of sets was improved greatly. Finally, No.4 coating machine was reconstructed which did not work uniform photo-resist thickness, so that uneven thickness probability of all coating photo-resist rails was decreased below 4%.On the process optimization, a check of the first exposure piece was added to detect early equipment failure which caused bad lithography line-width and handled it in time; In order to get better lithography line-width, the exposure energy setting of proximity lithography was reduced and the step of plasma etching residual photo-resists was added, thereby the quality of lithography was enhanced obviously.