The Module Design for Critical Dimension Bias Correction of Slanted Line on High Level Large Area Mask

In order to mass-produce the TFT array and the color filter of TFT-LCD panels, the technology of photolithography must be used to transfer the photomask graphics onto the base material of LCD panels. Therefore, the precision of photomask has critical affection to the quality of TFT-LCD panel. In plain terms of mask manufacture procedure, it starts by applying photoresist onto quartz blanks which then will be drawn various geometry by using the devices of laser or electron beam. After the developing process, the exposed photoresist on the blanks will be removed and then the procedure goes through the etching process to eliminate the chrome which was not covered by the photoresist. Finally, we clean the remained photoresist and leave the chrome geometry on the blanks. On the other hand, panel manufacturers use the photomasks as the master mask of LCD panels in production. Same as taking photos, we use a film to develop thousands of pictures. Similarly, one photomask can generate electronic circuits on TFT-LCD base material and lead to massive production. Film quality would affect its resulted pictures so photomask quality would same affect its resulted TFT-LCD panels. Currently, high-level large area photomasks are GTM (Gray Tone Mask), HTM (Half Tone Mask), and Slit mainly. The trend of high-level large area photomask is that the mask size is going larger and the design of line size and gap is going thinner. Also, the uniformity requirement of the entire photomask is getting stricter. Presently, the line size and gap of Korean made high-level panel are as small as below 1um and the acceptable tolerance is ±100nm. These are very close to the limitation of laser writers. Besides, masks are quite large in size so it´s hard to conquer technically while the micro size design on the entire mask needs to follow its specification. As the result, there are greatly increased difficulties of mask making and we need a special graphic process to assist it. Eventually, ph- - otomask manufacturers can gain more profit if they can improve their technique and yield rate of high-level mask production. Usually, we use MICRONIC writer for large size mask production and need to convert the data before writing. Considering the side etching effect caused by the etching process, it is required that to apply process bias onto mask graphics in advance. The compensation design has no problem with vertical and horizontal graphics while inaccuracy may happen when applied on oblique graphics. Comparing with vertical and horizontal graphics, for example, there will be a 125nm offset error on a 45 degree slope if we gave 300nm as the process bias value. The goal of this research is to develop a slope correction program to conquer the slope offset error caused by the process bias and promote the yield of producing high-level photomask.