Since several years, there has been continuous focus on legacy tools for mask making and the critical requirements to address the end of life of equipment which has been workhorse for volume production. Toppan Photomask Company, Ltd. (TPC) has presented several papers on this subject and brought this to attention to many equipment manufacturers and other mask shops who have also shown keen interest to support the manufacturers who are willing to take up this task to provide solutions. HTL Co. Japan Ltd. And V Technology Japan has teamed up to manufacture equipment for the semiconductor mask making legacy tools and one such example is successfully manufacturing the mask repair system with support from TPC. Mask inspection, Registration, FIB repair and others also being addressed, and one attractive feature is to give an opportunity to enhance the performance of these new replacement tools by using AI software for defect classification for the system. We will discus our development process and capabilities served for legacy tool replacement.
The purpose of this trial is how an AI-based approach can contribute to improving the operability of photomask inspection equipment. It is important for the equipment operation how to efficiently identify photomask defects. In particular, it is essential to accurately perform the filtering of erroneous judgments of inspection equipment called false defects. Furthermore, for actual defects, it is necessary to classify the defect types as accurately as possible. This paper describes how to implement AI approach into the “Defect Review System”. Especially, in case that the equipment can capture both transmission and reflection images simultaneously, effective utilization of both images has been shown to result in more effective identification of defects.
KEYWORDS: Data processing, Transistors, Electron beams, Optical proximity correction, Photomasks, Resolution enhancement technologies, Vestigial sideband modulation, Electron beam melting, Data conversion, Data modeling
The optical lithography still remains to be the mainstream coupled with RETs (resolution enhancement techniques)
because of the various and serious difficulties other NGL candidates (Electron beam direct writing, EUV and etc.) are
facing now. Development of OPC have made pattern data complexity large so that increasing rate of pattern data
volume is higher than the number of transistors in a chip. We studied key issues of development of mask writer
especially for throughput.
Optical proximity effect correction (OPC) now is a prerequisite technique to improve common process windows of the present optical lithography process. It will be also applied to 0.13 micrometer device processes. Although the technology is now widely used, there are still issues to be solved in terms of choice of OPC methods, pattern fidelity specs, software/data processing limitations, mask manufacturing equipments and manufacturing yields with costs. Photomask Japan '99 Symposium (PMJ '99) had a panel discussion this year covering such issues. For 0.13 micrometer generation, critical dimension (CD) accuracy of plus or minus 4 nm on wafer is given for error budget derived from masks, which OPC masks must also achieve. Mask defects with a size of 70 nm must be repaired, which also requires mask repair accuracy of OPC geometry copy features with high performance. As OPC is sometimes applied to the corner part of figure shapes, it is also required to clarify CD specifications for such portions depending on desired pattern layouts. A mask process with zero defects will also be required as a countermeasure of such mask making difficulty. As a consensus, it is also proposed that acceleration of collaboration between device makers, equipment/software makers and mask shops is much required.
This panel discussion was focused on the key issues on mask fabrication for 0.18 micrometer rule devices and beyond. The requirements for mask fabrication specifications from the logic and DRAM device manufacturers, and the limits and key issues for mask technologies from the mask suppliers and the equipment suppliers were presented and discussed. The CD accuracy, defect inspection, and cost were listed up in the critical requirement list from the device manufacturers. On the other hand, the mask suppliers gave the critical issues such as the capabilities of inspection and repair, dry etching technology, 230 mm reticle, the throughput of mask writers, and so on. According to the revised 1997's SIA roadmap, technologies were pulled-in about 2 years, so that the panelists pointed out some expanded gap between the requirements and current performances. CD uniformity was listed as the most important issue to be improved, and requested CD range was less than 20 nm. Compared with mask suppliers target of 30 nm, there are still some critical issues to overcome to achieve the requested value. In addition to the improvement of equipment and process, the studies of metrology, specification clarification, and error budget analysis were required for action items.
A panel discussion on mask technologies for 0.2-micrometer rule devices was held at Photomask Japan '97. This paper summarizes the discussion to make clear what is really needed to the mask, and what is a key issue to overcome. Required CD uniformity is satisfied by the improvement in resist/etching process and pattern writing accuracy. PSM key issues are defect inspection and repair. OPC is indispensable for 0.2 micrometer device, so the improvement in mask pattern fidelity and defect inspection technology is strongly required, but some limitation in OPC pattern design will be necessary to realize the OPC technology in mass production. To achieve both technology and cost, the partnership of captive and merchant mask shop, and the partnership of lithography, device, mask, equipment, and material vendors will be very important.
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