Haruo Kokubo

Defect repair performance using the nanomachining repair technique

Nanomachining is a new technique for repairing photomask defects. The advantages of this technique are no substrate damage, precise edge placement position and Z height accuracy when compared with current Laser zapper or FIB GAE repair techniques. This technique can be applied to any type of opaque defects at any type of film materials and quartz bump defects on Alternating Aperture Phase Sifting Masks (AAPSM). Furthermore, these characteristics enable complex pattern repairs of most advanced photomasks for 193nm lithography and enables iterative repair to achieve improved printing performance when analyzed with an AIMS 193nm tool. Dai Nippon Printing Co., Ltd. (DNP) has been producing AAPSMs in mass production for quite some time. The standard type of AAPSMs manufactured has been etched quartz, single trench with an undercut structure. On this structure, there is a potential for quartz defects underneath the chrome overhang based on the combination of dry and wet etching to create the undercut. For this study, we fabricated this kind of designed quartz defects and repaired them using the nanomachining system. These types of defects are particularly difficult to repair perfectly because they exist underneath the chrome overhang. We will show some options to achieve better printing results through the repair of these kinds of defects. In this report, we confirmed basic performance of this technique such as edge placement accuracy, Z height accuracy and AIMS printability. Additionally, we also tried to repair some complex defects such as quartz defects of AAPSM, quartz defects of CPL mask and oversized Serifs for application options. We will show these nanomachining repairs with evaluation results of printing performance simulated by the AIMS 193nm tool.

Feasibility study of manufacturing process and quality control for the new alternating PSM structure

Alternating phase-shifting mask (Alt.PSM) technology is the most effective approach to expand resolution limitation and expand the process window of lithography. Currently, etched quartz Alt.PSMs have been introduced not only for device development but also for production use. We have been supplying Alt.PSMs with Single trench + Undercut structures for the mass-production of KrF lithography and reported this structure is applicable for ArF lithography. On the other hand, we have introduced preliminary manufacturing results of the new Alt.PSM structure. This structure has the advantages, which are exempted from biasing issues and narrow chrome width limitations. In order to make sure the adaptability of this new Alt.PSM structure in mass-manufacturing, we started to investigate productivity for this structure. In this paper, we will discuss about the feasibility study of manufacturing process and quality control which include CD performance results, alignment error tolerance evaluations and defect assurance evaluations.

Photomask repeater strategy for high quality and low cost reticle fabrication

The severe mask specification makes mask cost increase drastically. Especially, the increase in the mask cost deals ASIC businesses a fatal blow due to its small chip volume per product. Pattern writing cost has always occupied the main part of the prime mask cost and the emphasis of this is still increasing. This paper reports on a Photomask Repeater strategy to be a solution for reducing mask cost in pattern writing, comparing with conventional EB system.

Feasibility study of SCAAM-type Alt-PSM for 157-nm lithography

Alternating Phase Shifting Mask (Alt-PSM) technology is one of the most effective Resolution Enhancement Technology (RET). It has been used for current optical lithography and will be used for 157nm lithography also. Considering about topographic structure of Alt-PSM, current etched quartz with undercut structure will be very difficult to be applied for 157nm Alt-PSM because undercut structure limits mechanical durability at narrower chrome width. To solve this problem, Side-wall Chrome Alternating Aperture Mask (SCAAM) is proposed. This structure has the characteristics of “There is no undercut”, “Ideal topographic structure for lithography (All quartz steps are covered by chrome film which means very few refracted light at quartz side-wall will go through chrome film and affect printing results compared with conventional etched quartz type Alt-PSM)”. We fabricated SCAAM type Alt-PSM for 157nm lithography and printed by using 157nm microstepper with a 0.85-NA lens. In this report, we will show preliminary printing results of using SCAAM and which will be compared with the results of using conventional etched quartz type Alt-PSM.

Feasibility study of manufacturing process and quality control for the new Alternating PSM structure

Alternating phase-shifting mask (Alt.PSM) technology is the most effective approach to expand resolution limitation and expand the process window of lithography. Currently, etched quartz Alt.PSMs have been introduced not only for device development but also for production use. We have been supplying Alt.PSMs with Single trench + Undercut structures for the mass-production of KrF lithography and reported this structure is applicable for ArF lithography. (*1,2,3) On the other hand, we have introduced preliminary manufacturing results of the new Alt.PSM structure. (*3) This structure has the advantages, which are exempted from biasing issues and narrow chrome width limitations. (*4) In order to make sure the adaptability of this new Alt.PSM structure in mass-manufacturing, we started to investigate productivity for this structure. In this report, we will discuss about the feasibility study of manufacturing process and quality control which include CD performance results, alignment error tolerance evaluations and defect assurance evaluations.

Improvement of photomask repeater for 130-nm lithography

Device masks for 180nm lithography was fabricated by PR system. These masks were verified by device yields comparing with masks written by other conventional systems. There were no differences in device yields between PR system and conventional system. Fine analysis of CD error was carried out for enhancement of CD uniformity to apply Photomask Repeater to 130nm lithography. It revealed that major CD error function is global CD error. By optimizing exposure dose of each shot to compensate global distribution, global CD error was reduced from 7.9nm to 5.5nm. Finally, CD uniformity of 8nm was achieved. PR system can afford to fulfill the requirement of CD uniformity for 130nm lithography. Simultaneously, the result of fine analysis indicates excellence of PR system in littleness of random error.

100-nm alternating PSM structure discussion for ArF lithography

Alternating phase-shifting mask (Alt.PSM) technology is the most effective approach to expand resolution limitation and expand the process window of lithography. Currently, etched quartz Alt.PSMs have been introduced not only for device development but also for production use. Adapting the etched quartz structure, we need to consider about transmission difference between etched and un-etched regions. So, side-etching method has been used for structure of Alt.PSMs. We have been supplying Alt.PSMs with side-etching and single trench structures for the mass-production of KrF lithography. As design rule of device pattern have been tightening, in 100nm node and further, narrow chrome width limits the undercut width and which should be optimized for ArF lithography. Moreover, proximity effect has been reported for the shifter edge type Alt.PSMs as pitch dependency of printed line CD. We will report about the side-etching optimization whether limited undercut width can compensate the CD imbalance between etched and un-etched regions. Or, how much bias adding at space width of etched regions can compensate it, or how undercut and space biasing combination affect CD imbalance. We also discuss about whether the line bias can correct to targeted line CD. Finally, we will summarize which structure is recommended for 100nm-node Alt.PSM for ArF lithography. On the other hand, for the case the undercut structure turns out to be difficult in the 100nm-Alt.PSM manufacturing, we will report preliminary manufacturing results of the new structure.