Hisatsugu Shirai

Improvement of ZEP process for advanced mask fabrication

In mask making, ZEP 7000 resist process with MEBES writing tool is widely adopted to produce advanced masks. This time, we tried to improve resist pattern CD uniformity in ZEP process using our special techniques. Resist sensitivity uniformity of mask blank is one of the most significant parameters for resist pattern CD uniformity. In ZEP7000 coating process, our original cooling method waw adopted in consideration of its resist sensitivity properties. Resist film thickness loss (RTL) uniformity during development was examined in order to analyze the resists sensitivity uniformity within a mask blank. It was clearly seen that resist pattern CD uniformity was 15nm with the optimum cooling condition. RTL uniformity and resist pattern CD uniformity were also examined using blanks which were commercially available from two vendors. And these results were compared with the results of our original cooling method. Based on the results of our study, we confirmed that our original cooling method was very effective for improvement of resist pattern CD uniformity on ZEP process.

Improvement of Cr dry etching characteristics with the MERIE system

Dry etching characteristics of Cr films were investigated and some improvements have ben done with magnetically enhanced reactive ion etching (MERIE) system. Clear field patterns and ark field ones exposed on thin EB resists, whose thickness was less than 300 nm, were etched. Although there had been some difficulties in etching of clear-field pattens with SAL-601, these situations were much improved with an appropriate etching condition of magnetic field. It was found that magnetic field intensity affected Cr etching distributions very much. In marked contrast to the above results, MFI condition showed little contributions to the etching distribution of dark field patterns exposed on ZEP- 7000. It was shown that some waveforms of magnetic field could be effective to improve the etching characteristics for the plate whose etching area was extremely small. Etching characteristics for these extremely varied Cr-loaded are considered through the above etching results. Discussions about more useful dry etching process with MERIE system are also described.

64-Mbit DRAM production with i-line stepper

This paper describes the exposure technology to manufacture 64M-bit DRAM chips with i-line (365-nm) stepper. The one-shot (conventional) exposure method was tried--a 64 M bit DRAM chip using the i-line lens of numerical aperture (NA)

Reticle cleaning process for 130-nm lithography and beyond

EG0.50 with or without a phase-shift method--but the process margin was not sufficient in a few layers. The authors have shown that the block exposure method can be used as an exposure technology when the one-shot exposure method cannot be used. The block exposure method divides a step-and-repeat pattern within a single chip into multiple blocks and allows high-resolution exposure of each of these blocks. The stepper with the i-line lens of NAequals0.65 was used. The authors also tried to clarify the effect of coherency caused by the illumination optical system of the i-line stepper. In addition, the alignment accuracy of the block exposure method is discussed.

Investigations of CD variation in Cr dry etching process

Three cleaning methods were examined to check their strong points. Cleaning results were analyzed from the aspects on removal of particles and chemicals. Starlight inspection results showed that conventional wet cleaning based on chemicals, such as H2SO4 and NH4OH, could remain small particles on chrome-oxide (CrOX). DUV irradiation could assist this traditional SC-1 (mixture of NH4OH and H2O2 and HH(subscript 2O) cleaning in removing these sticking particles. Electrolyzed water, contained anode and cathode water, showed same tendency as SC-1 treatment, which could easily attract particles to CrOX surface. Mechanism of particle removal and attraction was considered from the aspect on electrostatic reaction between particles and photomask surface. ArF ((lambda) =193nm) lithography could cloud quartz surface with crystallized substances. Analytical results implied that they had been generated by optical-chemical reaction between ArF light and chemical residue after cleaning. Experimental results showed that DUV treatment before cleaning was effective to prevent reticle surface from chemical contamination. From the above knowledge, suggestion about reticle cleaning process for ArF lithography is described as a conclusion.

Knack for reticle cleaning

In this report, origins of CD error caused through Cr dry etching were investigated and some process conditions were evaluated for the advanced reticle productions. It is shown that resist patterns of ZEP-7000 written with MEBES-4500 showed a little CD deviation between the sparse and dense regions. These errors could be easily emphasized after Cr dry etching. Some dry etching conditions were examined and slight improvements were confirmed after the addition of etching assist gas and adequate intensity of AC magnetic field of MERIE (Magnetically Enhanced Reactive Ion Etching) system. It is also shown that resist profiles after development play important role in the CD distribution after dry etching for the reticle contained both sparse and dense region on the same plate. With our conventional condition, resist profile of ZEP-7000 showed a gentle slope after development. It is proved that this lower pattern contrast makes the Cr CD difference due to pattern loading much worse. Minimum CD error could be obtained through the process that made resist profile almost vertical. These results imply that total adjustments, not only for dry etching conditions but also for resist process that gives us the highest pattern contrast, are needed to solve the complex issues for the advanced CD control.

Overlay accuracy of reticles

Cleaning is one of the most important processes in mask making, because it decides final quality. In cleaning process, it is necessary for reticle cleanliness to not only remove particles from reticle but also prevent adsorption and re-deposition onto reticle. There is the knack for reticle cleaning, and we introduce three keys in this paper. The first key is the rinse after chemical treatment. By the rinse sequence modification, the cleaner was refined and the particle removal ability was improved. The second key is quality control to grasp the situation of cleaner. By the daily check, cleaners abnormal condition is found at an early stage, quick action is taken, and then stable cleaning quality is kept every day. And the third key is proper choice of cleaners. We have adopted pre-cleaning process and selected the adequate cleaner for each cleaning level and improved cleaning yield and quality.

Method for fabricating semiconductor devices that prevents pattern contamination

This paper describes the study on overlay accuracy of reticles, using a reticle set for DRAM. It is found that single reticle pattern placement has to be higher accuracy than overlay of reticles, which may be a majority in the total overlay accuracy. Concerning some points of a reticle set, we found that there is a very large value. To match overlay accuracy of reticles with the demand of devices, we have shown that the suitable reticle exposure system has to be used and managed exactly. In order to assure overlay accuracy of a reticle set, it was proposed that single reticle pattern placement accuracy must be higher than overlay accuracy demand and the overlay accuracy yield also should be shown in some cases.