Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1117/1.JMM.19.4.044401

DOI： 10.1117/1.JMM.19.4.044401

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1143/JJAP.50.117301

DOI： 10.1143/JJAP.50.117301

Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

Freeze cleaning involves the selective separation of particles from the substrate surface by utilizing the volume expansion that occurs when water in a supercooling state changes to ice. This allows particles to be efficiently and easily removed without causing pattern collapse. However, this method has a long processing time because of the following two factors: (i) the particles tend to remain at the four corners of a rectangular substrate; (ii) particle removal efficiency (PRE) per freeze-thaw cycle is low. These factors necessitated 30 repetitions of the freeze-thaw cycle to obtain sufficient removability
over the entire substrate surface, which prolonged the processing time. Therefore, we attempted to improve the
removability at the four corners of the substrate and PRE per freeze-thaw cycle. The experimental results showed that removability at the four corners of the substrate was enhanced by improving the discharge efficiency of particles separated from the substrate. Furthermore, the PRE per freeze-thaw cycle was improved by achieving a uniform temperature distribution across the substrate at the end of supercooling. These measures reduced the processing time to 1/6 and allowed
us to successfully develop a device for mass production.

DOI： 10.1117/12.3034592

Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

We propose freeze cleaning as a method of photomask cleaning in which particles small enough to be embedded in the region less than 100 nm from the substrate surface, where there is virtually no fluid flow, are selectively removed without causing pattern collapse. In freeze cleaning, a high particle removal efficiency is achieved by repeating the sequence of liquid (deionized water) being poured onto the substrate, freezing, and thawing (rinsing) multiple times. Based on the mechanism of particle removal, the timings at which the water freezes, ice growth, and freezing of the entire surface are important parameters that govern freeze cleaning performance. In contrast, when these timings were monitored during repeated processing, a maximum variation of about 16% was observed. The most significant cause of these fluctuations is attributed to the process performed in a system that is open to the atmosphere at room temperature, despite the use of
cryogenic N2 at -120°C. Even with these timing fluctuations, by developing and applying an algorithm that monitors individual changes and automatically determines step switching using this monitor information, it is possible to construct a stable and highly efficient processing system without any tool modification.

DOI： 10.1117/12.2640652

Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)  

Other Link： https://iopscience.iop.org/issue/1938-5862/108/4

Event date： 2024.9 - 2024.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Monterey, California, USA   Country：United States  

With the down-scaling in semiconductor device, the size of minimum particle required to be removed from EUV masks have become smaller and smaller. Accordingly, critical dimensions of patterns and surface of films have being easily affected by chemicals during being cleaned and from the viewpoint of reducing environmental impacts, decreasing an amount of used chemicals has become one of the most significant challenges at production sites. Spray and mega sonic cleaning are known as conventional cleaning method; however, it usually cannot simultaneously satisfy small particle removals and not collapsing small patterns due to their trade-off relationship. Therefore, we have developed the cleaning technology called "the Freeze Cleaning method"[1],[2] that can discriminate between particles and patterns perfectly and only particles can be removed selectively. In the Freeze Cleaning method developed by Shibaura, the water intruded into gaps between particles and substrate surface is frozen to expand its volume and volume expansion leads to weakening strength of sticking between them. As a result, particles are selectively separated from substrate surface, and they can be efficiency and easily removed from substrate surface. And this innovative cleaning technology is capable of removing small particles only without giving any physical shocks to patterns. Moreover, we optimized the cooling method for a quartz plate with low thermal conductivity in order to obtain high uniformity of temperature across a whole plate, which can shorten a cooling time. And we established the special method that particles are prevented from sticking to substrate surface again, which can drastically enhance removal efficiency of particles per a freeze cycle. Through these our unique measures, we can reduce cleaning time significantly

Event date： 2024.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：新潟市朱鷺メッセ   Country：Japan  

半導体デバイスの露光原版であるフォトマスクの配線パターンに欠陥があると、露光されたすべてのウェハにその欠陥が転写される。そのため、フォトマスクに要求される清浄度は厳しく、また配線パターンの微細化により欠陥要因となる異物の最小サイズが小さくなってきている。一方で一般的な薬液洗浄では、基板表面からおよそ100nm 以下の領域(stagnant layer：停滞層)で流れが実
質的にゼロになるため、その領域にトラップされた微小異物の除去は困難である。
薬液より強力な洗浄手法として、スプレーや超音波洗浄等の物理力を利用する洗浄手法が利用されている。それらの手法では物理力を大きくすることで停滞層内の微小異物まで除去可能であるが、フォトマスクの微細な配線パターンに対してはパターンが倒壊し、欠陥になるという問題があっ
た。
芝浦メカトロニクス(株)が開発した凍結洗浄[1]，[2]では、基板上の水を凍らせることにより、異物を起点として形成される氷の体積膨張を利用している。膨張する氷が異物と基板の隙間を広げ、凍結と解凍を繰り返すことでやがて異物が基板から剥離され、解凍時に液化する水ごと基板上から排出される。そのため、基板に直接形成された配線パターンにはダメージを与えず、停滞層内の微小異物を除去可能である。
本研究では、解凍時の基板の面内温度分布がPRE(particle removal efficiency：異物除去率)に与える影響を評価した。評価用基板として、ブランクスの石英基板(152mm×152mm)を用い、洗浄液には純水のみを使用した。基板の温度分布を直接測定することが困難であったため、放射温度計で測定した基板上の水の温度分布を基板の温度分布と仮定した。Fig.1 に測定した基板の温度分布画像例を、Table1 にPRE の面内温度差依存性を示す。この表から、面内の温度差が小さいほどPRE が向上することがわかる。その要因は、基板温度分布が不均一であるほど水平方向に氷が成長しやすく、異物を核とする氷が成長する前に、基板全面で水が凍結するためと考えている。基板温度分布の均一化により凍結回数の低減が可能となり、処理時間の大幅な短縮が実現され
た。
【参考文献】
[1] Kei Hattori. et al., J. Micro/ Nanolithography, MEMS, and MOEMS, 044401-1(2020).
[2] M. Kamiya. et al., “Freeze point monitoring system for freeze cleaning”, Proc. Photomask Japan,
123250B (2022).

Event date： 2024.4

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：名古屋大学・EI創発工学館FUJIホール   Country：Japan  

Event date： 2022.5 - 2022.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Vancouver, BC, Canada, and Online   Country：Canada  

Event date： 2022.4

Language：English   Presentation type：Oral presentation (general)  

Country：Japan