27 December 2002 Preserving EAPSM Phase and Transmission in the Clean Process
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The cleaning of embedded-attenuated phase shift masks (EAPSMs) is one of the most important enabling capabilities in the production of high-quality masks. Particles are commonly generated during Cr and MoSiON etching using inductively coupled plasma (ICP) tools. The cleaning process of EAPSMs requires not only the removal of particles on the phase shifting layer (MoSiON) and glass, but also the ability to leave the phase and transmission properties intact. Megasonic cleaning is a technique commonly used for removing particles on the surfaces of photomasks. However, megasonic processes employing SC-1 chemistry (specifically ammonium hydroxide) cannot be applied to a MoSiON PSM. Chemical erosion of the alkali-soluble phase shifting layer will drive phase and transmission performance outside of customer specifications. Therefore, EAPSM cleaning must balance simultaneously the complete removal of particles with the prevention physical damage. For these reasons, the cleaning process requires a high degree of control. In this paper, a new cleaning method was applied to MoSiON-based masks utilizing megasonic cleaning because it had a little change on phase and transmission. Traditional SC-1 chemistry was not used at all. Results obtained through this method showed a little change on phase and transmission. The particles on glass also can be sufficiently removed using megasonic process with the dilute SC-1 chemistry. The cleaning technique for the fabrication of EAPSMs with no variation in phase and transmission after the cleaning process will be presented.
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Se-Jong Choi, Si-Yeul Yoon, Yong-Dae Kim, Hak-Weon Lee, Dae-Hong Kim, Si-Woo Lee, Dong-Heok Lee, Jin-Min Kim, Sang-Soo Choi, Soo Hong Jeong, "Preserving EAPSM Phase and Transmission in the Clean Process", Proc. SPIE 4889, 22nd Annual BACUS Symposium on Photomask Technology, (27 December 2002); doi: 10.1117/12.467480; https://doi.org/10.1117/12.467480

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