8 October 2014 Plasma technology for advanced quartz mask etching
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Abstract
We review the state-of-art and issues of dry etching of masks for nano-device photo lithography. After introducing the basics of photo-mask structures and their plasma etching, we discuss the specifics of mask etching as compared to the etching of silicon wafers, focusing on processes for the two most-challenging cases: phase-shift masks and NGL where it is achieved by etching the quartz exactly to the prescribed depth. State-of the art solutions for the etching of such masks must provide stringent etching uniformity and accurate end-point monitoring. This can be addressed by either reducing the lithography fields to half or even quarter of their present area, with two to four times worse productivity, or working with larger masks of 9 and later 12 inch. The pressure for such development is becoming stronger with the wider adoption of 450 mm wafers. The new masks may need to be thicker to prevent unwanted deformations. Etching uniformity will have to be sustained over much wider areas. Furthermore, RF bias control for thicker substrates is not straightforward due to the quartz impedance preventing effective RF coupling. Our etching experiments in Ar and Cl2 showed that well established mask etching conditions can be reproduced for moderately thicker substrates, while further increase of substrate thickness may require essentially different approach, such as a series resonance of the inductive plasma bulk and the capacitive sheath.
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Munenori Iwami, Munenori Iwami, Hirotsugu Ita, Hirotsugu Ita, Yoshihisa Kase, Yoshihisa Kase, Hidehito Azumano, Hidehito Azumano, Kazuki Nakazawa, Kazuki Nakazawa, Yoshie Okamoto, Yoshie Okamoto, Hiroki Shirahama, Hiroki Shirahama, Tomoaki Yoshimori, Tomoaki Yoshimori, Makoto Muto, Makoto Muto, Ivan Ganachev, Ivan Ganachev, } "Plasma technology for advanced quartz mask etching", Proc. SPIE 9235, Photomask Technology 2014, 92350D (8 October 2014); doi: 10.1117/12.2073069; https://doi.org/10.1117/12.2073069
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