The effect of mask substrate and mask process steps on patterned photomask flatness

Kenneth Racette; Monica Barrett; Michael Hibbs; Max Levy

doi:10.1117/12.599598

10 May 2005 The effect of mask substrate and mask process steps on patterned photomask flatness

Kenneth Racette, Monica Barrett, Michael Hibbs, Max Levy

Proceedings Volume 5752, Metrology, Inspection, and Process Control for Microlithography XIX; (2005) https://doi.org/10.1117/12.599598
Event: Microlithography 2005, 2005, San Jose, California, United States

Abstract

Photomask substrate, blank, and finished mask flatness are becoming more serious concerns for photomask fabrication. Most commercial and captive mask houses now use a combination of mask blanks at various flatness levels from >2.0um to <0.5um, measured as total indicated range, or TIR. As mask feature sizes are reduced, depth of focus becomes significantly smaller, driving the need for tighter flatness specifications. Photomask blank suppliers generally specify mask blank flatness based on measurements of quartz substrates before films are deposited. The mask substrates start with unique, non-flat shapes resulting from polishing and are further deformed by the stress of deposited films. Mask patterning, which removes some of the deposited films, has the potential to change the shape and flatness of the mask. The attachment of a pellicle and frame also has the potential to distort the mask. Since the goal of the mask maker is to provide a finished mask meeting all requirements, including flatness, it is important to understand the effects of each step in the flatness life of the photomask. This paper provides flatness data from the following process steps: quartz substrate, chromium coating, phase shifter coating, resist coating, patterned mask and pelliclized mask. A correlation is made of substrate and blank flatness and shape to finished mask flatness, with proposed practical guidelines for control of final mask flatness.

Citation Download Citation

Kenneth Racette, Monica Barrett, Michael Hibbs, and Max Levy "The effect of mask substrate and mask process steps on patterned photomask flatness", Proc. SPIE 5752, Metrology, Inspection, and Process Control for Microlithography XIX, (10 May 2005); https://doi.org/10.1117/12.599598

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