Gautam Meda

13.2: Support Design for Reducing the Sag of Horizontally Supported Sheets

At some stages in the manufacture of liquid crystal display panels, thin glass sheets are stacked horizontally in cassettes. The sheets sag to gravity; with the ever-increasing sheet size and decreasing sheet thickness, the amount of sag has been increasing. Excessive sag is undesirable, since it limits the number of sheets that can be tracked in a cassette of given height. In this note, I describe some support designs that lead to reduced sag.

Reflecting-surface distortion when mirrors are cut to shape

Sometimes, glass mirrors are cut to final shape after they are polished. The cuts may relieve residual stresses in the glass, thereby leading to distortion of the carefully polished reflecting surfaces. To aid in selecting a glass blank for making a mirror, it would be useful if we could predict the amount of post-polish distortion that a specific choice of blank would lead to. In this note, I describe how to make such predictions, using an example. Cases considered so far indicate that Corning Ultra Low Expansion glass (ULE) blanks, if properly chosen, lead to post-polish distortion that is low enough to be acceptable for extreme ultraviolet lithography applications.