Photolithographic Mask Sets with Improved Overlay
Original Publication Date: 1980-Aug-01
Included in the Prior Art Database: 2005-Feb-13
Photolithographic masks with their repeated patterns (chip areas) have to be very accurately positioned, to obtain an optimal overlay when the masks are printed on circuit substrates with patterns previously produced by other masks of the set. Existing step and repeat cameras are not sufficiently accurate for this purpose, even if their position reproduction is interferometrically controlled.