Deep-UV Conformable-Contact Photolithography for Bubble Circuits
by B. J. Lin
The techniques of deep-ultraviolet (UV) conformable-contact photolithography are described and some preliminary work reported on their application to the fabrication of high-density bubble memory circuits by single-level masking. A quantitative analysis of tolerance requirements for linewidth, mask-to-wafer gap, and exposure is made for printing with conventional UV and deep-UV, for feature sizes in the range 2.5 μm to 0.1 μm. A new type of mask-to-wafer holder is described, utilizing a diaphragm to achieve contact. The holder can be used for either a conformable wafer or a conformable mask, or for both conformable wafer and mask, and for the liquid gap technique. Developmental bubble memory circuits on amorphous and garnet materials have been fabricated using deep-UV conformable-contact photolithography, electroplating, liftoff, and ion milling.