A soft photo-mask with embedded carbon black and its application in contact photolithography

This paper presents a new type of soft photo-mask which can be used in contact photolithography for achieving small line-width, large area, and high throughput ultraviolet (UV) patterning. It starts from a polydimethylsiloxane (PDMS) mold replicated from a silicon master mold. A carbon black photo-resist (PR) is spin-coated on top of the PDMS mold and then thermally cured. After a contact transfer process, the solidified carbon black PR exists only in the concave region of the PDMS mold, which converts the PDMS mold into a carbon-black/PDMS soft photo-mask. Due to its flexibility, this soft photo-mask can be used in contact photolithography on a slightly curved substrate. Experiments on preparing this new soft photo-mask and its application for fabricating patterned sapphire substrates (PSSs) used in the light-emitting-diode (LED) industry are carried out. Successful results are observed.