Contact photolithography using a carbon-black embedded soft photomask and ultraviolet light emitting diodes with application on patterned sapphire substrates

This paper presents a contact photolithography method for large-area ultraviolet (UV) patterning using a soft polydimethylsiloxane (PDMS) photomask and a planar light source consisting of arrayed light-emitting diodes (LEDs). With simple design and construction, the UV light source can achieve uniformly distributed UV light intensity over an area of 4′ in diameter but its divergent angle is 15°. To overcome this large divergent angle, a PDMS soft mold embedded with carbon-black inserts as the UV light blocking materials is applied. It is demonstrated that, when increasing the aspect ratio of the carbon-black inserts, one can achieve excellent UV patterning results. Both experimental data and simulation results are presented. This contact photolithography system has been successfully used for manufacturing patterned sapphire substrates (PSSs) in LED industry. The advantages and potential applications of the proposed method will be addresses.