This paper reports the application of novel contact printing lithography to fabricating patterned sapphire substrates (PSSs) used in light emitting diodes (LEDs). This contact printing lithography method can directly transfer a metal film pattern from a silicon mold to a sapphire substrate, and subsequently use the transferred metal film pattern as the etching mask for inductively coupled plasma etching on the sapphire substrate. The strength of this new approach lies on its capability of achieving sub-micrometer-or nanometer-scaled patterning in a direct, easy and large-area way as well as for obtaining deeper etching depth on sapphire because of excellent etching selectivity of metal films. Experiments have been carried out to demonstrate the feasibility of using this new approach for obtaining sub-micrometer surface structures on the complete surface area of a 2 sapphire substrate. The PSSs can be used for high brightness LEDs.

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.

This paper reports an improved method that combines a metal film contact printing method with traditional photolithography for fabrication of submicrometer-scale patterned sapphire substrates (PSSs) used for high-brightness light-emitting diodes (LEDs). First, a patterned metal thin film is transferred from the surface of a mold onto a photoresist (PR) layer deposited on top of the sapphire substrate. The transferred metal pattern acts as a photomask for subsequent photolithographic processes. PR structures with a high aspect ratio of 5 and a small line width of 500 nm are fabricated on 2 and 4 in. sapphire wafers. Finally, inductively coupled plasma etching is performed on the sapphire substrates to obtain PSSs by using the patterned PR microstructures as an etching mask. Experiments have been performed and both 2 and 4 in. PSSs with submicrometer-scaled and cone-shaped surface features were successfully obtained. These PSSs can be used in the LED industry to obtain high-brightness LEDs.

The influences of pattern size and etching depth of patterned sapphire substrates (PSSs) on crystal quality and light output power of light-emitting diodes (LEDs) were investigated by contact-transferred and mask-embedded lithography. The present results indicate that a smaller pattern size facilitates superior light extraction efficiency. However, a suitable pattern size and etching depth should be chosen to obtain the highest quality of GaN film. In comparison with the conventional sapphire substrate, the largest light output enhancement (∼28.9%) was observed when the pattern diameter and the etching depth of PSS were 400 and 400 nm, respectively.