Metal contact printing photolithography for fabrication of submicrometer patterned sapphire substrates for light-emitting diodes

Abstract

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.

Fabrication of a hierarchical patterned sapphire substrate for GaN-based light-emitting diodes

“…The PSS can get more photons generated in the active layer into the air to enhance the LEE. [7,8] To date, different types and morphologies of PSS, from micropatterns to nanopatterns, such as cone-shaped PSS, [9] pyramidally PSS, [10,11] volcano-shaped PSS, [12,13] micro-hole patterns, [14] concave-hexagonal PSS, [15] lensshaped PSS, [16] have been employed in use of GaN-based LEDs. The micro-patterned sapphire substrates (MPSSs) show great performance in both enhancing the LEE and reducing the TD.…”

Fabrication of wafer-scale nanopatterned sapphire substrate by hybrid nanoimprint lithography

“…Recent theoretical and experimental studies 7,8 have suggested that greater light output power (LOP) may be achieved for GaN-based LEDs when nanopatterned sapphire substrates (NPSSs) are used rather than micropatterned sapphire substrates (MPSSs). In recent studies, various state-of-the-art techniques, such as e-beam lithography, 10 metal contact printing photolithography, 11 nanoimprint lithography (NIL), 12 and nanosphere lithography 13 have been used to fabricate NPSSs. 9 However, contact photolithography, which is used for production of MPSSs, is not suitable for patterning in the submicrometer range.…”