Femtosecond laser lithography technique for submicron <inline-formula><math display="inline" overflow="scroll"><mrow><mi>T</mi></mrow></math></inline-formula>-gate fabrication on positive photoresist

Abstract

Femtosecond lasers have been found suitable for maskless photolithography with submicron resolution, which is very attractive for solving the problem of high photomask cost. Direct femtosecond laser writing of lithographic patterns is reported with submicron feature width on thin positive photoresist film. We use a scanning electron microscope to investigate the feature sizes of femtosecond laser lithography, which are determined by the incident laser power, the number of scan times and the substrate materials. Submicron T -shaped gates have been fabricated using a two-step process of femtosecond laser lithography where the gate foot and head can be separately defined on positive AZ4620 photoresist film. This work has led to the stable fabrication of sub-300 nm T -gates on the samples of GaN on sapphire substrate and AlGaN/GaN on Si substrate.

Two-photon nanolithography of positive photoresist thin film with ultrafast laser direct writing

“…By combining TPNL of positive photoresist with semiconductor devices processing techniques, we have fabricated a T-gate with a gate length of about 200 nm on the AlGaN/GaN substrate. 17,18 In this letter, we report a smallest trench width of 85 nm achieved by using TPNL of a commercial positive photoresist thin film and study the mechanism of the cross-section shape formation and spatial resolution theoretically and experimentally.…”

Tunable reflection coating to reduce exposure power threshold for interference-assisted two-photon polymerization lithography

“…The development of TPP lithography for more than two decades has demonstrated enormous advantages in the field of 3D photonic devices, but there are few reports on the fabrication of 2D semiconductor electronic devices. 7) Different from traditional TPP on glass substrates, [8][9][10] semiconductor devices require lithographic substrates to be SOI, 11) silicon, 12,13) silicon nitride, 14) metal, 15,16) and other reflective/opaque substrates, 17) etc. However, due to the high spatial coherence of the light source in TPP, when the laser is focused on the photoresist-substrate interface, the incident light and the reflected light interfere and superimpose to form a standing wave, resulting in periodic undulating oscillations at the side wall of the photoresist pattern.…”