Laser-induced photoelectrochemical lithography

Abstract

While photolithography stands as the predominant industrial methodology for the fabrication of functional three-dimensional micro-/nano-structures (3D-MNSs) in micro-/nano-devices, researchers continue to pursue an alternative avenue of using laser-induced photoelectrochemical (PEC) lithography directly on a semiconductor wafer. This innovative approach avoids the use of photoresists, auxiliary processes, and high-power laser sources. Unfortunately, the continuous use of strong chemical etchants employed in semiconductor industry, e.g., concentrated H₂SO₄/H₂O₂ or KOH solutions, poses challenges in excluding the interference of chemical etching on PEC etching processes. This challenge manifests in the notable deterioration of shape preservation, i.e., the feature sizes of the obtained 3D-MNSs seriously deviate from the structured photo-field. To address this, we developed a laser-induced PEC lithography (PECL) approach by employing a special etchant that acts as the acceptor of photogenerated electrons without chemically reacting with gallium arsenide (GaAs). Because excessive chemical etching was avoided, the illuminated GaA wafer undergoing PEC etching by the photogenerated holes is more significant, resulting in the anticipated machining accuracy. We systematically investigated technical parameters and controllably fabricated sinusoidal holographic grating within minutes, with the grating period aligning with the structured photo-field. The mean squared error of the feature size was controlled to as low as 0.96%. Its exceptional accuracy and efficiency make PECL a competitive technique for realizing functional 3D-MNSs in semiconductor micro-optical devices.