Ultrasonic-Assisted Electrochemical Nanoimprint Lithography: Forcing Mass Transfer to Enhance the Localized Etching Rate of GaAs.

Electrochemical nanoimprint lithography (ECNL) has emerged as a promising technique for fabricating three-dimensional micro/nano-structures (3D-MNSs) directly on semiconductor wafers. This technique is based on a localized corrosion reaction induced by the contact potential across the metal/semiconductor boundaries. The anodic etching of semiconductor and the cathodic reduction of electron acceptors occur at the metal/semiconductor/electrolyte interface and the Pt mold surface, respectively. However, the etching rate is limited by the mass transfer of species in the ultrathin electrolyte layer between the mold and the workpiece. To overcome this challenge, we introduce the ultrasonics effect into the ECNL process to facilitate the mass exchange between the ultrathin electrolyte layer and the bulk solution, thereby improving the imprinting efficiency. Experimental investigations demonstrate a positive linear relationship between the reciprocal of the area duty ratio of the mold and the imprinting efficiency. Furthermore, the introduction of ultrasonics improves the imprinting efficiency by approximately 80 %, irrespective of the area duty ratio. The enhanced imprinting efficiency enables the fabrication of 3D-MNSs with higher aspect ratios, resulting in a stronger light trapping effect. These results indicate the prospective applications of ECNL in semiconductor functional devices, such as photoelectric detection and photovoltaics.