Kinetic Investigation on the Confined Etching System of n-Type Gallium Arsenide by Scanning Electrochemical Microscopy

Abstract

Confined etchant layer technique (CELT) has been proved an effective electrochemical microfabrication method for both 3D microstructures and a supersmooth surface. From a physical chemistry viewpoint, the confined etching system of n-GaAs includes an etchant generation reaction from Br– to Br2 (E) followed by two parallel reactions: the confining reaction between Br2 and l-cystine (C1), and the etching reaction between Br2 and n-GaAs (C2). In this paper, the homogeneous EC1 process is investigated first through the tip generation/substrate collection (TG/SC) mode of scanning electrochemical microscopy (SECM), and the reaction rate of C1 is determined as (8.0 ± 1.0) × 103 dm3 mol–1 s–1; second, the heterogeneous EC2 process is investigated through the feedback mode of SECM, and the reaction rate of C2 is determined as (3.2 ± 0.5) × 10–2 cm s–1; third, a deformed geometry finite element model is established to simulate the etching topography coupling E(C1∥C2) processes by using the obtained data. The theoretical profiles of pits etched at different concentrations of scavenger, l-cystine, are analyzed and compared with experimental results. This model allows the prediction of spatial resolution of CELT as a function of reaction rates of C1 and C2 but also of the concentration of scavenger.