Electrochemistry of Silicon Carbide Semiconductors

Abstract

Due to the distinctive chemical and physical properties of silicon carbide, interest in the material as a substrate for semiconductor industry has risen significantly during the past two decades. As a wide bandgap semiconductor, SiC is known to be highly chemically inert. On one hand, this high stability opens up a wide field of possible applications, on the other hand it introduces new challenges regarding surface processing. (Photo-assisted) anodic etching as a specific form of wet etching represents a possible approach, for which the particular mechanisms and surface reactions are not elucidated yet. Modification of n-type SiC is done using a combination of anodic polarization and irradiation with UV light in a liquid electrolyte. In this work, the Si face of SiC wafers is investigated. Different electrolytes relevant for etching, e.g. hydrofluoric acid (HF), sulfuric acid (H2SO4), potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH), are used. Etching in n-SiC occurs according to three fundamental steps: (1) Generation of electron-hole pairs through UV illumination (2) oxidation of Si and C (3) dissolution of SiOx in the electrolyte [1]. The electrochemical measurements are evaluated using highly surface sensitive analytical techniques, such as X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Angle resolved XPS (ARXPS) further allows qualitative and quantitative analysis of surface species in dependence of depth distribution. Gathering information about surface elements and their quantities, binding states and depth distribution permits to draw a connection between electrochemical processes and measureable surface conditions. Further aspects, like the effect of etching on surface morphology and roughness, need to be taken into consideration. References [1] Zhuang and Edgar, "Wet etching of GaN, AlN, and SiC: A review," Materials Science and Engineering: Reports, vol. 48, no. 1, pp. 1-46, 2005.