Wet Etching and Surface Analysis of Chemically Treated InGaN Films

Abstract

This paper discusses the performance of different wet chemical etchants on InGaN. It is shown that certain etchants can be used to chemically etch and remove appreciable amounts of InGaN even though the etch rate is not as high as observed for other III-V materials. The performance of etchants studied here were (i) two different ratios of HF, HNO 3 , (ii) cyclic usage of NH 4 OH followed by HCl, (iii) hot H 2 SO 4 and H 3 PO 4 mixture, and (iv) conc. NH 4 OH. The etched surfaces have then been analyzed by x-ray photoelectron spectroscopy (XPS). Different etch residues were observed on the top surface. These results suggest an alternative to reactive plasma etching or photo-enhanced electrochemical etching of InGaN type materials. Based on the observed performance of the etchants studied, it was also possible to segregate the surface cleaning protocols and etchants. It is well known that in semiconductor materials and device fabrication, the important issues are materials' purity, growth, defect control, lithography, etching, contact formation, and device performance.1,2 Among these, etching is an important process in which the grown material is required to be partially removed using specific patterns for subsequent doping, metalization, device structure formation, etc. In such processes, the rate of material removal has to be fast and repeatable. There is another associated process, in which the top layer of a material is cleaned before subsequent growth by removing a few angstroms and associated top layer contaminants. In this cleaning process, it is essential that the top layers are removed with care and the least amount of material is wasted. Thus, this chemical cleaning process has to be one with a slow material removal rate and with the least amount of interfering residues.Such etching and cleaning may be done by electrochemical, wet chemical methods, reactive ion or sputter ion cleaning.3 Electrochemical processes are not always very selective while removing materials and often require very tight control over bias voltages and currents. Wet chemical etching is a method of removing the top layer of a material in a solvent leading to its dissolution in the reaction medium. Often the etchants are a combination of acids or a combination of bases. In wet chemical methods, with proper calibration, it is possible to retain better material crystalline quality of the etched material and by controlling the concentration of chemicals in the reaction, the material removal rate can also be rigorously controlled. However in all etch steps, residues from etching steps are present; these need to be understood to evaluate the likely effects on the subsequent electrical properties of the device created. Wet chemical etching is thus often the preferred etching mechanism for lithographic process. It has often been seen that the traditional wet chemical or electrochemical processes may also have their other limitations, even though they are quite cost effective. Inability to get high etching rates or reaction induced surface p...

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