Damage characterisation of InP after reactive ion etching using the low-frequency noise measurement technique

Abstract

Reactive ion etching (RIE) is a basic tool in the processing of InP optoelectronic and photonic integrated circuits (OEICs and PICs). However, due to the bombardment of the high energy ions of the plasma, heavy damage of the semiconductor surface occurs. Additionally, when using a CH 4 + Ar + H 2 plasma significant proton implantation also takes place. Investigating n-type InP etched by specific RIE processes, we show, that the low-frequency noise (LFN) generated in an appropriately designed planar resistor pattern is affected in a characteristic manner depending on the process-parameters. Further, a decrease of the pattern resistance and also significant surface leakage currents were observed, due to a strong enhancement of the surface electron concentration. In n-type material the 1 f noise component is enhanced as the damaged portion of the current path increases. Additionally, generation-recombination (g-r) components are also present in the spectrum indicating that specific deep levels appear in the damaged region. Using rapid thermal annealing (RTA) as a post-process step, the 1 f noise component decreases and the sample resistance increases. At the same time the surface leakage currents disappear. These observations are due to the fact, that an out diffusion of the implanted H + takes place and it is likely that process-induced modifications of the surface layer will tend to recover. To avoid proton implantation, etching only by Ar plasma was investigated. Damage and an enhanced surface conduction were observed. Applying a short HF-dip, a slight increase of the g-r noise intensity was detected.