Optimization of InP etching using inductively coupled plasma

Abstract

The etching of semiconductor components is one of the most critical process steps in the manufacturing process of semiconductor devices, as the desired pattern can be transferred into the semiconductor wafer with lithography and etching steps. In this Bachelor’s thesis, plasma etching of InP-based semiconductor wafers is optimized in cooperation with Modulight Corporation. The goals are to transfer the etching process from reactive ion etching (RIE) equipment to inductively coupled plasma (ICP) RIE equipment, decrease the etching time, and improve the etching profile.In the future, the process is planned to be used in production. A total of fve 3" InP-based wafers were etched, one reference wafer with RIE and four wafers with ICP-RIE, varying the etching time. Etch depths were measured with a contact proflometer and scanning electron microscope (SEM) to compare the etch depths and the profles of the ridges. The etch depth next to the ridge was also looked at because it is signifcant for the operation of semiconductor devices. The etching process used gave reliable results. It was observed from the results that the etch rate increased, and the etch profle was better in ICP-RIE processes than in the RIE reference. In addition, a profle with undercutting was not formed. It was also found that the etch rate was up to 500 nm/min in ICP-RIE processes, which was 15 times faster than in the RIE reference. On the other hand, the footing value was higher in ICP-RIE etchings when compared to the RIE reference. Moreover, it was observed that possibly the hard mask ran out from the edges of the pattern during longer ICP-RIE etchings, which was caused by mask erosion. Still, after all, the profles were smoother. Overall, the results were promising, and the etching process can be transferred from RIE to ICP-RIE. In the future, a thicker hard mask could be tested to see if the same etch depth can be reached with a mask surviving the whole etch time. In addition, the process parameters could be optimized to decrease the footing. Also, other InP-based compound semiconductors could be tested to see if similar results can be achieved with them.