Use of electrical test structures to characterize trench profiles etched on SOI wafers

This paper demonstrates the use of electrical test structures patterned on silicon-on-insulator (SOI) material to evaluate the performance of the plasma etching process. Electrical characterization is performed by capacitance and resistance measurements. The measurements are used to compare the etch results of slightly varied plasma etch processes. Subtle differences in submicron trench profiles are very difficult to distinguish and quantify when using scanning electron microscopy (SEM). The electrical measurements can reveal these differences, facilitating etch process development. Experimental results are presented and compared to cross-sectional SEM analysis. The goal of the development of test structures presented here is to establish a fast, low cost, and nondestructive method to characterize and optimize deep trench etching process cycles needed in the fabrication of micromachined devices.