Evaluation of plasma-induced damaged structure in InP substrates using conductance analysis

Abstract

III-V semiconductors have attracted attention as high mobility channel materials exceeding the performance limit of Si. However, the electrical characteristics may deteriorate due to the damage caused by dry etching processes. In addition, the analysis method has not been sufficiently established for InP substrate. For example, the C-V characteristics of InP substrate are significantly different from those of Si, so it has become clear that the conventional methods using C-V characteristics are not applicable. In this study, the conductance method using a parallel circuit model was demonstrated for the plasma induced damage analysis in InP substrate.
A 500 nm-epitaxial InP layer grown on InP substrate and p-type Si substrate were prepared. About 5.8nm SiO2 were deposited on each substrate by atomic layer deposition. A dual frequency capacitively coupled plasma (CCP) reactor was used for Ar plasma exposure. The process time was varied from 3 to 300 s, and the peak-to-peak voltage (Vpp) was changed from 270 to 630 V. The equivalent parallel conductance– frequency (Gp/ω–f) characteristics were measured by a mercury probe system. The created defects in the depletion region were quantitatively evaluated in terms of the conductance. By fitting a theoretical model to experimental data, we estimated the defect density and its characteristic relaxation time in the case of Ar plasma exposure.
We found that the plasma exposure changed its conductance in a specific frequency band, and the peak intensity, which was correspond to the defect density, strongly depends on the plasma exposure conditions. The conductance method clarified that one kind of defect level is generated in the InP substrate and a plurality of defect levels are generated on the Si substrate. Having one defect level means that there could be also one type of defect.
We found that the modified conductance method with an equivalent circuit model including the damaged layer can identify the latent defects created in InP substrates after plasma exposures. The obtained results suggest that the modified conductance method is an effective tool to quantify the dynamic behaviors of latent defects in InP substrates, and it enables not only process optimization but also elucidation of defect structures induced by the plasma exposure.