Quantitative Characterization of Plasma-Induced Defect Generation Process in Exposed Thin Si Surface Layers

Abstract

The defect generation process in Si surface layer induced by plasma exposures is studied by two optical analyses, spectroscopic ellipsometry (SE) and photoreflectance spectroscopy (PR). Two plasma sources with Ar-gas mixtures are employed; one is DC plasma and the other, electron cyclotron resonance (ECR) plasma. In the case of Ar-DC plasma exposure with 300 V bias, the SE analysis with an optimized optical model determines 1-nm-thick interfacial layer (IL) between the surface layer and the substrate, while in the case of the ECR, approximately 0.5-nm-thick interfacial layer is identified. This difference is attributed to that in self-bias voltages (Vdc) between two plasma sources. In order to quantify the damage, we have modified the PR analysis technique in order to evaluate the plasma-induced carrier trap site density, by correlating the Si surface potential change to the trapped carrier density. Combined with the results by plasma diagnostics, we found that the calculated defect generation probabilities by an impinging ion were the orders of 10-2 and 10-5 in the present DC and ECR plasma conditions, respectively, and that the probability depends on the Vdc. The obtained results enable us to predict the plasma-induced physical damage to the devices in advance at the stage of plasma process designs.