Electrochemical and Analytical Study of the Si Etching Mechanism in HF

Abstract

In this work a methodology and metrology for the Si substrate loss characterization during cleaning and etching of Si semiconductor substrate has been developed. Using this methodology, the substrate loss in different HF based cleaning solutions can be investigated, both in situ and ex situ. The etching mechanism in different HF mixtures is studied, where the effect of dissolved O 2 , illumination, free F-ions and additives can be explored. Etch rates are determined ex situ by measuring the Si concentration as function of time with Inductively Coupled Plasma -Mass Spectrometry (ICP-MS). By combining both electrochemical and ICP-MS data, the number of electrons n involved in the electron transfer reaction are determined both in darkness and illumination. Results confirm the existing Si etching mechanism under illumination, with n=2. It is shown that in darkness a low etch rate is observed, and even under deoxygenated HF conditions pointing to some chemical etching mechanism.