Defect Reactions Induced by Reactive Ion Etching

Abstract

ABSTRACTReactive ion etching (RIE) causes substrate surface contamination, substrate damage, and induces defect reactions to produce carrier traps at depths into μm range. We have developed a model describing the indiffusion of interstitials and the subsequent reactions in the defect reaction region to predict the defect depth profiles. We formulate the reaction kinetics as a series of 1-D coupled interstitial diffusion-reaction partial differential equations (PDEs) with a moving boundary. The predicted defect depth profiles are consistent with those measured in the photoluminescence (PL) experiments. We conclude that the defect depth profiles are determined by interstitial diffusion coefficient (Di), etch rate (υE), etch time (tE), defect reaction rate (K), and background dopant and impurity concentrations ([C], [B] and [O]) in the Si substrate. The μm range defect depth profiles can be explained as: (i) fast diffuser Si self-interstitial (Sii) indiffusion to a μm depth range of (Di/K)1/2 limited by [C] and [B]; (ii) the generation of carbon and boron interstitials (Ci and Bi) through the Watkins replacement reactions, and (iii) the formation of Ci- and Bi-related defect pairs through diffusion limited pairing reactions. Ci and Bi indiffusion are limited by υE and extremely shallow (Di/υE) during a typical RIE process with υE≈1000Å/min and tE≈10min. The indiffusion of vacancies (V), contamination from the etching plasma and enhanced diffusion effects are also considered in the model.