Experimental quantitative study into the effects of electromigration field moderation on step bunching instability development on Si(111)

摘要

We experimentally studied the effects of a moderated electromigration field on the dynamics of the step bunching process on the Si(l11) surface at 1130 ℃ (regime Ⅱ) and 1270 ℃ (regime Ⅲ). The surfaces with step bunch morphologies were created by annealing vicinal Si(111) at fixed temperatures while the applied electric field E was adjusted for every experiment. Scaling relations, y_m ~ h~step bunch y_m, step bunch height h, and electromigration field E were experimentally probed. Scaling exponents a≈2/3 and q≈1/3 were extracted from the step bunch morphologies created by annealing Si(111) in the regime Ⅲ (1270 ℃), which are in good agreement with the predictions of the generalized BCF theory. Scaling exponents a ≈ 3/5 and q ≈ 1/3 were extracted from the morphologies created by annealing in regime Ⅱ (1130 ℃). This result was compared to the scaling relations derived within the frame of the transparent step model, which correctly predicts the formation of the step bunching instability by step-up adatom electromigration. The scaling relation obtained by experiment was found to differ from the model predictions. We measured values of critical electric field (E_(cr)), i.e., minimum electric field required for the step bunching to take place. A relatively weak field of E > 0.5 V/cm was found to be sufficient to initiate the step bunching process in regime Ⅱ. This contrasts with regime III, where E_(cr) = 1.0 and 2.0 V/cm were measured for Si miscut from the (111) plane by 1.1° and 2.5°, respectively. The increased values of E_(cr) were attributed to the enhanced step-step repulsion in regime Ⅲ. The theoretically predicted formation of compressed step density waves was observed upon annealing in both regimes with E < E_(cr).