Evolution of Morphology During Etching of Si

Abstract

The step morphology of clean Si surfaces has been studied under conditions of thermal etching in the temperature range 950–1250°C. Kinetic-bunching of steps is caused by direct current in the step-down direction around 950°C. By comparing the rate of thermal decay of these structures with and without direct current, the electromigration force causing this step bunching is estimated to be due to an effective charge of less than or approximately 0.01 electron units. Around 1150°C, step-bunching is caused by direct current in the step-up direction. By analysis of the patterns of step structure, the effective charge of the driving force is found to be approximately -0.1 electron units. Oxygen-induced etching of Si(001) and Si(111) has been studied in the temperature range of 700–900 °C, and at a pressure of 5 x 10⁷ torr, conditions under which the surface is etched by the desorption of SiO. On Si(001), the original narrow distribution of double-layer height steps is preserved during the oxygen-etching process. On Si(111), the original narrow distribution of mixed single- and triple-layer height steps changes dramatically during oxygen-etching, leaving wide terraces of flat (111) surface separated by regions of high step density. At low etching temperatures (700°C), the steps remain straight within the step bunches and retain their distinct character as single- and triple-height steps. However, following higher temperature etching, the steps begin to merge into facets in the vicinity of defect structures. Following etching at the highest temperatures studied (815 and 830°C), the pinning action of the defect structures becomes apparent, and the pinned step-bunches become identifiable as (113) facets.