The formation of etch hillocks during step-flow etching of Si(111)

The formation of etch hillocks during NH4F etching of vicinal Si(111) surfaces was investigated by scanning tunneling microscopy and kinetic Monte Carlo simulations. Simple, site-specific reaction kinetics are shown to produce two- and three-dimensional etch hillocks. Two-dimensional hillocks are nucleated at self-propagating defect sites. Their size is kinetically controlled. Simulations showed that three-dimensional hillocks can be caused by the collisions of two-dimensional hillocks.