Real-time observation of ion beam eroded silicon surfaces: Ripple propagation, coherence and noise effects in surface erosion

The evolution of ion beam eroded Silicon surfaces was measured in real-time by combining focused ion beam technology with scanning electron microscopy. By detecting the secondary electrons emitted during implantation the surface was monitored in-situ during the erosion process of a Gallium focused ion beam. Repetitive scanning of the ion beam over the surface effectuates a coherent erosion of the exposed surface area, with the continuum theory of erosion as the ergodic limitation. Surface ripple as proposed by linear erosion theory were observed for oblique incidence of the ion beam and their propagation with progressing erosion time as well as their velocity dispersion were monitored. The ripple wavelength has been observed to increase with the erosion time and the value of the ripple velocity was observed to agree qualitatively with the results of Monte-Carlo simulations of the erosion process. Noise effects acompanying the erosion process are found to be responsible for the reorientation of the ripples when the orientation of the ion beam onto the surface is varied. This mechanism is discussed to stimulate further efforts in this field of surface erosion.