Simulations of side-wall profiles in reactive ion etching

Side-wall profiles have been calculated for sputtering of amorphous Si substrates using an Ar plasma, under conditions typically used for reactive ion etching of semiconductor materials. The authors combine ion energy and angular distributions, calculated for ions travelling through the oscillating RF sheath, with a description of the interaction of these ions with an amorphous Si surface. Resultant side-wall profiles are presented for a range of plasma parameters, including reactor pressure, applied RF voltage and frequency, resist erosion rates and chemical etching component. Calculated profiles show the generic forms of profiles seen in experimental etch processes. Low-pressure plasmas give rise to vertical, anisotropic side-walls with rough surfaces, whilst higher pressure plasmas produce smoother surfaces and exhibit a degree of mask undercut. Resist erosion during the etch process gives rise to sloping side-walls, whilst chemical etching effects produce isotropic profiles characteristic of wet etching.