The deposition of carbon-rich film during etching of aluminum and aluminum oxide surface is studied. When the etching is carried out using a BCl3/CH3OH plasma excited in a parallel-plate magnetron-reactive ion etching reactor, deposits are observed on both aluminum and aluminum oxide surfaces. Analyses of the etched surfaces by x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy show that the deposits consist mainly of carbon with C-C bonds. The analyses also suggest that the deposit is accumulated more easily on the aluminum surface than on the aluminum oxide surface when a small amount of CH3OH is added to BCl3. We consider that this difference in the deposition characteristics is dependent on the oxidation rate of the deposits due to the existence of oxygen on the etched surface. When we selectively etch aluminum oxide against aluminum as an application of these deposition phenomena, a good etching selectivity of more than ten is obtained.