Secondary ion mass spectrometry analyses were carried out using a metal cluster complex ion of Ir4(CO)7+ as a primary ion beam. Depth resolution was evaluated as a function of primary ion species, energy, and incident angle. The depth resolution obtained using cluster ion bombardment was considerably better than that obtained by oxygen ion bombardment under the same experimental condition due to reduction of atomic mixing in the depth. The authors obtained a depth resolution of ∼1 nm under 5 keV, 45° condition. Depth resolution was degraded by ion-bombardment-induced surface roughness at 5 keV with higher incident angles.