Polycrystalline silicon (poly-Si) films on glass were prepared by aluminium-induced crystallisation of amorphous silicon (a-Si). During an annealing step at temperatures well below the eutectic temperature of the Al/Si system (Tu = 577 degreesC) a glass/Al/a-Si stack is transformed into a glass/poly-Si/Al + Si stack. In this aluminium-induced layer exchange process the oxidation of the Al layer during the preparation of the initial glass/Al/a-Si stack plays an important role. Here we show that the aluminium oxide layer, which was formed during the preparation of the initial stack, is still present after the annealing step. The Al2O3 layer has corundum structure. The thickness of this layer is laterally inhomogeneous. The nucleation of the poly-Si layer starts at the Al/Al2O3 interface.