We have examined the structure of ultrathin ZrO(2) layers on Si(001) using medium energy ion scattering and cross-sectional transmission electron microscopy. Films can be deposited on SiO(2) layers with highly abrupt interfaces by atomic layer deposition. On HF stripped Si(001), nucleation was inhibited, resulting in poorer film morphology. ZrO(2) showed remarkable stability against silicate formation, with no intermixing even after high temperature oxidation. The oxide is vulnerable to high temperature vacuum annealing, with silicidation occurring at temperatures above 900 degrees C. (C) 2000 American Institute of Physics. [S0003- 6951(00)03204-6].