In this investigation, two kinds of ZrO2 samples were prepared. The ZrO2 films of about 150 Angstrom by PVD were used for physical characterization and the ultrathin ZrO2 films of about 40 Angstrom by RTCVD were used for electrical characterization of MOS capacitors. The samples were annealed in a rapid thermal processing (RTP) system at temperatures of 400-1050 degreesC in various gas ambients, including O-2, N-2, forming gas (H-2/Ar), wet H-2 (15% H2O in H-2), and wet O-2 (15% H2O in O-2). Spectroscopic ellipsometry (SE) with a two layer BEMA optical model was used to characterize the ZrO2 thickness and evaluate the microstructure. A wet etch rate test of ZrO2 films in 1:100 HF solution using SE indicated two distinct etch rates, with a slower initial rate followed by a faster rate. The measured etch rates are dependent of temperature, indicating 4.85 and 38.9 Angstrom /min at 25 and 45 degreesC, respectively. The RTP annealing temperature and gas ambients have a significant effect on the ZrO2 film etch rate. Rutherford backscattering spectrometry (RBS) and x-ray photoelectron spectroscopy depth profile were used to characterize the films. Three ZrO2 samples were measured by both cross section transmission electron microscopy and SE, indicating that the thickness difference between two techniques is only 1 A. A mercury probe was used to characterize the electrical properties of the physical vapor deposition dielectric films. The electrical characterization of ultrathin ZrO2 films show that the gas ambients in postdeposition anneal affect the equivalent oxide thickness (EOT) and leakage current significantly. The lowest EOT achieved in this study is 10.9 Angstrom for the sample spike annealed in N-2. The RTP effect on electrical properties of ultrathin ZrO2 was also discussed.