Characterization of high-K dielectric ZrO2 films annealed by rapid thermal processing

Abstract

In this investigation, two kinds of ZrO2 samples were prepared. The ZrO2 films of about 150 Å by PVD were used for physical characterization and the ultrathin ZrO2 films of about 40 Å 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 °C in various gas ambients, including O2, N2, forming gas (H2/Ar), wet H2 (15% H2O in H2), and wet O2 (15% H2O in O2). 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 Å/min at 25 and 45 °C, 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 Å. 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 Å for the sample spike annealed in N2. The RTP effect on electrical properties of ultrathin ZrO2 was also discussed.