Impact of Hf-Precursor Choice on Scaling and Performance of High-k Gate Dielectrics

Abstract

Downscaling of CMOS gate stacks requires introduction of ultra-thin high-k dielectrics such as HfO2. Atomic Layer Deposition has excellent characteristics for depositing such films. We have compared HfCl4/H2O and TEMAH/O3 ALD between 245ºC and 370ºC. Growth behavior and electrical performance are discussed as function of process parameters. Precursor choice has a clear impact on HfO2 deposition process and device performance. Both precursors demonstrate good growth nucleation on -OH rich starting surfaces. TEMAH shows better nucleation on low -OH density surfaces, suggesting a potential advantage for interface optimization towards low EOT. However, with HfCl4 lowest leakage currents were obtained as well as excellent interface scaling results by using well chosen interface layers. The leakage current of TEMAH/O3 layers strongly depends on the ALD process temperature and oxidizer dose, suggesting the impact of C impurities on the dielectric properties. Overall the HfCl4 approach seems to be the most promising solution.