Paper EM-FrM5
A Comparison of the Nucleation and Growth of HfO₂ Thin Films Deposited by ALD Using TEMAH and TDMAH Precursors

Friday, October 19, 2007, 9:20 am, Room 612

A hot wall Atomic Layer Deposition (ALD) flow reactor has been used for the comparison of two different HfO₂ ALD chemistries: tetrakis (ethylmethylamino) hafnium (TEMAH) and H₂O, and tetrakis (dimethylamino) hafnium (TDMAH) with H₂O on H-terminated Si and SC1 chemical oxide starting surfaces. Spectroscopic ellipsometry (SE) confirms linear growth of the films with a growth rate of ~1.2 Å/cycle at 250°C for the TEMAH process, and ~1.0 Å/cycle at 275°C for the TDMAH process. Nucleation and initial growth behavior of the films were examined using x-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS). RBS indicates an initial 4-7 cycle nucleation barrier for the Si-H surface with both metal-organic precursors, before the growth rates on that surface match those on SC1. Steady-state coverage is attained after a ‘conditioning’ period of about 45 ALD cycles for TEMAH, as opposed to only 20 cycles with TDMAH. However, TEMAH results in a higher steady-state coverage rate of 3.1x10¹⁴ Hf/cm² on both starting surfaces, compared to 2.4x10¹⁴ Hf/cm² and 2.7x10¹⁴ Hf/cm² for the Si-H and SC1 surfaces with TDMAH. A comparison of the growth rate measurements with RBS and SE indicates that the HfO₂ films grown from TEMAH appear to reach about 85% of their bulk density on both starting surfaces while TDMAH results in 85% bulk density for the Si-H surface and 95% density on the SC1 surface. XPS is implemented to examine the Si/HfO₂ interfacial region for films grown on the Si-H starting surface. Angle-resolved scans ranging from 0-60° (measured from the surface normal) are taken for samples prepared with both precursors, ranging from 4-25 ALD cycles. For the TEMAH films, we detect a ~7 Å SiO_x/silicate interfacial layer which remains practically unchanged up to 50 ALD cycles as indicated by HRTEM data. In the TDMAH/H₂O process, the interface appears to be initially unstable, and the interfacial layer increases from ~6 Å at 4 cycles up to ~18 Å at 25 cycles. This unstable interface may be due to a more porous film structure, and/or the slightly higher deposition temperature than that of the TEMAH process (275 vs. 250 °C) which may enhance interface oxidation.