Deposition of HfO2, Gd2O3 and PrOx by liquid injection ALD techniques

Thin films of hafnium oxide (HfO 2 ), gadolinium oxide (Gd 2 O 3 ), and praseodymium oxide (PrO x ) have been deposited by liquid injection atomic layer deposition (ALD) and for comparison, have also been deposited by thermal metal-organic (MO) CVD using the same reactor. The ALD-grown films were deposited on Si(100) over a range of substrate temperatures (150-450 °C) using alternate pulses of [Hf(mmp) 4 ], [Gd(rump) 3 ], or [Pr(mnip) 3 ] (mmp = OCMe 2 CH 2 OMe) and water vapor. X-ray> diffraction (XRD) analysis showed that as-grown films of HiO 2 were amorphous hut these crystallized into the monoclinic phase after annealing in air at 800 °C. XRD analysis showed that as-grown Gd 2 O 3 and PrO x films had some degree of crystallinity. Residual carbon (0.8-3.3 at.-%) was detected in the HfO 2 and PrO, films by Auger electron spectroscopy (AF-S). but not in the Gd 2 O 3 films. The self-limiting behavior of the precursors was investigated at 225 °C by varying the volume of precursor injected during each ALD cycle and, in each case, oxide growth was not fully self-limiting. We propose a mechanism for this involving β-hydride elimination of the mmp group, and also propose some general mechanistic principles which may influence the growth of oxides by ALD using other precursors.