Deposition of HfO2, Gd2O3 and PrOx by Liquid Injection ALD Techniques

Thin films of hafnium oxide (HfO2), gadolinium oxide (Gd2O3), and praseodymium oxide (PrOx) 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(mmp)3], or [Pr(mmp)3] (mmp = OCMe2CH2OMe) and water vapor. X‐ray diffraction (XRD) analysis showed that as‐grown films of HfO2 were amorphous, but these crystallized into the monoclinic phase after annealing in air at 800 °C. XRD analysis showed that as‐grown Gd2O3 and PrOx films had some degree of crystallinity. Residual carbon (0.8–3.3 at.‐%) was detected in the HfO2 and PrOx films by Auger electron spectroscopy (AES), but not in the Gd2O3 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. Thin films of HfO2, (Figure) Gd2O3, and PrOx have been deposited by liquid injection ALD. XRD analysis shows that as‐grown films of HfO2 are amorphous, but crystallize into the monoclinic phase after annealing in air; as‐grown Gd2O3 and PrOx films have some degree of crystallinity. In each case, ALD growth was not fully self‐limiting; this is attributed to the β‐hydride elimination of the mmp (OCMe2CH2OMe) group of the precursors, liberating alkene and generating reactive [M‐OH] surface sites during each ALD cycle.