Selective Atomic Layer Deposition Mechanism for Titanium Dioxide Films with (EtCp)Ti(NMe₂)₃: Ozone versus Water

The need for the conformal deposition of TiO₂ thin films in device fabrication has motivated a search for thermally robust titania precursors with noncorrosive byproducts. Alkylamido-cyclopentadienyl precursors are attractive because they are readily oxidized, yet stable, and afford environmentally mild byproducts. We have explored the deposition of TiO₂ films on OH-terminated SiO₂ surfaces by in situ Fourier transform infrared spectroscopy using a novel titanium precursor [(EtCp)­Ti­(NMe₂)₃ (<b>1</b>), Et = CH₂CH₃] with either ozone or water. This precursor initially reacts with surface hydroxyl groups at ≥150 °C through the loss of its NMe₂ groups. However, once the precursor is chemisorbed, its subsequent reactivities toward ozone and water are very different. There is a clear reaction with ozone, characterized by the formation of monodentate formate and/or chelate bidentate carbonate surface species; in contrast, there is no detectable reaction with water. For the ozone-based ALD process, the surface formate/carbonate species react with the NMe₂ groups during the subsequent pulse of <b>1</b>, forming TiOTi bonds. Ligand exchange is observed within the 250–300 °C ALD window. X-ray photoelectron spectroscopy confirms the deposition of stoichiometric TiO₂ films with no detectable impurities. For the water-based process, ligand exchange is not observed. Once <b>1</b> is adsorbed, there is no spectroscopic evidence for further reaction. However, there is still TiO₂ deposition under typical ALD conditions. Co-adsorption experiments with controlled vapor pressures of water and <b>1</b> indicate that deposition arises solely from <b>1</b>/water <i>gas-phase</i> reactions. This striking lack of reactivity between chemisorbed <b>1</b> and water is attributed to the electronic and steric effects of the EtCp group and facilitates the observation of gas-phase reactions

Highly Conformal Amorphous W–Si–N Thin Films by Plasma-Enhanced Atomic Layer Deposition as a Diffusion Barrier for Cu Metallization

Ternary and amorphous tungsten silicon nitride (W-Si-N) thin films were grown by atomic layer deposition (ALD) using a sequential supply of a new fluorine-free, silylamide-based W metallorganic precursor, bis(tert-butylimido)bis(bis(trimethylsilylamido))tungsten(VI) [W(NtBu)(2){N(SiMe3)(2)}(2)], and H-2 plasma at a substrate temperature of 300 degrees C. Here, W(NtBu)(2){N(SiMe3)(2)}(2) was prepared through a metathesis reaction of W(NtBu)(2)Cl-2(py)(2) (py = pyridine) with 2 equiv of LiN(SiMe3)2 [Li(btsa)]. The newly proposed ALD system exhibited typical ALD characteristics, such as self-limited film growth and linear dependency of the film growth on the number of ALD cycles, and showed a high growth rate of 0.072 nm/cycle on a thermally grown SiO2 substrate with a nearly zero incubation cycle. Such ideal ALD growth characteristics enabled excellent step coverage of ALD-grown W-Si-N film, similar to 100%, onto nanotrenches with a width of 25 nm and an aspect ratio similar to 4.5. Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy analysis confirmed that the incorporated Si and W were mostly bonded to N, as in Si-N and W-N chemical bonds. The film kept its amorphous nature until annealing at 800 degrees C, and crystallization happened at local areas after annealing at a very high temperature of 900 degrees C. An ultrathin (only similar to 4 nm thick) ALD-grown W-Si-N film effectively prevented diffusion of Cu into Si after annealing at a temperature up to 600 degrees C

Direct solvothermal synthesis of early transition metal nitrides

Solvothermal reactions of TaCl5 with LiNH2 in benzene result in nanocrystalline Ta3N5 at 500 or 550 °C. The 25 nm Ta3N5 particles have a band gap of 2.08?2.10 eV. The same reactions in mesitylene resulted in a higher crystallization temperature and large amounts of carbon incorporation due to solvent decomposition. Reactions of Ta(NMe2)5 with LiNH2 under the same conditions resulted in TaN. Rocksalt-type MN phases are obtained for Zr, Hf, or Nb when their chlorides (ZrCl4, HfCl4, or NbCl5) or dialkylamides (M(NEtMe)4, M = Zr, Hf) are reacted with LiNH2 under similar conditions. With the amides, there is some evidence for nitrogen-rich compositions (HfN&gt;1), and carbon is incorporated into the products through pyrolysis of the dialkylamide groups