Nicolas Blasco

Semiconductor-metal transition in thin VO2 films grown by ozone based atomic layer deposition

Vanadium dioxide (VO2) has the interesting feature that it undergoes a reversible semiconductor-metal transition (SMT) when the temperature is varied near its transition temperature at 68°C.1 The variation in optical constants makes VO2 useful as a coating material for e.g. thermochromic windows,2 while the associated change in resistivity could be interesting for applications in microelectronics, e.g. for resistive switches and memories.3 Due to aggressive scaling and increasing integration complexity, atomic layer deposition (ALD) is gaining importance for depositing oxides in microelectronics. However, attempts to deposit VO2 by ALD result in most cases in the undesirable V2O5. In the present work, we demonstrate the growth of VO2 by using Tetrakis[EthylMethylAmino]Vanadium and ozone in an ALD process at only 150°C. XPS reveals a 4+ oxidation state for the vanadium, related to VO2. Films deposited on SiO2 are amorphous, but during a thermal treatment in inert gas at 450°C VO2(R) is formed as the first and only crystalline phase. The semiconductor-metal transition has been observed both with in-situ X-ray diffraction and resistivity measurements. Near a temperature of 67°C, the crystal structure changes from VO2(M1) below the transition temperature to VO2(R) above with a hysteresis of 12°C. Correlated to this phase change, the resistivity varies over more than 2 orders of magnitude.

Novel mixed alkylamido-cyclopentadienyl precursors for ALD of ZrO2 thin films

Mixed alkylamido-cyclopentadienyl compounds of zirconium, (RCp)Zr(NMe2)3 (R = H, Me or Et) are introduced as precursors for atomic layer deposition (ALD) of high permittivity zirconium oxide thin films. Ozone was used as the oxygen source. Only slight differences were observed in the ALD growth characteristics between the three liquid precursors. The ALD-type growth mode was verified at 300 °C with a growth rate of about 0.9 A cycle−1. Good film conformality was observed, as step coverages of 80–90% were measured for films deposited onto high aspect ratio (60 : 1) trenches. As compared to the commonly used Zr(NEtMe)4 precursor, these novel precursors showed comparative volatility and growth rate but higher thermal stability, as well as lower impurity content in the deposited stoichiometric ZrO2 films. The films deposited by the (RCp)Zr(NMe2)3/O3 processes tended to crystallize in the high temperature cubic form even when the film thickness exceeded 50 nm, while the Zr(NEtMe)4/O3 process resulted in films with mixed phases. The cubic phase ensures high permittivity and thus the capacitance equivalent thickness remained extremely low, even below 0.8 nm, with low leakage current density of 10−7 A cm−2 at 1 V when a 6.4 nm ZrO2 film was deposited on TiN.

Low temperature plasma-enhanced atomic layer deposition of thin vanadium nitride layers for copper diffusion barriers

Thin vanadium nitride (VN) layers were grown by atomic layer deposition using tetrakis(ethylmethylamino)vanadium and NH3 plasma at deposition temperatures between 70 °C and 150 °C on silicon substrates and polymer foil. X-ray photoelectron spectroscopy revealed a composition close to stoichiometric VN, while x-ray diffraction showed the δ-VN crystal structure. The resistivity was as low as 200 μΩ cm for the as deposited films and further reduced to 143 μΩ cm and 93 μΩ cm by annealing in N2 and H2/He/N2, respectively. A 5 nm VN layer proved to be effective as a diffusion barrier for copper up to a temperature of 720 °C.