Christian Dussarrat

Controllable synthesis of molybdenum tungsten disulfide alloy for vertically composition-controlled multilayer

The effective synthesis of two-dimensional transition metal dichalcogenides alloy is essential for successful application in electronic and optical devices based on a tunable band gap. Here we show a synthesis process for Mo1−xWxS2 alloy using sulfurization of super-cycle atomic layer deposition Mo1−xWxOy. Various spectroscopic and microscopic results indicate that the synthesized Mo1−xWxS2 alloys have complete mixing of Mo and W atoms and tunable band gap by systematically controlled composition and layer number. Based on this, we synthesize a vertically composition-controlled (VCC) Mo1−xWxS2 multilayer using five continuous super-cycles with different cycle ratios for each super-cycle. Angle-resolved X-ray photoemission spectroscopy, Raman and ultraviolet–visible spectrophotometer results reveal that a VCC Mo1−xWxS2 multilayer has different vertical composition and broadband light absorption with strong interlayer coupling within a VCC Mo1−xWxS2 multilayer. Further, we demonstrate that a VCC Mo1−xWxS2 multilayer photodetector generates three to four times greater photocurrent than MoS2- and WS2-based devices, owing to the broadband light absorption.

A review of cation-ordered rock salt superstructureoxides

The types of structures formed when two or more cations occupy the sodium sites in the NaCl unit cell in a non-random manner are reviewed with reference to the cation arrangement in layers of close-packed octahedra and the cation arrangement in the NaCl subcell. Factors influencing the stability of particular structure types, including bond valence and radius ratios, are discussed.

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.

Atomic layer deposition and characterization of vanadium oxide thin films

In this study, VOx films were grown by atomic layer deposition (ALD) using V(NEtMe)4 as the vanadium precursor and either ozone or water as the oxygen source. V(NEtMe)4 is liquid at room temperature and shows good evaporation properties. The growth was investigated at deposition temperatures from as low as 75 °C, up to 250 °C. When using water as the oxygen source, a region of constant growth rate (ca. 0.8 A/cycle) was observed between 125 and 200 °C, with the ozone process the growth rate was significantly lower (0.31–0.34 A/cycle). The effect of the process conditions and post-deposition annealing on the film structure was investigated. By varying the atmosphere under which the films were annealed, it was possible to preferably form either VO2 or V2O5. Atomic force microscopy revealed that the films were smooth (rms < 0.5 nm) and uniform. The composition and stoichiometry of the films were determined by X-ray photoelectron spectroscopy. Conformal deposition was achieved in demanding high aspect ratio structure.

Improvement in the leakage current characteristic of metal-insulator-metal capacitor by adopting RuO2 film as bottom electrode

The dielectric constant, equivalent oxide thickness (tox), and leakage current properties of Pt/(Al-doped)TiO2/RuO2 capacitors were examined in comparison with Pt/(Al-doped)TiO2/Ru capacitors. The Al-doped TiO2 and undoped TiO2 films grown on RuO2 showed high dielectric constants of 60 and 102, respectively. The minimum tox of these films were 0.46 nm and 0.56 nm, respectively, while still satisfying the dynamic random access memory leakage current density specification (< 1 × 10−7 Acm−2 at capacitor voltage of 0.8 V). These excellent electrical properties of (Al-doped) TiO2 on RuO2 were attributed to the high work function and the reduced interfacial effect on RuO2.

Preparation, thermal stability and crystal structure of a newruthenium(V) oxide containing peroxide ions:Ba5Ru2O9(O2). Structuralrelationships to thehexagonal-type perovskite

The compound Ba 5 Ru 2 O 11 has been synthesized by solid state reactions at 980 °C and 1 atm oxygen pressure. The crystal structure has been determined on a single crystal (R 1 =0.027, wR 2 =0.058). The symmetry is hexagonal (P6 3 /mmc) with the cell parameters a=5.9470(5) A, c=18.0428(10) A, Z=2. Perpendicular to the c-axis, the structure is built up by the periodic stacking of three hexagonal close packed [BaO 3 ] layers separated by a layer of composition [Ba 2 O 2 ] containing (O 2 ) 2- peroxide ions. The detailed formula is then Ba 5 Ru 2 O 9 (O 2 ) if we emphasize the formation of peroxide ions in the phase. The ruthenium(v) ions occupy the octahedral sites formed between the [BaO 3 ] layers (hexagonal perovskite slabs) and then constitute isolated [Ru 2 O 9 ] pairs. Ba 5 Ru 2 O 9 (O 2 ) belongs to a new family of compounds, generically formulated as [A 2 (O 2 )][A n B n -1 O 3n ] wheren represents the number of [AO 3 ] successive layers in the hexagonal perovskite slabs. Each member of the series is an intergrowth of [A 2 (O 2 )] and hexagonal perovskite layers; n=3 corresponds to Ba 5 Ru 2 O 9 (O 2 ). The isostructural phase has been observed when ruthenium is replaced by niobium. The n=4 member and the intergrowth between the n=3 and n=4 members of this family has been observed in the Ba–Nb(Ta)–S ternary systems. The former proposed formula for the ternary barium sulfides is discussed in the light of the framework of this new family.

Ti Source Precursors for Atomic Layer Deposition of TiO2, STO and BST

In this study we evaluated several precursors such as tetrakis(dimethylamino) titanium (TDMAT), tetrakis (diethylamino) titanium (TDEAT), tetrakis(ethylmethylamino) titanium (TEMAT) along with novel PrimeTiTM, StarTiTM and TyALDTM for TiO2 ALD application with both water and ozone as the oxidizer. Each precursor is evaluated with respect to some of the important characteristics like growth rate of TiO2 per ALD cycle, range and upper limit of process temperature window, volatility and stability of precursor, chemistry with desired oxidizer etc., that are critical for the selection of the precursor. All amino-compounds had a narrow process window. Precursor decomposition was observed for TDMAT, TDEAT and TEMAT at temperature higher than 225 oC limiting the deposition process at 225 {degree sign}C. On the other hand, TiO2 ALD using PrimeTiTM and StarTiTM is observed up to 325 and 400 {degree sign}C respectively. Finally, photoelectron spectroscopy analysis of some the films will be discussed.

Plasma-Enhanced Atomic Layer Deposition of Cobalt Using Cyclopentadienyl Isopropyl Acetamidinato-Cobalt as a Precursor

Cobalt plasma-enhanced atomic layer deposition (PE-ALD) using cyclopentadienyl isopropyl acetamidinato-cobalt [Co(CpAMD)] precursor and NH3 plasma was investigated. The PE-ALD Co thin films were produced well on both SiO2 and Si(001) substrates. The deposition characteristics and films properties such as resistivity, chemical bonding states and quantitative impurity level contents were investigated. Especially, Co deposition using this precursor was possible at very low growth temperature as low as 100 °C, which enable the deposition on polymer-based substrate. We demonstrate that this low growth temperature PE-ALD can be applicable to patterning of Co film by lift-off method, which was realized by direct deposition of Co on photoresist patterned substrate.

Tuning of Material and Electrical Properties of Strontium Titanates using Process Chemistry and Composition

In this work, we study the compatibility of a highly volatile strontium precursor, HyperSr, which has a low melting point, good thermal stability and good reactivity, with various Ti precursors for atomic layer deposition (ALD) of strontium titanates (STO). Novel Ti precursors studied for STO deposition include PrimeTi & StarTi. We will then discuss the interesting trends in material properties observed in STO films deposited with various compositions. X-ray photoelectron spectroscopic analysis of ALD SrO films showed the presence of carbonate groups in the film. There is the potential that this carbonate species is inherent to the ALD process; however, it has been reported that SrCO3 forms when SrO films are exposed to atmospheric CO2. To isolate the effects of atmospheric exposure on the carbonate formation in the film, a TiO2 capping layer is used on the surface of ALD SrO films and the resulting film structures are analyzed.

Mitigation of plasma-induced damage in porous low-k dielectrics by cryogenic precursor condensation

The present work describes the plasma etch properties of porous organo-silicate materials at cryogenic temperature. The mechanism of plasma damage is studied by means of in situ ellipsometry and post-etch material evaluation. Using conventional volatile reactants such as SF6, it is found that low plasma damage can be achieved below -120 degrees C through two main channels: pore sidewall passivation by molecular SF6 and partial condensation of non-volatile etch by-products. The protection can be enhanced by means of gas phase precursors with low saturated vapor pressure. Using C4F8, complete pore filling is achieved at -110 degrees C and negligible plasma-induced damage is demonstrated on both blanket and patterned low-k films. The characteristics of the precursor condensation process are described and discussed in detail, establishing an optimal process window. It is shown that the condensation temperature can be raised by using precursors with even lower vapor pressure. The reported in situ densification through precursor condensation could enable damage-free plasma processing of mesoporous media.