Guo-Ping Ru

Atomic layer deposition of TiO2 from tetrakis-dimethyl-amido titanium or Ti isopropoxide precursors and H2O

Atomic layer deposition (ALD) of TiO2 thin films using Ti isopropoxide and tetrakis-dimethyl-amido titanium (TDMAT) as two kinds of Ti precursors and water as another reactant was investigated. TiO2 films with high purity can be grown in a self-limited ALD growth mode by using either Ti isopropoxide or TDMAT as Ti precursors. Different growth behaviors as a function of deposition temperature were observed. A typical growth rate curve-increased growth rate per cycle (GPC) with increasing temperatures was observed for the TiO2 film deposited by Ti isopropoxide and H2O, while surprisingly high GPC was observed at low temperatures for the TiO2 film deposited by TDMAT and H2O. An energetic model was proposed to explain the different growth behaviors with different precursors. Density functional theory (DFT) calculation was made. The GPC in the low temperature region is determined by the reaction energy barrier. From the experimental results and DFT calculation, we found that the intermediate product stability ...

Improved barrier properties of ultrathin Ru film with TaN interlayer for copper metallization

The properties of ultrathin ruthenium (∼5nm)∕TaN(∼5nm) bilayer as the copper diffusion barrier are studied. Cu, Ru, and TaN thin films are deposited by using the ion beam sputtering technique. The experimental results show that the thermal stability of the Cu∕Ru∕TaN∕Si structure is much more improved than that of the Cu∕Ru∕Si structure, which should be attributed to the insertion of the amorphous TaN interlayer. The microstructure evolution of the Cu∕Ru∕TaN∕Si structure during annealing is also discussed. The results show that the Ru∕TaN bilayer can be a very promising diffusion barrier in the future seedless Cu interconnect technology.

Growth Kinetics and Crystallization Behavior of TiO2 Films Prepared by Plasma Enhanced Atomic Layer Deposition

cSCK-CEN, Boeretang 200, B-2400 Mol, Belgium Atomic layer deposition ALD of TiO2 films from tetrakisdimethylamido titanium TDMAT or titanium tetraisopropoxide TTIP precursors was investigated. The growth kinetics, chemical composition, and crystallization behavior of the TiO2 films were compared for combinations of the two precursors with three different sources of oxygen thermal ALD using H2O and plasma-enhanced ALD PEALD using H2 Oo r O 2 plasma. For TDMAT, the growth rate per cycle GPC decreased with increasing temperature; while for TTIP with either water plasma or O2 plasma, a relatively constant growth rate per cycle was observed as a function of substrate temperature. It was found that the crystallization temperature of the TiO2 films depends both on film thickness and on the deposition conditions. A correlation was observed between the TiO2 crystallization temperature and the C impurity concentration in the film. The TiO2 films grown using a H2O plasma exhibit the lowest crystallization temperature and have no detectable C impurities. In situ X-ray diffraction measurements were used to test the diffusion barrier properties of the TiO2 layers and proved that all TiO2 films grown using either H2 Oo r O2 plasma are dense and continuous.

The effect of postannealing on the electrical properties of well-aligned n-ZnO nanorods/p-Si heterojunction

This work investigates the effects of postannealing on the electrical properties of the n-ZnO nanorods/p-Si heterojunction. Well-aligned ZnO nanorods are grown on the p-Si substrate with a ZnO seed layer through a hydrothermal method. The as-grown ZnO nanorods are grown along the preferential [0001] direction with high single crystalline quality. The rectifying characteristics of the heterojunction are effectively improved and the rectification ratio is increased tens of times after annealing in air. The leakage current is decreased by two orders of magnitude and the forward-bias injection efficiency is largely enhanced after annealing. The photoluminescence and x-ray photoelectron spectroscopy results show that annealing in the air ambient can effectively reduce the loosely adsorbed oxygen on the surface of the ZnO nanorods so that the bound free electrons can be released, which can result in larger carrier concentration and improve the injection efficiency of the n-ZnO nanorods/p-Si structure in the for...

Ni/Si solid phase reaction studied by temperature-dependent current-voltage technique

The temperature-dependent current–voltage (I–V–T) technique has been used to study the Ni/Si solid phase reaction by measuring the Schottky barrier height (SBH) inhomogeneity of Ni-silicide/Si Schottky diodes. The experimental results show the strong dependence of SBH inhomogeneity on the Ni/Si solid phase reaction. The SBH distribution of the diodes annealed at 500 and 600 °C can be described by a single-Gaussian function and the diode annealed at 500 °C is found to have the best homogeneity and the smallest leakage current. The SBH distribution of the diodes annealed at 400, 700, and 800 °C can be described by a double-Gaussian function in which the mean value of the second Gaussian function is substantially smaller than that of the dominant Gaussian function. The variation of SBH inhomogeneity, an interface property, is related to the phase evolution process in the Ni/Si solid phase reaction, and verified by reverse I–V measurements. Our results indicate that the I–V–T technique may be developed as a w...

Nickel silicidation on n and p-type junctions at 300°C

The electrical and materials properties of ∼20nm nickel silicide films, formed at 300°C, on n+∕p and p+∕n junctions are investigated. The sheet resistance of the silicide on p+∕n junctions is found to be more than twice as high as that of the silicide on n+∕p junctions. Cross section transmission electron microscopy, Rutherford backscattering spectroscopy, and x-ray photoelectron energy spectroscopy reveal that a pure Ni2Si layer forms on n+∕p junctions while a thicker Ni2Si∕NiSi double layer (∼60% Ni2Si) forms on p+∕n junctions. But the electrical differences are found to correlate only with differences in grain size and dopant concentration in the silicide.

A BEEM study of Schottky barrier height distributions of ultrathin CoSi2/n-Si(100) formed by solid phase epitaxy

The spatial distributions of the Schottky barrier heights of ultrathin CoSi2 films (~10 nm) on n-Si(100), obtained by multilayer solid state reaction of Co/Ti/n-Si, Co/a-Si/Ti/n-Si, Ti/Co/a-Si/Ti/n-Si and Co/n-Si systems, are studied by ballistic electron emission microscopy (BEEM) and spectroscopy (BEES) at low temperature (~-80 °C). The barrier heights determined from BEEM spectra range between 520 meV and 700 meV, with an approximate Gaussian distribution. The mean barrier heights of the epitaxial CoSi2 /Si contacts are 0.60-0.61 eV, lower than the 0.64 eV for polycrystalline CoSi2 /Si contacts. Adding a thin amorphous Si interlayer (1 nm) slightly increases the probability of higher barrier heights, while a thin Ti capping layer (1 nm) has no significant influence on the mean barrier height. The BEEM results are compared to those from I -V /C -V measurements.

Epitaxial growth of CoSi2 film by Co/a-Si/Ti/Si(100) multilayer solid state reaction

Epitaxial growth of CoSi2 by solid state reaction of Co/a-Si/Ti/Si(100) is investigated. A Ti/a-Si composite interlayer is used to modify the diffusion barrier and influence the epitaxial growth process. The epitaxial quality of the CoSi2 is improved compared to the film grown by Co/Ti/Si reaction. A multielement amorphous layer is formed by a solid-state amorphization reaction at the initial stage of the multilayer reaction. This layer acts as a diffusion barrier, which controls the atomic interdiffusion of Co and Si while limiting the supply of Co atoms. CoSi2 grows as the first phase and the growth interface of the epitaxial CoSi2 is at both the CoSi2/Si and CoSi2/CoSi interfaces. Investigation of the growth kinetics shows that the activation energy of CoSi2 formation is larger than that without an amorphous Si layer.

Growth of pinhole-free ytterbium silicide film by solid-state reaction on Si(001) with a thin amorphous Si interlayer

A thin amorphous Si (α‐Si) interlayer is produced between the sputtering deposited ytterbium layer and Si(001) substrate, and the growth of the ytterbium silicide (YbSi2−x) film is investigated in this paper. Formation of YbSi2−x was verified by x-ray diffraction (XRD). The silicide film morphology was examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). SEM results reveal that without the α‐Si interlayer, pinholes form during YbSi2−x formation on Si(001). Furthermore, the XRD results demonstrate that there is a strong epitaxial relationship between the formed YbSi2−x and Si(001) substrate, and it is believed to be the reason for the formation of pinholes. To suppress the formation of pinholes, a thin α‐Si interlayer with different thicknesses is introduced on the Si(001) substrate prior to Yb film deposition. The α‐Si interlayer is produced by either sputter deposition employing a Si target or by Si ion implantation induced amorphization. In the presence of this thin α‐Si int...

Cu adhesion on tantalum and ruthenium surface: Density functional theory study

This work reports a first-principles study of copper adhesion on Ta(110) and Ru(0001) surface with the density functional theory. Adsorption energy, electron density difference, and geometrical structures of Cu on pure, oxygen, and nitrogen doped Ta(110), Ru(0001) surfaces, and Ru doped Ta(110) surface were investigated. By analyzing the calculated results and the existing experimental results, it is found that although Ta has stronger chemical interaction with Cu, its larger lattice mismatch with Cu, and easy oxidation and nitridation make Ta a poorer Cu adhesion layer in comparison with Ru. The adhesion ability of Cu on Ta can be improved by doping Ru in Ta. The agglomeration of Cu on Ta or Ru is also studied. The calculation results show that Cu adsorbed on Ta(110) surface is more likely to be desorbed and agglomerated on the top of the second Cu atom layer. The substitutional oxygen O Ta in Ta will stimulate the agglomeration of Cu on the Ta surface.