Xin-Ping Qu

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 ...

Germanium surface passivation and atomic layer deposition of high-k dielectrics?a tutorial review on Ge-based MOS capacitors

Due to its high intrinsic mobility, germanium (Ge) is a promising candidate as a channel material (offering a mobility gain of approximately??2 for electrons and??4 for holes when compared to conventional Si channels). However, many issues still need to be addressed before Ge can be implemented in high-performance field-effect-transistor (FET) devices. One of the key issues is to provide a high-quality interfacial layer, which does not lead to substantial drive current degradation in both low equivalent oxide thickness and short channel regime. In recent years, a wide range of materials and processes have been investigated to obtain proper interfacial properties, including different methods for Ge surface passivation, various high-k dielectrics and metal gate materials and deposition methods, and different post-deposition annealing treatments. It is observed that each process step can significantly affect the overall metal?oxide?semiconductor (MOS)-FET device performance. In this review, we describe and compare combinations of the most commonly used Ge surface passivation methods (e.g. epi-Si passivation, surface oxidation and/or nitridation, and S-passivation) with various high-k dielectrics. In particular, plasma-based processes for surface passivation in combination with plasma-enhanced atomic layer deposition for high-k depositions are shown to result in high-quality MOS structures. To further improve properties, the gate stack can be annealed after deposition. The effects of annealing temperature and ambient on the electrical properties of the MOS structure are also discussed.

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.

Mixing entropy and the nucleation of silicides: Ni-Pd-Si and Co-Mn-Si ternary systems

Nucleation can play an important role during the formation of silicides, especially when the difference in Gibbs free energy AG between the existing and newly formed phase is small. In this work, it is shown that the addition of elements that form a solid solution with either the existing or nucleating phase influences the entropy of mixing and thus changes AG. In this way, the height of the nucleation barrier may be controlled, thus controlling the nucleation temperature. The influence of mixing entropy on silicide nucleation is illustrated by experiments for two ternary systems: Co-Mn-Si and Ni-Pd-Si. It is shown that the nucleation temperature of CoSi 2 is increased by the addition of Mn, the nucleation temperature of MnSi 1 7 is increased by the presence of Co, the nucleation temperature of NiSi 2 is increased by the addition of Pd, and the nucleation temperature of PdSi is decreased by the addition of Ni. In all four cases, the effect of the alloying element on the nucleation temperature can be explained by a model on the basis of the concept of mixing entropy.

Spatially Selective Photochemical Reduction of Silver on Nanoembossed Ferroelectric PZT Nanowires

It is well known that photochemical reaction in an aqueous solution can be chosen by selectively patterning the domain structures of ferroelectrics. In this work, we investigate the photochemically induced deposition of Ag particles on ferroelectric lead zirconate titanate [Pb(Zr(x),Ti(1 - x))O(3)] nanowires fabricated by nanoembossing technology. The photochemical reduction of Ag particles is found to occur preferentially along the embossed nanowires. By imaging domain configurations of the embossed films using the piezoresponse force microscope, the spatially selective deposition of Ag particles can be associated with the underlying ferroelectric domain structures created by the nanoembossing process. The controllable and selective deposition of metal species onto nanoembossed ferroelectric nanostructures without the need for an external electrical field is promising for providing a new route to nanoferroelectric lithography.

Ultrathin GeOxNy interlayer formed by in situ NH3 plasma pretreatment for passivation of germanium metal-oxide-semiconductor devices

In situ NH3 plasma surface-nitridation treatments at 250 °C on both p- and n-type Ge(100) wafers were investigated. An ultrathin high quality GeOxNy interlayer was formed and exhibited dielectric breakdown for electric fields greater than 15 MV/cm. Well behaved capacitance-voltage characteristics were obtained for the complementary metal-oxide-semiconductor capacitors (CMOSCAPs) with HfO2(3 nm)/GeOxNy(1 nm) gate stacks. Gate leakage current density was below 5×10−7 A/cm2 at VFB±1 V for both MOSCAPs with an equivalent oxide thickness of 1.1 nm. Promising electrical properties of the CMOSCAPs indicate effective passivation of the Ge interface with GeOxNy interlayer formed by in situ NH3 plasma treatment.