Nanopatterning of diamond films with composite oxide mask of metal octylates in electron beam lithography

The fabrication of diamond nanopatterns by electron cyclotron resonance (ECR) oxygen plasma with a composite metal octylate mask was investigated using electron beam lithography technology. A high etching selectivity of 14 was obtained with Bi₄Ti₃O₁₂ octylate film as a mask under the plasma-etching conditions of microwave power of 300 W and oxygen gas flow rate of 3 sccm. The metal naphthenates and metal octylates exhibited negative exposure characteristics. The sensitivity of metal naphthenates (1.2×10^–3 C cm^–2) was ten times lower than that of polymethyl methacrylate (PMMA) resist, while that of octylates (8.0×10^–5 C cm^–2) was in good agreement with that of PMMA resist (6.0×10^–5 C cm^–2). The resulting minimum chemical vapor deposited (CVD) diamond line-width of 100 nm with a height of approximately 1 m was fabricated with a Bi₄Ti₃O₁₂ octylate mask.     

Nanocrystalline wurtzite Si–nickel silicide composite thin films with large band gap and high resistivity

Stabilization of wurtzite Si nanocrystals embedded in a metal/metal silicide matrix by the metal induced crystallization process is demonstrated. The process involves the growth of 50 nm thick Ni films on borosilicate glass (BSG) substrates followed by 700 nm thick amorphous Si films and annealing of this multilayered stack at 550 °C in furnace atmosphere for 1 h. The presence of wurtzite Si is established based on electron diffraction studies and is also confirmed by the Raman signature of wurtzite Si at 504 cm⁻¹. It is shown that the growth of wurtzite Si is mediated by the formation of Nickel Silicide, as evidenced by the Raman signal at 294 cm⁻¹. The films exhibit a band gap greater than 1.9 eV with dc resistances of the order of 10 GΩ. It is proposed that such high resistivities should make this form of Si ideal for PV and microwave device applications.     

Superconducting properties of ion beam modified YBCO microbridges

We prepared ion beam modified microbridges based on thin sputtered or laser ablated YBCO films on SrTiO₃ substrates. The microbridges with a width of 10 μm were irradiated through slits in a 700 nm thick double layer resist mask. In our experiments we used O⁺ ions with an ion energy of 30 keV or 100 keV varying the dose between 10¹³ ions·cm⁻² and 10¹⁴ ions·cm⁻². We investigated the influence of film thickness and slit width on the superconducting properties of these junctions. We show the temperature dependence of the junctions properties on microwave radiation or external magnetic fields.     

Sol–gel synthesis and electrical characterization of (Pb, Ca)TiO3 thin films

Calcium modified lead titanate films have been prepared on Pt/Ti/SiO₂/Si substrates using a sol–gel route. The sols were prepared from propanediol solutions of Pb(CH₃COO)₂·xH₂O, Ti(OC₃H₇)₂(CH₃COCHCOCH₃)₂ and Ca(NO₃)₂·xH₂O. Tetragonal phase (Pb, Ca)TiO3 films could be produced by firing the coatings at 650°C for 30 min. The limiting thickness of crack-free single layers was ∼0.4 μm, but 3 μm thick films could be made by a multiple deposition technique. Dielectric and ferroelectric parameters were determined for single layer 0.5 μm films for compositions up to 30 mol% Ca. The average values of remanent polarization, P_r and coercive field, E_c decreased with increasing Ca content from ∼11 μC cm⁻² and ∼125 Kv cm⁻¹ for a 10 mol% Ca composition to ∼8 μC cm⁻² and 80 kV cm⁻¹ for 30 mol% Ca films. It was noted that the statistical variation in electrical values across each film was greater than in PZT films made by a similar sol–gel route. Reasons for this are discussed in terms of the incidence of physical defects in the films. This revised version was published online in November 2006 with corrections to the Cover Date.     

The ferroelectric and optical properties of (Pb0.92La0.08)(Zr0.65Ti0.35)O3 thin films deposited by radio-frequency magnetron sputtering

Ferroelectric (Pb_0.92La_0.08)(Zr_0.65Ti_0.35)O₃ (PLZT) films have been prepared on Pt/Ti/SiO₂/Si and fused quartz substrates using radio-frequency (rf) magnetron sputtering at a deposition temperature of 650°C. X-ray diffraction analysis shows that the PLZT thin films on platinized silicon are polycrystalline with (100)-preferential orientation. A Al/PLZT/Pt capacitor has been fabricated and it shows that the films have excellent ferroelectric character, with saturation polarization (P _s), remanent polarization (P _r) and coercive field (E _c) of 32.8μC/cm², 24.3μC/cm² and 142 kV/cm, respectively. The PLZT thin films exhibit good insulating property and the leakage current density of the films on platinized silicon is only about 0.86 × 10⁻⁷ A/cm² at 200 kV/cm. By the optical transmission spectra measurements, the energy gap (E _g) of the PLZT films on fused quartz is found to be about 3.54 eV. The optical constants (n and k) of the films in the wavelength range of 250–900 nm are obtained by a Filmetrics F20 reflectance spectrometer.     

Growth and characterization of HfO2 high-k gate dielectric films by laser molecular beam epitaxy (LMBE)

The HfO₂ gate dielectric films were fabricated by the laser molecular beam epitaxy (LMBE) technique. High-resolution transmission electron microscopy (HRTEM) observation showed that under optimized condition, there is no detectable SiO₂ interfacial layer in the as-deposited film and a SiO₂ interfacial layer of about 0.4 nm was formed at the Si interface due to the post deposition annealing. Capacitance–voltage (C–V) measurement of the film revealed that the equivalent oxide thickness was about 1.3 nm. Such a film showed very low leakage current density of 1.5 × 10⁻² A cm⁻² at 1 V gate bias from the current–voltage (I–V) analysis. The conduction mechanisms as a function of temperature T and electric field E were also systematically studied.     

Au agglomerates observed in the out-diffusion process of supersaturated high-temperature substitutional Au in Si

Out-diffusion profiles of supersaturated substitutional Au in Si annealed at 900 °C for 90 h have been measured by SIMS and ICTS methods over a distance of 80 μm from the specimen surface. The tendency of the profile of total Au atoms measured by SIMS and that of electrically active substitutional Au measured by ICTS agrees well, but the very small regions containing high-concentration of Au atoms, 3 × 10²² cm⁻³, are observed sporadically at the distance deeper than 10 μm from the surface by SIMS method. The size of the high-concentration region is estimated to be about 20 nm and its density is about 2 × 10¹⁰ cm⁻³. The small agglomerates contain 10⁵–10⁷ Au atoms and many of them contain about 2 × 10⁵ atoms. The observed agglomerate is a new agglomeration of Au in Si. The state of the agglomeration (namely, precipitates of Au, agglomeration of substitutional Au in Si, or a new state) is not clear by SIMS measurement.     

Profile of the wafer level ECD gold bumps under variable parameters

The uniformity and deformation of electrochemical deposition (ECD) bumps get more and more important with the pitch shrinking and density increasing according to the requirement of modern electronic industry. In this paper, wafer level diameter and thickness distribution, surface roughness and hardness of Au bumps were characterized under different electroplating current densities and bath temperatures. Some valuable results were obtained. First, the diameter of ECD Au bumps was enlarged for 5–30 μm at all positions on the wafer for both the bumps of 10–100 μm diameters. Electroplated at 40 °C, the diameter distribution of Au bumps was similar to that of photoresist. While electroplated at 60 °C, its distribution was more symmetric. Second, more uniform thickness distribution of Au bumps was obtained when the bath temperature increased from 40 to 60 °C or the electroplating current density decreased from 8 to 3 mA/cm². Third, the Au bumps electroplated at 60 °C exhibited the surface roughness of 105–125 nm independent of electroplating current densities. The Au bumps electroplated at 40 °C exhibited the surface roughness of 40–45 nm for 3 mA/cm² and 5 mA/cm² and 923.45 nm for 8 mA/cm². Fourth, the hardness of Au bumps decreased with electroplating temperature increasing from 40 to 60 °C. The difference of hardness got at between 40 and 60 °C can be vanished by the following anneal process at 60 °C. In addition, the big differences among different current densities electroplated at 40 °C can also be vanished by the anneal process. Finally, possible reasons leading to above results were discussed.     

Mixing induced by swift heavy ion irradiation at Fe/Si interface

The present work deals with the mixing of metal and silicon by swift heavy ions in high-energy range. Threshold value for the defect creation in metal Fe calculated was found to be ∼ 40 keV/nm. A thin film of Fe (10 nm) was deposited on Si (100) at a pressure of 4 × 10⁻⁸ Torr and was irradiated with 95 MeV Au ions. Irradiation was done at RT, to a dose of 10¹³ ions/cm² and 1 pna current. The electronic energy loss was found to be 29.23 keV/nm for 95 MeV Au ions in Fe using TRIM calculation. Compositional analysis of samples was done by Rutherford backscattering spectroscopy. Reflectivity studies were carried out on the pre-annealed and post-annealed samples to study irradiation effects. Grazing incidence X-ray diffraction was done to study the interface. It was observed that ion beam mixing reactions at RT lead to mixing as a result of high electronic excitations.     

Effect of film thickness on ferroelectric domain structure and properties of Pb(Zr0.35Ti0.65)O3/SrRuO3/SrTiO3 heterostructures

Epitaxial Pb(Zr_0.35Ti_0.65)O₃ (PZT) thin films with tetragonal symmetry and thicknesses ranging from 45 to 230 nm were grown at 540 °C on SrRuO₃-coated (001)SrTiO₃ substrates by pulse-injected metalorganic chemical vapor deposition. The effect of the film thickness on the ferroelectric domain structure and the dielectric and ferroelectric properties were systematically investigated. Domain structure analysis of epitaxial PZT films was accomplished with high-resolution X-ray diffraction reciprocal space mapping and high-resolution transmission electron microscopy. Fully polar-axis (c-axis)-oriented epitaxial PZT thin films with high ferroelectric polarization values [e.g., remanent polarization (P _r) ~ 90 μC/cm²] were observed for film thicknesses below 70 nm. Films thicker than 70 nm had a c/a/c/a polydomain structure and the relative volume fraction of c-domains monotonously decreased to about 72% on increasing the film thickness up to 230 nm , and finally P _r diminished to about 64 μC/cm² for the 230-nm-thick epitaxial film. These polarization values were in good agreement with the estimated values taking into account the volume fraction of the c-axis-oriented domains while assuming a negligible contribution of 90° domain reorientation caused by an externally applied electric field.     

The application of a statistical methodology to investigate deposition parameters in CdTe/CdS solar cells grown by MOCVD

A L₈ matrix of experiments has been carried out to investigate various deposition parameters of Cadmium telluride (CdTe)/Cadmium sulphide (CdS) solar cells grown using metal organic chemical vapour deposition (MOCVD). The results of the matrix were analysed using a criterion to establish which growth parameters are significant and warrant further investigation. The most significant parameters were CdTe growth temperature and in situ arsenic doping of the CdTe absorber layer. Characterisation of the device structures showed that CdTe grain enlargement from 1 μm to ∼3 μm occurred at the higher CdTe deposition temperature of 390 °C. SIMS depth profiles verified that arsenic concentrations, within the device structures, of 2.5 × 10¹⁸ and 2 × 10¹⁹ atoms cm⁻³ were achieved for the different partial pressures. A model for the behaviour of arsenic in polycrystalline CdTe material, based on only partial passivation of grain boundaries and saturation of the grain boundaries at As concentrations above >2.5 × 10¹⁸ atoms cm⁻³ is presented and discussed.     

Proximity-effect correction in electron-beam lithography on metal multi-layers

We report a proximity-effect correction in electron beam patterning when fabricating a spin valve device with a junction size of 100 nm × 100 nm. Since the spin valve device has a stack of magnetic/non-magnetic/magnetic metal multi-layers on oxidized Si substrate, its proximity effect should be appropriately corrected to realize a nano-scale junction. ZEP 520A was chosen as an electron beam resist because its dry-etching resistance is high enough to serve as an etching mask in the post-process. A set of proximity parameters, α, β, and η of ZEP 520A coated metal multi-layers was evaluated by using the doughnut pattern method. A simulation was carried out based on given proximity parameters in order to obtain effective dose factors of each segment of the exposure pattern. The junction with a desired shape and size on a metal multi-layer was successfully fabricated with a help of efficient proximity-effect correction.     

Microstructural analysis of Au/Pt/Ti contacts to p-type InGaAs

A detailed study on the microstructural changes that occur on annealing of Au/Pt/Ti ohmic contacts to n-type InGaAs has been carried out. The metal layers were deposited sequentially by electron beam evaporation onto InGaAs, doped with Zn to a level of 7 × 10¹⁸ cm^–3, that was epitaxially grown on < 100 > InP substrates. The deposition sequence and metal layer thicknesses were: Ti (25 or 30 nm), Pt (25 or 30 nm) and Au (250 or 300 nm). Samples were annealed at temperatures ranging from 250–425 C in a nitrogen atmosphere. As-deposited contacts were Schottky barriers, while a minimum contact resistance of 2 × 10^–5 cm² was obtained by annealing in the 375–425 C range. Annealing resulted in the inward diffusion of Ti and outward diffusion of In and As, leading to the formation of TiAs, metallic In and Ga-rich InGaAs at the Ti/InGaAs interface. The Pt diffusion barrier was effective in preventing In diffusion into the outer Au layer and minimizing Au diffusion to the semiconductor.     

Symmetric growth of Pt ultrathin nanowires from dumbbell nuclei for use as oxygen reduction catalysts

This work demonstrates the synthesis of Pt ultrathin nanowires assisted by chromium hexacarbonyl [Cr(CO)₆]. The nanowires exhibit a uniform diameter of 2–3 nm. The length can reach up to several microns. It was found that Cr species produced dumbbell-like nuclei which play a pivotal role in the formation of the Pt nanowires. Such Pt nanowires can be tuned to nanocubes by simply decreasing the concentration of [Cr(CO)₆]. Compared to a commercial Pt/C catalyst (45 wt%, Vulcan, Tanaka) and Pt black (fuel cell grade, Sigma), the synthesized Pt nanowires exhibit superior performance in electrocatalytic oxygen reduction with a specific activity of 0.368 mA/cm², which was 2.7 and 1.8 times greater than that of Pt/C (0.138 mA/cm²) and Pt black (0.202 mA/cm²), respectively. The mass activity of Pt nanowires (0.088 mA/μg) is 2.3 times that of Pt black (0.038 mA/μg) and comparable to that of Pt/C (0.085 mA/μg).      

Pulsed laser deposition of crystalline ZrC thin films

ZrC thin films were grown on Si substrates by the pulsed laser deposition (PLD) technique under various conditions. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), X-ray diffraction and reflectivity, spectroscopic ellipsometry, and four point probe measurements were used to characterize the properties of the deposited films. It has been found that crystalline films could be grown only by using laser fluences higher than 5 J/cm² and substrate temperatures in excess of 500 °C. For a fluence of 10 J/cm² and a substrate temperature of 700 °C, cubic ZrC films (a = 0.469 nm) exhibiting a (200)-texture were deposited under vacuum or low pressure C₂H₂ atmosphere. These films were smooth, with surface roughness values below 1.0 nm and mass densities around the tabulated value of 6.7 g/cm³. AES depth profiling investigations showed oxygen contamination around 7% in the bulk region. Despite the relatively high levels of oxygen contamination, the deposited ZrC films were very conductive. The use of a low C₂H₂ pressure atmosphere during deposition had a small beneficial effect on crystallinity and stoichiometry of the films.     

Selective growth of well-aligned carbon nanotubes by APCVD

Well-aligned good-quality carbon nanotube (CNT) array was grown on silicon substrate by atmospheric pressure chemical vapor deposition (APCVD) through SiO₂ masking. First, the patterned substrate was pretreated with NH₃ and then CNTs were synthesized at 800 °C using Ni as the catalyst, acetylene (C₂H₂) as the carbon source material and N₂ as the carrier gas. Effects of the NH₃-pretreatment time, the flow ratio of [C₂H₂]/[NH₃] and the CNT growth time on the qualities of CNT array were analyzed in detail. It was found that good-quality CNTs with an average length of around 15 μm could be grown by pretreating the Si substrate with NH₃ for 10 min and then conducting the CNT growth with a flow ratio of [C₂H₂]/[NH₃] = 30/100. Furthermore, the field emission property of CNT array was investigated using a diode structure. It was found that the turn-on electric field decreased with increasing CNT length. The turn-on electric field as low as about 2 V/μm with an emission current density of 10 μA/cm² was achieved for a CNT-array diode with the tube length near 18 μm. For the same device, the emission current density could be elevated to 10 mA/cm² with the applied voltage of 3.26 V/μm.     

Change in the properties of BT-23 titanium alloy induced by implantation of iron and zirconium ions followed by exposure to a low-energy high-current electron beam

Atomic physics methods, atomic force microscopy, and testing of microhardness, wear resistance, and friction coefficient were used to investigate Ti₄₁-V₄₁-Al₁₈ samples implanted with iron (60 kV) and zirconium (40 kV) ions, and then exposed to a high-current electron beam with energy fluxes of 2.7 and 5.5 J/cm². The maximum concentration of iron ions is 16.5 at.% at a depth of 85 nm and that of zirconium ions 0.85 at.% at 56 nm. After double implantation, the friction coefficient decreases and the wear resistance increases. After implantation and high-current electron beam treatment, the depth of the hardened layer and the wear resistance increase. Pis’ma Zh. Tekh. Fiz. 25, 66–73 (August 12, 1999)     

Preparation of ferroelectric PZT films by thermal decomposition of organometallic compounds

Transparent PZT thin films with perovskite structure were successfully obtained by thermal decomposition of organometallic compounds at the temperatures of 500 to 700° C. The films deposited on platinum substrates were smooth and uniform, but microcrackings were observed in the films deposited on fused silica substrates. The ratio of metal composition in the PZT film agreed with that in the mixture of starting materials. Films obtained at 700° C on platinum substrate showed a hysteresis loop. A spontaneous polarization was 35.65μC cm⁻², a saturation remanent polarization was 30.56μC cm⁻² and a coercive field was 45 kV cm⁻¹. Dielectric constant and dielectric loss angle were about 300 and 0.05, respectively.     

Photocurrent enhancement of d.c. sputtered copper oxide thin films

Copper oxide (CuO) thin films with photocurrent as high as 25 μA/cm² were deposited on conductive glass substrates using d.c. reactive sputtering. This was the highest reported photocurrent for sputteredp- type copper oxide measured in the electrolyte KI. The photocurrent drastically increased up to 25 (μA/cm² as the sputtering pressure and the substrate temperature were increased up to 8.5 mbar and 192°C, respectively. All the synthesized films contained single phase of CuO in this range of pressure and substrate temperature. Variation of the photocurrent, photovoltage, structure and absorbance with deposition conditions were studied in detail.     

Fabrication of micro-Ni arrays by electroless and electrochemical depositions with etched porous aluminum template

Nickel micro-arrays were fabricated by electroless and electrochemical deposition in an etched porous aluminum membrane. The aluminum membrane with metal characteristic could be fabricated from high-purity aluminium by electrochemical method. The aluminum reduced Ni²⁺ into Ni and the formed Ni nuclei served as the catalyst for further reduction of Ni²⁺ in electroless solution. With the help of the membrane, nickel micro-columns of about 1–2 μm diameter were obtained. The surface-deposited nickel layer served as a substrate for the nickel micro-columns, and the resulting material possessed strong mechanical strength. Electrochemical deposition was operated without preparing a conductive layer on the template due to the conductivity of the aluminum membrane. Nickel micro-tubes with an outer diameter of about 1–2 μm and a wall thickness in the order of tens of nm were obtained. The nickel micro-arrays were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).