Toshiaki Tatsuta

Structural and Electrical Properties of Ta2O5 Grown by the Plasma-Enhanced Liquid Source CVD Using Penta Ethoxy Tantalum Source

We report on structural and electrical properties of tantalum penta oxide (Ta2O5) material with a high dielectric constant grown from a penta ethoxy tantalum [Ta(OC2H5)5] liquid source by the plasma-enhanced liquid source chemical vapor deposition (PE-LS-CVD) technique. We have investigated several basic plasma deposition conditions. Structural properties investigated by θ-2θ X-ray measurements showed the amorphous nature of the films, and Auger electron spectrosopy (AES) and secondary ion mass spectroscopy (SIMS) indicated growth of Ta2O5 films having proper stoichiometry (Ta/O=0.4). Optical transmission spectroscopy showed that the band gap (Eg) of Ta2O5 is 5.28 eV. Electrical measurements performed on Au/Ta2O5/n, p-Si metal oxide semiconductor (MOS) structure exhibited very well defined capacitance-voltage (C-V) characteristics with flat band voltage as low as -0.1 eV, low leakage current, high breakdown voltage and high dielectric constant (25-38). As a hitherto unreported step in Ta2O5 processing we also performed rapid thermal (RTA) annealing at 700°C and 900°C for 5 min which resulted in much improved electrical properties. All results suggest growth of high-quality Ta2O5 films from a carbon-based Ta liquid source, due to an effect of plasma-enhanced deposition process.

Conformal oxide coating of carbon nanotubes

The International Roadmap for Ferroelectric Memories requires three-dimensional integration of high-dielectric materials onto metal interconnects or bottom electrodes by 2010. Here, we demonstrate the possibility of conformally coating carbon nanotubes with high-dielectric oxide as a first step toward ultrahigh integration density of three-dimensional ferroelectric random access memories.

Submicron three-dimensional trenched electrodes and capacitors for DRAMs and FRAMs: Fabrication and electrical testing

We report conformal deposition of both RuO2 electrodes and PbZrxTi1−xO3 (PZT) capacitors in submicron Si trenches through the same in situ liquid source mist processing. The step coverage for the RuO2 electrodes is 75% at 225 °C. After electroding, we deposited Pb(Zr,Ti)O3 thin films and nanotubes using the same apparatus with remanent polarization of ∼15 μC/cm2. The step coverage was 59% on the sidewall and 79% on the bottom wall. Electrical testing showed charge storage (capacitance/trench) was 13±2 pF, with a breakdown voltage of 11.3±0.2 V and dielectric constant e=166±30. This shows that a single inexpensive processing can produce fully electroded dynamic random access memory trenched capacitors with high aspect ratios and commercial electrical performance.

Preparation of hydrophilic plasma-polymers derived from oxygen-containing organic monomers

Plasma polymerization of nine oxygen-containing organic monomers was surveyed for producing hydrophilic films on solid substrates on due consideration of chemical structures of the monomers, operative conditions for plasma polymerization, and resultant film characters. The wettability of the polymer films were evaluated by measuring the contact angles of water on the film surfaces while the power consumption was compared as the lowest wattage needed for sustaining normal deposition rates of the polymer films. It has been found that the monomers involving the triple bond in the chemical structure conducted plasma polymerization under very low wattage of radiofrequency power, and at the same time the deposition rate was relatively high. With respect to the chemical structures of the monomers, the hydroxyl group tended to initiate and sustain the electric discharge at somewhat lower power than other functional groups. Highly hydrophilic polymer films could, thus, be obtained under a soft plasma condition by using propargyl alcohol (2-propyn-1-ol) as a monomer having the triple bond and the hydroxyl group. X-Ray photoelectron spectra of the polymers suggested that the wettability was not simply dependent upon oxygen atom content of the polymers, but also dependent upon spatial arrangement of the oxygen atoms within the polymer molecules.

Use of the 'mist' (liquid-source) deposition system to produce new high-dielectric devices: ferroelectric-filled photonic crystals and Hf-oxide and related buffer layers for ferroelectric-gate FETs

We describe the application of misted chemical solution deposition (CSD) techniques to processing of ferroelectric-filled porous silicon photonic devices and of novel precursor medium- and high-dielectric constant films for gate oxide and memory applications.

Fabrication Of InP Sub-micron Pillars For Two-dimensional Photonic Crystals By Reactive Ion Etching

We have fabricated periodic arrays of InP pillars for two-dimensional (2D) photonic crystals by reactive ion etching (RIE) with SiCl4/Ar inductively coupled plasma (ICP) and Cl2 electron cyclotron resonance (ECR) plasma chemistry. Prior to the fabrication of the arrays, photonic band structures for electromagnetic waves are calculated theoretically, and photonic band gaps are predicted to appear in the optical wavelength region. Periodic arrays of InP micron pillars with fairly smooth etched surfaces are fabricated by ICP-RIE with SiCl4/Ar. The reflective properties of the arrays have been characterized in the optical wavelength region by Fourier-transformed infrared reflection absorption spectrometry (FTIR-RAS). FTIR-RAS spectra of the arrays exhibit characteristic features such as a blue shift with decreasing period of pillars. In ECR-RIE, we systematically investigate InP etch characteristics as functions of various etching parameters, and successfully fabricate periodic arrays of vertical submicron pillars with smooth surfaces.

Deposition of Cathode Coupled Plasma Enhanced Chemical Vapor Deposition SiN Films Using Liquid Source Material

Silicon nitride (SiN) films were prepared using 1,1,1,3,3,3-Hexamethyldisilazane (HMDS) instead of monosilane (SiH4) by the cathode coupled plasma enhanced chemical vapor deposition (PE-CVD). As HMDS and NH3 were used, SiN film prepared at RF power of 300 W shows high insulation performance, breakdown voltage of which is 7 MV/cm. This value is same as Si3N4 films deposited by thermal CVD. These films can be used for insulating films in various semiconductor devices. In addition, because it has higher optical transparency than SiN films deposited using SiH4, it can be used for optical coating films.

Improvement in Homogeneity and Ferroelectric Property of Mist Deposition Derived Pb(Zr,Ti)O3 Thin Films by Substrate Surface Treatment

Pt/TiO2/SiO2/Si substrate UV surface treatment was carried out with O3 or N2/O2 atmosphere before film deposition to improve the homogeneity of mist deposition (MD)-derived Pb(Zr, Ti)O3 (PZT) films. The effect of the surface treatment was determined by measuring the contact angle of the distilled water on Pt substrates. The largest improvement in wettability was achieved in the N2/O2 atmosphere at the O2 partial pressure of approximately 10%. The macroscopic homogeneity of PZT films deposited onto the surface-treated Pt substrates was dramatically improved with a decrease in the contact angle. Although the contact angle of 0° was achieved by over 5 min UV treatment in any atmosphere, the P–E hysteresis properties and J–E characteristics were further improved with treatment time, even after the contact angle of 0° was reached. The improvement in electrical properties corresponded closely to the improvement in microscopic surface roughness. The PZT film deposited onto UV/N2-treated Pt substrates for 30 min showed the two fold remanent polarization (2Pr) of 52 µC/cm2, while the PZT film on the 5-min-treated substrate showed 44 µC/cm2.

Fabrication of two-dimensional InP photonic band-gap crystals by reactive ion etching with inductively coupled plasma

We fabricated two-dimensional (2D) InP photonic band-gap crystals by reactive ion etching (RIE) with a SiCl 4 /Ar inductively coupled plasma (ICP) chemistry, and characterized their reflective characteristics in the optical wavelength region by Fourier-transformed infrared reflection absorption spectrometry (FTIR-RAS). The photonic band-gap crystals consisted of a periodic array of parallel air rods of circular cross section whose intersections with a perpendicular plane form a triangular lattice in InP substrates. Prior to the fabrication of the periodic array of air rods, the photonic band structure for electromagnetic waves was calculated theoretically in the sample structure and was predicted to appear in the optical wavelength region. In RIE with the SiCl 4 /Ar ICP chemistry, we systematically investigated the InP etch rate and the etch selectivity of InP over SiO 2 as functions of various etching parameters, to fabricate deep air rods with a vertical profile. The effect of the N 2 O addition to the SiCl 4 /Ar ICP chemistry was investigated and it was revealed that the addition of a small amount of N 2 O results in an improvement in the vertical profile with a slight increase in the InP etch rate. The InP etch rate and the etch selectivity of InP over SiO 2 depended strongly on the SiCl 4 flow rate. In FTIR-RAS measurements, characteristic features were observed in the optical wavelength region, depending on the diameter of the air rods. Behaviors of the features were discussed in relation to theoretically calculated densities of states.

Optimization of Amorphous Carbon-Deposited Antireflective Layer for Advanced Lithography

Critical dimension variation due to the multiple interference effect is the greatest problem for improving the actual resolution limit in optical lithography. To overcome this problem, amorphous carbon-deposited antireflective layer has been developed. This paper reports on the results of optimization for the antireflective layer film and application to advanced lithography. First, we optimized the deposition process of antireflective layer by measuring the reflectivity. Second, we applied the antireflective layer films in i-line (365 nm) and KrF excimer laser (248 nm) lithography. With the antireflective layer films, the reflectivity from the substrate reduces to less than 20%, which leads to a multiple interference effect of less than 1/7. With optimized antireflective layer films, resolution and depth-of-focus are almost same as those of the films without antireflective layer.