Jacobus W. Swart

Deposition of silicon nitride by low-pressure electron cyclotron resonance plasma enhanced chemical vapor deposition in N2/Ar/SiH4

Plasma deposition of silicon nitride on silicon substrates in a microwave electron cyclotron resonance N2/Ar/SiH4 discharge was studied as a function of gas pressure (1–5 mTorr), gas composition, and discharge power (250–1000 W). The dependencies of deposition parameters on discharge characteristics obtained at 1 mTorr appear to be essentially different from those at higher pressures. Optical emission spectroscopy was used for plasma characterization. A high degree of ionization and dissociation of gas molecules was observed under present plasma conditions. It is shown that the contribution of ionized species to film deposition is comparable with that of neutral ones under high power and low pressure conditions. The best quality of films was obtained at a moderate rather than the highest available dissociation degree of silane.

Silicon nitride deposited by ECR–CVD at room temperature for LOCOS isolation technology

For LOCOS application, silicon nitride (SiNx) insulators have been deposited by ECR–CVD at room temperature and with N2 flows of 2.5, 5, 10 and 20 sccm on pad-SiO2/Si or on Si substrates. The obtained SiNx/Si structures were used to analyze the SiNx characteristics. FTIR analyses reveal the presence of Si–N and N–H bonds. The refractive indexes between 1.88 and 2.48 and the thickness between 120 and 139 nm were determined by ellipsometry. With these thickness values, the deposition rates of 9.6– 10.1 nm/min and the BHF etch rates of 2–86 nm/min were determined. On the SiNx/pad-SiO2/Si structures, the LOCOS process was performed. Optical and SEM microscopy analyses were used to investigate the SiNx resistance to thermal oxidation, made at 1000 8C, and the bird’s beak in the obtained LOCOS structures, respectively. These analyses reveal that SiNx insulator performed with N2 flows higher than 2.5 sccm presented high quality to LOCOS isolation technology. # 2003 Elsevier Science B.V. All rights reserved. PACS: 85.40.Ls; 77.84.Bw; 85.40.Sz; 81.15.Gh

Platinum thin films deposited on silicon oxide by focused ion beam: characterization and application

Focused ion beam system was used for deposition of platinum (Pt) thin films on thermally oxidized silicon (Si). Various test patterns (squares and lines) were deposited for electrical characterization of the films, using 2- and 4-terminal measurements. Tests with parallel Pt lines were also carried out, and considerable leakage was detected for the interline distances in the sub-micron range. We investigated two ways to decrease the leakage current: inducing surfaces roughness and using an oxygen plasma after patterns deposition. A method of dielectrophoresis with an AC electric field was applied to align and deposit metallic multi-wall carbon nanotubes (CNT) between pre-fabricated metal, gold, and palladium electrodes with a micron-scale separation. Further, using focused electron and ion beam-deposited Pt contacts in two different configurations (“Pt-on-CNT” and “CNT-on-Pt”), 4-terminal measurements have been performed to evaluate intrinsic nanotube resistances.

Analysis of The Etching Mechanisms of Tungsten in Fluorine Containing Plasmas

Tungsten and polysilicon layers were etched in three different types of etching equipment, in different etching modes. Etch rates and wall profiles were determined. Partially etched tungsten layers were analyzed through Auger spectroscopy. Combining all these results, it was possible to determine the etch rate limiting subprocesses for tungsten etching. For most process conditions, the arrival of atomic fluorine at the wafer surface is the etch rate limiting mechanism. For other processes, the removal of products with low volatility is the limiting mechanism.

Fabrication of high-aspect ratio silicon nanopillars and nanocones using deep reactive ion etching

Bosch type processes have been employed to fabricate nanostructured Si surfaces. Nanopillars and nanocones in Si have been fabricated using different techniques for Ni micromasking. Plasma redeposition of Ni was found to be responsible for Si pillar formation with diameters varying in the submicron range. A possibility to produce tilted nanopillars with tilt angles up to as high as 25° has been demonstrated. In other method, previously deposited and annealed thin Ni films were employed. Smaller Ni nanoislands were obtained, and the formation of Si nanocones was demonstrated using longer passivation steps. In this case, reflection coefficients as low as 1.2% were obtained for the optimized etching process time.

Photodetection With Gate-Controlled Lateral BJTs From Standard CMOS Technology

The silicon-based gate-controlled lateral bipolar junction transistor (BJT) is a controllable four-terminal photodetector with very high responsivity at low-light intensities. It is a hybrid device composed of a MOSFET, a lateral BJT, and a vertical BJT. Using sufficient gate bias to operate the MOS transistor in inversion mode, the photodetector allows for increasing the photocurrent gain by 106 at low light intensities when the base-emitter voltage is smaller than 0.4 V, and BJT is off. Two operation modes, with constant voltage bias between gate and emitter/source terminals and between gate and base/body terminals, allow for tuning the photoresponse from sublinear to slightly above linear, satisfying the application requirements for wide dynamic range, high-contrast, or linear imaging. MOSFETs from a standard 0.18-μm triple-well complementary-metal oxide semiconductor technology with a width to length ratio of 8 μm /2 μm and a total area of ~ 500 μm2 are used. When using this area, the responsivities are 16-20 kA/W.

Electrical Characterization of Platinum Thin Films Deposited by Focused Ion Beam

Dual beam FIB (focused ion beam)/SEM (scanning elelctron microscope) systems are commonly used for imaging, selective etch and deposition of materials like platinum. The paper presents the results of electrical characterization of platinum thin films deposited by focused ion beam. For measurements, two types of test structures were fabricated: (i) 150x150 :m and 20x20 :m squares with thickness of 5, 10, 30 and 100 nm, and (ii) 30 :m long resistors with variable cross - section (50 nm x 50nm to 1:m x 1:m). The Pt film resistivity has been measured by a four points probe method, to give the value of ~10 x 10-4 A.cm.

Different carbon nanostructured materials obtained in catalytic chemical vapor deposition

Different carbon nanostructured materials, such as nanotubes, nanofibers, nanosprings and nanooctopus, were grown by changing the metal catalyst and experimental parameters of the thermal chemical vapor deposition process. These experiments were performed using a tubular furnace and methane or acetylene as carbon feedstock gases. Thin films of Ni or Cu were deposited onto a SiO2/Si substrate and employed as catalysts. The effect of the growth temperature, metal catalyst and carbon gas precursor (methane or acetylene) on the final carbon nanoestructured material was studied by scanning electron microscopy, Raman spectroscopy and grazing incidence X-ray diffraction. Growth of multiwall carbon nanotubes (MWCNTs) was observed using both metal films and carbon precursor gases, whereas partially oxidized Ni films promoted formation of nanosprings. Experiments with reduced supply of methane resulted in octopus-like carbon nanostructures when a Cu film was used as a catalyst.

Study of Conditions for Anisotropic Plasma Etching of Tungsten and Tungsten Nitride Using SF 6 / Ar Gas Mixtures

Results of the study of reactive ion etching of tungsten, tungsten nitride, and silicon in SF 6 /Ar gas mixtures are presented. For plasma diagnostics, optical emission spectroscopy ~actinometry! was used. Using the actinometry technique, it was possible to show that etching mechanisms were different for Si-F and W-F chemistries. Anisotropic etching of tungsten/tungsten nitride using conventional reactive ion etcher has been obtained, and conditions of achieving anisotropic etching have been analyzed. A correlation is found between anisotropy of tungsten etching and the ratio of Si/W etch rates. Mechanisms of fluorine redistribution between the bottom/sidewall surfaces due to surface diffusion and/or reflection are proposed as possible reasons for the observed correlation.

Characterization and modeling of antireflective coatings of SiO2, Si3N4, and SiOxNy deposited by electron cyclotron resonance enhanced plasma chemical vapor deposition

In this work the optical transmission spectra of silicon oxide (SiO2), silicon nitrides (Si3N4), silicon-rich oxynitrides (SiOxNy), and antireflective coatings (ARCs), deposited by the electron cyclotron resonance enhanced plasma chemical vapor deposition onto a silicon substrate at room temperature, are studied. Simulations carried out with the MATHEMATICA program, from 0to1000nm thick coatings, showed maximum transmittance in the three basic colors at 620, 480, and 560nm for the SiO2, Si3N4, and SiOxNy ARCs, respectively. However, a highly significant transmittance over a broad spectral range from visible (VIS) to near the infrared region, with optical gain in the three basic colors above 20%, is observed only at thicknesses of 80, 70, and 60nm, respectively, for SiO2, Si3N4, and SiOxNy ARCs. Among the three evaluated films, the highest transmittance in the broad spectral band in the VIS range was observed for 60nm thick Si3N4 films. The Fourier transform infrared spectroscopy of these films reveal high...