Satoshi Hamaguchi

Simulation of surface topography evolution during plasma etching by the method of characteristics

Application of the method of characteristics to the general case of ion or plasma etching is reviewed, yielding a topography evolution algorithm which is simultaneously accurate, flexible, and efficient. The behavior of initial slope discontinuities is computed by mapping the characteristic locus in the region of the discontinuity and removing any closed loops which appear in the locus. The new method is shown to produce profiles which satisfy the required entropy and jump conditions for any given variation of etching rate with surface slope, while allowing the use of longer integration time steps than conventional methods. Previously published ‘‘string’’ algorithms [W. G. Oldham, S. N. Nandgaonkar, A. R. Neureuther, and M. O’Toole, IEEE Trans. Electron Devices ED‐26, 717 (1979); A. R. Neureuther, C. Y. Liu, and C. H. Ting, J. Vac. Sci. Technol. 16, 1767 (1979)] are compared to the new method, and are shown to be capable of generating correct profiles only under limited conditions, i.e., for specific etch...

Rapid formation of electric field profiles in repetitively pulsed high-voltage high-pressure nanosecond discharges

Rapid formation of electric field profiles has been observed directly for the first time in nanosecond narrow-gap parallel-plate discharges at near-atmospheric pressure. The plasmas examined here are of hydrogen, and the field measurement is based on coherent Raman scattering (CRS) by hydrogen molecules. Combined with the observation of spatio-temporal light emission profiles by a high speed camera, it has been found that the rapid formation of a high-voltage thin cathode sheath is accompanied by fast propagation of an ionization front from a region near the anode. Unlike well-known parallel-plate discharges at low pressure, the discharge formation process at high pressure is almost entirely driven by electron dynamics as ions and neutral species are nearly immobile during the rapid process.

Nonlinear Evolution of q = 1 Triple Tearing Modes in a Tokamak Plasma

In magnetic configurations with two or three q=1 (with q being the safety factor) resonant surfaces in a tokamak plasma, resistive magnetohydrodynamic modes with poloidal mode numbers m much larger than 1 are found to be linearly unstable. It is found that these high-m double or triple tearing modes significantly enhance through nonlinear interactions the growth of the m=1 mode. This may account for the sudden onset of the internal resistive kink, i.e., the fast sawtooth trigger. Based on the subsequent reconnection dynamics that can proceed without formation of the m=1 islands, it is proposed that high-m triple tearing modes are a possible mechanism for precursor-free partial collapses during sawtooth oscillations.

Across-wafer nonuniformity of long throw sputter deposition

Physical sputter deposition has been used at longer-than-normal cathode-to-sample distances for semi-directional deposition within high aspect ratio features. “Long throw” sputter deposition can be advantageous over other means of directional sputtering, such as collimated sputter deposition, because of the absence of collimators and related problems. However, due to the finite target size and sample geometry, an asymmetry is observed at the wafer edge with a thicker deposit on the inward-facing walls of trench and via structures compared with the outward-facing walls. We have used numerical simulation as well as metal sputter deposition experiments to characterize this asymmetry, which is typically 2–3:1 at the wafer edge. We also discuss how ionized sputter deposition would alter the deposition profile in the edge region.

Magnetic neutral loop discharge (NLD) plasmas for surface processing

A neutral loop discharge (NLD) is a plasma generated along a magnetic neutral (i.e. null field) loop at magnetic cusps by an externally applied radio frequency (RF) electric field. Due to partial electron cyclotron resonance and good electron confinement by the magnetic cusps, the NLD plasma can efficiently absorb power from the RF field. For applications to material surface processing, NLD plasmas have two important advantages. One is the high ionization rates, which allow the production of high-density plasmas with relatively low electron temperatures at low gas pressures. The other is the spatial and temporal controllability of magnetic field configuration, which allows optimization of plasma configuration during processing. For example, highly uniform plasma processing over a large wafer can be achieved with time-varying shape control of an NLD plasma. In this paper, some basic properties of NLD plasmas as well as several examples of their applications to plasma processing are reviewed. It is shown that, due to their high plasma densities and low collisionality, NLD plasmas are especially suited for highly anisotropic high-throughput etching processes such as those for fabrication of micro-electromechanical systems/nano-electromechanical systems.

Fast growing double tearing modes in a tokamak plasma

Configurations with nearby multiple resonant surfaces have broad spectra of linearly unstable coupled tearing modes with dominant high poloidal mode numbers m. This was recently shown for the case of multiple q=1 resonances [Bierwage et al., Phys. Rev. Lett. 94 65001 (2005)]. In the present work, similar behavior is found for double tearing modes (DTM) on resonant surfaces with q⩾1. A detailed analysis of linear instability characteristics of DTMs with various mode numbers m is performed using numerical simulations. The mode structures and dispersion relations for linearly unstable modes are calculated. Comparisons between low- and higher-m modes are carried out, and the roles of the inter-resonance distance and of the magnetic Reynolds number SHp are investigated. High-m modes are found to be destabilized when the distance between the resonant surfaces is small. They dominate over low-m modes in a wide range of SHp, including regimes relevant for tokamak operation. These results may be readily applied to...

Electric field measurement in an atmospheric or higher pressure gas by coherent Raman scattering of nitrogen

The feasibility of electric field measurement based on field-induced coherent Raman scattering is demonstrated for the first time in a nitrogen containing gas at atmospheric or higher pressure, including open air. The technique is especially useful for the determination of temporal and spatial profiles of the electric field in air-based microdischarges, where nitrogen is abundant. In our current experimental setup, the minimum detectable field strength in open air is about 100?V?mm?1, which is sufficiently small compared with the average field present in typical microdischarges. No further knowledge of other gas/plasma parameters such as the nitrogen density is required.

Hydrogen effects in hydrofluorocarbon plasma etching of silicon nitride: Beam study with CF+, CF2+, CHF2+, and CH2F+ ions

Hydrogen in hydrofluorocarbon plasmas plays an important role in silicon nitride (Si3N4) reactive ion etching. This study focuses on the elementary reactions of energetic CHF2+ and CH2F+ ions with Si3N4 surfaces. In the experiments, Si3N4 surfaces were irradiated by monoenergetic (500–1500 eV) beams of CHF2+ and CH2F+ ions as well as hydrogen-free CF2+ and CF+ ions generated by a mass-selected ion beam system and their etching yields and surface properties were examined. It has been found that, when etching takes place, the etching rates of Si3N4 by hydrofluorocarbon ions, i.e., CHF2+ and CH2F+, are higher than those by the corresponding fluorocarbon ions, i.e., CF2+ and CF+, respectively. When carbon film deposition takes place, it has been found that hydrogen of incident hydrofluorocarbon ions tends to scavenge fluorine of the deposited film, reducing its fluorine content.

Fragment ions of dimethylsilane produced by hot tungsten wires

Fragment ions produced from dimethylsilane with a hot tungsten wire (i.e., catalyzer) in catalytic chemical vapor deposition (Cat-CVD, which is also known as hot wire CVD) processes are identified with a use of a low-energy mass analyzed ion beam system. The mass analysis shows that dominant fragment ions from dimethylsilane are H1+, H2+, CH3+, Si+, SiH3+, SiCH4+, SiC2H+, and SiC2H7+. The energy distributions of these ions are also measured. It is found that the spreads of the energy distributions are narrow and no energetic ions are produced, suggesting that the produced ions are unlikely to cause any significant damage to the deposited films in actual dimethylsilane Cat-CVD processes. The ion production rates are found to be strongly dependent on the catalyzer temperature.

Molecular-dynamics simulations of organic polymer etching by hydrocarbon beams

Molecular-dynamics simulations of hydrocarbon beam injections into a poly (1,4-phenylene) substrate surface are carried out with the use of classical potential functions for covalent bonds of carbon and hydrogen atoms. Van der Waals interactions among carbon atoms are also taken into account. In the low injection energy (50eV) regime, we have observed that injected carbon atoms tend to be deposited on the surface, whereas hydrogen atoms tend to chemically break carbon bonds in the substrate. With the combination of chemical effects by hydrogen with large momenta carried by the injected carbon atoms, hydrogen-rich carbon clusters can etch organic polymer surfaces with relatively high efficiency. Implications of our simulation results on etching processes of low-dielectric-constant organic polymers by hydrogen-nitrogen plasmas are also discussed.