Lin I

SiO2 thin film deposition by radio frequency oxygen plasma enhanced laser ablation from Si

A novel process of room temperature deposition of thin SiO2 film by laser ablation from a c‐Si target in a low pressure (<5 mTorr) rf oxygen magnetron plasma background was developed. The gas phase reactions which usually dominate in other high pressure reactive ablation processes are suppressed and the energetic particles from the target have good transport to the substrate in the low pressure background. The surface reactions are continuously enhanced after the arrival of Si particles by the high fluxes of oxygen radicals and ions from the steady state magnetron discharge. The deposition of stoichiometric, less disorder, dense, and water free films are demonstrated.

Steady‐state rf magnetron discharges

A study of the steady‐state discharges and the spatial distributions of plasma parameters vertical to the magnetic field was made in an rf magnetron with oval cross section. Langmuir probes were used for the major diagnostics. The device generates low‐ion energy, high‐ion flux stable plasma (Ei∼102 eV, Γi∼5 mA/cm2 at 1 W/cm2 rf power). Ion transport toward the positive sheath is enhanced by the rf induced dc electric field in the uniform glow. The state of the glow is independent of rf power except ion density ni∝ (rf power)α. The voltage drop across the sheath follows V∝(rf power) β with 0<α<β<1. The discharge strongly depends on magnetic field strength and system pressure, and weakly depends on the gas chemistry. Generally, the state of the discharge is determined by charged particle generation, transport and loss processes, and in turn controlled by the system operating parameters. The experimental results obey the conservation laws and the steady‐state criterion. The correlations between plasma parame...

Fine silicon oxide particles in rf hollow magnetron discharges

The formation and the properties of fine silicon oxide particles in a hollow post‐type rf magnetron discharge in SiH4/O2/Ar gas mixtures were studied. For P≳30 mTorr, primary fine particles (PFPs) with a diameter of about 20 nm are formed through homogeneous reactions. Their diameter increases with the system pressure. PFPs with sufficient negative charge are suspended in the plasma. They can further aggregate with other PFPs to form aggregated fine particles (AFP) with nearly spherical shape and larger diameter. The size of the AFP depends on the duration of the rf power. In the cw mode, AFPs gradually drift axially to both ends of the discharge system. The accumulation of AFPs at the end trap causes low‐frequency oscillation of the discharge. The films consisting of fine particles are loose and brittle. Infrared‐absorption spectrum shows that oxide formed in the homogeneous reaction has similar Si—O bond strain relaxation to that of the thermal oxides and the annealed oxide from chemical‐vapor deposition.

Fine particles in dusty plasmas

Dusty plasma is a four-component plasma system with fine particles suspended in a gaseous background with electrons, ions, and neutrals. The dust particles are usually negatively charged. The capability of forming fine particles in discharges opens a new window for various applications. The large mass and charges drastically alter the nature of the background plasma and generate many interesting collective behaviors. In this paper, we briefly review the recent researches on the fine particles in dusty plasmas, including the forces on the single particles, particle formation mechanisms, particle manipulation and removal, dust plasma crystals and liquids, and collective waves in dusty plasmas.

Hollow oval magnetron for large‐area low‐energy ions

A novel device, the ‘‘hollow oval magnetron,’’ was designed and characterized. The device has a hollow electrode with an oval cross section. It sustains a large‐area uniform plasma with low‐energy ions under low pressure and moderate rf power (Ni ∼1011 cm−3, Γi ∼0.5 mA/cm2, Ei ∼30 eV, and P∼5 mTorr). The energy distribution of ion current onto the hollow electrode has a broad spread ΔEi /Ei ∼1 in the rf mode, and a narrow peak ΔEi/ Ei ∼0.1 with a low‐energy tail in the dc mode. The device is a good candidate for low‐energy high‐rate plasma‐material processing.

Observation of 3D defect mediated dust acoustic wave turbulence with fluctuating defects and amplitude hole filaments

We experimentally demonstrate the direct observation of defect mediated wave turbulence with fluctuating defects and low amplitude hole filaments, from a 3D self-excited plane dust acoustic wave in a dusty plasma by reducing dissipation. The waveform undulation is found to be the origin for the amplitude and the phase modulations of the local dust density oscillation, the broadening of the sharp peaks in the frequency spectrum, and the fluctuating defects. The corrugated wave crest surface also causes the observed high and low density patches in the transverse (xy) plane. Low oscillation amplitude spots (holes) share the same positions with the defects. Their trajectories in the xyt space appear in the form of chaotic filaments without long term predictability, through uncertain pair generation, propagation, and pair annihilation.

Strongly coupled dusty plasmas: crystals, liquids, clusters and waves

The dusty plasma is a system that consists of many strongly-charged fine dust particles suspended in a plasma background. The slow dynamics and strong coupling due to the large mass and charges lead to the formation of highly-ordered dust crystal structures suspended in the plasma background, which can be directly observed. The dusty plasma forms a link to the area of condensed matter physics for the study of many interesting microscopic phenomena from order to disorder. In this paper, we introduce the special properties of this system from the viewpoint of conventional plasma physics, then we briefly review past works on the structure and dynamical behaviour from the highly-ordered state, through the melting and liquid states with associated vortex-type excitation and anomalous diffusion, to the state with self-organized macroscopic dust waves after losing microscopic order. The first observation of strongly-coupled dust Coulomb clusters with small numbers of particles from a few to a few hundred, which resemble classical atoms, is also demonstrated.

Ionization‐drift turbulence in rf magnetron plasmas

Electron density fluctuations in a rf hollow magnetron system are investigated. The weakly ionized and axially magnetized (B∼80 G) discharge supports nonlinear ionization‐drift waves in the presence of the nonuniform rf‐induced dc electric field and density gradient along the normal of the hollow electrode surface. The fluctuations have good coherence along B and are turbulent in the transverse plane. The turbulence is inhomogeneous along the density gradient. The power spectrum shows two major bands. The amplitude of the high‐frequency oscillation is modulated by the low‐frequency oscillation. In the transverse plane, the phase velocity is about the same as the diamagnetic drift velocity. It has one component along the diamagnetic drift direction and the other toward the electrode surface. The turbulence also induces anomalous cross‐field electron current which deteriorates the electron confinement in the low‐pressure regime. Generally, the system combines the nature of the reaction diffusion and the dri...

Projectile channeling in chain bundle dusty plasma liquids: Wave excitation and projectile-wave interaction

The microscopic channeling dynamics of projectiles in subexcitable chain bundle dusty plasma liquids consisting of long chains of negatively charged dusts suspended in low pressureglow discharges is investigated experimentally using fast video-microscopy. The long distance channeling of the projectile in the channel formed by the surrounding dust chain bundles and the excitation of a narrow wake associated with the elliptical motions of the background dusts are demonstrated. In the high projectile speed regime, the drag force due to wake wave excitation increases with the decreasing projectile speed. The excited wave then leads the slowed down projectile after the projectile speed is decreased below the resonant speed of wave excitation. The wave-projectile interaction causes the increasing projectile drag below the resonant speed and the subsequent oscillation around a descending average level, until the projectile settles down to the equilibrium point. Long distance projectile surfing through the resonant crest trapping by the externally excited large amplitude solitary wave is also demonstrated.

INFRARED STUDIES OF ROOM TEMPERATURE DEPOSITION OF HYDROGENATED SILICON OXIDE FILMS IN RF MAGNETRON DISCHARGES

The properties of a‐SiOx:H thin films deposited at low temperature (∼ 50 °C) in a low energy magnetron rf plasma system with Ar/SiH4/O2 gas mixtures are investigated. In the low pressure regime (about 5 mTorr reactive gases), the surface reaction dominates in the film formation process. As the partial pressure ratio (ROS) of oxygen to silane increases, the Si‐H related vibrational modes gradually disappear, and the film becomes stoichiometric SiO2 for ROS≥1. High quality oxide film can be deposited due to the low pressure environment and the plasma promoted surface process. In the high pressure regime (tens of mTorr) the deposited SiO2 films contain fine particles (tens of nanometer in size) and are porous (15% void) due to the gas phase homogeneous reaction and aggregation. The infrared absorbance spectra with normal and oblique incidence imply different origins of the half width and the shoulder intensity of the 1070 cm−1 Si‐O(s) mode. In comparison with the low pressure dense films, the narrow half wid...