Yoko Maemura

Particle formation and a-Si:H film deposition in narrow-gap RF plasma CVD

The effects of electrode distance are discussed in a diode type plasma enhanced chemical vapor deposition (PECVD) system as an important external control parameter for the preparation of hydrogenated amorphous silicon (a-Si:H) using an RF silane (SiH4) plasma. The electron temperature is increased by shortening the electrode distance due to a plasma self-organization mechanisms, leading to an increase in the growth rate of a-Si:H films. Furthermore, shortening the distance between the heated electrodes (anode and/or cathode) gives rise to decrease in SiH4 density in the discharge space near the electrodes resulting in suppression of the particle formation. Through the control of particle formation by changing the electrode distance, the defect properties in the resulting films are successfully controlled.

Transport of negatively charged particles by E × B drift in silane plasmas

Abstract The motion of dust particles in glow discharge plasmas is influenced by the applied magnetic field, B , perpendicular to the discharge electric field, E . The negatively charged particles in a weakly magnetized plasma can be transported by the ambipolar electric field due to the E × B drift of the magnetized electrons. In this paper we propose a transport model to indicate the behavior of dust particles and evaluate “the ambipolar E × B drift” in weakly magnetized plasmas, in which only electrons can be magnetized, in terms of the drift velocities of charged particles (electrons, ions and negatively charged massive particles) calculated from the equations of motion. The calculation results in the present model agree qualitatively with the experimental results.

Mechanism of particle transport in magnetized silane plasmas

Particle transport phenomena were investigated in silane plasmas in the presence of a magnetic field B perpendicular to a discharge electric field E. From the experimental results, it was concluded that silicon particles were transported in the opposite direction to the drift, and the particle density decreased with increasing applied magnetic flux density. Theoretical calculations on particle drift show that negatively charged particles can be transported in the opposite direction to drift and the drift velocity increases with B for the present experimental conditions. Both experimental and theoretical results suggest that transport by modified ambipolar drift can eliminate particles from discharge space.

Effects of Crossed Magnetic Fields on Silicon Particles in Plasma Chemical Vapor Deposition Process

In order to realize the preparation of large-area uniform hydrogenated amorphous silicon thin films for solar cells under-dust particle-free process conditions, the scanning plasma method (SPM) using a crossed magnetic field has been investigated to remove silicon particles produced in silane discharge. The silicon particles collected on the substrates were observed by scanning electron microscopy (SEM) to identify the crossed magnetic field effects on particle removal and suppression in the present SPM process. In this paper, the relationship between the externally applied crossed magnetic field and the particle behavior in silane plasma are reviewed from the viewpoint of particle removal and suppression.

Influence of a modulated magnetic field on the behavior of particulates in silane plasma CVD

The spatio-temporal evolution of silicon particles has been investigated by using a laser light scattering method in a static and/or modulated magnetic field. If the crossed static magnetic field is applied at the same time as the discharge starts, then the appearance times of the Mie scattering intensity by silicon particles become later with increasing applied magnetic flux density and the density of silicon particles decreases with increasing applied magnetic flux density. If the modulated magnetic field is applied, the particle density decreases more than in the case of static applied magnetic field; however, the appearance time of silicon particles has an optimum frequency for the discharge condition. Finally, it is considered that the fluctuation of discharge current in the presence of a modulated magnetic field is caused by the effects of both generation of silicon particles in the discharge space and the deposition of a-Si:H thin film on the cathode surface.

a-Si:H film deposition using same phase modulated scanning plasma method

The effects of a magnetic field perpendicular to a discharge electric field (cross-magnetic field) and their modulation phase are discussed in a plasma enhanced chemical vapor deposition (PECVD) system as important external control parameters for the preparation of hydrogenated amorphous silicon (a-Si:H) using silane (SiH4) plasmas. In this paper, a-Si:H thin films are prepared under the conditions of the same and random phase modulations of an electric field (E) and a magnetic field (B). The effects of removal and growth suppression on silicon particles owing to the same phase modulation of E and B fields can suppress the disorder parameter and the surface roughness of the deposited films.

Correlation between silicon particles and modulated crossed magnetic field in silane plasmas

The influence of a modulated crossed magnetic field on silicon particles have been investigated by a laser light scattering method and a field emission scanning electron microscopy (FESEM) in SiH 4 (10%)/Ar plasmas. In the initial stage of silane discharge, the fluctuation of discharge current due to the modulated crossed magnetic field being applied is drastically decreased, then the density of silicon particles removed from the discharge space is increased and the average radius of the removed silicon particles is kept smaller than 10 nm of the detecting limit of FESEM. It is suggested that the small silicon particles in the stage of the initial growth are effectively removed from the discharge space and the fluctuation of discharge current is related to the nucleation and the growth of silicon particles.

Large-area uniform dust-free plasma CVD

In the weak magnetic field perpendicular to the discharge electric field, both the electrons and positive ions are transported in the direction of E×B drift by the space charge electric field produced by the preceded electrons. As a result, radicals are generated uniformly outside of discharge space between the electrodes in the direction of E×B drift. On the other hand, negatively charged heavy particles such as dust particles can be removed from discharge space in the direction opposite to E×B drift of plasmas. The authors have studied the transport mechanisms of magnetized dusty plasmas and its applications for the large-area uniform a-Si:H thin film deposition in plasma CVD methods. This paper reviews the transport phenomena and the transport mechanisms of dust particles and the results of film preparation under particle-free process conditions.

Experimental Verification of Dust Particle's Transport by Ambipolar ExB Drift

Publisher Summary This chapter explores the transport mechanisms of dust particles in simplified system, utilizing the process of injection of the small Cu particles into parallel-plates DC argon discharges. Based on this understanding, the chapter discusses the process of experimental measurement of dust particles in the —E x B direction. The space charge electric field enhanced by the E x B drift of electrons is calculated as a driving force acting on the dust particles. The chapter also presents a comparison of the drift velocities of dust particles and the results from the calculations and experiments. The results suggest that when the magnetic field from 0 Gauss to 50 Gauss is applied, the injected Cu particles are removed from discharge space in the direction opposite to E x B drift of plasmas with a drift velocity from 2 mm/sec–15 mm/sec. The drift velocities from the experiments agree qualitatively with the results obtained from the calculation model based on the ambipolar condition of electrons, ions and negatively charged dust particles, where the space charge electric field is enhanced by the magnetized electrons and it acts on the particle drift towards the —ExB direction in weakly magnetized plasmas.