Plasma molding over surface topography: simulation and measurement of ion fluxes, energies and angular distributions over trenches in RF high density plasmas

In atmospheric pressure discharges, such as dielectric barrier discharges (DBDs), it is common to have transient sheaths having electric fields of hundreds of kV cm −1. With these sheaths, even with short mean free paths, it may be possible to deliver short pulses of energetic ions (tens to hundreds of eV) to surfaces. The energies of these ions can be controlled to some extent by selecting the relative permittivity (ε/ε 0) of the underlying surface. In using DBDs to treat sensitive materials or tissue in plasma medicine where control of ion energies may be desirable, one has a very limited ability, if any, to modify the dielectric properties of the tissue. In this paper, we use results from a computational study to propose a method to control the characteristics of the transient sheath formed at the surface of sensitive materials or biological tissue by using a thin porous film placed on top of the surface. By controlling the transient sheath, one can control the ion energies delivered to the surface. We show that ion energies delivered to the underlying surface through the pores can be controlled by the capacitance and thickness of the film and the width of the pore. Results are discussed for streamer penetration and ion energies delivered to the surface when the plasma filament directly strikes the pore and is offset from the pore.

Section: Ieads Through a Pore To Underlying Skinmentioning

confidence: 99%

Control of ion activation energy delivered to tissue and sensitive materials in atmospheric pressure plasmas using thin porous dielectric sheets

Babaeva

Kushner²

2013

“…The properties (flux, energy, directionality) of neutral beams generated by simultaneous extraction and neutralization of ions through grid holes depend critically on the interaction of the plasma with the holes (plasma moulding). Plasma moulding [44][45][46][47] refers to the ability of the plasma-sheath interface to 'contour' along the topography of surface features in contact with the plasma. In the case of plasma in contact with a grid, plasma moulding depends primarily on the diameter of the grid hole, D, as compared with the plasma-sheath thickness, L sh .…”

Section: Fundamentals Of Ion Extraction and Neutralization Through Gr...mentioning

confidence: 99%

Fast (tens to hundreds of eV) neutral beams for materials processing

Economou¹

2008

Fast neutral beams (beam energy of tens to hundreds of eV) may be useful for mitigating charging damage that can occur in conventional plasma processing of materials. For neutral beam processing to be viable, however, the beam energy, flux and directionality must be comparable to those in traditional reactive ion etching or reactive ion beam technologies. This paper provides a review of fast neutral beams for materials processing. Neutral beam generation techniques are outlined. Characterization of neutral beams is important to measure the beam flux, energy and angular distributions. Neutral beam materials processing is discussed with emphasis on etching of thin films.

“…The anisotropic etching profile can be achieved as a result of the competition between bottom etching and sidewall passivation. Plasma moulding is an important issue in deep-Si etching [7,8]. When the sheath thickness in front of the wafer is comparable to or even smaller than the pattern size, the ion angular distribution deviates from the normal incidence under the distorted electric field caused by plasma moulding.…”

Section: Introductionmentioning

confidence: 99%

Numerical investigation of relationship between micro-scale pattern, interfacial plasma structure and feature profile during deep-Si etching in two-frequency capacitively coupled plasmas in SF₆/O₂

Hamaoka¹,

Yagisawa²,

Makabe³

2009

The feature profile of deep-Si etching in the presence of plasma moulding in two-frequency capacitively coupled plasmas in SF6/O2 has been numerically simulated to investigate the relationship between the micro-scale pattern on a Si wafer, the interfacial structure of the plasma (i.e. the sheath) and the etching profile. We have also discussed the deep-Si etching profile as functions of the SF6/O2 gas mixture ratio and the total gas pressure. The result shows that the plasma moulding has no influence on the sheath structure when the sheath thickness is an order of magnitude longer than the width of the hole pattern. In the presence of a large number of F radicals, the chemical etching of Si causes isotropic etching with a significant undercut profile, reducing the plasma moulding's influence on the etching profile due to the F radicals' much higher Si etching rate compared with the rate of etching by ions. On the other hand, with the increase in the oxygen mixture ratio, a passivation layer grows up on the inside wall, and the removal of the layer at the bottom corner is strengthened by the distorted ion by plasma moulding. Thus, the etching is enhanced particularly at the bottom corner. As the pattern width decreases and the oxygen mixture ratio increases, the etching profile becomes anisotropic by the formation of the passivation layer at the sidewall. In addition, the bottom profile becomes flat because of the uniform ion flux under the reduced influence of the plasma moulding.