Magnetic neutral loop discharge (NLD) plasmas for surface processing

Abstract

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.

Effects of Micromachining Processes on Electro-Osmotic Flow Mobility of Glass Surfaces

“…While deep reactive ion etching of silicon has been extensively used in manufacturing MEMS for decades [68,69], the etching of glass using neutral loop discharge (NLD) is a promising technology for manufacturing glass micro/nano structures [70][71][72][73]. NLD employs plasma generated along a closed magnetic neutral line by a radio frequency (RF) electric field.…”

Experimental studies on ion acceleration and stream line detachment in a diverging magnetic field

“…In plasma applications, a directed ion flux is used to obtain an efficient momentum exhaust for electric propulsion, e.g., variable specific impulse magnetoplasma rocket, 4 and to achieve high aspect ratios in material processing ͑plasma etching͒. [5][6][7] Diverging magnetic field configurations are often used to obtain a unidirectional flow, [8][9][10][11][12][13] where we may anticipate that the magnetization of ions breaks down in the low magnetic field region. For realizing and controlling the plasma flow, it is important to have the knowledge on flow structure in the low magnetic field region, in which the detachment of ion stream line from the magnetic field line takes place.…”

Scattering-Based Stochastic Process Attracting Electrons Inward under Antiparallel Gradient Magnetic Fields

“…Step (3) of the outline is a convincing inference from step (2). Because the opportunity of electron-molecule collisions during a flight time τ is more or less proportional to τ as τ 0 Nq(v(t))v(t)dt ≈ ντ , x scat tends to be in the inner region of longer residence time than in the outer region.…”

“…The NLD plasma is a low-pressure inductively coupled magnetized plasma used for dry etching. 1,2) The NLD plasma is generated along a ring of zero magnetic field named the neutral loop (NL), and the magnetic field around the NL consists of two pairs of APGMFs.…”