Vacuum ultraviolet (VUV) radiations generated in low temperature plasmas (e.g., CCP and ICP) has been reported to cause wafer damage, alteration of morphology of polymers and electrical properties of dielectrics. Electron-hole pairs generated in dielectric films by VUV radiations can be trapped in dielectrics and interfaces. This results in charge buildup and dielectric breakdown as well as the decrease of device reliability. Synergistic effects of VUV exposure and energetic ion bombardment have been addressed to increase photoresist roughening. In order to improve the device and plasma process reliability, monitoring and evaluation of plasma generated VUV radiations have become important and highly demanded in plasma processing. Herein, characterization and spatial evolution of VUV radiations generated in a microwave surface-wave plasma is reported. Microwave surface-wave discharges operating within a wide power and pressure window can be used to produce large area plasmas of high density. Due to its inherent diffusion characteristics, apart from the discharge source, quiescent, uniform, and low-temperature Maxwellian plasma near wafer region can be obtained. In spite of these promising features, understanding the evolution of plasma generated VUV radiations can help the development of microwave surface-wave plasma based hardware and the design of process recipes. The plasma source used in this work consists of a radial line slot antenna (RLSA) which transmits 2.45 GHz microwaves into a large quartz resonator disk which then couples to the plasma. VUV radiations in RLSA plasma are monitored by measuring VUV induced electron-hole pair generation in dielectric films using VUV monitoring sensors developed by Samukawa et al.¹ Three kinds of VUV sensors consisting of SiO₂, Si₃N₄, and SiO₂/Si₃N₄ films are used, which monitor VUV radiations in the wavelength range of <140 nm, <250 nm, and >250 nm, respectively. Measurements in N₂, Ar, and O₂ plasma are carried out from 23 mm to 203 mm below top plate surface. A wide pressure-power spectrum has been investigated. Experimental results indicate that VUV radiations in RLSA plasma are dramatically reduced as a function of distance from the top plate. For better understanding on the evolution of VUV radiations in RLSA plasma, the electron energy distribution functions (EEDFs) are also measured using a Langmuir probe as a function of vertical location. Mechanisms on the evolution of VUV radiations are discussed based on the measured EEDFs and VUV absorption process.

¹ S. Samukawa et al., J. Vac. Sci. Technol. A 23(6), 1509 (2005)

Helicon discharges are known to very efficient in generating high plasma densities at low pressures for such applications as etching. The reason for this efficiency is that helicon plasmas depend on resonant waves in a magnetic field which couple the rf energy into electrons in a complicated way involving nonlinear physics. To generate the magnetic field, commercial helicon reactors employ large, heavy electromagnets and a correspondingly large dc power supply to drive them. A new type of helicon discharge has been developed that uses the remote field of annular permanent magnets (PMs) and an array of small tubes that incorporate constructive interference of a reflected helicon wave [1-3]. With 3kW at 13.56 MHz, an 8-tube test device has produced argon plasmas of density 2-6 x 10¹¹ cm^-3 over ~20 x 50 cm areas with +/- 3-5% uniformity [4]. The source needs only 15 cm of vertical space. A code HELIC is used for the design of the wave properties, and a new code EQM has recently been developed to predict the equilibrium profiles of plasma and neutral densities and of electron temperature, With 27.12 MHz it is possible to design a very compact plasma thruster for spacecraft.

*mail to:ffchen@ee.ucla.edu

1. F.F. Chen and H. Torreblanca, Plasma Phys. Control. Fusion 49, A81 (2007).

2. F.F. Chen and H. Torreblanca, Phys. Plasmas 16, 057102 (2009).

3. F.F. Chen and H. Torreblanca, Plasma Sources Sci. Technol. 16, 593 (2007).

Technical plasmas are often generated by radio-frequency (RF) fields in the MHz regime. In particular, capacitively coupled RF plasmas have found wide industrial application ranging from semiconductor etching to thin film deposition as e.g. in large area production of solar-cells. In all cases the processes on the substrate surface are critically dependent on the energy and flux of the impinging ions. Therefore, independent control of these parameters is the major aim of various alternative concepts developed in the past. Despite some general progress, in practice independent control has been realized only within certain constrains.

The recently invented electrical asymmetry effect provides a novel solution by adjusting as a control parameter the relative phase between two harmonic RF frequencies [1]. This meets not only the above requirements in an almost ideal way but allows in addition for the first time breaking the symmetry in geometrically geometric discharges, which are common in large area processing. There the phase can be set so that the ion energy is increased on one electrode and reduced on the other or vice versa. The physics of the resulting non-linear system can be reduced to a few basic principles that allow an analytic treatment. The results of the analytical model are compared with particle-in-cell (PIC) / Monte Carlo (MC) simulations and experiments [1-6]. Although the system is characterized by a high degree of complexity all three approaches show remarkable agreements. Ultimately this leads to a detailed understanding not only of the dynamics of the electrical asymmetry effect but also of the physics of capacitively coupled plasmas in general.

Finally, first applications in industry on thin-film solar-cell production demonstrate superior performance by immediately more than doubling the deposition rate of silicon without loss in quantum efficiency.

References:

[1] Brian G. Heil, U. Czarnetzki, R. P. Brinkmann, T. Mussenbrock, Journal of Physics D: Applied Physics. 42, 165202 (2008)

[2] Z. Donkó, J. Schulze, B.G. Heil and U. Czarnetzki, Journal of Physics D: Applied Physics 42, 025205 (2009)

[3] Z. Donkó, J. Schulze, U. Czarnetzki, and D. Luggenhölscher, Applied Physics Letters 94, 131501 (2009)

[4] J. Schulze, E. Schüngel and U Czarnetzki, Journal of Physics D: Applied Physics 42, 092005 (2009)

[5] J. Schulze, E. Schüngel, U. Czarnetzki and Z. Donkó, Journal of Applied Physics 106, 063307 (2009)

[6] J. Schulze, E. Schüngel, Z. Donkó, and U. Czarnetzki, Journal of Physics D: Applied Physics, in print (2010)

In electric discharge-pumped excimer lasers as used for photolithography sources in microelectronics fabrication, corona discharges are often used to provide UV photons to preionize the gas mixture. The preionization source, often called a corona bar, typically consists of a cylindrical metal rod surrounded by a dielectric. A discharge initiated by a high voltage pulse propagates around the surface of the corona bar, producing a surface-hugging avalanche wave similar to a gas phase streamer. The high electron temperature in the avalanche front produces radiating excited states that in turn produce the desired UV photons. We present results from a numerical study of an idealized corona bar discharge sustained in a multi-atmosphere Ne/Ar/F₂/Xe gas mixture as used in ArF excimer lasers. The corona bar consists of a grounded metal cylinder surrounded by an annular dielectric layer of a few cm diameter. A point electrode (cathode) is located on the surface of the dielectric layer and is subject to a stepwise initial voltage change. The ensuing corona surface discharge was investigated using a 2-dimensional plasma hydrodynamics model with radiation photon transport. Continuity equations for charged and neutral species, and Poisson's equation are solved coincident with the electron energy equation with transport coefficients obtained from solutions of Boltzmann's equation. The ionization front, initiated from the point electrode, propagates along the cylinder surface (with speeds up to 3 x 10⁸ cm/s that depend on the dielectric constant) charging the surface as it propagates. The ionization front usually stops before completing a full circle as the corona bar becomes progressively charged. The strength and propagation speed of the ionization wave are characterized by the electron density and temperature distributions along the cylinder circumference. The photon fluxes are collected on a surrounding circular surface. With radiation from short lived states such as Ne₂*, the UV emission sweeps around the corona bar coincident with the ionization wave. The effects of dielectric constants, gas mixture and voltage on the corona discharge dynamics will be presented.

* Work supported by Cymer, Inc. and the Department of Energy Office of Fusion Energy Sciences.