Filling the vacuum chamber of a technological system with homogeneous plasma using a stationary glow discharge
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TEMPERATURE PLASMA
Filling the Vacuum Chamber of a Technological System with Homogeneous Plasma Using a Stationary Glow Discharge1 A. S. Metel, S. N. Grigoriev, Yu. A. Melnik, and V. V. Panin Moscow State University of Technology “Stankin,” Vadkovsky per. 3a, Moscow, 127994 Russia email: [email protected] Received October 31, 2008; in final form, April 3, 2009
Abstract—Experimental study of a glow discharge with electrostatic confinement of electrons is carried out in the vacuum chamber volume V ≈ 0.12 m3 of a technological system “Bulat6” in argon pressure range 0.005–5 Pa. The chamber is used as a hollow cathode of the discharge with the inner surface area S ≈ 1.5 m2. It is equipped with two feedthroughs, which make it possible to immerse in the discharge plasma interchange able anodes with surface area Sa ranging from ~0.001 to ~0.1 m2, as well as floating electrodes isolated from both the chamber and the anode. Dependences of the cathode fall Uc = 0.4–3 kV on the pressure p at a con stant discharge current in the range I = 0.2–2 A proved that aperture of the electron escape out of the elec trostatic trap is equal to the sum So = Sa + Sf of the anode surface Sa and the floating electrode surface Sf. The sum So defines the lower limit po of the pressure range, in which Uc is independent of p. At p < po the cathode fall Uc grows up dramatically, when the pressure decreases, and the pressure p tends to the limit pex, which is in fact the discharge extinction pressure. At p ≈ pex electrons emitted by the cathode and the first generation of fast electrons produced in the cathode sheath spend almost all their energy up to 3 keV on heating the anode and the floating electrode up to 600–800°C and higher. In this case the gas in the chamber is being ionized by the next generations of electrons produced in the cathode sheath, their energy being one order of magnitude lower. When Sa < (2m/M)1/2S, where m is the electron mass and M is the ion mass, the anode may be additionally heated by plasma electrons accelerated by the anode fall of potential Ua up to 0.5 kV. PACS numbers: 52.25.Tx DOI: 10.1134/S1063780X09120095 1
1. INTRODUCTION A whole number of plasma immersion technologi cal processes may be carried out only at the gas pres sure p < 0.1 Pa, when the mean free pass λ of atoms and ions exceeds 0.1 m. For instance, the sheath width d between the plasma and a substrate being subjected to plasma immersion ion implantation may reach 0.5 m at the 100kV amplitude of negative bias voltage pulses applied to the substrate [1]. Energy of ions bom barding the substrate is not less than 100 keV only in that case when their charge exchange length, which is approximately equal to λ, exceeds the width d at least several times. And to achieve it the pressure p should not exceed 0.01 Pa. Lowering of the working gas pressure down to p < 0.1 Pa may also substantially improve effectiveness of some other material treatment processes, for instance, ion nitriding. According to the results of Günther schulze [2] at the cathode fal
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