Density Profile of a Plasma Layer Formed by an Electron Beam
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TEMPERATURE PLASMA
Density Profile of a Plasma Layer Formed by an Electron Beam I. A. Sorokina, b, * and E. G. Shustina, b a
Kotelnikov Institute of Radio Engineering and Electronics (Fryazino Branch), Russian Academy of Sciences, Fryazino, Moscow oblast, 141190 Russia b National Research Nuclear University “MEPhI,” Moscow, 115409 Russia *e-mail: [email protected] Received June 9, 2018; in final form, July 31, 2018
Abstract—Results of particle-in-cell simulation of the formation of a near-wall plasma layer produced by an ionization source remote from the chamber walls are verified experimentally. The measured profiles of the density and temperature of the plasma produced by an electron beam in two modes are compared: (i) gas is ionized by a low-density electron beam, while collective interactions are almost absent (beam-induced plasma), and (ii) gas is mainly ionized by plasma electrons heated due to the development of two-stream instability (beam−plasma discharge). The measured spatial profiles of the parameters of the beam-induced plasma are found to qualitatively agree with the model ones. DOI: 10.1134/S1063780X18120061
1. INTRODUCTION
cannot be lower than the values determined by the electron temperature [1],
Plasmachemical reactors currently used in manufacturing of semiconductor and quantum electronic devices provide a variety of technological operations required for their mass production: surface cleaning, selective and anisotropic etching, implantation, and deposition of dielectric and semiconductor films. The tendencies to increase the speed and memory and reduce the dimensions of telecommunications systems necessitate increasing attention to the corresponding technologies.
kTe (1) ln πm , 2e 2M where Vf is the floating potential, Vs is the plasma potential, Te is the electron temperature, m is the electron mass, M is the ion mass, and k is the Boltzmann constant. The width of the near-wall layer in which plasma quasineutrality is violated is estimated as
High-density plasma sources, such as inductively coupled plasma (ICP) and electron cyclotron resonance (ECR) discharge, are the key technological means for the development of high-precision etching processes. However, these plasma sources inflict several types of radiation damages caused by the bombardment of the treated surface with energetic ions. It is especially important to minimize the charging of the treated surface when manufacturing nanosized structures. As is known [1], the potential of the substrate surface is formed as a superposition of the potential formed due to the difference between the electron and ion mobilities (the Debye layer) and the bias potential applied to the substrate from outside or the high-frequency potential arising upon surface detection of the field of the RF power source producing the discharge (the Child–Langmuir layer). The plasma potential and, accordingly, the energy of the ions hitting the wall
⎛ 2V ⎞4 (2) d = 2 ⎜ 0 ⎟ λD, 3 ⎝ Te ⎠ where V0 is the potential at the layer boundary and λD is the Debye length. When
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