Simulation of Thin Carbon Film Deposition in a Radio‐Frequency Methane Plasma Reactor

Abstract

Radio-frequency (rf) methane and methane/hydrogen plasmas are used extensively for the deposition of hard-coating of diamond-like carbon films. 1 The prediction of the deposition of thin carbon films in nanoscale is a technological challenge. The discharge in typical reactors being essentially two dimensional, a two-dimensional modeling of the glow discharge physics is essential to identify the axial and radial variations of the species and their fluxes. Multidimensional discharge modeling for a polyatomic gas like methane is challenging in terms of computational effort and time. A methane discharge contains a number of positive and negative ions and radicals. The gas phase chemistry and surface deposition models need to be coupled with the discharge physics model to predict the radial and axial variations of radicals. The radical and ion fluxes to the cathode are required for the prediction of the diamond-like carbon film deposition rate on the wafer. The motivation of the present research is to develop a comprehensive plasma model for the prediction of the deposition of thin diamond-like carbon film under reactor operating conditions.Capacitively coupled rf discharges are extensively used in the semiconductor industry for etching and deposition processes, and their use is important for ultralarge-scale integration (ULSI) device fabrications. Recently, diamond-like carbon (DLC) film deposition has been investigated for its potential applications as a low dielectric constant material for the back end of the line interconnect structures in ULSI circuits. 2 A number of one-dimensional fluid models for rf discharges has been developed in the last decade. Recently, some of these models have been extended to two-dimensions to capture both the axial and radial variations of plasma properties.Considerable research has been performed for modeling monatomic gas discharges in capacitively coupled reactors. By using three moments of the Boltzmann equation, one-and two-dimensional rf He discharges 3 were simulated for plasma density, electric field, mean energy, and ionization rates. A two-dimensional fluid model for an rf Ar discharge in a cylindrical chamber 4 was presented where self-induced dc bias was computed using a trial-and-error method. An asymmetric axial ion density profile was predicted that peaked toward the smaller, powered electrode. The electron energy in the presheath region in front of the powered electrode was several electron-volts higher than that in the bulk plasma. The off-axis maximum in electron density was observed in a two-dimensional Ar discharge model with metastable neutral transport. 5 An Ar discharge model for the Gaseous Electronics Conference reference reactor 6 also predicted an off-axis maximum for plasma density. The electron and ion current densities on the powered electrode were observed to increase radially outward. A three-moment approach 7 for both electrons and ions to model the two-dimensional rf Ar discharge was used to predict the electron density, potential and electron-excitat...

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