A three-dimensional model for inductively coupled plasma etching reactors: Azimuthal symmetry, coil properties, and comparison to experiments

Abstract

Inductively coupled plasma ͑ICP͒ etching reactors are rapidly becoming the tool of choice for low gas pressure, high plasma density etching of semiconductor materials. Due to their symmetry of excitation, these devices tend to have quite uniform etch rates across the wafer. However, side to side and azimuthal variations in these rates have been observed, and have been attributed to various asymmetries in pumping, reactor structure and coil properties. In this article, a three-dimensional computer model for an ICP etching reactor is reported whose purposes is to investigate these asymmetries. The model system is an ICP reactor powered at 13.56 MHz having flat coils of nested annuli powering Ar/N 2 and Cl 2 plasmas over a 20-cm diam wafer. For demonstration purposes, asymmetries were built into the reactor geometry which include a wafer-load lock bay, wafer clamps, electrical feeds to the coil, and specifics of the coil design. Comparisons are made between computed and experimentally measured ion densities and poly-silicon etch rates in Cl 2 plasmas. We find that the electrical transmission line properties of the coil have a large influence on the uniformity of plasma generation and ion fluxes to the wafer.

Issues and status of “modelling industrial plasmas” from papers and discussions

“…Recent references to this specific work are given in Refs. [1][2][3][4], although numerous other groups also do similar modelling. These simulations typically treat 3-D geometry, but some approximations are made so that only some of the components are tully 3-D.…”

A Numerical Method to Simulate Radio-Frequency Plasma Discharges

“…Upwind biasing the spatial discretization of the electron flux (and sometimes the ion flux) is used almost universally to circumvent the stability problems posed by steep gradients at the sheath edges and very low electron densities (see, for example, Barnes et al [13], Sommerer and Kushner [23], Gogolides et al [24], Kushner et al [8], and Colella et al [25]). However, some simulations have been published with a nondissipative discretization for the electron and ion equations.…”

“…Prior to 1990, simulations were typically one dimensional, either with a fluid model or a particle model of the plasma; since then, two-and three-dimensional models with detailed chemistry have been developed [1]. Some examples of two-dimensional simulations can be found in [2]- [7]; three-dimensional simulations are more rare, but [8]- [10] contain representative calculations. Numerical tools are actually being used by industry as part of the design process [1].…”

The effect of discharge conditions of ICP etching reactor on plasma parameters

“…These simulations are instructional in the study of plasma discharge, component transport and plasma chemistry. The layout of coil directly influence the uniformity of plasma density, and the related simulation and experiment results were also introduced by some researchers [2,13]. The impact of coil structure on plasma density is expected to be further studied.…”

“…Many computational models [2,[8][9][10][11][12][13][14][15][16] were developed to investigate the parameters that can influence the uniformity of plasma flow to the wafer and to shorten the R&D cycle with the theory on fluid kinetics, electromagnetic, and plasma discharge theories. These simulations are instructional in the study of plasma discharge, component transport and plasma chemistry.…”