Investigation of electron source and ion flux uniformity in high plasma density inductively coupled etching tools using two-dimensional modeling

Abstract

Inductively coupled plasma (ICP) sources are being developed as reactors for high plasma density (1011–1012 cm−3), low-pressure (<10–20 mTorr) etching of semiconductors and metals for microelectronics fabrication. Transformer coupled plasmas (TCPs) are one variant of ICP etching tools which use a flat spiral coil having a rectangular cross section powered at radio frequencies (rf) to produce a dense plasma in a cylindrical plasma chamber. Capacitive rf biasing of the substrate may also be used to independently control ion energies incident on the wafer. The uniformity of generating the plasma and the uniformity of the flux of reactants to the substrate are functions of the geometry and placement of the coil; and of the materials used in the construction of the chamber. In this article, we use results from a two-dimensional model to investigate design issues in TCPs for etching. We parametrize the number of turns and locations of the coil; and material properties of the reactor. We find that at low pressure, designs which produce ionization predominantly at larger radii near the edge of the wafer produce more uniform ion fluxes to the substrate. This results from a ‘‘converging’’ ion flux which compensates for losses to lateral surfaces. Careful attention must be paid to metal structures in the vicinity of the coils which restrict the azimuthal electrical field. This situation results in reduced power deposition at large radii, which can be compensated by over sizing the coil or by using auxiliary solenoidal coils. The plasma and neutral transport, dominated by diffusion, treats the advective flow from the gas inlets and pump port as local sources and sinks which are rapidly volume averaged.

Three-dimensional discharge simulation of inductively coupled plasma (ICP) etching reactor

“…The conductivity of plasma consists of all species discharged, including electron and ions. In practical use electron plays a so important role that other ion's contributions can be neglected in the estimate of conductivity [1] . Electron collision frequency v m is the distribution function of electron energy.…”

“…The first design uses a solenoid coil wrapped around the outer diameter of the chamber; while the second one uses a spiral planar coil placed on the top of the chamber. If the coil is driven at the frequency of 10 s MHz with the energy of 100 1000 s watts deposited in the etching reactor, the plasma whose density ranged from10 11 to 10 12 cm 3 will be generated at the pressure of 5 20 mTorr and flow rates of 10 100 s Sccm [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.…”

“…With the pressure of 5-20 mTorr (0.666-2.667 Pa) and the flow rate of 10-100 sccm, if the coil is driven at the frequency of 10 MHz with the energy of 100-1,000 W deposited in the etching reactor, the plasma whose density ranged from 10 11 to 10 12 cm −3 will be generated [2].…”

“…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.…”