Inductively coupled plasma sources are being developed to address the need for high plasma density (1011–1012 cm−3), low pressure (a few to 10–20 mTorr) etching of semiconductor materials. One such device uses a flat spiral coil of rectangular cross section to generate radio-frequency (rf) electric fields in a cylindrical plasma chamber, and capacitive rf biasing on the substrate to independently control ion energies incident on the wafer. To investigate these devices we have developed a two-dimensional hybrid model consisting of electromagnetic, electron Monte Carlo, and hydrodynamic modules; and an off line plasma chemistry Monte Carlo simulation. The results from the model for plasma densities, plasma potentials, and ion fluxes for Ar, O2, Ar/CF4/O2 gas mixtures will be presented.
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.
Inductively coupled plasmas (ICPs) are currently being investigated as high density (> lo"-10" cmB3), low pressure (< l-20 mTorr) sources for semiconductor etching and deposition. We have developed a two-dimensional (Y,z) hybrid model for ICP sources and have used the model to investigate Ar/C!Fd02 mixtures for etching applications. The simulation consists of electromagnetic, electron Monte Carlo, and hydrodynamic modules with an "off-line" plasma chemistry Monte Carlo simulation. The model produces the temporally and spatially dependent magnetic and electric fields (both inductively and capacitively coupled), plasma densities, and the energy resolved flux of ions and radicals to the substrate. We discuss-results for densities, power deposition, and ion energies to the substrate as a function of position.
A molecular dynamics model is used to understand the layer-by-layer etching of Si and SiO2 using fluorocarbon and Ar+ ions. In these two-step etch processes, a nanometer-scale fluorocarbon passivation layer is grown on the material’s surface using low energy CFx+ ions or radicals. The top layers of the material are then reactive ion etched by Ar+ ions utilizing the fluorocarbon already present on the material surface. By repeating these two steps, Si or SiO2 can be etched with nanometer-scale precision and the etch rate is considerably faster than what traditional atomic layer etching techniques provide. The modeling results show that fluorocarbon passivation films can be grown in a self-limiting manner on both Si and SiO2 using low energy CF2+ and CF3+ ions. The fluorocarbon passivation layer is a few angstroms thick, and its thickness increases with the fluorocarbon ion’s energy. Increasing the ion energy, however, amorphizes the top atomic layers of the material. In addition, the fluorocarbon film becomes F rich with increasing ion energy. Simulations of fluorocarbon passivated SiO2 surface show that Ar+ ions with energy below 50eV etch Si (within SiO2) in a self-limiting manner. Si etching stops once F in the fluorocarbon passivation layer is exhausted or is pushed too deep into the substrate. Oxygen within SiO2 is more easily sputtered from the material surface than Si, and the top layers of SiO2 are expected to become O deficient during Ar+ ion bombardment. Ar+ ion etching of fluorocarbon passivated Si also appears to be self-limiting below 30eV ion energy, and etching stops once F on the material surface is either consumed or becomes inaccessible.
One of the most challenging and recurring problems when modeling plasmas is the lack of data on the key atomic and molecular reactions that drive plasma processes. Even when there are data for
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