Inductively coupled plasma reactors: Modeling, simulation, and experimental validation

A combined experimental and numerical study of inductively coupled plasma (ICP) reactors of the type used for microelectronic device fabrication was performed. A hierarchy of models with increasing degree of sophistication was developed and tested with experimental data. A reduced order model which couples a CSTR treatment of the "bulk" plasma with a sheath model was developed. This model is most useful for sorting out the complex plasma and surface chemistry. Then, a two-dimensional finite element simulation of ICPs based on the "fluid" equations was developed. By taking advantage of the relevant physics, a modular approach was employed to address the disparate time and length scales of the system. This resulted in dramatic reduction in computation time which makes the simulation tool suitable for Technology Computer-Aided Design (TCAD) applications. The simulation was verified by comparison to published data on a variety of key plasma parameters in both electronegative and electropositive discharges, without fitting any reaction rate coefficients. The two-dimensional simulation included a novel circuit model of a radio frequency biased substrate. Furthermore, a two-dimensional fluid simulation for electrons was coupled to a Direct Simulation Monte Carlo (DSMC) for ions and neutrals to generate a sophisticated hybrid simulation of plasma flow. This simulation runs most efficiently on massively parallel supercomputers. The hybrid simulation revealed important nonequilibrium effects, such as significant temperature differences even between neutral species, and temperature jumps at the walls. Local loading of neutral radical species was observed even in very low pressure (10 mTorr) plasmas.; Nonintrusive optical diagnostics were performed in an inductively coupled plasma reactor. It was discovered that the widely used noble gas optical emission actinometry is invalid for high density plasmas, due to the actinometer chemistry. Laser-induced fluorescence (LIF) probing of optically allowed transitions was also performed to further test the accuracy of the numerical simulation. Measured spatially resolved plasma emission from Cl radicals and LIF from argon metastables compared favorably to the finite element simulation. Finally, multiple steady states of the plasma and formation of a "plasmoid" were discovered.