Simulation of transients and transport in plasma processing reactors

Low temperature, high plasma density reactors are widely used for etching and deposition during microelectronics fabrication. As the wafer size increases, the requirements for azimuthal symmetry and side-to-side uniformity become more stringent. The development of plasma equipment models (PEMs) for investigating chemical, physical, and engineering scaling issues for plasma processing has significantly advanced in the recent years. PEMs in two and three dimensions have been developed with the goals of both investigating basic physical processes and for use in the design of plasma equipment. In spite of the success of these activities, issues related to three-dimensional (3D) phenomena have come to the forefront and cannot be adequately addressed by the present generation of PEMs. To design reactors with good side-to-side symmetry, design engineers require 3D information of plasma properties. The lack of inexpensive azimuthal measurement techniques for plasma properties in inductively coupled plasma (ICP) reactors makes it more difficult for experiments to provide this information.; In this thesis, two-dimensional (2D) and 3D hybrid models were developed to investigate transient phenomena (time variation of plasma properties) during pulsed operation of ICP reactors. Employing the 2D model, it was demonstrated that utilizing transients during pulsed operation, energetic negative ions can be extracted from pulsed ICPs that can aid in reducing charge buildup on wafers. Energetic negative ions can be extracted from Ar/Cl₂ pulsed ICPs with pulsed low frequency (1–2 MHz) substrate biases. Employing the 3D model, the impact of asymmetric pumping on plasma properties during continuous wave (CW) ICP operation and the effect of transients on these flow-induced asymmetries were quantified. Asymmetric pumping results in non-uniform species densities, which then feed back through plasma conductivity making the power deposition azimuthally asymmetric. The asymmetries in plasma properties increase with increase in power and gas flow rate. Pulsed operation of ICPs improves the uniformity of plasma properties as it reduces the positive feedback between species density and power deposition. In Ar ICPs, the plasma parameters were more uniform relative to CW operation on decreasing duty cycle or pulse repetition frequency (PRF).