The goal of this project is to investigate the science and technology of pulsed plasma processing of semiconductor wafers aimed towards developing a knowledge base that will enable pulsed plasmas to be optimized for materials modification. Plasma assisted materials processing is largely responsible for the impressive progress that continues to be made in production of microelectronics devices of ever increasing capability. Plasma etching is the only known, industrially implementable method to fabricate the nanometer sized features in logic and memory chips. During plasma etching, fluxes of ions and neutral particles are directed towards the wafer being processed. The energy and angle of impact of the particles onto the surface of wafers are the critical parameters for the fabrication of microelectronic devices, as well as nanostructured and biocompatible materials. Control of these parameters allows for finer control of the surface composition and, in microelectronics fabrication, etch rate. Low temperature plasmas for plasma materials processing have traditionally used continuously excited plasmas. However, all major semiconductor chip and equipment manufacturers are predicting that pulsed plasmas will be the enabling technology for achieving sub-10 nanometer feature sizes. The most direct impact of this research is addressing fundamental science issues that are of paramount importance to the plasma processing of high performance microelectronics, nanostructures and biocompatible materials. In addition to the technological broader impacts, this project will be highly focused on educational outreach. Prof. Gekelman is one of the founders of LAPTAG (Los Angeles Physics Teachers Alliance Group) and several LAPTAG students and will be involved in these plasma processing studies. Prof. Kushner, director of the Michigan Institute of Plasma Science and Engineering, will leverage those resources to launch the Plasma Picture of the Day website with the goal of providing informative images of plasmas to educate the general public and school children about plasmas.
The lack of fundamental understanding of the dynamics of pulsed plasma systems is the current impediment to widespread adoption. For example, instabilities and waves are nearly universally observed in pulsed plasmas, and particularly in electronegative plasmas, which sometimes prevents operation in desirable parameters spaces. The sources of these instabilities and the means to prevent them are not understood. Pulsed plasma processing can be arbitrarily complex. For example, modern capacitively coupled plasma etching tools may be driven by up to 3 separate power supplies at different frequencies which can be pulsed independently at different repetition rates and different duty cycles. The combinations of parameters can number into the millions. This extremely large parameter space places a large premium on having a fundamental understanding of pulsed plasma processing and so be able to predict plasma performance. In this research project, a highly collaborative experimental-modeling effort will investigate the fundamental properties of pulsed plasmas as used in materials processing, with an emphasis on instabilities and waves, diagnosing and modeling the dynamics of the transition from interpulse afterglow to powered plasma, and the means to improve uniformity through pulsing. Laser induced fluorescence will be used to characterize the trajectory of ions as they are accelerated through the transient sheaths produced by pulsed plasmas; and will be correlated with Langmuir probe measurements of plasma properties. Multi-dimensional computer modeling will be validated by these measurements and will be further used to illuminate fundamental issues related to plasma transport in pulsed systems.
