| AVS 60th International Symposium and Exhibition | |
| Plasma Science and Technology | Tuesday Sessions |
| Session PS1-TuM |
| Session: | Plasma Sources |
| Presenter: | M.D. Logue, University of Michigan |
| Authors: | M.D. Logue, University of Michigan W. Zhu, University of Houston H. Shin, University of Houston L. Liu, University of Houston S. Sridhar, University of Houston V.M. Donnelly, University of Houston D.J. Economou, University of Houston M.J. Kushner, University of Michigan |
| Correspondent: | Click to Email |
In plasma materials processing, finer control of the electron energy distribution, f(ε), enables better selectivity of generating reactants produced by electron impact excitation and dissociation. This is particularly important in low pressure, inductively coupled plasmas (ICPs) where dissociation products often react with surfaces before interacting with other gas phase species. Under these conditions, fluxes to surfaces are more directly a function of electron impact rate coefficients than gas phase chemistry. Externally sustained discharges are able to control f(ε) by, for example, augmenting ionization independent of the f(ε) of the bulk plasma so that f(ε) can be better matched to lower threshold processes. In this case, the tail the f(ε) is lowered. Following the same logic, introducing additional losses by external means will produce an increase in the tail of f(ε). To achieve this control, a tandem (dual) ICP source has been developed. In this device, the primary (lower) source is coupled to the secondary (upper) source through a biasable grid to control the transfer of species between the two sources with the intent of controlling f(ε) in the primary source. A boundary electrode (BE) at the top of the system, along with the grid, can be dc biased to shift the plasma potential. This controls the energy of charged species passing into the primary source as well as ion energy distributions (IEDs) to surfaces.
Results will be discussed from a computational investigation of the control of and IEDs, in a tandem source ICP system at pressures of tens of mTorr. The model used in this study is the Hybrid Plasma Equipment Model (HPEM) with which f(ε) and IEADs as a function of position and time are obtained using a Monte Carlo simulation. f(ε) and IEDs will be discussed while varying the relative power in the primary and secondary sources, and dc biases (BE and grids) in continuous and pulsed formats. Results from the model will be compared to experimental data of f(ε) and IED obtained using a Langmuir probe and a gridded retarding field ion energy analyzer.
* Work supported by the DOE Office of Fusion Energy Science, Semiconductor Research Corp. and the National Science Foundation.