Studies of Electron Behavior in Magnetic Neutral-Loop Discharge (NLD) Plasmas for Processing Applications

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In this project, the formation mechanism of a magnetic neutral-loop discharge (NLD) plasma was studied theoretically and experimentally. Also, application possibilities of the NLD plasma were studied.Electron behavior in the NLD plasma was theoretically modeled using a two-dimensional electromagnetic field configuration. The model predicted that the electron motion around the neutral loop (NL) became chaotic, and electrons could be effectively heated by the rf electric field in the collisionless low pressure regime. Then, the electron behavior was examined experimentally. The experimental results showed that the energy deposition to electrons in the vicinity of the NL played an essential role in the formation of the NLD plasma. This result was consistent with the prediction of the two-dimensional model. However, the dependence of the plasma production efficiency on the gradient of the magnetic field strength showed disagreement between the experiment and the model. The model predicted … More that plasma production became more efficient for a smaller magnetic field gradient. On the other hand, the experimental results showed the existence of an optimum value of the magnetic field gradient. In order to improve the situation, a new model which included effects of the three-dimensional electromagnetic field configuration, a spatially varied rf electric field and electron collisions with neutral particles was proposed. The model gave optimum values of the magnetic field strength for given discharge conditions, and those predictions were found to be consistent with experimental results. In conclusion, the model gives a guideline for the design of NLD plasma devices.NLD plasmas were successfully applied to a high-rate etch process with satisfactory uniformity. In the application to the SiO_2 etch process, an etch rate of about 1 mum/min was obtained. When the hole pattern was etched, the etched profile was almost vertical. These results were found to be superior to the etching results using an inductively coupled plasma. In order to open sputtering applications, an NLD plasma based on capacitive coupling was proposed and a prototype device was designed. Less