Paper PS1-WeA11
Model-based Ion Energy Control in ICP Etcher

Wednesday, October 31, 2012, 5:20 pm, Room 24

In particular for III-V semiconductors, plasma processes close to active zones of surface-sensitive devices are critical, demanding low damage through ion bombardment and so an excellent process understanding and control. In order to get the ion energy into the right range, the bias power is switched off working then a downstream-like mode. A complete model of the entire system with this special setup is presented and validated. It demonstrates that the bias matchbox capacitances are excellent control elements for the ion energy. We can also show that the Vp measurement is not representing the ion energy here. The ion energy is estimated by the sheath voltage from the model and shows a reasonable correlation to the etch rate observed.

This paper focuses on a general method to characterize equipment and plasma by a combination of off-line and real-time measurements. The first major goal of this paper is to show how reduced models of plasma equipment can be used to estimated important plasma parameters as to understand how the plasma process works. The equivalent circuit i only a tools to explain the over all plasma physical picture, it does mean that an equivalent circuit is always the right tool to describe a plasma. This resulting, reduced and so also not self-consistent model must be verified and then used for the ion energy control in an ICP etcher.

The model is based on an combined plasma and RF model in the special case of an existing bias matchbox but zero bias power. The control elements are the capacitance in the bias matchbox. We show the tune capacitance to be an excellent control element, but we can also demonstrate that – at least in this case – an RF peak voltage measurement is not representing the ion energy and alone not very useful.

Trikon/Aviza Omega 201 ICP etcher was used. A 100 mm electrode, a cylindrical coil around a ceramic chamber wall, and a Al chamber lid are main parts of the chamber.

Usually two generators are running at 13.56 MHz as master and slave with an adjustable phase shift between source and bias generator. In our case the bias generator is switched off in order to achieve a very low ion energy and thus almost no damage at the wafer. First investigations have shown that the position of load and tune capacitance in the bias matchbox to be very important for etch rate and wafer damage. Therefore a model was built to understand and finally to utilize these effects for process control.