Paper PS1-WeA1
Real-Time and Wafer-to-Wafer Control Strategies to Address Seasoning of Plasma Etching Reactors¹

Wednesday, October 17, 2007, 1:40 pm, Room 606

Seasoning of plasma etching reactors refers to the deposition of materials on the wafer and non-wafer surfaces of the chamber that change the fluxes of reactants to the wafer. This influence results from changes in reactive sticking coefficients of radicals and ions on surfaces that change the density of gas phase reactants, the removal of materials that add to the reactive fluxes to the wafer and changes in electrical properties. The negative consequences include drift, either during a process or wafer-to-wafer, in etch rates or uniformity of the process. In this paper, we discuss results from a computational investigation of the seasoning of reactors and, in particular, the use of real-time and wafer-to-wafer control strategies to eliminate process drift. These results were obtained using the Virtual Plasma Equipment Model, an implementation of sensors, actuators and control algorithms in the Hybrid Plasma Equipment Model.² The demonstration system is Ar/Cl₂ of Si in inductively coupled and capacitively coupled plasmas in which redeposition of etch products on walls and the wafer change reactive sticking coefficients and produce etch blocks. Sputtering of dielectrics in contact with the plasma introduce additional etch-block capable species. The diagnostics include etch rate sensors, optical emission and bias power. Actuators include power supply voltage, gas flow rate and gas mixture. We found that use of real-time-control to stabilize processes during a single etch and wafer-to-wafer control are sometimes complicated by the changing state of the wafer compared to the walls. For example, the wall conditions at the end of the prior wafer and beginning of the next wafer do not necessarily change however the new wafer does not have redeposition products. As such, actuators must be reset for the new wafer. Multiple sensors-and-actuators may be needed to account for the transition between neutral limited to ion limited processes as wall and wafer conditions change.

¹Work supported by the Semiconductor Research Corporation and National Science Foundation.
² S. Rauf and M. J. Kushner, "Virtual Plasma Equipment Model: A Tool for Investigating Feedback Control in Plasma Processing Equipment", IEEE Trans. Semiconductor Manufact. 11, 486 (1998).