Real-time plasma control in a dual-frequency, confined plasma etcher

摘要

The physics issues of developing model-based control of plasma etching are presented. A novel\udmethodology for incorporating real-time model-based control of plasma processing systems is\uddeveloped. The methodology is developed for control of two dependent variables (ion flux and\udchemical densities) by two independent controls (27 MHz power and O2 flow). A phenomenological\udphysics model of the nonlinear coupling between the independent controls and the dependent\udvariables of the plasma is presented. By using a design of experiment, the functional dependencies\udof the response surface are determined. In conjunction with the physical model, the dependencies\udare used to deconvolve the sensor signals onto the control inputs, allowing compensation of the\udinteraction between control paths. The compensated sensor signals and compensated set–points are\udthen used as inputs to proportional-integral-derivative controllers to adjust radio frequency power\udand oxygen flow to yield the desired ion flux and chemical density. To illustrate the methodology,\udmodel-based real-time control is realized in a commercial semiconductor dielectric etch chamber.\udThe two radio frequency symmetric diode operates with typical commercial fluorocarbon feed-gas\udmixtures (Ar/O2 /C4F8). Key parameters for dielectric etching are known to include ion flux to the\udsurface and surface flux of oxygen containing species. Control is demonstrated using diagnostics of\udelectrode-surface ion current, and chemical densities of O, O2, and CO measured by optical\udemission spectrometry and/or mass spectrometry. Using our model-based real-time control, the\udset-point tracking accuracy to changes in chemical species density and ion flux is enhanced.