Towards closed loop control of a plasma tool using OES

Potential candidate methods for closed loop control using OES have been evaluated for SF(6) etching of Si and for fluorocarbon etching of SiO(2). In the case of SF(6) etching of Si it was found that a spectrum matching method could be used to recover the plasma state from a deliberate change in all process parameters, or even a doubling of the silicon load present in the chamber. The etch rate of silicon after process recovery matched that before the doubling of the load. For fluorocarbon etching of SiO(2) the OES CF(2):F peak height ratio was found to be related to the polymer deposition rate and hence also the SiO(2) etch rate. A closed loop control method using the CF(2):F relationship was demonstrated via in-situ laser interferometer (LI) monitoring of the etching of (or polymer deposition onto) SiO(2). (C) 2008 Elsevier B.V. All rights reserved.