Advanced multi-objective control for epitaxial silicon deposition

Semiconductor fabrication requires tight specification limits on thickness and resistivity for epitaxially deposited silicon films. A testbed system for integrated, model-based, run-to-run control of epi films is under development, incorporating a Centura tool with an epi deposition chamber, an in-line epi film thickness measurement tool, and off-line thickness and resistivity measurement systems. Automated single-input-single-output, run-to-run control of epi thickness has been successfully demonstrated. An advanced multi-objective controller is currently under development, which seeks to provide simultaneous epi thickness control on a run-to-run basis using the in-line sensor, as well as combined thickness and resistivity uniformity control on a lot-to-lot basis using off-line thickness and resistivity sensors. Control strategies are introduced for performing combined run-to-run and lot-to-lot control, based on the availability of measurements. Also discussed are issues involved with using multiple site measurements of multiple film characteristics, as well as the use of time-based inputs and rate-based models. Such techniques are widely applicable for semiconductor processing.