Model-based uniformity control for epitaxial silicon deposition

Semiconductor fabrication requires tight specification limits on thickness and resistivity for epitaxially deposited silicon films. Our testbed system for integrated, model-based, run-to-run control of epi films incorporates 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 described, 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. Techniques are proposed for dealing with multiple site measurements of multiple film characteristics taken at different sampling rates, as well as the use of time-based inputs and rate-based models. These concepts are widely applicable for semiconductor fabrication processes.