Run-to-run control for wafer patterning in semiconductor manufacturing.

Abstract

The semiconductor manufacturing technology is getting closer to manufacturing sub-0.1mu<italic>m</italic> devices. As a consequence, tighter manufacturing tolerances are demanded. Due to the lack of <italic>in situ</italic> sensors, Run-to-Run (R2R) control has proven to be a good candidate to reduce the process variance. We have investigated the use of R2R control techniques in lithography and etch processes. These processes are crucial steps in meeting device specifications. Lithography control is a challenging problem due to the many variables that interact in complex ways. The process materials, the equipment, and the processing environment experience time-varying disturbances that negatively impact the resist profile. We addressed this problem by designing R2R feedback controllers. The controllers manipulate the dose and focus inputs and include Kalman filtering schemes that update the disturbance dynamics. We tested the performances of these controllers using the lithography simulator PRO-LITH. The results showed reduction of the effect of the process disturbances on the critical dimension <italic> CD</italic>, the sidewall angle <italic>SW A</italic> and the <italic>CD</italic> print bias of the isolated and dense lines. The etch process also has its own control challenges. One of them is integrating feedforward and feedback control to reduce the effect of the etch disturbances on the post-etch <italic> CD</italic>. We first developed a feedforward and feedback controller that reduces the effect of autocorrelated etch disturbances on the post-etch <italic> CD</italic>. The designed controller is called Feedforward and Feedback Recipe Selection Control (FFRSC). It updates the disturbance dynamics using Kalman filtering techniques and selects a recipe from an allowable set of qualified recipes. We tested the FFRSC performance using simulations based on real data and the results showed more reduction in the post-etch <italic>CD</italic> variance. We then developed a feedforward and feedback (FF/FB) controller to reduce the effect of an oxygen flow disturbance applied during resist trim on the post-etch <italic>CD</italic>. The controller also uses Kalman filtering techniques to update the disturbance model. Simulations and experimental results quantify the significant benefit of integrating feedforward and feedback control in addition to only using a feedforward control in minimizing the polysilicon <italic> CD</italic> deviations from the etch target.