Steven T. Jenkins

Adaptive optimization of run-to-run controllers: the EWMA example

This paper presents a recursive scheme for optimizing the gain of an exponentially weighted moving average (EWMA) controller under stability constraints. The objective is to minimize the asymptotic mean square error in the output with minimal a priori information. The algorithm hinges on a simple representation of the optimal EWMA gain. Both step and drift disturbances are considered. It is shown that the gain sequence generated by the algorithm always yields a stable system. Furthermore, this sequence is shown to converge to a suboptimal value. Extensions to the algorithm to the case where there is model uncertainty are also presented. The algorithm is verified via simulation. Data from a manufacturing implementation are presented.

Device dependent control of chemical-mechanical polishing of dielectric films

This paper presents a control scheme for run-to-run control of chemical-mechanical polishing (CMP). The control scheme tracks both device pattern dependent and equipment induced disturbances. The structure of the controller is such that sensitivity to qual (unpatterned blanket oxide) wafer frequency is minimized. Additionally, prethickness variation and metrology delay are accounted for in the design. Results from applying this scheme in volume production are presented.

In situ estimation of blanket polish rates and wafer-to-wafer variation

Presents a scheme for extracting information from interferometry signals off patterned wafer polish during nonendpointed chemical-mechanical polishing (CMP). This enables one to obtain blanket removal rates immediately after a patterned wafer finishes polishing as well as estimate post-polish within lot thickness variation. A nonlinear regression algorithm is presented that enables one to estimate this information from less than a full interferometry trace cycle and with a lower sampling rate compared to peak-valley detection schemes.

Sin/cosine encoder interpolation methods: encoder to digital tracking converters for rate and position loop controllers

Pointing and tracking applications usually require relative gimbal angles to be measured for reporting and controlling the line-of-sight angular position. Depending on the application, angular resolution and/or accuracy might jointly or independently determine the angle transducer requirements. In the past decade, encoders have been increasingly taking the place of inductive devices where the measurement of angles over a wide range is required. This is primarily due to the fact that encoders are now achieving very high resolution in smaller sizes than was previously possible. These advances in resolution are primarily due to improved encoder disk and detector technology along with developments in interpolation techniques. Measurement accuracy, on the other hand, is primarily determined by mounting and bearing eccentricity as it is with all angular measurement devices. For very demanding accuracy requirements, some type of calibration of the assembled system may be the only solution, in which case transducer repeatability is paramount. This paper describes a unique encoder-to-digital tracking converter concept for improving interpolation of optical encoders. The new method relies on Fraunhofer diffraction models to correct the non-ideal sin/cos outputs of the encoder detectors. Diffraction model concepts are used in the interpolation filters to predict the phase of non-ideal sin and cosine encoder outputs. The new method also minimizes many of the open loop pre-processing requirements and assumptions that limit interpolation accuracy and rate loop noise performance in ratiometric tracking converter designs.