Patent Number: 
Section: claims

1. A method, comprising:processing a workpiece using a processing tool;measuring an output characteristic of the processed workpiece;modifying a previously estimated state of the processing tool based at least on the measured output characteristic;estimating, using a filter, a next state of the processing tool based at least on the modified previously estimated state; andprocessing a workpiece based on the estimated next state of the processing tool. 2. The method of claim 1, wherein processing comprises etching the semiconductor wafer and wherein measuring the output characteristic comprises measuring an etched depth of the semiconductor wafer. 3. The method of claim 1, wherein estimating the next state comprises providing the modified estimated process state to a Kalman filter to estimate the next state. 4. The method of claim 3, wherein modifying the previously estimated state comprises modifying the estimated state based on the measured output characteristic of the processed workpiece and on a measured output characteristic of a workpiece processed prior to the processed workpiece. 5. The method of claim 4, wherein modifying the previously estimated state comprises modifying the estimated state based on an average of the two measured output characteristics. 6. The method of claim 3, wherein the estimated next state includes a process rate state and a process drift state, further comprising limiting an amount of change in the process drift state to a preselected threshold value. 7. The method of claim 3, further comprising applying an exponentially weighted moving average filtering technique to the next state. 8. The method of claim 1, wherein estimating the next processing-tool state comprises providing the modified previously estimated process state to the filter to estimate the next processing-tool state. 9. An apparatus, comprising:an interface adapted to receive an output characteristic of a processed workpiece; anda control unit communicatively coupled to the interface, the control unit adapted to:modify a previously estimated processing-tool state based at least on the received output characteristic;determine, using a filter, a next processing-tool state based at least on the modified previously estimated state; andprovide the determined next processing-tool state to process a workpiece. 10. The apparatus of claim 9, wherein the control unit is adapted to etch the semiconductor wafer and to measure an etched depth of the semiconductor wafer. 11. The apparatus of claim 9, wherein the control unit is adapted to provide the modified estimated state to a Kalman filter to estimate the next processing-tool state. 12. The apparatus of claim 11, wherein the control unit is adapted to modify the estimated state based on the received output characteristic of the processed workpiece and on a received output characteristic of a workpiece processed prior to the processed workpiece. 13. The apparatus of claim 12, wherein the control unit is adapted to modify the estimated state based on an average of the two received output characteristics. 14. The apparatus of claim 11, wherein the estimated next processing-tool state includes a process rate state and a process drift state, and wherein the control unit is adapted to limit an amount of change in the process drift state to a preselected threshold value. 15. The apparatus of claim 11, wherein the control unit is adapted to apply an exponentially weighted moving average filtering technique to the next processing-tool state. 16. The apparatus of claim 9, wherein the control unit is adapted to provide the modified previously estimated processing-tool state to the filter to determine the next processing-tool state. 17. An apparatus, comprising:means for processing a workpiece;means for measuring an output characteristic of the processed workpiece; andmeans for:modifying a previously estimated processing-tool state based at least on the measured output characteristic;providing the modified estimated state to a filter to determine a next processing-tool state, wherein the next processing-tool state is determined based at least on modified previously estimated state; andproviding the determined next processing-tool state to process a workpiece. 18. An article comprising one or more machine-readable storage media containing instructions that when executed enable a processor to:receive a measured output characteristic of a processed workpiece;modify a previously estimated processing-tool state based at least on the received output characteristic;estimate a next processing-tool state based at least on the modified estimated state, wherein estimating the next processing-tool state comprises providing the modified estimated state to a filter to calculate the next processing-tool state; andprovide the estimated next processing-tool state to process a workpiece. 19. The article of claim 18, wherein the instructions when executed enable the processor to etch a semiconductor wafer and to measure an etched depth of the semiconductor wafer. 20. The article of claim 19, wherein the instructions when executed enable the processor to provide the modified estimated state to a Kalman filter to estimate the next processing-tool state. 21. The article of claim 20, wherein the instructions when executed enable the processor to modify the previously estimated state based on the received output characteristic of the processed workpiece and on a received output characteristic of a workpiece processed prior to the processed workpiece. 22. The article of claim 21, wherein the instructions when executed enable the processor to modify the previously estimated state based on an average of the two received output characteristics. 23. The article of claim 20, wherein the estimated next processing-tool state includes a process rate state and a process drift state, wherein the instructions when executed enable the processor to limit an amount of change in the process drift state to a preselected threshold value. 24. The article of claim 20, wherein the instructions when executed enable the processor to apply an exponentially weighted moving average filtering technique to the next processing-tool state. 25. A system, comprising:a processing tool adapted to process a workpiece;a controller adapted to:receive a measured output characteristic associated with the processed workpiece;modify a previous estimated process state of the processing tool based at least on the measured output characteristic;provide the modified previous estimated process state to a filter to calculate a next process state, wherein the next process state is calculated based at least on modified previous estimated process state; andprovide the next process state to process a workpiece. 26. The system of claim 25, wherein an advanced process control framework is coupled between the processing tool and the controller.