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On a Sampling Decision System using Virtual Metrology

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The common approach to semiconductor process control is based on physical measurements of a certain number of processed wafers. Therefore, the status of the process is just controlled within certain …

The common approach to semiconductor process control is based on physical measurements of a certain number of processed wafers. Therefore, the status of the process is just controlled within certain time lags, which might result in delayed observations of process abnormalities. Moreover, the measurement rules are typically of a statical nature meaning that the measurement policy is not adapted to current production conditions. In this master thesis, we propose a novel approach to semiconductor process control based on virtual measurements. These are predictions on the location of the real measurements in the control chart depending on the status of the equipment while processing. The advantage of the application of virtual measurements is that they are available for every wafer. Therefore, the status of the process can be steadily controlled and process deviations can be realized earlier. Moreover, the usage of virtual measurements allows for adapting the measurement policy to current process conditions. Whenever virtual measurements provide sufficiently strong evidence that the process is running within the control limits, there is no need of triggering physical measurements. However, if process abnormalities are signalized by the virtual measurement, a physical measurement needs to be triggered. Therefore, physical metrology operations can be scheduled in a more efficient way.

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  • 1. On a Sampling Decision System using Virtual Metrology D. Kurz O. Univ.-Prof. Dr. J. Pilz AAU Klagenfurt, Department of Statistics Dr. C. De Luca Infineon Technologies Austria AG 4 December 2013 D. Kurz On a Sampling Decision System usingVirtual Metrology
  • 2. Innovation 1 2 3 4 5 6 7 8 9 Semiconductor process control: the current state-of-the-art Based on physical measurements Only certain number of wafers measured Statical measurement rules UCL Semiconductor process control with a sampling decision system Based on virtual measurements Virtual measurements for every wafer Target Dynamical measurement rules a a a a a a a LCL D. Kurz On a Sampling Decision System usingVirtual Metrology
  • 3. 2.0 Applied statistical methods Expected utility of measurement information 0.5 1.0 VM: N(0,10²) VM: N(0,15²) 0.0 Decision-theoretical modeling of virtual measurements Density 1.5 Sampling decision evaluation 0.0 0.2 0.4 0.6 0.8 PIT Lindley information and wafer quality risk values Monitoring reliability of virtual measurements Quantification of performance of virtual measurements Detection of unreliable virtual measurements Update of precision of virtual measurements a ¥ ¥ a e e e µVMk ¥ yk D. Kurz On a Sampling Decision System usingVirtual Metrology 1.0
  • 4. 50 real metrology virtual metrology q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q −50 q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q −150 mean 150 Results 0 10 20 30 40 50 0.20 50 q 0.10 49 q 0.00 EVofMI 0.30 wafer no. q q q q q q q q q 0 q q q q q q q q q q 10 q q q q q q q q q q 20 q q q q q q q q q q 30 q q q q q q q q q 40 50 wafer no. q q 0.2 prior risk preposterior risk q q q 0 q q q q q q q q q q 0.0 exp.loss 0.4 q q q q q q q q q q q 10 q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q 20 q q q q 30 q q q q q q q q q q q q q q q q q q q q q q q q 40 q q q q q q q q q 50 wafer no. D. Kurz On a Sampling Decision System usingVirtual Metrology