11/8/99 1 Autonomous On-Wafer Sensor Arrays SFR Workshop November 8, 1999 Mason Freed, Kameshwar Poolla, and Costas Spanos Berkeley, CA This project involves the incorporation of sensors, a communication system, and a power supply onto a standard silicon wafer, for the purpose of supplying wafer-state information during a process step. 11/8/99 2 Overview Motivation Certain wafer-state variables are difficult or destructive to measure, and many are impossible to measure in real-time Add-on in-situ measurement devices are costly and cumbersome Proposal: distributed sensor array on a wafer 11/8/99 3 Test-Case: Etch Rate Polysilicon etch rate sensors based on van der Pauw probe electrical film-thickness measurement: Use wired connections for power and communications Initial testing in XeF 2, an isotropic, gaseous etchant No problem making connections to wafer No electrical or physical isolation necessary I I V Poly-Si 11/8/99 4 Design #1 Connections made using edge-board connector: Edge-board connector Sensors 11/8/99 5 Results (Design #1) Eleven etch cycles performed, interferometric thickness measurements made between each cycle. Repeatability: Accuracy: 45.9 Stability: 3.2 drift in 15 minutes. 11/8/99 6 Design #2 Surface mount multiplexers Edge-board pads Temperature-referenced Sensors 11/8/99 7 Results (Design #2) Preliminary test of a single sensor only, during etch 11/8/99 8 Progress vs Milestones Year 1 Demonstrate tethered, real-time etch-rate measurements in chemical, non-plasma etch. (Done) Year 2 Demonstrate un-tethered real-time measurements with integrated power and data processing. (Work in progress) 11/8/99 9 Future Work Next Year Conduct testing of new sensor design. Research isolation schemes to allow operation in plasma conditions. Work on integrating power and communications modules onto sensor wafer, for wireless operation Develop additional integrated sensors for plasma. Develop sensors for other processes (DUV resist processing, Rapid Thermal Processing steps.)