GE Energy Silicon Wafer Measurement System Team 10 Olin Biddy Scott Johnson Chetwyn Jones Rob McCoy Tim Weber

Project Overview Design a device that can measure the thickness of a silicon wafer Silicon wafer production has to be precise Wafers come off a conveyer belt from oven Immediate feedback for production adjustments Important Requirements – Accurate within 10 microns – 9 or more measurement points – Completes process in 30 seconds – Repeatable and Reproducible

Goals of Prototype Detects faulty wafers Outputs thickness measurements in user friendly format Store data for further research / analysis Easy to operate for workstation user Graphical representation of surface geometry

Design Requirements: Wants Precision- Degree to which future measurements will show similar results. Accuracy- Degree of conformity of measured value to its true value.

Design Requirements: Metrics Prioritized List of Metrics Gage Reproducibility and Repeatability – Measures Precision using Statistical Process Control equation.

Concept Selection Infrared Laser- Two laser heads fixed in place. Wafer slides between lasers on XY Table Precision Linear Gauges- Two grids of 9 linear gauges fixed, one grid on each side of wafer

Complete Concept Two lasers for subtraction measurement method XY Table to transverse wafer Stage to hold wafer between laser heads Stationary frame for laser heads Labview to control XY Table, lasers and analyze data System Components

LK-G Laser Accurate up to.05 microns Fast 20,000 measurements a second Auto-adjusts intensity for changing reflectivity Wide Spot of 850 microns to average over pits on surface Connectivity with Labview for data collection

XY- Table (Velmex, Inc.) Stable movement – Stepper motor drives – 9”x9” travel of 12”x12” work surface –.001” resolution – Vmax = 4.0 in/s LabView interface Easy attachment for wafer stage

Wafer Stage Two stage platforms to accommodate both 6”x6” and 9”x7” wafers Press fit pins allow for quick change between top wafer platforms Rubber surface to eliminate wafer movement (not shown)

Laser Mounting Frame Prefab Aluminum Framing System (Bosch Rexroth) – 30mm x 30mm cut-to-length extrusion – Prefabricated fasteners/accessories – Highly Modular – Rapid build time – Stable “H” Frame – Accommodates both laser heads – Data cable conduit

Completed Prototype

Roadblocks Unforeseen Obstacles Electronics Box – Safely house laser controller and power supply module (~120V) – Provide a point of electrical entry from wall outlet Connectivity with lasers and Labview – Changed from USB to RS232 input Labview Programming – Particular version of Labview limited graphical data output

Calibration & Testing Accuracy Calibrate- Use known thickness object (high tolerance steel gauge blocks) Subtraction method to calculate thickness Test- Measure multiple repeated points on steel gauge blocks (5) to validate thickness accuracy to 10 microns

Testing Gauge R&R (Abbreviated Overview) Gauge R&R is a Statistical Process Control measure of an instrument in Six Sigma practices Measure 10 wafers using standard measurement process under normal operating conditions Find statistical range & average Calculate combined repeatability (instrument error) & reproducibility (operator error) from a standardize expression: Gauge Error (Gauge R&R) Gauge Error < 10% to be successful

Testing Steps and Time One combined test to validate: – Operator steps – Average measurement time (per wafer) Run of 10 wafers by a familiarized operator – Define and count steps – Divided total test time by number of wafers to find average time per wafer Under 10 operator steps meets target Under 30 seconds average measurement time meets target

Testing Results Completion Time: 35 seconds Operator Steps: 5 simple steps Accuracy: 6.3 microns Gauge R&R: 24.6% (point repeatability error included) Gauge R&R: 5.4% (without changing placement)

Final Bill of Materials Laser System$11,233 XY Table$3,014 Wafer Platform$177 Laser Support System$138 Electronics Box$60 Platform$14 Total $14,693

Conclusion Successful system designed to measure true thickness of a silicon wafer Design can be immediately implemented upon completion Further programming needed to add Statistical Process Control graphs as well as graphical representation of warp Instructions and materials provided for duplicate systems in other GE applications

Working System

Questions?

Subtraction Method

Computer Display