GE Energy Silicon Wafer Measurement System Team 10 Olin Biddy Scott Johnson Chetwyn Jones Rob McCoy Tim Weber
Dec 22, 2015
GE Energy Silicon Wafer Measurement System
Team 10Olin 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
Final % Rate ofRanking Importance
1 412 203 174 145 46 3
Easy to Use
Wants
PreciseAccurate
EconomicalStable
Quick
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.
Metrics % Rate Target ValueImportance
Gage R&R Error 32 Gage R&R Error less than 10%Measurement Accuracy 22 Accurate to less than 10 microns# Measurement Points 13 Greater than 9 points of measurementCompletion Time 12 Less than 30 seconds# Operater Steps 11 Less than 10 operater stepsCost 5 Less than 25,000 dollarsRange of wafer size measureable 5 Ablility to measure thickness less than 2 mm
and width and length range of 15.2 - 22.9 cm
Concept Selection
Infrared Laser- Two laser heads fixed in place. Wafer slides between lasers on XY TablePrecision Linear Gauges- Two grids of 9 linear gauges fixed, one grid on each side of wafer
Key Metrics Infrared Laser Linear GaugesGage R&R Small MediumMeasurement Accuracy .05 microns 3 microns# Measurement Points 20,000/sec 9Completion Time 25 seconds 10 secondsCost 15,400 13,000
Concepts
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
RoadblocksUnforeseen 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
19.1
15.5 R
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