1. Autonomous temperature sensor for bake plate calibration
SFR Workshop
November 8, 1999
Michiel Krüger, Darin Fisher,
Andy Gleckman, Scott Eitapence
Berkeley, CA
In this project we investigate the feasibility of wireless, autonomous sensors, riding on dummy wafers to measure the temperature distribution across a wafer during semiconductor processing. Off-the-shelf components are used to test the concept.
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2. Motivation Why autonomous smart dummy wafers? Why temperature?
spatial distribution of process variables over area and time
real-time wafer-state information useful for:
Process design / modeling / control
Equipment design / diagnosis
Why temperature?
Temperature information can be used for feedback control during photo resist baking and plasma etching.
DUV photo resist is very sensitive to bake process: temperature transient info can be used to:
calibrate detailed DUV photo resist models
accurately determine overall thermal budget of photo resist
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3. Temperature sensor Technology set Features surface mount components
minimal processing of host wafer
on-board microprocessor with integrated 4 channel A/D
off-the-shelf battery technology
infrared data transfer (IrDA compliant) with error detection (CRC)
Features
Distributed array of temperature sensors (0.5 °C resolution)
real-time data acquisition
wireless power & data transfer
PalmPilot interoperability
Sensor P
Ir-LED
Batteries
Voltage
regulator
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4. PalmPilot Interface
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5. Experimental setup
Computer controlled bake-plate used for calibration and validation of measurements.
Probes used for external powering / measuring.
Data from wafer stored on computer via Ir-receiver.
Data transmitted at 2Hz.
Tethered and untethered.
Tests conducted:
repeatability (hrs.)
fast transients (min.)
power consumption (sec.)
Wafer
Ir-receiver
Probes
Bake-plate
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6. Results: tethered power, untethered communication
Repeatability test up to 120 °C; externally powered
Average current  1mA, current spikes due to data transmission via Ir-LED
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7. Results: totally autonomous run
Button cell/UCLA batteries used for power supply
Good result up to 140 °C.
Slow and fast transients measured.
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8. Milestones
Year 1
Demonstrate untethered temperature measurements in plasma. (in progress)
Year 2
Demonstrate un-tethered real-time temperature and etch rate measurements with integrated power and data processing in plasma. (in progress)
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9. Future work ( )
Integrate thick film UCLA batteries in current sensor design
RF isolation of sensors for use in
plasma chamber
Low profile temperature sensors
(flip-chip components)
Total enclosure of components
Close the control loop
Include other sensors in design (etch rate / stress / ion density)
Thermal isolation of electronics / high temp ASIC for operation up to 160 °C
battery
sensor
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