Autonomous On-Wafer Sensor Arrays

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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.
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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

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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 XeF2, an isotropic, gaseous
  etchant
• No problem making connections to wafer
• No electrical or physical isolation necessary

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Design 1

• Connections made using edge-board connector

Sensors
Edge-board connector
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Results (Design 1)

• Eleven etch cycles performed, interferometric
  thickness measurements made between each cycle.
• Repeatability ? 12.89 Å
• Accuracy ? 45.9 Å
• Stability 3.2 Å drift in 15 minutes.

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Design 2
Temperature-referenced Sensors
Surface mount multiplexers
Edge-board pads
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Results (Design 2)

• Preliminary test of a single sensor only, during
  etch

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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)

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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.
• 2000-2002
• Develop additional integrated sensors for plasma.
• Develop sensors for other processes (DUV resist
  processing, Rapid Thermal Processing steps.)