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Wafer Charge Exit Specification using LSF
Larry LevitChief Scientist
Ion Systems CorpBerkeley, CA
Andy RudackATDF Equipment Engineer
International SematechAustin TX
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• Why do end users see static charge on their wafers, but Tool Manufacturers do not?
• How can E78 audits be streamlined?
• Does an E78 test depend upon the chemistry of the wafer used for the test?
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• Wet Cleaning 20k V
• Wet processing: 5k V• Litho 3k V
• Plasma Etch 2k V• Wafer Aligners 1k V
• Wet Cleaning 2 k V
• Wet processing: 1 k V• Litho 0 V
• Plasma Etch 200 V• Wafer Aligners 0 V
End User Tool Manufacturer
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Wafer aligners look through glass and quartz wafers!!!
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• How to do it?– Place wafer in tool– Check charge on wafer– Process wafer– Stop and open tool– Measure field with a fieldometer
• What geometry to use?– q=CV
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Fixed geometry and readout without tool stoppage
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• Use iFOUP• Wafers
– Bare– Thermox wafers (5000 �������������� ������������
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Wafer enters tool Wafer leaves tool
The FOUP does not dissipate the static charge.
250 V/div
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The FOUP door is charged and holds its charge.Door events cause field changes and move contamination within the FOUP.
250 V/div 500 V/div 250 V/div
Door closes Door openedDoor closed
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Ions off
Ions On
Ions On 10 sec. less time (no pre-align)
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Ions Off Ions On
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• FOUP doors electrostatic problem• Oxide coated wafers
– Do not show dissipation in FOUP
– Hold charge efficiently
• Bare wafers– Discharge on end effector
• The iFOUP works
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Now: Confusion
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Bare Oxide
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The end effector is beginning to charge.
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Ions on, oxideDI and IPA
Ions on, oxideDI no IPA
Ions off, oxideDI and IPA
Ions on, bareDI and IPA
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• Contrary to experience!!• Recent Measurements with Faraday Cup
and 300 mm Etch Tool. Exit Charge:– Bare wafer <1 nC– Oxide wafer ~ 3-5 nC– Customer wafer 200 nC
• The Solution is in the chemistry of processed wafers
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• All E78 Ionizer evaluations should be done with oxide, glass or quartz wafers
• All E78 testing needs to be done with process wafers or some other wafers that emulate worst case
• The iFOUP will greatly speed E78 testing• More work is required to identify good
specimen wafer type