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