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Dark Field counting

We have an application where we are counting defects in a thin film coating. The setup is a dark field measurement with a 20x objective. We are looking for defects that are possibly down to 1um in diameter on a 100mm diameter sample. We have a macro that measures and NxN grid over the part. The trouble is in focusing. The program estimates focus at each location and adjusts the z-axis thru motor control. The trouble is focus may be slightly off and defects are missed or blurry resulting in errors in the data. Is there a method accurately controlling focus thru a script and motor control? We are using an version 7.0 of IPP on WIndows XP.



  • BCharles --

    Since you have control of the Z AXIS, have you considered:

    ** Capturing multiple Z IMAGES at each XY LOCATION
    ** Using the IPP 7 EXTENDED DEPTH OF FIELD / FOCUS FUNCTION to combine the images
    ** Analyzing the EDOF IMAGE for DEFECTS

    Another possibility would be for each XY LOCATION to:

    1) Capture Z(0)
    2) Analyze Z(0)
    3) Capture Z(n)
    4) Mask out DEFECTS found in Z(0) to Z(n-1)
    5) Analyze Z(n)
    6) Repeat 3 to 5 as required

    You could potentially combine these two suggestions and do an EDOF on 2 or three images make that a Z(?) image and then analyze.

    I hope these suggestions are helpful.

    -- Matt
  • Matt,
    Thanks for the ideas. Having no experience with IPP prior to this project it has been a learning curve. I did come across the EDOF feature as well as the autofocus. I am working on getting the autofocus working, yet having issues. I click the button and nothing happens. Any ideas? I did perform a z-axis calibration.

  • bcharles --

    I have been away from my desk and my normal computer resources so I'm sorry I'm slow to respond.

    I would be willing to WEBEX with you and your machine to brainstorm and see if we can find a quick resolution to your issue.

    Please send me your contact information if this sounds like a good plan. 

    If if my contact info isn't visible to you within the FORUM, google


    Good luck.

    -- Matt
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