Defect Inspection

Deep saw marks detection on solar wafers

Silicon ingots are sliced into wafers using diamond wires. Small deviation of these wires during the sawing process may results in relatively deep marks that make the wafer fragile. This application describes such defect inspection on solar wafers.

Speed is a key requirement for this application, and the unrivaled acquisition speed of DHM® is a necessity:

  • High throughput: 1 wafer per second !
  • Measurements performed on a rubber band convey tray, without stopping the samples.
  • Presence of vibrations due to surrounding of production facilities.
Saw mark depth measurement on solar wafers. 1 wafer per seconds
5mm x 150mm 3D profile



  • Wafer size: 150 x 150 mm
  • Inspected area: 150 x 5 mm
  • Typical Depth Threshold: 10 micrometers


  • Speed: 214 mm/s
  • Height variation: < 300 μm
  • Inspection time for each wafer: 0.7 second


  • 3D Measurement of a 150 mm x 5 mm rough surface at a rate of 1 wafer per second
  • Saw marks detection on the entire 3D surface measured


  • 2 OEM reflection DHM® heads:
    • top and bottom surface inspection
    • synthetic wavelength of 58.6 μm. Solar wafers have a rough surface that produces speckle. This specific optical configuration allows DHM® to extract precise profile cut.
  • Size: 430 x 230 x 60 mm
  • Weight:  10kg
  • Magnification: 1.25x

Automated Process

  • Measurement start: triggered by an optical barrier
  • Acquisition and stitching: 50 3D measurements in less than 1 second
  • Decision Go/NoGo: based on topography measurement analysis
  • Software: Dedicated acquisition and analysis software based on the Software Development Kit

Automated Defect detection over the complete sphere surface

This application demonstrates automated defects detection over the entire surface of a semi-transparent microshell. The sample is hold by a small vacuum nozzle. Two rotation axes allow to cover its entire surface. Defects are detected and their geometrical characteristics measured. DHM® has been chosen among other techniques for this application considering:

  • Manipulation complexity: sample wobbles if the rotation center and the sample center do not coincide
  • Automated re-centering and focalization to compensate for the inevitable wobble
  • Fast image stitching on a curved surface
  • Need for short acquisition time


Microshell Sample

  • Material: CHGe sphere with an internal solid layer of Deuterium-Tritium (D-T)
  • Diameter: 0.8 mm


  • DHM® R1000
  • Motorized stage XYZ
  • Two customized  rotation axes for sample rotation
  • Vacuum chuck to hold the sample with 2 small nozzles


  • LabView and the Remote TCP/IP and  to control simultaneously the motorized stage and the DHM®

Automated measurement process

  • Sample rotation to cover the entire microshell surface
  • At each position
    • Sample centering
    • Sample focalization
  • Automated stitching, digital curvature compensation, extraction of data along a band


  • Defects (bumps) detection and diameter, height, and volume measurements over the entire sample surface
Sample description
Handling of micro-shell
Measurement along complete circumference of the micro-shell and representation along a band


Characterization of the Microshell Surface Using Holography

ANS / Publications / Journals / Fusion Science and Technology / Volume 59 / Number 1 / Pages 110-115

Home / Publications / Journals / Fusion Science and Technology / Volume 59 / Number 1