CASE STUDY #2 Wafer Inspection

The Challenge

Wafer Inspection Machine

The client, a wafer die manufacturer, appointed PSB Tech to design and develop a machine to inspect wafers for die alignment, surface defects, contamination and dimple depths. This machine afforded the client flexibility since it could be configured as an inline or standalone machine.

Inline inspection allowed wafers to be inspected as part of the production process, sieving out reject dies, thus ensuring good final product quality. Standalone inspection allowed for batch processing and ad-hoc inspection, located offline from the production flow, thus allowing flexibility in shopfloor layout.

The wafer inspection machine must be able to detect specific size and unique patterns on the wafer. Accordingly, specially customized image processing routines had to be developed to detect and characterize the various defects and patterns found in the wafers.


  • • Use of high resolution, auto-zoom optics to achieve sub-micron accuracy in the measurement of die misalignment and surface defects.
  • • Incorporation of various customized image processing techniques to enable the machine to detect glue smears, contaminants, scratches, dents and missing features
  • • Ability to measure dimple depths with a resolution of 2nm
  • • Ability to tap wafer contour with a resolution of 0.1 micron
  • • Application of high precision linear motor stages that enables the machine to achieve high-speed positioning

The Result

Inspection of wafer

The wafer inspection machine developed by PSB Tech allowed for the switching of inspections of different product types automatically. Furthermore, the inspection sampling scheme was user-configurable.

Through this new machine, the client was able to conduct a better quality control on its wafer dies, as the machine is able to consistently detect and classify defects not discernible to the human eye. Moreover, the defects are detected at a much faster rate using the machine than human, thus reducing manpower requirements for the client.