Laser Particle Inspection, Laser, Cutting, Engraving, Machining, Processing, Scribing, Shaping, California.

Application Notes

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Laser Particle Inspection

The WIS 850 is a tool SQI uses to inspect the surface quality of a wafer. It accomplishes this by scanning the surface with a laser on the surface and measuring the reflection. If there is something at any point that disrupts the reflection by scattering the incident light – such as a particle, scratch, or crystallographic defect – the WIS will detect the deviation in the reflected light and classify it based on its properties. Simply speaking, the amount of scattering relates directly to the size of the particle. Dark and light channel detectors are used to find different types of defects, Particles in the dark channel and mounds, dimples etc in the light channel. After the machine has scanned the entire surface, it provides Run Time Data, as seen on the following page.

The WIS-850 has no capability to measure haze. The smallest particles that can be detected are 0.17um, though SQI only uses down to 0.2um in current Production recipes. It is currently set-up to run 6” and 8” wafers.

This tool is periodically calibrated using NIST traceable PSL (Polystyrene Latex) sphere standards at 0.2, 0.3 and 0.5um.

Here are some definitions:

RECIPE – Deals with how the machine functions during a scan; recipes may be defined by SQI and can affect how such variables as the flaws are categorized, the maximum acceptable flaw count, and how much power is used (details for one recipe are on the third page)

THRSHLDS – Values selected during calibration process which define the sensitivity of the tool, i.e. the thresholds below which there is only noise and above which defect are counted.

WAFER SIZE – Nominal wafer diameter, expressed in inches and mm

EDGE EXCLUS – The WIS does not scan near the very edge of the wafer, and this field defines how far in from the nominal edge it begins, expressed in inches and mm.

FL – flaws detected; the output lists the number of flaws detected in each category

FL 1 Particle 0.2 to 0.3 μm

FL 2 Particle 0.3 to 0.5 μm

FL 3 Particle 0.5 to 5.0 μm

FL 4 Particle above 0.3 μm*

FL 5 Scratch (defect on more than 4 adjacent pixels)

FL 6 Area Defect (defect on more than 8 adjacent pixels)

FL 7 Medium Distortion – Light Channel Defect**

FL 8 Large Distortion – Light Channel Defect

FL 9 Small Distortion – Light Channel Defect

FL A Particle 5 to 20 μm

FL B Very Large Distortion – Light Channel Defect

FL C Particle greater than 20 μm

FL G Large Flaw – Huge Defect

* Cumulative measurement of 2, 3, A, and C

** Light Channel Defects are typically mounds, dimples, etc.