Two Types of Wafer Inspection Equipment Used in QA


June 1, 2022

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Silicon wafer suppliers have to pay attention to many details in the manufacturing process. They have to cut wafers into specific thicknesses, use a predetermined temperature in the crystal growth, be diligent in quality control, etc.

As the final part of the process, quality assurance prevents any defective product from making it to the market. QA specialists may use the following visual inspection systems to identify flawed wafers from the functioning ones in the batch.

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Optical Pattern Wafer Inspection

Optical pattern inspection systems scan the wafer surface and compare the resulting picture against the circuit diagrams or a defect-free chip. Two types of illumination are used in OPWI: bright-field and dark-field. They are often used in tandem to increase the rate of detection.

This inspection technique shines a light on the wafer surface, reflecting the beam back to a detector. Perfect surfaces will show up with even lighting on the final image. On the other hand, defects will appear as dark spots against a bright field. Once the defects have been identified, technicians can create a “defect map” to demonstrate how many flaws are in the final product.

Electron Beam Inspection

The e-beam inspection system is similar to an electron microscope. It bombards the chips with electrons from a generator and scans the reflected electrons to create a high-resolution image. EBI is distinct for its high resolution and sensitivities of up to 1 nanometer. Any imaging with EBI systems can output more details than the optical gear.

However, one downside of EBI is its speed. The technology is not ideal for inspections that require real-time results. Operators must wait hours for the final image if they are checking out the whole safer. Hence, electron beam inspections focus only on specific parts of the wafer rather than the entire semiconductor. It may also be used for verification if optical inspection does not yield any defects.

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