Automated Imaging for Semiconductor Inspection

Increasing throughput and ensuring quality with high-speed, high-precision positioning and autofocus

Semiconductor inspection requires extreme precision and reliability because the slightest imperfections can affect chip performance. 

With wafer features measured at the nanometer scale, inspection systems must deliver sub-micron accuracy, consistent repeatability, and stable positioning.

Advanced imaging, combined with vibration control, is essential for effectively detecting imperfections. Automating these processes not only enhances accuracy but also improves efficiency, reducing human error, and increasing throughput for high-volume manufacturing.

A wide range of imaging modalities may be used. Some examples and applications are:

Detecting surface defects: 
•    Bright field and darkfield microscopy
•    Atomic force microscopy 
•    Confocal microscopy 

Examining the internal structure of the wafers:
•    Infrared microscopy
•    SWIR (Short Wave Infrared) imaging

Challenges for semiconductor inspection

Precise imaging of wafers at the nanometer scale, without compromising speed

While the detail of a semiconductor wafer is small, the wafers themselves are large – up to 300 mm (12 inches) in diameter. The imaging system must be able to move the sample quickly to cover the entire area, while offering sub-nanometer resolution. 

Weight is another challenge. For imaging, wafers are often mounted in carriers, cassettes, vacuum chucks, or environmental enclosures that add additional weight. For high-resolution imaging, some equipment – such as heavy objectives – may be mounted directly on the stage. The combined weight is often several kilograms. 

Prior Scientific Solution:

ProScan H112 Motorized Stage with Queensgate WP120A Single Axis Wafer Piezo Stage

The WP120A piezo wafer stage from Queensgate holds 300 mm wafers, has a Z-axis travel range of 120 µm, with 5.5 nm repeatability. It is compatible with the H112 large-format motorized stage from Prior, which has 302 mm XY travel. The H112 features a 2 mm ballscrew for speed, together with Intelligent Scanning Technology (IST) for enhanced linearity and accuracy. 

High-load, high-accuracy piezo z-stages from Queensgate

The NPS-X-60D, NPS-X-100D, and NPS-Z-250B are high-load nanopositioning piezo stages. When configured for vertical travel (Z-axis), they precisely position and hold the heavy optical assemblies used for semiconductor inspection.  

Flexure guidance and low-noise capacitive sensors ensure precise positioning and stability. Learn more about Queensgate’s solutions for semiconductor and hard disk inspection.

OpenStand-L: Large Format Microscopy Platform

Because each semiconductor fab is unique, a complete, customized inspection system is often required. The OpenStand-L is modular and compatible with Prior’s large-format motorized stages and other components; Queensgate’s piezo nanopositioning stages; and a host of third-party integrations are possible. 

Maintain sharp focus across the wafer surface

Silicon wafers aren’t perfectly flat and may have thickness variations, both within the wafer and due to raised features in the patterning. Imaging systems will need to refocus continually during the inspection, which can slow down the entire process.

Prior Scientific Solution:

PureFocus850 and PureFocus690 Laser Autofocus Systems

PureFocus adjusts in real time to uneven surfaces or inconsistent reflectivity – such as the surface of a silicon wafer. PureFocus’ line mode ensures stability for industrial samples by averaging the focus across the field of view.

It uses interface detection recognition to target the correct surface when the sample has multiple reflective layers, which eliminates time-consuming recalibrations. 

CASE STUDY: Rapid scanning of Silicon Carbide wafers using Prior Scientific’s PureFocus 850 Autofocus

Environmental factors can compromise measurement stability

The inspection is often carried out under carefully controlled conditions – such as in a vacuum – to eliminate contaminants and reduce optical distortion. Temperature changes affect materials, so it's important to select nanopositioning products with low thermal expansion. Effective vibration control is also essential. 

Prior Scientific Solution:

Many Queensgate nanopositioning piezo stages are designed to operate in UHV conditions. Both the Queensgate NPS-XYP-250Q 300 mm Wafer Mask Alignment Stage and WP120A wafer stage operate in high vacuum and have low thermal expansion properties, making them suitable for a wide range of semiconductor applications. 

Passive vibration control workstations and optical tables. 

Kinetic Systems offers vibration control for automation and testing equipment. As well as off-the-shelf workstations and control platforms, they work with customers to develop custom products for specific applications in the semiconductor industry.