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

Posted in Application notesAutofocusPureFocus 850 Jul 7th 2020


May 2019 saw the release of Prior Scientific’s PureFocus 850, an extremely versatile hardware autofocus system capable of accommodating a variety of imaging techniques. In 2020, numerous PureFocus 850 autofocus systems are in the field, enhancing productivity in areas from biological research to industrial component scanning.

PureFocus 850 Autofocus: Benefits for Wafer Inspection

The PureFocus 850 is highly effective for wafer inspection and has been used with particular success for analysis of defect selective etching. The PureFocus 850 has enabled STMicroelectronics, the multinational electronics and semiconductor manufacturer, to overcome a number of challenges associated with traditional autofocus systems and reduce scanning time per sample. STMicroelectronics has used the PureFocus 850 with automatic image recognition software to analyze the quality of Silicon Carbide wafers at their manufacturing facility in Sweden.

When wafer quality is analyzed through defect-selective etching, it creates etch pits on the Silicon Carbide wafer surface, and the morphology, number, and distribution of these pits indicate the type and location of potential defects within a sample. Traditional laser autofocus systems analyze signals reflected from the center of the field of view to calculate the optimal focus position. If the sample surface is not flat, however, peripheral areas of the image may still be out of focus.

The PureFocus 850 supplied to STMicroelectronics was calibrated to analyze signal reflected from across the field of view, allowing the consistent focus to be maintained throughout every autofocus wafer scan.

Image analysis is performed while focusing on the bottom of the pits to analyze their morphology, meaning the imaging plane of interest is different from the main reflective surface of the Silicon Carbide wafer. This analysis is made possible by the motorized optics of the PureFocus 850, which allows the imaging plane to be offset from the wafer surface.

STMicroelectronics also wanted to generate both brightfield and darkfield images to assist with their image analysis. The intuitive PureFocus 850 user interface allowed STMicroelectronics to optimize their Autofocus settings for each imaging technique based on the intensity of illumination, rather than having to find a compromise between the two.

PureFocus 850 Autofocus: User Benefits

Engineers using the PureFocus 850 deem it a highly effective autofocus system, drastically improving their sample analysis throughput.

Erik Sörman, a development engineer at STMicroelectronics, said, “I use it for all my routine inspections. Inspection times [have been] reduced from 45 minutes to 7 minutes.”

“I use it for all my routine inspections. Inspection times [have been] reduced from 45 minutes to 7 minutes.”

The PureFocus 850 has allowed the engineers to acquire higher quality images, with a focus error of less than 10 microns, with an 85% reduction in scanning time.

Prior worked with BergmanLabora AB, one of Sweden’s leading suppliers of analytical instruments, to provide this autofocus solution to STMicroelectronics.

“PF850 is an excellent addition to any microscope that lacks hardware autofocus,” said product specialist Marie Andersson, who was one of the first to attend Prior’s PureFocus 850 training sessions.

“The time savings for our customers are incredibly advantageous. It has also been easy to install and maintain the PF850, as Prior’s training and support have been very good and in-depth. [The] PF850 is simply a really good product!”

BergmanLabora AB has since gone on to demonstrate and supply further PureFocus 850 autofocus systems to other users in their region.


The PureFocus 850’s reach extends far further than Silicon Carbide autofocus wafer analysis, and greater time efficiency and enhanced image quality make the PureFocus 850 the autofocus system of the future. Capable of significantly improving throughput in a huge array of applications, the PureFocus 850 makes for versatile image analysis hardware that is set to achieve prevalence throughout the industry.