Efficiency is important in semiconductor manufacturing for maintaining a competitive edge. A semiconductor manufacturer aimed to improve low production yields due to the wafer material not being perfectly flat and the effects of the fabrication process. Their existing mask-based system had a yield rate of approximately 66%, meaning only two-thirds of the chips on each wafer were suitable for packaging.
This led them to seek methods to increase their yields and reduce costs associated with their high scrap rate. By investing in an MLA 300 maskless aligner system from Heidelberg Instruments, with embedded Cognex vision software, they increased their yield rate to 95%.
High scrap costs drive the need for change
While investigating upgrades to the production line, this manufacturer connected with Heidelberg Instruments, who recommended their MLA 300 maskless aligner to improve the yield.
Exposure testing showed a significant improvement in yield from 66% to 95%. Although the cycle time per wafer was slower, the higher yield rate and subsequent savings on scrap and waste outweighed the increase in production times. The advanced Cognex imaging tools in the MLA 300 pr
ovided the necessary detail to properly align the projected circuit pattern onto each die despite the challenges of surface irregularities.
Non-silicon materials require an alternative manufacturing method
Mask-based lithography is the most common way to produce semiconductors and has been in use for decades. It’s most effective on perfectly flat wafer materials, like silicon. Alternative materials used in micro-scale production present challenges for mask-based lithography. Surface warpage and height variations cause areas on the substrate to be out of focus with mask-based systems. Similarly, the fixed mask does not allow for compensation of lateral distortions caused by thermal processing.
Maintaining high yield rates and minimizing scrap in the most cost-effective way possible is the main goal of semiconductor manufacturers. Throughput is also important, but not at the expense of too much scrap. Fortunately, Heidelberg Instruments has a solution – maskless aligners.
Maskless lithography provides an exceptionally precise and adaptable solution
Maskless lithography offers an alternative to traditional mask-based lithography by directly projecting designs onto wafers without needing photomasks. This allows for dynamic compensation of distortions, increasing uniformity and alignment and reducing scrap. Maskless aligners are a cost-efficient solution for device serialization due to a flexible framework that allows dynamic pattern adjustments and dynamically generated features.
Heidelberg Instruments in Germany specializes in advanced maskless laser lithography equipment for research and industry. Using Cognex's machine vision technology, it produces state-of-the-art maskless aligners to enhance the efficiency of micron-level production applications. These systems use spatial light modulators, optical devices that convert a data stream into a light pattern that is projected onto the substrate surface.
Cognex alignment technology solves “quality of fit” challenge
In semiconductor manufacturing, multiple layers of circuitry are applied onto a base material, requiring several steps for accurate pattern transfer. The circuit will only function properly if the connections are precisely aligned. Heidelberg Instruments uses Cognex machine vision technology to ensure that the projected microchip die patterns align with the base material's alignment marks, ensuring that the exposures across multiple layers are properly aligned.
Heidelberg Instruments created algorithms to compute “quality of fit" to ensure the substrate could properly receive the pattern. If this calculation is too low, the substrate is flagged for secondary inspection and rejected for automatic processing. If rejections occur frequently, the automated processing is slowed down, which is costly and can lead to lower performance. Increasing the alignment robustness allows for greater variability in the condition of the alignment fiducials on the substrate.
Cognex plays a key role here. Heidelberg Instruments’ maskless aligners employ pattern-matching capabilities in Cognex VisionPro to rapidly locate alignment marks and verify positioning, ensuring accurate circuit pattern transfers even on more challenging substrates.
Leveraging Cognex’s reputation for robust vision tools now and in the future
Heidelberg Instruments develops many products with their own technology, but they acknowledge the importance of partnering with specialists like Cognex to enhance their solutions. Konrad Roessler, CEO of Heidelberg Instruments, said, “By using imaging specialists like Cognex, we can implement modules such as their image recognition into our toolset and achieve improved output compared to using only our solution.”
As for the future, Heidelberg Instruments expects to lean on Cognex vision tools to provide additional functionality to their customers, such as measurement or other tasks.
“We appreciate having an extensive toolbox from Cognex so we can react very quickly to different imaging challenges without having to write new software,” said Philip Paul, Product Manager of MLA 300 at Heidelberg Instruments.
When asked to summarize his perception of Cognex in a few words, Paul said, “Powerful, versatile image processing.”