Precision layers, perfect chips

The production of advanced optical filters is a core area of expertise for Bühler Leybold Optics. The company's vacuum coating technology is used to apply microscopically thin layers of different materials to glass and other substrates. Varying the thickness of those layers and selecting materials with different optical properties allows the creation of filters that reflect some wavelengths of light while allowing others to pass through.

Wavelength-specific imaging systems can use a separate filter made of coated glass, but integrating the filter into the sensor offers several key advantages, allowing devices to be thinner and more durable, and eliminating spaces where contaminants can lodge. Having the filter on the chip also means that there are fewer mechanical parts that need to be aligned and packaged within the final device.

Chip production takes place in tightly controlled cleanrooms. Workers in these environments wear hooded suits, masks, and gloves, but every time they move or interact with something, there is a risk of contamination. However, even manipulating a silicon wafer with a tool in order to load it into a machine can generate potentially damaging particles. This means reducing the number of people in the production environment as far as possible. The reason is simple: people produce particles. Automation is therefore key.

In precision optics applications, most HELIOS machines operate as standalone systems, producing small batches of varied products. To achieve this level of flexibility, the substrate is loaded and unloaded in a semi-automated, semi-manual way, while keeping particle contamination low. In semiconductor applications, by contrast, the products are uniform wafers. As there is no requirement for flexibility, the manual steps can be removed, and robotic systems used instead that not only streamline the workflow but also reduce particle contamination to a minimum. 

Bühler is collaborating with RECIF Technologies to integrate automated wafer handling technology into its 300 mm HELIOS machines. In high-volume semiconductor production, wafers are transported in standardized plastic cassettes called Front Opening Universal Pods. These airtight units usually hold a stack of 25 wafers and can be gas purged to create an ultra-clean atmosphere around the wafers.

The missing link between the HELIOS and the plastic cassettes is provided by RECIF’s Equipment Front End Module or EFEM. It uses the company’s Advanced Contact Technology to extract wafers one by one. It identifies the wafer by scanning etched markings on the surface, orients the wafer using a notch on its edge, flips it upside down if needed, and finally places the wafer into the HELIOS. For unloading, this sequence is reversed. To reduce particle contamination, the EFEM passes the wafers in via an airlock that helps to preserve the vacuum conditions inside the machine.
 

The first HELIOS machine equipped with a RECIF EFEM is currently undergoing commissioning at a semiconductor customer in Europe. Bühler engineers are operating another development machine at the headquarters of Bühler Leybold Optics in Alzenau, Germany, and work is ongoing to build a third machine for customer use.

“Bühler and RECIF have complemented each other very effectively in this project,” says Schaefer. “RECIF technology is helping our world-leading optical technology to integrate seamlessly into the most advanced semiconductor manufacturing systems. Together with RECIF we bring the coating know-how from Bühler into state-of-the-art semiconductor production.”