Optical sensors
From facial recognition to autonomous vehicles, many future technologies rely on optical sensors for mobile devices. Making these work requires not only the development of sophisticated optical filters for optical sensors, but also the technology and systems to apply these directly to semiconductors quickly, efficiently, and precisely. Through Bühler Leybold Optics’ collaboration with Belgian research institute imec, this technology is now market ready.
Markus Reber, November 2022
Optical Technologies are the enablers of many important innovations that make our lives easier, healthier, and more energy efficient. From consumer electronics to electromobility and life sciences, there is already a wide range of applications. And these technologies are growing in importance.
LiDAR scanners for example, which are used in today’s premium cars, are likely to become standard. Acting as the car’s “eyes”, they scan the environment and recognize potential dangers. Today they support the driver to react faster, keep a safe distance from the vehicle in front, or trigger emergency braking in critical situations. In future, they will enable cars to drive autonomously, communicating with their environment and other road users via projectors integrated into the headlights.
The potential for these technologies is vast and crosses many sectors. Taking LiDAR again, it can also enable drones to fly autonomously. In combination with hyper-spectral imaging sensors, this can be used in agriculture to scan fields. With the data acquired, farmers can make smarter decisions about the amount of water and fertilizer needed, improving crop yields while lessening the impact on the environment. Sensors are also already in use in life sciences. They are found in smart watches, for example, where they are used to monitor human vital functions. With this information, the wearer can react quickly before a problem becomes more serious. In future, smartphones equipped with hyperspectral imaging can help users avoid foods that are not good for them. By taking a picture in which every pixel can be analyzed, the user can, for example, detect high sugar levels, or even bacterial contamination.
Around 2 billion smart devices are currently sold worldwide, and going forward more and more optical sensors and projectors will be integrated into mobile devices offering new functionalities.
To benefit from these promising technologies, optical sensors need to be smaller, cheaper, and more easily integrated. “This is what we are working on with our customers,” explains Dr. Steffen Runkel, Director and Global Head of Optics at Bühler Leybold Optics. “We are already well-known as a leader in precision optics. Now we want to expand our expertise to the semiconductor industry.”
We are transferring our experience and expertise gained over many decades in precision optics to the semiconductor industry.
DR. STEFFEN RUNKEL ,
Director and Global Head of Optics at Bühler Leybold Optics
Bühler Leybold Optics is specialized in the manufacture of thin film vacuum coating equipment and coating processes with a focus on optical layers. It produced the world’s first light sensor that combines multiple filters and optical elements, such as lenses and apertures, in a very small space. Last year, as part of the HIOS project with AMS, the company began the journey of adapting its coating technology to the requirements of the semiconductor industry.
The technology is based on a vacuum coating process known as sputter deposition. It can be used to create nanometer-thin layers of different materials on an object. This stack of layers acts as the optical filter. Depending on its composition, it reflects or transmits different wavelengths of light. With Leybold Optics’ technology, optical filters with the highest performance can be applied to an object.
To drive this development forward, Bühler Leybold Optics has been collaborating with imec in Belgium, a world-leading R&D and innovation hub in nanoelectronics and digital technologies since 2019. As an institute that bridges university research and industry, imec brings early-stage developments to the point of application and enables volume production in industry.
The aim of the collaboration was to develop a new process for manufacturing optical filters with unprecedented speed and precision in a cost-efficient manner that allows them to be applied directly to CMOS wafers and to adapt the sputter coater to the needs of the semiconductor industry.
“imec was producing hyperspectral imaging filters with state-of-the-art chip production equipment. However, these tools were not designed with such optical applications in mind,” says Stephan Mingels, Bühler Leybold Optics’ project lead for the imec collaboration. “As a result, imec was not able to achieve the most demanding specifications as they were not able to control the coating process in situ while producing the optical filters. So they came to us to see if we could help. In exchange, we had the chance to qualify our machine for the semiconductor industry. This was a very interesting opportunity for us.”
By adapting precision optics requirements to the needs of semiconductor customers we have taken the machine platform to the next level.
PHILIPP SPINDLER ,
Head of Market Segment Semiconductor at Bühler Leybold Optics
At the heart of the project is the HELIOS 800 Gen II sputter coater. The machine was installed in a cleanroom at imec, and the process testing began. There were three requirements the machine had to meet if it was to be qualified for use in the semiconductor industry. First, it had to prove it could meet the required standards of cleanliness, avoiding any contamination with metals such as iron or copper, as these can adversely affect device performance. Next, it had to prove it could prevent dust particles landing on the wafers during deposition, as this can render chips defective and reduce yield. Finally, the team had to develop a new automated process so that the machine could load the production pieces without an operator touching them.
“To keep the wafer clean, the operator can never touch it directly,” Mingels explains. “The wafer is in a cassette encapsulated in a box. We needed to develop a way to load the wafer from the box into
our machine. That might not sound complex, but it needs to be 100 percent reliable and free of any source of particles. We are talking about particles in the nanometer range. If one of these is in the wrong position, the chip will be defective and that means your mobile phone or camera will not work. It was quite a challenge.”
The pressure to get the handling system right was high, as mistakes can be costly. “When the wafers reach HELIOS, they have sometimes already gone through hundreds of processing steps, meaning that they can be worth in excess of EUR 10,000,” explains Runkel. “To damage such a wafer would be a disaster.” The handling system was therefore developed to be highly sensitive. It carefully puts the wafer into the machine, applies the coatings, and then takes the wafer out and places it back in the standardized box to move on to the next step.
Over the course of the collaboration, HELIOS has proven itself capable of meeting all the demands. It has demonstrated that it can apply complex filters directly on CMOS wafers, which are typically 200 or 300 mm in diameter, with a coating thickness that is consistent to +/- 0.5 percent. Furthermore, it can coat up to 12 substrates in just a few hours. With conventional semiconductor tools this process might take weeks, as each layer has to be added individually.
“We are transferring the experience and expertise that we have gained over many decades in precision optics to the semiconductor industry,” says Runkel. “The advantage we have over the traditional suppliers is that we have innovative tools that enable us to put complex optical filters directly on CMOS wafers with unmatched precision.” Via the collaboration with imec, HELIOS has proven itself for the semiconductor industry and Bühler Leybold Optics has acquired valuable experience. A follow-up project has already been agreed to further optimize and automate the use of HELIOS in advanced semiconductor and photonics device manufacturing.
“With HELIOS we had a mature platform ready for creating high-end coatings for precision optics that had already been optimized over many years,” says Philipp Spindler, Head of Market Segment Semiconductor at Bühler Leybold Optics. “By adapting precision optics requirements to the needs of semiconductor customers we have brought the machine platform to the next level. Now we have qualified it, and we are enjoying the first success stories with customers in this new field.” With the machine now being sold to big players, the team is adapting it further to market requirements.
“Sensor technologies are already driving innovations that bring many benefits to our lives,” explains Runkel. “The value we bring to our customers is that we can apply the filters that control precisely which part of light hits the sensor. This is what enables the sensor to work. With the production tools the semiconductor industry had, they could only build up filters with tens of layers. With HELIOS they can apply hundreds of layers uniformly on wafers – quickly, efficiently, and cost effectively. That means our customers can produce at scale the next-generation sensors that enable new functionalities and bring new benefits to our lives.”
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