CMOS image sensor features UV-optimized coating

Nov. 11, 2014

At last week’s VISION 2014 exhibition, imec presented a backside-illuminated (BSI) CMOS image sensor chip featuring a new anti-reflective coating (ARC) optimized for UV light. Targeting imaging solutions in new markets such as life sciences, the achievement is an important addition to imec’s customized 200-mm CMOS fab. This 200-mm process line enables imec to offer design, prototyping, and low-volume manufacturing of custom specialty chip solutions such as highly specialized CMOS image sensors.

Known for its superior enhanced light sensitivity compared with image sensors using front side illumination (FSI), BSI sensors are top candidates to further improve the performance of CMOS image sensors. Widely spread today in consumer applications such as smart phones, BSI imagers are expected to enter the higher-end application space—for example, industrial inspection.

BSI imagers have a clear advantage when it comes to fill factor for the pixel area, angular response, and the complete avoidance of absorption or scattering losses in the metal interconnect layers. The cost for these light gathering improvement are the extra process complexity for the backside fabrication and possible electrical and optical losses at the new backside silicon interface. Therefore the engineering of the backside layers and interfaces is key to develop high performance BSI devices.

Imec is tackling these challenges to exploit the benefits of BSI imagers for highly specialized customized imagers for space applications, high speed cameras, semiconductor inspection, and medical applications. To minimize reflection losses and maximize transmission of light to the sensor, specific anti-reflective coatings (ARC) are developed for various applications targeting different regions of the light spectrum. The coatings are applied at wafer level as part of the BSI process flow.

Imec has already developed an ARC for visible light range (400 nm to 800 nm) with >70% QE over the entire spectral range. Imec’s new ARC, targeting the UV range, shows excellent performance at near UV wavelengths, with Quantum Efficiency (QE) values above 50% over the entire spectral range from 260 nm to 400 nm.

“This is an important milestone for imec’s customized 200-mm CMOS process line, demonstrating our expertise and capability to design, prototype, and manufacture high-end CMOS image sensors,” said Rudi Cartuyvels, senior vice president, Smart Systems & Energy Technologies, imec. “The development widens our portfolio towards new markets, offering solutions for both visible and UV imaging in semiconductor equipment applications, such as advanced lithography and wafer and mask inspection.”

In other news, mec announced that it has successfully qualified a set of custom high-quality electron detector die products for FEI. The dies are manufactured at imec and integrated in FEI’s scanning electron microscopes (SEMs), helping to enhance the tools’ performance and reliability. This milestone achievement is another confirmation of the capability of imec’s 200-mm process line, developing and manufacturing custom specialty chip solutions.

Imec developed and processed the back scattered and stem electron sensors according to FEI’s custom designs and specifications, with focus on superior sensitivity to low energy electrons and high reliability.

Imec offers companies all the services needed to turn innovative ideas into customized microsystem products. The imec toolbox contains a wide variety of device technologies on 200 mm (for example, CMOS, Si-photonics, MEMS, image sensors, and packaging) as well as design, testing, and reliability. Imec’s services range from feasibility studies over design and technology development to prototyping and low-volume manufacturing. And through its alliances, imec can also offer a path to transfer the technology to a foundry for volume production.

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