Vision 2014: Imec presents 'improved' back-side lit CMOS sensor

05 Nov 2014

With its UV-optimized antireflective coating, new chip targets high-res UV imaging applications in machine vision.

At this week’s VISION 2014 exhibition, Belgian-based research center imec has presented a backside-illuminated (BSI) CMOS image sensor chip with a new anti-reflective coating (ARC) optimized for UV light.

Targeting imaging solutions in markets such as life sciences, its developers say this achievement is an important addition to imec’s customized 200mm CMOS fab. This process line enables imec to offer design, prototyping and low-volume manufacturing of custom specialty chip solutions such as highly specialized CMOS image sensors.

BSI sensors, which imec describes as offering superior enhanced light sensitivity compared with front side illuminated sensors (FSI), are leading candidates to further improve the performance of CMOS image sensors. Widely deployed today in consumer applications such as smart phones, BSI imagers are expected to enter higher-end application markets – such as industrial inspection.

BSI imagers have advantages in, for example, fill factor for the pixel area, angular response, and the complete avoidance of absorption or scattering losses in the metal interconnect layers. The downside of these light gathering improvements are typically the extra process complexity for the backside fabrication and possible electrical and optical losses at the new backside silicon interface. Therefore, imprving the engineering of the backside layers and interfaces is key to developing high performance BSI devices.

Imec says it is tackling these challenges to exploit the benefits of BSI imagers for highly specialized customized imagers such as 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.

Visible and UV performance

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

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

About the Author

Matthew Peach is a contributing editor to optics.org.