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Backside-illuminated CMOS image sensor optimised for UV light

Posted: 06 Nov 2014 ?? ?Print Version ?Bookmark and Share

Keywords:Imec? CMOS? image sensor? backside-illuminated? BSI imager?

Imec has recently unveiled a backside-illuminated (BSI) CMOS image sensor chip boasting an innovative anti-reflective coating (ARC) optimised for UV light. Described by the organisation as an important addition its customised 200mm CMOS fab, the device is aimed in various markets, particularly, life sciences.

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 in consumer applications such as smartphones, BSI imagers are expected to enter the higher-end application space of e.g. 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 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 specialised customised imagers for space applications such as high speed cameras, semiconductor inspection and medical applications. To cut reflection losses and maximise 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 developed an ARC for visible light range (400-800nm) with >70 per cent QE over the entire spectral range. Imec's latest ARC, targeting the UV range, shows excellent performance at near UV wavelengths, with Quantum Efficiency (Q.E.) values above 50 per cent over the entire spectral range from 260-400nm wavelength.

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