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CMOS-Back-End-of-Line-Prozesse für optische Bauelemente

 
: Hochschulz, Frank
: Vogt, Holger; Tegude, Franz-Josef

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Volltext (PDF; )

Duisburg-Essen, 2012, 213 S.
Duisburg-Essen, Univ., Diss., 2012
Deutsch
Dissertation, Elektronische Publikation
Fraunhofer IMS ()

Abstract
When CMOS image sensors are to be employed in scientific and technical applications problems arise that are negligible in common imaging applications. Specifically, when the spectral width of the illumination is small, strong variations of the sensitivity dependent on the wavelength, process-induced thickness variations, the angle of incidence and the spectral width of the incident radiation become dominant. Furthermore, in scientific and technical applications a larger spectral range is of interest than in common imaging applications. In this thesis three Back-End-of-Line processes for CMOS photo detectors are investigated, which intend to improve the applicability of CMOS image sensors for scientific and technical imaging applications. All three processes can be used with standard CMOS manufacturing tools. By developing an UV-transparent silicon nitride passivation the sensitivity of photo detectors could be extended into the far UV-range of the spectrum, while maintaining good protective properties. This process is interesting for the development of any image sensor, especially for spectroscopic applications where interesting spectral lines are in the UV-range of the spectrum. Using the so called step etching, which introduces multiple optical path lengths into a single photo detector, the variations of the sensitivity dependent on all above-mentioned parameters could be reduced significantly, without changing the average sensitivity. This process is especially interesting for applications that feature laser illumination, like 3D-time-of-flight-imaging, where a reduction of the variations of the sensitivity simplifies the manufacturing and usage. Using the so called deep optical stack etching, where the Back-End-of-Line in photo-active areas is removed down to thin layers, the variations of the sensitivity could be removed and the sensitivity could be extended into the extreme UV-range of the spectrum. However, this process introduces possible reliability risks. Applications for this process include microscopy. An image sensor using this process has been manufactured, which is intended for mask blank inspection tools for the coming EUV-lithography and is currently waiting for its characterization. Using the investigated Back-End-of-Line processes the variations of the sensitivity could be reduced and the usable spectral range of photo detectors could be increased. These processes therefore improve the applicability of CMOS image sensors for scientific and technical applications.

: http://publica.fraunhofer.de/dokumente/N-442413.html