New Ultrathin Solar Blind EUV Imager

At the International Electron Devices Meeting this week, the Interuniversity Microelectronics Centre (IMEC) presented an ultrathin hybrid AlGaN-on-silicon extreme ultraviolet (EUV) imager with a 10-µm pixel-to-pixel pitch. The wide-bandgap AlGaN provides insensitivity to visible wavelengths and enhanced UV radiation hardness compared to silicon. Backside illumination in a hybrid design was used to achieve the very small pitch. The novel imager shows an excellent detection down to a wavelength of 1 nm.

Ultraviolet detection is of particular interest for solar science, EUV microscopy and advanced EUV lithography tools. Sensors using wide-bandgap materials overcome the drawbacks of silicon-based sensors such as their sensitivity to UV radiation damage and the need for filters to block the unnecessary visible and infrared radiation.

IMEC’S backside-illuminated EUV imager is based on a state-of-the-art hybrid design integrating an AlGaN sensor on a silicon readout chip. A submicron-thick AlGaN layer was grown on a Si(111) wafer using molecular beam epitaxy and a focal plane array of 256 × 256 pixels with a 10-μm pitch was processed. Each pixel contains a Schottky diode optimized for backside illumination. A custom read-out chip, based on capacitance transimpedance amplifiers, was fabricated in 0.35-µm CMOS technology. The AlGaN wafer and read-out chip were postprocessed with indium solder bumps also with 10-µm pitch, achieving excellent uniformity. The focal plane array and read-out chip were assembled using flip-chip bonding and subsequently the silicon substrate was locally removed to enable backside illumination of the active AlGaN layer. Finally, the imager was packaged and wire-bonded.

These results were obtained in collaboration with Centre de Recherche sur l'Hétéro-Epitaxie et ses Applications/Centre National de la Recherche Scientifique (CRHEA/CNRS) of France and the Royal Observatory of Belgium in the framework of the BOLD project of the European Space Agency.

For more information, visit: www2.imec.be