10 μm Pixel-to-Pixel Pitch Hybrid Backside Illuminated AlGaN-on-Si Imagers for Solar Blind EUV Radiation Detection Pawel E. Malinowski *,1,2 , Jean Yves Duboz 3 , Piet De Moor 1 , Joachim John 1 , Kyriaki Minoglou 1 , Puneet Srivastava 1,2 , Ybe Creten 1 , Tom Torfs 1 , Jan Putzeys 1 , Fabrice Semond 3 , Eric Frayssinet 3 , Boris Giordanengo 4 , Ali BenMoussa 4 , Jean Francois Hochedez 4 , Robert Mertens 1,2 , and Chris Van Hoof 1,2 1 IMEC, Kapeldreef 75, Leuven, Belgium 2 ESAT, Katholieke Universiteit Leuven, Leuven, Belgium 3 CRHEA/CNRS, Valbonne, France 4 Royal Observatory of Belgium, Brussels, Belgium *e-mail: Pawel.Malinowski@imec.be Abstract We present the first measurement results from hybrid AlGaN-on-Si-based Extreme Ultraviolet (EUV) imagers with 10 μm pixel-to-pixel pitch. The 256x256 backside illuminated Focal Plane Arrays (FPAs) were hybridized to dedicated Si-based CMOS Readouts (ROICs). The AlGaN active layer with 40% Al concentration provides an intrinsic rejection of wavelengths larger than 280 nm (solar blindness), together with enhanced radiation hardness (1). Sensitivity in Deep UV (DUV), Far UV (FUV) and Extreme UV (EUV) was verified using synchrotron radiation down to a wavelength of 1 nm. Introduction Ultraviolet detection is of particular interest for solar science, EUV microscopy and modern EUV lithography tools (2). Having 2D imaging capability with wide bandgap semiconductors such as Aluminum Gallium Nitride (AlGaN) provides an interesting alternative to the currently used Si electronics, prone to radiation damage and requiring filters for blocking the unnecessary visible and infrared radiation (3). Backside illumination in a hybrid design eliminates absorption in metal contacts shadowing the active layer (4). Using Si as a substrate for AlGaN growth enables increasing the wafer size to 200 mm. Fabrication AlGaN layers were grown on Si(111) wafers using Molecular Beam Epitaxy. Two layer types were processed, with an n- doped layer requiring MESA etching (Layer 1, Fig. 1a) or without MESA (Layer 2, Fig. 1b). The latter was designed for a backside ohmic contact, producing a vertical Schottky diode. The growth started with a 40 nm AlN nucleation layer and was followed by the undoped active layer. Al concentration was decreasing towards the surface, reaching 40%. For the Layer 1, the n-doping was introduced for the top 100 nm. A total thickness of the AlGaN layer was 440 nm for Layer 1 and 340 nm for Layer 2. For the Layer 1, a Cl 2 -based Reactive Ion Etching (RIE) was used to access the undoped layer, with the resulting MESA depth of 200 nm. The FPA pixels are 4 μm Schottky contacts and were deposited by sputtering 20 nm of Au (Fig. 2a). The ohmic grid (common contact surrounding the array) consisted of a Ti/Al/Mo/Au stack, annealed for 1 minute at 850°C. After that, 100 nm of SiO 2 was sputtered to act as an isolation layer. It was opened on top of the pixel contacts with SF 6 - based RIE. Furthermore, in the post-processing step, arrays of 256x256 In bumps with 10 μm pixel-to-pixel pitch and height of 2 μm were deposited by evaporation on top of the AlGaN arrays (Fig. 2b). Figure 1 – AlGaN-on-Si active layers in two versions: a) with n-doped layer for the ohmic contact and requiring MESA etching; and b) simpler, with no MESA etching required. The active layer is AlGaN with a 40% Al concentration. Both layers were grown on Si(111). Figure 2 – SEM micrographs of AlGaN Schottky-photodiode-based pixels with 10 μm pitch: a) front side view before post-processing, showing the MESA structures and the ohmic grid; and b) In bumps deposited on each pixel, with a height of approximately 2 μm. undoped Al 0.4 Ga 0.6 N undoped AlN 300 nm AlN 40 nm Si(111) 300 µm b) Layer 2 no MESA a) Layer 1 Ω contact + MESA AlN 40 nm Si(111) 300 µm n-Al 0.4 Ga 0.6 N MESA 200 nm 200 nm undoped AlN b) a) 14.5.1 IEDM10-348 978-1-4244-7419-6/10/$26.00 ©2010 IEEE