Thin detectors for the CHICSi ΔE-E telescope

A pilot series of 10 μm to 15 μm thin silicon detectors has been made for the ΔE-E telescopes in the CHICSi experiment at the Celsius Heavy Ion Collider in Uppsala, Sweden. ΔE-E telescopes provide ion type identification and energy determination of collision fragments. The thin detectors are made as p-i-n diodes in thin etched membranes on 280 μm thick silicon wafers. The membranes are made with anisotropic etching using 25 w% tetramethylammonium hydroxide (TMAH) solution. The etch speed of this solution is very uniform across a wafer. As a result detectors with uniform thickness can be produced. The etch depth varies with less than 0.3 μm and the surface roughness is in the 2-4 nm range. Each detector has a 10.0×10.0 mm² active area on a 10.2×10.2 mm² membrane surrounded by a 1.1 mm wide supporting frame. The detectors have active area leakage currents of approximately 0.5 nA at 20 V. The breakdown voltage of the detectors is above 100 V. Test experiments with telescopes consisting of a thin detector in combination with a thick detector have shown excellent ion separation capabilities. Isotope separation of the isotope ⁷Be and the isotopes ⁹Be and ¹⁰Be can be seen