Thin detectors for the CHICSi /spl Delta/E-E telescope

Abstract

A pilot series of 10 /spl mu/m to 15 /spl mu/m thin silicon detectors has been made for the /spl Delta/E-E telescopes in the CHICSi detector system. This system will operate at the CELSIUS heavy ion storage ring in Uppsala, Sweden. /spl Delta/E-E telescopes provide isotope identification and energy determination of fragments from nuclear collisions. The thin detectors are made as p-i-n diodes in thin etched membranes in 280 /spl mu/m thick silicon wafers. The membranes are made with anisotropic etching using 25 wt.% 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 /spl plusmn/0.3 /spl mu/m over a wafer and the surface microroughness is in the range from 2 to 4 nm. Each detector has a 10.0 mm/spl times/10.0 mm active area on a 10.2 mm/spl times/10.2 mm membrane surrounded by a 1.1 mm wide supporting frame. The detectors have leakage currents in the active area of approximately 0.5 nA at 20 V. The breakdown voltage of the detectors is above 100 V. Evaluation experiments with telescopes consisting of a thin detector in combination with a thick detector have shown excellent isotope separation capabilities. Mass separation of /sup 6/Li and /sup 7/Li is clearly observable.