A new technique for the fabrication of thin silicon radiation detectors

The fabrication of silicon radiation detectors with thicknesses lower than 30 um requires non-standard processing equipment and procedures. Such detectors are commonly manufactured by vias in thick silicon wafers of typically 300 urn in order to locally create on small areas thin detectors. Since the etching step controls the thickness and uniformity of the detector, it must provide a constant and controllable etch rate and should not modify the surface micro-roughness, rendering this manufacturing technique critical. As an alternative, we have developed a new technique for the fabrication of thin detectors based on the use of substrates presenting a buried etch-stop layer. The detector thickness, its uniformity and the surface roughness are fixed and controlled by the substrate specifications. 5 to 30 μm thick pin silicon diodes with surfaces ranging from 1 to 100 mm ² have been fabricated. Using this technique, thickness uniformity as low as ±0.05 μm can be obtained on 5 μm thick detectors over 100 mm ² area. 30 μm thick pin detectors (S = 64 mm ²) are fully depleted at zero bias and exhibit an energy resolution of less than 120 keV (∼ 2 %) for 5.5 MeV alpha particles. This constitutes a breakthrough towards the low cost fabrication of thin silicon radiation detectors using planar technology.