Fabrication of Electrical Contacts on Pyramid-Shaped NTD-Ge Microcalorimeters Using Free-Standing Shadow Masks

In our effort to fabricate arrays of germanium microcalorimeters for X-ray detection, a truncated square-based pyramid shape has been identified as a suitable geometry for the sensors. It allows to obtain a uniform current spreading across each sensor, and represents a good compromise between having a large support area for the radiation absorber and for maintaining an overall small bolometer volume. This three-dimensional geometry, however, does not allow to create the electrical contacts for the sensors using a regular photoresist-based lift-off metallization process. In this paper we show how to deposit metal contacts on the lateral faces of the pyramidal sensors by metal evaporation through a butterfly shaped shadow mask, made of a five microns thick free-standing microstructured copper film. The process to fabricate the shadow mask, using microlithography and electrodeposition techniques, is also described.