Fabrication of a MEMS-based fine-pitch cantilever-type probe unit

We report a MEMS-based cantilever-type probe unit, which corresponds to the fine pitch less than 20 mum and to a fritting force more than 3 gf. The proposed micro probe has been designed to have more than 100 mum of overdrive in single-tip loading that is required to achieve uniform and simultaneous electrical contacts to the high-density testing electrodes having possible nonuniform heights. The probe structure is optimized based on the stress distribution measurement for various lengths and thicknesses of the cantilever. Metal lines are formed by sputtering on the front side of substrate and 10 mum-high metal tips at the end edge of the cantilever by electroplating. Because the probe tips are entirely composed of metal, the wearing out of the metal tips is minimized during touching test and it extends the life time of the probe unit. The cantilevers are released by combination of back-side etching using tetramethyl ammonium hydroxide (TMAH) and following front-side etching by deep reactive ion etch (DRIE). In multi loading test, the limit of the overdrive on the elastic region has reached to 185 mum and the maximum load force to 3.5 gf.