In manufacturing diaphragm sensors using surface micromechanics, it is necessary when providing thermally insulated diaphragms, to remove the silicon below the diaphragms. As a rule, this is accomplished through access openings in the diaphragm layer, through which the silicon below it is removed by CIF3 etching, for example. To prevent dirt, moisture or other foreign matter from depositing between the diaphragm and the silicon substrate, or to be able to set a differential pressure between the front side and the back side of the diaphragm, these access openings must be closed again after the etching process. However, because of the large opening diameters attainable using standard methods, the closing of the access openings calls for thick closing layers.
In principle, this problem can be met by small access openings having a diameter <500 nm, as can be realized, for example, by stepper exposure in photoresist. However, the stepper necessary for this demands a large capital outlay. In transferring the photoresist structure into, for example, an oxide layer, however, the structure is enlarged, and therefore the hole diameter becomes larger. In the best case, the smallest hole diameter is identical to the structure realized in the photoresist layer.