Mask aligner for ultrahigh vacuum with capacitive distance control

We present an ultrahigh vacuum mask aligner driven by three piezoelectric motors which guide and align a SiN shadow mask under capacitive control towards a conductive sample surface. The three capacitors for read out are located at the backside of the thin mask. The mask can be placed in micrometer distance from the sample surface without touching it, while deliberately keeping it parallel to the sample surface. The sample can additionally be displaced laterally with respect to the mask with a precision of few nanometers. Samples and masks can be exchanged in-situ with a wobble stick. We demonstrate an edge sharpness of the deposited structures below 100 nm, which is likely limited by the diffusion of the deposited Au on Si(111).