In this paper, we present technologies for measuring inner dimensions of sm
all holes. In the first method with a single probe system, the electrical c
ontact between a vibrating probe and the inner surface of a hole is detecte
d and the duty factor of the contact is measured. Through controlled scanni
ng by a probe with a constant duty factor, data on the ups and downs of the
surface profile are obtained. To characterize inside profiles of micro-hol
es regardless of materials, we developed a new technology with a twin-probe
system. With a silicon-based micro-twin probe 3 mm in length, a micro-hole
with a diameter of around 125 mu m was measured and the estimated imprecis
ion of measurement on this set-up is smaller than 0.5 mu m.