Measurements of the diameter, roundness and sidewall profile of micro- and nanoholes

Inhalt:
Small holes with a size at micro- and nanometre scale are widely applied in industry. This paper presents research pro-gresses at the Physikalisch-Technische Bundesanstalt, the national metrology institute of Germany, for measurements of diameter, roundness and sidewall profile of micro- and nanoholes. Of two metrology tools introduced, one is a profils-canner which applies a slender silicon cantilever type microprobe. The smallest microprobe availlable has a length of 1.5 mm, width of 30 µm, thickness of 25 µm and tip heights of 22 µm. It is therefore capable of measuring the inner surface roughness and sidewall profile inside microholes with a diameter down to 35 µm. Three laser interferometers are applied in the metrology frame of the profilscanner, which measures in full compliance with the Abbe measurement principle. The tool is capable of traceable measurements with an expanded uncertainty down to 5.2 nm. The second tool is a 3D-AFM which applies a kind of flared AFM tip. Such tip has an extended geometry near its free end which enables the measurements of steep and even undercut sidewalls of holes. Commercial flared tips are available with diameters ranging from 15 nm to 850 nm and with effective tip length ranging from 130 nm to 7500 nm. Therefore, such probes allow measurements of very small nanoholes. For measuring deep holes, however, tips with larger tip length are needed. Two measurement examples on a micro Sonic nozzle with throat diameters of 200 µm to 800 µm, and on a Through Silicon Vias (TSV) with a diameter of 3 µm are demonstrated, showing interesting application capabilities of the developed tools.