High-speed microprobe for roughness measurements in high-aspect-ratio microstructures

Abstract

Cantilever-type silicon microprobes with an integrated tip and a piezoresistive signal read out have successfully proven to bridge the gap between scanning force microscopy and stylus profilometry. Roughness measurements in high-aspect-ratio microstructures (HARMS) with depths down to 5 mm and widths down to 50 µm have been demonstrated. To improve the scanning speed up to 15 mm s−1, the wear of the tip has to be reduced. The atomic layer deposition (ALD) technique with alumina (Al2O3) has been tested for this purpose. Repeated wear measurements with coated and uncoated microprobe cantilevers have been carried out on a roughness standard at a speed of 15 mm s−1. The tip shape and the wear have been measured using a new probing tip reference standard containing rectangular silicon grooves with widths from 0.3 µm to 3 µm. The penetration depth of the microprobe allows one to measure the wear of the tip as well as the tip width and the opening angle of the tip. The roughness parameters obtained on the roughness standard during wear experiments agree well with the reference values measured with a calibrated stylus instrument, nevertheless a small amount of wear still is observable. Further research is necessary in order to obtain wear resistant microprobe tips for non-destructive inspection of microstructures in industry and microform measurements, for example in injection nozzles.

Long Slender Piezo-Resistive Silicon Microprobes for Fast Measurements of Roughness and Mechanical Properties inside Micro-Holes with Diameters below 100 µm

“…At the maximum possible traverse speed of these microprobes, which currently amounts to 15 mm/s [7], wear increases in such a way that, after a measurement length as short as 2 m on the roughness standard RN6531, the radius of the tip reaches more than 2 μm (see Figure 18) increasing to 3 µm after a total scan length of 300 m (Figure 19). For these measurements, we used a small static probing force of 50 µN along with a measurement length of 7 mm and, for roughness evaluation, a cut-off wavelength of 0.8 mm and software written by researchers in LabView were used.…”

“…Besides the capability to measure inside micro-nozzles, these light weight sensors have the potential to deliver very fast measurements, since their mass (0.12 mg) is orders of magnitude smaller than that of conventional roughness probes (1 g). The first fast measurements with traverse speeds up to 15 mm/s were successfully made on roughness standards [7].…”

“…At fast roughness measurements, a continuous small wear of the integrated silicon tip was observed [7]. To overcome the wear problem, two methods are tested here: a hard coating of the tips and the gluing of full diamond tips to the probes.…”

Sensor characterization by comparative measurements using a multi-sensor measuring system

“…However, the tip may influence the sample to be measured and also limits the measuring speed typically up to 1 mm s −1 . Therefore, there are efforts to increase the measuring speed of tactile sensors and to reduce the wear of the stylus tip (Morrison, 1996;Doering et al, 2017). Doering et al (2017) present a microprobe which allows tactile roughness measurements with a lateral scanning speed of 15 mm s −1 .…”

“…However, depending on the surface topography, more or less systematic measurement errors may also occur. Examples are artefacts known as batwings (Harasaki and Wyant, 2000;Xie et al, 2017), phase jumps resulting from the slope effect in white-light interferometry and also laser interferometry (Schake et al, 2015), artefacts from crosstalk between neighbouring pinholes of a spinning disc of a confocal microscope (Fewer et al, 1997), and artefacts occurring by equal curvature of the wavefront and the measuring surface (Mauch et al, 2012). For an investigation of these effects it is necessary to distinguish between the real and the measured surface.…”