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Production sequence of Si-spheres and interferometrical determination of the sphere volume




A new metrological large range magnetic force microscope (Met. LR-MFM) with a measurement volume up to 25 mm x 25 mm x 5 mm has been built up. The instrument works in a scanning sample principle. A dual-stage design, which combines a highly dynamic piezo stage and a large range precision mechanical positioning stage (referred to as a nanomeasuring machine, NMM), has been applied for scanning samples along three axes. The dual-stage design enables both a large range MFM measurements and a high scanning speed. The NMM applies high precision nanometric laser interferometers and angular sensors for measuring all six degree-of-freedoms of the sample position in full compliance with the Abbe principle, offering excellent positioning and measurement accuracy at the nm level. Experimental results show that its position stability reaches 0.15 nm, 0.2 nm and 0.6 nm along the x-, y- and z-axes, respectively. A home-built atomic force microscopy (AFM) head is applied in the instrument. It utilizes the optical lever principle for measuring the bending and torsion of cantilevers. The AFM head is capable of measuring in the contact, intermittent- and non-contact AFM mode. Three different measurement strategies referred to as Topo&MFM, MFMXY and MFMZ, respectively, have been developed for MFM measurements. The Topo&MFM measures the topography profile of the surface in the intermittent-contact mode first, and then the tip is lifted with a given height for non-contact MFM measurements, which is similar to conventional MFMs. The MFMXY differs from the Topo&MFM such that it does not measure the topography profile of surfaces at the 2nd and successive lines, thus reducing the tip wear and saving measurement time. To account for the influence of the instrument drift particularly along the z-axis, a drift compensation mechanism is implemented in the measurement strategy. The measurement strategy MFMZ offers the capability for imaging the stray field in the XZ or YZ planes. A number of measurement examples on a multilayered thin film reference sample made of [Co(0.4nm)/Pt(0.9nm)]100 and on a patterned magnetic multilayer [Co(0.4nm)/Pt(0.9nm)]10 with stripes with 9.9 μm line width and 20 μm periodicity are demonstrated, indicating the excellent measurement performance of the developed instrument.

Schematic diagram of three different MFM measurement strategies, shown as (a) Topo&MFM, (b) MFMXY and (c) MFMZ.

Demonstration of a large range MFM measurement, shown as (a) an MFM phase image measured on a patterned magnetic multilayer sample over an area of 204.7 µm x 51.1 µm (x,y); (b) a cross-sectional profile at the marked line in (a) and an illustration of the cross-section of the patterned structure, and (c) a zoom-In MFM phase image measured over an area of 15.33 µm x 15.33 µm marked as the dashed square in (a).

For more details of this research task, please refer to some selected publications listed below:
[1] Gaoliang Dai et al. Metrological large range magnetic force microscopy, Rev. Sci. Instrum. 89, 093703 (2018)
[2] PTB News