Topography-free sample for thermal spatial response measurement of scanning thermal microscopy

Abstract

A novel fabrication technique is described for the production of multimaterial, lithographically defined, topography-free samples for use in experiments to investigate the nature of contrast in scanning probe microscopy (SPM). The approach uses a flat sacrificial substrate as the base for fabrication, which is deleted in the final step. This leaves an exposed, flat surface with patterns of materials contrast defined during the lithography stages. In the example application presented, these are designed to challenge the detection ability of a scanning thermal microscopy (SThM) probe, although many other applications can be envisioned. There are many instances in SPM where images can exhibit topographically induced artifacts. In SThM, these can result in a change of the thermal signal which can easily be misinterpreted as changes in the sample thermal conductivity or temperature. The elimination of these artifacts through postprocessing requires a knowledge of how the probe responds thermal features of differing sizes. The complete sample fabrication process, followed by successful topographic/thermal scanning is demonstrated, showing sub-1.5 nm topography with a clear artifact-free thermal signal from sub-100 nm gold wires. The thermal spatial resolution is determined for the sample materials and probe used in this study to be in the range of 35-75 nm.

Quantification of probe–sample interactions of a scanning thermal microscope using a nanofabricated calibration sample having programmable size

“…The temperature variation of the probe can be determined from the output voltage (U), from which probe resistance is derived using parameters of the circuit (peak-peak AC voltage supplying the bridge, Vac) and gain of the lock-in amplifier (A). We have previously shown that the temperature coefficient of resistance (α) of the whole probe, consisting the cantilever, gold wires, pads, and the platinum tip, is 0.000961 ± 0.0000106 K -1 [50].…”

Dimension- and shape-dependent thermal transport in nano-patterned thin films investigated by scanning thermal microscopy

“…The apex radius was estimated to be the same as the tip radius of curvature (~ 50 nm) 15,16 and the temperature coefficient of resistance (") was measured as 0.000961 K -1 . 29 The probe was used in contact mode under ambient conditions, and operated in constant power mode (P = 1.02 × 10 -4 W) configured in a Wheatstone bridge. Any increase in electrical resistance was converted to temperature above ambient.…”

“…This results in data that is inaccurate and open to misinterpretation. To avoid the issue, we have employed a recently developed approach to fabricate topography-free samples [29]. These samples have enabled us to make the first systematic demonstration illustrating the effect of feature dimensions on thermal spreading resistance as measured by SThM independent of topographic artefacts.…”

Scanning thermal microscopy for accurate nanoscale device thermography

“…Heat conduction via the point of contact between the probe and the sample is expected to be the dominant heat transport mechanism in SThM. However, when scanning in ambient air and pressure, presence of water meniscus surrounding the tip at the point of contact not only hinders the lateral resolution, but also enables additional heat convection to the tip [37,38]. This effect is temperature dependent; it is reduced at temperatures close to water boiling temperature, and can be further reduced or completely mitigated by introducing of dry inert atmosphere (N, Ar) or vacuum, respectively.…”