Abstract
Scanning thermal microscopy (SThM) enables thermal conductivity (λ) measurements with a lateral resolution down to a few tens of nanometers. The present work investigates ways to improve SThM images recorded with resistive probes. Probes based on resistance thermometry act both as a thermometer and as a Joule heated nanoscale heat source. The influence of amplitude and frequency of the applied heating voltage on the SThM image quality was systematically studied. To connect the investigated heating parameters to the temperature change at the apex of the SThM probe, electrical–thermal finite element simulations were performed. Image quality was assessed according to three criteria. The first criterion was the thermal contrast (thermal resolution) between materials of different λ’s. To convert measured SThM signals (in mV) into thermal resolution (in W m−1 K−1), reference measurements were performed by time-domain thermoreflectance, and an implicit calibration method was employed. The second criterion was the distortion of the thermal image by topography. To illustrate the image distortion, the standard deviation of the thermal trace-minus-retrace profile was taken, which could be reduced nearly ten times by changing the heating parameters of the used SThM setup. The third criterion was the spatial resolution of the thermal images. To assess the spatial resolution, gradients in the thermal signal at interfaces between materials were extracted from profiles through thermal images.
Highlights
High-resolution images of thermal conductivity (λ) and temperature distributions are possible by scanning thermal microscopy (SThM), a variant of scanning probe microscopy (SPM).[1,2] Owing to a spatial resolution down to a few tens of nanometers, Scanning thermal microscopy (SThM) has become an integral part of the experimental landscape in submicron heat transfer studies
To compare thermal signals recorded at different settings of the heating amplitude and frequency, the difference in the thermal signal between layer and Si-substrate was defined as ΔVlayer
It is to note that the BPSG/SiO2 layer had the highest ΔVlayer because its thermal conductivity was most different from the reference Si layer
Summary
High-resolution images of thermal conductivity (λ) and temperature distributions are possible by scanning thermal microscopy (SThM), a variant of scanning probe microscopy (SPM).[1,2] Owing to a spatial resolution down to a few tens of nanometers, SThM has become an integral part of the experimental landscape in submicron heat transfer studies. Accurate thermal characterization at the nanoscale helps to understand failure mechanisms (reliability and lifetime) in micro- or nanoelectronic devices and study the impact of nanometer-scale heat transfer on engineered systems.[1]. The hot tip apex acts as a heat source, exciting the sample and, at the same time, allows measuring the tip temperature in contact with the sample due to the temperature dependency of its electrical resistance. The tip temperature depends on the applied heating power and the heat transfer from the tip to the sample, which depends upon other parameters on the local λ of the sample.[12,13]
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