Novel nanoscale method for thermal conductivity measurements

As the downscaling of electronic devices pushes dimensions of its components towards the atomic limits, new measurement tools need to be developed to address new challenges. In particular, nanoscale heat transfer is a key mechanism which is known to limit the performance of nanoscale sized transistors in the processor chips and thus invalidate of a major component Moore’s law of the processor speed increase [1]. Measurements of thermal conductivity for simple geometry such as thin films present many difficulties to traditional techniques for layer thicknesses smaller than 100 nm [2]. For example, decoupling the thermal conductivity from the interfacial resistances between the film and the substrate as well as the probe and the film is often difficult. In this report, we develop a novel approach addressing these challenges. We combine a unique cross-sectional tool and a heated probe – scanning thermal microscopy, or SThM, we were able to measure intrinsic thermal conductivity of few tens of um thin layer-on-substrate and to deduce the interfacial thermal resistance. Beam-exit cross-sectional polishing (BEXP) uses Ar-ion beams impinging on a sample at shallow angle (<10 ) [3,4]. The cross-sectioned surface obtained has preferential geometry and sub-nm surface roughness making it easily suitable for studies via standard scanning probe microscopy methods (Fig. 1). Nanothermal microscopy techniques are gaining interest as they resolve thermal properties below the diffraction limit [5,6]. SThM uses the atomic force microscopy principles to raster a thermosensitive probe on a surface. The electrical resistance of the probe is monitored as it scans the sample and by relating this resistance with the temperature, heat transfer properties of the sample can be deduced [7]. To validate our approach, we apply this method on different commonly used materials from semiconductors to insulators such as silicon dioxide, spin-on-glass and spin-onpolymers. The BEXP cross-sectioning process enables the measurements of the SThM ...