Quantifying thermal transport in buried semiconductor nanostructures via cross-sectional scanning thermal microscopy

Managing thermal transport in nanostructures became a major challenge in the development of active microelectronic, optoelectronic and thermoelectric devices, stalling the famous Moore's law of clock speed increase of microprocessors for more than a decade. To find the solution to this and linked problems, one needs to quantify the ability of these nanostructures to conduct heat with adequate precision, nanoscale resolution, and, essentially, for the internal layers buried in the 3D structure of modern semiconductor devices. Existing thermoreflectance measurements and “hot wire” 3ω methods cannot be effectively used at lateral dimensions of a layer below a micrometre; moreover, they are sensitive mainly to the surface layers of a relatively high thickness of above 100 nm. Scanning thermal microscopy (SThM), while providing the required lateral resolution, provides mainly qualitative data of the layer conductance due to undefined tip–surface and interlayer contact resistances. In this study, we used cross-sectional SThM (xSThM), a new method combining scanning probe microscopy compatible Ar-ion beam exit nano-cross-sectioning (BEXP) and SThM, to quantify thermal conductance in complex multilayer nanostructures and to measure local thermal conductivity of oxide and semiconductor materials, such as SiO2, SiGex and GeSny. By using the new method that provides 10 nm thickness and few tens of nm lateral resolution, we pinpoint crystalline defects in SiGe/GeSn optoelectronic materials by measuring nanoscale thermal transport and quantifying thermal conductivity and interfacial thermal resistance in thin spin-on materials used in extreme ultraviolet lithography (eUV) fabrication processing. The new capability of xSThM demonstrated here for the first time is poised to provide vital insights into thermal transport in advanced nanoscale materials and devices.
The authors acknowledge the EU QUANTIHEAT FP7 project no. 604668 and the Horizon 2020 Graphene Flagship Core 3 project no. 881603, EPSRC EP/G015570/1 EP/K023373/1, EP/G06556X/1. EP/V00767X/1 and EP/P006973/1 and Faraday Institution NEXGENNA project for the overall support, and Paul Instrument Fund, c/o The Royal Society grant on “Infrared non-contact atomic force microscopy (ncAFM-IR)” for the equipment support. We are also grateful to our industrial collaborators Leica Microsystems, Lancaster Materials Analysis Ltd and Bruker for the financial and instrumentation support. LTD to ICN2 is supported by the Spanish MINECO (Severo Ochoa Centers of Excellence Program under Grant SEV-2017-0706 and CEX2019-000917-S) and by the Generalitat de Catalunya (Grants 2017SGR806, 2017SGR488, and the CERCA Program). We thank Severine Gomès from CNRS and Harry Hoster from Lancaster Energy for the helpful discussions on the measurements, and Andy Cockburn and Mike Kocsic from IMEC for the interesting materials and discussion of applications.