The Role of Interfacial Thickness and Quality on Thermal Boundary Conductance at Pt-silicide/Si Interfaces

As devices continue to shrink in size towards the nano-length scale, solid-solid interfaces serve as a primary scattering center for energy carriers (phonons), often creating a thermal bottleneck within the device. The optimization of thermal boundary conductance, hBD, at solid-solid interfaces is complicated since the innate phonon spectra of materials often limits the maximum thermal boundary conductance achievable for a solid-solid interface. To offset this constraint, researchers have shown that inserting a thin instertitual layer between two vibrationally mismatched materials can serve as a “phonon bridge” to mediate scattering. More recent computational studies by the Norris group demonstrated that a mass-graded “phonon bridge” can enhance the thermal boundary conductance by up to 300% at vibrationally mismatched materials. The aim of this research is to experimentally measure the role of a compositionally-graded interstitial layer on the thermal boundary conductance at a vibrationally mismatched alloy/semiconductor interface.
A series of Pt-based metallic silicides/Si were deposited through plasma vapor deposition and heat treatments at a range of temperatures were used to encourage diffusion and formation of intermetallic compounds within the interfacial region. The silicide films and the interfacial region were characterized through x-ray diffraction and x-ray photoelectron spectroscopy. The resulting thermal boundary conductance of the sample series was measured with time-domain thermoreflectance (TDTR). The thermal boundary conductance values of the Pt-silicide/Si interfaces were directly correlated to the size of the interfacial region and the thermal boundary conductance could be enhanced by up to 60%. The thermal boundary conductance values were also dependent upon the transition rate and phase composition of the intermediate layer. Overall, the results support that the thermal boundary conductance can be enhanced by promoting a compositionally-mixed gradient at the interface at carefully selected interfaces. Utilizing purposeful mixing layers at an interface remains a promising avenue for controlling the thermal boundary conductance at alloy/semiconductor interfaces. Methods for optimizing the thermal boundary conductance at the understudied alloy/semiconductor interfaces are crucial for continued optimization of electronic devices.