Ion irradiation of the native oxide/silicon surface increases the thermal boundary conductance across aluminum/silicon interfaces

Abstract

The thermal boundary conductance across solid-solid interfaces can be affected by the physical properties of the solid boundary. Atomic composition, disorder, and bonding between materials can result in large deviations in the phonon scattering mechanisms contributing to thermal boundary conductance. Theoretical and computational studies have suggested that the mixing of atoms around an interface can lead to an increase in thermal boundary conductance by creating a region with an average vibrational spectra of the two materials forming the interface. In this paper, we experimentally demonstrate that ion irradiation and subsequent modification of atoms at solid surfaces can increase the thermal boundary conductance across solid interfaces due to a change in the acoustic impedance of the surface. We measure the thermal boundary conductance between thin aluminum films and silicon substrates with native silicon dioxide layers that have been subjected to proton irradiation and post-irradiation surface cleaning procedures. The thermal boundary conductance across the Al/native oxide/Si interfacial region increases with an increase in proton dose. Supported with statistical simulations, we hypothesize that ion beam mixing of the native oxide and silicon substrate within ∼2.2 nm of the silicon surface results in the observed increase in thermal boundary conductance. This ion mixing leads to the spatial gradation of the silicon native oxide into the silicon substrate, which alters the acoustic impedance and vibrational characteristics at the interface of the aluminum film and native oxide/silicon substrate. We confirm this assertion with picosecond acoustic analyses. Our results demonstrate that under specific conditions, a "more disordered and defected" interfacial region can have a lower resistance than a more "perfect" interface.

Thermal Conductance across Phosphonic Acid Molecules and Interfaces: Ballistic versus Diffusive Vibrational Transport in Molecular Monolayers

“…This is consistent with our previous analyses of thermal boundary conductance across Al/silicon interfaces with and without a native oxide and varying degrees of interfacial roughness and disorder. [12][13][14]21 Page 15 of 38…”

“…For example, changes in thermal conductance across solid boundaries have been experimentally observed by considering geometric roughness, [12][13][14] chemical mixing, 10,[15][16] crystalline orientation, [17][18] strain, 19 and defects. [20][21][22] Where these structural modifications to the interfaces often rely on some disorder driven by the atomic arrangement, several recent measurements have confirmed an additional, if 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 4 not more effective, avenue to tune the thermal boundary conductance between two solids driven by the chemical bond at the interface. [23][24][25][26][27] With the availability of a wide array of molecules and functional groups, new materials and composite interfaces that utilize interfacial chemistries and bonding have provided a pathway to alter thermal transport at the molecular level, including: functionalized fullerene derivatives that set new extremes to the lowest thermal conductivity for a fully dense solid, [28][29][30]...…”

Thermal boundary conductance across metal-gallium nitride interfaces from 80 to 450 K

“…We have also included the measurements of thermal boundary conductance across Al-GaN and Cr-GaN interfaces by Stevens et al, 37 the discrepancy seen here could be due to the work of Stevens et al pre-Al sputtering procedure to remove the native oxide layer on GaN. 37 We have previously shown that removing the native oxide layer between Al and Si will increase the thermal boundary conductance, 23,43 consistent with our assertion about the discrepancy between our and Al-GaN data of Stevens et al. Understanding the contributions of the various metal systems measured and reported here provide a starting point in the basic thermal science of GaN-metal interactions and enable design of the much more complex contacts needed to operate high power devices.…”

“…16 These thin oxide layers prevent direct interaction between the metal and GaN, and can contribute to the mechanisms described above to further limit the thermal boundary conductance. 23,43 While interfaces in GaN-based devices vary significantly in material constituents and methods of processing, the interfaces chosen in this study aim to provide a reference for fundamental understanding of the GaN-metal interface that is critical to establishing a framework for thermal engineering of the contact component of devices. A comparison of the findings in this work to previous works concentrated on the GaN-substrate interface helps to give context to the metal-GaN interface with respect to thermal management.…”

Design rules for interfacial thermal conductance: Building better bridges

“…Nevertheless, the full potential of this revolution is still to be seen because there is a gap between our fundamental understanding of heat flow across single and multiple interfaces and the outcome of experimental measurements [6]. For instance, while many simulations predict an enhancement of thermal conductance when a thin layer is inserted at a well bonded interface [7][8][9][10][11][12][13], only one experiment backs up that prediction so far [14]. Other experiments reporting conductance enhancement attribute the increase to a strengthening of the bonds at the boundaries [15][16][17].…”