Hydrogen thermal reductive Cu nanowires in low temperature Cu–Cu bonding

Abstract

Nanostructures have attracted great interest in interconnect applications. Herein, we present a novel low temperature, templateless method for directly preparing Cu nanowires through a hydrogen thermal decompositionreduction route of Cu(OH) 2 → CuO → Cu. The thermal treatments are performed at relatively low temperatures of 180 °C-200 °C to meet the low thermal budget in the semiconductor industry. Cu(OH) 2 nanowires are completely transformed into Cu nanowires and the morphologies of the nanowires are successfully preserved without shrinkage of volume and size. Sintering of Cu nanowires occurs at a low temperature of 400 °C in Ar ambient and 350 °C in H 2 ambient, respectively. Based on this phenomenon, we innovatively apply the assynthesized Cu nanowires in Cu-Cu bonding at 150 °C-400 °C. The bonded samples exhibit high shear strengths where Cu nanowires have transformed into Cu nanoparticles, mainly attributed to the enhanced atom diffusion with the existence of nanowires. The present work demonstrates the feasibility of hydrogen thermal reductive Cu nanowires in low temperature Cu-Cu bonding.

Ultra-Broadband and Omnidirectional Perfect Absorber Based on Copper Nanowire/Carbon Nanotube Hierarchical Structure

“…Conventionally, high-quality CNTs are grown on Cu substrates at elevated temperatures (700–900 °C) in Ar/H 2 atmospheres using extrinsic Ni catalysts − due to the poor catalytic activity of copper for CNT growth . However, thermally reduced Cu NWs (Figure a­(ii)) can easily collapse under these conditions, , and extrinsic catalysts act as impurities in the structure. To obtain our hierarchical structure, instead, we used a low-temperature self-catalytic CVD growth process by using acetylene gas (C 2 H 2 ) as a carbon precursor due to its low decomposition temperature (∼600 °C) .…”

“…To obtain our hierarchical structure, instead, we used a low-temperature self-catalytic CVD growth process by using acetylene gas (C 2 H 2 ) as a carbon precursor due to its low decomposition temperature (∼600 °C) . We also minimized the CNT growth time to prevent any significant morphological change of the Cu NW structure in the inert atmosphere. , Elemental analysis results of the final Cu-CNT NWs structure in Figure S1 consistently show the vast predominance of carbon and copper in the structure, indicating that the CNT-coated NWs remain in the Cu metallic state after exposure to ambient air. The very low oxygen content (ca.…”

“…Importantly, a comparison of Figure b,d confirms that the morphology of the NWs is largely preserved during CNT growth. A mechanical strain gradient, due to surface reduction of the NWs during the H 2 treatment process, is responsible for the slight bending of the Cu NWs. , On the contrary, samples prepared by using methane gas as the carbon precursor (growth temperature ∼ 900 °C) suffered from sintering, with complete loss of the NW morphology (see Supporting Information S1.2 and Figure S3). Interestingly, the high-magnification SEM images reveal that, during our acetylene-based growth, short-length and coil-shaped CNTs are radially grown on individual Cu NWs, fully covering them throughout their entire length (Figure e).…”

“…The as-grown CuO NWs appeared black and were used as a 3D support for the later CNT branch growth, which avoids aggregation of CNTs. Before CVD growth of CNTs, a hydrogen thermal reduction process was performed on the as-grown CuO NWs at 350 °C for 10 min in a low concentration H 2 environment (300 sccm Ar/30 sccm H 2 ) to reduce the CuO NWs into Cu NWs, which can act as a catalyst for random growth of CNTs (Figure a­(ii)). ,, Then, the CNTs were directly grown on the surface of Cu NW arrays via a self-catalytic mechanism at 600 °C for 10 min by using a mixture of acetylene (C 2 H 2 ) gas (300 sccm Ar/40 sccm C 2 H 2 ) as a carbon precursor with a low decomposition temperature (Figure a­(iii)). After CVD growth of CNTs, the system was rapidly cooled down to room temperature (∼30 K/min) under Ar cover to prevent oxidation and preserve the morphology of Cu NWs.…”