Direct Cu-Cu bonding by low-temperature sintering using three-dimensional nanostructured plated Cu films

This work examined low-temperature sintering of three-dimensional (3D) nanostructured plated Cu films (3D-Cu films), followed by direct Cu-Cu bonding using these films. The 3D-Cu films were prepared by electrodeposition, employing a Cu plating bath containing polyacrylic acid. These films were subsequently heated under a vacuum of approximately 1 Pa, after which their microstructure was characterized. Direct bonding between the films was performed at 200, 250 or 300 degrees C in air with a joint load of 10 MPa, and the strength of the resulting bonds was measured. Low-temperature sintering of the films was evident at temperatures above 180 degrees C. The bonding strength for films processed at 200, 250 and 300 degrees C was determined to be about 5, 23 and 34 MPa, respectively, demonstrating the feasibility of direct Cu-Cu bonding via low-temperature sintering of 3D-Cu films.