Formation of subsurface Cu-O-Si system through laser-induced plasma-assisted copper penetration for fabricating robust adhesive copper wire on glass substrate

This study reports an approach, laser-induced plasma-assisted penetration (LIPAP), to facilitate copper diffusion to the glass interior using a femtosecond laser. TEM images and EDS analysis showed copper particles could diffuse into the glass up to 300 nm from the surface. The diffusion was driven by the local high temperatures generated by consecutively incident highly repetitive laser pulses. Furthermore, the HR-TEM images showed that, between the surface copper layer and the internal amorphous SiO₂, there were crystalline regions of copper nanoparticles and copper oxides and an amorphous zone, belonging to the Cu-O-Si system, through which, the surface copper layer was firmly connected with the glass substrate. The LIPAPed copper layer then served as a patterning seed for electroless-plating of highly conductive copper wires. Consequently, copper wires with a resistivity of 9.9×10^-8Ωm were obtained. Finally, a scratch adhesion test was performed to quantify the adhesion of the resulting copper films. Results showed that copper remained adhered to the surface before reaching the ultimate glass crush load of 30 N, corresponding to normal scratch stress of 240 MPa. Accordingly, based on the LIPAP-formed special subsurface nanostructures serving as the mechanical anchoring basis, highly conductive and adhesive electroless-plated copper wires were achieved.