Laser enhanced electroless plating of micron-scale copper wires

A technique for laser direct writing of micron-scale copper conductor lines from Cu(HCOO)(2) and CuSO4 on Si substrates using the laser enhanced elect roless plating (LEEP) technique was developed. In this process a focused Ar ion laser beam was used to induce a temperature rise on Si substrate surfa ces immersed in reactant solutions. Increasing the Si surface temperature e nhances the reducing reaction and results in Cu deposition. Glucose and gly cerol were used as reducing agents for copper sulfate and copper formate, r espectively. Line geometries of 2-12 mu m width by 0.25-1.2 mu m thickness were achieved for scan rates of 0.1-0.8 mm/s for Cu(HCOO)(2)/glycerol, for example. The maximum deposition rate for the LEEP of Cu from CuSO4/glucose on Si is 80 mu m/s which is approximately five orders of magnitude faster t han deposition rates produced by conventional electroless plating of Cu. Th e deposited copper films from CuSO4 have a minimum resistivity of 3.6 mu Om ega-cm, approximately twice the resistivity of pure copper (1.68 mu Omega-c m). The resistivity of the Cu deposits shows strong pH dependence. The opti mum resistivity for deposition from copper sulfate is produced at a pH leve l of approximately 13. Out experiments show that there is no significant et ching of Si at pH values less than or equal to 13. To keep the copper ion i n solution at high pH levels, ethylenediaminetetraacetic acid was added to the solution as a complexing agent. (C) 2000 The Electrochemical Society. S 0013-4651(99)04-021-5. All rights reserved.