THE INFLUENCE OF LITHOGRAPHIC PATTERNING ON CURRENT DISTRIBUTION IN ELECTRODEPOSITION - EXPERIMENTAL-STUDY AND MASS-TRANSFER EFFECTS

The effect of lithographic patterning on electrodeposit thickness uniformity was investigated in a series of experiments. Copper was electrodeposited from an acid-sulfate solution onto a specially patterned cathode under controlled agitation provided by a reciprocating paddle. The thickness nonuniformity resulting from a difference in ''active-area-density'' between adjacent zones was measured by profilometry. At current densities far below the mass-transfer limit, the thickness distributions agreed well with predictions from a recently developed secondary-current-distribution model, in which each zone is treated as a continuum. Since this ''secondary'' model was found to be insufficient to describe behavior at higher current densities, it was extended to include a simple treatment of mass transfer. The resulting ''tertiary'' model better described the observed behavior. it was discovered that the influence of mass transfer can either decrease or increase the nonuniformity, depending on the importance of radially enhanced diffusion at individual features.