Method for forming via holes in multilayer circuits

A method for rapidly forming a high density patterned array of via holes of predetermined size in an unfired layer comprising finely divided particles of dielectric solids dispersed in an ablatable organic medium containing substantially no volatile organic solvents, the layer having a thickness of 1-1,000 micrometers, comprising the sequential steps of:

• (a) providing a beam dividing device which splits a single excimer laser light beam into a plurality of smaller beams of predetermined size arranged in the pattern of a selected segment of the patterned array of via holes;
• (b) adjusting the relative position of the beam dividing device between the upper exposed surface of the unfired layer and a source of excimer laser light to enable directing the plurality of smaller excimer laser light beams in a patterned array from the beam dividing device onto a preselected area of the surface of the unfired layer;
• (c) directing the plurality of smaller excimer laser light beams onto the surface of the dielectric layer at (1) a power level of 0.1-10 J/cm.sup.2 and (2) a drilling rate of 0.2-2 micrometer per pulse to effect complete ablation of the organic medium from the areas of the dielectric layer exposed to the laser beams without incurring densification of the dielectric solids therein;
• and
• (d) repeating steps (b) and (c) in further preselected areas of the unfired layer until the patterned array of via holes in the unfired layer has been completed.