The effect of core material surface roughness on line accuracy using electrodeposited photoresist

Miniaturization in electronics means finer lines and smaller vias in substrate technology. Very fine lines on the substrate are difficult to produce by conventional means. Thick copper layers are difficult to etch and the accuracy of conventional dry film photoresist is not necessarily sufficient. One very promising means of achieving fine lines is the etching of sputtered thin films on the substrate and growth of the copper with an additive method on the tiny lines. It has been shown that use of dry film photoresist is unsuitable for very narrow lines. Spinning the photoresist is an alternative, but in the test, its adhesion was not good enough. Most narrow resist lines were washed away in the development stage. To meet requirements for accuracy, the best method seemed to be the electrodeposited method, in which a very thin, even, homogenous photoresist layer can be generated. This fine layer is developed easily, thus allowing the transfer of fine line images to the substrate. For good accuracy on the metal lines, the core material beneath the sputtered metal layer must be smooth; the best accuracy can be achieved only with the smoothest surface. The differences between the original and only slightly brushed surfaces are not very obvious.