Etch resistance, photo-resist material

In contrast to the si tion processes in i ch the near-surface region is modified, far fewer aiq>roadies exist for direct man ulation of the top oaf ace of a substrate to provide high resolution patterns of etch resistant materials. The initial report of top-surface imaging (TSfi utilized selective deposition of TIOj on the photo-oxidized surface of hydrophobic pofymers (4, 5). 

Wilkins and coworkers have redesigned both the sensitizer and the matrix resin (78-79). They have tested a variety of o-nitrobenzyl esters of cholic acid as sensitizers. These substances, like the diazoquinones, are insoluble in aqueous base but undergo a photo-reaction that yields base soluble products. The matrix resin chosen for the new sensitizer materials is a copolymer of methyl methacrylate and methacrylic acid that is far more transparent than novolac resins in the DUV. The new resist materials are reported to have useful sensitivity (ca. 00mJ/cm ) and extremely high contrast. The resist formulation is essentially aliphatic in nature and would be expected to be less stable to dry etching environments than the aromatic-based novolac resin materials (24). 

A pre-cleaning process is required to remove the stains and oxidations on the surface of the copper foils prior to the coating of photo resist materials. Several adhesiveless laminates have extremely shiny copper surface, therefore the chemical cleaning has an important function in making a better affinity with the etching resist, especially for the fine trace etching. 

Treatment of natural rubber with an ENPCAF-type material containing cinnamate ester groups enables the rubber to be cross-linked by photodimerization in the presence of a photosensitizer. (K. Dawes unpublished—quoted by Porter, 1977). This technique has been used to develop a photo-resist system used in the etching of printed electrical circuit boards. 

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