Factors controlling the performance of film patterns of cured sol-gel-derived positive-type photosensitive oligomeric silsesquioxanes with random structure

We investigated the effect of heating rates during post-baking on the minimum resolution widths of film patterns prepared from positive-type photosensitive random-structure oligomeric silsesquioxanes (oligo-SQs) with only phenyl (Ph) or both Ph and methyl (Me) groups (Ph group content ≥50 mol%) as substituents. Previously, increasing the Me group content produced 20 μm minimum widths. This was attributed to flow, fusion, and wrinkling during post-baking at 60 °C/min, and partly attributed to enhanced silanol (Si-OH) group reactivity during early stages of post-baking. Here, film patterns for high-definition optical devices fabricated from oligo-SQs with only Ph groups, or with the highest Me group content, produced desired 10 μm widths when heated slowly at 6 °C/min or 3 °C/min, respectively. The decreased widths were attributed to reduced flowability because of enhanced Si-OH group reactivity during heating and the changes and bulkiness of the oligo-SQ molecular structure. The Si-OH reactivity may have been enhanced by the activation of molecular chain motions with increased Me group content and the lower weight-average molecular weight. Structural changes and substituent bulkiness may have also suppressed the chain motions.