Critical factors for nanoscale injection molding

Injection molding technology offers the most competitive potential to meet the growing demand for cost-effective manufacturing of components with micro and nanoscale features due to its far greater production rates than the other techniques. Since conventional mold tooling materials and techniques are not suitable for sub-micron scale molding, mature silicon processing technology were evaluated as tooling for these features. Simple pattern geometries of trench lines were employed to simplify the analysis and all parts were molded using optical grade high-flow polycarbonate. Replication quality was evaluated in terms of depth ratio (height of molded feature/depth of corresponding tooling feature) and root-mean-square roughness. Although perfect replication has not been achieved with the given system, several factors including surface adhesion and feature aspect ratio were found to be critical for replication of nanoscalefeatures. Of four factors possibly affecting replication, adhesion of the polymer to silicon surface during ejection was found to be critical and is influenced by processing temperatures, cooling times, tooling mounting systems, and tooling surface roughness. Trapped of air in tooling trenches, damage to the silicon tooling during molding, and shrinkage of polymer during cooling may also have contributed to less-than-perfect replication. All factors seem synergistic and the effects are greater for small feature geometries.