Critical Parameters Soft lithography appears to be a promising route to nanostructures and nanosystems. Many issues remain to be solved, however, before the techniques can be brought to the market. Some critical parameters are applicable to all the techniques, while others apply only to specific techniques. Multilevel structures and devices necessitate the ability to accurately place one layer on top of another. Distortion currently limits soft lithographic techniques to the fabrication of single-layer structures and devices.
Registration is possible on micron-sized features using a mask aligner.
Studies are also underway in our group to quantify the distortion in elastomeric stamps and to limit this distortion by using thick stamps and rigid backings. The formation and distribution of defects also must be controlled if these techniques are to be used in device fabrication. Defects arise from dust particles, poor adhesion to the substrate and poor release from the stamp, bubbles in the precursor, and contamination from low molecular weight monomers in the stamp. The presence of the underlayer makes etching and lift-off difficult. Although reactive ion etching can be used to remove thin layers, the time necessary to remove thick layers would damage small features.