Multilevel resists systems

Table 1.1. Organosilicon Resists for Bilayer Multilevel Resist Systems...

Multileaf spiral-wound modules, 15 819 Multilevel 157-nm resist systems, 15 188-189... 

X-ray lithography also takes advantage of the increased resist sensitivity due to the thinner imaging films of multilayer systems. Thinner imaging films further improve X-ray resolution by minimizing the penumbra effect, a problem associated with an uncollimated X-ray beam. Consequently, the oblique exposure of features near pattern edges are minimized by multilevel resist processes, thereby restoring the desired profile. 

One technique for reducing this proximity effect is to replace the single layer of resist with a multilevel resist (MLR) system. In this case, a thin radiation sensitive resist is separated from the substrate by a thick layer of organic material (1). The utility of this approach has been demonstrated experimentally in several laboratories and also investigated by various computer modeling studies. 

SO multilevel resists have not yet seen widespread manufacturing use. The limited selection of polymeric materials suitable for 157-nm resist formulation has brought renewed interest in multilevel systems. 

Photosensitizers can also be used to great advantage in multilevel photoresists. A typical system incorporates a long wavelength uv or visible light photosensitized resist on the top level and a deep uv sensitive resist on the bottom. Both resists may be based on cationic photoinitiators or one may be of this type while the other may be a conventional resist material. 

---