Multilayer resist systems

Resist systems may be classified into two broad categories, namely, SLR (singlelayer resist) systems and ML (multilayer) resist systems. 

Each approach has its characteristic advantages and disadvantages due to the underlying technology and the materials issues involved (see the remainder of this section). In contrast, SLR schemes are relatively simple processes, can have moderate levels of resolution and etch resistance, and good hnearity, but they suffer from reflective swing problems and small depths of focus, and are limited to low aspect ratios. Irrespective of the resist process approach chosen, chemical amplification continues to be the dominant exposure mechanism of the imaging layer. 

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Photoresist compositions have been prepared that consist of silsesquioxanes containing sulfonamide substituents. These materials are useful in multilayer resist systems that provide contrast upon exposure to photogenerated acid. 

Multilayer resist systems can improve the performance of optical, electron beam. X-ray, and ion beam lithography (83,86). Whereas these schemes increase processing complexity, they appear to be gaining popularity and are currently used in several manufacturing areas. Both DUV blanket-ex-posure-PCM and DUV imaging and RIE-PCM schemes are strong candidates for submicrometer lithography. 

Fig. 32.5 A multilayer resist system incorporating polyaniline as a conducting interlayer.

Fig. 23-1 Three possible ways that conductive discharge layer can be incorporated into a multilayer resist system. After Reference [953], reproduced with permission.

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