Resist imaging methods

MLR systems offer many advantages in optical, e-beam, x-ray, and ion-beam lithography. An advantage common to all imaging methods is in enhancement of resist sensitivity. As the resolution and the aspect ratio requirements are separated in an MLR system, faster resists that are usable only for low aspect ratio images can now be candidates for the top layer. Other advantages of MLR systems differ from one imaging method to the other. They will be discussed separately. 

When working with this type of resist to make VLSI devices there are several problems that come up, particularly the need for improved thermal stability from the resist images emd a method to control light that is reflected or scattered in a nonimagewise manner. The function of a development enhancement agent is to increase the dissolution rate of the photoresist so that polymers with better physical properties but slow dissolution rates may be used. The dyes... 

The reticulation problem is also encountered in the plasma resist image stabilization method (PRIST) (38) where the crosslinking reactions are more superficial than in UV-hardeniog. In PRIST, resist images are exposed to a CF4 plasma for a short period, providing a surface cross-linked by interaction with the reactive environment. The oxidation and fluorine incorporation are limited to a very shallow surface. 

The RPL values obtained by puddle development for PC-129 and HPR-204 are both larger than those obtained by dip development, thus indicating that the dip method is better with the developers employed. In addition, resist image clearing uniformity across the 3" test wafers was better for the dip developed wafers than for those puddle developed. Furthermore, the dip development method yielded statistically better wafer to wafer development reproducibility for PC-129. This is not to say that puddle development is not a useable entity but that dip is preferred. In fact, Leonard and coworkers (6) have developed a puddle development method with production capability. Similarly, the RPL data for KTI-II favors dip development over that of spin/spray, therefore, dip development is the favored development method overall for these three example resists. 

One important area of resist research in recent years is the development of plasma-developable resist systems. The aim of plasma developable resists is to use nonsolvent, all dry development methods to avoid the problems of swelling and consequent resolution limitation associated with conventional resists. Much of the semiconductor fabrication process now utilizes plasma techniques as they are capable of providing high resolution images. An important consideration in this is that the plasma-developable resist images should stand up well to the plasma etching treatments. 

Because of the changes in the cell membrane resistance during electroporation, the technique can be controlled and monitored with electrical impedance tomography, a realtime imaging method that maps the electrical impedance distribution inside the tissue (Davalos et al., 2004). Ivorra et al. concluded in (Ivorra and Rubinsky, 2(X)7) that... 

Spray Coating. Although very thin and uniform coatings are possible with this method, its use in resist imaging has been limited due to concerns about waste caused by overspray. 

Sano, H. Yamada, M. Ink-jet recording method using magenta inks to give light-resistant images. Jpn. Kokai Xokkyo Koho JP 2000265099, 2000 Chem. Abstr. 2000, 133, 268387. 

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