Dry-developed resist system

Methods 1 and 3 have been utilized in dry developed resist systems. To our knowledge, there are no resist systems commercially available that depend on post-exposure treatment other than the post-curing effect in negative electron beam resists mentioned earlier. Since such systems are still largely in the research phase we will not discuss them here but rather refer the reader to the literature for more detailed descriptions (44-50). 

Coopmans, F. Ronald, B. DESIRE a novel dry developed resist system. Proc. SPIE 1986, 631, 34-39. 

The latest addition to this list of dry developing resist materials is a contribution from IBM s San Jose Research Laboratory (66-67) that evolved from efforts to design positive-tone resist materials that incorporate chemical amplification. These efforts were stimulated by the fact that the quantum yield of typical diazoquinones of the sort used in the formulation of positive photoresists is 0.2 to 0.3 thus, three or four photons are required to transform a single molecule of sensitizer. This places a fundamental limit on the photo-sensitivity of such systems. 

These experiments confirm the potential advantage of combining low energy e-beam exposure with a dry develop resist scheme proposed in 1984 by G. N. Taylor, L. E. Stillwagon, and T. Venkatesan (5). At that time lack of a high resolution, low voltage e-beam exposure system prevented these workers from experimentally verifying the concept. 

The third class of dry-developable resists involves heating the exposed resist films in a development step. This development method does not require expensive etching tools, is therefore economical, and could alleviate the potential problem of exposure tool contamination associated with the self-developing resist systems. Many of the plasma-developable resist systems involving a relief-bake step, as discussed in Section 3.2.4.1, have the thermal development characteristics to a certain extent. In the thermally developable resist scheme, development is minimal during irradiation but completed to the substrate upon postbaking. 

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. 

With respect to single layer systems (conventional, ImRe, Promote and dry developable resists), we expect that computer programs that can simulate latent image formation and development processes will become of great importance in the near future. A better understanding of the mechanism which underlies the dissolution or etching of resist layers in a developer or plasma respectively is also crucial in order to achieve the ultimate resolution of single layer photoresists. In this respect, well chosen and perfectly defined polymers are required. 

The product temperatures were -21.2°C for KC1 and -31.0°C for povidone. The arrows mark the values of the vapor pressure of ice at the operating temperatures. The normalized dried product resistances increase smoothly with pressure as the vapor pressure of ice is approached and exceeded. Thus, the sublimation rate decreases smoothly throughout this pressure range and does not drop to zero at a total system pressure which exceeds the vapor pressure of ice. This observation is completely consistent with the theoretical concepts developed... 

Although other resist systems have been described in the literature, it does not appear that these newer resist formulations will displace the older more established resists for conventional wavelengths. Much more interest is being shown in dry-developable photoresists which will be discussed later. 

Optimum design was made theoretically on P(CMS-2VN) system. Design method was developed based on theoretical analysis for copolymer resist sensitivity and on dry etch rate dependence on polymer structure obtained by a series of experiments. P(CMSq -2VN9i) (Mw =7.8 x 10, Mw /Mp = 1.3) proved to have high sensitivity (Dg=0.9 jtC / cm2) and high resolution (<0.5 /nm) as well as high dry etch resistance. This resist is suitable for microfabrication especially for dry etching processes. 

---