Image-reversal resist

Fig. 4.3. SEM micrograph of image-reversal resist stripes of a test pattern after photolithography. The resist shows an rmdercut profile as desired for the lift-off process...

Figure 3. Sensitivity curves of SPP image reversal (solid line) after 20kV EB exposure compared with a novolac-based resist (dashed line). A 0.3 //m thick resist layer was exposed to EB followed by a flood exposure using near UV radiation and then dip-developed in an aqueous THAH solution for 60 s at 25°C. TMAH concentration A 0.65 wt%, B 0.70 wt%, C 0.80 wt%, D 1.2 wt%.

Although DNQ sensitizers react with X-rays, very little ICA is formed. This observation was made even when exposure was conducted under ambient conditions in which water vapor was present. The net result is that the irradiated areas of the resist have very poor solubility in aqueous base. In fact, if a UV flood exposure is used after imagewise X-ray irradiation, the areas exposed only to the UV can be selectively removed with a developer, a process that leads to an image-reversal scheme. 

As discussed previously, an optional postexposure, predevelopment bake can reduce problems with the standing-wave effect in DNQ-novolac positive resists. However, such a postexposure bake step is indispensable in the image reversal of positive resists (37-41) and certain resists based on chemical amplification of a photogenerated catalyst (64-67, 77, 78). For both types of resists, the chemistry that differentiates between exposed and unexposed areas does not occur solely during irradiation. Instead, differentiation occurs predominantly during a subsequent bake. Therefore, to obtain acceptable CD control in these systems, the bake conditions must be carefully optimized and monitored. 

One approach to minimize these problems is the image-reversal process described in Section 2.2 (28, 29). Another approach has been to increase the nonbleachable absorbance of the resist by adding a dye (30). This ap-... 

Figure 2.21. Resist hardening and image-reversal processes for the Rohm 6-...

The photoresists are exposed through a mask by contact or projection printing with the 3650, 4050, and 4350A° mercury lines. Electron beams 5-30KV and x-rays 2-lOA have also been employed. The positive resist reproduces the mask or image in a direct positive replication while a negative resist reproduces an image reversal of the opaque portions of the mask. 

R. Dammel, Diazonaphthoquinone based Resists, pp. 140 141, SPIE Press, Bellingham, WA (1993) R.M.R. Gijsen, H.J.J. Kroon, F.A. Vollenbroek, and R. Vervoordeldonk, A quantitative assessment of image reversal, a candidate for a submicron process with improved line width, Proc. SPIE 631, 108 (1986). 

Fig. 5a-c. Image Reversal. After imagewise exposure (a) the irradiated areas are insolubilized by decarboxylation of the indene carboxylic acid, followed by blanket exposure to near UV (c). During development, the slope of the resist wall changes from positive to negative. The linewidth is determined by the top width of the insolubilized area... 

Fig. 8a-c. Schematic representation of the lift-off procedure a a resist pattern with negatively sloping profiles is made either by the soak procedure or by image reversal b metal is deposited on the patterned resist, so that a discontinuity exists between metal on the substrate and metal on the resist c the metal on, the resist has been lifted off by dissolution of the resist pattern... 

Apply and pattern photo resist mask using image reversal technique. 

Pichler A, Prior JL, Piwnica-Worms D. Imaging reversal of multidrug resistance in living mice with bioluminescence MDRl P-glycoprotein transports coelenterazine. Proc Natl Acad Sci USA 2004 101 1702-1707. 

In other areas, POD has been used to improve the wear resistance of a mbber latex binder by incorporation of 25% of Oksalon fibers. Heat-resistant laminate films, made by coating a polyester film with POD, have been used as electrical insulators and show good resistance to abrasion and are capable of 126% elongation. In some instances, thin sheets of PODs have been used as mold release agents. For this appHcation a resin is placed between the two sheets of POD, which is then pressed in a mold, and the sheets simply peel off from the object and mold after the resin has cured. POD-based membranes exhibit salt rejection properties and hence find potential as reverse osmosis membranes in the purification of seawater. PODs have also been used in the manufacturing of electrophotographic plates as binders between the toner and plate. These improved binders produce sharper images than were possible before. 

Use of D-amino acids in the synthesis of a hairpin loop portion from the CD4 receptor provides a stable CD4 receptor mimic, which blocks experimental allergic encephalomyelitis (144). This synthetic constmct is not simply the mirror image or enantiomer of the CD4 hairpin loop, but rather an aH-D-constmct in the reverse sequence, thus providing stereochemicaHy similar side-chain projections of the now inverted backbone (Fig. 11). This peptide mimetic, unlike its aH-L amino acid counterpart, is resistant to en2yme degradation. As one would expect, the aH-D amino acid CD4 hairpin loop, synthesi2ed in the natural direction, the enantiomer of the natural constmct, is inactive. 

Figure 10. Kleitz s reaction pathway model for solid-state gas-diffusion electrodes. Traditionally, losses in reversible work at an electrochemical interface can be described as a series of contiguous drops in electrical state along a current pathway, for example. A—E—B. However, if charge transfer at point E is limited by the availability of a neutral electroactive intermediate (in this case ad (b) sorbed oxygen at the interface), a thermodynamic (Nernstian) step in electrical state [d/j) develops, related to the displacement in concentration of that intermediate from equilibrium. In this way it is possible for irreversibilities along a current-independent pathway (in this case formation and transport of electroactive oxygen) to manifest themselves as electrical resistance. This type of chemical valve , as Kleitz calls it, may also involve a significant reservoir of intermediates that appears as a capacitance in transient measurements such as impedance. Portions of this image are adapted from ref 46. (Adapted with permission from ref 46. Copyright 1993 Rise National Laboratory, Denmark.)...

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