Image reversal

Haque TS, Little JC, Gellman SH (1994) Mirror-image reverse turns promote beta- hairpin formation. J Am Chem Soc 116 4105 106... 

Figure 6 Image reversal process and related chemistry based on a...

Preparation of a Novel Silicone-Based Positive Photoresist and Its Application to an Image Reversal Process... 

This paper describes the preparation of SPP and its application to an image reversal process, as well as the chemistry of the SPP image reversal. 

Application to image reversal process a)Electron beam lithography... 

Figure 4 shows an SEM photograph of 0.3 urn line and 0.5 m space pattern delineated in an SPP 2LR system with a dose of 5 u C/cm2. The combination of this SPP image reversal process and EB direct wafer-writing technology represents a promising approach for achieving sub-halfmicron resolution. 

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%.

Figure 5. Sensitivity curve of SPP Image reversal to X-rays compared with that of FBM-G. A 0.4 /ui thick SPP layer was exposed to X-rays both In air and In vacuum followed by a flood exposure and then dip-developed In a 0.8 wt% TMAH solution for...

The deep UV induced reactions appear to be slightly different from X-ray and EB induced reactions. Deep UV exposure in air can induce an increase in solubility of SPP, indicating that indenecar-boxylic acid is produced. IR spectra of SPP exposed to deep UV are shown in Figure 11. In this case, we used a mono-functional dissolution inhibitor, tert-amylphenol diazonaphthoquinone sulfonyl ester, instead of a multi-functional sensitizer, DNQ, because the IR spectrum of a mono-functional ester is easier to interpret than that of DNQ. The SPP containing this mono-functional ester also exhibits an image reversal reaction with almost the same characteristics as the SPP with DNQ. 

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 24. Process sequence for image reversal in a positive photoresist. The chemical transformations of the sensitizer that occur in each process...

Figure 8. Schematic representation of monazoline process for image reversal of positive photoresists. (Reproduced with premission from Ref. 1.)...

Recently, other thermally induced image-reversal processes have been... 

Scheme HI. Decarboxylation of indenecarboxylic acid (ICA) photoproducts during image reversal. The process involves treatment with base to form a carboxylate salt, followed by baking to generate ultimately a base-insoluble...

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. 

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