Positive tone image

Fig. 35. Process flow for thin-film imaging lithography (a) bilayer process and (b) top surface imaging. The bilayer process shown here employs a positive-tone imaging layer. The TSI process illustrated refles on preferential silicon incorporation in the exposed regions of the imaging layer to give a...

One final example of the application of onium salt photochemistry in positive resist materials should be mentioned, because it does not include any postexposure acid-catalyzed processes and therefore does not encompass the principle of chemical amplification (79). Interestingly, Newman (79) has determined that onium salts themselves can inhibit the dissolution of novolac in aqueous base and that irradiation of such an onium salt-novolac resist restores the solubility of the resin in developer and leads to a positive-tone image. In this application, the onium salt behaves like diazonaphthoquinone in a typical positive resist. Recently, Ito (80) has reported also the use of onium salts as novolac dissolution inhibitors. 

The developed resist patterns were heated at 200°C for 1 hour in a convection oven. Scanning electron microscopy shows no thermal deformation in the negative tone images (Figure 10). The positive tone images lost thickness consistent with thermolysis of the t-BOC side chain but also do not show evidence of thermal flow deformation. 

The SEMs shown in Figure 3.29 were made from a single wafer of poly( p-formyloxystyrene) that had been exposed on a Perkin-Elmer M500 scanner in the UV-2 mode and then broken in half One half was developed in a polar solvent to generate a positive-tone image, whereas the other was developed in a nonpolar solvent to produce a negative-tone image. 

In positive-tone imaging, a high-sensitivity photoresist is usually composed of a photoinitiator and a polymer, the degradation of which is typically based on chemical... 

Figure 7. Deep UV polymer patterns obtained with a matrix resist of poly(2-methyl-l-pentene sulfone) and Varcum resin positive tone images on the left and negative tone images on the right.

The reverse polarity change mechanism to convert polar polymer to nonpolar polymer could be an excellent basis to design a resist that could provide positive-tone images upon development with supercritical C02. 

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