UV HARDENING

Glass transition temperatures of the uv-hardened films were measured with a Perkin Elmer Model DSC-4 differential scanning calorimeter (DSC) that was calibrated with an indium standard. The films were scraped from silicon substrates and placed in DSC sample pans. Temperature scans were run from -40 to 100-200 °C at a rate of 20 ° C/min and the temperature at the midpoint of the transition was assigned to Tg. 

Table VI shows a comparison of the leveling properties of the ortho-cresol novolac film that was baked at 225 C for 15 min with those for a uv-hardened film of a 7 3 mixture of NA and EBDMA. The mixture had a viscosity of 75 cs and a 10 min leveling period was used before uv hardening. Both films had a final film thickness of about 2 fJ.m.

Table VII. Glass Transition Temperatures and Film Shrinkage of UV-Hardened and Baked 7/3 NA-EBDMA Films...

Films of 7 3 mixtures of 1-naphthyl acrylate and ethoxylated bisphenol-A dimethacrylate had better planarizing properties than any of the resins that were examined and may be useful as layers for etchback processing. For use as bottom layers in multilayer-resist structures it will be necessary to bake the films after uv hardening to increase the Tg, and if the exposure wavelength is above 300 nm, an appropriate dye must be added to eliminate substrate reflections that degrade resolution. 

Figure 3.58. SEMs demonstrating UV hardening of a photoresist. Top, AZ1470 patterns baked at 180 °C for 30 min after exposure to a low-pressure Hg lamp containing DUV output and bottom, AZ1470 patterns under the same conditions except that the patterns were exposed through a glass filter. Reproduced with permission from reference 201. Copyright 1982 Electrochemical...

Fig. 12 (Right) Comparison of thermal flows of 3.5 fim thick resist images at 250°C (a) no treatment, (b) electron beam hardening, (c) Deep UV-hardening.

It is also possible to smoothen the walls of patterned resist features, using standard post-lithographic processing techniques such as UV hardening, electron-beam irradiation, and thermal flow. The use of surfactant rinse liquids has also been shown to improve LER of patterned resist features to acceptable values. ... 

Self-condensation of benzaldehyde produces benzoin, which is used as a photoinitiator for UV hardening of paints. Benzil, which is obtained by oxidation of benzoin, has the same application. 

UV hardening resin was first reported in 1968. From the report, UV hardening resins have been applied to many industrial fields, such as wood coating, electronic equipment, printing inks, and adhesive reagents. UV adhesive resin is one of the most important applications of UV hardening. The merits of UV adhesive resins are ... 

Photoinitiators are seldomly used in commercial applications, because large reaction volumes cannot be irradiated easily in a uniform way. Still, there are some applications in the area of UV hardening lacquers and printing inks. In research, on the other hand, photoinitiators are used frequently, for they allow to precisely define the beginning and end of the initiation process by flash photolysis of the initiator. Also, most photoinitiators show almost no temperature dependence of the decomposition rate, but a strong dependence on the (UV) light intensity. 

---