Photoresists, nitrenes

The efficient light-initiated decomposition of azides has been the basis for commercially important photoresist formulations for the semiconductor industry. A common approach is to mix a diazide, such as diazadibenzylidenecyclohexanone (I), with an unsaturated hydrocarbon polymer. Excitation of the difunction-al sensitizer produces highly reactive nitrenes which crosslink the polymer by a variety of paths including insertion into both carbon-carbon double bonds and carbon-hydrogen bonds, and by generation of radicals. The polymer component in the most widely used resists is polyisoprene which has been partially eye Iized by reaction with p-toluenesulfonic acid G). Other polymers used include polycyclopentadiene and the copolymer of cyclopentadiene and a-methyI styrene ( ). 

Bis(aryl)azide rubber resist is a common negative photoresist. In a photoreaction, the evolution of nitrogen from the acylazide produces a highly reactive intermediate, nitrene. Through a series of reactions the nitrene intermediate leads to the formation of polymer by cross-linking the resin. The unreacted negative photoresist can then be dissolved in organic solvent, and xylene is commonly used. 

The photochemistry of aromatic azides reeeives eontinuous attention because of their useful applications in heterocyclic syntheses, photoresist techniques and photoaflfinity labeling [1,2,3,4,5]. The key reaction in all cases is the photoinduced N-N2 bond dissociation with formation of highly reactive intermediate, nitrene. The main quantitative parameter of this reaction is the photodissociation quantum yield (cp), which determines the azide photoactivity. 

---