Strategies for deep-UV patterning of half-micron contacts using negative photoresists

Contact structures represent some of the most challenging features to image using deep UV excimer laser lithography. A single resist process, exposure dose, and focal setting must compensate not only for variations in the reflectivities of gate (Le, polysilicon) and diffusion (i.e., oxide) substrates, but must deal with variations in underlying topographical features which create a non-uniform resist film over a non-planar imaging surface. Commercially available deep UV photoresists are negative toned, requiring the use of clear field photomasks for imaging of submicron contact structures. In this paper, we describe three strategies for enhancing the ability to image contact structures using currently available negative toned chemically amplified deep UV photoresists: (1) optimization of central exposing laser wavelength, (2) incorporation of anti-reflective coatings, and (3) optimization of resist film thickness for sidewall profile enhancement. These approaches should also enhance imaging of contacts using positive tone photoresists, once they are commercially available