Multiphoton patterning processes also allow subtractive manufacturing of positive-tone resists. Here, the nonlinear light absorption triggers a local "depolymerization" of the material that can be easily washed away in a developer bath in post processing. This enables a high-resolution lithography of thin-film resists on a broad range of transparent (e.g. glass) as well as opaque (e.g. silicon) substrates without the need of photomasks. Along the list of compatible positive-tone photoresists are AZ® MIR 701, AZ® 5214, AZ® 9260, and AZ® 40XT. Surface patterning of photopolymers can also be achieved by using negative-tone photoresists like SU-8 or Nanoscribe's IP resins. For the latter, these photoresists enable a very robust and reliable process as the local light-triggered polymerization results in a cross-linking of polymer chains. Pre- and post-processing parameters therefore have marginal influence on the polymerization result.
SEM micrographs of various 2D patterns in positive and negative tone photoresists fabricated with a Photonic Professional GT.