Observing hydrogen silsesquioxane cross-linking with broadband CARS

Broadband coherent anti-Stokes Raman scattering microscopy (CARS microscopy) is used for real-time measurements of in situ cross-linking of the photoresist material hydrogen silsesquioxane (HSQ). Using samples baked at different temperatures, and therefore cross-linked to varying degrees, characteristic Raman bands are identified for the open 'cage' structure (345 cm(-1), 454 cm(-1) and 562 cm(-1)) as well as the cross-linked 'network' structure (484 cm(-1)). Cross-linking can also be induced by absorption of high intensity near-infrared (IR) laser light (similar to 10(13) W cm(-2)) and followed in real time by monitoring the characteristic Raman bands. Using the time resolution of CARS to follow the HSQ reaction during the laser exposure, a two-stage kinetic process is observed and associated time constants of 20 +/- 10 s and 3 +/- 1 min are determined for the IR laser-induced cross-linking in films of similar to 1 mu m thickness. Copyright (C) 2009 John Wiley & Sons, Ltd.