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 (∼1013 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 ∼1 µm thickness. Copyright © 2009 John Wiley & Sons, Ltd. Using broadband CARS microscopy to monitor multiple Raman bands simultaneously on a sub‐second time scale, the near‐IR laser‐induced cross‐linking kinetics of hydrogen silsesquioxane (HSQ) are measured in situ, and a two‐stage cross‐linking mechanism is observed. Understanding the reaction mechanisms of HSQ is important for making reproducible nanostructures in this novel spin‐on dielectric via e‐beam and photolithography.