Evidence from simulation, linewidth measurements, and in situ Fourier-transform infrared (FTIR) data are presented which suggests that a type II diffusion front is moving through positive tone t-BOC material during postexposure bake. A steady increase in linespace of 50 nm/min is observed in IBM APEX-E and even faster rates can be found in generic t-BOC resists. The simultaneous reaction and three-dimensional deprotection dependent diffusion simulation was carried out with a massively parallel approach. A novel FTIR measurement of transmission versus time of patterned and unpatterned wafers during postexposure bake corroborated scanning electron microscope linewidth measurements.