Real-time Fourier transform infrared spectroscopy study of the kinetics of acid-catalyzed negative-tone resists based on hexamethoxymethylmelamine and phenolic resins

The kinetics of the acid-catalyzed reaction in the novolac-based, negative-tone resist SAL 605 (Shipley Co.) and similar formulations were studied with Fourier transform infrared spectroscopy with an in situ hot plate. Real-time measurements of the reaction kinetics were made in a matrix identical to the lithographic conditions and without interference from the development step. The reaction order in the acid concentration was measured to be 1.2 +/- 0.15 at 113 degrees C, and the overall activation energy was measured to be 113 +/- 11 kJ/mol for SAL 605. A kinetic model was explored to explain the observed results. The model invoked the general acid catalysis shown in a prior publication [P. M. Dentinger, K. G. Knapp, G. W. Reynolds, J. W. Taylor, T. H. Fedynyshyn, and T. A. Richardson, Proc. SPIE 3331, 568 (1998)], and that the rate constant for the first link of a hexamethoxymethylmelamine (HMMM) was significantly greater than the rate constant for a second link. This model can be simplified to aid in chemically amplified resist modeling efforts and all parameters may be determined experimentally under similar conditions as the lithography and without interference from the dissolution process. A direct comparison of novolac-based and poly(4-hydroxy)styrene (PHS)-based negative resist formulations showed that the reaction rate was slightly faster for the PHS resin near lithographic bake times. The PHS system also appeared more able to form additional Links per HMMM than novolac. However, a difference in dose to print between similar formulations of the two phenolic resins appears to arise largely from a reaction of the resin/HMMM matrix to the developer and is only a small function of the postexposure bake kinetics. (C) 1998 American Vacuum Society. [S0734-211X(98)08306-1].