Quantification of the extent of reaction in a negative, novolac-based, chemically amplified resist

A technique for determining the extent of reaction and the molar absorptivity of the Fourier transform infrared (FTIR) peak created during the postexposure bake (PEB) reaction of the negative e-beam/x-ray Shipley resist, SAL 605, is described. Wafers were oven baked within a gas-tight bomb. The product of the linking reaction, methanol, was quantified from the gas in the bomb and within the resist film after the PEB. The ether peak, corresponding to the reaction between hexamethoxymethylmelamine (HMMM) and novolac was measured on the same wafer using FTIR. In addition, the absolute number of HMMM molecules reacted was measured by,eel permeation chromatography to yield the number of moles methanol produced/HMMM reacted. The molar absorptivity for the ether peak, resulting from a reaction between an HMMM and a phenolic site on the novolac is 3.14 +/- 0.53 x 10(5) cm(2)/mole. Under conditions sufficient for imaging in a 0.5 mu m thick film, the average number of reactions/HMMM molecule is 1.27 +/- 0.24. From previous work on the acid concentration in this resist [P. M. Dentinger, C. M. Nelson, S. J. Rhyner, J. W. Taylor, T. H. Fedynyshyn, and M. F. Cronin, J. Vac. Sci. Technol. B 14, 4239 (1996)] each acid moiety created was found to catalyze an average of 26 +/- 8 events during the PEB process. It appears that no more than 1.5%-2% of the available phenolic sites in the film need to be reacted for the required differential dissolution rate, and that the film does not crosslink. The ramifications of this work on modeling this type of resist will also be discussed. (C) 1997 American Vacuum Society.