The exposure of certain positive photoresists has been shown by Dill and co-workers to be modelable in terms of a local inhibitor concentration which results in a local development rate. The development process is assumed to be a surface etching reaction in which the surface velocity is the local development rate. The characterization of resists for the purpose of line-edge profile simulation therefore involves the measurement of development rate for controlled exposure dose profiles. In this paper a technique is described in which the resist thickness is continuously plotted during development. The low frequency capacitance is measured using a conducting substrate as one plate, and the highly conductive developer as the other plate of the capacitor. The inverse capacitance, proportional to the composite resist-oxide thickness, is obtained using an analog divider. Examples of standing wave effects in Shipley Az 1350 resists, and resist development rate modification using chlorobenzene are presented.
W. G. Oldham,
"In SITU Characterization Of Positive Resist Development", Proc. SPIE 0135, Developments in Semiconductor Microlithography III, (6 September 1978); doi: 10.1117/12.956125; http://dx.doi.org/10.1117/12.956125