Langmuir—Blodgett Deposition To Evaluate Dissolution Behavior of Multicomponent Resists

Abstract

The development behavior of diazonaphthoquinone resists has been studied extensively. Our work focuses on the influence exerted by photoactive compound (PAC) on the dissolution of an unexposed resist. In particular, we have evaluated the effect of the sensitzer's spatial distribution in the film. Stratified resist films have been fabricated through the combined use of spin casting and Langmuir-Blodgett deposition. With these resist structures, not only can the effect of locally high PAC concentrations on dissolution be evaluated, but the mobility of the sensitizer in the matrix can also be studied. We have found that embedding as little as three monolayers (30 Å) of PAC between two thicker layers of polymer (1000 Å each) causes a significant induction period when the solvent front reaches the PAC layer. In addition, the dissolution rate of the pure spin cast polymer layer underlying the PAC is reduced significantly. Thermal treatment of these resist structures has demonstrated that the PAC appears to be more mobile in Langmuir-Blodgett polymer films than in spin cast polymer films.As integrated circuit features shrink below 0.5 /im, the need for optimization of all lithographic steps is crucial. In order to define such features with high precision, the processing behavior of the photoresist materials used for patterning must be well-characterized. Hence, we need a fundamental understanding of their development behavior. Although much of the current semiconductor industry uses diazonaphthoquinone-based positive resists, many details of the dissolution mechanism of these materials are still unknown.Thin film dissolution behavior has been the subject of study for many applications. In the case of positive photoresists, a number of techniques have been used to characterize the kinetics of dissolution (1-12). The earliest such experiments were performed by exposing the resist to a solvent for a fixed time and then measuring the thickness of the remaining film (1). From repeated measurements of this type, a bulk development rate could be determined.

A review of polymer dissolution

“…As the film dissolves and the mass decreases, the frequency will rise until the base frequency of the crystal is reached. The change in frequency can then be subsequently correlated with the film thickness through density, substrate area and instrument parameters [116]. The main advantage of this system is that highly accurate frequency measurements can be made.…”

Understanding nonlinear dissolution rates in photoresists

“…The bulk dissolution rate slows as the temperature is increased, due to the known decrease in residual casting solvent. 8,9 There is also a dramatic change in the extent of surface inhibition. However, the HD experiments, 15 the model by Mack 16 and the results of Ficner 26 suggest that the change in surface inhibition is not related to a residual solvent concentration gradient in the film.…”

“…6,7 Several researchers have shown that bulk dissolution rates are dependent upon the residual solvent concentration 8,9 so it follows that a concentration gradient in residual casting solvent would result in a nonlinear dissolution rate. Beauchemin et.…”