New development model: Aggregate extraction development

We propose a new development model (Aggregate Extraction Model), which can explain the generation process of linewidth fluctuations. This model is inherently different from some previously proposed development models in that polymer aggregates, not a single polymer, are treated as the dissolution units. We found that the polymer aggregates about 20 - 30 nm in size are naturally contained in resist films. These aggregates can be observed in the cross section of a resist film and on the lightly exposed resist pattern surface after development. A polymer aggregate dissolves more slowly than the surrounding polymer probably because the polymer density is slightly higher inside the aggregate. Once the surrounding polymer dissolves, the aggregates are extracted and float away into the developer. The polymer aggregates trapped on the pattern sidewall, on the other hand, cause the roughness of the pattern size wall surface, which is responsible for the linewidth fluctuations. We have succeeded in a direct observation of aggregate extraction during the development by AFM observations. The validity of the Aggregate Extraction Model is also discussed from the point of view of the polymer density.