We have established experimental techniques for polymer dissolution that can provide insight into details of the dissolution process^1-3. Our experimental protocol for characterizing polymer thin film dissolution combines high-sensitivity gravimetric analysis using a quartz crystal microbalance (QCM) with an analysis of film depth structure by visible and infrared reflectance spectroscopy (see figure below). These techniques provide complementary information about the time evolution of the film undergoing dissolution. From such measurements a detailed picture can be constructed of the chemical and physical changes that comprise the dissolution process.

A simple example is shown below. The dissolving film is the copolymer poly(methyl methacrylate-co-methacrylic acid), a model for a 193 nm photoresist. When dissolved by an aqueous solution of hydroxide ion, an initial swollen interfacial layer is formed, with a net increase in film mass detected by QCM and characteristic changes in the reflectance spectrum of the film. The thickness and rate of formation of the interfacial layer depends on the hydroxide concentration. Both the rate of formation and the composition of the swollen layer are available from the measurements. Swelling is followed by dissolution of the film in a linear manner while the thickness of the interfacial layer remains constant. Mechanistic information can be inferred from such data; in this instance, it can be shown that the dissolution process is controlled by the rate of diffusion of hydroxide ion through the interfacial layer.

 References

1. S. Lee, W. Hinsberg and K. Kanazawa, Anal. Chem., 74, 125-131 (2002).
2. F. Houle, W. Hinsberg and M. Sanchez, Macromolecules, 35, 3591-3600 (2002).
3. W. Hinsberg, F.A. Houle, S-W Lee H. Ito and K. Kanazawa, Macromolecules, 38, 1882-1898 (2005).