Interfacial effects on moisture absorption in thin polymer films

TY - JOUR

T1 - Interfacial effects on moisture absorption in thin polymer films

AU - Vogt, Bryan D.

AU - Soles, Christopher L.

AU - Jones, Ronald L.

AU - Wang, Chia Ying

AU - Lin, Eric K.

AU - Wu, Wen Li

AU - Satija, Sushil K.

AU - Goldfarb, Dario L.

AU - Angelopoulos, Marie

PY - 2004/6/22

Y1 - 2004/6/22

N2 - Moisture absorption in model photoresist films of poly(4-hydroxystryene) (PHOSt) and poly(tert-butoxycarboxystyrene) (PBOCSt) supported on silicon wafers was measured by X-ray and neutron reflectivity. The overall thickness change in the films upon moisture exposure was found to be dependent upon the initial film thickness. As the film becomes thinner, the swelling is enhanced. The enhanced swelling in the thin films is due to the attractive nature of the hydrophilic substrate, leading to an accumulation of water at the silicon/polymer interface and subsequently a gradient in concentration from the enhancement at the interface to the bulk concentration. As films become thinner, this interfacial excess dominates the swelling response of the film. This accumulation was confirmed experimentally using neutron reflectivity. The water rich layer extends 25 ± 10 Å into the film with a maximum water concentration of ∼30 vol %. The excess layer was found to be polymer independent despite the order of magnitude difference in the water solubility in the bulk of the film. To test if the source of the thickness dependent behavior was the enhanced swelling at the interface, a simple, zero adjustable parameter model consisting of a fixed water rich layer at the interface and bulk swelling through the remainder of the film was developed and found to reasonably correspond to the measured thickness dependent swelling.

AB - Moisture absorption in model photoresist films of poly(4-hydroxystryene) (PHOSt) and poly(tert-butoxycarboxystyrene) (PBOCSt) supported on silicon wafers was measured by X-ray and neutron reflectivity. The overall thickness change in the films upon moisture exposure was found to be dependent upon the initial film thickness. As the film becomes thinner, the swelling is enhanced. The enhanced swelling in the thin films is due to the attractive nature of the hydrophilic substrate, leading to an accumulation of water at the silicon/polymer interface and subsequently a gradient in concentration from the enhancement at the interface to the bulk concentration. As films become thinner, this interfacial excess dominates the swelling response of the film. This accumulation was confirmed experimentally using neutron reflectivity. The water rich layer extends 25 ± 10 Å into the film with a maximum water concentration of ∼30 vol %. The excess layer was found to be polymer independent despite the order of magnitude difference in the water solubility in the bulk of the film. To test if the source of the thickness dependent behavior was the enhanced swelling at the interface, a simple, zero adjustable parameter model consisting of a fixed water rich layer at the interface and bulk swelling through the remainder of the film was developed and found to reasonably correspond to the measured thickness dependent swelling.

UR - http://www.scopus.com/inward/record.url?scp=3042587325&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=3042587325&partnerID=8YFLogxK

U2 - 10.1021/la035830f

DO - 10.1021/la035830f

M3 - Article

C2 - 15986664

SN - 0743-7463

VL - 20

SP - 5285

EP - 5290

JO - Langmuir

JF - Langmuir

IS - 13

ER -