Monitoring photo-polymerization of thin films using SH acoustic plate mode sensors

Abstract

Abstract The use of shear-horizontal (SH) acoustic plate mode (APM) devices to monitor the cross-linking of polymer films in real time has been demonstrated. The SH-APM, which is excited and detected in a thinned quartz plate by interdigital transducers patterned on the surface, has displacement in the plane of the surface and normal to the direction of mode propagation. Because APM propagation velocity is affected by the shear stiffness (but not the bulk modulus) of a thin film in contact with the device surface, the APM acts as a sensitive probe of this film property. Using an APM sensor, the changes in shear modulus which accompany the photocross-linking of a negative photoresist polymer film were monitored as a function of time and of the wavelength of the cross-linking radiation.