(664f) Reactive Rinse Treatment to Enhance the Mechanical Properties of Photoresist Thin Film

As integrated circuit fabrication continues to advance towards the 32 nm node and below, it has become increasingly apparent that the use of ultrathin films and polymer features will be required. Though it has been widely accepted that the properties of polymers on the nanoscale can differ significantly from their bulk counterparts, the extent of such deviation is the subject of much debate and concern. Furthermore, most studies have focused on elucidating the differences in the thermal properties of micro- and nano-scale polymer films as determining the mechanical properties of ultrathin films can be somewhat cumbersome. In order to we have implemented a thin film buckling technique wherein a polymer film is floated onto a pre-strained polydimethylsiloxane (PDMS) substrate. Release of the strain, the polymer film undergoes periodic buckling at a wavelength that minimizes the total strain energy in the system and provides the opportunity to accurately determine the modulus of polymer thin films with thicknesses down to 20 nm. A reactive rinse method was employed whereby the hydroxyl functional groups of the resist were cross-linked via a dicarboxylic acid using carbodiimide chemistry as a potential method to ultimately enhance lithographic patterning performance. The effect of the reactive rinse on the modulus of the polymer thin films was analyzed and it was found that the application of the reactive rinse resulted in a clear increase in the modulus of the polymer films. The use of crosslinkers with the different numbers of carboxylic acid functionalities as well as a comparison of the corresponding enhancement the mechanical properties will be provided. IR and X-ray photoelectron spectroscopy (XPS) data supporting the confinement of the crosslinking agents to the surface will be discussed. Also, the thickness of the crosslinking layer will be estimated by quartz crystal microbalance (QCM). Application of a simplified multi-layer model to describe the observed modulus dependence on film thickness will also be shown.