Investigating buried polymer interfaces using sum frequency generation vibrational spectroscopy

Abstract

This paper reviews recent progress in the studies of buried polymer interfaces using sum frequency generation (SFG) vibrational spectroscopy. Both buried solid/liquid and solid/solid interfaces involving polymeric materials are discussed. SFG studies of polymer/water interfaces show that different polymers exhibit varied surface restructuring behavior in water, indicating the importance of probing polymer/water interfaces in situ. SFG has also been applied to the investigation of interfaces between polymers and other liquids. It has been found that molecular interactions at such polymer/liquid interfaces dictate interfacial polymer structures. The molecular structures of silane molecules, which are widely used as adhesion promoters, have been investigated using SFG at buried polymer/silane and polymer/polymer interfaces, providing molecular-level understanding of polymer adhesion promotion. The molecular structures of polymer/solid interfaces have been examined using SFG with several different experimental geometries. These results have provided molecular-level information about polymer friction, adhesion, interfacial chemical reactions, interfacial electronic properties, and the structure of layer-by-layer deposited polymers. Such research has demonstrated that SFG is a powerful tool to probe buried interfaces involving polymeric materials, which are difficult to study by conventional surface sensitive analytical techniques.

Adhesion Investigation Between Metal and Benzocyclobutene (BCB) Polymer Dielectric Materials in 3-D Integration Applications

“…5(a) shows the SFG spectrum of an air/BCB interface (3-μm thickness of BCB on Si). Two main peaks are observed at 2870 and 2930 cm −1 , which are consistent with the methyl group symmetric C-H stretching mode and the Fermi resonance [18], [24].The SFG spectral results indicate that the methyl groups are ordered at the air/BCB interface. The general C-H spectral range, i.e., 2800-3000 cm −1 , can be detected through SFG vibrational spectroscopy [16]- [18], [24].…”

“…Therefore, C-H spectral peaks at different locations may be detected in each individual case [18], [24]. Fig.…”

“…In addition, a peak at 2850 cm −1 (negative peak) is detected in the case of titanium/BCB because of methylene symmetric stretching [24], [26]. Due to interference between resonant and nonresonant contributions or between contributions from different resonant modes, the resonant peaks in the SFG spectra (from a metal/polymer interface) may appear negative or asymmetric [18]. In fact, the significance values of the positive and negative peaks are the same.…”

“…Furthermore, SFG vibrational spectroscopy can be used to examine interfacial molecular interactions and interfacial chemical structures, such as interfacial bonding formation, interfacial diffusion, orientation distribution of interfacial functional groups, etc. [15]- [18]. In this paper, we investigate the adhesion strength between copper and BCB polymer dielectric to develop the guidelines for copper and BCB bonding.…”

Probing Electronic Structures of Organic Semiconductors at Buried Interfaces by Electronic Sum Frequency Generation Spectroscopy

“…We emphasize this equation differs from the formula for vibrational sum frequency generation (VSFG) 4,[41][42][43][44][45][46][47][48][49][50] , in which one of the two incoming pulses are tuned in resonant with molecular transitions. First, all states are electronic states and the contribution from vibrational states are treated implicitly.…”