Probing the molecular structures of plasma-damaged and surface-repaired low-k dielectrics

Abstract

Fully understanding the effect and the molecular mechanisms of plasma damage and silylation repair on low dielectric constant (low-k) materials is essential to the design of low-k dielectrics with defined properties and the integration of low-k dielectrics into advanced interconnects of modern electronics. Here, analytical techniques including sum frequency generation vibrational spectroscopy (SFG), Fourier transform infrared spectroscopy (FTIR), contact angle goniometry (CA) and X-ray photoelectron spectroscopy (XPS) have been employed to provide a comprehensive characterization of the surface and bulk structure changes of poly(methyl)silsesquioxane (PMSQ) low-k thin films before and after O2 plasma treatment and silylation repair. O2 plasma treatment altered drastically both the molecular structures and water structures at the surfaces of the PMSQ film while no bulk structural change was detected. For example, ∼34% Si-CH3 groups were removed from the PMSQ surface, and the Si-CH3 groups at the film surface tilted toward the surface after the O2 plasma treatment. The oxidation by the O2 plasma made the PMSQ film surface more hydrophilic and thus enhanced the water adsorption at the film surface. Both strongly and weakly hydrogen bonded water were detected at the plasma-damaged film surface during exposure to water with the former being the dominate component. It is postulated that this enhancement of both chemisorbed and physisorbed water after the O2 plasma treatment leads to the degradation of low-k properties and reliability. The degradation of the PMSQ low-k film can be recovered by repairing the plasma-damaged surface using a silylation reaction. The silylation method, however, cannot fully recover the plasma induced damage at the PMSQ film surface as evidenced by the existence of hydrophilic groups, including C-O/C[double bond, length as m-dash]O and residual Si-OH groups. This work provides a molecular level picture on the surface structural changes of low-k materials after plasma treatment and the subsequent silylation repair.

Probing molecular structures at buried solid/solid interfaces involving low-k materials or polymers in situ nondestructively: a review

“…SFG is a second-order nonlinear optical spectroscopic technique 11 – 44 According to the selection rule of a second-order nonlinear optical process, SFG signal can only be generated from a medium with no inversion symmetry under the electric dipole approximation 11 – 44 Most bulk materials possess inversion symmetry, therefore, no SFG signal can be produced.…”

“… – 44 According to the selection rule of a second-order nonlinear optical process, SFG signal can only be generated from a medium with no inversion symmetry under the electric dipole approximation 11 – 44 Most bulk materials possess inversion symmetry, therefore, no SFG signal can be produced. Surfaces and interfaces lack inversion symmetry, thus, they can produce SFG signals.…”

Studying Polymer Surfaces and Interfaces with Sum Frequency Generation Vibrational Spectroscopy

“…The damaged surface can be repaired using silylation. 171 We then applied the above developed data analysis method to investigate surface and buried interfacial structures of commercial low-k samples provided by Intel and IBM. SFG was used to investigate molecular structures of surfaces and buried interfaces of pSiCOH films on Si provided by Intel.…”

“…It was reported that the surface and interfacial molecular structures of a low-k pSiCOH thin film deposited on silicon wafer could be characterized using SFG. − The methodology was developed on the basis of the approach used to study polymer thin films on metal surfaces with a series of different film thicknesses. The SFG spectra collected from a model low-k film (PMSQ, Figure a, model for pSiCOH) have contributions from both the PMSQ surface and the buried PMSQ/silicon interface.…”

“…It was found that only 5 s of oxygen plasma treatment can greatly modify the surface structure of a PMSQ film. The damaged surface can be repaired using silylation . We then applied the above developed data analysis method to investigate surface and buried interfacial structures of commercial low-k samples provided by Intel and IBM.…”