Study of Wet Surface Activation Routes to Enable the Deposition of Monomolecular Organic Thin Films on k 2.0 Porous Dielectrics

Abstract

This paper explores the effects of different wet surface treatments on low dielectric constant (low-k) materials and the consequences for the growth behavior of self-assembled monolayers (SAMs) from 11-cyanoundecyltrichlorosilane precursor on these modified substrates. Hydrofluoric acid (HF), tetramethylammonium hydroxyde (TMAH) and sulfuric peroxide mixture (SPM) treatments were performed on SiCOH low-k films to modify their chemical surface groups. Transmission FTIR and water contact angle analysis showed that the SPM and TMAH treatments changed the hydrophobic surface completely into a hydrophilic surface, while the HF changed it only partially. In particular, low-k surface hydrophilicity, thickness loss and refractive index increase associated with the TMAH activation are reported as a function of TMAH concentration, contact time and temperature. The density of the SAM molecules deposited from the vapor phase and their penetration degree in the bulk of the low-k films were found to be proportional to the density and depth of the hydroxyl groups created during the wet pre-activation, respectively. In a subsequent step, an HfO2 Atomic Layer Deposition was applied on top of the SAMs. The film stacks were exhaustively characterized after each step in terms of k damage and pore sealing by ellipsometric porosimetry, and Rutherford Backscattering Spectroscopy.