A vapor phase based silylation process was used to restore plasma damaged porous ultra low-kappa SiOCH dielectric films. The process was carried out with 11 different silylation agents. After the processing of blanked wafers, the restoration performance was analyzed by different analytic techniques such as Fourier infrared and Auger electron spectroscopy as well as contact angle, ellipsometric porosimetry, and mercury probe measurements. Quantum mechanic calculations and practical results suggest three repair chemicals having two reactive groups to be most promising. However, a comparable electrical improvement, i.e., kappa-value improvement, was achieved with chemicals having one reactive group. The removal of water during the high temperature silylation process is suggested to be the main contributor to the kappa-value improvement. The recovery of the surface free energy inhibits or retards water from returning after the silylation process. The chemicals with two reactive groups providing the highest degree of silylation are found to be most appropriate for ultra low-kappa dielectric (ULK) recovery. But, depending on the requirement for ULK restoration (e.g., kappa-value, surface recovery, etc.), chemicals having one reactive group can be sufficient as well. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3503596] All rights reserved.