A highly selective and low-damage damascene process for porous methyl-silsesquioxane (porous MSQ, k-2.2) films has been realized using a neutral beam system we have developed. Use of a SF6 or CF4 neutral beam enables etching of porous MSQ with higher selectivity to the photoresist than what can be obtained in a conventional plasma. This is considered to be because the neutral. beam eliminates exposure to ultraviolet (UV) light which enhances the resist etching. Anisotropic, low-dimension-shift damascene etching of porous MSQ is achieved through the neutral beam system. In addition, an O-2 neutral beam reduces damage to the sidewall of porous MSQ during the resist ashing process. Also, a modified layer generated on porous MSQ during ashing using a H-2 or H-2/N-2 beam could prevent damage by UV light, which allows more effective resist ashing in a dual damascene structure of porous MSQ. Accordingly, this neutral beam system is a promising candidate for use in porous MSQ damascene processes. (C) 2005 American Vacuum Society.