We have investigated the impact of Hz-plasma treatment on porous organosilicate glass (POSG) with etching process. The etching rate of trenches of nanoporous silica film was about 650 nm/min using fluorocarbon plasma. It is 1.6 times the etching rate of CVD oxide for the same etching condition due to the high porosity of POSG. We found that the profile of the intrinsic sample had mask undercutting. By the contrary, the mask undercutting effect was suppressed in the H-2,-plasma-treated sample. Based on the FTIR spectra analysis, the Si-H bonding was appeared after H-2-plasma treatment. The existence of Si-H bonds enhances to possess high C/F ratio and high polymerization rate at the sidewall surface. As a result, the spontaneous reactive etching at sidewall was suppressed. We also observed the pattern profile of porous silica was distorted after O-2-plasma ashing. This is due to the oxidation of hydrophobic groups and the formation of Si-OH bonds in the bulk. The interaction between the siloxanol groups and the gelation reaction occurred in the internal of porous organosilicates predominate stress evolution, leading to the deformation of patterned porous organosilicate films. (C) 2004 Published by Elsevier B.V.