SIMS is a powerful technique to observe the low levels of copper diffusion. However, change in chemical structure of low-k dielectrics has been observed under electron irradiation for charge compensation using a magnetic sector instrument. The depth of implanted Cu peak from SIMS depth profiles decrease with increase of irradiation time. This peak shift to shallower direction is simply proportional to decrease in film thickness. Decrease in the thickness is ascribed to the formation of SiON (x less than or equal to 2) network via decomposition of CH3 group as well as SiOH formation. These changes occurred uniformly throughout the films. (C) 2002 Elsevier Science B.V. All rights reserved.