Oxygen radical and plasma damage of low- k organosilicate glass materials: Diffusion-controlled mechanism for carbon depletion

Fourier transform infrared (FTIR) analyses of low- k materials exposed to either oxygen radicals or to capacitively coupled O₂ plasma indicate that carbon depletion from these materials is dominated by O radical diffusion. FTIR measurements of changes in absorbance related to silanol formation (3500 cm^-1) and carbon depletion (2980 cm^-1, 900-700 cm ^-1) exhibit a linear dependence on the square root of the exposure time. Diffusion is faster for a sample of higher porosity and interconnectedness (k=2.54) than for a sample with lower porosity (k=3.0). However, a sample with high porosity (k=2.57) but low interconnectedness (as measured by liquid diffusion) exhibits a high initial rate of carbon loss, followed by no further carbon loss at longer times. Further, pretreatment of k=3.0 material by 500 eV noble gas ions results in a sharp decrease in the rate of carbon loss upon subsequent exposure to oxygen radicals. The data indicate that the main mechanism of carbon depletion in organosilicate glass (OSG) materials during oxygen plasma exposure is loss due to a reaction front created by oxygen radicals diffusing through interconnected pores. Further, carbon depletion can be minimized for low- k OSG materials either by formation of high porosity/low interconnectedness samples, or by pretreatment by noble gas ion bombardment, which seals surface pores.