Pore Sealing vs. Surface Densification in Inhibition of O$_{2}$ Plasma Damage in Organosilicates*

XPS and FTIR were used to determine effects of surface densification vs. pore sealing on O$_{2}$ plasma-induced carbon loss from organosilicate glass (OSG). O$_{2}$ plasma exposure during photoresist removal induces carbon loss and increased dielectric constant in OSG. He plasma-induced SiO$_{2}$ formation (surface densification) is considered the chief damage inhibition mechanism. However, comparison of OSG pretreatments involving (a) direct He plasma, or (b) He plasma exposure in the presence of a MgF$_{2}$ window (He/MgF$_{2})$, indicates that UV-induced pore sealing in the OSG interior plays a dominant role in inhibition of carbon loss. He plasma pretreatment results in the formation of a $\sim $ 50 angstrom thick SiO$_{2}$ surface layer, whereas He/MgF$_{2}$ pretreatment--which transmits only UV results in $<$ 3 angstroms SiO$_{2}$ formation; yet both He plasma and He/MgF$_{2}$ pretreatments inhibit carbon loss at longer O$_{2}$ plasma exposure times. Results are consistent with findings concerning the role of O radical diffusion down nanopores in the carbon loss process, and O radical diffusion through SiO$_{2}$. UV radiation blocks interconnections between pores in OSG, inhibiting carbon loss.