Molecular structures at the surface and buried interface of an amorphous ultralow-k pSiCOH dielectric film were quantitatively characterized before and after reactive ion etching (RIE) and subsequent dielectric repair using sum frequency generation (SFG) vibrational spectroscopy and Auger electron spectroscopy. SFG results indicated that RIE treatment of the pSiCOH film resulted in a depletion of ∼66% of the surface methyl groups and changed the orientation of surface methyl groups from ∼47° to ∼40°. After a dielectric recovery process that followed the RIE treatment, the surface molecular structure was dominated by methyl groups with an orientation of ∼55° and the methyl surface coverage at the repaired surface was 271% relative to the pristine surface. Auger depth profiling indicated that the RIE treatment altered the top ∼25 nm of the film and that the dielectric recovery treatment repaired the top ∼9 nm of the film. Both SFG and Auger profiling results indicated that the buried SiCNH/pSiCOH interface was not affected by the RIE or the dielectric recovery process. Beyond characterizing low-k materials, the developed methodology is general and can be used to distinguish and characterize different molecular structures and elemental compositions at the surface, in the bulk, and at the buried interface of many different polymer or organic thin films.