Paper EM-WeA9
Pore Sealing of Low-k Films by UV Assisted CVD Processes

Wednesday, October 21, 2015, 5:00 pm, Room 210E

Porous ultra-low k (ULK) dielectric films with high porosity and larger pore size (k<2.4 and beyond) pose a serious challenge for their integration into next-generation microchips. In this paper, we report the formation of a thin layer of SiCxNy based pore sealing film deposited by UV assisted CVD. This film when deposited on damaged ULK surface assists in sealing the interconnected pores to prevent diffusion of metal liner and barrier metal precursors during the subsequent metallization steps. In addition pore sealing also enables an efficient sidewall protection to ULK thereby reducing its degradation by radical penetration during subsequent wet clean processes. A side benefit of this method is replenishment of depleted methyl species in damaged subsurface sites thereby improving hydrophobicity and recovery of k damage. A very thin pore seal film ~15 Ang is found to be sufficient to prevent metal precursor diffusion into a porous ULK k2.4 material. Porosimetry and backside SIMS were used to assess sealing behavior on surface pores of damaged ULK. On pattern wafers pore sealing treatment has been shown to significantly improve VBD and TDDB of k2.4 ULK to a level comparable to that observed for industry standard ULK k2.55 material. No structural change is observed in pattern CD for up to 15A of pore-seal deposition. Although this deposition is highly selective to surface sites available on damaged ULK, a thin layer (i.e. < 5A) of pore seal residue formed on Cu via bottom has been shown to be completely removed by typical CuOx wet clean solutions. Kelvin via measurements on structure wafers show that pore-seal with wet clean yields comparable via resistance as compared to wafers without pore-seal.