Improved nucleation of TiN atomic layer deposition films on SiLK low-k polymer dielectric using an Al2O3 atomic layer deposition adhesion layer

Abstract

Diffusion barriers are required to prevent copper from diffusing into low-k polymer dielectrics in backend interconnects. The ability to deposit conformal diffusion barriers onto high aspect ratio, low-k polymer features requires atomic layer deposition (ALD) techniques. This study examined TiN ALD on SiLK (a trademark of the Dow Chemical Company) low-k polymer dielectric using tetrakis-dimethylamino titanium and NH3. X-ray fluorescence spectroscopy (XRFS), optical microscopy, and surface profiling of the TiN ALD films deposited on SiLK revealed discontinuous films displaying distinct patchy regions. The patches corresponded to a thinner TiN coating and were attributed to difficulties for TiN ALD nucleation on SiLK. To study TiN ALD nucleation, in situ quartz-crystal microbalance (QCM) measurements were performed by spincoating SiLK onto the QCM sensor. Subsequent QCM measurements during TiN ALD revealed very low initial TiN ALD growth rates indicating poor nucleation. Al2O3 ALD was then performed on the SiLK film using trimethyl aluminum and H2O. Surface profiling, XRFS, QCM, and transmission electron microscopy measurements revealed that the Al2O3 ALD film nucleates immediately on SiLK producing a continuous Al2O3 film. In addition, QCM measurements showed that TiN ALD nucleates readily on the Al2O3 surface. The Al2O3 ALD adhesion layer facilitated the growth of a continuous TiN ALD film on SiLK. Examination of TiN ALD films prepared on SiLK with progressively thinner Al2O3 ALD adhesion layers revealed that 10 Al2O3 ALD cycles were sufficient to promote the nucleation of the TiN ALD film.