Nucleation and growth during Al 2 O 3 atomic layer deposition (ALD) were explored on a variety of polymer films at 85 °C. Al 2 O 3 ALD was performed using sequential exposures of Al(CH 3 ) 3 [trimethylaluminum (TMA)] and H 2 O. The polymer films were polystyrene (PS), polypropylene (PP), poly(methyl methacrylate) (PMMA), polyethylene (PE), and poly(vinyl chloride) (PVC). These polymer films were prepared by spin-coating onto the surface of a quartz crystal microbalance (QCM) sensor or the surface of a Si(100) wafer. Al 2 O 3 ALD during the sequential TMA and H 2 O exposures was monitored in situ on the various polymers using the QCM. The QCM measurements revealed distinct differences for each polymer in the initial nucleation period during Al 2 O 3 ALD. Following the initial nucleation period, linear Al 2 O 3 ALD growth was observed on all the polymers. The thickness of the Al 2 O 3 ALD films was also characterized by ex situ surface profilometry. Based on the QCM measurements and recent FTIR measurements of Al 2 O 3 ALD on low-density PE, a model is proposed for Al 2 O 3 ALD nucleation and growth on polymers. This model is based on the adsorption of TMA onto the surface and absorption into the near-surface region of the polymer. The adsorbed and absorbed TMA is then available for subsequent reaction with the H 2 O exposure. This model for Al 2 O 3 ALD does not require specific chemical groups on the polymer surface to initiate Al 2 O 3 ALD. This model should be valuable to understand and optimize the use of these Al 2 O 3 ALD films as seed layers and gas diffusion barriers on polymers.
Atomic layer deposition (ALD) was employed to grow coaxial thin films of Al(2)O(3) and Al(2)O(3) /W bilayers on multi-walled carbon nanotubes (MWCNTs). Although the MWCNTs have an extremely high surface area, a rotary ALD reactor was successfully employed to perform ALD on gram quantities of MWCNTs. The uncoated and ALD-coated MWCNTs were characterized with transmission electron microscopy and x-ray photoelectron spectroscopy. Al(2)O(3) ALD on untreated MWCNTs was characterized by nucleation difficulties that resulted in the growth of isolated Al(2)O(3) nanospheres on the MWCNT surface. The formation of a physisorbed NO(2) monolayer provided an adhesion layer for the nucleation and growth of Al(2)O(3) ALD films. The NO(2) monolayer facilitated the growth of extremely conformal coaxial Al(2)O(3) ALD coatings on the MWCNTs. Cracks were also observed in the coaxial Al(2)O(3) ALD films on the MWCNTs. After cracking, the coaxial Al(2)O(3) ALD films were observed to slide on the surface of the MWCNTs and expose regions of bare MWCNTs. The Al(2)O(3) ALD film also served as a seed layer for the growth of W ALD on the MWCNTs. The W ALD films can significantly reduce the resistance of the W/Al(2)O(3)/MWCNT wire. The results demonstrate the potential for ALD films to tune the properties of gram quantities of very high surface area MWCNTs.
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 ͑ALD͒ techniques. This study examined TiN ALD on SiLK ͑a trademark of the Dow Chemical Company͒ low-k polymer dielectric using tetrakis-dimethylamino titanium and NH 3 . X-ray fluorescence spectroscopy ͑XRFS͒, 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 ͑QCM͒ 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. Al 2 O 3 ALD was then performed on the SiLK film using trimethyl aluminum and H 2 O. Surface profiling, XRFS, QCM, and transmission electron microscopy measurements revealed that the Al 2 O 3 ALD film nucleates immediately on SiLK producing a continuous Al 2 O 3 film. In addition, QCM measurements showed that TiN ALD nucleates readily on the Al 2 O 3 surface. The Al 2 O 3 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 Al 2 O 3 ALD adhesion layers revealed that 10 Al 2 O 3 ALD cycles were sufficient to promote the nucleation of the TiN ALD film.
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