|AVS 57th International Symposium & Exhibition|
|Thin Film||Wednesday Sessions|
|Session:||High K Dielectrics for Si Electronics|
|Presenter:||J. Swerts, IMEC, Belgium|
|Authors:||J. Swerts, IMEC, Belgium
S. Armini, IMEC, Belgium
L. Carbonell, IMEC, Belgium
D.A. Annelies, IMEC, Belgium
F.A. Alexis, IMEC, Belgium
S. Mertens, IMEC, Belgium
T. Witters, IMEC, Belgium
M. Schaekers, IMEC, Belgium
Z. Tökei, IMEC, Belgium
G. Beyer, IMEC, Belgium
V. Gravey, Applied Materials Inc.
A. Cockburn, Applied Materials Inc.
K. Shah, Applied Materials Inc.
J. Aubuchon, Applied Materials Inc.
S. Van Elshocht, IMEC, Belgium
|Correspondent:||Click to Email|
Electrochemical deposition of Cu for interconnect metallization traditionally uses Physical Vapor Deposition (PVD) of a Cu seed layer on top of a PVD Ta/TaN barrier to conduct the current. However, the limitations of PVD in respect of step coverage compromise its use in future technology nodes. Atomic Layer Deposition (ALD) for barrier deposition combined with seedless Cu electroplating is one of the metallization routes explored for sub-25 nm line widths. However, compatibility with seedless electroplating seriously limits the choice of materials. Among the different candidates, Ru-based layers have been identified as very promising.
We report the growth and scalability of Ru films by plasma-enhanced ALD (PE-ALD) from MethylCyclopentadienylPyrrolylRuthenium (MeCpPyRu) and N2/NH3 plasma. The layers were deposited using a 300 mm showerhead type reactor (AMAT) with direct plasma capability. The substrate temperature during deposition was 330C. The Ru growth per cycle was 0.04 nm. As substrates we used Si wafers with 100-300 nm SiO2 on which a thin TaN or TiN layer was deposited by ALD or PVD.
The metal nitride is needed as a growth enabler since Rutherford backscattering spectrometry (RBS) showed that only 1E14 Ru atoms/cm2, i.e. less than a monolayer, were deposited on SiO2 after 120 PE-ALD cycles. The minimal thickness of the metal nitride to enable Ru growth has been determined to be as low as 0.7-0.8 nm which is promising for scaling. Growth studies on scaled and thick ALD TiN or TaN still showed a limited growth inhibition during the first 40 cycles followed by a linear growth behavior. Static time-of-flight secondary ion mass spectroscopy (TOFSIMS) suggests Ru layer closure for a film thickness around 2 nm.
Atomic force microscopy revealed that the root mean square roughness values were below 0.4 nm for film thicknesses up to 20 nm. X-ray diffraction showed that the Ru layers have a hexagonal structure. The density of the Ru layer was 11.75 g/cm3 as derived from X-ray reflectivity and RBS. Elastic recoil detection analysis and TOFSIMS indicate that the N, O, C-levels in the bulk Ru layers were << 1%. Surface analysis by static TOFSIMS showed the presence of organic contamination identified as MeCp ligands from the Ru precursor. In contrast, the Pyrrolyl ligand was not observed. A post deposition thermal treatment of the Ru film removes the ligand organic contamination. The impact of this surface contamination on the seedless Cu electroplating efficiency will be discussed. Finally, the step coverage of TiN/Ru and TaN/Ru stacks in narrow lines (65-15 nm width) was evaluated by transmission electron microscopy.