Plasma-assisted Atomic Layer Deposition of TiN Films at low Deposition Temperature for High-aspect Ratio Applications
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Plasma-assisted atomic layer deposition of TiN films at low deposition temperature for high-aspect ratio applications S.B.S. Heil1, E. Langereis1, F. Roozeboom2, A. Kemmeren2, N.P. Pham3, P.M. Sarro3, M.C.M. van de Sanden1, and W.M.M. Kessels1 1
Eindhoven University of Technology, Dept. of Applied Physics, P.O. Box 513, 5600 MB Eindhoven, The Netherlands 2 Philips Research, Prof. Holstlaan 4, 5656 AA Eindhoven, The Netherlands 3 Delft University of Technology, DIMES-ECTM, P.O. Box 5053, 2600 GB Delft, The Netherlands
ABSTRACT A plasma-assisted atomic layer deposition (PA-ALD) process of titanium nitride (TiN) using TiCl4 precursor dosing and H2/N2 plasma exposure is presented. In situ spectroscopic ellipsometry revealed a growth rate at 400 °C of ~0.7 Å/cycle independent of precursor dosing. Varying the plasma exposure time changed the stoichiometry [N]/[Ti] of the films within the range ~0.93-1.15. At 100 °C a relatively low chlorine impurity level (~2 at. %) and low resistivity (~200 µΩ·cm) were obtained for a ~45 nm thick film. The growth rate was found to be considerably lower (~0.3 Å/cycle) at this temperature. Using TEM imaging we found that PAALD TiN films can be deposited conformally in 20:1 aspect-ratio features (1.5 µm width) but that the step coverage still needs to be improved, probably by a prolonged plasma exposure step.
INTRODUCTION Titanium nitride (TiN) films can be found in a broad range of applications, for instance as diffusion barrier and metallization layer in back-end interconnect technology. For this application a low resistivity (90%) in these high aspect ratio structures (AR>5) is desired. Moreover, back-end and passive integration require process temperatures to be preferentially 40 nm) deposited at 100 °C, however, lower resistivities (~200 µΩ·cm) and lower Cl impurity levels (~2 at. %) were found. These values are relatively low for an ALD process at these low temperatures. RBS measurements of these thicker films also revealed that the Cl is predominantly present on the film interfaces. Also ex situ four-point probe measurements of the resistivity were performed and for thick films the obtained resistivities were in agreement with the SE values. However, for the ~10 nm films the four-point probe measurements yielded somewhat higher values most probably due to oxidation after exposing the films to air. In situ measurements by SE are therefore preferred over the ex situ measurement by the four-point probe.
APPLICATION OF PA-ALD TiN FILMS High-density MOS capacitors are fabricated on highly-doped Si-wafers with arrays of highaspect ratio features with a diameter of ~1.5 µm referred to as “macropores” [8]. Using the Bosch process the macropores are dry-etched to a depth of ~30 µm or more and the surface is
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subsequently covered with an ONO (oxide/nitride/oxide) dielectric stack. The top electrode usually consists of n-doped poly-Si and requires a furnace anneal of 1000 °C step to improve conductivity. In the future, the capacitance per area can be improved by using a hig
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