%20(1).png)
Commonly titanium
nitride (TiN) thickness and resistivity wafer fab in-line metrology is based on
ellipsometry and 4-point probe resistivity mapping. Alternative and relatively
slower or more complex methods are X-ray photoelectron spectroscopy
(XPS), X-ray reflectivity (XRR) and X-ray fluorescence (XRFS). TiN thin
films are highly conductive and lose transparency for thicker layers which can
make it challenging to accurately measure the thickness by ellipsometry above
10-20 nm. At about 50 nm layer thickness TiN is non-transparent and has a
bronze color changing to gold for even thicker layers. In the case of resistivity
mapping, 4-point probe is a destructive method leaving scratches from the
needles that penetrates the TiN layer and possibly also damages the underlying
layers and devices.
Atomic
Layer Deposition of TiN on 200 mm wafers
TiN
is used as a metal gate in complementary metal-oxide-semiconductor (CMOS)
technology as it has low resistivity and is compatible with gate dielectrics.
TiN is also deposited as a wear resistant coating, and barrier layer for copper
diffusion due to its chemical and thermal stability. Traditionally TiN was
deposited using physical vapour deposition techniques which suffer from as poor
step coverage in deep contacts and via trenches due to the shadowing effects
especially in high aspect ratio structures.
Atomic
layer deposition (ALD) is a thin film deposition technique which allows for
Å-level control of the film thickness, excellent uniformity, and conformal
coating of high aspect ratio features.
Therefore,
non-destructive characterization of thickness and electrical uniformity across
the entire surface covered by the deposition is critical to ensure the quality
of the final film. Oxford Instruments demonstrate the deposition of conductive
TiN by plasma enhanced ALD with excellent thickness uniformity and collaborate
with das-nano to map the resistivity uniformity using THz
spectroscopy on 200 mm wafers.
