18
THROUGH SILICON VIAS
PVD with resputtering have been used to across the substrate). Electrografting
achieve better step coverage, but this is enables conformal layers to be deposited
extremely expensive and pushes up the on structures regardless of their
cost of via metallisation beyond orientation or aspect ratio, with excellent
acceptable limits. It is the technological uniformity at the wafer scale and very
and economical limitations of these dry high adhesion to the substrate. Figure 1
processes that have thus far held up the shows a conformal electrografted copper
adoption of 3D IC packaging. seed layer over 10:1 AR TSVs. It is
possible to control the thickness of
Enabling technology electrografted material on the nanometer
Alchimer has developed a technology scale, between 5 and 500nm.
called electrografting which uses specific Electrografting is a wet process, that is, Figure 4: High density vias coated
liquid chemical precursors to it uses wet chemistry, in contrast to the with conformal isolation, barrier and
electrochemically grow conformal dry techniques used by PVD, CVD and seed layers using AquiVia
nanometric films on the surface of ALD.
conducting or semiconducting substrates, Applied to through silicon vias,
with the application of a small electrical electrografting can be used to create highly scalloped sidewalls created by the
current (typically 1 to 10µA/cm2 is copper seed layers that are uniform and Bosch process. Figure 2 shows such a
enough to control the processes uniformly completely conformal, even on TSVs with layer obtained by Alchimer’s eG ViaCoat,
a process specifically designed for
electrografting copper seed layers inside
high density, high aspect ratio TSVs.
Using this technology, it is possible to
grow conformal copper seed layers on
TSVs with aspect ratios of 10:1 and
beyond, reliably, making eG ViaCoat the
enabling technology of 3D IC packaging.
Another important feature of
electrografting and eG ViaCoat is that the
technology is very easy to implement on
industry standard electroplating
equipment. Fabs can avoid investing in
new expensive equipment by simply
reusing existing tools. eG ViaCoat has
been tested on high end and legacy
systems and demonstrates repeatable
results every time. It is compatible with
commercially used barrier materials and
standard CMP. eG ViaCoat is
commercially available to license now and
cuts cost of ownership of the copper seed
layer deposition by up to 75% for high
aspect ratio TSVs.
Expansion to all three
layers
Alchimer recently announced that it has
applied its wet deposition technology to
the deposition of isolation and barrier
layers inside high aspect ratio TSVs. The
isolation layer is deposited using
electrografting, the same technology that
powers eG ViaCoat. Since electrografting
requires a conducting or semiconducting
substrate, a slightly different approach
must be used to apply the barrier layer
onto the isolation layer. This process is
Figure 3: Alchimerís AquiVia process flow consists entirely of wet processes, referred to as chemical grafting, and
drastically reducing cost of operation although it uses a similar mechanism to
www.euroasiasemiconductor.com August 2008
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