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THROUGH SILICON VIAS
19
electrografting, it doesn’t require an
applied current. The barrier material used
is a proprietary metal alloy. Alchimer
calls the process flow consisting of
electrografted isolation layer, chemical
grafted barrier and electrografted seed
“AquiVia” (see figures 3 and 4).
The implications of using three wet
processes instead of CVD for isolation and
PVD for barrier and seed layers are
significant. Firstly, all three processes
plus the electroplating copper fill can be
performed by the same tool. Alchimer
anticipates that most of its customers will
set up a separate line for TSV and
electrografting eliminates the need to buy
expensive equipment - plating tools are
less than half the cost of their PVD/CVD
counterparts. Secondly, elimination of
PVD and CVD frees up capacity on these
tools which no longer need be involved in
TSV metallisation. Thirdly, cost of
ownership (CoO) of isolation, barrier, seed
and fill processes is reduced by 50%
overall compared to PVD/CVD.
Today the cost of creating TSVs on a
300mm wafer is close to $400, far too
expensive for a step that basically delivers Figure 5: Alchimer has calculated the CoO per wafer for a 50k wafer/month
an interconnect function. The major operation based on equipment, facilities, operating and consumable costs,
contributors are bonding, via fill throughput and utilization. This analysis shows how AquiVia compares to
processing and wafer thinning. The traditional methods of TSV metallisation
industry has set a target cost of $200 for
this technology, so innovative approaches
like Alchimer’s are needed to reduce CoO assumptions as the current benchmark and performance benefits to other types
by the required 50% and bring TSVs into process described above, the CoO of of TSV. For example, in sectors such as
an industrially viable range. AquiVia produced TSVs is $43 per wafer, CMOS image sensors and MEMS where
Alchimer has calculated the CoO per a greater than 50% cut in the cost of relatively low aspect ratio vias are
wafer for a 50k wafer/month operation these four steps. required, AquiVia still brings cost
based on equipment, facilities, operating It is worth noting that this 50% advantages.
and consumable costs, throughput and reduction in CoO may be a conservative Companies producing this kind of
utilisation (see figure 5). We assumed two estimate. Since electrografting lends itself product are not necessarily equipped with
deposition chambers per dry vacuum to producing uniform coatings on all the latest tools so the concept of
process and eight cells for the surfaces, step coverage is excellent. A metallising and filling TSVs using
electroplating tool. According to this traditional process using PVD/CVD may standard plating equipment is extremely
model, CoO for 10:1 aspect ratio vias is have to deposit close to 1000nm on the attractive.
$89 per wafer minimum using existing top surfaces to ensure a 100nm coating Since Alchimer’s technology consists
technologies. The most critical step is on the sidewalls of a TSV, a tremendous entirely of wet processes, it presents a
barrier/seed deposition, so it was assumed overburden. Compared to Alchimer’s completely different approach to
that a high-performance iPVD tool was process which features over 40% step metallisation of TSVs compared to the
available. Any lesser performance tool coverage, much less resources need be dry vapour deposition processes presently
would increase the cost of consumables spent on process engineering-intensive used. It is these differences which allow
and decrease throughput and yield. CMP and post-CMP cleaning steps, as such radical reductions in cost of
Alchimer’s AquiVia process flow can there is a fraction of the amount of ownership and such dramatic
be implemented using either current material to be removed. improvements in performance. Alchimer’s
plating tools for isolation, barrier and electrografting based technologies,
seed, and another for via fill; or one large Application areas including eG ViaCoat and AquiVia, are
cluster tool, depending on via volume and Alchimer’s primary focus was on high set to enable the widespread adoption of
line balance. Based on a split tool density, high aspect ratio TSVs, but it’s 3D ICs by solving the industry’s TSV
configuration and using the same becoming clear that AquiVia brings cost related problems.
August 2008 www.euroasiasemiconductor.com
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