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F E B R U A R Y 2 0 1 0 i s s u e n ° 1 4
N e w s l e t t e r o n 3 D I C , T S V , W L P & E m b e d d e d T e c h n o l o g i e s
OmniBSI™: the third approach to Backside
Illuminated (BSI) Sensor Integration
In summary, BSI technology for small pixel CMOS image sensors (CIS) enables increased fill factor and quantum efficiency,
reduced pixel cross talk, and thinner camera modules. Image sensor technologists migrating to a BSI configuration have
many new (for them) engineering problems to solve.
he choices of starting substrate (bulk metallization to the edge in front illuminated layer, a flip of the image sensor substrate had
vs. SOI), carrier wafer bond, substrate sensors was easily transferrable to the BSI minimal impact on the new packaging. Despite the
thickness, surface passivation, and solution. By going horizontal first, and then radical reengineering of the now 2.1 µm thick CIS
pixel isolation can influence both the sensor’s connecting the traces with a sidewall redistribution substrate, OmniVision/TSMC were able to avoid
manufacturing cost and performance. Once the
BSI sensor’s desired performance is set at the
silicon level, it still needs to be integrated into
the camera module supply chain. To achieve this
integration, companies need to choose a course
for packaging, whether it be through licensing or
innovation. Making this decision is not optional;
the reality of a thin substrate BSI sensor forces an
engineering response.
Three avenues exist for BSI sensor integration:
wafer level chip scale packaging (WL-CSP) both
with and without through silicon vias (TSVs), and
backside wire bonding. Being early adopters of
WL-CSP packaging for their front illuminated
sensors, OmniVision and foundry partner TSMC
were fortuitously able to recycle their existing
solution for their bulk BSI process. A quick review
of OmniVision’s advanced packaging roadmap
begins with its 2003 investment in Taiwanese
wafer level packaging (WLP) company Xintec
Inc. TSMC has also been a longtime investor in
Xintec, finally taking a controlling share in 2007.
Xintec licensed Shellcase/Tessera’s ShellOP WLP
technology in 2002, making it an attractive partner Figure 1 Xintec WL-CSP for BSI – Cross Section Overview
for OmniVision/TSMC. Chipworks found this in use
in 2007, in an OmniVision 2 Mp front illuminated
camera module. The sensor had a thickness of
700 µm, as measured from the top of Glass 1 to
the bottom of Glass 2.

OmniVision chose to insert its BSI technology
at the 1.4 µm pixel generation. After having co-
developed the process flow with TSMC, mass
production began in early 2009, with Xintec
continuing to handle the packaging. Chipworks
analyzed a 5 Mp OmniBSI CIS (OV5642), a cross
section of which is shown in Figure 1. At a glance,
the cross section could be mistaken for a front
illuminated sensor. Closer inspection reveals the
ultrathin BSI sensor substrate bonded to a silicon
carrier wafer, and the absence of a lower glass
support. Xintec’s WL-CSP BSI version is only 570
µm thick, a thickness reduction of about 0.13 mm
compared to the front illuminated device.

Figure 2 shows a detailed view of the “T” contact
modified for use in the BSI configuration. As it
turns out, the philosophy of extending the die
Figure 2 Xintec WL-CSP for BSI – Cross Section Detail
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