research activities in 2007 - CSEM

Optoelectronic Test Equipment for Image Sensors and Systems Qualification
A. Baumgartner
The testing of a circuit is an essential but quite expensive step in the production flow of semiconductor devices. Frequently CSEM customers are
looking for small volume production with a high quality level. Therefore a testing environment has been set up to support production verification and
qualification in-house with moderate investments and in a very short time after prototype evaluation. This is achieved thanks to the development of
very similar routines for both evaluation measurements at the prototype level and for production verification.
Following the evaluation of the first prototypes, the set-up of a
fully automatic test system for production testing typically
requires a large effort and high investments.
Quite often for products resulting from “leading edge” research
projects, the standard industry levels of quality are expected
but for significantly lower quantities. Furthermore the
development of test plans for automatic test equipments
(ATE) can be quite costly due to the high time pressure for
rapid development cycles and a quick ramp up of the
production.
Prototype evaluation is a key phase in the development of
novel image sensors. This evaluation can be very timeconsuming
and needs to be repeated for each new sensor
circuit. The measurements done during evaluation are similar
to the testing cycles for the production verification. For largevolume
production, testing is normally done on dedicated test
systems. In this project, a cost-effective evaluation system for
production testing was investigated and implemented for low
volume production.
To be able to verify a device in a short time, special testing
features and design for test (DfT) generally have to be
implemented:
• Insertion of structural testing for digital design (blocks)
such as the exchange of flip-flops with scan flip-flops
• Insertion of special dedicated “test“ registers to guarantee
the control- and observability of analogue blocks
This work has to be done during the design phase and the
fault coverage of these tests has to be checked before the end
of the design phase. Therefore, a test concept for production
testing needs to be done and elaborated before the project
design phase starts.
For manufactured optical semiconductors, the following
procedure is used:
• Manufacture wafers with PCM structures (=dedicated test
structures), verify PCM structures in wafer fabrication site
• Samples are first tested using a (wafer) prober and a
needlecard (probecard) to contact the pads. The failing
samples are marked. This first measurement is done in a
clean atmosphere (open wafers) in the pre-test site, e.g. in
a clean room at CSEM in Zurich. To guarantee correct
operation over the full temperature range, this first test is
done at one temperature within the specified limits (e.g.
hot)
• The good samples are packaged in single-die
packages,on multi-die “chip-carriers” like Multi-Chip-
Packages/Multi-Chip-Modules (MCP/MCM) or bonded
directly on circuit boards (e.g. on “flexprints”)
• The packaged samples are tested a second time at a
different temperature.
An automatic test system for evaluation and small-volume
production testing using a National Instruments LabVIEW® -
based system was chosen as a solution for CSEM. For cost
reasons the measurement hardware is based on PC
components. It consists of a PC with 19 PXI cards (in 2
external racks), a semiautomatic prober in a dark cabinet and
an Ulbricht sphere.
With the above described hardware the main challenge is the
capability to test semiconductors very fast. Therefore,
additional external equipment consisting of a logic analyzer
and a pattern generator were integrated into the system. The
complete testing set-up is controlled from LabVIEW with the
TestStand add-on LabVIEW tool.
The test equipment looks as displayed in Figure 1.
PXI link
Logic
Analyzer
PXI
System
Ulbricht
sphere
RS232
GPIB
PC1: LabVIEW 8.5
XP
DUT
Prober
RS232
PC2: Proberbech
NT4.0
Figure 1: Schematics of the test equipement.
Dark Room
Clean Room
With this setup, small volume production testing can be
performed and an automatic system evaluation flow (system
qualification) can/will be easily implemented. CSEM has now
the possibility to test optical circuits on wafer as well as on
packaged samples.
Due to the high flexibility of this system, circuits with high
frequency requirements and/or with a high pin count can be
tested. Moreover new equipment can be easily integrated in
the future.
This system implementation was possible thanks to the
support of the Wilsdorf foundation which CSEM would like to
acknowledge.
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