A Step by Step Guide to Practical RF Device Measurement
Transcript of A Step by Step Guide to Practical RF Device Measurement
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PHDVXUHPHQWGavin Fisher
Cascade Microtech Europe
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Device measurement at its simplest requires the following
steps
Probe and accessory physical Set-up for calibration
Calibration instrumentation setting preparation
Calibration raw measurement steps, error computation andcalset delivery to instrument
Calibration verification
Wafer alignment and test plan set-up Device measurement, including biasing
Measurement of de-embedding structures and post process
activities to remove unwanted parasitics
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Vector Network
Analyzer
Cables
Probes
Probe positioners
Probe station
Contact Substrate
Calibration Substrate
Calibration Software
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Dry, Frost Freeenvironment
Auxiliary Chucks Roll-out chuck
Stable repeatableplaten
Top-Hat
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*definition: planarization -
the ability to ensure all
contacts are at the same
height
Use Contact
Substrate to
planarise probes
Equalprobemarks
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Contact Substrate
PN 005-018
Dull gold finish
Bright contact marks
Adjust planarity until
equal marks from all
probe contacts
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Electrical behavior of standards
Standard dimensions Probe pitch
Probe placement (Use Alignment marks)
Cal coefficients supplied with probe & ISS
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Sets probes overtravel & spacing
for calibration
Initial Contact (zero overtravel)
Line the edges of the probes to
edge of flags
Center the contacts with X & Ymicrometers
Final Contact (2 3 mils overtravel)
Tips lined up with flag centers
Center the contacts with Z
micrometer only
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Tools for the novice
Guided Wizards
Multi-media Tutorials
Intelligence in setups
Tools for expert Enhanced verification
Real time measurement
validation Enhanced reports
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Measurement System Setup
Define the measurement system
VNA, prober, ISS and probes
VNA Qualification
Test that the VNA is functional
and repeatable
Probe Qualification
Check that the probe is making
contact
ISS management
What structures to use
Is a structure good?
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Important to initialise instrument settings paying attention to power, number of points, Start and stop
and particularly IF bandwidth
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Probe characteristics are
displayed both graphically
and numerically. Probes can
be identified by serialisation
Probe data required to
check calibration
compatability and where
necessary provide lumped
element data
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Individually serialised iss
data can be loaded
This information is
important to keep track of
correct iss for calibration
and determine location of
alignment structure
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ISS Reference location
determines the correct orientation
and alignment of the probes withrespect to the entire iss
A similar tool is used to inform
the software of damaged or
untrimmed lcations
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Automatic calibration will use the prober to automatically move from
standard to standard
On pressing autocal the procedure is as follows
Repeatability check measures raw open multiple times in order to
check the system is repeatable (often picks up problems relating to
cabling, system directivity, Excessively high If bandwidth) Calibration moves though all standards for the calibration,
computes calibration and sends to instrument
Verification will look at a verification standard to compare against
known values (typically an open)
Monitoring measurement will store data for future checks against
system stability (is cal still good)
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Wincal measures open to check repeatability of measurement system
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System re-measures open for the calibration. At times the
open measurement uses substrate opens hence the need
for remeasurement
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It is important that only 50 ohm loads are used for this part
of the calibration
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Wincal applies the selected calibration to the measureddata (typically we recommend LRRM) and error set is sent
to the instrument
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Following calibration a validation is carried out against a known standard. Typically thisis an open whose capacitance is known by the probe pitch, but can be a golden dutwhose characteristics are pre-measured and stored. For lrrm the open is the raw openmeasured during the cal and corrected by the calibration (post corrected)
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Following validation wincal will take a measurement of a
standard for use in later monitoring tests.
Monitoring test allow Wincal to gain a metric of system
drift and thus the continuing validity of the calibration.
An open is an easy standard to reproduce and is affectedlittle by probe movement ie this can often be measured
just above the device under test
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Openstub
GROUND
GROUND
SIGNAL
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0.81
1.5
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40.0 GHz
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[dB]
[GHz]
Linear Phase Lag
50ohm to stub Z miss-match
Fringing C at stub open end
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Prior to carrying out any
multi-die test the wafer
should be aligned to the
system axes and
appropriately sized.
Nucleus can carry out this
activity automatically using
optical pattern recognition
If an exisiting wafermap is
available his can spped up
alignment process
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Using Evue microscope multi ccd view makes location of usable
optical alignment points straightforward
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Nucleus wafermap allows test plan to be visible and test progress to
be tracked
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Subdie allow for multiple devices to be identified and
tested within each die
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Wafermaps can also be used to see the distribution of
single point data for die and subdie as the test progresses
This tool is most useful for spotting set-up issues during
the test sequence
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