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Excerpt Edition
This PDF is an excerpt from Chapter 4
of the Parametric Measurement Handbook.
The
Parametric Measurement
Handbook

Third Edition
March 2012
Chapter 4: On-Wafer Parametric Measurement

"One must learn by doing the thing; for though you think you know it, you have
no certainty until you try." -- Sophocles

Introduction
The vast majority of parametric measurements are performed on-wafer.
Obviously, this implies that you need some sort of a wafer prober to make these
measurements. What is often missed by many engineers performing on-wafer
parametric measurements are the profound effects that various factors such as
the wafer chuck, cables, wafer probes and switching matrix (if used) can have
upon their measurement results.

Fully automatic versus analytical wafer probers
Fully automatic wafer probers are designed to be used in production environ-
ments in conjunction with either parametric or functional test equipment. Fully
automatic wafer probers can test an entire cassette or FOUP (front-opening
unified pod) of wafers at a time, and they have the ability to automatically load
and align a wafer for testing. Fully automatic wafer probers are virtually always
used with some sort of a probe card and switching matrix. Due to their size,
cost, and complexity, fully automatic wafer probers are used almost exclusively
in production test environments with high-volume production testers. Since this
handbook is primarily focused on parametric test instruments, we will not spend
any additional space discussing them.

Analytical wafer probers are designed to be used in laboratory environments,
and they come in both manual and semi-automatic versions. Manual wafer
probers do not possess any electrical motors to automate any part of the wafer
alignment and stepping process, but must instead (as their name implies) be
manually adjusted each time that you want to move to a new location on the
wafer. In contrast, most semi-automatic wafer probers possess the capability to
automatically align an individual wafer; however, they typically do not support
any sort of automated wafer loading and they require the manual loading of
each wafer. Semi-automatic wafer probers can be used with probe cards and
switching matrices, but it is more common to see them used with multiple
individual positioners (probes) for maximum measurement flexibility. Most semi-
automatic wafer probers also do support automated testing across an entire
wafer in conjunction with some sort of parametric instrumentation.

Figure 4.1. Some examples of semi-automatic wafer probers.
64
Wafer prober measurement concerns
It should be clear upon some reflection that the wafer prober measurement
environment has a significant impact on the quality of parametric measurements
that you can obtain. Unfortunately, many times these effects are not adequately
accounted for by users trying to make parametric measurements. Some of the
key issues are as follows.
1. Limited current noise floor