semi合集-English.pdf - 第6473页
SEMI G78-0699 © SE MI 1999 6 Figure 4 Recommended Dice and P ads to be used f or Data Collect ion 6.6.3 I t is im porta nt tha t the w afers u s ed with thi s method are probed only once, or else multiple scr ub marks ma…
SEMI G78-0699 © SEMI 19995
X offset =
(right – left)/2 + left
Die pad
Cente
r
Lef
t
X
Y
Y Pads- Scrub mark &
scrub mark cente
r
X
Die pad
Cente
r
Top
Bottom
Y
X Pads- Scrub mark &
scrub mark cente
r
Y offset =
(top – bottom)/2 + bottom
Right
Offset
Offset
Figure 2
X and Y Offset
Scrub mark
and scrub mark
center
Die pad
Passivation opening and best fit
rectangle
Best fit
rectangle
Die pad center
Y
X
Figure 3
Scrub Mark Analysis
6.4.1 Vision system measurements will be made
establishing offset distances from the die pad center to
the scrub mark. The stability of the measurement is
greater when made perpendicular to the direction of the
scrub mark. This will establish X and Y offsets via
measurement of offsets for pads in the X and Y plane of
the die.
6.4.2 Once the offsets are established, a two-step
procedure will manipulate 1296 X and 1296 Y offset
values. The end result of the algorithm will be a
relative measure of the total probe system accuracy and
repeatability for the pads analyzed. Figure 5 represents
a visual summary of the method.
6.5 Considerations of Scale — When evaluating the
suitability of a particular probe system to probe a
particular size of bond pad, or to probe accurately at a
particular pad-to-pad pitch, a good rule of thumb is that
the prober’s positional accuracy, as stated in its
specifications, should be 1/10 that of the scale of the
features to be probed. For example, if the probe system
being evaluated has an overall placement accuracy of
5µm, it would be inappropriate to analyze wafers using
this method and this probe system for dice that have
pads less than 50 µm square (this would be less than
10x).
6.5.1 Regardless, when this method is used for
evaluation of multiple systems, it is essential that die
and bond pad size/pitch consistency be maintained from
evaluation to evaluation if the results are to be
meaningful.
6.5.2 The same 10× rule applies to the vision system
or automated Probe Mark Analysis system employed to
make the pad offset measurements. These systems
should have a pixel resolution that is at least 10× finer
than the die pad dimensions associated with the scrub
marks being measured.
6.6 Conclusion — It is assumed th at the user of this
method has a wafer probe system or systems, or is
planning to make a selection from the various systems
available in the market place, and requires objective
comparative analysis for accuracy, repeatability and
throughput.
6.6.1 It should be clear that this method employs a
three-step process of probing, probe mark data
collection, and data analysis.
6.6.2 When probing, every die on ea ch of the ten
wafers is to be “tested” and probed. Of those ten
wafers, the last nine with 12 die per wafer will be used
for scrub mark data collection. At least 24 pads per die
will be used for the analysis. The first wafer is meant
only to allow stabilization for the probe system and its
probe card.
SEMI G78-0699 © SEMI 1999 6
Figure 4
Recommended Dice and Pads to be used for Data Collection
6.6.3 It is important that the wafers used with this
method are probed only once, or else multiple scrub
marks may be difficult for the measurement system to
deal with and will most likely influence the analysis
results. This method assumes the wafer is ideal, having
no die skew due to wafer process anomalies.
NOTE: It is possible that a not so perfect probe tip to pad
alignment (PTTPA) may create misleading results for this
method. It is recommended that PTTPA be done on die
located at the edge of the wafer, as shown in Figure 4. This is
opposed to having PTTPA done on die in the center of the
wafer. An offset error incurred in the context of a PTTPA
done in the center may result in an incremental and continuing
error as testing moves across the wafer. With this method that
error may be averaged-out.
6.6.4 Probe system index time is device and probe
system dependent. Probe system index time is
determined by acceleration, maximum achievable
velocity, and distance traveled die to die by the chuck.
Thus, the device type chosen for use with this method
should be representative of typical die size if
meaningful index time and throughput data are to be
gathered.
SEMI G78-0699 © SEMI 19997
6.6.5 If the results of this method tu rn out to be
unfavorable, the user has the option of applying a more
detailed, enhanced data analysis application of this
method. That application is contained in Appendix 1.
The enhanced method uses the same data, but it
requires more manipulation of the data during data
analysis. The detail contained in the enhanced
algorithm will provide the user with greater insight as
to the cause of unfavorable results related to the probe
system under evaluation. A summary of the enhanced
method is shown in Figure 6.
6.7 Alternatives — What has been left undefined to
this point is availability of an automated approach to
data collection per the requirements of this method.
Regardless, data collection can be manually
accomplished. The manual process is laborious and
requires a video measuring system to make offset
measurements on the die pads, and a spreadsheet to
analyze the resulting data.
6.7.1 If manual operation is not desi rable or practical,
automated Probe Mark Analysis Systems do exist in the
market place as an item to be purchased. Providers are
also available to accept probed wafers and execute
probe mark analysis under contract as a service.
NOTE: A Final Note to the User of This Method — This
method provides sufficient data for sophisticated analysis of
probe system performance across die-to-die, wafer-to-wafer,
and setup-to-setup. It also provides a simple metric. It is easy
to make comparisons with simple "single number" metrics,
but that has the potential for oversight, distortion and
subsequent inappropriate comparisons. The test engineer,
working with the probe system supplier, must be the ultimate
judge of the applicability of this method and the correct
interpretation of the results.
DIE
3
σ
σσ
σ
Average Die Offset
Three sigma calculation of Die Offset Values
Die to Die X and Die to Die Y variation
[REPEATABILITY]
VISION SYSTEM or PROBE MARK ANALYSIS SYSTEM
ESTABLISH
PAD OFFSETS
Offset from the center of the bond pad to the center of the scrub mark for Lot-X and Lot-Y
Average Die Offset
Average all Pad Offsets by die
(Avg. of 108 Lot-X and Avg. of 108
Lot-Y values)
SETUP LOT
1
2
WAFER
Figure 5
Pad Offset and Two-Step Analysis Algorithm for Determining Probe System Error