U.S. patent application number 11/975243 was filed with the patent office on 2008-02-21 for probe station.
This patent application is currently assigned to Cascade Microtech, Inc.. Invention is credited to John Dunklee, Greg Nordgren.
Application Number | 20080042376 11/975243 |
Document ID | / |
Family ID | 26924344 |
Filed Date | 2008-02-21 |
United States Patent
Application |
20080042376 |
Kind Code |
A1 |
Nordgren; Greg ; et
al. |
February 21, 2008 |
Probe station
Abstract
A probe station for testing a wafer.
Inventors: |
Nordgren; Greg; (Logan,
UT) ; Dunklee; John; (Tigard, OR) |
Correspondence
Address: |
CHERNOFF, VILHAUER, MCCLUNG & STENZEL
1600 ODS TOWER
601 SW SECOND AVENUE
PORTLAND
OR
97204-3157
US
|
Assignee: |
Cascade Microtech, Inc.
|
Family ID: |
26924344 |
Appl. No.: |
11/975243 |
Filed: |
October 18, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11083677 |
Mar 16, 2005 |
|
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11975243 |
Oct 18, 2007 |
|
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|
09881312 |
Jun 12, 2001 |
6914423 |
|
|
11083677 |
Mar 16, 2005 |
|
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60230552 |
Sep 5, 2000 |
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Current U.S.
Class: |
279/137 ;
324/750.22 |
Current CPC
Class: |
G01R 31/2886 20130101;
G01R 31/2887 20130101; Y10T 279/29 20150115 |
Class at
Publication: |
279/137 ;
324/158.1 |
International
Class: |
G01R 31/26 20060101
G01R031/26 |
Claims
1. A chuck assembly including a rotational member and an auxiliary
chuck comprising: (a) rotational-member suitable for supporting a
chuck thereon wherein said rotational member is rotatable with
respect to said chuck assembly; (b) said auxiliary chuck being free
from rotating with respect to said chuck assembly; (c) wherein said
auxiliary chuck is free from supporting said rotational member.
2. The chuck assembly of claim 1 wherein said auxiliary chuck
having an upper surface thereon having an elevation that is above
an upper surface of said rotational member.
3. The chuck assembly of claim 1 wherein said rotational member has
a planar upper surface.
4. The chuck assembly of claim 2 wherein said chuck assembly has a
planar upper surface.
5. The chuck assembly of claim 4 wherein said rotational member
planar upper surface and said chuck assembly planar upper surface
are substantially coplanar.
6. The chuck assembly of claim 1 wherein chuck assembly includes a
movement assembly for moving said rotational member in a lateral
direction.
7. The chuck assembly of claim 1 wherein said auxiliary chuck is
suitable to support at least one test substrate thereon.
8. The chuck assembly of claim 1 wherein said auxiliary chuck
supports said test substrate at a location above said rotational
member.
9. The chuck assembly of claim 5 wherein said auxiliary chuck moves
together with said rotational member in a lateral direction.
10. A chuck assembly including a rotational member and a movement
member comprising: (a) said rotational member suitable for
supporting a chuck thereon wherein said rotational member is
rotatable with respect to said chuck assembly; (b) said movement
member mechanically interconnected with said rotational member so
as to selectively rotate said rotational member; (c) said
rotational member being substantially free from exerting a
downwardly directed force on said movement member while testing a
device under test.
11. The chuck assembly of claim 10 wherein rotational member
includes a tab, said movement member includes a slot that engages
said tab.
12. The chuck assembly of claim 11 wherein rotational movement of
said slot causes rotational movement of said rotational member.
13. The chuck assembly of claim 10 wherein said rotational member
is supported by a positioning stage.
14. The chuck assembly of claim 13 wherein said positioning stage
includes a pair of spaced apart linear bearings.
15. The chuck assembly of claim 14 wherein said positioning stage
is the primarily support for said rotational member.
16. The chuck assembly of claim 10 wherein a substantially constant
vertical spacing is maintained between said movement member and
said rotational member while said rotational member is being
rotated.
17. The chuck assembly of claim 16 wherein said chuck assembly
provides z-axis movement of said rotational member while
maintaining said substantially constant vertical spacing.
18. A chuck assembly including a rotational member and a base
assembly comprising: (a) said rotational member suitable for
supporting a chuck thereon wherein said rotational member is
rotatable with respect to said chuck assembly; (b) said rotational
member laterally movable with respect to said base assembly when
said rotational member is in a predefined rotational orientation;
(c) said rotational member free from being laterally movable with
respect to said base assembly selectively based upon the
orientation of said rotational member.
19. The chuck assembly of claim 18 wherein said predefined
rotational orientation is zero degrees.
20. The chuck assembly of claim 18 wherein said predefined
rotational orientation is a predefined range of values.
21. The chuck assembly of claim 18 wherein said rotational member
is maintained free from substantially all rotational movement while
said rotational member is in an extended position with respect to
said base.
22. A chuck assembly including a rotational member comprising: (a)
said rotational member supporting a chuck thereon; (b) a plurality
of adjustment members suitable to adjust the orientation of said
chuck in a plane generally co-planar with an upper surface of said
chuck with respect to said rotational member while maintaining said
rotational member and said chuck in a tensioned state while
adjusting said orientation.
23. The chuck assembly of claim 22 wherein said tensioned state is
provided by said adjustment members maintaining the spacing between
said rotational member and said chuck.
24. The chuck assembly of claim 23 wherein said adjustment members
are threaded screws.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a division of U.S. patent application
Ser. No. 11/083,677, filed Mar. 16, 2005, which is a continuation
of U.S. patent application Ser. No. 09/881,312, filed Jun. 12,
2001, now U.S. Pat. No. 6,914,423, which claims the benefit of U.S.
Provisional App. No. 60/230,552, filed Sep. 5, 2000.
BACKGROUND OF THE INVENTION
[0002] The present application relates to a probe station.
BRIEF SUMMARY OF THE INVENTION
[0003] With reference to FIGS. 1, 2 and 3, a probe station
comprises a base 10 (shown partially) which supports a platen 12
through a number of jacks 14a, 14b, 14c, 14d which selectively
raise and lower the platen vertically relative to the base by a
small increment (approximately one-tenth of an inch) for purposes
to be described hereafter. Also supported by the base 10 of the
probe station is a motorized positioner 16 having a rectangular
plunger 18 which supports a movable chuck-assembly 20 for
supporting a wafer or other test device. The chuck assembly 20
passes freely through a large aperture 22 in the platen 12 which
permits the chuck assembly to be moved independently of the platen
by the positioner 16 along X, Y and Z axes, i.e., horizontally
along two mutually-perpendicular axes X and Y, and vertically along
the Z axis. Likewise, the platen 12, when moved vertically by the
jacks 14, moves independently of the chuck assembly 20 and the
positioner 16.
[0004] Mounted atop the platen 12 are multiple individual probe
positioners such as 24 (only one of which is shown), each having an
extending member 26 to which is mounted a probe holder 28 which in
turn supports a respective probe 30 for contacting wafers and other
test devices mounted atop the chuck assembly 20. The probe
positioner 24 has micrometer adjustments 34, 36 and 38 for
adjusting the position of the probe holder 28, and thus the probe
30, along the X, Y and Z axes, respectively, relative to the chuck
assembly 20. The Z axis is exemplary of what is referred to herein
loosely as the "axis of approach" between the probe holder 28 and
the chuck assembly 20, although directions of approach which are
neither vertical nor linear, along which the probe tip and wafer or
other test device are brought into contact with each other, are
also intended to be included within the meaning of the term "axis
of approach." A further micrometer adjustment 40 adjustably tilts
the probe holder 28 to adjust planarity of the probe with respect
to the wafer or other test device supported by the chuck assembly
20. As many as twelve individual probe positioners 24, each
supporting a respective probe, may be arranged on the platen 12
around the chuck assembly 20 so as to converge radially toward the
chuck assembly similarly to the spokes of a wheel. With such an
arrangement, each individual positioner 24 can independently adjust
its respective probe in the X, Y and Z directions, while the jacks
14 can be actuated to raise or lower the platen 12 and thus all of
the positioners 24 and their respective probes in unison.
[0005] An environment control enclosure is composed of an upper box
portion 42 rigidly attached to the platen 12, and a lower box
portion 44 rigidly attached to the base 10. Both portions are made
of steel or other suitable electrically conductive material to
provide EMI shielding. To accommodate the small vertical movement
between the two box portions 42 and 44 when the jacks 14 are
actuated to raise or lower the platen 12, an electrically
conductive resilient foam gasket 46, preferably composed of silver
or carbon-impregnated silicone, is interposed peripherally at their
mating juncture at the front of the enclosure and between the lower
portion 44 and the platen 12 so that an EMI, substantially
hermetic, and light seal are all maintained despite relative
vertical movement between the two box portions 42 and 44. Even
though the upper box portion 42 is rigidly attached to the platen
12, a similar gasket 47 is preferably interposed between the
portion 42 and the top of the platen to maximize sealing.
[0006] With reference to FIGS. 5A and 5B, the top of the upper box
portion 42 comprises an octagonal steel box 48 having eight side
panels such as 49a and 49b through which the extending members 26
of the respective probe positioners 24 can penetrate movably. Each
panel comprises a hollow housing in which a respective sheet 50 of
resilient foam, which may be similar to the above-identified gasket
material, is placed. Slits such as 52 are partially cut vertically
in the foam in alignment with slots 54 formed in the inner and
outer surfaces of each panel housing, through which a respective
extending member 26 of a respective probe positioner 24 can pass
movably. The slitted foam permits X, Y and Z movement of the
extending members 26 of each probe positioner, while maintaining
the EMI, substantially hermetic, and light seal provided by the
enclosure. In four of the panels, to enable a greater range of X
and Y movement, the foam sheet 50 is sandwiched between a pair of
steel plates 55 having slots 54 therein, such plates being slidable
transversely within the panel housing through a range of movement
encompassed by larger slots 56 in the inner and outer surfaces of
the panel housing.
[0007] Atop the octagonal box 48, a circular viewing aperture 58 is
provided, having a recessed circular transparent sealing window 60
therein. A bracket 62 holds an apertured sliding shutter 64 to
selectively permit or prevent the passage of light through the
window. A stereoscope (not shown) connected to a CRT monitor can be
placed above the window to provide a magnified display of the wafer
or other test device and the probe tip for proper probe placement
during set-up or operation. Alternatively, the window 60 can be
removed and a microscope lens (not shown) surrounded by a foam
gasket can be inserted through the viewing aperture 58 with the
foam providing EMI, hermetic and light sealing. The upper box
portion 42 of the environment control enclosure also includes a
hinged steel door 68 which pivots outwardly about the pivot axis of
a hinge 70 as shown in FIG. 2A. The hinge biases the door
downwardly toward the top of the upper box portion 42 so that it
forms a tight, overlapping, sliding peripheral seal 68a with the
top of the upper box portion. When the door is open, and the chuck
assembly 20 is moved by the positioner 16 beneath the door opening
as shown in FIG. 2A, the chuck assembly is accessible for loading
and unloading.
[0008] With reference to FIGS. 3 and 4, the sealing integrity of
the enclosure is likewise maintained throughout positioning
movements by the motorized positioner 16 due to the provision of a
series of four sealing plates 72, 74, 76 and 78 stacked slidably
atop one another. The sizes of the plates progress increasingly
from the top to the bottom one, as do the respective sizes of the
central apertures 72a, 74a, 76a and 78a formed in the respective
plates 72, 74, 76 and 78, and the aperture 79a formed in the bottom
44a of the lower box portion 44. The central aperture 72a in the
top plate 72 mates closely around the bearing housing 18a of the
vertically-movable plunger 18. The next plate in the downward
progression, plate 74, has an upwardly-projecting peripheral margin
74b which limits the extent to which the plate 72 can slide across
the top of the plate 74. The central aperture 74a in the plate 74
is of a size to permit the positioner 16 to move the plunger 18 and
its bearing housing 18 a transversely along the X and Y axes until
the edge of the top plate 72 abuts against the margin 74b of the
plate 74. The size of the aperture 74a is, however, too small to be
uncovered by the top plate 72 when such abutment occurs, and
therefore a seal is maintained between the plates 72 and 74
regardless of the movement of the plunger 18 and its bearing
housing along the X and Y axes. Further movement of the plunger 18
and bearing housing in the direction of abutment of the plate 72
with the margin 74b results in the sliding of the plate 74 toward
the peripheral margin 76b of the next underlying plate 76. Again,
the central aperture 76a in the plate 76 is large enough to permit
abutment of the plate 74 with the margin 76b, but small enough to
prevent the plate 74 from uncovering the aperture 76a, thereby
likewise maintaining the seal between the plates 74 and 76. Still
further movement of the plunger 18 and bearing-housing in the same
direction causes similar sliding of the plates 76 and 78 relative
to their underlying plates into abutment with the margin 78b and
the side of the box portion 44, respectively, without the apertures
78a and 79a becoming uncovered. This combination of sliding plates
and central apertures of progressively increasing size permits a
full range of movement of the plunger 18 along the X and Y axes by
the positioner 16, while maintaining the enclosure in a sealed
condition despite such positioning movement. The EMI sealing
provided by this structure is effective even with respect to the
electric motors of the positioner 16, since they are located below
the sliding plates.
[0009] With particular reference to FIGS. 3, 6 and 7, the chuck
assembly 20 is a modular construction usable either with or without
an environment control enclosure. The plunger 18 supports an
adjustment plate 79 which in turn supports first, second and third
chuck assembly elements 80, 81 and 83, respectively, positioned at
progressively greater distances from the probe(s) along the axis of
approach. Element 83 is a conductive rectangular stage or shield 83
which detachably mounts conductive elements 80 and 81 of circular
shape. The element 80 has a planar upwardly-facing wafer-supporting
surface 82 having an array of vertical apertures 84 therein. These
apertures communicate with respective chambers separated by O-rings
88, the chambers in turn being connected separately to different
vacuum lines 90a, 90b, 90c (FIG. 6) communicating through
separately-controlled vacuum valves (not shown) with a source of
vacuum. The respective vacuum lines selectively connect the
respective chambers and their apertures to the source of vacuum to
hold the wafer, or alternatively isolate the apertures from the
source of vacuum to release the wafer, in a conventional manner.
The separate operability of the respective chambers and their
corresponding apertures enables the chuck to hold wafers of
different diameters.
[0010] In addition to the circular elements 80 and 81, auxiliary
chucks such as 92 and 94 are detachably mounted on the corners of
the element 83 by screws (not shown) independently of the elements
80 and 81 for the purpose of supporting contact substrates and
calibration substrates while a wafer or other test device is
simultaneously supported by the element 80. Each auxiliary chuck
92, 94 has its own separate upwardly-facing planar surface 100, 102
respectively, in parallel relationship to the surface 82 of the
element 80. Vacuum apertures 104 protrude through the surfaces 100
and 102 from communication with respective chambers within the body
of each auxiliary chuck. Each of these chambers in turn
communicates through a separate vacuum line and a separate
independently-actuated vacuum valve (not shown) with a source of
vacuum, each such valve selectively connecting or isolating the
respective sets of apertures 104 with respect to the source of
vacuum independently of the operation of the apertures 84 of the
element 80, so as to selectively hold or release a contact
substrate or calibration substrate located on the respective
surfaces 100 and 102 independently of the wafer or other test
device. An optional metal shield 106 may protrude upwardly from the
edges of the element 83 to surround the other elements 80, 81 and
the auxiliary chucks 92, 94.
[0011] All of the chuck assembly elements 80, 81 and 83, as well as
the additional chuck assembly element 79, are electrically
insulated from one another even though they are constructed of
electrically conductive metal and interconnected detachably by
metallic screws such as 96. With reference to FIGS. 3 and 3A, the
electrical insulation results from the fact that, in addition to
the resilient dielectric O-rings 88, dielectric spacers 85 and
dielectric washers 86 are provided. These, coupled with the fact
that the screws 96 pass through oversized apertures in the lower
one of the two elements which each screw joins together thereby
preventing electrical contact between the shank of the screw and
the lower element, provide the desired insulation. As is apparent
in FIG. 3, the dielectric spacers 85 extend over only minor
portions of the opposing surface areas of the interconnected chuck
assembly elements, thereby leaving air gaps between the opposing
surfaces over major portions of their respective areas. Such air
gaps minimize the dielectric constant in the spaces between the
respective chuck assembly elements, thereby correspondingly
minimizing the capacitance between them and the ability for
electrical current to leak from one element to another. Preferably,
the spacers and washers 85 and 86, respectively, are constructed of
a material having the lowest possible dielectric constant
consistent with high dimensional stability and high volume
resistivity. A suitable material for the spacers and washers is
glass epoxy, or acetyl homopolymer marketed under the trademark
Delrin by E. I. DuPont.
[0012] With reference to FIGS. 6 and 7, the chuck assembly 20 also
includes a pair of detachable electrical connector assemblies
designated generally as 108 and 110, each having at least two
conductive connector elements 108a, 108b and 110a, 110b,
respectively, electrically insulated from each other, with the
connector elements 108b and 110b preferably coaxially surrounding
the connector elements 108a and 110a as guards therefor. If
desired, the connector assemblies 108 and 110 can be triaxial in
configuration so as to include respective outer shields 108c, 110c
surrounding the respective connector elements 108b and 110b, as
shown in FIG. 7. The outer shields 108c and 110c may, if desired,
be connected electrically through a shielding box 112 and a
connector supporting bracket 113 to the chuck assembly element 83,
although such electrical connection is optional particularly in
view of the surrounding EMI shielding enclosure 42, 44. In any
case, the respective connector elements 108a and 110a are
electrically connected in parallel to a connector plate 114
matingly and detachably connected along a curved contact surface
114a by screws 114b and 114c to the curved edge of the chuck
assembly element 80. Conversely, the connector elements 108b and
110b are connected in parallel to a connector plate 116 similarly
matingly connected detachably to element 81. The connector elements
pass freely through a rectangular opening 112a in the box 112,
being electrically insulated from the box 112 and therefore from
the element 83, as well as being electrically insulated from each
other. Set screws such as 118 detachably fasten the connector
elements to the respective connector plates 114 and 116.
[0013] Either coaxial or, as shown, triaxial cables 118 and 120
form portions of the respective detachable electrical connector
assemblies 108 and 110, as do their respective triaxial detachable
connectors 122 and 124 which penetrate a wall of the lower portion
44 of the environment control enclosure so that the outer shields
of the triaxial connectors 122, 124 are electrically connected to
the enclosure. Further triaxial cables 122a, 124a are detachably
connectable to the connectors 122 and 124 from suitable test
equipment such as a Hewlett-Packard 4142B modular DC source/monitor
or a Hewlett-Packard 4284A precision LCR meter, depending upon the
test application. If the cables 118 and 120 are merely coaxial
cables or other types of cables having only two conductors, one
conductor interconnects the inner (signal) connector element of a
respective connector 122 or 124 with a respective connector element
108a or 110a, while the other conductor connects the intermediate
(guard) connector element of a respective connector 122 or 124 with
a respective connector element 108b, 110b. U.S. Pat. No. 5,532,609
discloses a probe station and chuck and is hereby incorporated by
reference.
[0014] The foregoing and other objectives, features, and advantages
of the invention will be more readily understood upon consideration
of the following detailed description of the invention, taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0015] FIG. 1 is a partial front view of an exemplary embodiment of
a wafer probe station constructed in accordance with the present
invention.
[0016] FIG. 2 is a top view of the wafer probe station of FIG.
1.
[0017] FIG. 2A is a partial top view of the wafer probe station of
FIG. 1 with the enclosure door shown partially open.
[0018] FIG. 3 is a partially sectional and partially schematic
front view of the probe station of FIG. 1.
[0019] FIG. 3A is an enlarged sectional view taken along line 3A-3A
of FIG. 3.
[0020] FIG. 4 is a top view of the sealing assembly where the
motorized positioning mechanism extends through the bottom of the
enclosure.
[0021] FIG. 5A is an enlarged top detail view taken along line
5A-5A of FIG. 1.
[0022] FIG. 5B is an enlarged top sectional view taken along line
5B-5B of FIG. 1.
[0023] FIG. 6 is a partially schematic top detail view of the chuck
assembly, taken along line 6-6 of FIG. 3.
[0024] FIG. 7 is a partially sectional front view of the chuck
assembly of FIG. 6.
[0025] FIG. 8 illustrates an adjustment plate and a surrounding
positional stage.
[0026] FIG. 9 illustrates an extended positional stage.
[0027] FIG. 10 illustrates a locking mechanism for the positional
stage.
[0028] FIG. 11 illustrates a locking mechanism for the adjustment
plate and a tab for rotational engagement of the adjustment
plate.
[0029] FIG. 12 illustrates traditional adjustment of the
orientation of the chuck.
[0030] FIG. 13 illustrates a modified adjustment of the orientation
of the chuck.
[0031] FIG. 14 illustrates a probe station supported by an
isolation stage, both of which are surrounded by a frame.
[0032] FIG. 15 illustrates the engagement of the sides of the
environmental control enclosure.
[0033] FIG. 16 illustrates the engagement of a door to the
environmental control enclosure.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
[0034] The probes may be calibrated by using test structures on the
calibration substrates supported by the auxiliary chucks 92 and 94.
During calibration the chuck assembly 20, as previously described
in the background, is normally aligned with the probes. A wafer
placed on the chuck assembly 20 is not normally accurately aligned
with the auxiliary chucks 92 and 94, and hence the probes. In order
to test the wafer the entire chuck assembly 20, including the
auxiliary chucks 92 and 94, is rotated to align the wafer with the
positioners 24 and their respective probes. Typically, during
testing the chuck assembly 20 is rotated to realign the test
structures on the calibration substrates supported by the auxiliary
chucks 92 and 94 with the probes. After further calibration, the
entire chuck assembly 20, including the auxiliary chucks 92 and 94,
is again rotated to align the wafer with the positioners 24 and
their respective probes. Unfortunately, the theta adjustment of the
chuck assembly 20 may not be sufficiently accurate for increasingly
small device structures. Multiple theta adjustments of the chuck
assembly 20 may result in a slight misalignment of the chuck
assembly 20. As a result of such misalignment it may become
necessary for the operator to painstakingly manually adjust the
theta orientation of the chuck assembly 20.
[0035] Smaller environmental control enclosures require less time
to create suitable environmental conditions within the
environmental control enclosure for accurate measurements. The
environmental control enclosure is sufficiently large to permit the
chuck assembly to move the entire wafer under the probes for
testing. However, if the chuck assembly 20 is rotatable with
respect to the environmental control enclosure then the
environmental control enclosure needs additional width to prevent
the corners of the chuck assembly 20 from impacting the sides of
the environmental control enclosure.
[0036] Normally the encoders within the stage supporting the chuck
assembly include software based compensation for non-proportional
movement to achieve accurate movement in the X and Y directions
over the entire range of movement. The software compensation of the
encoders also depends on the X and Y position of the chuck relative
to the probes. In other words, at different X and Y positions over
the entire range of movement of the chuck the amount of
compensation provided to the encoders may vary. This variable
compensation depending on the X and Y position of the chuck results
in complicated spatial calculations for appropriate encoder
control. The spatial calculations are further complicated when the
chuck is rotated to accommodate the auxiliary chuck
calibration.
[0037] To overcome the limitations associated with misalignment of
the theta orientation of the wafer, to reduce the size of the
environmental control enclosure, and/or to simplify the
compensation for the encoders over the X and Y movement, the
present inventors came to the realization that the chuck supporting
the wafer should rotate with respect to the auxiliary chuck, as
illustrated by FIG. 8. FIG. 8 illustrates the adjustment plate 182
and a surrounding positional stage 184. Accordingly, auxiliary
chucks 180 preferably maintain a fixed X and Y orientation with
respect to the probe positioners and their respective probes. In
this manner, the auxiliary chucks are always properly orientated
with the probes positioners and the probes. During use, the chuck
(supported by the adjustment plate 182) with a wafer thereon is
rotated to the proper theta position with respect to the probes for
probing the wafer. Thereafter, the theta adjustment of the chuck
may remain stationary during subsequent probing of the wafer and
recalibration using the auxiliary chucks. In this manner, typically
the chuck assembly needs to only be moved in X, Y, and potentially
Z directions to achieve complete probing of an entire wafer.
Accordingly, the environmental control enclosure does not
necessarily need to be sufficiently wide to accommodate rotation of
the positional stage. Also, the encoder compensation may be
simplified.
[0038] During probing with the chuck assembly 20, as described in
the background, it became apparent that probing toward the edges of
the wafer tended to result in "wobble" of the wafer and chuck
assembly 20. In addition, some existing probe assemblies include
the chuck assembly elements supported by a set of linear bearings
that permit the upper chuck assembly elements together with the
bearing to be slid out of the environment enclosure for loading the
wafer onto the chuck assembly. The resulting structure is heavy,
and positioned on top of and supported by a plunger affixed to the
top of the Z-axis movement of the chuck assembly 20.
[0039] To reduce the wobble occurring during probing and reduce the
stress applied to the plunger, the present inventors developed a
modified arrangement to nearly eliminate the vertical loads on the
plunger. Referring to FIG. 9, a modified arrangement includes a
central plunger 200 providing rotational movement to the adjustment
plate 182 and hence a chuck supported thereon. The central plunger
200 may include a receptacle 201 that moves within a tab 203. The
positional stage 184 and auxiliary chucks 180 are supported by the
stage 204 surrounding the central plunger 200 which provides the X,
Y, and Z movement. Preferably, the stage includes the central
plunger 200. The positional stage 184 includes an internal bearing
(not shown) upon which the adjustment plate 182 rotates.
Accordingly, the positional stage 184 is the primary load bearing
member for the adjustment plate 182 and chuck thereon. Spaced apart
linear bearings 206 provide a vertical and lateral load bearing
support to the rotational chuck while the central plunger 200
provides the rotational movement to the chuck without (free from)
being the primary load bearing member. The plunger 200 preferably
maintains substantially constant vertical position with respect to
the adjustment plate 182 when the stage 204 provides vertical "Z"
movement of the positional stage.
[0040] Unlocking a lock permits the positional stage 184, including
the rotational chuck, to slide out of the probe station for easier
placement of wafers thereon. Normally when the positional stage 184
is extended, the wafer thereon is adjusted or otherwise replaced
with a different wafer for subsequent testing. After repeated
movement of the stage in and out of the probe station, together
with rotational movement of the chuck (theta adjustment), the
present inventors determined that the resulting theta movement of
the chuck may be significantly different than the initial "zero"
theta. In other words, after repeated use the adjustment plate 182
may be offset by a significant theta offset. Such significant
potential theta offset may result in the cabling to the chuck,
normally provided by a rollout service loop, being wound about the
chuck assembly creating a significantly greater tension thereon or
otherwise damaging the cabling or chuck. The adjustment plate 182
may include a rotational theta limit about "zero" to minimize
potential damage. A suitable rotational limit may be ..+-..7.5
degrees. A further limitation exists in the case that the
adjustment plate 182 is rotated to a position near its rotational
limit because the user may not be permitted further rotational
movement in that direction when aligning another wafer thereby
resulting in frustration to the user. To overcome these limitations
the rotational orientation of the adjustment plate 182 (chuck) is
returned to "zero" prior to sliding the positional stage 184 out of
the probe station. In this manner, the chuck is always at a
constant rotational position, such as 0 degrees, when a wafer is
positioned thereon so that the likelihood of damaging the probe
station by unintended tension on the wires and other
interconnections to the chuck assembly is reduced. In addition, the
range where the chuck is orientated prior to sliding out the
positional stage 184 may be any predefined range of values. Also,
the user maintains the ability to rotate the adjustment plate 182
as necessary during further alignment.
[0041] While the positional stage 184 is extended the user may
attempt to rotate the adjustment plate 182. Unfortunately, this may
result in difficulty engaging the tab 203 with the receptacle 201
when the positional stage 184 is retracted. This difficulty is the
result of the rotation of the lunger 200 not likewise rotating the
positional stage as in existing designs.
[0042] Referring to FIG. 10, the "zero" theta lockout may be
provided by a mechanical arrangement together with a locking
mechanism. A rotational handle 210 is secured to the upper plate
212 of the positional stage 184. A block 216 as secured to the
lower plate 214 of the positional stage 184, which is rigidly
attached to the housing 204. A finger 218 is inserted within a slot
220 defined by the block 216 to rigidly lock the upper plate 212 in
position. The handle 210 is rotated to remove the finger 218 from
the slot 220 to permit relative movement of the upper plate 212
with respect to the lower plate 214.
[0043] Referring to FIG. 11, the handle 210 includes a shaft 230
with a slot 232 in the end thereof. With the handle 210 in the
closed position, the slot 232 is aligned with an alignment plate
234 attached to the rear of the adjustment plate 182. The
adjustment plate 182 may be rotated to properly align the wafer
thereon, with the alignment plate 234 traveling within the slot
232. To unlock the handle 210 the adjustment plate 182 is realigned
to "zero" thus permitting rotational movement of the handle 210,
while simultaneously preventing rotational movement (substantially
all) of the adjustment plate 182. It is to be understood that any
suitable lock out mechanism may likewise be used.
[0044] When one or more chuck assembly elements are supported by
the adjustment plate 182, the upper surface of the chuck assembly
should have a suitable orientation with respect to the probes, such
as co-planar. Referring to FIG. 12, to adjust the orientation of
the chuck assembly, the positional stage 184 is extended to provide
convenient access to loosen threaded screws 240. The threaded
screws 240 interconnect the chuck to the adjustment plate 182. Next
an adjusting screw 242, such as a jack screw, is rotated to adjust
the spacing between the adjustment plate and the chuck. Then the
threaded screw 240 is tightened to rigidly secure the adjustment
plate to the chuck. The positional stage is then slid back into the
probe station and locked in place. At this point the actual
orientation of the upper surface of the chuck assembly may be
determined. Normally, the positional stage is adjusted several
times to achieve accurate orientation. Unfortunately, this trial
and error process of extending the positioning stage from the probe
station, adjusting the orientation of the upper surface of the
chuck assembly by adjusting one or more adjusting screws 242, and
repositioning the positioning stage in the probe station, may take
considerable time.
[0045] After consideration of this prolonged process of adjusting
the orientation of the upper surface of the probe assembly, the
present inventors came to the realization that loosening the
threaded screw 240 relaxes the chuck from the adjustment plate 182.
The amount of relaxation is hard to determine because the weight of
the chuck assembly would make it appear that the chuck, jack screw,
and adjustment plate are held together. Also, by adjusting the jack
screw 242 and measuring the resulting movement of the chuck
assembly provides an inaccurate result. In order to reduce the
relaxation of the chuck and the adjustment plate, the present
inventors determined that the threaded screw 240 should be
tensioned so that the chuck does not significantly relax with
respect to the adjustment plate. Referring to FIG. 13, one
technique to tension the threaded screw is to provide a set of
springs 250 under the head of the screw to provide an outwardly
pressing force thereon when the threaded screw 240 is loosened. In
this manner the relaxation between the chuck and the adjustment
plate is reduced, resulting in a more accurate estimate of the
adjustment of the orientation of the upper chuck assembly element.
This reduces the frustration experienced by the operator of the
probe station in properly orientating the chuck assembly. In
addition, by loosening the threaded screws slightly, the chuck
assembly may be more easily oriented by adjusting the jack screws
while the probe station is in its locked position within the probe
station. Thereafter, the positioning stage is extended and the
threaded screws are tightened. It is to be understood that any
structure may likewise be used to provide tension between the chuck
assembly element and the adjustment plate while allowing adjustment
of the spacing between the adjustment plate and the chuck assembly
element, or otherwise adjusting the orientation of the chuck.
[0046] Normally it is important during testing to isolate the probe
station from the earth and other nearby devices that may impose
vibrations or other movement to the probe station, and hence the
device under test. With proper isolation, the probe station may
provide more accurate measurements. Typically the probe station is
placed on a flat table having a surface somewhat larger than the
probe station itself to provide a stable surface and reduce the
likelihood of inadvertently sliding the probe station off the
table. The table includes isolation, such as pneumatic cylinders,
between the floor and the table surface. Also, it is difficult to
lift the probe station onto the table in a controlled manner that
does not damage the table and/or probe station. Further, the probe
station is prone to being damaged by being bumped.
[0047] To overcome the aforementioned limitations regarding the
size of the probe station, the present inventors came to the
realization that an integrated isolation stage, probe station, and
frame provides the desired benefits, as illustrated in FIG. 14. The
integrated isolation stage and probe station eliminates the
likelihood of the probe station falling off the isolation stage.
The top of the isolation stage may likewise form the base for the
probe station, which reduces the overall height of the probe
station, while simultaneously providing a stable support for the
probe station. To protect against inadvertently damaging the probe
station a frame at least partially surrounds the isolation stage
and the probe station.
[0048] Even with extensive shielding and guarding existing
environmental enclosures still seem to be inherently prone to low
levels of noise. After consideration of the potential sources of
noise, the present inventors determined that the construction of
the environmental control enclosure itself permits small leakage
currents to exist. Existing environmental control enclosures
include one plate screwed or otherwise attached to an adjoining
plate. In this manner, there exists a straight line path from the
interior of the environmental control enclosure to outside of the
environmental control enclosure. These joints are also prone to
misalignment and small gaps there between. The gaps, or otherwise
straight paths, provide a convenient path for leakage currents.
Referring to FIGS. 15 and 16, to overcome the limitation of this
source of leakage currents the present inventors redesigned the
environmental control enclosure to include all (or substantial
portion) joints having an overlapping characteristic. In this
manner, the number of joints that include a straight path from the
interior to the exterior of the environmental control enclosure is
substantially reduced, or otherwise eliminated.
[0049] The terms and expressions which have been employed in the
foregoing specification are used therein as terms of description
and not of limitation, and there is no intention, in the use of
such terms and expressions, of excluding equivalents of the
features shown and described or portions thereof, it being
recognized that the scope of the invention is defined and limited
only by the claims which follow.
* * * * *