Holder mechanism for simultaneously tilting and rotating a wafer cassette

A holder mechanism tilts and rotates a vertically oriented wafer-loaded cassette for proper presentation in a horizontal orientation to the robotic arm of a workstation. The mechanism includes a cassette holder, a support member, and a motor. The cassette holder has first and second supports that define orthogonal first and second planes. In two embodiments, the support member connects the cassette holder to the motor shaft and, as the motor shaft rotates, the cassette holder is rotated about a single pivot axis that is oblique to the first and second planes. This rotation tilts a cassette placed in the holder through a tilt angle of about 45.degree. to 90.degree., and simultaneous rotates the cassette through an angle .theta. about the vertical axis. The support member shape determines whether tilting and rotation is away from or toward the motor, and also determines the angle of rotation .theta. and the tilt angle. After workstation processing, the motor rotates in the opposite direction to produce a counter-tilt and counter-rotation that returns the cassette to a vertical orientation. In a third embodiment, the support member is coupled to a horizontal shaft that is coupled to a worm gear assembly. Vertical motor shaft rotation rotates the horizontal shaft through a tilt angle, and simultaneously rotates the cassette holder through the rotation angle .theta..

FIELD OF THE INVENTION 
The present invention relates generally to handling semiconductor wafers 
during fabrication, and more specifically to an automated mechanism for 
tilting and rotating a wafer cassette when it is holding semiconductor 
wafers. 
BACKGROUND OF THE INVENTION 
Integrated circuits ("IC's") and discrete semiconductor devices such as 
transistors are fabricated on substrate wafers. Using techniques well 
known in the art, raw silicon is refined and grown into a single-crystal 
cylinder (known in the art as a "boule") whose diameter may range from 
about 4" to 12" or more. The cylinder is then sliced into a plurality of 
single-crystal wafers that are lapped, chemically etched and polished to 
form finished wafers. 
The finished wafers serve as the starting substrate upon which various 
semiconductor devices and integrated circuits may be formed. During their 
fabrication and subsequent handling, the wafers are loaded into a cassette 
that typically can hold up to 25 wafers. FIGS. 1A and 1B depict a cassette 
2 respectively in vertical and horizontal orientations loaded with wafers 
4. 
As used herein when the wafers are vertically oriented as shown in FIG. 1A, 
the cassette is said to be vertically oriented, and when the wafers are 
horizontally oriented as shown in FIG. 1B, the cassette is said to be 
horizontally oriented. An "arrow marker" 6 is shown in FIG. 1B to ease 
following the change in orientation and rotation of the cassette. It will 
be recognized, though, that actual cassettes probably will not include 
such an arrow marker. 
Cassette 2 in FIGS. 1A and 1B is a representation of an actual cassette, 
although most cassettes can hold up to 25 finished wafers. For ease of 
illustration, cassette 2 is depicted as having the capacity to hold 9 
rather than 25 wafers. Only six finished wafers are shown to illustrate 
that it is not necessary that all of the wafer positions be used. 
Formation of semiconductor devices and ICs upon the finished wafers occurs 
at a semiconductor fabrication facility, referred to in the art as a 
"fab". A modern fab can include 150 work stations, at which the wafers 
undergo specific processes, e.g., introduction of dopant materials, 
formation of oxides, etching, wafer sorting, and so forth. FIG. 2 depicts 
a generic fab 8 as including a number of workstations WS1, WS2, WS3. 
Associated with each workstation is at least one robotic arm mechanism 12, 
often referred to as an "end effector" or "extractor". In general, 
mechanism 12 unloads wafers from a cassette and reloads the wafers into 
the cassette after processing at the workstation. 
Wafers to be treated are typically transported between workstations in a 
cassette. To protect the wafers against spillage, the wafer-loaded 
cassettes are moved between workstations in a vertical orientation as 
shown in FIG. 1A. This inter-workstation orientation is depicted in FIG. 2 
by vertically-oriented cassettes 2-V, which hold wafers 4-V, the "V" 
notation indicating the vertical orientation of the cassette. In the 
present state of the art, the vertically oriented wafer-loaded cassettes 
typically are hand-carried between workstations by human operators. 
The workstations have a generally horizontal work surface 10 upon which one 
or more wafer-loaded cassettes 4 are placed in a horizontal orientation, 
such as shown in FIG. 1B. Robotic arm 12 then withdraws a horizontally 
oriented wafer, e.g., wafer 4-H, from a generally horizontally oriented 
cassette, e.g., cassette 2-H, the "H" notation indicating the horizontal 
orientation. 
The robotic arm then moves the wafer into a working position at the 
workstation for processing. Workstation WS1, for example, is depicted as 
including mechanism denoted as WS1-P1 that performs a specific procedure 
upon each horizontally oriented wafer 4-H in a cassette 2-H. Workstation 
WS2 is shown as generically including two mechanisms, WS2-P1 and WS2-P2, 
that each perform a process upon the horizontally oriented wafers at that 
station. 
Thus, at each workstation the cassette must be tilted from a vertical 
orientation required for safe wafer handling between workstations, to a 
generally horizontal orientation required by a workstation robotic arm. 
Generally, the required tilt angle will be about 90.degree.. In addition, 
once horizontally oriented, it will usually be necessary to rotate the 
wafer-loaded cassette through some angle .theta. about the vertical Z-axis 
for proper presentation of the wafers to the robotic arm. The rotation 
angle .theta. will generally range from about 0.degree. to 90.degree.. 
Mechanical guides 14 that are attached to the horizontal workstation 
surface 10 can assist the operator in achieving the necessary degree of 
rotation about the vertical axis. 
In a present-day fab, a small percentage (perhaps 10%) of the workstations 
may include a mechanism that receives the cassette in a vertical 
orientation and tilts the holder 90.degree. into a horizontal orientation. 
However, the majority of workstations require that the human operator 
carrying the cassette, manually tilt the cassette approximately 90.degree. 
(to achieve a horizontal orientation) and also rotate the cassette some 
angle .theta. about the vertical axis to achieve a proper orientation for 
the robotic arm to access the now horizontally oriented wafers. 
Unfortunately, manually tilting and rotating a wafer-loaded cassette can be 
ergonometrically challenging. Fab procedures dictate not only minimum 
clean room standards, but also minimum ergonometric standards for the 
human operators who hand-carry cassettes. A cassette fully loaded with 
wafers can present a sufficiently heavy load that precludes tilting 
90.degree. and rotating through an angle .theta., in a sound ergometric 
manner. For example, a cassette containing 25 12" diameter wafers can 
weigh perhaps 20 pounds (9 Kg). In the future, when even larger diameter 
cylinders can be grown, manually tilting and rotating a fully loaded 
cassette may not be ergonometrically feasible. In addition, at some 
workstations, the space in which the wafer-loaded cassette must be tilted 
and rotated may be quite limited. Such space limitations can further 
hamper operator maneuverability in tilting and rotating a loaded cassette. 
In future fabs, it is likely that an automated conveyer belt will replace 
human operators in transporting the cassettes, in a vertical orientation, 
from workstation to workstation. However, upon arrival at the majority of 
the workstations, the wafer-loaded cassettes will still have to be tilted 
90.degree. into a horizontal orientation and then be rotated some angle 
.theta. about the vertical axis. Upon completion of processing at a given 
workstation, the cassette must then be tilted 90.degree. from a horizontal 
to a vertical orientation, counter-rotated through an angle -.theta. about 
the vertical axis, and then returned to the conveyor belt. 
In summary, there is a need for a mechanism that can tilt a wafer-loaded 
cassette approximately 90.degree. from a generally vertical to generally 
horizontal orientation. Such mechanism should simultaneously rotate the 
cassette through a desired angle .theta. about the vertical axis for 
proper presentation of the wafers to the robotic arm of a workstation. 
After workstation processing is complete, the mechanism should receive the 
horizontally oriented cassette, and then provide a counter-tilt and 
counter-rotation of -.theta. about the vertical axis, and counter-tilt the 
holder approximately 90.degree., returning the cassette to a vertical 
orientation. Preferably such mechanism should not require excessive 
workstation space for implementation and operation. 
The present invention discloses such a mechanism. 
SUMMARY OF THE INVENTION 
In one aspect, a mechanism for tilting and rotating a wafer-loaded cassette 
includes a cassette holder, a support member, and a motor. The cassette 
holder has first and second supports that define orthogonal first and 
second planes. The support member mechanically connects the cassette 
holder to the motor shaft. As the motor shaft rotates, the cassette holder 
is rotated about a single pivot axis that is oblique to the first and 
second planes. 
Rotating the holder about the single pivot axis results in simultaneous 
tilting of a cassette placed in the holder through a tilt angle, and 
rotation of the cassette through an angle .theta. about the vertical axis. 
The shape of the support member determines the magnitude of the rotation 
angle and the tilt angle resulting from a given amount of motor shaft 
rotation. Further, the shape of the support member governs whether tilting 
and rotation movement is away from or toward the motor. 
In a second aspect, a mechanism for tilting and rotating a wafer-loaded 
cassette advantageously may be constructed beneath the surface of a 
workstation. The mechanism includes a cassette holder providing first and 
second supports defining orthogonal first and second planes, a support 
member, and a motor. Vertical motor shaft rotation is converted through 
pulleys and belts, a bearing unit and a worm gear assembly into rotation 
of a horizontal axis connected to the support member through a tilt angle, 
and into simultaneous rotation of the cassette holder through a desired 
angle .theta. about the vertical axis. 
With either aspect, semiconductor wafers placed in the cassette may be 
carried in a vertical orientation from workstation to workstation, and 
then placed in the cassette holder. The present invention then 
simultaneously tilts the cassette and wafers therein through a tilt angle 
ranging from about 45.degree. to 90.degree. from a vertical to a generally 
horizontal orientation, and also rotates the cassette through an angle 
.theta. ranging from about 0.degree. to 90.degree. for proper wafer 
presentation to a robotic arm associated with the workstation. 
In a third aspect, a workstation is constructed to include at least two 
mechanisms for simultaneously tilting and rotating a wafer-loaded 
cassette. 
Other features and advantages of the invention will appear from the 
following description in which the preferred embodiments have been set 
forth in detail, in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIGS. 3A and 3B depict a first embodiment of the present invention. In FIG. 
3A, a cassette 2 loaded with wafers 4 (only two of which are shown for 
ease of illustration) is shown placed in a vertical orientation on a 
tilt/rotation rotation mechanism 20 of the present invention. For ease of 
illustration, the slots that define the wafer holding positions in 
cassette 2 are not drawn. In the figures, the X-axis and Y-axis together 
define a horizontal plane, and the Z-axis denotes the vertical dimension. 
Mechanism 20 includes a cassette holder 22 having a support member 32, and 
a motor 24 that rotates holder 22 about a single pivot axis represented by 
26. In FIGS. 3A and 3B, mechanism 20 is shown on a planar and typically 
horizontal surface 10 of a workstation WS that includes a robotic arm, 
shown generically as 12. Robotic arm 12 can withdraw wafers 4 from 
cassette 2 if the wafers are in a generally horizontal orientation and if 
the cassette has been rotated through an angle .theta. about the Z-axis so 
that the wafer edges face the robotic arm. It is the purpose of mechanism 
20 to provide such wafer tilting and rotation in a simultaneous fashion. 
Cassette holder 22 includes a first support 28 and a second support 30 that 
define respective orthogonal first and second planes. In the embodiment of 
FIG. 3A, the first and second supports are planar, and the first and 
second planes are thus coincident with these planar support surfaces. In 
general, supports 28 and/or 30 need not be planar as shown in the figures. 
For example, supports 28 and/or 30 could comprise two or more fork-like 
tines against which cassette 2 may be supported. However, even if the 
supports are substantially planar, they may include indentations, 
mechanical stops or other features (not shown) that can assist rapid 
manual or mechanical placement of a cassette on holder 22. 
The single pivot axis 26 is oblique to the first and second planes. By 
"oblique" it is meant that axis 26 is not parallel to either of the 
planes. In FIG. 3A, the pivot axis 26 traverses cassette 2 somewhat 
diagonally, going from approximately the lower right corner to 
approximately the upper rear corner. 
In the embodiment of FIGS. 3A and 3B, cassette holder 22 includes a rigidly 
attached support member 32 that is inclined at an angle .PHI. relative to 
the first plane. The intersection of the inclined portion 34 of support 
member 32 and a longitudinal axis of the first plane defines an angle 
.beta.. If desired, supports 28, 30 and support member 32 may be 
integrally formed, for example from a single piece of metal or from molded 
plastic. Motor 24 includes a rotatable shaft 36 that is fixedly attached 
to the distal portion of support member 32, and whose rotational axis 
defines pivot axis 26. 
Proper selection of support member 32 angles .PHI. and .beta. will cause 
rotation of holder 22 about pivot axis 26 through an angle .omega., to 
produce a desired amount of simultaneous tilting and rotation. Generally, 
if .PHI.&gt;90.degree. holder 22 will be tilted and rotated away from the 
motor (as is the case for the embodiment of FIGS. 3A and 3B). Thus in FIG. 
3B, after tilting and rotation have occurred, holder 22 faces generally to 
the left, whereas the motor 24 is disposed to the right. The amount of 
time required for the simultaneous tilting and rotation about axis 26 
preferably is in the range of a few seconds to perhaps ten seconds, and 
depends upon the motor speed. Tilting and rotating the cassette holder too 
rapidly may cause the wafers to fall out or be otherwise damaged, and 
tilting and rotating too slowly will needlessly waste time. 
The orientation of pivot axis 26 relative to cassette 2 affects the volume 
of work space needed to tilt and rotate the cassette. For example, if 
pivot axis 26 traverses the geometric center of the cassette 2, the volume 
of space required to achieve the desired tilting/rotation is minimized. 
For some workstations, the volume of work space available for the 
tilting/rotation action may dictate the design of mechanism 20. 
When the motor is energized, e.g., by applying operating voltage, motor 
shaft 36 will rotate cassette holder 22 and a supported cassette 2 and 
wafers 4 through an angle .omega. about the pivot axis 26. In an 
implementation of this preferred embodiment, .PHI..apprxeq.105.degree., 
.beta..apprxeq.15.degree.. As a result, a motor shaft rotation 
.omega..apprxeq.90.degree. produces approximately 90.degree. of tilt, and 
approximately .theta.=30.degree. simultaneous rotation about the Z-axis 
Because .PHI.&gt;90.degree., tilting and rotation will cause holder 22 to 
move away from the motor, as shown by FIG. 3B. In the embodiment of FIGS. 
3A and 3B, motor 24 preferably produces a shaft rotation of about 5 
revolutions/minute. 
Of course support member angles .PHI. and/or .beta. may be varied to 
produce different results. For example, the tilt angle need not be 
precisely 90.degree. and may range from about 45.degree. to about 
90.degree.. The precise tilt angle will depend upon the workstation 
configuration, including the plane of surface 10, which may not be 
precisely horizontal. The necessary rotation angle .theta. may range from 
about 0.degree. to about 90.degree., and typically depends upon robotic 
arm 12 and the number of cassettes present at the workstation. 
After rotation through angle .omega. about pivot axis 26, wafers 4 will be 
in a substantially horizontal orientation and will have a desired 
alignment angle .theta., as shown in FIG. 3B. This orientation and 
alignment is chosen to permit mechanical removal of the wafers from the 
cassette by the robotic arm, to facilitate processing of the wafers at the 
workstation. 
After processing at workstation WS is complete, robotic arm 12 will 
mechanically return the wafers, one at a time, to cassette 2, which is 
still in the horizontal orientation of FIG. 3B. Motor 24 is then energized 
to produce rotation in the opposite direction, e.g., through -.omega., 
about the pivot axis 26. Preferably motor 24 is a direct current motor, 
and counter-rotation may be produced by reversing the polarity of the 
power source coupled to the motor. 
The result of this counter-rotation is that holder 22, cassette 2 and 
wafers 4 are rotated through an angle -.theta. about the Z-axis, and are 
tilted approximately -90.degree.. Thus, holder 22, cassette 2 and wafers 4 
are together returned to the substantially vertical orientation of FIG. 
3A. A human operator (or mechanical device) may then remove the 
wafer-loaded cassette 2 from holder 22 for conveyance to another 
workstation. At such other workstation, the vertically oriented cassette 
may be placed in a similar mechanism 20, according to the present 
invention, for tilting and rotation, as required by that workstation. 
In the embodiment of FIGS. 3A and 3B, motor 24 is attached to motor mount 
members 38 and 40 that are inclined at the angle .theta. relative to each 
other. In the preferred embodiment, mount members 38 and 40 are integrally 
formed from a sheet of metal that is bent along a fold-line 42 to define 
the angle .PHI.. As such, motor shaft 36 extends orthogonally from mount 
member 40 and extends orthogonally into the distal portion of support 
member 38. Mount member 38 may be secured to the workstation surface 10 
using screws 44 or the like. 
As noted, in the embodiment of FIGS. 3A and 3B, .PHI.&gt;90.degree. and 
tilting/rotation moves the holder and cassette away from the motor. This 
embodiment is convenient for use with workstations that provide sufficient 
space to the right of the cassette holder for a drive motor, but not to 
the left. However, space restrictions at other workstations may require 
that the motor be mounted to the left of the cassette holder, and that the 
cassette rotate toward the motor. As described below, FIGS. 4A and 4B 
depict such an alternate embodiment. 
The embodiment of FIGS. 4A and 4B is similar in several aspects to the 
above-described first embodiment. In each embodiment, a mechanism 20 
includes a cassette holder 22, and a motor 24 that rotates holder 22 about 
a single pivot axis 26. In FIGS. 4A and 4B, it is the function of 
mechanism 20 to simultaneously tilt and rotate a wafer-loaded cassette 2 
to permit a robotic arm 12 to access wafers 4 within the cassette. Unlike 
the first embodiment, in FIGS. 4A and 4B, the simultaneous 
tilting/rotation action moves the cassette holder toward the motor. As 
such, the embodiment of FIGS. 4A and 4B may be required if the workstation 
configuration dictates mounting the motor such that there is insufficient 
space to the left of the motor through which the holder may be tilted and 
rotated. 
More specifically, in the embodiment of FIGS. 4A and 4B, the motor is 
disposed to the left of the cassette holder 22, and is mounted to the 
generally horizontal surface 10 of the workstation WS using a bracket 50 
and screws, or the like, 52. Rotation of the motor shaft 36 causes holder 
22 to simultaneously tilt and rotate, toward the motor, as shown in FIG. 
4B. 
To facilitate such tilting and rotation, a support member 32 is rigidly 
attached to support 28. Support member 32 comprises first and second 
elements 56, 54, respectively between which is defined an angle .PHI.. 
Further, second element 56 defines an angle .beta. in the X-Y plane 
relative to a longitudinal axis of the first plane. Analogously to what 
was described with respect to the first embodiment, the magnitude of 
angles .PHI. and .beta. determine the amount of tilt angle and rotation 
.theta. that will result from a given amount of motor shaft rotation 
.omega.. Further, if .PHI.&lt;90.degree., tilting and rotation about pivot 
axis 26 will move cassette 2 toward the motor (as shown in FIG. 4B). 
Support member 32 elements 54 and 56 may be integrally formed with each 
other and with cassette holder 22, using metal, or plastic, among other 
materials. The shaft 36 of motor 24 is attached orthogonally to the distal 
portion of element 54. 
Rotation of the motor shaft 36 through an angle .omega. will rotate 
cassette holder 22, cassette 2 and wafers 4 therein about the single pivot 
axis 26. 
In the preferred embodiment, .PHI..apprxeq.75.degree., 
.beta..apprxeq.15.degree.. Rotation of motor shaft 36 through an angle 
.omega..apprxeq.90.degree. simultaneously tilts cassette holder 22 
substantially 90.degree. (from the vertical orientation of FIG. 4A to the 
horizontal orientation of FIG. 4B) and produces a .theta. rotation about 
the Z-axis of about 30.degree.. 
Motor shaft 36 preferably rotates at about 5 revolution/minute and the 
simultaneous tilting and rotation may be accomplished in a period of time 
ranging from several seconds to perhaps ten seconds. Depending upon the 
workstation configuration, the tilt angle required may range from about 
45.degree. to 90.degree., and the rotation angle .theta. may vary from 
about 0.degree. to about 90.degree.. Of course different amounts of 
tilting and/or rotation may be achieved by varying .PHI. and/or .beta. to 
thus change the relationship of support member elements 54 and 56. 
After such tilting and rotation, cassette 2 will be in the substantially 
horizontal orientation shown in FIG. 4B, and will have been rotated 
through a required angle .theta.. So oriented, the wafers 4 within the 
cassette may now be mechanically removed from cassette 2 by robotic arm 12 
for processing at the workstation. 
After workstation processing, robotic arm 12 will return the processed 
wafers to the cassette, which is still in the horizontal orientation shown 
in FIG. 4B. The motor 24 is then energized to produce a counter-rotation 
of -.omega., which results in a horizontal-to-vertical tilt reorientation 
and a counter-rotation -.theta. about the Z-axis. The cassette is thus 
returned to the vertical orientation of FIG. 4A, and may be removed 
manually or otherwise from holder 22 and safely conveyed to another 
workstation. 
Although the embodiments of FIGS. 3A and 3B, and 4A and 4B provide design 
flexibility in locating the motor on the right or left side of the 
cassette holder, neither embodiment readily permits locating the motor 
below the horizontal surface 10 of the workstation WS. In the embodiment 
of FIGS. 3A and 3B, for example, although motor 24 could be mounted 
beneath surface 10, the shaft 36 would extend from surface 10 at an angle 
of about 75.degree. (e.g., the complement of .PHI.). Further, the extended 
shaft length might have to be 10" (25.4 cm) or more to provide the 
necessary volume of work space through which the cassette holder is tilted 
and rotated. The resultant shaft length may project over more workstation 
space than is available and could also create excessive torque 
requirements for motor 24. 
As noted, while the embodiments of FIGS. 3A-3B, and 4A-4B provide 
flexibility in controlling whether tilting and rotation motion is away 
from or toward the motor, it is difficult to implement these embodiments 
and locate the motor beneath the workstation surface. This problem of 
locating the motor beneath the workstation surface is addressed by the 
third embodiment of the present invention depicted in FIG. 5. 
In FIG. 5, mechanism 20 simultaneously tilts and rotates a cassette 2 
loaded with wafers 4. However, in contrast to the embodiments of FIGS. 
3A-4B, in this third embodiment motor 24 is located beneath surface 10 of 
a workstation WS. The workstation WS and its robotic arm 12 are shown in 
phantom in FIG. 5 as they are drawn in perspective, whereas mechanism 20 
is depicted in a frontal cross-sectional view. 
In FIG. 5, cassette 2 is shown in a horizontal orientation, with the plane 
of the wafers 4 normal to the printed page. Mechanism 20 includes a 
cassette holder 22, a motor 24, and assorted pulleys, belts, shafts and 
worm gear mechanism, described below. As in the embodiments of FIGS. 
3A-4B, holder 22 includes supports 28 and 30 that define orthogonal first 
and second planes. A support member 32 may be integrally formed with 
holder 22. 
Mechanism 20 further includes a vertical shaft 60 and a horizontal shaft 
62. Rotation of motor shaft 36 is coupled by pulley 64 and pulley belt 66 
to pulley 68, causing rotation of vertical shaft 60. The rotation of 
vertical shaft 60 is coupled to a reduction worm gear assembly 70 that 
rotates horizontal shaft 62 through the necessary tilt angle, typically 
45.degree. to about 90.degree.. 
As shown in FIG. 5, a pulley 72 is also coupled to the vertical shaft 60, 
whose rotation is carried by pulley belt 74 to a pulley 76. The lower end 
of pulley 76 is rigidly attached to the housing of motor 24. The upper end 
of pulley 76 is rotatably and coaxially attached to a bearing unit and 
support cylinder 78. The upper end of the bearing unit and support 
cylinder 78 is fixedly attached to a preferably circular support plate 80 
that is free to rotate in the X-Y plane about the vertical axis of motor 
shaft 36. 
Rotation of motor shaft 36 causes rotation of vertical shaft 60. The 
rotation of vertical shaft 60 is then coupled by pulley 72, belt 74 and 
pulley 76 to the bearing unit and support cylinder 78. As shown in FIG. 5, 
motor 24 is fixedly attached to the workstation by motor mount member 82. 
As a result, the support plate 80, and thus pulleys 64, 68, 72, 76, pulley 
belts 66, 74, bearing unit and support cylinder 78 and support plate 80 
all rotate through an angle .theta. in the X-Y plane, about the vertical 
axis of motor shaft 36. 
The rotating support plate 80 may protrude through a circular opening in 
the surface 10 of the workstation and be flush with surface 10. 
Alternatively, as shown in FIG. 5, support plate 80 may be disposed below 
surface 10, and an arcuate-shaped opening 84 may be formed in surface 10. 
Vertical shaft 10 protrudes through opening 84, to be moved in an arc 
through the rotation angle .theta. about the axis of motor shaft 36. 
As noted above, rotation of vertical shaft 60 also produces tilting of 
cassette holder 22 through a desired tilt angle, due to the action of worm 
gear assembly 70 upon the horizontal shaft 62. The resultant simultaneous 
tilting and rotation action tilts cassette holder 22 through a tilt angle 
that typically is in the range of about 45.degree. to 90.degree., and 
produces a rotation about the Z-axis through an angle .theta. that ranges 
from about 0.degree. to about 90.degree.. 
In the preferred embodiment, the shaft 36 of motor 24 rotates at about 100 
revolutions/minute, and worm gear assembly 70 has a reduction of about 
15:1, although other motor speeds and reduction ratios could of course be 
used. The resultant simultaneous tilting and rotation of cassette holder 
22 preferably takes from a few seconds to perhaps ten seconds to complete. 
In addition to providing a configuration most of which may be disposed 
beneath the workstation surface 10, the embodiment of FIG. 5 minimizes the 
volume of space required as the cassette 2 is tilted and rotated, as 
contrasted to the embodiments of FIGS. 3A-4B. Although FIG. 5 depicts the 
motor axis 36 as roughly bisecting the horizontal width of support 30, the 
length of horizontal shaft 62 may be changed to produce a non-bisecting 
configuration. Similarly, although horizontal shaft 62 could bisect the 
vertical length of support 28, such need not be the case (as indeed FIG. 5 
indicates). 
After mechanism 20 has tilted and rotated cassette holder 22 into a 
horizontal orientation, a robotic arm 12 associated with workstation WS 
removes the wafers 4 from cassette 2 for processing. After workstation 
processing, robotic arm 12 returns the wafers to cassette 2, and motor 24 
is energized to rotate shaft 36 in the opposite direction. This 
counter-rotation produces a counter-tilt and counter-rotation that returns 
cassette 2 to a vertical orientation, such as was shown in FIG. 1A. 
To recapitulate, any of the embodiments of FIGS. 3A-5 may be used in 
existing fabs in which wafer-loaded cassettes 2 will have been carried in 
a vertical orientation to the workstation and placed on cassette holder 22 
by a human operator. However, the various embodiments of the present 
invention may also be used in future fabs, in which an automatic conveyor 
belt will convey vertically oriented wafer-loaded cassettes from 
workstation to workstation. In such fabs, once the wafer-loaded cassettes 
have been conveyed to a workstation, they can be automatically and 
mechanically removed from the conveyor and may be mechanically placed upon 
a holder 22, according to the present invention. 
Although the various embodiments of the present invention may be 
retrofitted to existing workstations, it is also intended that 
workstations WS be constructed to include the present invention. FIG. 6, 
for example, depicts a workstation WS constructed to include mechanism 20 
and mechanism 20' for tilting and rotation wafer-loaded cassettes 2 and 
2', respectively. Shown generically are WS-P1 and WS-P2, representing 
procedures that may be carried out at the workstation upon a wafer 4 that 
has been removed from cassette 2 or 2' by robotic arm 12. 
Generally each mechanism 20, 20' will tilt a cassette through the same tilt 
angle, although individual tilt angles may also be provided. Typically 
each mechanism will require a different angle of rotation, depending upon 
the configuration of the workstation. Thus, as shown in FIG. 6, mechanism 
20 may rotate cassette 2 through angle .theta., whereas mechanism 20' may 
rotate cassette 2' through a different angle .theta.'. 
Rotational power to the various mechanisms 20, 20' may be energized 
sequentially or simultaneously and in some configurations, rotation from a 
single motor may be coupled to rotate more than one mechanism. Although 
FIG. 6 depicts two mechanisms 20 and 20' that are identical, e.g., each is 
the embodiment of FIG. 5, if desired each mechanism could be implemented 
with a different embodiment of the present invention. Finally, although 
FIG. 6 shows a workstation constructed to include two mechanisms according 
to the present invention, a different number of mechanisms may be 
provided. Modifications and variations may be made to the disclosed 
embodiments without departing from the subject and spirit of the invention 
as defined by the following claims.