Wafer softlanding system and cooperative door assembly

A wafer softlanding system and cooperative door assembly are disclosed for gently and reliably loading and unloading a batch of wafers onto and off of the floor of a processing furnace tube. The disclosed softlanding system is coupled to a wafer receiving paddle and is operable to both linearly move the paddle as a whole in Z either upwardly or downwardly and to selectively rotatably move the paddle so that it tilts about an axis as it is moved linearly up and down. A door assembly is disclosed that includes a resiliently mounted furnace closure that is operative to provide a self-seating action at the mouth of the processing furnace tube. The door assembly includes in one embodiment a vacuum door closure and in another embodiment an atmospheric process door closure. In both embodiments, the closure members are readily releasable to provide for each of interchangeability, maintenance, and differential door size accommodation.

FIELD OF THE INVENTION 
This invention is directed to the field of semiconductor wafer processing, 
and more particularly, to a novel wafer softlanding system and cooperative 
door assembly. 
BACKGROUND OF THE INVENTION 
Semiconductor wafers are batch processed in the thermal reaction chambers 
of one or more processing furnace tubes to form various thin-films and 
other structures thereon during the several phases of the integrated 
circuit fabrication process. The wafers are typically loaded into 
so-called boats provided therefor, and a boat loading mechanism is 
provided for inserting and removing plural wafer loaded boats operatively 
coupled to the boat loading mechanism into and out of the thermal reaction 
chambers. The boat loading mechanisms are called upon to be as reliable as 
is practicably possible, so that system throughput, and consequent revenue 
generation, are not thereby compromised. As the dimensions of the 
microstructures formed on the wafers become smaller, the risk of batch 
contamination proportionately increases making even comparatively small 
quantities of particulates generated during the loading and unloading 
procedures approach unacceptable limits. In view of the extremely small 
dimensions of the microstructures now capable of being fabricated by 
todays technology, such boat loading mechanisms then are further called 
upon to operate in such a way that particulate generation is either 
eliminated or constrained to a level sufficiently low to prevent the 
possibility of contaiminating the wafers being processed in the one or 
more processing furnace tubes. 
SUMMARY OF THE INVENTION 
The novel softlanding system and cooperative door assembly of the present 
invention is operative to produce little if any particulates, and has such 
a construction as to be both reliable in operation and readily 
maintainable. The present invention thus achieves a high system 
throughput, and makes possible the micro-fabrication of intended 
structures of very small dimensions on plural wafers, in one or more 
processing furnace tubes, in a manner that is substantially free from the 
deleleterious effects of particulate generation. 
The disclosed softlanding system includes a cantilevered paddle. An 
X-actuator is coupled to the paddle for moving plural wafer-loaded boats 
placed on the free end of the paddle into and out of the thermal reaction 
chamber of a processing furnace tube. A combination Z and .theta. actuator 
assembly coupled to the supported end of the cantilevered paddle is 
selectively operative in a load mode and in an unload mode to so move the 
paddle in the Z direction and in the .theta. direction as to gently place 
and remove the plural boat-loaded wafers onto and off of the floor of the 
thermal reaction chamber. In the preferred embodiment, the Z and .theta. 
motions are selected such that the paddle approaches and departs from the 
floor of the processing furnace tube at an oblique angle during 
softlanding and liftoff. Any particulate generation that would otherwise 
arise from the sticking of the plural wafer loading boats to the floor of 
the thermal reaction chamber thereby is circumvented. A door assembly is 
disclosed that is cooperative with the softlanding system to provide a 
closure at the mouth of the thermal reaction chamber except during the 
load and unload modes. Means are disclosed for removably mounting the 
closure to the door assembly, which therewith allows its ready repair and 
replacement, and the capability to accept doors of varying physical 
dimensions. Resilient means are disclosed cooperative with the removable 
mounting means for providing a self-seating action thereof. A vaccum door 
closure and an atmospheric door closure are disclosed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1, generally designated at 10 is a furnace system 
having the wafer softlanding system and cooperative door assembly of the 
present invention. The system 10 includes a furnace generally designated 
12 having a plurality of vertically stacked processing furnace tubes, not 
specifically shown, that are accessible via a corresponding one of plural 
mouths 14. A vertically stacked array of load shelves 16, corresponding in 
number to the number of processing furnace tubes, are provided in 
longitudinal alignment with the processing tubes and confronting a 
corresponding mouth 14 thereof. An X, .theta., and Z moveable wafer 
softlander 18 to be described, and cooperative electronics 20, are 
provided on each of the load shelves 16 of the furnace 12, one being 
specifically illustrated. A cantilevered paddle 22 is mounted to each of 
the wafer softlanders 18, and a scavenger shield 24 is mounted thereto 
adjacent the supported end of the cantilevered paddle 22. A door assembly 
26 to be described is mounted to the furnace 12 adjacent corresponding 
ones of the mouths 14 of the several processing furnace tubes. 
In operation and referring now to FIG. 2A, plural wafers 30 are placed on 
the cantilevered paddle 22 of the wafer softlander 18 for processing in 
the associated furnace tube. The wafers 30 are supported in a quartz 
member 32 of any suitable design that receives the several wafers and that 
receives the free end of the paddle 22. Prior to and after processing, the 
door assembly 26 is in its closed condition as illustrated. 
After the door 26 is moved into its open condition out of the mouth of the 
associated processing furnace tube, the wafer softlander 18 moves in a 
direction designated "X" for inserting the plural wafers 30 into the 
processing tube as shown in FIG. 2B. As the softlander 18 moves in the X 
direction, of the cantilevered paddle 22 therewith moves into the thermal 
reaction chamber of the processing furnace tube, and no particulates or 
other contaminates are thereby generated. The scavenger shield 24, 
illustrated dashed in FIG. 2B, is then in abutting relation with the mouth 
of the processing tube. A scavenger manifold, not shown, is typically 
provided intermediate the mouths 14 and the several processing furnace 
tubes, and the shields 24 help maintain a desired gas environment during 
loading and unloading. 
As shown in FIG. 2C, the wafer softlander 18 then moves in .theta. and in Z 
such that the cantilevered paddle 22 changes its pitch as it moves 
downwardly. In the presently preferred embodiment, the pitch is changed 
such that its free end is more downwardly inclined than its supported end 
during controlled descent, although, as appears more fully below, the 
softlander 18 is selectively operable to pitch the paddle 22 in, among 
other modes, the converse manner. The resulting motion of the cantilevered 
paddle 22 is such that the end of the support 32 remote from the 
softlander 18 softly touches down on the floor of the processing furnace 
tube before the end thereof adjacent the softlander 18. 
As shown in FIG. 2D, with continued controlled .theta. and Z movement of 
the paddle, the entire surface of the support 32 lands softly on the 
confronting wall of the floor of the processing furnace tube. As will be 
appreciated, the support 32 does not scrape along the floor of the 
processing tube during its controlled descent so that particulate 
generation thereby is either wholly eliminated or kept well within 
prescribed bounds. 
As shown in FIG. 2E, the softlander 18 then moves the paddle along the X 
axis, preferably while executing a Z, .theta. motion that is the reverse 
of that described above in connection with the description of FIGS. 2B-2D, 
out of both the support 32 and the furnace processing tube without 
touching the floor of the processing furnace tube. The door 26 is then 
moved into its closed condition, and the wafers 30 are processed in the 
furnace tube to form the intended structures thereon. 
After processing of each batch of wafers 30, the door is moved into its 
opened condition, and the softlander 18 is operative to move the paddle in 
X, .theta., and Z so as to be received in the support 32 as shown in FIG. 
2D. Thereafter, the softlander is operative to so move the paddle in 
.theta. and in Z that the support 32 is gently lifted off of the floor of 
the processing furnace tube, with the end thereof proximate the softlander 
18 being lifted off before the free end thereof as illustrated in FIG. 2C. 
It will be appreciated that the pitch of the paddle is able to break any 
sticking of the support 32 to the floor of the furnace without generating 
any significant particulates therebecause. With continued .theta. and Z 
motion, the paddle, and therewith the wafers 30 and support 32, are moved 
above the floor of the processing furnace tube as illustrated in FIG. 2B. 
Thereafter, the softlander moves in X, and therewith the batch of 
processed wafers on the paddle 22 are removed from the furnace as shown in 
FIG. 2A. It will be appreciated that the same or another process is then 
repeated on the same or on another batch of wafers. 
Referring now to FIGS. 3, 4 and 5, the softlander 18 preferably includes a 
carriage 34 slidably mounted on linear bearings 36 for reciprocating 
motion along the X direction. First and second spaced-apart upstanding 
plates 38 are fastened to the carriage 34. A shaft 40 is journaled for 
rotation in the upstanding plates 38, and first and second disks 42 (best 
seen in FIG. 5) are mounted for rotation with the shaft 40 individually 
confronting a corresponding one of the opposed surfaces of the upstanding 
plates 38. The shaft 40 is mounted for rotation with the shaft 44 of a 
motor 46 via a flexible coupling 48 and limit-switch tripping cams 50 
(best seen in FIG. 5). A phase adjusting coupling 52 is mounted in the 
shaft 40 and between the confronting surfaces of the plates 38. 
The paddle 22 is slidably received in and removably retained by a housing 
member 54, and first and second spaced upstanding plates 56 are fastened 
to the housing 54 individually confronting a corresponding one of the 
opposed surfaces of the upstanding plates 38 that are fastened to the 
carriage 34. The upstanding plates 56 each have an elongated slot 
generally designated 58 therethrough (best seen in FIG. 4) that is 
elongated in a direction generally transverse the direction of elongation 
of the upstanding plates. Posts 60 having roller bearing surfaces 61 are 
eccentrically fastened to the disks 42, and the posts 60 are individually 
slidably received in corresponding ones of the slots 58. The housing 54, 
and therewith the cantilevered paddle 22, is thereby suspended off of the 
upstanding plates 38 fastened to the carriage 34. The relative phase of 
the eccentric posts 60 is selected to control the pitch of the paddle 22 
as it controllably descends and as it controllably ascends. 
A shaft 62 is mounted to a linear bearing 64 that is fastened to the 
housing 54 at a point along its side intermediate the upstanding plates 38 
so that it extends in a direction perpendicular to the direction of 
elongation of the paddle 22. The shaft 62 is journaled for rotation in a 
plate 66 that is fastened to the confronting surfaces of the upstanding 
plates 38. The linear bearing 64 accommodates movement of the housing 54 
in the Z direction. The shaft 62 journaled in the plate 66 accommodates 
movement of the housing 54 angularly about the axis of the shaft 62 in the 
.theta. direction. 
The plates 56 have linear cam follower bearing surfaces 70, and bearing 
posts 72 that are fastened to the plates 38 follow the bearing surfaces 70 
during Z motion of the housing 54. The bearing surfaces 70 and posts 72 
stabilize the assembly during controlled Z and .theta. motion. 
The coupling 52 is adjusted such that the relative angular position of the 
posts 60 are in selected phase relation with each other. In the preferred 
embodiment, the eccentric posts 60 are so phased that the proximate post 
is in phase lead relation to the distal post for a given angular position 
of the shaft 40. As the shaft 40 is controllably rotated by the motor 46, 
the posts 60 thus gang the confronting walls of the slots 58 in such a way 
that the plates 56 are differentially driven downwardly as can best be 
seen in FIG. 4. The housing 54 therewith moves vertically downwardly on 
the linear bearing plate 64, and the housing 54 rotates about the shaft 62 
in the .theta. direction. The cantilevered paddle 22 therewith tilts about 
the axis of the shaft 62 in the .theta. direction such that its free end 
leads its supported end while it undergoes as a whole a vertical 
displacement downwardly along the Z direction. As described above in 
connection with the description of FIG. 2, with continued .theta. and Z 
motion a batch of wafers to be processed is therewith gently softlanded on 
the floor of an associated processing tube. 
By angularly rotating the motor 46 in the reverse angular direction, the 
same motion occurs but in reverse. In the latter case, the distal 
eccentric leads the proximate eccentric such that the supported end of the 
cantilevered paddle moves vertically before its free end whereby the batch 
of wafers is gently lifted-off the floor of the processing furnace tube. 
In the preferred embodiment, it may be noted that a typical displacement 
in the vertical direction is about three-fourths of an inch, that a 
typical rotation of the shaft of the motor typically subtends less than 
180! of arc, and that the pitch of the paddle is controllable 
approximately between 0 minute to +3 minute of arc. The limit switch 
tripping cams control the end points of angular travel of the shaft. It 
will be noted that the eccentrics can be selectively phased to provide any 
controlled .theta. and Z motion without departing from the inventive 
concept. 
Referring now to FIGS. 6-8A, the door assembly 26 includes an arm 74. A 
closure member generally designated 76 to be described is fastened to the 
arm 74. The arm 74 is slidably mounted on a pair of parallel shafts 78, 80 
that are fastened to a pair of spaced-apart stabilizing and tie plates 82. 
The shaft 80 is journaled for rotation in spaced apart plates 83 and is 
mounted for rotation with the shaft of a motor 84 as best seen in FIG. 8A. 
With the rotation of the motor 84 the shaft 80 rotates, and therewith the 
stabilizing and tie plates 82 pivot about the axis of the shaft 80 moving 
the door assembly 76 clockwise from its closed position to the open 
position illustrated in dashed line in FIG. 7. It will be appreciated that 
any other suitable means for pivoting the door 74 in response to rotation 
of the shaft of the motor 84, such as a rectangular shaft, can be employed 
as well without departing from the inventive concept. 
The arm 74 on its end remote from the door closure member 76 is received 
between two upstanding posts 86 that are fastened to a leg 88. The leg 88 
is fastened to a slide 90 that is slidably mounted on a shaft 92 mounted 
for rotation by a X motor 94. A stabilizing annulus 91 fastened to the 
slide 90 is mounted for sliding motion along the shaft 80. Although any 
suitable means for converting the rotary motion of the shaft 92 into 
translating motion of the slide 90 may be employed, a so-called ROHLIX 
drive 98 is preferred insofar as this type of drive slips when its motion 
is resisted, such as when the closure member 76 hits an abutment or 
otherwise is impeded in its controlled motion so that any damage that 
could otherwise result from overtravel thereof is thereby substantially 
eliminated. 
As best seen in FIGS. 1, 7, and 8A, the door assembly 26 preferably has 
three positions. A first outboard position designated 94 and illustrated 
in FIGS. 1 and 7 is provided where the door assembly 76 is located 
laterally outwardly adjacent and axially spaced from a corresponding mouth 
14 of a furnace tube so as to allow the paddle 22 free and unimpeded 
ingress thereinto and egress thereout. An inboard second position 
designated 96 and illustrated in FIGS. 7 and 8A is provided where the door 
assembly 26 is rotated inwardly and is axially confronting the processing 
furnace tube so as to provide a closure of the corresponding mouth 14. An 
axially and rotationally intermediate position designated 98 and 
illustrated in FIG. 8A is provided to allow the door to move between its 
outboard and its inboard positions 94, 96. Axial position sensors 100, 
102, 104 are responsive to the location of the arm along the X direction 
to control the motion of the door assembly. A cover 106 (FIG. 7) is 
slidably mounted in the door assembly 26 to prevent dirt, dust, and other 
contaminants from penetrating into and jamming or otherwise interferring 
with the action of the door assembly as it is controllably moved between 
its three positions. 
As shown in FIG. 8A, a first embodiment of the closure member 76 of the 
door assembly 26 includes a shaft 106 generally perpendicular to and 
mounted for rotation with the arm 74. A scavenger shield 103, preferably 
of stainless steel, is fastened to the arm 76 and concentric with the 
shaft 106, and an annulus 110 is provided surrounding and spaced from the 
shaft 106. A process tube closure 114, preferably fashioned of quartz, is 
provided with an annulus 116 that terminates in a radially outwardly 
extending flange 118. The annulus 116 is slidably mounted around the shaft 
106 and within the annulus 110. A removable abutment such as a pin 112 is 
slidably mounted through an aperture, not shown, provided therefore in the 
peripheral wall of the annulus 110 that abuts and limits the travel of the 
flange 118 of the annulus 116. A spring 120 slidably mounted on the shaft 
106 bears against the flange 118 and urges the members 112, 118 into 
abutment. The closure 114 thereby is allowed to flex about the shaft 106, 
which is advantageous insofar as this feature eliminates the need for a 
precise stopping position control while providing a self-seating action. 
The closure member 114 is able to be readily removably replaced simply by 
removing and replacing the pins 112, and different size closures for 
different size process tubes can thereby be readily accommodated. As will 
be appreciated by those skilled in the art, the embodiment of the door 
shown in FIG. 8A is particularly useful for processing furnace tubes 
running atmospheric processes. 
Referring now to FIG. 8B, generally shown at 121 is a door assembly 
particularly well-suited for vacuum processes. The door 121 includes a 
plate 122 mounted for rotation with the arm 76. A vacuum door tube closure 
124 is mounted in spaced relation to the member 122 on elongated headed 
fasteners 126 slidably mounted in apertures provided therefore in the door 
122 such that their enlarged heads abut the member 126 and their other 
ends are threadably fastened to the vacuum tube closure 124. Springs 128 
are slidably mounted on the fasteners 126 for urging the door 124 away 
from the member 122. A sealing ring 130 is mounted in an annular recess 
provided therefor in the tube closure 124 for providing an air-tight seal 
with the mouth of the processing furnace tube. The tube closure 124 in the 
embodiment of FIG. 8B, as in the embodiment of the closure of FIG. 8A, is 
able to flex, which eliminates the need for precise stopping position 
control, and provides a self-seating action. The closure 124 is readily 
replaceable by the action of the fasteners 126. 
The softlanding system of the present invention in the way that the paddle 
is tilted during lifting makes possible the gentle removal of wafers off 
of the floor of the furnace tube that may be stuck thereto as by coating 
bridges without generating any significant levels of particulates. The 
lifting motion is itself gentle, and it pries the support off of the floor 
in a controlled wedge-like manner. Because of the gentle prying release of 
the support, vibration in the paddle is reduced and in such a way that 
wafer movement is minimized. Any particulate generation that would 
otherwise be induced by a large vibration is thereby substantially 
circumvented. 
The paddle itself is not present in the thermal reaction chamber during 
processing. The lower thermal mass in the processing furnace tube results 
in quicker thermal recovery. An improved intrachamber gas flow and the 
possibility for more flexible quartzware design are further advantages 
that attend the absence of the paddle during processing. 
The cooperative door assembly that maintains the closure member at the 
mouth of the processing furnace tubes results in cleaner furnaces, no 
unwanted contaminants being admitted thereto. Further, the door assembly 
acts to better maintain the intended pressure and other conditions in the 
processing furnace tubes, and results in more uniform system operation. 
Many modifications of the presently disclosed invention will become 
apparent to those skilled in the art without departing from the scope of 
the appended claims.