United States Patent 3823836

An apparatus is provided for handling generally flat sheets such as discs or rectangles of fragile silicon. The apparatus includes a supply carrier with a plurality of ledges to hold the sheets and a withdrawing means of a vacuum chuck to lift and hold the sheets between the adjacent ledges, attached to an elevator to raise and lower the chuck, the level of which is indexed by a control to progressively higher ledge levels as the lower sheets are removed. A horizontal movement means is provided to bring the sheets clear of the supply carrier. In particular, the level control includes a spiral staircase the steps of which act as stops to hold the elevator at predetermined levels between the adjacent ledges so as to prevent the sheets from touching the carrier except when they are gently raised off of or lowered onto the ledges.

Cheney, Oliver F. (Philadelphia, PA)
Dobo, Tamas (Philadelphia, PA)
Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
414/744.1, 414/937
International Classes:
H01L21/677; (IPC1-7): B65G1/06
Field of Search:
View Patent Images:
US Patent References:
3683849COATING APPARATUS1972-08-15Atchley et al.
3158381Vacuum chuck1964-11-24Yamamura
2906239Can body side seam cooling and spraying apparatus1959-09-29Socke
2833434Article handling mechanisms1958-05-06Stover et al.

Primary Examiner:
Makay, Albert J.
Assistant Examiner:
Johnson R. B.
Attorney, Agent or Firm:
Caesar, Rivise, Bernstein & Cohen
We claim

1. An apparatus for handling of generally flat shapes, such as sheets comprising,

2. an upward facing vacuum chuck to lift and hold the shapes when the chuck is positioned and moved upwardly under the shapes,

3. an elevator assembly to raise and lower the vacuum chuck,

4. an elevator level control for indexing the chuck position to progressively higher ledge levels, and

5. horizontal movement means causing the vacuum chuck holding the shape to move horizontally to a position where the shape is clear of the supply carrier.

6. The apparatus of claim 1 wherein the deposition means comprises,

7. an upward facing vacuum chuck to lift and hold the shapes at a level over a ledge of the discharge carrier,

8. an elevator assembly to raise and lower the vacuum chuck,

9. an elevator level control for indexing the chuck position to progressively lower ledge levels,

10. movement means causing the vacuum chuck holding the shape to move horizontally to a position where the shape is above the ledge and not touching the discharge carrier such that when the vacuum chuck is lowered and the vacuum released, the shape will be deposited on the ledge,

11. The apparatus of claim 1 wherein a transfer means is included to transport the shapes from the withdrawing means to the work station comprising,

12. an upward vacuum chuck for holding the shape when presented thereto from the withdrawing means,

13. an arm holding the vacuum chuck capable of horizontal movement of the vacuum chuck from the withdrawing means to the work station to sequentially remove and deposit the shapes presented thereto.

14. The apparatus of claim 3 wherein a transfer means is added to transport the shapes from the work station to the deposition means comprising,

15. an upward vacuum chuck for holding the shape when presented thereto from the work station,

16. an arm holding the vacuum chuck capable of horizontal movement of the vacuum chuck from the work station to the work station to sequentially remove and deposit the shapes presented thereto.

17. The apparatus of claim 1 wherein the elevator level control comprises,

18. a vertical column rotatable predetermined incremental distances, and

19. a series of stops extending horizontally outwardly from the vertical column positioned to form a spiral staircase,

20. The apparatus of claim 5 wherein the vertical column is rotated the incremental distances by a ratchet and pawl.

21. The apparatus of claim 1 wherein the supply carrier comprises,

22. two parallel adjacent walls spacedly separated from each other,

23. a series of ledges on the inside surface of the walls extending into the space between the walls, the ledges being vertically spaced from each other providing open slots defined by vertically adjacent pairs of these ledges, and

24. connecting means to rigidly and spacedly connect the walls such that there is no obstruction past the center of the space between the walls in a horizontal direction at at least one end of the carrier.

25. The apparatus of claim 7 wherein the elevator level control comprises,

26. a vertical column rotatable predetermined incremental distances,

27. a series of circular rods extending outwardly horizontally from the vertical column positioned to form a spiral staircase,

28. wherein the horizontal rods are positioned to stop the rise of the elevator against which the elevator is held after its upward movement such that the vacuum chuck is positioned to lift and hold the shape in one of the slots of the supply carrier.

29. The apparatus of claim 8 wherein the vertical column is rotated the incremental distances by a ratchet and pawl.

30. The apparatus of claim 7 wherein the connecting means of the walls of the supply carrier provides no obstruction past the center of the space between the walls in a horizontal direction at both ends of the carrier, and

31. The apparatus of claim 4 wherein the transfer means from the withdrawing means to the work station and the transfer means from the work station to the deposition means, both rotate horizontally in 90° arcs from pickup to deposit.

32. The apparatus of claim 11 wherein at least one orientation means is utilized to control orientation of the shapes from the supply carrier to the discharge carrier.

33. The apparatus of claim 1 wherein at least one orientation device is utilized to control orientation of the shapes from the supply carrier to the discharge carrier.


This invention relates to an apparatus for handling sheets, particularly those of a rigid, fragile nature. More particularly, this invention relates to an apparatus to allow movement of sheets from a carrier containing a plurality of sheets to a work station where the sheet is subjected to conditioning and the subsequent removal of the sheets from the work station to a discharge carrier for storage of the sheets. The apparatus eliminates the necessity of manual handling and essentially eliminates breakage and damage to the sheets.

In particular, this invention relates to the handling of delicate sheets such as silicon wafers, glass masks, ceramic substrates and other sheets that are valuable and are easily damaged by handling in an uncontrolled manner. These sheets are typical of those employed by the electronics industry in the manufacture of various semiconductor devices such as integrated circuits, transistors and memory circuits. This apparatus provides handling for many operations including that for coating such as described in U.S. Pat. No. 3,538,883 to J. Polin on Nov. 10, 1970. It is also quite useful in handling semiconductor slices before and after the use of the brush cleaning apparatus described in U.S. Pat. No. 3,585,668 to R.J. Jaccobine, et al. on June 22, 1971. The apparatus is also useful where the sheet is to be transported to various predesignated positions on an x-y table for test purposes, such as under a high powered microscope, even though no processing is performed at this station.

More particularly, this invention relates to a withdrawing means by which the sheets are removed from a carrier by a vacuum chuck which lifts and holds the sheets in the slots between respective adjacent pairs of ledges on which the sheet was placed and then caused to move horizontally to a position where the sheet is clear of the carrier. More particularly, an embodiment of this invention relates to the level control for indexing the vertical chuck position such that the sheets do not touch the carrier after they are lifted off the ledges before removal for processing or as they are inserted into the discharge carrier after the work has been applied to the sheet. A more particular embodiment relates to a spiral staircase series of stops against which the elevator is held to position the vaccum chuck at precisely the correct level to allow safe removal or safe deposition of the sheet in or out of the carrier.

This invention furthermore relates to an improved double open ended carrier which allows the removal of the sheets for processing on either side. In addition, the construction of the ledges in an embodiment provide that essentially only the edge of the sheet rests on the ledges of the carrier thereby limiting the damage to the surface of the sheets.

Specifically, this invention relates to an improved handling system for transporting sheets to and from cleaning, testing and coating operations for sheets of various shapes, such as discs or rectangles, like fragile silicon wafers. The work performed on the wafers includes the application of a photoresist material extensively used in the electronics industry. This photoresist material is typically in the form of a viscous solvent based clear liquid coating that is applied to the sheet. After application of the liquid coating the sheet is rotated at a high speed to obtain the desired thickness of the deposition across the sheet. As the coated sheet is removed from the coating apparatus it is still tacky to the touch. The sheets are later subjected to heat to finally bake the coating. Any handling or touching of the surface coated with the unbaked photoresist material will damage the surface. Sometimes a foreign object touching the coating will remove a portion of the coating which will adhere to the foreign object. Of course, this invention is not limited to this specific use but the advantages of the invention are demonstrated by this particular usage.


During the manufacturing of semiconductors an unpredictable factor has been wafer processing. Manual handling of the wafers through the production processes using tweezers or other tools to move them to and from a work position within a station causes the wafers to be contaminated, broken, chipped or otherwise damaged. The yield from a single silicon wafer is up to 10,000 transistors.

The loss due to handling greatly affects the yield of these minute electronic components. In this highly competitive field, where piece price is extremely important to survival in the marketplace, manual handling is no longer feasible. Even limited damage around the edge of the silicon sheets is a serious problem.

The placement of larger and more sophisticated memory circuits on silicon wafers produces a more expensive sheet. The potential yield is only about ten to twenty per wafer. Damage during handling of these sheets containing the more complicated circuits by contamination or by physical damage to the wafer continues to be a major problem to the industry.

Apparatus and methods for handling treated silicon wafers have been disclosed including U.S. Pat. No. 3,645,581 to Lasch, Jr., et al. on Feb. 29, 1972, which utilize a gas bearing track structure to transport the wafers from a magazine to a centering unit and finally to the spinning and coating unit. Using this system, the wafers travel at significant speeds and if they strike a stop or a side of the track there may be significant damage to the edge of the wafer. The cross-section of the wafer is thin and impact is usually at a point thus raising the possibility of damage. In addition, the coated wafers with the unbaked photoresist material are removed using the same pneumatic system and it is easily seen how a deposit of the unbaked coating can be removed from the edge of the wafer and left as a residue on the track and the equipment. The possibility of semidried coating reaching a later coated wafer is significant and poses a threat of a rejected circuit. Small airborne particles are a major concern as the presence of a foreign object during the processing can destroy the miniturized circuit. Directionality of the circuit containing wafers is difficult to control in an air track where the part tends to spin.

Other devices have been disclosed in the past for handling various shapes including discs. These include U.S. Pat. No. 2,294,273 to E. K. Buxbaum on Aug. 25, 1942, U.S. Pat. No. 2,941,499 to E. R. Gutzmer on June 21, 1960, U.S. Pat. No. 2,881,929 to J. Lo Giffen on Apr. 14, 1959, U.S. Pat. No. 2,185,089 to A. L. Kronquest on Dec. 26, 1939, U.S. Pat. No. 3,552,584 to R. G. Heinrich on June 5, 1971, and U.S. Pat. No. 3,516,386 to G. L. Lanewehr et al. on June 23, 1970. While some methods utilize vacuum chucks, they are not useful for fragile parts and there is no indexed movement of the vacuum chuck. Typically the parts are merely stacked and are not separated from each other on shoulders as is necessary for which this invention is particularly useful.

It has also been found that any method which "shoves" the fragile silicon wafers results in damaging of the edges. In addition, any sliding of the silicon sheet on any surface abrades and removes surface particles that are a source of contamination for that wafer and subsequent wafers moving through the apparatus. A belt system for the movement of the wafers raises similar and additional difficulties.

The deficiencies and difficulties using these methods are eliminated or at least greatly improved upon by the present invention. These and additional objects are listed below.


The present invention is an apparatus for handling sheets. Specifically, it is directed to handling fragile sheets, no matter what the shape, such as silicon wafers, glass sheets and the like. This apparatus transports the sheets from one location to another during the processing or testing of the sheets.

In particular, this invention is an apparatus comprising a supply carrier in which there is a plurality of ledges designed to hold the sheets at their outermost edges on only two sides; a withdrawing means to remove the sheets, one at a time, from the carrier which does not move, from the lowest horizontal pair of ledges upwards to the highest pair of ledges on which a sheet rests; a work station capable of receiving the sheets and performing the necessary process on the sheets; a discharge carrier similar to the supply carrier capable of receiving the sheets, one at a time, on ledges; and deposition means for transfering the sheets from the transfer means onto the discharge carrier. The withdrawing means includes an upward facing vacuum chuck to lift and hold the sheets above the surface of the ledges in the carrier in the horizontal slot space between adjacent ledges; an elevator assembly to raise and lower the vacuum chuck; an elevator level control for indexing the chuck position to progressively higher ledge levels as each sheet is removed; and an apparatus causing the vacuum chuck holding the sheet to move horizontally to a position where the sheet is clear of the supply carrier. The deposition apparatus for transporting the sheets from the transfer means to the discharge carrier is similar and can work in tandem, but deposits the sheets at progressively lower ledge levels until the carrier is filled.

An object of this invention is to provide a handling system for fragile sheets which elminates the need for manual handling and virtually eliminates the possibility of damage to the fragile parts. An additional object is to provide a handling system which avoids the common causes of introduction of contaminents during the handling processes. An additional object is to provide a handling apparatus which avoids any collision with the edges of the fragile sheets inasmuch as it is the most easily damaged part of the structure. It is an additional object to provide an apparatus that avoids collision damage to sheets by firm positive guidance at all times. This positive guidance seeks to avoid all sliding contact with the handling apparatus including the carrier of the sheets.

An additional object of this invention is to provide a withdrawing apparatus which accurately and gently lifts the fragile sheet off the ledges on which it rests in the carrier and accurately moves it away from the ledges and out of the carrier without physical contact with the apparatus other than the vacuum chuck lifting from below. A more specific object is to provide an elevator and elevator level control which is adjusted to the pitch and the slot space between adjacent ledges in the carrier which in turn depends upon the thickness of the sheet to be handled such that the vacuum chuck position when picking up a sheet may be accurately indexed to avoid any contact of the sheet with the carrier. An additional object is to provide a withdrawing means to the work station, wherein the transfer mechanism also provides a ready supply of the sheets for processing.

These and other objects of the overall invention will become apparent in the following detail disclosure of the more specific embodiments.


FIG. 1 is a perspective view of a sheet handling apparatus of the present invention.

FIG. 2 is a schematic flow diagram illustrating the horizontal movement of a wafer through the entire handling apparatus shown in FIG. 1.

FIG. 3 is a front elevational view of a withdrawing and deposition apparatus of the present invention.

FIG. 4 is a closeup elevational view of a vacuum chuck holding a sheet in the center of a carrier slot in FIG. 3.

FIG. 5 is a sectional view of a carrier taken in the plane of line 5--5 of FIG. 3.

FIG. 6 is a sectional view of a carrier taken in the plane of line 6--6 of FIG. 3.

FIG. 7 is a perspective of a preferred open brace for a two sided carrier.

FIG. 8 is a sectional view along 8--8 of FIG. 3 illustrating a ratchet system controlling the movement of a spiral staircase.

FIG. 9 is a side elevational view showing the construction of a slide assembly for a withdrawing apparatus.

FIG. 10 is a schematic side elevational view of an orientation device at the work station.


Referring to FIG. 1, that portion of the apparatus actually touching the sheets to be processed is pictured. The sheets pictured are thin silicon wafers in one of the preparatory stages towards transformation into semiconductor devices. At the same time, it will be helpful to refer to FIG. 2 which schematically pictures the travel path of the discs through the apparatus. The discs are pictured on FIG. 2 as round, but they may be flattened on one or more sides in order to provide an indication of directionality. The apparatus is equally applicable for rectangular sheets and the composition of the sheets may be glass or any other suitable substance.

In this embodiment of the invention a supply carrier 1 is filled with silicon wafers resting on a series of ledges. Supply carrier 1 is placed on base 2 and at the start vertical unload arm 10 attached to vacuum chuck 11 is in the bottom vertical rest position and away from the carrier 1 along path 12. As operation begins, unload arm 10 moves horizontally along path 12 towards carrier 1 at the height of the rest position. After unload arm 10 enters into the supply carrier and under the lower wafer in carrier 1, vacuum chuck 11 is raised to an indexed level determined by an elevator level control system to be described hereinafter. This indexed level of the vacuum chuck 11 is sufficient to lift the wafer and clear the ledge surfaces on which the wafer rests. As soon as the wafer is held securely by chuck 11, as indicated by a vacuum detector, vertical unload arm 10 moves horizontally along path 12 at its index level to stop 13 at the end of path 12 away from carrier 1. For clarification, reference may be made to FIG. 2 showing the horizontal movement of chuck 11 on vertical unload arm 10 moving horizontally to stop position 13 such that a portion of the wafer is over vacuum chuck 14 attached to transfer arm 15 horizontally rotated on shaft 16 pictured on FIG. 2. Upon reaching stop 13 away from carrier 1, the vertical unload arm 10 is lowered to the bottom rest position which is chosen to place the top of vacuum chuck 11 slightly above the vacuum chuck 14 on transfer arm 15. Upon a signal that the wafer is required at work station 17 and is available from chuck 14, transfer arm is elevated on shaft 16 by a vertical cam such that vacuum chuck 14 with vacuum on contacts the wafer at a position leaving the center of the bottom face of the wafer clear. The vacuum is released from chuck 11 so that the wafer is physically transferred to vacuum chuck 14 which it is elevated above chuck 4. The transfer arm 15 rotates 90 degrees as shown on FIG. 2 to place the wafer in a centered position on vacuum chuck 18 on spindle 19 at work station 17. When spindle load transfer arm 15 moves out to spindle 19, it moves for not other reason than to carry a wafer to the spindle. Therefore, when transfer arm 15 returns to the rest position ready to receive another wafer, there should be a vacuum detected on chuck 18. If there is no vacuum detected on the spindle chuck, the wafer is presumed dropped and the apparatus is shut down. Centering of the wafer on spindle 19 is accomplished by adjustment of the stop position 13 and the degree of turn transfer arm 15, no matter what size or shape sheet is required.

The rotating arm 15 to load spindle 19 and arm 21 to unload spindle 19 are operated by cams driven by AC motors. Each time the arms move to spin spindle 19, the cam will take a full turn and stop. Once started the cam will finish the full turn without stopping. Arms 15 and 21 each have their own separate cam and motor drive. The cams also control the up and down motion of arms 15 and 21, the rotation of the arms, and control the sequencing ofthe vacuum to chucks 14 and 22 on the tips of the arms. The typical lift of the load arm 15 cam is about 3/32 inch. In the same fashion, the lift of spindle unload arm 21 cam is about 5/32 inch.

The rotary motion of the spindle load arm 15 and spindle unload arm 21 is driven by a springloaded cam follower. It is preferred that arms 15 and 21 point directly to the spindle chuck 19 at the point of maximum swing. While in rest position, both the load and unload arms should point directly to the appropriate vertical load arm 23 or unload arm 10. When orientation is necessary, however, it is more important that the arm swing exactly 90° .

At work station 17, there is pictured a coating applicator 20 for depositing on the silcon wafer a material such as photoresist coating. The amount of coating applied to the silicon wafers and the timing of the various process steps varys greatly from manufacturer to manufacturer. A typical processing time will vary from 10 to 30 seconds wherein a premeasured amount of coating liquid is applied to the wafer. The centrifical force applied to wafer spreads the liquid evenly over the surface of the wafer. The spindle 19 should be capable of a rapid acceleration to about 10,000 revolutions per minute. The construction of the work station and in particular the spin chuck and spindle is well known in the art and a typical construction useful in this apparatus is provided in U.S. Pat. No. 3,538,883 to Polin on Nov. 10, 1970. A spin motor connected to chuck 8 is used for may steps in the processing of silicon wafers to spin the photoresist and other liquids from the wafer surface and then to spin the wafer at high speeds to hasten the drying process. The spin speed and timing is controlled by each of the several process steps to the specification of the manufacturer of the electronic devices. Acceleration control of the spin motor is obtained by variation of the capacitor charge in current or other methods all well known to those skilled in the art of constructing spin coating apparatus.

During this processing time, the handling apparatus continues to operate to the point of placing a fresh wafer on arm 10 so that delay inserting a fresh wafer to work station 17 after the coated wafer is removed is minimal. This storage facility of chuck 11 greatly reduces the total cycle time per piece. When the programmed processing at the work station is completed a signal is directed to transfer unload arm 24 which moves horizontally 90° such that vacuum chuck 22 is positioned under the freshly coated wafer. A slight upward cammed movement of transfer arm 21, with the vacuum suction on, allows contact with the wafer and removal from spindle chuck 18 from which all vacuum pressure has been removed after spindle 19 has stopped rotating.

The logic of the accompanying electronic system assumes that vacuum chuck 22 has picked up the wafer, and spindle unload transfer arm 21 rotates 90° to a position where vertical carrier load arm 14 is directly under the center of the wafer. When spindle unload arm 21 moves out to spindle 19, it does so only to unload a wafer from the spindle. When arm 21 returns to rest position away from the spindle, it should transfer a wafer to vertical carrier load arm 23. Thus, a vacuum should be detected on vacuum chuck 24 on the top of vertical arm 23. Obviously, this vacuum test of the transfer cannot be made immediately since the vaccum to the detector must have time to build up on chuck 24. This delayed transfer test indicates if removal has been effected and if no vacuum is detected, the apparatus is shut down. Reference is again made to FIG. 2 showing the movement of transfer arm 21 to the work station and back to the rest position along with the flow of the wafer on the apparatus. Vertical load arm 23 is then raised to the proper level by an elevator assembly and elevator control described hereinafter. That level provides sufficient clearance above the pair of ledges in carrier 30, on which the wafer is to be placed. The level is below the ledge on which the last wafer was inserted, or in the case of the start of the operation, on the uppermost ledge. Arm 23 is then lowered gently allowing the coated wafer come to rest on the ledge contacting only the very edges of the wafer.

As wafers are transferred from point ot point in the apparatus, the electronic system associated with the apparatus is continually checking to see that the wafers are not being lost. If a wafer is dropped or if certain events occur, the system is shut down to prevent continued loss of wafers. If at any time there is a vacuum loss in any of the chucks at a time in the cycle when a wafer should be being firmly held, a signal is received directly shut down of the apparatus. After the problem is recitified, the apparatus is ready to continue at the very point in which it was stopped inasmuch as the "mechanical memory" hereinafter described maintains the exact place in the cycle before stoppage occurred. The vacuum detector system by indicating the placement of the wafers in the apparatus aids in this "memory determination."

This is the entire transport trip for a single wafer. Obviously, while one wafer is passing through a particular station, other functions are taking place such as the supply characteristics of arm 10. As arm 23 is depositing a coated wafer in carrier 30, a fresh wafer may be simultaneously removed from carrier 1 by pickup arm 10. The entire operation is synchronized such that the wafers are handled in sequence in an orderly and efficient manner.

For the processing of some sheets orientation of the piece as it leaves the handling system is unimportant, but it is becoming increasingly necessary to assure that orientation is controlled. Orientation is accomplished in a preferred embodiment of the invention by the inclusion of devices at two points: first, on the spin motor driving spindle 19 at work station 17, and, second, while the sheet is being held by vertical load arm 23 before deposition in discharge carrier 30.

An orientation device on the work station spin motor system is schematically shown on FIG. 10. In this embodiment of the orientation device, spindle 19 holding vacuum chuck 18 is extended as a hollow motor shaft (also 19) through which vacuum is supplied to through hole 150. The characteristics of spin motor 151 have been described hereinabove as controlled by tachometer system 152. On an extension of shaft 19, disc 153 of clear Plexiglas acrylic plastic sheet is firmly attached. A single black line 154 is marked as a radii. A photodetector optic sensing device 155 comprising two arms 156 and 157 which sandwich but not touch disc 153 is electrically connected to spin motor 151 power imput. As the rotation speed of shaft 19 is slowed, black line 154 is sensed between photocell 158 and light source 159, so as to stop spindle 19 at the same radial position in which it started. Thus, the sheet leaves spindle 19 oriented in the same direction as it was placed.

In this embodiment is critical that the transfer arms 15 and 21 rotate exactly 90° in the placement of sheet on and removal of sheet from spindle 19. If this is provided the sheet leaves the work station rotated exactly 180° from the orientation of entry. Where orientation is not critical the radial swing of arms 15 and 21 may vary significantly from 90° as long as other adjustments are made to insure centering of the sheet on spindle 19.

A second orientation device shown in FIG. 3 improves the accuracy of the spin motor orientation control of FIG. 10 comprising at least one air cylinder 26 with moving shaft 27 having an at least one upright soft pin 28, and at least one soft pin stop 29 up against which the sheet is oriented by moving pin 28. The total number of pins of the stops and the moving shaft are at least three with the preferred embodiment being one pin 28 on shaft 27 and two stop pins 29.

Although the embodiment hereinabove illustrates the use radial moving transfer arms 15 and 21 to load and unload spindle 19 at work station 17, they are not required for the invention. It is apparent that paths 12 and 25 may be angled directly to spindle 19 and that vertical arm 10 and vertical arm 23 may directly load spindle 19. Of course, it is necessary that vacuum chucks 11 and 24 lift up the sheets leaving the center section free so as not to interfere with the area required for work station chuck 18.


A critical stage of the operation of the apparatus handling sheets, in particular silicon wafers, is the removal from or deposition in a carrier. An embodiment of the invention utilizes carriers as shown on FIGS. 3 through 7. On FIG. 3 carriers 1 and 30 are shown as placed on base plates 2 and 31. Adjustable guides 3 and 32 insure proper allignment of the carriers.

A closeup view of vertical removal arm 10 and vacuum chuck 11 holding a wafer in position ready to be removed from carrier 1 is shown on FIG. 4. The wafer has been gently lifted off horizontal ledge pair 4 and 5 and is being firmly held in about the middle of slots 6 and 7 so as not to touch the carrier. Slot 6 is the horizontal space between adjacent ledges 4 and 8 and slot 7 is the horizontal space between adjacent ledges 5 and 9. The slots, such as 6 and 7 open toward the direction the wafer is removed from or deposited into the carrier. An important characteristic of the carriers is that the upper and lower surfaces are not horizontal. As shown on FIG. 4, upper surface 33 of the ledge is inclined downward from the horizontal toward the center of the carrier at angel 34. Similarly the bottom surface 35 of the ledge is inclined upward from the horizontal toward the center of the carrier at angle 36. These angles vary from about 1° to abut 15°. The inclined upper surface 33 allows the wafer to rest on a minimum of surface area. The inclined lower surface 35 facilitates removal of sheets without touching the carrier.

Referring to FIG. 3 and more specifically to FIG. 5, a carrier is constructed such that walls 37 and 38 are spacedly and rigidly held in position by bar 50. Bar 50 is placed such that pickup arms 10 or 23 may readily move under the center of the wafers, if desired. If the carrier is desired to be only one side up, the uppermost bars 51 and 52 are placed so as to prevent the movement of the vertical arms 10 or 23 into position. This prevents inadvertent application of coating to the wrong side of the wafer.

On the other hand, a preferred embodiment provides a carrier which will allow coating of the wafers from both sides. The construction of this improved carrier end plate is pictured in FIG. 7. This generally U-shaped brace and end plate 53 is constructed to fasten to walls 37 and 38 on faces 54 and 55. Cavity 56 is provided to allow the vertical arms 10 or 23 to enter under the center of the wafers. End plates 53 are connected at both the top and bottom of the carrier so that the wafers may be processed on both faces without the necessity of individually turning the wafers over.

The composition of the carrier is not critical to the invention. However, this invention prevents friction and abrasion of the carrier ledge surfaces. As a consequence, a highly finished, virtually indestructable carrier may be utilized such that it can withstand the high temperatures of baking the coating on the silicon wafers. Therefore, the preferred composition of the carriers useful in this invention is aluminum and other structural materials. Of course, plastics may be used without interfering with the operation of the apparatus.

The preferred carrier is symmetrical in regard to ledge and slot positioning.


Of particular importance to the apparatus of this invention, is the removal means 60 by which a wafer is removed from the carrier without damage. The requirements of means 60 is to firmly lift the wafer off a pair of ledges of carrier 1, and remove it from the carrier without damage to either the wafer or the carrier, and present it to work station 17. Referring first to FIG. 3, this horizontal view shows vertical unload arm 10 in a raised position holding a wafer ready for removal form carrier 1. Vertical unload arm 10 is a rigid hollow rod holding vacuum chuck 11 rigidly attached to elevator 70. Elevator 70 is a hollow body 71 riding up and down on track guides 72 and 73 on bearings. The elevator is raised cable 74 riding over pulley 75. Elevator body 71 is returned to the down rest position by gravity and by spring 76 attached to base plate 77. The vacuum chuck 11 is supplied through a flexible tube attached to connection 78. Inasmuch as some of the elevator lifting mechanism is hidden in FIG. 3, it is of interest to consider the essentially identical system for elevator 80 for raising and lowering vertical load arm 23 on which vacuum chuck 24 is attached. Similarly to elevator 70, elevator 80 includes hollow body 81 to which hollow rod arm 23 is rigidly attached. Body 81 rides up and down on track guide 82 and 83 on bearings 84 and 85. Elevator body 81 is raised by cable 86 attached to body 81, passing up and over pulley 87, down and around pulley 88, over and around movable pulley 89 which is attached to air cylinder slide 90, and finally attached to base plate 77, movement of slide 90 by introducing compressed air through nozzle 91 into air cylinder 92 raises elevator body 81 at a 2 to 1 ratio. Spring 93 and gravity bring body 81 back to bottom rest position.

The elevator level control 100 is a spiral staircase comprising metal column 101 from which extend a plurality of cantilever rod stops 102. These cantilever rods 102 act as positive stops preventing further upward motion of elevator body 71 by meeting should 79 on the elevator housing. Thus the radial position of column 101 controls the distance elevator 70 can move in an upward direction. The downward movement of the elevator is not restricted by the single spiral staircase. The radial position of column 101 aligns a particular rod 102 with shoulder 79 indexing the vertical position of chuck 11 to meet with and slightly lift the sheet above the corresponding ledge level of carrier 1. The position of the particular rod 102 allows the sheet to be lifted clear of the pair of ledges on which the sheet rests but prevents lifting the sheet too high such that it will touch the next higher adjacent pair of ledges. The spacing and placement of cantilever pin stops 102 depend upon the space between the adjacent ledge surfaces of carrier 1 as well as the pitch between the ledges. A typical slot space for thin silicon wafers is about 3/32 inch and a typical pitch is 1/8 inch which will provide room for about 25 wafers on an easily handleable carrier. These distances and numbers vary greatly depending upon the type of sheets to be processed. Glass plates typically require a 1/4 inch wide slot and the carrier holds about a dozen sheets.

The radial position of column 101 is moved and controlled by ratchet system 110 which includes air cylinder 111 actuated by air pressure through nozzle 51. Arm 113 moved by the air pressure moves gear 114 through a standard detent notch system, illustrated in FIG. 8. Arm 113 driven by air cylinder 111 is connected by coupler 115 to offset cam 116 connected to pawl spring 117. Position of gear 114 is controlled by spring 118 bearing against ball 119 which abutts detents 120 on the bottom of gear 114. Gear 114 is rigidly attached to column 101 such that the radial movement of the gear is identical to the radial movement of the column.

The ratchet system of radial control of the level control of this embodiment of the invention provides an advantage particularly for coating or cleaning operations on sheets such as for silicon wafers. The spiral staircase 100 is held in rigid position by ratchet system 110 thereby limiting the vertical upward travel of elevator 70. In case of power failure or the necessity of turning off machine operation, there is a built-in "mechanical memory" which does not depend on any electrical circuit. The ratchet position is left unchanged by the interruption power and upon restarting the apparatus, the power position for the elevator is not in doubt. The electronic circuit controlling the operation of the apparatus need not be supplied with a memory system or back-up power source for emergency use. The previous position of elevator 70 is determined and the apparatus will begin operating where it left off.

There are alternative methods of controlling the radial position of spiral staircase 100. These include a servo-motor which will accurately move and control the radial position with the advantage of reduced weight and space. The disadvantage of a servo-motor control is that the system has not mechanical memory in that the servo-motor will automatically return the spiral staircase 100 to the "start position."

Ratchet 120 is a stepping control which radially moves the spiral staircase and rod stops 102. In the embodiment shown, the ratchet moves one step per wafer. The apparatus may be programmed to adjust to carriers with different pitches between ledges in carrier 1 to allow for thicker wafers. For example, for handling masks for the semiconductor industry, the ratchet may be programmed to take two steps so that the elevator will move double the normal stop distance or 1/4, inch. The ratchet is activated by timed pulses typically about 0.2 seconds long.

The ratcheting typically occurs at the time the entire elevator assembly returns to the bottom rest position. When all of the wafers in supply carrier 1 have been processed, the ratchet movement which follows the last wafer will place spiral elevator 100 in a position ready to start all over again. In order to stop the operation a switch is activated by arm 103 indicating that the last wafer has been removed and the withdrawing means need not continue to hunt for wafers in the carrier. The transfer means to the work station continues as well as the deposition in the discharge carrier until it is filled. Arm 123 on spiral elevator 120 provides a similar service when the discharge carrier is full.

There is a series of systems identical to the withdrawing means described hereinabove in the typical overall handling apparatus. This part of the apparatus is referred to as the deposition means inasmuch as it provides transfer of the sheets and deposition of them on discharge carrier 30. The components are equivalent in function to those found on the unload or removal side of the apparatus including elevator 80 with its level control, the spiral staircase 120, which is radially indexed by ratchet 130. Elevator 80 is shown in the down-rest position ready to be raised by cable 86 and to be returned to the rest position by spring 93. The upward movement is restrained by abuttment of shoulder 94 against the chosen pin 122 of spiral staircase 120. The radial movement and control is provided by ratchet system 130 which is identical to that of ratchet system 110 described hereinabove. The spiral of staircase 120 is in the opposite direction to that of staircase 100.

The entire withdrawing and deposition means 60 hangs from table 140 on guide rods 141 and 142. Referring to FIG. 9, hangers 143 and 144 ride on bearings 145 and 146, which in turn ride on rod 142. Means 60 hangs in a similar way at the other end on rod 141. Movement horizontally in or out of the entire withdrawing and deposition means 60 is accomplished by air cylinder 147. This horizontal, in and out, movement of the entire means 60 provides for movement of vertical unload arm 10 along path 12 and for movement of vertical unload arm 23 along path 25.

The rest position of this elevator assembly is such that these vertical load and unload arms are at the far end of paths 12 and 25 away from the carriers. Means 60 receives instructions to move out to the carriers if either vertical unload arm 10 needs a wafer or if carrier load arm 23 has a wafer to place in the discharge carrier 30. Means 60 may also move out for both reasons at once.

It should be understood that while the present invention has been described in considerable detail with respect to specific embodiments thereof, it is not to be considered limited to those embodiments but may be used other ways without departure from the spirit of the invention or the scope of the appended claims.