The present invention relates in general to semiconductor wafer treatment systems and in particular to systems including apparatus and methods for transferring wafers to and from a process chamber.
Semiconductor wafer treatment systems, including wafer handling systems therefor, are well known in the art. Such systems typically employ automated pickup elements for delivering unprocessed wafers to a process chamber and removing processed wafers from the process chamber. While generally effective, presently existing wafer handling systems may encounter difficulty when their pickups fail to positively grip a wafer and deliver it to the process chamber. Wafer grip failures sometimes arise from excessive gaps between the gripping members of the pickups and the faces of the wafers to be treated. The gaps frequently occur because the wafers assume inconsistent out-of-vertical positions in the cassettes in which they reside. That is to say, because of slot tolerances in the cassettes which are necessary to permit unhindered insertion of the wafers into and withdrawal of the wafers from the cassettes, some wafers may lean in one direction whereas others may lean in the opposite direction. As a consequence, the pickup element may not be able to grip certain ones of the wafers. Such grip failures can result in incomplete or improper processing of a batch of wafers, thereby resulting in less than optimum wafer treatment efficiency.
An advantage exists, therefore, for a wafer handling system including apparatus and methods for simply and reliably gripping wafers and placing them into and removing them from a processing chamber.
The present invention provides a system including apparatus and methods for effectively treating semiconductor wafers. The apparatus includes a load lock chamber in communication with a process chamber. The load lock chamber is connected to a vacuum pump whereby a vacuum may be drawn inside the chamber as a precursor to wafer treatment in the process chamber. Accordingly to a preferred embodiment, a carousel located in the load lock chamber carries a plurality of radially directed cradles, each of which is adapted to receive a wafer-containing cassette. The cradles are sloped or canted with respect to horizontal. As a consequence, the wafers contained in the cassettes are urged by gravity to lean in a desired justified position.
A multiaxial transfer unit picks up wafers from the cassettes and delivers them to the process chamber for treatment after which they are returned to the cassettes. The multiaxial transfer unit comprises cooperating x-axis and z-axis transfer mechanisms. The z-axis transfer mechanism is inclined with respect to vertical at an angle substantially equal to the angle of slope of the cradles whereby the x-axis transfer mechanism is correspondingly sloped with respect to horizontal to extend substantially parallel to the cradles. Because all of the wafers are justified, i.e., lean in the same direction and essentially to the same degree in their cassette slots, the wafers present essentially uniformly inclined and stable surfaces that a wafer pickup element or end effector carried by the x-axis transfer mechanism can reliably capture and release in order to consistently remove and replace the wafers from and into the cassettes.
A method of wafer treatment is also provided which capitalizes on the beneficial features of the wafer handling apparatus according to the invention.
Other details, objects and advantages of the present invention will become apparent as the following description of the presently preferred embodiments and presently preferred methods of practicing the invention proceeds.
The invention will become more readily apparent from the following description of preferred embodiments thereof shown, by way of example only, in the accompanying drawings wherein:
Referring to the drawings wherein like or similar references indicate like or similar elements throughout the several views, there is shown in
Referring in particular to
Removably received in each cradle 24 is a slotted cassette 30 which is adapted to hold a plurality of wafers “W”, e.g., twenty-five for standard cassettes, although the cassettes may hold more or less as may be desired or necessary. According to the invention, cradles 24, and thus the cassettes received therein are sloped at an acute angle “A” with respect to horizontal. Although not limited thereto, angle “A” may range from about 2°-10°, with a preferred angle being about 3°-5°. It has been observed that cradles pitched at such an angle provide wafer justification sufficient to enable reliable withdrawal of wafers from and insertion of wafers into cassettes 30 as described in greater detail below. Further, although shown as being downwardly sloped or canted from their proximal to their distal ends, it will be appreciated that the cradle slope may be reversed, i.e., the cradles may be upwardly sloped from their proximal to distal ends.
The load lock chamber 12 further includes a multiaxial Cartesian carrier or transfer unit 32 which is capable of effectuating reciprocating movement of an end effector 34, discussed below, along “X” and “Z” axes. A suitable transfer unit for this purpose may be obtained from Bell-Everman, Inc. of Goleta, Calif. Unit 32 includes a first beam 36 that is secured by spacer means 38 to a ceiling plate 40. Spacer means 38 may consist of a plurality of stub shafts as illustrated in
First beam 36 is a component of an x-axis transfer mechanism the structure of which is perhaps most clearly illustrated in
Affixed to second carriage 48 is one end of a third beam 52 the opposite end of which carries end effector 34. Third beam 52 preferably extends perpendicular to second beam 46 and parallel to first beam 36. Many commercially available wafer-handling end effectors may be used in the present system. Accordingly, the particular structure of end effector 34 will not be described in detail as it does not form a critical part of the present invention. In any event, however, it is imperative that the chosen end effector 34 be effective for reliably capturing and releasing wafers “W” such that they may be effectively removed from and placed into the cassette slots 31 (
The operation sequence of the wafer treatment system according to the invention is generally as follows.
The load lock chamber 12 is vented to atmospheric pressure by placing valve 22 into a venting position. Preferably concurrently therewith, the x-axis and z-axis transfer mechanisms are moved to a home position wherein the end effector 34 is clear of any possible obstructions.
Once the load lock chamber is vented to the atmosphere, a load lock chamber access door 54 (
Once the load lock chamber 12 is vented to atmosphere and the access door 54 is opened, a worker may begin to place wafers into the load lock chamber. More specifically, a slotted cassette 30 containing one or more wafers “W” is placed into a first sloped cradle 24. Once the first cradle is loaded with a cassette, the carousel 26 is rotated by a worker-initiated operation or by an automated command a sufficient angular distance to bring a second cradle into alignment with the access door opening whereby a second wafer-carrying cassette may be loaded into the next cradle. This process is repeated as necessary to load a desired batch of wafers into the load lock chamber 12 for processing by process chamber 14.
After the desired number of cassettes are loaded into the load lock chamber, access door 54 is closed, the valve 22 is placed into a vacuum position and vacuum pump 20 is activated to draw a vacuum within the load lock chamber. Upon reaching the desired reduced pressure interiorly of the load lock chamber, typically about 50-150 millitorr, the isolation gate 16 between the load lock and process chambers is opened. Thereafter, the carousel 26 is homed, either by the worker or automatically, the carousel is rotated again to bring a first loaded cassette 30 into a process chamber loading position and the x-axis and z-axis transfer mechanisms of the multiaxial transfer unit 32 move the end effector 34 into a waiting position in alignment with a wafer on the waiting cassette. The z-axis transfer mechanism is then activated to lower the end effector to a position whereby it can grab or capture a wafer. Once in proper vertical position, the end effector is activated to grab the wafer. Upon capturing of the wafer by the end effector, the z-axis transfer mechanism is activated to raise the wafer to an elevation suitable for insertion into the process chamber 14. Once at the proper insertion elevation, the x-axis transfer mechanism is activated to insert the wafer into the process chamber. Following this, the z-axis transfer mechanism is activated to lower the wafer into a slot of an awaiting receptacle located inside the process chamber 14. In this regard, and although not shown, the awaiting wafer-receiving receptacle in the process chamber includes slots likewise angled with respect to vertical at an angle substantially equal to angle “C” such that the wafers are angularly justified therein and may be readily and reliably removed therefrom once wafer processing is completed. Upon placement of the wafer into the receptacle in process chamber 14, the end effector releases the wafer, the z-axis transfer mechanism raises the end effector, and the x-axis transfer mechanism retracts the end effector into the load lock chamber whereby it assumes a ready position above the next wafer to be treated. The foregoing procedure, which is preferably fully automated, continues until the first cassette in the load lock chamber is unloaded and its counterpart receptacle in the process chamber is loaded.
Upon depletion of a first cassette 30 of its wafer supply, the carousel is rotated to an extent that a second cassette is brought into position beneath the end effector. Simultaneously, another receptacle is brought into wafer receiving position within process chamber 14. Once both the second cassette and the second receptacle are in their appropriate positions, the foregoing cassette unloading and process chamber receptacle filling process begins anew and proceeds until unloading of the second cassette is completed. It will be appreciated that all of the unloading and filling steps are repeated until all cassettes in the load lock chamber are emptied of their wafers and such wafers are placed into corresponding receptacles in the process chamber.
Once all wafers in a batch are loaded into the process chamber, the isolation gate 16 is closed and processing of the wafers within process chamber 14 begins. Upon completion of wafer processing, the isolation gate 16 is opened and the entire loading process described above is reversed. That is to say, coated wafers are removed one-by one from the process chamber receptacles and placed into corresponding cassettes 30 in load lock chamber 12. Once unloading of the wafers from the processing chamber is finished, the isolation gate 16 is again closed and the valve 22 is placed into venting position whereby the load lock chamber is again vented to atmospheric pressure. And, once the load lock chamber has achieved atmospheric pressure, access door 54 and cassettes 30 containing processed wafers are sequentially removed from their cradles until all cassettes are removed whereby the entire process described above may begin again.
Although the invention has been described in detail for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention as claimed herein.
For example, while shown as being rotatable about a vertical axis “V”, it will be understood that carousel 26 may rotate about axes of other angular orientations up to and including a horizontal axis. In any event, however, the cradles 26 must be sloped or inclined in one direction or another in order to achieve effective justification of wafers “W” such that they may be reliably captured by the inclined gripping fingers of end effector 34. In addition, while a carousel is the preferred mode of supporting cradle(s) 24, it is also contemplated that the cradle(s) may be carried by a reciprocating platform or the like, whereby one or more cradles may be brought into a position in alignment with the end effector 34.
In addition, while the present invention has been disclosed with respect to sloped/inclined cradles and cassettes, it will be understood that a comparable effect may be achieved by using horizontally oriented cradles with cassettes having slots inclined with respect to vertical at an acute angle substantially equal to angle “C” discussed above.
This application claims the benefit of U.S. Provisional Application No. 61/542,320, filed Oct. 3, 2011, the disclosure of which is incorporated in its entirety by reference thereto.
Number | Date | Country | |
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61542320 | Oct 2011 | US |