Edwin Den Hartog
ASM International N.V.
Dean J. Kramer
Knobbe, Martens, Olson & Bear, LLP
An end effector alternately (or simultaneously) transports susceptors and wafers. Separate contact surfaces are provided for wafer transport and for susceptor transport. In one embodiment, the wafer contact surface is spaced above the susceptor contact surface, and the susceptor is a plate with a recess sized and deep enough to accommodate the wafer contact surface without touching it, while being supported upon the susceptor contact surface. The wafer contact surface is a complete or C-shaped ring having an annular opening connected to a vacuum pump. In another embodiment, the wafer contact surface is spaced below the susceptor contact surface, and both comprise peripheral edge support surfaces. The edge support surfaces can be formed from a single sloped surface for each contact pad, with a smaller wafer supported below the position of a larger susceptor plate. Alternatively, a stepped surface is provided for each pad, with the lower inner contact surfaces supporting a wafer and the upper outer contact surfaces supporting the susceptor.
This application claims the priority benefit under 35 U.S.C. 119(e) of U.S. provisional application No. 60/377,904, filed May 2, 2002. Additionally, this application claims the priority benefit under 35 U.S.C. 119(e) of U.S. provisional application No. 60/365,122, filed Mar. 15, 2002 and U.S. Provisional application No. 60/379,885, filed May 10, 2002.
The invention relates to the transfer of articles, such as semiconductor wafers and more particularly to an improved end effector for handling and transferring of wafers.
For the batch processing of wafers in vertical furnaces at very high temperatures it is proposed in U.S. provisional application No. 60/365,122, filed Mar. 15, 2002 (incorporated herein by reference) to support wafers, accommodated in a wafer boat, by susceptor plates. A susceptor plate supports a wafer over its entire surface to prevent slip of the wafer during the high temperature processing. Loading/unloading of wafers into a wafer boat with susceptor plates can be carried out according to the loading/unloading procedure described in the above reference application. The '122 application proposes to have the susceptor plates removably accommodated in the wafer boat. In the loading procedure, a wafer is transported by a wafer handling robot to a transfer station where it is placed onto a susceptor plate. The susceptor plate, accommodating the wafer on its upper surface, is transported from the transfer station to the wafer boat by the wafer handling robot. The susceptor plates are contacted by the same generic end effector as the wafers.
Susceptor plates used for high temperature applications are generally made from silicon carbide (SiC). A common problem of a SiC-object is its surface roughness. The contact surface of the end effector can be damaged by the rough surface of the susceptor plate and subsequently is a potential source for damaging wafers handled by this end effector.
One way to avoid damage of the wafer is to use two end effectors instead of one end effector. The first end effector is used to handle semiconductor wafers and the second end effector is used to handle susceptor plates. Extra space inside the semiconductor processing tool would be needed to accommodate a second end effector. The space necessary is not always available and, when available, could be more productively employed in other fashions. Furthermore, the logistics of such a solution are very complex.
Hence, it is an object of the present invention to provide a single end effector that is able to handle susceptor plates and wafers, desirably without the susceptor plate ever touching the contact surface of said end effector on which the wafer is to be supported.
According to one aspect of the invention, an end effector is provided with a first contact surface to support a semiconductor wafer and a second contact surface, displaced relative to the first contact surface, to support a susceptor plate. Preferably, the first contact surface is on a first vertical level and the second contact surface is on a second vertical level.
According to one embodiment, the second surface (for supporting the susceptor plate) is positioned below the first surface. The susceptor plate is provided with a recess in an underside thereof, configured to prevent contact with said first contact surface while the susceptor plate is supported by the second contact surface. The recess faces the first contact surface and has a diameter significantly smaller than the outer diameter of the second contact surface but a large enough to accommodate the first contact surface. The depth of the recess is such that no contact of the susceptor plate is made with the first contact surface while it is supported by the second contact surface.
In another embodiment, an edge support end effector supports a disk-like object at a contact surface at the edge of the object. With this edge support end effector, a wafer is supported at a first, lower level and a susceptor plate with a larger diameter than the wafer is supported at a second higher level. The contact surface can be upwardly and outwardly sloped so that the object to be supported is only contacted at its outer edge. In another embodiment, the contact surface can also comprise steps.
According to preferred embodiments of the invention, an end effector is provided with a first contact surface to support a semiconductor wafer and a second contact surface, displaced relative to the first contact surface, to support a susceptor plate. The second contact surface can be laterally displaced relative to the first contact surface. Typically, the susceptor plate has a diameter slightly larger than the wafer. In this case, the wafer can be supported by a first contact surface being disposed within a peripheral edge of the wafer and the susceptor plate can be supported on a second contact surface, positioned outside a peripheral edge of the wafer but positioned within a peripheral edge of the susceptor plate. The second surface is also preferably positioned vertically displaced with respect to the first surface.
In one embodiment, the susceptor plate, supported by the second contact surface, contains a recess to prevent contact of the susceptor plate with the first contact surface. The recess faces the first contact surface and is sized to accommodate the first contact surface. The depth of the recess is such that the susceptor plate makes no contact with the first contact surface while the susceptor is supported by the second contact or support surface. In this case, the first contact surface is vertically above the second contact surface.
A blow-up of the area inside the dotted line of
As mentioned above, the inner rings 12 and 13 of the end effector 1 are preferably formed of a relatively soft material to avoid damaging of a wafer during transfer. Unfortunately, such a material scratches very easily. If a scratch in the radial direction is present on the contact surface of the inner ring 12, connecting the annular groove 30 and the free volume 9 located above the disc 23, an unwanted vacuum in free volume 9 will be created when evacuating the groove 30. Firstly, the unwanted vacuum results in large forces on the wafer 3, resulting in bending of the wafer, which is undesirable. Secondly, during release of the wafer it will take a relatively long time before the vacuum in the relatively large free volume 9 is filled to atmospheric pressure again. This delay would cause unwanted sticking of the wafer 3 onto the first contact surface 5 and in uncontrollable and abrupt release of the wafer, which may induce damage and inaccurate positioning of the wafer in the wafer cassette.
With reference to
With reference now to
While not shown, it will be understood that the end effectors 40, 50 of
In this manner, the end effector 40 or 50 can fit between the posts of a standard cassette designed to support wafers 42, or the cassette disclosed in U.S. Provisional Patent Application No. 60/365,122, filed Mar. 15, 2002, which is designed to support a plurality of susceptor plates 43. U.S. Provisional Application No. 60/365,122, filed Mar. 15, 2002 is incorporated herein by reference. It will be understood that the stepped platforms of
The end effectors disclosed herein are particularly useful for transporting susceptors to a transshipment or transfer station designed for loading wafers onto susceptors for transporting the wafer susceptor combination together into a boat for batch processing, and for transporting wafers on the same end effector to the transfer station.
Inside the housing 102, a support structure 120 is provided, mounted at the lower side of the housing 102 with bolts 122. Attached to the support structure 100 are vertically extending support beams 130 and 136, provided with supports 132 and 138, respectively, to hold susceptors, which take the form of support plates 140 in the illustrated embodiment. Each support 132 is provided with a support ridge 134 with sloped sides, fitting in a hole 142 in a corresponding susceptor plate or support plate 140 to provide centering and positioning capabilities for the support plates 140. In total, 23 accommodations for support plates 140 are provided, of which the bottom one is shown empty in
At the lower end of the FOUP 100, where two more slots are ordinarily found in standard cassettes designed for accommodating 25 wafers, a transshipment or transfer station is provided. The transfer station comprises three pins 150, each provided with a conical lower end 152, on which a susceptor or support plate 140 can be supported, and a cylindrical upper part, on top of which a wafer 160 can be supported. Preferably the material of the pins 150 is PEEK or any other material that is not damaging the wafer, like Teflon or polypropylene. Each support plate 140 is provided with three holes 142 to accommodate the cylindrical upper part of the pins 150.
In order to load a wafer onto a support plate, a robot end effector 154 contacts a support plate in one of the storage accommodations of the FOUP 100 from the bottom and the robot transports the support plate from the storage accommodation to the transfer station provided at the lower end of the FOUP 100. The end effector 154 is configured, as described above, to have wafer supporting surfaces and separate susceptor supporting surfaces. The robot holds a support plate 140 upon susceptor contact surfaces such that the support plate does not touch the wafer contact surfaces, and places the support plate at the conical part 152 of the support pins 150. Because the position of the support plates is locked in the storage accommodations, through support ridges 134, it is ensured that the orientation of the support plates is correct, such that the position of the holes 142 in the support plate 140 corresponds with the positions of the pins 150.
Then a wafer 160 is transported upon wafer contact surfaces of the robot end effector to the transfer station and is placed on top of the pins 150. Desirably, the wafer 160 does not touch the susceptor contact surfaces of the robot end effector. Next, the robot retracts, moves downward and extends again so that the end effector 154 is now placed below the support plate 140 that is positioned on the pins 150. Finally, the end effector 154 moves upward until the support plate 140 is lifted from and raised above the pins 150, the wafer 160 is supported by the support plate 140 and the wafer/plate combination is raised above pins 150. Then the robot can transport the support plate 140 upon susceptor contact surfaces of the end effector, together with the wafer 160, to the support plate holder or boat (not shown).
Although the transfer station is preferably provided at the lower end of the FOUP, it can be placed alternatively at the upper end or at a selected point between the upper and lower ends.
As an alternative to use with the transfer station of
Advantageously, the end effectors disclosed herein are designed to avoid damage to the wafer supporting surfaces on the end effector. In particular, damage to the wafer supporting surfaces is avoided by transporting the susceptor on susceptor supporting surfaces of the same end effector in a manner that avoids susceptor plate contact with the wafer supporting surfaces.
It will be appreciated by those skilled in the art that various omissions, additions and modifications may be made to the structures and processes described above without departing from the scope of the invention. All such modifications and changes are intended to fall within the scope of the invention, as defined by the appended claims.