US20030026683A1

US20030026683A1 - Gripper for supporting substrate in a vertical orientation

Info

Publication number: US20030026683A1
Application number: US10/255,325
Authority: US
Inventors: Boris Govzman; Manoocher Birang; Michael Sugarman; Anwar Husain
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-05-15
Filing date: 2002-09-26
Publication date: 2003-02-06
Also published as: JP2001024052A; TW461011B; EP1054439A1; US6474712B1

Abstract

A gripper assembly is provided which supports a substrate in a vertical orientation. The gripper assembly's end effectors contact only the edge of the substrate. In a first aspect the end effectors each comprise a first pair of opposed surfaces and an second pair of opposed surfaces, all of which simultaneously contact the substrate, holding the substrate in a clamp-type manner. In a second aspect the end effectors each comprise a lower pair of opposed surfaces which simultaneously contact the substrate, and an upper pair of opposed surfaces, larger than the thickness of the substrate, which limit the substrate from horizontal tilting. In the second aspect the end effectors can close at a first elevation where they do not contact the substrate, and can then elevate to gently contact and support the substrate in a pocket-like manner. In a third aspect one of the end effectors has two pairs of opposed surfaces which simultaneously contact the substrate, and the other end effector has two pairs of opposed surfaces which limit the substrate from horizontal tilting. In any aspect no moving parts are required to limit the substrate's vertical and horizontal movement. In a further aspect, fingers to which the end effectors are coupled, are bent so that the gripper is not positioned above the substrate.

Description

This application is a continuation of U.S. patent application Ser. No. 09/559,889, filed Apr. 26, 2000, which is hereby incorporated by reference herein in its entirety.[0001]

BACKGROUND OF THE INVENTION

When designing an automated semiconductor substrate handler, three main concerns prevail; 1) substrate handler reliability; 2) substrate handler particle generation and potential for substrate contamination; and 3) substrate handler size. Each of these concerns is essentially aimed at reducing costs associated with damaged or defective substrates. Increasing substrate handler reliability prevents substrate damage which can occur when a substrate is incorrectly grasped, etc., and prevents downtime associated with repair and/or recalibration. Reducing particle generation helps reduce defects which result when particles contact substrate surfaces, and reducing substrate handler size allows processing chamber openings to be smaller and to thereby reduce the possibility of particle entry to the chamber and the possibility of substrate contamination thereby.

A major source of particles results when a substrate slides along the surface of the substrate handler's end effector. Accordingly, after a wafer is placed/loaded onto an end effector, a pin or other holding mechanism conventionally moves into place to secure the substrate and prevent the substrate from sliding against the end effector during transport. However sliding and the particles that result therefrom, may occur as part of the loading process. Further, the holding mechanisms, being moving parts themselves, can generate particles and can introduce reliability issues, increasing substrate handler costs. Moreover, during the entire load and transfer process, particles and other contaminants may collect on the substrate or between the end effectors and the substrate.

Accordingly, a need exists for an improved substrate handler, and particularly for a substrate handler having an improved end effector which will reduce substrate sliding and the associated need for moving parts to control substrate sliding. Such a substrate handler and end effector should be streamlined, and should reduce the probability of contaminant contact with substrate surfaces and/or the probability of trapped contaminants between the end effector and the substrate.

SUMMARY OF THE INVENTION

The present invention provides an inventive gripper assembly having a pair of fingers operatively coupled to the gripper so as to move between an open and a closed position; each finger has an end effector coupled thereto, and adapted to support a vertically oriented substrate therebetween. Each end effector has a first pair of opposed surfaces and a second pair of opposed surfaces. Each pair of opposed surfaces is adapted either to simultaneously contact the edge of a vertically oriented substrate supported by the end effector, (clamp-type contact) or to limit horizontal movement of a vertically oriented substrate supported by the end effectors (pockettype contact). Each of the opposed surfaces preferably does not move relative to the other. A pair of opposed surfaces that do not move relative to each other is referred to herein as unitary, whether made of one or more pieces. Preferably, both the first and second opposed surfaces are radiused to mimic the circumference of the wafer so as to deter fluid and contaminants from collecting between the substrate and the surfaces of the end effector.

In operation, the end effectors are positioned on opposite sides of a vertically oriented substrate, and preferably pick up or grasp the substrate in either of the two manners described below. Specifically, in the case of a gripper assembly configured for clamp-type contact, the end effectors are moved to a position at which the end effectors may stabily support the vertically oriented substrate. Thereafter, the end effectors are closed such that the end effector's first and second pairs of opposed surfaces contact the substrate's edge and thereby support the substrate.

Similarly, in the case of a gripper assembly configured for pocket-type contact, the gripper assembly may simply close such that the two pairs of opposed surfaces positioned closest to the bottom edge of the substrate contact the substrate. Alternatively, the pocket-type end effectors may move to a position in line with the substrate, yet at an elevation below which the pair of opposed surfaces would contact the substrate when the end effectors are in a closed position. This elevation may be entirely below the substrate or anywhere below the substrate's horizontal diameter. Thereafter the closed pair of end effectors are elevated such that the end effectors' lower pairs of opposed surfaces contact and support the substrate via the substrate's edges. Note that a pocket type gripper need not have an open and closed position, as the gripper may pick up and deposit a substrate by raising and lowering around the substrate as will be apparent with reference to the detailed description of the preferred embodiments.

The clamp-type gripper is advantageous because it is able to grasp wafers that are within a relatively wide tolerance of a desired position, and thus reduces the time required for initial robot calibration and chamber alignment, as well as reducing the frequency and time required for recalibration and alignment.

The pocket-type gripper is advantageous because it reduces the risk of substrate damage. The pocket-type grippers close below the substrate forming a pocket, and then elevate such that the substrate gently contacts the bottom of the pocket (e.g., contacts the lower pair of opposed surfaces), and such that the upper pair of opposed surfaces surround the substrate and prevent the substrate from excessive tilting in the horizontal direction. Accordingly, the only force applied to the substrate is a purely vertical lifting force, which tends to generate fewer particles than do multidirectional forces. Further, because there is no external force opposing the vertical lifting force, the substrate is not acted on by external opposing forces, and is less likely to be damaged.

When the gripper assembly is configured such that the gripper is at a higher elevation than the end effectors, the fingers are preferably bent such that the gripper is positioned to the front, back or most preferably the side of the substrate rather than directly above the substrate. Thus, particles from the gripper are less likely to contaminate the substrate.

The end effectors of the inventive gripper assembly, whether clamp-type or pocket-type, preferably have no moving parts, and are therefore inexpensive and less likely to malfunction. Further, the absence of moving parts enable a streamlined design, which in addition to the fact that the gripper assembly grasps a substrate by the substrate's edges, allows the inventive gripper assembly to move substrates through narrow openings such as those found in semiconductor manufacturing equipment.

Because the inventive gripper assembly is streamlined and inexpensive, and because the gripper assembly experiences reduced calibration time, reduced particle generation, and reduced risk of substrate damage, a substrate handler employing the inventive gripper assembly is ideally suited for semiconductor applications. Moreover, because the inventive gripper assembly supports a substrate in a vertical orientation, contaminants are less likely to collect on the substrate's surfaces. Further contamination reduction may be achieved with the use of radiused end effector surfaces which are radiused to mimic the circumference of the wafer, and thus may minimize or eliminate contact with the front or back surface of the wafer and may contact only the beveled edge of the wafer.

Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side perspective view of a clamp-type end effector of a first aspect of the inventive gripper assembly; [0014]
FIG. 1A is a cross-sectional view showing contact between a substrate and opposed surfaces of the end effector of FIG. 1; [0015]
FIGS. 2A and 2B are front elevational views of a gripper assembly employing the clamp-type end effector of FIG. 1, showing the gripper assembly in an open and a closed position, respectively; [0016]
FIG. 3 is a side perspective view of a pocket-type end effector of a second aspect of the inventive gripper assembly; [0017]
FIGS. [0018] 4A-B are front elevational views of a gripper assembly employing the pocket-type end effector of FIG. 3, showing the gripper assembly in a closed no-substrate-contact position and a closed substrate-contact position, respectively;
FIG. 5 is a front elevational view of an alternative pocket-type gripper assembly; and [0019]
FIG. 6 is a schematic side view of a substrate handler that includes the gripper assembly of FIGS. [0020] 4A-B.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a side perspective view of a clamp-[0021] type end effector 11 of a first aspect of the inventive gripper assembly. The clamp-type end effector 11 comprises a first pair of opposed surfaces 13 a-b, adapted to simultaneously contact an edge of a vertically oriented substrate to be supported thereby (FIGS. 2A-B), and a second pair of opposed surfaces 15 a-b adapted to simultaneously contact a vertically oriented substrate to be supported thereby. The first pair of opposed surfaces 13 a-b and the second pair of opposed surfaces 15 a-b preferably comprise a groove adapted to support a substrate with minimum contact (e.g., via two opposing points), such as a “v” shaped groove, as shown in FIG. 1A. Preferably, to deter particles and fluid contaminants from being trapped between the first pair of opposed surfaces 13 a-b and/or the second pair of opposed surfaces 15 a-b, and the substrate surface, the first pair of opposed surfaces 13 a-b and the second pair of opposed surfaces 15 a-b are radiused to mimic the circumference of the wafer, and thus may minimize or eliminate contact with the front or back surface of the wafer and may contact only the beveled edge of the wafer, as shown in FIG. 1. Further, the first pair of opposed surfaces 13 a-b and the second pair of opposed surfaces 15 a-b are preferably unitary, thereby minimizing moving parts.
The first pair of opposed surfaces [0022] 13 a-b and the second pair of opposed surfaces 15 a-b preferably extend the same (with reference to FIG. 1 horizontal distance) distance x and the same (with reference to FIG. 1 vertical distance) distance y, from a point C which is to be centered on the substrate's diameter (e.g., in the configuration shown the point C is to be centered on the substrate's horizontal diameter), such that when the point C is centered along the diameter of a substrate (where the clamp-type end effector 11 provides maximum stability) the first pair of opposed surfaces 13 a-b and the second pair of opposed surfaces 15 a-b provide the only contact points with the substrate, and for maximum stability, contact the substrate at equal distances from the substrate's diameter, as shown in FIGS. 2A-B.
FIGS. [0023] 2A-B are front elevational views of a gripper assembly 17 which employs a pair of the end effector 11 of FIG. 1, and which show the gripper assembly 17 in an open and a closed position, respectively. The gripper assembly 17 comprises a gripper 19, a pair of fingers 21 a-b operatively coupled to the gripper 19 so that the gripper 19 can move the pair of fingers 2la-b between an open and a closed position. Coupled to the ends of the pair of fingers 21 a-b opposite the gripper 19, are a pair of clamp-type end effectors 11 a-b, configured as described with reference to FIG. 1. The clamp-type end effectors 11 a-b are coupled to the pair of fingers 21 a-b so that the first end effector 11 a's first pair of opposed surfaces 13 a-b and second pair of opposed surfaces 15 a-b are opposite the second end effector 11 b's first pair of opposed surfaces 13 a-b and second pair of opposed surfaces 15 a-b, respectively.
Grippers for moving a pair of fingers between open and closed positions are well known in the art, and are therefore not described in detail herein. Similarly, although shown in a scissors linkage configuration, the pair of fingers [0024] 21 a-b may be coupled in any manner to achieve open and closed positions. However, in the scissors linkage configuration shown, the distance between the clamptype end effectors 11 a-b in the open and closed position can be easily adjusted via a set screw 23 which controls relative movement between the pair of fingers 21 a-b by sliding back and forth within a slot 25, as is known in the art.
When the pair of fingers [0025] 21 a-b are configured in the scissors linkage, the gripper 19 moves the base of the pair of fingers 21 a-b apart, causing the ends of the pair of fingers 2la-b to move apart thereby assuming an open position wherein the first pair of opposed surfaces 13 a-b and the second pair of opposed surfaces are positioned farther apart than the diameter of a substrate supported thereby (as shown in FIG. 2A). To assume the closed position, the gripper 19 moves the base of the pair of fingers 21 a-b toward each other, causing the ends of the pair of fingers 2la-b to move toward each other to a position where the first pair of opposed surfaces 13 a-b and the second pair of opposed surfaces 15-a-b are positioned such that each of the first pair of opposed surfaces 13 a-b and each of the second pair of opposed surfaces 15 a-b contact the substrate S (as shown in FIG. 2B). Preferably, the lower of the two first pairs and the two second pairs of opposed surfaces are positioned where the substrate S is narrower than at its diameter (e.g., below the substrate's horizontal diameter or adjacent but off-set from the substrate's vertical diameter, etc.) Thus, due to the fact that the substrate's width increases as its diameter is approached, the substrate S cannot slide downwardly through the lower pair of opposed surfaces (e.g., with reference to FIG. 2 the first pair of opposed surfaces 13 a-b).
In operation a substrate handler (not shown) having the [0026] gripper assembly 17 coupled thereto, moves the gripper assembly 17 to a position at which the clamp-type end effectors 11 a-b can stabily support the vertically oriented substrate S. The position at which the first pair of opposed surfaces 13 a-b and the second pair of opposed surfaces 15 a-b can stabily support the substrate S varies depending on the specific configuration of the first pair of opposed surfaces 13 a-b and the second pair of opposed surfaces 15 a-b (e.g., the distances x and y to which the first pair of opposed surfaces 13 a-b and the second pair of opposed surfaces 15 a-b extend, whether equal or differing distances, etc.). However, the position at which the clamptype end effectors 11 a-b can stabily support the substrate S, preferably positions the center C of the clamp-type end effector 11 a-b at the diameter of the substrate S (e.g., as shown in FIGS. 2A-B the horizontal diameter). Thereafter, the gripper assembly 17 assumes the closed position such that the first pair of opposed surfaces 13 a-b and the second pair of opposed surfaces 15 a-b each contact the edge of the substrate S and the substrate S is supported thereby.
The clamp-type gripper assembly of FIGS. [0027] 2A-B can support a substrate in a vertical orientation regardless of the position of the gripper relative to the substrate. Thus, by turning FIGS. 2A-B to view them from various orientations, one can view various orientations of the gripper assembly 17 which still support a vertically oriented substrate by its edges. The gripper assembly of FIGS. 2A-B are thus easily adaptable to transfer substrates to and from variously configured substrate supports. However, because most vertical substrate supports support a substrate along its lower hemisphere, the gripper assembly 17 is preferably configured with the gripper 19 at a higher elevation than the end effectors 11 a-b. Accordingly, to reduce potential substrate contamination, the fingers 21 a-b are bent (e.g., as shown in FIGS. 2A-B) to place the gripper 19 to the side of the substrate S (where particles are less likely to travel to the substrates front surface). Although less preferred, the fingers 21 a-b may be bent so as to position the gripper 19 to the front, or preferably to the back of the substrate S.
The clamp type gripper assembly of FIGS. [0028] 2A-B may be able to pick up a flatted substrate regardless of its oreintation, because each of the end effectors 11 a-b may be sized so as to be longer than the length of a flat portion of a substrate to be gripped thereby. Accordingly at least three of the pairs of opposed surfaces 13 a-b will contact a flatted substrate at any given time. Three points of contact are sufficient to securely grip a substrate.
FIG. 3 is a side perspective view of a pocket-[0029] type end effector 31 of a pocket-type aspect of the inventive gripper assembly. Like the clamp-type end effector 11 of FIG. 1, the pocket-type end effector 31 of FIG. 3 comprises a first and second pair of opposed surfaces, best described with reference to FIGS. 4A-B as a lower pair of opposed surfaces 33 a-b adapted to simultaneously contact (e.g., via two opposing points) an edge of a vertically oriented substrate S to be supported thereby. The pocket-type gripper assembly 31 also comprises an upper pair of opposed surfaces 35 a-b. However in the embodiment of FIG. 3, the upper pair of opposed surfaces 35 a-b are adapted to limit the horizontal movement of a vertically oriented substrate S supported by the lower pair of opposed surfaces 33 a-b, rather than to clamp the substrate S. Thus the upper pair of opposed surfaces 35 a-b are positioned far enough apart to allow some horizontal movement (both into and out of the page).
Preferably both the lower pair of opposed surfaces [0030] 33 a-b and the upper pair of opposed surfaces 35 a-b comprise a groove adapted to minimize contact with the substrate S's front and back surfaces, such as a “v” shaped grove. Preferably, to deter particles and fluid contaminants from being trapped between the lower pair of opposed surfaces 33 a-b and/or the upper pair of opposed surfaces 35 a-b and the substrate S, the lower pair of opposed surfaces 33 a-b and/or the upper pair of opposed surfaces 35 a-b are radiused to mimic the circumference of the wafer, and thus may minimize or eliminate contact with the front or back surface of the wafer and may contact only the beveled edge of the wafer, as shown in FIG. 3. Further, the lower pair of opposed surfaces 33 a-b and the upper pair of opposed surfaces 35 a-b are preferably unitary, thereby minimizing moving parts.
The lower pair of opposed surfaces [0031] 33 a-b preferably extend a further horizontal distance (X₁), than do the upper pair of opposed surfaces 35 a-b (X₂). Similarly, the lower pair of opposed surfaces 33 a-b are located a greater vertical distance Y₁from a point C which is to be centered on the substrate S's horizontal diameter, than are the upper pair of opposed surfaces 35 a-b (Y₂)
In this configuration a pair of pocket-[0032] type end effectors 31 a-b can close when positioned along a narrower portion of the substrate S (e.g., below the elevation at which the lower pairs of opposed surfaces 33 a-b contact the substrate S). Thus, when the end effectors 31 a-b elevate, the upper pair of opposed surfaces 35 a-b (which do not extend inwardly as far as the lower pair of opposed surfaces 33 a-b) will not contact the substrate S, as described further with reference to FIGS. 4A-B. Alternatively, much like the clamp-type end effectors of FIGS. 2A-B, the pockettype end effectors may open and close around the substrate S from an elevation at which the lower pair of opposed surfaces will contact the substrate S when in the closed position.
FIGS. [0033] 4A-B are front elevational views of a gripper assembly 37 employing a pair of the end effectors of FIG. 3 and showing the gripper assembly in a closed no-substrate-contact position and closed substrate-contact position, respectively. Aside from the pocket-type end effectors 31 a-b, the gripper assembly 37 of FIGS. 4A-B is identical to the gripper assembly 17 of FIGS. 2A-B. Accordingly, the description thereof is not repeated with reference to FIGS. 4A-B.
In operation a substrate handler (not shown) having the [0034] gripper assembly 37 coupled thereto, lowers the gripper assembly 37 to an elevation below an elevation at which the lower pair of opposed surfaces 33 a-b would intersect the substrate S when in the closed position. Thereafter, if the gripper assembly 37 is not already closed, the gripper assembly 37 assumes the closed position such that the upper pair of opposed surfaces 35 a-b close around the substrate S, but do not contact the substrate S (FIG. 4A). The substrate handler (not shown) then elevates the gripper assembly 37 causing the lower pair of opposed surfaces 33 a-b to gently contact and support the substrate S in a pocket-like manner (FIG. 4B). The force exerted between the substrate S and the lower pair of opposed surfaces 33 a-b preferably is purely vertical and thus particle generation is minimized. During substrate pick-up and transport, the upper pair of opposed surfaces 35 a-b (which are further apart than the thickness of the substrate S's edge) do not contact the substrate S unless the substrate S tilts horizontally forward or backward.
FIG. 5 is a front elevational view of an alternative pocket-[0035] type gripper assembly 41. The pocket-type gripper assembly 41 is oriented such that the gripper 19 is positioned beside the substrate S. Aside from a bottom end effector 43 and a top end effector 45 the remainder of the gripper assembly 41 comprises components like those of FIGS. 1-4B. Accordingly, only those aspects of the gripper assembly 41 which differ from the gripper assemblies 17 and 37 will be described with reference to FIG. 5. Specifically, the bottom end effector 43 is positioned such that the first and second pair of opposed surfaces 33 a ₁-b ₁, 33 a ₂-b ₂are in a horizontal line. The first and second pair of opposed surfaces 33 a ₁-b ₁, 33 a ₂-b ₂are configured such that both opposing surfaces simultaneously contact the substrate S to thereby support the substrate S. The top end effector 45 is also positioned such that the first and second pair of opposed surfaces 35 a ₁-b ₁, 35 a ₂-b ₂are in a horizontal line. However, the first and second pair of opposed surfaces 35 a ₁-b ₁, 35 a ₂-b ₂of the top end effector 45 are configured like the upper pairs of opposed surfaces 35 a-b of FIGS. 4A-B. Specifically, the first and second pair of opposed surfaces 35 a ₁-b ₁, 35 a ₁-b ₁of the top end effector 45 are adapted to limit the horizontal movement of a vertically oriented substrate S supported by the bottom end effector 43.
In operation the [0036] gripper assembly 41 assumes an open position and moves to position the center points C of the top and bottom end effector 43, 45 along the vertical diameter of the substrate S and then closes, as shown in FIG. 5. As the gripper assembly 41 closes, the bottom end effector 43 gently contacts the substrate S and lifts it from the substrate support (not shown), and the top end effector 45 lowers to an elevation wherein the opposed surfaces thereof limit the horizontal movement of the substrate S but do not clamp the substrate S (e.g., to an elevation wherein the substrate S is not inserted far enough within the groove formed by the opposed surfaces to contact the edges thereof, unless the substrate moves horizontally forward or backward).
The gripper of each of the [0037] gripper assemblies 17, 37 and 41, preferably are normally biased to a closed position (e.g., via a spring 47 shown in FIG. 5). Thus, in the event a power failure occurs while the gripper assembly 17, 37, 41 supports a substrate S, the gripper assembly maintains its closed position and does not drop the substrate S. Also, each of the gripper assemblies 17, 37 and 41, may be advantageously coupled to a substrate handler 51 having a moveable arm 53 for lifting and lowering the gripper assembly as shown in the schematic side view of FIG. 6. Such a wafer handler may be advantageously used with the end effectors described herein, and particularly with the pocket type end effectors. Thus, as shown in FIG. 6, the gripper is at an elevation higher than that of the end effectors, and at least one of the fingers is bent so that the gripper is not above the substrate supported by the end effectors.
The foregoing description discloses only the preferred embodiments of the invention, modifications of the above disclosed apparatus and method which fall within the scope of the invention will be readily apparent to those of ordinary skill in the art. For instance, as previously mentioned, the [0038] end effectors 11 and/or 31, rather than being unitary, may comprise moving parts which move the opposing surfaces horizontally together and apart, so as to selectively contact the substrate S. Further, although both the clamp-type and pocket-type end effectors are preferably positioned along the diameter of the substrate S, other positions will also support the substrate. Of course, for both types of end effectors the lengths of the upper and lower pairs of opposed surfaces will vary according to the position at which they contact the substrate. The opposed surfaces need not be v-shaped, any pair of surfaces which can support the substrate may be employed. Thus, the invention encompasses any gripper assembly which clamps or pockets a vertically oriented substrate by contacting the substrate's edges.
Further, the clamp type end effectors may be advantageously employed for gripping other, non-vertically oriented substrates (e.g., horizontal, etc.). In such embodiments the substrate need not slide relative to the end effectors (e.g., relative to a bottom plate of the end effector) as may occur in conventional horizontal end effectors. Specifically the inventive end effectors are each mounted to an individual gripper finger which may move the respective end effector in a “tong” like motion rather than a pushing/sliding motion. [0039]
The gripper actuators and gripper finger configurations disclosed herein are merely exemplary. The gripper fingers need not cross, as shown herein, and the gripper actuators may comprise scissors type actuators, sliding type actuators, etc. [0040]
Accordingly, while the present invention has been disclosed in connection with the preferred embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claims. [0041]

Claims

The invention claimed is

1. A method of handling a semiconductor substrate, comprising:

positioning along opposite edges of a semiconductor substrate, a pair of end effectors adapted to support the substrate and coupled to ends of a pair of fingers that respectively extend along the opposite edges of the substrate;

moving the end effectors to a position at which the end effectors may stabily support the substrate; and

closing the end effectors by moving the ends of the fingers toward each other such that the end effectors each contact an edge of the substrate.

2. The method of claim 1 wherein closing the end effectors such that the end effectors contact and support the substrate comprises contacting the substrate with a plurality of grooves, each adapted to contact the substrate's edge at two opposing points.

3. The method of claim 1 wherein closing the end effectors such that the end effectors contact and support the substrate comprises contacting the substrate with four pairs of opposing surfaces.

4. The method of claim 2 wherein contacting the substrate with a plurality of grooves comprises contacting the substrate with two supporting grooves, and wherein the method further comprises preventing horizontal substrate tilting.

5. A gripper assembly comprising:

a gripper;

a pair of fingers operatively coupled to the gripper; and

a pair of end effectors coupled to ends of the fingers and adapted to support a substrate therebetween, each end effector comprising:

a first pair of opposed surfaces adapted to simultaneously contact an edge of a substrate to be supported by the end effectors; and

a second pair of opposed surfaces adapted to simultaneously contact the edge of a substrate to be supported by the end effectors;

wherein the fingers are adapted to respectively extend along opposite edges of the substrate.

6. A substrate handler, comprising:

a mechanical arm capable of lifting and lowering; and

the gripper assembly of claim 5 coupled to an end of the moveable arm.

7. The apparatus of claim 5 wherein the grippers are normally biased closed.

8. The gripper assembly of claim 5 wherein the fingers are movably linked to each other at a point between the gripper and the ends of the fingers.

9. The gripper assembly of claim 5 wherein the first and second pair of opposed surfaces are radiused.

10. A gripper assembly comprising:

a gripper;

a pair of fingers operatively coupled to the gripper and adapted to extend along opposite edges of a substrate to be supported by the gripper assembly; and

a pair of end effectors, one coupled to an end of each of the fingers, adapted to support a substrate by its edges.

11. The apparatus of claim 10 wherein the gripper is at an elevation higher than the end effectors, and at least one of the fingers is bent so that the gripper is horizontally displaced relative to a substrate supported by the end effectors.

12. The apparatus of claim 10 wherein the grippers are normally biased closed.

13. The gripper assembly of claim 10 wherein the fingers are movably linked to each other at a point between the gripper and the ends of the fingers.

14. The gripper assembly of claim 10 wherein the first and second pair of opposed surfaces are radiused.

15. A gripper assembly comprising:

a gripper;

a pair of fingers operatively coupled to the gripper; and

a first pair of opposed surfaces and a second pair of opposed surfaces;

wherein the fingers are movably linked to each other at a point between the gripper and the ends of the fingers.

16. The apparatus of claim 15 wherein the first pair of opposed surfaces are radiused.

17. The apparatus of claim 15 wherein the second pair of opposed surfaces are radiused.

18. The apparatus of claim 15 wherein the first and second pairs of opposed surfaces of one of the end effectors are both adapted to limit horizontal movement of a vertically oriented substrate supported by the first and second pairs of opposed surfaces of the other of the end effectors.

19. The apparatus of claim 15 wherein the second pair of opposed surfaces of each of the end effectors are both adapted to limit horizontal movement of a vertically oriented substrate supported by the first pair of opposed surfaces of each of the end effectors.

20. The apparatus of claim 15 wherein the first pair of opposed surfaces of each of the end effectors and the second pair of opposed surfaces of each of the end effectors are adapted to simultaneously contact a substrate supported thereby.

21. The apparatus of claim 15 wherein the grippers are normally biased closed.

22. The gripper assembly of claim 15 wherein the fingers are movably linked to each other at a point between the gripper and the ends of the fingers.

23. The gripper assembly of claim 15 wherein the first and second pair of opposed surfaces are radiused.

24. The gripper assembly of claim 5 wherein each of the pair of end effectors is sized so as to be longer than the length of a flat portion of a substrate to be gripped thereby.

25. The gripper assembly of claim 10 wherein each of the pair of end effectors is sized so as to be longer than the length of a flat portion of a substrate to be gripped thereby.

26. The gripper assembly of claim 15 wherein each of the pair of end effectors is sized so as to be longer than the length of a flat portion of a substrate to be gripped thereby.