WO2003006705A2

WO2003006705A2 - Wafer fabrication buffer station

Info

Publication number: WO2003006705A2
Application number: PCT/US2002/022160
Authority: WO
Inventors: Paul Bacchi; Paul S. Filipski
Original assignee: Newport Corporation
Priority date: 2001-07-13
Filing date: 2002-07-12
Publication date: 2003-01-23
Also published as: WO2003006705A3

Abstract

A buffer station (10) includes a base (14) and multiple posts (27) that extend from a base (14). A moveable arm (22) is coupled to each post (27) and moves between specimen (16) supporting and releasing positions. The buffer station (10) may further include supporting fingers (18) extending from the base (14) to support a specimen (16). Alternatively, the buffer station may include movable lower arms that each couple to a corresponding post. The movable lower arms move from specimen supporting and releasing positions. The movable lower arms may also couple to their own individual posts. Movement of the lower arms is independent from that of the upper arms. The buffer station supports specimens at two different elevations.

Description

WAFER FABRICATION BUFFER STATION

Related Application This application claims benefit of United States Provisional Patent Application

No. 60/305,420, filed July 13, 2001. Field of the Invention

This invention relates to semiconductor wafer handling and robotics systems and, in particular, to a buffer station for increasing the throughput of such systems. Background of the Invention

Semiconductor wafer process environments typically include a processing unit, such as a chemical mechanical polisher, at least one wafer carrier station, an optional prealigner station, and a robotic arm for transferring wafers among the stations.

In a typical operation, the sequence for exchanging wafers on a processing station requires the robotic arm to pickup a processed wafer and return it to another location. The robotic arm then retrieves an unprocessed wafer and loads it to the processing station. Unfortunately, the processing station is idled while the robotic arm is performing the aforementioned wafer exchange function.

Prior workers have addressed this bottleneck in multiple ways, such as employing multiple robots, multiple end-effectors or multiple arm robots, all of which require more complex automation systems. These more complex systems result in increased system costs as well as requiring additional footprint that may be a drawback in crowded processing environments. Another process is described in U.S. Patent No. 6,212,961 for BUFFER SYSTEM FOR A WAFER HANDLING SYSTEM, in which a wafer buffer station includes at least one pair of supporting elements and a motion unit. The supporting elements are capable of supporting at least two wafers and are located to support the wafers within the operational pathway of a measurement station. The motion unit moves the supporting elements to either support wafers placed thereon within the pathway or to be separated to allow motion of the handling system during wafer handling. Unfortunately, the handling system is unduly complex and grips or releases the multiple wafers simultaneously. Moreover, in the event of a power failure, the motion unit may drop a wafer. Summary of the Invention

The present invention provides an apparatus and a method for overcoming the limitations of the prior art. The semiconductor buffer station disclosed herein is relatively simple, grips or releases wafers independently and, does not drop a wafer in the event of a power failure.

A specimen buffer station of this invention is suitable for use in a specimen processing system including a robotic arm. The buffer station is beneficial for use in any processing environment where a specimen, such as a semiconductor wafer, is unloaded by the robotic arm (hereafter "robot") at a specimen processing location from which the specimen is later reloaded by the same robot or another robot. The buffer station is advantageous because the processing station is less dependent on, or even independent of, specimen movements associated with the robot, resulting in increased specimen processing throughput. The buffer station includes a base in which a wafer receptor is mounted. The wafer receptor supports and optionally elevates a wafer specimen. In one embodiment, multiple specimen supporting fingers protrude a first distance above the base. The station fiirther includes multiple rotatable arms each having a specimen supporting surface that is located a second distance above the base. The rotatable arms extend from posts that support, and impart rotating motion to, the rotatable arms. The optional wafer receptor and posts preferably, but not necessarily, rotate about parallel axes. The base is preferably mounted on a translation stage providing specimen- positioning capability. The supporting fingers and rotatable arms coact with the wafer receptor or chuck motion in support of a wafer processing method of this invention. The chuck is not mandatory, and its function can be readily replaced by another specimen holding device. In an alternative embodiment of this invention, the supporting fingers, rotatable arms, and posts are replaced by multiple coaxially actuated upper and lower specimen supporting arms. The posts are replaced by outer and inner posts that are coaxially and independently rotatable about a common longitudinal axis. An upper arm protrudes from the outer post, and a lower arm protrudes from the inner post. The upper and lower arms have specimen supporting surfaces that are positioned to support wafers at first and second distances above the base. The upper and lower arms are independently rotatable to the above-described wafer supporting and releasing positions in support of a wafer processing method of this invention. In another alternative embodiment of this invention, the supporting arms, rotatable arms, and posts are replaced by multiple non-coaxially actuated upper and lower specimen supporting arms. An upper arm protrudes from the one rotatable post, and a lower arm protrudes from a different rotatable post. The upper and lower arms have specimen supporting surfaces that are positioned to support wafers at the first and second distances above the base. The upper and lower arms are independently rotatable to the above-described wafer supporting and releasing positions in support of a wafer processing method of this invention.

Additional features and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof that proceed with reference to the accompanying drawings. Brief Description of the Drawings

Fig. 1 is an isometric view of a wafer buffer station of this invention showing wafer supporting fingers at a first elevation and three rotatable arms at a second elevation in alternate wafer supporting and releasing positions. Figs. 2A and 2B are respective plan and side elevation views of the buffer station of Fig. 1 showing the rotatable arms in the wafer supporting position for supporting a wafer at the second elevation.

Figs. 3 A and 3B are respective plan and side elevation views of the buffer station of Fig. 1 showing the rotatable arms in the wafer releasing position and the fingers supporting a wafer at the first elevation. Figs. 4A and 4B are respective plan and side elevation fragmentary views of the buffer station of this invention showing the rotatable arms in the wafer releasing position and an optional chuck supporting a first wafer at an inspection elevation.

Figs. 5 A and 5B are respective plan and side elevation fragmentary views of the buffer station of this invention showing the rotatable arms in the wafer releasing position and the first wafer lowered by the chuck and being supported by the wafer supporting fingers.

Figs. 6A and 6B are respective plan and side elevation fragmentary views of the buffer station of this invention showing the rotatable arms in the wafer supporting position and the first wafer supported by the wafer supporting fingers.

Figs. 7A and 7B are respective plan and side elevation fragmentary views of the buffer station of this invention showing the rotatable arms in the wafer supporting position and supporting a second wafer while the first wafer is still supported by the wafer supporting fingers. Figs. 8 A and 8B are respective plan and side elevation fragmentary views of the buffer station of this invention showing the rotatable arms in the wafer supporting position and supporting the second wafer, the first wafer having been removed from the supporting fingers by a robot.

Figs. 9 A and 9B are respective plan and side elevation fragmentary views of the buffer station of this invention showing the rotatable arms in the wafer supporting position, and the optional chuck elevating the second wafer to the inspection elevation.

Figs. 10A and 10B are respective plan and side elevation fragmentary views of the buffer station of this invention showing the rotatable arms in the wafer releasing position and the optional chuck lowering the second wafer from the inspection elevation toward the supporting fingers.

Figs. 11 A to 1 lH are plan and sectional elevation views of an alternative rotatable arm embodiment of this invention shown in a series of views representing a multiple wafer inspection operation.

Figs. 12A and 12B are respective plan and side elevation views of an alternative buffer station of this invention showing upper and lower rotatable arms in the wafer supporting positions for supporting wafers at first and second elevations. Figs. 13 A and 13B are respective side elevation and plan views of an alternative post and a linearly extensible arm that moves between wafer supporting and releasing positions.

Figs. 14A and 14B are respective side elevation and plan views of an alternative post and a hinged arm that moves between wafer supporting and releasing positions. Detailed Description of Preferred Embodiments

Figs. 1-3 show a specimen buffer station 10 of this invention for use in a specimen processing system including a robot (not shown). Buffer station 10 is beneficial for use in any processing environment where a specimen 12, such as a semiconductor wafer is unloaded by the robot at a specimen processing location from which the specimen 12 is later reloaded by the same robot or another robot. Buffer station 10 is advantageous because robot operation is less dependent, or even independent of, specimen movements associated with buffer station 10, resulting in increased specimen processing throughput. Buffer station 10 includes a base 14 that provides a planar surface. Base 14 further includes at least two, but preferably three specimen supporting fingers 18 that protrude a first distance 20 above base 14 and at least two, but preferably three rotatable arms 22. Rotatable arms 22 extend from posts 27 that support, and impart rotating motion to rotatable arms 22. Each arm 22 has a specimen supporting surface 24 that is located a second distance 26 above base 14. The specimen supporting surface 24 may be configured as a step in arm 22 which provides an edge to limit movement of the specimen 12. However, the specimen supporting surface 24 may be configured with alternative shapes provided that the surface 24 provides a generally planar support. The buffer station 10 operates in conjunction with a handling system for elevating specimens 12 to an appropriate position for processing. The handling system may be embodied in various ways known in the art. In the embodiment shown in Figs. 1-3, the handling system includes a chuck 16 that nests within an aperture in the base 14. The aperture is concentrically disposed between the fingers 18 and the posts 27. The chuck 16 vertically extends between the fingers 18 and posts 27 and supports, elevates, and rotates a specimen 12. As shown in Figs. 1-3, the chuck 16 and posts 27 rotate about parallel axes. Alternatively, the handling system may include an arm that lowers from above the specimen 12 to retain the specimen 12. The arm may be connected to a vacuum grip that secures the specimen 12 upon contact. One of skill in the art will appreciate that a handling system may be configured in various implementations that would operate with the present invention.

Base 14 may be mounted on or otherwise connected to x- and y-axis translation stages 28 and 30 for providing specimen positioning capability.

Fig. 1 shows rotatable arms 22 in a specimen supporting position and, in dashed lines, in a specimen releasing position. Rotatable arms 22 rotate concurrently by any of various well-known means, such as driving posts 27 with an actuator, belt, solenoid(s), gear(s), or pulleys.

Figs. 2A and 2B show rotatable arms 22 in the specimen supporting position for supporting specimen 12 at the second distance 26 above base 14. Specimen 12 is shown by way of example only in phantom lines to represent a transparent specimen. Specimen 12 may be a semiconductor wafer having a finite thickness. Fig. 2B shows chuck 16 elevated to a distance between first and second distances 20 and 26.

Figs. 3 A and 3B show rotatable arms 22 in the specimen releasing position in which specimen supporting fingers 18 can support specimen 12 at first distance 20 above base 14. Fig. 3B shows chuck 16 (or a robot) elevated to a distance less than first distance 20. Chuck 16 can be elevated over distances ranging from substantially less than the first distance 20 to substantially greater than the second distance 26. Chuck 16 is movable by any of various well-known means. Other handling systems would likewise elevate the specimen 12 to the same heights.

A method of processing semiconductor wafers by employing buffer station 10 is described below with reference to Figs. 4-10.

Figs. 4A and 4B show a first wafer processing operation in which rotatable arms 22 are in the wafer releasing position and chuck 16 supports a first wafer 40 at a processing distance 42 above base 14.

Figs. 5A and 5B show a first wafer storage operation in which rotatable arms 22 remain in the wafer releasing position and first wafer 40 is lowered by chuck 16 for storage on wafer supporting fingers 18. Figs. 6A and 6B show an intermediate operation in which rotatable arms 22 rotate to the wafer supporting position while first wafer 40 remains stored on wafer supporting fingers 18.

Figs. 7A and 7B show a second wafer storing operation in which rotatable arms 22 remain in the wafer supporting position and receive a second wafer 44 from a robot (not shown) while first wafer 40 remains stored on wafer supporting fingers 18. The robot serves to deliver unprocessed specimens to the buffer station 10 and retrieve processed specimens 12.

Figs. 8A and 8B show a first wafer retrieving operation in which rotatable arms 22 continue supporting second wafer 44 while first wafer 40 (no longer shown) was retrieved from supporting fingers 18 by the robot.

Figs. 9A and 9B show a second wafer processing operation in which rotatable arms 22 remain in the wafer supporting position and chuck 16 elevates second wafer 44 to processing distance 42 above base 14. When the second wafer processing operation is completed, the buffer station has returned to substantially the state shown in Figs. 4A and 4B.

Figs. 10A and 10B show a second wafer storing operation in which rotatable arms 22 rotate to the wafer releasing position and chuck 16 lowers second wafer 44 toward supporting fingers 18. When the second wafer storing operation is completed, the buffer station has returned to substantially the state shown in Figs. 5A and 5B.

In an alternative embodiment of this invention, supporting fingers 18, rotatable arms 22, and posts 27 are replaced by at least two, and preferably three pairs of coaxially actuated upper and lower specimen supporting arms. Figs. 11 A to 11H show a series of views representing how the alternative embodiment carries out the method of inspecting semiconductor wafers that was described with reference to Figs. 4-10.

Fig. 1 IE best shows the structure of this embodiment. Posts 27 and fingers 18 (Figs. 1-10) are replaced by outer post 50 and inner post 52 that are coaxially and independently rotatable about a common longitudinal axis 54. An upper arm 56 protrudes from outer post 50, and a lower arm 58 protrudes from inner post 52 and through an opening in outer post 50. Upper arm 56 and lower arm 58 have respective specimen supporting surfaces 60 and 62 that are positioned to support wafers at the respective second and first distances 26 and 20 above base 14. Upper and lower arms 56 and 58 are independently rotatable to the above-described wafer supporting and releasing positions.

Employing the alternative embodiment to carry out the method of inspecting semiconductor wafers is described below. Fig. 11 A shows the first wafer processing operation in which upper and lower arms 56 and 58 are both in the wafer releasing position and chuck 16 supports first wafer 40 at processing distance 42 above base 14.

Fig. 1 IB shows a rotation operation in which inner post 52 rotates lower arm 58 to the wafer supporting position while upper arm 56 remains in the wafer releasing position.

Fig. 11C shows the first wafer storage operation in which first wafer 40 is lowered by chuck 16 for storage on lower arm 58.

Fig. 1 ID shows another rotation operation in which outer post 50 rotates upper arm 56 to the wafer supporting position while lower arm 58 continues supporting first wafer 40.

Fig. 1 IE shows the second wafer storing operation in which upper and lower arms 56 and 58 remain in the wafer supporting position and upper arm 56 receives second wafer 44 from the robot (not shown) while first wafer 40 remains stored on lower arm 58. Fig. 1 IF shows the first wafer retrieving operation in which upper arm 56 continues supporting second wafer 44 while first wafer 40 (no longer shown) was retrieved from lower arm 58 by the robot.

Fig. 11G shows the second wafer processing operation in which upper and lower arms 56 and 58 remain in the wafer supporting position and chuck 16 elevates second wafer 44 to processing distance 42 above base 14.

Fig. 11H shows yet another rotation operation in which upper and lower arms 56 and 58 both rotate to the wafer releasing position, which returns the buffer station to substantially the processing operation state shown in Fig. 11 A.

Figs. 12A and 12B show an alternative embodiment of the present invention in which fingers 18 (Figs. 1-10) are replaced by lower posts 70. Lower posts 70 may be disposed non-coaxially relative to posts 27. Each lower post 70 may be disposed equidistantly between posts 27, adjacent posts 27, or at other suitable locations. Lower posts 70 are each connected to a corresponding lower arm 72. Arms 22 and 72 have specimen supporting surfaces that are positioned to support wafers at the respective second and first distances 26 and 20 above base 14. Lower arms 72 rotate independently from arms 22 to the above-described wafer supporting and releasing positions in support of a wafer processing method described in reference to Figs. 11A-11H.

Figs. 13 A and 13B show an alternative embodiment for a post 76 and an extensible arm 78. Arm 78 is linearly actuated to horizontally extend and retract to specimen supporting and releasing positions, with the supporting position shown in phantom. Accordingly, arm 78 does not rotate but extends and retracts through mechanisms well known in the art. In one embodiment, arm 78 is configured for telescoping extension and retraction as shown. As before, arm 78 includes a supporting surface 24 for supporting a specimen. Skilled persons will appreciate that arm 78 may be substituted for arms 22, 56, 58, and 72 in previously disclosed embodiments. Figs. 14A and 14B show an alternative embodiment for a post 80 and a hinged arm 82. Arm 82 vertically rotates to specimen supporting and releasing positions, with the supporting position shown in phantom. Arm 82 may include a hinge 84 to enable vertical rotation. Post 80 may include some or all of the mechanisms commonly known in the art for movement of arm 82. As in previous embodiments, arm 82 includes a supporting surface 24. Arm 82 maybe substituted for arms 22, 56, 58, and 72 in previously disclosed embodiments. Skilled persons will appreciate that arms 78 and 82 of Figs. 13A, 13B, 14A, and 14B maybe operated in support of wafer processing methods disclosed above.

Skilled persons will recognize that portions of this invention may be implemented differently from the implementations described above for preferred embodiments. Fingers 18 and rotatable arms 22 may vary in their configurations and still be included within the scope of the present invention. Buffer station 10 of the present invention can operate with a robot that simultaneously carries two or more wafers, and can be readily modified to include a pre-alignment unit. It will be obvious to those having skill in the art that many changes may be made to the details of the above-described embodiments of this invention without departing from the underlying principles thereof. Accordingly, it will be appreciated that this invention is also applicable to specimen handling applications other than those found in semiconductor processing. The scope of the invention should, therefore, be determined only by the following claims.

Claims

1. A buffer apparatus for use in handling wafer specimens, comprising: a base; a plurality of fingers disposed on the base and protruding a first distance from the base for supporting a specimen; a plurality of posts disposed on the base; and a plurality of movable arms, each arm extending from a corresponding post and having a supporting surface for supporting a specimen, the arms movable between a first position wherein the supporting surface supports a specimen a second distance from the base and a second position for releasing a specimen.

2. The buffer apparatus of claim 1, wherein the apparatus comprises three fingers, three posts, and three movable arms.

3. The buffer apparatus of claim 1, wherein the base includes an aperture disposed concentrically within the base.

4. The buffer apparatus of claim 1, further comprising x-axis and y-axis translation stages connected to the base for providing operable movement of the base.

5. The buffer apparatus of claim 1, wherein in the first position the movable arms extend over an adjacently disposed finger.

6. The buffer apparatus of claim 1, wherein the arms horizontally rotate between the first and second positions.

7. The buffer apparatus of claim 1, wherein the arms horizontally extend and retract between the first and second positions.

8. The buffer apparatus of claim 1, wherein the arms vertically rotate between the first and second positions.

9. A buffer apparatus for use in handling wafer specimens, comprising: a base having an aperture; a plurality of fingers disposed on the base, the fingers protruding a first distance from the base for supporting a specimen; a plurality of posts disposed on the base; a plurality of movable arms, each arm extending from a corresponding post and having a supporting surface for supporting a specimen, the arms movable between a first position wherein the supporting surface supports a specimen a second distance from the base and a second position for releasing a specimen; and a chuck disposed within the aperture and extendable between the posts and fingers to thereby contact and elevate a specimen.

10. The buffer apparatus of claim 9, wherein the apparatus comprises three fingers, three posts, and three movable arms.

11. The buffer apparatus of claim 9, further comprising x-axis and y-axis translation stages connected to the base and providing operable movement of the base.

12. The buffer apparatus of claim 9, wherein the arms rotate horizontally between the first and second positions.

13. The buffer apparatus of claim 9, wherein the arms horizontally extend and retract between the first and second positions.

14. The buffer apparatus of claim 9, wherein the arms vertically rotate between the first and second positions.

15. A buffer apparatus for use in handling wafer specimens, comprising: a base; a plurality of posts disposed on the base; a plurality of movable lower arms, each lower arm extending from a corresponding post and having a supporting surface for supporting a specimen, the lower arms movable between a first position wherein the supporting surface supports a specimen a first distance from the base and a second position for releasing a specimen; and a plurality of movable upper arms, independently movable from the lower arms, each upper arm extending from a corresponding post and having a supporting surface for supporting a specimen, the upper arms movable between a first position wherein the supporting surface supports a specimen a second distance from the base and a second position for releasing a specimen.

16. The buffer apparatus of claim 15, wherein the apparatus comprises three posts, three lower arms, and three upper arms.

17. The buffer apparatus of claim 15, wherem the base includes an aperture disposed concentrically within the base.

18. The buffer apparatus of claim 15, further comprising x-axis and y-axis translation stages connected to the base for providing operable movement of the base.

19. The buffer apparatus of claim 15, wherein each post includes: an outer post coupled to a corresponding upper arm and providing rotatable movement of the upper arm, the outer post having, an interior cavity, and a gap in communication with the cavity; and an inner post disposed within the interior cavity and coupled to a corresponding lower arm extending through the gap, the inner post providing rotatable movement of the lower arm.

20. The buffer apparatus of claim 15, wherein the lower and upper arms horizontally extend and retract between first and second positions.

21. The buffer apparatus of claim 15, wherein the lower and upper arms vertically rotate between first and second positions.

22. A buffer apparatus for use in handling wafer specimens, comprising: a base having an aperture; a plurality of posts disposed on the base; a plurality of movable lower arms, each lower arm extending from a corresponding post and having a supporting surface for supporting a specimen, the lower arms movable between a first position wherein the supporting surface supports a specimen a first distance from the base and a second position for releasing a specimen; and a plurality of movable upper arms, independently movable from the lower arms, each upper arm extending from a corresponding post and having a supporting surface for supporting a specimen, the upper arms movable between a first position wherein the supporting surface supports a specimen a second distance from the base and a second position for releasing a specimen; and a chuck disposed within the aperture and extendable between the posts to thereby contact and elevate a specimen.

23. The buffer apparatus of claim 22, wherein the apparatus comprises three posts, three lower arms, and three upper arms.

24. The buffer apparatus of claim 22, further comprising x-axis and y-axis translation stages connected to the base for providing operable movement of the base.

25. The buffer apparatus of claim 22, wherein each post includes: an outer post coupled to a corresponding upper arm and providing rotatable movement of the upper arm, the outer post having, an interior cavity, and a gap in communication with the cavity; and an inner post disposed within the interior cavity and coupled to a corresponding lower arm extending through the gap, the inner post providing rotatable movement of the lower arm.

26. The buffer apparatus of claim 22, wherein the lower and upper arms horizontally extend and retract between first and second positions.

27. The buffer apparatus of claim 22, wherein the lower and upper arms vertically rotate between first and second positions.

28. A buffer apparatus for use in handling wafer specimens, comprising: a base; a plurality of lower posts disposed on the base; a plurality of movable lower arms, each lower arm extending from a corresponding lower post and having a supporting surface for supporting a specimen, the lower arms movable between a first position wherein the supporting surface supports a specimen a first distance from the base and a second position for releasing a specimen; a plurality of upper posts disposed on the base; and a plurality of movable upper arms, independently movable from the lower arms, each upper arm extending from a corresponding upper post and having a supporting surface for supporting a specimen, the upper arms movable between a first position wherein the supporting surface supports a specimen a second distance from the base and a second position for releasing a specimen.

29. The buffer apparatus of claim 28, wherein the apparatus comprises three lower posts, three lower arms, three upper posts, and three upper arms.

30. The buffer apparatus of claim 28, wherein the base includes an aperture disposed concentrically within the base.

31. The buffer apparatus of claim 28, further comprising x-axis and y-axis translation stages connected to the base for providing operable movement of the base.

32. The buffer apparatus of claim 28, wherein the lower and upper arms horizontally rotate between first and second positions.

33. The buffer apparatus of claim 28, wherein the lower and upper arms horizontally extend and retract between first and second positions.

34. The buffer apparatus of claim 28, wherein the lower and upper arms vertically rotate between first and second positions.