US20020081948A1

US20020081948A1 - Flexible bending member for a workpiece carrier apparatus

Info

Publication number: US20020081948A1
Application number: US09/748,608
Authority: US
Inventors: Clinton Fruitman
Original assignee: Speedfam IPEC Corp
Current assignee: Speedfam IPEC Corp
Priority date: 2000-12-26
Filing date: 2000-12-26
Publication date: 2002-06-27

Abstract

A flexible membrane for a wafer polishing apparatus has a central contact portion, an annular bending element connected to the central contact portion and an outer annual ring connected to the annular bending element. The membrane is configured to apply uniform pressure to a workpiece during polishing.

Description

FIELD OF THE INVENTION

The present invention relates, generally, to systems for polishing or planarizing workpieces such as semiconductor wafers. More particularly, the present invention relates to a flexible bending member for a workpiece carrier apparatus that improves the uniform polishing of workpieces during a polishing procedure.

BACKGROUND OF THE INVENTION

Many electronic and computer-related products such as semiconductors, CD-ROMs, and computer hard disks require highly polished surfaces to achieve optimum operational characteristics. For example, high-quality and extremely precise wafer surfaces are often needed during the production of semiconductor-based integrated circuits. During the fabrication process, the wafers generally undergo multiple masking, etching, and dielectric and conductor deposition processes. Because of the high-precision required in the production of these integrated circuits, an extremely flat surface is generally needed on at least one side of the semiconductor wafer to ensure proper accuracy and performance of the microelectronic structures created on the wafer surface. As the size of integrated circuits decreases and the density of microstructures on integrated circuits increases, the need for accurate and precise wafer surface polishing increases.

Chemical Mechanical Polishing (“CMP”) machines have been developed to polish or planarize semiconductor wafer surfaces to the flat condition desired for integrated circuit components and the like. For examples of conventional CMP processes and machines, see U.S. Pat. No. 4,805,348, issued Feb. 21, 1989 to Arai et al.; U.S. Pat. No. 4,811,522, issued Mar. 14, 1989 to Gill; U.S. Pat. No. 5,099,614, issued Mar. 31, 1992 to Arai et al.; U.S. Pat. No. 5,329,732, issued Jul. 19, 1994 to Karlsrud et al.; U.S. Pat. No. 5,498,196, issued Mar. 12, 1996 to Karlsrud et al.; U.S. Pat. No. 5,498,199, issued Mar. 12, 1996 to Karlsrud et al.; U.S. Pat. No. 5,558,568, issued Sep. 24, 1996 to Talieh et al.; and U.S. Pat. No. 5,584,751, issued Dec. 17, 1996 to Kobayashi et al.

Typically, a CMP machine includes a wafer carrier configured to hold, rotate, and transport a wafer during the process of polishing or planarizing the wafer. The wafer carrier is rotated to cause relative lateral motion between the polishing surface and the wafer to produce a substantially uniform thickness. In general, the polishing surface includes a horizontal polishing pad, the hardness and density of which depends on the material that is to be polished and the degree of precision required in the polishing process.

During a polishing operation, the wafer carrier applies pressure such that the wafer engages the polishing surface with a desired amount of force. The carrier and the polishing pad are rotated or orbited, typically at different velocities, to cause relative lateral motion between the polishing pad and the wafer to promote uniform polishing.

A variety of wafer carrier designs have been used in CMP systems. Earlier wafer carrier designs used a flat pressure plate to press the wafer against a polishing surface. However, flat plates were not able to adjust to the nonconformities of the wafers and thus were not able to apply uniform pressure to the wafer. In addition, flat pressure plate carriers often resulted in greater abrasion in a small region adjacent to the edge of the wafer. To address this problem, some wafer carrier designs utilize a bladder or other flexible membrane element in an attempt to apply uniform pressure to the wafer. For examples of wafer carriers employing flexible membrane elements, see U.S. Pat. No. 5,851,140, issued Dec. 22, 1998 to Barns, et al.; U.S. Pat. No. 6,056,632, issued May 2, 2000 to Mitchel et al.; and U.S. Pat. No. 6,106,378, issued Aug. 22, 2000 to Perlov et al., which patents are herein incorporated by this reference.

Conventional types of membrane carriers include three types, those in which the bladder is vertically suspended, those in which the bladder is vertically suspended with enhanced wafer axis movement devices, such as bellows or toroidal walls, and those in which the bladder is horizontally suspended. While the first two types of bladder carriers provide good translation of the wafer in the vertical direction, shear effects of both torsional and lash natures cause wrinkling of the bladder at the edges of the wafer and pressure differentials across the surface of the wafer. The third type of wafer carrier, while resistant to torsional and lash effects, typically exhibits poor vertical movement and requires other adaptations such as separately gimbaled edges to maintain uniform pressure across the wafer.

A need therefore exists for a system for pressing a wafer against a polishing surface while applying uniform pressure to a wafer.

SUMMARY OF INVENTION

These and other aspects of the present invention will become more apparent to those skilled in the art from the following non-limiting detailed description of preferred embodiments of the invention taken with reference to the accompanying figures.

In accordance with an exemplary embodiment of the present invention, a flexible membrane for a wafer polishing apparatus has a central contact portion, an annular bending element connected to the central contact portion, and an outer annular ring connected to the annular bending element. The membrane is configured to apply uniform pressure to a workpiece during polishing.

In accordance with another exemplary embodiment of the present invention, the annular bending element has a first thickness and the outer annular ring has a second thickness and the first thickness of the annular bending element is approximately equal to the second thickness of the outer annular ring.

In accordance with a further exemplary embodiment of the present invention, the annular bending element has a first thickness and the outer annular ring has a second thickness and the first thickness of the annular bending element is less than the second thickness of the outer annular ring.

In accordance with yet another exemplary embodiment, the central contact portion has a third thickness. The first thickness of the annular bending element is approximately half the third thickness of the central contact portion.

In accordance with yet a further exemplary embodiment of the present invention, a workpiece carrier head for a chemical mechanical polishing apparatus has a carrier plate and a flexible membrane. The flexible membrane has an outer peripheral edge, an annular bending element positioned proximate to the outer peripheral edge, and a central contact portion disposed proximate to the annual bending element. The flexible membrane is connected to the carrier plate at the outer peripheral edge, forming a cavity between the central contact portion of the flexible membrane and the carrier plate. The workpiece carrier head also includes an annular retaining ring disposed adjacent the peripheral edge of the flexible membrane.

In accordance with another exemplary embodiment of the present invention, a method of polishing a workpiece includes loading a workpiece into a workpiece carrier head. The workpiece carrier head comprises a carrier plate and a circular flexible membrane. The circular flexible membrane has an outer peripheral edge, an annular bending element positioned proximate to the outer peripheral edge and a central contact portion disposed proximate to the annular bending element. The membrane is connected to the carrier plate at the outer peripheral edge, forming a cavity between the central contact portion of the flexible membrane and the carrier plate. The workpiece carrier head also has an annular retaining ring disposed adjacent the peripheral edge of the flexible membrane. The method further includes moving the workpiece carrier head until the workpiece is adjacent a polishing pad. The cavity is pressurized such that the flexible membrane bends at the annular bending element and the central contact portion applies pressure to the workpiece, urging the workpiece against the polishing pad. Relative motion is caused between the workpiece and the polishing pad.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Exemplary embodiments of the present invention will hereafter be described in conjunction with the appended drawing figures, wherein like designations denote like elements, and: [0016]
FIG. 1 is a side cross-sectional view of an exemplary embodiment of a wafer carrier head with a flexible membrane of the present invention; [0017]
FIG. 2 is a side cross-sectional view of the wafer carrier head of FIG. 1 with a pressurized cavity; [0018]
FIG. 3 is a side cross-sectional view of an alternative exemplary embodiment of a wafer carrier head with a flexible membrane of the present invention; and [0019]
FIG. 4 is a side cross-sectional view of an alternative exemplary embodiment of the flexible membrane of the present invention.[0020]
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention. [0021]

DETAILED DESCRIPTION OF THE INVENTION

The following description is of exemplary embodiments only and is not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention as set forth. [0022]
Referring to FIG. 1, a wafer carrier apparatus of the present invention includes a [0023] wafer carrier head 10 having a rigid carrier plate 12. The wafer carrier head 10 is suitably configured to connect to a rotational drive mechanism (not shown) by a plurality of screws (not shown) which are received within threaded apertures 38 positioned within carrier plate 12. Carrier plate 12 has a planar upper surface 14 and a parallel lower surface 16. The lower surface 16 has a plurality of recessed plenums 18 which are in fluid communication with a top surface 20 of upper surface 14 via secondary apertures 22. Lower surface 16 of carrier plate 12 also has a central recessed area 24 which is in fluid communication with top surface 20 of upper surface 14 via a primary aperture 26.
A retaining [0024] ring 28 is connected to the lower surface 16 of carrier plate 12. A circular flexible membrane 30 is held between carrier plate 12 and retaining ring 28 stretching across the lower surface 16 of carrier plate 12 to form a flexible diaphragm beneath the carrier plate. Membrane 30 preferably is formed of EPDM rubber, natural rubber or SBR rubber, although it will be appreciated that a thin sheet of any suitable soft, elastic material may be used. To minimize torsional effects, membrane 30 may be reinforced with Kevlar® fibers or any other suitable reinforcing material. A cavity 34 is formed between carrier plate 12 and membrane 30.
As shown in FIG. 1, [0025] membrane 30 has an annular recess 32 proximate its peripheral edge which forms an annular integral bending element 36 of membrane 30. Bending element 36 is surrounded by an annular outer ring 42. A relatively planar, circular wafer contact portion 40 of membrane 30 is surrounded circumferentially by annular recess 32. Bending element 36 has a thickness T₁which may be less than the thickness T₂of outer ring 42 or thickness T₃of contact portion 40 of membrane 30. Alternatively, thickness T₁of bending element 36 may be equal to the thickness T₂of the outer ring 42 of membrane 30 and less than the thickness T₃of the contact portion 40 of membrane 30. Preferably, thickness T₁of bending element 36 is approximately half the thickness T₃of contact portion 40 of membrane 30.
The outside diameter of [0026] annular recess 32 may be positioned a distance W₁from the outside peripheral edge of membrane 30, where W₁is equal to the width of retaining ring 28 and annular outer ring 42. In an alternative embodiment, as shown in FIG. 3, the outside diameter of annular recess 32 may be positioned a distance W₂from the outside peripheral edge of membrane 30 where W₂is the width of annual outer ring 42 and is less than the width of retaining ring 28. In this embodiment bending element 36 is longer and is thus able to bend in the vertical direction a greater distance. Alternatively, W₂may be greater than the width of retaining ring 28. Wafer contact portion 40 may have a diameter greater than, equal to or less than the diameter of the wafer. However, with wafer contact portion 40 having a diameter less than the wafer, edge effects may be further reduced.
[0027] Membrane 30 may be fabricated from one piece of material, as illustrated in FIG. 1, or, alternatively, membrane 30 may be fabricated from layers laminated together. For example, as illustrated in FIG. 4, membrane 30 may include ring member 200 and flexible center disc 210, both of which are fixedly attached to a support member 220 to form recess 32.
Referring again to FIG. 1, retaining [0028] ring 28 is fixedly attached to membrane 30 by any suitable glue, epoxy, cement or the like. Membrane 30 is similarly fixedly attached to carrier plate 12 by any suitable glue, epoxy, cement or the like. Alternatively, carrier plate 12, membrane 30 and retaining ring 28 may be connected by a screw, pin or any other suitable fixation device. In a further alternative embodiment, retaining ring 28 may be attached directly to carrier plate 12 with membrane 30 securely sandwiched in between.
Referring to FIG. 2, in order to polish a wafer, [0029] carrier head 10 is moved over a wafer storage area and lowered onto a wafer 110. Carrier head 10 is connected to a vacuum source (not shown) which effects a vacuum in cavity 34 through plenums 18 and central recessed area 24 and secondary apertures 22 and primary aperture 26. When a vacuum is effected within cavity 34, the vacuum draws membrane 30 up and into plenums 18 and central recessed area 24, thereby causing a vacuum between wafer 110 and portions of membrane 30 adjacent plenums 18 and central recessed area 24. This action causes wafer 110 to be drawn up against membrane 30. Alternatively, wafer contact portion 40 may have a plurality of apertures (not shown) extending therethrough such that when a vacuum is effected within cavity 34, a suction is created which draws wafer 110 against membrane 30.
The [0030] carrier head 10 then moves wafer 110 adjacent a polishing pad 100 and presses wafer 110 against polishing pad 100, which is mounted on a platen (not shown). The platen may be configured to rotate, orbit, dither or otherwise effect lateral movement between polishing pad 100 and wafer 110. A pressurized fluid is introduced to carrier plate 12 and flows through secondary apertures 22 and primary aperture 26. The fluid is preferably a gas, such as dry air or nitrogen. It will be appreciated that liquids such as deionized water also may be employed. The fluid flows through the secondary apertures 22 and primary aperture 26 in the carrier plate 12 to the plurality of recessed plenums 18 and central recessed area 24, thereby filling cavity 34 between the carrier plate 12 and the flexible membrane 30. This action inflates cavity 34 and exerts pressure against membrane 30 in the direction of arrows A120. The downward force of the fluid causes membrane 30 to bend at bending element 36, thereby exerting a uniform pressure against wafer 110.
Because [0031] membrane 30 is thin, it conforms to the top surface of wafer 110. Membrane 30 is soft and highly flexible conforming to even the minute variations in the wafer surface. As a consequence, wafer 110 is pressed evenly against polishing pad 100. In addition, carrier head 10 applies extremely uniform polish pressure across the entire area of wafer 110, including the edge of the wafer. The extreme flexibility of membrane 30 with bending element 36 allows membrane 30 to respond to small disturbances on the face of wafer 110 which may be caused by some aspect of the polishing process such as pad variation, conditioning of the pad, and slurry flow rate. The flexible membrane is thus able to automatically compensate for such variations and provide uniform pressure between wafer 110 and polishing pad 100. Any energy associated with these disturbances is absorbed by the fluid in cavity 34 instead of increasing the local polishing rate of the semiconductor wafer. In addition, because movement of flexible membrane 30 in the horizontal direction is limited, membrane 30 provides advantages over membranes utilizing bellows or torroidal elements, as membrane 30 is resistant to lash effects that may result from shear stress across the surface of the wafer being polished.
Although the subject invention has been described herein in conjunction with the appended drawing Figures, it will be appreciated that the scope of the invention is not so limited. Various modifications in the arrangement of the components discussed and the steps described herein for using the subject device may be made without departing from the spirit and scope of the invention as set forth in the appended claims. [0032]

Claims

I claim:

1. A flexible membrane for a wafer polishing apparatus comprising:

a) a central contact portion;

b) an annular bending element connected to said central contact portion; and

c) an outer annular ring connected to said annular bending element; wherein said membrane is configured to apply uniform pressure to a workpiece during polishing.

2. The flexible membrane of claim 1, wherein said annular bending element is integrally connected to said outer annular ring.

3. The flexible membrane of claim 1, wherein said annular bending element is integrally connected said central contact portion.

4. The flexible membrane of claim 1, wherein said membrane comprises at least one of EPDM rubber, natural rubber and SBR rubber.

5. The flexible membrane of claim 1, wherein said annular bending element has a first thickness and said outer annular ring has a second thickness and said first thickness is approximately equal to said second thickness.

6. The flexible membrane of claim 1, wherein said annular bending element has a first thickness and said outer annular ring has a second thickness and said second thickness is greater than said first thickness.

7. The flexible membrane of claim 1, wherein said annular bending element has a first thickness and said central contact portion has a third thickness and wherein said first thickness is approximately half of the third thickness.

8. A workpiece carrier head for a chemical mechanical polishing apparatus comprising:

a) a carrier plate;

b) a flexible membrane having an outer peripheral edge, an annular bending element positioned proximate to said outer peripheral edge, and a central contact portion disposed proximate to said annular bending element, wherein said membrane is connected to said carrier plate at said outer peripheral edge, thereby forming a cavity between said central contact portion of said flexible membrane and said carrier plate; and

c) an annular retaining ring disposed adjacent said outer peripheral edge of said flexible membrane.

9. The workpiece carrier head of claim 8, wherein said annular bending element of said flexible membrane has a first thickness and said outer peripheral edge of said flexible membrane has a second thickness, said first thickness being approximately equal to said second thickness.

10. The workpiece carrier head of claim 8, wherein said annular bending element of said flexible membrane has a first thickness and said outer peripheral edge of said flexible membrane has a second thickness, said second thickness being greater than said first thickness.

11. The workpiece carrier head of claim 8, wherein said annular bending element of said flexible membrane has a first thickness and said central contact portion has a second thickness, said first thickness being approximately half said second thickness.

12. The workpiece carrier head of claim 8, wherein said carrier plate comprises at least one fluid conduit by which a source of a vacuum and a source of a pressurized fluid are alternatively connected to the cavity.

13. The workpiece carrier head of claim 8, wherein said outer peripheral edge of said membrane has a first width and said retaining ring has a second width and wherein said first width and said second width are approximately equal.

14. The workpiece carrier head of claim 8, wherein said outer peripheral edge of said membrane has a first width and said retaining ring has a second width and wherein said first width is less than said second width.

15. The workpiece carrier head of claim 8, wherein said outer peripheral edge of said membrane has a first width and said retaining ring has a second width and wherein said first width is greater than said second width.

16. The workpiece carrier head of claim 8, wherein said membrane comprises EPDM rubber.

17. The workpiece carrier head of claim 8, wherein said outer peripheral edge of said flexible membrane is integrally connected to said annular bending element.

18. The workpiece carrier head of claim 8, wherein said central contact portion is integrally connected to said annular bending element.

19. The workpiece carrier element of claim 12, wherein said central contact portion of said flexible membrane comprises a plurality of apertures configured so that when said source of a vacuum is connected to said cavity, a workpiece is drawn against said flexible membrane.

20. A method of polishing a workpiece comprising the steps of:

a) loading a workpiece into a workpiece carrier head comprising:

i) a carrier plate;

ii) a circular flexible membrane having an outer peripheral edge, an annular bending element positioned proximate to said outer peripheral edge and a central contact portion disposed proximate to said annular bending element, wherein said membrane is connected to said carrier plate at said outer peripheral edge, thereby forming a cavity between said central contact portion of said flexible membrane and said carrier plate, and

iii) an annular retaining ring disposed adjacent said peripheral edge of said flexible membrane;

b) moving the workpiece carrier head until the workpiece is adjacent a polishing pad;

c) pressurizing said cavity such that said flexible membrane bends at said annular bending element and said central contact portion applies pressure to said workpiece and urges said workpiece against said polishing pad; and

d) causing relative motion between said workpiece and said polishing pad.

21. The method of claim 20, wherein said loading step further comprises loading said workpiece into said workpiece carrier head, wherein said workpiece carrier head has a plurality of recesses.

22. The method of claim 21, wherein said step of loading further comprises effecting a vacuum in said cavity so that said central contact portion of said flexible membrane adjacent said recesses are drawn into said recesses, thereby effecting a vacuum between said central contact portion and said workpiece.

23. The method of claim 20, wherein said loading step further comprises loading said workpiece into said workpiece carrier head, wherein said central contact portion has a plurality of apertures.

24. The method of claim 23, wherein said loading step further comprises effecting a vacuum in said cavity and within said apertures such that said workpiece is drawn against said central contact portion of said flexible membrane.