Carrier including a multi-volume diaphragm for polishing a semiconductor wafer and a method therefor

BACKGROUND OF THE INVENTION

The present invention relates to semiconductor processing equipment, and more particularly to carriers for holding a semiconductor wafer during chemical-mechanical planarization.

Semiconductor wafers are planarized or polished to achieve a smooth, flat finish before performing process steps that create electrical circuits on the wafer. This polishing is accomplished by securing the wafer to a carrier, rotating the carrier and placing a rotating polishing pad in contact with the rotating wafer. The art is replete with various types of wafer carriers for use during this polishing operation. A common type of carrier is securely attached to a shaft which is rotated by a motor. A wet polishing slurry, usually comprising a polishing abrasive suspended in a liquid, is applied to the polishing pad. A downward polishing pressure is applied between the rotating wafer and the rotating polishing pad during the polishing operation. This system required that the wafer carrier and polishing pad be aligned perfectly parallel in order to properly polish the semiconductor wafer surface.

The wafer carrier typically was a hard, flat plate which did not conform to the surface of the wafer which is opposite to the surface being polished. As a consequence, the carrier plate was not capable of applying a uniform polish pressure across the entire area of the wafer, especially at the edge of the wafer. In an attempt to overcome this problem, the hard carrier plate often was covered by a softer carrier film. The purpose of the film was to transmit uniform pressure to the back surface of the wafer to aid in uniform polishing. In addition to compensating for surface irregularities between the carrier plate and the back wafer surface, the film also was supposed to smooth over minor contaminants on the wafer surface. Such contaminants could produce high pressure areas in the absence of such a carrier film. Unfortunately, the films were only partially effective with limited flexibility and tended to take a “set” after repeated usage. In particular, the set appeared to be worse at the edges of the semiconductor wafer.

The wafer carrier described in U.S. Pat. No. 5,762,544 typifies another problem associated with many prior wafer carrier designs. U.S. Pat. No. 5,762,544 discloses use of a flat, rigid carrier base that was connected to a shaft through a gimballing mechanism intended to keep the carrier base surface parallel to the semiconductor wafer surface during polishing. Typically, the arrangement resulted in applying one pressure across the entire semiconductor wafer surface. Thus, changing the force transferred through the shaft to the carrier base resulted in altering the applied pressure across the entire surface of the semiconductor wafer. The problem with using wafer carriers like the one described in U.S. Pat. No. 5,762,544 is that despite the apparent application of uniform pressure over the wafer surface, some planarization methods form one or more annular depressions near the perimeter of the wafer on the surface upon which circuit deposition is to occur. Only sufficiently smooth, flat portions of the wafer surface can be effectively used for circuit deposition. Thus, the annular depressions limit the useful area of the semiconductor wafer.

Other wafer carrier designs, such as described in U.S. Pat. No. 5,762,539, implement means for applying more than one pressure region across the back surface of the semiconductor wafer to attempt to compensate for uneven removal patterns, such as the annular depressions noted above. Specifically, the carrier described in U.S. Pat. No. 5,762,539 provides a top plate with a plurality of internal chambers that may be independently pressurized. A plurality of holes penetrate the top plate and a pad abutting the bottom surface of the top plate. By pressurizing the individual chambers in the top plate to different magnitudes, different pressure distributions can be established across the wafer surface abutting the pad; however, the pressure distributions are not sufficiently controllable to establish distinct areas across the back surface of the wafer having the same applied pressure. This is because pressurized fluid is directly applied to the back surface of the wafer through the tiny holes in the top plate, and the pressurized fluid is substantially free to move across the wafer's back surface. Thus, pressurized fluid applied to one area of the back surface of the wafer moves into adjacent areas of the wafer's back surface being supplied with a pressurized fluid at a different pressure. Therefore, the ability to control the applied pressure across specified, distinct sections of the wafer is limited, thereby restricting the ability of the design to compensate for anticipated removal problems.

There therefore was a need to provide a carrier design permitting controlled application of multiple pressure regions across the back surface of a semiconductor wafer during polishing.

BRIEF SUMMARY OF THE INVENTION

A general object of the present invention is to provide an improved wafer carrier for polishing semiconductor wafers.

Another object is to provide a wafer carrier which applies uniform pressure over the entire area of the semiconductor wafer, if desired.

Yet another object of the present invention is to provide a wafer carrier which applies non-uniform, yet controlled pressure over the entire area of the semiconductor wafer to compensate for anticipated, troublesome removal patterns such as a perimeter annular depression or a centrally located bulge typically referred to as a center slow problem.

A further object of the present invention is to provide a surface on the carrier which contacts the back surface of the semiconductor wafer and conforms to any irregularities of that back surface. Preferably, the surface of the carrier should conform to even minute irregularities in the back surface of the semiconductor wafer.

These and other objectives are satisfied by a carrier for an apparatus which performs chemical-mechanical planarization of a surface of a workpiece that includes a rigid plate having a major surface. The carrier also includes a first diaphragm of soft, flexible material with a first section for contacting a first surface portion of the workpiece. The first diaphragm is connected to the rigid plate and extends across at least a first portion of the major surface, thereby defining a first cavity therebetween.

The carrier also includes a second diaphragm of soft, flexible material with a second section for contacting a second surface portion of the workpiece. The second diaphragm is also connected to the rigid plate and extends across at least a second portion of the major surface, thereby defining a second cavity therebetween. A plurality of fluid conduits provides pressurized fluid, such as a gas, that is connected to one or more of the cavities.

By pressurizing the cavities to the same or to different pressures, as desired, one can apply a uniform or a controlled, non-uniform pressure distribution over the workpiece surface, respectively. Additionally, since the diaphragms are made from a soft, flexible material, such as polyurethane, or nitrile rubber, or butyl rubber, the diaphragms, which contact the back surface of the workpiece, conform to any irregularities of that back surface.

In the preferred apparatus embodiment of the present invention, only two diaphragms having associated cavities and an inter-diaphragm cavity are included; however, in general, any desired number of diaphragms with their respective cavities and inter-diaphragm cavities may be implemented. Additionally, regardless of the selected number of diaphragms, they may be separate diaphragms connected together or one integral diaphragm having the desired number of independent cavities.

In another embodiment of the present invention, the carrier comprises a rigid plate having a major surface with a plurality of cavities formed therein, a diaphragm of flexible material coupled to and abutting a portion of the major surface, a first member coupled to and abutting a lower surface of the diaphragm, a second member coupled to and abutting the lower surface of the diaphragm, and a plurality of fluid conduits by which a source of pressurized fluid, such as a gas, is connected to at least one of the cavities. As in the prior embodiment of the carrier, appropriate pressurization of the carrier cavities in this later embodiment can compensate for otherwise uneven removal rates during polishing of the workpiece.

The present invention also provides a method for controlling the chemical-mechanical planarization of a surface of a workpiece to compensate for uneven removal rates on the surface comprising: providing a rigid plate having a major surface; pressurizing a first cavity formed by a first diaphragm of soft, flexible material and by a first portion of the major surface of the rigid plate to permit a first section of the first diaphragm to contact a first surface portion of the workpiece which is located on a side that is opposite the surface of the workpiece; pressurizing a second cavity formed by a second diaphragm of soft, flexible material and by a second portion of the major surface of the rigid plate to permit a second section of the second diaphragm to contact a second surface portion of the workpiece which is located on a side that is opposite the surface of the workpiece; selecting pressurization of the cavities to compensate for the uneven removal rates; and polishing the surface of the workpiece.

During polishing, the cavities are pressurized with fluid, such as a gas, which causes the diaphragms to exert force against the workpiece pushing the workpiece into an adjacent polishing pad. Because the diaphragms are made from a thin, soft, and highly flexible material, the diaphragms conform to the back surface of the workpiece which is opposite to the surface to be polished. By conforming to even minute variations in the workpiece surface, the diaphragms exert pressure evenly over the entire back surface of the workpiece, thereby producing uniform polishing.

These and other objects, advantages and aspects of the invention will become apparent from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention and reference is made therefor, to the claims herein for interpreting the scope of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1

is a diametric, cross-sectional, exploded view of a polishing apparatus in accordance with a preferred embodiment of the present invention;

FIG. 2

is a diametric, cross-sectional, fully-assembled view of the polishing apparatus from

FIG. 1

in accordance with a preferred embodiment of the present invention;

FIG. 3

is a diametric cross-sectional view of a portion of the carrier from

FIG. 1

in accordance with a preferred embodiment of the present invention;

FIG. 4

is a diametric cross-sectional view of a portion of the carrier from

FIG. 1

in accordance with an alternate embodiment of the present invention;

FIG. 5

is a perspective view of a portion of a unitary diaphragm in accordance with an alternate embodiment of the present invention;

FIG. 6

is a simplified, cross-sectional view of a plurality of diaphragms that may be coupled together with the carrier in accordance with another alternate embodiment of the present invention;

FIG. 7

is a flowchart of a method for operating the carrier in order to polish a workpiece in accordance with a preferred embodiment of the present invention;

FIG. 8

is a diametric, cross-sectional, fully-assembled view of the carrier in accordance with another alternate embodiment of the present invention;

FIG. 9

is diametric cross-sectional view of a portion of the carrier from

FIG. 8

; and

FIG. 10

is another diametric cross-sectional view of a portion of the carrier from FIG.

8

.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, wherein like reference characters represent corresponding elements throughout the several views, and more specifically referring to

FIG. 1

, a diametric, cross-sectional, exploded view of a polishing apparatus

10

is shown in accordance with a preferred embodiment of the present invention. In the preferred embodiment, apparatus

10

is used to planarize or polish a front surface of a semiconductor wafer; however, apparatus

10

may be used to polish a “workpiece” which is generally defined to include: semiconductor wafers, both bare silicon or other semiconductor substrates such as those with or without active devices or circuitry, and partially processed wafers, as well as silicon on insulator, hybrid assemblies, flat panel displays, Micro Electro-Mechanical Sensors (MEMS), MEMS wafers, hard computer disks or other materials that would benefit from planarization.

Apparatus

10

has a carrier

12

mounted on a spindle shaft

14

that is connected to a rotational drive mechanism by a gimbal assembly (not shown). One end of spindle shaft

14

is connected to a rotating coupling

16

. Rotating coupling

16

is of a type well known to those skilled in the art, such as the rotary coupling manufactured under Rotary Systems Part No. 202196. Rotating coupling

16

permits the transfer of pressurized fluid, such as a gas, through multiple conduits that are fixed on the supply side of rotating coupling

16

, yet moving on the carrier side of rotating coupling

16

. Specifically, tubing

26

a,

26

b,

and

26

c

is stationary. Element

20

represents a source for providing pressurized fluid (e.g., gas) or vacuum. Elements

22

a,

22

b,

and

22

c

represent regulators that control either the degree of pressurization of the fluid (e.g., gas) or the magnitude of supplied vacuum. Pressure and vacuum regulators, such as those manufactured by SMC Pneumatics, Inc. under Part No. IT2011-N32, are well known to those skilled in the art.

Tubing

24

a,

24

b,

and

24

c

is provided between the combination pressurization/vacuum source and the respective regulators

22

a,

22

b,

and

22

c

that are connected to the rotating coupling

16

through tubing

26

a,

26

b,

and

26

c.

Tubing

26

a,

26

b,

and

26

c

is respectively connected to tubing

28

a,

28

b,

and

28

c

through rotating coupling

16

. Tubing

28

a,

28

b,

and

28

c

is shown within an internal cavity of spindle shaft

14

; however, tubing

28

a,

28

b,

and

28

c

need not reside within spindle shaft

14

. Tubing

28

a,

28

b,

and

28

c

is respectively connected to tubing fittings

30

a,

30

b,

and

30

c.

Tubing fittings

30

a,

30

b,

and

30

c

penetrate an upper surface

36

of rigid plate

34

and permit fluid communication through to a lower surface

38

of rigid plate

34

, thereby establishing fluid communication from the combination pressurization/vacuum source

20

all the way through to the lower surface

38

of rigid plate

34

. Tubing

24

a-

24

c,

26

a-

26

c,

and

28

a-

28

c

is preferably flexible and lightweight, though tubing materials of various different flexibilities and weights may be employed. Such tubing is well known to those skilled in the art. Additionally, any one of a variety of different types of tubing fittings well known to those skilled in the art may be used for tubing fittings

30

a-

30

c.

Thus, a plurality of conduits run from the combination pressurization/vacuum source

20

to the major or lower surface

38

of rigid plate

34

, and the conduits provide a source of “pressurized” fluids or gasses to cavities (discussed below). However, the term, “pressurized,” is intended to refer to absolute pressure. Thus, a positive absolute pressure means the fluid, such as a gas, within the conduits is pressurized, and an absolute pressure of zero means vacuum is supplied through the conduits.

Spindle shaft

14

preferably comprises a sturdy, rigid material such as stainless steel; however, any sturdy, rigid, and preferably lightweight material may be used for spindle shaft

14

. Spindle shaft

14

is coupled at one end to rotating coupling

16

, and is connected at an opposite end to rigid plate

34

. Spindle shaft

14

is also supported with journal bearing

18

. The detailed connection of spindle shaft

14

to rigid plate

34

is not shown, as any one of a number of different types of connection may be implemented. A cover is provided comprising an upper section

32

a,

a middle section

32

b,

and a lower section

32

c.

The cover

32

a-

32

c

is connected over rigid plate

34

in order to protect spindle shaft

14

, tubing

28

a-

28

c,

and tubing fittings

30

a-

30

c

from debris. Cover

32

a

-

32

c

is preferably made from a lightweight material, and may be connected to rigid plate

34

in any one of a number of different manners well known to those skilled in the art.

Focusing on the lower surface

38

of rigid plate

34

, as viewed from left to right in

FIG. 1

, lower surface

38

includes an annular recess between positions

38

a,

and

38

b,

a raised annular portion between positions

38

b

and

38

c,

another annular recess between positions

38

c

and

38

d,

and a raised cylindrical portion bounded by position

38

d.

Rigid plate

34

is preferably made of stainless steel, although any sturdy, rigid material may be substituted if desired. A diaphragm

40

is coupled to the rigid plate

34

. Diaphragm

40

includes a centrally disposed section between positions

40

a

and

40

b

for contacting a surface portion of an upper surface of a workpiece (e.g., a semiconductor wafer

56

, FIG.

2

). The contact section of diaphragm

40

is substantially circular. Diaphragm

40

also includes a rim

40

c

facilitating connection with rigid plate

34

, and a bellows

40

d

located between the rim

40

c

and the wafer contact section bounded by positions

40

a

and

40

b.

Another diaphragm

42

also includes a section for contacting a surface portion of upper surface

56

u

of semiconductor wafer

56

. The wafer contact section for diaphragm

42

comprises an annular area bounded by positions

42

a

and

42

b

. Diaphragm

42

includes an inner rim

42

c

and an outer rim

42

d

facilitating connection with rigid plate

34

. Diaphragm

42

also includes a bellows

42

e

between the diaphragm's wafer contact section and rims

42

c

and

42

d.

Both diaphragms

40

and

42

are preferably made of a soft, flexible material, such as polyurethane; however, any soft, flexible and substantially thin material may be used for diaphragms

40

and

42

.

An annular clamp

44

is fastened to rigid plate

34

using fasteners

46

(e.g., screws or other connectors) and corresponding threaded cavities

51

, thereby securely fastening rims

40

c

and

42

c

against the lower surface

38

of rigid plate

34

. Similarly, wear ring

48

is fastened against the lower surface

38

of rigid plate

34

using fasteners

49

and threaded cavities

55

. When fastened to rigid plate

34

, wear ring

48

clamps outer rim

42

d

of diaphragm

42

against lower surface

38

of rigid plate

34

. A protruding rib in outer rim

42

d

is inserted into a notch

53

located in lower surface

38

of rigid plate

34

to facilitate proper positioning of diaphragm

42

. As such, the wear ring

48

clamps outer rim

42

d

against lower surface

38

.

FIG. 2

is a diametric, cross-sectional, fully-assembled view of the polishing apparatus from

FIG. 1

in accordance with a preferred embodiment of the present invention.

FIG. 2

shows the polishing apparatus in contact with the back or upper surface

56

u

of a workpiece

56

(e.g., a semiconductor wafer). Workpiece

56

also has a front or lower surface

56

l

which is polished when placed in contact with a polishing pad (not shown).

A cavity

50

is formed between diaphragm

40

and lower surface

38

of rigid plate

34

. Similarly, a cavity

52

is formed between diaphragm

42

and lower surface

38

of rigid plate

34

. Additionally, a cavity

54

is formed between a portion of diaphragm

40

, a portion of diaphragm

42

, and a portion of the semiconductor wafer

56

. Cavity

54

is referred to as the “inter-diaphragm cavity.” Cavity

50

is generally cylindrical in shape, while cavities

52

and

54

are generally annular in shape and are concentrically located with respect to cavity

50

.

Referring to

FIG. 3

, a diametric cross-sectional view of a portion of carrier

12

is shown in accordance with a preferred embodiment of the present invention. The carrier portion is shown with diaphragm sections conformably engaged with the upper surface of a semiconductor wafer

56

. Tubing or conduits

28

a,

28

b,

and

28

c

provide pressurized fluid (e.g., gas) or vacuum through rigid plate

34

to their respective cavities

52

,

54

, and

50

. Diaphragm

40

and rigid plate

34

form cavity

50

, while diaphragm

42

and rigid plate

34

form cavity

52

. Inter-diaphragm cavity

54

is formed by portions of diaphragm

40

and

42

, as well as a portion of semiconductor wafer

56

. In this version of inter-diaphragm cavity

54

, the side boundaries of cavity

54

are formed by portions of diaphragms

40

and

42

, while the upper boundary of cavity

54

is formed by rigid plate

34

, and the lower boundary is formed by semiconductor wafer

56

. In this regard, substantially no portion of the lower boundary of inter-diaphragm cavity

54

is provided by diaphragms

40

and

42

. The contact sections of diaphragms

40

and

42

are slightly bent or angled due to their conforming to minute variations in the upper surface

56

u

(

FIG. 2

) of semiconductor wafer

56

.

Referring to

FIG. 4

, a diametric cross-sectional view of a portion of carrier

12

is shown in accordance with an alternate embodiment of the present invention. The portion of carrier

12

is shown with diaphragm sections conformably engaged with the upper surface of a semiconductor wafer

56

. The version of carrier

12

shown in

FIG. 4

is substantially similar to that shown in FIG.

3

. One difference between these two versions of carrier

12

is that the lower boundary of inter-diaphragm cavity

54

is partially formed by diaphragms

40

and

42

. In

FIG. 3

, the lower boundary of the inter-diaphragm cavity

54

is exclusively formed by the semiconductor wafer

56

.

Another difference depicted in the carrier

12

of

FIG. 4

is that diaphragms

40

and

42

include one or more apertures

58

through their respective contact sections. One or more apertures

58

may be located in one or more of the contact sections corresponding to cavities

50

,

52

, and

54

. As described in more detail in conjunction with

FIG. 7

, apertures

58

enable chucking of the semiconductor wafer prior to polishing. Although apertures

58

are shown in each of cavities

50

,

52

, and

54

in

FIG. 4

, it is not necessary that apertures

58

are present in each cavity.

Referring to

FIG. 5

, a perspective view of a portion of a unitary diaphragm

60

is shown in accordance with an alternate embodiment of the present invention. As shown, diaphragm

60

provides a plurality of cavities when connected to the carrier's rigid plate.

Diaphragm

60

is substantially identical to diaphragms

40

and

42

from

FIGS. 1 and 2

, when diaphragms

40

and

42

are taken in combination. In other words, the only difference between diaphragms

40

and

42

, and diaphragm

60

is that diaphragm

60

comprises a single, integral diaphragm. Therefore, diaphragm

60

could be used in lieu of diaphragms

40

and

42

in carrier

12

as shown in

FIGS. 1-4

.

Diaphragm

60

includes a central, circular-shaped contact section

62

bounded by positions

64

and

66

. A bellows portion

68

extends up from central contact section

62

. An annular connecting section

70

includes apertures

72

used in fastening diaphragm

60

to rigid plate

34

(FIG.

1

). The majority of apertures

72

are used to fasten diaphragm

60

to rigid plate

34

; however, at least one of the apertures

72

is used to pressurize the inter-diaphragm cavity

54

(

FIG. 2

) formed between bellows portions

68

and

74

. An annular contact section

78

is bounded by positions

80

and

82

. Another bellows portion

76

extends upwardly from annular contact section

78

. An annular rim

84

and protruding rib portion

86

are used to align and securely fasten diaphragm

60

between wear ring

48

(

FIG. 1

) and rigid plate

34

. Cavity

50

(

FIG. 2

) is formed between bellows

68

, central contact section

62

, and rigid plate

34

. The inter-diaphragm cavity

54

(

FIG. 2

) is formed between bellows portion

68

, bellows portion

74

, annular connecting section

70

, and wafer

56

(FIG.

2

). Cavity

52

(

FIG. 2

) is formed between annular contact section

78

, bellows portions

74

and

76

, and rigid plate

34

.

FIG. 6

shows a simplified, cross-sectional view of a plurality of diaphragms that may be coupled together with the carrier in accordance with another alternate embodiment of the present invention. The distinct diaphragm sections

40

,

42

, and

88

, may be coupled together in a manner analogous to that described in conjunction with

FIGS. 1 and 2

.

As described previously, the coupling of diaphragm sections

40

and

42

shown in

FIGS. 1 and 2

resulted in formation of three cavities

50

,

52

, and

54

which could be individually pressurized.

FIG. 6

illustrates that at least one additional diaphragm section

88

could also be employed, which would result in formation of two additional cavities (not shown). These additional cavities also could be individually pressurized. Thus, where the diaphragm sections

40

and

42

of

FIGS. 1 and 2

enable precise control of the pressures applied to the center region and one annular region of the semiconductor wafer, the additional diaphragm section

88

enables the pressure applied to a second annular region of the wafer to be more precisely controlled. This precise control during the polishing process could yield an even more flat wafer surface than is achievable using embodiments which include two or fewer diaphragm sections. In other alternate embodiments, even more diaphragm sections could be employed.

FIG. 7

illustrates a flowchart of a method for operating the carrier in order to polish a workpiece in accordance with a preferred embodiment of the present invention. The method begins, in step

90

, by providing a carrier which includes a rigid plate as described herein. In step

92

, the semiconductor wafer or other workpiece to be polished is chucked. This is achieved by suspending carrier

12

over one or more semiconductor wafers

56

to be processed. Carrier

12

is lowered to a position slightly above the top wafer

56

.

If no apertures

58

(

FIG. 4

) are provided in diaphragms

40

and

42

, the inter diaphragm diaphragm cavity

54

(

FIG. 2

) is used to chuck the wafer. Accordingly, the conduit linked to inter-diaphragm cavity

54

is connected to a vacuum source, while the conduits associated with cavities

50

and

52

(

FIG. 2

) are initially pressurized, if desired, to help establish a seal against semiconductor wafer

56

in order to have it chucked against diaphragms

40

and

42

. Alternatively, one or more apertures

58

(

FIG. 4

) may be included through the contact sections for diaphragms

40

and/or

42

. In this latter case, any one or more of the cavities

50

,

52

, and

54

, may be evacuated to chuck the semiconductor wafer

56

.

Next in step

96

, the carrier

12

and wafer

56

are moved over a polishing pad and platen (not shown) and then lowered, in step

98

, such that the lower surface

56

l

(

FIG. 2

) of wafer

56

makes contact with the polishing pad. From this point, any polishing technique well known to those skilled in the art may be used, such as rotational, orbital, or a combination thereof.

Regardless of the polishing technique used, in step

99

, the user may adjust the pressure in cavities

50

-

54

to the same pressure in an effort to establish uniform polishing pressure across the entire surface of semiconductor wafer

56

. Alternatively, the user may adjust the pressure in cavities

50

-

54

(

FIG. 2

) to different levels, thereby establishing a non-uniform, yet controlled force distribution across the entire surface of the semiconductor wafer

56

.

In this manner, a user can increase the force distribution across an area which would otherwise experience slow removal rates if a uniform force distribution was implemented across the surface of the semiconductor wafer

56

. For example, one problem experienced in the industry is referred to as a “center slow removal rate.” A center slow removal rate of a polished semiconductor wafer

56

is exemplified by a central portion of the semiconductor wafer

56

having a hemispherical or dome-like bulge.

It would be advantageous to apply a greater force distribution across the central portion of the semiconductor wafer

56

in order to avoid the center slow problem. In this instance, the user would apply a relatively higher pressure to cavity

50

than to cavities

52

and

54

in order to establish a greater force distribution across the central portion of semiconductor wafer

56

. The greater force distribution across the central portion of semiconductor wafer

56

equates to a higher removal rate in this region of the semiconductor wafer

56

. Thus, a smoother, flat finish may be established on the lower or working surface

56

l

(

FIG. 2

) of semiconductor wafer

56

.

After polishing has been completed, the method ends. The method could be applied to each of the embodiments shown in

FIGS. 1-6

, and, with a few modifications, also to the embodiments shown in

FIGS. 8-10

, described below. Depending on the embodiment, a different number of cavities may need to be pressurized in order to best achieve the advantages of the present invention.

FIG. 8

is a diametric, cross-sectional, fully-assembled view of the carrier

100

in accordance with another alternate embodiment of the present invention.

FIGS. 9 and 10

are diametric cross-sectional views of a portion of the carrier from FIG.

8

.

Like carrier

12

shown in

FIGS. 1-4

, carrier

100

is part of an apparatus for performing chemical-mechanical planarization of a front surface of a workpiece, such as a semiconductor wafer. Thus, while carrier

100

is not shown as part of a larger planarization apparatus, it is understood that carrier

100

is preferably coupled to the various elements comprising a planarization apparatus (e.g., the spindle shaft

14

, rotating coupling

16

, etc. of FIGS.

1

-

2

).

Carrier

100

includes a rigid plate

102

having upper

102

u

and lower

102

l

surfaces. Focusing on the lower surface

102

l

of rigid plate

102

, as viewed from left to right in

FIG. 8

, lower or major surface

102

l

includes a generally flat outer annular area

103

, and a plurality of cavities

138

,

104

, and

106

formed in lower surface

102

l.

In a preferred embodiment, the relatively small annular cavity

138

retains an O-ring. In other embodiments, annular cavity

138

would not be included. Continuing to move toward the right, a larger annular cavity

104

is formed in lower surface

102

l

, and a cylindrical cavity

106

is concentrically located with respect to annular cavity

104

. The rigid plate

102

is preferably made of stainless steel, though any suitably strong, rigid material may be implemented.

A plurality of fluid conduits

108

,

110

, and

112

pass through rigid member

102

. Fluid conduits

108

,

110

, and

112

are coupled to independent pressurization sources (not shown) that can supply either vacuum or fluid (e.g., gas) at a selected pressure to any one of the conduits

108

,

110

, and

112

. In a preferred embodiment, the vacuum or fluid (e.g., gas) are supplied in a manner similar to that described in conjunction with

FIGS. 1-2

. Fluid conduits

108

and

112

are in communication with their respective cavities

104

and

106

, while fluid conduit

110

is in communication with intermediate cavity

140

(to be discussed below).

As more easily viewed in

FIG. 9

, a diaphragm

114

of flexible material is coupled to and abuts certain portions

102

a

of the lower surface

102

l

of plate

102

.

Diaphragm

114

preferably comprises a round piece of suitably flexible, resilient material (e.g., neoprene).

Referring back to

FIG. 8

, wear ring

116

clamps an upper surface of diaphragm

114

against the portions

102

a

of the lower surface

102

l

of plate

102

using fasteners

118

(e.g., screws or other connectors) which pass through apertures (not shown) in diaphragm

114

. Wear ring

116

preferably comprises a ceramic type or plastic material well known to those skilled in the art.

A cylindrical member

119

is coupled to a lower surface of diaphragm

114

using annular clamp

126

and connectors

128

, which also pass through apertures (not shown) in diaphragm

114

. As shown more clearly in

FIG. 9

, annular clamp

126

includes a notch

127

located above diaphragm

114

to facilitate a retaining lip

129

of rigid plate

102

.

cylindrical member

119

is located below cavity

106

, and centered with respect to rigid plate

102

and semiconductor wafer

124

. Cylindrical member

119

and annular clamp

126

are preferably made of stainless steel, though any rigid material may be implemented.

An annular member

120

is also coupled to the lower surface of diaphragm

114

using annular clamp

130

and fasteners

132

(e.g., screws or other connectors) which pass through apertures (not shown) in diaphragm

114

. Annular clamp

130

fits within cavity

104

, though it does not completely occupy the cavity volume as evident in FIG.

9

. Annular member

120

is concentrically located with respect to cylindrical member

119

. Moreover, annular member

120

is located below cavity

104

and above a peripheral annular area of semiconductor wafer

124

. Annular member

120

and annular clamp

130

are also preferably made of stainless steel, though any rigid material may be implemented.

The lower surfaces of members

119

and

120

essentially provide pressure directly to a center portion and an annular portion of the back surface of semiconductor wafer

124

, although a relatively thin carrier film

122

(described below) is disposed between the lower surfaces of members

119

,

120

and the back surface of semiconductor wafer

124

. Therefore, the lower surfaces of members

119

and

120

are desirably as flat and smooth as possible in order to ensure that even pressures will be applied to the wafer

124

across members

119

and

120

.

As is easily viewed in

FIG. 9

, an intermediate cavity

140

is formed between cylindrical member

119

and annular member

120

. Intermediate cavity

140

is defined by a retaining ring

134

, diaphragm

114

, cylindrical member

119

, annular member

120

, and carrier film

122

. In a preferred embodiment, the retaining ring

134

is coupled to rigid plate

102

using connectors (not shown) that penetrate apertures (not shown) in diaphragm

114

.

Retaining ring

134

holds diaphragm

114

tightly against rigid plate

102

, even when intermediate cavity

140

is positively or negatively pressurized. In order to permit pressurized fluid (e.g., gas) or vacuum supplied through conduit

110

to reach intermediate cavity

140

, an aperture

111

in diaphragm

114

is aligned with fluid conduit

110

and an aperture

113

through retaining ring

134

.

As described previously, carrier film

122

is disposed between lower surfaces of members

119

,

120

and a semiconductor wafer

124

. Carrier film

122

preferably includes one or more apertures

142

to facilitate chucking the wafer

124

using vacuum applied to intermediate cavity

140

. Chucking the wafer is described in more detail in conjunction with FIG.

7

.

Carrier film

122

is placed in contact with the lower surfaces of annular

120

and cylindrical

119

members, and typically extends in between the two members

119

and

120

across the intermediate cavity

140

, though carrier film

122

need not extend across cavity

140

. Carrier film

122

preferably comprises DF-200 carrier film manufactured by Rodel Inc. of Newark, Del., though any soft resilient carrier film may be used.

Referring to

FIG. 9

, it is clear that there is sufficient space around annular clamp

130

to permit application of pressurized fluid (e.g., gas) or vacuum to cavity

104

. The same is true for the space around annular clamp

126

, permitting application of pressurized fluid (e.g., gas) or vacuum throughout cavity

106

.

In a preferred embodiment, carrier

100

is assembled in a particular sequence, although other assembly sequences also could be employed. In a preferred embodiment, members

119

and

120

first are fastened to diaphragm

114

. Then, annular clamps

126

and

130

are inserted into their respective cavities

106

and

104

. In this regard, retaining lip

129

is keyed to permit insertion of annular clamp

126

into cavity

106

. Then, annular clamp

126

is rotated to a position preventing it from falling through the keyed slots (not shown) in retaining lip

129

. The retaining ring

134

and wear ring

116

are next fastened to hold the diaphragm

114

in place, as well as to isolate the independent pressurization zones (e.g., three in this case corresponding to cavities

104

,

106

, and

140

) from each other.

FIG. 10

demonstrates that wear ring

116

and retaining lip

129

act as mechanical stops to limit downward motion of annular clamps

126

and

130

, and therefore, members

119

and

120

. It is assumed that gravitational force pulls members

119

and

120

down to the mechanical stops of clamps

126

and

130

. However, when a semiconductor wafer

124

is in place between the carrier

100

and a polishing platen (not shown), the thickness of the wafer

124

tends to prevent clamps

126

and

130

from reaching their mechanical stops. When positive or negative pressures are applied to cavities

104

and

106

, clamps

126

and

130

are forced to move toward or away, respectively, from their mechanical stops. In this manner, differential pressures can be applied to the semiconductor wafer

124

via clamps

126

,

130

and members

119

,

120

.

The method of operating carrier

100

is very much analogous to the method described in conjunction with

FIG. 7

, which referred to operation of carrier

12

, The method begins by chucking the semiconductor wafer

124

or other workpiece to be polished. This is achieved by suspending carrier

100

over one or more semiconductor wafers

124

to be processed. Carrier

100

is lowered to a position slightly above the top wafer

124

. Conduit

110

is connected to a vacuum source which applies a negative pressure in cavity

140

to chuck semiconductor wafer

124

using apertures

142

in carrier film

122

. Positive pressure may also be supplied to cavities

104

and

106

to help maintain a seal with the wafer

124

during chucking.

Next the carrier

100

and wafer

124

are moved over a polishing pad and platen (not shown), and then lowered such that the lower surface of wafer

124

makes contact with the polishing pad. From this point, any polishing technique well known to those skilled in the art may be used, such as rotational, orbital, or a combination thereof. The user may pressurize cavities

104

,

106

, and

140

to the same pressure in an effort to establish uniform polishing pressure across the entire surface of semiconductor wafer

124

. Alternatively, the user may pressurize cavities

104

,

106

, and

140

to different levels, thereby establishing a non-uniform, yet controlled force distributed across the entire surface of the semiconductor wafer

124

.

In this manner, a user can increase the force distribution across an area which would otherwise experience slow removal rates if a uniform force distribution was implemented across the surface of the semiconductor wafer

124

. As is clearly illustrated in

FIG. 10

, this result is made possible by the fact that as one increases the supply pressure in cavity

104

, diaphragm

114

expands slightly to cause greater applied force from the annular member

120

against wafer

124

. The same is true for pressure supplied to cavity

106

, and to a lesser extent to cavity

140

. After polishing has been completed, the method ends.

It should be understood that the methods and apparatuses described above are only exemplary and do not limit the scope of the invention, and that various modifications could be made by those skilled in the art that would fall under the scope of the invention. For example, while the pressurized fluid mentioned herein is preferably a pressurized gas, a pressured liquid may be employed in the alternative.

To apprise the public of the scope of this invention, the following claims are provided:

Number	Name	Date	Kind
5205082	Shendon et al.	Apr 1993	A
5230184	Bukham	Jul 1993	A
5584746	Tanaka et al.	Dec 1996	A
5584751	Kobayashi et al.	Dec 1996	A
5605488	Ohashi et al.	Feb 1997	A
5624299	Shendon	Apr 1997	A
5660517	Thomson et al.	Aug 1997	A
5681215	Sherwood et al.	Oct 1997	A
5738574	Tolles et al.	Apr 1998	A
5762539	Nakashiba et al.	Jun 1998	A
5762544	Zuniga et al.	Jun 1998	A
5762546	James et al.	Jun 1998	A
5795215	Guthrie et al.	Aug 1998	A
5820448	Shamouilian et al.	Oct 1998	A
5964653	Perlov et al.	Oct 1999	A
6056632	Mitchel et al.	May 2000	A
6106378	Perlov et al.	Aug 2000	A

Carrier including a multi-volume diaphragm for polishing a semiconductor wafer and a method therefor

Information

Patent Number

Date Filed

Date Issued

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Agents

CPC

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Abstract

Description

Claims

US Referenced Citations (17)