Polishing head for polishing semiconductor wafers

This application is entitled to the benefit of U.S. Provisional Patent Application Ser. No. 60/778,675, filed on Mar. 3, 2006, 60/800,468, filed on May 15, 2006, 60/834,890, filed on Aug. 1, 2006, 60/837,109, filed on Aug. 11, 2006 and 60/844,737, filed on Sep. 15, 2006, which are all incorporated herein by reference.

The invention relates generally to semiconductor processing equipments, and more particularly to a polishing head and method for handling and polishing semiconductor wafers.

Local and global planarization of semiconductor wafers becomes increasingly important as more metal layers and interlayer dielectric layers are stacked on the wafers. A preferred method to planarize semiconductor wafers is the chemical mechanical polishing (CMP) method, where a surface of a semiconductor wafer is polished using a slurry solution supplied between the wafer and a polishing pad. The CMP method is also widely used for damascene process to form copper structures on the semiconductor wafers.

In general, a CMP equipment includes a polishing table where a polishing pad is placed and a wafer carrier that supports a semiconductor wafer and presses the wafer against the polishing pad. The CMP equipment may also include a wafer cleaner to clean and dry the polished wafers.

An important component of a CMP equipment is the polishing head that holds a semiconductor wafer to be polished on a polishing surface. The polishing head is designed to chuck (load) and de-chuck (unload) the wafer, and to apply pressure to the wafer onto the polishing surface. After a wafer is polished, a strong bond may exist between the wafer and the polishing surface, which makes chucking the wafer onto the polishing head challenging. The polishing head must be designed to overcome this bond between the wafer and the polishing surface to chuck the wafer onto the polishing head. During the wafer polishing, the polishing head must apply proper pressure to the wafer to minimize uneven polishing.

In view of the above issues, what is needed is a polishing head and method for handling and polishing semiconductor wafers that overcomes these issues to properly handle and polish the wafers.

A polishing head and method for handling and polishing semiconductor wafers uses a base structure with at least one recess region and an outer flexible membrane that can conform to the at least one recess region to form at least one depression to hold a semiconductor wafer onto the outer flexible membrane when suction is applied to the at least one depression. The at least one depression allows a wide area of the wafer to be subjected to the applied suction to secure the wafer onto the outer flexible membrane.

A polishing head in accordance with an embodiment of the invention comprises a base structure, an outer flexible membrane, a first fluid channel and a second fluid channel. The base structure has a lower surface. The base structure is configured to include at least one recess region on the lower surface. The outer flexible membrane is positioned below the base structure. The outer flexible membrane and the base structure define a chamber below the base structure. The first fluid channel is operatively connected to the chamber to apply suction to at least a portion of the chamber. The suction causes the outer flexible membrane to conform to the at least one recess region of the base structure such that at least one depression is formed on a bottom surface of the outer flexible membrane. The second fluid channel is configured to extend through the outer flexible membrane such that an opening of the second fluid channel is positioned in the at least one depression when the suction is applied to the chamber. The second fluid channel is used to apply another suction to the at least one depression to hold a semiconductor wafer onto the outer flexible membrane.

A method for handling and polishing a semiconductor wafer in accordance with an embodiment of the invention comprises moving the polishing head such that an outer flexible membrane of the polishing head is at least in close proximity to a surface of the semiconductor wafer, applying suction to at least a portion of a chamber of the polishing head defined by the outer flexible membrane and a base structure of the polishing head, the base structure being configured to include at least one recess region on a lower surface of the base structure, the applying of the suction to at least a portion the chamber causing the outer flexible membrane to conform to the at least one recess region of the base structure such that at least one depression is formed on a bottom surface of the outer flexible membrane, and applying another suction to the at least one depression on the bottom surface of the outer flexible membrane to hold the semiconductor wafer onto the outer flexible membrane of the polishing head.

Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrated by way of example of the principles of the invention.

FIG. 1 is a vertical cross-sectional view of a polishing head in accordance with an embodiment of the present invention.

FIG. 2 is a bottom view of the polishing head of FIG. 1 with an outer flexible membrane being partially cut away to show first, second and third inner annular flexible membranes in accordance with an embodiment of the invention.

FIG. 3A is a bottom view of a first annular disc of the polishing head of FIG. 1 in accordance with an embodiment of the invention.

FIG. 3B is a cross-sectional view of the first annular disc of FIG. 3A .

FIG. 4A is a perspective view of an inner annular flexible membrane of the polishing head of FIG. 1 in accordance with an embodiment of the invention.

FIG. 4B is a cross-sectional view of the inner annular flexible membrane of FIG. 4A .

FIG. 5 is a cross-sectional view of an annular disc and an inner annular flexible membrane in accordance with an embodiment of the invention.

FIG. 6A is a cross-sectional view of an example of second and third annular discs with the second and third inner annular flexible membranes in accordance with an embodiment of the invention.

FIG. 6B is a cross-sectional view of another example of the second and third annular discs with the second and third inner annular flexible membranes in accordance with an embodiment of the invention.

FIG. 7A is a block diagram of a valve-and-regulator assembly of the polishing head of FIG. 1 in accordance with an embodiment of the invention.

FIG. 7B is a block diagram of the valve-and-regulator assembly of the polishing head of FIG. 1 in accordance with an alternative embodiment of the invention.

FIG. 8 is another vertical cross-sectional view of the polishing head of FIG. 1 with a semiconductor wafer chucked onto the polishing head in accordance with an embodiment of the present invention.

FIG. 9 is a bottom view of the first, second and third annular discs with interconnected recess regions in accordance with an embodiment of the invention.

FIG. 10 is a bottom view of the outer flexible membrane that has conformed to the interconnected recess regions of the annular discs in accordance with an embodiment of the invention.

FIG. 11A is a cross-sectional view showing a portion of the outer flexible membrane with an annular flap in accordance with an embodiment of the invention.

FIG. 11B is a cross-sectional view showing the portion of the outer flexible membrane with the annular flap in accordance with an alternative embodiment of the invention.

FIG. 12 is a process flow diagram of a method of handling and polishing a semiconductor wafer in accordance with an embodiment of the invention.

With reference to FIG. 1 , a polishing head 10 for polishing a semiconductor wafer W according to an embodiment of the present invention is described. FIG. 1 is a vertical cross-sectional view of the polishing head 10 after it is assembled. The polishing head 10 is used to remove material from the wafer that is being polished. The polishing head 10 is configured to hold the wafer and polish it by rotating and pressing the wafer on a polishing surface 11 . Abrasive slurry and/or chemical can be used during the polishing of the wafer.

The polishing head 10 includes a housing 12 , a base 14 and a retainer ring 16 . The housing 12 is connected to a drive shaft 18 , which is used to move and rotate the polishing head 10 . The drive shaft 18 is connected to a motor (not shown) that rotates the drive shaft. The drive shaft 18 is also connected to a vertical drive mechanism (not shown), such as a pneumatic actuator, to displace the polishing head 10 vertically toward the polishing surface 11 . The base 14 is connected to the housing 12 via a flexure 20 .

The flexure 20 is a thin circular disc made of a flexible material. As an example, the flexure 20 can be a thin metal circular disc. However, the flexure 20 can be made of other flexible materials. The interior region of the flexure 20 is attached to the housing 12 and the base 14 using joint screws, adhesive material or any other means to physically attach the flexure to the housing and the base. The outer edge of the flexure 20 is attached to the retainer ring 16 using joint screws, adhesive material or any other means to physically attach the flexure to the retainer ring. The flexure 20 is configured to be reversibly flexible in a vertical manner. The flexure 20 is further configured to bear shear stress applied to the flexure in a parallel manner to the base 14 .

The polishing head 10 further includes an annular tube 22 , which is positioned over the retainer ring 16 between the housing 12 and the flexure 20 . The annular tube 22 is attached to the housing 12 and the retainer ring 16 through the flexure 20 . The annular tube 22 is a sealed tube such that the interior region of the tube contains a fluid 24 , such as air, water, oil, silicon, gelatin or other gas or liquid, at a predefined pressure. The fluid 24 may be a viscous material.

The annular tube 22 is pressurized when a downward force is applied to the annular tube by the housing 12 at a time when the retainer ring 16 is in contact with the polishing surface 11 . The pressurized annular tube 22 transfers the downward force to the retainer ring 16 . In an embodiment, the annular tube 22 is made of elastic material such that the tube is not subject to permanent deformation during repeated pressing processes of the retainer ring 16 against the polishing surface 11 .

When the retainer ring 16 presses the polishing surface 11 , the annular tube 22 operates as a vibration absorber. The vibrations generated during a polishing process of the wafer W due to friction between the polishing surface 11 and the bottom surface of the retainer ring 16 are absorbed by the annular tube 22 . Therefore, the vibrations that are transferred to the housing 12 of the polishing head 10 can be minimized.

Since the pressure of the fluid 24 in the annular tube 22 does not have to be controlled to adjust the pressure applied to the polishing surface 11 through the retainer ring 16 , the annular tube 22 does not have to be connected to any fluid source in the polishing head 10 . However, in other embodiments, the annular tube 22 can be connected to a fluid source in the polishing head 10 such that the fluid 24 can be supplied to the tube or removed from the tube to control the volume of the fluid in the tube.

The polishing head 10 further includes a controller 26 and a valve-and-regulator assembly 28 . In the illustrated embodiment, the controller 26 and the valve-and-regulator assembly 28 are situated within the housing 12 above the base 14 . The controller 26 is configured to control the components of the valve-and-regulator assembly 28 , as described below. The controller 26 is connected to an external controller (not shown), which may be a computer system, via wires 30 for power and data communication. The controller 26 is also connected to the valve-and-regulator assembly 28 via wires 32 for power and data communication. The valve-and-regulator assembly 28 is connected to fluid channels 36 A- 36 D. The fluid channel 36 A is used to receive pressurized gas, such as air. The fluid channel 36 B is used as an exhaust to release excess gas. The fluid channel 36 C is used to provide vacuum or suction. The fluid channel 36 D is used to receive deionized (D.I.) water. The valve-and-regulator assembly 28 is also connected to a number of fluid channels 34 A- 34 E, which are described below.

The polishing head 10 also includes a first annular disc 40 A, a second annular disc 40 B, a third annular disc 40 C, a first inner annular flexible membrane 42 A, a second inner annular flexible membrane 42 B, a third inner annular flexible membrane 42 C and an outer flexible membrane 44 . The first, second and third annular discs 40 A- 40 C are attached to the base 14 using joint screws, adhesive material or any other means to physically attach the annular discs to the base. The first, second and third annular discs 40 A- 40 C are positioned within the confines of the retainer ring 16 . The base 14 and the annular discs 40 A- 40 C form a base structure of the polishing head 10 .

The first annular disc 40 A is shown in more detail in FIGS. 3A and 3B . FIG. 3A is a bottom view of the first annular disc 40 A, while FIG. 3B is a cross-sectional view of the first annular disc. As shown in FIGS. 3A and 3B , the first annular disc 40 A includes a circular hole 302 at its center and a circular recess region 304 on its bottom surface. The circular recess region 304 is positioned about the circular hole 302 such that the circular hole is positioned at the center of the circular recess region 304 . Some of the advantages of the configuration of the first annular disc 40 A are described below.

Turning back to FIG. 1 , the inner and outer diameters of the first, second and third annular discs 40 A- 40 C at their bottom surfaces are determined such that the third annular disc 40 C surrounds the second annular disc 40 B, and the second annular disc 40 B surrounds the first annular disc 40 A. In an embodiment, the outer edge of the second annular disc 40 B is configured to have a step and the inner edge of the third annular disc 40 C is configured to have an inverted step. Thus, the outer edge of the second annular disc 40 B and the inner edge of the third annular disc 40 C can be fitted together to interlock the second and third annular discs. Some of the advantages of the configuration of the second and third annular discs 40 B and 40 C are described below.

The first inner annular flexible membrane 42 A is connected to the first annular disc 40 A such that a first annular chamber 46 A is defined by the first annular disc 40 A and the first inner annular flexible membrane 42 A. The second inner annular flexible membrane 42 B is connected to the second annular disc 40 B such that a second annular chamber 46 B is defined by the second annular disc 40 B and the second inner annular flexible membrane 42 B. The third inner annular flexible membrane 42 C is connected to the third annular disc 40 C such that a third annular chamber 46 C is defined by the third annular disc 40 C and the third inner annular flexible membrane 42 C. The first, second and third inner annular flexible membranes 42 A- 42 C can be bonded to their respective annular discs 40 A- 40 C using adhesive material. When one or more of the inner annular flexible membranes 42 A- 42 C need to be changed, the respective annular discs 40 A, 40 B and/or 40 C that have the respective bonded inner annular flexible membranes can be changed.

An example of an inner annular flexible membrane 400 is illustrated in FIG. 4A and 4B . As shown in FIGS. 4A and 4B , the inner annular flexible membrane 400 includes an inner circular sidewall 402 with a circular top flap 404 that extends outward away from the center of the membrane. The inner annular flexible membrane 400 also includes an outer circular sidewall 408 with a circular top flap 410 that extends inward toward the center of the membrane. The circular top flaps 404 and 410 are used to secure the inner annular flexible membrane 400 to the respective annular disc 40 A, 40 B or 40 C. The inner circular sidewall 402 defines a circular aperture 406 at the center of the inner annular flexible membrane 400 . The size of the aperture 406 corresponds to the inner diameter D 1 of the inner annular flexible membrane 400 . The outer circular sidewall 408 defines the outer diameter D 2 of the inner annular flexible membrane 400 . The inner and outer diameters D 1 and D 2 of the inner annular flexible membrane 400 depend on whether the inner annular flexible membrane is to be used as the first flexible membrane 42 A, the second flexible membrane 42 B or the third flexible membrane 42 C of the polishing head 10 .

Even though the polishing head 10 is illustrated and described as comprising the three annular chambers 46 A- 46 C associated with their respective annular discs 40 A- 40 C, the polishing head 10 can be configured to comprise other number of annular chambers associated with their respective annular discs in other embodiments.

Turning back to FIG. 1 , the outer flexible membrane 44 is attached to the base 14 and the retainer ring 16 such that the outer flexible membrane covers the first, second and third inner annular flexible membranes 42 A, 42 B and 42 C. In the illustrated embodiment, the outer flexible membrane 44 is configured to include a circular recess region 48 at its center that conforms to the center circular hole of the first annular disc 40 A. The circular recess region 48 of the outer flexible membrane 44 forms a circular central cavity 50 . The center of the outer flexible membrane 44 is attached to the base 14 using an adhesive material, one or more joint screws or any other means to physically attach the outer flexible membrane to the base. The outer edge of the outer flexible membrane 44 is attached to the retainer ring 16 using one or more outer membrane holders 52 , which may be joint screws. In other embodiments, the outer edge of the outer flexible membrane 44 may be attached to the retainer ring 16 using an adhesive material or any other means to physically attach the outer flexible membrane to the retainer ring. The outer flexible membrane 44 and the annular discs 40 A- 40 C define a large annular chamber, which contains the annular chambers 46 A- 46 C created by the inner annular flexible membranes 42 A- 42 C.

The outer flexible membrane 44 is configured to have an annular periphery portion 54 and an annular central portion 56 . The annular periphery portion 54 is shaped to have an annular upside down U-shape such that the annular periphery portion is situated between the base 14 and the retainer ring 16 . The annular central portion 56 of the outer flexible membrane 44 is also shaped to have an annular upside down U-shape such that the top of the upside down U-shaped portion 56 faces an annular recess 58 that is formed near the center of the base 14 . The upside down U-shaped portions 54 and 56 are made to keep their shape reversibly after repeated changes of their shape. The upside down U-shaped portions 54 and 56 of the outer flexible membrane 44 allow the outer flexible membrane 44 to expand downward toward the wafer W and to contract upward away from the wafer without having to stretch or without having to stretch significantly. Thus, the outer flexible membrane 44 can be made of inelastic material and still function properly, i.e., expand and contract. However, in some embodiments, the outer flexible membrane 44 can still be made of elastic material.

The bottom surface of the outer flexible membrane 44 is used as the surface that contacts the wafer W. The outer flexible membrane 44 and the first, second and third inner annular flexible membranes 42 A- 42 C can be made of any flexible materials including rubbers and plastic materials. In some embodiments, plastic material such as PVC, Polystyrene, Nylon, and Polyethylene is used for the first, second and third inner annular flexible membranes 42 A- 42 C. In some embodiments, elastic material such as rubber, elastomer, silicon rubber, and polyurethane rubber is used for the outer flexible membrane 44 . In other embodiments, non-elastic material is used for the outer flexible membrane 44 .

In some embodiments, the thicknesses of the first, second and third inner annular flexible membranes 42 A- 42 C are substantially thinner than the thickness of the outer flexible membrane 44 . By using thin flexible membranes for the first, second and third inner annular flexible membranes 42 A- 42 C, any pressure differential at the boundaries of the inner flexible membranes 42 A- 42 C on the outer flexible membrane 44 and the wafer W by the first, second and third inner annular flexible membranes 42 A- 42 C is minimized. As an example, the first, second and third inner annular flexible membranes 42 A- 42 C can be films with thicknesses less than 0.2 mm. In this example, the outer flexible membrane 44 can be a film with a thickness greater than 0.5 mm. As another example, the first, second and third inner annular flexible membranes 42 A- 42 C can be films with thicknesses between 0.06 mm and 0.09 mm. In this example, the outer flexible membrane 44 can be a film with a thickness between 0.6 and 0.9 mm.

The outer flexible membrane 44 and the first, second and third inner annular flexible membranes 42 A- 42 C are shown in FIG. 2 , which is a bottom view of the polishing head 10 with the outer flexible membrane being partially cut away to show the first, second and third inner annular flexible membranes. As illustrated in FIG. 2 , D 1 , D 2 and D 3 are widths of the first, second and third inner annular flexible membranes 42 A- 42 C, respectively, and thus, the widths of the annular chambers 46 A- 46 C, respectively, which are defined by the first, second and third inner annular flexible membranes 42 A- 42 C. These widths D 1 , D 2 and D 3 also correspond to the widths of the first, second and third annular discs 40 A- 40 C, respectively. Thus, by adjusting the widths D 1 , D 2 and D 3 of the discs 40 A- 40 C, the widths of the annular chambers 46 A- 46 C associated with the respective discs can be adjusted.

Turning back to FIG. 1 , the first annular disc 40 A and the base 14 comprise at least one fluid channel 34 A such that the first annular chamber 46 A is connected to the valve-and-regulator assembly 28 via the fluid channel 34 A to receive pressurized gas. The second annular disc 40 B and the base 14 comprise at least one fluid channel 34 B such that the second annular chamber 46 B is connected to the valve-and-regulator assembly 28 via the fluid channel 34 B to receive pressurized gas. The third annular disc 40 C and the base 14 comprise at least one fluid channel 34 C such that the third annular chamber 46 C is connected to the valve-and-regulator assembly 28 via the fluid channel 34 C to receive pressurized gas. The pressurized gas may include air, nitrogen or a combination of different gases. The valve-and-regulator assembly 28 controls the pressure of the gas such that gas having different pressures can be supplied to the first, second and third annular chambers 46 A- 46 C through the respective fluid channels 34 A- 34 C.

The base 14 also comprises a central fluid channel 34 D, which connects the central cavity 50 to the valve-and-regulator assembly 28 through the outer flexible membrane 44 to apply a vacuum/suction and to provide DI water to the central cavity 50 . The fluid channel 34 D includes an opening 35 , which is located at the center of the outer flexible membrane 44 , and extends through outer flexible membrane. The base 14 further comprises at least one fluid channel 34 E, which connects a space 60 between the outer flexible membrane 44 and the inner annular flexible membranes 42 A- 42 C to the valve-and-regulator assembly 28 to apply a vacuum/suction to the space 60 . The fluid channel 34 E allows a vacuum/suction to be applied to the space 60 so that the annular chambers 46 A- 46 C can be efficiently deflated when needed.

In an embodiment, at least some of the inner annular flexible membranes 42 A- 42 C are configured to include annular wrinkled portions to allow the membranes to expand and contract without having to stretch or without having to stretch significantly. FIG. 5 shows a cross-section of an inner annular flexible membrane 500 attached to an annular disc 502 . The membrane 500 is configured to include an annular wrinkled portion 504 on an inner sidewall 506 of the membrane and an annular wrinkled portion 508 on an outer sidewall 510 of the membrane. The wrinkled portion 504 on the inner sidewall 506 is configured to protrude outward toward the outer sidewall 510 or toward the annular disc 502 . The wrinkled portion 508 on the outer sidewall 510 is configured to protrude inward toward the inner sidewall 506 or toward the annular disc 502 . Thus, the wrinkled portions 504 and 508 both protrude toward the annular disc 502 . In this embodiment, the wrinkled portion 504 of the membrane 500 faces an annular recess 512 that is formed at an inner side of the annular disc 502 . The wrinkled portion 508 of the membrane 500 faces an annular recess 514 that is formed at an outer side of the annular disc 502 . The wrinkled portions 504 and 508 of the inner annular membrane 500 serve a similar function as the upside down U-shaped portions 54 and 56 of the outer flexible membrane 44 . The wrinkled portions 504 and 508 of the inner annular membrane 500 allow the membrane 500 to expand downward toward the wafer W (not shown in FIG. 5 ) and to contract upward away from the wafer without having to stretch or without having to stretch significantly. Thus, the inner annular flexible membrane 500 can be made of inelastic material and still function properly, i.e., expand and contract. However, in some embodiments, the inner annular flexible membrane 500 can still be made of elastic material.

Turning now to FIGS. 6A and 6B , an example of adjusting the widths of the second and third annular chambers 46 B and 46 C, which are defined by the annular discs 40 B and 40 C, respectively, is described. FIG. 6A shows a first set of the second and third annular discs 40 B and 40 C, which are coupled by a joint screw 600 . FIG. 6B shows a second set of the second and third annular discs 40 B and 40 C, which are also coupled by the joint screw 600 . In FIG. 6A , the width D 2 of the second annular disc 40 B is 13 mm and the width D 3 of the third annular disc 40 C is 7 mm. In FIG. 6B , the width D 2 of the second annular disc 40 B has been changed to 17 mm and the width D 3 of the third annular disc 40 C has been changed to 3 mm. Consequently, the widths of the second and third annular chambers 46 B and 46 C have been adjusted. However, the total width of the second and third annular discs 40 B and 40 C has not been changed. Thus, the widths of the second and third annular chambers 46 B and 46 C can be adjusted by changing only the annular discs 40 B and 40 C and the attached inner annular flexible membranes 42 B and 42 C. That is, the annular disc 40 A and the inner annular flexible membrane 42 A do not have to be changed to adjust the widths of the second and third annular chambers 46 B and 46 C.

Turning now to FIG. 7A , the components of the valve-and-regulator assembly 28 in accordance with an embodiment of the invention are shown. The valve-and-regulator assembly 28 includes manifolds 702 A, 702 B and 702 C, pressure regulators 704 A, 704 B and 704 C, a three-way valve 706 and a water trap 708 . The manifold 702 A is connected to the fluid channel 36 A to receive pressurized gas. The manifold 702 A is also connected to the pressure regulators 704 A, 704 B and 704 C to distribute the pressurized gas from the fluid channel 36 A to the pressure regulators. The pressure regulators 704 A, 704 B and 704 C are connected to the first, second and third annular chambers 46 A, 46 B and 46 C, respectively, through the fluid channels 34 A, 34 B and 34 C, respectively. The pressure regulators 704 A, 704 B and 704 C are also connected to the manifold 702 B, which is connected to the fluid channel 36 B. The pressure regulator 704 A is configured to selectively direct pressurized gas to the first annular chamber 46 A. The pressure regular 704 A is also configured to selectively release pressurized gas through the fluid channel 36 B via the manifold 702 B. Thus, the pressure regulator 704 A can control the pressure within the first annular chamber 46 A. Similarly, the pressure regulators 704 B and 704 C can control the pressure within the annular chambers 46 B and 46 C. Although not illustrated, the pressure regulators 704 A- 704 C are connected to the controller 26 via the wires 32 (shown in FIG. 1 ) to receive power and control signals.

The manifold 702 C is connected to the fluid channel 36 C, which provides a vacuum/suction. The manifold 702 C is also connected to the space 60 between the outer flexible membrane 44 and the inner annular flexible membranes 42 A- 42 C via the fluid channel 34 E to apply a vacuum/suction to the space 60 . The space 60 may also be connected the manifold 702 B such that the space 60 can be connected to the fluid channel 36 B. The manifold 702 C is also connected to the central cavity 50 via the fluid channel 34 D through the valve 706 and the water trap 708 to apply a vacuum/suction to the cavity 50 . The three-way valve 706 is connected to the manifold 702 C and the central cavity 50 via the water trap 708 . The three-way valve 706 is also connected to the fluid channel 36 D to receive D.I. water. Thus, the valve 706 can selectively provide D.I. water to the central cavity 50 or apply a vacuum/suction to the central cavity 50 . Although not illustrated, the three-way valve 706 is connected to the controller 26 via the wires 32 (shown in FIG. 1 ) to receive power and control signals. The water trap 708 is connected to the fluid channel 34 D to trap contaminated water from the central cavity 50 when a vacuum/suction is being applied to the central cavity 50 . The contaminated water in the water trap 708 can be released through the central cavity 50 by D.I. water received through the fluid channel 36 D during an appropriate period.

Turning now to FIG. 7B , the components of the valve-and-regulator assembly 28 in accordance with an alternative embodiment of the invention are shown. In this alternative embodiment, the valve-and-regulator assembly 28 further includes three-way valves 710 A, 710 B and 710 C. The three-way valve 710 A is connected to the pressure regulator 704 A, the manifold 702 C and the first annular chamber 46 A. Since the manifold 702 C is connected to the fluid channel 36 C, which provides a vacuum/suction, the three-way valve 710 A is able to selectively connect the annular chamber 46 A to the manifold 702 C to apply suction to the first annular chamber 46 A to deflate the annular chamber 46 A. The three-way valve 710 B is similarly connected to the pressure regulator 704 B, the manifold 702 C and the second annular chamber 46 B, and the three-way valve 710 C is similarly connected to the pressure regulator 704 C, the manifold 702 C and the third annular chamber 46 C. Thus, the three-way valve 710 B is able to selectively connect the second annular chamber 46 B to the manifold 702 C to apply suction to the second annular chamber to deflate the second annular chamber. Similarly, the three-way valve 710 C is able to selectively connect the third annular chamber 46 C to the manifold 702 C to apply suction to the third annular chamber to deflate the third annular chamber.

With reference to FIGS. 1 and 8 , processes of chucking (loading) the wafer W onto the polishing head 10 , polishing the wafer on the polishing surface 11 using the polishing head and de-chucking (unloading) the wafer from the polishing head are described. FIG. 8 shows a vertical cross-section of the polishing head 10 , which has the wafer W chucked onto it. In FIG. 1 , the outer flexible membrane 44 of the wafer carrier 10 is in contact with the back surface of wafer W.

In order to chuck the wafer W onto the polishing head 10 , suction is applied to the central cavity 50 via the fluid channel 34 D. Suction is also applied to the space 60 between the inner annular flexible membranes 42 A- 42 C and the outer flexible membrane 44 via the fluid channel 34 E. As a result, gas in the annular chambers 46 A- 46 C is evacuated and the annular chambers 46 A- 46 C are deflated, as illustrated in FIG. 8 . Alternatively, suction is applied directly to the annular chambers 46 A- 46 C via the fluid channels 34 A- 34 C, respectively, to evacuate the gas in the annular chambers and deflate the annular chambers. Suction can also be applied to the space 60 between the inner annular flexible membranes 42 A- 42 C and the outer flexible membrane 44 to further assist in deflating the annular chambers 46 A- 46 C.

As the annular chambers 46 A- 46 C are deflated, the inner annular flexible membrane 42 A and the outer flexible membrane 44 are sucked into the circular recess region 304 of the first annular disc 40 A, forming a large circular depression on the bottom surface of the outer flexible membrane that conforms to the circular recess region 304 . In effect, the circular depression formed on the bottom surface of the outer flexible membrane 44 increases the size or diameter of the central cavity 50 . As a result of the suction, a vacuum is created in the central cavity 50 between the outer flexible membrane 44 and the back surface of the wafer W, which causes the wafer to be chucked onto the polishing head 10 . The circular recess region 304 of the first annular disc 40 A allows more area of the wafer W to be subjected to the suction, which increase chucking power of the polishing head. The circular recess region 304 allows the polishing head 10 to have a smaller central cavity 50 . As an example, the diameter of the central cavity 50 may be less than 5 mm, e.g., 2.5 mm. In a conventional polishing head, the diameter of a similar central cavity is typically much greater than 5 mm, e.g., 10 mm, so that the suction created in the central cavity has enough suction power to chuck a semiconductor wafer. Since the diameter of the central cavity is relatively large, the conventional polishing head may need to provide pressure in the central cavity during a wafer polishing process to provide sufficient downward force to the zone of a semiconductor wafer below the central cavity. However, such pressure in the central cavity 50 of the polishing head 10 is not necessary since the central cavity 50 is sufficiently small.

In order to polish the wafer W on the polishing surface 11 , the polishing head 10 with the chucked wafer is moved over the polishing surface. The polishing head 10 is then lowered onto the polishing surface 11 such that the retainer ring 16 contacts the polishing surface. Next, the first, second and third annular chambers 46 A- 46 C are inflated by supplying pressurized gas with same or different pressures to the annular chambers 46 A- 46 C through the pressure regulators 704 A- 704 C, respectively, of the valve-and-regulator assembly 28 . As a result, the annular chambers 46 A- 46 C are inflated, which push the bottom surface of the outer flexible membrane 44 toward the polishing surface 11 , and thus, applies same or different pressures to the wafer on the polishing surface 11 during the polishing process.

In this manner, the pressures applied to the wafer W can be controlled in terms of zones of the wafer. The pressure applied to a central zone that is under the first annular chamber 46 A is controlled by the pressure in that chamber. The pressure applied to an intermediate annular zone surrounding the central zone that is under the second annular chamber 46 B is controlled by that chamber. The pressure applied to an outer annular zone surrounding the intermediate annular zone that is under the third annular chamber 46 C is controlled by that chamber. By applying different pressures to the respective zones, polishing rates at the respective zones can be controlled individually.

As the bottom surface of the outer flexible membrane 44 is pushed downward, the shapes of the annular upside down U-shaped portions 54 and 56 of the outer flexible membrane 44 are changed such that the heights of these upside down U-shaped portions are decreased. That is, the annular upside down U-shaped portions 54 and 56 of the outer flexible membrane 44 are at least partially straightened. These changes in shape of the annular upside down U-shaped portions 54 and 56 allow the bottom surface of the outer flexible membrane 44 to move downward more easily. Without the upside down U-shaped portions 54 and 56 , the sidewalls of the outer flexible membrane 44 need to be elongated or stretched, which would not allow the bottom surface of the outer flexible membrane 44 to move downward easily.

During the polishing process, the suction applied to the central cavity 50 may be removed. Alternatively, instead of removing the suction applied to the central cavity 50 during the polishing process, the applied suction can be used to detect wafer slippage. If the wafer W is slipped out from the polishing head 10 during the polishing process, the pressure of the suction will be changed. By detecting this pressure change, the wafer slippage can be detected.

After the polishing process is finished, the suction is again applied to the central cavity 50 in order to hold the wafer W. After the wafer is held by the suction onto the outer flexible membrane 44 , the pressurized gas is no longer applied to the first, second and third annular chambers 46 A- 46 C. In addition, another suction is applied to the space 60 between the inner annular flexible membranes 42 A- 42 C and the outer flexible membrane 44 to deflate the annular chambers 46 A- 46 C, which raises the bottom surface of the outer membrane 44 toward the base 14 . Since the suction applied to the central cavity 50 attracts the wafer toward the base 14 , the wafer is lifted from the polishing surface 11 and moved toward the base 14 as the annular chambers 46 A- 46 C are deflated.

As the bottom surface of the outer flexible membrane 44 is moved upward, the shapes of the annular upside down U-shaped portions 54 and 56 of the outer flexible membrane are recovered to their original upside down U-shapes.

Next, the polishing head 10 is transferred to a wafer unload station (not shown) and then the wafer is unloaded or de-chucked to the wafer unload station. In order to de-chuck the wafer from the polishing head 10 , the suction is no longer applied to the central cavity 50 and the space 60 between the inner annular flexible membranes 42 A- 42 C and the outer flexible membrane 44 . Furthermore, pressurized gas is applied to at least one of the inner annular flexible membranes 42 A- 42 C through the respective fluid channels 34 A- 34 C in order to unload the wafer onto the wafer unload station. Alternatively, D.I. water can be applied to the wafer through the central cavity 50 via the fluid channel 34 D in order to unload the wafer onto the wafer unload station.

Turning now to FIG. 9 , the first, second and third annular discs 40 A- 40 C in accordance with another embodiment of the invention are shown. In this embodiment, at least some of the annular discs 40 A- 40 C are configured to include interconnected recess regions 900 A- 900 D. The interconnected recess regions 900 A- 900 D of the first, second and third annular discs 40 A- 40 C are similar to the recess region 304 of the first annular disc 40 A, which is illustrated in FIGS. 3A and 3B . The interconnected recess regions 900 A- 900 D of the first, second and third annular discs 40 A- 40 C allow the outer flexible membrane 44 , as well as the inner annular flexible membranes 42 A- 42 C, to conform to the interconnected recess regions 900 A- 900 D when the inner annular flexible membranes 42 A- 42 C are deflated and suction is applied to one or more of the annular chambers 46 A- 46 C and/or the space 60 between the inner annular flexible membranes 42 - 42 C and the outer flexible membrane 44 .

As illustrated in FIG. 10 , when the outer flexible membrane 44 is conformed to the interconnected recess regions 900 due to the applied suction, the lower surface of the outer flexible membrane 44 forms interconnected depressions 1002 A- 1002 D, which allow a vacuum to be created in the interconnected depressions 1002 A- 1002 D through the opening 35 of the fluid channel 34 D when a wafer is in contact with the outer flexible membrane. Since the interconnected recess regions 900 A- 900 D are distributed throughout the annular discs 40 A- 40 C, the corresponding interconnected depressions are also distributed throughout the lower surface of the outer flexible membrane 44 . Thus, when a wafer is in contact with the lower surface of the outer flexible membrane 44 and suction is applied to the interconnected depressions 1002 A- 1002 D, a vacuum can be created and applied over most of the back surface of the wafer. In effect, the vacuum in the interconnected depressions 1002 A- 1002 D creates a bond between the wafer and the outer flexible membrane 44 over a large area of the wafer that corresponds to the area of the interconnected depressions 1002 A- 1002 D.

In FIG. 9 , the interconnected recess regions 900 A- 900 D include a circular recess region 900 A and annular recess regions 900 B and 900 C, which are located on the bottom surface of the annular disc 40 A. In addition, the interconnected recess regions 900 A- 900 D include an annular recess regions 900 D, which is located on the bottom surface of the annular disc 40 B. In this illustrated embodiment, there are no recess regions on the bottom surface of the annular disc 40 C. However, in other embodiments, the annular disc 40 C may include one or more interconnected recess regions.

In other embodiments, one or more of the annular discs 40 A- 40 C may have interconnected recess regions having different configurations than the interconnected recess regions 900 A- 900 D. As an example, one or more of the annular discs 40 A- 40 C may have interconnected recess regions that extend in a radial direction. As another example, one or more of the annular discs 40 A- 40 C may have interconnected recess regions that are geometrical in shape.

The operation of a polishing head with the annular discs 40 A- 40 C of FIG. 9 is similar to the operation of the polishing head 10 of FIG. 1 . Thus, the chucking process, the polishing process and the de-chucking process using the polishing head with the annular discs 40 A- 40 C of FIG. 9 are similar to the corresponding processes using the polishing head 10 of FIG. 1 .

A concern with the polishing head 10 using the annular discs 40 A- 40 C of FIG. 1 or FIG. 9 is that the third annular chamber 46 C defined by the third inner annular flexible membrane 42 C may over inflate when the pressure in the third annular chamber 46 C is significantly higher than the pressure in the second annular chamber 46 B. As a result, the thickness of the third annular chamber 46 C may be greater than the desired thickness D 3 , which is illustrated in FIG. 2 .

Turning now to FIG. 11A , a portion of the outer flexible membrane 44 in accordance with an embodiment of the invention is shown. In this embodiment, the outer flexible membrane 44 includes an annular flap 45 that extends upward toward the base 14 . The annular flap 45 is attached to the upper surface 47 of the lower portion 49 of the outer flexible membrane 44 such that the annular flap is positioned between adjacent sidewalls of the second and third inner annular flexible membranes 42 B and 42 C. The annular flap 45 provides a barrier between the second annular chamber 46 B produced by the second inner annular flexible membrane 42 B and the third annular chamber 46 C produced by the third inner annular flexible membrane 42 C so that the third annular chamber does not over inflate into the region below the lower surface of the second annular disc 40 B for the second annular chamber. Thus, the annular flap 45 of the outer flexible membrane 44 serves to maintain the thickness D 3 of the third annular chamber 46 C even when the pressure in the third annular chamber is significantly higher than the pressure in the second annular chamber 46 B, which allows the polishing head 10 to control the zone of the wafer that is affected by the third annular chamber during polishing. In the embodiment shown in FIG. 11A , the annular flap 45 is an integral part of the outer flexible membrane 44 . That is, the outer flexible membrane 44 with the annular flap 45 is made of a single piece of material. Thus, in this embodiment, the annular flap 45 is made of the same material as the rest of the outer flexible membrane 44 .

In an alternative embodiment, the annular flap 45 of the outer flexible membrane 44 may be a separate piece that is attached to bottom portion 49 of the outer flexible membrane, as illustrated in FIG. 11B . In this embodiment, the bottom portion 49 of the outer flexible membrane 44 includes an annular groove 51 on its upper surface 47 . The annular flap 45 is situated in the annular groove 51 of the bottom portion 49 of the outer flexible membrane 44 . The annular flap 45 may be attached to the bottom portion 49 of the outer flexible membrane 44 using an adhesive material. In this embodiment, the annular flap 45 can be made of a material that is different than the rest of the outer flexible membrane 44 . As an example, the annular flap 45 can be made of a material that is harder than the material for the rest of the outer flexible membrane 44 to provide a stronger barrier between the second annular chamber 46 B and the third annular chamber 46 C.

With reference to a process flow diagram of FIG. 12 , a method for handling and polishing a semiconductor wafer using a polishing head is described. At block 1202 , the polishing head is moved such that an outer flexible membrane of the polishing head is at least in close proximity to a surface of the semiconductor wafer. Next, at block 1204 , suction is applied to a chamber of the polishing head defined by the outer flexible membrane and a base structure of the polishing head. The base structure is configured to include at least one recess region on a lower surface of the base structure. The applying of the suction to the chamber causes the outer flexible membrane to conform to the at least one recess region of the base structure such that at least one depression is formed on a bottom surface of the outer flexible membrane. Next, at block 1206 , another suction is applied to the at least one depression on the bottom surface of the outer flexible membrane to hold the semiconductor wafer onto the outer flexible membrane of the polishing head.

Although the foregoing description sets forth preferred exemplary embodiments and methods of operation of the invention, the scope of the invention is not limited to these specific embodiments or described methods of operation. Many details have been disclosed that are not necessary to practice the invention, but have been included to sufficiently disclose the best mode of operation and manner and process of making and using the invention. Modification may be made to the specific form and design of the invention without departing from its spirit and scope as expressed in the following claims.