Configuration for polishing disk-shaped objects

ABSTRACT

A polish head for Chemical Mechanical Polishing includes a backing film of silicone on a rigid support element, preferably, of amorphous ceramic. The silicone backing film is fabricated by molding, thereby enabling an appropriate cross-sectional shape for specific polishing needs. The head provides a uniform polishing of a semiconductor wafer.

INFORMATION

DETAILED DESCRIPTION OF THE INVENTION

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown a configuration for polishing disk-shaped objects according to the invention. The configuration is especially applicable for polishing semiconductor wafers for the manufacturing of integrated circuits. The configuration includes a table or polish platen on which a polish pad is attached. A polish head holds a wafer , the front side of which is moved across the polish pad for polishing. A liquid slurry or a polish pad with fixed abrasive inside of the polish pad is inserted to control friction and to accomplish the Chemical Mechanical Polishing. A configuration of, for example, three or four polish heads is provided, each rotating around its own axis and all of them rotating around the axis of the head configuration. The wafer is pressed onto the polish pad by the polish head . The wafer backside is in direct contact with the backing film. In particular, there is no material disposed between the backing film and the wafer backside. The downforce is applied through a backing film or backing pad . The backing film is supported through the polish head by a backing film support . The backing film support is rigid having an incompressible, indistortable constant shape. The support withstands the downforce applied to the wafer without any relaxation. According to the invention, the backing film is made of silicone. A retainer ring withstands the radial forces during polish. The support applies a vacuum to the backside of the wafer through a vacuum chamber and vacuum holes . By applying the vacuum the wafer is sucked to the backing film . By switching off the vacuum, the wafer is released from the backing film . Further, a vacuum is supplied to suck the silicone backing film to the support .

FIG. 2 shows a preferred embodiment of the polish head . The support element for the backing film is a ceramic chuck . A vacuum chamber is provided above the ceramic chuck . A channel connects the vacuum chamber to a non-illustrated vacuum generator. The ceramic chuck , being amorphous, enables the vacuum in the chamber to reach the silicone backing film to suck it to the ceramic chuck . With the amorphous ceramic chuck , the vacuum in the chamber is evenly distributed across the surface that contacts the silicone backing film. Because silicone does not leak air, the backing film is tightly held on the ceramic chuck and can be released easily by switching off the vacuum in the chamber . Compared to a polyurethane backing film, no glue is necessary to stick the backing film to the support (chuck ) so that a replacement of a used backing film is facilitated and non-uniformities due to air bubbles enclosed by the glue are avoided. The surface of the ceramic chuck is rigid and has a constant shape even when the polish head is pressed onto the platen .

An additional vacuum chamber provided with a vacuum by another vacuum channel is disposed above the vacuum chamber . Vacuum tubes range from the vacuum chamber through the vacuum chamber also protruding through the ceramic chuck as well as the backing film . The tubes are on the backside of the wafer . When a vacuum is applied to the backside of the wafer through the vacuum tubes , the wafer is tightly held to the backing film . When switching off the vacuum after polishing, the wafer is released from the polish head .

The backing film is fabricated by a molding process in a molding form shown in cross-sectional view in FIG. . The molding or casting form has a bottom part and a top part . Liquid silicone is inserted through a channel between the top and the bottom parts and is transformed to a solid film. Due to the fact that the silicone film is produced from a liquid, the solid silicone backing film is very homogeneous, having substantially no variation in density and compressibility. Further, the cross-sectional shape of the backing film can be adapted to various requirements. It is also possible to provide the surface of the silicone backing film, which is facing the backside of the wafer to be polished, with a microstructure as explained below. Further, it is possible to insert additional components into the silicone to adopt specific hardness requirements to various radial and/or concentric zones of the silicone backing film.

The silicone backing film is impermeable for air. To ease the removal of the wafer from the backing film after polishing of the surface , the silicone backing film facing to the backside of the wafer is provided with a microstructure. Preferred embodiments of the microstructure are shown in FIG. 4A, B, and C. The microstructure has projecting or enhanced portions and recessed portions . The enhanced portions make contact to the backside of the wafer , whereas the recessed portions do not contact the backside wafer surface . With enhanced and recessed portions , forming a microstructure, the contact area between the backing film and the wafer backside surface is reduced. The height of the projections is to be adjusted in the range 5 to 500 μm. The sequence of projections and recesses is regular. Two neighboring projections repeat after 100 to 1000 μm. A cross-section through a projecting element can be of rectangular shape as shown in FIG. 4A or of tapered shape as shown in FIG. 4B or of triangular shape as shown in FIG. C.

The complementary shape of the microstructure is provided by the molding or casting form of FIG. 3 including a bottom part and a top part . The top part is provided with the microstructure . The microstructure is formed by a lithography process. The top part is, preferably, a metal plate or a glass plate. The top part is coated with a photoresist and structured by light exposure. After developing the photoresist and removal of the developed portions (or undeveloped portions depending on the type of the photoresist), the exposed metal or glass sections are etched by a wet etching chemical or by dry etching (plasma etch). As a result, the structures as shown in FIG. 4A through 4C are achieved. Liquid silicone is fed into the molding form through feeding channel and is then molded.

By appropriate macroscopic shaping of the molding in FIG. 3, the various cross-sectional shapes as shown in FIG. 5A through 5C are obtained. The convex form shown in FIG. 5A has a crosssectional shape where the thickness decreases from the center to the circumference. Polishing a wafer with the backside film of FIG. 5A in a polish head of FIGS. 1 or provides faster polishing at the center of the wafer than at the outside portions of the wafer. The macroscopic shape is easily achieved by the appropriate shaping of the top part of the molding form . The convex cross-sectional shape of the backing film in FIG. 5B has a smaller thickness in the center that increases radially to its circumference. The concaveness of the backside film can be obtained by an appropriate shape of the top part of the molding form . With the concave backing film as shown in FIG. 5B, the center of the wafer is polished more slowly as compared to the outer parts of the wafer. Another preferred shape of the backside film is depicted in FIG. C. The macroscopic cross-sectional structure of the circular backing film is U-shaped and has a macroscopic recess at the center and a projecting portion at the circumference. The surface touching the backside of the wafer of the projecting portion has a microstructure as is explained with respect to FIG. . The recess section encloses an air cushion behind the wafer.

As shown in principle in FIG. 5D, the backing film can have portions of different hardness. For example, the portion in the center of the backing film is harder and has less compressibility than the circular portion surrounding the inner portion . The center is polished faster than the outer part of the wafer. Different hardness is achieved by adding particles to the silicone rubber. The particles are mixed into the liquid silicone before the molding form is filled with liquid silicone. The particles may include silicon or aluminum-oxide or a mixture of both. Other particles that do not introduce any contamination to silicon wafers are also possible.

The invention as disclosed above achieves better uniformity of Chemical Mechanical Polishing of semiconductor wafers by various effects. The silicone backing film can, easily, be drawn to the ceramic chuck or support plate within the polish head by the application of a vacuum, thereby avoiding any glue. Such a configuration provides a uniform adhesion of the silicone backing film to the polish head. The replacement of a used and mature backing film is easy and safe, enabling high turnaround time by simply switching the vacuum on and off provided through the amorphous ceramic chuck. The ability to manufacture silicone by molding in an appropriately configured molding/casting form enables the backing film to be adopted to specific polishing characteristics. By appropriate macroscopical shape of the silicone backing film achieved by the molding form, different removal speeds of the material to be polished can be achieved across the wafer surface. A comparable effect can be achieved by an appropriate adding of particles into the silicone. In addition, a microstructure on the contact surface of the backing film to the backside of the wafer serves for good adhesion to the backing film during polishing and easy removal from the backing film when the polish process is finished. Overall, the use of a silicone backing film in a polish configuration according to the invention provides a more accurate polishing and a high turnaround time, thereby providing better quality integrated circuits.

BRIEF DESCRIPTION OF THE DRAWINGS:

FIG. 1 is a fragmentary, cross-sectional view of a first embodiment of a configuration for polishing a semiconductor wafer according to the invention;

FIG. 2 is a fragmentary, cross-sectional view of a second embodiment of the configuration of FIG. 1;

FIG. 3 is a cross-sectional view of a molding form for the fabrication of a silicone backing film according to the invention;

FIGS. 4A, B, and C are fragmentary, diagrammatic, enlarged cross-sectional views of various embodiments of a microstructure of the surface of a silicone backing film according to the invention; and

FIGS. 5A to D are diagrammatic, enlarged, cross-sectional views through a silicone backing film according to the invention.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of copending International Application No. PCT/EP01/10186, filed Sep. 4, 2001, which designated the United States.

CLAIMS

1. A configuration for polishing disk-shaped objects having a first surface and a second surface opposite the first surface, comprising: a platen adapted to contact the first surface of an object to be polished; and a polish head having: a backing film removably attached to said polish head and adapted to directly contact the second surface, said backing film being of silicone; and a rigid support element carrying said backing film.

2. The configuration according to claim 1, wherein the object is a semiconductor wafer.

3. The configuration according to claim 1, wherein the object is a silicon wafer.

4. The configuration according to claim 1, wherein said support element is an amorphous ceramic.

5. The configuration according to claim 4, wherein said polish head has a vacuum generator supplying a vacuum to said ceramic support element to hold said backing film on said ceramic support element.

6. The configuration according to claim 5, wherein said polish head has: a first vacuum chamber supplying a vacuum to said ceramic support element; a second vacuum chamber above said first vacuum chamber; and a plurality of tubes projecting from said second vacuum chamber through said first chamber, through said ceramic support element, and through said backing film to end above the second surface of the object, said tubes supplying a vacuum to said second surface of the object to hold the object onto said backing film.

7. The configuration according to claim 1, wherein said backing film has a surface adapted to directly contact the second surface of the object, said surface of said backing film having a microstructure with: a plurality of enhanced portions contacting the second surface of the object; and a plurality of recessed portions not contacting the second surface of the object.

8. The configuration according to claim 7, wherein said surface of said backing film is: concave; convex; or U-shaped defining a macroscopic recess in a center thereof, said recess not contacting the object.

9. The configuration according to claim 1, wherein said backing film has concentric zones of different hardnesses.

10. The configuration according to claim 1, wherein said backing film has additives of solid particles.

11. The configuration according to claim 10, wherein said particles are of silicon or aluminum oxide.

12. A configuration for polishing semiconductor wafers having a first surface and a second surface opposite the first surface, comprising: a platen adapted to contact the first surface of a wafer to be polished; and a polish head having: a backing film removably attached to said polish head and adapted to directly contact the second surface, said backing film being of silicone; a rigid support element carrying said backing film; and a vacuum generator holding said backing film on said support element.

13. The configuration according to claim 12, wherein said vacuum generator supplies a vacuum to said support element to hold said backing film on said support element.

14. The configuration according to claim 12, wherein said vacuum generator has: a first vacuum chamber supplying a vacuum to said support element; a second vacuum chamber above said first vacuum chamber; and a plurality of tubes projecting from said second vacuum chamber through said first chamber, through said support element, and through said backing film to end above the second surface of the wafer, said tubes supplying a vacuum to said second surface of the wafer to hold the wafer onto said backing film.

15. The configuration according to claim 12, wherein said backing film has a surface adapted to directly contact the second surface of the wafer, said surface of said backing film having a microstructure with: a plurality of enhanced portions contacting the second surface of the wafer; and a plurality of recessed portions not contacting the second surface of the wafer.

16. The configuration according to claim 15, wherein said surface of said backing film is: concave; convex; or U-shaped defining a macroscopic recess in a center thereof, said recess not contacting the wafer.

17. The configuration according to claim 12, wherein said support element is an amorphous ceramic.

18. The configuration according to claim 12, wherein said backing film has concentric zones of different hardnesses.

19. The configuration according to claim 2, wherein said backing film has additives of solid particles.

20. The configuration according to claim 19, wherein said particles are of silicon or aluminum oxide.

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