Using backgrind wafer tape to enable wafer mounting of bumped wafers
A method and apparatus are disclosed for mounting a wafer on a mount and thinning the wafer. The wafer includes a front surface having bumps with an adhesive tape having a backing attached thereto and a back surface. The front surface of the wafer is mounted facedown on a suction surface with the backing of the adhesive tape abutting the surface. The wafer is then suctioned, after which the back surface of the wafer undergoes a grinding process to thin the wafer. Since the backing attached to the bumps on the wafer is substantially planar and sits substantially flat on the suction surface of the wafer mount, the force exerted on the wafer from the thinning process does not overcome the suction force holding the wafer on the wafer mount. Thus, the bumped wafer may be thinned without damaging the bumps and the active surface of the wafer.
This application is a continuation of application Ser. No. 09/854,759, filed May 14, 2001, pending.
BACKGROUND1. Field of the Invention
The present invention relates to a method and apparatus for mounting and thinning a wafer. In particular, the present invention relates to a method and apparatus for mounting a bumped wafer to a wafer mounting chuck and thinning the wafer to a predetermined thickness.
2. State of the Art
Typically, in a manufacturing process, a plurality of integrated circuits is simultaneously patterned and defined on the front surface of a single silicon wafer. The circuits are generally aligned in rows and columns in an orthogonal format. After the integrated circuits are fully defined, the wafer is diced by a singulation machine along lines between the rows and columns, separating the wafer into a plurality of individual integrated circuit dice. The integrated circuit dice can then be secured within individual packages and/or incorporated into electronic devices.
In the typical manufacturing process, the silicon wafer is sliced from a generally cylindrical ingot. The wafer is at first sliced sufficiently thick so as not to warp or break during the various manufacturing processes. However, in some instances, the desired thickness for the finished dice is less than the initial thickness of the sliced wafer. Therefore, after the integrated circuit patterns are formed on the wafer, it has been necessary to grind the back surface of the wafer to reduce its thickness as desired for the individual integrated circuit die.
Grinding machines for grinding down the back surfaces of silicon wafers are known in the art. The known machines have chuck tables for securing a plurality of wafers in position to be ground by one or more grinding wheels. Examples of such grinding machines are illustrated in U.S. Pat. No. 5,679,060 (Leonard), U.S. Pat. No. 4,753,049 (Mori), U.S. Pat. No. 5,632,667 (Earl), and U.S. Pat. No. 5,035,087 (Nishiguchi).
Currently available wafer processing systems are unsatisfactory, particularly for grinding wafers after the contact pads of the integrated circuits thereon are bumped, known as bumped wafers. Recently, the market demands the thinning of wafers to about 6 mils or less for chips utilized in ultra-compact applications such as in cell phones. For example, see U.S. Pat. No. 5,476,566 (Cavasin), which discloses a method for thinning wafers by adhesively attaching the wafers to a supporting substrate, but does not disclose thinning wafers after being bumped. Also, U.S. Pat. No. 6,162,703 (Muntifering et al.), assigned to the assignee of the present invention, discloses a method for thinning and singulating dice from an unbumped wafer by adhesively attaching the unbumped wafer to a table and precutting notches in the unbumped wafer prior to the thinning thereof. However, for bumped wafers, it is necessary to thin the wafer after bumping because, currently, the wafer must be at least 12 mils thick to undergo the bumping process without the likelihood of damage thereto. Further, it is important that the wafer be held tightly in place during the thinning process, typically with a vacuum chuck.
Vacuum chucks include a series of apertures in the surface of the chuck to which a vacuum source is connected. The suction created between the surface of the chuck and the bottom of the wafer securely holds the wafer in place. For example, see U.S. Pat. No. 6,120,360, assigned to the assignee of the present invention, which discloses a vacuum chuck made for securing to the planar face surface of a wafer. However, the vacuum chuck is segmented into quarters and also requires the wafer to be quartered, resulting in additional process steps and potential for error in handling four times the number of wafer parts per wafer.
Although vacuum chucks perform very well for wafers having a planar face surface through which air cannot pass, such vacuum chucks will not work well for a bumped wafer. Specifically, the required suction force between the surface of the chuck and the active surface of the wafer cannot be achieved since the suctioned air will pass through the gap provided by the bumps formed on the bond pads of the integrated circuits formed on the surface of the wafer. To overcome such problems, vacuum chucks for bumped wafers are typically made to provide the suction on the active surface's periphery where there are no bumps. However, such vacuum chucks do not provide the necessary suction at the wafer's periphery for effectively holding a bumped wafer for the thinning thereof because there is not enough surface area proximate the wafer's periphery without the integrated circuits and bumps thereon. As a result, it has been suggested to increase the area proximate the wafer's periphery without the integrated circuits and bumps formed on the bond pads thereof to provide greater suction on the wafer. However, this would unacceptably limit the number of bumped dice per wafer, thereby resulting in a reduction of yield.
Therefore, it would be advantageous to provide a method and apparatus for thinning bumped wafers that provide the necessary area for suction without limiting the number of bumped dice on the wafer.
SUMMARY OF THE INVENTIONThe present invention relates to a method and apparatus for mounting a bumped wafer. The present invention further relates to a method and apparatus for mounting a bumped wafer to a wafer mounting chuck and thinning the wafer.
In a preferred embodiment of the present invention, the wafer includes a front surface and a back surface, the front surface including conductive bumps on the bond pads of the integrated circuits located thereon. The present invention includes an adhesive tape having an adhesive and a backing, the adhesive of the adhesive tape attaching the tape to the front surface of the wafer and, particularly, to the bumps on the bond pads of the integrated circuits located on the front surface of the wafer. According to the present invention, the adhesive and the tape attaches to the bumps so that an outer surface of the backing of the tape is substantially planar.
With the adhesive tape attached to the front surface of the wafer, the wafer is mounted, facedown, to a wafer mounting chuck. The wafer mounting chuck includes a suction surface with apertures therein which communicate a suction force to the wafer. The suction surface is configured to hold the wafer by the suction force applied thereto and, particularly, to hold the outer surface of the adhesive tape which is adhesively attached to the wafer using the suction force applied thereto. Thus, the outer surface of the adhesive tape provides a large surface area for holding the wafer via the suction force.
Once the wafer is suctioned facedown to the wafer mounting chuck, the wafer is ready for a thinning process. In particular, the wafer is thinned by removing material from the back surface of the wafer by grinding or chemical mechanical polishing. In this manner, bumped wafers may be thinned to less than 12 mils and, preferably, between about 6 mils and about 12 mils. After the thinning process, a wafer mount tape is applied to the back surface of the wafer. The adhesive tape is then removed from the active surface of the wafer with the aid of de-tape. The de-tape has a stronger adhesive than that of the adhesive tape so that the de-tape may be applied to an end portion of the adhesive tape for peeling the adhesive tape from the front surface of the wafer. The wafer may then undergo singulation or, rather, the wafer may be segmented into separate integrated circuit dice and/or a plurality of integrated circuit dice.
In an aspect of the present invention, the adhesive tape overlying the bumps on the bond pads of the integrated circuits and the front surface of the wafer provides an outer surface that is substantially planer so that the outer surface of the tape is suctionable. Further, the suction force is applied to substantially the whole outer surface of the backing in the desired areas so that the force exerted on the wafer from the thinning process does not overcome the suction force holding the wafer on the wafer mounting chuck. In this manner, the bumped wafer may be thinned to a desired level or an ultra thin level without damaging the bumps on the bond pads and the integrated circuits formed on the front surface of the wafer.
Another aspect of the invention provides that the bumped wafer be thinned to less than 12 mils thick. Since wafers being bumped are currently required to be at least 12 mils thick, it is necessary for the bumps to be formed on the wafer before thinning the wafer to the desired thickness between the preferred range of about 6 mils to about 12 mils.
Other features and advantages of the present invention will become apparent to those of skill in the art through a consideration of the ensuing description, the accompanying drawings and the appended claims.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGSWhile the specification concludes with claims particularly pointing out and distinctly claiming that which is regarded as the present invention, the advantages of this invention may be ascertained from the following description of the invention when read in conjunction with the accompanying drawings.
Preferred embodiments of the present invention will be hereinafter described with reference to the accompanying drawings. It should be understood that the illustrations are not meant to be actual views of any particular apparatus and/or method, but are merely idealized representations which are employed to more clearly and fully depict the present invention than would otherwise be possible. Additionally, elements and features common between the figures retain the same numerical designation.
Depicted in drawing
Depicted in drawing
Depicted in drawing
Referring to drawing
As depicted in drawing
Referring to drawing
As shown in drawing
The back surface 114 of the wafer 110 is then processed through a normal back-grind or back-lap process to thin the wafer to a desired thickness by a grinder 164. The grinder 164, as depicted in drawing
According to the present invention, it is well appreciated that the planarity of the outer surface 138 of the adhesive tape 130 provides sufficient suction force to be applied on the suction surface 152 of the wafer mounting chuck 150 and on the wafer 110 to undergo grinding without damaging the wafer 110 or without wafer movement. Further, the increased application of a suction force that the adhesive tape 130 provides allows thinning of the wafer 110 to the predetermined thickness 168 after being bumped.
After backgrinding the wafer 110, the wafer 110 may remain on the wafer mounting chuck 150 or be moved to another type of wafer mount chuck 170, such as a chuck 170 with vacuum ports 174 about a chuck periphery 172 and an air gap 176 at a center portion of the chuck 170 (as shown in drawing
As illustrated in drawing
The wafer 110 with the wafer mount tape 180 on its back surface 114 is then prepared for dicing or a singulating process. As illustrated in drawing
The above descriptions and drawings are only illustrative of preferred embodiments which achieve the objects, features and advantages of the present invention, and it is not intended that the present invention be limited thereto. Any modification of the present invention which comes within the spirit and scope of the following claims is considered part of the present invention.
Claims
1. A wafer having bumps on a surface thereof for a material removal operation, comprising:
- a tape having an adhesive and a backing attached to at least a portion of said bumps of said surface having bumps thereon of said wafer, said tape conforming at least a portion of said adhesive of said tape to said bumps, said backing of said tape has a substantially planar surface after said conforming.
2. The wafer of claim 1, further comprising:
- a wafer mount having a suction surface temporarily connected to the backing of said tape using a suction force.
3. The wafer of claim 2, further comprising:
- said wafer cut to form at least one semiconductor die after removing wafer material from said back surface.
4. The wafer of claim 3, further comprising a portion of said adhesive removed from said wafer prior to said cutting.
5. The wafer of claim 1, wherein said attaching a tape having an adhesive and a backing conforms said backing to include a substantially planar surface on at least a portion thereof.
6. The wafer of claim 1, wherein said attaching a tape having an adhesive and a backing conforms at least a portion of said adhesive of said tape to said bumps to form a substantially planar surface on said backing of said tape.
7. The wafer of claim 1, wherein said wafer comprises a wafer having a thickness of at least about 12 mils.
8. The wafer of claim 1, wherein said wafer has a thickness in the range of between about 6 mils and about 12 mils.
9. The wafer of claim 1, wherein said wafer has a back surface ground to remove material therefrom.
10. The wafer of claim 1, wherein said wafer has material removed therefrom by chemical-mechanical polishing said back surface of said wafer.
11. The combination of a wafer having bumps on a surface thereof and a mount for a material removal operation comprising:
- a tape having an adhesive and a backing attached to at least a portion of said bumps of said surface having bumps thereon of said wafer, said tape conforming at least a portion of said adhesive of said tape to said bumps, said backing of said tape has a substantially planar surface after said conforming; and
- a wafer mount having a suction surface temporarily connected to the backing of said tape using a suction force.
12. The combination of claim 11, wherein said attaching a tape having an adhesive and a backing conforms said backing to include a substantially planar surface on at least a portion thereof.
13. The combination of claim 11, wherein said attaching a tape having an adhesive and a backing conforms at least a portion of said adhesive of said tape to said bumps to form a substantially planar surface on said backing of said tape.
14. The combination of claim 11, wherein said wafer comprises a wafer having a thickness of at least about 12 mils.
15. The combination of claim 11, wherein said wafer has a thickness in the range of between about 6 mils and about 12 mils.
16. The combination of claim 11, wherein said wafer has a back surface ground to remove material therefrom.
17. The combination of claim 11, wherein said wafer has material removed therefrom by chemical-mechanical polishing said back surface of said wafer.
18. An in-process wafer having bumps on a surface thereof for a material removal operation, comprising:
- a tape having an adhesive and a backing attached to at least a portion of said bumps of said surface having bumps thereon of said wafer, said tape conforming at least a portion of said adhesive of said tape to said bumps, said backing of said tape has a substantially planar surface after said conforming.
19. The wafer of claim 18, further comprising:
- a wafer mount having a suction surface temporarily connected to the backing of said tape using a suction force.
20. The wafer of claim 19, further comprising:
- said wafer cut to form at least one semiconductor die after removing wafer material from said back surface.
21. The wafer of claim 20, further comprising a portion of said adhesive removed from said wafer prior to said cutting.
22. The wafer of claim 18, wherein said attaching a tape having an adhesive and a backing conforms said backing to include a substantially planar surface on at least a portion thereof.
23. The wafer of claim 18, wherein said- attaching a tape having an adhesive and a backing conforms at least a portion of said adhesive of said tape to said bumps to form a substantially planar surface on said backing of said tape.
24. The wafer of claim 18, wherein said wafer comprises a wafer having a thickness of at least about 12 mils.
25. The wafer of claim 18, wherein said wafer has a thickness in the range of between about 6 mils and about 12 mils.
26. The wafer of claim 18, wherein said wafer has a back surface ground to remove material therefrom.
27. The wafer of claim 18, wherein said wafer has material removed therefrom by chemical-mechanical polishing said back surface of said wafer.
28. A wafer having bumps on a surface thereof in a process for a material removal operation, comprising:
- a tape having an adhesive and a backing attached to at least a portion of said bumps of said surface having bumps thereon of said wafer, said tape conforming at least a portion of said adhesive of said tape to said bumps, said backing of said tape has a substantially planar surface after said conforming.
29. The wafer of claim 28, further comprising:
- a wafer mount having a suction surface temporarily connected to the backing of said tape using a suction force.
30. The wafer of claim 29, further comprising:
- said wafer cut to form at least one semiconductor die after removing wafer material from said back surface.
31. The wafer of claim 30, further comprising a portion of said adhesive removed from said wafer prior to said cutting.
32. The wafer of claim 28, wherein said attaching a tape having an adhesive and a backing conforms said backing to include a substantially planar surface on at least a portion thereof.
33. The wafer of claim 28, wherein said attaching a tape having an adhesive and a backing conforms at least a portion of said adhesive of said tape to said bumps to form a substantially planar surface on said backing of said tape.
34. The wafer of claim 28, wherein said wafer comprises a wafer having a thickness of at least about 12 mils.
35. The wafer of claim 28, wherein said wafer has a thickness in the range of between about 6 mils and about 12 mils.
36. The wafer of claim 28, wherein said wafer has a back surface ground to remove material therefrom.
37. The wafer of claim 28, wherein said wafer has material removed therefrom by chemical-mechanical polishing said back surface of said wafer.
38. A wafer having bumps on a surface thereof in a material removal operation, comprising:
- a tape having an adhesive and a backing attached to at least a portion of said bumps of said surface having bumps thereon of said wafer, said tape conforming at least a portion of said adhesive of said tape to said bumps, said backing of said tape has a substantially planar surface after said conforming.
39. The wafer of claim 38, further comprising:
- a wafer mount having a suction surface temporarily connected to the backing of said tape using a suction force.
40. The wafer of claim 39, further comprising:
- said wafer cut to form at least one semiconductor die after removing wafer material from said back surface.
41. The wafer of claim 40, further comprising a portion of said adhesive removed from said wafer prior to said cutting.
42. The wafer of claim 38, wherein said attaching a tape having an adhesive and a backing conforms said backing to include a substantially planar surface on at least a portion thereof.
43. The wafer of claim 38, wherein said attaching a tape having an adhesive and a backing conforms at least a portion of said adhesive of said tape to said bumps to form a substantially planar surface on said backing of said tape.
44. The wafer of claim 38, wherein said wafer comprises a wafer having a thickness of at least about 12 mils.
45. The wafer of claim 38, wherein said wafer has a thickness in the range of between about 6 mils and about 12 mils.
46. The wafer of claim 38, wherein said wafer has a back surface ground to remove material therefrom.
47. The wafer of claim 38, wherein said wafer has material removed therefrom by chemical-mechanical polishing said back surface of said wafer.
48. The combination of a wafer having bumps on a surface thereof and a mount in a material removal operation comprising:
- a tape having an adhesive and a backing attached to at least a portion of said bumps of said surface having bumps thereon of said wafer, said tape conforming at least a portion of said adhesive of said tape to said bumps, said backing of said tape has a substantially planar surface after said conforming; and
- a wafer mount having a suction surface temporarily connected to the backing of said tape using a suction force.
49. The combination of claim 48, wherein said attaching a tape having an adhesive and a backing conforms said backing to include a substantially planar surface on at least a portion thereof.
50. The combination of claim 48, wherein said attaching a tape having an adhesive and a backing conforms at least a portion of said adhesive of said tape to said bumps to form a substantially planar surface on said backing of said tape.
51. The combination of claim 48, wherein said wafer comprises a wafer having a thickness of at least about 12 mils.
52. The combination of claim 48, wherein said wafer has a thickness in the range of between about 6 mils and about 12 mils.
53. The combination of claim 48, wherein said wafer has a back surface ground to remove material therefrom.
54. The combination of claim 48, wherein said wafer has material removed therefrom by chemical-mechanical polishing said back surface of said wafer.
55. A wafer mount assembly and a wafer having a front surface having at least one bump thereon and a back surface, comprising:
- an adhesive tape having an adhesive and a planar backing for a vacuum attachment, said adhesive tape for adhesively attaching a portion of said front surface of said wafer having said at least one bump thereon to a portion of said wafer mount assembly by said planar backing for a vacuum attachment.
56. The assembly of claim 55, further comprising:
- a wafer mount having a vacuum surface thereon, said vacuum surface of said wafer mount for abutting at least a portion of said backing of said adhesive tape, said vacuum surface including apertures therein for communicating a vacuum therethrough.
57. The assembly of claim 55, wherein said backing of said adhesive tape includes a substantially planar surface for overlying said at least one bump.
58. The assembly of claim 57, wherein said substantially planar surface of said backing of said adhesive tape provides an area for the application of a vacuum to at least a portion of said front surface of said wafer.
59. The assembly of claim 55, wherein said backing includes a substantially planar surface overlying said at least one bump.
60. The assembly of claim 55, wherein said adhesive attaches to said at least one bump.
61. The assembly of claim 55, wherein said adhesive conforms to said at least one bump to form a substantially planar surface on at least a portion of said backing.
62. The assembly of claim 55, wherein said adhesive tape substantially overlies another bump.
63. The assembly of claim 55, wherein said wafer comprises a wafer having a thickness of at least 12 mils.
64. The assembly of claim 55, wherein said at least one bump comprises a conductive bump for electrical connection.
65. An assembly of a bumped wafer and a wafer mount for grinding, the assembly comprising:
- a wafer having a front surface and a back surface thereof, said front surface having at least one bump thereon; and
- a tape having an adhesive and a planar backing for vacuum attachment, said tape for adhesively attaching a portion of said front surface of said wafer having said at least one bump thereon.
66. The assembly of claim 65, wherein said backing includes a substantially planar surface overlying said at least one bump.
67. The assembly of claim 65, wherein said adhesive attaches to said at least one bump for forming a substantially planar surface oh said backing.
68. The assembly of claim 65, wherein said adhesive conforms to said at least one bump to form a substantially planar surface on a portion of said backing.
69. The assembly of claim 65, wherein said tape substantially covers said front surface of said wafer.
70. The assembly of claim 65, wherein said at least one bump comprises a conductive bump for electrical connection.
71. The assembly of claim 65, wherein said backing comprises a resilient material.
72. The assembly of claim 65, wherein said wafer comprises a thickness of at least 12 mils prior to being mounted to said wafer mount.
73. The assembly of claim 65, wherein said wafer comprises another thickness of one of about less than 6 mils and greater than about 6 mils and less than about 12 mils after grinding said back surface of said wafer.
Type: Application
Filed: Dec 3, 2004
Publication Date: May 12, 2005
Inventors: Michael Ball (Boise, ID), Jose Sanchez (Boise, ID)
Application Number: 11/004,208