METHOD FOR FORMING INTERCONNECTS ON THIN WAFERS
A method of forming a semiconductor interconnect including, in the order recited: (a) providing a semiconductor wafer; (b) forming bonding pads in a terminal wiring level on the frontside of the wafer; (c) reducing the thickness of the wafer; (d) forming solder bumps on the bonding pads; and (e) dicing the wafer into bumped semiconductor chips.
This Application is a division of U.S. patent application Ser. No. 11/184,695 filed on Jul. 19, 2005, which is a division of U.S. patent application Ser. No. 10/604,164 filed on Jun. 28, 2003, now U.S. Pat. No. 6,951,775.
FIELD OF THE INVENTIONThe present invention relates to the field of semiconductor processing; more specifically, it relates to a method of forming a solder interconnect structure on a thin wafer.
BACKGROUND OF THE INVENTIONIncreasing density of semiconductor devices has allowed semiconductor chips to decrease in area. Along with the decrease in chip area, has come a need to make the semiconductor chips thinner. Current methods of thinning semiconductor wafers often lead to damage of the semiconductor chips.
SUMMARY OF THE INVENTIONA first aspect of the present invention is a method of forming a semiconductor interconnect comprising, in the order recited: (a) providing a semiconductor wafer; (b) forming bonding pads in a terminal wiring level on the frontside of the wafer; (c) reducing the thickness of the wafer; (d) forming solder bumps on the bonding pads; and (e) dicing the wafer into bumped semiconductor chips.
A second aspect of the present invention is a method of forming a semiconductor interconnect comprising, in the order recited: (a) providing a semiconductor wafer; (b) forming bonding pads in a terminal wiring level on the frontside of the wafer; (c) reducing the thickness of the wafer to produce a reduced thickness wafer; (d) providing an evaporation fixture comprising a bottom ring, a shim, an evaporation mask and a top ring; (e) placing the shim into the bottom ring; (f) placing the reduced thickness wafer on the shim; (g) placing on and aligning the mask to the reduced thickness wafer; (h) placing said top ring over said mask and temporarily fastening said top ring to said bottom ring; (i) evaporating solder bumps on the bonding pads through the mask; (j) removing the reduced thickness wafer from the fixture; and (k) dicing the reduced thickness wafer into bumped semiconductor chips.
A third aspect of the present invention is A fixture for holding wafer and an evaporative mask comprising: a bottom ring having a inner periphery and an outer periphery, the bottom ring having a raised inner lip formed along the inner periphery and a raised outer lip formed along the outer periphery, the height of the inner lip above a surface of the bottom ring being greater than a height of the outer lip above the surface of the bottom ring; a shim having a inner and an outer periphery, the outer periphery of the shim fitting inside and in proximity to the outer lip of the bottom ring, a bottom surface of the shim proximate to the inner periphery of the shim contacting an upper surface of the inner lip of the bottom ring; a top ring having an inner periphery and an outer periphery, the top ring having a lower raised lip formed along the inner periphery of the bottom ring and extending below a bottom surface of the top ring; and the bottom ring and the top ring adapted to press a bottom surface of the wafer against an upper surface of the shim and to press a top surface of the wafer against a bottom surface of the mask and to press a top surface of the mask proximate to the periphery of the mask against a lower surface of the lower raised lip of the top ring.
BRIEF DESCRIPTION OF DRAWINGSThe features of the invention are set forth in the appended claims. The invention itself, however, will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:
For the purposes of the present invention, the terms substrate and wafer may be used interchangeably.
In
In one example of thinning, a 200 mm diameter wafer having an initial thickness T1 of about 650 to 780 microns is thinned to a new thickness T2 of about 150 to 450 microns. The present invention may be practiced using any diameter wafer including 100 mm, 125 mm and 300 mm wafer of any initial thickness T1, reducing the wafer to any final thickness T2 as required by the use of the finished chip.
In
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The evaporation process for forming PLMs 165 and solder bumps 170 (see
Retaining post 282 passes through retaining post hole 262 in mask 250, retaining post notches 297 in shim 290 and retaining post hole 227 in bottom ring 200. A spring clip 310 engages retaining post 305 and temporarily fastens assembled fixture 300 together.
The second method is to experimentally determine for a given thinned wafer thickness (T2) a shim thickness (T3) that yields the same wafer deflection (D4) (see
The description of the embodiments of the present invention is given above for the understanding of the present invention. It will be understood that the invention is not limited to the particular embodiments described herein, but is capable of various modifications, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, it is intended that the following claims cover all such modifications and changes as fall within the true spirit and scope of the invention.
Claims
1. A fixture for holding a wafer and an evaporative mask comprising:
- a bottom ring having a inner periphery and an outer periphery, said bottom ring having a raised inner lip formed along said inner periphery and a raised outer lip formed along said outer periphery, the height of said inner lip above a surface of said bottom ring being greater than a height of said outer lip above said surface of said bottom ring;
- a shim having a inner and an outer periphery, the outer periphery of said shim fitting inside and in proximity to said outer lip of said bottom ring, a bottom surface of said shim proximate to said inner periphery of said shim contacting an upper surface of said inner lip of said bottom ring; and
- a top ring having an inner periphery and an outer periphery, said top ring having a lower raised lip formed along said inner periphery of said bottom ring and extending below a bottom surface of said top ring.
2. The fixture of claim 1, wherein said bottom ring and said top ring are adapted to press a bottom surface of said wafer against an upper surface of said shim and to press a top surface of said wafer against a bottom surface of said evaporative mask and to press a top surface of said evaporative mask proximate to said periphery of said evaporative mask against a lower surface of said lower raised lip of said top ring.
3. The fixture of claim 1, wherein the combined thicknesses of said wafer and said shim are substantially equal to a thickness of a thicker wafer, said fixture designed to hold said thicker wafer without said shim being present.
4. The fixture of claim 1, wherein said shim has thickness such that said wafer is bowed substantially a same amount as a thicker wafer would be bowed without said shim being present, said fixture designed to hold said thicker wafer.
5. A fixture, comprising:
- a bottom ring having opposite top and bottom surfaces and inner and outer raised lips on said top surface;
- a shim having a circular opening and opposite top and bottom surfaces;
- a top ring having opposite top and bottom surface surfaces; and
- said bottom ring and said top ring adapted to press said bottom surface of said shim adjacent to said circular opening against said inner raised lip, to press a bottom surface of a wafer against said upper surface of said shim, to press a top surface of said wafer against a bottom surface of a mask and to press a top surface of said mask proximate to a periphery of said mask against said lower surface of said top ring.
6. The fixture of claim 5, wherein said shim, said top ring and said bottom ring are adapted to impart a bow to said wafer and said mask, a central part of said wafer and a central part of said mask bowed away from said bottom ring and peripheral portions of said wafer and said mask bowed toward said bottom ring.
7. The fixture of claim 5, wherein the combined thicknesses of said wafer and said shim are substantially equal to a thickness of a thicker wafer said fixture is designed to hold without said shim being present.
8. The fixture of claim 5, wherein said shim has thickness such that said wafer is bowed substantially a same amount as a thicker wafer would be bowed without said shim being present, said fixture designed to hold said thicker wafer.
9. The fixture of claim 5, wherein said inner raised lip extends a first distance above said top surface of said bottom ring, said outer raised lip extends a second distance above said top surface of said bottom ring, said first distance is greater than said second distance.
10. A fixture, comprising:
- a bottom ring having a inner periphery and an outer periphery, said bottom ring having a raised inner lip formed along said inner periphery and a raised outer lip formed along said outer periphery;
- a shim having a inner and an outer periphery, the outer periphery of said shim fitting inside and in proximity to said outer lip of said bottom ring, a bottom surface of said shim proximate to said inner periphery of said shim contacting an upper surface of said inner lip of said bottom ring; and
- a top ring having an inner periphery and an outer periphery, said top ring having a lower raised lip formed along said inner periphery of said bottom ring and extending below a bottom surface of said top ring.
11. The fixture of claim 10, wherein the height of said inner lip above a surface of said bottom ring being greater than a height of said outer lip above said surface of said bottom ring.
12. The fixture of claim 11, wherein said height of said inner lip is about 0.080 inches and said height of said outer lip is about 0.073 inches.
13. The fixture of claim 10, wherein said bottom ring includes openings extending between said surface and an opposite surface of said bottom ring, said opening located between said inner and outer lips.
14. The fixture of claim 10, wherein a thickness of said shim is substantially equal to a difference between a thickness of said wafer and a thickness of a thicker wafer after said thicker wafer has been thinned, said fixture designed to hold said thicker wafer.
Type: Application
Filed: Jul 3, 2007
Publication Date: Dec 6, 2007
Inventors: Leonard Gardecki (Essex, VT), James Palmer (Williston, VT), Erik Probstfield (Fairfax, VT), Adolf Wirsing (South Hero, VT)
Application Number: 11/772,862
International Classification: B25B 5/16 (20060101);