This invention relates to the manufacture of ultrathin semiconductor wafers and die and to the packaging of such die.
Ultra thin semiconductor die which are thinner than about 100 μm are well known. Such die can be formed as vertical conduction MOSFETs or other semiconductor devices with a very low on resistance (RDSON).
However, when such wafers are thinned to below about 100 μm, they are very fragile and hard to handle in present day fabrication and packaging equipment.
The present invention provides a novel process for the handling of such die and their subsequent packaging in conventional packaging equipment.
In accordance with the invention the front or top surface of a full thickness die is conventionally processed to receive the requisite junctions but without the formation of the front metal and the front metal patterning. A thick rigid front carrier plate is then adhesively applied to the unmetallized front surface with an adhesive that can be easily dissolved.
The back side of the wafer is then ground back to some desired thickness, for example, to less than 50 μm. After a conventional stress relief process, a suitable back metal which becomes, for example, the drain electrode of thinned MOSFETs, is applied to the wafer back surface as by sputtering or the like.
A relatively thick and rigid conductive back plate, which may be copper, aluminum or other conductive material is then permanently conductively bonded to the back metal, and the front carrier plate is removed by disabling the adhesive.
The front surface of the thinned wafer is then metallized and patterned with the thick conductive back plate providing rigidity to enable the easy handling of the die.
The wafer may then be mounted and sawn (or singulated) into separate die. The conductive back plate is an integral part of the singulated die which has the thinned silicon die fixed thereto to provide physical strength to the assembly and to further reduce RDSON.
The individual die assemblies can now be handled as conventional thick die for mounting in a can such as a DirectFET package (U.S. Pat. No. 6,624,522) or in any other package.
It will be noted also that there is no front metal induced stress on the thinned silicon until after the backside conductor has been bonded to the wafer. Further, front metal features cannot pattern through to the wafer back during the grind-to-thin operation. Further, higher temperature bonding for the adhesive and for connecting the thick back plate to the silicon can be used since the front metal is not yet in place.
As a further feature of the invention, the wafer can be diced before grinding. With this embodiment, the glue used to bond the front carrier plate will flow into the saw lines and prevent the back metal and back plate bonding material from going up the die side walls.
A rigid front side carrier 30 is then glued or otherwise releasably adhered to the front side 21 (which is not yet metallized) as shown in
The back side 31 of the wafer 20 of
The thinned wafer 20 with carrier 30 is next processed to have a back metal 40 applied thereto, as by a conventional sputter process, as shown in
Thereafter, and as shown in
As next shown in
The back metal plate 50 will now serve as a permanent support for the wafer during dicing at vertical dotted lines 61, 62 (die separation by sawing or the like) and for packaging of the die. Conventional packaging equipment can be used for the thick, strong die assembly.
Thereafter, as shown in
Thereafter, as shown in
The metal 60 is then patterned as shown in
Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein.
This application claims the benefit and priority of U.S. Provisional Application No. 60/688,453, filed Jun. 8, 2005 the entire disclosure of which is incorporated by reference herein.
Number | Name | Date | Kind |
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5047833 | Gould | Sep 1991 | A |
5324687 | Wojnarowski | Jun 1994 | A |
6465353 | Francis | Oct 2002 | B1 |
6506664 | Beyne et al. | Jan 2003 | B1 |
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Number | Date | Country | |
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20060281315 A1 | Dec 2006 | US |
Number | Date | Country | |
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60688453 | Jun 2005 | US |