Method for reducing the thickness of substrates
View Patent ↗The current invention presents a method for thinning wafers. The method uses a two-step process, whereby first the carrier wafer ( 2 ) is thinned and in a second step the device wafer ( 1 ) is thinned. The method is based on imprinting the combined thickness non-uniformities of carrier ( 2 ) and glue layer ( 3 ) essentially on the carrier ( 2 ), with a resulting low TTV of the wafer ( 100 ) after thinning.
1. A method for thinning a wafer, comprising:
providing a device wafer having a first surface and a second surface essentially parallel to each other;
providing a carrier having a first surface and a second surface essentially parallel to each other;
bonding the first surface of the device wafer to the first surface of the carrier, whereby a composite substrate is obtained;
clamping the second surface of the device wafer to a first reference surface; thereafter
removing material from the second surface of the carrier in the composite substrate; thereafter
clamping the second surface of the carrier to a second reference surface; thereafter
removing material from the second surface of the device wafer in the composite substrate; and
removing the wafer from the carrier, whereby a thinned wafer is obtained.
2. The method of claim 1 , wherein at least one of removing material from the second surface of the carrier in the composite substrate and removing material from the second surface of the device wafer in the composite substrate is done by grinding.
3. The method of claim 1 , wherein bonding the first surface of the wafer to the first surface of the carrier comprises applying a glue layer between the first surface of the wafer and the first surface of the carrier.
4. The method of claim 1 , wherein the thinned device wafer has a thickness below 50 microns and a total thickness variation below 2 microns.
5. The method of claim 1 , wherein at least one of removing material from the second surface of the carrier in the composite substrate or removing material from the second surface of the device wafer in the composite substrate is done by a method selected from the group consisting of fly cutting and chemical mechanical polishing.
6. The method of claim 1 , wherein the device wafer has a thickness of more than 600 microns before thinning.
7. The method of claim 1 , wherein the device wafer has a thickness of more than 400 microns before thinning.
8. The method of claim 1 , wherein the device wafer has a thickness of more than 200 microns before thinning.
9. The method of claim 1 , wherein at least one of the device wafer and the carrier comprises a semiconductor material.
10. The method of claim 1 , wherein at least one of the device wafer or the carrier comprises at least one material selected from the group consisting of silicon, germanium, compound semiconductors, and glass.
11. The method of claim 1 , wherein removing material from the second surface of the carrier in the composite substrate comprises removing material such that the second surface of the carrier is essentially parallel to the first reference surface; and wherein removing material from the second surface of the device wafer in the composite substrate comprises removing material such that the second surface of the wafer is essentially parallel to the second reference surface.
12. The method of claim 11 , wherein the first reference surface and the second reference surface are the same.
13. The method of claim 11 , wherein the first reference surface is a first chuck and the second reference surface is a second chuck.
14. The method of claim 1 , wherein the device wafer has a thickness of more than 100 microns before thinning.
15. The method of claim 14 , wherein the thinned wafer has a thickness of below 50 microns.
16. The method of claim 14 , wherein the thinned wafer has a thickness of below 40 microns.
17. The method of claim 14 , wherein the thinned wafer has a thickness of below 30 microns.
18. The method of claim 14 , wherein the thinned wafer has a thickness of below 20 microns.
19. The method of claim 14 , wherein the thinned wafer has a thickness of below 10 microns.
20. The method of claim 14 , wherein the thinned wafer has a thickness of below 5 microns.