Methods for minimizing edge peeling in the manufacturing of BSI chips
A method includes forming top metal lines over a semiconductor substrate, wherein the semiconductor substrate is a portion of a wafer having a bevel. When the top metal lines are exposed, an etchant is supplied on the bevel, wherein regions of the wafer sprayed with the etchant has an inner defining line forming a first ring having a first diameter. A trimming step is performed to trim an edge portion of the wafer, wherein an edge of a remaining portion of the wafer has a second diameter substantially equal to or smaller than the first diameter.
1. A method comprising:
forming top metal lines over a semiconductor substrate, wherein the semiconductor substrate is a portion of a wafer comprising a bevel;
wherein the top metal lines are exposed, supplying an etchant to the bevel, wherein a region of the wafer supplied with the etchant has an inner defining line forming a first ring having a first diameter; and
performing a trimming step to trim an edge portion of the wafer, wherein an edge of a remaining portion of the wafer has a second diameter substantially equal to or smaller than the first diameter.
2. The method of claim 1 , wherein the second diameter is smaller than the first diameter.
3. The method of claim 2 , wherein the second diameter is smaller than the first diameter by greater than about 2 mm.
4. The method of claim 1 , wherein the trimming is performed after the supplying the etchant to the bevel.
5. The method of claim 1 further comprising:
after the step of supplying the etchant, forming a passivation layer over the top metal lines;
bonding a carrier on the passivation layer; and
performing a thin down process from a backside of the semiconductor substrate to thin down the semiconductor substrate.
6. The method of claim 5 , wherein the trimming step is performed after the step of performing the thin down process, and wherein the method further comprises, after the trimming step, performing an additional thin down process from the backside of the semiconductor substrate to further thin down the semiconductor substrate.
7. The method of claim 5 , wherein during the step of supplying the etchant, edge portions of the top metal lines are etched by the etchant, and inner portions of the top metal lines closer to a center of the wafer than the edge portions are not etched, and wherein in the step of forming the passivation layer, trenches left by the etched edge portions of the top metal lines are filled with the passivation layer.
8. The method of claim 5 further comprising:
performing an additional trimming step to form a recess extending from a front surface of the wafer to an intermediate level of the wafer, with an edge portion of the wafer aligned to the recess, and wherein in the thin down process, the edge portion of the wafer is removed.
9. The method of claim 1 , wherein in the step of supplying the etchant, a metallic material on the bevel is removed, wherein the metallic material comprises a same metal as the top metal lines.
10. A method comprising:
forming an image sensor at a front side of a semiconductor substrate, wherein the semiconductor substrate is comprised in a semiconductor wafer comprising a bevel;
forming top metal lines over the semiconductor substrate, wherein the top metal lines comprise edge portions adjacent to the bevel, and inner portions closer to a center of the semiconductor wafer than the edge portions;
performing an edge bevel removal using an etchant to remove a metallic material from the bevel of the wafer, wherein the edge portions of the top metal lines are removed during the edge bevel removal, and wherein portions of the wafer receiving the etchant form a first ring having an inner defining line, with portions of a top surface of the wafer inside the inner ring not receiving the etchant;
performing a first thin down process for thinning down a semiconductor substrate of the wafer; and
from a backside of the semiconductor wafer, performing a trimming step after the first thin down process, with a trim line forming a second ring, wherein the second ring is located inside the first ring.
11. The method of claim 10 , wherein the first ring and the second ring has a spacing greater than about 1 mm.
12. The method of claim 10 , further comprising, after the step of performing the edge bevel removal, forming a dielectric layer over the top metal lines, wherein the trimming step is performed after the edge bevel removal and the forming the dielectric layer.
13. The method of claim 10 further comprising a second thin down process after the step of trimming to further thin down the semiconductor substrate.
14. The method of claim 10 , wherein the edge bevel removal is performed by spraying an acid to the bevel of the wafer.
15. The method of claim 10 further comprising:
performing an additional trimming step to form a recess extending from a front surface of the wafer to an intermediate level of the wafer, with an edge portion of the wafer aligned to the recess, and wherein in the first thin down process, the edge portion of the wafer is removed.
16. A method comprising:
forming a front-side structure of a wafer;
wherein top metal lines of the front-side structure are exposed, performing an Edge Bevel Removal (EBR) on an edge portion of the wafer to remove a metallic material from a bevel of the wafer, wherein outer portions of the top metal lines in an EBR region of the wafer are etched during the EBR, and wherein inner portions of the top metal lines closer to a center of the wafer than an inner defining line of the EBR region are not etched; and
performing a trimming step to trim off all portions of the wafer that are farther away from the center of the wafer than the inner defining line of the EBR region.
17. The method of claim 16 , wherein a trim line of trimming step is on an inner side of the inner defining line of the EBR region, and the trimming step is performed after the performing the EBR.
18. The method of claim 17 , wherein a spacing between the trim line and the inner defining line of the EBR region is greater than about 1 millimeter.
19. The method of claim 16 further comprising, after the step of performing the EBR, forming a dielectric layer on the front side of the wafer and over the top metal lines, wherein the dielectric layer is filled into trenches left by etched outer portions of the top metal lines in the EBR region.
20. The method of claim 16 further comprising:
performing a first thin down process for thinning down a semiconductor substrate of the wafer, wherein the trimming step is performed after the first thin down process; and
performing a second thin down process to further thin down the semiconductor substrate, wherein the second thin down process is performed after the trimming step.
21. The method of claim 16 further comprising forming an image sensor in the wafer.
22. The method of claim 20 further comprising:
performing an additional trimming step to form a recess extending from a front surface of the wafer to an intermediate level of the wafer, with an edge portion of the wafer aligned to the recess, and wherein in the first thin down process, the edge portion of the wafer is removed.