Method for forming image sensor devices

1 . A method, comprising:

forming an opening extending from a second surface of a semiconductor layer to a first surface of the semiconductor layer;

forming a buffer oxide layer lining the opening;

forming, according to a patternable layer, at least one recess in the buffer oxide layer that partially extends into the buffer oxide layer and terminates before a conductive structure disposed below the first surface of the semiconductor layer is exposed;

removing the patternable layer after forming the at least one recess and while the conductive structure remains covered by the buffer oxide layer under the at least one recess; and

extending the at least one recess through the buffer oxide layer to expose a corresponding portion of the conductive structure.

2 . The method of claim 1 , further comprising filling the at least one recess with a conductive material to form at least one pad structure configured to provide electrical connection to the conductive structure.

3 . The method of claim 1 , wherein at least a portion of the patternable layer has a thickness of at least about 8 μm.

4 . The method of claim 1 , wherein the semiconductor layer having a thickness of about 3 μm to 6 μm.

5 . The method of claim 1 , wherein the buffer oxide layer includes a material selected from a group consisting of: silicon oxide, undoped silicate glass (USG), phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), fluorine-doped silicate glass (FSG), and combinations thereof.

6 . The method of claim 1 , wherein the buffer oxide layer includes polyethyloxazoline (PEOX).

7 . The method of claim 1 , wherein removing the patternable layer further comprises ashing the patternable layer using an oxygen-based plasma.

8 . The method of claim 1 , wherein removing the patternable layer is performed in situ or ex situ with forming the at least one recess in the buffer oxide layer.

9 . The method of claim 1 , wherein extending the at least one recess through the buffer oxide layer further comprises etching the buffer oxide layer using a fluoride-based etching gas.

10 . The method of claim 1 , wherein the conductive structure includes a lateral copper interconnect structure and a nitride-based conductive layer wrapping the lateral copper interconnect structure.

11 . The method of claim 1 , further comprising forming one or more radiation sensitive regions in the semiconductor layer, wherein the one or more radiation sensitive regions are surrounded by at least one pad structure.

12 . The method of claim 1 , further comprising:

forming one or more semiconductor devices along the first surface of the semiconductor layer;

depositing a nitride layer on the first surface of the semiconductor layer, wherein the nitride layer surrounds the one or more semiconductor devices;

depositing a dielectric layer over the nitride layer; and forming the conductive structure in the dielectric layer.

13 . A method, comprising:

forming, over a first surface of a semiconductor layer, a plurality of radiation sensing regions;

forming a dielectric layer over the first surface of the semiconductor layer, the dielectric layer including a conductive structure that is disposed below the first surface of the semiconductor layer;

etching through a second surface of the semiconductor layer to form an opening that exposes the dielectric layer;

forming a buffer oxide layer lining the opening;

forming a patternable layer having a pattern in the opening;

forming, according to the pattern of the patternable layer, a recess in the buffer oxide layer that partially extends into the buffer oxide layer and terminates before the conductive structure is exposed;

removing the patternable layer after forming the recess and while the conductive structure remains covered by the buffer oxide layer under the recess;

etching, based on the recess, the buffer oxide layer and a portion of the dielectric layer to expose a corresponding portion of the conductive structure; and

filling the recess with a conductive material to form a pad structure.

14 . The method of claim 13 , wherein removing the patternable layer is performed in situ or ex situ with forming the recess in the buffer oxide layer.

15 . The method of claim 13 , wherein removing the patternable layer further comprises:

ashing the patternable layer using an oxygen-based plasma.

16 . The method of claim 13 , further comprising:

forming one or more semiconductor devices over the first surface of the semiconductor layer;

depositing a nitride layer on the first surface of the semiconductor layer, wherein the nitride layer surrounds the one or more semiconductor devices;

depositing the dielectric layer; and

forming one or more vertical conductive structures in the dielectric layer to electrically connect the one or more semiconductor devices to the conductive structure.

17 . The method of claim 13 , wherein the patternable layer has a thickness of at least about 8 μm.

18 . The method of claim 12 , wherein the semiconductor layer having a thickness of about 3 μm to 6 μm.

19 . A method, comprising:

forming, over a first surface of a semiconductor layer, a plurality of pixels configured to absorb radiation from a second surface of the semiconductor layer;

forming a dielectric layer over the first surface of the semiconductor layer, the dielectric layer including a conductive structure that is disposed below the first surface;

etching through the second surface of the semiconductor layer to form an opening laterally spaced from the plurality of pixels;

lining the opening with a buffer oxide layer;

forming a patternable layer having a pattern in the opening;

forming, according to the pattern of the patternable layer, a recess in the buffer oxide layer that partially extends into the buffer oxide layer and terminates before the conductive structure is exposed;

ashing the patternable layer using an oxygen-based plasma while keeping the conductive structure covered by at least the buffer oxide layer after forming the recess and while the conductive structure remains covered by the buffer oxide layer under the recess;

etching, based on the recess, the buffer oxide layer and a portion of the dielectric layer to expose a corresponding portion of the conductive structure; and

filling the recess with a conductive material to form a pad structure in electrical contact with the conductive structure.

20 . The method of claim 19 , wherein the patternable layer has a thickness of at least about 8 μm.