Image sensor with epitaxial sealing layer for front-side deep trench isolation and manufacturing method thereof
A method includes forming a doped region in a substrate; forming a doped well vertically extending from a front side of the substrate into the doped region; forming a transfer gate over the front side of the substrate and laterally between a first portion of the doped well and a second portion of the doped well; forming a trench vertically extending form the front side of the substrate through the doped well toward a back side of the substrate; depositing an dielectric material over the front side of the substrate and in the trench; recessing the dielectric material; performing a selective epitaxial growth process to form a sealing layer in the trench and over the recessed dielectric material from the front side of the substrate; forming an electrode in the trench and over the sealing layer from the front side of the substrate.
1 . A method, comprising:
forming a doped region in a semiconductor substrate, wherein the doped region is of a first conductivity type;
forming a doped well vertically extending from a front side of the semiconductor substrate into the doped region, wherein the doped well is of a second conductivity type opposite to the first conductivity type;
forming a transfer gate over the front side of the semiconductor substrate and laterally between a first portion of the doped well and a second portion of the doped well;
forming a trench vertically extending form the front side of the semiconductor substrate through the doped well toward a back side of the semiconductor substrate;
depositing an dielectric material over the front side of the semiconductor substrate and in the trench;
recessing the dielectric material, such that the recessed dielectric material has a top surface lower than the front side of the semiconductor substrate;
performing a selective epitaxial growth process to form a sealing layer in the trench and over the recessed dielectric material from the front side of the semiconductor substrate; and
forming an electrode in the trench and over the sealing layer from the front side of the semiconductor substrate.
2 . The method of claim 1 , wherein the step of recessing the dielectric material comprises:
performing a planarization process to remove the dielectric material located outside the trench; and
after performing the planarization process, performing a dry etching process to recess the dielectric material.
3 . The method of claim 2 , wherein the dry etching process comprises an etchant including C 4 F 8 .
4 . The method of claim 2 , wherein the dry etching process is performed such that the recessed dielectric material has a sharp protrusion on a top thereof.
5 . The method of claim 2 , further comprising:
after performing the dry etching process, performing a pre-clean process on the recessed dielectric material to scale down the sharp protrusion.
6 . The method of claim 5 , wherein the pre-clean process comprises an etchant including HF and NH 3 .
7 . The method of claim 1 , wherein the selective epitaxial growth process comprises a repetitive cycle, and the each cycle comprises an epitaxial deposition step and an annealing step following the epitaxial deposition step.
8 . The method of claim 1 , further comprising:
forming a floating diffusion node in the first portion of the doped well, wherein the electrode is formed in the floating diffusion node.
9 . The method of claim 1 , further comprising:
after forming the electrode, removing the dielectric material in the trench from the back side of the semiconductor substrate to expose the sealing layer;
after removing the dielectric material, forming a high-k dielectric liner lining a sidewall of the trench from the back side of the semiconductor substrate; and
after forming the high-k dielectric liner, forming a dielectric filler in the trench from the back side of the semiconductor substrate to form a deep trench isolation structure.
10 . The method of claim 1 , further comprising:
forming a plurality of micro-lenses over the back side of the semiconductor substrate.
11 . A method, comprising:
forming a doped well vertically extending from a front side of a substrate into the substrate and surrounding a pixel region of an image sensor;
forming a trench vertically extending form the front side of the substrate through the doped well toward a back side of the substrate;
forming a dielectric structure in the trench from the front side of the substrate;
performing a selective epitaxial growth process to form a epitaxial silicon layer in the trench and over a front side of the dielectric structure, wherein the selective epitaxial growth process comprises a repetitive cycle, and the each cycle comprises an epitaxial deposition step and an annealing step following the epitaxial deposition step;
forming a dielectric layer in the trench and over a front side of the epitaxial silicon layer;
forming a polysilicon layer in the trench and over a front side of the dielectric layer; and
replacing the dielectric structure with a deep trench isolation structure from the back side of the substrate.
12 . The method of claim 11 , wherein the epitaxial deposition step in the selective epitaxial growth process is performed at a temperature in a range from about 600 to 900° C.
13 . The method of claim 11 , wherein forming the dielectric structure comprises:
depositing an dielectric material over the front side of the semiconductor substrate and in the trench; and
recessing the dielectric material, such that the recessed dielectric material has a top surface lower than the front side of the semiconductor substrate.
14 . The method of claim 11 , wherein from a top view, the deep trench isolation structure has a grid pattern that has a grid line, and from a cross-sectional view taken along a direction intersecting with a lengthwise direction of the grid line, the epitaxial silicon layer has a flat back-side surface.
15 . The method of claim 11 , wherein from a top view, the deep trench isolation structure has a grid pattern that has a grid line, and from a cross-sectional view taken along a lengthwise direction of the grid line, the epitaxial silicon layer has a convex back-side surface.
16 . The method of claim 11 , wherein the step of replacing the dielectric structure with the deep trench isolation structure comprises:
thinning down the substrate to expose the dielectric structure from the back side of the substrate;
removing the dielectric structure in the trench from the back side of the substrate; and
forming the deep trench isolation structure in the trench.
17 . An image sensor, comprising:
a first conductivity type doped region in a pixel region of a substrate;
a second conductivity type doped well vertically extending from a front side of the substrate into the first conductivity type doped region, wherein from a top view, the second conductivity type doped well laterally surrounds the pixel region;
a deep trench isolation structure in the substrate and laterally surrounding the pixel region, wherein a footprint of the deep trench isolation structure is within a footprint of the second conductivity type doped well;
an epitaxial sealing layer over a front side of the deep trench isolation structure and in the second conductivity type doped well; and
a polysilicon layer over a front side of the epitaxial sealing layer and embedded in the second conductivity type doped well.
18 . The image sensor of claim 17 , wherein the epitaxial sealing layer has a flat back side surface.
19 . The image sensor of claim 17 , wherein the deep trench isolation structure has a flat front side surface.
20 . The image sensor of claim 17 , wherein the deep trench isolation structure has a vertical sidewall wall.