# US 12,765,101 B2 · Frontside deep trench isolation (FDTI) structure for CMOS image sensor

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- Number: US 12,765,101 B2
- Document ID: US12765101B2
- Status: Granted
- Kind: B2
- Application number: 18/314,184
- Filed: 2023-05-09
- Published: 2024-08-08
- Granted: 2026-10-13
- Earliest claimed: 2023-02-02
- Assignees: Taiwan Semiconductor Manufacturing Company, Ltd.
- Applicants: Taiwan Semiconductor Manufacturing Company, Ltd.
- Inventors: Chao-Te Liu; Yen-Chen Lin; Szu-Ying Chen; Chen-Jong Wang; Dun-Nian Yaung
- Web page: https://patentgrep.com/patent/US12765101B2

## CPC

- H10F 39/807: {Pixel isolation structures}
- H10F 39/014: {of CMOS image sensors}
- H10F 39/18: Complementary metal-oxide-semiconductor [CMOS] image sensors; Photodiode array image sensors
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION

## Abstract

In some embodiments, the present disclosure relates to a method for forming an image sensor and associated device structure. A FDTI trench is formed from a frontside of a substrate between a first pixel region and a second pixel region and then filled to form a FDTI structure. A cap layer is formed over the FDTI structure overlying the first pixel region and the second pixel region of the substrate. A first photodiode is formed in the first pixel region and a second photodiode is formed in the second pixel region. A FD node is formed within the cap layer between the first pixel region and the second pixel region overlying the FDTI structure. The FD node may be shared by a group of pixel regions not separated by the FDTI structure, such that few metal contacts are needed and thus reduce parasitic capacitance issues of proximity metal contacts.

## Claims

### Claim 1

A method for forming an image sensor, the method comprising:
forming a frontside deep trench isolation (FDTI) trench from a frontside of a substrate between a first pixel region and a second pixel region adjacent to the first pixel region;
partially filling the FDTI trench with a FDTI structure to form a FDTI structure with a first depth;
forming a cap layer in a remaining upper portion of the FDTI trench over the FDTI structure and overlying the first pixel region and the second pixel region of the substrate;
forming a first photodiode in the first pixel region and a second photodiode in the second pixel region, wherein the first photodiode and the second photodiode are of a first doping type; and
forming a floating diffusion (FD) node of the first doping type within the cap layer between the first pixel region and the second pixel region, wherein the FD node overlies the FDTI structure.

### Claim 2 (depends on 1)

The method of claim 1, wherein the FD node is formed to be spaced apart from the FDTI structure by the cap layer.

### Claim 3 (depends on 1)

The method of claim 1, wherein the cap layer is formed contacting an upper surface of the FDTI structure.

### Claim 4 (depends on 1)

The method of claim 1, wherein the cap layer is formed with a cap-shaped stop layer formed between the cap layer and the FDTI structure.

### Claim 5 (depends on 1)

The method of claim 1, further comprising:
forming a stop layer between the cap layer and the FDTI structure in a remaining upper portion of the FDTI trench contacting the FDTI structure.

### Claim 6 (depends on 5)

The method of claim 5, wherein both the cap layer and the stop layer contact the FDTI structure.

### Claim 7 (depends on 1)

The method of claim 1, further comprising:
after forming the cap layer, forming a first gate structure over the first photodiode and a second gate structure over the second photodiode; and
forming an interlayer dielectric (ILD) layer over the first gate structure and the second gate structure and the cap layer.

### Claim 8 (depends on 7)

The method of claim 7, further comprising:
forming a first gate contact and a second gate contact through the ILD layer and respectively reaching the first gate structure and the second gate structure; and
forming a FD contact through the ILD layer and reaching the FD node, wherein the FD node is configured to be shared by the first pixel region and the second pixel region.

### Claim 9 (depends on 1)

The method of claim 1, further comprising:
flipping the substrate and performing a thinning down process from a backside of the substrate to expose the FDTI structure; and
removing and replacing the FDTI structure with a replaced FDTI structure comprising a high-k dielectric liner.

### Claim 10 (depends on 1)

The method of claim 1, wherein the cap layer includes polysilicon.

### Claim 11

A method for forming an image sensor, the method comprising:
forming a frontside deep trench isolation (FDTI) trench from a frontside of a substrate separating a plurality of pixel regions arranged in rows and columns from a top view;
filling the FDTI trench followed by a recessing process to form a dummy FDTI structure with a first depth;
replacing the dummy FDTI structure with a FDTI structure comprising a stack of metal and dielectric layers including a high-k dielectric liner;
forming a cap layer over the FDTI structure and overlying the plurality of pixel regions;
forming a plurality of photodiodes of a first doping type from the cap layer and extending in the substrate; and
forming a floating diffusion (FD) node of the first doping type within the cap layer shared by a group of pixel regions within the plurality of pixel regions, wherein the FD node is arranged at a crossroad of the group of pixel regions overlying the FDTI structure.

### Claim 12 (depends on 11)

The method of claim 11, wherein the cap layer is formed by thermal melting or epitaxy with a conical-shaped void formed between the cap layer and the FDTI structure.

### Claim 13 (depends on 11)

The method of claim 11, further comprising forming a stop layer with a conical shape between the cap layer and the FDTI structure and in a remaining upper portion of the FDTI trench contacting the FDTI structure.

### Claim 14 (depends on 11)

The method of claim 11, further comprising:
forming a plurality of gate structures over the plurality of photodiodes;
forming an interlayer dielectric (ILD) layer over the plurality of gate structures and the cap layer; and
forming a single FD contact through the ILD layer and reaching the FD node.

### Claim 15 (depends on 11)

The method of claim 11, further comprising forming a stop layer contacting the FDTI structure prior to the formation of the cap layer.

### Claim 16 (depends on 11)

The method of claim 11, further comprising forming a plurality of color filters at a backside of the substrate corresponding to the plurality of photodiodes, wherein the plurality of color filters meet the plurality of photodiodes at interfaces overlying the FDTI structure.

### Claim 17

A method, comprising:
a substrate having a first pixel region and a second pixel region adjacent to the first pixel region;
forming a cap layer over a frontside of a substrate;
forming a first photodiode and a second photodiode extending from the cap layer into the substrate, wherein the first photodiode and the second photodiode are of a first doping type;
forming a stop layer on the cap layer;
forming a frontside deep trench isolation (FDTI) structure between the first photodiode and the second photodiode on the stop layer; and
forming a floating diffusion (FD) node of the first doping type within the cap layer and spaced apart from the FDTI structure by the cap layer.

### Claim 18 (depends on 17)

The method of claim 17, wherein the FDTI structure is formed with a width monotonically increasing from a backside of the substrate to a position within the substrate.

### Claim 19 (depends on 17)

The method of claim 17, wherein the stop layer contacts upper surfaces of the cap layer and the FDTI structure.

### Claim 20 (depends on 19)

The method of claim 19, wherein the FDTI structure is formed with a planar-shaped bottom sitting on the stop layer.