# US 11,114,491 B2 · Back-illuminated sensor and a method of manufacturing a sensor

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- Number: US 11,114,491 B2
- Document ID: US11114491B2
- Status: Granted
- Kind: B2
- Application number: 16/562,396
- Filed: 2019-09-05
- Published: 2020-06-18
- Granted: 2021-09-07
- Earliest claimed: 2018-12-12
- Assignees: KLA Corporation
- Applicants: KLA Corporation
- Inventors: Yung-Ho Alex Chuang; Jehn-Huar Chern; John Fielden; Jingjing Zhang; David L. Brown; Sisir Yalamanchili
- Web page: https://patentgrep.com/patent/US11114491B2

## CPC

- H10F 39/199: {Back-illuminated image sensors}
- H10F 39/024: {of coatings or optical elements}
- H10F 39/026: {Wafer-level processing}
- H10F 39/80: {Constructional details of image sensors}
- H10F 39/805: {Coatings}
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION

## Abstract

An image sensor utilizes a pure boron layer and a second epitaxial layer having a p-type dopant concentration gradient to enhance sensing DUV, VUV or EUV radiation. Sensing (circuit) elements and associated metal interconnects are fabricated on an upper surface of a first epitaxial layer, then the second epitaxial layer is formed on a lower surface of the first epitaxial layer, and then a pure boron layer is formed on the second epitaxial layer. The p-type dopant concentration gradient is generated by systematically increasing a concentration of p-type dopant in the gas used during deposition/growth of the second epitaxial layer such that a lowest p-type dopant concentration of the second epitaxial layer occurs immediately adjacent to the interface with the first epitaxial layer, and such that a highest p-type dopant concentration of the second epitaxial layer occurs immediately adjacent to the interface with pure boron layer.

## Claims

### Claim 1

A method of fabricating an image sensor, the method comprising:
forming a first epitaxial layer on a substrate;
forming a circuit element on a first surface of the first epitaxial layer;
thinning the substrate to generate a thinned substrate, the thinned substrate exposing at least a surface portion of a second surface of the first epitaxial layer, said second surface being opposed to the first surface on which said circuit element is disposed;
forming a second epitaxial layer on the exposed portion of the first epitaxial layer; and
forming a pure boron layer on the second epitaxial layer,
wherein forming the second epitaxial layer includes generating a p-type dopant concentration gradient in the second epitaxial layer by gradually increasing a concentration of a p-type dopant used during formation of the second epitaxial layer such that a first layer portion of the second epitaxial layer has a lower p-type dopant concentration than a subsequently formed second layer portion of the second epitaxial layer, and a highest p-type dopant concentration of the second epitaxial layer is adjacent to the pure boron layer.

### Claim 2 (depends on 1)

The method of claim 1, wherein the p-type dopant comprises boron.

### Claim 3 (depends on 1)

The method of claim 1, wherein forming the second epitaxial layer comprises utilizing a gas containing elemental boron at a temperature lower than about 350° C.

### Claim 4 (depends on 3)

The method of claim 3, wherein forming the second epitaxial layer comprises growing said second epitaxial layer using molecular-beam epitaxial growth.

### Claim 5 (depends on 1)

The method of claim 1, wherein the method further comprises depositing an anti-reflection layer on a surface of the pure boron layer.

### Claim 6 (depends on 1)

The method of claim 1, wherein the method further comprises depositing a metal protective layer on the surface of the pure boron layer.

### Claim 7 (depends on 1)

The method of claim 1, wherein the method further comprises attaching a handling wafer to the first epitaxial layer over the circuit elements prior to thinning the substrate.

### Claim 8 (depends on 1)

The method of claim 1, wherein forming the second epitaxial layer comprises utilizing a plasma-enhanced chemical vapor deposition process at a temperature lower than about 450° C.

### Claim 9

A method of fabricating an image sensor, the method comprising:
forming a first epitaxial layer on a substrate;
forming a circuit element on said first epitaxial layer;
thinning the substrate to generate a thinned substrate, the thinned substrate exposing at least a surface portion of the first epitaxial layer;
forming a second epitaxial layer on the exposed portion of the first epitaxial layer; and
forming a pure boron layer on the second epitaxial layer,
wherein forming the second epitaxial layer includes generating a p-type dopant concentration gradient in the second epitaxial layer by gradually increasing a concentration of a p-type dopant used during formation of the second epitaxial layer such that a first layer portion of the second epitaxial layer has a lower p-type dopant concentration than a subsequently formed second layer portion of the second epitaxial layer, and a highest p-type dopant concentration of the second epitaxial layer is adjacent to the pure boron layer, and
wherein the method further comprises:
attaching a handling wafer to the first epitaxial layer over the circuit elements prior to thinning the substrate, and
forming vias in at least one of the first epitaxial layer and the handling wafer prior to thinning the substrate.

### Claim 10 (depends on 9)

The method of claim 9, wherein the method further comprises exposing the vias after forming the pure boron layer.

### Claim 11 (depends on 9)

The method of claim 9, wherein the p-type dopant comprises boron.

### Claim 12 (depends on 9)

The method of claim 9, wherein forming the second epitaxial layer comprises utilizing a gas containing elemental boron at a temperature lower than about 350° C.

### Claim 13 (depends on 12)

The method of claim 12, wherein forming the second epitaxial layer comprises growing said second epitaxial layer using molecular-beam epitaxial growth.

### Claim 14 (depends on 9)

The method of claim 9, wherein the method further comprises depositing an anti-reflection layer on a surface of the pure boron layer.

### Claim 15 (depends on 9)

The method of claim 9, wherein the method further comprises depositing a metal protective layer on the surface of the pure boron layer.

### Claim 16 (depends on 9)

The method of claim 9, wherein forming the second epitaxial layer comprises utilizing a plasma-enhanced chemical vapor deposition process at a temperature lower than about 450° C.