# US 7,608,908 B1 · Robust deep trench isolation

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- Number: US 7,608,908 B1
- Document ID: US7608908B1
- Status: Granted
- Kind: B1
- Application number: 12/125,613
- Filed: 2008-05-22
- Granted: 2009-10-27
- Earliest claimed: 2008-05-22
- Assignees: Freescale Semiconductor, Inc.
- Inventors: Vishnu Khemka; Amitava Bose; Michael C. Butner; Bernhard H. Grote; Tahir A. Khan; Shifeng Shen; Ronghua Zhu
- Web page: https://patentgrep.com/patent/US7608908B1

## CPC

- H10P 90/1906: {Preparing SOI wafers}
- H10W 10/061: {using SOI processes together with lateral isolation, e.g. combinations of SOI and shallow trench isolations}
- H10W 10/181: {Semiconductor-on-insulator [SOI] isolation regions, e.g. buried oxide regions of SOI wafers}
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
- H10W: GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10

## Abstract

Higher voltage device isolation structures (40, 60, 70, 80, 90, 90′) are provided for semiconductor integrated circuits having strongly doped buried layers (24, 24″). One or more dielectric lined deep isolation trenches (27, 27′, 27″, 27′″) separates adjacent device regions (411, 412; 611, 612; 711, 712; 811, 812; 911, 912). Electrical breakdown (BVdss) between the device regions (411, 412; 611, 612; 711, 712; 811, 812; 911, 912) and the oppositely doped substrate (22, 22″) is found to occur preferentially where the buried layer (24, 24″) intersects the dielectric sidewalls (273, 274; 273′, 274′; 273″, 274″) of the trench (27, 27′, 27″, 27′″). The breakdown voltage (BVdss) is increased by providing a more lightly doped region (42, 42″, 62, 72, 82) of the same conductivity type as the buried layer (24, 24″), underlying the buried layer (24, 24″) at the trench sidewalls (273, 274; 273′, 274′; 273″, 274″). The more lightly doped region's (42, 42″, 62, 72, 82) dopant concentration is desirably 1E4 to 2E2 times less than the buried layer (24, 24″) and it extends substantially entirely beneath the buried layer (24, 24″) or to a distance (724, 824) extending about 0.5 to 2.0 micro-meters from the trench sidewall (273, 274; 273′, 274′; 273″, 274″). In a preferred embodiment, the trench (27, 27′) is split into two portions (271, 272; 271′, 272′) with the semiconductor therein (475, 675, 775, 875) ohmically coupled to the substrate (22).

## Claims

### Claim 1

An integrated electronic circuit (IC) embodying an isolation wall, comprising:
a semiconductor (SC) substrate of a first conductivity type and substrate doping concentration;
a further semiconductor (SC) layer overlying the substrate and having an upper surface, wherein the further SC layer comprises a first region of the first conductivity type and a first doping concentration less than the substrate doping concentration overlying the substrate, a second region of a second, opposite, conductivity type and a second doping concentration overlying the first region, a third region of the second conductivity type and third doping concentration higher than the second doping concentration overlying the second region, and a fourth region of the second conductivity type and fourth dopant concentration less than the third doping concentration overlying the third region and extending substantially to at least a part of the upper surface; and
a dielectric lined isolation trench extending from the upper surface through the fourth, third, second and part of the first regions toward the substrate.

### Claim 2 (depends on 1)

The circuit of claim 1, wherein a sidewall of the dielectric lined isolation trench is in contact with the fourth, third, second and part of the first regions.

### Claim 3 (depends on 2)

The circuit of claim 2, wherein the dielectric lined isolation trench has two portions, a left portion and a right portion, with a part of the further SC layer in between the two portions, and wherein the part of the further SC layer in between the two portions has the same doping type as the substrate and makes Ohmic contact thereto.

### Claim 4 (depends on 3)

The circuit of claim 3, wherein the further SC layer has a left device region and a right device region, the left device region contacting a left surface of the left portion of the dielectric lined isolation trench and the right portion contacting a right surface of the right portion of the dielectric lined isolation trench.

### Claim 5 (depends on 1)

The circuit of claim 1, wherein the doping concentration of the third region is C(3) atoms/cc and the doping concentration of the second region is C(2) atoms/cc and the ratio C(3)/C(2) is in the range of about 2E2 to 1E4.

### Claim 6 (depends on 5)

The circuit of claim 5, wherein the ratio C(3)/C(2) is in the range of about 5E2 to 5E3.

### Claim 7 (depends on 1)

The circuit of claim 1, wherein the doping concentration of the first region is C(1) atoms/cc and the doping concentration of the second region is C(2) atoms/cc and the ratio C(2)/C(1) is in the range of about 5E0 to 5E1.

### Claim 8 (depends on 1)

The circuit of claim 1, wherein the third region and the second region are in contact.

### Claim 9 (depends on 1)

The circuit of claim 1, wherein the first region has two portions a first portion underlying the second region and a second portion lying between the second and third regions.

### Claim 10 (depends on 9)

The circuit of claim 9, wherein the second portion has a thickness such that the second portion is fully depleted of mobile carriers at a voltage less than or equal to a breakdown voltage between the third region and the substrate.

### Claim 11

An electronic device comprising:
a semiconductor body having a substrate layer and a further layer extending from the substrate layer to a first surface spaced apart from the substrate layer;
a dielectric lined isolation trench in the semiconductor body extending from the first surface toward the substrate layer and dividing the further layer into at least two regions, a first region on a first side of the dielectric lined isolation trench and a second region on a second side of the dielectric lined isolation trench;
wherein at least one of the first and second regions has first, second, third and fourth portions abutting one of the first or second sides of the dielectric lined isolation trench; and
wherein the first portion of a first conductivity type and first dopant concentration C1 overlies the substrate layer, the second portion of a second, opposite conductivity type and second dopant concentration C2 overlies at least part of the first portion, the third portion of the second conductivity type and a third dopant concentration C3 overlies the second portion, and the fourth portion of the second conductivity type and a fourth dopant concentration C4 overlies the third portion; and wherein C1<C2<C3>C4.

### Claim 12 (depends on 11)

The device of claim 11, wherein the dielectric lined isolation trench has a polycrystalline semiconductor core.

### Claim 13 (depends on 11)

The device of claim 11, wherein the dielectric lined isolation trench has first and second separated parts, wherein a left side of the first part abuts the first semiconductor region and a right side of the second part abuts the second semiconductor region, and a third region of the further layer lies between the first and second separated parts of the dielectric lined isolation trench.

### Claim 14 (depends on 13)

The device of claim 13, wherein both parts of the dielectric lined isolation trench have a polycrystalline semiconductor core.

### Claim 15 (depends on 11)

The device of claim 11, wherein the second portion extends laterally from the one of the first or second sides of the dielectric lined isolation trench for a distance smaller than a lateral extent of the first or third portion.

### Claim 16

A semiconductor device, comprising:
a semiconductor body having a substrate layer and a further layer extending from the substrate layer to a first surface of the semiconductor body;
a dielectric lined isolation trench extending into the semiconductor body from the first surface so that at least one dielectric lined sidewall is in contact with stacked portions of the further layer; and
wherein a first portion of the further layer has a first dopant concentration C1, a second overlying portion of the further layer has a second dopant concentration C2, and a third overlying portion of the further layer has a third dopant concentration C3, such that C1<C2<C3 and that C1 and C2 are of opposite conductivity type and C2 and C3 are of the same conductivity type.

### Claim 17 (depends on 16)

The semiconductor device of claim 16, wherein the further layer comprises a fourth overlying portion of dopant concentration C4 such that C4<C3 and C4 and C3 are of the same conductivity type.

### Claim 18 (depends on 17)

The semiconductor device of claim 17, wherein the second portion extends laterally from the at least one dielectric sidewall for a predetermined distance D2 and the third portion extends laterally from the at least one dielectric sidewall for a predetermined distance D3, such that D2<D3.

### Claim 19 (depends on 18)

The semiconductor device of claim 18 wherein D2 is in the range of about 0.3 to about 3.0 micrometers.

### Claim 20 (depends on 16)

The semiconductor device of claim 16 wherein the dielectric lined isolation trench comprises two parts separated by another part of the further layer ohmically coupled to the substrate layer.