# US 2013/0157433 A1 · Methods for forming electrostatic discharge protection clamps with increased current capabilities

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- Number: US 2013/0157433 A1
- Document ID: US20130157433A1
- Status: Published application
- Kind: A1
- Application number: 13/770,548
- Filed: 2013-02-19
- Published: 2013-06-20
- Earliest claimed: 2010-01-19
- Assignees: Freescale Semiconductor, Inc.
- Inventors: Rouying Zhan; Amaury Gendron; Chai Ean Gill
- Web page: https://patentgrep.com/patent/US20130157433A1

## CPC

- H10D 84/038: {using silicon technology, e.g. SiGe}
- H10D 10/01: Manufacture or treatment
- H10D 84/0119: {the components including complementary BJTs}
- H10D 89/711: {using bipolar transistors as protective elements}
- H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES

## Abstract

Methods for forming an electrostatic discharge protection (ESD) clamps are provided. In one embodiment, the method includes forming at least one transistor having a first well region of a first conductivity type extending into a substrate. At least one transistor is formed having another well region of a second opposite conductivity type, which extends into the substrate to partially form a collector. The lateral edges of the transistor well regions are separated by a distance D, which at least partially determines a threshold voltage Vt1 of the ESD clamp. A base contact of the first conductivity type is formed in the first well region and separated from an emitter of the second conductivity type by a lateral distance Lbe. The first doping density and the lateral distance Lbe are selected to provide a parasitic base-emitter resistance Rbe in the range of 1<Rbe<800 Ohms

## Claims

### Claim 1

A method for forming an electrostatic discharge protection (ESD) clamp, comprising:
providing a semiconductor substrate of a first conductivity type and having an upper surface;
forming at least one transistor having a first well region of a first conductivity type and first doping density extending into the substrate from the first surface, the first well region having a first lateral edge;
forming in the at least one transistor another well region of a second opposite conductivity type extending into the substrate from the first surface, the another well region forming part of a collector of the transistor and having another lateral edge laterally separated from the first lateral edge by a distance D adapted to determine in part a threshold voltage Vt1 of the ESD clamp;
forming in the first well region a base contact of the first conductivity type and an emitter of the second conductivity type separated by a lateral distance Lbe; and
wherein the first doping density and the lateral distance Lbe are selected to provide a parasitic base-emitter resistance Rbe in the range of 1<Rbe<800 Ohms

### Claim 2 (depends on 1)

The method of claim 1 wherein the first well region has a first base portion of a first base portion doping density and containing the base contact and the emitter, and wherein the first well region also has a second base portion of a second base portion doping density, located between the first base portion and the first lateral edge, and wherein the second base portion doping density is greater than the first base portion doping density.

### Claim 3 (depends on 1)

The method of claim 1 wherein the first base portion has a first sheet resistance and the second base portion has a second sheet resistance and the first sheet resistance is at least about twice the second sheet resistance.

### Claim 4 (depends on 1)

The method of claim 1 wherein the emitter and the base contact region are separated by a lateral distance Lbe in the range of about 0.7<Lbe<23 micrometers.

### Claim 5 (depends on 2)

The method of claim 2 wherein the first base doping density is in the range of about 1E16 cm−3 to 1E18 cm−3.

### Claim 6

A method for forming an electrostatic discharge protection (ESD) clamp having a predetermined threshold voltage Vt1, the method comprising:
providing a semiconductor substrate having a first surface;
producing at least a first bipolar transistor on the semiconductor substrate comprising a base of a first conductivity type underlying the first surface, a base contact of the first conductivity type extending into the base from the first surface, an emitter of a second, opposite, conductivity type extending into the base from the first surface and laterally separated from the base contact at the first surface by a distance Lbe, and a collector proximate the base;
wherein the base is formed to include:
a first base portion containing the base contact and the emitter and having a first base dopant concentration;
a second base portion located laterally between the first portion and a first boundary and having a second base dopant concentration; and
a third base portion of width D located laterally between the boundary and a portion of the collector and having a third base dopant concentration, wherein the threshold Vt1 is determined at least in part by the width D;
wherein the first base dopant concentration is less than the second base dopant concentration; and
wherein Lbe is in the range of about 0.7 to 23 micrometers.

### Claim 7 (depends on 6)

The method of claim 6 wherein Lbe is in the range of about 1 to 15 micrometers.

### Claim 8 (depends on 6)

The method of claim 6 wherein the first base portion has a doping density in the range of about 1E16 to 1E18 cm−3.

### Claim 9 (depends on 6)

The method of claim 6 wherein the second base doping density is at least twice the first base doping density.

### Claim 10 (depends on 6)

The method of claim 6 wherein the transistor has a parasitic emitter-base resistance Rbe in the range of 1<Rbe<800 Ohms

### Claim 11 (depends on 6)

The method of claim 6 wherein the first base portion has a first base sheet resistance and the second base portion has a second base sheet resistance, and the first base sheet resistance is larger than the second base sheet resistance.

### Claim 12 (depends on 11)

The method of claim 11 wherein the first base sheet resistance is at least twice the second base sheet resistance.

### Claim 13

A method for forming an electrostatic discharge protection (ESD) clamp having a predetermined threshold voltage Vt1, comprising:
providing a semiconductor substrate having a first surface;
producing at least a first bipolar transistor on the semiconductor substrate comprising a base of a first conductivity type underlying the first surface, a base contact of the first conductivity type extending into the base from the first surface, an emitter of a second, opposite, conductivity type extending into the base from the first surface and laterally separated from the base contact at the first surface by a distance Lbe, and a collector proximate the base;
wherein the base comprises a first base portion containing the base contact and the emitter and having a first base dopant concentration, a second base portion located laterally between the first portion and a first boundary and having a second base dopant concentration, and a third base portion of width D located laterally between the boundary and a portion of the collector and having a third base dopant concentration, wherein the threshold Vt1 is determined at least in part by the width D;
wherein the first base dopant concentration is less than the second base dopant concentration; and
wherein the first base portion has a first base sheet resistance and the second base portion has a second base sheet resistance, and the first base sheet resistance is larger than the second base sheet resistance.

### Claim 14 (depends on 13)

The method of claim 13 wherein the first base sheet resistance is at least twice the second base sheet resistance.

### Claim 15 (depends on 13)

The method of claim 13 wherein the first base sheet resistance is at least 2 to 20 times the second base sheet resistance.

### Claim 16 (depends on 13)

The method of claim 13 wherein Lbe is in the range of about 0.7 to 23 micrometers.

### Claim 17 (depends on 13)

The method of claim 13 wherein the first base portion has a doping density in the range of about 1E16 to 1E18 cm−3.

### Claim 18 (depends on 13)

The method of claim 13 wherein the second base doping density is at least twice the first base doping density.

### Claim 19 (depends on 13)

The method of claim 13 wherein the first bipolar transistor has a parasitic emitter-base resistance Rbe in the range of 1<Rbe<800 Ohms

### Claim 20 (depends on 13)

The method of claim 13 wherein the first bipolar transistor has a distance D=D1, and wherein method further comprises producing a second bipolar transistor analogous to the first transistor but having a distance D′=D2 different than D1.