# US 8,785,307 B2 · Method of forming a memory cell by reducing diffusion of dopants under a gate

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- Number: US 8,785,307 B2
- Document ID: US8785307B2
- Status: Granted
- Kind: B2
- Application number: 13/593,448
- Filed: 2012-08-23
- Published: 2014-02-27
- Granted: 2014-07-22
- Earliest claimed: 2012-08-23
- Assignees: Silicon Storage Technology, Inc.
- Applicants: Xian Liu; Mandana Tadayoni; Chien-Sheng Su; Nhan Do
- Inventors: Xian Liu; Mandana Tadayoni; Chien-Sheng Su; Nhan Do
- Web page: https://patentgrep.com/patent/US8785307B2

## CPC

- H10D 64/035: {comprising conductor-insulator-conductor-insulator-semiconductor structures}
- H10B 41/30: characterised by the memory core region
- H10D 30/0411: {of FETs having floating gates}
- H10D 30/681: {having only two programming levels (Floating gate IGFETs programmable by two single electrons H10D30/688)}
- H10D 30/6892: {having at least one additional gate other than the floating gate and the control gate, e.g. program gate, erase gate or select gate}
- H10P 30/222: {characterised by the angle between the ion beam and the crystal planes or the main crystal surface (characterised by the angle between the ion beam and the mask H10P30/221)}
- H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
- H10B: ELECTRONIC MEMORY DEVICES
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10

## Abstract

A method of forming a memory cell includes forming a conductive floating gate over the substrate, forming a conductive control gate over the floating gate, forming a conductive erase gate laterally to one side of the floating gate and forming a conductive select gate laterally to an opposite side of the one side of the floating gate. After the forming of the floating and select gates, the method includes implanting a dopant into a portion of a channel region underneath the select gate using an implant process that injects the dopant at an angle with respect to a surface of the substrate that is less than ninety degrees and greater than zero degrees.

## Claims

### Claim 1

A method of forming a memory cell, comprising:
providing a substrate of semiconductor material of a first conductivity type;
forming first and second spaced-apart regions in the substrate of a second conductivity type, with a channel region therebetween;
forming a conductive floating gate over and insulated from the substrate;
forming a conductive control gate over and insulated from the floating gate;
forming a conductive erase gate laterally to one side of, and insulated from, the floating gate;
forming a conductive select gate laterally to an opposite side of the one side of, and insulated from, the floating gate; and
implanting, after the forming of the floating gate and the select gate, a dopant into a portion of the channel region underneath the select gate using an implant process that injects the dopant at an angle with respect to a surface of the substrate that is less than ninety degrees and greater than zero degrees.

### Claim 2 (depends on 1)

The method of claim 1, wherein the dopant is not implanted into a portion of the channel region underneath the floating gate.

### Claim 3 (depends on 1)

The method of claim 1, wherein the dopant is of the first conductivity type.

### Claim 4 (depends on 1)

The method of claim 1, wherein the dopant includes boron.

### Claim 5 (depends on 1)

The method of claim 1, wherein the angle with respect to a normal N to the surface of the substrate is generally 30°.

### Claim 6 (depends on 1)

The method of claim 1, wherein the dopant is injected with an implant energy of 15 KeV.

### Claim 7 (depends on 1)

The method of claim 1, wherein the dopant is injected with a total dose of 4E13.

### Claim 8 (depends on 1)

The method of claim 1, further comprising:
horizontally rotating the substrate 90 degrees; and
repeating the implanting for a second time.

### Claim 9 (depends on 8)

The method of claim 8, further comprising:
after the implanting for a second time, horizontally rotating the substrate another 90 degrees; and
repeating the implanting for a third time.

### Claim 10 (depends on 9)

The method of claim 9, further comprising:
after the implanting for a third time, horizontally rotating the substrate another 90 degrees; and
repeating the implanting for a fourth time.