US4732871A — Process for producing undercut dummy gate mask pr…

Claim 1

Independent Claim 143 words

A process for fabricating undercut mask profiles for use in semiconductor device manufacturing comprising the steps of: depositing a first layer of dielectric material on the surface of a substrate in a plasma enhanced chemical vapor deposition reactor at a first plasma excitation frequency to impart a given etch rate to said first layer, depositing a second layer of dielectric material on said first layer at a second plasma excitation frequency to impart an etch rate lower than said given etch rate to said second layer, patterning said first and second layers such that at least one vertical edge of each of said layers is exposed, and etching said first and second layers at said at least one vertical edge to remove portions of said first layer at a rate higher than the rate at which portions of said second layer are removed.

Claim 2

Dependent Claim 143 words

A process for fabricating undercut mask profiles for use in semiconductor device manufacturing comprising the steps of: depositing a first layer of dielectric material on the surface of a substrate in a plasma enhanced chemical vapor deposition reactor at a first plasma excitation frequency to impart a given etch rate to said first layer, depositing a second layer of dielectric material on said first layer at a second plasma excitation frequency to impart an etch rate lower than said given etch rate to said second layer, patterning said first and second layers such that at least one vertical edge of each of said layers is exposed, and etching said first and second layers at said at least one vertical edge to remove portions of said first layer at a rate higher than the rate at which portions of said second layer are removed.

Claim 3

Dependent Claim 17 words

A process according to claim 1 wherein said first and second layers of dielectric material are nitrides.

Claim 4

Dependent Claim 15 words

A process according to claim 1 wherein said substrate is made of a semiconductor material.

Claim 5

Dependent Claim 20 words

A process according to claim 1 wherein said first and second layers of dielectric material are made of silicon nitride.

Claim 6

Dependent Claim 20 words

A process according to claim 1 wherein said first and second layers of dielectric material are made of boron nitride.

Claim 7

Dependent Claim 29 words

A process according to claim 1 wherein said first and second layers of dielectric material are made of nitrides selected from the group consisting of silicon and boron nitride.

Claim 8

Dependent Claim 30 words

A process according to claim 1 wherein said first plasma excitation frequency is in a range of 1 to 50 MHz and said second excitation frequency is below 100 kHz.

Claim 9

Dependent Claim 13 words

A process according to claim 1 wherein said substrate is made of silicon.

Claim 10

Dependent Claim 13 words

A process according to claim 1 wherein said substrate is made of gallium-arsenide.

Claim 11

Dependent Claim 87 words

A process according to claim 1 wherein the step of depositing a first layer of dielectric material includes the steps of: introducing into said reactor a gas comprising NH 3 :N 2 :SiH 4 in the proportions 18:3:55, respectively, at a pressure of about 0.1 Pa, heating said substrate to a temperature of 300° C., and exciting said gas at a frequency of 13 MHz and a power of 75 watts to deposit a layer of silicon nitride at a rate of 20-30 nm/min. on said substrate.

Claim 12

Dependent Claim 86 words

A process according to claim 1 wherein the step of depositing a second layer of dielectric material includes the steps of: introducing into said reactor a gas comprising N 2 :SiH 4 in the proportions 4:50, respectively, at a pressure of about 0.1 Pa, heating said substrate to a temperature of 300° C., and exciting said gas at a frequency of 50 kHz and a power of 75 watts to deposit a layer of silicon nitride at a rate of 20-30 nm/min. on said first layer.

Claim 13

Dependent Claim 49 words

A process according to claim 1 wherein the step of patterning said first and second layers includes the steps of: forming a photoresist mask on the surface of said second layer, and etching said first and second layers to remove portions of said layers not covered by said mask.

Claim 14

Dependent Claim 57 words

A process according to claim 1 wherein the step of etching said first and second layers includes the step of exposing said at least one vertical edge of said first and second layers to a wet chemical etch so that portions of said first layer are removed at a higher rate than portions of said second layer.

Claim 15

Dependent Claim 57 words

A process according to claim 1 wherein the step of etching said first and second layers includes the steps of exposing said at least one vertical edge of said first and second layers to a dry plasma etch so that portions of said first layer are removed at a higher rate than portions of said second layer.

Claim 16

Dependent Claim 178 words

A process for fabricating undercut mask profiles for use in the fabricating of a fully self-aligned field effect transistor which includes a gate and source and drain elements formed in a semiconductor substrate having a current channel disposed therebetween comprising the steps of: depositing a first layer of nitride on the surface of said substrate in a plasma enhanced chemical vapor deposition reactor at a first plasma excitation frequency to impart a given etch rate to said first layer, depositing a second layer of nitride on said first layer at a second plasma excitation frequency to impart an etch rate lower than said given etch rate to said second layer, patterning said first and second layers such that at least one vertical edge of each of said layers is exposed, and etching said first and second layers at said at least one vertical edge to remove portions of said first layer at a rate higher than the rate at which portions of said second layer are removed and provide an undercut mask structure having a T-shaped cross section.

Claim 17

Dependent Claim 178 words

A process for fabricating undercut mask profiles for use in the fabricating of a fully self-aligned field effect transistor which includes a gate and source and drain elements formed in a semiconductor substrate having a current channel disposed therebetween comprising the steps of: depositing a first layer of nitride on the surface of said substrate in a plasma enhanced chemical vapor deposition reactor at a first plasma excitation frequency to impart a given etch rate to said first layer, depositing a second layer of nitride on said first layer at a second plasma excitation frequency to impart an etch rate lower than said given etch rate to said second layer, patterning said first and second layers such that at least one vertical edge of each of said layers is exposed, and etching said first and second layers at said at least one vertical edge to remove portions of said first layer at a rate higher than the rate at which portions of said second layer are removed and provide an undercut mask structure having a T-shaped cross section.

Claim 18

Dependent Claim 118 words

A process according to claim 15 further including the steps of: ion implanting to form source and drain regions within said semiconductor substrate at both ends of said current channel using said T-shaped structure as a mask, depositing ohmic contact metallization onto said source and drain regions, applying and planarizing a reflowable dielectric to embed said T-shaped structure, removing the portion of said dielectric that covers the top of said T-shaped structure, removing said T-shaped structure to expose the surface region over said current channel where said gate electrode is to be formed, depositing a gate metallization, and removing the remaining portion of said dielectric together with those sections of said gate metallization deposited on top of it.

Claim 19

Dependent Claim 19 words

A process according to claim 15 wherein said first and second layers of nitride are made of silicon nitride.

Claim 20

Dependent Claim 19 words

A process according to claim 15 wherein said first and second layers of nitride are made of boron nitride.

Claim 21

Dependent Claim 26 words

A process according to claim 15 wherein said first and second layers of nitrides are nitrides selected from the group consisting of silicon and boron nitride.

Claim 22

Dependent Claim 30 words

A process according to claim 15 wherein said first plasma excitation frequency is in a range of 1 to 50 MHz and said second excitation frequency is below 100 kHz.

Claim 23

Dependent Claim 11 words

A process according to claim 15 wherein said semiconductor is silicon.

Claim 24

Dependent Claim 11 words

A process according to claim 15 wherein said semiconductor is galliumarsenide.

Claim 25

Dependent Claim 86 words

A process according to claim 15 wherein the step of depositing a first layer of nitride includes the steps of: introducing into said reactor a gas comprising NH 3 :N 2 :SiH 4 in the proportions 18:3:55, respectively, at a pressure of about 0.1 Pa, heating said substrate to a temperature of 300° C., and exciting said gas at a frequency of 13 MHz and a power of 75 watts to deposit a layer of silicon nitride at a rate of 20-30 nm/min. on said substrate.

Claim 26

Dependent Claim 85 words

A process according to claim 15 wherein the step of depositing a second layer of nitride includes the steps of: introducing into said reactor a gas comprising N 2 :SiH 4 in the proportions 4:50, respectively, at a pressure of about 0.1 Pa, heating said substrate to a temperature of 300° C., and exciting said gas at a frequency of 50 kHz and a power of 75 watts to deposit a layer of silicon nitride at a rate of 20-30 nm/min. on said first layer.

Claim 27

Dependent Claim 49 words

A process according to claim 15 wherein the step of patterning said first and second layers includes the steps of: forming a photoresist mask on the surface of said second layer, and etching said first and second layers to remove portions of said layers not covered by said mask.

Claim 28

Dependent Claim 57 words

A process according to claim 15 wherein the step of etching said first and second layers includes the step of exposing said at least one vertical edge of said first and second layers to a wet chemical etch so that portions of said first layer are removed at a higher rate than portions of said second layer.

Claim 29

Dependent Claim 57 words

A process according to claim 15 wherein the step of etching said first and second layers includes the steps of exposing said at least one vertical edge of said first and second layers to a dry plasma etch so that portions of said first layer are removed at a higher rate than portions of said second layer.

Claim 30

Dependent Claim 20 words

A process according to claim 16 whrein said gate forms a Schottky barrier at an interface with said current channel.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1991-03-22	1991-09-21	1992-03-22	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1995-03-22	1995-09-21	1996-03-22	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	1999-03-22	1999-09-21	2000-03-22	$7700.00	Window Closed / Lapsed

Process for producing undercut dummy gate mask profiles for MESFETs

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