US5008207A — Method of fabricating a narrow base transistor

Claim 1

Independent Claim 95 words

A method of forming a semiconductor structure comprising the steps of: providing a substrate of semiconductor material including a region of first conductivity type; forming a first layer of second conductivity type epitaxial semiconductor material over said region; forming a second layer of second conductivity type epitaxial semiconductor material over said first layer, said second layer having a relatively higher dopant concentration than said first layer; oxidizing a portion of said second layer through to said first layer; and removing said oxidized portion of said second layer to expose a portion of said first layer.

Claim 2

Independent Claim 95 words

A method of forming a semiconductor structure comprising the steps of: providing a substrate of semiconductor material including a region of first conductivity type; forming a first layer of second conductivity type epitaxial semiconductor material over said region; forming a second layer of second conductivity type epitaxial semiconductor material over said first layer, said second layer having a relatively higher dopant concentration than said first layer; oxidizing a portion of said second layer through to said first layer; and removing said oxidized portion of said second layer to expose a portion of said first layer.

Claim 3

Dependent Claim 21 words

A method in accordance with claim 1 wherein: said semiconductor material comprises silicon; and said first and second layers comprise silicon.

Claim 4

Dependent Claim 50 words

A method in accordance with claim 1 wherein: said steps of forming said first and second layers each include epitaxially growing said semiconductor material at a temperature in the range of about 500-800 degrees centigrade and a pressure in the range of about 10 -4 -10 -2 torr during deposition.

Claim 5

Dependent Claim 46 words

A method in accordance with claim 1 wherein said step of oxidizing said portion of said second layer of said semiconductor material includes the step of exposing said second layer to steam at a temperature selected to oxidize said second layer selectively over said first layer.

Claim 6

Dependent Claim 30 words

A method in accordance with claim 1 wherein said step of removing said oxidized portion of said second layer includes the step of etching with a wet or dry etchant.

Claim 7

Dependent Claim 55 words

A method in accordance with claim 1 and further including the steps of: forming a third layer of intrinsic epitaxial semiconductor material intermediate said first and second layers, said oxidizing step extending at least through said second layer to said third layer; and said removing step exposing at least a portion of said third layer.

Claim 8

Dependent Claim 52 words

A method in accordance with claim 1 wherein: said region of said first conductivity type is framed within a window of insulating material overlying said substrate; and said first and second layers being of monocrystalline structure over said region of said first conductivity type and of polycrystalline structure over said insulating material.

Claim 9

Dependent Claim 25 words

The method of claim 1 wherein said exposed portion of said first layer comprises an intrinsic base region of a subsequently formed vertical bipolar transistor.

Claim 10

Dependent Claim 13 words

The method of claim 1 wherein said first layer includes a silicon-germanium compound.

Claim 11

Dependent Claim 57 words

The method of claim 1 and further including the step of heating said substrate, after performing said oxidizing and removing steps, to drive dopant from the remaining portion of said second layer into said first layer such that the remaining portion of said second layer forms an electrical contact to said exposed portion of said first layer.

Claim 12

Independent Claim 134 words

A method of forming a semiconductor structure comprising the steps of: providing a substrate of semiconductor material including a region of first conductivity type; forming a first layer of second conductivity type epitaxial semiconductor material over said region; forming a second layer of second conductivity type epitaxial semiconductor material over said first layer, said second layer having a relatively higher dopant concentration than said first layer; forming a third layer of protective material over said second layer; anisotropically etching said third layer to expose a portion of said second layer; oxidizing the exposed portion of said second layer through to said first layer; removing an oxidized portion of said second layer to expose a portion of said first layer; and forming a spacer of insulating material on the exposed edge of said second layer.

Claim 13

Independent Claim 134 words

A method of forming a semiconductor structure comprising the steps of: providing a substrate of semiconductor material including a region of first conductivity type; forming a first layer of second conductivity type epitaxial semiconductor material over said region; forming a second layer of second conductivity type epitaxial semiconductor material over said first layer, said second layer having a relatively higher dopant concentration than said first layer; forming a third layer of protective material over said second layer; anisotropically etching said third layer to expose a portion of said second layer; oxidizing the exposed portion of said second layer through to said first layer; removing an oxidized portion of said second layer to expose a portion of said first layer; and forming a spacer of insulating material on the exposed edge of said second layer.

Claim 14

Dependent Claim 21 words

A method in accordance with claim 11 wherein: said semiconductor material comprises silicon; and said first and second layers comprise silicon.

Claim 15

Dependent Claim 50 words

A method in accordance with claim 11 wherein: said steps of forming said first and second layers each include epitaxially growing said semiconductor material at a temperature in the range of about 500-800 degrees centigrade and a pressure in the range of about 10 -4 -10 -2 torr during deposition.

Claim 16

Dependent Claim 46 words

A method in accordance with claim 11 wherein said step of oxidizing said portion of said second layer of said semiconductor material includes the step of exposing said second layer to steam at a temperature selected to oxidize said second layer selectively over said first layer.

Claim 17

Dependent Claim 30 words

A method in accordance with claim 11 wherein said step of removing said oxidized portion of said second layer includes the step of etching with a wet or dry etchant.

Claim 18

Dependent Claim 55 words

A method in accordance with claim 11 and further including the steps of: forming a third layer of intrinsic epitaxial semiconductor material intermediate said first and second layers, said oxidizing step extending at least through said second layer to said third layer; and said removing sep exposing at least a portion of said third layer.

Claim 19

Dependent Claim 52 words

A method in accordance with claim 11 wherein: said region of said first conductivity type is framed within a window of insulating material overlying said substrate; and said first and second layers being of monocrystalline structure over said region of said first conductivity type and of polycrystaline structure over said insulating material.

Claim 20

Dependent Claim 27 words

A method in accordance with claim 11 wherein said step of removing said oxidized portion of said second layer includes dipping said layer in a wet etch.

Claim 21

Dependent Claim 85 words

A method in accordance with claim 18 wherein said step of forming said spacer of insulating material includes the steps of: oxidizing the exposed portions of said first and second layers; forming a layer of silicon nitride over the oxidized portions of said first and second layers; forming a layer of silicon dioxide over the layer of silicon nitride; and removing portions of said layers of silicon dioxide and silicon nitride and portions of the oxidized region of said first layer to leave said spacer.

Claim 22

Dependent Claim 35 words

A method in accordance with claim 19 wherein said third layer of protective material comprises a stack including: a layer of oxide-resistant material; and a layer of insulating material over said layer of oxide-resistant material.

Claim 23

Dependent Claim 34 words

A method in accordance with claim 11 wherein said step of removing an oxidized portion of said second layer includes reactive ion etching a horizontal region of the oxidized portion of said second layer.

Claim 24

Dependent Claim 85 words

A method in accordance with claim 21 wherein said step of forming said spacer of insulating material comprises the steps of: oxidizing the exposed portions of said first and second layers; forming a layer of silicon nitride over the oxidized regions of said first and second layers; forming a layer of silicon dioxide over the silicon nitride; and removing portions of said layers of silicon dioxide and silicon nitride and portions of the oxidized regions of said first and second layers to form said spacer.

Claim 25

Dependent Claim 47 words

A method in accordance with claim 22 wherein said third layer comprises a stack including: a layer of intrinsic silicon overlying said second layer; a layer of silicon nitride overlying said layer of intrinsic polysilicon; and a layer of silicon dioxide overlying said layer of silicon nitride.

Claim 26

Dependent Claim 25 words

The method of claim 11 wherein said exposed portion of said first layer comprises an intrinisic base region of a subsequently formed vertical bipolar transistor.

Claim 27

Dependent Claim 13 words

The method of claim 11 wherein said first layer includes a silicon-germanium compound.

Claim 28

Dependent Claim 56 words

The method of claim 11 and further including the step of heating said substrate, after said oxidizing and removing steps, to drive dopant from the remaining portion of said second layer into said first layer such that the remaining portion of said second layer forms an electrical contact to said exposed portion of said first layer.

Claim 29

Independent Claim 184 words

A method of forming a vertical bipolar transistor comprising the steps of: providing a substrate of semiconductor material including a first device region of a first conductivity type; forming a first layer of second conductivity type epitaxial semiconductor material over said first device region; forming a second layer of second conductivity type epitaxial semiconductor material over said first layer, said second layer having a relatively higher dopant concentration than said first layer; forming a third layer of protective material over said second layer; etching said third layer to expose a portion of said second layer; oxidizing the exposed portion of said second layer through to said first layer; removing the oxidized portion of said second layer to expose a portion of said first layer; forming a spacer of insulating material on the exposed edge of said second layer; forming a second region of said first conductivity type in the surface of said exposed portion of said first layer; and heating said substrate to drive dopant from the remaining portions of said second layer into said first layer; whereby to form a vertical bipolar transistor.

Claim 30

Independent Claim 184 words

A method of forming a vertical bipolar transistor comprising the steps of: providing a substrate of semiconductor material including a first device region of a first conductivity type; forming a first layer of second conductivity type epitaxial semiconductor material over said first device region; forming a second layer of second conductivity type epitaxial semiconductor material over said first layer, said second layer having a relatively higher dopant concentration than said first layer; forming a third layer of protective material over said second layer; etching said third layer to expose a portion of said second layer; oxidizing the exposed portion of said second layer through to said first layer; removing the oxidized portion of said second layer to expose a portion of said first layer; forming a spacer of insulating material on the exposed edge of said second layer; forming a second region of said first conductivity type in the surface of said exposed portion of said first layer; and heating said substrate to drive dopant from the remaining portions of said second layer into said first layer; whereby to form a vertical bipolar transistor.

Claim 31

Dependent Claim 47 words

The method of claim 27 wherein said steps of forming said first and second layers each include epitaxially growing semiconductor material at a temperature in the range of about 500-800 degrees centigrade and a pressure in the range of about 10 -4 -10 -2 torr during deposition.

Claim 32

Dependent Claim 54 words

The method of claim 27 wherein said step of forming said second region comprises the step of: forming a layer of doped conductive material over the surface of said exposed portion of said first layer; and said heating step driving dopant from said doped conductive material into said exposed portion of said first layer.

Claim 33

Dependent Claim 13 words

The method of claim 27 wherein said first layer includes a silicon-germanium compound.

Claim 34

Dependent Claim 40 words

The method of claim 27 wherein said step of oxidizing said portion of said second layer includes the step of exposing said second layer to steam at a temperature selected to oxidize said second layer selectively over said first layer.

Claim 35

Dependent Claim 50 words

The method of claim 27 wherein: said region of said first conductivity type is framed within a window of insulating material overlying said substrate; and said first and second layers being of monocrystalline structure over said region of said first conductivity type and of polycrystalline structure over said insulating material.

Claim 36

Dependent Claim 53 words

The method of claim 27 and further including the steps of: forming a third layer of intrinsic epitaxial semiconductor material intermediate said first and second layers, said oxidizing step extending at least through said second layer to said third layer; and said removing step exposing at least a portion of said third layer.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1994-04-15	1994-10-15	1995-04-16	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1998-04-15	1998-10-15	1999-04-16	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2002-04-15	2002-10-15	2003-04-16	$7700.00	Window Closed / Lapsed

Method of fabricating a narrow base transistor

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