Process for forming a self-aligned low resistance path in semiconductor devices

• US 4,669,178 A
• Filed: 05/23/1986
• Issued: 06/02/1987
• Est. Priority Date: 05/23/1986
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Johnson, Eric D.
• Primary Examiner(s): Smith, John D.
• Assistant Examiner(s): Dang, Vi D.
• Application Number:
  US06/866,411
• Time in Patent Office: 375 Days
• Field of Search: 427/85, 427/84, 427/93, 29/571, 29/576 B, 148/DIG. 70, 357/52, 156/662
• US Class Current: 438/529
• CPC Class Codes: H01L 21/02238 silicon in uncombined form, i.e. pure silicon
• CPC Class Codes: H01L 21/02255 formation by thermal treatment H01L21/02252 takes precedence; after treatment of an insulating film H01L21/3105 and subgroups
• CPC Class Codes: H01L 21/02299 pre-treatment
• CPC Class Codes: H01L 21/033 comprising inorganic layers
• CPC Class Codes: H01L 21/266 using masks H01L21/26586 takes precedence
• CPC Class Codes: H01L 21/31662 of silicon in uncombined form
• CPC Class Codes: H01L 21/761 PN junctions

Abstract

A method of forming a low resistance path, e.g., to serve as a guard ring, in a silicon semiconductor device is disclosed.

An opening is defined in an upper protective layer and an underlying lower protective layer. Normally these layers are silicon nitride and silicon dioxide, respectively. The lower protective layer is isotropically wet etched so that the upper protective layer overhangs the lower protective layer and protects a part of the silicon wafer surface.

A first impurity is implanted in the exposed silicon wafer surface except in the annular area protected by the upper protective layer overhang.

A silicon dioxide layer is grown on the entire exposed surface of the silicon wafer which is inherently thicker over the area where the impurity has been implanted and inherently thinner over the annular area where the impurity has not been implanted. The upper protective layer is then preferably removed.

A second impurity is implanted through the annular thinner silicon dioxide layer, which optionally may be etched away, to create, e.g., a guard ring in the silicon wafer around the perimeter of the thicker silicon dioxide layer which has protected the silicon wafer from the implant.

Claims

1. A method of forming a guard ring in a silicon semiconductor device comprising the steps of:

(a) forming a first protective layer on the surface of a silicon wafer;

(b) forming a second protective layer on the first protective layer;

(c) defining an opening in the first protective layer and the second protective layer to expose a selected portion of the silicon wafer surface with the opening in the second protective layer being smaller than the opening in the first protective layer such that the second protective layer overhangs the first protective layer and protects a portion of the silicon wafer;

(d) implanting a first impurity in a portion of the exposed silicon wafer surface the same size as the opening in the second protective layer and smaller than the opening in the first protective layer;

(e) thermally growing a silicon dioxide layer on the entire exposed surface of the silicon wafer, wherein the thermally grown silicon dioxide layer is thicker over the area where the impurity has been implanted and thinner over the area where the impurity has not been implanted, thereby forming a central thicker silicon dioxide area and an annular thinner silicon dioxide area therearound;

(f) implanting a second impurity, the second impurity being implanted through the thinner annular silicon oxide to create a guard ring in the silicon wafer around the perimeter of the thicker silicon dioxide layer which remains; and

(g) removing any protective layer from the silicon wafer surface.

2. A method as in claim 1, wherein the first protective layer is silicon dioxide and the second protective layer is silicon nitride.

3. A method as in claim 1, wherein the second protective layer is removed between steps (d) and (f).

4. A method as in claim 2, wherein the second protective layer is removed between steps (d) and (f).

5. A method as in claim 2, wherein in step (e) the silicon dioxide layer is a second silicon dioxide layer, and wherein between steps (e) and (f) the following step (e) is conducted:

etching the second silicon dioxide layer to remove the annular thinner silicon dioxide area while permitting the thicker silicon dioxide area to remain to thereby expose an annular region on the surface of the underlying silicon wafer around the thicker silicon dioxide area.

6. A method as in claim 4, wherein:

in step (a) the silicon wafer is P-type;

in step (d) the first impurity is N-type; and

in step (f) the second impurity is N-type, but differs from the first impurity which is N-type.

7. A method as in claim 1, wherein the thicker silicon dioxide area has a thickness from about 1.5 to about 10 times the thickness of the annular thinner silicon dioxide layer.

8. A method as in claim 7, wherein the annular thinner silicon dioxide layer is about 200 Å

to about 300 Å

thick and the thicker silicon dioxide layer is about 2,000 Å

to about 3,000 Å

thick.

9. A method as in claim 8, wherein the first impurity is implanted to a concentration of at least 10²⁰ atoms/cc.

10. A method as in claim 1, wherein the opening in the first protective layer is formed by a wet etch, whereby said first protective layer is isotropically etched to result in said second protective layer overhanging the first protective layer.

11. A method of forming a guard ring in a P-type silicon semiconductor device comprising the steps of:

thermally growing a first layer of silicon dioxide on the surface of the body;

forming a layer of silicon nitride on the first layer of silicon dioxide;

defining an opening in said layers to expose a selected portion of the silicon surface with the opening in the silicon nitride layer being smaller than the opening in the silicon dioxide layer such that the silicon nitride layer overhangs the opening in the silicon dioxide layer;

implanting an N-type impurity in a portion of the exposed silicon surface the same size as the opening in the silicon nitride material and smaller than the opening in the first layer of silicon dioxide;

thermally growing a second silicon dioxide layer on the entire exposed surface of said silicon body;

the thermally grown layer being thicker over the implanted area than over the unimplanted area;

diffusing an N-type impurity of a different type into the exposed annular silicon surface to create a guard ring in the body, around the perimeter of the thick oxide, the silicon nitride layer being removed prior to this diffusing step; and

removing all the oxide layers from said silicon surface.

12. A method of forming a guard ring in a P-type silicon semiconductor device comprising the steps of:

thermally growing a first layer of silicon dioxide on the surface of the body;

forming a layer of silicon nitride on the first layer of silicon dioxide;

defining an opening in said layers to expose a selected portion of the silicon surface with the opening in the silicon nitride layer being smaller than the opening in the silicon dioxide layer such that the silicon nitride layer overhangs the opening in the silicon dioxide layer;

implanting an N-type impurity in a portion of the exposed silicon surface the same size as the opening in the silicon nitride material and smaller than the opening in the first layer of silicon dioxide;

thermally growing a second silicon dioxide layer on the entire exposed surface of said silicon body;

the thermally grown second silicon dioxide layer being thicker over the implanted area than over the unimplanted area;

etching the second silicon dioxide layer to remove the thinner silicon dioxide over the unimplanted area to expose an annular region on the surface of the underlying silicon body around the thicker silicon dioxide deposit;

diffusing an N-type impurity of a different type into the exposed annular silicon surface to create a guard ring in the body, around the perimeter of the thicker silicon dioxide; and

removing all the silicon dioxide layers from said silicon surface.