Browse Prior Art Database

REDUCED DOPING ADJACENT FIELD IMPLANT

IP.com Disclosure Number: IPCOM000025757D
Original Publication Date: 1987-Oct-31
Included in the Prior Art Database: 2004-Apr-04
Document File: 2 page(s) / 104K

Publishing Venue

Xerox Disclosure Journal

Abstract

A field implant is conventionally formed to prevent leakage between neighboring diffused regions of a silicon semiconductor substrate. For example, Fig. 1 shows very lightly P-doped substrate 10, with heavily N-doped diffused regions 12 and 14 separated by heavily P-doped field implant 16. Field oxide 18 is formed over implant 16 between diffused regions 12 and 14 for device isolation. Reducing device dimensions requires increasing the P-concentration necessary for implant 16 to prevent inversion or leakage around oxide 18. This high concentration decreases the breakdown voltage at junctions 20 and 22 and leads to narrow width effects. Therefore, device dimensions cannot be reduced below the level at which avalanche breakdown occurs.

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XEROX DISCLOSURE JOURNAL

REDUCED DOPING ADJACENT Proposed Classification FIELD IMPLANT U.S. C1.427/85 Russel Martin Int. C1. B05d 5/12

12

\

OXIDE

<

FIG. 1

-

P-

16 FIG. 2

FIG. 3A

34 \

FIG. 38

FIG. 3C

FIG. 30

34.

Volume 12 Number 5 September/October 1987 249

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REDUCED DOPING ADJACENT FIELD IMPLANT (Cont'd)

A field implant is conventionally formed to prevent leakage between neighboring diffused regions of a silicon semiconductor substrate. For example, Fig. 1 shows very lightly P-doped substrate 10, with heavily N-doped diffused regions 12 and 14 separated by heavily P-doped field implant 16. Field oxide 18 is formed over implant 16 between diffused regions 12 and 14 for device isolation. Reducing device dimensions requires increasing the P- concentration necessary for implant 16 to prevent inversion or leakage around oxide 18. This high concentration decreases the breakdown voltage at junctions 20 and 22 and leads to narrow width effects. Therefore, device dimensions cannot be reduced below the level at which avalanche breakdown occurs.

This problem can be solved by providing a region of lower doping between diffused regions 12 and 14 and heavily doped implant 16. Fig. 2 shows lightly doped regions 24 and 26, which serve to increase the breakdown voltage, permitting smaller device dimensions.

Figs. 3A-3D show steps in a process which creates lightly doped regions 24 and
26. Fig. 3A shows local oxidation stacks 32 and 34, which could be conventio...