Vertical thyristor-based memory with trench isolation and its method of fabrication

• US 7,456,439 B1
• Filed: 07/01/2004
• Issued: 11/25/2008
• Est. Priority Date: 03/22/2001
• Status: Expired due to Fees

• Current Assignee: T-Ram, LLC
• Original Assignee: T-RAM Semiconductor, Inc.
• Inventors: Horch, Andrew E.
• Primary Examiner(s): Wilczewski, M.
• Assistant Examiner(s): Chiu, Tsz K
• Application Number:
  US10/884,337
• Time in Patent Office: 1,608 Days
• Field of Search: 257/302, 257/133, 257/E21.661, 257/147, 257/155, 438/268, 438/212, 438/270, 438/279, 438/587, 438/138
• US Class Current: 257/133
• CPC Class Codes: G11C 11/39 using thyristors or the avalanche or negative resistance type, e.g. PNPN, SCR, SCS, UJT
• CPC Class Codes: H01L 21/76229 Concurrent filling of a plurality of trenches having a different trench shape or dimension, e.g. rectangular and V-shaped trenches, wide and narrow trenches, shallow and deep trenches
• CPC Class Codes: H01L 21/76237 introducing impurities in trench side or bottom walls, e.g. for forming channel stoppers or alter isolation behavior
• CPC Class Codes: H01L 21/763 Polycrystalline semiconductor regions H01L21/76264 takes precedence
• CPC Class Codes: H01L 27/0617 comprising components of the field-effect type H01L27/0251 takes precedence
• CPC Class Codes: H01L 27/0817 Thyristors only
• CPC Class Codes: H01L 27/1027 Thyristors
• CPC Class Codes: H01L 29/0657 characterised by the shape of the body
• CPC Class Codes: H01L 29/66363 Thyristors
• CPC Class Codes: H01L 29/74 Thyristor-type devices, e.g. having four-zone regenerative action two-terminal thyristors H01L29/87
• CPC Class Codes: H10B 99/00 Subject matter not provided for in other groups of this subclass

Abstract

A semiconductor device may comprise a plurality of memory cells. A memory cell may comprise a thyristor, at least a portion of which is formed in a pillar of semiconductor material. The pillar may comprise sidewalls defining a cylindrical circumference of a first diameter. In a particular embodiment, the pillars associated with the plurality of memory cells may define rows and columns of an array. In a further embodiment, a pillar may be spaced by a first distance of magnitude up to the first diameter relative to a neighboring pillar within its row. In an additional further embodiment, the pillar may be spaced by a second distance of a magnitude up to twice the first diameter, relative to a neighboring pillar within its column.

Claims

1. A semiconductor device, comprising:

a plurality of thyristor-based memory cells each comprising a thyristor formed in a pillar of semiconductor material that has a cylindrical circumference of a first diameter;

the pillars associated with the plurality of thyristor-based memory cells defining rows and columns of an array; and

a given pillar of the plurality spaced by a first distance of magnitude up to the first diameter relative to a first pillar of the same row, and

a second pillar of the plurality spaced from the given pillar by a second distance of magnitude up to twice the first diameter within the same column;

in which the pillars each further comprise an access device in electrical series relationship and vertically aligned with the associated thyristor.

2. The device of claim 1, in which the pillars of semiconductor material each comprise alternating layers of opposite type conductivities that define the access device in series and vertical relationship with the thyristor.

3. The device of claim 1, in which the at least a portion of the access device comprises source, channel and drain regions of a MOSFET;

and

the at least a portion of the thyristor comprises cathode-emitter, p-base, and a-base regions.

4. The device of claim 3, in which the cathode-emitter region is disposed above the p-base region and in common with the drain/source region of the MOSFET.

5. The device of claim 3, further comprising:

an anode-emitter region of the thyristor defining in part a portion of the second given pillar; and

a buried n-region disposed exterior to the anode-emitter region within the semiconductor substrate.

6. The device of claim 5, in which the anode-emitter region comprises a further portion that extends below the second given pillar and is electrically coupled in common to respective portions of the anode-emitter regions of at least one neighboring pillar.

7. A semiconductor thyristor-based memory array comprising:

an array of memory cells comprising a plurality of rows and columns of semiconductor pillars;

first and second row wordlines comprising respective first and second layers of conductive material;

the first and the second layers of conductive material vertically offset relative to each other;

each of the first and the second wordlines for a given row of the semiconductor pillars comprising a plurality of apertures;

the apertures defined by the first wordline aligned vertically to apertures of the second wordline;

the pillars of semiconductor material for the given row extending through the aligned apertures; and

dielectric disposed between the pillars and the conductive material of the first and second wordlines;

in which the semiconductor pillars comprise vertically aligned alternating regions of opposite conductivity type to define at least part of a thyristor in series with an access transistor therein.

8. The memory array of claim 7, the conductive material for the first wordline operable collectively as a gate electrode capacitively coupled to a body region of the respective access transistors for the pillars of a given row.

9. The memory array of claim 8, in which the layer of conductive material for the second wordline is operable as a capacitor electrode capacitively coupled to a base region of the respective thyristors for the pillars associated with the given row.

10. A semiconductor thyristor-based memory array comprising:

an array of memory cells comprising a plurality of rows and columns of semiconductor pillars;

first and second row wordlines comprising respective first and second layers of conductive material;

the first and the second layers of conductive material vertically offset relative to each other;

each of the first and the second wordlines for a given row of the semiconductor pillars comprising a plurality of apertures;

the apertures defined by the first wordline aligned vertically to apertures of the second wordline;

the pillars of semiconductor material for the given row extending through the aligned apertures; and

dielectric disposed between the pillars and the conductive material of the first and second wordlines;

in which;

the semiconductor pillars comprise vertically aligned alternating regions of opposite conductivity type to define at least part of a thyristor in series with an access transistor therein;

the conductive material for the first wordline operable collectively as a gate electrode capacitively coupled to a body region of the respective access transistors for the pillars of a given row;

the layer of conductive material for the second wordline is operable as a capacitor electrode capacitively coupled to a base region of the respective thyristors for the pillars associated with the given row; and

at least one of the first and second wordlines is formed from sleeves of conductive material conformally deposited about the pillars with a radial thickness of magnitude greater than half the distance interspacing the neighboring pillars within the given row.

11. The memory array of claim 10, in which the layer of conductive material for the first wordline comprises a depth sufficient to span a channel length for the body region between and to overlap at least respective portions of source and drain regions of the access transistors.

12. The memory array of claim 11, the conductive material for the second wordline being limited to a depth of magnitude less than that for the base region of the thyristors to which it is capacitively coupled.

13. The memory array of claim 12, in which

pillars of the plurality associated with a given row are interspaced by a lateral distance less than the lateral diameter;

and

a different row of the pillars that neighbors the given row is separated therefrom by a longitudinal distance greater than the longitudinal diameter.