Reverse construction memory cell

• US 7,776,715 B2
• Filed: 07/26/2005
• Issued: 08/17/2010
• Est. Priority Date: 07/26/2005
• Status: Active Grant

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Micron Technology, Inc.
• Inventors: Manning, H. Montgomery, Wells, David H.
• Primary Examiner(s): Gurley; Lynne A
• Assistant Examiner(s): Gebremariam; Samuel A
• Application Number:
  US11/189,945
• Publication Number:
  US 20070023805A1
• Time in Patent Office: 1,848 Days
• Field of Search: 438455-460, 438/463, 438405-406, 438/424, 438/427, 438294-296, 438/396
• US Class Current: 438/455
• CPC Class Codes: H01L 21/76254 with separation/delamination along an ion implanted layer, e.g. Smart-cut, Unibond
• CPC Class Codes: H01L 21/84 the substrate being other than a semiconductor body, e.g. being an insulating body
• CPC Class Codes: H10B 12/053 the transistor being at least partially in a trench in the substrate vertical transistor in combination with a capacitor formed in a substrate trench H10B12/0383
• CPC Class Codes: H10B 12/48 Data lines or contacts therefor
• CPC Class Codes: H10B 12/482 Bit lines

Abstract

A method of fabricating a memory cell comprises forming a plurality of doped semiconductor layers on a carrier substrate. The method further comprises forming a plurality of digit lines separated by an insulating material. The digit lines are arrayed over the doped semiconductor layers. The method further comprises etching a plurality of trenches into the doped semiconductor layers. The method further comprises depositing an insulating material into the plurality of trenches to form a plurality of electrically isolated transistor pillars. The method further comprises bonding at least a portion of the structure formed on the carrier substrate to a host substrate. The method further comprises separating the carrier substrate from the host substrate.

Claims

1. A method of fabricating a memory array, the method comprising:

forming at least three vertically stacked doped semiconductor layers of alternating conductivity type on a carrier substrate;

forming a plurality of digit lines for the memory array separated by an insulating material, wherein the digit lines are arrayed over the vertically stacked doped semiconductor layers on the carrier substrate;

bonding at least a portion of a structure formed on the carrier substrate to a host substrate, wherein the structure comprises the vertically stacked doped semiconductor layers and the plurality of digit lines; and

separating a portion of the carrier substrate from the host substrate while leaving the structure on the host substrate.

2. The method of claim 1, further comprising performing a chemical mechanical planarization process on a semiconductor surface, wherein the semiconductor surface is exposed by separating the portion of the carrier substrate from the host substrate.

3. The method of claim 1, further comprising implanting hydrogen ions in a region in one of the at least three vertically stacked doped semiconductor layers, wherein the carrier substrate is separated in the region of hydrogen ion implantation.

4. The method of claim 1, wherein the at least three vertically stacked doped semiconductor layers comprises a p⁻

doped layer positioned between an n⁺ doped layer and an n⁻

doped layer.

5. The method of claim 1, wherein one of the at least three vertically stacked doped semiconductor layers comprises doped silicon.

6. The method of claim 1, wherein the plurality of trenches have feature size F is between about 50 μ

m and about 150 μ

m.

7. The method of claim 1, wherein the digit lines comprise a material selected from the group consisting of tungsten, titanium, nickel and cobalt.

8. The method of claim 1, wherein the insulating material is an oxide material.

9. The method of claim 1, further comprising inverting the at least three vertically stacked doped semiconductor layers after bonding at least a portion of the structure formed on the carrier substrate to a host substrate.

10. The method of claim 1, further comprising forming a layer of insulating material over the vertically stacked doped semiconductor layers and the plurality of digit lines prior to the bonding.

11. The method of claim 1, further comprising:

etching a plurality of trenches through at least two of the doped semiconductor layers; and

depositing an insulating material into the plurality of trenches to form a plurality of transistor pillars before bonding and separating.

12. The method of claim 11, wherein the plurality of trenches are etched to a depth above a separation line along which the carrier substrate is separated.

13. The method of claim 11, wherein etching a plurality of trenches through at least two of the doped semiconductor layers comprises etching a plurality of trenches through at least three of the doped semiconductor layers before the carrier substrate is separated.

14. The method of claim 11, wherein the plurality of trenches are etched to a depth below a separation line along which the carrier substrate is separated.

15. A method comprising:

forming a plurality of at least partially fabricated vertical transistor structures on a carrier substrate;

forming a plurality of digit lines over the at least partially fabricated vertical transistor structures;

separating the digit lines and the at least partially fabricated vertical transistor structures from the carrier substrate;

bonding the digit lines and the at least partially fabricated vertical transistor structures to a host substrate, such that the digit lines are positioned between the host substrate and the at least partially fabricated vertical transistor structures.

16. The method of claim 15, wherein the at least partially fabricated vertical transistor structures comprise a transistor pillars separated by a plurality of orthogonally arrayed trenches.

17. The method of claim 15, further comprising performing a chemical mechanical planarization process on a semiconductor surface, wherein the semiconductor surface is exposed by separating the portion of the carrier substrate from the host substrate.

18. The method of claim 15, further comprising implanting hydrogen ions in a region in one of the plurality of at least partially fabricated vertical transistor structures, wherein the carrier substrate is separated in the region of hydrogen ion implantation.

19. The method of claim 15, wherein the plurality of digit lines comprise a material selected from the group consisting of copper, aluminum, gold, nickel and cobalt.

20. The method of claim 15, further comprising forming a complete memory array after bonding and separating, wherein the memory array comprises a plurality of transistors formed from the partially fabricated vertical transistor structures and the plurality of digit lines.