Fabrication of a gate structures having a longer length toward the top for formation of a rectangular shaped spacer

• US 6,306,710 B1
• Filed: 02/03/2000
• Issued: 10/23/2001
• Est. Priority Date: 02/03/2000
• Status: Expired due to Term

• Current Assignee: GlobalFoundries, Inc.
• Original Assignee: Advanced Micro Devices, Inc.
• Inventors: Bell, Scott, Long, Wei, Liu, Bill, Karlsson, Olov
• Primary Examiner(s): Niebling, John F.
• Assistant Examiner(s): LINDSAY JR, WALTER LEE
• Application Number:
  US09/498,231
• Time in Patent Office: 628 Days
• Field of Search: 438/261, 438/182, 438/279, 438/303, 438/305, 438/622, 438/595
• US Class Current: 438/279
• CPC Class Codes: H01L 21/28035 the final conductor layer next to the insulator being silicon, e.g. polysilicon, with or without impurities H01L21/28105 takes precedence
• CPC Class Codes: H01L 21/28114 characterised by the sectional shape, e.g. T, inverted-T
• CPC Class Codes: H01L 29/4925 with a multiple layer structure, e.g. several silicon layers with different crystal structure or grain arrangement with only a vertical doping structure or vertical doping variation H01L29/4916
• CPC Class Codes: H01L 29/665 using self aligned silicidation, i.e. salicide formation of conductive layers comprising silicides H01L21/28518

Abstract

The gate structure of the MOSFET of the present invention is formed to have a longer length toward the top of the gate structure such that a spacer having a substantially rectangular shaped is formed at the sidewalls of the gate structure. For fabricating a gate structure of a field effect transistor on a semiconductor substrate, a layer of gate structure material is deposited on the semiconductor substrate. The composition of the layer of gate structure material is adjusted along a depth of the layer of gate structure material for a slower etch rate toward a top of the layer of gate structure material that is further from the semiconductor substrate. The gate structure is then formed by patterning and etching the layer of gate structure material. The slower etch rate toward the top of the layer of gate structure material results in a longer length toward a top of the gate structure that is further from the semiconductor substrate. Spacer dielectric is deposited conformally on exposed surfaces of the gate structure. The spacer dielectric is anisotropically etched such that the spacer dielectric remains on sidewalls of the gate structure. The longer length toward the top of the gate structure results in a substantially rectangular shaped spacer dielectric remaining on the sidewalls of the gate structure. The present invention may be used to particular advantage when the gate structure and the spacer having the rectangular shape are formed as part of a field effect transistor such as a MOSFET.

Claims

1. A method for fabricating a gate structure of a field effect transistor on a semiconductor substrate, the method including the steps of:

A. depositing a layer of gate structure material on said semiconductor substrate;

B. adjusting a composition of said layer of gate structure material along a depth of said layer of gate structure material for a slower etch rate toward a top of said layer of gate structure material that is further from said semiconductor substrate;

C. forming said gate structure by patterning and etching said layer of gate structure material, wherein said slower etch rate toward said top of said layer of gate structure material results in a longer length toward a top of said gate structure that is further from said semiconductor substrate;

D. depositing spacer dielectric on exposed surfaces of said gate structure; and

E. anisotropically etching said spacer dielectric such that said spacer dielectric remains on sidewalls of said gate structure,

wherein said longer length toward said top of said gate structure results in a substantially rectangular shaped spacer dielectric remaining on said sidewalls of said gate structure.

2. The method of claim 1, wherein said gate structure material is comprised of polysilicon and wherein said gate dielectric is comprised of silicon dioxide (SiO₂).

8. The method of claim 1, wherein said step B includes the step of:

implanting a dopant into said layer of gate structure material, wherein a concentration of said dopant varies along said depth of said layer of gate structure material, and wherein a lower concentration of said dopant toward said top of said layer of gate structure material results in said slower etch rate toward said top of said layer of gate structure material.

9. The method of claim 8, wherein said layer of gate structure material is comprised of polysilicon, and wherein said dopant is comprised of nitrogen (N).

10. The method of claim 8, wherein said layer of gate structure material is comprised of polysilicon, and wherein said dopant is comprised of silicon (Si).

11. The method of claim 1, wherein said step B includes the steps of:

depositing a bottom layer of amorphous silicon closer to said semiconductor substrate as part of said layer of gate structure material; and

depositing a top layer of polysilicon further from said semiconductor substrate as part of said layer of gate structure material,

wherein said top layer of polysilicon etches with said slower etch rate than said bottom layer of amorphous silicon.

12. The method of claim 1, wherein said gate structure with said longer length toward said top of said gate structure has a T-shape.

13. The method of claim 1, wherein said gate structure with said longer length toward said top of said gate structure has an I-shape.

3. A method for fabricating a gate structure of a field effect transistor on a semiconductor substrate, the method including the steps of:

A. depositing a layer of gate structure material on said semiconductor substrate;

B. adjusting a composition of said layer of gate structure material along a depth of said layer of gate structure material for a slower etch rate toward a top of said layer of gate structure material that is further from said semiconductor substrate;

C. forming said gate structure by patterning and etching said layer of gate structure material, wherein said slower etch rate toward said top of said layer of gate structure material results in a longer length toward a top of said gate structure that is further from said semiconductor substrate;

D. implanting halo dopant toward said semiconductor substrate having said gate structure to form a drain pocket and a source pocket of said field effect transistor in said semiconductor substrate around said gate structure; and

E. implanting source and drain extension dopant toward said semiconductor substrate to form a drain extension and a source extension of said field effect transistor in said semiconductor substrate around said gate structure,

wherein said halo dopant is implanted at an angle toward said gate structure and wherein said source and drain extension dopant is implanted vertically toward said semiconductor substrate such that said drain pocket surrounds said drain extension and such that said source pocket surrounds said source extension toward a channel of said field effect transistor.

4. The method of claim 3, further including the steps of:

depositing spacer dielectric on exposed surfaces of said gate structure; and

anisotropically etching said spacer dielectric such that said spacer dielectric remains on sidewalls of said gate structure,

wherein said longer length toward said top of said gate structure results in a substantially rectangular shaped spacer dielectric remaining on said sidewalls of said gate structure.

5. The method of claim 4, further including the step of:

implanting source and drain contact dopant toward said semiconductor substrate to form a drain contact junction and a source contact junction of said field effect transistor in said semiconductor substrate around said spacer dielectric,

wherein said source and drain contact dopant is implanted vertically toward said semiconductor substrate.

6. The method of claim 5, further including the step of:

forming silicide within said gate structure and said drain contact junction and said source contact junction of said field effect transistor.

7. A method of fabricating a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) within a silicon substrate, the method including the steps of:

A. depositing a layer of polysilicon on said silicon substrate;

B. implanting nitrogen dopant into said layer of polysilicon, wherein a concentration of said nitrogen dopant varies along a depth of said layer of polysilicon, and wherein a lower concentration of said nitrogen dopant toward a top of said layer of polysilicon that is further from said silicon substrate results in a slower etch rate toward said top of said layer of polysilicon;

C. patterning and etching said layer of polysilicon to form a gate structure of said MOSFET, wherein said slower etch rate toward said top of said layer of polysilicon results in a longer length toward a top of said gate structure that is further from said silicon substrate, and wherein said gate structure with said longer length toward said top of said gate structure has a T-shape;

D. implanting halo dopant toward said silicon substrate having said gate structure to form a drain pocket and a source pocket of said MOSFET in said silicon substrate around said gate structure;

E. implanting source and drain extension dopant toward said silicon substrate to form a drain extension and a source extension of said MOSFET in said silicon substrate around said gate structure,

wherein said halo dopant is implanted at an angle toward said gate structure and wherein said source and drain extension dopant is implanted vertically toward said silicon substrate such that said drain pocket surrounds said drain extension and such that said source pocket surrounds said source extension toward a channel of said MOSFET;

F. depositing spacer dielectric of silicon dioxide (SiO₂) on exposed surfaces of said gate structure;

G. anisotropically etching said spacer dielectric such that said spacer dielectric remains on sidewalls of said gate structure,

wherein said longer length toward said top of said gate structure results in a substantially rectangular shaped spacer dielectric remaining on said sidewalls of said gate structure;

H. implanting source and drain contact dopant toward said silicon substrate to form a drain contact junction and a source contact junction of said MOSFET in said silicon substrate around said spacer dielectric,

wherein said source and drain contact dopant is implanted vertically toward said silicon substrate; and

forming silicide within said gate structure and said drain contact junction and said source contact junction of said MOSFET.