Etch depth determination for SGT technology

• US 8,021,563 B2
• Filed: 03/23/2007
• Issued: 09/20/2011
• Est. Priority Date: 03/23/2007
• Status: Active Grant

• Current Assignee: Alpha & Omega Semiconductor, Ltd.
• Original Assignee: Alpha & Omega Semiconductor, Ltd.
• Inventors: Lou, Yingying, Wang, Yu, Bhalla, Anup, Li, Tiesheng
• Primary Examiner(s): ALANKO, ANITA KAREN
• Application Number:
  US11/690,546
• Publication Number:
  US 20080233748A1
• Time in Patent Office: 1,642 Days
• Field of Search: None
• US Class Current: 216/59
• CPC Class Codes: H01L 22/12 for structural parameters, e.g. thickness, line width, refractive index, temperature, warp, bond strength, defects, optical inspection, electrical measurement of structural dimensions, metallurgic measurement of diffusions electrical measurement of diffusions H01L22/14
• CPC Class Codes: H01L 29/407 Recessed field plates, e.g. trench field plates, buried field plates
• CPC Class Codes: H01L 29/66734 with a step of recessing the gate electrode, e.g. to form a trench gate electrode
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Abstract

A method for determining the depth etch, a method of forming a shielded gate trench (SGT) structure and a semiconductor device wafer are disclosed. A material layer is formed over part of a substrate having a trench. The material fills the trench. A resist mask is placed over a test portion of the layer of material. The resist mask does not cover the trench. The layer of material is isotropically etched. An etch depth may be determined from a characteristic of etching of the material underneath the mask. Such a method may be used for forming SGT structures. The wafer may comprise a layer of material disposed on at least a portion of a surface of semiconductor wafer; a resist mask comprising an angle-shaped test portion disposed over a portion of the layer of material; and a ruler marking on the surface of the substrate proximate the test portion.

Claims

1. A method for determining etch depth, comprising:

a) forming a layer of material over a portion of a substrate having a trench formed thereon in such a way that the material fills the trench;

b) placing a mask over a test portion of the layer of material, wherein the mask does not cover the trench;

c) isotropically etching the layer of material;

d) determining a depth D_T of etching of the material in the trench based on a characteristic of etching of the material underneath a portion of the mask, wherein the characteristic of etching is an amount of lateral undercut D_L of the test portion underneath the mask.

2. The method of claim 1 wherein d) comprises:

measuring the amount of lateral undercut D_L; and

determining the depth of etched length of the material in the trench from the amount of undercut D_L.

3. The method of claim 2 wherein the mask comprises a rectangular shape.

4. The method of claim 2, wherein the mask comprises a circular shape.

5. The method of claim 2 wherein the mask comprises a portion having an angled shape having a tip angle θ

.

6. The method of claim 5 wherein the mask over the test portion comprises a chevron shape.

7. The method of claim 5, wherein the mask over the test portion comprises a triangular or dagger shape.

8. The method of claim 5 wherein measuring the amount of lateral undercut D_L comprises measuring a change in length Δ

L of the test portion and determining the amount of lateral undercut D_L from the change in length Δ

L.

9. The method of claim 8, further comprising:

e) forming a marking ruler proximate the test portion, wherein the ruler is adapted to facilitate measurement of the change length Δ

L of the test portion.

10. The method of claim 8 wherein determining the amount of lateral undercut D_L from the change in length Δ

L comprises approximating the amount of undercut D_L as

D_L≈

Δ

L×

tan θ

/2.

11. The method of claim 2 wherein the mask is made of a transparent material.

12. The method of claim 11 wherein the transparent material comprises a transparent oxide material.

13. The method of claim 2 wherein the layer of material comprises a layer of polysilicon.

14. A method of forming a shielded gate trench (SGT) structure, comprising:

a) filling a trench with polysilicon wherein a polysilicon film is formed over the trench;

b) placing a mask over a portion of the polysilicon;

c) isotropically etching the polysilicon;

d) determining a depth of etching of the polysilicon in the trench based on a characteristic of etching of the polysilicon portion underneath the mask, wherein the characteristic of etching is an amount of lateral undercut D_L of the test portion underneath the mask.

15. The method of claim 14, wherein d) comprises:

measuring the amount of lateral undercut D_L; and

determining the depth of etched length of the polysilicon in the trench from the amount of undercut D_L.

16. The method of claim 15 wherein the mask comprises a layer of material having an angled shape test portion having a tip angle θ

.

17. The method of claim 16 wherein measuring the amount of lateral undercut D_L comprises measuring a change in length Δ

L of the test portion and determining the amount of lateral undercut D_L from the change in length Δ

L.

18. The method of claim 17, further comprising:

e) placing a marking ruler proximate the test portion, wherein the ruler is adapted to facilitate measurement of the change in length Δ

L of the test portion.

19. The method of claim 17 wherein determining the amount of lateral undercut D_L from the change in length Δ

L comprises approximating the amount of undercut D_L as

D_L≈

Δ

L×

tan θ

/2.