Method for forming horizontal buried channels or cavities in wafers of monocrystalline semiconductor material

• US 6,670,257 B1
• Filed: 04/07/2000
• Issued: 12/30/2003
• Est. Priority Date: 04/09/1999
• Status: Expired due to Term

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Villa, Flavio, Barlocchi, Gabriele
• Primary Examiner(s): Everhart, Caridad
• Assistant Examiner(s): Lee, Calvin
• Application Number:
  US09/545,260
• Time in Patent Office: 1,362 Days
• Field of Search: 438/52, 438/107, 438/627-667, 438/700, 438/960, 438/456, 438/421, 438/422, 438/411, 216/2-87, 735/14, 257/418, 257/419, 257/434, 257/619
• US Class Current: 438/422
• CPC Class Codes: H01L 21/2007 Bonding of semiconductor wafers to insulating substrates or to semiconducting substrates using an intermediate insulating layer H01L21/2011 takes precedence; bonding of semiconductor wafers to semiconductor wafers for junction formation H01L21/187
• CPC Class Codes: H01L 21/30608 Anisotropic liquid etching H01L21/3063 takes precedence
• CPC Class Codes: H01L 21/3086 characterised by the process involved to create the mask, e.g. lift-off masks, sidewalls, or to modify the mask, e.g. pre-treatment, post-treatment
• CPC Class Codes: H01L 21/76251 using bonding techniques
• CPC Class Codes: H01L 21/76262 using selective deposition of single crystal silicon, i.e. SEG techniques
• CPC Class Codes: H01L 21/764 Air gaps H01L21/76264 takes precedence

Abstract

A method of forming buried cavities in a wafer of monocrystalline semiconductor material with at least one cavity formed in a substrate of monocrystalline semiconductor material by timed TMAH etching silicon; covering the cavity with a material inhibiting epitaxial growth; and growing a monocrystalline epitaxial layer above the substrate and the cavities. Thereby, the cavity is completely surrounded by monocrystalline material. Starting from this wafer, it is possible to form a thin membrane. The original wafer must have a plurality of elongate cavities or channels, parallel and adjacent to one another. Trenches are then excavated in the epitaxial layer as far as the channels, and the dividers between the channels are removed by timed TMAH etching.

Claims

1. A method for forming a membrane of monocrystalline semiconductor material, arranged above an air gap, comprising:

forming a wafer of monocrystalline semiconductor material, comprising forming a plurality of cavities in the material and growing a monocrystalline epitaxial layer on the material to encase the plurality of cavities to thereby form a plurality of buried channels adjacent and separated from each other by dividers;

forming trenches in said epitaxial layer, said trenches extending transversely to said buried channels from a surface of said wafer, as far as said buried channels; and

removing said dividers.

2. The method of claim 1 wherein said buried channels have walls covered by a layer inhibiting epitaxial growth, and wherein removing said dividers comprises:

removing said layer inhibiting epitaxial growth; and

anisotropically etching said semiconductor material.

3. The method of claim 2 wherein said anisotropic etching comprises TMAH timed etching.

4. The method of claim 1, further comprising, after forming third trenches, the forming of second regions extending on the walls of said trenches.

5. A method of forming encased cavities in a substrate of monocrystalline semiconductor material, comprising:

forming a plurality of trenches in the substrate;

coating lateral walls of the plurality of trenches with material resistant to etching;

anisotropically etching the substrate through each of the plurality of trenches to form a cavity below each of the plurality of trenches; and

further comprising forming third trenches in the substrate, the third trenches extending transversely to the cavities from a surface of the substrate; and

removing monocrystalline semiconductor material through the third trenches to connect the plurality of cavities and form an air gap in the substrate with a membrane of monocrystalline semiconductor material arranged above the air gap;

coating the walls of the cavity with a material inhibiting epitaxial growth; and

growing a monocrystalline epitaxial layer on the substrate to encase the at least one trench and cavity.

6. A method for forming buried cavities in a wafer of monocrystalline semiconductor material, comprising:

forming at least one cavity in a substrate of monocrystalline semiconductor material wherein forming at least one cavity comprises forming at least one first trench in said substrate;

covering lateral walls of said at least one first trench with first protective regions of a material resistant to etching of said monocrystalline semiconductor material;

forming at least one second trench aligned with, and arranged below the at least one first trench;

anisotropically etching said substrate below said at least one first trench;

coating the cavity with TEOS to inhibit epitaxial growth; and

growing a monocrystalline epitaxial layer on said substrate and said at least one cavity to thereby obtain a wafer of monocrystalline semiconductor material containing at least one buried cavity completely surrounded by said monocrystalline material.

7. The method of claim 6, wherein the anisotropic etching comprises timed etching.

8. A method for forming buried cavities in a wafer of monocrystalline semiconductor material, comprising:

forming at least one cavity in a substrate of monocrystalline semiconductor material wherein forming at least one cavity comprises forming at least one first trench in said substrate;

covering lateral walls of said at least one first trench with first protective regions of a material resistant to etching of said monocrystalline semiconductor material;

forming at least one second trench aligned with, and arranged below the at least one first trench;

anisotropically etching said substrate below said at least one first trench;

coating the cavity with nitride to inhibit epitaxial growth; and

growing a monocrystalline epitaxial layer on said substrate and said at least one cavity to thereby obtain a wafer of monocrystalline semiconductor material containing at least one buried cavity completely surrounded by said monocrystalline material.

9. The method of claim 8 wherein the anisotropic etching comprises timed etching.