Optical Backplane Mirror

• US 20140363120A1
• Filed: 06/10/2013
• Published: 12/11/2014
• Est. Priority Date: 06/10/2013
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Stephens, Tab A., Pelley, Perry H., McShane, Michael B.
• Granted Patent: US 9,810,843 B2
• Time in Patent Office: Days
• US Class Current: 385/14
• CPC Class Codes: G02B 2006/12061 Silicon
• CPC Class Codes: G02B 2006/12104 Mirror; Reflectors or the like
• CPC Class Codes: G02B 6/125 Bends, branchings or intersections
• CPC Class Codes: G02B 6/131 by using epitaxial growth epitaxial growth for semiconductors H01L21/02365
• CPC Class Codes: G02B 6/136 by etching
• CPC Class Codes: G02B 6/4214 the intermediate optical element having redirecting reflective means, e.g. mirrors, prisms for deflecting the radiation from horizontal to down- or upward direction toward a device G02B6/4246 takes precedence
• CPC Class Codes: G02B 6/43 Arrangements comprising a plurality of opto-electronic elements and associated optical interconnections

Abstract

An integrated circuit optical backplane die and associated semiconductor fabrication process are described for forming optical backplane mirror structures for perpendicularly deflecting optical signals out of the plane of the optical backplane die by selectively etching an optical waveguide semiconductor layer (103) on an optical backplane die wafer using an orientation-dependent anisotropic wet etch process to form a first recess opening (107) with angled semiconductor sidewall surfaces (106) on the optical waveguide semiconductor layer, where the angled semiconductor sidewall surfaces (106) are processed to form an optical backplane mirror (116) for perpendicularly deflecting optical signals to and from a lateral plane of the optical waveguide semiconductor layer.

Claims

1. A semiconductor fabrication process comprising:

providing a wafer comprising an optical waveguide semiconductor structure;

selectively etching the optical waveguide semiconductor structure with an anisotropic wet etch process to form an angled semiconductor sidewall surface on the optical waveguide semiconductor structure; and

processing the angled semiconductor sidewall surface on the optical waveguide semiconductor structure to form a mirror for deflecting optical signals into and out of a lateral plane that is parallel to a major wafer substrate surface.

2. The process of claim 1, where providing the wafer comprises providing an semiconductor-on-insulator substrate comprising an optical waveguide silicon layer formed over a buried oxide layer.

3. The process of claim 1, where providing the wafer comprises providing an semiconductor-on-insulator (SOT) substrate with an optical through-semiconductor via formed in the SOI substrate in optical alignment with the mirror.

4. The process of claim 1, where the optical waveguide semiconductor structure comprises a silicon layer located over a buried oxide layer.

5. The process of claim 1, where the anisotropic wet etch process comprises an etchant having high crystallographic plane selectivity, said etchant including at least one of the group consisting of KOH, EDP, TMAH, N₂H₄, and CsOH.

6. The process of claim 1, where the anisotropic wet etch process comprises a silicon orientation-dependent wet etch process that produces a first recess opening with 45 degree angled semiconductor sidewall surfaces.

7. The process of claim 1, where processing the angled semiconductor sidewall surface comprises:

selectively forming one or more patterned oxidation protection layers on the angled semiconductor sidewall surface of the optical waveguide semiconductor structure to expose a first portion of the optical waveguide semiconductor structure defining a first angled semiconductor sidewall surface and to cover a second portion of the optical waveguide semiconductor structure;

oxidizing the first portion of the optical waveguide semiconductor structure with a semiconductor oxidation process to produce an oxide layer with an angled oxide sidewall surface substantially parallel to where the first angled semiconductor sidewall surface was located prior to oxidation;

removing at least the one or more patterned oxidation protection layers to form a recess opening in the wafer; and

growing an epitaxial semiconductor layer in the recess opening from at least the second portion of the optical waveguide semiconductor structure to form the mirror at an interface between the epitaxial semiconductor layer and the angled oxide sidewall surface.

8. The process of claim 7, where oxidizing the first portion of the optical waveguide semiconductor structure comprises performing a LOCal Oxidation of Silicon (LOCOS) process to thermally oxidize the first portion of the optical waveguide semiconductor structure.

9. The process of claim 1, where processing the angled semiconductor sidewall surface comprises:

selectively forming one or more patterned oxidation protection layers to cover a first angled semiconductor sidewall surface of the optical waveguide semiconductor structure and to expose a second angled semiconductor sidewall surface of the optical waveguide semiconductor structure;

oxidizing the second angled semiconductor sidewall surface with a semiconductor oxidation process to produce an oxide mirror layer substantially parallel to the second angled semiconductor sidewall surface was located prior to oxidation;

removing at least the one or more patterned oxidation protection layers to form a recess opening in the wafer which exposes the first angled semiconductor sidewall surface; and

growing an epitaxial semiconductor layer in the recess opening from at least the first angled semiconductor sidewall surface of the optical waveguide semiconductor structure to form the mirror at an interface between the epitaxial semiconductor layer and the oxide mirror layer.

10. The process of claim 3, where processing the angled semiconductor sidewall surface comprises:

selectively forming one or more patterned dielectric mirror layers to directly cover a first angled semiconductor sidewall surface of the optical waveguide semiconductor structure which is aligned with the optical through-silicon via formed in the substrate, and to expose a second angled semiconductor sidewall surface of the optical waveguide semiconductor structure; and

forming a planarized optical semiconductor layer over the one or more patterned dielectric mirror layers on the first angled semiconductor sidewall surface by growing an epitaxial semiconductor layer from at least the exposed second angled semiconductor sidewall surface of the optical waveguide semiconductor structure.

11. The process of claim 1, where processing the angled semiconductor sidewall surface comprises forming a mirror for perpendicularly deflecting optical signals into and out of the lateral plane.

12. A method comprising:

providing a wafer comprising a semiconductor optical beam structure;

forming a patterned etch mask layer over the semiconductor optical beam structure to provide a first etch opening over a predetermined optical mirror location;

selectively etching the semiconductor optical beam structure with an anisotropic wet etch process using the patterned etch mask layer to form a first recess opening in the semiconductor optical beam structure with a first angled sidewall surface;

using the first angled sidewall surface to form a dielectric structure having a second angled sidewall surface, wherein the second angled sidewall surface of the dielectric structure is used to form an optical mirror for deflecting optical signals into and out of a lateral plane that is parallel to a major lateral surface of the semiconductor optical beam structure.

13. The method of claim 12, where using the first angled sidewall surface to form the dielectric structure comprises:

selectively forming one or more patterned dielectric layers to cover a first angled semiconductor sidewall surface of the semiconductor optical beam structure and a first portion of the semiconductor optical beam structure defining the first angled semiconductor sidewall surface, and to expose a second portion of the semiconductor optical beam structure defining a second angled semiconductor sidewall surface;

oxidizing the second portion of the semiconductor optical beam structure to produce an oxide layer with an angled oxide sidewall surface at the predetermined optical mirror location;

removing the one or more patterned dielectric layers to form a second recess opening over at least the angled oxide sidewall surface at the predetermined optical mirror location; and

growing an epitaxial semiconductor layer in the second recess opening from at least the first portion of the semiconductor optical beam structure to form the optical mirror at an interface between the epitaxial semiconductor layer and the angled oxide sidewall surface.

14. The method of claim 12, where selectively etching the semiconductor optical beam structure comprises applying an anisotropic wet etchant having high crystallographic plane selectivity, said etchant selected from the group consisting of KOH, EDP, TMAH, N₂H₄, or CsOH.

15. The method of claim 14, where the anisotropic wet etchant comprises a silicon orientation-dependent wet etchant that produces the first recess opening with 45 degree angled sidewall surfaces.

16. A semiconductor device, comprising

a first optical waveguide semiconductor structure comprising a lateral waveguide portion with an end portion for conveying optical signals in a lateral plane;

and

an optical mirror located at the end portion of the optical waveguide semiconductor structure for deflecting optical signals into and/or out of the lateral waveguide portion of the first optical waveguide semiconductor structure.

17. The semiconductor device of claim 16, where the optical mirror comprises an angled interface surface between a silicon structure and an adjacent oxide layer, where the angled interface surface is offset by 45 degrees from the lateral plane.

18. The semiconductor device of claim 16, where the optical mirror comprises a full mirror.

19. The semiconductor device of claim 16, where the optical mirror comprises a half mirror.

20. The semiconductor device of claim 16, further comprising a second optical waveguide semiconductor structure positioned on an opposite side of the optical mirror from the first optical waveguide semiconductor structure to receive a portion of an optical signal that is not reflected by the optical mirror.

21. The semiconductor device of claim 20, where the second optical waveguide semiconductor structure is a lateral structure positioned in the lateral plane.

22. The semiconductor device of claim 20, where the second optical waveguide semiconductor structure is a vertical structure positioned perpendicularly to the lateral plane.

23. The semiconductor device of claim 16, where the optical mirror deflects optical signals above the lateral plane.

24. The semiconductor device of claim 16, where the optical mirror deflects optical signals below the lateral plane and into an optical through hole via structure formed in a substrate.