Semiconductor buried grating fabrication method

• US 20090246707A1
• Filed: 03/27/2008
• Published: 10/01/2009
• Est. Priority Date: 03/27/2008
• Status: Active Grant

• Current Assignee: Thorlabs Quantum Electronics, Inc. (Thorlabs Incorporated)
• Original Assignee: Corning Incorporated
• Inventors: Zah, Chung-En, Song, Kechang, Li, Yabo, Visovsky, Nicholas John
• Granted Patent: US 7,981,591 B2
• Time in Patent Office: Days
• US Class Current: 430/314
• CPC Class Codes: G02B 6/124 Geodesic lenses or integrated gratings
• CPC Class Codes: G02B 6/136 by etching
• CPC Class Codes: G03F 7/0005 Production of optical devices or components in so far as characterised by the lithographic processes or materials used therefor
• CPC Class Codes: H01S 5/12 the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers comprising a photonic bandgap structure H01S5/11; surface-emitting lasers H01S5/18

Abstract

Methods for forming grating profiles in semiconductor laser structures comprise the steps of providing a semiconductor wafer comprising a wafer substrate, an etch stop layer disposed over the wafer substrate, a grating layer disposed over the etch stop layer, an etch mask layer disposed over the grating layer, and a photoresist layer disposed over the etch mask layer, forming a photoresist grating pattern, transferring the photoresist grating pattern into the grating layers via dry etching, and removing the photoresist layer, selectively wet etching the grating layer to form the grating profile in the grating layer. The placement of the grating layer between the etch mask and etch stop layers controls the selective wet etching step. The method also comprises removing the etch mask layer via selective wet etching without altering the grating profile, and regrowing an upper cladding layer to produce the semiconductor laser structure.

Claims

1. A method of forming a grating profile in a semiconductor laser structure comprising:

providing a semiconductor wafer comprising a wafer substrate, an etch stop layer disposed over the wafer substrate, a grating layer disposed over the etch stop layer, an etch mask layer disposed over the grating layer, and a photoresist layer disposed over the etch mask layer, wherein the wafer substrate comprises an active lasing region;

forming a photoresist grating pattern in the photoresist layer;

transferring the photoresist grating pattern into the grating layer via dry etching;

removing the photoresist layer;

selectively wet etching the grating layer to form the grating profile in the grating layer, wherein the placement of the grating layer between the etch mask layer and the etch stop layer controls the selective wet etching;

removing the etch mask layer without altering the grating profile of the grating layer through selective wet etching; and

regrowing an upper cladding layer over the grating layer to produce the semiconductor laser structure.

2. The method of claim 1 wherein the wafer substrate is a graded index separate confinement heterostructure (GRINSCH).

3. The method of claim 1 wherein the semiconductor wafer undergoes quantum well intermixing prior to forming the photoresist grating pattern in the photoresist layer.

4. The method of claim 1 wherein the etch stop layer comprises InGaAsP and defines a thickness of about 50 nm.

5. The method of claim 1 wherein the grating layer comprises GaAs, GaInP, other group III-V semiconductor compositions, or combinations thereof, and defines a thickness of about 100 nm.

6. The method of claim 1 wherein the etch mask layer comprises GaAs, GaInP, group III-V semiconductor compositions, or combinations thereof, and defines a thickness of about 50 nm.

7. The method of claim 1 wherein the photoresist layer comprises a positive photoresist or negative photoresist, a further comprises a thickness in a range from about 25 nm to about 500 nm.

8. The method of claim 1 wherein the upper cladding layer comprises AlGaAs.

9. The method of claim 1 further comprising a contact layer comprising GaAs disposed over the upper cladding layer.

10. The method of claim 1 wherein the semiconductor laser structure is a distributed Bragg reflector (DBR) laser.

11. The method of claim 10 wherein the DBR laser is a raise ridge waveguide DBR laser.

12. The method of claim 10 wherein the DBR laser produces a power output of 700 mW at a 1060 nm wavelength.

13. The method of claim 1 wherein the layers of the semiconductor wafer are grown onto the wafer substrate via low pressure Organometallic Vapor Phase Epitaxy (MOVPE).

14. The method of claim 1 wherein the photoresist grating pattern is formed through a holography system.

15. The method of claim 14 wherein the holography system is a two beam interference holography system.

16. The method of claim 1 further comprising performing a descum procedure on the photoresist layer to produce a descumed photoresist grating pattern prior to dry etching.

17. The method of claim 1 wherein the descumed photoresist grating pattern defines a duty cycle of about 0.25 to about 0.3, or about 0.75 to about 0.8.

18. The method of claim 1 wherein the photoresist grating pattern is dry etched into the etch mask layer and the grating layer using reactive ion etching (RIE).

19. The method of claim 1 wherein the photoresist layer is removed via etching with oxygen plasma.

20. The method of claim 1 wherein the wet etching utilizes a solution of sulfuric acid and hydrogen peroxide, a solution of phosphoric acid and hydrochloride acid, or combinations thereof.

21. The method of claim 1 further comprising analyzing the grating profile using an atomic force microscope (AFM).

22. The method of claim 1 further comprising etching the semiconductor wafer prior to the regrowth step.

23. The method of claim 1 further comprising conducting a UV/Ozone treatment prior to the regrowth step.

24. A method of forming a grating profile in a semiconductor laser structure comprising:

providing a semiconductor wafer comprising a wafer substrate, an etch stop layer comprising GaAsInP disposed over the wafer substrate, a grating layer comprising GaAs disposed over the etch stop layer, an etch mask layer comprising GaInP disposed over the grating layer, and a photoresist layer disposed over the etch mask layer, wherein the wafer substrate comprises an active lasing region;

forming a photoresist grating pattern in the photoresist layer through a holography system;

conducting a descum procedure on the photoresist layer to produce a descumed photoresist grating pattern;

transferring the descumed photoresist grating pattern into the grating layer via dry etching;

removing the photoresist layer via etching;

selectively wet etching the grating layer to form the grating profile in the grating layer, wherein the placement of the grating layer between the etch mask layer and the etch stop layer controls the selective wet etching;

removing the etch mask layer without altering the grating profile of the grating layer through selective wet etching; and

regrowing an upper cladding layer over the grating layer to produce the semiconductor laser structure.