Process for making optical waveguides

• US 6,231,771 B1
• Filed: 04/05/1999
• Issued: 05/15/2001
• Est. Priority Date: 12/14/1998
• Status: Expired due to Fees

• Current Assignee: Bookham Incorporated (Oclaro (North America), Inc.)
• Original Assignee: Bookham Incorporated (Oclaro (North America), Inc.)
• Inventors: Drake, John Paul
• Primary Examiner(s): ALANKO, ANITA KAREN
• Application Number:
  US09/286,415
• Time in Patent Office: 771 Days
• Field of Search: 216/2, 216/24
• US Class Current: 216/24
• CPC Class Codes: G02B 2006/12097 Ridge, rib or the like
• CPC Class Codes: G02B 2006/12176 Etching
• CPC Class Codes: G02B 6/122 Basic optical elements, e.g. light-guiding paths
• CPC Class Codes: G02B 6/131 by using epitaxial growth epitaxial growth for semiconductors H01L21/02365
• CPC Class Codes: G02B 6/30 for use between fibre and thin-film device

Abstract

A process for treating a waveguide structure which comprises a silicon substrate with an integrally formed rib waveguide is described. The waveguide has an end portion with a facet, the end portion overhanging the silicon substrate and having an oxide layer on its underside protruding from the facet of the waveguide. A nitride layer extends over the upper surface of the waveguide and the facet. The treatment process involves etching the oxide layer from the underside, growing a new oxide layer, etching the nitride layer and then depositing a new nitride layer.

Claims

1. A process for treating a waveguide structure comprising:

a silicon substrate with an integrally formed rib waveguide, the waveguide comprising an end portion with a facet, the end portion overhanging the silicon substrate and having an oxide layer on its underside protruding from the facet of the waveguide, and a nitride layer extending over the upper surface of the waveguide and the facet, the process comprising;

i) carrying out an oxide etch step to remove the oxide layer from the underside;

ii) carrying out an oxide growth step to form a new oxide layer on exposed silicon on the underside, said new oxide layer terminating at the facet;

iii) carrying out a nitride etch step to remove the nitride layer; and

iv) depositing a new nitride layer extending over the upper surface and facet without protruding beyond the facet, such that silicon nitride is formed on the facet.

2. A process according to claim 1, wherein the waveguide structure comprises an unwanted layer of oxide on the facet and wherein the process comprises an additional step (v) after step (iii) of removing the unwanted oxide layer.

3. A process according to claim 1, wherein step (iv) is a blanket deposition step.

4. A process according to claim 1, wherein the thickness of the new nitride layer is controlled to control the optical properties of the facet.

5. A process for making a waveguide structure in a silicon-on-insulator wafer comprising a silicon substrate, a layer of oxide on top of the silicon substrate and a layer of epitaxial silicon on top of the layer of oxide, the process comprising:

defining a rib waveguide in the epitaxial layer;

etching through the epitaxial layer on either side of the rib waveguide at an end portion thereof to expose the buried oxide layer;

depositing oxide and nitride layers successively on the rib waveguide;

undercutting the end portion to form a V-groove in the silicon substrate for aligning an optical fibre to the waveguide structure, said undercutting step leaving an unwanted part of the buried oxide layer extending beyond an end facet of the rib waveguide; and

treating the waveguide structure by a process as defined hereinabove in accordance with claim 1.

6. A process according to claim 2, wherein the waveguide structure comprises an unwanted layer of oxide on the facet and wherein the process comprises an additional step (v) after step (iii) of removing the unwanted oxide layer.

7. A process according to claim 3, wherein step (iv) is a blanket deposition step.

8. A process according to claim 4, wherein the thickness of the new nitride layer is controlled to control the optical properties of the facet.