Method of fabricating a modulator of the propagation losses and of the index of propagation of an optical signal

Patent metadata

Field	Value
Publication number	US-10705354-B2
Application number	US-201716319902-A
Country	US
Kind code	B2
Filing date	Jul 27, 2017
Priority date	Aug 8, 2016
Publication date	Jul 7, 2020
Grant date	Jul 7, 2020

Abstract

A method of fabricating a modulator of propagation losses and of index of propagation of an optical signal, including: following bonding of a substrate onto an encapsulated semiconductor layer including a first electrode of the modulator and prior to forming a second electrode of the modulator, the method includes: removing a base substrate onto which the encapsulated semiconductor layer is deposited to expose a face of a buried layer of dielectric material, situated under the buried semiconductor layer, without modifying thickness of the buried layer by more than 5 nm; and forming the second electrode is implemented directly on this exposed face of the buried layer such that, once the second electrode has been formed, it is the buried layer which directly forms a dielectric layer interposed between proximal ends of the electrodes of the modulator.

First claim

The invention claimed is:

1. A method of fabricating a modulator of propagation losses and of index of propagation of a guided optical signal, the method comprising:
providing a stack comprising, successively, a base substrate, a buried layer of first dielectric material, and a semiconductor layer, thickness at every point of the buried layer being equal to e 2ini to within approximately 5 nm, wherein e 2ini is a constant equal to an average thickness of the buried layer; then
etching the semiconductor layer to form a first electrode of the modulator, the first electrode including a proximal end, a distal end, and an intermediate part extending from the proximal end to the distal end to mechanically and electrically connect the proximal end and the distal end, then
encapsulating the semiconductor layer in a second dielectric material; then
bonding a substrate onto the encapsulated semiconductor layer; then
forming a second electrode of the modulator having a proximal end facing the proximal end of the first electrode, the proximal end of the first electrode and the proximal end of the second electrode being separated from each other only by a third dielectric layer, the proximal end of the first electrode, the proximal end of the second electrode, and the third dielectric layer forming a waveguide to guide the optical signal to be modulated;
wherein following the bonding of the substrate onto the encapsulated semiconductor layer and prior to the forming of the second electrode, the method comprises removing the base substrate to expose one face of the buried layer without modifying the thickness of the buried layer by more than 5 nm; and
the forming the second electrode is implemented directly on the exposed face of the buried layer such that, once the second electrode has been formed, the buried layer forms the third dielectric layer interposed between the proximal end of the first electrode and the proximal end of the second electrode.

2. The method as claimed in claim 1 , wherein:
the providing the stack comprises provision of a stack in which:
the base substrate is made of silicon,
the buried layer is a layer of thermal silicon oxide, obtained by oxidation of a surface of the base substrate at a temperature higher than 700° C.; and

the forming the second electrode comprises:
direct bonding of a layer of semiconductor material onto the exposed face of the buried layer; then
localized etching of the layer of semiconductor material to form the second electrode.

3. The method as claimed in claim 1 , wherein:
the etching of the semiconductor layer comprises a localized etching which thins the intermediate part of the first electrode without thinning the proximal end of the first electrode such that the intermediate part is thinner than the proximal end of the first electrode; and
the forming the second electrode comprises positioning of the second electrode with respect to the proximal end of the first electrode such that the proximal end of the second electrode extends on either side of the proximal end of the first electrode.

4. The method as claimed in claim 1 , wherein the forming the second electrode comprises:
localized etching which thins an intermediate part of the second electrode, the intermediate part being situated between a distal end and the proximal end of the second electrode such that the intermediate part is thinner than the proximal end of the second electrode; and
positioning of the second electrode with respect to the proximal end of the first electrode such that the first electrode extends on either side of the proximal end of the second electrode.

5. The method as claimed in claim 1 , further comprising localized doping of the semiconductor layer at a location of the proximal end of the first electrode or of the second electrode to dope a first region of the proximal end of the first electrode or of the second electrode directly in contact with the third dielectric layer more highly than a second region further away from the third dielectric layer, thickness of the first region being greater than or equal to 70 nm.

6. The method as claimed in claim 1 , wherein the thickness of the buried layer is less than or equal to 25 nm.

7. The method as claimed in claim 1 , wherein:
the etching of the semiconductor layer forms a first waveguide at a same time as the first electrode; then
the method further comprises forming, on the exposed face of the buried layer, facing the first waveguide, a second waveguide made of III-V material to amplify the optical signal, the second waveguide being coupled to the first waveguide through the buried layer.

8. The method as claimed in claim 1 , wherein the removing the base substrate comprises an operation of selective etching of at least a residual thin layer of the base substrate directly in contact with the buried layer, using a chemical agent which etches the base substrate at least 500 times faster than the buried layer.

9. The modulator of propagation losses and of index of propagation of the optical signal, fabricated by the method of fabrication in accordance with claim 1 , the modulator comprising:
a substrate extending in a plane;
the semiconductor layer encapsulated in the second dielectric material, the encapsulated semiconductor layer comprising a lower face directly facing the substrate and an upper face facing a side opposite to the substrate, the encapsulated semiconductor layer further comprising at least the first electrode of the modulator formed in the semiconductor layer, the first electrode extending, in a transverse direction parallel to the plane of the substrate, from the proximal end of the first electrode to the distal end of the first electrode via the intermediate part of the first electrode and the second dielectric material continuing, in the transverse direction, until the second dielectric material directly touches the proximal end of the first electrode, the proximal and distal ends and the intermediate part of the first electrode being flush with the upper face of the encapsulated semiconductor layer;
the second electrode made of semiconductor material having a doping of opposite sign to a doping of the first electrode, the second electrode extending from the proximal end of the second electrode to a distal end of the second electrode via an intermediate part of the second electrode, the proximal end of the second electrode being situated facing the proximal end of the first electrode and the distal end of the second electrode being situated on an opposite side to the distal end of the first electrode with respect to a plane perpendicular to the transverse direction and going through the proximal ends of the first electrode and the second electrode;
the buried layer of the first dielectric material interposed between the proximal ends of the first electrode and the second electrode, superposition of the proximal ends of the first electrode and the second electrode and of the third dielectric layer forming the waveguide configured to guide the optical signal to be modulated;
bump contacts in direct mechanical and electrical contact with, respectively, the distal ends of the first electrode and the second electrode for electrically connecting the first electrode and the second electrode to different electrical potentials to modify a density of charge carriers in the waveguide;
wherein the proximal end of the first electrode is thicker than the intermediate part of the first electrode.

10. The modulator as claimed in claim 9 , wherein the proximal end of the first electrode or of the second electrode comprises a first region directly in contact with the third dielectric layer, the first region is more highly d

Assignees

• Commissariat Energie Atomique

Inventors

• Menezo Sylvie
• Girard Olivier

Classifications

• G02F1/212

  Mach-Zehnder type · CPC title

• G02F1/025 Primary

  in an optical waveguide structure (G02F1/017, {G02F1/2257} take precedence) · CPC title

• G02F1/2257

  the optical waveguides being made of semiconducting material · CPC title

• G02F2001/212

  Physics · mapped topic