U.S. patent application number 10/341408 was filed with the patent office on 2004-02-05 for method of producing a rib waveguide.
This patent application is currently assigned to BOOKHAM TECHNOLOGY, PLC.. Invention is credited to Drake, John Paul, Tomlinson, Andrew, Zekak, Abdel Karim.
Application Number | 20040020893 10/341408 |
Document ID | / |
Family ID | 9929244 |
Filed Date | 2004-02-05 |
United States Patent
Application |
20040020893 |
Kind Code |
A1 |
Drake, John Paul ; et
al. |
February 5, 2004 |
Method of producing a rib waveguide
Abstract
A method of producing an optical grating component including
only a single continuous grating field formed in a longitudinal
waveguide rib, the method including the steps of defining a grating
in an optic chip including a portion thereof through which the
longitudinal waveguide rib is to extend, and then defining the
lateral edges of the longitudinal rib in the optic chip, whereby
any portion of the grating extending laterally beyond the lateral
width of the rib is removed in the step of defining the lateral
edges of the rib leaving a single continuous grating field that has
straight lateral grating boundaries that are laterally aligned with
the straight lateral edges of the rib.
Inventors: |
Drake, John Paul;
(Berkshire, GB) ; Tomlinson, Andrew; (Oxford,
GB) ; Zekak, Abdel Karim; (Didcot, GB) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 Pennsylvania Avenue, NW
Washington
DC
20037-3213
US
|
Assignee: |
BOOKHAM TECHNOLOGY, PLC.
|
Family ID: |
9929244 |
Appl. No.: |
10/341408 |
Filed: |
January 14, 2003 |
Current U.S.
Class: |
216/3 ;
216/2 |
Current CPC
Class: |
G02B 2006/12061
20130101; G02B 6/124 20130101; G02B 2006/12097 20130101 |
Class at
Publication: |
216/3 ;
216/2 |
International
Class: |
C23F 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 17, 2002 |
GB |
8201091.2 |
Claims
What is claimed is:
1. A method of producing an optical grating component including
only a single continuous grating field formed in a longitudinal
waveguide rib, the method including the steps of defining a grating
in an optic chip including a portion thereof through which the
longitudinal waveguide rib is to extend, and then defining the
lateral edges of the longitudinal rib in the optic chip, whereby
any portion of the grating extending laterally beyond the lateral
width of the rib is removed in the step of defining the lateral
edges of the rib leaving a single continuous grating field that is
laterally aligned with the lateral edges of the rib.
2. A method of producing an optical grating component including a
grating with straight lateral grating boundaries in a length of
longitudinal waveguide rib of uniform lateral width, the method
including the steps of (a) defining a grating in an optic chip
including a portion thereof through which said length of the
longitudinal rib is to extend, and then (b) defining the lateral
edges of said length of the longitudinal rib in the optic chip,
whereby any portion of the grating extending laterally beyond the
lateral uniform width of said length of the rib is removed in the
step of defining the lateral edges of the rib leaving a grating
with straight lateral grating boundaries that are laterally aligned
with the lateral edges of said length the rib.
3. A method of producing an optical grating component according to
claim 1, wherein the longitudinal waveguide rib includes a first
section having the grating formed therein and a second section
extending longitudinally from the first section without a grating
formed therein, and wherein the grating is defined in a selected
portion of an optic chip including a portion thereof through which
said first section of the longitudinal rib is to extend but
excluding any portion of the optic chip through which the second
section is to extend.
4. A method of producing an optical grating component according to
claim 2, wherein the longitudinal waveguide rib includes a first
section having the grating formed therein and a second section
extending longitudinally from the first section without a grating
formed therein, and wherein the grating is defined in a selected
portion of an optic chip including a portion thereof through which
said first section of the longitudinal rib is to extend but
excluding any portion of the optic chip through which the second
section is to extend.
5. A method according to claim 1, wherein the grating is formed by
a non-mask technique.
6. A method according to claim 2, wherein the grating is formed by
a non-mask technique.
7. A method according to claim 1, wherein the optic chip is a
silicon optic chip.
8. A method according to claim 2, wherein the optic chip is a
silicon optic chip.
9. A method of producing a silicon rib waveguide including a
grating in a portion thereof, the method including the steps of:
(a) providing a grating mask over a selected portion of a silicon
optic chip for use in defining the grating; (b) then defining a rib
in the silicon optic chip using a rib mask formed over the grating
mask, the step of defining the rib removing any of the grating mask
that may extend laterally beyond the lateral width of the rib; and
(c) etching the optic chip through the grating mask to define a
grating in the rib, whereby the grating is aligned laterally with
the lateral edges of the rib; wherein photoresist is used to form
the rib mask
10. A method of producing a silicon rib waveguide including a
grating in a portion thereof, the method including the steps of:
(a) providing a grating mask over a selected portion of a silicon
optic chip for use in defining the grating; (b) then defining a rib
in the silicon optic chip using a rib mask formed over the grating
mask, the step of defining the rib removing any of the grating mask
that may extend laterally beyond the lateral width of the rib; and
(c) etching the optic chip through the grating mask to define a
grating in the rib, whereby the grating is aligned laterally with
the lateral edges of the rib; wherein the grating mask is a thermal
oxide mask.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method of producing a rib
waveguide including a grating in a portion thereof.
BACKGROUND OF THE INVENTION
[0002] An integrated optic device may include a rib waveguide
including a grating formed in a portion thereof. The grating
typically comprises a parallel array of lateral trenches of
relatively small depth formed in the top surface of a longitudinal
rib of relatively large height. Such a grating has, for example,
application as a reflective element in laser devices.
[0003] Gratings are typically submicron features, whose performance
is strongly dependent on the process used to produce them.
[0004] According to one conventional method, rib waveguides
including a grating in a portion thereof are produced by first
etching selected portions of the optic chip to form a rib, then
forming a patterned grating mask over a portion of the top surface
of the rib, and etching through the patterned mask to form the
grating However this technique can suffer from "overspilling" of
the grating etch onto the low ground on one or both sides of the
rib as a result of the patterned grating mask not being correctly
aligned with the rib.
[0005] An alternative technique has been developed which involves
first forming a patterned grating mask on a portion of the optic
chip through which the rib is to extend, selectively protecting the
portion of the chip through which the rib is to extend including
also protecting the patterned grating mask, etching to define the
rib, and then etching through the patterned grating mask to define
the grating in a portion of the rib.
[0006] It is an aim of the present invention to provide a process
for producing a silicon rib waveguide including a grating in a
portion thereof.
SUMMARY OF THE INVENTION
[0007] According to a first aspect of the present invention, there
is provided a method of producing an optical grating component
including only a single continuous grating field formed in a
longitudinal waveguide rib, the method including the steps of
defining a grating in an optic chip including a portion thereof
through which the longitudinal waveguide rib is to extend, and then
defining the lateral edges of the longitudinal rib in the optic
chip, whereby any portion of the grating extending laterally beyond
the lateral width of the rib is removed in the step of defining the
lateral edges of the rib leaving a single continuous grating field
that is laterally aligned with the lateral edges of the rib.
[0008] According to a second aspect of the present invention, there
is provided a method of producing an optical grating component
including a grating with straight lateral grating boundaries in a
length of longitudinal waveguide rib of uniform lateral width, ,
the method including the steps of (a) defining a grating in an
optic chip including a portion thereof through which said length of
the longitudinal rib is to extend, and then (b) defining the
lateral edges of said length of the longitudinal rib in the optic
chip, whereby any portion of the grating extending laterally beyond
the lateral uniform width of said length of the rib is removed in
the step of defining the lateral edges of the rib leaving a grating
with straight lateral grating boundaries that are laterally aligned
with the lateral edges of said length the rib.
[0009] In one embodiment, the grating is formed by a non-mask
technique.
[0010] According to a third aspect of the present invention, there
is provided a method of producing a silicon rib waveguide including
a grating in a portion thereof, the method including the steps of:
(a) providing a grating mask over a selected portion of a silicon
optic chip for use in defining the grating; (b) then defining a rib
in the silicon optic chip using a rib mask formed over the grating
mask, the step of defining the rib removing any of the grating mask
that may extend laterally beyond the lateral width of the rib; and
(c) etching the optic chip through the grating mask to define a
grating in the rib, whereby the grating is aligned laterally with
the lateral edges of the rib; wherein photoresist is used to form
the rib mask.
[0011] According to a fourth aspect of the present invention, there
is provided a method of producing a silicon rib waveguide including
a grating in a portion thereof, the method including the steps of:
(a) providing a grating mask over a selected portion of a silicon
optic chip for use in defining the grating; (b) then defining a rib
in the silicon optic chip using a rib mask formed over the grating
mask the step of defining the rib removing any of the grating mask
that may extend laterally beyond the lateral width of the rib; and
(c) etching the optic chip through the grating mask to define a
grating in the rib, whereby the grating is aligned laterally with
the lateral edges of the rib; wherein the grating mask is a thermal
oxide mask.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Embodiments of the present invention are described
hereunder, by way of non-limiting example only, with reference to
the accompanying drawings, in which:-
[0013] FIGS. 1(a) to 1(i) show a method according to a first
embodiment of the present invention;
[0014] FIGS. 2(a) to 2(i) show a method according to a second
embodiment of the present invention; and
[0015] FIGS. 3 and 4 are schematic overhead and perspective views
of an example of an optical grating component to which the method
of the present invention is applicable.
DESCRIPTION OF A PREFERRED EMBODIMENT
[0016] In FIGS. 1(a) to 1(i), the left side shows cross-sectional
views at a portion of the optic chip at which a trench of the
grating is located in the final product, and the right side shows
cross-sectional views of a portion. of the optic chip at which a
ridge of the grating is located in the final product. Taken
together, they show how the grating is formed. For the purposes of
simplicity, the supporting silicon substrate which would normally
underlie the silicon oxide lower confinement layer 6 is not
shown
[0017] A selected portion of the thermal oxide layer 4 formed at
the top surface of the epitaxial silicon layer 2 is selectively
removed by etching to define a window 7 exposing a portion of the
surface of the silicon layer including at least the portion of the
optic chip at which the grating is to be formed (FIG. 1(b)). The
grating is then directly defined in the exposed silicon layer (FIG.
1(c)) using a technique such as ebeam writing, holography or phase
mask.
[0018] In this embodiment, lateral trenches are etched which extend
laterally beyond the width of the rib to be formed in a later step;
those portions of the lateral trenches extending laterally beyond
the width of the rib are removed in the later step of forming the
rib. This makes it possible to ensure that the grating extends
laterally right across the longitudinal rib in the final
product.
[0019] For example, the grating may comprise a parallel array of
lateral trenches of about 150 nm depth at a period of about 220
nm.
[0020] Next, a thin layer 8 of LPCVD nitride is formed over the
entire top surface of the optic chip (FIG. 1(d)). The nitride layer
serves to protect the grating from oxidation in subsequent thermal
processes.
[0021] Photoresist is used in a photolithographical technique to
then provide a rib mask 10 on the nitride layer 8 over only the
portion of the optic chip in which the rib is to be located in the
final product (FIG. 1(e)). Because the resist patterning is carried
out before the ribs are formed, i.e. on a relatively flat surface,
high resolution patterning can be carried out with greater
repeatability.
[0022] The optic chip is then subject to etching using an etchant
to which only the photoresist mask is resistant to define a rib 12
in the silicon layer, and the photoresist mask is then removed
(FIG. 1(f)). The optic chip is then heated in an oxidising
environment to form a thermal oxide layer 14 at the exposed silicon
surfaces (FIG. 1(g)). The nitride layer 8 is then stripped (FIG.
1(h)) and the thermal oxide layer 14 removed (FIG. 1(i)).
[0023] This process provides automatic alignment of the lateral
edges of the grating with the lateral edges of the rib. It is also
a relatively clean, accurate and quick process as it is a
metal-free process that does not involve a lift off
photolithography step.
[0024] Furthermore, since the grating is formed without the use of
a grating mask in this preferred embodiment, the process can be
carried out relatively quickly.
[0025] In FIGS. 2(a) to 2(i), the left side shows cross-sectional
views at a portion of the optic chip at which a trench of the
grating is located in the final product, and the right side shows
cross-sectional views of a portion of the optic chip at which a
ridge of the grating is located in the final product. Taken
together, they show how the grating is formed. For the purposes of
simplicity, the supporting silicon substrate which would normally
underlie the silicon oxide lower confinement layer 6 is not
shown.
[0026] Selected portions of the thermal oxide layer 4 formed at the
top surface of the silicon layer 2 are selectively removed by a
technique such as ebeam writing, holography or phase mask to
produce a patterned thermal oxide mask 7 which will be used at a
later stage to produce the grating (FIG. 2(b)). Such a thermal
oxide mask is relatively reliable as it can be made to be pinhole
free and of high density.
[0027] In this embodiment, the thermal oxide mask extends laterally
on either side beyond the portion of the optic chip in which the
rib is located in the final product; those portions of the mask
extending laterally beyond the width of the rib are removed in the
later step of forming the rib. This makes it possible to ensure
that the mask extends laterally right across the rib after the rib
is formed, so that the grating extends laterally right across the
longitudinal rib in the final product.
[0028] Next, a thin layer 8 of LPCVD nitride is formed over the
entire top surface of the optic chip, including over the patterned
mask 7 (FIG. 2(c)). The nitride layer serves to protect the
patterned mask during subsequent thermal processes. Photoresist is
used in a photolithographic technique to then provide a patterned
rib mask 10 on the nitride layer 8 over only the portion of the
optic chip in which the rib is to be located in the final product
(FIG. 2(d)).
[0029] The optic chip is then subject to etching with an etchant to
which only the photoresist mask is resistant to define a rib 12 in
the silicon layer (FIG. 2(e)), and the photoresist mask is then
removed (FIG. 2(f)). The optic chip is then heated in an oxidising
environment to form a thermal oxide layer 14 at the exposed silicon
surfaces (FIG. 2(f)). The nitride layer 8 is then stripped to
expose the original thermal oxide layer 4 defining the patterned
mask for producing the grating (FIG. 2(g)).
[0030] The optic chip is then subject to silicon etching using an
etchant to which the thermal oxide is resistant, such as reactive
ion etching using CHF.sub.3, to produce an array of parallel
laterally extending trenches in the top surface of the longitudinal
silicon rib 12 and thus define a grating in the top surface of the
silicon rib (FIG. 2(h)). The thermal oxide layers 8, 14 are then
removed (FIG. 2(i)).
[0031] FIGS. 3 and 4 are schematic overhead and perspective views
of an example of an optical grating component to which the
production method of the present invention is applicable. They show
a portion of an optic chip including a longitudinal rib waveguide
including an optical grating in a portion of the upper surface of
the rib. As shown in the figures, the grating is only formed along
a selected length of the rib; the rib also includes upstream and
downstream of said selected length portions that do not include a
grating. As also shown in the figures, the grating component
consists of a single continuous grating field having straight
lateral boundaries aligned with the straight lateral edges of the
rib.
* * * * *