Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD OF MANUFACTURING OPTICAL WAVEGUIDE DEVICE
USING INDUCTIVELY COUPLED PLASMA SYSTEM
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a device for
optical communications, and more particularly, to a method of manufacturing an
optical waveguide device.
2. Description of the Related Art
An optical waveguide device is a basic optical transmission device for
transmitting an optical signal, among several optical devices constituting a
lightwave circuit.
The optical waveguide device includes lower and upper cladding layers
formed on a substrate, and an optical waveguide for waveguiding light formed
between the lower and upper cladding layers. The optical waveguide must be
uniformly patterned to transmit light. To do this, a process for forming a core layer
on the lower cladding layer and patterning the core layer is required.
The core layer is patterned by an etch process using a reactive ion etching
(RIE) system as shown in FIG. 1.
To be more specific, a core layer and a mask pattern exposing a
predetermined area of the core layer are sequentially formed on a substrate 40.
The mask pattern is usually formed of photoresist. The resultant substrate 40 isloaded on a cathode electrode 43 of the RIE system as shown in FIG. 1. Radio
frequency (RF) power generated by a RF power generator 41 is applied to the
cathode electrode 43, and a direct current (DC) bias is applied to an upper
electrode 45 spaced apart a predetermined distance and opposite to the cathode
electrode 43. Simultaneously, a reactive gas is supplied into the RIE system to
allow plasma to be generated from the reactive gas by the RF power applied to
the cathode electrode 43. The thus-generated plasma reaches the substrate 40
and reacts with the core layer exposed by the mask pattern, thereby patterning the
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core layer. Then, the mask pattern, i.e., a remaining photoresist pattern, is removed.
In such an etching method using the RIE system, the etch speed is low.
For example, when a silica layer is used as the core layer, the etch speed is very
low, i.e., about 300A/min to 500~/min. Thus, in order to form an optical
waveguide by etching a core layer having a thickness of about 8,um or more,
etching for period of about 3 to 5 hours is required. Therefore, the productivity of
a process for manufacturing an optical waveguide device is degraded.
A method of increasing RF power can be used to increase the etch speed.
In this method, the concentration of the generated plasma is increased by
increasing the RF power, to thus increase the energy for etching. However, when
increasing the RF power, another problem may occur in that the DC bias voltage
applied to the upper electrode 45 increases to an abnormal level. Such an
increase in DC bias may damage the optical waveguide or the lower cladding
layer and substrate. This kind of damage lowers the characteristics of a lightwave
circuit including an optical waveguide device.
Meanwhile, when the mask pattern is formed of photoresist, failure in
photoresist pattern may be produced due to a restriction in the resolution
depending on the thickness of the photoresist. This failure in photoresist pattern
may generate defects in the profile or shape of the core layer pattern, i.e., optical
waveguide. Thus, an optical transmission error may be generated.
To be more specific, the optical waveguide must generally be about 8,um
high. Thus, the photoresist pattern thickness required for an etching process must
be kept without being completely consumed until the core layer is completely
etched out. An etch selection ratio of a material layer, i.e., a silica layer, used as
the core layer to the photoresist pattern is about 1:1. Thus, a photoresist pattern
having a thickness of about 10,um or more is required to etch the core layer
having a thickness of around 8,um.
The restriction in the resolution is accompanied by exposure and
development process for forming the photoresist pattern having the above-
mentioned large thickness. Accordingly, photoresist pattern failures may begenerated by the exposure or development inferiorities. Also, failure may be
generated on the profile or shape of the core layer pattern, i.e., ihe optical
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waveguide obtained by the process for patterning the core layer using the failedphotoresist pattern.
SUMMARY OF THE INVENTION
To solve the above problems, it is an objective of the present invention to
provide a method of manufacturing an optical waveguide, by which productivity isincreased since a core layer patterning process can be performed at high speeds.It is another objective of the present invention to provide a method of
manufacturing an optical waveguide, by which the profile, shape, or another
aspect of an optical waveguide formed by achieving a thinner mask pattern can beimproved by introducing a mask pattern having a high etch selectivity with respect
to a core layer.
To achieve the first objective, in a method of manufacturing an optical
waveguide, first, a lower cladding layer and a core layer are formed on a
substrate. The core layer is a silica layer, an optical polymer layer, or a single
crystal oxide layer.
A mask pattern exposing the core layer is formed on the core layer. The
mask pattern is formed of a photoresist layer, an amorphous silicon layer, or a
silicide layer. Alternatively, the mask pattern may be formed of a metal layer such
as a chrome layer or a titanium layer. The metal layer is formed by sputtering or
electron beam deposition.
The step of forming the mask pattern is performed as follows. A photoresist
pattern exposing the core layer is formed on the core layer. The metal layer is
formed on the resultant structure on which the photoresist pattern is formed. A
metal mask pattern exposing the core layer is formed by removing the photoresistpattern while simultaneously removing a part of the metal layer formed on the
photoresist pattern.
Alternatively, the step of forming the mask pattern may be formed as
follows. The metal layer is formed on the core layer. A photoresist pattern
exposing the metal layer is formed on the metal layer. A metal mask pattern
exposing the core layer is formed by patterning the exposed metal layer using the
photoresist pattern as a patterning mask. The step of patterning the exposed
metal layer is performed using a dry or wet etching method.
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The substrate having the mask pattern formed thereon is formed on a
cathode electrode of an inductively coupled plasma system including the cathode
electrode, an upper electrode opposing the cathode electrode at predetermined
intervals, and an inductively coupled plasma coil interposed between the upper
electrode and the cathode electrode.
A plasma from a reaction gas is generated by supplying the reaction gas to
the inductively coupled plasma system and applying first and second RF power
respectively to the cathode electrode and the inductively coupled plasma coil, to
pattern the core layer exposed by the mask pattern, into an optical waveguide.
The reaction gas includes a fluoride gas such as a carbon tetrafluoride gas or asulfur hexafluoride gas. Then, an upper cladding layer covering the optical
waveguide is formed.
To achieve the second objective, in a method of manufacturing an optical
waveguide device, a lower cladding layer and a core layer are sequentially on a
substrate. The core layer is a silica layer, an optical polymer layer, or a single
crystal oxide layer.
A metal mask pattern exposing the core layer is formed on the core layer.
The metal mask pattern is formed of a chrome layer or a titanium layer. The
metal mask pattern is formed by sputtering or electron beam deposition.
The step of forming the metal mask pattern is performed as follows. A
photoresist pattern exposing the core layer is formed on the core layer. The metal
layer is formed on the resultant structure on which the photoresist pattern is
formed. A metal mask pattern exposing the core layer is formed by removing the
photoresist pattern while simultaneously removing a part of the metal layer formed
on the photoresist pattern.
Alternatively, the step of forming the metal mask pattern may be performed
as follows. The metal layer is formed on the core layer. A photoresist pattern
exposing the metal layer is formed on the metal layer. A metal mask pattern
exposing the core layer is formed by patterning the exposed metal layer using the
photoresist pattern as a patterning mask. The step of patterning the exposed
metal layer is performed using a dry or wet etching method.
The substrate having the metal mask pattern formed thereon is formed on a
cathode electrode of an inductively coupled plasma system including the cathode
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electrode, an upper electrode opposing the cathode electrode at predetermined
intervals, and an inductively coupled plasma coil interposed between the upper
electrode and the cathode electrode.
A plasma from a reaction gas is generated by supplying the reaction gas to
the inductively coupled plasma system and applying first and second RF power
respectively to the cathode electrode and the inductively coupled plasma coil, to
pattern the core layer exposed by the mask pattern, into an optical waveguide.
The reaction gas includes a fluoride gas such as a carbon tetrafluoride gas or asulfur hexafluoride gas. Then, an upper cladding layer covering the optical
waveguide is formed.
According to the present invention, productivity is increased since a core
layer patterning process can be performed at high speeds. Also, a mask pattern
having a high etch selectivity with respect to the core layer is employed, thus
allowing improvement of the profile or shape of the optical waveguide formed by
accomplishing a thinner mask pattern.
BRIEF DESCRIPTION OF THE DRAWINGS
The above objectives and advantages of the present invention will become
more apparent by describing in detail preferred embodiments thereof with
reference to the attached drawings in which:
FIG. 1 is a cross-section of a reactive ion etching (RIE) system;
FIGS. 2 through 5 are cross-sectional views illustrating a method of
preparing a mask pattern which is used in manufacturing an optical waveguide
device according to a first embodiment of the present invention;
FIG. 6 is a cross-sectional view illustrating a step for manufacturing an
optical waveguide using the mask pattern prepared according to the first
embodiment of the present invention;
FIG. 7 is a cross-section of an inductively coupled plasma system which is
used in manufacturing an optical waveguide;
FIG. 8 is a cross-sectional view illustrating a step of completing the optical
waveguide device according to the first embodiment of the present invention; and
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FIGS. 9 through 11 are cross-sectional views illustrating a method of
manufacturing an optical waveguide device according to a second embodiment of
the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The embodiments of the present invention can be modified into various
other forms, and the scope of the present invention must not be interpreted as
being restricted by the embodiments. The embodiments are provided to more
completely explain the present invention to those skilled in the art. In the
drawings, the shapes or else of members are exaggerated or simplified for clarity.
Like reference numerals in the drawings denote the same members.
FIGS. 2 through 5 are cross-sectional views illustrating a method of
preparing a mask pattern which is used in manufacturing an optical waveguide
device according to a first embodiment of the present invention.
FIG. 2 shows the step of forming a lower cladding layer 200 and a core
layer 300 on a substrate 100.
To be more specific, the lower cladding layer 200 and the core layer 300
are sequentially formed on a flat substrate 100 made of silicon or glass. The core
layer 300 is patterned later as an optical waveguide. Thus, the core layer 300 is
formed of a material through which light can be guided or propagated. Also, the
core layer 300 is formed of a material having a larger refractive index than thelower cladding layer 200.
For example, in the case of a silica optical waveguide, a silica layer
containing oxidized silicon (SiO2) as a main component is used as the core layer300. Alternatively, the core layer 300 may be formed as an organic material layer
such as a single crystal oxide layer or an optical polymer. The present
embodiment takes as an example the case of using a silica layer as the core layer
300, but the present invention is not limited to the embodiment.
FIG. 3 shows the step of forming a photoresist pattern 450 on the core
layer 300.
To be more specific, the photoresist pattern 450 exposing a predetermined
area of the core layer 300 is formed on the core layer 300. Here, the photoresist
pattern 450 covers a portion of the core layer 300 to be etched out later.
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FIG. 4 shows the step of forming a metal layer 500 on the entire surface of
the resultant structure on which the photoresist pattern 450 is formed.
The metal layer 500 is formed on the entire surface of the resultant
structure on which the photoresist pattern 450 is formed. The metal layer 500 isformed of a metal having a large etch selectivity with respect to the core layer300. That is, when the silica layer is used as the core layer 300, the metal layer
500 is formed of titanium (Ti) or chromium (Cr). Preferably, the metal layer 500 is
formed of chromium (Cr).
The metal layer 500 is formed by a deposition method using a sputtering
system or an electron beam deposition system.
FIG. 5 shows the step of forming a mask pattern 550.
The mask pattern 550 is formed by removing the photoresist pattern 450
and the metal layer 500 formed on the photoresist pattern 450 using a lift-off
method. The lift-off method is performed using a chemical solvent. Here, the
chemical solvent must be able to solve and remove the photoresist pattern 450
according to the quality of the material of the photoresist pattern 450. For
example, acetone or the like is used as the chemical solvent. The chemical
solvent solves and removes the photoresist pattern 450.
When the photoresist pattern 450 is solved, the metal layer 500 deposited
on the photoresist pattern 450 is also removed. Thus, only the metal layer 500
deposited directly on the core layer 300 exposed by the photoresist pattern 450
remains, thereby forming the mask pattern 550.
As described above, the mask pattern 550 is formed of a material having a
large etch selectivity with respect to the lower core layer 300. Accordingly, the
mask pattern 550 can be formed more thinly than a mask pattern formed of
photoresist. Thus, the metal mask pattern 550 can be accurately formed by the
lift-off method.
The present embodiment describes the mask pattern 550 formed of the
chrome layer as described above, but the material of the mask pattern 550 can
vary according to the material of the core layer 300 to be patterned later. For
example, the mask pattern 550 can use a metal layer such as titanium layer, a
polymer layer such as a photoresist layer, an oxide layer such as an oxidized
silicon layer, a dielectric layer such as amorphous silicon layer, or a silicide layer.
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FIG. 6 is a cross-sectional view illustrating a step for forming an optical
waveguide 350 by patterning the core layer 300. FIG. 7is a cross-section of an
inductively coupled plasma (ICP) system which is used in forming the optical
waveguide 350.
The ICP system is comprised of a cathode electrode 600, an upper
electrode 700 spaced apart a predetermined distance and opposite to the cathode
electrode 600, and an ICP coil 900. A first RF power generated by a first RF
power generator 800 is applied to the cathode electrode 600, and a DC bias is
applied to the upper electrode 700. Also, a second RF power is applied to the
ICP coil 900. The entire configuration of the ICP system is similar to that of aconventional RIE system, except that the ICP coil 900 is introduced, and that the
second RF power is applied to the ICP coil 900.
As described above, a substrate 100 on which the core layer 300 and the
mask pattern 550 are formed is loaded on the cathode electrode 600 of the ICP
system. A reactive gas is supplied into the ICP system via a gas supply line (not
shown). A first RF power is applied to the cathode electrode 600, a second RF
power is applied to the ICP coil, and a DC bias is applied to the upper electrode
700.
The elements of the reaction gas supplied into the ICP system are excited
to a plasma phase by the first and second RF powers applied respectively to the
cathode electrode 600 and the ICP coil 900. Here, the plasma is generated in
various forms according to conditions such as the first RF power, the second RF
power, a partial pressure in the ICP system, the type of reaction gas, the supply
amount of the reaction gas, or the output of the ICP system.
The plasma contains elements of the reaction gas, ions excited from the
reaction gas, a reactive radical, electrons, etc. Here, the excited ions are
accelerated by the first RF power applied to the cathode electrode 600, and the
accelerated ions collide with the substrate 100. This ion bombardment causes
selective etching of the core layer 300 exposed by the mask pattern 550.
At this time, the movement of electrons (e~) in the plasma is changed by the
second RF power applied to the ICP coil 900. That is, the electrons in the plasma
make a spiraling motion as well as a rectilinear motion. Accordingly, the electrons
and the elements of the reaction gas, or the electrons and the ions in the plasma
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are more likely to collide with each other. Thus, the probability of generating
plasma increases, to thus increase the concentration of plasma.
This increase in the concentration of plasma indicates an increase in the
concentration of the ions in the plasma, radicals, or electrons. Such an increase
in ions, etc. augments an ion bombardment effect, thus allowing faster etching of
the core layer 300 exposed by the mask pattern 550.
In the present embodiment, a reaction gas including a fluoride gas is used
as the reaction gas. For example, a carbon tetrafluoride gas (CF4) which can
generate carbon fluoride ion (CFX) and fluorine radical, or a sulfur hexafluoride
gas (SF6) which can generate fluorine ion and fluorine radical is supplied as the
reaction gas.
This supplied fluoride gas is excited into a plasma phase by the first RF
power applied to the cathode electrode 600 and the second RF power applied to
the ICP coil 900. At this time, CFX, CFX, Fx, F-, F and electron (e-) exist
within plasma which is generated when CF4 is used as the reaction gas. Also,
SFX; SFX+, Fx, F+, F and e- exist within a plasma which is generated when SF6
is used as the reaction gas.
Here, the F+ or CFX is accelerated by the first RF power applied to the
cathode electrode 600, and collides with the substrate 100. Accordingly, the core
layer 300 is etched by the ion bombardment due to the F+ or CFX.
As described above, the concentration of ions which causes the ion
bombardment due to the spiral motion of the e- within the plasma by the second
RF power applied to the ICP coil 900, such as F+ or CFx, is increased. Thus,
the etch speed of the core layer 300 becomes higher.
In the present embodiment, an optical waveguide 350 having a thickness of
about 8,um or more can be formed using concrete etch conditions which will be
exemplified later. For example, about 10sccm (standard cubic centimeter per
minute) to 50sccm of an SF6 or CF4 gas is supplied to an ICP system. Here, the
air pressure in the lCP system is maintained at about 3 to 30mTorr. Also, about
10 to 400W of the first RF power is applied to the cathode electrode 600, and
about 100 to 1500W of the second RF power is applied to the ICP coil 900.
Under the above-described etch conditions, the silica layer used as the core
layer 300 can be etched at an etch speed of about 3000A/min or higher. Here,
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when a chrome layer is used as the mask pattern 550, it can accomplish the etch
selectivity with the core layer 300 (i.e., the chrome layer) of about 1 :65. That is,
when the chrome layer used as the mask pattern 550 is consumed by about 1A,
the silica layer used as the core layer 300 is etched by a thickness of about 65A
and removed.
Accordingly, the mask pattern 550, i.e., the chrome layer, can be introduced
more thinly. A thinner lower photoresist layer for patterning the chrome layer
using the lift-off method can also be introduced, allowing accomplishment of a
photoresist pattern in high-resolution. Thus, the profile or shape of the chromelayer pattern formed by the lift-off method, i.e., the mask pattern 550, is improved,
so that a mask pattern 550 having a more accurate pattern is achieved.
An etch method performed under the etch condition of using the fluoride-
family gas provides high anisotropic etching characteristics. Thus, the sidewalls of
the optical waveguide 350 are sloped at almost right angles to the surface of the
substrate 100. That is, the optical waveguide 350 having an excellent sidewall
profile can be achieved, and more uniform sidewall characteristics can be
obtained.
According to the first embodiment of the present invention, the optical
waveguide 350 of 8,um or higher thickness having an excellent profile can be
formed in a shorter time by the above-described effect.
FIG. 8 is a cross-sectional view illustrating a step of completing the optical
waveguide device by forming an upper cladding layer 250 covering the optical
waveguide 350.
After the mask pattern 550 remaining on the waveguide 350 is removed, the
upper cladding layer 250 covering the waveguide 350 is formed. The upper
cladding layer 250 is formed of a material having a lower refractive index than the
material of the waveguide 350. Preferably, the upper cladding layer 250 is formed
of the same material as that of the lower cladding layer 200.
FIGS. 9 through 11 are cross-sectional views illustrating a method of
manufacturing an optical waveguide device according to a second embodiment of
the present invention.
The same reference numerals in the second embodiment as those in the
first embodiment denote the same members. In the first embodiment, the mask
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pattern 550 is formed by patterning the metal layer 500 using the lift-off method.
However, in the second embodiment, a mask pattern 550a is formed by patterning
a metal layer 500a using a selective etching process.
Referring to FIG. 9, the lower cladding layer 200 and the core layer 300 are
sequentially formed on the substrate 100 as in the hrst embodiment. The metal
layer 500a having a large etch selectivity with respect to the core layer 300 isformed on the core layer 300 according to the material of the core layer 300 to be
etched. For example, the metal layer 500a is formed of Ti or Cr. The metal layer500a is formed by sputtering or electron beam deposition.
FIG. 10 is a cross-sectional view illustrating the step of forming the mask
pattern 550a by patterning the metal layer 500a.
A photoresist pattern 450a exposing a part of the metal layer 500a is
formed on the metal layer 500a. The exposed metal layer 500a is etched by using
the photoresist pattern 450a as an etch mask, thereby forming the mask pattern
550a, i.e., a metal mask pattern, exposing a part of the core layer 300. A wet
etching method or a dry etching method using a plasma can be used to etch the
metal layer 500a.
The mask pattern 550a is formed of a metal having a large etch selectivity
with respect to the lower core layer 300, so that it can be formed thinly. The
photoresist pattern 450a for forming the mask pattern 550a can also be formed
thinly, thus allowing formation of a photoresist pattern 450a in high-resolution.
Therefore, the profile or shape of the mask pattern 550a is improved.
FIG. 11 is a cross-sectional view illustrating the step of forming an optical
waveguide 350 by patterning the core layer 300.
The optical waveguide 350 is formed by etching a part of the exposed core
layer 300 using an etching method using an ICP system. For example, the core
layer 300 is selectively patterned by a reaction gas such as SF6 or CF4 gas.
Thus, the effect as described in the first embodiment can be obtained. Then, theremaining etch mask 550a is removed, thus forming the upper cladding layer 250
as shown in FIG. 8.
As described above, the core layer can be patterned more quickly by using
the reaction gas such as SF6 orCF4 and the ICP system which can generate
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fluorine ions or fluorocarbon ions. Therefore, productivity of manufacturing theoptical waveguide device can be improved.
Also, a high etch selectivity with the core layer can be accomplished by
introducing a metal mask pattern, etc., so that a thinner mask pattern can be
introduced. Furthermore, high anisotropic etching characteristics can be achieved,
allowing an excellent profile close to the perpendicularity of the optical waveguide
to be formed.
The present invention was described in detail with reference to the above-
described embodiments, but the present invention is not limited to the
embodiments. It is apparent that various modifications or improvements may be
effected within the technical spirit of the present invention by those skilled in the
art.
