Optical waveguides – Having particular optical characteristic modifying chemical... – Of waveguide core
Reexamination Certificate
1999-11-22
2004-05-04
Sanghavi, Hemang (Department: 2874)
Optical waveguides
Having particular optical characteristic modifying chemical...
Of waveguide core
C385S129000
Reexamination Certificate
active
06731856
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an organic waveguide having a core section made of organic polymer, which is used for optical parts such as optical integrated circuits, optical communications devices, and optical interconnections, and a manufacturing method thereof.
BACKGROUND OF THE INVENTION
As a core material of an organic waveguide, inorganic materials such as quartz glass and multi-component glass have been widely used conventionally. The feature of waveguides made of these materials is that the propagation loss is small and the propagation band is wide. Meanwhile, organic materials, despite their large propagation loss compared with inorganic materials, have been catching attention as a waveguide material due to among other things the property which allows the film to be desirably processed and to be easily made thick as well as the low costs they offer.
A common manufacturing method of an organic waveguide starts with formation of a core section by forming an organic film in an appropriate thickness and thereafter by patterning the organic film, followed by application of organic polymer as an overclad having a refractive index lower than that of the core section.
As the method of a patterning process, a method by cutting and a method by wet etching, etc., as disclosed in Japanese Unexamined Patent Publication No. 222524/1997 (Tokukaihei 9-222524) (Published Date : Aug. 26, 1997) have been available. However, the method which is widely adopted is the method by reactive ion etching (RIE) using an oxygen gas, which is convenient and which allows a high precision process.
However, RIE using an oxygen gas does not allow the use of a positive resist of novolak resin as a mask due to its small etching selective ratio with respect to the organic polymer.
Thus, there has been a method in which a silicon contained resist having a large etching selective ratio with respect to the organic polymer is used as a mask. However, in this method, it is -required to remove the resist after RIE, and due to the fact that the surface of the resist is changed in property by the oxygen ion, removal of the resist by an organic solvent is difficult.
Further, as disclosed in Japanese Unexamined Patent Publication No. 9807/1992 (Tokukaihei 4-9807) (Published Date: Jan. 14, 1992) and No. 75942/1996 (Tokukaihei 8-75942) (Published Date : Mar. 22, 1996), there has been a method available in which the core section is processed by RIE using an oxygen gas with the use of a metal such as copper or aluminium on which the photosensitive resist pattern has been transferred, wherein the metal is used as an intermediate mask on the organic polymer.
The following describes the manufacturing method of the organic waveguide employing the above method referring to FIG.
5
.
(1) First, as shown in FIG.
5
(
a
), organic polymer is applied as a buffer layer
32
on a substrate
31
by spin-coating and the substrate complex is baked.
(2) Then, organic polymer, to be a core section
33
, having a higher refractive index than that of the buffer layer
32
is applied by spin-coating followed by baking.
(3) Then, on the substrate complex, copper or aluminium is deposited as a metal mask
37
, for example, by sputtering.
(4) Then, a photoresist
36
is applied, and the photoresist
36
is patterned by photolithography.
(5) Then, as shown in FIG.
5
(
b
), the mask pattern is transferred onto the metal mask
37
by ion-milling or wet etching.
(6) Then, as shown in FIG.
5
(
c
), the organic polymer is etched by RIE using an oxygen gas to form the core section
33
.
(7) Then, as shown in FIG.
5
(
d
), the metal mask
37
is removed by wet etching, and as shown in FIG.
5
(
e
) and FIG.
5
(
f
), organic polymer having a lower refractive index than that of the core section
33
is applied as an overclad
35
followed by baking. The conventional organic waveguide is manufactured by the described steps.
However, in the described waveguide having the overclad made of organic polymer, the organic polymer is applied by spin-coating so as to cover the core section
33
having a step-difference. Thus, as shown in FIG.
5
(
e
), the overclad
35
tends to be thick at side portions of the organic waveguide, or a waveguide of a buried type as shown in FIG.
5
(
f
) results.
When such a organic waveguide is to be coupled with other optical elements such as a semiconductor laser, a further process is required on the overclad
35
on the side portions, and for this reason it has been difficult in conventional organic waveguides to realize integration of other optical elements on the same substrate.
Alternatively, air may be utilized as an overclad instead of forming the overclad
35
. However, this is not without problems that a difference in refractive index becomes too large and the core section cannot be protected, to name a few.
Further, when the process is to be carried out by RIE using a metal mask or a silicon contained resist as a mask, a residue is likely to be generated on the organic polymer by the mask material, and it becomes difficult to remove the mask after RIE. Furthermore, because the adhesion between metal and organic polymer is generally poor, when used as a mask, the metal is easily removed and it becomes difficult to carry out high precision patterning.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an organic waveguide which can be easily integrated with other optical elements, and which generates less residue in an RIE process, and which can be manufactured with less steps, and a manufacturing method thereof, and also to provide an optical part on which such an organic waveguide and an optical element such as a semiconductor laser or photoreceptive element are integrated on the same substrate.
In order to achieve this object, an organic waveguide in accordance with the present invention includes a core section made of organic polymer, and a clad section covering the core section and made of inorganic dielectric having a lower refractive index than that of the core section. Further, in the organic waveguide in accordance with the present invention, it is preferable that the inorganic dielectric to be the clad section is formed by a sputtering method, CVD method, or vapor deposition method.
Further, in order to achieve the above object, a manufacturing method of the organic waveguide of the present invention includes the step of forming an inorganic dielectric layer as the clad section on an organic polymer layer processed into the core section, and the inorganic dielectric layer is formed by a CVD method, sputtering method, or vapor deposition method.
With the above arrangement and method, because the clad section is made of inorganic dielectric having a lower refractive index than that of the core section, it is possible to use the sputtering method, CVD method, or vapor deposition method, etc., to form the clad section, which were not allowed with the organic polymer, thus forming the clad section in the same shape as that of the core section with ease.
As a result, an organic waveguide which can be desirably coupled with other optical elements can be obtained without the conventional process on the side portions of the clad section, thereby allowing integration with other optical elements and simplifying manufacturing steps.
In the organic waveguide of the present invention, it is further preferable that a portion of the clad section constitutes a masking clad section which serves as a mask when processing the core section.
Further, the manufacturing method of the organic waveguide of the present invention may include the steps of forming an organic polymer layer which becomes a core section by processing; forming an inorganic dielectric layer to be a clad section on the organic polymer layer; processing the inorganic dielectric layer into a shape covering only an upper surface of the core section; and processing the inorganic dielectric layer into the core section by dry etching using as a mask the inorganic dielectric layer processed.
With this arrangement
Fujita Hideaki
Ishii Yorishige
Kurata Yukio
Tamura Toshihiro
Knauss Scott
Sanghavi Hemang
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