JP4449075B2 - Optical waveguide and method for manufacturing the same - Google Patents

Description

  The present invention relates to a polymer optical waveguide film and a method for producing the same.

  With the recent spread of personal computers and the Internet, information transmission demand is rapidly increasing. For this reason, it is desired to spread optical transmission having a high transmission speed to an end information processing apparatus such as a personal computer. In order to realize this, it is necessary to manufacture a high-performance optical waveguide for optical interconnection at low cost and in large quantities.

As a material for the optical waveguide, one using a resin has been conventionally known, and a polyimide having a high glass transition temperature (Tg) and excellent heat resistance is particularly expected. When the core and the clad of the optical waveguide are formed using polyimide, long-term reliability can be expected and it can withstand soldering.
Such a polymer optical waveguide is formed by, for example, forming a clad layer on a substrate such as silicon, etching the clad layer into a core shape, and coating and forming a core resin film thereon. It is manufactured by providing a clad layer made of the same material as the lower and side portions on the core (see FIG. 3).
In this way, a film-shaped optical waveguide by peeling the substrate from the polymer optical waveguide formed on the substrate is excellent in flexibility. For example, a connecting element having a curved portion that could not be realized by a conventional optical waveguide The scene of utilization is spreading.
However, in a film-like polymer optical waveguide without such a substrate, a so-called polarization dependent loss (PDL) in which the propagation loss for TM light becomes larger than the loss for TE light is observed. As a result, the insertion loss fluctuated.
Conventionally, in polymer optical waveguides manufactured on a substrate, it is known that PDLs with different propagation losses of the waveguides depending on the polarization direction of light are generated. It is considered that the polymer resin film formed exhibits birefringence (see Patent Document 1). That is, since the thermal expansion coefficient of the polymer material is one digit or more larger than the value of the substrate material such as Si, an internal stress is generated in the polymer optical waveguide in which the polymer material is laminated on the substrate. It is considered that PDL occurs due to the above. On the other hand, since the internal stress is released in the film-like polymer optical waveguide from which the substrate is peeled off, it is theoretically considered that PDL hardly occurs. However, it has now been found that PDL also occurs in a film-like polymer optical waveguide.

Japanese Patent Laid-Open No. 11-133254

  Accordingly, an object of the present invention is to provide a polymer optical waveguide film having a small PDL and a small insertion loss.

It has been found that the above problems are solved by the following polymer optical waveguide film. That is, the polymer optical waveguide film of the present invention has a first upper part formed so as to cover the lower clad (refractive index n ₁ ), the core (refractive index n ₂ ), at least the lower clad upper surface and the core side surface. A polymer optical waveguide film having a clad (refractive index n ₃ ), a first upper clad and a second upper clad (refractive index n ₄ ) formed above the core, wherein n ₁ , n ₂ , n ₃ And n ₄ satisfies the following relationship: a polymer optical waveguide film: n ₂ > n ₃ > n ₁ ≧ n ₄

The present invention also provides
A first step of forming a lower cladding (refractive index n ₁ ) on a substrate;
A second step of forming a core (refractive index n ₂ ) on the lower cladding;
A third step of forming a first upper clad (refractive index n ₃ ) so as to cover at least the upper clad upper surface and the core side surface; and a second upper portion above the first upper clad and the core A fourth step of forming a clad (refractive index n ₄ );
A fifth step of peeling the polymer optical waveguide including the lower clad, the core, the first upper clad and the second upper clad from the substrate;
(Where n ₂ > n ₃ > n ₁ ≧ n ₄ )
The manufacturing method of the polymer optical waveguide film containing this.

  According to the present invention, it is possible to provide a polymer optical waveguide film having a small PDL and, as a result, a small maximum insertion loss, and a method for producing the same.

The polymer optical waveguide film of the present invention will be described.
The polymer optical waveguide film of the present invention includes a first upper clad formed so as to cover a lower clad (refractive index n ₁ ), a core (refractive index n ₂ ), at least the lower clad upper surface and the core side surface. a polymeric optical waveguide film having a refractive index n ₃₎ and said first upper cladding and the second upper cladding formed from the top of the core (refractive index _{n 4), n 1, n} 2, n 3 and n ₄ satisfies the following relationship: Polymer optical waveguide film: n ₂ > n ₃ > n ₁ ≧ n ₄ .

  In this specification, the polymer optical waveguide film is an optical waveguide in which either a clad and a core or a clad and a core are made of a polymer material and does not include a substrate portion.

In the present specification, the lower clad is a clad layer in contact with the bottom surface of the core, for example, a layer represented by symbol 2 in the optical waveguide of the embodiment of the present invention shown in FIG. In this specification, the refractive index of the polymer resin of the lower clad is represented by n ₁ .

In the present specification, the first upper clad is a clad layer formed so as to cover at least the lower clad upper surface and the core side surface. For example, in the embodiment of the present invention shown in FIG. The layer represented. The first upper clad may be formed at the same height as the core and may not exist on the core upper surface. That is, the second upper clad may be laminated directly on the core upper surface. Alternatively, the first upper clad may be formed higher than the height of the core and cover the core upper surface. When the core upper surface is covered, the thickness of the first upper clad on the core is preferably 1/3 or less of the core height, and more preferably 2 μm or less. That is, the height of the first upper cladding on the core is preferably 1/3 or less of the core height from the core upper surface, and more preferably 2 μm or less. If the thickness of the first upper clad on the core becomes too thick, the asymmetry of the refractive index distribution structure in the vertical direction of the core becomes remarkable, and the PDL tends to increase, which is not preferable. In order to reduce the insertion loss, the surface of the first upper clad is preferably a plane parallel to the core upper surface. In this specification, the refractive index of the polymer resin of the first upper cladding is represented by n ₃ .

The second upper clad is a clad layer formed so as to cover the core upper surface and the first upper clad upper surface when the first upper clad does not cover the core upper surface. For example, in FIG. It is a layer represented by symbol 5. When the core upper surface is covered with the first upper clad, the second upper clad is a layer formed on the first upper clad. In this specification, the refractive index of the polymer resin of the second upper cladding is represented by n ₄ . The refractive index n ₁ of the lower clad and the refractive index n ₄ of the second upper clad may be different, but the difference between the two is preferably smaller and more preferably the same. When the refractive indexes of the lower cladding and the second upper cladding are greatly different, the asymmetry of the refractive index distribution structure in the vertical direction of the core becomes remarkable, and therefore the mode field shape becomes asymmetric. When the optical waveguide of the present invention is used by being bonded to an optical fiber, if the asymmetry of the mode field between the optical waveguide and the optical fiber increases, the coupling loss between the optical fiber increases and the insertion loss may increase. is there. When the first upper cladding is thin on the core, the refractive index above the core is affected according to the refractive index of the first upper cladding and the thickness on the core. It is preferable to make a slight difference between the refractive indexes of the lower clad and the second upper clad so as to ensure the symmetry of the mode field.
In this specification, the refractive index of the core 3 is represented by n ₂ .

The height and / or width of the core is about 2 μm to 10 μm. The size of the core and the thickness of the clad are appropriately selected in consideration of the respective refractive index values. For example, when the optical waveguide of the present invention is used by being joined to an optical fiber, it is effective for reducing the coupling loss that the mode fields of the optical waveguide and the optical fiber are approximate. Therefore, by selecting the size and shape of the mode field of the optical waveguide to approximate those of the optical fiber, the coupling loss can be reduced and the insertion loss can be reduced.
The thicknesses of the lower cladding, the first upper cladding, and the second upper cladding are appropriately selected as described above. For example, the thickness is about 5 μm to 30 μm (lower cladding), about 4 μm to 17 μm (first upper cladding). ) And about 5 μm to 30 μm (second upper clad).

In the polymer optical waveguide film of the present invention, the difference in refractive index between the core and the first upper clad, ie, (n ₂ −n ₃ ) is smaller than 0.2% with respect to the refractive index n ₂ of the core, and the core and the lower portion The refractive index difference from the clad or the second upper clad, that is, (n ₂ −n ₁ ) or (n ₂ −n ₄ ) is preferably smaller than 0.5% with respect to the refractive index n _{2 of the} core. That is, n ₁ , n ₂ , n _3, and n ₄ preferably satisfy the following relationship: (n ₂ −n ₃ ) / n ₂ <0.002, (n ₂ −n ₁ ) / n ₂ <0 0.005, (n ₂ −n ₄ ) / n ₂ <0.005, where n ₂ > n ₃ > n ₁ ≧ n ₄ . It has been found that the insertion loss and PDL of a polymer optical waveguide having a refractive index satisfying such a relationship are further reduced. In addition, a polymer optical waveguide having a refractive index satisfying such a relationship has an advantage that even if a relatively large core is manufactured, it does not become a multimode, and as a result, a coupling loss with an optical fiber or the like can be reduced.
In the case of a fixed optical waveguide such as a crossed optical waveguide, the smaller the difference in refractive index between n ₂ and n ₁ , the smaller the light loss at the intersection of the optical waveguide. Therefore, from such a viewpoint, in the optical waveguide film of the present invention, it is particularly preferable that (n ₂ −n ₁ ) / n ₂ <0.005.

Also, when an optical fiber is connected to the optical waveguide, the positional deviation between the optical fiber center and the core may occur in the range of about ± 1 μm. In such a case, an optical waveguide that can suppress the coupling loss as low as possible is provided. desirable. The polymer optical waveguide film of the present invention has an advantage that the coupling loss can be suppressed relatively low compared to the conventional one even when the optical fiber center and the core are misaligned when connected to the optical fiber. .
In particular, there is an advantage that the tolerance for the positional deviation in the left-right (horizontal) direction of the core is increased. For example, when an end face where a plurality of optical waveguides of the present invention are arranged in parallel is connected to an optical fiber array or the like, an allowable range between the pitch error of the optical fiber array and the pitch error of the polymer optical waveguide is increased. In addition, for example, when a guide groove for connecting an optical fiber is arranged at the end of the optical waveguide of the present invention, the tolerance of misalignment between the central axis of the optical waveguide and the central axis of the guide groove is growing.

In the polymer optical waveguide film of the present invention, the specific refractive index range of the core and each clad varies depending on the input wavelength, the core and the clad material, etc., but as an example, a specific fluorinated polyimide resin as the core and clad material And measured at an input wavelength of 1.31 μm, n ₁ = n ₄ = 1.524 to 1.521, n ₂ = 1.528 to 1.530, n ₃ = 1.525 to 1.527 It is.

  In the embodiment of the present invention, specific examples of the core material and the polymer of the lower and upper cladding materials include polyimide resins (eg, polyimide resins, poly (imide / isoindoloquinazolinedioneimide) resins, polyetherimide resins, Polyether ketone resins, polyester imide resins, etc.), silicone resins, acrylic resins, polystyrene resins, polycarbonate resins, polyamide resins, polyester resins, phenol resins, polyquinoline resins, polyquinoxaline resins, polybenzos Oxazole resins, polybenzothiazole resins, polybenzimidazole resins, and photobleaching resins (eg, polysilanes described in JP-A-2001-296438, silicone resins having a nitrone compound, DMAPN {(4 Poly (methyl methacrylate) containing N, N-dimethylaminophenyl) -N-phenylnitrone}, a dye polymer, a polyimide resin or an epoxy resin containing a nitrone compound, and water added as described in JP-A-2000-66051 Decomposable silane compounds, etc.). The resin may have a fluorine atom. Preferred examples of the polymer include a polyimide resin because of its high glass transition temperature (Tg) and excellent heat resistance, and among these, a fluorinated polyimide resin is particularly preferred.

Among the fluorinated polyimide resins, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride and 2,2′-bis (trifluoromethyl) -4,4′-diaminobiphenyl or 4 Polyimide resin synthesized from 4,4′-oxydianiline is preferred.
In the polymer optical waveguide film of the present invention, the refractive index of the core and the clad can be changed by appropriately changing the kind of the resin, whereby the core and the clad having a refractive index satisfying a certain formula of the present invention. The resulting polymer optical waveguide film can be produced.

The polymer optical waveguide film of the present invention described above is
A first step of forming a lower cladding (refractive index n ₁ ) on a substrate;
A second step of forming a core (refractive index n ₂ ) on the lower cladding;
A third step of forming a first upper clad (refractive index n ₃ ) so as to cover at least the upper clad upper surface and the core side surface; and a second upper portion above the first upper clad and the core A fourth step of forming a clad (refractive index n ₄ );
A fifth step of peeling the polymer optical waveguide including the lower clad, the core, the first upper clad and the second upper clad from the substrate;
(Where n ₂ > n ₃ > n ₁ ≧ n ₄ )
It can manufacture with the manufacturing method of a polymer optical waveguide film containing these.

The polymer optical waveguide film of the present invention is preferably
A first step of forming a lower clad (refractive index n ₁ ) by applying and drying a lower clad material solution on a substrate;
A second step of forming a core layer by applying a core material solution on the lower clad, and patterning the core layer into an optical waveguide shape to form a core (refractive index n ₂ );
A third step of forming a first upper clad (refractive index n ₃ ) by applying and drying a first upper clad material solution so as to cover the lower clad upper surface and the core side surface; A fourth step of forming a second upper clad (refractive index n ₄ ) by applying and drying a second upper clad material solution on the upper clad and the core;
A fifth step of peeling the polymer optical waveguide including the lower clad, the core, the first upper clad and the second upper clad from the substrate;
It can manufacture with the manufacturing method of a polymer optical waveguide film containing these.
Here, n ₂ > n ₃ > n ₁ ≧ n ₄ , and more preferably n ₁ , n ₂ , n ₃ and n ₄ have the following relationship:
(N ₂ −n ₃ ) / n ₂ <0.002, (n ₂ −n ₁ ) / n ₂ <0.005, (n ₂ −n ₄ ) / n ₂ <0.005, where n ₂ > n ₃ > n ₁ ≧ n ₄ is satisfied.

Any substrate may be used in the production method of the present invention, but examples include inorganic materials such as glass, quartz, silicon, silicon oxide, silicon nitride, aluminum, aluminum oxide, aluminum nitride, tantalum oxide, and gallium arsenide. A material substrate is mentioned.
In the manufacturing method, patterning the core layer into an optical waveguide shape means forming the core layer into a core (optical waveguide) shape. Specifically, for example, after a layer such as a photosensitive resist is provided on the core layer, the core-shaped resist is formed on the core layer by performing image exposure, development, etc. using the core-shaped pattern, Using this resist pattern as a mask, the core layer is used to remove unnecessary portions by, for example, etching to obtain a core, and the resist is then removed.

  In a preferred embodiment of the present invention, the third step of the manufacturing method further includes forming a first upper cladding so as to cover the core upper surface. More specifically, the third step of the manufacturing method further includes applying a first upper clad material solution until the upper portion of the core is completely covered. Further, in the third step, when the thickness of the first upper clad on the core after drying is thicker than 2 μm, the first upper clad may be removed to a height of at least 2 μm from the core upper surface. In the third step, the first upper clad covering the upper portion of the core may be removed until the core upper surface is exposed. If the thickness of the first upper clad on the core exceeds 2 μm, the PDL becomes large, which is not preferable. In order to reduce the insertion loss, the surface of the first upper cladding is preferably a plane parallel to the core upper surface, but by removing a part of the first upper cladding by a method such as etching or polishing. The upper portion of the first upper clad can be processed into a flat surface.

In addition, the manufacturing method of the polymer optical waveguide film mentioned above is an example, and it is natural that it can manufacture by the various methods known to those skilled in the art. For example, the above-described polymer optical waveguide film of the present invention covers the upper surface of the lower clad, the first step of forming the lower clad (refractive index n ₁ ) by applying and drying the lower clad material solution on the substrate. As described above, the first upper clad material solution is applied and dried to form a layer (first upper clad layer) made of the first upper clad material, and the first upper clad layer is patterned into an optical waveguide shape. Then, etching is performed to provide a groove portion for the core, and a third step of forming the first upper clad (refractive index n ₃ ), the core material solution is poured into the groove portion for the core, and the core is dried. A fourth step of forming (refractive index n ₂ ), and a second upper clad material solution is applied on the first upper clad and the core and dried to form a second upper clad (refractive index n ₄ ). First Step, the substrate, a lower cladding includes a core, a sixth step of removing the polymer optical waveguide comprising a first upper cladding and the second upper cladding, and can be manufactured by the manufacturing method of the polymer optical waveguide film.

  Hereinafter, one embodiment of the method for producing a polymer optical waveguide film of the present invention will be described with reference to FIGS. In the following example, polyimide resin is used as the core and cladding material. FIG. 1 shows a schematic perspective view of a polymer optical waveguide film of the present invention. 2 is a cross-sectional view taken along the line I-I ′ of the optical waveguide of FIG. 1. 1 and 2, the optical waveguide is formed on the lower clad 2, the core 3 mounted thereon, the first upper clad 4 formed on the side surface of the core 3, and the core 3 and the first upper clad 4. And a second upper clad 5 formed.

The core, lower clad, first upper clad, and second upper clad used for the following materials have refractive indexes satisfying the above-described formula.
First, a lower clad polyimide precursor solution is applied to the entire upper surface of the silicon substrate 1 to form a material solution film, which is dried by heating to evaporate the solvent, and then heated at a higher temperature to cure the resin. The lower clad 2 made of a polyimide resin film is formed. The lower clad polyimide precursor solution is applied by, for example, a spin coating method.

  On this lower clad 2, a core polyimide precursor solution is applied to form a material solution film, which is heated and dried to mainly evaporate the solvent, and then heated at a higher temperature to cure the resin. Then, a core layer made of a polyimide resin film is formed. As a coating method, the same method as the coating method of the polyimide precursor solution for lower clad is mentioned.

A resist is applied onto the core layer by a spin coater, dried, image exposed, and developed to form a resist pattern layer. This resist pattern layer is used as a mask for processing the core layer into the shape of the core.
By using this resist pattern layer as a mask, the core layer made of a polyimide resin film is subjected to reactive ion etching (O ₂ -RIE) with a gas mainly composed of oxygen, whereby the core 3 can be obtained. Thereafter, the resist pattern layer is peeled off.
In forming the core, it is necessary to select a method according to the required dimensional accuracy. In general, when high accuracy is required, dry etching is better than wet etching. In the case of dry etching, the surface roughness of the side surface of the core may become rough. When the surface is rough, particularly when the surface roughness is 1/20 or more of the wavelength used, it may cause scattering loss. The scattering loss becomes more prominent as the difference in refractive index between both sides of the interface increases. In addition, the rougher the surface roughness, the more prominent. Therefore, in order to reduce scattering loss, it is effective to select a method that reduces the roughness of the surface formed by etching. When it is difficult to reduce the roughness of the etch-back surface, reducing the difference in refractive index between the layers on both sides of the interface is effective in reducing scattering loss. In the configuration of the optical waveguide of the present invention, the core and the first upper clad form an interface on the side surface of the core, and the difference in refractive index between the layers on both sides of the interface is smaller than in the conventional configuration. Therefore, there is an advantage that the scattering loss can be reduced and the insertion loss can be reduced.

Next, a first upper clad polyimide precursor solution is applied so as to cover the core 3 and the lower clad 2. Examples of the application method include the methods described above.
Next, the first upper clad polyimide precursor solution film is dried by heating to evaporate the solvent, and then heated at a higher temperature to cure the resin, thereby forming a first upper clad polyimide resin film.

  Further, the first upper clad polyimide resin film is removed by, for example, etching (hereinafter also referred to as etch back) to form the first upper clad 4 made of the clad polyimide resin film. The removal of the first upper clad polyimide resin film is preferably performed to a height of at least 2 μm from the upper surface of the core 3, more preferably until the upper surface of the core 3 is exposed. FIG. 2 shows a case where the core 3 is formed by removing until the upper surface is exposed.

Thereafter, a second upper clad polyimide resin film is applied on the first upper clad 4 and the core 3, and dried and heat-cured to form the second upper clad 5. If the upper surface of the core 3 is not exposed and the core is covered with the first upper clad 4, a second upper clad polyimide resin film is applied onto the first upper clad 4, dried and The second upper clad 5 is formed by heat curing.
When the second upper cladding is formed after the first upper cladding is formed and etched back, it is preferable to pay attention to the following points depending on the etching back method. When the roughness of the surface formed by the etch-back is rough, particularly when the roughness is 1/20 or more of the wavelength used, it may cause scattering loss. The scattering loss becomes more prominent as the difference in refractive index between both sides of the interface increases. In addition, the rougher the surface roughness, the more prominent. Therefore, in order to reduce scattering loss, it is effective to select a method that reduces the roughness of the etched back surface. When it is difficult to reduce the roughness of the etch-back surface, reducing the difference in refractive index between the layers on both sides of the interface is effective in reducing scattering loss. In the case of the present invention, the first upper clad can be formed thick, and the whole can be etched back later. However, when this etch back is used to etch back to the position where the upper surface of the core is exposed, the scattering loss is reduced. The size is governed by the difference in refractive index between the core and the second upper cladding. On the other hand, when etching back to a position just before the upper surface of the core is exposed (the extent that the first upper clad of 2 μm or less remains on the core), the magnitude of the scattering loss is as follows. Dominated by the refractive index difference from the clad (the interface between the core and the first upper clad has a very small surface roughness because the upper surface of the core is not an etching surface but a spin coat film formation surface, and the scattering loss Is negligible). Since the refractive index difference between the core and the second upper cladding is larger than the refractive index difference between the first upper cladding and the second upper cladding, when the etch back is performed up to the position where the upper surface of the core is exposed, There is a risk that the impact will be greater.
Next, the substrate 1 and the polymer optical waveguide composed of the core 3 and the clad (2, 4, and 5) are peeled off by immersing the obtained wafer in water. The substrate is usually peeled by immersing it in water, but it can also be peeled by further ultrasonic treatment or contact with an acid such as hydrogen fluoride. In addition, a method is known in which a metal (copper) is used as a sacrificial layer between the substrate and the polymer optical waveguide in advance, and the metal (copper) is dissolved and removed with the etching solution. Other examples of such sacrificial layer and etchant combinations include, for example, Patrick J. French, MEMS / MOEMS Technology Capabilities and Trends, p. 16, MEMS and MOEMS Technology and Applications, Ed. P. Rai-Choudhury , SPIE, 2000. However, the method using such a sacrificial layer also has a drawback that the number of steps increases.
As described above, a polymer optical waveguide film having a cross section shown in FIG. 2 is prepared.

Examples of means for removing the first upper clad polyimide resin film include dry etching, wet etching, and polishing with an abrasive.
Examples of dry etching include plasma etching, reactive ion etching, reactive sputter etching, ion beam etching, and the like. Reactive ion etching is preferable because anisotropic etching is possible. For these, the gas composition, pressure, temperature, frequency, output, and the like are control factors, and conditions suitable for the purpose may be appropriately selected.

Wet etching is etching using a chemical reaction using a liquid phase. For example, an acid such as hydrogen fluoride, an alkali hydroxide, an alkali such as ethylenediamine, or an oxidizing agent such as potassium permanganate is used. Examples of the reaction method include immersion, flowing water, spray, jet, electrolysis and the like, and the liquid composition, pH, viscosity, temperature, stirring conditions, treatment time, treated area, etc. are the control factors and are suitable for the purpose. What is necessary is just to select conditions suitably.
In the present invention, since a polyimide resin is used, an aqueous solution of potassium hydroxide or sodium hydroxide, a mixed solution of hydrazine and isopropyl alcohol, a mixed aqueous solution of ethylenediamine and pyrocatechol, or the like can be used by heating.

  For polishing with an abrasive, an abrasive such as colloidal silica, barium carbonate, iron oxide, calcium carbonate, silica, cerium oxide, or diamond is used, and mechanical polishing or mechanochemical polishing is used. This method is preferable because the surface is uniformly polished, but care must be taken not to scratch the surface.

In addition, you may provide a solvent-resistant protective layer in order to protect the clad surface from a damage | wound, a solvent, etc. on both surfaces or one side of the polymer optical waveguide film of this invention. Examples of the polymer material constituting such a solvent-resistant protective layer include a polyimide resin not containing fluorine, an acrylic resin, and an epoxy resin. The film thickness of the protective layer made of a polymer material having better solvent resistance than the clad is preferably 0.5 to 10 μm. If the thickness is less than 0.5 μm, pinholes are generated in the protective layer, which may not play the role of the protective layer. If the thickness is more than 10 μm, the stress increases and the film may curl.
The solution for forming the solvent-resistant protective layer is applied onto the substrate surface by a method such as a spinner or printing, and heat-treated at a final temperature of 350 ° C. or lower to be cured to form a solvent-resistant protective film.

[Example 1]
Optical waveguide films A and B were manufactured using the following materials and conditions.
[material]
The polyimide used for the core and the clad is represented by the following formula.

Material of film A / Polyimide for lower clad: Polyimide with X = 0.11 in the above formula (refractive index n ₁ = 1.5227)
-Core polyimide: X = 0.26 in the above formula (refractive index n ₂ = 1.5291)
First polyimide for upper clad: Polyimide with X = 0.20 in the above formula (refractive index n ₃ = 1.5267)
Second polyimide for upper cladding: Polyimide with X = 0.11 in the above formula (refractive index n ₄ = 1.5227)
Photoresist: RU-1600P (manufactured by Hitachi Chemical Co., Ltd.)

Material of film B / Polyimide for lower clad: Polyimide with X = 0.11 in the above formula (refractive index n ₁ = 1.5227)
-Core polyimide: In the above formula, polyimide with X = 0.30 (refractive index n ₂ = 1.5307)
First polyimide for upper clad: polyimide with X = 0.26 in the above formula (refractive index n ₃ = 1.5291)
Second polyimide for upper cladding: Polyimide with X = 0.11 in the above formula (refractive index n ₄ = 1.5227)
Photoresist: RU-1600P (manufactured by Hitachi Chemical Co., Ltd.)

[Manufacturing]
In the following production, the polyimide precursor solution for the core and the lower clad, the first upper clad and the second upper clad polyimide precursor solution were applied using a spin coater.
First, a fluorine-free polyimide resin precursor solution (made by Hitachi Chemical Co., Ltd., trade name PIQ13) for forming a solvent-resistant protective layer is dropped on the entire upper surface of the silicon substrate 1, and spin coating (2000 rpm / 30 seconds) and then dried on a hot plate (200 ° C./5 minutes) to form a solvent-resistant protective layer (film thickness of about 4 μm). On top of this, a polyimide precursor solution for lower cladding is applied to form a material solution film, which is heated at 100 ° C. for 30 minutes and then at 200 ° C. for 30 minutes to evaporate the solvent, and at 370 ° C. for 60 minutes. The lower clad 2 made of the lower clad polyimide resin film was formed by heating and curing (film thickness was about 6 μm). On this lower clad 2, a core polyimide precursor solution is applied to form a material solution film, which is heated at 100 ° C. for 30 minutes and then at 200 ° C. for 30 minutes to evaporate the solvent, and further 350 A core layer made of a polyimide resin film for the core was formed by heating at 60 ° C. for 60 minutes to cure.

A photoresist was applied onto the core layer by a spin coater, dried, exposed and developed to form a resist pattern layer.
Using this resist pattern layer as a mask, the core polyimide resin film was subjected to reactive ion etching (O ₂ -RIE) with oxygen to obtain the core 3 (the film thickness was about 6 μm and the width was about 6 μm). Thereafter, the resist pattern layer was peeled off.
Next, the polyimide precursor solution for the first upper clad was applied so as to cover the core 3 and the lower clad 2. Next, this was heated at 100 ° C. for 30 minutes, then at 200 ° C. for 30 minutes to evaporate the solvent, and heated at 370 ° C. for 60 minutes to be cured to form a first upper clad polyimide resin film.

Further, the first upper clad polyimide resin film is removed by reactive ion etching (O ₂ -RIE) until the upper surface of the core 3 is exposed, and the first upper clad polyimide resin film is formed. A clad 4 was formed (the film thickness from the lower clad surface was about 6 μm).
Thereafter, a polyimide resin film for the second upper clad is applied on the first upper clad 4 and the core 3, and the solvent is evaporated by heating at 100 ° C. for 30 minutes and then at 200 ° C. for 30 minutes, and at 370 ° C. for 60 minutes. The second upper clad 5 was formed by heating and curing (film thickness was about 6 μm) (two-layer clad).
Further, a fluorine-free polyimide resin precursor solution (trade name PIQ13, manufactured by Hitachi Chemical Co., Ltd.) for forming a solvent-resistant protective layer is dropped on the second upper clad layer, and spin coating (2000 rpm / 30) is performed. Second) and then dried on a hot plate (200 ° C./5 minutes) to form a solvent-resistant protective layer (film thickness of about 4 μm).
The optical waveguide on the obtained substrate was cut out with a dicer to produce an optical waveguide with a substrate. When the optical waveguide with a substrate was immersed in water (temperature of 100 ° C.) for 30 minutes, the optical waveguide was easily peeled from the substrate, and the optical waveguide films A and B of the present invention having solvent-resistant protective layers on both surfaces were obtained, respectively. . In addition, the thing before removing the board | substrate of the optical waveguide film A of this invention was made into the optical waveguide C with a board | substrate (comparative example).

  In the production of the optical waveguide C with the substrate, the lower clad, the first upper clad, and the second upper clad material are all made of the same material (the same material as the lower clad and the second upper clad material used in Example 1). An optical waveguide was produced (see FIG. 3). That is, after the lower clad made of the clad material and the core made of the core material are produced on the wafer in the same manner as the film A, the thickness from the lower clad surface is about 12 μm (the film pressure on the core is about 6 μm). The same clad material as the lower clad was applied and dried to form an upper clad (one-layer clad), and an optical waveguide D with substrate (Comparative Example) was manufactured. Next, the substrate was peeled off to produce an optical waveguide film D (Comparative Example).

Evaluation PDL of the optical waveguide C with substrate, optical waveguide films A and B, optical waveguide D with substrate, and optical waveguide film D manufactured as described above was measured. Optical waveguide films A, B, and D were measured with glass substrates sandwiched from both sides.
Using a fiber optic block with a glass block, each of a state in which the surfaces of the fiber blocks are coupled to each other and a state in which an optical waveguide is inserted between the surfaces of the fiber block are measured using a polarization controller. PDL was determined by measuring the difference between the maximum loss and the minimum loss at 31 μm. The measurement results are shown in Table 1.

（単位：ｄＢ／ｃｍ）
光導波路フィルムのＰＤＬを非常に小さくすることができた（本発明の光導波路フィルムＡ：０．０４、本発明の光導波路フィルムＢ：０．０５）。なお、光導波路フィルムにおける２層クラッドとしたことによるＰＤＬ低減効果（光導波路フィルムＡ／光導波路フィルムＤ：０．０４／０．２）は、従来の１層クラッドの基板付き光導波路を２層クラッドとしたことによる効果（基板付き光導波路Ｃ／基板付き光導波路Ｄ：０．１／０．３）に比して非常に大きなものであった。 Table 1

(Unit: dB / cm)
The PDL of the optical waveguide film could be made very small (optical waveguide film A of the present invention: 0.04, optical waveguide film B of the present invention: 0.05). Note that the effect of reducing PDL (optical waveguide film A / optical waveguide film D: 0.04 / 0.2) due to the two-layer cladding in the optical waveguide film is that the conventional optical waveguide with a single-layer clad substrate has two layers. Compared to the effect of the clad (optical waveguide with substrate C / optical waveguide with substrate D: 0.1 / 0.3), it was very large.

It is a perspective view which shows one embodiment of the optical waveguide of this invention. It is sectional drawing which shows one embodiment of the optical waveguide of this invention. It is sectional drawing which shows the conventional optical waveguide.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Silicon substrate 2 ... Lower clad 3 ... Core 4 ... 1st upper clad 5 ... 2nd upper clad 6 ... Cladding

Claims (7)

A lower cladding (refractive index n ₁ ), a core (refractive index n ₂ ), a first upper cladding (refractive index n ₃ ) formed so as to cover at least the lower cladding upper surface and the core side surface, and the first A polymer optical waveguide film not including a substrate, comprising a polymer optical waveguide having an upper cladding and a second upper cladding (refractive index n ₄ ) formed above the core, wherein the first upper cladding comprises: It is formed at the same height as the core and does not exist on the core upper surface, or covers the core upper surface so that the thickness on the core is 2 μm or less, and n ₁ , n ₂ , n ₃ and n ₄ Satisfying the following relationship: n ₂ > n ₃ > n ₁ ≧ n ₄ , (n ₂ −n ₃ ) / n ₂ <0.002, (n ₂ −n ₁ ) / N ₂ <0.005, (n ₂ −n ₄ ) / N ₂ <0.005. The polymer optical waveguide film according to claim 1, wherein the core and the clad material are fluorinated polyimide resins. The polymer optical waveguide film according to claim 1 or 2, wherein the polymer optical waveguide film has a form of a crossed optical waveguide or a plurality of optical waveguides arranged in parallel. A first step of forming a lower cladding (refractive index n ₁ ) on a substrate;
A second step of forming a core (refractive index n ₂ ) on the lower cladding;
The core upper surface so as to cover at least the lower clad upper surface and the core side surface, and is formed at the same height as the core and does not exist on the core upper surface, or the thickness on the core is 2 μm or less. A third step of forming a first upper clad (refractive index n ₃ ) so as to cover, and a fourth step of forming a second upper clad (refractive index n ₄ ) above the first upper clad and the core The process of
A fifth step of peeling the polymer optical waveguide including the lower clad, the core, the first upper clad and the second upper clad from the substrate;
(Where n ₂ > n ₃ > n ₁ ≧ n ₄ , (n ₂ −n ₃ ) / n ₂ <0.002, (n ₂ −n ₁ ) / n ₂ <0.005, (n ₂ − n ₄ ) / n ₂ <0.005 )
A method for producing a polymer optical waveguide film containing no substrate. The method of claim 4 wherein the core and cladding material is a fluorinated polyimide resin. The method according to claim 4 or 5 , wherein the optical waveguide has the form of a crossed optical waveguide or a plurality of optical waveguides arranged in parallel. Forming a first upper cladding so as to cover the core upper surface so that the thickness on the core is 2 μm or less in a third step;
The method according to any one of claims 4 to 6 , further comprising a step of etching the first upper clad to a position immediately before the upper surface of the core is exposed before the fourth step.

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