JP3472512B2 - Optical waveguide forming method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an optical waveguide in an optical wiring board, an optical device, an optical functional circuit or the like.

[0002]

2. Description of the Related Art An optical waveguide using a polymer material is generally formed by a spin coating method in which a liquid or varnished polymer material is dropped on a silicon (Si) wafer to obtain a desired film thickness. While rotating the Si wafer by a number, the lower clad layer and the core layer are sequentially formed and heat-treated, and then the core layer is etched through the etching mask formed on the surface of the core layer to form a core with a rectangular cross section. After forming, the upper clad layer is laminated so that the core is completely embedded to form an embedded optical waveguide.

[0003]

However, when the heat treatment is performed in forming the optical waveguide layer, the difference in the coefficient of thermal expansion between the substrate such as the Si wafer and the polymer forming the optical waveguide layer is large by about one digit or more. In this case, when the temperature is lowered to room temperature, the shrinkage of the polymer is larger than that of the substrate, and “warpage” occurs in the substrate with the optical waveguide layer inside. Therefore, when the core layer is formed by reactive ion etching through the mask to form the core, the angle formed by the direction of the etching beam and the surface of the core layer is not a right angle, and as shown in FIG.
The cross section of the core 15 tends to have a distorted rectangular shape. In addition, since the stress remains inside the core layer due to the difference in the thermal expansion coefficient, when the core layer is etched, the etching region not covered with the mask and the non-etched region covered with the mask will remain in the core layer. Since the stress distribution is generated and the stress difference becomes large especially near the region interface, the etching rate tends to become non-uniform, and the cross section of the etching region becomes as shown in FIG. Therefore, there is a problem that a part of the core layer 13 'is likely to remain, which causes optical crosstalk between the cores and makes it difficult to narrow the pitch between the cores. 4 and 5, 11 is a substrate such as Si, 12 is a lower clad layer, 13 is a core layer, 14 is a mask, 15 is a core, and 16 is an upper clad layer.

An object of the present invention is to provide a technique capable of reducing the stress distribution in the core layer even if the difference in the coefficient of thermal expansion between the polymer forming the optical waveguide layer and the substrate is large. is there. Another object of the present invention is to provide a technique capable of improving the yield of forming an optical waveguide. Another object of the present invention is to provide a technique capable of reducing optical crosstalk and narrowing the pitch between cores. The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[0005]

Among the inventions disclosed in the present application, a brief description will be given to the outline of typical ones.
It is as follows.

(1) A lower clad layer and a core layer having a refractive index higher than that of the lower clad layer are sequentially laminated on a substrate, and the core layer is processed into a rectangular cross section in the thickness direction.
Method of forming an optical waveguide by forming cores arranged in one or more arrays and completely filling the cores arranged in the array with an upper clad layer having a refractive index equal to that of the lower clad layer And forming a first mask on the surface of the core layer, the first mask having the same pattern as the core on the substrate arranged in the array, and forming the first mask on the surface of the first mask within the cross-sectional shape of the second mask. Forming a second mask covering the first mask so as to include a cross-sectional shape;
Chemically from the surface of the core layer on which the second mask is formed,
Alternatively, the core layer is mechanically etched and the second
Method of forming a rectangular core by etching the core layer or the core layer and the lower clad layer through the first mask after removing the first mask, and removing the first mask. Is.

(2) A lower clad layer and a core layer having a refractive index higher than that of the lower clad layer are sequentially laminated on a substrate, and the cross section in the thickness direction of the core layer is processed into a rectangular shape.
A method of forming an optical waveguide by forming cores arranged in one or more arrays and completely filling the cores arranged in the array with an upper clad layer having a refractive index equal to that of the lower clad layer. Then, a first mask having the same pattern as the core in the plane of the substrate arranged in the array is formed on the surface of the core layer, and the first mask is formed on the surface of the second mask in the cross-sectional shape of the second mask. A second mask is formed so as to cover the first mask so as to include the cross-sectional shape, and a third mask having a pattern in which the cross-sectional shape is included in the cross-sectional shape of the inverted pattern of the first or second mask. Is formed on the surface of the lower clad layer, and the core layer is chemically or mechanically etched from the surface of the core layer on which the second mask is laminated, and the second mask is removed. Previous The core layer is etched through the first mask, the first is a method of removing the third mask to form a rectangular core.

(3) A lower clad layer and a core layer having a refractive index higher than that of the lower clad layer are sequentially laminated on a substrate, and the cross section of the core layer in the thickness direction is processed into a rectangular shape.
A method of forming an optical waveguide by forming cores arranged in one or more arrays and completely filling the cores arranged in the array with an upper clad layer having a refractive index equal to that of the lower clad layer. And forming the fourth mask on the surface of the lower clad so as to completely cover the first mask with a pattern in which the cross-sectional shape of the first mask is included in the cross-sectional shape of the fourth mask. Then, after chemically or mechanically etching the lower clad layer from the surface of the lower clad layer on which the fourth mask is formed, the fourth mask is removed to remove the core layer and the first mask. In this method, the core layers are sequentially laminated, the core layer is etched through the first mask, and the first mask is removed to form a rectangular core.

(4) In the method for forming an optical waveguide according to any one of the means (1) to (3), the core layer, the lower and upper clad layers are made of a polymer.

(5) In the method for forming an optical waveguide according to any one of the means (1) to (4), the first to fourth
Of the masks, at least the first and third masks are made of metal.

According to the method of forming an optical waveguide of the present invention, a groove having a width narrower than the core pitch is formed in the core layer or the lower clad layer projecting between the cores before forming the rectangular core. Even if the difference in the coefficient of thermal expansion between the polymer forming the layer and the substrate is large, the stress distribution in the core layer can be reduced in advance. Therefore, "warpage" of the substrate can be suppressed, and the angle between the etching beam direction and the surface of the core layer can be made right. Further, the etching rate in the etching region can be made uniform.

Hereinafter, the present invention will be described in detail with reference to the drawings together with embodiments (embodiments). In all the drawings for explaining the embodiments (examples), components having the same function are designated by the same reference numeral, and repeated description thereof will be omitted.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) FIGS. 1A to 1C are cross-sectional views in each step for explaining an optical waveguide forming method according to Embodiment 1 of the present invention. In FIG.
1 is a substrate such as Si, 2 is a lower clad layer, 3 is a core layer,
Reference numeral 4 is a first mask, 5 is a second mask, 6 is a groove, 7 is a core, and 8 is an upper clad layer. This embodiment (example)
The optical waveguide forming method of No. 1 will be described for the case where, for example, a polyimide resin is used as the lower clad layer 2, the core layer 3, and the upper clad layer 8.

As shown in FIG. 1 (a), the lower clad layer 2 has a thickness of, for example, 40 μm, and is spin-coated with a varnish-like polyimide resin and then cured by heating at, for example, 350 ° C. or above to form a substrate 1 of the substrate 1. Form on top. The core layer 3 has, for example, a refractive index higher than that of the lower clad layer 2 (for example, a relative refractive index of 1.2%) and a thickness of 50 μm. Form on top. The first mask 4 formed on the surface of the core layer 3 is made of, for example, titanium (Ti) having a width of 50 μm,
The gap between the adjacent first masks 4 in FIG. 1A is, for example, 250 μm. The second mask 5 is made of resist, for example, and completely covers the first mask 4 so that the cross-sectional shape of the second mask 5 includes the cross-sectional shape of the first mask 4. The gap between the adjacent second masks 5 in FIG. 1A is 125 μm, for example.

In this state, reactive ion etching is performed in, for example, an oxygen atmosphere, and as shown in FIG.
A groove 6 having a width of about 125 μm is formed in the core layer 3.
The remaining second mask is removed with a stripping solution to expose the first mask 4 on the outermost surface. Then, reactive ion etching is performed in, for example, an oxygen atmosphere to form a core 7 of 50 μm square as shown in FIG. After removing the first mask 4 with, for example, hydrofluoric nitric acid, as shown in FIG. 1D, an upper clad layer having the same composition as that of the lower clad layer 2 and having a thickness of, for example, 40 μm from the upper surface of the core 7 is formed. 8 is laminated in the same manner as the lower clad layer 2 to form an optical waveguide.

(Embodiment 2) FIG. 2 is a sectional view in each step for explaining an optical waveguide forming method according to Embodiment 2 of the present invention. Reference numeral 9 is a third mask. In the optical waveguide forming method according to the present embodiment (Example) 2, the lower clad layer 2, the core layer 3, and the upper clad layer 8 are formed.
As an example, a case of using a polyimide resin will be described.

As shown in FIG. 2A, the lower clad layer 2 has a thickness of, for example, 40 μm, and is spin-coated with a varnish-shaped polyimide resin, and then cured by heating at, for example, 350 ° C. or higher. To form. The third mask 9 formed on the surface of the lower cladding layer 2 is made of, for example, titanium (Ti), and the third mask 9 is formed in the cross-sectional shape of the inverted pattern of the first or second mask 4 or 5. It is arranged at a position including the sectional shape. The pattern width of the third mask 9 is, for example, 200 μm. The core layer 3 has, for example, a refractive index higher than that of the lower clad layer 2 (for example, a relative refractive index of 1.2%) and a thickness of 50 μm, and is formed on the lower clad layer 2 in the same manner as the lower clad layer 2. Form. The first mask 4 is made of, for example, titanium (Ti) having a width of 50 μm, and the gap between the adjacent first masks 4 in FIG. 2A is, for example, 250 μm.
The second mask 5 is made of, for example, a resist, and completely covers the first mask 4 so that the cross-sectional shape of the second mask 5 includes the cross-sectional shape of the first mask 4. The gap between the adjacent second masks 5 in FIG. 2A is, for example, 125 μm.

In this state, reactive ion etching is performed in, for example, an oxygen atmosphere, and as shown in FIG.
A groove 6 having a width of about 125 μm is formed in the core layer 3.
The remaining second mask is removed with a stripping solution to expose the first mask 4 on the surface. After that, reactive ion etching is performed in, for example, an oxygen atmosphere to form a core 7 of 50 μm square as shown in FIG. In this case, the third
The presence of the mask 9 makes it possible to prevent the etching from reaching the lower clad layer 2 as shown in FIG.

After removing the first and third masks 4 and 9 with, for example, hydrofluoric nitric acid, as shown in FIG.
An optical waveguide is formed by stacking an upper clad layer 8 having the same composition as the lower clad layer 2 and having a thickness of, for example, 40 μm from the upper surface of the core 7 in the same manner as the lower clad layer 2.

(Embodiment 3) FIG. 3 is a sectional view in each step for explaining an optical waveguide forming method according to Embodiment 3 of the present invention, and 10 is a fourth mask. The optical waveguide forming method according to the present embodiment (Example) 3 includes the lower clad layer 2, the core layer 3, and the upper clad layer 8.
As an example, a case of using a polyimide resin will be described.

As shown in FIG. 3 (a), the lower clad layer 2 has a thickness of, for example, 40 μm, and is spin-coated with a varnish-shaped polyimide resin, and then cured by heating at, for example, 350 ° C. or above, onto the substrate 1. To form. On the outermost surface of the lower clad layer 2, a fourth mask 10 made of, for example, a resist and having a dimension that includes the cross-sectional shape of the first mask 4 in its cross-sectional shape is formed. The gap between the adjacent fourth masks 10 in FIG. 3A is, for example, 125 μm.
Is.

In this state, reactive ion etching is performed in, for example, an oxygen atmosphere, and as shown in FIG.
A groove 6 having a width of about 125 μm is formed in the core layer 3.
After the remaining fourth mask 10 is removed with a stripping solution, the core layer 3 is laminated. The core layer 3 has, for example, a higher refractive index than the lower cladding layer 2 (for example, a relative refractive index of 1.2%).
The thickness is 50 μm, and the same method as that for the lower clad layer 2
It is formed on the lower clad layer 2. The first mask 4 formed on the core layer 3 is made of, for example, titanium (Ti) having a width of 50 μm, and the gap between the adjacent first masks 4 in FIG. 3B is, for example, 250 μm. Is.

In this state, reactive ion etching is performed in, for example, an oxygen atmosphere, and as shown in FIG.
A 50 μm square core 7 is formed. After removing the first mask 4 with, for example, hydrofluoric nitric acid, as shown in FIG. 3D, an upper portion having a composition similar to that of the lower cladding layer 2 and having a thickness of 40 μm from the upper surface of the core 7 is formed. Clad layer 8
Are laminated in the same manner as the lower clad layer 2 to form an optical waveguide.

The optical waveguide material is not limited to the polyimide resin, and the material such as acrylic resin or silicone resin is not particularly limited. Further, the substrate is not limited to the Si wafer, but may be a ceramic substrate, and the substrate shape may be a square shape. The material of the first and third masks 4 and 9 is not limited to titanium (Ti), and any material having a high selection ratio with respect to the optical waveguide material may be used. The thickness of the clad layers 8 and 2 above and below the optical waveguide is not limited to 40 μm, and the size of the core 7 is 50 μm.
For example, it may be 8 μm square instead of m square. Further, the difference in refractive index between the core 7 and the cladding layers 2 and 8 is not limited to 1.2%. Further, the etching method is not limited to reactive ion etching, and may be chemical etching. Further, after irradiating ultraviolet rays or the like through a mask to optically form the core 7, the non-irradiated portion is removed by chemical etching. It goes without saying that it is okay.

Although the present invention has been specifically described based on the embodiments, the present invention is not limited to the above-mentioned embodiments, and various modifications can be made without departing from the scope of the invention. is there.

[0026]

As described above, according to the present invention,
Before forming the rectangular core, a groove having a width narrower than the core pitch is formed in the core layer or the lower clad layer projecting between the cores in advance, so that the gap between the polymer forming the optical waveguide layer and the substrate is formed. Even if the difference in the coefficient of thermal expansion is large, the stress distribution in the core layer can be reduced. Therefore, "warpage" of the substrate can be suppressed, and the cross-sectional shape of the etched core can be made rectangular. Further, by reducing the stress distribution, the etching rate in the etching region can be made uniform, so that the yield of forming the optical waveguide can be improved. Further, it becomes possible to reduce the optical crosstalk and narrow the pitch between the cores.

[Brief description of drawings]

FIG. 1 is a cross-sectional view in each step for explaining an optical waveguide forming method according to an embodiment (Example) 1 of the present invention.

FIG. 2 is a cross-sectional view in each step for explaining an optical waveguide forming method according to an embodiment (Example) 2 of the present invention.

FIG. 3 is a cross-sectional view in each step for explaining an optical waveguide forming method according to a third embodiment (embodiment) of the present invention.

FIG. 4 is a cross-sectional view illustrating a problem of a conventional optical waveguide forming method.

FIG. 5 is a cross-sectional view for explaining a problem of the conventional optical waveguide forming method.

[Explanation of symbols]

1, 11 ... Substrate such as Si, 2, 12 ... Lower clad layer,
3, 13 ... Core layer, 4 ... First mask, 5 ... Second mask, 6 ... Groove, 7, 15 ... Core, 8, 16 ... Upper clad layer, 9 ... Third mask, 10 ... Fourth Mask of 13 '...
Part of the core layer, 14 ... Mask.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-29632 (JP, A) JP-A-63-43105 (JP, A) JP-A-8-43654 (JP, A) JP-A-5- 224055 (JP, A) JP 10-311922 (JP, A) JP 8-15540 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 6/12-6 /14

Claims (5)

(57) [Claims] 1. A lower clad layer and a core layer having a refractive index higher than that of the lower clad layer are sequentially laminated on a substrate, and the core layer is processed into a rectangular cross-section in the thickness direction to form one or more layers. A method of forming an optical waveguide, comprising forming cores arranged in an array and completely filling the cores arranged in the array with an upper clad layer having a refractive index equal to that of the lower clad layer. Forming a first mask on the surface of the core layer having the same pattern as that of the cores on the substrate arranged in the array, and setting the cross-sectional shape of the first mask within the cross-sectional shape of the second mask. Forming a second mask overlying the first mask to include and chemically or mechanically etching the core layer from the surface of the core layer on which the second mask is formed, Removed the mask And etching the core layer, or the core layer and the lower cladding layer through the first mask, and removing the first mask to form the rectangular core. Waveguide formation method. 2. A lower clad layer and a core layer having a refractive index higher than that of the lower clad layer are sequentially laminated on a substrate, and the cross section in the thickness direction of the core layer is processed into a rectangular shape to form one or more layers. An optical waveguide forming method for forming an optical waveguide by forming cores arranged in an array and completely filling the cores arranged in the array with an upper cladding layer having a refractive index equal to that of the lower cladding layer, A first mask having the same pattern as the cores in the plane of the substrate arranged in the array is formed on the surface of the core layer, and the cross-sectional shape of the first mask is formed on the cross-sectional shape of the second mask. A second mask is formed to cover the first mask so as to be included, and the third mask having a pattern in which the cross-sectional shape is included in the cross-sectional shape of the inversion pattern of the first or second mask is formed on the lower portion. Clad layer surface Formed in,
Chemically from the surface of the core layer on which the second mask is formed,
Alternatively, the core layer is mechanically etched and the second
Method for forming an optical waveguide, wherein the core layer is etched through the first mask after removing the first mask, and the first and third masks are removed to form a rectangular core. . 3. A lower clad layer and a core layer having a refractive index higher than that of the lower clad layer are sequentially laminated on a substrate, and the cross section in the thickness direction of the core layer is processed into a rectangular shape to form one or more layers. An optical waveguide forming method for forming an optical waveguide by forming cores arranged in an array and completely filling the cores arranged in the array with an upper cladding layer having a refractive index equal to that of the lower cladding layer, The fourth mask is formed on the surface of the lower clad so as to cover the first mask in a pattern such that the cross-sectional shape of the fourth mask is included in the cross-sectional shape of the fourth mask. After chemically or mechanically etching the lower clad layer from the surface of the lower clad layer having the mask No. 4, the fourth mask is removed, and the core layer and the first mask are sequentially laminated. hand, Serial through the first mask by etching the core layer, the optical waveguide forming method comprising forming a rectangular core by removing the first mask. 4. The method of forming an optical waveguide according to claim 1, wherein the core layer, the lower and upper clad layers are made of a polymer. 5. The optical waveguide forming method according to claim 1, wherein at least the first and third masks of the first to fourth masks are made of metal. An optical waveguide forming method characterized by the above.