JP3079401B2 - Method for forming end mirror of optical waveguide - 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 a mirror at an end of an optical waveguide in a thin film optical component.

[0002]

2. Description of the Related Art When optical components such as prisms used in an optical communication system or an optical disk system are bulk-type individual components, adjustment of the optical axis of the individual components is troublesome, and environmental factors such as temperature and vibration. However, there are problems such as instability and inability to be miniaturized or mass-produced. Therefore, research on thinning and arranging them on one substrate for integration has been advanced.

In such a thin film optical component, a thin film waveguide having a higher refractive index than its surroundings may be formed on a substrate. As a basic structure, a two-dimensional waveguide (slab-like waveguide) or a three-dimensional waveguide (channel-like waveguide) is used. , Lip shape, etc.). When the guided light in the three-dimensional waveguide is taken out perpendicular to the space, a reflection mirror is formed in the waveguide. FIG. 4 shows a conventional manufacturing method for forming a reflecting mirror in a three-dimensional optical waveguide by ion beam processing. This figure shows L.
R. Harriott, R.E.Scotti, KD Cummings, and AFAmbro
se, "Micromachining of optical structure with focus
ed ion beam ", J. Vac.Sci.Technol, B5 (1), 207-210, (198
It is quoted from 7).

In the conventional mirror forming technique shown in FIG.
An optical waveguide core layer 1 is formed on a dielectric substrate 2 such as a thermally oxidized silicon substrate, and a mirror forming position of the optical waveguide core layer 1 is irradiated with an ion beam B. By gradually reducing the beam irradiation area, the reflection mirror 8 having an inclined structure is formed.

[0005]

However, in the above-described conventional method using an ion beam, mirrors are formed one by one while scanning the ion beam. Was inefficient and unsuitable for forming

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to enable simultaneous formation of mirrors in a large number of optical waveguides at the same time, which greatly shortens the mirror formation time. An object of the present invention is to provide a method for forming an optical waveguide end mirror that can be shortened.

[0007]

The present invention has the following configuration to achieve the above object. That is, according to the mirror forming method of the present invention, the phenomenon that the shape of the etching photomask made of the photoresist is transferred to the processed shape of the etching material, and that the shape of the photoresist to be the etching photomask can be controlled by the exposure amount It is an application of

A first method for forming an end mirror of an optical waveguide according to the present invention is a method for integrally forming a mirror in a ridge-type optical waveguide. (A) A dielectric substrate (such as a thermally oxidized silicon substrate) After forming an optical waveguide core material (such as fluorinated polyimide) on the optical waveguide core material, forming a photoresist (such as a silicon-based positive type photoresist) on the optical waveguide core material; Patterning the photoresist using a photomask partially provided with a mask pattern whose height or density gradually increases or decreases in the longitudinal direction of the optical waveguide, and (c) the patterned photoresist and the lower layer thereof And a step of etching the film by dry etching (reactive ion etching, excimer laser etching, etc.).

A second method of forming an end mirror of an optical waveguide according to the present invention is a method of integrally forming a mirror in a ridge type optical waveguide. (A) A dielectric substrate (such as a thermally oxidized silicon substrate) Forming a base cladding material of the optical waveguide (such as fluorinated polyimide having a lower refractive index than that of the optical waveguide core); and (b) forming an optical waveguide core material (such as fluorinated polyimide) on the base cladding material. After the film is formed, a step of forming a photoresist (eg, a silicon-based positive type photoresist) on the optical waveguide core material, and (c) the size or density of the opening gradually increases or decreases in the longitudinal direction of the optical waveguide. Patterning the photoresist using a photomask partially provided with a mask pattern to be etched, and (d) dry-etching the patterned photoresist and the underlying film. Etching (reactive ion etching, excimer laser etching, etc.).

A third method for forming an optical waveguide end mirror according to the present invention is a method for integrally forming a mirror in a buried type optical waveguide, and comprises the following steps: (a) a dielectric substrate (such as a thermally oxidized silicon substrate); An underlayer cladding material for the optical waveguide (fluorinated polyimide with a lower refractive index than the optical waveguide core)
And (b) forming an optical waveguide core material (such as fluorinated polyimide) on the underlying cladding material, and then forming a photoresist (such as a silicon-based positive photoresist) on the optical waveguide core material. (C) patterning the photoresist using a photomask, and then etching and forming an optical waveguide core by a dry etching method; and (d) an upper cladding (silicon) on the optical waveguide core. (E) a step of forming a photoresist (such as a silicon-based positive photoresist) on the upper clad;
Patterning the photoresist using a photomask partially provided with a mask pattern in which the size or density of the opening gradually increases or decreases in the longitudinal direction of the optical waveguide; and (d) the patterned photo The step of etching the resist and the underlying film by a dry etching method (reactive ion etching, excimer laser etching, etc.).

[0011]

In the above structure, an etching mask (photoresist) having a slope structure is formed at a position corresponding to the reflection mirror portion by using a photomask in which the exposure amount is partially controlled. By performing reactive ion etching or the like, a reflection mirror is formed on the optical waveguide core.

That is, since the pattern shape of the photoresist changes depending on the amount of exposure, the photoresist is exposed to light using a photomask having a pattern configuration in which the amount of transmitted ultraviolet light gradually increases, thereby etching the photoresist having a slope structure. A mask can be obtained. On the other hand, in a general etching process, although the etching mask and the etching material are processed in the same manner, the photoresist etching mask has higher resistance to the etchant, so that
A desired processing shape is obtained. However, when the thickness of the etching mask is small, the etching mask is also etched, so that the etching material is exposed and etched. The time until the etching material is exposed is proportional to the thickness of the etching mask, and the longer the etching mask thickness, the longer the time. Therefore, when an etching mask having a gradually changing thickness is used in the slope structure of the present invention, a slope reflection mirror is formed on a corresponding optical waveguide core or the like after the etching is completed.

According to the above-described mirror forming method, even in an optical waveguide circuit configuration requiring a large area and a large number of mirrors, the mirrors can be formed collectively by ordinary photolithography technology. The time can be significantly reduced.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the illustrated embodiments. FIG. 1 is a first embodiment of a mirror forming method in a ridge optical waveguide component of the present invention, FIG. 2 is a second embodiment of a mirror forming method in a similar ridge optical waveguide component, and FIG. 3 is a buried optical waveguide component. 11 is a third embodiment of the mirror forming method.

<First Embodiment> This first embodiment is shown in FIG.
As shown in (6), this is an example of a ridge-type optical component in which a plurality of rows of optical waveguide cores (here, fluorinated polyimide material) 1 are protruded on a thermally oxidized silicon substrate 2. An etching mask (for example, a silicon-based positive photoresist) 3 is formed on the polyimide film A ₁ , and a slope structure 7 is formed on the etching mask 3 by using the photomask 4 on which a light amount gradually increasing mask pattern 6 is formed. Waveguide core 1 by reactive ion etching
The reflection mirror 8 is formed. Hereinafter, the process will be described in detail.

(1) A fluorinated polyimide material to be an optical waveguide core 1 is spin-coated on a thermally oxidized silicon substrate 2 by a spin coating method, and a fluorinated polyimide film A ₁ having a thickness of, for example, 10 μm or less is passed through a curing process. A film is formed by (2) fluorinated polyimide film A ₁ etching mask 3 on
Become a silicon-based positive photoresist A ₃ was spin coated, deposited by prebaking.

(3) Silicon-based positive photoresist A ₃
The photomask 4 is placed on the substrate to perform patterning. The photomask 4 includes a plurality of parallel linear patterns 5 spaced apart from each other, and transmits light at the time of exposure due to the area / density of minute rectangular patterns 6a arranged at an end of the linear pattern at an interval of, for example, 1 μm or less. A light amount increasing mask pattern 6 (see FIG. 1C) having a structure in which the amount gradually increases in the longitudinal direction of the optical waveguide is provided.

(4) The exposed portion of the silicon-based positive photoresist A ₃ undergoes a structural change due to the exposure, and is dissolved by the solvent treatment, so that a linear pattern etching mask 3 is obtained and the light amount of the photo mask 4 is gradually increased. The pattern of the etching mask 3 corresponding to the portion has a slope structure 7 that is inclined in proportion to the transmission amount. (5) by reactive ion etching using oxygen plasma P, performs fluorinated etching of the polyimide film A ₁ other than the portion to be the optical waveguide core 1.

(6) At this time, since the etching mask 3 is also etched by the oxygen plasma, a portion having a small etching mask thickness (for example, 2 μm or less) is formed of the fluorinated polyimide film A ₁ (for example, 10 μm) to a desired thickness. It is etched before the end of the etching. Therefore, the slope structure 7 of the etching mask 3 having a thickness was gradually changed gradually mask from the thin portion is completed etched, the drive starts the etching exposed fluorinated polyimide film A ₁ is gradually, according to the inclination thickness Since the etching proceeds, the inclined reflecting mirror 8 is formed in the optical waveguide core 1 corresponding to the inclined structure 7.

In the thin-film optical waveguide component manufactured as described above, the guided light L propagating in the ridge-type optical waveguide composed of a silicon thermal oxide film, fluorinated polyimide, and air is emitted from the waveguide, The light was reflected by the formed reflecting mirror 8 and taken out into the space.

<Second Embodiment> This second embodiment is similar to that of FIG.
As shown in (7), an underlayer cladding 11 (fluorinated polyimide having a lower refractive index than that of the optical waveguide core 1) of the optical waveguide is formed on the thermally oxidized silicon substrate 2.
This is an example of a ridge-type optical component in which a plurality of optical waveguide cores (fluorinated polyimide materials) 1 are protruded on an optical waveguide core 1.
1, an etching mask (for example, a silicon-based positive photoresist) 3 is formed in the same manner as in the first embodiment, and a slope structure 7 is formed on the etching mask 3 by using a photomask 4 on which a light amount gradually increasing mask pattern 6 is formed. Then, the optical waveguide core 1 is formed by reactive ion etching of oxygen plasma.
Forming the reflection mirror 8 on the base cladding 11; Less than,
The details will be described in the order of steps.

(1) A fluorinated polyimide material to be an optical waveguide base clad 11 is spin-coated on a thermally oxidized silicon substrate 2 by a spin coating method, and a curing process is performed.
A fluorinated polyimide film A fluorinated polyimide film A ₁₁ having a refractive index lower than ₁ is deposited by, for example, 20μm or less in thickness. (2) on the base clad 11, a fluorinated polyimide material as the optical waveguide core 1 was spin coated by a spin coating method, through the curing process, forming a fluorinated polyimide film A ₁ for example, 10μm or less in thickness .

[0023] (3) a fluorinated polyimide film A ₁ silicon as an etching mask 3 on positive photoresist A
₃ is spin-coated and pre-baked to form a film. (4) performing the patterning by placing the photomask 4 in the silicon-based positive photoresist A _3. This photo mask 4
Comprises a plurality of parallel linear patterns 5 spaced apart from each other,
The light amount gradually increasing mask pattern 6 (FIG. 2) in which the transmission amount at the time of exposure gradually increases in the longitudinal direction of the optical waveguide due to the area / density of the minute rectangular patterns 6a arranged at intervals of, for example, 1 μm or less at the end of the linear pattern (C).

(5) The exposed portion of the silicon-based positive photoresist A ₃ undergoes a structural change due to the exposure, and is dissolved by the solvent treatment, so that a linear pattern of the etching mask 3 is obtained and the light amount of the photo mask 4 is gradually increased. The pattern of the etching mask 3 corresponding to the portion has a slope structure 7 that is inclined in proportion to the transmission amount. (6) by reactive ion etching using oxygen plasma is performed fluorinated etching of the polyimide film A ₁ other than the portion to be the optical waveguide core 1.

(7) At this time, since the etching mask 3 is also etched by the oxygen plasma, the portion having a small etching mask thickness (for example, 2 μm or less) is formed of the fluorinated polyimide film A ₁ (for example, 10 μm) to a desired thickness. It is etched before the end of the etching. Therefore, in the inclined structure 7 of the etching mask 3 whose thickness is gradually changed, the etching of the mask is gradually completed from the thin portion, and the fluorinated polyimide films A ₁ and A ₁₁ are gradually exposed and the etching is started. Since the etching proceeds according to the thickness, the inclined reflecting mirror 8 is formed on the optical waveguide core 1 and the base clad 11 corresponding to the inclined structure 7.

In the thin-film optical waveguide component manufactured as described above, the guided light L propagating through the ridge-type optical waveguide composed of the silicon thermal oxide film, the fluorinated polyimide of the base clad core and air is the waveguide. After being emitted from the mirror, the light was reflected by the formed reflecting mirror 8 and taken out into the space.

<Third Embodiment> This third embodiment is similar to that of FIG.
As shown in 1), an optical waveguide core (a fluorinated polyimide material as in the first embodiment) 1 is composed of an under cladding 11 (a fluorinated polyimide having a lower refractive index than the optical waveguide core 1) and an upper cladding 12 (an optical waveguide core). This is an example of an embedded optical component embedded between a cladding 11 and a fluorinated polyimide having a refractive index lower than that of the optical waveguide core 1. Mask (for example, silicon-based positive photoresist) 3
Is formed, a slope structure 7 is formed on the etching mask 3 by using the photomask 4 on which the light amount increasing mask pattern 6 is formed, and a reflection mirror 8 is formed on the upper clad 12 and the base clad 11 by reactive ion etching of oxygen plasma. I do. Hereinafter, the process will be described in detail.

(1) A fluorinated polyimide material to be an optical waveguide base clad 11 is spin-coated on a thermally oxidized silicon substrate 2 by a spin coating method, and is subjected to a curing process.
A fluorinated polyimide film A fluorinated polyimide film A ₁₁ having a refractive index lower than ₁ is deposited by, for example, 20μm or less in thickness. (2) on the base clad 11, a fluorinated polyimide material as the optical waveguide core 1 was spin coated by a spin coating method, through the curing process, forming a fluorinated polyimide film A ₁ for example, 10μm or less in thickness .

(3) A silicon-based positive photoresist A ₃ ′ serving as an etching mask 3 ′ is spin-coated on the fluorinated polyimide film A ₁ , and is prebaked to form a film. (4) A photomask (not shown) is placed on the silicon-based positive photoresist A ₃ ′ to perform patterning. The photomask has an opening at a portion on the optical waveguide core 1 (portion forming a reflection mirror), and the exposed portion of the silicon-based positive photoresist A ₃ ′ undergoes a structural change due to exposure, and the solvent changes. The process dissolves, and an opening 6 'is formed in the etching mask 3'.

[0030] (5) by reactive ion etching using oxygen plasma, the etching mask 3 'and etched fluorinated polyimide film A _1, given that a portion 1a of the optical waveguide core 1 is removed the optical waveguide circuit pattern Is formed. (6) On such a circuit pattern of the optical waveguide core 1,
Fluorinated polyimide material comprising an optical waveguide upper cladding 12 was spin-coated, through the curing process, forming a fluorinated polyimide film A fluorinated polyimide film A ₁₂ having a refractive index lower than _1.

(7) Silicon-based positive photoresist A serving as an etching mask 3 on the upper cladding 12 of the optical waveguide
₃ is spin-coated and pre-baked to form a film. (8) performing the patterning by placing the photomask 4 in the silicon-based positive photoresist A _3. This photo mask 4
In the configuration, the amount of light transmitted during exposure gradually increases in the longitudinal direction of the optical waveguide due to the area / density of the minute rectangular patterns 6a arranged at intervals of, for example, 1 μm or less in the removed portion 1a of the optical waveguide core 1. The mask pattern 6 is provided.

(9) Silicon-based positive photoresist A ₃
The portion irradiated with light changes its structure by the exposure, is dissolved by the solvent treatment, and the pattern of the etching mask 3 corresponding to the gradually increasing portion of the light amount of the photomask 4 becomes a slope structure 7 having an inclination proportional to the transmission amount. (10) by reactive ion etching using oxygen plasma, to etch the fluorinated polyimide film A _12.

(11) At this time, since the etching mask 3 is also etched by the oxygen plasma, the thin portions of the etching mask (for example, 2 μm or less) are fluorinated polyimide films A ₁₂ and A ₁₁ (for example, Etching is performed before the etching of 40 μm or less). Therefore,
In the inclined structure 7 of the etching mask 3 whose thickness is gradually changed, the etching is gradually finished from the thin portion, the fluorinated polyimide films A ₁₁ and A ₁₂ are gradually exposed, and the etching is started. Since the etching proceeds in response, the inclined reflecting mirror 8 is formed on the upper cladding 12 and the underlying cladding 11 corresponding to the slope structure 7.

In the thin film optical waveguide component manufactured as described above, the guided light L propagating in the buried optical waveguide composed of fluorinated polyimide for both the core and the upper and lower claddings was formed after exiting from the waveguide. The light is reflected by the reflection mirror 8 and taken out into the space.

Although the present invention has been described in detail with reference to the embodiments, the present invention is not limited to the above-described embodiments and can be variously modified without departing from the gist thereof. Of course. For example, in the above embodiment, the mirror surface is left as a polyimide surface, but metal evaporation may be performed on the formed mirror surface in order to increase the reflection efficiency.

Further, in the above-described embodiment, the mask pattern structure in which the light quantity is gradually increased / decreased by changing the density and area of the rectangular pattern is used. Needless to say, a configuration may be adopted. Furthermore, the reactive ion etching method was taken up as an etching method,
An etching method using an excimer laser may be used.

[0037]

As described above, according to the mirror forming method of the present invention, the mirror forming position is determined by using a photomask partially having a mask pattern in which the size or density of the opening gradually increases and decreases in the longitudinal direction of the optical waveguide. An etching mask of a photoresist having a slope structure is formed on the substrate, and dry etching such as reactive ion etching is performed using such an etching mask. Therefore, a mirror is integrally formed in the optical waveguide by a photolithography technique. In a thin-film optical waveguide circuit configuration requiring a large area and a large number of mirrors, the mirrors can be manufactured collectively in a short time, and the manufacturing efficiency can be greatly improved.

[Brief description of the drawings]

1A is a longitudinal sectional view showing a mirror forming method according to a first embodiment of the present invention in the order of steps, FIG. 1B is a transverse sectional view thereof, and FIG. It is a graph which shows the change of the transmission amount.

2A is a longitudinal sectional view showing a mirror forming method according to a second embodiment of the present invention in the order of steps, FIG. 2B is a transverse sectional view thereof, and FIG. It is a graph which shows the change of the transmission amount.

3A is a longitudinal sectional view showing a mirror forming method according to a third embodiment of the present invention in the order of steps, and FIG. 3B is a transverse sectional view thereof.

FIG. 4 is a cross-sectional view showing a conventional mirror forming method.

[Explanation of symbols]

Reference Signs List 1 optical waveguide core (A ₁ fluorinated polyimide film) 2 thermally oxidized silicon substrate 3 etching mask (A ₃ silicon-based positive photoresist) 4 photo mask 5 linear pattern 6 light amount increasing mask pattern 6 a minute rectangular pattern 7 slope structure 8 reflection Mirror 11 Under cladding 12 Upper cladding

Claims (3)

(57) [Claims] 1. An optical waveguide formed on a dielectric substrate,
This is a method of integrally forming a mirror that reflects the guided light in the optical waveguide, and (a) forming an optical waveguide core material on a dielectric substrate and then forming a photoresist on the optical waveguide core material. Filming, and (b) using a photomask partially provided with a mask pattern in which the size or density of the opening gradually increases or decreases in the longitudinal direction of the optical waveguide, and patterning the photoresist, (c) a method of forming an optical waveguide end mirror, comprising a step of etching the patterned photoresist and the underlying film by dry etching. 2. An optical waveguide formed on a dielectric substrate,
A method for integrally forming a mirror for reflecting guided light in an optical waveguide, comprising: (a) forming a base clad material of an optical waveguide on a dielectric substrate; and Forming a photoresist on the optical waveguide core material after forming the optical waveguide core material on the optical waveguide core, and (c) a mask in which the size or density of the opening gradually increases or decreases in the longitudinal direction of the optical waveguide. Patterning the photoresist using a photomask partially provided with a pattern,
and (d) a step of etching the patterned photoresist and the underlying film by dry etching. 3. An optical waveguide formed on a dielectric substrate,
A method for integrally forming a mirror for reflecting guided light in an optical waveguide, comprising: (a) forming a base clad material of an optical waveguide on a dielectric substrate; and After forming an optical waveguide core material on the optical waveguide core material, a step of forming a photoresist on the optical waveguide core material, and (c) after patterning the photoresist using a photomask, the optical waveguide core by dry etching method (D) forming an upper cladding on the optical waveguide core, and then forming a photoresist on the upper cladding; and (e) controlling the size or density of the opening by light guiding. Patterning the photoresist using a photomask partially provided with a mask pattern that gradually increases or decreases in the longitudinal direction of the wave path, and (d) the patterned photoresist and a lower layer thereof. Method of forming an optical waveguide end mirror, comprising the step of etching by dry etching and.