JP3488800B2 - Optical platform manufacturing 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 manufacturing an optical platform used in the fields of optical communication systems and optical information processing systems using optical network cables.

[0002]

2. Description of the Related Art A conventional optical platform is shown in FIG. In this optical platform, a V groove 22 for precisely positioning and fixing an optical fiber (not shown) on the surface of a silicon substrate 21, and an optical fiber and a device such as a laser oscillator or an optical modulator are optically coupled. An optical waveguide 23 and a device positioning marker 24 such as a mounted laser oscillator or optical modulator are formed.

A method of manufacturing the optical waveguide portion of this conventional optical platform will be described with reference to FIG. First, as shown in FIG. 3A, the optical waveguide 2 is formed on the silicon substrate 21.
In order to form the lower clad layer No. 3, a recess 25 having a depth of about 40 μm is formed by photolithographic etching.

Next, as shown in FIG. 2B, in order to form the lower clad layer 26, glass particles are deposited on the entire surface of the substrate 21 by the flame deposition (FHD) method, and the temperature is about 1300 ° C. A glass layer is formed by baking at a high temperature.

Next, as shown in FIG. 1C, polishing is performed to eliminate surface irregularities. Next, as shown in FIG. 4D, glass particles to be the lower cladding layer 26a and glass particles to be the core portion 27 having a controlled refractive index and having a thickness of about 8 μm are deposited by the FHD method. The reason why the glass fine particles to be the lower clad layer 26a are further deposited is that the laser light emission port is slightly higher than the laser mounting surface. The glass fine particles are baked and solidified at a high temperature of 1300 ° C. as before. The core portion 2 has a refractive index of the cladding portions 26 and 26a.
If the refractive index of 7 is 0.25% higher, the thickness of the core portion 27 needs to be 8 μm.

Next, as shown in FIG. 1E, the cladding portion 2 is formed using Al having a thickness of about 2 μm as a mask.
The portions other than the waveguide 23 portion composed of 6, 26a and the core portion 27 are etched by reactive ion etching (RIE) or the like.

Next, as shown in FIG. 1F, in order to form the upper clad layer 28, glass fine particles are deposited by the FHD method and baked at a high temperature of about 1300 ° C. to form a glass layer. To do.

Finally, as shown in FIG. 2G, the glass layer 28 in the portion where the V-groove and the device are mounted is removed by using, for example, Al as a mask by, for example, the reactive ion etching method.

In the V groove portion of the conventional optical platform, as shown in FIG. 8A, a predetermined portion of the (1, 0, 0) surface of the silicon substrate 21 is covered with a resist film 29, and then, as shown in FIG. ), It is formed by immersing in a potassium hydroxide solution. That is, the silicon substrate 2
When the resist film 29 is coated so as to expose a predetermined portion of No. 1 and is dipped in a potassium hydroxide solution, anisotropic etching proceeds from the exposed portion to expose the (1, 1, 1) plane, so that the V groove 22 is formed. Is formed. The V groove 22 may be formed by dicing instead of anisotropic etching. When the V groove 22 is formed by dicing, it is formed by cutting a required portion with a cutter to a required depth.

[0010]

However, in this conventional method for manufacturing an optical platform, when the V groove 22 is formed by anisotropic etching, dislocation concentration and impurities in the solution adhere to the silicon substrate 21. Then, there are problems that the etching interface becomes uneven, the positioning accuracy of the optical fiber is deteriorated, and the in-plane uniformity in the V groove 22 is deteriorated due to the wet etching.

Further, in the method by dicing, a necessary portion is cut by a cutter to a required depth, but since it is a physical processing, stress is applied to the silicon substrate 21 and particles at the time of cutting are generated on the silicon substrate 21. There was also a problem that a large amount of them adhered to, and sufficient cleaning was necessary.

Furthermore, when the device positioning marker 24 such as a laser to be mounted is to be formed by a photolithography process after the V groove 22 is formed by anisotropic etching or dicing, the resist film in the V groove 22 portion becomes uneven. There is also a problem that it cannot be applied uniformly.

Furthermore, in the conventional optical platform, the device and the optical waveguide 23 or the optical waveguide 23 and the optical fiber must be positioned with an accuracy of 1 μm or less in order to reduce the connection loss. The platform requires active alignment such as positioning while measuring the light intensity, and there is a problem in that it takes time and cost to create.

The method of manufacturing an optical platform according to the present invention has been made in view of the above problems of the conventional device, and it is possible to accurately form a groove for fixing an optical fiber. It is intended to provide a manufacturing method.

[0015]

In order to achieve the above object, in the method of manufacturing an optical platform according to the present invention,
In a method of manufacturing an optical platform in which a groove is formed on a surface portion of a silicon substrate and an optical fiber is fixed to the groove portion, a mask is formed so that the optical fiber fixing groove portion and the optical waveguide forming portion on the surface portion of the silicon substrate are exposed. By providing anodization treatment to make the exposed portion of the silicon substrate porous, and etching the optical fiber fixing groove portion in the porous region to form the groove, An optical waveguide is formed by doping a part of the optical waveguide forming portion with an impurity having a high refractive index and performing anodization treatment in the converted region, and then fixing the optical fiber to the groove portion.

[0016]

Further, it is desirable to position the device positioning marker mounted on the silicon substrate with the mask.

[0018]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a diagram showing an embodiment of a method for manufacturing an optical platform according to the present invention. As the silicon substrate 1, either p-type or n-type can be used, but p-type low resistance (usually 10 m
Ω to 1 Ωcm) is desirable. This is because it is easy to control the porosity of porous silicon and the diameter of pores.

First, as shown in FIG. 1A, a mask 2 having an opening only in a portion where a groove 4 is formed is formed by using a photolithography technique. This mask 2 has SiN _x , aS
i, Au, Pt, or a resist film having hydrofluoric acid resistance is used. These films have a multilayer structure,
It is also possible to increase resistance. This mask 2 has a width of 0.5
An opening 2a of about 5 μm is provided. When simultaneously forming an optical waveguide and a device positioning marker, a mask 2 in which an optical fiber fixing groove 4 and an optical waveguide and a device positioning marker are opened is provided on a silicon substrate 1.

Next, as shown in FIG. 3B, anodization treatment is performed in a hydrofluoric acid solution to form a region 3 in which the silicon substrate 1 is selectively made porous through the opening 2a of the mask 2. Set up.

FIG. 2 shows an apparatus for performing anodizing treatment. In FIG. 2, 1 is a silicon substrate, 5 is a chemical conversion chamber, 6 is an anode platinum electrode, 7 is a cathode platinum electrode, 8 is a hydrofluoric acid solution, and 9 is a DC power source. The chemical conversion chamber 5 is made of fluororesin or the like. In this apparatus, the hydrofluoric acid solution 8 on the anode platinum electrode 6 side and the cathode platinum electrode 7 side are separated via the silicon substrate 1. The hydrofluoric acid solution 8 containing the cathode platinum electrode 7 is made porous from the surface of the silicon substrate 1. The hydrofluoric acid solution 8 used in the anodizing treatment is a mixed solution of hydrofluoric acid, ethanol, and water, and the hydrofluoric acid concentration is 15 to 50.
%. Current density during anodization is 10 to 250.
It is mA / cm ² . When an n-type substrate is used as the silicon substrate 1, it is necessary to irradiate light with a tungsten lamp or the like during anodization, but when a p-type substrate is used, light irradiation is not necessary.

As shown in FIG. 1B, the porosity progresses from the opening 2a of the mask 2 in a fan-shaped semicircular shape. The size of the porous region 3 can be controlled by the concentration of hydrofluoric acid, the formation current density, the formation time, and the substrate resistance. Formation time 2 to 120 minutes, substrate resistance 0.005 to several tens Ωc
It forms in about m. The depth and porosity of the porous region 3 can be arbitrarily set within ± 1% in terms of in-plane distribution and reproducibility. In order to fix the optical fiber, the depth of the porous region 3 is 80 to 150 μm, and the porosity is 35 to 35 μm.
Set to 70%.

FIG. 3 is a graph showing the relationship between the anodization time and the thickness of the porous region 3. As shown in FIG.
There is an approximately proportional relationship between the anodization time and the thickness of the porous region.

Finally, as shown in FIG. 1 (c), when it is immersed in a solution such as phosphoric acid that is not normally attacked by silicon, since the porous region 3 has a large surface area, only this region 3 dissolves and becomes half. A circular groove 4 can be formed.

FIG. 4 is a diagram showing a method of forming an optical waveguide portion. First, as shown in FIG. 3A, the fixing groove 4 is formed on the mask 2 for forming the optical fiber fixing groove 4.
Then, the optical waveguide portion and the positioning marker portion are simultaneously exposed by performing batch exposure so that the optical waveguide portion and the device positioning marker portion are opened. This mask 2 has Si
_Nx , a-Si, Au, Pt, or a resist film having a hydrofluoric acid resistance is used. It is also possible to make these films a multi-layer structure to increase the durability. The mask 2 is provided with an opening 2b having a width of about 0.5 to 5 μm. This step is the same as the step shown in FIG.

Next, as shown in FIG. 4 (b), an anodization treatment is performed in a hydrofluoric acid solution to selectively make the silicon substrate 1 porous from the opening 2b of the mask 2. A region 10 is provided. This porous second region 1
0 is continuously provided in the porous region 3 for forming the optical fiber fixing groove 4 of FIG. 1 (b). The porosity proceeds from the opening 2b of the mask 2 in a fan-shaped semicircular shape. The size of the porous second region 10 can be controlled by the hydrofluoric acid concentration, the formation current density, the formation time, and the substrate resistance. The formation time is about 2 to 120 minutes and the substrate resistance is about 0.005 to several tens Ωcm. The depth of the porous second region 8 is 80 to 150 μm, and the porosity is 3
Set to 5-70%. This step is the same as the step shown in FIG.

Next, as shown in FIG. 4C, another portion is covered with a resist 11 so that the optical fiber fixing groove 4 portion (see FIG. 1) is opened. Since it suffices that the optical waveguide forming portion and the porous silicon of the device positioning marker portion are covered, the accuracy does not matter.

Next, it is immersed in phosphoric acid to remove only the optical fiber fixing groove 4 portion by etching. (FIG. 1 (c)). When immersed in a solution such as phosphoric acid that is not normally attacked by silicon,
Since the porous region has a large surface area, only the porous region can be melted to form a semicircular groove. The portions other than the optical fiber fixing groove 4 are covered with the resist 11 and are not etched.

Next, as shown in FIG. 4D, the resist 11 is removed by washing with acetone.

Next, as shown in FIG. 4E, the impurity 12 is doped into the optical waveguide forming portion. As impurities, Be, Mg, Al, Cd, Y, Pb, Ti, La,
There are Nb, S, B, Sr, Ge, oxides thereof, compounds containing them, and the like, and an impurity-containing layer is formed and doped on the silicon substrate 1 by a method such as vapor deposition, spin coating, or electrodeposition. . The doping amount depends on the doping material. Normally, the core part and the clad part (Si
O ₂ ) relative refractive index difference (Δn (%)) is 0.25 to 2.0
Impurity doping is performed so as to obtain the desired level. Titanium oxide formed by doping Ti has a refractive index of 2.
The refractive index of 71 and quartz is extremely high compared to the refractive index of 1.14, and the refractive index of the core portion can be increased even with a small amount.

Finally, as shown in FIG. 3F, an oxidation process is performed. This oxidation treatment is performed in three stages, for example. First, the pore surface of the second region 10 made porous at 300 ° C. is oxidized, the second region 10 made porous at 900 ° C. is completely oxidized, and the melt densification and impurities are made at 1150 ° C. Spread. Due to the oxidation, impurities such as Ti are distributed with a concentration gradient from the surface layer portion toward the inside.
This completes the optical waveguide. When it is necessary to provide the upper clad layer, spin-on-glass method, CV
It can be formed by the D method, the FHD method, or the like.

The positioning marker for mounting the device is
By patterning the optical fiber fixing groove 4 at the same time as the mask 2 for producing, the optical fiber can be produced without error. By using the above method, the silicon substrate 1
The optical fiber fixing groove 4 can be formed on the top with high accuracy and good reproducibility. Further, since the mask 2 used when forming the optical fiber fixing groove 4 can form the optical waveguide and the device positioning marker to be mounted by collective exposure, the optical fiber fixing groove 4 and the optical waveguide and the device positioning marker can be formed between the optical waveguide fixing groove 4 and the optical waveguide. It is possible to create an optical platform with no displacement. Therefore, it becomes possible to fix an optical fiber by passive alignment and mount a device using a positioning marker, and there is no need for active alignment such as alignment while measuring light intensity.

[0033]

【Example】

-Example 1-As a substrate, P-type 0.05 Ωc in the (1, 0, 0) plane orientation
A silicon substrate having a resistance of m was used. P-C on the substrate
A 2000 Å SiN film was formed using a VD apparatus. A pattern in which a portion for forming an optical fiber fixing groove was opened to a width of 1 μm was prepared by a photolithography process. SiN etching is performed by reactive ion etching (R
IE) equipment, CF ₄ (60 sccm) and O ₂ (5
sccm) at a power of 700 kW for 5 minutes.

The anodizing treatment was performed using the jig shown in FIG. Hydrofluoric acid concentration is 20%, formation current is 200mA / c
When it is m ² , the formation depth can be determined as shown in FIG. 3, so formation was carried out for about 30 minutes to form anodization to a depth of 121 μm. An almost semicircular cross section was obtained.

Next, it was immersed in phosphoric acid. Normally, silicon did not dissolve in phosphoric acid, but the porous portion had a large surface area and could be completely removed. This groove has an outer diameter of 120
It was possible to mount an optical fiber of μm with high accuracy of ± 0.5 μm.

Example 2 The mask for forming the optical fiber fixing groove shown in Example 1 was collectively exposed so that the optical waveguide and the device positioning marker portion were opened (FIG. 1A and FIG. 1A). Four
(A)). 200 m using 20% HF as in Example 1.
A chemical conversion treatment was performed at a current density of A / cm ² for 30 minutes (FIGS. 1B and 4B). Next, the optical fiber fixing groove was covered with a resist by a photolithography process so as to open (FIG. 4C). Since it suffices that the waveguide forming portion and the porous silicon of the device positioning marker portion are covered, the accuracy does not matter. The groove was formed by immersing in phosphoric acid (FIG. 1 (c)). The resist was removed by washing with acetone (FIG. 4 (d)). Next, it was immersed in a thin film coating type solution containing 5% of organic Ti for 3 minutes, and was shaken and washed in acetone for 3 minutes before the surface was dried. Ti for controlling the refractive index enters near the surface layer of the pores (FIG. 4 (e)).
Finally, oxidation treatment was performed. The oxidation profile has three stages. At 300 ° C, the inner surface of the pores of porous silicon is oxidized, and at 900 ° C, the porous silicon is completely oxidized.
It was performed at 50 ° C. for melt densification and diffusion of impurities.
Due to the oxidation, Ti was distributed with a concentration gradient from the surface layer to the inside.

A near field pattern (NF) when a 1.55 μm laser beam is guided through this optical waveguide
P) was as shown in FIG. Note that FIG. 5A shows a horizontal near-field pattern, and FIG.
Is a vertical near-field pattern.

[0038]

As described above, according to the method of manufacturing the optical platform of the present invention, the surface portion of the silicon substrate is linearly made porous, and the porous region is removed by etching to form the groove. At the same time, the groove for fixing this optical fiber and the optical waveguide are formed with the same mask pattern,
Then, since the optical fiber is fixed in this groove portion, the optical fiber fixing groove can be accurately formed, the optical fiber can be accurately fixed in the groove portion, and the groove for fixing the optical fiber and the optical waveguide are the same mask. Since the pattern is formed, the positioning with respect to the optical waveguide and the device can be accurately performed.

[Brief description of drawings]

FIG. 1 is a process drawing showing an embodiment of a method for manufacturing an optical platform according to the present invention.

FIG. 2 is a schematic configuration diagram of an anodizing apparatus used in the method for manufacturing an optical platform according to the present invention.

FIG. 3 is a diagram showing the relationship between the formation time and the depth of the porous silicon region in the method for manufacturing an optical platform according to the present invention.

FIG. 4 is a diagram showing another embodiment of a method for manufacturing an optical platform according to the present invention.

FIG. 5 is a diagram showing a light intensity profile obtained from a near-field pattern in an optical waveguide manufactured by the method for manufacturing an optical platform according to the present invention.

FIG. 6 is a diagram showing a conventional optical platform.

FIG. 7 is a diagram showing a method of manufacturing an optical waveguide portion of a conventional optical platform.

FIG. 8 is a diagram showing a method of manufacturing a V groove portion of a conventional optical platform.

[Explanation of symbols]

1 ... Silicon substrate, 2 ... Mask, 3 ... Porous area, 4 ... Optical fiber fixing groove, 8 ...
Porous second region

─────────────────────────────────────────────────── --- Continuation of the front page (56) Reference JP-A-8-83955 (JP, A) JP-A-6-347665 (JP, A) JP-A-5-90242 (JP, A) JP-A-9- 17733 (JP, A) JP 10-292540 (JP, A) JP 10-133047 (JP, A) JP 10-133048 (JP, A) JP 10-160950 (JP, A) International Publication 91/010931 (WO, A1) V.I. P. Bondarenko et. al. , Microelectronic Engineering, Vol. 28 No. 1-4 (June 1995), pp. 447-450 A. Loni et. al. , IEEE Colloquium on Microengineering Applications in Optoelectronics, February 27, 1996, pp. 8 / 1-8 / 5 (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02B 6/12-6/14 G02B 6/30

Claims (2)

(57) [Claims] 1. A method of manufacturing an optical platform in which a groove is formed on a surface portion of a silicon substrate and an optical fiber is fixed to the groove portion, the optical fiber being formed on the surface portion of the silicon substrate.
The exposed portion of the silicon substrate is made porous by providing a mask so that the fiber fixing groove portion and the optical waveguide formation portion are exposed, and the exposed portion of the silicon substrate is fixed to the optical fiber fixing portion. The groove portion is etched to form the groove, and the porous region
Among them, the refractive index becomes high in a part of the optical waveguide formation part.
Forming an optical waveguide by oxidizing the impurities by doping UNA method for manufacturing an optical platform, characterized by fixing the optical fiber and thereafter the groove portion. 2. A method of manufacturing an optical platform according to claim 1, characterized in that the positioning device positioning markers to be mounted on the silicon substrate in the mask.