JP3208312B2 - Tapered waveguide and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a tapered waveguide in an optical integrated circuit device and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, miniaturization and integration of optical parts have been promoted, and fine processing techniques on the order of submicrons have been established. In the usual manufacturing method by film formation and etching,
It is general to make the speed as uniform as possible and make the film thickness and etching depth uniform, that is, to process in a plane parallel to the substrate and suppress the distribution in that plane, but in some cases, There is a case where a tapered structure is machined by intentionally giving a distribution to those velocities.

The above processing method is applied to a tapered portion (tapered waveguide) in an optical waveguide.
A tapered waveguide bends light without loss in its thickness direction,
This is an important structure used when crossing the boundary between regions having different effective refractive indices without loss.

In a tapered waveguide, the tapered shape is
Partial shielding by processing methods such as dry or wet etching, ion milling, and cutting, or known film forming techniques such as sputtering, vapor deposition, and CVD, prevents particles from entering the shielding part. It is produced by the shadow mask method used. Here, the etching method and the shadow mask method will be described with reference to the drawings.

FIG. 7 shows a step of forming a tapered shape by etching disclosed in Japanese Patent Application Laid-Open No. 4-55802. A thermally oxidized SiO ₂ film 52 is provided on a Si substrate 51, and a _second layer capable of controlling an etching rate is provided thereon.
SiO ₂ film 53 and a photoresist 5 thereon
4 is patterned. The thermally oxidized SiO ₂ film 52 functions as a buffer layer of the optical waveguide. When these SiO ₂ films are etched with an appropriate etchant, the second SiO ₂ film 53 is etched first because the etching rate is higher than that of the thermally oxidized SiO ₂ film 52. However, since the thermally oxidized SiO ₂ film 52 below this has a relatively low etching rate, the etching proceeds gradually, and is etched in proportion to the time of contact with the etchant. Thus, SiO ₂ as in FIG. 7 (F)
The portion of the film 52 that is not covered with the photoresist 54 is large, and the inside thereof is etched to be small. As a result, the tapered portion 55 as shown in FIG.
Is obtained. 56 is an optical waveguide laminated on these structures.

FIG. 8 shows the Journal of Lightwave Technolog.
y (Vol. 8, No. 4, pp. 587-593, April 1990) showing the principle of the shadow mask method disclosed in Japanese Patent Application Laid-Open (Kokai) No. H10-15083. A metal mask 61 is arranged at a certain distance from the substrate 63 by a spacer 62. When a film is formed from above in this state, the film is distributed around the masked portion in the shade of the mask 61 and the film thickness is distributed, and a tapered structure portion 64 as shown is obtained. The shape of the taper is determined by the cross-sectional shape of the mask 61, the distance from the mask to the substrate, the size of the film-forming particle source and the distance from the substrate, and the like. This causes the shadow of the mask 61 to be unclear.

An application of the shadow mask method is disclosed in
A manufacturing method shown in FIG. 9 disclosed in JP-A-134216 is also known. The substrate 72 on which the photoresist pattern 71 is formed is positioned so as to lean between the film forming particle source 75 of the film forming apparatus and the sample table 76. Since the substrate 72 is separated from the cooled sample table 76 by being leaned in this manner, the substrate 72 is set with a metal jig 74 having good heat conductivity. During the film formation, the film-forming particles 79 fly obliquely with respect to the photoresist pattern 71 on the substrate 72, and are stacked on the surface of the substrate without the photoresist with a film thickness distribution corresponding to a shadow. After film formation, an operation called lift-off is performed. Specifically, the photoresist pattern 71 and the unnecessary film 78 laminated thereon are removed by a solvent such as acetone in which the photoresist is soluble, and a film 77 having a desired tapered end is obtained.

[0008]

A film laminated by a deposition method such as vapor deposition, sputtering, or CVD has an advantage that a material can be selected widely as compared with a case where a thermal oxidation method is used. However, films formed from these materials are more likely to have grain boundaries than, for example, SiO ₂ films formed by a thermal oxidation method, and generally have a rough and porous surface. Since the surface roughness is increased as compared with the case of the above, there is a problem that the optical loss of the tapered waveguide manufactured by this method is larger than that of the thermally oxidized SiO ₂ film, and the material is limited. Was the current situation. Also, in the step of removing the SiO ₂ film used to control the etching rate, a step is generated in the tapered portion due to the difference in the etching rate of each material, which also greatly increases the optical loss of the tapered waveguide. Had an effect.

Further, in the taper processing by etching, ions in the etchant invade the substrate or the etching itself reaches the substrate, and these effects on the substrate may cause fluctuations in device characteristics. Was.

The taper obtained by the shadow mask method has a taper length of several mm since the mask and gap are about 1 mm, which hinders miniaturization and integration of elements. Further, there is a problem that mass production is difficult due to operations such as attachment and detachment of the shadow mask used in this method and cleaning.

When film formation from an oblique direction is applied,
The film thickness distribution and the refractive index distribution of the film forming material in the device have often been problems.

In view of these problems, the present invention makes use of the advantages of a tapered waveguide having a small increase in surface roughness and having no step, and a wide selection of tapered materials, while reducing the surface roughness by tapering by etching. The object of the present invention is to provide a method of manufacturing a tapered waveguide that does not increase and that no step is left, and further provides a method of manufacturing a tapered waveguide suitable for mass production without damage to a semiconductor substrate during taper processing. I have.

[0013]

In order to achieve the above object, according to the present invention, an optical waveguide layer is provided on a semiconductor substrate via a dielectric layer having a tapered portion, and a light detecting layer is provided on a substrate portion at a tapered end. In the method of manufacturing a tapered waveguide provided with a vessel, a step of forming the dielectric layer by deposition, a step of processing a part of the formed dielectric layer into a tapered shape by etching , by polishing the etched surface to make, to the steps of the gently tapered portion of the surface is smooth and inclined, laminating an optical waveguide layer on the dielectric layer, characterized by having a .

Further, according to the present invention, a taper is formed on the semiconductor substrate.
Providing an optical waveguide layer via a dielectric layer having a shape portion
At the same time, a taper with a photodetector
In the method of manufacturing a waveguide, the dielectric layer is formed by deposition.
And forming a part of the formed dielectric layer by etching.
Processing to form a tapered shape by
Filling SOG on the body layer and polishing the SOG
The surface is smooth and the slope is gently tapered.
And forming an optical waveguide layer on the dielectric layer
And a step of performing In addition, the present invention
Now, a dielectric layer having a tapered portion on a semiconductor substrate
The optical waveguide layer is provided through the
In the manufacturing method of the tapered waveguide provided with the photodetector in the part
Forming the dielectric layer by deposition,
Part of the dielectric layer that has been processed into a tapered shape by etching
And filling SOG on the processed dielectric layer
Process and polishing the SOG by making an edge grind
This makes the surface smooth and gently tapered
Forming an optical waveguide layer on the dielectric layer;
And a step of layering.

Further, according to the present invention, a taper is formed on a semiconductor substrate.
Providing an optical waveguide layer via a dielectric layer having a shape portion
At the same time, a taper with a photodetector
In the method of manufacturing a waveguide, the dielectric layer is formed by deposition.
And forming a part of the formed dielectric layer by etching.
Process to form a tapered shape by etching
While removing the mask material by polishing,
Polish the surface of the dielectric layer by making an edge grind
This makes the surface smooth and gently tapered
Forming a shape, and laminating an optical waveguide layer on the dielectric layer.
And

Further, a polishing cloth in the polishing step is used.
And a soft material is used. Also, the polishing
As a polishing cloth in the process, use a soft polishing cloth or
Or suede.

Further, between the substrate and the light detector and the dielectric layer, characterized in that a protective film as a stop layer for the etching process, the protective film comprising the same or silicon LPCVD nitride film Laminate or CVDSiO
It is characterized by being composed of _two films or a laminate including the _two films.

Further, according to the present invention, in the tapered waveguide provided with an optical waveguide layer on a semiconductor substrate via a dielectric layer having a tapered portion and a photodetector provided on a substrate portion at a tapered end, The body layer is sharpened at the edge.
Were polished to make the surface is characterized by having a gently tapered for smooth and inclined.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing a process of the first embodiment. As shown in FIG.
On a substrate 11, a dielectric layer 12 functioning as a buffer layer of an optical waveguide is patterned, and
3 has occurred. This step is generated, for example, by patterning a photoresist on the dielectric layer 12 and performing etching using the photoresist as a mask. The surface of the dielectric layer 12 is desirably smooth because the surface roughness may be large enough to affect the propagation loss of the waveguide depending on the thickness of the layer and the film forming method. The step 13 processed by etching generally has a larger surface roughness than the surface of the dielectric layer 12.

Subsequently, the surface is polished. Polishing conditions vary depending on the material of the film and the state of lamination, but an example is shown below.

Substrate: 4 "silicon wafer Dielectric layer: PSG (Phospho-Silicate Glass) Thickness
2.3μm Abrasive: 0.5μm diameter diamond slurry Polishing cloth: Soft polishing cloth manufactured by Maruto Co. PSG and B, which have never been used as a material for the dielectric layer, are porous and have a rough surface.
PSG (Boron-doped Phosho-Silicate Glass) can be used. By using these materials for the dielectric layer, it is possible to reduce the film stress, suppress the occurrence of cracks in the laminated portion, and stabilize the device characteristics.

As the polishing cloth, a soft material such as polishing cloth or suede is used. Polishing sagging of the edge can be intentionally made by using these soft materials, and a desired tapered waveguide can be obtained by using this.

By this polishing step, the step 13 is formed as shown in FIG.
A gentle taper 14 as shown in FIG. 2B is obtained, and the surface of the dielectric layer 12 becomes sufficiently smooth.

FIG. 2 shows a taper shape measured by a surface roughness meter. FIG. 2A shows the measurement result of the taper before polishing, and FIG. 2B shows the measurement result of the gentle taper (tip portion) after polishing, which correspond to the process of FIG. According to FIG. 2, a PSG buffer layer having a thickness of about 2 μm has a taper length of about 5 μm.
It can be seen that a gentle taper of 0 μm is formed. In addition, the surface roughness of the PSG layer is reduced by this polishing.
(Peak to Valley) value from about 80 nm to 5 nm before polishing (measured on the polished surface 200 μm away from the tapered tip)
And it is sufficiently smooth as a buffer layer of the optical waveguide.

Next, as shown in FIG.
5 is laminated. The optical waveguide layer is made of a material having a higher refractive index than the dielectric layer 21, for example, a # 7059 glass film (N = 1.56) manufactured by Corning and having a thickness of 0.6 μm.

Through the above process, a tapered waveguide having a tapered shape with a gentle inclination can be obtained. Substrate portion at the tapered end (the substrate here is a semiconductor material)
A light detector 19 is formed, and light propagating through the optical waveguide is guided to the light receiving portion of the photo detector by the tapered waveguide, and a light signal is converted into an electric signal. Is composed.

As for the substrate 11, if a dielectric substrate made of a material having an optical property or a composite thereof having a function as a buffer layer, for example, a quartz glass substrate is used, two optical waveguides having different effective refractive indices are coupled. A tapered waveguide can be manufactured.

FIGS. 3A and 3B show a refraction mode splitter utilizing the structure. FIG. 9A is a sectional view showing the configuration of the mode splitter, and FIG. 3B is a plan view showing the principle. is there. The effective refractive index in each region can be changed by a combination of the film forming material and the thickness. In this example, as shown in FIG. 3A, a dielectric substrate 91, for example, a dielectric layer 92 having a higher refractive index than a quartz glass substrate,
For example, a region A having a large effective refractive index is formed by laminating a TiO ₂ film. The propagating light is refracted when passing through this boundary portion connected by the gentle taper 94 (region B → region A, region A → region B), and as shown in FIG. Due to the difference, the optical path is separated (separation angle θ). The light propagating in the optical waveguide 95 (the traveling direction is from left to right in the drawing) can be transmitted without loss through different boundaries of the structure by the tapered waveguide having a smooth surface and a gentle slope.

The second embodiment will be described with reference to FIG.

In this embodiment, as shown in FIG. 4A, an SOG (Spin On Glass) 26 is coated on a dielectric layer 22 having a step patterned on a substrate 21. By this coating, the step is formed into a rather gentle taper. It is needless to say that this SOG needs to have an optical characteristic that particularly functions as a buffer layer of the waveguide.

If an optical waveguide is laminated as it is, a tapered waveguide can be obtained. In the case of a waveguide type photodetector, the SOG 26 acting as a buffer layer on the light receiving portion of the photodetector 29 is used.
Prevent the coupling of light to the substrate side, the buffer layer is removed by polishing. In polishing, unlike the removal by etching, the surface is not roughened.

When the polishing process is performed, a further gentle taper 24 is obtained as shown in FIG. And FIG.
By laminating the optical waveguides as shown in (c), a tapered waveguide having a gently tapered shape can be obtained.
The optical waveguide layer is made of, for example, Corning # 7059 glass having a thickness of 0.6 μm.

Through the above process, a tapered waveguide having a tapered shape with a gentle inclination can be obtained.
A photodetector 29 is formed on the substrate (here, a semiconductor material) at the tapered end, and light that has propagated through the optical waveguide is guided to the light receiving portion of the photodetector 29 by the tapered waveguide, and an optical signal is converted into an electric signal. This constitutes a so-called waveguide type photodetector.

The third embodiment will be described with reference to FIG. When the taper processing is performed by the method shown in FIG. 7 described in the conventional example, the etching rate control material 37 remains on the surface of the dielectric layer 32 as shown in FIG. Conventionally, the etching rate control material in this portion was removed by performing wet etching for a short time, but in this embodiment, direct polishing is performed. As shown in FIG.
As shown in (b), the etching rate control material 37 is removed, and in addition, a rough tapered surface can be made smooth at the time of taper etching. Actually, the etching rate control material can be removed by wet etching for a short time and then polished. However, in this case, a step is formed on the tapered surface by etching or the substrate 31 is etched. There is a risk.

Subsequently, by laminating an optical waveguide on this,
A tapered waveguide as shown in FIG. 5C can be manufactured. The optical waveguide layer is, for example, a 0.6 μm-thick Corning #
It is made of 7059 glass.

Through the above process, a tapered waveguide having a tapered shape with a gentle inclination can be obtained.
A photodetector 39 is formed on the substrate (here, a semiconductor material) at the tapered end, and the light propagating through the optical waveguide is guided to the light receiving portion of the photodetector 39 by the tapered waveguide, and the optical signal is converted into an electric signal. This constitutes a so-called waveguide type photodetector.

If the substrate 31 is made of a dielectric substrate made of a material having optical characteristics or a composite thereof having a function as a buffer layer, for example, a quartz glass substrate, two optical waveguides having different effective refractive indices are used. Can be manufactured. The configuration and principle of the application are the same as those described with reference to FIG.

A fourth embodiment will be described with reference to FIG.

When a semiconductor element is formed on a substrate like a waveguide type photodetector, the element in the semiconductor substrate is damaged by etching or polishing for forming a smooth tapered shape. Sometimes. Therefore, in this embodiment, as shown in FIG. 6, a protective film 48 for protecting the semiconductor element from damage due to etching or polishing is previously laminated between the semiconductor substrate 40 and the dielectric layer 42. Considering a semiconductor process, an LPCVD silicon nitride film or a laminate including the same is most suitable as the protective film.

As shown in FIG. 6A, when the taper 44 is processed using the etching rate control material 47, the etching rate of the protective film 48 is sufficiently smaller than the etching rate of the buffer layer. The etching does not proceed to the substrate beyond the substrate, and the semiconductor substrate 40 is not affected by the etchant.

Subsequently, etching is performed for a short time to remove the etching rate control material. Since the protective film 48 functions effectively also at this time, there is no concern that the semiconductor substrate 40 is attacked by the etchant during the removal of the etching rate control material. At this time, since the tapered portion 42 is also etched for the same time,
Steps as shown in FIG. 6B remain in the dielectric layer 42.
In order to eliminate this step and smooth the tapered surface,
Here, a polishing process is performed. By polishing, a gentle taper 44 as shown in FIG. 6C is obtained. The protective film 48 effectively functions for polishing at this time, and the semiconductor substrate 40 is not affected by the abrasive.

Finally, as shown in FIG.
5 is laminated. The optical waveguide layer is made of, for example, Corning # 7059 glass having a thickness of 0.6 μm.

Through the above process, a tapered waveguide having a tapered shape with a gentle inclination can be obtained.
A photodetector 49 is formed on the substrate portion at the tapered end, and light propagating through the optical waveguide 45 is guided to the light receiving portion of the photodetector 49 by the tapered waveguide, and an optical signal is converted into an electric signal. This constitutes a so-called waveguide type photodetector.

In the case where the substrate has a function as a buffer layer, for example, a glass substrate, there is no particular need for a protective film as long as the substrate itself has resistance to the above-described tapering. However, when a protective film is used on a substrate having a problem in resistance, the protective film needs to have optical characteristics to function as a buffer layer. As a material having such properties, withstanding the above-described processing, and being used in the semiconductor process, a CVD SiO ₂ film (including a thermal annealing treatment in some cases) or a laminate including the same is most suitable.

[0046]

According to the method for manufacturing a tapered waveguide of the present invention, the step formed in the buffer layer is removed by polishing at the edge.
Since it is made and polished to make it gentle and the optical waveguide is laminated thereon, it is not necessary to strictly process the step portion of the buffer layer into a gently tapered shape in advance, thereby improving the yield and reducing the cost. Further, since the deposition film forming method can be used, the selection of the taper material is expanded, and integration with various devices becomes possible. In particular, by using PSG or BPSG as the taper material, the film stress is reduced, and it is possible to prevent problems such as generation of cracks and changes in the characteristics of the semiconductor device at the portion where the films are laminated, thereby improving the device manufacturing efficiency and the yield. And reliability is improved. In addition, even if the surface roughness is increased by processing such as etching, the surface can be smoothed by polishing, so that optical loss does not become a problem, which leads to higher characteristics and improved reliability of the element.

Further, SO is formed at the stepped portion generated in the buffer layer.
G is filled to make it more gradual, and this is polished to suppress the shape change at the tapered tip, and then the optical waveguide is laminated, so that a tapered waveguide with smaller optical loss is manufactured. Therefore, the characteristics of the element are improved.

The etching rate control material used when processing the taper in the buffer layer is removed by polishing, and the surface of the tapered portion is smoothed and the slope is made gentle, and the optical waveguide is laminated on the tapered portion. Even if a step of removing the control material is not particularly provided, a tapered shape without a step can be obtained, and a tapered waveguide with small optical loss can be manufactured. Therefore, the number of processes can be reduced, so that the cost can be reduced, the performance of the device can be improved, and the reliability can be improved.

In the above polishing, a soft material or a soft material
By using a quality polishing cloth or suede , it is possible to intentionally create a sagging sag of the edge and use it for the fabrication of a tapered waveguide, thereby obtaining a tapered shape with a smooth surface and a gentle slope, and optical loss. Can be manufactured. Therefore, cost reduction and higher performance of the element can be achieved.

By providing a protective film between the substrate and the buffer layer as a stop layer when the taper processing is performed by wet etching or polishing, damage to the substrate by an etchant, an abrasive, etc. can be suppressed. In addition, the cost can be reduced and the reliability of the device can be improved.

Further, by using a hard and dense LPCVD silicon nitride film used in a semiconductor process or a laminate containing the same, or a CVD SiO ₂ film or a laminate containing the same as the protective film, protection of the substrate can be achieved. Since it can be more effectively achieved, cost reduction and improvement of the reliability of the element can be achieved.

[0052] Further, the tapered waveguide of the present invention, the edge
It has a buffer layer that has a smooth surface and a gently sloped surface that has been polished and polished, and an optical waveguide layer has been laminated on it. And reliability can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a first embodiment of the present invention.

FIG. 2 is a measurement result of a sectional shape of a taper.

FIG. 3 is a cross-sectional view and a plan view illustrating an application example of the embodiment of the present invention.

FIG. 4 is a sectional view showing a second embodiment of the present invention.

FIG. 5 is a sectional view showing a third embodiment of the present invention.

FIG. 6 is a sectional view showing a fourth embodiment of the present invention.

FIG. 7 is a sectional view showing a conventional example.

FIG. 8 is a perspective view showing another conventional example.

FIG. 9 is a cross-sectional view showing another conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Substrate 12 Dielectric layer 13 Step 14 Slow taper 15 Optical waveguide 19 Photodetector

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-55802 (JP, A) JP-A-7-134216 (JP, A) JP-A-6-140620 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G02B 6/122 G02B 6/13 G02B 6/42

Claims (9)

(57) [Claims] 1. A method of manufacturing a tapered waveguide, comprising: providing an optical waveguide layer on a semiconductor substrate via a dielectric layer having a tapered portion; and providing a photodetector on a substrate portion at a tapered end. A step of forming a layer by deposition, a step of processing a part of the formed dielectric layer into a tapered shape by etching, and a step of polishing the etched surface by forming a polishing sag of an edge, so that the surface is smooth and smooth. A method for manufacturing a tapered waveguide, comprising: a step of forming a tapered portion having a gentle inclination; and a step of laminating an optical waveguide layer on the dielectric layer. 2. A method for manufacturing a tapered waveguide, comprising: providing an optical waveguide layer on a semiconductor substrate via a dielectric layer having a tapered portion; and providing a photodetector on a substrate portion at a tapered end. Forming a layer by deposition, processing a part of the formed dielectric layer into a tapered shape by etching, filling SOG on the processed dielectric layer, and polishing the SOG A step of forming a tapered portion having a smooth surface and a gentle slope, and a step of laminating an optical waveguide layer on the dielectric layer. 3. A semiconductor substrate having a tapered portion.
An optical waveguide layer is provided via a dielectric layer, and a taper is provided.
How to make a tapered waveguide with a photodetector on the edge substrate
In law, a step of forming by depositing the dielectric layer was deposited induced
Process a part of the electric conductor layer into a tapered shape by etching
And a step of filling SOG on the processed dielectric layer
And polishing the SOG by making an edge grind
The surface is smooth and the slope is gently tapered
And forming an optical waveguide layer on the dielectric layer.
And forming a tapered waveguide.
Construction method. 4. A method of manufacturing a tapered waveguide, comprising: providing an optical waveguide layer on a semiconductor substrate via a dielectric layer having a tapered portion; and providing a photodetector on a substrate portion at a tapered end. A step of forming a layer by deposition, a step of processing a part of the formed dielectric layer into a taper shape by etching, and removing a mask material in the etching step by polishing and forming a polishing sagging of an edge. wherein by polishing the dielectric layer surface, tapers the steps of a gently tapered surface is smooth and inclined, laminating an optical waveguide layer on the dielectric layer, characterized by having a Waveguide manufacturing method. 5. The polishing cloth in the polishing step is a soft cloth.
5. The method according to claim 1, wherein a material is used.
13. A method for manufacturing a tapered waveguide according to 6. A soft cloth as the polishing cloth in the polishing step.
It is important to use quality polishing cloth or suede.
The tapered waveguide according to any one of claims 1 to 4,
Road manufacturing method. 7. The tapered conductive film according to claim 1 , wherein a protective film is provided between the substrate and the photodetector and the dielectric layer as an etching stop layer. Waveguide manufacturing method. 8. The tapered waveguide according to claim 7 , wherein the protective film is formed of an LPCVD silicon nitride film or a laminate including the same, or a CVD SiO ₂ film or a laminate including the same. Production method. 9. A tapered waveguide in which an optical waveguide layer is provided on a semiconductor substrate via a dielectric layer having a tapered portion and a photodetector is provided on a substrate portion at a tapered end, wherein the dielectric layer comprises: Make and polish the edge
A tapered waveguide having a smooth surface and a tapered shape with a gentle slope.