JPH10206665A - Manufacture of quartz type optical waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten thickness of a resist film which is equipped for creating pattern of an optical waveguide, and increase of accuracy in relation to the created pattern. SOLUTION: A dummy layer 20 is formed on a quarts film 26 forming a core layer. In the dummy layer 20, several layers are piled such that thickness of one layer is smaller than that of its lower layer in turn. A resist film 34 is formed on the dummy layer 20. An optical waveguide pattern 34a is formed by creating pattern of the resist film 34, and the dummy layer 2 is etched using the pattern 34a as a mask. A quartz film 26 is etched using the etched dummy layer 20 as a mask.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a planar optical waveguide using quartz as a material.

[0002]

2. Description of the Related Art Conventionally, a silica-based optical waveguide having a thickness of about 50 .mu.m that matches an optical fiber is formed by the following manufacturing process. That is, an amorphous silicon (hereinafter abbreviated as α-Si) film is formed on the surface of the quartz film,
A step of forming an organic resist film on the upper surface of the α-Si film, a step of patterning the organic resist film by photolithography and etching, and a step of etching the α-Si film using the patterned organic resist film as a mask And etching the quartz film using the etched α-Si film as a mask. The above-described etching of the α-Si film can be performed by, for example, dry etching using CBrF ₃ gas as an etching gas. The etching of the quartz film can be performed, for example, by dry etching using a mixed gas of C ₂ F ₆ and C ₂ H ₄ as an etching gas.

However, when the above-mentioned etching gas is used, the etching rate ratio between the α-Si film and the quartz film is 1: 1.
Since it is about 0, an α-Si film having a thickness of about 10 μm is required to etch a quartz film having a thickness of about 50 μm. Further, since the etching rate ratio between the α-Si film and the organic resist film is about 4: 1, the α-Si film and the organic resist film have a thickness of 10 μm.
In order to etch the Si film, an organic resist film having a thickness of about 3 μm is required. Generally, it is difficult to form a pattern with high precision on such a thick resist film. Therefore, even if the lower layer is etched using this resist film, a high-precision pattern cannot be formed, so that the optical waveguide cannot be processed with high accuracy.

[0004] Therefore, for example, in the document “Japanese Patent Laid-Open No.
7407, a fluoride having a high dry etching selectivity to quartz is used as an etching mask for a quartz film.

[0005]

However, when processing a fluoride, there is no suitable chemical reaction for performing dry etching, so that there is a problem that a high-precision pattern cannot be formed. Although a lift-off method may be used as described in the above document, the cross-sectional shape of the pattern cannot be formed better than that of dry etching. Further, the ion milling method is a method in which fluoride atoms are physically beaten by inert atoms, but cannot be used because there is no appropriate mask material.

Therefore, there has been a demand for a manufacturing method capable of accurately forming a pattern of a silica-based optical waveguide with high accuracy.

[0007]

Therefore, according to the method of manufacturing a quartz optical waveguide of the present invention, a dummy layer is formed above a quartz film for forming a core layer, and a resist film is formed on the upper surface of the dummy layer. A step of forming a pattern of the resist film, etching the dummy layer using the pattern as a mask, and etching the quartz film using the etched dummy layer as a mask. In the method for manufacturing an optical waveguide, the dummy layer is provided as a stack in which first and second mask materials are alternately stacked,
Each layer of the stack is provided such that the thickness of the upper layer on the lower side of the quartz film is smaller in order than the thickness of the lower layer on the quartz film side.

Thus, the first and second mask materials are
Since the upper layer is alternately laminated so that the upper layer has a smaller thickness than the lower layer, the uppermost mask material (hereinafter abbreviated as the uppermost layer) of the dummy layer can have an appropriate thickness.
Then, a resist film is formed on the upper surface of the uppermost layer. The thickness of the resist film can be appropriately determined according to the thickness of the uppermost layer. Therefore, the thickness of the resist film can be a thickness that functions as a mask for etching the uppermost layer, and that can form a pattern on the resist film with sufficiently high precision. Since the resist film can be formed thin in this manner, a pattern having excellent resolution can be formed.

In the method of manufacturing a quartz-based optical waveguide according to the present invention, preferably, the dummy layer is etched in order from an upper layer constituting the dummy layer to a layer on the quartz film side. The upper layer is used as a mask to sequentially perform the lower layer below the upper layer, and the etching rate for the lower layer is preferably set to be higher than the etching rate for the etched upper layer.

In this manner, the dummy layers in which the first and second mask materials are alternately stacked can be etched one by one sequentially from the upper side. That is, the first
When the mask material layer is to be etched, the already etched second mask material layer immediately above this layer is used as a mask, and the etching rate of the first mask material is reduced with respect to the second mask material. To be faster. For example, when dry etching is used, a specific etching gas that achieves the above-described etching rate ratio is used. As a result, the pattern of the second mask material can be transferred to the first mask material with good accuracy. Further, when etching the layer of the second mask material, the etching may be performed such that the etching rate of the second mask material is faster than that of the first mask material.

Therefore, the etched layer can be used as a mask for etching the lower layer, and the pattern of the dummy layer can be formed sequentially from the upper layer. Finally, a pattern of a quartz film is formed using the etched dummy layer. As described above, since the good patterns formed on the resist film can be sequentially transferred to the lower layer, the quartz film pattern can be accurately formed.

In the method for manufacturing a quartz optical waveguide according to the present invention, preferably, the first and second mask materials are made of amorphous Si and SiO ₂ , respectively, and the lowermost layer of the dummy layer is made of amorphous Si. Good to be.

In the method for manufacturing a quartz-based optical waveguide according to the present invention, preferably, the etching of the amorphous Si is performed by using an HBr gas as an etching gas,
The etching of SiO ₂ is preferably performed using a mixed gas of C ₂ F ₆ and C ₂ H ₄ as an etching gas.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. It should be noted that the figures schematically show the size, shape and arrangement relationship to the extent that the method, process and configuration of the present invention can be understood, and the numerical conditions and the like described below are merely examples, and However, the present invention is not limited to this embodiment.

Prior to the description of an embodiment of the method for manufacturing a silica-based optical waveguide of the present invention, an example of the structure of an optical waveguide produced by the method of the present invention will be briefly described. FIG.
FIG. 4A is a plan view showing the structure of the silica-based optical waveguide formed in this step, and FIG. 4B is a plan view taken along line II of FIG.
It is a figure which shows the cut surface of the cross section cut by the line. FIG.
(A) shows the upper cladding layer 16 removed. As shown in FIGS. 4A and 4B, the optical waveguide has a lower clad layer 12
2 is provided with a patterned core layer 14 on the upper side, and the upper side of the core layer 14 is covered with an upper cladding layer 16. The substrate 10 is a Si wafer, and the lower cladding layer 12, the core layer 14, and the upper cladding layer 16 are quartz (SiO ₂ ) films. The core layer 14 is doped with impurities, and has a higher refractive index than the cladding layers 14 and 16. The core layer 14 shown in FIG. 4 is formed in a pattern so as to have a Y-shape in plan view, and constitutes a Y-branch waveguide.

Hereinafter, with reference to FIGS. 1, 2 and 3,
The manufacturing method according to the embodiment will be described. FIGS. 1, 2 and 3 are views showing, as an example, a process of manufacturing the above-described Y-branch waveguide. FIGS. 1 to 3 show cross-sections of the structure obtained in the main process steps, which are taken along a section corresponding to a section taken along line II of FIG.

In this embodiment, a dummy layer 20 is formed above a quartz film 26 for forming a core layer.
0, a step of forming a pattern of the resist film 34, a step of etching the dummy layer 20 using this pattern as a mask, and a step of etching the dummy layer 20 using the etched dummy layer as a mask. The optical waveguide is formed by the step of performing the etching.

First, a 1 mm thick Si wafer 22 is used as a substrate, and a lower cladding layer is formed on the substrate. This formation is carried out at 10 sccm of tetraethoxysilane.
(Standard Cubic Centimeter per Minute) and a plasma CVD method with a substrate temperature of 400 ° C. and a discharge power of 300 W in an atmosphere in which F ₂ gas of 0.2 sccm is mixed with 1 sccm of oxygen. As a result, a 25 μm-thick fluorine-doped SiO ₂ film 24 is formed as a lower clad layer on the Si wafer 22 (FIG. 1A).

Next, a quartz (SiO ₂ ) film 26 for forming a core layer is formed on the upper surface of the fluorine-doped SiO ₂ film 24. This formation is based on tetraethoxysilane 10 scc
substrate temperature in a mixed gas of m and oxygen 1 sccm.
Plasma C at 00 ° C. and discharge power of 300 W
This is performed by the VD method. Thereby, fluorine-doped SiO ₂
A structure in which a 10 μm-thick SiO ₂ film 26 is formed on the film 24 is obtained (FIG. 1A).

Next, the dummy layer 2 is formed on the upper side of the SiO ₂ film 26.
The step of forming 0 will be described. In this embodiment, the dummy layer 20 has a required number of layers such that the upper and lower layers of the first and second mask materials are sequentially thinner than the lower layer of the quartz film 26. Each layer is formed as a laminate that is alternately and sequentially stacked.

For this purpose, first, an α-Si film 28 to be the lowermost layer of the dummy layer is formed. The structure shown in FIG. 1A is formed by sputtering using an Si target in argon (Ar) gas under the conditions of a partial pressure of Ar gas of 1 Pa and a discharge power of 300 W. Then, an α-Si film 28 having a thickness of 1.5 μm is formed on the upper surface of the SiO ₂ film 26 (FIG. 1B).

Next, continuously on the upper surface of the α-Si film 28,
An SiO ₂ film 30 is formed (FIG. 1B). Thus, the first mask material is α-Si, and the second mask material is Si
As O ₂ , the first and second mask materials are alternately laminated. SiO _{2 serving as a} second layer of the dummy layer
The film 30 is formed by Ar + O ₂ (15%) gas (85% A
r gas and a 15% O ₂ gas mixture)
This is performed by a sputtering method using a Si target under the conditions of a gas partial pressure of 1 Pa and a discharge power of 500 W. The thickness of the formed SiO ₂ film 30 is 0.5 μm.

Then, an α-Si film 32 having a thickness of 0.2 μm is formed on the upper surface of the SiO ₂ film 30 as the uppermost layer of the dummy layer (FIG. 1B). The formation of the α-Si film 32 can be performed in the same manner as the formation of the α-Si film 28 described above. As described above, the dummy layer 20 including the α-Si film 28, the SiO ₂ film 30, and the α-Si film 32 is formed on the quartz film 26 for forming the core layer. The thicknesses of the α-Si film 28, the SiO ₂ film 30 and the α-Si film 32 are 1.5 μm, 0.5 μm and 0.2 μm, respectively. As described above, in this example, the dummy layer 20 is formed as a layer in which α-Si and SiO ₂ are alternately stacked only three layers so that the thickness of the upper layer is smaller than the thickness of the lower layer. .

Next, the upper surface of the dummy layer 20, that is, α-S
An organic resist film 34 is formed on the upper surface of the i-film 32 (FIG. 1).
(C)). For the organic resist film 34, a resist material OFPR8600 (trade name) manufactured by Tokyo Applied Chemical Industry Co., Ltd.
Is applied by a spin coater so as to have a thickness of 0.2 μm. Then, a pattern is formed on the organic resist film 34 (FIG. 1D). This pattern is formed by using ordinary photolithography and etching techniques.
4a is formed.

Next, a process of etching the dummy layer 20 using the formed waveguide pattern 34a as a mask will be described. The etching of the dummy layer 20 is performed in order from the upper layer constituting the dummy layer 20 using the etched layer on the upper surface of the layer to be etched as a mask, and the etching rate of the layer to be etched is reduced. The etching is performed at a speed higher than the etching rate.

First, α-S which is the uppermost layer of the dummy layer 20
The i-film 32 is etched. For this, a reactive ion etching (RIE) method is used. Further, HBr gas is used as an etching gas, and the gas pressure is set to 5P.
a, and the discharge power is set to 200 W. By this etching, the α-Si film 32 is patterned according to the waveguide pattern 34a formed from the resist film 34 (FIG. 2).
(A)). At this time, the etching selectivity of the organic resist to α-Si is ３, and the cross section formed by the etching has a substantially rectangular shape. Further, the amount of side etching on the lower side of the resist pattern 34a is substantially negligible.
It can be considered that there is substantially no dimensional change between the pattern shape of the film 32a (referred to as a residual α-Si film) and the pattern shape of the resist. Thus, the waveguide pattern 34a is transferred to the remaining α-Si film (also referred to as a first α-Si film pattern) 32a. The remaining portion of the resist film 34, that is, the resist pattern 34a is used as a mask for etching the SiO ₂ film 30 together with the remaining α-Si film pattern 32a.

Then, the lower SiO ₂ film 30 is etched using the first α-Si film pattern 32a as a mask. This etching uses C ₂ as an etching gas.
The mixed gas of F ₆ gas and C ₂ H ₄ gas is used, and the gas pressure of the mixture is set to 6 Pa and the discharge power is set to 200 W by the RIE method. In this case, the etching selectivity of α-Si to SiO ₂ is 1/10.
As described above, the etching rate of the layer 30 to be etched is reduced by using the portion of the etched α-Si film 32 on the upper surface of the SiO ₂ film 30 as the layer to be etched, that is, the first α-Si film pattern 32a as a mask. Layer 32 of
Etching is performed at a rate higher than the etching rate a. Since the film thickness and the selection ratio are as described above, pattern formation can be performed with good accuracy. Therefore, by this etching step, the waveguide pattern of the first α-Si film pattern 32a is transferred to the SiO ₂ film pattern 30a (FIG. 2B). The remaining α-Si film pattern 32a
Is used together with the SiO ₂ film pattern 30a as a mask for etching the underlying α-Si film 28.

Then, the α-Si film 28 is etched using the SiO ₂ film pattern 30a as a mask. This etching is also performed by the RIE method, and an HBr gas is used as an etching gas. In this case, the etching selectivity of SiO _{2 to} α-Si is 1/20. As described above, the portion of the etched SiO ₂ film 30 on the upper surface of the α-Si film 28 as the layer to be etched, that is, the Si
Using the O ₂ film pattern 30a as a mask, the layer to be etched 2
The etching is performed at an etching rate of 8 higher than the etching rate of the etched layer 30a. By this etching step, the waveguide pattern composed of the remaining portion of the SiO ₂ film 30 is transferred to the second α-Si film pattern 28a (FIG. 2C). The remaining SiO ₂ film 3
The 0 portion 30a is used as a mask for forming the core layer by etching the SiO ₂ film 26 together with the _second α-Si film pattern 28a.

Next, to etch the dummy layer 20 and the lower quartz alpha-Si film pattern 28a of the bottom layer obtained by etching a mask (SiO ₂₎ film 26 as described above (FIG. 3 (A)). The SiO ₂ film 26 is etched by RIE using a mixed gas of C ₂ F ₆ gas and C ₂ H ₄ gas as an etching gas. As described above, the etching selectivity of α-Si to SiO ₂ is 1/10. Accordingly, since each layer has the above-mentioned film thickness, the waveguide pattern 28a comprising the remaining portion of the α-Si film 28 can be transferred to the SiO ₂ film pattern, that is, the core layer 26a with good accuracy. As a result, the waveguide pattern-shaped core layer 26a (ie, FIG. 4A)
And (B) correspond to the core layer 14. ) Is formed.

The α-Si film pattern 28a remaining on the upper surface of the remaining portion 26a of the SiO ₂ film converted into the waveguide pattern is used.
For example, 10 Pa SF gas is used as an etching gas, and
By RIE with a discharge power of 0 W, it can be selectively removed without affecting the core layer (FIG. 3B).

Subsequently, an upper clad layer 36 is formed so as to cover the upper side of the core layer 26a (FIG. 3C).
The upper cladding layer 36 can be formed under the same conditions as the formation of the lower cladding layer 24. Here, as the upper cladding layer 36, a fluorine-doped SiO of 20 μm thickness is used.
_Two films 36 are formed.

Through the steps described above, a quartz-based planar optical waveguide is formed. According to this embodiment, it is possible to solve the conventional problem that the resist film for forming the pattern of the optical waveguide becomes thick and cannot be etched with high accuracy. That is, as described above, the dummy layer is formed by alternately laminating two types of mask materials such that the thickness of the upper layer is smaller than the thickness of the lower layer. Can be made thinner than before. Therefore, the resolution can be greatly increased during the photolithography process. Usually, when a pattern is formed on a part of a wide surface, the exposure conditions for forming a 10 μm-wide waveguide with high precision and the conditions for forming a Y-branch waveguide shown in FIG. The smaller the film thickness, the closer it is. Therefore, simultaneous high-precision pattern formation of both becomes possible. Using the optical waveguide formed in this way, a Mach-Zehnder filter, an N × N star coupler,
Light propagation loss in various optical elements such as a subscriber optical circuit unit element and an arrayed waveguide grating type multiplexing / demultiplexing circuit element can be reduced.

In this embodiment, α-Si and SiO ₂ are used as a combination of the mask material constituting the dummy layer. However, the present invention is not limited to this.
₂ , Cr and SiO ₂ , Al and Si, Al and SiO _{2, and the} like. In these combinations, poly (poly) -Si is used instead of α-Si.
(Polycrystalline silicon) may be used, or SiN _x (where x represents a composition ratio; x> 0) may be used instead of SiO ₂ . In the etching of Ti and Al, it is preferable to use Cl ₂ gas as an etching gas. And in the above-described embodiment,
Although a mixed gas of C ₂ F ₆ gas and C ₂ H ₄ gas was used as an etching gas for SiO ₂ , CHF ₃ gas is also suitable.

[0034]

According to the method for manufacturing a quartz optical waveguide of the present invention, the first and second mask members are alternately stacked so that the upper layer has a smaller thickness than the lower layer. The mask material at the top of the layer can be of a suitable thickness. Then, a resist film is formed on the upper surface of the uppermost layer. The thickness of the resist film can be appropriately determined according to the thickness of the uppermost layer. Therefore, the thickness of the resist film can be a thickness that functions as a mask for etching the uppermost layer, and that can form a pattern on the resist film with sufficiently high precision. Since the resist film can be made thinner in this manner, a pattern having excellent resolution can be formed.

Further, according to the preferred embodiment of the method for manufacturing a quartz optical waveguide of the present invention, the dummy layers formed by alternately laminating the first and second mask materials are sequentially stacked one by one from the upper side.
Can be etched. That is, the etched layer can be used as a mask for etching the lower layer, and the pattern formation of the dummy layer can be performed sequentially from the upper layer. Finally, a pattern of a quartz film is formed using the etched dummy layer. Therefore, good patterns formed on the resist film can be successively transferred to the lower layer, and a quartz film pattern can be formed with high accuracy.

[Brief description of the drawings]

FIG. 1 is a diagram showing a manufacturing process of an embodiment.

FIG. 2 is a view showing a manufacturing step of the embodiment, following FIG. 1;

FIG. 3 is a diagram illustrating a manufacturing step of the embodiment, following FIG. 2;

FIG. 4 is a diagram illustrating a structure of an optical waveguide according to an embodiment.

[Explanation of symbols]

10: substrate 12: a lower cladding layer 14: core layer 16: upper clad layer 20: Dummy layer 22: Si wafer 24, 36: fluorine-doped SiO ₂ film 26, 30: SiO ₂ film 26a: core layer 28, 32: alpha -Si film 34: Organic resist film 28a: Second α-Si film pattern 30a: SiO ₂ film pattern 32a: Residual α-Si film (first α-Si film pattern) 34a: Waveguide pattern

Claims (4)

[Claims] 1. A step of forming a dummy layer on a quartz film for forming a core layer, forming a resist film on an upper surface of the dummy layer, forming a pattern of the resist film, and using the pattern as a mask, A method for manufacturing a silica-based optical waveguide, comprising: a step of etching a dummy layer; and a step of etching the quartz film using the etched dummy layer as a mask, wherein the dummy layer is formed by first and second mask materials. It is provided as alternately stacked layers, and each layer of the layer is provided such that the film thickness of the upper layer above the lower layer is sequentially smaller than the film thickness of the lower layer of the quartz film side of the layer. Of producing a silica-based optical waveguide. 2. The method for manufacturing a quartz-based optical waveguide according to claim 1, wherein the etching of the dummy layer is performed in order from an upper layer constituting the dummy layer to a layer on the quartz film side. Using the upper layer as a mask, sequentially to the lower layer below the upper layer, and performing the etching at a lower rate than the etching rate for the etched upper layer. Method. 3. The method according to claim 1, wherein the first and second mask materials are made of amorphous Si and SiO ₂ , respectively, and the lowermost layer of the dummy layer is made of amorphous Si. A method for manufacturing a silica-based optical waveguide. 4. The method for manufacturing a quartz optical waveguide according to claim 3, wherein the etching of the amorphous Si is performed using an HBr gas as an etching gas, and the etching of the SiO _{2 is} performed using an etching gas. Using a mixed gas of C ₂ F ₆ and C ₂ H ₄ .