JPH0727888B2 - Dry etching method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a dry etching method, and more particularly to a dry etching method effective for manufacturing a circuit component having a laminated structure such as an optical integrated circuit.

[Technical background of the invention]

In recent years, research on circuit components having large steps and a laminated structure such as an optical integrated circuit and a three-dimensional integrated circuit has become active. Accompanying this, the processing of substrates having steps and a laminated structure cannot be handled by conventional photolithography technology, and it is necessary to develop a precision processing method suitable for this. For example, optical integrated circuits are expected in the fields of optical communication and optical information processing. A silica-based optical waveguide circuit in which an optical waveguide and a light emitting / receiving element are combined and integrated is an effective means for realizing an optical integrated circuit (for example, Japanese Patent Application No. 59-167677).
No., M. Kawachi et al, Electron. Lerr., 21, 31, (198
Four)〕.

The application of this silica-based optical waveguide circuit to a multimode optical circuit has been studied so far, and for example, a ridge-shaped optical circuit has been produced as shown in FIG. FIG. 1 is a perspective view showing a ridge-shaped optical circuit, in which 1 is a substrate, 2 is an optical waveguide, 3 is a fiber guide, 4 is a laser guide, 5 is a light receiving element guide,
6 is a fiber, 7 is a semiconductor laser, 8 is a small reflecting mirror, 9
Is an avalanche photodiode.

In forming the optical waveguide 2, the fiber guide 3, the laser guide 4, and the light receiving element guide 5 of such an optical circuit, one photomask pattern 10 as shown in FIG.
It can be formed by removing an unnecessary portion of the silica-based optical waveguide film by dry etching using.
Since the positions of the optical waveguide 2 and the guides 3, 4, 5 are determined by the photomask pattern 10, alignment between the optical waveguide 2 and the guides 3, 4, 5 is not necessary during the process, and high precision is achieved. The alignment can be realized automatically with.

By the way, when the silica-based optical waveguide circuit is applied to a single-mode system, a thick clad layer is formed instead of the ridge shape as in the optical circuit shown in FIG. 1, and as shown in FIG. It is desirable to have a structure in which the core is embedded. This is because, in the case of a single mode system, an optical electric field is more likely to seep into the clad layer, so that a thick clad layer is required. That is, the waveguide buffer layer 2b is formed on the substrate 1, the core 2a is formed on the buffer layer 2b, and
A thick clad layer is formed around the core 2a and the buffer layer 2b.
It has a structure in which the core 2a and the like are embedded by being covered with 2c.

In the case of manufacturing such an embedded optical waveguide circuit, conventionally, the guide and the optical waveguide cannot be manufactured at the same time by using one photomask, and thus FIG. 4A to FIG.
It was manufactured based on the process shown in.

First, as shown in FIG. 4 (a), a mask pattern is formed on the silica-based optical waveguide film 2'formed on the substrate 1 by the photolithography technique using the photomask pattern 10a. Reference numeral 21 is a mask material. Next, the optical waveguide 2 is formed by dry etching (Fig. 4 (b)), the embedded clad layer 2c is formed thereon (Fig. 4 (c)), and the optical waveguide embedded with the embedded clad layer 2c is formed. A mask material 21 is formed again on the surface 2 and the guide portion 2d is patterned by the photomask pattern 10b (FIG. 4 (d)). Further, the clad layer 2c is dry-etched to form a fiber connecting guide 2d for the optical waveguide 2 (FIG. 4 (e)).

In such a step, in the step shown in FIG. 4 (d), it is necessary to pattern the guide pattern 10b with respect to the position of the already formed optical waveguide 2 with an accuracy within an error of 1 μm. is there. However, since the mask material 21 is already laminated on the clad layer 2c, it is impossible to directly visually observe the optical waveguide 2 formed in the lower layer. Therefore, in the conventional dry etching process,
It was extremely difficult to perform precise alignment between the guide and the waveguide.

[Outline of Invention]

The present invention has been made in view of the above points, and when processing a circuit component having a laminated structure, such as an embedded silica optical waveguide, a dry structure capable of accurately aligning an upper layer structure and a lower layer structure. It is an object to provide an etching method.

Therefore, the dry etching method according to the present invention, after forming a buried mask of a desired pattern on the surface of the first material to be processed, remove unnecessary portions by etching to form a lower layer structure on the surface of the first material to be processed, A second work material is laminated and formed on the surface of the first work material in which the embedded mask remains, and a surface mask having a desired pattern is formed on the second work material, and the surface mask and embedding are performed. It is characterized in that a desired structure is formed on the surfaces of the first processing material and the second processing material by etching using the mask as a mask to remove unnecessary portions.

According to the present invention, for example, when etching a circuit component having a laminated structure, not only a mask material is formed on the surface, but also between the upper second processing material and the lower second processing material. A mask material can be formed, and the upper layer and the lower layer can be collectively processed by dry etching using the surface mask and the buried mask, and therefore, the upper layer structure and the lower layer structure can be accurately aligned.

[Specific Description of the Invention]

FIG. 5 shows an example of a process when the dry etching method according to the present invention is applied to manufacture of a buried quartz optical waveguide with a guide. In the drawing, 31 is an amorphous Si (a-
Si) mask and 32 are Cr masks, and the same reference numerals as in FIG.

First, as shown in FIG. 5 (a), a silica-based waveguide thin film 2'is formed on a substrate 1, and a mask is patterned into an optical waveguide and a guide shape. In this embodiment, an amorphous Si (a-Si) mask 31 is used as a mask material for forming an optical waveguide, and an amorphous Si (a-Si) mask 31 and a Cr mask 32 are used for forming a guide portion. It uses a stack.

Next, reactive ion etching is performed by using the amorphous Si (a-Si) mask 31 and the Cr mask 32 as masks to remove unnecessary portions of the silica-based optical waveguide film 2 '(Fig. 5 (b)), and the optical waveguide The path 2 and the guide portion 2d are formed. At this time, the mask on the guide portion 2d is made of amorphous Si (a-S
i) Since the mask 31 and the Cr mask 32 have two layers, the mask thickness is thicker than the mask on the optical waveguide 2 and the mask on the guide portion 2d at the end of etching. Therefore, after the etching is completed, the amorphous Si (a-Si) mask 31 on the waveguide 2 is removed, and the guide portion is removed.
It is possible to leave the mask 31 on 2d left. Amorphous Si (a-Si) on the waveguide 2
To remove the mask 31, for example, a reactive ion etching method can be used.

Next, a clad layer 2c is formed on it and the whole is embedded (FIG. 5 (c)). This clad layer 2c is made of, for example, Si
Source gases such as Cl ₄ and TiCl ₄ are hydrolyzed in an oxyhydrogen flame,
A method of depositing glass fine particles on the substrate 1 and then making the glass vitrified at a high temperature in electricity [Japanese Patent Application No. 58-1473].
Issue, M. Kawachi et al. Electron Lett., 19 (1983), 58.
3] can be formed. By forming the clad layer 2c in this way, the guide portion 2d is masked.
While the 31 is still attached, it is embedded in the cladding layer 2c and becomes the embedded mask 31a.

After forming the cladding layer 2c in this way, at least the upper surface of the waveguide 2 is covered, but the upper surface of the glass portion 2d is not covered.
An amorphous Si (a-Si) mask 31 is formed (FIG. (D)), and reactive ion etching is performed to form the mask 31.
The portion of the clad layer 2c in which the clad is not formed is removed (fifth
Figure (e). At this time, an embedded mask is placed on the guide portion 2d.
Since 31a is formed, the guide portion 2d is not removed by etching. As a result, a buried optical waveguide with a guide having the guide 2d on the substrate 1 and the core 2a buried in the cladding layer 2c can be formed.

In the above embodiment, as a method of forming the amorphous Si (a-Si) mask 31 and the Cr mask 32 in the step of FIG. 5A, for example, the method shown in FIG. 6 can be used.

In FIG. 6, 31 'is an amorphous silicon film and 32' is Cr.
Films, 40 and 41 are photomasks, and 33 is a photoresist pattern.

First, as shown in FIG. 6 (a), the optical waveguide film 2'is formed on the substrate 1.
Then, an amorphous Si film 31 'is formed on the entire surface, and then a photomask 40 is used to perform a lift-off method.
A Cr mask film 32 'is formed.

Next, using the photomask 41, a resist pattern 33 is formed by a normal photolithographic technique. An optical waveguide portion and a guide portion are drawn on the photomask 41. Therefore, it is not necessary to align the guide and the waveguide during the processing process, and highly accurate alignment can be realized automatically. The guide pattern here is
The waveguide pattern is formed on the Cr film 32 'by the amorphous Si film 31'.
Although it requires some alignment as formed above, it is extremely easy because the Cr pattern in the lower layer has a simple shape and a large amount of misalignment is possible (FIG. 6 (b)).

Next, using the resist pattern 33 as a mask, unnecessary portions of Cr
The film 32 'is removed so that the Cr film 32' remains only in the guide portion 2d (Fig. 6 (c)). Finally this resist pattern 33
By removing the unnecessary portion of the amorphous Si film 31 'by reactive ion etching using the mask as a mask, the state shown in FIG. 5 (a) can be formed.

Further, in the step of FIG. 5D in the above-mentioned embodiment, the amorphous Si (a-Si) mask 31 is formed only on the upper portion of the waveguide 2, and the amorphous Si (a-Si) mask is formed on the upper portion of the guide 2d.
In order to prevent the -Si) mask from being formed, for example, the method shown in FIG. 7 may be used.

FIG. 7 is a side view of FIGS. 5 and 6. First, as shown in FIG. 7 (a), an amorphous resin is formed on the cladding layer 2c in the state of FIG. 5 (c). A Si film 31 'is formed. As a result, the embedded Si mask 31a cannot be seen directly from the material information. However, if a sufficiently large pattern is formed as the guide portion 2d, the surface is not flat when the clad layer 2c is formed, and the guide portion 2d is slightly raised. Therefore, when the resist film 33 is applied with this as a mark, alignment is performed using the photomask 40, and the photolithography technique is applied, the resist mask 33 is formed only on the upper portion of the waveguide 2 as shown in FIG. 7B. It is formed. At this time, since the positional deviation tolerance of the photomask 40 is sufficiently large, the photomask 40 is formed by the above-described means.
It doesn't matter if you install. Also, the influence of the step on the substrate surface does not matter.

Finally, the resist pattern 33 is used as a mask to remove the unnecessary portion of the amorphous Si film 31 ', whereby the state shown in FIG. 5D can be realized.

As described above, according to the present invention, there is an advantage that a buried waveguide with a guide having high positional accuracy can be easily manufactured.

Although three types of resist, amorphous Si (a-Si) and Cr film were used as the mask material in this embodiment, the present invention is not limited to this. As such a mask material, any material may be used as long as it has a sufficient etching selection ratio with respect to a material to be processed, for example, quartz, and can be patterned by a dry etching process. In the case of manufacturing the above-mentioned optical waveguide, it is preferable that the material is stable even when exposed to the glass-clearing temperature and does not diffuse into the glass.

In any case, such a mask material should be functionally selected in consideration of the type of material to be processed.

As described above, in the present embodiment, when manufacturing the embedded waveguide with a guide, the upper Cr layer is laminated while the mask is mounted on the guide, the mask is embedded, and this is used as an embedded mask on the surface of the Cr layer. Since the formed surface mask can be collectively processed by dry etching, precise alignment of the guide and the buried waveguide, which was difficult in the past, could be easily achieved.

FIG. 9 is a diagram showing steps of another embodiment of the dry etching method according to the present invention, which is for manufacturing the optical waveguide shown in FIG.

FIG. 8 shows 2 manufactured by the process shown in FIG.
FIG. 3 is a perspective view of a layer-stacked optical waveguide, in which 50 is a lower optical waveguide, 51 is a core layer thereof, 60 is an upper optical waveguide, 61 is a core layer thereof, and 62 is a clad layer. As is clear from this figure, a plurality of optical waveguides 50 each having a core layer 51 are provided in parallel in the longitudinal direction in the figure on the substrate 1.
A plurality of upper optical waveguides 60 each having a core layer 61 formed on a clad layer 62 are provided at right angles to 50.

In manufacturing such a two-layer laminated optical waveguide,
First, as shown in FIG. 9, a core film 51a for forming the core layer 51 is formed on the substrate 1 to form a portion 50a to be the lower optical waveguide 50 (FIG. 7 (a)).

Next, the lower layer optical waveguide 50 is formed by dry etching using the photomask 70 having a predetermined pattern and the mask material 21 (FIG. 7B).

Further, the clad layer 62a, the core layer 61a, and the clad layer 62a that constitute the upper optical waveguide 60 are sequentially laminated to form the upper optical waveguide 60.
A layer 60a is formed (FIG. 9 (c)). At this time, the mask 21 provided on the lower optical waveguide 60 is embedded as it is, and becomes the embedded mask 21a.

Next, the mask material 21 provided on the upper waveguide film layer 60a is processed into the upper optical waveguide pattern shape by the photomask mask 71 having a predetermined pattern on the surface of the upper optical waveguide film layer 60a (FIG. 9). (D)).

After the above structure, the mask 21 and the buried mask 21a formed on the upper optical waveguide film layer 60a are used as a mask to perform dry etching to remove unnecessary portions, thereby removing the unnecessary portion, thereby forming the two-layer laminated optical waveguide shown in FIG. Can be manufactured.

In this embodiment, in the step of FIG. 9 (d), it is necessary to slightly align the mask of the pattern of the upper layer structure with the lower layer structure. However, even in this case, the error tolerance of the mask alignment is large. The mask alignment can be easily performed.

〔The invention's effect〕

As described above, according to the dry etching method of the present invention, the mask formed on the surface and the lower layer structure are formed,
There is an advantage that an upper layer structure and a lower layer structure can be collectively formed by dry etching using a two-layer mask including an embedded mask, and it is possible to manufacture a circuit component having a large step or a laminated structure, which is difficult by the conventional method. It has the advantage that it can be done easily. Therefore, it is advantageous in the dry etching method according to the present invention, particularly in the production of an optical integrated circuit having a large level difference.

[Brief description of drawings]

FIG. 1 is a perspective view of a conventional silica-based optical waveguide circuit, FIG. 2 is a view showing a photomask pattern used for manufacturing the optical waveguide circuit of FIG. 1, and FIG. 3 is a cross section of a buried waveguide. 4 and 5 are views showing a conventional manufacturing process of a buried waveguide with a guide, FIG. 5 is a process drawing showing a process of one embodiment of dry etching according to the present invention, and FIG. 6 is a guide and an optical waveguide. FIG. 7 is a process drawing for patterning the mask material, FIG. 7 is a process drawing for explaining the process of forming a mask only on the upper portion of the waveguide, and FIG. 8 is a perspective view of a two-layer laminated optical waveguide.
The drawings are process diagrams of another embodiment of the dry etching method according to the present invention. 1 ... Board, 2 ... Optical waveguide, 2d ... Guide part, 31 ...
Mask, 31a ... Embedded mask.

Front page continuation (72) Masao Kawachi Inventor Masao Kouchi Tokai-mura, Naka-gun, Ibaraki Prefecture 162 Shirahane, Shirahane, Nippon Telegraph and Telephone Corporation Ibaraki Telecommunications Research Institute (72) Morio Kobayashi Tokai-mura, Naka-gun, Ibaraki Prefecture 162 Shirakuji Shirane, Nippon Telegraph and Telephone Corporation, Ibaraki Electro-Communications Research Laboratory (72) Inventor, Anko Mitsuho Tokai-mura, Naka-gun, Ibaraki Prefecture In-house (56) Reference JP-A-60-17406 (JP, A) JP-A-60-90305 (JP, A) JP-A-61-46911 (JP, A) JP-A-61-73107 (JP, A)

Claims (1)

[Claims] 1. A buried mask having a desired pattern is formed on the surface of a first material to be processed, and an unnecessary portion is removed by etching to form a lower layer structure on the surface of the first material to be processed. A second work material is laminated and formed on the surface of the first work material while remaining, and a surface mask having a desired pattern is formed on the second work material,
A dry etching method characterized by forming a desired structure on the surfaces of the first processing material and the second processing material by removing unnecessary portions by etching using the surface mask and the embedded mask as masks.