JPH0983073A - Formation of grating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a grating with high reproducibility for the dimensional accuracy especially in the direction of depth. SOLUTION: A first etching control layer 21 having etching rate different from a substrate 20 is formed on the substrate 20, a second etching control layer 22 having etching rate different from the first etching control layer 21 is formed on the first etching control layer 21, and a mask pattern 26 is formed on the second etching control layer 22. The second etching control layer 22 is then etched using the mask pattern 26 as a mask and the first etching control layer 21 as an etching stop layer to form a second control layer pattern 27. Subsequently, the first etching control layer 21 is etched using the second control layer pattern 27 as a mask to form a first control layer pattern 28 which is then used as a mask for etching the substrate 20 thus forming a grating pattern 29 on the surface layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DFB (distributed fem) used for a light source or the like which is indispensable for an optical communication system.
ed back) Laser and DBR (distributed Bragg reflec)
tor) relates to a method of manufacturing a grating such as a laser.

[0002]

2. Description of the Related Art Generally, in an optical circuit element such as a distributed feedback laser such as a DFB laser or a DBR laser, a grating having a periodic uneven structure on its surface is often used. In order to manufacture a grating used for such a distributed feedback laser, etc., first, a mask corresponding to the pattern of the grating to be manufactured is formed on a substrate, and then dry etching or chemical etching is performed using this mask. As a result, a method of forming a grating pattern on the surface layer of the substrate is adopted.

By the way, in the production of such a grating, a two-beam interference exposure method is usually employed to form a mask corresponding to the grating pattern.
This two-beam interference exposure method uses He--Cd as shown in FIG.
The laser light from the laser 1 is reflected by the plane mirror 2, and the reflected light is passed through the lens 3 and the pinhole 4 and split by the beam splitter 5. Then, the two light fluxes are reflected on the mirror 6 to interfere with each other on the sample 7 coated with the photoresist in advance, and a grating pattern is printed on the sample 7.

A conventional grating manufacturing method using such a two-beam interference exposure method will be specifically described. First, as shown in FIG. 3A, an InP substrate 10 to be a grating manufacturing substrate is dry-etched. An Au film 11 having resistance is formed by a sputtering method, and a photoresist is applied on the Au film 11 to form a photoresist layer 12. Next, as shown in FIG.
The photoresist layer 12 is exposed (baked) to the grating pattern by the light flux interference exposure method, and further developed using an appropriate developing solution to obtain a resist grating 13 as shown in FIG. 3B. Then, dry etching such as IBE (ion etching beam) method is performed using the resist grating 13 as a mask to etch the Au film 11 into a grating pattern as shown in FIG. 3C. Then, by continuing this dry etching, the InP substrate 10
As a grating pattern, and the remaining Au
If the film 11 and the resist grating 13 are present, they are removed, and the grating 14 as shown in FIG.
Get.

Here, when a 1.3 μm to 1.6 μm band long wavelength laser grating is produced, the period of the primary grating is 210 to 260 nm. In addition,
The photoresist layer 12 is not provided directly on the InP substrate 10 and is formed via the Au film 11. The photoresist layer 12 is provided directly and the photoresist layer 12 is burned on the InP substrate 10 after dry etching. This is because it becomes difficult to peel it off. That is, A, which has a high etching rate by dry etching
By providing the u film 11 between the InP substrate 10 and the photoresist layer 12, the photoresist layer 12 and the Au film 11 can be easily removed by dry etching.

[0006]

However, in the above-described grating manufacturing method, the shape of the grating
In particular, there is a drawback that the controllability of the etching amount in the depth direction is poor. However, when the grating to be manufactured is used for a long-wavelength laser, the pitch thereof needs to be controlled to about 210 to 240 nm and the depth to be controlled to about 100 nm with a minute etching amount. With the method, it is extremely difficult to control this etching amount with good reproducibility. In addition, since the reproducibility of the etching amount is insufficient in this way, there arises a disadvantage that the characteristics of the optical circuit element using the grating obtained in the related art cannot be stabilized.

The present invention has been made in view of the above circumstances. An object of the present invention is to manufacture a grating with good reproducibility, particularly with respect to dimensional accuracy in the depth direction. An object of the present invention is to provide a method for manufacturing a grating that enables provision of an optical circuit element having characteristics.

[0008]

According to the method of manufacturing a grating of the present invention, a step of forming a first etching control layer made of a material having an etching rate different from that of the substrate on the grating manufacturing substrate, On the etching control layer, the step of forming a second etching control layer made of a material having a different etching rate from the first etching control layer, and on the second etching control layer,
A step of forming a mask pattern corresponding to the pattern of the grating to be produced, using the mask pattern as a mask, and etching the second etching control layer by causing the first etching control layer to function as an etching stop layer, A step of forming a second control layer pattern corresponding to the pattern of the grating to be produced, and etching the first etching control layer using the second control layer pattern as a mask, corresponding to the pattern of the grating to be produced. And a step of forming one control layer pattern, and a step of etching the grating production substrate using the first control layer pattern as a mask to form a grating pattern in the surface layer portion of the grating production substrate, It was used as a solution to the problem.

According to the method for producing a grating of the present invention, a first etching control layer and a second etching control layer having different etching rates are formed on a grating production substrate, and then these are sequentially patterned to form A mask corresponding to the grating pattern is formed from the first and second etching control layers, and etching is performed using this mask to form the grating pattern on the surface layer of the grating-fabricating substrate. It becomes possible to fabricate a rectangular wave-shaped grating having a depth determined by the thickness of the etching control layer.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a grating of the present invention will be described in detail below with reference to its embodiments. 1 (a) to 1 (f) are views for explaining an example of an embodiment in which the present invention is applied to manufacture of a grating for a 1.55 μm band DFB laser, and reference numeral 20 in FIG. 1 is a grating. It is an InP substrate that is a fabrication substrate.

In this method, first, as shown in FIG. 1A, a first etching control layer 21 made of a material having an etching rate different from that of the substrate, InGaAsP in this example, is formed on the InP substrate 20. Next, on the first etching control layer 21, the first etching control layer 21 is formed.
And the second etching control layer 22 made of InP in this example. Then, a SiO ₂ film 23 is formed on the second etching control layer 22. Then, a photoresist is applied on the SiO ₂ film 23 to form a photoresist layer 24. Here, for example, the MOCVD method (metal organic chemical vapor deposition method) is adopted for forming the first etching control layer 21 and the second etching control layer 22, and the thermal CVD method is used for forming the SiO ₂ film 23. Adopted. Also,
In this example, the first etching control layer 21 and the second etching control layer 22 are formed to have the same film thickness.

Next, the photoresist layer 24 is exposed to a desired grating pattern by the two-beam interference exposure method described above, and this is developed to form a resist grating 25 as shown in FIG. 1 (b). . Then, using the formed resist grating 25 as a mask, the SiO ₂ film 23 is etched with HF, and the SiO ₂ film 23 is etched as shown in FIG.
As shown in, a SiO ₂ grating mask 26 is formed, which becomes a mask pattern corresponding to the grating pattern to be manufactured.

Next, using the obtained SiO ₂ grating mask 26 as a mask, the second etching control layer 22 is etched by using an HCl-based etchant.
As shown in (c), the second control layer pattern 27 corresponding to the grating pattern to be produced is formed. Here, in selecting the etchant used for etching the second etching control layer 22, the fact that the etching rates of the second etching control layer 22 and the first etching control layer 21 are different is used, An etchant is selected such that the etching rate for the one etching control layer 21 is sufficiently slower than the etching rate for the second etching control layer 22, so that the first etching control layer 21 functions as an etching stop layer.

Next, the SiO ₂ grating mask 2
6 is removed by HF or the like, and then the whole is dry-etched. Specifically, as the dry etching, Cl
Reactive ion etching apparatus using a ₂ and Ar (RI
Etching by the E device) is adopted. According to such dry etching, the second etching control layer 22
Although the (second control layer pattern 27) and the first etching control layer 21 are both etched, the etching rate of the second etching control layer 22 is about 0.1 μm / min. And the first etching control layer 21, InGaAsP
Etching rate of 0.05 to 0.06 μm / min
Becomes Therefore, in the dry etching under the above conditions, the etching rate of the second etching control layer 22 is about twice that of the first etching control layer 21.

Therefore, in the present invention, a square-wave grating is produced by utilizing this difference in etching rate. That is, in this dry etching, the second control layer pattern 27 is completely etched so that the first etching control layer 21 is reduced to half its thickness as shown in FIG. 1D. Etching. Then, by further advancing this dry etching and continuing the etching of only the first etching control layer 28 until a part of the InP substrate 20 is exposed, as shown in FIG. A corresponding first control layer pattern 28 is formed.

After that, dry etching under the above conditions is continued using the first control layer pattern 28 as a mask until the first control layer pattern 28 disappears. Then, InGaAsP and In forming the first control layer pattern 28 are formed.
Due to the difference in etching rate from the InP forming the P substrate 20, the grating 29 having a depth determined by the film thickness of the first etching control layer 21 and the second etching control layer 22 as shown in FIG. However, it is formed on the surface layer portion of the InP substrate 20 while maintaining the square wave shape.

In such a method of manufacturing the grating 29, the grating 29 having a depth determined by the film thicknesses of the first etching control layer 21 and the second etching control layer 22 is kept in a square wave shape. InP as it is
The dimensional accuracy in the depth direction of the grating 29, which can be formed in the surface layer portion of the substrate 20 and therefore improves the controllability in the depth direction, can be improved.
That is, if the first etching control layer 21 and the second etching control layer 22 are grown and formed by, for example, the MOCVD method (metal organic chemical vapor deposition method), this MO with relatively high accuracy is obtained.
The depth of the grating 29 can be determined by the film forming accuracy (film thickness accuracy) by the CVD method, and thus a desired grating shape can be easily obtained.

Further, in this method, unlike the conventional method shown in FIG. 3, since the Au film 11 serving as a dry etching resistant mask is not directly formed on the InP substrate 10,
By sputtering the dry etching resistant mask material, the surface of the InP substrate 20 which is a grating fabrication substrate is not roughened, and therefore, the deterioration of the optical characteristics of the obtained grating 29 due to the roughened surface can be prevented.

In the above embodiment, the InP substrate 20 was used as the grating fabrication substrate, InGaAsP was used as the first etching control layer 21, and InP was used as the second etching control layer 22. For, the etching rates of the grating fabrication substrate and the first etching control layer 21 are different,
Further, other materials may be used as long as the first etching control layer 21 and the second etching control layer 22 have different etching rates. Further, the thicknesses of the first etching control layer 21 and the second etching control layer 22 can be set arbitrarily according to the difference in etching rate between them, instead of being the same as in the above example.

[0020]

As described above, according to the method for producing a grating of the present invention, the first etching control layer and the second etching control layer having different etching rates are formed on the grating production substrate, and then these are formed. A mask corresponding to the grating pattern is formed by sequentially patterning, and etching is performed using this mask to form a square wave grating with a depth determined by the thicknesses of the first and second etching control layers on the surface layer of the grating fabrication substrate. Since this is a method of forming a pattern, the controllability in the depth direction is improved, and the dimensional accuracy in the depth direction of the resulting grating can be improved. Therefore, a grating such as a DFB laser or a DBR laser can be manufactured with high dimensional accuracy and good reproducibility, which makes it possible to provide an optical circuit device having stable device characteristics.

[Brief description of drawings]

1 (a) to 1 (f) are side cross-sectional views of relevant parts for explaining a method of manufacturing a grating of the present invention in order of steps.

FIG. 2 is a diagram for explaining a two-beam interference exposure method.

3 (a) to 3 (d) are side cross-sectional views of relevant parts for explaining a conventional method of manufacturing a grating in the order of steps.

[Explanation of symbols]

20 InP Substrate 21 First Etching Control Layer 22 Second Etching Control Layer 23 SiO
₂ film 24 photoresist layer 25 resist grating 26 SiO ₂ grating mask 27 second control layer pattern 28 first control layer pattern 29 grating

Claims (1)

[Claims] 1. A step of forming a first etching control layer made of a material having an etching rate different from that of the substrate on which the grating is formed, and the first etching control layer being formed on the first etching control layer. Forming a second etching control layer made of a material having a different etching rate from the control layer; forming a mask pattern corresponding to the pattern of the grating to be produced on the second etching control layer; The second etching control layer is etched by using the mask pattern as a mask and causing the first etching control layer to function as an etching stop layer to form a second control layer pattern corresponding to the pattern of the grating to be produced. And a step of etching the first etching control layer using the second control layer pattern as a mask. And forming a first control layer pattern corresponding to the pattern of the grating to be produced, and etching the grating production substrate using the first control layer pattern as a mask to form a grating pattern on the surface layer of the grating production substrate. And a step of forming a grating.