JPH0653600A - Method for forming diffraction grating for semiconductor light emitting element - Google Patents

Abstract

PURPOSE:To form easily and in a good reproducibility the diffraction gratings which are provided with grooves of uneven depths for a semiconductor light emitting element. CONSTITUTION:A layer 20 for first pattern is partially formed on an InP base board. On this layer 20 for the first pattern, and the base board which is exposed to an aperture 22, a layer 30 is formed for a second pattern having the same pattern as that of the diffraction gratings. With this layer 30 for the first pattern being used as a mask, the InP base board is ion etched reactively to form deep grooves 40 on the part where the layer 20 for the first pattern does is absent. On the part where the layer 20 for the first patter is present, the base substrate is etched subsequent to the etching of the layer for the first pattern, and shallow grooves 42 are formed at the same time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diffraction grating of a semiconductor light emitting device, and more particularly to a method of forming a diffraction grating having grooves with uneven depth.

[0002]

2. Description of the Related Art Conventionally, there is a distributed feedback semiconductor light emitting device (hereinafter abbreviated as DFB laser). This light emitting element
It has a diffraction grating in which gratings are arranged in the cavity axis direction. To make each grating of this diffraction grating, it is usual to form trenches of uniform depth in a suitable substrate and fill these trenches with a suitable layer of the same material.

The depths of these grooves were uniform, but recently, as disclosed in the literature: "Proceedings of the Joint Lecture on Spring Applied Physics, 1991, 29p-D-1," A diffraction grating with grooves of non-uniform depth is formed and these grooves are filled with a suitable material to form a DFB laser. The reason is that the coupling coefficient is distributed in the axial direction of the resonator in order to control the optical intensity distribution in the axial direction of the resonator of the DFB laser used for long-distance optical communication and increase the difference in oscillation gain threshold between longitudinal modes.

Hereinafter, an example of the structure of the conventional DFB laser and an example of a method of manufacturing a diffraction grating having non-uniform groove depths will be described with reference to FIGS. 5B and 6A to 6D, respectively.
Also, a brief description will be given with reference to FIGS. 6 (A) to (D) and FIG. 7 (A) to
Although the contour of the cross section of the groove shown in (D) is different from the contour of the cross section of the corresponding groove shown in FIG. 5 (B), it is shown more schematically in FIGS. 6 and 7. It is shown more realistically in (B) of 5 and the contour and shape of the groove itself are not changed in any of the drawings.

FIG. 5B is an explanatory view of a light emitting device with a diffraction grating, and is a sectional view showing an outline of an example of the structure of a DFB laser. A deep groove 54 and a shallow groove 56 are formed on the surface of the InP substrate 50 in a state of being symmetrically arranged with the phase shift portion 52 as the center along the resonator axis direction. A guide layer 58, an active layer 60, and a clad layer 62 are laminated thereon.

FIGS. 6A to 6D are process diagrams of the first half for explaining a method of manufacturing a diffraction grating of a semiconductor light emitting device having grooves of nonuniform depth, and FIG. A) to (D)
FIG. 7C is a second half of the process drawing following FIG. 6C. Each figure schematically shows a cross-sectional view at a main process step.

First, a film of silicon dioxide is formed as a preliminary film 64 for forming an etching mask on the InP substrate 50 by the CVD method, and a portion 52a which becomes a boundary forming a phase shift portion is formed on the preliminary film 64. A positive resist film 66 and a negative resist film 68 are formed side by side with the film sandwiched therebetween ((A) of FIG. 6).

Next, the positive resist film 66 and the negative resist film 68 are exposed by the two-beam interference exposure method, and then a resist mask 70 is formed by development (FIG. 6B).

After that, the preliminary film 64 is etched by etching, and the pattern of the resist mask 70 is transferred to the preliminary film 64 to form a first etching mask 72 (FIG. 6C).

After removing the resist mask 70, the shallow groove 56 is first formed in the InP substrate 50 by reactive ion etching (hereinafter abbreviated as RIE).
It is formed in the portion exposed in the opening between the first etching masks 72 ((D) of FIG. 6).

Next, another preliminary film (not shown) for forming another etching mask is formed once again, and the second etching mask 78 is formed on this preliminary film by using ordinary photolithography and etching techniques. ((A) of FIG. 7).

Then, by RIE again, only the portion not covered by the second etching mask 78 is further etched by using the first etching mask, and the shallow groove 56 already formed in the opening is further etched to form the deep groove 54. It is formed ((B) of FIG. 7).

Finally, the first and second etching masks 7
2 and 78 were removed (FIG. 7C), and then the guide layer 58, the active layer 60 and the glad layer 62 were provided by a conventional method to provide the grooves 54 and 56 having uneven depths. A semiconductor light emitting device having a structure in which a diffraction grating is formed was obtained ((D) of FIG. 7).

[0014]

However, in the above-described conventional method of forming a groove having a non-uniform depth for making a diffraction grating which constitutes a light emitting element, an etching mask is formed twice and RIE is performed. The InP substrate is etched twice by. For this reason, the process becomes complicated, and a difference between the shape of the deep groove and the shape of the shallow groove is likely to occur. If there is a difference in the shape of the grooves, when a diffraction grating is built using these grooves, the diffraction efficiency will deteriorate and the coupling coefficient will also change. There are drawbacks such as poor reproducibility and low yield.

Therefore, an object of the present invention is to form a groove having a non-uniform depth for forming a diffraction grating of a semiconductor light emitting device.
An object of the present invention is to provide a method of forming by a simple method with high accuracy.

[0016]

In order to achieve this object, according to the method of forming a diffraction grating having grooves of non-uniform depth of a semiconductor light emitting device of the present invention, the following steps are taken. It has the characteristics of.

(A) On the base on which the groove is to be formed, the opening is located on the region where the deep groove is to be formed, and the first pattern layer is located on the region where the shallow groove is to be formed. The first pattern layer is formed as described above.

(B) A second pattern layer having the same pattern as the pattern of the diffraction grating to be formed is formed on the first pattern layer and the underlayer exposed in the opening. .

(C) Using this second pattern layer as a mask, dry etching is performed once to form a deep groove in the region where the deep groove is to be formed from the surface of the underlayer, and at the same time a shallow groove is formed. Grooves extending from the first pattern layer to the underlying regions are formed in the regions to be formed.

In carrying out the present invention, preferably, two pattern layers are simultaneously exposed by a two-beam interference exposure method using a positive resist film and a negative resist film to both resist films. After this, it is preferable to develop both resist films to form them.

According to another preferred embodiment of the present invention, the second pattern layer is formed by using one kind of resist film.
The resist film is preferably formed by exposing the resist film by an electron beam exposure method and then developing the resist film.

Further, in carrying out the present invention, it is more preferable that the etching rate of the first pattern layer is made higher than the etching rates of the second pattern layer and the underlying layer.

[0023]

According to the above-described structure of the present invention, an etching mask having a one-layer structure consisting only of the second pattern layer is provided in the region where the deep groove is to be formed in the base, and the shallow groove in the base is formed. The first pattern layer and the second pattern layer are formed in the planned formation area.
A two-layered structure including an insulating layer. Then, using the etching mask layers having the one-layer structure and the two-layer structure, dry etching is performed once on the surface of the underlayer from a direction perpendicular to the surface. A portion of the first pattern layer exposed on the opening between the second pattern layers and a portion of the first pattern layer are respectively etched to form a portion of the first pattern layer on the area where the shallow groove is to be formed in the underlying layer. Are removed and the base is partially exposed. When the base portion on the shallow groove formation region is exposed, the base portion of the deep groove formation region is etched to a depth corresponding to the etching time until then.

If this dry etching is continued, the underlying portion of the shallow groove formation region starts to be etched. This etching time is an arbitrary time according to the design, and the depth of the shallow groove is determined thereby. At the same time, the thickness of the first pattern layer can be set in advance to determine the etching time of the first pattern layer.

As described above, according to the structure of the present invention, the grooves having different etching depths, that is, the grooves having the non-uniform depth are simultaneously formed by one dry etching, so that the shape of the deep groove and the shallow groove are formed. Match the shape. As a result, a diffraction grating having good diffraction efficiency and a desired coupling coefficient can be easily formed with high yield. Therefore, these grooves can be filled with a suitable semiconductor material having light propagation characteristics to form a semiconductor light emitting device.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method for forming a diffraction grating having grooves of non-uniform depth according to the present invention will be described below with reference to the drawings. It should be noted that the drawings referred to below only schematically show the sizes, shapes, and arrangement relationships of the respective constituent components to the extent that the present invention can be understood. Therefore, it is obvious that the present invention is not limited to the illustrated example.

First, referring to FIGS. 1A to 1C,
A basic embodiment of the present invention will be described. Figure 1 (A)
6A to 6C are process drawings for explaining a method of forming a diffraction grating having grooves of non-uniform depth, each of which is a schematic cross-sectional view of a structure obtained at a main stage of the process. Is shown in.

First, in the present invention, the first pattern layer 20 is formed on the underlayer 10 on which the groove is to be formed, by using a usual technique ((A) of FIG. 1). This first pattern layer 20
Is provided in the shallow groove formation region 12 of the base 10 with an appropriate film thickness, and the deep groove formation region 1 of the base 10 is formed.
The openings 2 other than the portion of the first pattern layer 20 are shown in FIG.
2 is positioned ((A) of FIG. 1).

Next, a second pattern layer 30 is formed on the first pattern layer 20 and on the base 10 exposed in the openings 22 (FIG. 1B). In this case, the pattern of the second pattern layer 30 is the same as the pattern of the diffraction grating to be formed. Therefore, the width, length, shape, arrangement interval and arrangement direction of each pattern layer are the same as the width, length, shape, arrangement interval and arrangement direction of each diffraction grating to be formed (Fig. 1 (B)). In this embodiment, a part of the second pattern layer 30 is constituted by an individual pattern layer 34 which is wider than the other individual pattern layers 32, and the individual pattern layer 34 is deep. The pattern patterns are provided on the lower surface of the groove forming region, and the individual pattern layers 32 of equal width are equally arranged on both sides of the wide individual pattern layer 34 on the first pattern layer 20 in sequence. ing. The opening other than the individual pattern layers 32 and 34 of the second pattern layer 30, which exposes a part of the first pattern layer 20, is indicated by 36, and the underlying layer is exposed. Open the opening at 38,
Shown respectively.

Next, using the second pattern layer 30 as an etching mask, the first pattern exposed in the opening 36 is formed.
A portion of the pattern layer 20 and a portion of the base 10 exposed in the opening 38 are dry-etched. This dry etching is continuously performed to penetrate the first pattern layer 20 to form a shallow groove 42 reaching a predetermined depth from the underlying surface. At this time, the etching of the portion of the base 10 exposed in the opening 38 also proceeds continuously, and the deep groove 40 is formed at the same time.
A structure as shown in FIG. 1C is obtained. Incidentally, FIG.
(C), since the opening 24 is formed in the first pattern layer 20 by this dry etching, the remaining portion of the first pattern layer 20 is shown as the remaining pattern layer 25. . In this embodiment, the wide individual pattern layer 34 is formed because, when a light emitting element is completed by forming a diffraction grating in a later step, light is propagated in the light emitting element. This is because the phase of light is shifted in the region corresponding to the individual pattern layer 34. Therefore, this portion is called a phase shift portion, and this individual pattern is also called a phase shift portion pattern layer. The position where the phase shift portion is provided can be appropriately determined according to the design.

Since this dry etching is continuously performed without interruption, the widths, lengths and shapes of the openings 36 and 38 are faithfully transferred to the base 10 to etch the deep groove 40 and the shallow groove 42. It is formed. Moreover, the shapes of both grooves 40 and 42 are made uniform by this etching.

Next, more specific embodiments of the present invention will be described. In this embodiment, the case where the second pattern layer is formed by using a positive resist film and a negative resist film will be described.

2A to 2E and FIG. 3A.
(E) is a process drawing for demonstrating the formation method of the diffraction grating provided with the groove | channel of nonuniform depth based on this invention. Each drawing is a cross-sectional view in a plane along the cavity axis direction of the light emitting element.

In this embodiment, the InP substrate 1 is used as a base.
0 is used to form the first pattern layer 20 on the substrate 10 ((E) in FIG. 2). Therefore, first, the first coating film 16 of silicon dioxide (SiO ₂ ) is formed on the substrate 10 (see FIG. 2).
(A)).

Next, a resist (Microposit (trade name), manufactured by Shiple Co.) film 18 is formed on the first coating 16 ((B) of FIG. 2).

Then, using the photolithography technique, an opening 18b is provided in the resist film 18 to leave the resist pattern 18a (FIG. 2C). The resist pattern 18a is formed in the shallow groove formation region 12 of the substrate 10.
The opening 18b is provided on the upper side, and is located on the region where the deep groove is to be formed.

Next, using the resist pattern 18a as a mask, the lower first coating 16 is etched to form a first pattern layer 20 (FIG. 2D).
In the figure, reference numeral 22 denotes an opening formed by etching the first coating film 16.

Then, after removing the resist pattern 18a ((E) of FIG. 2), a second pattern is formed on the surface of the substrate 10 exposed on the first pattern layer 20 and the opening 22. An insulating layer 30 is provided ((B) of FIG. 3). Therefore, in this embodiment, first, the positive resist film 26 and the negative resist film 28 are formed side by side symmetrically along the resonator axis with the center of the opening 22 (see FIG. 2E) as a boundary. ((A) of FIG. 3). In the illustrated example, the positive resist film 26 is provided on the entire left side of the boundary C, and the negative resist film 28 is provided on the entire right side.

After forming the resist films 26 and 28, the resist films 26 and 28 are formed by the two-beam interference exposure method.
Is exposed, and thereafter, development is performed to obtain resist patterns 26a and 28a as shown in FIG. These resist patterns 26a and 28a are formed such that individual pattern layers are continuously formed in contact with each other at the boundary C, but at the positions apart from the boundary C along the resonator axial direction, It is formed as an individual pattern layer, which is spaced apart at a pitch. In this embodiment, the resist patterns 26a and 28a are combined to form the second pattern layer 30.
Are configured. Then, these resist patterns 26
a and 28a correspond to the respective grating patterns of the diffraction grating to be formed. By this etching, openings are formed in each of the resist films 26 and 28 in the same manner as already described with reference to FIG. These openings on the shallow groove forming area 12 and the deep groove forming area 14 are indicated by 36 and 38, respectively.

Next, using the second pattern layer 30 as an etching mask, this substrate is dry-etched by an RIE apparatus. In this etching, as is well known, the portions exposed without the etching mask 30 in the openings 36 and 38 are etched in the shape of the pattern of the resist mask 26, while the portions with the etching mask 30 are present. Only the etching mask 30 is exposed to etching. In the case of this embodiment, the opening 36
The portion of the first pattern layer 20 exposed on the substrate is the substrate 10.
First, the surface is etched to form the opening 24 in the first pattern layer 20 and the remaining pattern layer 25 (FIG. 3C). During the etching time of the first pattern layer 20, the portion of the InP substrate 10 exposed in the opening 38 is also etched to form the groove 40a (FIG. 3C).

When the etching is further advanced, the portion of the InP substrate 10 exposed in the opening 38 is further etched from the groove 40a and becomes deeper into the deep groove 40. On the other hand, the opening 3
The portions of the InP substrate 10 exposed in the communication holes 6 and 24 start to be etched. If the etching time is set in advance so that the etching depth of the latter InP substrate 10 portion becomes a depth according to the design, the groove formed by the etching in this portion becomes the shallow groove 42. .
Then, the groove 40a is deepened only in the depth portion of the shallow groove 42 to obtain the deep groove 40 ((D) of FIG. 3). In this way, since the shallow and deep grooves 40 and 42 are formed by one dry etching, the shape and shape of these grooves are not disturbed or disturbed. Finally, the second pattern layer 30 and the remaining pattern layer 25 are removed, and the grooves 40 having a non-uniform depth are formed.
A diffraction grating for a semiconductor light emitting device including and 42 is obtained ((E) of FIG. 3).

On the thus obtained diffraction grating having grooves of non-uniform depth, required layers such as the optical guide layer 58, the active layer 60 and the glad layer 62 are sequentially formed in the same manner as in the conventional case. By forming the semiconductor light emitting device, the semiconductor light emitting device can be completed. The state of the semiconductor light emitting device thus obtained is shown in FIG. In this embodiment, a guide layer is embedded in a deep groove and a shallow groove to form a diffraction grating.

In the embodiment shown in FIG. 5 (A), the cross-sectional cuts of each groove are square, but when forming these grooves by etching, in practice,
The pattern of the cross-section cut has a rounded and wavy shape with rounded corners as shown in FIG. 5 (B).

Next, another embodiment will be described in which an etching mask is partially formed on a substrate by using a photoresist and a lift-off method.

First, a resist film 80 is formed on the InP substrate as the base 10 ((A) of FIG. 4).

Next, the resist film 80 is partially removed by using the photolithography technique to remove the resist pattern 8.
2 is formed (FIG. 4 (B)). This resist pattern is formed so as to be located on the deep groove formation planned region 14 in the region of the underlying substrate 10.

Subsequently, coatings 84, 84a and 84b for forming the first pattern layer are formed on the substrate 10 on which the resist pattern 82 is formed ((C) in FIG. 4).
The coating 84a is a portion formed on the resist pattern 82, and the coating 84b is a portion formed on the base substrate 10, and both portions are cut off.

Then, the lift-off technique is used to form the first pattern layer 20 by removing the resist pattern 82 and the remaining film portion 84b (FIG. 4D). After that, the groove may be formed through the steps of (A) to (E) of FIG.

It will be clear that the invention is not limited to the embodiments described above, but that many variants or modifications can be made. For example, in the above-described embodiment, an example was described in which an InP substrate is used as a base and a groove having a nonuniform depth for forming a nonuniform diffraction grating is formed in the substrate, but in the present invention, a GaAs substrate, or Substrates of other suitable compound semiconductor materials can be used. Further, an optical guide layer provided on the substrate can be used as the base. In addition, the base may be any layer as long as it can form a diffraction grating of the light emitting element.

Further, in the above-mentioned embodiment, as the exposure method for forming the mask used for etching the groove,
Although the two-beam interference method is used, it may be formed using an electron beam exposure method. Further, in the above-described embodiment, the groove depth is formed so as to be symmetrical in both directions along the resonator axis with the phase shift portion sandwiched therebetween, but the groove depth does not necessarily have to be symmetrical.

Further, in the above-mentioned embodiments, the shapes, dimensions, materials, arrangement relations and other conditions of each constituent component are not particularly mentioned, but these may be arbitrarily set according to the design. In the present invention, it is sufficient to use various conditions that allow the deep groove and the shallow groove suitable for the pattern of the diffraction grating to be built to be manufactured with high precision and without disturbing the shape. Therefore, the etching for forming the groove may be one dry etching step, and other conditions relating to the etching may be arbitrarily set.

[0052]

According to the method of forming a diffraction grating having a groove of a non-uniform depth for a semiconductor light emitting device of the present invention, a second pattern is formed in a region of the underlying deep groove to be formed. An etching mask having a single-layer structure consisting of only layers is provided, and the first pattern layer and the second pattern layer are formed in the underlying region where shallow trenches are to be formed.
A layer having a two-layer structure including a pattern layer is provided. And
By utilizing these one-layer and two-layer structure etching mask layers, the surface of the underlying layer is dry-etched once from a direction perpendicular to the surface. A portion of the first pattern layer exposed on the opening between the second pattern layers and a portion of the first pattern layer are respectively etched to form a portion of the first pattern layer on the area where the shallow groove is to be formed in the underlying layer. Are removed and the base is partially exposed. When the base portion on the shallow groove formation region is exposed, the base portion of the deep groove formation region is etched to a depth corresponding to the etching time until then.

When this dry etching is continued, the underlying portion of the shallow groove formation region starts to be etched. This etching time is an arbitrary time according to the design, and the etching depth of the shallow groove is determined thereby. At the same time, the thickness of the first pattern layer can be set in advance to determine the etching time of the first pattern layer.

As described above, according to the structure of the present invention, the grooves having different etching depths, that is, the grooves having the non-uniform depths are simultaneously formed by one dry etching. Match the shape. As a result, a diffraction grating having good diffraction efficiency and a desired coupling coefficient can be easily formed with high yield. Therefore, it is possible to form a semiconductor light emitting device by embedding a diffraction grating having these grooves with an appropriate semiconductor material having a light propagation characteristic.

[Brief description of drawings]

FIG. 1A to FIG. 1C are process diagrams for explaining a method of forming a groove having a non-uniform depth for a semiconductor light emitting device of the present invention.

FIG. 2A to FIG. 2E are process diagrams of the first half used for explaining a method of forming a diffraction grating having grooves of non-uniform depth according to the present invention.

3A to 3E are process diagrams of the latter half of FIG. 2 for explaining a method of forming a diffraction grating having grooves of non-uniform depth according to the present invention.

4 (A) to (D) are explanatory views of another embodiment.

5A and 5B are cross-sectional views for explaining the structure of a distributed feedback semiconductor light emitting device.

6A to 6D are process diagrams of the first half used to describe a conventional method for forming a diffraction grating having grooves of non-uniform depth.

7A to 7D are process diagrams of the latter half of FIG. 5 for explaining a conventional method of forming a groove having a non-uniform depth.

[Explanation of symbols]

 10: Base 12: Area where shallow groove is to be formed 14: Area where deep groove is to be formed 16: First film 18: Resist film 18a: Resist pattern 18b: Opening 20: First pattern layer 22: Opening 24 : Opening 25: Remaining pattern layer 26: Positive resist film 26a: Resist pattern 28: Negative resist film 28a: Resist pattern 30: Second pattern layer 32: Individual pattern layer 34: Individual pattern Layer 36: opening 38: opening 40: deep groove 40a: groove 42: shallow groove 58: guide layer 60: active layer 62: clad layer 80: resist film 82: resist pattern 84: film 84a: film 84b: Coating C: Boundary

Claims (4)

[Claims] 1. A method for forming a diffraction grating having grooves of non-uniform depth in a semiconductor light emitting device, wherein an opening is located on a base on which a groove is to be formed and on a region where a deep groove is to be formed. And a step of forming the first pattern layer so as to position the first pattern layer on the area where the shallow groove is to be formed, and exposing on the first pattern layer and the opening. A step of forming a second pattern layer having the same pattern as the pattern of the diffraction grating to be formed on the lower surface, and a single dry etching using the second pattern layer as a mask Then, a deep groove is formed from the surface of the base in the deep groove formation planned region, and at the same time, a groove reaching the base region from the first pattern layer is formed in the shallow groove formation planned region. And a step of forming each of Method of forming a diffraction grating with grooves of non-uniform depth. 2. The method of forming a diffraction grating having grooves of non-uniform depth according to claim 1, wherein the second pattern layer is formed by using a positive resist film and a negative resist film. A method of forming a diffraction grating having grooves of non-uniform depth, characterized in that both resist films are simultaneously exposed by a two-beam interference exposure method, and then both resist films are developed and formed. . 3. The method of forming a diffraction grating having grooves of non-uniform depth according to claim 1, wherein the second pattern layer is formed on this resist film by using one kind of resist film. On the other hand, a method of forming a diffraction grating having a groove having a non-uniform depth, which is characterized in that the resist film is developed and then exposed by an electron beam exposure method. 4. The method of forming a diffraction grating having grooves of non-uniform depth according to claim 1, wherein the etching rate of the first pattern layer is the etching rate of the second pattern layer and the underlying layer. A method of forming a diffraction grating having a groove having a non-uniform depth, which is characterized in that it is larger than the groove.