JP6292361B1 - Manufacturing method of optical semiconductor device - Google Patents

Abstract

A ridge structure (9) having a ridge lower part (6) on a semiconductor substrate (1) and a ridge upper part (8) disposed on the ridge lower part (6) and having a width wider than that of the ridge lower part (6). Form. A depression (11) in the ridge structure (9) caused by the difference between the width of the ridge lower part (6) and the ridge upper part (8) is that the ridge lower part (6) is recessed in the lateral direction with respect to the ridge upper part (8). The semiconductor substrate (1), the ridge structure (9), and the insulating film (10) form a convex shape (19) having no step on the side surface by being completely filled with the insulating film (10) by atomic layer deposition.

Description

  The present invention relates to a method for manufacturing an optical semiconductor device in which a recessed portion of a ridge structure is embedded with an insulating film.

  In a semiconductor laser having a ridge structure, it is necessary to secure the area of the ridge upper part for reducing the resistance and to narrow the width of the lower part of the ridge for realizing a high-speed response. For this reason, the ridge structure is an inverted mesa ridge structure, a T-shaped structure, or a Y-shaped structure. Further, a method for realizing a stable ridge size as a device structure for realizing a high-speed response is disclosed (for example, see Patent Document 1).

Japanese Patent No. 5454381

  In the inverted mesa ridge structure, the T-shaped structure, or the Y-shaped structure, there is a recessed portion in which the lower portion of the ridge is recessed in the lateral direction with respect to the upper portion of the ridge. Conventionally, since the sputtering method or the plasma CVD method has been used to form the insulating film, the insulating film has insufficient coverage, and the recessed portion of the ridge structure cannot be completely filled with the insulating film. As a result, there has been a problem that the ridge structure is vulnerable to external environmental changes such as temperature, aging, or mechanical stress applied during assembly.

  The present invention has been made to solve the above-described problems, and an object thereof is to obtain a method for manufacturing an optical semiconductor device capable of improving the mechanical strength of a ridge structure.

The method of manufacturing an optical semiconductor device according to the present invention includes a step of forming a ridge structure on a semiconductor substrate having a ridge lower portion and a ridge upper portion disposed on the ridge lower portion and having a width wider than the ridge lower portion. In addition, a recess portion of the ridge structure, which is caused by a difference in width between the lower portion of the ridge and the upper portion of the ridge, is recessed in the lateral direction with respect to the upper portion of the ridge, is completely filled with an insulating film by an atomic layer deposition method. the write Mukoto, characterized in that it comprises a step of forming a convex shape without a step on the semiconductor substrate on a side surface of the insulating film provided on a side surface of the ridge structure.

  In the present invention, the recessed portion of the ridge structure in which the lower portion of the ridge is recessed laterally with respect to the upper portion of the ridge is completely filled with the insulating film by the atomic layer deposition method. Thereby, the mechanical strength of the ridge structure can be improved.

It is sectional drawing which shows the manufacturing method of the optical semiconductor device which concerns on Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing method of the optical semiconductor device which concerns on Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing method of the optical semiconductor device which concerns on Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing method of the optical semiconductor device which concerns on Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing method of the optical semiconductor device which concerns on Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing method of the optical semiconductor device which concerns on Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing method of the optical semiconductor device which concerns on Embodiment 1 of this invention. It is sectional drawing which shows the optical semiconductor device which concerns on a comparative example. It is sectional drawing which shows the manufacturing method of the optical semiconductor device which concerns on Embodiment 2 of this invention. It is sectional drawing which shows the manufacturing method of the optical semiconductor device which concerns on Embodiment 2 of this invention. It is sectional drawing which shows the manufacturing method of the optical semiconductor device which concerns on Embodiment 2 of this invention. It is sectional drawing which shows the manufacturing method of the optical semiconductor device which concerns on Embodiment 2 of this invention. It is sectional drawing which shows the manufacturing method of the optical semiconductor device which concerns on Embodiment 2 of this invention. It is sectional drawing which shows the manufacturing method of the optical semiconductor device which concerns on Embodiment 2 of this invention. It is sectional drawing which shows the manufacturing method of the optical semiconductor device which concerns on Embodiment 2 of this invention. It is sectional drawing which shows the manufacturing method of the optical semiconductor device which concerns on Embodiment 2 of this invention.

  A method for manufacturing an optical semiconductor device according to an embodiment of the present invention will be described with reference to the drawings. The same or corresponding components are denoted by the same reference numerals, and repeated description may be omitted.

Embodiment 1 FIG.
1 to 7 are sectional views showing a method for manufacturing an optical semiconductor device according to the first embodiment of the present invention. First, as shown in FIG. 1, an active layer 2 is formed on a semiconductor substrate 1. The outermost surface layer 2a of the active layer 2 is an InP layer. A sacrificial layer 3 made of a material different from that of the outermost surface layer 2 a of the active layer 2 is formed on the active layer 2. The sacrificial layer 3 is required to have a selection ratio between InP and etching, and is, for example, an InGaAsP layer. A thin InP layer may be formed on the InGaAsP layer as a cap layer. The thickness of the sacrificial layer 3 matches the height of the lower portion of the ridge that will be formed later.

  Next, as shown in FIG. 2, a part of the sacrificial layer 3 is removed by wet etching or dry etching to form an opening 4. Next, as shown in FIG. 3, an InP layer 5 made of a material different from that of the sacrificial layer 3 is formed on the active layer 2 and the sacrificial layer 3, and a lower ridge 6 is formed inside the opening 4. An InGaAs contact layer 7 is formed on the InP layer 5. A thin InP layer may be formed on the InGaAs contact layer 7 as a cap layer.

Next, as shown in FIG. 4, an insulating film hard mask such as SiO ₂ or the like, by dry etching or wet etching the InP layer 5 and the InGaAs contact layer 7 to the sacrificial layer 3 is required to the characteristics The ridge upper part 8 is formed by patterning to a desired ridge width. Next, as shown in FIG. 5, the sacrificial layer 3 is selectively removed by wet etching with respect to the outermost surface layer 2 a of the active layer 2 and the InP layer 5. Thereby, a ridge structure 9 having a ridge lower part 6 and a ridge upper part 8 disposed on the ridge lower part 6 and having a width wider than that of the ridge lower part 6 is formed on the semiconductor substrate 1. Since the width of the ridge upper part 8 is wider than the ridge lower part 6, a recessed portion 11 of the ridge structure 9 is formed in which the ridge lower part 6 is recessed laterally with respect to the ridge upper part 8, and a step 17 is generated on the side surface of the ridge structure 9. Due to this step, a space 18 is formed between the outermost surface layer 2 a of the active layer 2 and the bottom surface 16 of the ridge top 8. The space 18 is a gap where no solid such as a semiconductor or an insulator exists. The mechanical strength of the ridge structure 9 is low when the step 17 including the space 18 exists on the side surface.

  Next, as shown in FIG. 6, an insulating film 10 is formed on the entire surface by atomic layer deposition (ALD), and the ridge lower portion 6 is changed to the ridge upper portion 8 due to the difference in width between the ridge upper portion 8 and the ridge lower portion 6. The recessed portion 11 of the ridge structure 9 caused by the recess in the lateral direction is completely filled with the insulating film 10. Finally, as shown in FIG. 7, an electrode 12 is formed by etching away a part of the insulating film 10 on the upper surface of the ridge structure 9.

  Subsequently, the effect of the present embodiment will be described in comparison with a comparative example. FIG. 8 is a cross-sectional view showing an optical semiconductor device according to a comparative example. In FIG. 8A, since the sputtering method or the plasma CVD method is used for forming the insulating film 13, the coverage of the insulating film 13 is insufficient, and the recessed portion 11 of the ridge structure 9 is completely filled with the insulating film 13. It is not possible. As a result, there is a problem that the ridge structure 9 is vulnerable to external environmental changes such as temperature, aging, or mechanical stress applied during assembly. On the other hand, in this embodiment, the recessed portion 11 of the ridge structure 9 is completely filled with the insulating film 10 by atomic layer deposition. Thereby, the mechanical strength of the ridge structure 9 can be improved. However, as shown in FIG. 8B, when the insulating film 13 is simply formed by using the atomic layer deposition method and the recessed portion 11 of the ridge structure 9 is not completely buried, the machine of the ridge structure 9 Strength cannot be increased. In the present embodiment, not only the atomic layer deposition method is used, but also the depression 11 of the ridge structure 9 is completely buried by using the atomic layer deposition method as shown in FIG. The step 19 is eliminated, the space 18 between the outermost surface layer 2a of the active layer 2 and the bottom surface 16 of the ridge upper portion 8 is eliminated, and the semiconductor substrate 1, the ridge structure 9 and the insulating film 13 have a convex shape 19 with no step on the side surface. By forming the ridge, the mechanical strength of the ridge structure 9 can be increased. Further, when the height of the ridge lower portion 6 is 300 nm or less and the lateral width is 3 μm or less, the recessed portion 11 of the ridge structure 9 can be completely filled with the insulating film 10, and high-speed response is good.

Embodiment 2. FIG.
9 to 16 are sectional views showing a method for manufacturing an optical semiconductor device according to the second embodiment of the present invention. First, as shown in FIG. 9, the active layer 2 is formed on the semiconductor substrate 1. The outermost surface layer 2a of the active layer 2 is an InP layer. An InP layer 14 is formed on the active layer 2.

  Next, as shown in FIG. 10, the InP layer 14 is patterned by dry etching to form the ridge lower portion 6. In addition, when the outermost surface layer 2a of the active layer 2 is made of InGaAsP, the lower ridge 6 can be formed only by wet etching or by a combination of dry etching and wet etching.

  Next, as shown in FIG. 11, the sacrificial layer 3 made of a material different from that of the outermost surface layer 2 a and the InP layer 14 of the active layer 2 is formed around the ridge lower portion 6 to a height that does not cover the upper surface of the ridge lower portion 6. . The sacrificial layer 3 is required to have a selection ratio between InP and etching, and is, for example, an InGaAsP layer.

  Next, as shown in FIG. 12, an InP layer 15 made of a material different from that of the sacrificial layer 3 is formed on the ridge lower portion 6 and the sacrificial layer 3. An InGaAs contact layer 7 is formed on the InP layer 15. A thin InP layer may be formed on the InGaAs contact layer 7 as a cap layer.

Next, as shown in FIG. 13, the InP layer 15 and the InGaAs contact layer 7 are dry-etched or wet-etched up to the sacrificial layer 3 using an insulating film hard mask or the like such as SIO ₂ and is required for the characteristics. The ridge upper part 8 is formed by patterning to a desired ridge width.

  Next, as shown in FIG. 14, the sacrificial layer 3 is selectively removed by wet etching with respect to the outermost surface layer 2 a of the active layer 2 and the InP layers 14 and 15. Next, as shown in FIG. 15, the insulating film 10 is formed on the entire surface by atomic layer deposition, and the recessed portion 11 of the ridge structure 9 is completely filled with the insulating film 10. Finally, as shown in FIG. 16, a part of the insulating film 10 is removed by etching on the upper surface of the ridge structure 9 to form the electrode 12.

  Also in the present embodiment, as in the first embodiment, the mechanical strength of the ridge structure 9 can be improved by completely embedding the recessed portion 11 of the ridge structure 9 with the insulating film 10 by the atomic layer deposition method. .

  In the first and second embodiments, if the recess 11 of the ridge structure 9 is completely filled with the insulating film 10 by the atomic layer deposition method, an insulating film is further formed using a sputtering method or a plasma CVD method. May be. The ridge lower portion 6 and the ridge upper portion 8 have a vertical ridge shape, and the ridge structure 9 is T-shaped. However, the ridge structure 9 is not limited to this, and may be a reverse mesa ridge structure or a Y-shaped structure. In addition, the optical semiconductor device of the present embodiment is an optical integrated device such as a DFB laser or a modulator laser, but the present invention is not limited thereto.

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate, 2 active layer, 2a outermost surface layer, 3 sacrificial layer, 4 opening, 5 InP layer (semiconductor layer), 6 ridge lower part, 8 ridge upper part, 9 ridge structure, 11 hollow part, 14 InP layer (1st Semiconductor layer), 15 InP layer (second semiconductor layer), 16 bottom surface of the ridge, 17 steps, 18 spaces, 19 convex shape

Claims (7)

Forming a ridge structure on a semiconductor substrate having a ridge lower portion and a ridge upper portion disposed on the ridge lower portion and having a width wider than the ridge lower portion;
By completely filling a recess portion of the ridge structure with an insulating film by an atomic layer deposition method, which is caused by a difference in width between the ridge lower portion and the ridge upper portion. the method of the previous SL optical semiconductor device, characterized in that it comprises a step of forming a convex shape without a step on the side surface of the insulating film provided on a side surface of the ridge structure on the semiconductor substrate. Forming an active layer on the semiconductor substrate;
Forming a sacrificial layer having a material different from that of the outermost surface layer of the active layer on the active layer;
Removing a portion of the sacrificial layer to form an opening;
Forming a semiconductor layer made of a material different from that of the sacrificial layer on the active layer and the sacrificial layer to form a ridge lower part inside the opening;
Patterning the semiconductor layer to form the ridge top;
And a step of selectively etching and removing the sacrificial layer with respect to the outermost surface layer and the semiconductor layer of the active layer after forming the ridge top and before forming the insulating film. The method of manufacturing an optical semiconductor device according to claim 1. Forming an active layer on the semiconductor substrate;
Forming a first semiconductor layer on the active layer;
Patterning the first semiconductor layer to form the lower portion of the ridge;
Forming a sacrificial layer made of a material different from that of the outermost surface layer of the active layer and the first semiconductor layer to a height around the lower portion of the ridge so as not to cover the upper surface of the lower portion of the ridge;
Forming a second semiconductor layer made of a material different from that of the sacrificial layer on the ridge and on the sacrificial layer;
Patterning the second semiconductor layer to form the ridge top;
After forming the ridge top and before forming the insulating film, the sacrificial layer is selectively etched and removed from the outermost surface layer of the active layer and the first and second semiconductor layers. The method for manufacturing an optical semiconductor device according to claim 1, further comprising a step.   4. The optical semiconductor device according to claim 2, wherein the material of the outermost surface layer of the active layer, the lower portion of the ridge and the upper portion of the ridge is InP, and the material of the sacrificial layer is InGaAsP. Method. The ridge lower part and the ridge upper part have a vertical ridge shape,
The method of manufacturing an optical semiconductor device according to claim 1, wherein the ridge structure is T-shaped.   The method of manufacturing an optical semiconductor device according to claim 1, wherein the optical semiconductor device is a DFB laser.   The method of manufacturing an optical semiconductor device according to claim 1, wherein the optical semiconductor device is an optical integrated device.

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