Method for manufacturing semiconductor device

Abstract

A purpose of the present invention is to provide a method for manufacturing a semiconductor device that makes it possible to align the heights of ridge structures of a plurality of semiconductor elements that each have an optical function in different wavelength bands. In the method for manufacturing a semiconductor device according to the present disclosure, first conductivity-type layers 3 and 6, non-doped layers 4 and 7, and second conductivity-type layers 5 and 8 are selectively epitaxially grown on the surface of a semiconductor substrate 1 for each semiconductor element to form mesa structures. Further, wet etching is simultaneously applied to the mesa structures of the plurality of semiconductor elements, and the non-doped layers 4 and 7 are exposed at inclined portions of the mesa structures. Selective wet etching is simultaneously applied to the mesa structures of the plurality of semiconductor elements, and the width of the non-doped layers 4 and 7 is made narrower than the width of the second conductive-type layers 5 and 8. Selective wet etching is applied to the mesa structures of the plurality of semiconductor elements to form inverted mesa structures. Further, dry etching is simultaneously applied to the inverted mesa structures of the plurality of semiconductor elements to form high-mesa structures.

Description

Semiconductor device manufacturing method

[0001] The present disclosure relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device having multiple semiconductor elements each performing an optical function in a different wavelength band.

[0002] Wavelength Division Multiplexing (WDM) communication is known as a technology for realizing large-capacity optical communication.

[0003] In the technology disclosed in Patent Document 1, a first semiconductor laser element having a ridge structure is first formed on a semiconductor substrate. Next, a layered structure of a second semiconductor laser element having an oscillation wavelength band different from that of the first semiconductor laser element is formed. The layered structure is then etched to form the ridge structure of the second semiconductor laser element. By forming a large number of semiconductor laser elements having mutually different oscillation wavelength bands in this way, high integration can be achieved.

[0004] Japanese Patent Application Laid-Open No. 2004-207588

[0005] Not only in multi-wavelength semiconductor laser devices, but also in semiconductor devices having multiple semiconductor elements each performing optical functions in different wavelength bands, it is desirable that the wavelength characteristics do not change, and therefore it is desirable that the height of the ridge structure in each semiconductor element is uniform.

[0006] In the conventional technology, semiconductor layers for the second semiconductor laser element are formed so as to cover the ridge structure of the first semiconductor laser element. Furthermore, the portion where the second semiconductor laser element is to be formed is masked with resist. Then, etching is performed to form the desired ridge structure. This etching also serves to remove the semiconductor layers covering the ridge structure of the first semiconductor laser element and restore it to its original state. However, the unmasked first semiconductor laser element is also etched, and the height of the ridge structure changes from when it was formed. As a result, the heights of the ridge structures of the first semiconductor laser element and the second semiconductor laser element are no longer the same.

[0007] In order to solve the above-mentioned problems, the present disclosure aims to provide a method for manufacturing a semiconductor device that can align the heights of the ridge structures of multiple semiconductor elements that each perform optical functions in different wavelength bands.

[0008] An aspect of the present disclosure is a method for manufacturing a semiconductor device having a plurality of semiconductor elements each performing an optical function in a different wavelength band, comprising the steps of: selectively epitaxially growing a first conductivity type layer, a non-doped layer, and a second conductivity type layer on a surface of a semiconductor substrate for each semiconductor element to individually form a mesa structure; simultaneously wet-etching the mesa structures of the plurality of semiconductor elements to expose the non-doped layer at an inclined portion of the mesa structure of the plurality of semiconductor elements; simultaneously wet-etching the mesa structures of the plurality of semiconductor elements using a chemical solution whose etching rate for the non-doped layer is greater than the etching rates for the first conductivity type layer and the second conductivity type layer to make the width of the non-doped layer narrower than the width of the second conductivity type layer; Preferably, the method for manufacturing a semiconductor device includes the steps of: simultaneously wet-etching the mesa structures of the plurality of semiconductor elements using a chemical solution in which etching does not proceed to the non-doped layer, and in which the etching rate in the depth direction of the first conductivity type layer and the second conductivity type layer is slower than the etching rate in the lateral direction, thereby forming inverted mesa structures of the plurality of semiconductor elements; masking the peripheries of the inverted mesa structures of the plurality of semiconductor elements and the surface of the semiconductor substrate; shaping the mask on the inverted mesa structures of the plurality of semiconductor elements to a predetermined width; and simultaneously dry-etching the regions of the inverted mesa structures of the plurality of semiconductor elements excluding the masked portions until the semiconductor substrate is exposed, thereby forming high mesa structures of the plurality of semiconductor elements.

[0009] According to an aspect of the present disclosure, mesa structures of multiple semiconductor elements, each performing optical functions in a different wavelength band, are selectively epitaxially grown on a semiconductor substrate. Then, the semiconductor layers of each semiconductor laser element are simultaneously subjected to wet and dry etching. This allows the heights of the ridge structures of the multiple semiconductor elements to be uniform.

[0010] FIG. 1 is a diagram illustrating a method for manufacturing a multi-wavelength semiconductor laser device according to a first embodiment. FIG. 2 is a diagram illustrating a method for manufacturing a multi-wavelength semiconductor laser device according to a first embodiment. FIG. 3 is a diagram illustrating a method for manufacturing a multi-wavelength semiconductor laser device according to a first embodiment. FIG. 4 is a diagram illustrating a method for manufacturing a multi-wavelength semiconductor laser device according to a first embodiment. FIG. 5 is a diagram illustrating a method for manufacturing a multi-wavelength semiconductor laser device according to a first embodiment. FIG. 6 is a diagram illustrating a method for manufacturing a multi-wavelength semiconductor laser device according to a first embodiment. FIG. 7 is a diagram illustrating a method for manufacturing a multi-wavelength semiconductor laser device according to a first embodiment. FIG. 8 is a diagram illustrating a method for manufacturing a multi-wavelength semiconductor laser device according to a first embodiment. FIG. 9 is a diagram illustrating a method for manufacturing a multi-wavelength semiconductor laser device according to a second embodiment. FIG. 10 is a diagram illustrating a method for manufacturing a multi-wavelength semiconductor laser device according to a second embodiment. 1 is a diagram for explaining a method for manufacturing a multi-wavelength semiconductor laser device according to a second embodiment; FIG. 2 is a diagram for explaining a method for manufacturing a multi-wavelength semiconductor laser device according to a second embodiment; FIG. 3 is a diagram for explaining a method for manufacturing a multi-wavelength semiconductor laser device according to a third embodiment; FIG. 4 is a diagram for explaining a method for manufacturing a multi-wavelength semiconductor laser device according to a third embodiment; FIG. 5 is a diagram for explaining a method for manufacturing a multi-wavelength semiconductor laser device according to a third embodiment; FIG. 6 is a diagram for explaining a method for manufacturing a multi-wavelength semiconductor laser device according to a third embodiment; FIG. 7 is a diagram for explaining a method for manufacturing a multi-wavelength semiconductor laser device according to a third embodiment; FIG. 8 is a diagram for explaining a method for manufacturing a multi-wavelength semiconductor laser device according to a third embodiment;39 is a diagram illustrating a method for manufacturing a multi-wavelength semiconductor laser device according to a third embodiment. 40 is a diagram illustrating a method for manufacturing a multi-wavelength semiconductor laser device according to the third embodiment. 41 is a top view at the position of a non-doped layer for a semiconductor laser element according to a fourth embodiment. 42 is a diagram illustrating a method for manufacturing a multi-wavelength semiconductor laser device according to the fourth embodiment. 43 is a diagram illustrating a method for manufacturing a multi-wavelength semiconductor laser device according to the fourth embodiment. 44 is a diagram illustrating a method for manufacturing a multi-wavelength semiconductor laser device according to the fourth embodiment. 45 is a diagram illustrating a method for manufacturing a multi-wavelength semiconductor laser device according to the fourth embodiment. 46 is a diagram illustrating a method for manufacturing a multi-wavelength semiconductor laser device according to the fourth embodiment. 47 is a diagram illustrating a top view at the position of a non-doped layer for a semiconductor laser element according to the fourth embodiment. 48 is a diagram illustrating a method for manufacturing a multi-wavelength semiconductor laser device according to the fourth embodiment. 49 is a diagram illustrating an arrangement of an insulating film 2 when dry etching is performed on a high mesa structure according to a comparative example of the present disclosure. 49 is a diagram illustrating a case where dry etching is performed on the mesa structure of FIG. 37 according to a comparative example of the present disclosure. 49 is a diagram illustrating a state of forming a second semiconductor laser element in the prior art. 49 is a diagram illustrating a case where etching is performed to a targeted depth on the structure of FIG. 39. 49 is a diagram illustrating a case where etching is performed to a targeted depth on the structure of FIG. 39 in the prior art. 49 is a diagram illustrating a case where etching is performed to an excessive depth beyond the targeted depth on the structure of FIG. 39.

[0011] A method for manufacturing a semiconductor device according to an embodiment of the present disclosure will be described with reference to the drawings. The same or corresponding components are designated by the same reference numerals, and repeated description may be omitted.

[0012] 1 to 15 are diagrams illustrating a method for manufacturing a multi-wavelength semiconductor laser device 100 according to a first embodiment. First, as shown in FIG. 1, an insulating film 2 is formed on a semiconductor substrate 1. Examples of materials for the insulating film 2 include SiO. ２ Alternatively, SiN may be used, but any material may be used as long as it can achieve epitaxial growth, which will be described later.

[0013] 2, an opening 19 is formed in the region of the insulating film 2 where the first semiconductor laser element 110 is to be formed, thereby exposing the semiconductor substrate 1. Examples of a method for processing the insulating film 2 include dry etching such as reactive ion etching (RIE) or inductively coupled plasma (ICP) etching.

[0014] 3, the first conductivity type layer 3, the non-doped layer 4, and the second conductivity type layer 5 of the first semiconductor laser element 110 are selectively epitaxially grown in the opening 19 to form a mesa structure. The first conductivity type layer 3 and the second conductivity type layer 5 are conductivity type layers such as p-type or n-type doped InP layers. The non-doped layer 4 is an active layer made of a ternary or quaternary compound semiconductor such as InGaAsP, AlGaInAs, or InGaAs. This point is not limited to the first semiconductor laser element 110, but is also common to semiconductor laser elements that oscillate in other wavelength bands.

[0015] Next, the insulating film 2 is removed. The insulating film 2 can be removed by wet etching using buffered hydrofluoric acid (BHF) or hydrofluoric acid (HF).

[0016] Furthermore, as shown in FIG. 4, the insulating film 24 is formed again.

[0017] 5, an opening 20 is formed in a region of the insulating film 24 where the second semiconductor laser element 120 will be formed, thereby exposing the semiconductor substrate 1. Thereafter, as shown in FIG. 6, the first conductivity type layer 6, the non-doped layer 7, and the second conductivity type layer 8 of the second semiconductor laser element 120 are selectively epitaxially grown in the opening 20 to form a mesa structure.

[0018] For simplicity of explanation, only the mesa structures for the first semiconductor laser element 110 and the second semiconductor laser element 120 are illustrated below. However, if necessary, mesa structures for the third and fourth semiconductor laser elements can be selectively epitaxially grown using a similar method. This allows the formation of multiple semiconductor layers for the semiconductor laser elements responsible for lasing in each wavelength band. The mesa structure is a layer including a first conductivity type layer, a non-doped layer, and a second conductivity type layer.

[0019] Next, the insulating film 24 is removed, and then an insulating film 25 is formed. Furthermore, the insulating film 25 is removed except for the portions on the second conductive type layers 5 and 8, as shown in FIG.

[0020] 8, the selectively epitaxially grown mesa structure is wet-etched to expose the non-doped layers 4 and 7 at the inclined portions of the mesa structure. For the wet etching, a chemical solution capable of isotropically etching the first conductivity type layers 3 and 6, the non-doped layers 4 and 7, and the second conductivity type layers 5 and 8 is preferred. An example of the chemical solution is sulfuric acid.

[0021] Thereafter, as shown in FIG. 9 , the non-doped layers 4 and 7 are selectively wet-etched from the sloped portion of the mesa structure. For the wet etching, a chemical solution is used that has a higher etching rate for the non-doped layers 4 and 7 than for the first conductivity-type layers 3 and 6 and the second conductivity-type layers 5 and 8. In the case of the non-doped layers 4 and 7 made of ternary or quaternary compound semiconductors as in the present disclosure, an example of a suitable chemical solution is tartaric acid. As a guideline for the amount of wet etching, it is desirable to etch until the width of the non-doped layers 4 and 7 is narrower than the width of the second conductivity-type layers 5 and 8.

[0022] Next, as shown in FIG. 10 , the first conductivity-type layers 3 and 6 and the second conductivity-type layers 5 and 8 are selectively wet-etched. The chemical used must not etch the non-doped layers 4 and 7. Additionally, the etching rate in the depth direction of the first conductivity-type layers 3 and 6 and the second conductivity-type layers 5 and 8 must be relatively slower than the etching rate in the lateral direction. Hydrogen bromide (HBr) is a suitable chemical for the first conductivity-type layers 3 and 6 and the second conductivity-type layers 5 and 8, which are p-type or n-type doped InP layers as in the present disclosure. By performing wet etching with an anisotropic chemical, semiconductor layers with an inverted mesa structure can be simultaneously formed in each semiconductor laser element. Here, the inverted mesa structure refers to a structure in which the width narrows from the insulating film 25 mask toward the semiconductor substrate 1.

[0023] Next, as shown in FIG. 11, an insulating film 26 is formed around the ridge portion of the inverted mesa structure and on the surface of the semiconductor substrate 1.

[0024] 12, both ends of the insulating film 26 on the ridge of the inverted mesa structure are removed to shape the insulating film 26 to a predetermined width. The predetermined width refers to the width of the high mesa structure described below. Note that, as shown in FIG. 12, the insulating film 26 formed on the slope of the inverted mesa structure and the insulating film 26 on the surface of the semiconductor substrate 1 are left.

[0025] 13, the first conductivity type layers 3 and 6, the non-doped layers 4 and 7, and the second conductivity type layers 5 and 8 are dry-etched to expose the semiconductor substrate 1. In the dry etching, the insulating film 26 serves as a mask. For the semiconductor layers on the sloped portions of the inverted mesa structure, the dry etching first reaches the second conductivity type layers 5 and 8, then the non-doped layers 4 and 7, and the first conductivity type layers 3 and 6, in that order, and finally reaches the insulating film 26 on the sloped portions. After reaching the insulating film 26 on the sloped portions, the dry etching does not proceed.

[0026] On the other hand, for the semiconductor layers on the semiconductor substrate 1, the dry etching first reaches the second conductivity type layers 5 and 8, then the non-doped layers 4 and 7, and the first conductivity type layers 3 and 6, in that order, and finally reaches the semiconductor substrate 1. By terminating the dry etching when it reaches the semiconductor substrate 1, the high mesa structure shown in FIG.

[0027] Thereafter, all of the insulating film 26 is removed as shown in Fig. 14. Furthermore, an insulating film 27 is formed on the sidewalls of the high mesa structure and on the semiconductor substrate 1 as shown in Fig. 15. Furthermore, a top electrode 51 is formed on the top of the high mesa structure, and a back electrode 52 is formed on the back surface of the semiconductor substrate 1. In this way, a multi-wavelength semiconductor laser device 100 including a first semiconductor laser element 110 and a second semiconductor laser element 120 can be fabricated.

[0028] As described above, in the present disclosure, the mesa structure of each semiconductor laser element is selectively epitaxially grown on the semiconductor substrate 1. Then, the mesa structure of each semiconductor laser element is simultaneously subjected to wet and dry etching. In this case, the etching process variations are uniform for the mesa structure of each semiconductor laser element. Therefore, the height of the ridge structure can be made uniform in the semiconductor laser elements responsible for lasing in each wavelength band.

[0029] <Modification of First Embodiment> The non-doped layers 4 and 7 are not limited to active layers for semiconductor lasers, but may also be light absorption layers for semiconductor modulators or core layers for semiconductor optical amplifiers. This makes it possible to fabricate multi-wavelength semiconductor modulators or semiconductor optical amplifiers, respectively. This point is common to all of the following embodiments.

[0030] Second Embodiment This embodiment shows a method for manufacturing a buried ridge type multi-wavelength semiconductor laser device 200. The explanations of Figures 1 to 13 of the first embodiment are common to this embodiment and will therefore be omitted here.

[0031] 16, the ridge portion of the high mesa structure is covered with a resist 9. Then, mask transfer exposure and development processes are carried out.

[0032] Next, as shown in FIG. 17, wet etching is performed to remove the insulating film 26 except for the insulating film 26 on the upper part of the high mesa structure covered with the resist 9.

[0033] Thereafter, the resist 9 is removed as shown in Fig. 18. Furthermore, as shown in Fig. 19, a current blocking layer 10 is epitaxially grown so as to fill the spaces between each high mesa structure. Note that the material for the current blocking layer 10 can be of any type as long as it has high resistance to the current flowing through the non-doped layer.

[0034] Furthermore, the insulating film 26 on the top of the ridge of the high mesa structure is removed. Furthermore, as shown in FIG. 20 , an insulating film 28 is formed on the top of the current blocking layer 10. A top electrode 51 is formed on the top of the ridge of the high mesa structure, and a back electrode 52 is formed on the back surface of the semiconductor substrate 1. This allows the fabrication of a buried ridge type multi-wavelength semiconductor laser device 200 in which the ridge portion of the high mesa structure is buried with the current blocking layer 10. The current blocking layer 10 limits the amount of current flowing between the top electrode 51 and the back electrode 52. This makes it possible to suppress heat generation during laser operation. In terms of stable operation, the multi-wavelength semiconductor laser device 200 of this embodiment exhibits a superior effect to the multi-wavelength semiconductor laser device 100 of the first embodiment.

[0035] Third Embodiment This embodiment shows a method for manufacturing a multiplexer-integrated multi-wavelength semiconductor laser device 300. The explanations of FIGS. 1 to 11 in the first embodiment are common to this embodiment and will therefore be omitted here.

[0036] Next, similarly to FIG. 12 , an insulating film 26 having a predetermined width is shaped on the ridge of the reverse mesa structure. However, as shown in FIG. 21 , in the first region 61 where the reverse mesa structure extends, the insulating film 26 on the reverse mesa structure is shaped to a predetermined width, and in the second region 62 where the reverse mesa structure extends, the insulating film 26 on the reverse mesa structure is removed. Here, FIG. 21 is a top view of the semiconductor substrate 1. Note that the cavity length direction of each semiconductor laser element is the vertical direction on the page. The second region 62 is disposed adjacent to the first region 61 in the cavity length direction. FIG. 22 is a cross-sectional view taken along the line a-a' of the first region 61 in FIG. 21 . Similarly, FIG. 23 is a cross-sectional view taken along the line b-b' of the second region 62.

[0037] Next, similarly to Fig. 13, dry etching is performed until the semiconductor substrate 1 is exposed in the region excluding the masked portion of the inverted mesa structure. Next, the same processes as those shown in Figs. 16 to 18 of the second embodiment are performed. As a result, as shown in Fig. 24, in the first region 61, only the ridge portion of the high mesa structure and the insulating film 26 thereon remain, and the semiconductor substrate 1 is exposed. On the other hand, in the second region 62, the semiconductor substrate 1 is exposed over the entire area. Fig. 25 is a cross-sectional view taken along the line a-a' of the first region 61 in Fig. 24.

[0038] Then, as shown in FIGS. 26 and 27 , waveguide layers including a waveguide core layer 12, a waveguide first cladding layer 11, and a waveguide second cladding layer 13 are laminated between each high mesa structure. As shown in FIG. 26 , waveguide layers are laminated not only in the first region 61 but also in the second region 62 where no high mesa structure exists. FIG. 27 is a cross-sectional view taken along the line a-a′ of the first region 61 in FIG. 26 . As shown in FIG. 27 , the waveguide core layer 12 is formed to connect the non-doped layer 4 and the non-doped layer 7. The waveguide first cladding layer 11 is formed to connect the first conductivity type layer 3 and the first conductivity type layer 6. The waveguide second cladding layer 13 is formed to connect the second conductivity type layer 5 and the second conductivity type layer 8.

[0039] Thereafter, the insulating film 26 in the first region 61 is removed. Furthermore, as shown in Fig. 28, the waveguide core layer 12, the waveguide first cladding layer 11, and the waveguide second cladding layer 13 are processed to form a waveguide. The waveguide includes an input section 21, a multiplexer 22, and an output section 23. As a result, the light oscillated from each semiconductor laser element can be multiplexed by the multiplexer 22 and emitted from the output section 23.

[0040] Furthermore, as shown in Fig. 29, an insulating film 29 is formed on the sidewalls of the high mesa structure, the semiconductor substrate 1, and the waveguide. Furthermore, a top electrode 51 is formed on the top of the ridge of the high mesa structure, and a back electrode 52 is formed on the back surface of the semiconductor substrate 1. This makes it possible to fabricate a multi-wavelength semiconductor laser device 300 with a built-in multiplexer. Fig. 30 is a cross-sectional view taken along the line aa' in Fig. 29.

[0041] Here, in order to minimize the optical waveguide loss from each semiconductor laser element to the combiner 22, it is desirable that the thickness of the waveguide core layer 12 and its height from the semiconductor substrate 1 are the same as those of the non-doped layers 4 and 7. As described above, in the present disclosure, the height of the ridge structure can be made uniform for each semiconductor laser element. Furthermore, the heights of the non-doped layers 4 and 7 can also be made uniform. Therefore, in the present disclosure, it is possible to match the height of the waveguide core layer 12 to the height of the non-doped layers 4 and 7 of each semiconductor laser element. As a result, the loss due to optical waveguide mode mismatch occurring at the boundary between the non-doped layers 4 and 7 and the input section 21 can be made uniform for each semiconductor laser element.

[0042] Modification of Third Embodiment The multi-wavelength semiconductor laser device 300 with a built-in multiplexer described in this embodiment can be modified to the buried ridge type described in the second embodiment. In this modification, after forming the high mesa structures shown in FIG. 25 , current blocking layers 10 are epitaxially grown in the first region 61 so as to fill the spaces between the high mesa structures. Meanwhile, in the second region 62, as shown in FIG. 26 , waveguide layers including a waveguide core layer 12, a first waveguide cladding layer 11, and a second waveguide cladding layer 13 are stacked. Furthermore, as shown in FIG. 28 , the waveguide layers are processed to form a waveguide. As a result, the multi-wavelength semiconductor laser device 300 has a structure in which each high mesa structure is buried with a current blocking layer 10. In this case, the effects of combining the second and third embodiments can be obtained.

[0043] Fourth Embodiment This embodiment describes a manufacturing method for a multi-wavelength semiconductor laser device 400 incorporating a modulator or an optical amplifier. The multi-wavelength semiconductor laser device 400 has a configuration in which the multi-wavelength semiconductor laser device 300 described in the third embodiment further includes a modulator or an optical amplifier. In the following description, a manufacturing method for the multi-wavelength semiconductor laser device 400 including a modulator will be described. Regarding the optical amplifier, in the following description, the modulator should be read as the optical amplifier.

[0044] 1 to 6, in which the semiconductor layers of each semiconductor laser element are selectively epitaxially grown, a mesa structure for a modulator is selectively epitaxially grown between the mesa structures of each semiconductor laser element. The mesa structure for a modulator includes a non-doped layer for the modulator, a first conductivity type layer for the modulator, and a second conductivity type layer for the modulator.

[0045] 31 is a top view at the position of the non-doped layers 4 and 7 for the semiconductor laser element according to the fourth embodiment. An non-doped layer 14 for the first modulator is formed between the non-doped layer 4 for the first semiconductor laser element 110 and the non-doped layer 7 for the second semiconductor laser element 120. The first modulator operates as a modulator for the oscillation wavelength of the first semiconductor laser element 110.

[0046] Similarly, an undoped layer 15 for the second modulator is formed between the undoped layer 7 for the second semiconductor laser element 120 and the undoped layer of a third semiconductor laser element (not shown). The second modulator operates as a modulator for the oscillation wavelength of the second semiconductor laser element 120. In this way, each modulator has a modulation function for the oscillation wavelength of the semiconductor laser element adjacent to itself, which does not overlap with the oscillation wavelength of other modulators.

[0047] The non-doped layer 14 for the first modulator and the non-doped layer 15 for the second modulator are selectively epitaxially grown to the same height as the non-doped layers 4 and 7 of the semiconductor laser element, thereby enabling the light oscillated from the non-doped layers 4 and 7 of the semiconductor laser element to be modulated by the modulator.

[0048] The mesa structure of the semiconductor laser element has a first extension 41 and a second extension 42 extending in the cavity length direction from one end and the other end of the semiconductor substrate 1 in the cavity length direction of the laser. The mesa structure further includes a crank portion 43 connecting the first extension 41 and the second extension 42 and having two obtuse angles alternately connected. The mesa structures for each modulator also have a similar shape. The first extension 41 of the first semiconductor laser element 110 and the second extension 42 of the first modulator are formed on the same line. Similarly, the first extension 41 of the second semiconductor laser element 120 and the second extension 42 of the second modulator are formed on the same line.

[0049] The patterns of the non-doped layers 4 and 7 for the semiconductor laser element, the non-doped layer 14 for the first modulator, and the non-doped layer 15 for the second modulator shown in FIG. 31 are merely examples, and the present invention is not limited to these.

[0050] Next, the same processes as those shown in FIGS. 7 to 11 are performed. As a result, the mesa structures for each semiconductor laser element and each modulator mesa structure become inverted mesa structures. Furthermore, as in FIG. 12, an insulating film 26 is formed on the ridge of the inverted mesa structure. However, in this embodiment, as shown in FIG. 32, the insulating film 26 is formed on the first extension portion 41 of each semiconductor laser element and the second extension portion 42 of the modulator corresponding to the oscillation wavelength of the semiconductor laser element. Note that the insulating film 26 formed on the second extension portion 42 of the modulator is not formed over the entire extension direction of the second extension portion 42, but is formed only on the first extension portion 41 side.

[0051] 13, dry etching is then performed until the semiconductor substrate 1 is exposed in the region excluding the masked portion of the inverted mesa structure. Next, the same steps as those in FIGS. 16 to 18 of the second embodiment are performed. As a result, as shown in FIG. 33, only the ridge portion of the high mesa structure in the first extension portion 41 of each semiconductor laser element and the second extension portion 42 of each modulator and the insulating film 26 thereon are left, and the semiconductor substrate 1 is exposed.

[0052] 26 of the third embodiment, a waveguide layer including a waveguide core layer 12, a first waveguide cladding layer 11, and a second waveguide cladding layer 13 is laminated between each high mesa structure and on the exposed portion of the semiconductor substrate 1. This results in the state shown in FIG.

[0053] Furthermore, the waveguide layer is processed to form a waveguide in the same manner as in Fig. 28. This results in the state shown in Fig. 35. Fig. 35 is a top view at the position of the non-doped layers 4 and 7 for the semiconductor laser element.

[0054] 36, an insulating film 30 is formed on the sidewalls of the high mesa structure of each semiconductor laser element and modulator, on the semiconductor substrate 1, and on the waveguide excluding the modulator. Furthermore, a top electrode 53 is disposed to cover the top of the high mesa structure of each semiconductor laser element and modulator. This completes the fabrication of a multi-wavelength semiconductor laser device 400 incorporating a modulator.

[0055] Similar to the modification of the third embodiment, the multi-wavelength semiconductor laser device 400 can also be modified into a buried ridge type. This configuration provides the combined effect of the second and fourth embodiments.

[0056] As described above, according to the present disclosure, it is possible to provide a method for manufacturing a semiconductor device that can align the height of ridge structures in semiconductor elements that perform optical functions in different wavelength bands.

[0057] The present disclosure is not limited to the above-described embodiments, and various modifications can be made in the implementation stage without departing from the spirit of the present disclosure. Furthermore, the embodiments may be implemented in appropriate combinations, and in such cases, the combined effects can be obtained.

[0058] Comparative Example 1 In the present disclosure, it has been described that a desired high mesa structure such as that shown in FIG. 14 can be obtained by dry etching an inverted mesa structure. It should be noted that even if dry etching is performed on a mesa structure, the desired high mesa structure cannot be formed. FIG. 37 is a diagram illustrating the arrangement of the insulating film 31 when dry etching is performed on a mesa structure according to a comparative example of the present disclosure. To obtain the structure shown in FIG. 37, the insulating film 2 is removed from the state shown in FIG. 6, and then the insulating film 31 is deposited again. Furthermore, both ends of the insulating film 31 on the ridge of the mesa structure are removed, leaving only the width of the high mesa structure. Furthermore, the insulating film 31 is also removed from the sloped portion of the mesa structure.

[0059] 38 is a diagram illustrating a comparative example of the present disclosure in which dry etching is performed on the mesa structure of FIG. 37 . Dry etching, by its very nature, progresses an equal distance in the depth direction from the surface in all regions except for the portion masked by the insulating film 31. As a result, the shape of the sloped portion of the mesa structure is reproduced exactly in the semiconductor substrate 1. For this reason, regardless of the arrangement of the insulating film 31 shown in FIG. 37 , the desired high mesa structure cannot be obtained as long as dry etching is performed on the semiconductor layer of the mesa structure. Alternatively, the desired high mesa structure can be obtained, but additional processing is required after dry etching.

[0060] Comparative Example 2 It has been mentioned that in the prior art, the heights of the ridge structures of the first semiconductor laser element 110 and the second semiconductor laser element 120 are not the same. Here, a more detailed explanation will be given with reference to the drawings. Note that the same reference numerals as in this disclosure are used. FIG. 39 is a diagram illustrating the formation of the second semiconductor laser element 120 in the prior art. A semiconductor layer for the second semiconductor laser element 120 is formed so as to cover the ridge structure of the first semiconductor laser element 110.

[0061] Fig. 40 is a diagram illustrating a case where etching is performed to a targeted depth on the structure of Fig. 39 in the prior art. By etching, the portion around the ridge structure of the first semiconductor laser element 110 that is covered with the semiconductor layer for the second semiconductor laser element 120 is removed. In this way, if etching can be performed to the targeted depth, the first semiconductor laser element 110 can be restored to its original ridge structure.

[0062] FIG. 41 illustrates a prior art example in which the structure of FIG. 39 is etched to a depth greater than the desired depth. The second conductivity-type layer 5 of the first semiconductor laser element 110 and even the semiconductor substrate 1 are etched. Thus, the thickness of the second conductivity-type layer 5 varies in the first semiconductor laser element 110, which is not masked with resist or the like. On the other hand, the second semiconductor laser element 120 is masked with resist, so the second conductivity-type layer 8 is not etched even if the etching is excessive. As a result, the heights of the ridge structures of the first semiconductor laser element 110 and the second semiconductor laser element 120 are no longer the same.

[0063] 1 semiconductor substrate, 2 insulating film, 3 first conductivity type layer, 4 non-doped layer, 5 second conductivity type layer, 6 first conductivity type layer, 7 non-doped layer, 8 second conductivity type layer, 9 resist, 10 current blocking layer, 11 waveguide first cladding layer, 12 waveguide core layer, 13 waveguide second cladding layer, 14 first non-doped layer for modulator, 15 second non-doped layer for modulator, 16 first conductivity type layer for modulator, 17 second conductivity type layer for modulator, 19 opening, 20 opening, 21 input section, 22 multiplexer, 23 output section, 24, 25, 26, 27, 28, 29, 30, 31 insulating film, 41 first extension section, 42 second extension section, 43 crank section, 51 upper electrode, 52 Back electrode, 53 top electrode, 61 first region, 62 second region, 100, 200, 300, 400 multi-wavelength semiconductor laser device, 110 first semiconductor laser element, 120 second semiconductor laser element

Claims

1. A method for manufacturing a semiconductor device having a plurality of semiconductor elements each performing an optical function in a different wavelength band, comprising: selectively epitaxially growing a first conductivity type layer, a non-doped layer, and a second conductivity type layer on a surface of a semiconductor substrate to individually form a mesa structure for each semiconductor element; simultaneously wet-etching the mesa structures of the plurality of semiconductor elements to expose the non-doped layer at the inclined portions of the mesa structures of the plurality of semiconductor elements; simultaneously wet-etching the mesa structures of the plurality of semiconductor elements using a chemical solution having a higher etching rate for the non-doped layer than for the first conductivity type layer and the second conductivity type layer, thereby making the width of the non-doped layer narrower than the width of the second conductivity type layer; a step of simultaneously wet-etching the mesa structures of the plurality of semiconductor elements using a chemical solution that does not cause etching to proceed on the non-doped layer and has a depth etching rate that is slower than a lateral etching rate on the first conductivity type layer and the second conductivity type layer, thereby forming an inverted mesa structure of the plurality of semiconductor elements; masking the periphery of the inverted mesa structure of the plurality of semiconductor elements and the surface of the semiconductor substrate; a step of shaping the mask on the inverted mesa structures of the plurality of semiconductor elements to a predetermined width; a step of simultaneously performing dry etching on the plurality of semiconductor elements in regions other than the masked portions of the inverted mesa structure until the semiconductor substrate is exposed, thereby forming a high mesa structure for the plurality of semiconductor elements; A method for manufacturing a semiconductor device, comprising:

2. 2. The method for manufacturing a semiconductor device according to claim 1, further comprising the step of burying each of said high mesa structures with a current blocking layer having a high resistance to a current flowing through said non-doped layer.

3. 3. The method for manufacturing a semiconductor device according to claim 1, wherein the high mesa structure is a high mesa structure for a laser, a modulator, or an optical amplifier.

4. stacking a waveguide core layer and a waveguide clad layer on the semiconductor substrate, the waveguide core layer and the waveguide clad layer connecting the high mesa structures of the plurality of semiconductor elements; a step of processing the waveguide core layer and the waveguide clad layer to form a waveguide including a multiplexer connected to each of the high mesa structures of the plurality of semiconductor elements; The method for manufacturing a semiconductor device according to claim 1 or 2, further comprising:

5. 3. The method for manufacturing a semiconductor device according to claim 1, wherein the high mesa structure includes a high mesa structure for a modulator or an optical amplifier and a high mesa structure for a laser, and the high mesa structure for the modulator or the optical amplifier and the high mesa structure for the laser are linearly connected by a waveguide.