Method for manufacturing multi-wavelength integrated semiconductor laser

Abstract

The purpose of the present disclosure is to provide a method for manufacturing a multi-wavelength integrated semiconductor laser in which it is possible to align the heights of active layers in a plurality of semiconductor laser parts which perform laser oscillations in different wavelength bands. The method for manufacturing a multi-wavelength integrated semiconductor laser according to the present invention includes: a step for epitaxially growing a semiconductor layer on a semiconductor substrate; a step for etching the semiconductor layer to simultaneously form a first groove and a second groove; a step for selectively epitaxially growing at least a first active layer within the first groove to form a first semiconductor laser part; a step for selectively epitaxially growing at least a second active layer within the second groove to form a second semiconductor laser part; and a step for partially masking the upper surface of the first semiconductor laser part and the upper surface of the second semiconductor laser part by using an insulation film and then performing a dry-etching to form mesa structures for the first semiconductor laser part and the second semiconductor laser part.

Description

Method for manufacturing multi-wavelength integrated semiconductor laser

[0001] The present disclosure relates to a method for manufacturing a multi-wavelength integrated semiconductor laser having a plurality of semiconductor lasers each responsible for laser oscillation in a different wavelength band.

[0002] Multi-wavelength integrated semiconductor lasers are required to achieve even higher speeds, higher functionality, and lower costs. In the technology disclosed in Patent Document 1, a ridge structure of a first semiconductor laser portion is first formed on a semiconductor substrate. Then, a ridge structure of a second semiconductor laser portion having an oscillation wavelength band different from that of the first semiconductor laser portion is formed. In this way, by sequentially forming a large number of semiconductor laser portions having mutually different oscillation wavelength bands, high integration can be achieved.

[0003] Japanese Patent Application Laid-Open No. 2004-207588

[0004] In a multi-wavelength integrated semiconductor laser, it is desirable that the wavelength characteristics do not change, and therefore it is desirable that the height of the active layer in each semiconductor laser portion is uniform.

[0005] In the conventional technology, first, the semiconductor layer of the first semiconductor laser portion is epitaxially grown. Then, etching is performed to form a ridge structure of the first semiconductor laser portion and expose the semiconductor substrate except for the ridge structure area. Then, the semiconductor layer of the second semiconductor laser portion is epitaxially grown so as to cover the ridge structure of the first semiconductor laser portion. Then, the portion where the second semiconductor laser portion is to be formed is masked with resist. Then, etching is performed to form the ridge structure of the second semiconductor laser portion.

[0006] In the prior art, if the etching for forming the ridge structure of the first semiconductor laser portion is excessive, the semiconductor substrate is also etched. As a result, the surface of the semiconductor substrate where epitaxial growth of the semiconductor layer of the second semiconductor laser portion starts differs from that of the first semiconductor laser portion. As a result, the heights of the active layers of the first and second semiconductor laser portions do not match.

[0007] In order to solve the above-mentioned problems, the present disclosure aims to provide a method for manufacturing a multi-wavelength integrated semiconductor laser that can align the heights of the active layers of multiple semiconductor laser sections, each of which is responsible for laser oscillation in a different wavelength band.

[0008] an upper surface of the semiconductor layer and a lower surface of the semiconductor layer, the upper surface of the semiconductor layer being masked with a second insulating film, and then epitaxially growing at least a second active layer in the upper surface of the semiconductor layer to form a first semiconductor laser portion; and an upper surface of the semiconductor layer being masked with a third insulating film, the upper surface of the first semiconductor laser portion being masked with a third insulating film, and then epitaxially growing at least a second active layer in the upper surface of the semiconductor layer to form a second semiconductor laser portion.

[0009] In the present disclosure, a semiconductor layer formed on a semiconductor substrate is etched to simultaneously form a first groove and a second groove. At least a first active layer is selectively epitaxially grown inside the first groove to form a first semiconductor laser portion, and at least a second active layer is selectively epitaxially grown inside the second groove to form a second semiconductor laser portion. Because the semiconductor layers of the first and second semiconductor laser portions can be epitaxially grown from the same etched surface of the semiconductor substrate, it is possible to align the heights of the first active layer and the second active layer.

[0010] 1. A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to a first embodiment. A cross-sectional view of FIG. 1. A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to a first embodiment. A cross-sectional view of FIG. 3. A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to a first embodiment. A cross-sectional view of FIG. 5. A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to a first embodiment. A cross-sectional view of FIG. 7. A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to a first embodiment. A cross-sectional view of FIG. 9. A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to a first embodiment. A cross-sectional view of FIG. 11. A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to a first embodiment. A cross-sectional view of FIG. 13. A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to a first embodiment. A cross-sectional view of FIG. 15. A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to a first embodiment. A cross-sectional view of FIG. 17. A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to a first embodiment. A cross-sectional view of FIG. 19. A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to a first embodiment. A cross-sectional view taken along the A-A line of FIG. 21. A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to a first embodiment. 23. A cross-sectional view taken along line A-A of FIG. 23. A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to the first embodiment. A cross-sectional view taken along line A-A of FIG. 25. A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to the first embodiment. A cross-sectional view taken along line A-A of FIG. 27. A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to the first embodiment. A cross-sectional view of FIG. 29. A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to the first embodiment. A cross-sectional view of FIG. 31. A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to the first embodiment. A cross-sectional view of FIG. 33. A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to the second embodiment. A cross-sectional view of FIG. 35. A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to the second embodiment. A cross-sectional view of FIG. 37. A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to the second embodiment. A cross-sectional view of FIG. 39.41 . A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to a second embodiment. A cross-sectional view of FIG. 41 . A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to a third embodiment. A cross-sectional view of FIG. 43 . A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to a third embodiment. A cross-sectional view of FIG. 45 . A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to a third embodiment. A cross-sectional view of FIG. 47 . A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to a fourth embodiment. A cross-sectional view along A-A′ of FIG. 49 . A cross-sectional view along B-B′ of FIG. 49 . A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to a fourth embodiment. A cross-sectional view along A-A′ of FIG. 52 . A cross-sectional view along B-B′ of FIG. 52 . A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to a fourth embodiment. A cross-sectional view along A-A′ of FIG. 55 . A cross-sectional view along B-B′ of FIG. 55 . A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to a fourth embodiment. A cross-sectional view along A-A′ of FIG. 58 . A cross-sectional view along B-B′ of FIG. 58 . A top view illustrating a method for manufacturing a multi-wavelength integrated semiconductor laser according to a fourth embodiment. 61. An A-A' cross-sectional view of FIG. 61. An B-B' cross-sectional view of FIG. 61. A top view explaining a method for manufacturing a multi-wavelength integrated semiconductor laser according to the fourth embodiment. An A-A' cross-sectional view of FIG. 64. An B-B' cross-sectional view of FIG. 64. A CC' cross-sectional view of FIG. 64. A top view explaining a method for manufacturing a multi-wavelength integrated semiconductor laser according to the fifth embodiment. An A-A' cross-sectional view of FIG. 68. An B-B' cross-sectional view of FIG. 68. A top view explaining a method for manufacturing a multi-wavelength integrated semiconductor laser according to the fifth embodiment. An A-A' cross-sectional view of FIG. 71. An B-B' cross-sectional view of FIG. 71. A top view explaining a method for manufacturing a multi-wavelength integrated semiconductor laser according to the fifth embodiment. An A-A' cross-sectional view of FIG. 74. An B-B' cross-sectional view of FIG. 74. A top view explaining a method for manufacturing a multi-wavelength integrated semiconductor laser according to the fifth embodiment. An A-A' cross-sectional view of FIG. 77. An B-B' cross-sectional view of FIG. 77. A top view explaining a method for manufacturing a multi-wavelength integrated semiconductor laser according to the fifth embodiment. An A-A' cross-sectional view of FIG. 80. An B-B' cross-sectional view of FIG. 80.

[0011] Embodiments of the present disclosure will be described with reference to the drawings. The same or corresponding components will be designated by the same reference numerals, and repeated description may be omitted.

[0012] First Embodiment Here, a method for manufacturing a multi-wavelength integrated semiconductor laser 100 having a first semiconductor laser portion 110 and a second semiconductor laser portion 120 having different oscillation wavelength bands will be described with reference to FIGS.

[0013] 1 and 2, a semiconductor layer 2 is epitaxially grown on a semiconductor substrate 1, and an insulating film 3 is formed on the upper surface of the semiconductor layer 2 by a plasma CVD method or the like. The semiconductor layer 2 is a conductive layer such as a p-type or n-type doped InP layer, or a non-doped layer. Examples of materials for the insulating film 3 include SiO ２ Alternatively, SiN can be used.

[0014] 3 and 4, the regions of the insulating film 3 that form the first semiconductor laser portion 110 and the second semiconductor laser portion 120 are removed to expose the semiconductor layer 2. Methods for processing the insulating film 3 include dry etching such as reactive ion etching or inductively coupled plasma etching.

[0015] 5 and 6, the semiconductor layer 2 is etched to simultaneously form two grooves, each having the semiconductor substrate 1 as its bottom surface and the semiconductor layer 2 as its side surface. Hereinafter, of the two grooves, the groove in which the first semiconductor laser portion 110 is formed will be referred to as the first groove 111, and the groove in which the second semiconductor laser portion 120 is formed will be referred to as the second groove 121.

[0016] Although the explanation is omitted, if necessary, grooves for the third, fourth, . . . , nth semiconductor laser portions may be formed at the same time.

[0017] 7 and 8, the insulating film 3-1 is re-deposited and removed from the inside of the first groove 111. Meanwhile, the inside of the second groove 121 and the top surface of the semiconductor layer 2 are masked with the insulating film 3-1 (first insulating film).

[0018] 9 and 10 , the semiconductor layers of the first semiconductor laser portion 110, namely, the first conductivity type layer 4, the first active layer 5, the second conductivity type layer 6, the non-doped layer 7, and the cap layer 8, are epitaxially grown in this order in the first groove 111. Because the insulating film 3-1 serves as a mask, the semiconductor layers of the first semiconductor laser portion 110 are not epitaxially grown on the insulating film 3-1, but are selectively epitaxially grown only in the first groove 111.

[0019] Here, the first conductivity type layer 4, the second conductivity type layer 6, and the cap layer 8 are layers of a conductivity type such as p-type or n-type doped InP. The first active layer 5 and the non-doped layer 7 are active layers made of a ternary or quaternary compound semiconductor such as InGaAsP, AlGaInAs, or InGaAs. This point is not limited to the first semiconductor laser section 110, but is also common to semiconductor laser sections responsible for lasing in other wavelength bands.

[0020] Examples of epitaxial growth methods include metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), and liquid phase epitaxy (LPE), but other methods may also be used.

[0021] A protruding crystal growth abnormality 9 is deposited on the upper surface of the cap layer 8 along the edge of the first groove 111 adjacent to the semiconductor layer 2. This crystal growth abnormality 9 is formed by the diffusion and deposition of atoms evaporated on the insulating film 3-1 during epitaxial growth of the semiconductor layer of the first semiconductor laser portion 110. The size of the crystal growth abnormality 9 is several μm.

[0022] Next, all of the insulating film 3-1 is removed and the insulating film 3-2 is deposited again. At this time, the crystal growth abnormality portion 9 is also covered with the insulating film 3-2. Furthermore, as shown in Figures 11 and 12, the insulating film 3-2 on the inside of the second groove 121 is removed. Meanwhile, the top surface of the first semiconductor laser portion 110 and the top surface of the semiconductor layer 2 are masked with the insulating film 3-2 (second insulating film).

[0023] 13 and 14 , the semiconductor layers of the second semiconductor laser portion 120, namely, the first conductivity type layer 10, the second active layer 11, the second conductivity type layer 12, the non-doped layer 13, and the cap layer 14, are epitaxially grown in this order in the second groove 121. At this time, similar to the case of the first semiconductor laser portion 110, a crystal growth abnormality portion 15 is deposited on the upper surface of the cap layer 14 along the edge of the second groove 121 adjacent to the semiconductor layer 2.

[0024] Although the explanation is omitted, if necessary, the semiconductor layers may be epitaxially grown in the grooves in the same manner for the third, fourth, . . . , nth semiconductor laser portions.

[0025] Next, the crystal growth abnormalities 9 and 15 are removed. First, the insulating film 3-2 is removed, and then an insulating film 3-3 (fourth insulating film) is re-deposited on the semiconductor layer 2 and the semiconductor layers of the first and second semiconductor laser portions 110 and 120. Furthermore, as shown in FIGS. 15 and 16, openings are formed in the insulating film 3-3 at the ends of the first and second semiconductor laser portions 110 and 120 adjacent to the semiconductor layer 2, thereby exposing the crystal growth abnormalities 9 and 15. Meanwhile, the upper surfaces of the semiconductor layers of the first and second semiconductor laser portions 110 and 120, which do not have the crystal growth abnormalities 9 and 15, and the upper surface of the semiconductor layer 2 are masked with the insulating film 3-3. Furthermore, wet etching is performed to selectively remove the crystal growth abnormalities 9 and 15, as shown in FIGS.

[0026] Since the components of the crystal growth abnormality portions 9 and 15 are considered to be the same as the components of the semiconductor layers of the first and second semiconductor laser portions 110 and 120, a chemical solution that can etch the semiconductor layers of the first and second semiconductor laser portions 110 and 120 is used for wet etching. It is also desirable that the etching rate of the chemical solution in the depth direction be relatively slower than the etching rate in the lateral direction. An example of such a chemical solution is acetic acid.

[0027] As described above, the size of the crystal growth abnormalities 9 and 15 is several μm, and unless they are removed, it will be impossible to uniformly apply the photoresist 16 to a thickness of several hundred nm in the next step. Therefore, it is necessary to remove the crystal growth abnormalities 9 and 15 before applying the photoresist 16.

[0028] Since the crystal growth abnormalities 9 and 15 are removed by wet etching rather than dry etching, it is not always necessary to mask them with the insulating film 3-3, and they may be masked with a resist.

[0029] In etching the crystal growth abnormalities 9 and 15, it is sufficient that at least the region on the top surface of the semiconductor layer of the first and second semiconductor laser portions 110 and 120 that will eventually become the mesa structure is masked by the insulating film 3-3.

[0030] Next, all of the insulating film 3-3 is removed. Then, an insulating film 3-4 is formed again as shown in Figures 19 and 20, and a photoresist 16 for EB (Electron Beam) exposure is applied onto the insulating film 3-4.

[0031] Next, the photoresist 16 is exposed to EB to form openings aligned at regular intervals along the laser cavity direction in the regions of the photoresist 16 where the first and second semiconductor laser portions 110 and 120 are to be formed, thereby exposing the insulating films 3-4. Furthermore, the exposed insulating films 3-4 are removed to expose the cap layers 8 and 14, respectively, as shown in FIGS.

[0032] Furthermore, wet etching or the like is performed to engrave the cap layer 8 and non-doped layer 7 of the first semiconductor laser portion 110 at the opening in the photoresist 16, thereby exposing the second conductivity type layer 6. At the same time, the cap layer 14 and non-doped layer 13 of the second semiconductor laser portion 120 are also engraved to expose the second conductivity type layer 12. Furthermore, the photoresist 16 is removed to obtain the states shown in FIGS.

[0033] 25 and 26, the insulating film 3-4 on the top surface is then removed. Furthermore, as shown in Figures 27 and 28, a burying layer 17 is epitaxially grown in the recessed portion of the non-doped layer 7 and cap layer 8 of the first semiconductor laser portion 110, thereby forming a diffraction grating made up of a lattice of the non-doped layer 7 and cap layer 8 arranged at regular intervals along the resonator direction of the laser. Similarly, a diffraction grating is formed in the second semiconductor laser portion 120 by burying the cap layer 14 and non-doped layer 13 with the burying layer 17.

[0034] The buried layer 17 is made of a ternary or quaternary mixed crystal semiconductor such as InGaAsP, AlGaInAs, or InGaAs.

[0035] Next, the contact layer 19 is epitaxially grown on the buried layer 17, and then the insulating film 3-5 is formed. Furthermore, as shown in Figures 29 and 30, the regions that will become the mesa structures of the first semiconductor laser portion 110 and the second semiconductor laser portion 120 are masked with the insulating film 3-5 (third insulating film), and the insulating film 3-5 in other regions is removed.

[0036] 31 and 32 , contact layer 19, buried layer 17, semiconductor layer 2, first conductivity type layer 4, first active layer 5, second conductivity type layer 6, non-doped layer 7 (not shown), and cap layer 8 (not shown) of first semiconductor laser portion 110, and further first conductivity type layer 10, second active layer 11, second conductivity type layer 12, non-doped layer 13 (not shown), and cap layer 14 (not shown) of second semiconductor laser portion 120 are removed by dry etching to expose semiconductor substrate 1. In this way, the mesa structure is formed collectively by simultaneously performing dry etching on first and second semiconductor laser portions 110 and 120.

[0037] Next, all of the insulating films 3-5 are removed. Furthermore, as shown in Figures 33 and 34, an insulating film 3 is formed on the sidewalls of the mesa structures of the first and second semiconductor laser portions 110 and 120 and on the semiconductor substrate 1, and an electrode 20 is formed on the top of each mesa structure. An electrode 20 is also formed on the back surface of the semiconductor substrate 1. This makes it possible to fabricate a multi-wavelength integrated semiconductor laser 100 comprising a mesa-type first semiconductor laser portion 110 and second semiconductor laser portion 120.

[0038] As described above, in the present disclosure, the semiconductor layer 2 formed on the semiconductor substrate 1 is etched to simultaneously form the first groove 111 and the second groove 121. The semiconductor layer of the first semiconductor laser section 110 is selectively epitaxially grown inside the first groove 111, and the semiconductor layer of the second semiconductor laser section 120 is selectively epitaxially grown inside the second groove 121. Because the semiconductor layers of the first and second semiconductor laser sections 110, 120 can be epitaxially grown from the same etched surface of the semiconductor substrate 1, it is possible to align the heights of the first active layer 5 and the second active layer 11.

[0039] <Variation 1> In the above description, the first conductivity type layer 4, first active layer 5, second conductivity type layer 6, non-doped layer 7, and cap layer 8 of the first semiconductor laser portion 110 are formed in the first groove 111. However, it is sufficient that at least the first active layer 5 is formed in the first groove 111. For example, the first conductivity type layer 4 may be formed outside the first groove 111 by being the same as the semiconductor substrate 1. Alternatively, the second conductivity type layer 6 may be formed on the first groove 111. Furthermore, the non-doped layer 7 and cap layer 8 are not necessarily required. Similarly, it is sufficient that at least the second active layer 11 is formed in the second groove 121. This point is common to all of the following embodiments.

[0040] Second Embodiment This embodiment shows a method for manufacturing a buried ridge type multi-wavelength integrated semiconductor laser 100. The explanations of Figures 1 to 32 of the first embodiment are common to this embodiment and will therefore be omitted here.

[0041] 35 and 36, the current blocking layer 18 is epitaxially grown so as to fill the mesa structures of the first and second semiconductor laser portions 110 and 120. The material for the current blocking layer 18 may be, for example, a structure in which p-type InP and n-type InP are alternately stacked, or a semi-insulating material such as Fe-doped InP, but any material may be used as long as it has high resistance to the current flowing through the first active layer 5 and the second active layer 11.

[0042] Crystal growth anomalies (not shown) may be deposited along the edges of the mesa structure on the upper surface of the current blocking layer 18. As in the first embodiment, these crystal growth anomalies are formed by the diffusion and deposition of atoms evaporated on the insulating film 3 during the epitaxial growth of the current blocking layer 18. The deposited crystal growth anomalies are masked in the same manner as in the first embodiment and then removed by wet etching.

[0043] 37 and 38, a contact layer 19 is epitaxially grown on the current blocking layer 18. The contact layer 19 can be made of a ternary or quaternary alloy semiconductor such as InGaAsP, AlGaInAs, or InGaAs.

[0044] Furthermore, the insulating film 3 is formed again on the contact layer 19, and the insulating film 3 above the mesa structures of the first and second semiconductor laser portions 110 and 120 is removed to expose the contact layer 19, as shown in FIGS.

[0045] 41 and 42, an electrode 20 is formed on the exposed upper part of the contact layer 19, and an electrode 20 is also formed on the back surface of the semiconductor substrate 1. This makes it possible to fabricate a buried ridge type multi-wavelength integrated semiconductor laser 100 in which each mesa structure is buried with a current blocking layer 18. The current blocking layer 18 limits the amount of current flowing between the electrodes 20 formed on the upper part of the contact layer 19 and on the back surface of the semiconductor substrate 1, respectively. This makes it possible to suppress heat generation during laser operation. In terms of stable operation, the multi-wavelength integrated semiconductor laser 100 of this embodiment exhibits an effect superior to that of the multi-wavelength integrated semiconductor laser 100 of the first embodiment.

[0046] In this embodiment, a method for manufacturing a multi-wavelength integrated semiconductor laser 100 will be described, which can more precisely align the heights of the first active layer 5 of the first semiconductor laser portion 110 and the second active layer 11 of the second semiconductor laser portion 120 than in embodiment 1. Note that the following describes changes from embodiment 1.

[0047] 43 and 44, an etching stopper layer 30 and a semiconductor layer 2 are epitaxially grown in this order on a semiconductor substrate 1, and an insulating film 3 is formed on the upper surface of the semiconductor layer 2. The etching stopper layer 30 is a semiconductor layer that stops the progress of etching into the semiconductor substrate 1, and is made of a material that can be selectively etched with respect to the semiconductor substrate 1. For example, if the semiconductor substrate 1 is InP, the etching stopper layer 30 can be made of a ternary or quaternary alloy semiconductor such as InGaAsP, AlGaInAs, or InGaAs.

[0048] Next, as shown in FIGS. 45 and 46, the regions of the insulating film 3 where the first semiconductor laser portion 110 and the second semiconductor laser portion 120 are to be formed are removed to expose the semiconductor layer 2.

[0049] Thereafter, the semiconductor layer 2 is wet-etched with a first chemical solution to form a first groove 111 and a second groove 121, and the etching stopper layer 30 is exposed at the bottom surfaces of both grooves. Furthermore, as shown in Figures 47 and 48, the exposed etching stopper layer 30 is wet-etched with a second chemical solution to expose the semiconductor substrate 1. The subsequent steps are the same as those shown in Figure 7 and subsequent figures of the first embodiment, and therefore a description thereof will be omitted.

[0050] Here, the first chemical liquid is a chemical liquid that has an etching rate for the semiconductor layer 2, and hydrochloric acid is often used. If the first chemical liquid also has an etching rate for the etching stopper layer 30, the semiconductor layer 2 through the etching stopper layer 30 may be etched all at once, but as described in the first embodiment, the semiconductor layer 2 is often made of InP. Hydrochloric acid has an etching rate for InP, but does not have an etching rate for InGaAsP, AlGaInAs, or InGaAs, and therefore etching of the etching stopper layer 30 does not proceed.

[0051] The second chemical liquid is a chemical liquid that realizes selective etching between the etching stopper layer 30 and the semiconductor substrate 1. That is, it is a chemical liquid that has a higher etching rate for the etching stopper layer 30 than for the semiconductor substrate 1, and for example, tartaric acid is used.

[0052] In this way, by forming the etching stopper layer 30 between the semiconductor substrate 1 and the semiconductor layer 2, which enables selective etching of the semiconductor substrate 1, it is possible to prevent over-etching of the semiconductor substrate 1. Since the height of the surface on the semiconductor substrate 1 at which epitaxial growth of the semiconductor layers of the first and second semiconductor laser portions 110 and 120 starts can be precisely controlled, the heights of the first active layer 5 of the first semiconductor laser portion 110 and the second active layer 11 of the second semiconductor laser portion 120 can be aligned more precisely than in the first embodiment.

[0053] <Modification 2> The etching of the semiconductor layer 2 and the etching stopper layer 30 does not necessarily have to be wet etching, but may be dry etching. By observing the plasma emission of elements contained in the etching stopper layer 30 and utilizing this for endpoint detection, over-etching of the semiconductor substrate 1 can be prevented even in dry etching. This provides the same effect as in the third embodiment.

[0054] Fourth Embodiment This embodiment shows a method for manufacturing a multi-wavelength integrated semiconductor laser 100 incorporating a modulator or an optical amplifier. In the following description, a manufacturing method for the multi-wavelength integrated semiconductor laser 100 incorporating a modulator will be described. Regarding the optical amplifier, in the following description, the term "modulator" should be read as "optical amplifier."

[0055] In the drawings of this embodiment, the cross section marked A-A' indicates the cross section of the region where the first and second semiconductor laser units 110 and 120 are present. The cross section marked B-B' indicates the cross section of the region where the first and second modulators 130 and 140 are present. The cross section marked C-C' indicates the cross section of the region where the first semiconductor laser unit 110 and the first modulator 130 are present.

[0056] First, a first cladding layer 21, a core layer 22, and a second cladding layer 23, which are waveguide layers, are epitaxially grown in this order on a semiconductor substrate 1 to form a semiconductor layer 2. Next, an insulating film 3 is formed on the upper surface of the second cladding layer 23. Next, as shown in Figures 49 to 51, the regions of the insulating film 3 that form the first and second semiconductor laser sections 110, 120 and the first and second modulators 130, 140 are removed to expose the second cladding layer 23.

[0057] Here, the first cladding layer 21 and the second cladding layer 23 are made of undoped InP, etc. The core layer 22 is made of a ternary or quaternary mixed crystal semiconductor such as undoped InGaAsP, AlGaInAs, or InGaAs.

[0058] 52 to 54, the second cladding layer 23, the core layer 22, and the first cladding layer 21 are then etched to expose the semiconductor substrate 1 except for the portion masked by the insulating film 3. As a result, four grooves are formed in the semiconductor layer 2 consisting of the first cladding layer 21, the core layer 22, and the second cladding layer 23. Hereinafter, the four grooves will be referred to as a first groove 111, a second groove 121, a third groove 131, and a fourth groove 141, respectively.

[0059] Next, the insides of the third and fourth grooves 131, 141 and the top surface of the second cladding layer 23 are masked with the insulating film 3, and then the first and second semiconductor laser portions 110, 120 are manufactured by the method shown in Figures 7 to 28 of the first embodiment. As a result, the semiconductor layers of the first and second semiconductor laser portions 110, 120 are formed, as shown in Figures 55 to 57. Meanwhile, the insides of the third and fourth grooves 131, 141 and the top surface of the second cladding layer 23 separating these grooves are masked with the insulating film 3.

[0060] 58 to 60, the first conductivity type layer 24, third active layer 25, and second conductivity type layer 26, which are semiconductor layers of the first modulator 130, are grown by selective epitaxial growth in that order in the third trench 131. Furthermore, the first conductivity type layer 27, fourth active layer 28, and second conductivity type layer 29, which are semiconductor layers of the second modulator 140, are grown by selective epitaxial growth in that order in the fourth trench 141.

[0061] Here, the first conductivity type layers 24 and 27 and the second conductivity type layers 26 and 29 are made of p-type or n-type doped InP or the like, and the third active layer 25 and the fourth active layer 28 are active layers made of a ternary or quaternary alloy semiconductor such as InGaAsP, AlGaInAs, or InGaAs.

[0062] Furthermore, the crystal growth abnormalities deposited on the upper surfaces of the semiconductor layers of the first and second modulators 130 and 140 are removed by the method shown in the first embodiment.

[0063] Next, a contact layer 19 is epitaxially grown on the upper surfaces of the semiconductor layers of the first and second semiconductor laser portions 110 and 120 and the semiconductor layers of the first and second modulators 130 and 140, and then an insulating film 3 is formed. Furthermore, the insulating film 3 is removed except for regions that will become the mesa structures of the first and second semiconductor laser portions 110 and 120 and the first and second modulators 130 and 140, to expose the contact layer 19 as shown in FIGS.

[0064] Next, the contact layer 19, the semiconductor layers of the first and second semiconductor laser portions 110 and 120, and the semiconductor layers of the first and second modulators 130 and 140 are removed by dry etching to expose the semiconductor substrate 1 except for the portions masked with the insulating film 3. This results in the mesa structures of the first and second semiconductor laser portions 110 and 120 and the first and second modulators 130 and 140 being formed all at once, as shown in Figures 64 to 67.

[0065] 67 , the first active layer 5 of the first semiconductor laser section 110 is connected to the third active layer 25 of the first modulator 130 by the core layer 22. In the present disclosure, the heights of the first active layer 5 and the third active layer 25 can be aligned, and therefore it is possible to guide the light oscillated from the first semiconductor laser section 110 to the first modulator 130 without loss. The same applies to the relationship between the second semiconductor laser section 120 and the second modulator 140.

[0066] 67 , the thickness of the core layer 22 in a side view is set to be greater than the thickness of the first active layer 5 of the first semiconductor laser section 110 and the thickness of the third active layer 25 of the first modulator 130. This makes it possible to mitigate the influence of an unintentional misalignment in height between the first active layer 5 and the third active layer 25. The same applies to the relationship between the second semiconductor laser section 120 and the second modulator 140.

[0067] Although not shown in the drawings, as explained in the first embodiment, an insulating film 3 is formed on the sidewalls of the mesa structures of the first and second semiconductor laser portions 110 and 120, the sidewalls of the mesa structures of the first and second modulators 130 and 140, the sidewalls of the mesa structure of the semiconductor layer 2, and on the semiconductor substrate 1. An electrode 20 is also formed on the top of these mesa structures. An electrode 20 is also formed on the back surface of the semiconductor substrate 1. This makes it possible to fabricate a multi-wavelength integrated semiconductor laser 100 with a built-in modulator.

[0068] Fifth Embodiment This embodiment shows a method for manufacturing a multi-wavelength integrated semiconductor laser 100 with a built-in optical coupler. In the drawings of this embodiment, the cross section indicated by A-A' indicates the cross section of the region where the first and second semiconductor laser portions 110 and 120 are present. The cross section indicated by B-B' indicates the cross section of the region where the optical coupler 150 is present.

[0069] First, a first cladding layer 21, a core layer 22, and a second cladding layer 23, which are waveguide layers, are epitaxially grown in this order on a semiconductor substrate 1 to form a semiconductor layer 2. Furthermore, an insulating film 3 is formed on the upper surface of the second cladding layer 23. Next, as shown in Figures 68 to 70, the regions of the insulating film 3 that form the first and second semiconductor laser sections 110 and 120 are removed to expose the second cladding layer 23. Meanwhile, the region of the second cladding layer 23 where the optical coupler 150 is to be formed is masked with the insulating film 3.

[0070] 71 to 73, the second cladding layer 23, the core layer 22, and the first cladding layer 21 are etched to expose the semiconductor substrate 1 except for the portion masked by the insulating film 3. As a result, the first groove 111 and the second groove 121 are formed.

[0071] Next, the first and second semiconductor laser portions 110, 120 are manufactured by the method shown in Figures 7 to 28 of the first embodiment. As a result, the semiconductor layers of the first and second semiconductor laser portions 110, 120 are formed, and the contact layer 19 is formed on the upper surfaces, as shown in Figures 74 to 76. Meanwhile, in the region where the optical coupler 150 is to be formed, the upper surface of the second cladding layer 23 is masked with the insulating film 3.

[0072] Next, the insulating film 3 is completely removed and a new insulating film 3 is deposited. Furthermore, as shown in Figures 77 to 79, the insulating film 3 is removed, leaving behind the regions that will become the mesa structures of the first and second semiconductor laser portions 110, 120 and the region that will become the optical coupler 150. As a result, in the regions where the first and second semiconductor laser portions 110, 120 will be formed, the contact layer 19 is exposed except for the portion masked by the insulating film 3, and in the region where the optical coupler 150 will be formed, the second cladding layer 23 is exposed except for the masked portion.

[0073] 80 to 82 , the contact layer 19, the semiconductor layers of the first and second semiconductor laser portions 110 and 120, and the semiconductor layers of the optical coupler 150 are removed by dry etching to expose the semiconductor substrate 1 except for the portion masked by the insulating film 3. This results in the mesa structures of the first and second semiconductor laser portions 110 and 120 and the optical coupler 150 being formed all at once. When the optical coupler 150 is a multi-mode interference waveguide, the optical coupler 150 includes a multiplexer, an input element branching from the multiplexer and connected to the first active layer 5 of the first semiconductor laser portion 110 and the second active layer 11 of the second semiconductor laser portion 120, and an output element extending from the multiplexer. However, the shape of the optical coupler 150 is not limited to this.

[0074] In the present disclosure, the heights of the first active layer 5 of the first semiconductor laser section 110, the second active layer 11 of the second semiconductor laser section 120, and the core layer 22 of the optical coupler 150 can be aligned, so that the light emitted from the semiconductor laser section can be guided to the optical coupler 150 without loss.

[0075] Although not shown in the drawings, as explained in the first embodiment, an insulating film 3 is formed on the side walls of the mesa structures of the first and second semiconductor laser portions 110 and 120, the side walls of the optical coupler 150, and on the semiconductor substrate 1. An electrode 20 is also formed on the top of the mesa structures of the first and second semiconductor laser portions 110 and 120. An electrode 20 is also formed on the back surface of the semiconductor substrate 1. This makes it possible to fabricate a multi-wavelength integrated semiconductor laser 100 incorporating an optical coupler 150.

[0076] As described above, the present disclosure can provide a method for manufacturing a multi-wavelength integrated semiconductor laser that can align the heights of the active layers of multiple semiconductor laser sections that are each responsible for laser oscillation in different wavelength bands.

[0077] 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 and modifications may be implemented in appropriate combinations, in which case the combined effects can be obtained.

[0078] REFERENCE SIGNS LIST 1 semiconductor substrate, 2 semiconductor layer, 3 insulating film, 4 first conductivity type layer, 5 first active layer, 6 second conductivity type layer, 7 non-doped layer, 8 cap layer, 9 crystal growth abnormality portion, 10 first conductivity type layer, 11 second active layer, 12 second conductivity type layer, 13 non-doped layer, 14 cap layer, 15 crystal growth abnormality portion, 16 photoresist, 17 buried layer, 18 current blocking layer, 19 contact layer, 20 electrode, 21 first cladding layer, 22 core layer, 23 second cladding layer, 24 first conductivity type layer, 25 third active layer, 26 second conductivity type layer, 27 first conductivity type layer, 28 fourth active layer, 29 second conductivity type layer, 30 etching stopper layer, 100 multi-wavelength integrated semiconductor laser, 110 first semiconductor laser portion, 111 First groove, 120: Second semiconductor laser portion, 121: Second groove, 130: First modulator, 131: Third groove, 140: Second modulator, 141: Fourth groove, 150: Optical coupler

Claims

1. The process of epitaxially growing a semiconductor layer on a semiconductor substrate, A step of etching the semiconductor layer to simultaneously form a first groove and a second groove, A step of forming a first semiconductor laser portion by masking the inside of the second groove and the upper surface of the semiconductor layer with a first insulating film, and then epitaxially growing at least a first active layer within the first groove, After removing the first insulating film, the upper surface of the first semiconductor laser portion and the upper surface of the semiconductor layer are masked with the second insulating film, and at least the second active layer is epitaxially grown in the second groove to form the second semiconductor laser portion; After removing the second insulating film, the upper surface of the first semiconductor laser portion and a portion of the upper surface of the second semiconductor laser portion are masked with a third insulating film, and then the first semiconductor laser portion, the second semiconductor laser portion and the semiconductor layer are dry-etched to form the mesa structure of the first semiconductor laser portion and the mesa structure of the second semiconductor laser portion. A method for manufacturing a multi-wavelength integrated semiconductor laser, including the method described above.

2. Before forming the third insulating film, a fourth insulating film or resist is formed on the semiconductor layer, the first semiconductor laser portion and the second semiconductor laser portion, and an opening is formed in the fourth insulating film or resist at the ends of the first semiconductor laser portion and the second semiconductor laser portion adjacent to the semiconductor layer. A step of selectively removing crystal growth abnormalities deposited on the edges of the first semiconductor laser portion and the second semiconductor laser portion by wet etching using the fourth insulating film or the resist on which the opening is formed as a mask, A method for manufacturing a multi-wavelength integrated semiconductor laser according to claim 1, further comprising:

3. The method for manufacturing a multi-wavelength integrated semiconductor laser according to claim 2, wherein in the wet etching, a chemical solution is used in which the etching rate in the depth direction is slower than the etching rate in the transverse direction.

4. The upper surface of the first active layer in the first groove and the upper surface of the second active layer in the second groove include a non-doped layer. A method for manufacturing a multi-wavelength integrated semiconductor laser according to claim 2 or 3, further comprising the step of removing the crystal growth anomaly portion and then forming a diffraction grating in which the grating including the non-doped layer is aligned in the resonator direction of the first semiconductor laser portion and the second semiconductor laser portion.

5. An etching stopper layer is formed on the semiconductor substrate, and the semiconductor layer is formed on the etching stopper layer. A method for manufacturing a multi-wavelength integrated semiconductor laser according to claim 1 or 2, further comprising the step of selectively etching the etching stopper layer exposed on the bottom surfaces of the first groove and the second groove with respect to the semiconductor substrate, after forming the first groove and the second groove in the semiconductor layer.

6. A method for manufacturing a multi-wavelength integrated semiconductor laser according to claim 5, wherein when etching the etching stopper layer, wet etching is performed using a chemical solution that has a higher etching rate to the etching stopper layer than the semiconductor substrate.

7. A method for manufacturing a multi-wavelength integrated semiconductor laser according to claim 5, wherein the etching endpoint is detected by observing the plasma emission of the etching stopper layer when dry etching the etching stopper layer.

8. A method for manufacturing a multi-wavelength integrated semiconductor laser according to claim 1 or 2, comprising the step of embedding the mesa structures of the first semiconductor laser portion and the second semiconductor laser portion, respectively, in a current blocking layer.

9. A third groove is formed in the semiconductor layer simultaneously with the first groove and the second groove. A method for manufacturing a multi-wavelength integrated semiconductor laser according to claim 1 or 2, further comprising the step of forming a modulator or optical amplifier in the third groove.

10. The semiconductor layer is a waveguide layer including a core layer, A method for manufacturing a multi-wavelength integrated semiconductor laser according to claim 9, wherein the thickness of the core layer in a side view is greater than the thickness of the first active layer and the second active layer, and the thickness of the active layer of the modulator or the optical amplifier.

11. The process further includes the step of forming an optical coupler on the semiconductor layer, The semiconductor layer has a waveguide layer, A method for manufacturing a multi-wavelength integrated semiconductor laser according to claim 1 or 2, wherein the first active layer and the second active layer are connected to the optical coupler via the waveguide layer.