JP2001168467A - Manufacturing method for semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a semiconductor laser of coordinated characteristics with satisfactory yield by improving adhesion between a photoresist and a mesa and preventing erosion or disappearance of a second growth block mask at a mesa top part. SOLUTION: After a mesa, comprising an active layer, is formed by selective growth between a pair of first growth block masks comprising dielectrics, a second growth block mask is formed at the mesa top part for growing of a current block layer. Furthermore, after the second growth block mask is removed, a clad layer and a contact layer are grown on the mesa and current block layer. Here, a process, where a dielectrics film which is to be a second growth block mask, is formed over the entire surface of semiconductor substrate is provided, after a first growth block mask is removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a semiconductor laser.

[0002]

2. Description of the Related Art An "all-MOVPE selective growth type semiconductor laser" in which a waveguide mesa is directly formed using narrow-width selective MOVPE growth is a method of forming a waveguide mesa by wet etching of a semiconductor having difficulty in controllability. It is known that very high uniform characteristics can be obtained because it is not necessary to use the CDMA.
2 "reports excellent properties and uniformity. The method of manufacturing this “all-MOVPE selective growth type semiconductor laser” is described in detail in Japanese Patent Application Laid-Open No. 8-330665, and this manufacturing method will be briefly described with reference to FIG.

On an n-type InP (100) plane substrate 101,
A pair of first growth inhibition masks 102 made of a stripe-shaped SiO ₂ film extending in the <011> direction is formed (FIG. 7A). The width W of the first growth blocking mask 102 is 5 μm.
m, an interval between masks (opening width d) is 1.5 μm.
Next, an n-type InP cladding layer 103 (layer thickness 100 nm), an InGaAsP waveguide layer 104 including a multiple quantum well active layer (layer thickness 200 nm), and a first p-type InP cladding layer 105 (layer thickness 150 nm) by selective MOVPE growth. Is formed (FIG. 7B). Note that the layer thickness here is the same as that of the opening 102 of the first growth inhibition mask 102.
It is a layer thickness in a. Therefore, the height of the mesa 106 including the active layer is 450 nm. Next, an SiO ₂ film 107 (400 nm thick) is formed on the entire surface of the wafer by thermal CVD (FIG. 7C). Subsequently, ion milling using an inert gas ion such as Ar is performed to remove the SiO ₂ film on the slope of the mesa 106 (FIG. 7D). Next, the portion including the mesa 106 was formed to a width of 5 μm by photolithography.
7 (e), and etching with buffered hydrofluoric acid, the SiO ₂ film 107 remains only on the top of the mesa 106 due to side etching as shown in FIG. 7 (f). After removing the photoresist 108, a p-type InP current blocking layer 110 and an n-type InP current blocking layer 111 are sequentially formed by selective MOVPE growth using the SiO ₂ film on the top of the mesa as the second growth inhibition mask 109 (FIG. 7 (g)). )) And after removing the second growth inhibition mask 109 with buffered hydrofluoric acid, the second p-type I
An nP cladding layer 112 and a p-type InGaAs contact layer 113 are sequentially formed (FIG. 7H).

[0004]

The semiconductor laser manufactured by the above method has excellent characteristics and uniformity. However, in the step of removing the SiO ₂ film by side etching (FIGS. 7E to 7F), the photoresist 10 is removed.
If the adhesion between the mesa 106 and the mesa 106 is not sufficient, the buffered hydrofluoric acid penetrates from the mesa slope to the top of the mesa 106, and the SiO ₂ film on the top of the mesa, that is, the second growth inhibition mask 109 disappears. Alternatively, there is a problem of being eroded. Also in the case of the above example, the adhesion between the photoresist 108 and the mesa 106 fluctuates due to process fluctuations, and a case where buffered hydrofluoric acid infiltrates the top of the mesa may occur. In such a case, the SiO ₂ film on the top of the mesa,
That is, the second growth blocking mask 109 disappears, and the current blocking layers 110 and 111 cannot be formed on both sides of the mesa 106. In addition, since the smaller the contact area between the photoresist 108 and the mesa 106 is, the smaller the contact area between the photoresist 108 and the mesa 106 is, the lower the height of the mesa 106 is required in the element design, or the smaller the mesa 106 is in the resonator direction. When there is a portion where the height of the mesa changes and the mesa height is low, the photoresist 108 and the mesa 106
This problem was more remarkable because the contact area with the substrate was small.

An object of the present invention is to solve the above problems,
Improve the adhesion between the photoresist and the mesa, prevent the disappearance and erosion of the second growth inhibition mask, and improve the process capability.
An object of the present invention is to provide a method of manufacturing a semiconductor laser capable of stable production.

[0006]

According to the present invention, there is provided a method of manufacturing a semiconductor laser, comprising the steps of: forming a first growth inhibition mask having a stripe-shaped opening on a first conductivity type semiconductor substrate; Forming, by selective growth, a stripe-shaped mesa having a multi-layered structure including an active layer that contributes to light emission, a step of removing the first growth inhibition mask, and a step of removing a dielectric film from the mesa. Forming the entire surface of the semiconductor substrate, leaving the dielectric film only on the top of the mesa, and using the dielectric film left on the top of the mesa as a second growth-inhibiting mask, by selective growth, on both sides of the mesa. Growing a current block layer in which a current block layer of the second conductivity type and a current block layer of the first conductivity type are sequentially stacked, or a current block layer made of a high-resistance semiconductor layer or a semi-insulating semiconductor layer; Removing the serial second growth blocking mask, is characterized by a step of sequentially growing a clad layer and a contact layer of the second conductivity type on said mesa and on the current block.

According to the method of manufacturing a semiconductor laser of the present invention in which a spot size converter is integrated, a stripe-shaped opening having a constant width is formed on a semiconductor substrate of a first conductivity type, and a portion having a constant width and a constant width are formed. Forming a first growth-inhibiting mask comprising a tapered portion that gradually narrows toward an end; and a stripe having a multilayer structure including an active layer for emitting light at an opening of the first growth-inhibiting mask. Forming a stepped mesa by selective growth, removing the first growth inhibition mask, forming a dielectric film over the semiconductor substrate over the mesa, and forming the dielectric film over the mesa. Leaving the second conductive type current blocking layer and the first conductive type current blocking layer on both sides of the mesa by selective growth using the dielectric film left on the top of the mesa as a second growth-inhibiting mask. Growing a current blocking layer, or a current blocking layer comprising a high resistance semiconductor layer or a semi-insulating semiconductor layer; removing the second growth blocking mask; and forming a layer on the mesa and the current block. A step of sequentially growing a cladding layer and a contact layer of the second conductivity type, wherein the portion formed at the opening of the tapered first growth inhibition mask becomes a spot size converter.

In this method of manufacturing a semiconductor laser integrated with a spot size converter, a step of forming regions having different carrier densities in the cladding layer of the second conductivity type is provided. When the concentration is lower than the concentration, the absorption of laser light due to absorption between valence bands in the spot size converter can be suppressed without impairing the device resistance of the laser unit, and a semiconductor laser with excellent slope efficiency and low threshold current can be obtained. .

According to a method of manufacturing a distributed feedback semiconductor laser of the present invention, a step of forming a first growth inhibition mask having a stripe-shaped opening on a first conductivity type semiconductor substrate, and an opening of the first growth inhibition mask are provided. Forming, by selective growth, a stripe-shaped mesa having a multilayer structure including an active layer that contributes to light emission; removing the first growth inhibition mask; and covering the mesa with a dielectric film covering the mesa. Forming the entire surface of the substrate, leaving the dielectric film only on the top of the mesa, and using the dielectric film left on the top of the mesa as a second growth inhibition mask, selectively growing the second dielectric film on both sides of the mesa by selective growth.
Growing a current blocking layer in which a conductive type current blocking layer, a first conductive type current blocking layer is sequentially laminated, or a current blocking layer made of a high-resistance semiconductor layer or a semi-insulating semiconductor layer; Removing, a step of forming a diffraction grating at least on the mesa, and a step of sequentially growing a cladding layer and a contact layer of a second conductivity type on the mesa and the current block on which the diffraction grating is formed. It is characterized by having.

[0010] In the above manufacturing method, the dielectric film is formed by thermal CV.
D, plasma CVD, ECR plasma CVD, bias sputtering, or ECR sputtering. When the dielectric film is formed by such a method, the etching rate of the dielectric film on the mesa side wall (mesa slope) is faster than the etching rate of the dielectric film on the top of the mesa. Even if the dielectric film is completely etched and removed, the dielectric film can be reliably left on the top of the mesa.

In the step of leaving the dielectric film only on the top of the mesa, the dielectric film is etched by ion milling to reduce the thickness of the dielectric film on the mesa slope, and then the dielectric film on the mesa slope is buffered with hydrofluoric acid. Removing the dielectric film on the top of the mesa and the flat portion on both sides of the mesa, and covering the mesa with a photoresist and etching the dielectric film on the flat portion on both sides of the mesa. It is characterized by.
Alternatively, a step of removing the dielectric film on the mesa slope by etching the dielectric film with buffered hydrofluoric acid and leaving the dielectric film on the top of the mesa and the flat portions on both sides of the mesa, and covering the mesa with a photoresist Etching the dielectric film on the flat portions on both sides of the mesa.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) As a first embodiment, an example of a 1.3 μm band all-select MOVPE grown semiconductor laser will be described with reference to FIG. FIG.
(B) to (h) show AA 'cross sections in FIG. 1 (a). The hatching indicating the cut surface is omitted.

On the n-type InP substrate 1 (100) surface, <0
A pair of first growth inhibition masks 2 (mask width W5 μm, opening width d1.5 μm, thickness 100 nm) formed of a stripe-shaped SiO ₂ film extending in the 11> direction are formed (FIG. 1).
(A)). Next, n-type In is grown by selective MOVPE growth.
P cladding layer 3 (layer thickness 100 nm, carrier concentration 1 × 1
0 ¹⁸ cm ^-3 ), InGaAsP guide layer (layer thickness 60 ⁿ )
m, wavelength composition 1130 nm) and InGaAsP barrier layer (layer thickness 8 nm, wavelength composition 1130 nm) and InGaAs
Multiple quantum well active layer (7 well layers) composed of a P well layer (layer thickness: 5 nm, wavelength composition: 1270 nm, compressive strain: 0.7%)
And InGaAsP guide layer (layer thickness 60 nm, wavelength composition 1
A stripe-shaped mesa 6 composed of an InGaAsP waveguide layer 4 of 130 nm) and a first p-type InP cladding layer 5 (layer thickness of 150 nm, carrier concentration of 7 × 10 ¹⁷ cm ⁻³ ) is formed (FIG. 1B). . Here, the layer thickness of each semiconductor layer is the layer thickness at the opening of the first growth inhibition mask 2. Therefore, the height of the mesa 6 including the active layer is 453.
nm.

Next, the first growth inhibition mask is formed with buffered hydrofluoric acid.
The mask 2 is removed, and the entire surface of the wafer is SiO 2 by thermal CVD._Two
A film 7 (thickness: 400 nm) is formed (FIG. 1C). Continued
Milling using inert gas ions such as Ar
The mesa slope SiO _TwoThin the film. Ionmi
When the ring is formed, the mesa 6 slope SiO_TwoMesa peak on membrane
Part and flat part SiO_TwoEtched faster compared to film
And the mesa slope SiO_TwoThe membrane is flat on the top of the mesa and on both sides of the mesa
Tan of SiO_TwoIt becomes thinner than the film 7. Next, the buffer
SiO on mesa 6 slope with dofluoric acid_TwoComplete removal of membrane 7
(FIG. 1 (d)). At this time, the mesa slope SiO_TwoFilm thickness
Is SiO on the top of the mesa and the flat on both sides of the mesa_TwoThan membrane 7
Since it is thin, SiO_Twofilm
7 remains. Thereafter, the mesa 6 is formed by photolithography.
The part including this is covered with a photoresist 8 having a width of 5 μm (FIG. 1).
(E)), etching with buffered hydrofluoric acid
As shown in FIG. 1 (f), the top of the mesa is formed by id etching.
Only SiO_TwoThe film 7 remains. Remove the photoresist 8
After the mesa top SiO_TwoThe film is formed as a second growth inhibition mask 9
P-type InP current block by selective MOVPE growth
Layer 10 (layer thickness 0.6 μm, carrier concentration 6 × 10¹⁷c
m^-3), N-type InP current blocking layer 11 (layer thickness 0.6 μm)
m, carrier concentration 3 × 10¹⁸cm^-3) On both sides of mesa 6
Formed sequentially (FIG. 1 (g)). After this, the buffered
After removing the second growth inhibition mask 9 with hydrofluoric acid, the second p-type I
nP cladding layer 12 (layer thickness 3.5 μm, carrier concentration 1
× 10¹⁸cm^-3), P-type InGaAs contact layer 13
(Layer thickness 0.3 μm, carrier concentration 1 × 10 ¹⁹cm^-3)
On the n-type InP current block layer 11 and the mesa 6
It is formed sequentially (FIG. 1 (h)). Finally, p-type InGaAs
A metal electrode is formed on the surface of the
A pole is formed and cleaved to obtain a semiconductor laser.

In the present embodiment, as is apparent from a comparison between FIG. 1E and FIG. 7E, the SiO ₂ film 7 is formed after the first growth inhibition mask 2 is removed. ,
The thickness of the SiO ₂ film in the flat portions on both sides of the mesa 6 is smaller than in the conventional example, and the adhesion area between the photoresist 8 and the mesa 6 is larger than in the conventional example. Therefore, even if the adhesion between the two fluctuates due to process variations, the buffered hydrofluoric acid, which is an etchant, does not easily penetrate into the top of the mesa because of the large adhesion area between the two, and the SiO ₂ film on the top of the mesa can be prevented from disappearing, Process capacity is improved and stable production is possible. (Second Embodiment) As a second embodiment, an example of a 1.48 μm band all-selective MOVPE growth type high power semiconductor laser for exciting a fiber amplifier is shown in FIG. 1 as in the first embodiment. It will be described using FIG. In such high-power semiconductor lasers, Optical Amp 1999
lifeers and their Applica
It is necessary to minimize the internal loss of the laser cavity as shown in Thions ThD11-1. Therefore, it is effective to reduce the number of well layers in the multiple quantum well active layer and to reduce the thickness of the waveguide layer in order to weaken optical confinement. The method for manufacturing the element will be described below.

On the n-type InP substrate 1 (100) surface, <0
11> a pair of first growth inhibition masks 2 (width 5 μm, opening width 3 μm) made of a stripe-shaped SiO ₂ film extending in the direction
m, thickness 100 nm) (FIG. 1A). Next, the n-type InP cladding layer 3 is formed by selective MOVPE growth.
(Layer thickness 100 nm, carrier concentration 1 × 10 ¹⁸ cm ⁻³ ),
InGaAsP guide layer (layer thickness 33 nm, wavelength composition 11
30 nm), an InGaAsP barrier layer (layer thickness 7 nm, wavelength composition 1200 nm), and an InGaAsP well layer (layer thickness 4n).
m, wavelength composition 1450 nm, compression strain 1%) and a multiquantum well active layer (3 well layers) and an InGaAsP guide layer (layer thickness 33 nm, wavelength composition 1130 nm).
nGaAsP waveguide layer 4, first p-type InP cladding layer 5
A stripe-shaped mesa 6 having a layer thickness of 150 nm and a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ is formed (FIG. 1).
(B)). Note that the layer thickness here is the layer thickness at the opening of the first growth inhibition mask 2. Therefore, the height of the mesa 6 including the active layer is 342 nm.

Next, the first growth inhibition mask 2 is removed with buffered hydrofluoric acid, and SiO
_Two films 7 (thickness: 400 nm) are formed (FIG. 1C).
Subsequently, ion milling using an inert gas ion such as Ar is performed to make the thickness of the SiO ₂ film on the slope of the mesa 6 smaller than the thickness of the SiO ₂ film on the top of the mesa or the flat portion. next,
After the SiO ₂ film on the slope of the mesa 6 is completely removed with buffered hydrofluoric acid (FIG. 1D), the portion including the mesa 6 is covered with a photoresist 8 having a width of 5 μm by photolithography (FIG. 1E). And etch with buffered hydrofluoric acid. At this time, the photoresist 8 has a SiO 2 partially flat surface.
Covers ₂ film, but is removed by side etching, as shown in FIG. 1 (f), only the mesa top SiO ₂
The film 7 remains. After removing the photoresist 8, the SiO ₂ film on the top of the mesa is used as a second growth inhibiting mask 9 for selective MOV.
The p-type InP current blocking layer 10 (layer thickness 0.6 μm, carrier concentration 6 × 10 ¹⁷ cm ⁻³ ) and n-type I
After sequentially forming an nP current blocking layer 11 (layer thickness: 0.6 μm, carrier concentration: 3 × 10 ¹⁸ cm ⁻³ ) on both sides of the mesa 6 (FIG. 1G), a second growth inhibition mask is formed by buffered hydrofluoric acid. 9 is removed, the second p-type InP cladding layer 12 (3.5 μm in thickness, carrier concentration of 1 × 10 ¹⁸ cm ⁻³ ), p-type I
An nGaAs contact layer 13 (layer thickness 0.3 μm, carrier concentration 1 × 10 ¹⁹ cm ⁻³ ) is sequentially formed on the n-type InP current block layer 11 and the mesa 6 (FIG. 1H).
Thereafter, metal electrodes are formed on the front surface of the p-type InGaAs contact layer 13 and the back surface of the InP substrate, and are cleaved to obtain a semiconductor laser.

In this embodiment, as in the first embodiment, the contact area between the photoresist 8 and the mesa 6 is larger than in the conventional example. Therefore, even if the adhesion between the two fluctuates due to process fluctuations, it is difficult for buffered hydrofluoric acid, which is an etchant, to penetrate into the top of the mesa because the adhesion area is large,
The disappearance of the SiO ₂ film on the top of the mesa can be prevented, the process capability is improved, and stable production is possible. Particularly, since the height of the mesa 6 is lower than that of the first embodiment, the effect is larger than that of the first embodiment. (Third Embodiment) As a third embodiment, FIG.
An example of the spot size converter integrated type semiconductor laser shown in (a) and (b) will be described. FIG. 2B is a cross-sectional view taken along line AA ′ of FIG.

As described in Japanese Patent Application No. 10-271020, the spot size converter integrated semiconductor laser comprises a laser section 30 in which laser oscillation occurs and a spot size converter 31 for converting the spot size. The waveguide layer thickness is constant in the laser unit 30 and the spot size conversion unit 31
Has a structure that becomes gradually thinner toward the end face. As a result, the spot size of the laser beam 32 is enlarged by the spot size converter 31, and the light can be coupled to the optical fiber without a lens. The spot size converter integrated type semiconductor laser of the present embodiment
Is 496 nm, and in the spot size converter 31, the mesa height is also reduced at the same time as the thickness of the waveguide layer, and is 170 nm which is about 1/3 of the laser portion at the light emitting end. Hereinafter, the manufacturing procedure will be described with reference to FIG.

First, as in the first embodiment, thermal CV
D, the surface of the n-type InP (100) plane substrate 1 is coated with SiO.
After deposition of the _two films, a striped SiO running in the <011> direction is formed by photolithography and etching.
_A pair of first growth inhibiting masks 2 made of _two films are formed.
The width of the first growth blocking mask 2 is constant (50 in the laser portion).
μm), the spot size converter gradually narrows from the boundary with the laser toward the end face (the width at the end face is 5 μm). The length of the first growth blocking mask 2 is 300 μm for the laser portion and 200 μm for the spot size conversion portion. The aperture width is constant at 1.5 μm for both the laser section and the spot size conversion section.

An n-type InP cladding layer 3 (layer thickness: 100 nm, carrier concentration: 1 × 10 ¹⁸ cm) is formed on the InP substrate on which the first growth inhibition mask 2 is formed by selective MOVPE growth.
^-3 ), waveguide layer 4, p-type InP cladding layer 5 (layer thickness 20).
0 nm and a carrier concentration of 7 × 10 ¹⁷ cm ⁻³ ) are sequentially stacked to form a mesa 6 serving as an active region in the opening (FIG. 3).
(A)). Here, the waveguide layer 4 is composed of an InGaAsP guide layer (layer thickness 60 nm, wavelength composition 1130 nm), InG
aAsP well layer (layer thickness 6 nm, wavelength composition 1270 nm,
Strain amount 0.7%) and InGaAsP barrier layer (layer thickness 10n)
m, a wavelength composition of 1130 nm) and a multiple quantum well active layer (the number of well layers is 6) and an InGaAsP guide layer (layer thickness of 60 nm, wavelength composition of 1130 nm) are sequentially laminated. The thickness, wavelength composition, and strain amount of each semiconductor layer are all values in the laser section.

In MOVPE, a region sandwiched between a pair of SiO ₂ films has a different growth rate depending on the width of the SiO ₂ film.
The width of the SiO ₂ film is about physician狹, semiconductor layers grown in a region sandwiched SiO ₂ film is thin is layer thickness, the composition quaternary semiconductor layer to shorter wavelengths. For this reason, the semiconductor layer of the spot size conversion section in which the SiO ₂ film is gradually narrowed is tapered so as to gradually become thinner from the connection with the laser section toward the end face, and the waveguide layer 4 is formed in the laser section. Has a shorter wavelength than that of the waveguide layer.

The cross section (AA 'cross section) of the laser portion shown in FIG. 3A in which the mesa 6 is formed is the same as that of the first embodiment, and is not shown. If an illustration is required, reference is made to FIG. FIGS. 3B to 3E show cross sections (BB ′ cross sections) of the spot size conversion section (SSC section). Less than,
The present embodiment will be described with reference to FIGS.

A mesa 6 is formed on the InP substrate (FIG. 3)
After (a)), the first growth inhibition mask is
The mask 2 is removed, and SiO 2 is formed on the entire surface by thermal CVD._TwoMembrane 7
(Thickness: 400 nm) is formed (FIG. 3B). Continued
Ion milling using inert gas ions such as Ar
And the SiO on the slope of the mesa 6_TwoMesa top or flat
Part of SiO_TwoMake it thinner than the film thickness. Next, the buffer
SiO on mesa 6 slope with dofluoric acid_TwoComplete removal of membrane
Later (FIG. 3C), the mesa 6 is formed by photolithography.
3 is covered with a photoresist 8 having a width of 5 μm (FIG. 3).
(D)), etching with buffered hydrofluoric acid
By etching, as shown in FIG.
Only SiO_TwoThe film 7 is left. Remove the photoresist 8
After that, the SiO remaining on the top of the mesa_TwoThe film is used for the second growth inhibition mass.
In the same manner as in the first embodiment, both sides of the mesa 6
The p-type InP current blocking layer 10 (carrier concentration 6 × 1
0¹⁷cm^-3), N-type InP current blocking layer 11 (carrier
A concentration 3 × 10¹⁸cm^-3) Are sequentially formed on both sides of the mesa 6
After that, the second growth inhibition mask 9 is removed with buffered hydrofluoric acid.
Then, the second p-type InP cladding layer 12 (the laser portion and the
Carrier size differs from the cut-size converter), p-type I
nGaAs contact layer 13 (carrier concentration 1 × 10¹⁹
cm ^-3) Is the upper part of the n-type InP current blocking layer and the mesa 6.
(FIG. 2A). After that, the laser mesa
SiO with opening directly above_TwoThe film 16 is made of p-type InGaAs
s formed on the s-contact layer and having an opening
_TwoThe metal electrodes 14 and 1 are formed on the film 16 and on the back surface of the InP substrate.
5 was formed and cleaved to obtain a semiconductor laser (FIG. 2).
(A), (b)). This spot size converter is integrated
The semiconductor laser is a p-type InGaAs contact layer 1
3 and the electrode 14, a stripe-shaped opening is formed in the laser section 30.
SiO with mouth_TwoA film 16 is provided and a laser unit 30 is provided.
Current flows only in the spot size conversion unit 31
Has a structure that does not flow.

In the present embodiment, the carrier concentration in the spot size converter of the second p-type InP cladding layer is set lower than the carrier concentration of the laser unit (for example, the spot size converter is 1 × 10 ¹⁷ cm ⁻³ , Laser part is 1 × 10 ¹⁸ cm
^-3 ) A semiconductor laser with excellent slope efficiency and low threshold current has a structure that suppresses the absorption of laser light due to valence band absorption in the spot size conversion section without impairing the element resistance of the laser section. can get. In this case, after forming a second p-type InP cladding layer 12 having a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ and forming a p-type InGaAs contact layer,
An SiO ₂ film having an opening directly above the mesa of the laser unit 30 is formed on the p-type InGaAs contact layer, and Zn is introduced only into the laser unit 30 by thermal diffusion or ion implantation to provide a Zn diffusion region 12a. 30 second p-type I
The carrier concentration of the nP cladding layer (at least the striped region (the hatched region in FIG. 2) above the mesa 6 in the second p-type InP cladding layer) is 1 × 10 ¹⁸ c
m ⁻³ (Zn diffusion region is the second p-type InP
After growing and forming a second p-type InP cladding layer of the laser section (or spot size conversion section), the second p-type of the spot size conversion section (or laser section) may be formed. Growing and forming an InP cladding layer, or a second p-type InP cladding layer, p-type InGaAs
After forming the s-contact layer, the second p-type InP clad layer of the spot size conversion part (or laser part), p-type I
After removing the nGaAs contact layer by etching,
Spot size converter (or laser unit) from which the second p-type InP cladding layer and p-type InGaAs contact layer have been removed
Then, a second p-type InP cladding layer and a p-type InGaAs contact layer having a carrier concentration different from the carrier concentration of the second p-type InP cladding layer of the laser portion (or spot size conversion portion) remaining without being etched are grown again. By forming the second p-type InP cladding layer, the carrier concentration is different between the laser portion and the spot size conversion portion. In the case of forming the second p-type InP cladding layer having a different carrier concentration between the laser portion and the spot size conversion portion by the third method, an etching stopper layer such as InGaAsP is formed before forming the second p-type InP cladding layer. To form a mesa and current blocking layer and a second p-type InP
It is desirable to provide an etching stopper layer between the cladding layer and the second p-type InP cladding layer to prevent the mesa and the current blocking layer from being etched when the second p-type InP cladding layer is etched.

In the present embodiment, the carrier concentration of the spot size converter of the second p-type InP cladding layer is lower than the carrier concentration of the laser unit. And the carrier concentration of the laser section may be the same (for example, 1 × 10 ¹⁸ cm ⁻³ ). In this case, the second p-type InP cladding layer 12 and the p-type InGaAs contact layer 13 may be formed in the same steps as in the first embodiment.

In a semiconductor laser in which a spot size converter is integrated, the height of the mesa 6 changes in the direction of the resonator,
The mesa height at the lowest mesa is only 170 nm. Even with such a mesa height, in the present embodiment, as in the first embodiment, the contact area between the photoresist 8 and the mesa 6 can be made sufficiently large as compared with the prior art. And the second growth inhibiting mask 9 can be prevented from disappearing on the top of the mesa,
An element can be manufactured stably. (Fourth Embodiment) As a fourth embodiment, an example in which the present invention is applied to a distributed feedback semiconductor laser having a diffraction grating in a laser resonator will be described. As described in Japanese Patent Application No. 11-239113, an example of an all-selective MOVPE growth type distributed feedback semiconductor laser is one in which a diffraction grating is provided above a mesa (FIGS. 4 and 5), or (FIG. 6) and the like in which a diffraction grating is provided underneath. Also for such a distributed feedback laser, a similar effect can be obtained by a method similar to that of the first embodiment. In the distributed feedback semiconductor laser shown in FIG. 5, the mesa 6 includes the n-type InP cladding layer 3 (layer thickness: 100 nm, carrier concentration: 1 × 10 ¹⁸ cm ⁻³ ).
In the distributed feedback semiconductor laser shown in FIG. 4 in which the mesa 6 has the n-type InP cladding layer 3 (having a thickness of 100 n), as in the first embodiment, which is composed of two layers, the GaAsP waveguide layer 4 and the GaAsP waveguide layer 4.
m, carrier concentration 1 × 10 ¹⁸ cm ⁻³ ) and InGaAsP
Waveguide layer 4 and first p-type cladding layer 5 (layer thickness 150 nm,
This is an example in which the carrier concentration is 7 × 10 ¹⁷ cm ⁻³ ). Here, the InGaAsP waveguide layer 4 is composed of an InGaAsP guide layer (layer thickness: 60 nm, wavelength composition: 1130 nm),
nGaAsP barrier layer (layer thickness 8 nm, wavelength composition 1130 n
m) and an InGaAsP well layer (layer thickness 5 nm, wavelength composition 1)
It is composed of a multiple quantum well active layer (well layer number: 7) having 270 nm and a compressive strain of 0.7%, and an InGaAsP guide layer (layer thickness: 60 nm, wavelength composition: 1130 nm).

In order to fabricate a distributed feedback semiconductor laser having a diffraction grating on the mesa, first, in the same procedure as in the first embodiment, stripe-shaped mesas 6 and p having an active layer on an InP substrate are formed. Forming the InP current blocking layer 10 and the n-type current blocking layer 11 (FIGS. 4A and 5)
(A)). Next, the mesa 6 and the n-type current blocking layer 11
A photoresist is applied to the surface of the substrate, a diffraction grating pattern is formed on the photoresist by interference exposure or electron beam exposure, and then the diffraction grating pattern is transferred to the surface of the mesa 6 and the n-type current blocking layer 11 by etching. (FIGS. 4B and 5B). Thereafter, in the same manner as in the first embodiment, the second p-type InP cladding layer 12 (thickness: 3.5 μm, carrier concentration: 1 × 10
¹⁸ cm ⁻³ ), a p-type InGaAs contact layer 13 (layer thickness: 0.3 μm, carrier concentration: 1 × 10 ¹⁹ cm ⁻³ ), an n-type InP current block layer 11 on which a diffraction grating 20 is formed, and an upper part of the mesa 6. (FIG. 4C, FIG. 5)
(C)). Finally, the p-type InGaAs contact layer 13
Metal electrodes 14 and 15 are formed on the front surface and the back surface of the InP substrate, and are cleaved to complete a distributed feedback semiconductor laser. In this embodiment, the diffraction grating 20 is formed also on the n-type current blocking layer 11, but is not formed on the n-type InP current blocking layer, but is formed only on the mesa. Is also good.

A distributed feedback semiconductor laser having a diffraction grating below the mesa (FIG. 6) is formed by photolithography.
After the diffraction grating 20 is formed on the P substrate 1, it can be manufactured by forming the respective semiconductor layers and electrodes through the same manufacturing steps as in the first embodiment. The diffraction grating 20 may not be formed on the entire surface of the substrate, but may be formed only on the portion where the mesa 6 is formed.
Further, the mesa 6 may be composed of two layers of the n-type InP cladding layer 3 and the InGaAsP waveguide layer 4 as in the distributed feedback semiconductor laser shown in FIG.

In the above four embodiments, SiO
_TwoAlthough thermal CVD was used to form the film 7, plasma CVD,
ECR plasma CVD, bias sputtering, ECR spa
SiO_TwoA film 7 may be formed. ECR
Plasma CVD including plasma CVD and ECR sputtering
Formed by bias sputtering containing_TwoThe membrane is
The etching rate on the mesa side wall (mesa slope) is
It has faster features than the top. Therefore, when etching
Process margin is large and mesa slope SiO_TwoMembrane
Even if it is completely etched and removed, SiO_Twofilm
Can be reliably left. In addition, ion milling and
SiO on mesa slope by buffed hydrofluoric acid _TwoRemove film 7
However, buffered hydrofluoric acid was used without ion milling.
Mesa slope SiO only_TwoThe film may be removed. This place
If the mesa slope SiO_TwoThe thickness of the film is
Side flat SiO_TwoIt is formed thinner than the film thickness
Therefore, the mesa slope SiO_Two
Even if the film is removed, the SiO on the top of the mesa and the flat portions on both sides of the mesa
_TwoThe entire film is not etched away. Only
Then, only the ion milling is performed,_TwoRemove film
What is done is etching to the semiconductor layer that constitutes the mesa
It is not preferable because it will do.

The current blocking layer has a structure in which a p-type current blocking layer and an n-type current blocking layer are stacked, but a semi-insulating or high-resistance semiconductor layer, for example, Fe-doped InP
And so on. The semiconductor material used is In.
Not limited to GaAsP / InP-based materials, but other materials such as InGaAsP / InAlAs-based materials and GaAsP / I
The present invention can be applied to an nGaAsP type or the like.

[0032]

According to the present invention, a mesa including an active layer is formed by selective growth, and a dielectric film covering the mesa is formed on the entire surface of the substrate after removing the first growth inhibition mask. After the dielectric film is removed, the thickness of the dielectric film on the flat portions on both sides of the mesa becomes thinner than before, and the contact area between the photoresist covering the mesa and the mesa becomes larger than before. As a result, even if the adhesion between the two fluctuates due to process fluctuations, the buffered hydrofluoric acid, which is an etchant, is unlikely to penetrate into the top of the mesa due to the large contact area between the two, and erosion and disappearance of the dielectric film on the top of the mesa are prevented. Can be prevented, the process capability is improved, and stable production is possible.

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram of the first and second embodiments.

FIG. 2 is a perspective view and a sectional view of a semiconductor laser in which a spot size converter is integrated.

FIG. 3 is a manufacturing process diagram of a third embodiment.

FIG. 4 is a manufacturing process diagram of a fourth embodiment.

FIG. 5 is a manufacturing process diagram of the fourth embodiment.

FIG. 6 is a perspective view of a semiconductor laser according to a fourth embodiment.

FIG. 7 is a manufacturing process diagram of a conventional semiconductor laser.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 n-type InP substrate 2 first growth blocking mask 3 n-type InP cladding layer 4 InGaAsP waveguide layer 5 first p-type InP cladding layer 6 mesa 7 SiO ₂ film 8 photoresist 9 second growth blocking mask 10 p-type current block Layer 11 n-type current blocking layer 12 second p-type InP cladding layer 12a Zn diffusion region 13 p-type InGaAs contact layer 14 electrode 15 electrode 16 SiO ₂ film 20 diffraction grating 30 laser unit 31 spot size conversion unit 32 laser light 101 n-type InP substrate 102 first growth blocking mask 102a opening 103 n-type InP cladding layer 104 InGaAsP waveguide layer 105 first p-type InP cladding layer 106 mesa 107 SiO ₂ film 108 photoresist 109 second growth blocking mask 110 p-type current blocking Layer 111 n-type current Lock layer 112 second p-type InP cladding layer 113 p-type InGaAs contact layer

Claims (9)

[Claims] Forming a first growth inhibition mask having a stripe-shaped opening on a first conductivity type semiconductor substrate;
Forming, by selective growth, a stripe-shaped mesa having a multilayer structure including an active layer contributing to light emission in an opening of the first growth inhibition mask; removing the first growth inhibition mask; Forming a film on the entire surface of the semiconductor substrate over the mesa, leaving the dielectric film only on the mesa top, and selecting the dielectric film left on the mesa as a second growth inhibition mask. Growing a current block layer on both sides of the mesa by growing, removing the second growth blocking mask, and sequentially growing a second conductivity type cladding layer and a contact layer on the mesa and the current block. A method of manufacturing a semiconductor laser. 2. A semiconductor device comprising: a first conductivity type semiconductor substrate having a stripe-shaped opening having a constant width on a first conductivity type semiconductor substrate and having a constant width portion and a tapered portion having a width gradually narrowing toward an end portion; Forming a growth inhibition mask, forming a stripe-shaped mesa having a multilayer structure including an active layer contributing to light emission in an opening of the first growth inhibition mask by selective growth, Removing the blocking mask, forming a dielectric film over the semiconductor substrate over the mesa, leaving the dielectric film only on the mesa top, and removing the dielectric film on the mesa top. Using the film as a second growth blocking mask, growing a current blocking layer on both sides of the mesa by selective growth, removing the second growth blocking mask, and forming a second conductive layer on the mesa and the current block. Type Sequentially growing a cladding layer and a contact layer. 3. The method according to claim 2, further comprising the step of providing regions having different carrier concentrations in the cladding layer of the second conductivity type. 4. A step of forming a first growth inhibition mask having a stripe-shaped opening on a first conductivity type semiconductor substrate;
Forming, by selective growth, a stripe-shaped mesa having a multilayer structure including an active layer contributing to light emission in an opening of the first growth inhibition mask; removing the first growth inhibition mask; Forming a film on the entire surface of the semiconductor substrate over the mesa, leaving the dielectric film only on the mesa top, and selecting the dielectric film left on the mesa as a second growth inhibition mask. Growing a current blocking layer on both sides of the mesa by growing; removing the second growth blocking mask; forming a diffraction grating on at least the mesa; and forming a diffraction grating on the mesa on which the diffraction grating is formed. And a step of sequentially growing a second conductivity type cladding layer and a contact layer on the current block. 5. The current block layer forming step according to claim 1, wherein the second conductivity type current block layer and the first conductivity type current block layer are sequentially laminated. A method for manufacturing a semiconductor laser. 6. The method of manufacturing a semiconductor laser according to claim 1, wherein the current block layer forming step is a step of growing a high resistance semiconductor layer or a semi-insulating semiconductor layer. 7. The method according to claim 1, wherein the dielectric film is formed by thermal CVD, plasma CVD,
The method of manufacturing a semiconductor laser according to claim 1, wherein the semiconductor laser is formed by any one of ECR plasma CVD, bias sputtering, and ECR sputtering. 8. The step of leaving the dielectric film only on the top of the mesa,
After the dielectric film is etched by ion milling to reduce the thickness of the dielectric film on the mesa slope, the dielectric film on the mesa slope is removed with buffered hydrofluoric acid, and the top of the mesa and the flat portions on both sides of the mesa are removed. The method according to claim 1, further comprising: a step of leaving a dielectric film; and a step of covering the mesa with a photoresist and etching a dielectric film in a flat portion on both sides of the mesa. A method for manufacturing a semiconductor laser. 9. The step of leaving the dielectric film only on the top of the mesa,
Removing the dielectric film on the mesa slope by etching the dielectric film with buffered hydrofluoric acid, leaving a dielectric film on the mesa top and flat portions on both sides of the mesa, and covering the mesa with a photoresist, Etching a dielectric film on a flat portion on both sides of the mesa.
The method for manufacturing a semiconductor laser according to any one of the above.