JP2523648B2 - Manufacturing method of semiconductor laser - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor laser device that stably oscillates in a transverse fundamental mode up to a high output.

[Conventional technology]

In order to stably operate the semiconductor laser in the transverse fundamental mode up to a high output, it is necessary to form a built-in waveguide in the resonator of the laser and efficiently inject current into the active region. For example, the structure of the semiconductor laser described in Japanese Patent Laid-Open No. 61-125184 has a structure in which a current is injected only into a narrow region near the center of the band-shaped convex portion for optical waveguide. The structure makes it difficult for the carrier density to decrease in the central portion of the light intensity distribution due to the burning effect. Therefore, by appropriately setting the structural parameters, there is the effect of stabilizing the transverse mode during high-power operation.

Use of a two-layer etching mask of SiO ₂ and photoresist for manufacturing a semiconductor laser is disclosed in Japanese Patent Application No. Sho 63-5002.
No. 79 publication. This example discloses a method of forming a mesa structure having no dents on the side surface by using a methanol solution of bromine in an InP-based semiconductor material.
When the current confinement layer is crystal-grown on the mesa formed by this method, the relationship between the mesa width and the growth suppressing SiO ₂ mask width is that the SiO ₂ mask width is not wider than 0.4 μm or more than the mesa width or slightly smaller than the mesa width. It is stated that a narrow range is preferable.

[Problems to be solved by the invention]

The above-mentioned prior art does not consider the controllability in the semiconductor laser device manufacturing process and the simplification of the process, and has the following problems.

The first problem of the prior art is that a photolithography process for providing a band-shaped convex shape for optical waveguide in the semiconductor cladding layer and a photolithography process for providing a narrow opening in the current confinement layer are individually performed. This is a point that a misalignment (center misalignment) is likely to occur between the light guide convex portion and the current injection opening due to the alignment error of the lithography. If this misalignment exists, the effect of stabilizing the transverse mode of the semiconductor laser cannot be fully realized. In the current-light output characteristic, the linearity decreases, and in the light emission characteristic, asymmetry or instability appears. Usually, the misalignment of photolithography is about 0.5 μm, and when it is large, it is over 1 μm. This misalignment tends to adversely affect the semiconductor laser characteristics as the width of the optical waveguide convex portion becomes narrower.

The second problem is that the device manufacturing process becomes complicated because there are two photolithography steps.

A third problem is that when the semiconductor cladding layer is composed of a compound semiconductor layer containing Al, the surface of the cladding layer is exposed to the atmosphere, and active Al is easily oxidized. That is, it may adversely affect the crystal growth and reduce the reliability of the semiconductor laser.

The present invention solves the problems of the prior art as described above,
An object of the present invention is to provide a method for manufacturing a semiconductor laser device or the like, which has good device manufacturing accuracy, can simplify the process, and has good device reliability.

[Means for solving problems]

In order to achieve the above object, the present invention adopts the following method in the case of the above conventional example.

First, as a method of forming a band-shaped convex portion (convex portion) for forming an optical waveguide on one of the semiconductor cladding layers (first semiconductor layer), a method of forming a band-shaped convex portion on the surface of the semiconductor cladding layer (first semiconductor layer) is used. , SiO ₂ , phosphorous glass (PSG), silicon nitride film, photoresist, etc., at least two layers are used to form an etching mask for projection formation by photolithography or the like, and chemical etching or dry etching is performed. Then, the semiconductor cladding layer (first semiconductor layer) is etched to form a band-shaped convex portion (convex portion) for optical waveguide. Secondly, the lower layer of the etching mask is side-etched by an etching method in which the etching speed is higher in the lower layer than in the upper layer, or by etching conditions, and the side surface of the third semiconductor cladding layer is less than the band-shaped convex portion width. As a narrow striped mask, the upper mask is removed and the lower mask having a narrow width is left on the semiconductor cladding layer, and the semiconductor current confinement layer (second semiconductor layer) is formed in a region other than the mask portion. ) Is selectively formed. Next, the mask is removed, and a semiconductor burying layer (third layer
Semiconductor layer) is formed.

In the case where the semiconductor cladding layer is a compound semiconductor containing Al, such as GaAlAs, a semiconductor cladding layer is
It is transparent to the oscillation wavelength of the laser, and is composed of two or more semiconductor layers having different Al composition ratios, and after etching the band-shaped convex portion, the Al composition ratio of the semiconductor layer to be in contact with the current confinement layer is The structure is such that the ratio is smaller than the Al composition ratio of the semiconductor layer that functions to keep carriers in the laser active layer.

[Action]

According to the manufacturing method of the present invention, an etching mask for forming the optical waveguide convex portion on the semiconductor cladding layer of the semiconductor laser device and a mask for selective crystal growth for confining the current to a narrow portion are provided. Since it can be produced in a self-aligning manner by one lithographic process, the positional accuracy can be remarkably improved. Further, for the same reason, it becomes possible to simplify the element manufacturing process, and as a result, the yield can be improved and the manufacturing cost can be reduced. Further, when the semiconductor cladding layer is composed of a compound semiconductor containing Al, according to the present invention, it is possible to reduce the oxidation development of Al of the layer exposed on the surface and improve the quality of crystal growth, The reliability of the semiconductor laser device or the like can be further improved.

〔Example〕

 Examples of the present invention will be described below.

Example 1 FIG. 1 shows a schematic view of a semiconductor element manufacturing process of Example 1 of the present invention. Phosphorus glass 2 (PSG, P ₂ O ₅ 2 mol
%) Is formed to a thickness of about 4000Å, and then a photoresist mask 3 with a stripe shape (width of about 5 μm is formed by a photolithography process.
m) is formed to a thickness of about 1.1 μm, and P
The SG film 2 was etched (Fig. 1 (a)). Next, as shown in FIG. 1 (b), using the PSG mask 2 and the photoresist mask 3, the GaAs semiconductor crystal 1 is reduced to about 0.8.
μm etching was carried out to form a mesa shape 4. Next, as shown in FIG. 1 (c), the PSG mask 2 is side-etched with the photoresist mask 3 left, and the mesa width (about 5
A stripe-shaped PSG mask 2 having a width of about 2 μm, which is narrower than the width of μm), was formed. Buffered HF was used as an etchant.
Next, as shown in FIG. 1D, the photoresist mask 3
Was removed, leaving only PSG mask 2 in the center of the mesa. Next, as shown in FIG. 1 (e), the n-type GaAs layer 5 (Se-doped, n to 4 × 10 ¹⁸ cm ⁻³ , thickness about 0.7 μm) is applied to a region other than the region of the striped PSG mask 2. Partly formed selectively. For crystal growth, metalorganic pyrolysis (MOCVD
Method) was used. Next, as shown in FIG. 1 (f), PSG
Mask 2 was removed. Next, as shown in FIG. 1 (g),
A p-type Ga _0.6 Al _0.4 As layer 6 was formed on the entire surface. The MOCVD method was used for the crystal growth method. As a result of this manufacturing method, it becomes possible to fabricate the mesa shape formed on the semiconductor crystal surface and the opening formation by selective crystal growth in a self-aligned manner, and the positional accuracy of both is significantly improved to about 0.2 μm or less. did it. In addition, in this example, the photolithography process can be performed once, and the process can be shortened.

Second Embodiment FIG. 2 is a sectional view of a semiconductor laser device according to a second embodiment of the present invention in a direction perpendicular to the light traveling direction.

{100} plane n-type GaAs substrate 7 (Si-doped, n ~ 1 x 10 ¹⁸ c
m ⁻³ ), n-type Ga _0.65 Al _0.35 As layer 8 (Se-doped, n-1)
× 10 ¹⁸ cm ^-3 , thickness 1.5 μm), n-type Ga _0.55 Al _0.45 As layer 9 (S
e-doped n-1 × 10 ¹⁸ cm ^-3 , thickness about 0.1 μm), undoped Ga _0.86 Al _0.14 As active layer 10 (thickness about 0.07 μm) P-type Ga
_0.55 Al _0.45 As layer 11 (Zn-doped, P ~ 6 × 10 ¹⁷ cm ^-3 , thickness approx.
0.1 μm), P-type Ga _0.65 Al _0.35 As layer 12 (Zn-doped, P ~ 6 × 1
0 ¹⁷ cm ^-3 , thickness about 1.2 μm, P-type GaAs layer 13 (Zn-doped, P ~
6 × 10 ¹⁷ cm ⁻³ , thickness about 0.1 μm) was formed by MOCVD method. Next, using the two-layer structure of the PCG film and the photoresist film, the P-type GaAs layer 13 and the P-type Ga layer 13 are formed as in the first embodiment.
_0.65 Al _0.35 As Layer 12 is etched to form P-type Ga _0.65 Al _0.35 As
A mesa shape for an optical waveguide was formed on the layer 12. (See FIGS. 1 (a) and 1 (b)). Etching depth is about 1.0 μm
And The width of the mesa was about 6 μm. Then, a PSG tripe-shaped mask having a width of about 3 μm is formed in the center of the mesa portion formed on the P-type Ga _0.65 Al _0.35 As layer 12 by the same method as in Example 1 (FIG. 1 (c), (See (d)), and using this, the n-type GaAs current confinement layer 14 is selectively crystal-grown (first
(See Fig. (E)), then, after removing the PSG mask, P on the entire surface
Ga _0.55 Al _0.45 As layer 15 (Zn-doped, P-1 × 10 ¹⁸ cm ^-3 , thickness about 2.0 μm) and P-type GaAs cap layer 16 (Zn-doped, P-1 × 10 ¹⁹ cm ^-3) , (Thickness 0.4 μm) formed (first
(See Figures (f) and (g)). Next, a P-side electrode 17 and an n-side electrode 18 were formed, cleaved and scribed to form a semiconductor laser chip. Finally, the chip passivation and assembly were performed.

In the present semiconductor laser, the light distributed around the Ga _0.86 Al _0.14 As active layer 10 is distributed on both sides of the n-type Ga _0.65 Al _0.35 As layer 8, the n-type Ga _0.55 Al _0.45 As layer 9, and the p-type Ga _0.55 Al. _0.45 As Layer 11
And p-type Ga _0.65 Al _0.35 As layer 12 is exuded and distributed. However, the thickness of the p-type Ga _0.65 Al _0.35 As layer 12 is thin outside the band-shaped convex portion for the optical waveguide.
It reaches the current constriction layer 14 and suffers absorption loss. As a result, an effective refractive index difference Δn is generated in the direction parallel to the active layer, light is guided to the optical waveguide convex portion, and the transverse mode is stabilized. In addition, the n-type Ga _0.65 Al _0.35 As layer 8 and the n-type Ga _0.55 Al _0.45
As layer 9 also acts as an n-type cladding layer, and p
The type Ga _0.55 Al _0.45 As layer 11 and the p-type Ga _0.65 Al _0.35 As layer 12 together serve as a p-type cladding layer. Carrier inclusion in the active layer is due to the high Al mixed crystal ratio of these layers, that is, the layer with a large band gap, n-type Ga
_{This is performed by the 0.55} Al _0.45 As layer 9 and the p-type Ga _0.55 Al _0.45 As layer 11.

Since this semiconductor laser has a relatively large optical waveguide region and a current injection aperture that is precisely aligned in the center of the region, it causes a dent in the carrier density due to the spatial hole burning effect even during high-power operation. Stable transverse fundamental mode oscillation was obtained even at light output of 40 mW or more, which is not likely to cause development. The oscillation wavelength was about 780 nm, and the oscillation threshold current value was 40 mA. Moreover, the quality of crystal growth was improved by reducing the mixed crystal ratio of Al in the interface layer where the liquid crystal growth was discontinuous, and stable operation was obtained even in the accelerated life test at 50 ° C for 5000 hours. There is. Further, since the self-alignment method is used as the device manufacturing process, not only the positional accuracy is improved, but also the device manufacturing process can be simplified and shortened. In addition, the device production yield was significantly improved.

Example 3 In Example 1, as the etching mask for forming the mesa, the same kind of manufacturing process was performed for the combination of SiO ₂ and photoresist, and the combination of SiO ₂ and silicon nitride film, and the same effect was obtained.

〔The invention's effect〕

As described above, according to the present invention, by making good use of the side etching of the etching mask and the selective crystal growth technique, the optical waveguide band-shaped convex portion of the semiconductor laser device and the width narrower than that are obtained. It is possible to remarkably improve the alignment accuracy with the current injection opening. As a result, a semiconductor laser that stably oscillates in the transverse fundamental mode up to a high output can be obtained with a high yield. Further, the device manufacturing process can be simplified and shortened. Further, by reducing the Al composition ratio of the semiconductor layer in which the crystal growth is discontinuous, the quality of crystal growth can be improved and the reliability of the device can be increased.

Although the present invention has been described above focusing on the GaAlAs-based semiconductor laser device, the present invention can be applied to other materials and other devices, and the technical effect thereof is great.

[Brief description of drawings]

FIG. 1 is a schematic view of the semiconductor device manufacturing process of the first embodiment, and FIG. 2 is a cross-sectional view of the semiconductor laser device of the second embodiment with respect to the direction of light emission. 1 ... Semiconductor crystal, 2 ... PSG film, 3 ... Photoresist film, 4 ... Mesa shape formed by etching, 5 ... Selective crystal growth layer, 6 ... Semiconductor crystal growth layer, 7 ... n-type GaAs
Substrate, 8 ... n-type Ga _0.65 Al _0.35 As layer, 9 ... n-type Ga _0.55 Al
_0.45 As layer, 10 …… Ga _0.86 Al _0.14 As active layer, 11 …… P-type Ga
_0.55 Al _0.45 As layer, 12 …… p-type Ga _0.65 Al _0.35 As layer, 13 ……
p-type GaAs layer, 14 ... n-type GaAs current confinement layer, 15 ... p-type Ga
_0.55 Al _0.45 As layer, 16 ... p-type GaAs cap layer, 17 ... p
Side electrode, 18 ... n side electrode.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiro Kono 1-280 Higashi Koigakubo, Kokubunji City Central Research Laboratory, Hitachi Ltd. (72) Inventor Toshiaki Tanaka 1-280 Higashi Koigakubo, Kokubunji City Central Research Laboratory, Hitachi Ltd. ( 56) References JP-A-63-208292 (JP, A) JP-A-62-200785 (JP, A)

Claims (3)

(57) [Claims] 1. At least a lower clad layer on a substrate crystal,
In a method for manufacturing a semiconductor laser having a first semiconductor layer in which an active layer and an upper cladding layer are laminated, (i) a step of forming a mask having a width W1 of at least two layers on the surface of the first semiconductor layer, (ii) ) Using the mask formed in the step (i) to form a convex portion on the upper clad layer, (iii) Side etching the lower layer portion of the mask formed in the step (i) to obtain a width W1 A step of forming a mask having a width W2 smaller than that of the mask, (iv) a step of leaving the mask having the width W2 formed in the step (iii) and removing other portions of the mask, (v) the step (iv) ) Step of selectively forming the second semiconductor layer in a region other than the mask of width W2 formed in the step of (vi), (vi) after removing the mask of width W2 used in the step of (v), A third semiconductor layer on the surface of the first semiconductor layer and on the second semiconductor layer. The method of manufacturing a semiconductor laser which comprises a step of forming a conductive layer. 2. The mask according to (i) of the first aspect is made of Si.
Claim 1 comprising at least two layers of O ₂ , phosphorus glass (PSG), silicon nitride, and photoresist.
Item 6. A method for manufacturing a semiconductor laser according to item. 3. The upper clad layer according to claim 1 has a layered structure of two or more layers made of a semiconductor material containing Al, and in the layered structure of the two or more layers, the first clad layer (iii). The method of manufacturing a semiconductor laser according to claim 1, wherein the layer to be the convex portion described in the step (1) has a smaller Al composition than the layer below the layer.