JP2917695B2 - Method for manufacturing optical semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical semiconductor device used for optical communication, optical information and the like.

[0002]

2. Description of the Related Art Semiconductor lasers used for optical communication and optical information are required to have higher performance.
On the other hand, in order to cope with an application requiring much cost and requiring a low price, such as a subscriber optical communication, it is necessary to manufacture a device with a high yield using a large-area wafer. In order to satisfy such requirements, it is necessary to perform crystal growth by a vapor phase growth method such as a metal organic vapor phase epitaxy (MOVPE) capable of large area and high uniform growth. Further, by using vapor phase growth, it is possible to manufacture a quantum well semiconductor laser having various features such as a low threshold value, a high efficiency operation, and a narrow spectral line width operation.

FIG. 3 and FIG.
Crystal Growth (Journal of Cry)
Stal Growth), Vol. 107, pages 226-230, shows a typical method for manufacturing a semiconductor laser for optical communication using MOVPE.

This semiconductor laser is a distributed feedback (DFB) laser that operates in a single mode, and current is narrowed by a buried ridge structure. First, n-type indium
After forming a grating on a phosphorus (InP) substrate 1, n-type indium, gallium, arsenic, phosphorus (InGaAs) is formed.
sP) guide layer 8, InGaAsP active layer 3, p-type In
A P cladding layer 4 is laminated (FIG. 3A), and then SiO 2
_{The two} films 21 are formed in a stripe shape having a width of 2 μm (FIG. 3).
(B)), mesa etching is performed until the substrate 1 is reached (FIG. 3 (c)). Thereafter, the p-type InP layer 5 and p ⁺
A type InGaAs cap layer 7 is grown (FIG. 4D),
The current is narrowed by forming a high-resistance region 31 into which protons are implanted around the active layer (FIG. 4E).

[0005]

In order to manufacture such a large number of semiconductor lasers, it is important to use a large-area wafer and to precisely control the layer structure.
The layer thickness can be sufficiently controlled by using a vapor phase growth method such as MOVPE, but the width of the waveguide is conventionally controlled by mesa etching using SiO ₂ or the like as a mask. There was a problem that sufficient controllability could not be obtained depending on the cause. For example, FIG.
In the mesa etching shown in (1), even if the width of the SiO ₂ film 21 is formed to be exactly 2 μm, the active layer varies due to variations in the mesa structure and side etching at the time of etching the active layer. In particular, in a process using a large-diameter wafer such as a 2-inch substrate, the variation in the wafer surface becomes considerably large. Also, there is a problem that the active layer is damaged even in the dry etching method having good controllability.

[0006] Variations in the width of the active layer and the waveguide and defects in the active layer affect device characteristics such as threshold current, oscillation wavelength, beam pattern, and reliability. However, there is a problem that it is difficult to obtain the operation as designed, and there is a need for improvement.

An object of the present invention is to solve the above problems,
It is an object of the present invention to provide a method for manufacturing an optical semiconductor device having a uniform active layer, a waveguide width, and a high yield.

[0008]

According to the present invention, there is provided a method of forming two opposing dielectric thin film stripes on a semiconductor substrate with an optical waveguide forming region interposed therebetween, and a method of forming a semiconductor substrate other than the dielectric thin film stripes. Above the dielectric thin film stripe
Growth by stacking a semiconductor multilayer without active layer
A method for manufacturing an optical semiconductor device including the step, prior to forming the dielectric thin film stripes, forming an etching stop layer and the current blocking layer, the current blocking layer dielectric thin film stripes as a mask for etching It is characterized by adding a step and a step of burying and growing an etched portion with a semiconductor of the same conductivity type as the substrate.

[0009]

According to the method of the present invention, two parallel dielectric thin film stripes such as a SiO ₂ film are formed in the [011] direction on the surface of a semiconductor substrate having a (100) orientation, and the double hetero (D) is formed.
H) When the structure is selectively grown by the MOVPE method, the portion sandwiched by the stripes grows in a ridge shape having a flat (100) surface and a smooth (111) B surface, so that the active layer is mesa-etched. It can be determined only by patterning of SiO ₂ without using a method lacking in uniformity such as.
Therefore, devices can be manufactured by batch growth / process excellent in uniformity and reproducibility using a large-area wafer, and the advantage of forming the active layer by selective growth can be maximized.

[0010]

Next, embodiments of the present invention will be described with reference to the drawings.

FIGS. 1 and 2 are cross-sectional views of a semiconductor laser having a buried ridge structure showing an embodiment of a method for manufacturing an optical semiconductor device according to the present invention.

In this embodiment, n in the (100) direction
Type InP substrate 1 is doped with Si-doped n by a reduced pressure MOVPE method.
-Type InGaAsP layer 9 (1.29 μm composition, layer thickness 100
Angstrom, carrier concentration 1 × 10 ¹⁸ cm ^-3 ),
Growing Zn-doped p-type InP layer 5 (layer thickness 0.5 μm, carrier concentration 5 × 10 ¹⁷ cm ⁻³ ) and Si-doped InP layer 6 (layer thickness 0.5 μm, carrier concentration 1 × 10 ¹⁸ cm ⁻³ ) I do.

Next, the SiO ₂ film 21 is formed by CVD.
(About 2000 angstroms thick) on the surface,
Using photolithography technique, width 10 μm, spacing 2
Two μm stripes are formed (FIG. 1A).

Next, the n-type InP layer 6 and the p-type InP layer 5 are etched using a mixture of hydrochloric acid (HCl) and phosphoric acid (H ₃ PO ₄ ) using the SiO ₂ film 21 as a mask (FIG. 1).
(B)).

Next, an n-type InP
Cladding layer 2 (layer thickness 1 μm, carrier concentration 1 × 10 ¹⁸ c
m ^-3 ), InGaAsP active layer 3 (1.55 μm composition,
P-type InP cladding layer 4 (layer thickness 0.5 μm, carrier concentration 5 × 10 ¹⁷ cm ⁻³ )
Is selectively grown (FIG. 1C). The layer thickness is a value in the active region sandwiched between the SiO ₂ films.

Next, the SiO ₂ film 21 is removed in the form of a stripe having a width of 6 μm around the active region.
_The p-type InP layer 5 (layer thickness 2 μm, carrier concentration 5 × 10 ¹⁷ cm ⁻³ ) and the p ⁺ type InGaAsP cap layer 7 (layer thickness 0.3 μm, carrier concentration 1 × 10 ¹⁹⁾
cm ⁻³ ) (FIG. 2D), and again only the upper part of the active region of the SiO ₂ film 21 formed on the entire surface has a width of 1.5 μm.
m (FIG. 2 (e)), and finally a p-side electrode 32 and an n-side electrode 33 are formed to complete the semiconductor laser (FIG. 2 (f)).

When this laser was evaluated at a cavity length of 300 μm, the threshold current was 15 mA on average, and the standard deviation was 0.1 μm.
2 mA, the slope efficiency was 0.3 W / A on average, and the standard deviation was 0.04 W / A. The active layer width is 2.0 μm on average,
The standard deviation was 0.12 μm. This result is improved compared with the result of the conventional example, and by using the present invention,
It was confirmed that the uniformity of the device characteristics was improved.

As described above, M which enables large area and high uniform growth
By using OVPE growth, high characteristic yield,
A low-cost semiconductor laser can be manufactured.

In this embodiment, the active layer is made of bulk InGa.
Although AsP is used, the characteristics can be further improved by using a quantum well structure (MQW).

In this embodiment, it is obvious that similar characteristics can be improved even if a structure in which Pn is all inverted is adopted.

[0021]

As described above, according to the method for manufacturing an optical semiconductor device of the present invention, the active layer width is determined only by the patterning of a dielectric thin film such as SiO _2, so that the uniform active layer and waveguide width can be obtained. Can be manufactured with good controllability. By performing batch growth / process using a large-area wafer by this method, a low-cost semiconductor laser with high characteristics can be manufactured at a high yield.

[Brief description of the drawings]

FIG. 1 is a sectional view showing one embodiment of a method for manufacturing an optical semiconductor device of the present invention.

FIG. 2 is a sectional view showing one embodiment of a method for manufacturing an optical semiconductor device of the present invention.

FIG. 3 is a sectional view showing one embodiment of a conventional method for manufacturing an optical semiconductor device.

FIG. 4 is a cross-sectional view showing one embodiment of a conventional method for manufacturing an optical semiconductor device.

[Explanation of symbols]

Reference Signs List 1 n-type InP substrate 2 n-type InP cladding layer 3 active layer (including quantum well structure) 4 p-type InP cladding layer 5 p-type InP layer 6 n-type InP layer 7 p ⁺ type InGaAsP cap layer 8 n-type InGaAsP guide layer 9 n-type InGaAsP layer 21 SiO ₂ film 31 proton injection region 32 p-side electrode 33 n-side electrode

Claims (1)

(57) [Claims] Induced to 1. A semiconductor substrate, forming a two dielectric thin film stripes to opposite sides of the optical waveguide forming region between, on the semiconductor substrate other than the dielectric thin film stripes
Semiconductors that do not include an active layer below the dielectric thin film stripe
Selective growth step of laminating a multilayer film.
A method for forming an etching stop layer and a current blocking layer before forming a dielectric thin film stripe; a step of etching the current blocking layer using the dielectric thin film stripe as a mask; and A step of burying and growing the semiconductor with the same conductivity type.