JP3488098B2 - Optical semiconductor device and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an optical semiconductor device using selective oxidation of an Al-containing layer and a method for manufacturing the same.

[0002]

2. Description of the Related Art Selective oxidation is a technique in which when a semiconductor substrate containing a high Al concentration layer is heat-treated in a steam atmosphere, only the high Al concentration layer is selectively oxidized. It is possible to partially oxidize the Al high concentration layer or to oxidize the entire surface by controlling the temperature and time of the heat treatment or by other methods. Since the oxidized layer serves as an insulator and has a lowered refractive index, it is possible to easily form a current and light confinement layer of a semiconductor laser (LD), and thus has been in the spotlight in recent years. .

Hereinafter, an AlGaAs LD will be described as an example in FIG. On a semiconductor substrate 1 such as n-type GaAs, n
Type Al _x Ga _1-x As lower cladding layer 2, active layer 3 such as GaAs, p-type Al _x Ga _1-x As intermediate cladding layer 4,
AlyGa _1-y As (0 <x <y ≦ 1) Oxidized layer 5, p
A type Al _x Ga _1-x As upper clad layer 6 and a GaAs cap layer 7 are laminated. This semiconductor substrate is mesa-etched to expose the end of the Al _y Ga _1-y As oxidized layer 5,
Heat treatment is performed at 400 to 500 ° C. in a steam atmosphere.
Then, the p-side electrode 8 and the n-side electrode 9 are formed.

AlGaAs is oxidized by water vapor to
It changes to l ₂ O ₃ and becomes a dielectric. However, since its oxidation rate remarkably changes depending on the Al composition, for example, the above x,
By setting y such that x <y = 0.9 to 1, the cladding layer and G
Only the layer 5 to be oxidized can be selectively oxidized with almost no influence on the layer of aAs. By appropriately adjusting the temperature and time of the heat treatment, part of the AlGaAs oxidized layer remains as the opening 10 that is not oxidized, and the current can be narrowed. A current is injected only into the active layer immediately below the opening 10 to have a gain and become the active region 11.

Further, the refractive index of semiconductors such as the active layer and the clad layer is 3.0 to 3.5, whereas the refractive index of oxidized Al ₂ O ₃ is lowered to about 1.5. Also, the equivalent refractive index outside the active region is lowered, and it becomes possible to confine light in the active region 11. In the case of a red light laser having a wavelength of 650 nm, the active layer 3 may be made of InGaP and the upper and lower cladding layers 2, 4, 6 may be made of InGaAlP.

Although it is possible to manufacture an LD operating at a low current with such a simple process, some problems still remain.
First, when the forward mesa is formed as shown in the figure, the p-side electrode 8 cannot be wide, and therefore the resistance increases and heat generation reduces the performance and life of the element. With respect to this problem, an inverted mesa as shown in FIG. 2 can increase the electrode area. However, in this case, stress is concentrated on the mesa base portion 21 and the mesa edge 22 particularly during mounting or wire bonding, which leads to deterioration of element performance or even destruction of the element.

In order to make the electrode pad 32 wider,
As shown in FIG. 3, it is necessary to extend the wiring film 33 on the adjacent mesa via the insulating film 31, but this is not easy with the reverse mesa or the vertical mesa. Even in the case of a forward mesa, the wiring film 3 is formed by the mesa end portion 34 and the step 35 at the semiconductor hetero interface.
There is a problem that there is a possibility that so-called step disconnection may occur, which is a break in 3.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to manufacture an optical semiconductor element having a large electrode area and a low resistance with a simple process and good reproducibility.

[0009]

According to the present invention, the base portion has an A
a plurality of semiconductor mesa structures sandwiching an oxide layer are arranged in parallel,
The problem is solved by mechanically and electrically bonding the upper parts of the mesa structure to each other by the semiconductor bonding layer.

In the manufacturing method, at least an Al-containing semiconductor layer is laminated on a semiconductor substrate, the Al-containing layer is partially removed, a sacrificial layer is buried in the removed region, and the Al-containing layer and the sacrificial layer are formed. Stacking a semiconductor junction layer on the layer, selectively removing the sacrificial layer, and then selectively oxidizing the Al-containing layer

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION
Taking as an example the case of being applied to a 1GaInP-based red LD,
As shown in FIG. First, as shown in FIG. 4A, an n-type InGaAlP film having a thickness of 1.1 μm, for example, is formed on the n-type GaAs substrate 41.
Lower cladding layer 42, i-type 35A with a thickness of 0.17 μm
(Angstrom) InGaAlP as a barrier,
Active layer 4 having a plurality of 40 A thick InGaP quantum wells
3, an intermediate cladding layer 44 made of p-type InGaAlP having a thickness of 0.2 μm, an InGaP etch stop layer 45 having a thickness of 50 A, an Al _x Ga _1-x As oxidized layer 46 having a thickness of 0.1 μm, and a thickness of 0. A 9 μm InGaAlP upper cladding layer 47, a 500 A thick InGaP conducting layer 48, and a 2 μm thick GaAs cap layer 49 are crystal-grown. Here, the Al composition X of the layer 46 to be oxidized is X = 0.9.

A SiO ₂ film 400 is mounted on this substrate, and a mesa process is performed as shown in FIG. 4B by a photolithography process. The GaAs cap layer 49 and the InGaP easy-current-carrying layer 48 can be removed with a Br-based etchant, and thereafter, when etching is performed with phosphoric acid, the etching is stopped at the InGaP etch stop layer 45. By selecting the crystal orientation, the inverted mesa-shaped mesa structures 401 and 402 as shown in FIG.
Is formed.

If the crystal is grown as it is, no crystal grows on the SiO ₂ , so that the AlAs sacrificial layer 40 is formed in the etching groove between the adjacent mesa structures as shown in FIG. 4C.
3. The GaAs second cap layer 404 can be embedded. Such buried growth is often used for forming a current block layer of an LD. In this case, in order to reduce the leak current, the crystallinity of the buried growth interface or the block layer itself,
It is necessary to strictly control the doping level and the like, and the growth conditions are largely restricted. However, in this case, since the sacrificial layer is removed as described later, there are few restrictions and crystal growth can be easily performed.

Then, as shown in FIG. 4D, the SiO ₂ film 40 is formed.
After 0 is removed and a GaAs junction layer 405 is grown on the entire surface, an etching hole 406 is further provided in the GaAs junction layer 405 by a photolithography process. This hole is Ga
It is not necessary to stop at the As / AlAs interface, AlA
The sacrificial layer 403 may be penetrated.

Usually, a step is formed on the surface of the interface of the burying layer. Therefore, if the size of the etching hole 406 is smaller than the space between the mesa structures, it is sufficient without providing a marker or the like. The etching hole can be provided with a margin. Sulfuric acid-based or bromine-based wet etching may be used, but if reactive ion beam etching (RIE) is used, vertical holes can be formed and the margin is expanded.

By removing the AlAs sacrificial layer 403 through this hole, a cavity is formed in the region where the sacrificial layer was present. That is, the upper parts of the mesa structures 401 and 402 are
The GaAs junction layer 405 forms a junction.

Since the sacrificial layer 403 is made of AlAs and has a thickness of 1 μm or more, it can be easily removed with an ammonium fluoride solution, for example. One side of the etching hole 406 is, for example, 5
By setting the thickness to be at least μm, the wrapping of the etchant will be sufficient and the removal of the sacrificial layer will be easy.

At this time, the oxidized layer of AlGaAs is also slightly dissolved, but since the etching rate is smaller than that of AlAs and the thickness is smaller than that of the sacrificial layer, the influence is small.

After that, as shown in FIG. 4E, the AlGaAs oxidized layer 46 at the base of the mesa structure is selectively oxidized in a water vapor atmosphere to form an Al oxide layer 407. At this time, if the widths of the mesa structures 401 and 402 are different, the base of the narrower mesa is completely oxidized and the support structure 4 is deenergized.
02, the element structure 40 in which the opening 10 is provided at the base of the thicker mesa and a current can flow only there
It becomes 1.

Since the p-side electrode 8 can be formed on the entire surface of the GaAs junction layer 405 and a larger area can be secured as compared with the LD having the conventional structure, the resistance is small and the device performance and reliability are improved.

FIG. 5 is a sectional perspective view of the red LD thus manufactured. However, a part is cut away.
Further, the detailed layer structure is omitted and only the main part is shown. The numbers are the same as described above. In this example, a plurality of support structures 402 are arranged around the stripe-shaped element structure 401, and a wide electrode area is secured. By arranging a plurality of element structures having the same width in parallel, an array laser can be supplied with electric power at the same time.

In any case, the etching hole 406 is not limited to the rectangular shape, but may be a circular shape or a polygonal shape. Alternatively, the holes may be wide, and the mesh-shaped bonding layer may bond the upper portions of the mesa structures together. Further, the cavity from which the sacrificial layer has been removed may be filled with a dielectric material such as polyimide.

The element structure and the support structure are not limited to the stripe shape, and may be circular or rectangular. In addition, the support structure does not necessarily have to have the same length as the element structure, and may be discontinuous or island-shaped. Further, each structure is not necessarily limited to the reverse mesa, and the gist of the present invention can be applied to a vertical mesa or a pure mesa.

FIG. 6A shows a rectangular element structure 401.
An example in which the support structure 402 surrounds the above is shown. If the width of the support structure is smaller than the width of the device structure, the base of the support structure can be completely oxidized leaving the opening 10. Although omitted in this figure, the upper portions of the structures 401 and 402 are also bonded by a bonding layer. If there is an active layer that emits light under the opening 10, it becomes a light emitting diode (LED),
Further, by mounting a multilayer reflective film on the upper and lower sides, it becomes a surface emitting laser.

In this case, since the emission of light is blocked when the electrode metal is mounted on the element structure, the electrode metal has an opening on the element structure 401 as shown by the hatched portion in FIG. Must have Even in this case, since the electrode metal is in contact with the bonding layer over a wide area, the resistance is low.

Needless to say, in this example as well, the support structure 402 does not necessarily have to completely surround the element structure, and it may be discontinuous or island-shaped.

The above is applicable to InGaAlP semiconductor lasers.
Although description has been made assuming that the 1GaAs oxidized layer is used, the application of the present invention is not limited to this.
For example, the oxidized layer is made of AlGaP, AlInAs, AlI.
It can be applied to any compound containing Al at a high concentration, such as nP, AlSb, and AlN, and non-oxidized layers such as the clad layer are GaAs, InP, InGaAsP, In
Any compound having a low Al concentration such as GaSb or InGaN may be used. Further, the semiconductor coupling layer is not limited to GaAs, and may be any as long as it has a low electric resistance with the electrode metal.

The sacrificial layer does not necessarily have to be a semiconductor such as AlAs. For example, using a lateral growth technique that has been actively studied in GaN-based materials in recent years, SiO ₂ is buried in the etching groove in the state of FIG.
_{2 The} film 400 is removed and crystal growth is performed. This allows
The semiconductor coupling layer 405 can be formed by crystal growth twice. Since the sacrificial layer is SiO ₂ , it is easy to embed and also easy to remove.

The semiconductor element need not be limited to the laser,
It is also applicable to optical semiconductor elements such as light emitting diodes and photodiodes .

[0030]

According to the present invention, a semiconductor element having a wide electrode area and a low resistance can be manufactured with good reproducibility in a simple process.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a conventional semiconductor device.

FIG. 2 is a cross-sectional view of a conventional semiconductor device.

FIG. 3 is a cross-sectional view of a conventional semiconductor device.

FIG. 4 is a sectional process drawing showing an embodiment of the present invention.

FIG. 5 is a sectional perspective view showing an embodiment of the present invention.

FIG. 6 is a sectional perspective view and a plan view showing an embodiment of the present invention.

[Explanation of symbols]

401, 402: Mesa structure 405: Semiconductor junction layer 407: Al oxide layer 8: Electrode metal 46: Al-containing semiconductor layer 403: Sacrificial layer

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Claims (4)

(57) [Claims] 1. A plurality of mesa structures are formed on a semiconductor substrate.
And an Al oxide layer is formed in the mesa structure.
And the mesa structure has a structure similar to that of the mesa structure.
The Al oxide layer is partially provided on the cross section of the structure.
A layered device structure and a cross-section of the mesa structure
A support structure in which an Al oxide layer is layered over the entire surface
The optical semiconductor element characterized by being configured, and upper portions of the element structure and the support structure is mechanically and electrically joined by the semiconductor junction layer between. 2. An Al oxide layered portion of the support structure.
Is thinner than the Al oxide layered portion of the device structure.
The optical semiconductor according to claim 1, wherein the optical semiconductor is formed.
Element . 3. A semiconductor junction layer upper portion above the support structure.
In the device structure, a metal electrode is mounted on the entire surface.
The light according to claim 1, wherein a metal electrode is attached to the upper part of the semiconductor bonding layer above the body by providing an opening.
Semiconductor device . 4. At least one layer of Al on a semiconductor substrate
A step of stacking a plurality of semiconductor layers including a containing semiconductor layer, before
The semiconductor layers are partially etched from the top surface side.
Of the mesa structure having the Al-containing semiconductor layer
Forming a child structure and a supporting structure , burying a sacrificial layer in a region between the structures removed in the previous step,
An element structure and a support structure, a step of stacking a semiconductor bonding layer on the sacrificial layer, a step of removing the sacrificial layer after stacking the semiconductor bonding layer, and a step of removing the sacrificial layer, Previous
The Al-containing semiconductor layer of the element structure is partially oxidized,
A method for manufacturing an optical semiconductor element , comprising a step of completely oxidizing the Al-containing semiconductor layer of the support structure .