JPH08130204A - Surface treatment method of ingap and manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE: To flatten the surface of InGaP, by performing flattening etching for the surface of InGaP, for a specified time, by using etching solution wherein hydrochloric acid is mixed in pure water with a specified volume ratio. CONSTITUTION: An InGaP clad layer 12, an active layer 14 and a P-InGaP clad layer 16 are laminated in order on an N-GaAs substrate 10 by an MOVPE method. A stripe type etching mask 18 composed of SiO2 is formed on a P- InGaP clad layer 16. Mesa stripe structure is formed by performing etching via the mask 18. The exposed part of the mesa stripe type N-InGaP clad layer 12 is etched for flattening for 3-7 seconds by using etching solution at 20 deg.C which solution is formed by mixing hydrochloric acid in pure water with the volume ratio of 2:1. Thereby protrusions of the surface are eliminated, and the surface of the N-InGaP clad layer can be flattened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a compound semiconductor, In
The present invention relates to a surface treatment method of InGaP suitable for use in a manufacturing process of a semiconductor device such as a semiconductor laser using GaP as a material and for obtaining a flat surface having a small amount of surface oxide for regrowth of InGaP.

[0002]

2. Description of the Related Art An example of a conventional method of manufacturing a semiconductor laser using InGaP as a material is disclosed in Reference 1: "ELECTR.
ONICS LETTERS, Vol. 29 (199
3) pp. 873-874 ". According to the method described in this document, a stripe-shaped etching mask of SiO ₂ is formed on the cladding layer, and the cladding layer is etched through this etching mask to form a mesa stripe structure. There is. still,
In Reference 1, HBr and H are used as etching liquids.
A mixture of ₂ O ₂ , H ₂ O and HCl is used.

[0003]

However, when the mesa stripe structure is formed by the method described in the above Document 1, a protrusion may be formed on the surface of the InGaP cladding layer at the skirt portion of the mesa structure. This protrusion cannot be removed even by surface treatment with sulfuric acid. For this reason,
When a current block layer or the like is regrown on the InGaP surface where the protrusion is formed, threading dislocations having the protrusion as a nucleus are generated. As a result, there is a problem that the current blocking effect of the current blocking layer deteriorates due to the threading dislocation.

On the surface of InGaP just below the SiO ₂ etching mask, In is deposited by etching mask deposition.
The surface of GaP is oxidized to cause damage. For this reason,
There is a problem that a flat InGaP surface cannot be obtained after removing the etching mask.

These two problems have a great adverse effect on the basic characteristics of the semiconductor laser.

On the other hand, not InGaP but InGaAs
An example of a method for manufacturing a semiconductor device having a MIS structure in which is used as a material is Document 2: “Jpn. J. Appl. Phy.
s. , Vol. 30 (1991) pp. 3744-37
49 ”. According to the method described in Reference 2, semiconductor InG
By inserting an interface control layer (Si-ICL) between the aAs layer and the insulating SiO ₂ layer, the interface state can be reduced and Fermi level pinning can be relaxed.

Further, Document 2 describes a method of removing the surface oxide formed on the surface of InGaAs by etching the surface of InGaAs with a phosphoric acid-based etching solution and then treating with hydrofluoric acid.

In order to obtain an excellent regrowth surface, it is important not only to remove the surface oxide but also to flatten the surface. However, InGaP is hardly etched by the above phosphoric acid-based etching solution. Therefore, the combination of the etching with the phosphoric acid-based etching solution and the hydrofluoric acid treatment disclosed in Document 3 above is
It has no effect on flattening the surface of P.

For this reason, a flat I suitable for a regrowth surface is used.
It has been desired to realize a surface treatment method capable of obtaining a surface of nGaP and a semiconductor laser manufacturing method using the surface treatment method.

[0010]

According to the InGaP surface treatment method of the first invention of the present application, hydrochloric acid and pure water are mixed in a volume ratio of 2: 1 with respect to the surface of InGaP. Planarization etching is performed for 3 to 7 by using an etching solution.
It is characterized by being performed for a second.

Further, preferably, InGa of the first invention is used.
In the P surface treatment method, it is preferable to perform hydrofluoric acid treatment on the InGaP surface on which the planarization etching has been performed.

According to the second method for manufacturing a semiconductor laser according to this application, in manufacturing a semiconductor laser having a buried hetero structure in which InGaP is used as a material,
a step of sequentially laminating a first conductivity type clad layer composed of nGaP, an active layer, and a second conductivity type clad layer composed of InGaP; and stripes on the second conductivity type clad layer. Forming an etching mask in the shape of a stripe, a step of forming a mesa stripe structure by performing etching through the etching mask,
The exposed portion of the first conductivity type clad layer of the mesa stripe is subjected to the first flattening etching for 3 to 3 times by using an etching solution in which hydrochloric acid and pure water are mixed at a volume ratio of 2: 1. Step of performing for 7 seconds, step of forming the current block layer on both sides in the width direction of the mesa stripe structure after performing the first flattening etching, and step of forming the current block layer and then removing the etching mask The second step is performed by using the etching solution in which hydrochloric acid and pure water are mixed at a volume ratio of 2: 1 with respect to the step and the surface of the second cladding layer exposed by removing the etching mask. The method is characterized by including a step of performing flattening etching for 3 to 7 seconds and a step of performing hydrofluoric acid treatment on the surface after performing the second flattening etching.

[0013]

According to the InGaP surface treatment method of the first aspect of the invention and the semiconductor laser manufacturing method of the second aspect of the invention, hydrochloric acid and pure water are added to the surface of the InGaP layer.
Planarization etching is performed for 3 to 7 seconds using an etching solution mixed in a volume ratio of 1: 1. By this etching, the surface of InGaP can be flattened. However, the time required for the flattening etching is empirically 3 to
It is desirable that the time is about 7 seconds. For example, it has been confirmed by observation with an atomic force microscope (AFM) that the flatness of the surface is rather deteriorated if the flattening etching is performed for 10 seconds or more. In FIG. 8, the InGaP surface was treated with hydrochloric acid (H
Cl) and pure water (H ₂ O) are mixed at a volume ratio of 2: 1 and an AFM image is reproduced after etching for 30 seconds using an etching solution at a temperature of 20 ° C. The island-shaped spots shown in FIG. 8 are partially deep on the surface (tens of nm deep).
This is the part that is being etched. This spot starts to be observed when the etching time is 10 seconds or more.

In particular, when manufacturing a semiconductor laser,
Since the projections on the surface of the cladding layer can be removed by this flattening etching, deterioration of the current blocking layer can be prevented.

After the planarization etching, I
By performing hydrofluoric acid treatment on the surface of nGaP, the surface oxide formed on the surface can be removed.

In particular, when manufacturing a semiconductor laser,
Damage due to the oxide formed on the surface of the InGaAs layer immediately below the etching mask can be eliminated. For this reason, carrier traps and recombination centers due to this damage are not formed in the current injection layer regrown on this surface. As a result, improvement in efficiency and reliability of the semiconductor laser can be expected.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS InG of the first invention will now be described with reference to the drawings.
An example of the surface treatment method of aP and the method of manufacturing the semiconductor laser of the second invention will be described together. It should be noted that the drawings to be referred to merely schematically show the shapes, sizes, and positional relationships of the respective constituent components to the extent that these inventions can be understood. Therefore, these inventions are not limited to the illustrated examples.

<Manufacture of Semiconductor Laser> FIG.
FIG. 6C is a sectional process diagram of the first half at a cut along the width direction of the stripe of the active layer, which is used for explaining the method for manufacturing the semiconductor laser of this example. In addition, FIGS. 2A and 2B are cross-sectional process diagrams of the latter half following FIG. 1C. In the drawing, hatching showing a cross section is partially omitted.

First, in this embodiment, when manufacturing a buried type semiconductor laser using InGaP as a material, an n-InGaP clad layer as a first conductivity type clad layer is formed on an n-GaAs substrate 10. 12, active layer 14
And p-InGaP as second-conductivity-type cladding layer
The clad layer 16 is sequentially laminated using a metal organic chemical vapor deposition (MOVPE) method. The active layer 14 has a strained quantum well structure in which an InGaAs layer is sandwiched between GaAs layers (not shown) ((A) in FIG. 1).

Next, a stripe-shaped etching mask 18 made of SiO ₂ is formed on the p-InGaP clad layer 16, and etching is performed through the etching mask 18 to form a mesa stripe structure. In this etching, a mixed solution of HBr, H ₂ O ₂ , H ₂ O and HCl is used as an etching solution ((B) of FIG. 1).

By the way, n-In exposed at the skirt portion of the mesa stripe structure formed by this etching.
On the surface of the GaP clad layer 12, many protrusions having a height of about 4 to 8 nm are formed. Here, in FIG.
The observation image by the atomic force microscope (AFM) of the surface of the n-InGaP clad layer in which this protrusion was generated is shown.

Next, the n-InGa of this mesa stripe is formed.
The exposed portion of the P-clad layer 16 is subjected to the first flattening etching for 5 seconds by using an etching solution in which hydrochloric acid and pure water are mixed in a volume ratio of 2: 1 at a temperature of 20 ° C. . By this flattening etching, the projections on the surface are removed, and the surface of the n-InGaP cladding layer can be flattened. Here, in FIG. 3B, the AFM of the surface of the n-InGaP cladding layer from which the protrusions are removed is shown.
The observation image by is shown. From this observed image, it can be seen that the flattening etching yielded a flat surface having irregularities of about 2 to 3 atomic layers.

Next, after the first flattening etching, p-InGaP layer 22 and n- are formed as current blocking layers 20 on both sides in the width direction of the mesa stripe structure.
The InGaP layer 24 is sequentially embedded and grown by the MOVPE method (FIG. 1C).

Next, after forming the current blocking layer 20, the SiO ₂ etching mask 18 is removed using hydrofluoric acid. After the removal, it is washed with water and blown with nitrogen ((A) of FIG. 2).

By the way, the surface 16a of the p-InGaP cladding layer 16 exposed by removing the etching mask 18 has irregularities due to damage caused by the formation of the etching mask 18. Here, FIG.
An observation image (AMF image) of the surface 16a of the p-InGaP cladding layer 16 by AFM is shown in FIG. From this observation image, it can be seen that the surface has irregularities with a height of 7 to 12 nm.

Next, the surface 1 of the p-InGaP cladding layer 16 exposed by removing the etching mask.
The second flattening etching is performed on 6a for 5 seconds by using an etching solution in which hydrochloric acid and pure water are mixed at a volume ratio of 2: 1 at a temperature of 20 ° C.

Next, after performing the second flattening etching, the surface 16a is subjected to hydrofluoric acid treatment.
Here, after immersing the sample in hydrofluoric acid in a nitrogen atmosphere,
Blow with nitrogen without washing with water. The oxide on the surface 16a can be removed by the hydrofluoric acid treatment.

Next, on the surface 16a, a second p-InGa is formed.
The P clad layer 26 and the contact layer 28 are formed by MOVPE.
It grows by the method ((B) of FIG. 2).

After that, a semiconductor laser can be manufactured through usual steps such as formation of an ohmic electrode (not shown).

<Measurement Result by XPS> Next, InGa
Referring to the measurement results of the P surface by X-ray photoelectron spectroscopy (XPS), planarization etching and hydrofluoric acid treatment (hereinafter,
The effect of "surface treatment" will be described together.

First, in FIGS. 5A and 5B, 2 p of gallium (Ga) on the InGaP surface before and after the surface treatment is shown.
The graphs of the XPS measurement results of the electrons in the _3/2 orbit are shown respectively. The horizontal axis of each graph represents the binding energy (eV), and the vertical axis represents the XPS signal intensity.

The polygonal line a _{1 in} the graph of FIG.
The measurement results before surface treatment are indicated by. The curve I ₁ in the graph is a calculated value fitted to the polygonal line a ₁ . In fitting, the peak position and the half width were mainly used as parameters. The signal intensity of the curve I _{1 is} the signal intensity derived from Ga shown in the curve II ₁ and the curve III ₁
The signal intensity derived from the Ga oxide indicated by is added. Therefore, the curve I ₁ becomes the curve III ₁
Under the influence of, the curve bulges to the left of curve II ₁ and the peak position also moves slightly to the left.

On the other hand, the polygonal line a _{2 in} the graph of FIG. 6B shows the measurement result after the surface treatment. After the surface treatment, as indicated by the curve I ₂ fitted to the polygonal line a ₂ , the signal intensity derived from the Ga oxide shown by the curve III ₂ is weakened. Therefore, the curve I ₂ fitted to the polygonal line a ₂ has a smaller leftward bulge than the curve II ₂ representing the signal intensity derived from Ga.

Next, in FIGS. 6A and 6B, 3d of indium (In) on the InGaP surface before and after the surface treatment is shown.
The graphs of the measurement results of _5/2 orbital electrons by XPS are shown respectively. The horizontal axis of each graph represents the binding energy (eV), and the vertical axis represents the signal intensity.

The polygonal line b _{1 in} the graph of FIG.
The measurement results before surface treatment are indicated by. Also, the curves in the graph
IV ₁ is a calculated value fitted to the polygonal line b ₁ . In fitting, the peak position and the half width were mainly used as parameters. The signal intensity of this curve IV _{1 is} the signal intensity derived from In shown by the curve V ₁ and the curve VI ₁
The signal intensity derived from the In oxide shown by is added. Therefore, the curve IV ₁ bulges to the left of the curve V ₁ due to the influence of the curve VI ₁ , and the peak position also moves slightly to the left.

On the other hand, the broken line b _{2 in} the graph of FIG. 6B shows the measurement result after the surface treatment. After the surface treatment, as indicated by the curve IV ₂ fitted to the polygonal line b ₂ , the signal intensity derived from the In oxide indicated by the curve VI ₂ is weakened. Therefore, the curve IV ₂ fitted to the polygonal line b ₂ has a smaller leftward bulge than the curve V ₂ representing the signal intensity derived from In.

Next, FIGS. 7A and 7B show graphs of the results of XPS measurement of the electrons of the 2p orbital of phosphorus (P) on the InGaP surface before and after the surface treatment, respectively. The horizontal axis of each graph represents the binding energy (eV), and the vertical axis represents the signal intensity.

The polygonal line c _{1 in} the graph of FIG.
The measurement results before surface treatment are shown. Also, the curve VI in the graph
I ₁ is a calculated value fitted to the polygonal line c ₁ .
In the fitting, the peak position and the half width were mainly used as parameters. The signal intensity of this curve VII ₁ has two peaks. The peak near 129 eV on the right side is the sum of the signal intensities of the electrons in the 2p _1/2 orbit of P shown by the curve VIII ₁ and the signals in the 2p _5/2 orbit of P shown by the curve IX _1. Has become. on the other hand,
The peak near 133.5 eV on the left side indicates the signal intensity derived from P oxide.

On the other hand, the broken line c _{2 in} the graph of FIG. 7B shows the measurement result after the surface treatment. After the surface treatment, as indicated by the curve VII ₂ fitted to the polygonal line c ₂ , the signal intensity derived from the P oxide near 133.5 eV almost disappeared. On the other hand, the signal intensity of the electron in the 2p _1/2 orbit of P shown by the curve VIII ₂ and the signal intensity of the electron in the 2p _5/2 orbit of P shown by the curve IX ₂ are summed up 1
The peak near 29 eV hardly changes before and after the surface treatment.

From the XPS measurement results described above, it can be seen that the oxide on the InGaAs surface can be removed by the surface treatment.

Although the method of manufacturing the semiconductor laser has been described in the above-mentioned embodiments, the surface treatment method of InGaP according to the first invention is not limited to the semiconductor laser, and a semiconductor electronic device using InGaP as a material, for example, HEMT. It is suitable for use in the production of

[0042]

EFFECT OF THE INVENTION InGaP of the first invention according to this application
According to the surface treatment method and the semiconductor laser manufacturing method of the second invention, the InGaP surface is planarized by using an etching solution in which hydrochloric acid and pure water are mixed at a volume ratio of 2: 1. Etching is performed for 3 to 7 seconds. By this etching, the surface of InGaP can be flattened.

After performing the flattening etching, I
By performing hydrofluoric acid treatment on the surface of nGaP, the surface oxide formed on the surface can be removed.

[Brief description of drawings]

FIG. 1A to FIG. 1C are sectional process diagrams of the first half used to explain an embodiment.

2A and 2B are sectional process diagrams of the latter half of FIG. 1C.

3 (A) and (B) are AF of InGaP surface.
It is an observation image by M.

FIG. 4 is an AFM observation image of the InGaP surface with the etching mask removed.

5 (A) and 5 (B) are graphs showing the measurement results of the InGaP surface by X-ray photoelectron spectroscopy (XPS).

6A and 6B are graphs showing the measurement results of the InGaP surface by X-ray photoelectron spectroscopy (XPS).

7A and 7B are graphs showing the measurement results of the InGaP surface by X-ray photoelectron spectroscopy (XPS).

FIG. 8 is a copy of an AFM image of the InGaP surface after etching for 30 seconds.

[Explanation of symbols]

 10: n-GaAs substrate 12: n-InGaP clad layer 14: active layer 16: p-InGaP clad layer 16a: surface 18: etching mask 20: current blocking layer 22: p-InGaP layer 24: n-InGaP layer 26: Second p-InGaP clad layer 28: Contact layer

Claims (3)

[Claims] 1. A flattening etching is performed on an InGaP surface for 3 to 7 seconds using an etching solution in which hydrochloric acid and pure water are mixed at a volume ratio of 2: 1. Surface treatment method. 2. The InGaP surface treatment method according to claim 1, wherein hydrofluoric acid treatment is performed on the surface of the InGaP on which the planarization etching has been performed.
Surface treatment method of P. 3. In manufacturing a buried type heterostructure semiconductor laser using InGaP as a material, a first conductivity type cladding layer made of InGaP,
A step of sequentially laminating an active layer and a second conductivity type clad layer made of InGaP; a step of forming a stripe-shaped etching mask on the second conductivity type clad layer; and a step of forming the etching mask. Through etching to form a mesa stripe structure, and hydrochloric acid and pure water are mixed in a volume ratio of 2: 1 to the exposed portion of the first conductivity type cladding layer of the mesa stripe. The first planarization etching is performed for 3 to 7 seconds by using the etching solution, and the current block layers are formed on both sides in the width direction of the mesa stripe structure after the first planarization etching. And a step of removing the etching mask after forming the current blocking layer, and exposing by removing the etching mask,
Hydrochloric acid and pure water are 2 to 1 on the surface of the second cladding layer.
A step of performing a second flattening etching for 3 to 7 seconds by using an etching solution mixed in a volume ratio of, and after performing the second flattening etching, hydrofluoric acid is applied to the surface. And a step of performing a treatment.