JP2003289174A - Method of forming groove in semiconductor light emitting element structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of forming groove in semiconductor light emitting element structure by which a groove having a fixed shape can be formed easily with relatively high reproducibility by preventing the occurrence of extensive side etching. <P>SOLUTION: This method of forming groove in semiconductor light emitting element structure includes a crystal growing step of successively epitaxially growing an MP (wherein, M denotes one, two, or more kinds of group IIIb elements) core layer (2), and an MAs upper layer (3) on the ä100} face of an MAs lower layer (1); a lithographic etching step of forming an etching window in a protective layer (4) after the layer (4) is formed on the upper layer (3); and a first etching step of selectively etching the upper layer (3). This method also includes a second etching step of selectively etching the surface of the core layer (2) other than the surface, on which the ä111} face is mainly exposed so that the surface on which the ä111} face is mainly exposed may reach the lower layer (1) without performing side etching from the end section of the etched upper layer (3). These steps are successively performed. In the second etching step, in addition, hydrochloric acid or a mixed solution of hydrochloric acid and phosphoric acid is used. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a groove in a semiconductor light emitting device structure, and more particularly, to a groove which can easily form a groove having a constant shape with relatively good reproducibility. The present invention relates to a forming method. The groove forming method of the present invention also includes a ridge forming method in the sense that a ridge is formed between the grooves.

[0002]

2. Description of the Related Art Conventionally, many semiconductor light emitting devices having a groove in a semiconductor light emitting device structure have been proposed. Specifically, for example, a semiconductor light emitting device having a groove formed by etching away a part of the current blocking layer provided on the active layer, a part of the upper clad layer provided on the active layer is etched. Examples thereof include a semiconductor light emitting element having a ridge formed by removal. In the latter example, the ridges are geometrically formed between the grooves.
Therefore, the groove forming method is an important technique in manufacturing a semiconductor light emitting device.

Further, in a semiconductor light emitting device, current narrowing is performed by a groove or a ridge. Therefore, it is important to prevent a large side etching caused by an etching process at the time of manufacturing the device and control the area of the groove bottom surface to be constant. Is. That is, when the area of the bottom surface of the groove changes greatly due to side etching,
For example, in a laser, the threshold current fluctuates,
Further, it is difficult to stably obtain an element that emits light of a single transverse mode.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a groove forming method capable of forming a groove having a constant shape easily and with relatively good reproducibility. To do. Still another object of the present invention is to provide a method for forming a groove that prevents large side etching.

[0005]

Means for Solving the Problems The inventors of the present invention have made extensive studies in order to achieve the above-mentioned object, and have obtained the following new findings. That is, for example, a mixed etching aqueous solution of an organic acid and hydrogen peroxide is known as an etching aqueous solution of an epitaxial layer composed of MAs (M represents one or two or more IIIb group elements). However,
The epitaxial layer made of InGaP is not etched by a mixed etching solution of organic acid and hydrogen peroxide. On the other hand, the epitaxial layer composed of InGaP is etched by, for example, a mixed etching aqueous solution of hydrochloric acid and phosphoric acid. When an epitaxial layer composed of MAs is formed on the surface of the epitaxial layer, a specific crystal plane is etched. Exist without. Then, in such etching, side etching is limited.

The present invention has been completed on the basis of the above findings, and the gist thereof is the lower layer {10 which is composed of MAs (M represents one or two or more IIIb group elements).
A crystal growth step of sequentially epitaxially growing a core layer made of InGaP and an upper layer made of MAs on the 0} plane, a lithography-etching step of forming an etching window in the protective layer after forming a protective layer in the upper layer,
The first etching step of selectively etching the upper layer, the {111} surface of the core layer is mainly exposed so that the surface of the core layer reaches the lower layer without side etching from the end of the etched upper layer. The second etching step of selectively etching the other surfaces except the surface where the} surface mainly appears is sequentially combined and included, and the method for forming the groove in the semiconductor light emitting device structure is characterized by the above.

The present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is an explanatory view showing each step of the groove forming method of the present invention, in which (1) is a lower layer,
(2) represents a core layer, (3) represents an upper layer, and (4) represents a protective layer. The lower layer (1), the core layer (2) and the upper layer (3) are sequentially formed as an epitaxial thin film on a single crystal substrate (not shown).

As the above single crystal substrate, a so-called II is usually used.
A group IV compound single crystal substrate (wafer) is used. III
The group-V compound single crystal substrate is obtained by cutting out a bulk crystal of a compound of a group IIIb element and a group Vb element of the periodic table. In the present invention, a wafer selected from the group consisting of GaP, GaAs, and InP is used in consideration of the lattice matching with the lower layer (1). Among these, especially GaAs
Is preferably used.

The lower layer (1) and the upper layer (3) are composed of MAs (M
Represents one or more IIIb group elements). As specific constituent materials, AlAs, GaAs,
InAs, InGaAs, AlGaAs and the like can be mentioned, but GaAs is particularly preferably used. Of course, the materials forming the lower layer (1) and the upper layer (3) do not have to be the same.

The core layer (2) is composed of InGaP,
In the semiconductor light emitting device structure, various functional layers, for example,
It constitutes a current blocking layer, a clad layer, and the like. As the dopant, Si, Se, Te or the like is usually used for the n-type, and Be, Zn, C, Mg or the like is usually used for the p-type. The thickness of the core layer (2) is 0.05 to 5 μm,
The lower layer (1) and the upper layer (3) are selected from the range of 0.05 to 2 μm.

First, in the crystal growth step, the core layer (2) and the upper layer (3) are sequentially epitaxially grown on the {100} plane of the lower layer (1). Although any known method can be adopted for the epitaxial growth, a vapor phase growth method, particularly a molecular beam epitaxial growth method (MBE).
Method) or a metal organic chemical vapor deposition method (MOCVD method). In the present invention, since a step is added to the crystal growth surface according to a known method using an off-substrate, a surface slightly tilted from the {100} plane can be used as the crystal growth surface. In this case, the inclination angle is usually appropriately selected from the range of 0.5 to 15 °.

Next, in a lithography-etching process, after forming a protective layer as an upper layer, an etching window is formed in the protective layer. That is, first, the protective layer (4) is provided on the upper layer (3), and, for example, stripes are formed by a lithography technique (photoresist coating, exposure, development, etc.), and then, the protective layer (4) is formed, for example, by a dry etching technique. Dry etching is performed on a part of the substrate to form a striped window. FIG. 1A shows a state in which the photoresist layer has been removed after etching the protective layer (4).

The protective layer (4) has a function as a window for protecting the upper layer (3) and selectively etching the upper layer (3) in the next first etching step. The constituent material of the protective layer (4) is usually SiNx, Si.
O ₂ or the like is used. The protective layer (4) is formed by, for example, a plasma CVD method.

Next, in the first etching step, as shown in FIG.
As shown in (b), the upper layer (3) is selectively etched.
As the etching agent, the upper layer (3) composed of MAs
An etchant is used which is capable of etching but not substantially etching the core layer (2) composed of InGaP. Examples of such an etching agent include a mixed etching aqueous solution of an organic acid and hydrogen peroxide.

Examples of the organic acid include carboxylic acid, sulfonic acid, sulfinic acid and the like, and carboxylic acid is usually used. Examples of the carboxylic acid include monobasic acids such as formic acid, acetic acid, and propionic acid, and polybasic acids such as tartaric acid, maleic acid, malic acid, and citric acid, but polybasic acids, particularly tartaric acid, are preferably used. To be done. The organic acid may be in the form of a metal salt with sodium, potassium, magnesium or the like, or an ammonium salt.

The ratio of the organic acid to hydrogen peroxide and the concentration in the aqueous solution are not particularly limited, and are appropriately selected depending on the thickness of the core layer (2) and the upper layer (3), the specific composition of each layer and the like. However, in order to enhance the side etching prevention effect, the ratio of hydrogen peroxide / organic acid is usually 1 /
It is preferable to select from the range of 10 to 1/50 (weight ratio). The concentration of the organic acid and hydrogen peroxide in the aqueous solution is usually 30 to 50% by weight. The etching is usually performed at room temperature.

Next, in the second etching step, as shown in FIG.
As shown in (b) to (c), the core layer (2) is selectively etched mainly on the faces other than the {111} face.
The crystal plane of the core layer (2) which is not etched is substantially the {111} plane, but there may be a crystal plane close to this. The crystal plane that is not etched has {1
In addition to the 11} plane, crystal planes ({211} plane and {311} plane) close to this may exist.

Therefore, when there are a plurality of crystal planes that are not etched, the proportion of the {111} planes as an angle match depends on the type of other planes close to the {111} planes, but is usually about 50% or more. Is. In other words,
The plurality of crystal planes that are not etched have one or both of {111} planes and {211} planes and {311} planes, and the proportion of {111} planes as an angle match is usually 50 or less. % Or more.

As the etching agent, the core layer (2) composed of InGaP can etch mainly other surfaces than the {111} plane, but the lower layer (1) composed of MAs is substantially used. A non-etching etchant is used. As a result, the {111} plane is exposed in the core layer (2), and the groove (5) having a constant shape is formed.
Is formed.

In the present invention, hydrochloric acid or a mixed solution of hydrochloric acid and phosphoric acid is used as the above selective etching agent, that is, the selective etching agent of InGaP for MAs. Hydrochloric acid is usually used in a concentration of 10 to 36% by weight. In the case of a mixed etching aqueous solution of hydrochloric acid and phosphoric acid, the ratio of hydrochloric acid / phosphoric acid is usually 1/10 to 10/1.
It is selected from the range of (weight ratio), and the concentration of hydrochloric acid and phosphoric acid in the aqueous solution is usually 10 to 80% by weight. The etching is usually performed at a temperature of 25 to 100 ° C.

InGa is used in the second etching step.
Since the upper layer (3) made of MAs is formed on the surface of the core layer (2) made of P, side etching is limited. That is, the etching of the core layer (2) is performed by etching the edges (31), (3) of the etched upper layer (3).
Without changing 1), in other words, the groove (5)
Is performed without entering each of the outwardly extending wall surfaces forming the lower surface side of the upper layer (3). As a result, the groove (5)
Has a shape extending from the end face of the lower surface of the upper layer (3).

Therefore, according to the groove forming method of the present invention, variation in the shape of the groove (5) can be prevented as compared with the conventional method in which large side etching is performed in which each wall surface of the groove enters the lower surface side of the upper layer. Few. Therefore, according to the groove forming method of the present invention, by the epitaxial crystal growth and the lithography technique that can be performed with high accuracy,
The shape of the groove (5) can be easily and relatively reproducibly determined. In other words, the shape of the groove (5) formed according to the present invention is substantially determined by the thickness of the core layer (2) and the width of the etching window formed in the protective layer (4).

When side etching does not occur on each wall surface of the groove, and only the {111} plane of the InGaP crystal is exposed, the inner angle from the lower layer (1) of each wall surface of the groove (5) formed to extend outward. (Α) is theoretically
It becomes 54.7 °. However, when a crystal plane close to the {111} plane of the InGaP crystal, for example, the {311} plane (angle: 25.2 °) is partially exposed, it is 54.7.
Be sharper than °. Therefore, the above-mentioned interior angle (α) is, as a measurement value based on the electron micrograph, {11 of the MP crystal.
In consideration of the type of crystal plane close to the 1} plane, the degree of lattice matching during epitaxial crystal growth, measurement error by electron micrograph, etc., the range is usually 45 to 60 °.

The thickness of the core layer (2) can be controlled accurately by the epitaxial crystal growth process, and the width of the etching window can be controlled by the lithography-etching process with high accuracy. The groove can be formed easily and with relatively good reproducibility. Moreover, since the etching step does not require strict condition control, only control of the epitaxial crystal growth step and the lithography-etching step is sufficient, so that process management is easy.

In the present invention, a third etching step of selectively etching the upper layer (3) and / or the lower layer (1) can be included after the second etching step, if necessary. The removal of the upper layer (3) and / or the lower layer (1) is appropriately determined depending on the structure of the intended semiconductor light emitting device. Third
In the etching process, for example, the etching agent used in the first etching process is used.

FIG. 2 is an explanatory view showing each step when the groove forming method of the present invention is applied to ridge formation. The ridge (6) is formed through the above-described steps shown in FIG. 1 except that the ridge (6) is formed in a protective layer (4), for example, in a stripe shape. In FIG. 2, the same symbols as those in FIG. 1 have the same meaning.

[0027]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

Example 1 First, GaA was formed on the surface of a GaAs substrate by the MBE method.
An epitaxial wafer was obtained by sequentially forming a lower layer (0.6 μm) made of s, a core layer (1.0 μm) made of In _0.5 Ga _0.5 P, and an upper layer (0.01 μm) made of GaAs.

Then, SiNx is formed on the upper layer as a protective film.
A film (0.1 μm) was formed, and a 5 μm-wide stripe-shaped etching window was formed in the SiNx film by lithography-dry etching. Then, after removing the photoresist film, the upper layer was selectively etched with a mixed etching aqueous solution having a tartaric acid aqueous solution (50% by weight): hydrogen peroxide solution (30% by weight) in a volume ratio of 20: 1. The etching temperature was 25 ° C. and the time was 2 minutes.

Next, hydrochloric acid (36% by weight): phosphoric acid (85
The core layer was selectively etched by a mixed etching aqueous solution having a volume ratio of 1 wt%) of 1: 3. The etching temperature was 70 ° C. and the time was 2 minutes. From the X-ray analysis pattern, it was confirmed that each wall surface of the groove formed in the core layer so as to extend outward was a {111} plane of In _0.5 Ga _0.5 P. Further, the internal angle (α) from the lower layer of each wall surface was measured based on the electron micrograph, and the result was 53 °.

[0031]

According to the present invention described above, a groove having a constant shape can be formed easily and with relatively good reproducibility, and further, side etching is limited to control the area of the groove bottom surface to be substantially constant. You can

[Brief description of drawings]

FIG. 1 is an explanatory view showing each step of a groove forming method of the present invention.

FIG. 2 is an explanatory view showing each step when the groove forming method of the present invention is applied to ridge formation.

[Explanation of symbols]

1: Lower layer 2: Core layer 3: Upper layer 4: Protective layer 5: Groove 6: Ridge 31: Edge of upper layer etched

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Satoshi Nagao             1000 Higashitanana-cho, Ushiku-shi, Ibaraki Mitsubishi Chemical             Within the corporation (72) Inventor Nobuyuki Hosoi             1000 Higashitanana-cho, Ushiku-shi, Ibaraki Mitsubishi Chemical             Within the corporation (72) Inventor Hideki Goto             1000 Higashitanana-cho, Ushiku-shi, Ibaraki Mitsubishi Chemical             Within the corporation F-term (reference) 5F043 AA03 AA04 AA14 AA15 FF01                 5F073 AA20 AA26 CA06 CB02 CB19                       DA05 DA06 DA22

Claims (5)

[Claims] 1. A core layer composed of InGaP and an upper layer composed of MAs are sequentially formed on a {100} plane of a lower layer composed of MAs (M represents one or more kinds of IIIb group elements). A crystal growth step of epitaxially growing the layer, a lithography-etching step of forming an etching window in the protective layer after forming the protective layer on the upper layer, a first etching step of selectively etching the upper layer, and a core layer of {11
So that the surface where the 1} plane mainly appears reaches the lower layer without side etching from the end of the etched upper layer,
A method of forming a groove in a semiconductor light emitting device structure, comprising a second etching step of selectively etching other surfaces except the surface where the {111} surface of the core layer mainly appears. 2. The upper layer MAs is GaAs.
The method for forming the groove according to [1]. 3. The lower layer MAs is GaAs.
Or the groove forming method described in 2. 4. The method of forming a groove according to claim 1, wherein the protective layer is SiNx or SiO ₂ . 5. An upper layer and / or after the second etching step.
Alternatively, the groove forming method according to claim 1, further comprising a third etching step of selectively etching the lower layer.