JP2005191285A - Etching solution for AlGaAs compound semiconductor layer, etching method, and semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an etching solution for an AlGaAs-based compound semiconductor layer, an etching method, and a semiconductor substrate having a step, in which the etching layer is hardly oxidized and a step is formed by etching, and the shape and etching width can be easily controlled. Provided.
A first compound semiconductor layer made of a solution containing hydrofluoric acid and a complexing agent and made of Al _x Ga _1-x As (0 ≦ x <0.45), Al _x Ga _1- The second compound semiconductor layer of the Al _x Ga _1-x As (0 ≦ x ≦ 1) based compound semiconductor layer having the second compound semiconductor layer made of _x As (0.45 ≦ x ≦ 1) is selected. Etch.
[Selection figure] None

Description

  The present invention is an etching solution capable of selectively etching a compound semiconductor layer having a predetermined Al composition or higher among AlGaAs-based compound semiconductor layers forming a semiconductor device such as a light emitting element such as a light emitting diode or a semiconductor laser or a high frequency element, The present invention relates to an etching method and a semiconductor substrate.

  Conventionally, when etching an AlGaAs compound semiconductor layer, a selective etching method has been employed in which a compound semiconductor layer having a relatively high Al composition is etched and etching is stopped at a compound semiconductor layer having a relatively low Al composition. .

The selective etching method uses an Al _x Ga _1-x As-based compound semiconductor layer having a relatively low Al composition as an etching stop layer. For this reason, the selective etching method has an advantage that the etching depth can be controlled and oxidation of the portion where the etching is stopped from a low Al composition can be prevented.

Regarding a selective etching solution, it has been reported that hydrochloric acid can be used when etching an Al _x Ga _1-x As compound semiconductor layer having an Al composition of x ≧ 0.6 (Non-patent Document 1: F). Stern and JM Woodall, J. Appl. Phys. 45 (1974) p3904-3906). However, in practice, hydrochloric acid alone has a drawback that the etching rate is slow, and a sufficient etching rate cannot be obtained unless the Al composition is x ≧ 0.7. For this reason, when hydrochloric acid is used as an etching solution, the etching layer in the device must have an Al composition of x ≧ 0.7, and such an etching layer with a high Al composition is easily oxidized and difficult to use. there were.

An etching solution using hydrofluoric acid is also known (Non-Patent Document 2: LA Coldren and JL Merz, ELECRONICS LETTERS, 21 (1985), p558-559). The etching solution is Al composition hardly etched Al _x Ga _1-x As-based compound semiconductor layer of x ≦ 0.4, in liquid temperature 21 ° C., the Al composition is x = 0.6 Al _x Ga It has been reported that a _1-x As compound semiconductor layer can be etched at a very high etching rate of 3.5 μm / min. However, when a device such as an LD or LED is manufactured, an AlGaAs compound semiconductor layer having a thickness of 1 μm or less is often etched, and there is a problem that it is difficult to control etching at such a high etching rate.

Furthermore, in order to improve the fast etching rate as described above, an etchant composed of a mixture of hydrofluoric acid and water has also been proposed (Non-patent Document 3: Y. Komatsu, S. Isozumi, T. Kotani, FUJITSU Scientific and Technical Journal (1976 March) p125-139). However, when etching is actually performed using this solution, the Al composition of the Al _x Ga _1-x As-based compound semiconductor layer to be etched is x ≧ 0.6, and the Al composition of the compound semiconductor layer that stops the etching is x It was necessary to make ≦ 0.4. Furthermore, when performing etching to form a step using an appropriate mask, it is difficult to control the etching width because the step cross section after etching has many irregularities and the spreading speed of the etching in the lateral direction is high. is there. As described above, an etching solution composed of a mixture of hydrofluoric acid and water has a problem that it is difficult to use as an etching solution in a process such as a high-frequency element or LD that requires control of the etching width and depth. It was.

  Furthermore, an etching solution made of a mixed solution of hydrofluoric acid and an acid (hydrochloric acid or the like) has also been proposed (for example, Patent Document 1: Japanese Patent Laid-Open No. 6-196801). However, this etching solution can etch the etching cross section very smoothly, but has a drawback that the etching rate is still high and it is difficult to control the etching width.

As described above, when etching an AlGaAs-based compound semiconductor layer, an etching solution and an etching method that can easily control the shape and the etching width have been developed even when the etching layer is not easily oxidized and a step is formed by etching. It was desired.
JP-A-6-196801 (Claims 33 to 39) F. Stern and JM Woodall, J. Appl. Phys. 45 (1974) p3904-3906 LA Coldren and JL Merz, ELECRONICS LETTERS, 21 (1985) p558-559 Y. Komatsu, S. Isozumi, T. Kotani, FUJITSU Scientific and Technical Journal (1976 March) p125-139

  The present invention has been made to solve the above problems, and the object of the present invention is to control the shape and etching width even when a step is formed by performing selective etching using an Al composition difference. It is an object to provide an etching solution for an AlGaAs compound semiconductor layer that is easy.

  Furthermore, the second object of the present invention is to provide a method for etching an AlGaAs compound semiconductor layer using the etching solution.

  A third object of the present invention is to provide a semiconductor substrate having a step formed by the etching method.

  In order to solve the above-mentioned problems, the present inventors diligently studied to develop a novel etching solution based on hydrofluoric acid. As a result, it has been found that the etching of the AlGaAs compound semiconductor layer can be controlled by combining the hydrofluoric acid and the complexing agent depending on the Al composition level, and the present invention has been completed.

That is, the first object of the present invention is achieved by the following etching solution.
(1) An etching solution for an Al _x Ga _1-x As (0 ≦ x ≦ 1) -based compound semiconductor layer comprising a solution containing hydrofluoric acid and a complexing agent.
(2) the first compound semiconductor layer in which the Al _x Ga _1-x As (0 ≦ x ≦ 1) -based compound semiconductor layer is made of Al _x Ga _1-x As (0 ≦ x <0.45); An etching solution according to (1), wherein the second compound semiconductor layer is made of Al _x Ga _1-x As (0.45 ≦ x ≦ 1), and the second compound semiconductor layer is selectively etched. .
(3) The etching solution according to (1) or (2), wherein the complexing agent is citric acid.
(4) The etching solution according to any one of (1) to (3), wherein the concentration of hydrofluoric acid is 3 to 12 mol / l and the concentration of the complexing agent is 1 to 5 mol / l.

Furthermore, the second object of the present invention is achieved by the following etching method.
(5) Etching characterized by etching an Al _x Ga _1-x As (0 ≦ x ≦ 1) compound semiconductor layer using the etching solution according to any one of (1) to (4). Method.
(6) As the Al _x Ga _1-x As (0 ≦ x ≦ 1) -based compound semiconductor layer, a first compound semiconductor layer made of Al _x Ga _1-x As (0 ≦ x <0.45); Using the compound semiconductor layer having a second compound semiconductor layer made of Al _x Ga _1-x As (0.45 ≦ x ≦ 1), the second compound semiconductor layer is selectively etched (5) The etching method as described.
(7) After forming a mask pattern on part of the surface of the Al _x Ga _1-x As (0 ≦ x ≦ 1) compound semiconductor layer, the etching solution according to any one of (1) to (4) is used. And etching the compound semiconductor layer to form a step in the compound semiconductor layer.
(8) The <011> direction on the (100) plane when the mask pattern is a Ga plane on the (111) plane of the Al _x Ga _1-x As (0 ≦ x ≦ 1) compound semiconductor layer (7) The etching method according to (7), wherein the step formed on the compound semiconductor layer after etching is a forward mesa shape.

Furthermore, the third object of the present invention is achieved by the following semiconductor substrate.
(9) A semiconductor substrate having a step formed by the etching method according to (7).
(10) A semiconductor substrate having a forward mesa-shaped step formed by the etching method according to (8).

The etching solution of the present invention comprises a solution containing hydrofluoric acid and a complexing agent, and the etching solution of the present invention is used in the etching method of the present invention. Therefore, according to the etching solution and etching method of the present invention, when the AlGaAs compound semiconductor layer is etched, the etching width can be easily controlled, and a step having a smooth surface can be formed easily and stably. be able to. Furthermore, according to the etching solution and etching method of the present invention, an appropriate etching rate can be obtained, so that the etching operation can be easily performed with good reproducibility and stability.
Further, when the etching solution and etching method of the present invention are used, when the (111) plane is a Ga plane, a forward mesa is formed on the AlGaAs compound semiconductor layer in which the mask pattern is formed in the <011> direction on the (100) plane. A step of the shape can be formed.

  Furthermore, if the semiconductor substrate of the present invention is formed with a waveguide having smooth side walls, a semiconductor substrate in which the in-plane uniformity of the stripe width is further improved can be provided.

[Etching solution of the present invention]
The etching solution of the present invention comprises a solution containing hydrofluoric acid and a complexing agent.

The hydrofluoric acid used in the etching solution of the present invention is a solution in which hydrogen fluoride is mixed with water at an arbitrary ratio, and includes HF-H ₂ O, 2HF-H ₂ O, and 4HF-H ₂ O. .

  The concentration of hydrofluoric acid in the etching solution of the present invention is adjusted to 1 liter when the entire etching solution is 1 liter (ie, the mixture is mixed with hydrofluoric acid and a complexing agent and a solvent is added). 3) to 12 mol / l, preferably 7 to 12 mol / l, and more preferably 10 to 11.5 mol / l. If the concentration of hydrofluoric acid is 3 mol / l or more, an appropriate etching rate can be obtained. Therefore, the etching rate is too slow, and the etched portion does not rattle and unevenness is not generated on the side wall. In addition, when the concentration of hydrofluoric acid is 12 mol / l or less, an appropriate etching rate can be obtained, so that the etching rate is not too high and it is not difficult to control the etching width.

  The etching solution of the present invention contains a complexing agent. By combining the hydrofluoric acid and the complexing agent at a predetermined concentration, the etching rate can be adjusted to a range that can be easily controlled, and the unevenness of the stepped portion formed by etching can be reduced.

The complexing agent (metal sealant) used in the etching solution of the present invention is not particularly limited as long as the complex stability constant with Al is 1 or more, but is preferably 3 or more. Here, the complex stability constant is, for example, K = −log ₁₀ ([A] [X] / [AX]) in a complex composed of AX, when the ionic state is not taken into consideration and expressed as AX = A + X. The value of A complex stability constant of 1 or more is preferable because it is stably present in the etching solution as complex ions.

Examples of the complexing agent include citric acid, ethylenediaminetetraacetic acid compound (EDTA), triethylenetetraminehexaacetic acid (TTHA), diethylenetriaminepentaacetic acid (DTPA), and the like. High citric acid is preferred.
The complexing agent of the present invention does not include tartaric acid, phosphoric acid, hydrochloric acid, sulfuric acid, acetic acid, etc., which do not have a complex stability constant with Al.

  The concentration of the complexing agent in the etching solution of the present invention is suitably 1 to 5 mol / l, preferably 1.5 to 3 mol / l, when the total solution is 1 liter. More preferably, it is 8-2.5 mol / l. When the concentration of the complexing agent is in the range of 1 to 5 mol / l, it is possible to suppress the occurrence of unevenness in the etched portion while maintaining the etching rate.

  As the solvent used in the etching solution of the present invention, water can be generally used, but filtered water, purified water, distilled water and the like are preferably used from the viewpoint of preventing mixing of impurities. An alcohol solvent such as ethyl alcohol or glycerin can also be used.

Next, the compound semiconductor layer etched with the etching solution of the present invention will be described.
The compound semiconductor layer etched with the etching solution of the present invention is an AlGaAs compound semiconductor layer. An AlGaAs compound semiconductor can be represented by a general formula Al _x Ga _1-x As (0 ≦ x ≦ 1).

When etching is performed using the etching solution of the present invention, the etching can be controlled depending on the Al composition level of the AlGaAs compound semiconductor layer. That is, when the AlGaAs compound semiconductor is represented by the general formula Al _x Ga _1-x As, the AlGaAs compound semiconductor layer can be etched when 0.45 ≦ x ≦ 1, and when 0 ≦ x <0.45. The AlGaAs compound semiconductor layer is not etched. That is, the AlGaAs-based compound semiconductor layer can function as an etching layer when the Al composition is 0.45 ≦ x ≦ 1, and can function as an etching stop layer when 0 ≦ x <0.45.

When the Al _x Ga _1-x As-based compound semiconductor layer functions as an etching layer, the composition of Al is 0.45 ≦ x ≦ 1, preferably 0.5 ≦ x ≦ 0.8. More preferably, 6 ≦ x ≦ 0.7. In particular, when 0.6 ≦ x ≦ 0.7, an appropriate etching rate can be maintained and the progress of oxidation can be suppressed.

The etching rate when the Al _x Ga _1-x As-based compound semiconductor layer functions as an etching layer varies depending on the type of complexing agent used, the mixing molar ratio of hydrofluoric acid and complexing agent, and the Al composition. It is preferable that the etching rate is such that etching control is easy. For example, when citric acid is used as the complexing agent and the Al composition is 0.6 ≦ x ≦ 0.65, 0.3 to 2 μm / min, preferably 0.5 to 1.5 μm / min, more preferably Can have an etching rate in the range of 0.7 to 1.3 μm / min.
In addition, when an inorganic acid or an organic acid is used instead of the complexing agent, it is as follows. When hydrochloric acid is used, for example, when the Al composition is x = 0.65, the etching rate is 3 μm / min or more, and when x = 0.6, the etching rate is 1.8 μm / min or more. Etching control is difficult. When other inorganic acid or organic acid is used, unevenness is generated on the etched step side wall.

On the other hand, when the Al _x Ga _1-x As compound semiconductor layer functions as an etching stop layer, 0 ≦ x <0.45, preferably 0 ≦ x ≦ 0.4, and 0 ≦ x More preferably, it is ≦ 0.2. In particular, it is preferable to set the Al composition to 0 ≦ x ≦ 0.2 because there is no problem of oxidation and etching can be suppressed even with a very thin layer.

  The etching stop layer may be a layer made of a compound semiconductor other than an AlGaAs compound semiconductor. For example, etching stop for Al-free compound semiconductor layers such as GaInP-based compound semiconductor layers and InP-based compound semiconductor layers, and layers with a low Al composition in group III elements, especially compound semiconductor layers with an Al composition of less than 0.45 Can be used as a layer.

The etching solution of the present invention utilizes the above-described etching characteristics, for example, to convert the Al _x Ga _1-x As (0 ≦ x ≦ 1) -based compound semiconductor layer into Al _x Ga _1-x As (0 ≦ x When formed with a first compound semiconductor layer made of <0.45) and a second compound semiconductor layer made of Al _x Ga _1-x As (0.45 ≦ x ≦ 1), the second compound The semiconductor layer can be selectively etched. In particular, when a compound semiconductor laser is formed using the etching solution of the present invention, it is preferable to perform such selective etching.

[Etching method of the present invention]
Next, the etching method of the present invention will be described.
In the etching method of the present invention, an Al _x Ga _1-x As (0 ≦ x ≦ 1) based compound semiconductor layer is etched using the above etching solution.

When performing etching, the first compound semiconductor layer made of Al _x Ga _1-x As (0 ≦ x <0.45) is used as the Al _x Ga _1-x As (0 ≦ x ≦ 1) compound semiconductor layer. And an Al _x Ga _1-x As (0 ≦ x) having a second compound semiconductor layer made of Al _x Ga _1-x As (0.45 ≦ x ≦ 1) in contact with the first compound semiconductor layer ≦ 1) The second compound semiconductor layer can be selectively etched by using a system compound semiconductor layer and bringing the etching liquid into contact with the compound semiconductor layer.

The etching method of the present invention comprises forming a mask pattern that is not etched by the etching solution of the present invention on a part of the surface of an Al _x Ga _1-x As (0 ≦ x ≦ 1) compound semiconductor layer, and then etching the etching solution of the present invention. A step can be formed on the surface of the compound semiconductor layer by performing etching of the compound semiconductor layer using.

The method for forming the mask pattern is not particularly limited, and the mask pattern can be formed using a general method. The mask pattern can be formed, for example, by applying a resist on the surface and then performing exposure using a photomask having a shape to be produced and a stripe width. The mask pattern can also be formed using a material that is not easily eroded by hydrofluoric acid, for example, a metal such as tungsten or gold. Furthermore, in the present invention, a material such as an Al-free GaAs compound semiconductor or a low Al composition (x <0.45) Al _x Ga _1-x As compound semiconductor that forms the etching stop layer is used. A mask pattern can also be formed.

FIG. 1 shows a step shape of an Al _x Ga _1-x As (0 ≦ x ≦ 1) -based compound semiconductor layer formed after etching with the etching solution of the present invention. As shown in FIG. 1, when the (111) plane of an Al _x Ga _1-x As (0 ≦ x ≦ 1) compound semiconductor layer is a Ga plane, conventional hydrofluoric acid and water, or fluoride When etching is performed with a mixed solution of hydrogen acid and hydrochloric acid, and the mask pattern is formed in the <011> direction (FIG. 1A) on the (100) plane, the shape of the etched portion is an inverted mesa shape ( The shape of the etched portion when the mask pattern is formed in the <0-11> direction (FIG. 1 (d)) is a forward mesa shape (FIG. 1 (e)). On the other hand, when etching is performed with the etching solution of the present invention, the shape of the etched portion on the (100) plane is the reverse mesa shape (FIG. 1B) as in the case of using the conventional etching solution. In other words, the side wall of the etched part has a slightly mesa shape (FIG. 1C). As a result, according to the etching method of the present invention, it is possible to form a step having a forward mesa shape that is substantially the same as that when the mask pattern is formed in the <0-11> direction and etching is performed (FIG. 1 (f)).
In this specification, the “forward mesa shape” refers to a shape in which an etching opening extends in a square shape toward the epitaxial growth direction, and includes a shape whose side is slightly curved (for example, FIG. 1C). It is.

  The mask pattern formed in the <011> direction on the (100) plane when the (111) plane is a Ga plane, which is formed when etching is performed using the etching solution of the present invention, is a stripe shape. However, a deviation within ± 45 °, preferably within ± 30 °, more preferably within ± 15 ° from the stripe in the <011> direction is also included.

[Semiconductor substrate of the present invention]
The semiconductor substrate of the present invention has a step formed by etching an Al _x Ga _1-x As (0 ≦ x ≦ 1) compound semiconductor layer with the etching solution of the present invention. Compared with the step formed with the conventional etching solution, this step has a smooth surface with no unevenness on the side wall surface of the etched portion. The shape of the step is not particularly limited, but is preferably a forward mesa shape. Further, the off-angle of the semiconductor substrate used in the present invention is preferably ± 20 ° or less, more preferably ± 15 ° or less, and most preferably ± 10 ° or less.

Hereinafter, the present invention will be described in more detail with reference to specific examples.
The materials, reagents, ratios, operations, and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

(Example 1)
1. Preparation of etching solution 225 ml of 6.4 mol / l hydrofluoric acid (HF 49 wt%), 270 g (1.3 mol) citric acid monohydrate and water were mixed to prepare a total of 600 ml. An etching solution was prepared.

2. Sample Preparation Using MOCVD, a GaAs buffer layer with a thickness of 1.0 μm, an Al _0.52 Ga _0.48 As layer with a thickness of 1.6 μm, a GaAs layer with a thickness of 3 nm, a thickness of 0 on a (100) surface of a GaAs substrate. A sample was prepared by laminating 0.7 μm Al _0.62 Ga _0.38 As layers in this order.
The Al _0.52 Ga _0.48 As layer was formed below the GaAs etching stop layer to confirm whether or not the etching was effectively stopped.
Next, an etching mask pattern having a stripe shape with a width of 1.5 μm was formed on the Al _0.62 Ga _0.38 As layer with a resist in the <0-11> direction using ordinary photolithography.

3. Etching The sample was etched using the etching solution. As a result, the GaAs layer was reached in about 40 seconds. At this time, the shape of the etched portion was a normal mesa shape, and the width of the step bottom portion was 1.8 μm.
Furthermore, when the formed step cross section was observed with a scanning electron microscope (SEM), no unevenness was found on the side wall of the step, and a very smooth plane was formed. The etching width was stable in the plane.

In the sample etched with the above etchant, the etching was stopped at the GaAs layer, and the Al _0.52 Ga _0.48 As layer below it was not etched at all. Further, a forward mesa-shaped step was formed in the Al _0.62 Ga _0.38 As layer etched with the etching solution.
Thus, according to the etching solution and the etching method of the present invention, only the Al _0.62 Ga _0.38 As layer having a high Al composition can be selectively etched, and a forward mesa-shaped step can be formed in the Al _0.62 Ga _0.38 As layer by etching. I understand.

(Example 2)
1. Preparation of Etching Solution Etching solution was prepared in the same manner as in Example 1.

2. Sample Preparation Using MOCVD on a (100) surface of a GaAs substrate, a 1.0 μm thick GaAs buffer layer, a 1.6 μm thick Al _0.52 Ga _0.48 As layer, a 3.0 nm thick GaAs layer, A sample was prepared by laminating 0.7 μm thick Al _0.55 Ga _0.45 As layers in this order. The Al _0.52 Ga _0.48 As layer was formed below the GaAs layer in order to confirm whether or not the etching was effectively stopped.
Next, a stripe-shaped etching mask pattern having a width of 1.5 μm was formed on the Al _0.55 Ga _0.45 As layer with a resist in the <0-11> direction using ordinary photolithography.

3. Etching of the sample was performed using the etching solution prepared in Etching Example 1. As a result, the GaAs layer was reached in about 190 seconds, but the etching was stopped at the GaAs layer, and the Al _0.52 Ga _0.48 As layer below it was not etched at all. The shape of the etched portion of the formed Al _0.55 Ga _0.45 As layer was a normal mesa shape, and the width of the bottom portion was about 1.9 μm.
Further, when the cross section of the formed step was observed with a scanning electron microscope (SEM), a very smooth plane was formed on the side wall of the step of the Al _0.55 Ga _0.45 As layer. The etching width was stable in the plane.

Thus, according to the etching solution and etching method of the present invention, the Al GaAs layer containing no Al is not etched, only the Al _0.55 Ga _0.45 As layer having a high Al composition is etched, and a forward mesa having a smooth plane is obtained. It can be seen that a step of the shape can be formed.

(Example 3)
1. Preparation of Etching Solution Etching solution was prepared in the same manner as in Example 1.

2. Sample Preparation Using MOCVD on a (100) surface of a GaAs substrate, a 1.0 μm thick GaAs buffer layer, a 1.6 μm thick Al _0.52 Ga _0.48 As layer, a 3.0 nm thick GaAs layer, A sample was prepared by laminating 0.7 μm thick Al _0.42 Ga _0.58 As layers in this order.
Next, a stripe-shaped etching mask pattern having a width of 1.5 μm was formed on the Al _0.42 Ga _0.58 As layer with a resist in the <0-11> direction using ordinary photolithography.

3. When the sample was etched using the etching solution prepared in Etching Example 1, the Al _0.42 Ga _0.58 As layer was not etched at all.

  Thus, according to the etching solution and etching method of the present invention, only the AlGaAs compound semiconductor layer having an Al composition of 0.45 or more is selectively etched without etching the AlGaAs compound semiconductor layer having an Al composition of less than 0.45. It turns out that it etches.

Example 4
1. Preparation of Etching Solution Etching solution was prepared in the same manner as in Example 1.

2. Sample Preparation Using MOCVD on a (100) surface of a GaAs substrate, a 1.0 μm thick GaAs buffer layer, a 1.6 μm thick Al _0.52 Ga _0.48 As layer, a 3.0 nm thick GaAs layer, A 1.0 μm thick Al _0.65 Ga _0.35 As layer was laminated in this order to prepare a sample. The Al _0.52 Ga _0.48 As layer was formed below the GaAs layer in order to confirm whether or not the etching was effectively stopped.
Next, a stripe-shaped etching mask pattern having a width of 1.5 μm was formed on the Al _0.65 Ga _0.35 As layer with a resist in the <011> direction by using ordinary photolithography.

3. When the above sample was etched using the etching solution produced in the etching example 1, it reached the GaAs layer in about 40 seconds, but the etching stopped at the GaAs layer, and the Al _0.52 Ga _0.48 As layer below it. Was not etched at all. At this time, the step shape of the Al _0.65 Ga _0.35 As layer was a mesa shape with slightly rounded side walls, and the width of the etched bottom portion was about 2.4 μm.

Thus, according to the etching solution and the etching method of the present invention, it is understood that only the Al _0.65 Ga _0.35 As layer having a high Al composition can be selectively etched without etching the GaAs layer not containing Al. Further, in the case of forming a striped mask pattern in the <011> direction in the conventional etching solution and the etching method, the step of the etched portion is different from the reverse mesa shape. The shape can be a mesa shape.

(Comparative Example 1)
The sample was prepared in the same manner as in Example 1 except that 600 ml of a mixture of 6.4 mol / l hydrofluoric acid (49 wt%): water = 1: 10 (volume ratio) was used as the etching solution. Etching was performed. As a result, the GaAs layer was reached in about 240 seconds. At this time, the width of the bottom portion of the etched portion was 2.1 μm.

When the cross section of the step formed by the etching solution was observed with a scanning electron microscope (SEM), irregularities were formed on the side wall of the step. In addition, the width of the etched portion was not constant in the plane and varied. Further, the etching spread in the lateral direction was large.
From this, it can be seen that the etching solution composed of hydrofluoric acid-water used in the comparative example can be easily formed with a wide etching width, but it is difficult to control the etching width with a thin etching liquid.

(Comparative Example 2)
The sample was etched in the same manner as in Comparative Example 1 except that the etching solution used in Comparative Example 1 and the sample prepared in Example 4 were used. As a result, the GaAs layer was reached in about 230 seconds, but the underlying Al _0.52 Ga _0.48 As layer was not etched at all. The formed step shape was an inverted mesa shape, and the bottom width of the etched portion was 3.0 μm.

  From this, it can be seen that when etching is performed using a conventional etching solution, the shape of the step formed is an inverted mesa shape, and a forward mesa shape is not formed.

  The etching solution and etching method of the present invention can control the etching by adjusting the Al composition of the AlGaAs compound semiconductor layer and make the etched portion a smooth surface without unevenness. It can be used for etching of light emitting elements such as light emitting diodes and semiconductor lasers and semiconductor devices such as high frequency elements.

A step of _{Al x Ga 1-x As (} 0 ≦ x ≦ 1) compound semiconductor layer formed after etching with an etching solution of the present invention; FIG.

Claims (10)

An etching solution for an Al _x Ga _1-x As (0 ≦ x ≦ 1) -based compound semiconductor layer, comprising a solution containing hydrofluoric acid and a complexing agent. The Al _x Ga _1-x As (0 ≦ x ≦ 1) compound semiconductor layer includes a first compound semiconductor layer made of Al _x Ga _1-x As (0 ≦ x <0.45), and an Al _x Ga. 2. The etching solution according to claim 1, further comprising a second compound semiconductor layer made of _1-x As (0.45 ≦ x ≦ 1) and selectively etching the second compound semiconductor layer.   The etching solution according to claim 1, wherein the complexing agent is citric acid.   The etching solution according to claim 1, wherein the concentration of the hydrofluoric acid is 3 to 12 mol / l, and the concentration of the complexing agent is 1 to 5 mol / l. An etching method comprising etching an Al _x Ga _1-x As (0 ≦ x ≦ 1) compound semiconductor layer using the etching solution according to claim 1. As the Al _x Ga _1-x As (0 ≦ x ≦ 1) -based compound semiconductor layer, a first compound semiconductor layer made of Al _x Ga _1-x As (0 ≦ x <0.45) and the first The second compound semiconductor layer is selectively used using a compound semiconductor layer having a second compound semiconductor layer made of Al _x Ga _1-x As (0.45 ≦ x ≦ 1) in contact with the compound semiconductor layer of The etching method according to claim 5, wherein the etching is performed. After forming the _{Al x Ga 1-x As (} 0 ≦ x ≦ 1) compound part on the mask pattern on the surface of the semiconductor layer, using the etching solution according to claim 1 wherein An etching method comprising etching a compound semiconductor layer to form a step in the compound semiconductor layer. The mask pattern is striped in the <011> direction on the (100) plane when the (111) plane of the Al _x Ga _1-x As (0 ≦ x ≦ 1) compound semiconductor layer is a Ga plane. The etching method according to claim 7, wherein the step formed in the compound semiconductor layer after etching has a forward mesa shape.   A semiconductor substrate having a step formed by the etching method according to claim 7.   A semiconductor substrate having a mesa-shaped step formed by the etching method according to claim 8.

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