JP3389658B2 - Selective etching method and film thickness measuring method for epitaxial crystal laminate structure - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention generally relates to AlGaA.
The present invention relates to a method of selectively etching a s / AlGaAs or GaAs / AlGaAs system laminated structure.
The present invention also relates to a method for measuring the film thickness of an epitaxially grown thin film using the method.

[0002]

2. Description of the Related Art Al composition values are (x, y; where 0 ≦ x <
Al _{x in} the combination of 1 and 0 <y ≦ 1 and x <y)
In _{Ga 1-x As / Al y} Ga 1-y As multilayer structure (see FIG. 1), without cutting the lower Al _y Ga _1-y As layer, cut only the upper layer of Al _x Ga _1-x As layer As such a selective etching technique, for example, (x = 0, 0.3
In the case of 5 <y ≦ 1), JP-A-52-14118
As disclosed in Japanese Patent Publication No. 9, the ammonia water (NH ₄ O
H) and hydrogen peroxide solution (H ₂ O ₂ ) are mixed so that the hydrogen peroxide solution is in excess (for example, ammonia water: hydrogen peroxide solution = 1: 30 by volume). Are known.

When this solution is used, GaAs (x =
For 0), the hydrogen peroxide solution that is an oxidant causes Ga
Etching progresses in the process of forming an oxide such as O and dissolving the oxide with aqueous ammonia which is a dissolving agent. On the other hand, this solution contains Al _y Ga _1-y As (0.
For 4 <y ≦ 1), since the hydrogen peroxide solution is excessive, the oxidizing power of the solution is too strong, so that passive Al is used.
Oxide film is formed, and etching does not proceed. Due to the above-mentioned actions, by using this solution, useful selective etching having a selectivity (ratio of etching rates for respective films) of 100 or more can be performed.

However, with this ammonia-based solution, it is impossible to perform selective etching on other combinations (x, y) of Al compositions. In addition, for the structure of the combination (x, y) that allows selective etching,
In the selective etching with this solution, the oxide layer formed to stop the etching is very thick, and the surface of the layer has a dark color. Therefore, it is necessary to add acid treatment or the like. Further, since this solution corrodes the photoresist used in ordinary lithography, it becomes difficult to form a pattern.

Among the above problems, the problem that the oxide layer is formed thick and the resistance of the photoresist is avoided by using RIE (reactive ion etching) which is a dry etching technique. It is well known that you can do it. If Freon 12 is used as the etching gas, the combination of Al compositions is (x = 0, 0.15 <y ≦
With respect to the laminated structure of 1), the oxide layer for stopping the etching is extremely thin, and the surface is not discolored, so that the preferable selective etching can be performed. The photoresist is not attacked by this dry etching.

Further, in the prior art, various methods (for example, MBE, MOCVD, LPE, V) are formed on a semiconductor substrate.
When it is necessary to examine the distribution of the thickness of the epitaxially grown GaAs thin film formed by PE etc. in the substrate surface,
The procedure was as follows.

First, GaAs / AlGaA as described above
After forming the s laminated structure, a resist pattern is formed by photolithography, and selective etching is performed by this dry etching to remove GaAs in a portion where the resist is not placed, and then the resist is removed.
The desired thickness distribution is obtained by measuring the thickness of GaAs in the portion which is protected by the resist and is not etched by the step measuring device. However, this etching requires expensive RIE equipment. In addition, since it has been decided that the etching gas, Freon 12, will be banned from being manufactured and sold in the near future from the standpoint of global environment protection to prevent the destruction of the ozone layer, there is a possibility that it cannot be used in the future. Also, the combination of Al compositions is (x = 0, 0.15 <y ≦ 1)
The selective etching can be performed only on the above laminated structure.

Another means is disclosed in Japanese Patent Laid-Open No. 63-68.
In the method shown in 465, by using an aqueous solution containing tartaric acid and hydrogen peroxide, the laminated structure in which the combination of Al compositions is (0 ≦ x <0.35, 0.45 <y ≦ 1) It becomes possible to selectively etch. In the case of this solution, the oxide layer formed to stop the etching is very thin and does not cause discoloration.
Subsequent acid treatment is unnecessary. Moreover, since it does not attack the photoresist, pattern formation is easy. However, in the case of the present solution, even if the mixing ratio of tartaric acid and hydrogen peroxide solution is variously changed, useful selective etching such that the selection ratio exceeds 100 is (0 ≦ x <0.35, 0.45 < y ≦
This can be done only for the combination 1).

[0009]

As described above, according to the conventional technique, selective etching with a high selective ratio is possible only for a combination (x, y) of Al composition values in a very limited range. In some cases, the etching forms a thick passivation oxide layer, which requires further acid treatment after etching, or it is difficult to form a pattern using a normal photoresist.

The present invention has been made to solve the above-mentioned problems, and has an arbitrary Al composition value (x, y;
However with respect to 0 ≦ x <1 and 0 <Al with a combination of y ≦ 1 and _{x <y) x Ga 1-} x As / Al y Ga 1-y As multilayer structure, underlying Al _y Ga _1-y An object of the present invention is to provide a selective etching method of an epitaxial crystal laminated structure that enables selective etching such that only the upper Al _x Ga _1-x As layer is removed without removing the As layer.

Another object of the present invention is to provide a method for measuring the thickness of an epitaxially grown laminated thin film using the above method.

[0012]

In the selective etching method of the epitaxial crystal laminated structure according to the first aspect of the present invention, first, the upper layer is an Al _x Ga _1-x As crystal layer (0 ≦ x <1). Then, a substrate on which an epitaxially grown crystal having a laminated structure in which the lower layer is an Al _y Ga _1-y As crystal layer (0 ≦ y ≦ 1, where x <y) is formed is prepared.
An etching solution in which ethylenediaminetetraacetic acid (hereinafter referred to as EDTA), which is a pH buffer, is added to a mixed solution of ammonia water and hydrogen peroxide to adjust the pH value of the solution to an appropriate value within the range of 6 to 9 is obtained. prepare. The Al _x Ga _1-x As crystal layer, which is the upper layer, is selectively etched using the etching solution.

In the method for measuring the film thickness of an epitaxially grown laminated thin film according to the second aspect of the present invention, first, the upper layer is an Al _x Ga _1-x As crystal layer (0 ≦ x <1),
A substrate on which an epitaxially grown crystal having a laminated structure in which the lower layer is an Al _y Ga _1-y As crystal layer (0 ≦ y ≦ 1, where x <y) is prepared is prepared. A pattern that is uniformly distributed in the plane is formed on the substrate by a normal lithography method. EDTA, which is a pH buffer, is added to a mixed solution of aqueous ammonia and hydrogen peroxide to prepare an etching solution in which the pH value of the solution is adjusted to an appropriate value within the range of 6 to 9. Using the above etching solution, the upper layer of Al _x
The portion of the Ga _1-x As crystal layer where the pattern is open is etched until the surface of the lower layer is exposed.
The film thickness of the upper layer is measured by removing the photoresist on the substrate and measuring the step difference between the etched portion and the non-etched portion.

[0014]

According to the first aspect of the present invention, the selective etching method for the epitaxial crystal laminated structure has an arbitrary Al composition value (x, y; where 0 ≦ x <1 and 0 <y ≦ 1 and x <
Al has a combination of _{y) x Ga 1-x As} / Al y Ga
Selection that has a sufficient selection ratio for the _1-y As layered structure, that the oxide layer for stopping etching is thin enough, that discoloration does not occur, and that it does not attack the photoresist for ordinary lithography. In order to perform etching, p solution is added to a solution of ammonia water and excess hydrogen peroxide solution.
Add an appropriate amount of EDTA, which is an H buffer, and add (x,
The selective etching method is characterized in that selective etching is performed using a solution adjusted so that the solution has an optimum pH value according to the value of y). As described above, in a solution obtained by mixing ammonia water and an excess of hydrogen peroxide water, a passive oxide film is formed on AlGaAs having an Al composition of 0.35 or more due to its excessive oxidizing power, Although etching is possible, the oxide film becomes thick because the oxidizing power is too strong with this solution.

By the way, when EDTA which is a pH buffer is added to this mixed solution, the pH value which was originally 10 or more can be freely lowered by adjusting the amount of EDTA. When the pH becomes 9 or less, the oxidizing power of the solution is significantly weakened, and the passivation oxide film layer formed during etching becomes very thin. Further, depending on the pH value, a passive oxide film is not formed during etching with respect to AlGaAs having an Al composition within a certain range. By utilizing this property, it becomes possible to perform the above-described selective etching with respect to a combination of (x, y) having an arbitrary value simply by adjusting the pH value, as will be described in detail later. . Further, the weakening of the oxidizing power not only thins the passive oxide film, but also does not attack the photoresist used in ordinary lithography.

FIG. 2 shows a summary of the characteristics of this etching solution system. The horizontal axis is the mixing volume ratio of ammonia water and hydrogen peroxide water, the vertical axis is the pH value, and the line in the graph is a certain Al.
The boundary of whether or not the composition of AlGaAs is dissolved or not is shown. The upper side of the line indicates that etching is possible, and the lower side indicates that etching cannot be performed. In addition, GaAs having an Al composition of 0 can be etched in the entire region of this figure. Here, etching is possible 5
Etching progresses at a rate of 00 Å (0.05 μm) / min or more, and if etching is not possible, it means that the etching rate is 0 or 500 Å / min or less, which means the line of each composition. However, since it is also the boundary of whether a passive oxide film is formed or not, the change in the etching rate above and below that is dramatic.

In FIG. 3, as an example, the Al composition is 0.
The relationship between pH and etching rate in the case of etching 35 AlGaAs with a solution having a mixture volume ratio of ammonia water and hydrogen peroxide water (hydrogen peroxide water / ammonia water) of 3 is shown. As is clear from this, it can be seen that the etching characteristics drastically change at pH = 8.1.

From the above characteristics, for example, AlGaA that can be etched by fixing the mixing volume ratio of ammonia water and hydrogen peroxide water to 3 and continuously decreasing the pH.
The Al composition of s also changes continuously (see FIG. 2). If this property is used in combination with the property that etching cannot be performed drastically (see FIG. 3), A having any combination of Al compositions (x, y: where x <y) is obtained.
_{l x Ga 1-x As /} Al y Ga 1-y with respect to As multilayer structure, upper Al is smaller side Al composition _x Ga _1-x A
The s layer is shaved, and the lower layer side Al _y, which is the side with a large Al composition,
It is possible to perform suitable selective etching with a selectivity of 100 or more without removing the Ga _{1 -y} As layer.

According to the method of measuring the film thickness of the epitaxially grown laminated thin film according to the second aspect of the present invention, since the above-mentioned method is used, an accurate value can be obtained.

[0020]

Example 1 In this example, the combination of Al compositions is (x = 0,0.15).
<As would be _{y ≦ 1) Al x Ga 1} -x As / Al y G
A method for performing suitable selective etching on the a _1-y As laminated structure will be described.

A sample having a structure similar to that shown in FIG. 1 was used for the selective etching of this embodiment. However, the upper layer side has a GaAs layer with a thickness of 1000 Å (0.1 μm), and the lower layer side has an Al composition y of 500 Å (0.05 μm) with a thickness of 0.
2 AlGaAs layer. As an etching solution, hydrogen peroxide solution (30
% Standard solution) 40, and the solution was diluted 50 times with pure water, and an aqueous solution of 0.2 mol / l EDTA (Na) ₂ (ethylenediaminetetraacetic acid disodium salt) was added in a volume ratio. The liquid added 4% was used. The pH value of this solution is 25 ℃
Was 7.5. The temperature is set to 2 during etching.
The temperature was controlled to 5 ° C., and appropriate vibration was continued.

FIG. 4 shows the relationship between the etching time and the etching amount in this embodiment. From FIG. 4, after about 1 minute, the etching stopped cleanly at the lower AlGaAs layer, and selective etching with a selectivity of 100 or more was realized. Further, on the surface after etching, the formed oxide layer was very thin, and the color did not change to blackish.

In the present embodiment, the lower layer AlGaAs
Although the Al composition y of the layer is set to 0.2, the present invention is not limited to this, and AlG in the range of 0.15 <y ≦ 1 is set.
It is effective for the aAs layer.

In the present embodiment, the volume ratio of ammonia water to hydrogen peroxide water is 30 and the pH is 7.5. However, the present invention is not limited to this, and as shown in FIG. , Volume ratio of 10 or more, pH 6.5 to 8.5 (2
Within the range of 5 ° C., suitable selective etching similar to the above can be performed.

Embodiment 2 In this embodiment, the combination of Al compositions is (0 ≦ x <0.2,
0.3 <y ≦ 1) is a _{Al x Ga 1-x As /} Al y G
A method for performing suitable selective etching on the a _1-y As laminated structure will be described.

A sample having a structure similar to that shown in FIG. 1 was used for the selective etching of this embodiment. However, the upper layer side is 1
Al composition x with a thickness of 000Å (0.1 μm) is 0.15
AlGaAs layer, lower layer side is 500Å (0.05μm)
Is an AlGaAs layer having an Al composition y of 0.35. Ammonia water (standard solution) 1 is used as the etching solution.
To, hydrogen peroxide solution (30% standard solution) 3 is mixed,
The solution was diluted 10 times with pure water to give 0.2 mol /
A solution obtained by adding 14% by volume of an aqueous solution of EDTA (Na) ₂ (disodium salt of ethylenediaminetetraacetic acid) was used. The pH value of this solution was 7.8 at 25 ° C. During the etching, the temperature was controlled at 25 ° C. and appropriate vibration was continued.

The relationship between the etching time and the etching amount in this embodiment is exactly the same as that in FIG. 4, and after about 1 minute, the etching stopped at the lower AlGaAs layer. Similar to the above-mentioned examples, a selective ratio of 100 or more, a preferable selective etching was obtained in which the oxide layer on the surface after etching was very thin and the color did not change to blackish.

In this embodiment, the Al composition x of the upper AlGaAs layer is 0.15, and the Al composition of the lower AlGaAs layer is Al.
The composition y is set to 0.35, but the present invention is not limited to this and is effective for combinations of Al compositions in the range of 0 ≦ x <0.2 and 0.3 <y ≦ 1. .

Further, in the present embodiment, the volume ratio of the ammonia water and the hydrogen peroxide water was 3 and the pH was 7.8, but the present invention is not limited to this, and as shown in FIG. , Volume ratio 1 to 5, pH 7.7 to 7.9 (25
In the range of (° C.), suitable selective etching similar to the above can be performed.

Example 3 In this example, the combination of Al compositions was (0 ≦ x <0.4,
0.5 <y ≦ 1) is a _{Al x Ga 1-x As /} Al y G
A method for performing suitable selective etching on the a _1-y As laminated structure will be described.

A sample having a structure similar to that shown in FIG. 1 was used for the selective etching of this embodiment. However, the upper layer side is 1
Al composition x with a thickness of 000Å (0.1 μm) is 0.35
AlGaAs layer, lower layer side is 500Å (0.05μm)
Is an AlGaAs layer having an Al composition y of 0.6.
As an etching solution, an aqueous ammonia solution (standard solution) 1 was mixed with hydrogen peroxide solution (30% standard solution) 3, and the solution was diluted 10 times with pure water to obtain 0.2 mol / mol. A solution obtained by adding 13% by volume of an aqueous solution of EDTA (Na) ₂ (disodium salt of ethylenediaminetetraacetic acid) was used. The pH value of this solution was 8.4 at 25 ° C.
During the etching, the temperature was controlled at 25 ° C. and appropriate vibration was continued.

The relationship between the etching time and the etching amount in this example is exactly the same as that in FIG. 4, and after about 1 minute, the etching stopped at the lower AlGaAs layer. Similar to the above-mentioned examples, a selective ratio of 100 or more, a preferable selective etching was obtained in which the oxide layer on the surface after etching was very thin and the color did not change to blackish.

In this embodiment, the Al composition x of the upper AlGaAs layer is 0.35, and the Al composition of the lower AlGaAs layer is Al.
Although the composition y is set to 0.6, the present invention is not limited to this and is effective for a combination of Al compositions in the range of 0 ≦ x <0.4 and 0.5 <y ≦ 1. .

In this embodiment, the volume ratio of ammonia water to hydrogen peroxide water is 3 and the pH is 8.4. However, the present invention is not limited to this, and as shown in FIG. , Volume ratio 1 to 5, pH 8.2 to 8.5 (25
In the range of (° C.), suitable selective etching similar to the above can be performed.

Example 4 In this example, an expensive means such as dry etching is used to measure the in-plane distribution of the epitaxially grown GaAs thin film grown on the semiconductor substrate by various epitaxial growth methods. Instead, a method of performing the selective etching, which is the inexpensive wet process described above, will be described.

The sample used in the method for measuring the film thickness distribution of the GaAs epitaxially grown thin film of this embodiment is shown in FIG.
It has a structure like, and the upper layer side is 5000 Å (0.
5 μm) thick GaAs layer, lower layer side is 1000 Å
AlGa with a thickness of (0.1 μm) and an Al composition y of 0.2
It is an As layer. As the growth method, MOCVD (metal organic chemical vapor deposition) method was used. A positive resist (manufactured by Fuji Hunt Electronics Co., Ltd .: HPR-118) was added to this sample.
2) was applied, and a grid pattern as shown in FIG. 6 was formed by exposing and developing. Ammonia water (standard solution) 1 against hydrogen peroxide solution (30% standard solution) 40
Was mixed and diluted to 50 times with pure water.
A solution obtained by adding 4% by volume of an aqueous solution of 0.2 mol / l EDTA (Na) ₂ (disodium salt of ethylenediaminetetraacetic acid) was used. The pH value of this solution is 7.
It was 5. The etching time was 10 minutes, and the temperature was controlled at 25 ° C. while applying appropriate vibration. Then, the resist was removed by ultrasonic cleaning in an organic solvent, and the resulting step difference was measured with a step difference measuring device. The film thickness distribution obtained by this is shown in FIG.
The results were exactly the same as those obtained with E. That is, by the selective etching which is an inexpensive wet process,
It was proved that it is possible to measure the film thickness distribution of the epitaxially grown thin film with extremely high accuracy.

In the present embodiment, the upper layer side is GaAs and the lower layer side is AlGaAs having an Al composition y of 0.2. However, the present invention is not limited to this, and etching is performed as shown above. By changing the composition of the liquid, any combination of Al compositions (x, y: where 0 ≦ x <
Al _x Ga _1-x A with 1 and 0 <y ≦ 1 and x <y)
s / Al _y Ga relative to _1-y As the laminated structure, the upper layer side A
It can be applied to the measurement of the film thickness distribution of the l _x Ga _1-x As layer.

The method of growing an epitaxial thin film is also M
Not limited to OCVD, MBE, LPE, VP
It can be applied to a thin film grown by E or the like.

Further, the lithography pattern is not limited to the lattice pattern, and any pattern can be used as long as it is a pattern uniformly distributed in the plane.

[0040]

As described above, according to the present invention,
It is possible to perform selective etching on AlGaAs having an arbitrary Al composition by an easy method without making use of expensive process technology, and to provide a simple and accurate thin film thickness distribution measuring means.

[Brief description of drawings]

FIG. 1 Al _x Ga _1-x As / Al which is the object of the present invention
It is a conceptual diagram of _y Ga _1-y As multilayer structure.

FIG. 2 is a summary view of etching characteristics of AlGaAs having various Al compositions in the etching solution system used in the present invention.

FIG. 3 is a pH value of a liquid having a volume ratio of ammonia water and hydrogen peroxide water (hydrogen peroxide water / ammonia water) of 3 in the etching liquid system used in the present invention and AlGaAs having an Al composition of 0.35. FIG. 4 is a relationship diagram of an etching rate with respect to.

FIG. 4 is a relational diagram with etching time and etching amount in Example 1.

FIG. 5 is a diagram showing a range of an etching solution composition that enables selective etching suitable for the laminated structure of each example. The area of 1 indicates the case of the first embodiment, the area of 2 indicates the case of the second embodiment, and the area of 2 indicates the case of the third embodiment.

FIG. 6 is a diagram of a pattern for measuring the in-plane distribution of the film thickness of the epitaxially grown thin film used in Example 4.

7 is an epitaxially grown Ga obtained in Example 4. FIG.
It is a figure of the measurement result of the in-plane distribution of the film thickness of an As layer. The measurement is from the OF (orientation flat) position in the opposite direction of OF, that is,
The steps are sequentially performed in the [011] direction in the (100) plane.

[Explanation of symbols]

1 Al _x Ga _1-x As layer 2 Al _y Ga _1-y As layer 3 Substrate or epitaxial wafer

Claims (5)

(57) [Claims] 1. The upper layer is an Al _x Ga _1-x As crystal layer (0 ≦
x <1), and the lower layer is an Al _y Ga _1-y As crystal layer (0
≦ y ≦ 1, where x <y), a step of preparing a substrate on which an epitaxially grown crystal having a laminated structure is formed, and a mixture of ammonia water and hydrogen peroxide are added to ethylenediaminetetraacetic acid as a pH buffer. Is added to prepare an etching solution in which the pH value of the solution is adjusted to an appropriate value within the range of 6 to 9, and the upper layer of Al _x Ga, which is the upper layer, is prepared by using the etching solution.
_And a step of etching a _1-x As crystal layer, the selective etching method of an epitaxial crystal laminated structure, comprising: 2. The combination of Al compositions of the upper layer and the lower layer is (x = 0, 0.15 <y ≦ 1), and the standard ammonia water and the standard ammonia water 1 are used as the etching solution. Then, a standard hydrogen peroxide solution having a volume ratio of 10 or more is mixed, and the ethylenediaminetetraacetic acid, which is a pH buffer, is further added to adjust the pH value of the solution to a range of 6.5 to 8.5. The method for selectively etching an epitaxial crystal laminated structure according to claim 1, wherein the method is used. 3. The combination of Al compositions of the upper layer and the lower layer is (0 ≦ x <0.2, 0.3 <y ≦ 1), and the standard ammonia water and the standard ammonia are used as the etching solution. A standard hydrogen peroxide solution having a volume ratio of 1 or more and 5 or less is mixed with 1 of water, and ethylenediaminetetraacetic acid as a pH buffer is further added to adjust the pH value of the solution from 7.7 to 7.
The selective etching method for an epitaxial crystal laminated structure according to claim 1, wherein a liquid adjusted to a range of 9 is used. 4. The combination of Al composition of the upper layer and the lower layer is (0 ≦ x <0.4, 0.5 <y ≦ 1), and the standard ammonia water and the standard ammonia are used as the etching solution. A standard hydrogen peroxide solution having a volume ratio of 1 or more and 5 or less is mixed with 1 of water, and ethylenediaminetetraacetic acid, which is a pH buffer, is further added to adjust the pH value of the solution from 8.2 to 8.
The selective etching method for an epitaxial crystal laminated structure according to claim 1, wherein a liquid adjusted to a range of 5 is used. 5. The upper layer is an Al _x Ga _1-x As crystal layer (0 ≦
x <1), and the lower layer is an Al _y Ga _1-y As crystal layer (0
≦ y ≦ 1, where x <y), a step of preparing a substrate on which an epitaxially grown crystal having a laminated structure is formed, and a mixture of ammonia water and hydrogen peroxide are added to ethylenediaminetetraacetic acid as a pH buffer. To prepare an etching solution in which the pH value of the solution is adjusted to an appropriate value in the range of 6 to 9, and using the etching solution, the upper layer of Al _x Ga
Etching a portion of the _1-x As crystal layer until the surface of the lower layer is exposed, and measuring the step difference between the etched portion and the non-etched portion to measure the film thickness on the upper layer side; A method for measuring the film thickness of an epitaxially grown laminated thin film, which is provided.