JPH10312988A - Etching method for compound semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform etching with high uniformity while eliminating the etching residue by etching InGaAs using a specified mixed water solution and then performing an additional etching at a moment of time when the etching rate is decreased. SOLUTION: InGaAs 12 deposited on InAlAs 11 can not be etched uniformly because the etching rate is varied significantly at the interface of InAlAs 11/ InGaAs 12. In order to solve the problem, the InGaAs 12 is etched using a mixed liquid of citric acid/hydrogen peroxide water/water. At a moment of time when the etching rate is decreased to 100-200 Å/min, additional etching is performed for at least 10 min. According to the method, the InGaAs 12 can be etched uniformly and surely.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method for etching a compound semiconductor film, and more particularly to a method for etching InGaAs / InAlA.
It relates to the selective etching of the s film.

[0002]

2. Description of the Related Art A light receiving device (HPT: het) as an O / E (optical-electrical) conversion element for a solar cell or optical communication.
ro-bicolor-phototransisto
InP compound semiconductors are used for r, PD (photodiode) and the like. An InGaAs film having good lattice matching with InP and a small band gap is used for the contact layer and the active layer.

FIG. 3 shows an example of a laminated structure used for a solar cell. In this figure, 1 is n ⁺ -InP substrate, 2 is formed on the n ⁺ -InP substrate 1 n ⁺ -
InP BSF layer (0.2 μm, 1 × 10 ¹⁸ cm ⁻³ ),
3 is an n-InP base layer (2.5 μm, 1 × 10 ¹⁷ cm ⁻³ ) formed on the BSF layer 2, and 4 is a p ⁺ -InP emitter layer (0 .
1 μm, 1 × 10 ¹⁸ cm ⁻³ ), 5 is a p ⁺ -InAlAs window layer (0.1 μm, 1 × 10 ¹⁸ cm ⁻³ ) formed on the InP emitter layer 4, 6 is on the window layer 5 2 shows a p ⁺ -InGaAs contact layer (0.3 μm, 1 × 10 ¹⁹ cm ⁻³ ) formed in FIG.

[0004]

As shown in FIG.
InGaAs formed on the nAlAs window layer 5
In the etching of the contact layer 6, citric acid / hydrogen peroxide (31%) / water is used as an etchant having good selectivity to the InAlAs window layer 5. For example, in a citric acid / hydrogen peroxide / water mixed solution (= 50 g / 50 cc / 50 cc), In alone
The etching rates of GaAs and InAlAs were about 1700 ° / min (min) and 60 ° / min, respectively, and the selectivity was 28.

[0005] However, in the case of stacking, there is a case where the etching of the InGaAs contact layer 6 formed on the InAlAs window layer 5 cannot be made uniform despite the selectivity. The present invention eliminates the above problems,
It is an object of the present invention to provide a method for etching a compound semiconductor film which can be etched uniformly with no etching residue.

[0006]

According to the present invention, in order to achieve the above object, [1] In etching an InGaAs / InAlAs film, a mixed solution of citric acid / hydrogen peroxide / water is used.
When the nGaAs film is etched and the etching rate becomes as low as 100 ° to 200 ° / min, additional etching is performed for at least 10 minutes or more.

[2] In the etching of the InGaAs / InAlAs film, the InGaAs film is etched using a mixed solution of citric acid / hydrogen peroxide / water, and when the etching rate is reduced to 100 ° -200 ° / min, The interlayer in which Al is diffused is etched using a phosphoric acid or a sulfuric acid / hydrogen peroxide aqueous etchant.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a cross-sectional view showing an InGaAs film formed on an InAlAs film (layer) to be etched according to the present invention. InAlAs
The problem that the etching of the InGaAs film 12 formed on the film 11 cannot be made uniform is that the InAlAs film 11 /
It is conceivable that the etching rate at the interface of the InGaAs film 12 changes greatly (the etching rate of the InGaAs film at the interface becomes smaller).

FIG. 2 is a characteristic diagram showing the relationship between the etching time (minute) and the etching depth (分) when an InGaAs film is formed on the InAlAs film. Where the curve a
Indicates the etching depth with respect to the etching time when an InGaAs film is formed 1.5 μm on an InAlAs film (1.1 μm) and etched with a mixed solution of citric acid / hydrogen peroxide / water, Curve b shows InGa
The etching depth with respect to the etching time when an As film is formed as thin as 0.3 μm and is etched with a mixed solution of citric acid / hydrogen peroxide / water is shown.

Here, a mixed solution of citric acid / hydrogen peroxide / water = 50 g / 50 cc / 50 cc = 83.3 cc / 5
0cc = 1.67, 30 ° C. As is apparent from FIG. 2, the etching rate at the interface between the InGaAs film and the InAlAs film is low. As is clear from the curve a, I at the interface of the InGaAs film / InAlAs film
It took 10 minutes to etch the nGaAs layer at 500 °, and this phenomenon caused etching instability that the InGaAs layer could not be completely removed.

Incidentally, the decrease in the etching rate is caused by I
The nGaAs film is formed from the remaining film thickness of 1000 ° to 500 °, and the etching rate at that time is 200 ° to 1 °.
00Å / min. Also, as shown by curve b,
Even if the InGaAs film is as thin as 0.3 μm on the InAlAs film (0.1 μm), it should be etched in 2 minutes according to the initial etching rate, but it requires a long time, here 13 minutes etching time. is there.

Although the mechanism of this phenomenon has not been elucidated yet, when the InGaAs film is formed, Al diffuses from the interface with the underlayer to form an interlayer into which Al is diffused. Therefore, when etching the InGaAs film formed on the InAlAs film, a single In
The citric acid / hydrogen peroxide solution /
Etching is performed for a required time, which will be etched with a water mixed solution, and then, etching is further performed for 10 minutes or more. Alternatively, the interlayer into which Al has been diffused is etched using a phosphoric acid or sulfuric acid / hydrogen peroxide-based etchant, that is, so-called slight etching is performed.

For example, if the thickness of the InGaAs film is 3000
場合 If a film is formed, the etching rate of
Since it is about 1700 ° / min, it should be possible to perform etching in 2 minutes. However, since the etching rate at the interface becomes smaller (<100 °), an additional 1
Etching for 0 minutes or more, or a new phosphoric acid or sulfuric acid / hydrogen peroxide based etchant (InGa
The problem can be avoided by performing the slight etching using an etchant capable of etching both As / InAlAs films.

As described above, according to the above-mentioned embodiment, InGaAs is formed using a mixed solution of citric acid / hydrogen peroxide / water.
/ InAlAs film etching, InGaAs
The etching rate at which the film thickness is etched is 100
At the time when it becomes as small as {-200} / min, at least 1
Perform additional etching for 0 minutes or more, or add phosphoric acid or sulfuric acid /
Slight etching is performed using a hydrogen peroxide aqueous etchant, and two-step etching is performed to obtain In.
The GaAs film can be uniformly and reliably etched.

It should be noted that the present invention is not limited to the above embodiment, and various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0016]

As described above in detail, according to the present invention, the etching rate at which the thickness of the InGaAs layer is etched using a mixed solution of citric acid / hydrogen peroxide / water is 100 ° to 200 °. / Min, perform additional etching for at least 10 minutes or
Slight etching is performed using a phosphoric acid or sulfuric acid / hydrogen peroxide aqueous etchant, and by performing the two-step etching, the InGaAs layer can be etched with high uniformity without etching residues in the InGaAs layer.

[Brief description of the drawings]

FIG. 1 shows InAl which is an object of an etching method of the present invention.
FIG. 3 is a cross-sectional view of an InGaAs film formed on an As film.

FIG. 2 shows an InAlAs film according to an embodiment of the present invention;
FIG. 4 is a diagram showing the etching depth versus etching time when a GaAs film is formed to a thickness of 1.5 μm and etched with a mixed solution of citric acid / hydrogen peroxide / water.

FIG. 3 is a diagram showing an example of a laminated structure used for a solar cell.

[Explanation of symbols]

 11 InAlAs film 12 InGaAs film

Claims (2)

[Claims] In the etching of an InGaAs / InAlAs film, (a) the etching of the InGaAs film is performed using a mixed solution of citric acid / hydrogen peroxide / water, and when the etching rate is reduced to 100 ° -200 ° / min. And (b) performing additional etching for at least 10 minutes or more. 2. In the etching of the InGaAs / InAlAs film, (a) the InGaAs film is etched using a mixed solution of citric acid / hydrogen peroxide / water, and when the etching rate is reduced to 100 ° -200 ° / min. (B) a method of etching a compound semiconductor film, comprising etching an interlayer in which Al is diffused using a phosphoric acid or a sulfuric acid / hydrogen peroxide aqueous etchant.