JP2626715B2 - Etching solution for CdTe crystal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal evaluation technique,
Particularly, the present invention relates to an etching solution suitable for use in evaluating CdTe crystals (compound semiconductor crystals of cadmium and tellurium).

[0002]

2. Description of the Related Art CdTe crystals are used for substrates for epitaxial growth of infrared detecting elements, solar cells, substrates of radiation detecting elements, and the like. In many cases, the characteristics of these devices depend on the defects of the crystal serving as the substrate. By examining the etch pits representing the crystal defects, the crystal can be evaluated and the characteristics of the device can be predicted. Conventionally, as an etchant for evaluating a CdTe crystal, for example, 85% by weight of lactic acid, 30% by weight of nitric acid, and 50% by weight of hydrofluoric acid have a volume ratio of 25: (5-1).
2): An etching solution mixed in (1-6) has been proposed (JP-A-63-62237).

[0003]

However, in the above-mentioned lactic acid-nitric acid-hydrofluoric acid type etching solution,
Although etch pits appear on the (111) B surface,
The (111) A plane, the (100) plane, and the (110) plane have a disadvantage that etch pits hardly appear. Also,
Etch pits appearing on the (111) B surface cannot be observed unless the magnification is 200 to 500 times using a microscope. When observing with a microscope at such a high magnification, there is a disadvantage that it takes time to move the visual field, and the number of observation points per wafer increases, which increases the time required for evaluation. In particular, in recent years, crystals tend to have a large diameter in order to increase the yield, so that the higher the magnification of observation, the longer the time required for evaluation.

The present invention has been made in view of the above-mentioned problems.
An object of the present invention is to provide an etchant for evaluating a CdTe crystal in which etch pits appear on a crystal plane other than the B-plane and the etch pits can be observed at a low magnification.

[0005]

In order to achieve the above-mentioned object, the present invention relates to a method for producing 85% by weight of lactic acid, 30% by weight of hydrogen peroxide and 36% by weight of hydrochloric acid in a volume ratio of 25:
(5-25): An etching solution for CdTe crystal characterized by being mixed in (1-12).
The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0006]

When a CdTe crystal is etched using an etching solution having the above composition, the (111) B plane and the (111) B
A triangular etch pit that can be observed at a low magnification appears on the A-plane, and a rectangular etch pit that can be observed at a low magnification coincides with the cleavage direction appears on the (100) plane. In addition, the orientation of the plane can be determined by looking at the direction of the etch pit.
Although high magnification is required, etch pits also appear on the (110) plane, so that crystal evaluation can be performed more strictly. Further, according to the etchant having the above composition, mesa etching and reverse mesa etching can be performed, so that the plane orientation can be determined without using X-rays and can be used as an etchant at the time of device fabrication.

[0007]

EXAMPLE 85% by weight of lactic acid, 30% by weight of hydrogen peroxide and 36% by weight of hydrochloric acid were mixed in a volume ratio of 25: (5-2).
5): A mixed solution mixed at a ratio of (1 to 12) is prepared. The CdTe single crystal from which the surface deteriorated layer has been removed is immersed in the mixture, and the mixture is stirred. After about 2 minutes, the above C
The dTe single crystal is taken out of the mixed solution, washed with water and dried. By the above method, the (111) B surface and the (100)
When a CdTe single crystal having a plane was etched, (1
11) Etch pits as shown in FIG. 1 appeared on plane B, and etch pits as shown in FIG. 2 appeared on (100) plane. A portion forming a triangle in FIG. 1 and a portion forming a rectangle in FIG. 2 are etch pits.

Further, when an etching experiment was conducted by changing the volume ratio of the mixed solution having the above composition, the volume ratio was found to be 2%.
5: (5 to 25): Observable etch pits appeared in the range of (1 to 12). However, if the ratio of hydrochloric acid in the mixture was higher than the above range, the etch pit could not be determined. The mechanism of etching with the mixture of the above composition is that the crystal surface is oxidized with hydrogen peroxide in the mixture and the generated oxide is removed with hydrochloric acid.
If the ratio of hydrochloric acid is more than the above range, the etching is performed to the point where there is no defect, and the etch pits are not clear. On the other hand, if the proportion of hydrogen peroxide in the mixture was higher than the above range, the crystal surface was blackened. This is because the oxidizing power of hydrogen peroxide is too strong, a thick oxide film is formed, and the removal amount by hydrochloric acid is insufficient. On the other hand, if the proportion of hydrogen peroxide in the mixed solution is smaller than the above range, no oxide film is formed, and if the proportion of hydrochloric acid is smaller than the above range, the etching power is weak, and neither etch pit appears.

In the above embodiment, 85% by weight of lactic acid, 30% by weight of hydrogen peroxide, and 36% by weight of hydrochloric acid were mixed to form an etching solution. However, other concentrations of lactic acid and peroxide were used. Of course, hydrogen and hydrochloric acid may be mixed to form an etching solution. In that case, the volume ratio of the usable liquid mixture is 21.25: (1.5 to
7.5): The range of (0.36 to 4.32) is preferably used as a reference. For example, when 50% by weight of hydrogen peroxide is used instead of 30% by weight of hydrogen peroxide (lactic acid is 85%).
Weight, hydrochloric acid is 36% by weight), the volume ratio is 25: (5-
25): What is mixed in the range of (1 to 12) may be used as an etching solution.

[0010]

As described above, the present invention has a
Weight% lactic acid, 30 weight% hydrogen peroxide and 36 weight% hydrochloric acid in a volume ratio of 25: (5-25) :( 1-1
Since the mixture obtained in 2) was used as an etchant for a CdTe crystal, etching the CdTe crystal using an etchant of this composition yielded a (111) B plane and a (111) B plane.
A triangular etch pit that can be observed at a low magnification appears on the A-plane, and a rectangular etch pit that can be observed at a low magnification coincides with the cleavage direction appears on the (100) plane. In addition, the orientation of the plane can be determined by looking at the direction of the etch pit.
Further, although high magnification is required, since etch pits also appear on the (110) plane, crystal evaluation can be performed more strictly. Further, according to the etching solution having the above composition, mesa etching and reverse mesa etching can be performed, so that the plane orientation can be determined without using X-rays.
There is an effect that it can be used also as an etchant at the time of device creation.

[Brief description of the drawings]

FIG. 1 shows CdTe using an etching solution according to the present invention.
It is a figure which shows the etch pit which appears on a (111) B plane when a single crystal is etched.

FIG. 2 shows CdTe using an etching solution according to the present invention.
It is a figure which shows the etch pit which appears on a (100) plane when a single crystal is etched.

Claims (1)

(57) [Claims] 1. A mixture of 85% by weight of lactic acid, 30% by weight of hydrogen peroxide and 36% by weight of hydrochloric acid in a volume ratio of 25: (5
~ 25): C characterized by being mixed in (1-12)
Etching solution for dTe crystal.