JPH04370948A - Evaluation of semiconductor crystal dislocation - Google Patents

Abstract

PURPOSE:To enable an evaluation for semiconductor crystal dislocation to measure the dislocation accurately for II-VI semiconductor crystals. CONSTITUTION:Two CdZn substrates 4 and 6 are bonded by an epoxy adhesive to allow its epitaxial surfaces to face each other in evaluating the dislocation of the semiconductor crystal on the B surface which is formed of the II-VI semiconductors the group II of which is composed of Hg, Cd, or an element containing a small amount of Mn and Zn in them, and the group VI of which is composed of Te or an element containing a small amount of Se in Te. An pressure of 40g/cm<-2> is given vertically to the bonding surface. The etching surface is polished after annealing for three hours in a vacuum of 80 deg.C. The polished crystal is etched for 20 seconds at room temperature using an etching solution for defective evaluation prepared by mixing 49weight% hydrofluoric acid, 30weight% hydrogen peroxide water, and water in a cubic ration of 3:2:9. Subsequently, an etching is performed in a static state with the etching surface vertically held for 10 second at room temperature using an etching solution for defective evaluation prepared by mixing 70weight% nitric acid, 36weight% hydrochloric acid, water, bromine, and acetic acid in a cubic ratio of 60:25:90:0.1:5.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a group II-VI semiconductor in which group II is Hg, Cd or a small amount of Mn.
, Zn, and the VI group is composed of Te or an element containing a small amount of Se.

0002

[Prior Art] Among II-VI group semiconductors, group II is H
Group VI is composed of Te or a small amount of S.
No etching solution for defect evaluation that acts on the B-plane of a crystal composed of elements containing e has been published, except for the {111} B-plane. Etching solutions for defect evaluation that act on other surface orientations include the following. However, the notation of surface orientation followed the original paper as much as possible, and clearly incorrect notations in the original paper were corrected.

[0003] Etching solution developed by Rockwell Corporation (
US Patent No. 4,897,152. (1990)) is (110), (100), (111)A, (111)
B, acts on the (311) plane. I. Haehnert and M. Schenk etching solution (J.Crystal
Growth 101 (1990) 251)) is {1
10}, {111}A, {1 (bar) 1 (bar) 1 (bar)}B, acts on the {115} plane.

However, for CdTe or CdZnTe, it acts only on the {111}A plane. Etching solutions that act on the HgTe or HgCdTe {111}A surface are described in the literature (J. Phys. Suppl. C6 40 (1)
979) 151)), Parker etc.
h, Straghan etch, Polisar
1, Polisar 2, Quelch etc.
Etching solutions such as H are introduced.

[0005] The etching solution that acts on the CdTe (111) A side is Nakagawa etchant (Applied Physics Letters (Appl. Phys. Lett. 3).
4 (1979) 574)), and for the CdTe (111) B side, T. H. Myers et al.'s etching solution (J.Vac.Sci.Technol.Al
(1983) 1598)) has been published.

Among these etching solutions, the following two are considered to be the most reliable and standard for dislocation evaluation. First, II-
For VI group semiconductors, an etching solution called Polisar 2 is used to remove defects by mixing concentrated nitric acid, concentrated hydrochloric acid, water, bromine, and acetic acid in a volume ratio of 60:25:90:0.1:5. This is an etching solution for evaluation. For II-VI group semiconductors with a composition similar to CdTe, there is an etching solution called Nakagawa etchant, which is a mixture of hydrofluoric acid, hydrogen peroxide, and water in a volume ratio of 3:2:2 for defect evaluation. It is an etching solution.

Both of these etching solutions are {111}A
Acts on the surface. These etching conditions are based on Polis etching conditions.
In the case of ar 2, it is 20 to 30 seconds at room temperature, and in the case of Nakagawa etchant, it is 20 seconds at room temperature.

[0008]

[Problems to be Solved by the Invention] No etching solution for defect evaluation that acts on the B-plane has been reported except for the {111}B-plane. Among the previously reported etching solutions for defect evaluation, Rockwell's etching solution is {111}B.
As a result of experiments by the present inventor, it was found that etch pits caused by dislocations are formed by acting not only on the B-plane of the HgCdTe crystal with a high surface index, but observable etch pits are formed on the B-plane. Therefore, it is necessary to etch at least 10 μm, making it difficult to apply to thin film crystals, and the number of etch pits formed varies widely, making it a standard etching solution. There are drawbacks such as the inability to reliably correspond to the number of etch pits produced by Polisar 2. In addition, it is not possible to investigate the relationship with dislocations in the substrate or buffer layer, or the occurrence of dislocations during growth, only by evaluating from the surface.

When evaluating the {110} hexagonal plane of a B-plane thin film crystal, it is possible to evaluate defects in HgCdTe, but
Since there is no etching solution for evaluating defects on the dTe {110} plane, it is not possible to investigate the relationship with dislocations in the CdTe substrate or CdTe buffer layer.

[0010] Furthermore, the dislocation density of HgCdTe does not correspond to the dislocation density determined by Polisar 2, which is standardly used in evaluating the dislocation density of bulk crystals.

[0011] Furthermore, even if one attempts to evaluate a cross section other than the cleavage plane of a B-plane thin film crystal, surface sagging occurs during polishing.
It is not possible to accurately expose a predetermined surface in a micro region in an epitaxial cross section.

Next, when etching the {111}A surface using a standard etching solution under specified etching conditions, Po
Both lisar 2 and Nakagawa etchant have a pit diameter of 5.
Since the diameter is on the order of μm, it is impossible to measure dislocation distribution in a micro region. In addition, when evaluating dislocations in a crystal with a high dislocation density, the pits overlap, making it impossible to measure the dislocation density or dislocation distribution.

The present invention has been made in view of the above-mentioned conventional circumstances, and it is an object of the present invention to provide a method for evaluating dislocations in semiconductor crystals that can accurately measure dislocations.

[0014]

[Means for Solving the Problems] In order to achieve the above object, in the method for evaluating dislocations in semiconductor crystals according to the present invention, I
Among Group I-VI semiconductors, Group II is composed of Hg, Cd, or elements containing small amounts of Mn and Zn,
This is a method for evaluating dislocations in B-plane thin film semiconductor crystals, in which group VI is composed of elements containing Te or a small amount of Se, in which the surfaces of two thin film crystals are laminated together with an adhesive and pressed together. Etch pits caused by dislocations are formed by performing vacuum annealing, using a surface close to the cross section as an etching surface, polishing that surface, and then etching.

Furthermore, among the II-VI group semiconductors, H
g, on the {111}A plane of a semiconductor crystal with a composition close to that of Te, 70% by weight of nitric acid, 36% by weight of hydrochloric acid, water, bromine, and acetic acid were mixed in a volume ratio of 60:25:90:0. .1
Etching is performed using the etching solution for defect evaluation mixed in step 5 at room temperature for a predetermined period of time with the etched surface standing vertically and in a stationary state to form etch pits caused by dislocations.

Furthermore, among the II-VI group semiconductors, C
A defect created by mixing 49% by weight of hydrofluoric acid, 30% by weight of hydrogen peroxide, and water in a volume ratio of 3:2:9 on the {111}A plane of a semiconductor crystal with a composition similar to that of dTe. Etching is performed for a predetermined time at room temperature using an etchant for evaluation to form etch pits caused by dislocations.

[0017]

[Function] (1) According to the method of the present invention, the thickness of 2 μm is obtained by crimping.
Since the epitaxial surfaces are bonded together with an extremely thin film of adhesive, it is possible to level out the surfaces as accurately as bulk polishing. At this time, the same effect can be obtained even if the epitaxial surface and the bulk crystal are bonded together. By performing vacuum annealing in a crimped state, it is possible to reduce the thickness of the adhesive and expel any air bubbles remaining inside, making it possible to accurately polish the desired surface in the entire epitaxial cross section. In this way, by presenting an accurate surface over the entire cross section, it becomes possible to arbitrarily select a reliable etching solution that has a proven track record for dislocation evaluation to perform dislocation evaluation. Additionally, dislocations in the substrate, buffer layer, and epitaxial layer can be investigated simultaneously.

(2) {11 of crystals close to the composition of HgTe
1} Side A was treated with 70% by weight nitric acid, 36% by weight hydrochloric acid, water, bromine, and acetic acid in a volume ratio of 60:25:90:
When etching is performed at room temperature using an etching solution for defect evaluation mixed at a ratio of 0.1:5, bubbles begin to generate at the same time as the reaction between the crystal and the etching solution starts around 5 seconds later. Thereafter, etch pits due to dislocations begin to form, and approximately 10 seconds after the start of etching, almost all of the etch pits appear. The pit diameter at this point is 1μm
It is as follows. Even if etching is continued further, the pit diameter only increases and no new etch pits are generated. Therefore, by etching for about 10 seconds at room temperature, all etch pits due to dislocations appear, and the pit diameter can be suppressed to 1 μm or less. By etching under these conditions, it is possible to evaluate the dislocation distribution in a micro region of the {111}A plane of a crystal close to the composition of HgTe and the dislocations of a high dislocation density crystal.

[0019] Etching conditions also vary greatly depending on the presence or absence of stirring. In the case of artificial stirring, variations occur each time. Therefore, if the etching surface is held vertically and etching is performed in a static state, the bubbles generated by the reaction stroke the surface of the etching surface and agitation is performed, making it possible to perform etching under the same conditions every time.

(3) {11 of a crystal close to the composition of CdTe
1} When the A-plane is etched with Nakagawa etchant at room temperature, the reaction between the crystal and the etching solution starts immediately after the etching starts, and etch pits due to dislocations begin to form. It seems that almost all the etch pits have appeared 2 to 3 seconds after starting etching, and 10 seconds after starting, the pit diameter will be about 3 μm, and even if you continue etching, the pit diameter will only increase. No new etch pits are generated. If the etching time is less than 10 seconds, the error in the etching time will be large and the stirring state of the etching solution will also differ each time, making it impossible to perform etching with reproducibility.

Therefore, 49% by weight of hydrofluoric acid and 3
0% by weight hydrogen peroxide solution and water at a volume ratio of 3:2:9
When etching is carried out using the etching solution for defect evaluation mixed in the above, etch pits due to dislocations begin to form after 10 seconds of etching at room temperature, and within about 20 seconds from the start, all etch pits are aligned and the pit diameter is 1 μm. It can be kept below.

By etching under these conditions, H
It is possible to evaluate the dislocation distribution in a micro region of the {111}A plane of a crystal close to the composition of gTe and the dislocations of a high dislocation density crystal. However, if etching is performed in a stationary state, there will be no change in etching conditions when the etching surface is placed vertically or when the etching surface is placed horizontally.

[0023]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows Cd obtained by the method of the present invention.
This is an example of the dislocation distribution in the cross section of a CdTe buffer layer and a HgCdTe epilayer grown on a ZnTe (1 (bar) 1 (bar) 2 (bar)) B substrate.

In the figure, an HgCdTe epilayer 1 and an HgCdTe epilayer 1 are shown.
The HgCdTe epilayer 1 is bonded to the gCdTe epilayer 2 using an adhesive 3, and the HgCdTe epilayer 1 is grown directly on the CdZnTe substrate 4.
is grown on a CdZnTe substrate 6 via a CdTe buffer layer 5. HgCdTe epi layer 1
, 2 and the cross section of the CdTe buffer layer 5. Etch pits are observed in the cross section of the CdTe buffer layer 5. Etch pits are also formed on the CdZnTe substrates 4 and 6, but they are not visible in this photograph because their density is low.

The two crystals are cut in the orientation shown in FIG. 2, and then glued together using an epoxy adhesive so that the etched surfaces 7 are in the same direction and the epitaxial surfaces face each other. If the number of substrates to be laminated at this time is an even number, many crystals may be laminated at once with their epitaxial surfaces facing each other.

Next, a pressure of 40 g/cm 2 was applied perpendicular to the bonded surface to the bonded crystal, and annealing was performed at 80° C. in vacuum for 3 hours. After that, the etched surface and its back side were roughly cut to make it planar, and the etched surface was polished. For polishing, mechano-chemical polishing was performed after lapping with No. 3000 alumina powder. With the above operations (1 (bar) 1 (bar) 2 (
The (1 (bar) 1 (bar) 1) A cross section of the (1 (bar) 1 (bar) 1) A plane of the (1 (bar) 1 (bar) 1) A plane of the (1 (bar) 1 (bar) 1) (bar)) B crystal can be accurately displayed on both the substrate and the epitaxial layer, and the (1 (bar) 1 (bar) 1) A mirror surface is free from damage. A polished surface was obtained.

Next, the crystal was bonded to a glass substrate with solid wax with the polished surface facing upward, thereby making it possible to better handle the crystal and at the same time accurately setting the angle of the etched surface during etching. Dislocation evaluation can then be performed by immersing each glass substrate in a predetermined etching solution.

[0029] The polished crystal was treated with an etching solution for defect evaluation, which is a mixture of 49% by weight of hydrofluoric acid, 30% by weight of hydrogen peroxide, and water in a volume ratio of 3:2:9. Etching was performed for 20 seconds at room temperature. As a result, Cd
Dislocation density of ZnTe substrate 4: 8.8 x 104 cm-2, C
A dislocation density of dZnTe substrate 6 of 2.6×10 5 cm −2 was obtained. In addition, the dislocation density of the CdTe buffer layer was too large to make accurate measurements;
It was found to be on the order of m-2.

Next, 70% by weight of nitric acid, 36% by weight of hydrochloric acid, water, bromine, and acetic acid were mixed in a volume ratio of 60:25:
Etching was performed at room temperature for 10 seconds using an etching solution for defect evaluation mixed at a ratio of 90:0.1:5 with the etched surface standing vertically and in a stationary state. As a result, the dislocation density of the HgCdTe epilayer 1 was 2.2×107 cm−2, and the HgCdTe
A dislocation density of e-epi layer 2 of 3.0×10 8 cm −2 was obtained.

[0031]

Effects of the Invention By the method of the present invention, among II-VI group semiconductors, group II is composed of Hg, Cd, or elements containing small amounts of Mn and Zn, and group VI is composed of Te or a small amount of Se. B is composed of elements containing
Dislocation density of plane thin film crystal or {111}A plane crystal,
and its dislocation distribution can be measured accurately. Furthermore, since a standard etching solution for defect evaluation can be used, the dislocation density obtained by this method is a reliable value that can be compared with values reported for bulk crystals and the like.

[Brief explanation of drawings]

FIG. 1 is a photograph of an example of a dislocation distribution in a cross section of a substrate, a buffer layer, and an epitaxial layer obtained by the method of the present invention.

FIG. 2 is an explanatory diagram of cutting directions of crystals.

[Explanation of symbols]

1 HgCdTe epilayer 2 HgCdTe epilayer 3. Adhesive 4 CdZnTe substrate 5 CdTe buffer layer 6 CdZnTe substrate 7 Etched surface

Claims (3)

[Claims] [Claim 1] Among II-VI group semiconductors, group II is composed of Hg, Cd, or an element containing a small amount of Mn or Zn, and group VI is composed of Te or an element containing a small amount of Se. This is a method for evaluating dislocations in B-plane thin film semiconductor crystals, in which the surfaces of two thin film crystals are laminated and pressed together with an adhesive and then vacuum annealed.
A method for evaluating dislocations in a semiconductor crystal, characterized in that a surface close to the cross section is set as an etching surface, and the surface is polished and then etched to form etch pits caused by dislocations. 2. Among the II-VI group semiconductors, Hg
, 70% by weight of nitric acid, 36% by weight of hydrochloric acid, water,
Bromine and acetic acid in a volume ratio of 60:25:90:0.1:
2. Etch pits caused by dislocations are formed by performing etching using the etching solution for defect evaluation mixed in step 5 at room temperature for a predetermined period of time with the etched surface standing vertically and in a stationary state. Dislocation evaluation method for semiconductor crystals. 3. Among the II-VI group semiconductors, Cd
A defect created by mixing 49% by weight of hydrofluoric acid, 30% by weight of hydrogen peroxide, and water in a volume ratio of 3:2:9 on the {111}A plane of a semiconductor crystal with a composition close to that of Te. 2. The method for evaluating dislocations in a semiconductor crystal according to claim 1, wherein etching is performed for a predetermined time at room temperature using an etchant for evaluation to form etch pits caused by dislocations.