KR100415366B1 - A Method for Surface Cleaning of II-VI Group Compound Semiconductor Crystal - Google Patents

Abstract

The present invention is to provide a method for cleaning the surface of a group II-VI compound semiconductor crystal, which is not deteriorated before and after etching, and is excellent in specular cleanliness, and suitable for epitaxial growth. In an aqueous solution in which sulfuric acid was mixed at a capacity ratio of 1 to 10 with respect to water 1, an etching solution obtained by saturating potassium dichromate was used to etch a II-VI compound semiconductor crystal in a temperature range of 10 to 80 ° C. Surface of group II-VI compound semiconductor crystals washed with water, methanol and isopropyl alcohol at a temperature of 10 ° C. or higher and below a boiling point, followed by ultrasonic cleaning or distillation with dichloromethane, trichloroethylene and acetone. It is a cleaning method.

Description

A method for surface cleaning of II-VI group compound semiconductor crystal

The present invention relates to a method for surface cleaning of II-VI compound semiconductor crystals such as ZnSe, ZnSSe, ZnS, ZnMgSe, ZnMgSSe, ZnTe.

Conventionally, ZnSe crystals are etched using NaOH aqueous solution or NH ₄ OH / H ₂ O ₂ aqueous solution or the like or etched using a saturated sulfuric acid solution of potassium dichromate at 90 ° C., and then treated with carbon disulfide to crystallize the crystal surface. Cleansing has been reported (see J. Crystal Growth, 86 (1988) pp. 324). After etching the ZnSe crystals with a bromine / methanol solution, ultrasonic cleaning in trichloroethylene (see Japanese Patent Application Laid-Open No. 59-18200), and etching the ZnSe crystals with a solution consisting of sulfuric acid / hydrogen peroxide / water, followed by carbon disulfide The removal of Se on the crystal surface has been reported (see Japanese Patent Application Laid-Open No. 5-109694).

However, in the above-described surface purification method, the crystal surface is rough, and irregularities are generated, Se is precipitated, and red is markedly red, pits are generated due to crystal defects, and impurities such as Na in the etching solution remain clean. A flat mirror surface could not be obtained. Therefore, it could not be etched deep enough to remove a process deterioration layer. As a result, it was impossible to grow a high quality epitaxial thin film on the crystal obtained by the above-mentioned surface purification method.

Therefore, the present invention solves the above problems, the surface smoothness of the II-VI compound semiconductor crystal does not deteriorate before and after etching, is excellent in the mirror surface cleanliness, suitable for epitaxial growth, etc. II-VI compound semiconductor crystal It is to provide a surface cleaning method of.

BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows the pattern of the crystal surface state after an etching process.

The present invention has made it possible to solve the above problems by combining an etching step using a specific etching solution and a specific post-treatment step. The configuration of the present invention is as follows.

(1) 10 to 80 using an etching solution obtained by saturating potassium dichromate in an aqueous solution in which sulfuric acid is mixed at a capacity ratio of 1 to 10 with respect to water 1, preferably at a capacity ratio of 3 to 7 with respect to water 1. A method for cleaning the surface of a II-VI compound semiconductor crystal, characterized by etching the II-VI compound semiconductor crystal in a temperature range of < RTI ID = 0.0 >

(2) After the treatment by the surface cleaning method described in (1) above, the etching solution is removed by washing with water at a temperature of 10 ° C or higher and a boiling point, preferably 20 to 50 ° C, to precipitate the Group VI element. Surface cleaning method of a II-VI compound semiconductor crystal, characterized by suppressing the

(3) A group II-VI compound semiconductor crystal characterized by removing the etching solution and suppressing the precipitation of group VI elements by treating with the surface cleaning method described in (1) above and then washing with methanol or isopropyl alcohol. Surface cleaning method.

(4) After being treated by the surface cleaning method described in any one of (2) to (3), a small amount of precipitated on the crystal surface is subjected to ultrasonic cleaning or boiling treatment in dichloromethane or trichloroethylene. A method for surface cleaning of a II-VI compound semiconductor crystal, characterized by removing the Group VI element.

(5) During the ultrasonic cleaning or boiling process of dichloromethane or trichloroethylene, by providing a process of ultrasonic washing or boiling process of acetone, a Group VI element deposited in trace amount on the crystal surface is removed. The surface cleaning method of group II-VI compound semiconductor crystal | crystallization as described in (4).

(6) VI which precipitated in trace amount on the crystal surface by heat-processing in the temperature range of 200 degreeC or more, Preferably it is 200-350 degreeC after processing by the surface cleaning method as described in said (2) or (3). A method for surface cleaning of a II-VI compound semiconductor crystal, characterized by removing a group element.

(7) After the treatment by the surface cleaning method described in (2) or (3) above, the Group VI element precipitated in a small amount on the crystal surface is removed by immersion treatment in a solution containing carbon disulfide and / or carbon tetrachloride. A method of surface cleaning of a II-VI compound semiconductor crystal, characterized by the above-mentioned.

(8) The crystal surface is treated by the surface cleaning method described in (2) or (3) above, followed by immersion in a solution containing hydrochloric acid, a solution containing ammonium hydroxide and methanol, or a solution containing hydrofluoric acid. A method for cleaning the surface of a II-VI compound semiconductor crystal, characterized in that the oxide of the compound is removed.

(9) After the treatment by the surface cleaning method according to any one of (4) to (7), immersion treatment in a solution containing hydrochloric acid or a solution containing ammonium hydroxide and methanol or a solution containing hydrofluoric acid. To remove an oxide on the crystal surface, thereby cleaning the surface of the II-VI compound semiconductor crystal.

According to the present invention, an etching solution obtained by saturating potassium dichromate in an aqueous solution in which sulfuric acid is mixed at a capacity ratio of 1 to 10 with respect to water 1 and preferably at a capacity ratio of 3 to 7 with respect to water 1 is used. It has been found that by etching the II-VI compound semiconductor crystals in the temperature range of 80 ° C, preferably in the range of 20 to 50 ° C, it is effective to reproduce the crystal surface in the mirror plane state flatly.

When the capacity ratio of sulfuric acid to water is less than 1, rough pits of a mountain-like surface are generated on the mirror surface of the crystal surface, and when the capacity ratio is more than 10, precipitation of group VI elements is severe on the crystal surface, and predetermined surface cleaning is performed. Cannot be done.

In addition, even when the above-mentioned mixed aqueous solution of water and sulfuric acid is used, if the potassium dichromate is an unsaturated etching solution, rough pits of a mountain-like surface are generated on the crystal surface, and therefore it is necessary to use a saturated solution of potassium dichromate.

In addition, the said etching process can be acquired by performing in the temperature range of 10-80 degreeC, Preferably it is 20-50 degreeC. When etching is performed at a temperature lower than 10 ° C, rough pit of a mountain-shaped surface is generated on the crystal surface, and when it exceeds 80 ° C, precipitation of group VI elements becomes severe on the crystal surface, and the above-mentioned (2) to (8) Even by the method, the Group VI element cannot be sufficiently removed.

On the other hand, when the II-VI compound semiconductor crystal is subjected to the etching treatment described above, the crystal surface can be obtained in the mirror surface state as flat as described above, but the crystal surface edge part and the like may be somewhat reddish. When this reddening was examined in detail, it observed during the washing | cleaning after completion | finish of an etching process. It is considered that sulfuric acid in the etching solution remains on the crystal surface and dissolves the Group II elements on the crystal surface, resulting in residual Group VI elements and reddening.

Therefore, the present invention, after performing the above etching treatment, (1) to the crystal surface by washing with water at a temperature of 10 ℃ or more boiling point, preferably 20 to 50 ℃ ℃, or ② with methanol or isopropyl alcohol. It is preferable to suppress precipitation of a group element.

In addition, when the treatment according to the method ① or ② above fails to sufficiently suppress the precipitation of group VI elements on the crystal surface, ultrasonic cleaning or self-cleaning is carried out again in dichloromethane, trichloroethylene and / or acetone. , ④ by heat treatment in an inert gas at a temperature of at least 200 ° C., preferably in the range of 200 to 350 ° C., or by immersion in a solution containing carbon disulfide and / or carbon tetrachloride. It is preferable to remove group VI elements and to make stoichiometric ratio of group II element / group VI element.

Furthermore, after treatment by the method of the above ③ to ⑤, it is immersed in the solution containing (6) hydrochloric acid, the solution containing ammonium hydroxide and methanol, or the solution containing hydrofluoric acid, and the group II element and / or VI of a crystal surface. It is preferable to remove oxide of a group element.

<Example>

<Example 1>

The cleansing test of the surface of the ZnSe single crystal substrate was done.

The etching process was immersed in the etching liquid which consists of potassium dichromate / sulfuric acid / water which has a composition shown in Table 1, and was etched at 25 degreeC for 10 minutes.

Condition Water: sulfuric acid Etching temperature Potassium Dichromate Concentration Surface condition (One) 1: 2 25 ℃ saturation Surface B (2) 1: 2 25 ℃ Desaturation Surface A (3) 1: 5 25 ℃ saturation Surface B (4) 1: 5 25 ℃ Desaturation Surface A (5) 1: 9 25 ℃ saturation Surface B (6) 1: 9 25 ℃ Desaturation Surface A (7) 1: 0.7 25 ℃ saturation Surface A (8) 1: 0.7 25 ℃ Desaturation Surface A (9) 1: 12 25 ℃ saturation Surface C 10 1: 12 25 ℃ Desaturation Surface C or A

The crystal surface after the etching treatment was observed using a Normalsky microscope, and it was found to be roughly divided into the following three types of patterns (see FIG. 1).

Surface (A): The rough surface of a mirror surface or a mountain range shape generate | occur | produced.

Surface (B): A minute pit occurred, but it is a mirror surface and there is no roughness on the base.

Surface (C): A large amount of Se precipitated on the surface. (This Se cannot be removed by the treatment of Examples 2 and 3.)

As shown in Table 1, by using an etching solution in which potassium dichromate is saturated in a mixed aqueous solution in which the ratio of sulfuric acid to water is in the range of 1: 1 to 10, a flat and mirror surface crystal surface corresponding to surface B is prepared. Could be reproduced. If the ratio of sulfuric acid to water is out of the above range, or potassium dichromate becomes unsaturated, the crystal surface becomes A or C, and a predetermined crystal surface cannot be obtained.

Under the condition (1) in Table 1, the etching temperature was changed as in Table 2, and the concentration of potassium dichromate was changed to etch to obtain the results in Table 2.

As shown in Table 2, when etching at a temperature of 10 to 80 ° C. using a saturated etching solution of potassium dichromate, the crystal surface in a flat mirror state corresponding to the surface B could be reproduced. On the other hand, when potassium dichromate is unsaturated or when the etching temperature is out of the above range, the crystal surface becomes A or C, and a predetermined crystal surface cannot be obtained.

Condition Water: sulfuric acid Etching temperature Potassium Dichromate Concentration Surface condition (11) 1: 2 12 ℃ saturation Surface B (12) 1: 2 12 ℃ Desaturation Surface A (13) 1: 2 25 ℃ saturation Surface B (14) 1: 2 25 ℃ Desaturation Surface A (15) 1: 2 75 ℃ saturation Surface B (16) 1: 2 75 ℃ Desaturation Surface A (17) 1: 2 8 ℃ saturation Surface A (18) 1: 2 8 ℃ Desaturation Surface A (19) 1: 2 85 ℃ saturation Surface C 20 1: 2 85 ℃ Desaturation Surface A or C

Comparative Example 1

When the etching solution of Example 1 was changed to an etching solution of hydrogen peroxide / sulfuric acid / water (ratio 1: 4: 1) and etched at 40 ° C., Se was precipitated in a large amount on the crystal surface.

<Example 2>

The crystal surface etched in the condition (1) of Table 1 of Example 1 was observed in detail, and the reddish part existed in the edge part. It is considered that sulfuric acid in the etching solution remains on the crystal surface, dissolves only Zn on the surface of ZnSe, and as a result, Se remains and becomes red.

Therefore, the crystal surface etched under the condition (1) in Table 1 of Example 1 was washed under the conditions shown in Table 3, and the Se, ie, Se / Zn ratio, remaining on the crystal surface was changed to XPS (X-ray photoelectron spectroscopy). I looked into). The results are shown in Table 3.

Condition Washing method Cleaning temperature Se / Zn (21) water 8 ℃ 1.60 (22) water 25 ℃ 1.30 (23) Methanol 25 ℃ 1.25 (24) water 12 ℃ 1.45 (25) water 40 ℃ 1.25

As shown in Table 3, the washing after the etching treatment is preferably water or methanol of 10 ° C or higher. It is preferable to adjust the molar ratio of Se / Zn to 1.50 or less by this washing | cleaning. As high as 1.60 as in condition (21), Se could not be completely removed even by the treatment described later, and epitaxial growth of a high quality II-VI compound semiconductor crystal could not be performed on the crystal surface after the treatment. .

In addition, this washing is preferable because the treatment at a higher temperature than the etching treatment temperature can reduce the Se / Zn ratio. Also, when the cleaning effect was examined using isopropyl alcohol instead of methanol, it was found that the same effect as methanol.

<Example 3>

The crystal surface wash | cleaned by the condition (22) of Table 3 of Example 2 was processed on condition of Table 4, and the Se / Zn ratio of the surface was examined by XPS. The results are shown in Table 4.

As shown in Table 4, it was found that treatment under the conditions of Table 4 can almost completely eliminate Se remaining on the crystal surface.

Condition Processing method Se / Zn (26) Trichlorethylene Ultrasonic Cleaning 10 minutes 1.15 (27) Trichlorethylene Ultrasonic Cleaning 10 minutes Acetone Ultrasonic Cleaning 5 minutes and Trichloroethylene Ultrasonic Cleaning 10 minutes 1.05 (28) Treatment 27 was repeated three times. 1.00 (29) 15 minutes heat treatment at 200 ° C under nitrogen atmosphere 1.00 (30) 30 seconds treatment at room temperature in carbon disulfide solution 1.10 (31) 30 seconds treatment at room temperature in carbon tetrachloride 1.05

Further, in the above treatment, the same treatment was carried out using dichloromethane instead of trichloroethylene, and the effect almost equivalent to trichloroethylene was obtained. In addition, when the treatment was carried out by self-cleaning instead of ultrasonic cleaning, the same effect as ultrasonic cleaning was obtained. In addition, the heat treatment temperature of the conditions (29) of Table 4, Preferably the range of 200-350 degreeC was suitable. When it exceeded 350 degreeC, defects, such as a roughening of a crystal surface, generate | occur | produced.

<Example 4>

In order to remove the oxide on the surface of the crystal | crystallization wash | cleaned by the condition (28) of Table 4 of Example 3, it was immersed in 10-fold dilution of hydrochloric acid (36 weight%) for 2 minutes at room temperature, or ② ammonia: methanol = The mixture was immersed in a mixed solution of 1: 3 for 2 minutes at room temperature, or (3) immersed in a 10-fold dilution of hydrofluoric acid (47% by weight) for 2 minutes at room temperature. The atomic arrangement of the obtained ZnSe crystal surface was examined.

This atomic arrangement structure was determined by introducing a processed crystal into a molecular beam epitaxial growth furnace (MBE furnace) and examining the atomic rearrangement pattern by a reflection high speed electron diffraction method (RHEED). When the oxide was removed to clean the crystal surface, a rearrangement (C (2 × 2)) pattern of Zn atoms or a rearrangement (2 × 1) pattern of Se atoms appeared. The pressure in the MBE furnace was 1 × 10 ⁻¹⁰ Torr, and the crystal was heated to 500 ° C. at a heating rate of 10 ° C./minute, and the Se molecular beam at a pressure of 5 × 10 ⁻⁶ Torr was obtained when the crystal temperature exceeded 200 ° C. Investigated.

When the ZnSe crystals treated under the conditions of ① and ② and ③ were irradiated with an RHEED atomic rearrangement pattern, the crystal reached 500 ° C and at the same time a rearrangement (C (2 × 2)) pattern of Zn atoms appeared. It was found that the oxide was removed from the crystal surface. Moreover, even if the process of said (1), (2), and (3) was performed immediately after etching, the same result was obtained.

For comparison, the ZnSe crystals obtained by the treatment of Example 3 were irradiated with RHEED to examine the atomic rearrangement pattern, and after 30 minutes to 1 hour after the crystal reached 500 ° C, the rearrangement of Zn atoms (C (2 × 2)) A pattern appeared.

Further, for comparison, the atomic rearrangement pattern of the ZnSe crystal obtained by the treatment of Example 2 was examined by RHEED, and the rearrangement pattern of the atoms was not observed even when the crystal was treated at 500 ° C for several hours.

By employing the above-described configuration, the surface of the II-VI compound semiconductor crystal is not degraded before and after etching, and the surface of the II-VI compound semiconductor crystal is excellent in cleanability and suitable for epitaxial growth and the like.

Claims (9)

A group II-VI compound semiconductor crystal is etched in a temperature range of 10 to 80 ° C using an etching solution obtained by saturating potassium dichromate in an aqueous solution in which sulfuric acid is mixed at a capacity ratio of 1 to 10 with respect to water 1. A method for surface cleaning of II-VI compound semiconductor crystals. 2. The group II-VI compound semiconductor crystal according to claim 1, wherein the etching solution is removed and the precipitation of the Group VI element is suppressed by washing with water having a temperature of 10 ° C or more and a boiling point after the treatment by the surface cleaning method. Surface cleaning method. The surface cleaning of the II-VI compound semiconductor crystal according to claim 1, wherein the etching solution is removed and the precipitation of the Group VI element is suppressed by washing with methanol or isopropyl alcohol after the treatment by the surface cleaning method. Way. The method according to claim 2 or 3, wherein after the treatment with the surface cleaning method, ultrasonic cleaning or boiling treatment is carried out in dichloromethane or trichloroethylene to remove the Group VI element precipitated in a small amount on the crystal surface. A method for surface cleaning of a II-VI compound semiconductor crystal. The method of claim 4, wherein during the ultrasonic cleaning or boiling process of dichloromethane or trichloroethylene, by performing the ultrasonic cleaning or boiling process of acetone, a small amount of Group VI precipitated on the crystal surface is removed. The surface cleaning method of the II-VI compound semiconductor crystal | crystallization which sets it as. The group II-VI compound semiconductor crystal according to claim 2 or 3, wherein after the treatment with the surface cleaning method, heat treatment is performed at a temperature of 200 DEG C or higher to remove the Group VI element deposited in a small amount on the crystal surface. Surface cleaning method. The method according to claim 2 or 3, wherein after treatment by the surface cleaning method, a Group VI element precipitated in a trace amount on the crystal surface is removed by immersion treatment in a solution containing carbon disulfide and / or carbon tetrachloride. A method for surface cleaning of II-VI compound semiconductor crystals. 4. The oxide of the crystal surface according to claim 2 or 3, which is treated by the surface cleaning method and then immersed in a solution containing hydrochloric acid, a solution containing ammonium hydroxide and methanol, or a solution containing hydrofluoric acid to remove oxides on the crystal surface. A method for surface cleaning of a II-VI compound semiconductor crystal, characterized by the above-mentioned. The method according to claim 4, wherein after the treatment by the surface cleaning method, immersion treatment in a solution containing hydrochloric acid, a solution containing ammonium hydroxide and methanol, or a solution containing hydrofluoric acid to remove oxides on the crystal surface. A method for surface cleaning of a II-VI compound semiconductor crystal.

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