JPH09199559A - Method for evaluating crystal defects in semiconductor single crystal film - Google Patents

Abstract

(57) Abstract: To evaluate crystal defects in a semiconductor single crystal film that is homoepitaxially or heteroepitaxially grown. A semiconductor single crystal film 1 epitaxially grown on a semiconductor single crystal substrate 10 with a liquid level of the melt 12 and a predetermined gap h ₁ , h ₂ or h ₃ above the KOH melt 12.
1 is arranged with the surface of the single crystal film 11 facing downward, and the crystal defects of the single crystal film 11 are evaluated. When the KOH vapor rising from the liquid surface of the KOH melt contacts the single crystal film 11, even if the thickness of the single crystal film 11 is extremely thin, this vapor etches only the single crystal film 11 and etches the single crystal film. Expose the pit.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for evaluating crystal defects in an epitaxially grown semiconductor single crystal film. More specifically, the present invention relates to a selective etching method using molten KOH, which is suitable for evaluating crystal defects in a semiconductor single crystal film grown by heteroepitaxial growth.

[0002]

2. Description of the Related Art Conventionally, as a method for evaluating a crystal defect of a semiconductor silicon wafer, H ₂ O-H ₂ called SC-1 is used.
A method of evaluating a crystal defect by cleaning a silicon wafer with this SC-1 cleaning solution using an O ₂ —NH ₄ OH mixed solution to increase the surface microroughness of the wafer has been proposed (J. Ryuta et al. , "Crystal-originated singulariti
es on Si wafer surface after SC1 cleaning ", Jpn.JA
ppl.Phys., 29, L1947-L1949). In this method, the strong oxidizing action of H ₂ O ₂ in the SC-1 cleaning solution, the dissolving action of NH ₄ OH and the compound formation reaction remove organic contaminants and some metal impurities on the silicon wafer surface, We observed the shallow etch pits and evaluated the cause of the pits as vacancy clusters introduced during crystal growth. Further, as-grown CZ silicon wafers are vertically immersed in a Secco etchant for about 30 minutes, and defects distributed in the crystal from the flow patterns appearing on the wafer surface during the chemical etching (flow pattern defects). Is known (H.Yamagishi
et al., "D-defects in silicon single crystals and t
heir effects on gate oxide integrity ", Proc.Symp.on
Advanced Science and Technology of Silicon Materi
als, pp.83-88, Japan Society for the Promotion of Sc
ience, The 145th Committee (1991)).

However, since these methods are mainly for evaluating defects in the silicon wafer itself, they are not suitable for evaluating crystal defects in a semiconductor single crystal film epitaxially grown on a silicon wafer. In particular, it was unsuitable for evaluating crystal defects in a semiconductor single crystal film such as a SiC film heteroepitaxially grown on a silicon wafer. Even when a semiconductor single crystal film is homoepitaxially grown, when a GaAs film is epitaxially grown on a GaAs wafer, GaAs which is usually used is grown.
The crystal defects of the GaAs film could not be substantially evaluated because there was no wet etching solution that accurately revealed the crystal defects of the (100) plane epitaxially grown film.

For a semiconductor single crystal film such as GaAs, a selective etching method using molten KOH has been disclosed (Japanese Patent Laid-Open No. 55-27671). In this method, a plurality of crystal layers of Ga _1-x Al _x As (0 ≦ x ≦ 1) are immersed in molten KOH, and the crystal layers are selectively selected based on the etching rate determined by the mixed crystal ratio. It is a method of etching. The KOH etching rate of the bulk crystal GaAs wafer is as shown in FIG.
The melt is about 1 μm / min at 420 ° C. According to this method, a silicon wafer having a SiC semiconductor single crystal film heteroepitaxially grown on a wafer is immersed as a sample in molten KOH, and after a lapse of a predetermined time, the sample is taken out from the molten KOH, washed and the etched surface is observed. It is possible.

[0005]

However, the above-mentioned molten KO
As shown in Table 1 below, the method of immersing a silicon wafer having a SiC semiconductor single crystal film heteroepitaxially grown in H has an extremely high etching rate of SiC as compared with the etching rate of the silicon wafer. That is, the silicon wafer is preferentially dissolved in the etching solution, or the SiC film is peeled off from the substrate, which makes handling thereafter difficult. Therefore, the melting K
The OH dipping method was also unsuitable for evaluating crystal defects in the epitaxially grown semiconductor single crystal film.

[0006]

[Table 1]

An object of the present invention is to provide a method capable of evaluating crystal defects in a semiconductor single crystal film that has been homoepitaxially or heteroepitaxially grown.

[0008]

As shown in FIG. 1, in the invention according to claim 1 of the present application, the liquid surface of the melt 12 and a predetermined gap h ₁ , h ₂ or h above the KOH melt 12. _The semiconductor single crystal film 11 epitaxially grown on the semiconductor single crystal substrate 10 with a gap ₃ is selectively etched by arranging the single crystal film 11 with the surface of the single crystal film 11 facing downward.
This is a method for evaluating the crystal defects of. When the KOH vapor rising from the liquid surface of the KOH melt touches the single crystal film 11, even if the thickness of the single crystal film 11 is as thin as about 1 to 10 μm, this vapor etches only the single crystal film 11, Exposing the etch pits of the crystal film.

The invention according to claim 2 of the present application is the invention according to claim 1, wherein the predetermined interval h ₁ , h ₂ or h ₃ is at most 3c.
m, the temperature of the KOH melt 12 is 450 ° C. or lower, and the epitaxially grown semiconductor single crystal film 11
The arrangement time is 20 to 30 minutes. When the single crystal film 11 is brought into direct contact with the KOH melt 12 without a predetermined gap, the etching rate of the single crystal film 11 is rapidly increased, and desired etch pits cannot be formed. If the predetermined interval exceeds 3 cm, the amount of KOH vapor contacting the single crystal film 11 decreases, and it is difficult to form a desired etch pit. To avoid unnecessary energy consumption, the temperature of the KOH melt is preferably 450 ° C. or lower. Further, in order to form a desired etch pit, the arrangement time is set within the range of 20 to 30 minutes according to the above-mentioned predetermined interval.

The invention according to claim 3 of the present application is the invention according to claim 1 or 2, wherein the semiconductor single crystal film 11 is a film grown by heteroepitaxial growth on the semiconductor single crystal substrate 10. K rising from the liquid surface of KOH melt
Since the OH vapor mainly contacts the single crystal film 11 and does not substantially touch the semiconductor single crystal substrate 10 located on the back surface of the single crystal film 11, the semiconductor having a faster dissolution rate than the heteroepitaxially grown single crystal film. Even a single crystal substrate will not dissolve.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION As shown in FIG.
In order to observe crystal defects on the surface of the semiconductor single crystal film epitaxially grown by the H melt, first, granular KOH is put into the graphite wide-mouth crucible 13 and heated to a temperature not lower than the melting point of KOH (360 ° C.) and not higher than 450 ° C. Heater 14
To heat. Next, when KOH becomes the melt 12 and the temperature thereof reaches a predetermined temperature, the pair of sample holders 15a and 15b are installed so as to sandwich the crucible 13. Slits 16a and 16b are formed at the same height in the vicinity of the upper edge of the crucible of the sample holders 15a and 15b.
Are provided in a plurality of stages. The slit 16a, which is suitable for the liquid amount of the KOH melt 12, the material of the single crystal film 11, the film thickness, and the like,
16b is selected, and a sample (semiconductor single crystal substrate 10 with semiconductor single crystal film 11 epitaxially grown) is placed therein. The sample and the liquid surface of the KOH melt define a predetermined interval h ₁ , h ₂ or h ₃ by the selected slit. The single crystal film 11 is exposed to KOH vapor for a predetermined time while being arranged in the slits 16a and 16b. KO like this
When etching with H vapor, KOH melt is 420 ℃
However, in the case of the sample in which the GaAs film is epitaxially grown on the GaAs wafer, the relationship of the etching rate with respect to the predetermined interval is generated as shown in FIG.
The sample subjected to the etching treatment is washed with pure water, further washed with an organic solvent such as acetone, and dried, and then the etch pits on the surface of the single crystal film are observed with an optical microscope to determine the presence or absence of crystal defects. .

When the sample is placed, the sample may be placed on the upper end of the crucible and the crucible may be covered without using the sample holder.
It is preferable to use the sample holder because the sample may adhere to the upper end of the crucible when the temperature of the KOH melt lowers after the etching of (3) and the predetermined interval can be appropriately selected. Further, as shown in FIG. 2, the sample holder 17 having the slits 17a and 17b formed at the lower end is hung from above and the slit 17
After arranging the sample 10 horizontally on a and 17b, its height is lowered to a desired position as shown by a solid arrow by a lifting device (not shown), where it is exposed to KOH vapor for a predetermined time, and further shown by a dashed arrow. Thus, the sample 10 may be taken out from the placement tool 17 by raising.

[0013]

Next, embodiments of the present invention will be described. The present invention is not limited to this embodiment. <Example 1> A semiconductor substrate obtained by epitaxially growing a GaAs single crystal film on a GaAs wafer was used as a sample. The GaAs film had a thickness of about 10 μm and its crystal orientation was (100). As shown in Figure 1, 420 ℃
Above the KOH melt maintained at
This sample was placed horizontally with the GaAs film facing downward with a gap of cm. After exposing the GaAs film of the sample to KOH vapor for 20 minutes, the sample is washed with pure water,
Further washed with acetone and dried. After drying, sample 5
It was observed with an optical microscope at a magnification of 0 times. The crystal structure is shown by the micrograph of FIG. FIG. 5 shows GaA after epitaxial growth of GaAs film and before etching.
It is a microscope picture figure which shows the crystal structure of the surface of the s wafer. Etch pits of the epitaxial crystal were clearly observed in the photograph of FIG. 4 in contrast to the photograph of FIG. 5 in which almost no crystal defects were observed. In order to compare the etching rates, based on the conventional method, the GaAs wafer before epitaxial growth was immersed in the KOH melt maintained at 420 ° C. for 20 minutes as above, then pulled up, washed with water and washed with acetone. This sample was similarly observed with a 50 × optical microscope. Its crystal structure is shown in FIG. Although the etching density according to the method of Example 1 (FIG. 4) was smaller than that according to the conventional method (FIG. 6), the KOH etching method of Example 1 was found to be a suitable method.

<Embodiment 2> SiC on a silicon wafer
The sample was a semiconductor substrate obtained by epitaxially growing the single crystal film of. The SiC film was a very thin epitaxial crystal film having a thickness of about 1 μm, and its crystal orientation was (100). KO maintained at 420 ° C. as in Example 1
The sample was placed horizontally above the H melt with the SiC film facing downward with a gap of about 1 cm from the liquid surface of the melt. After exposing the SiC film of the sample to the vapor of KOH for 30 minutes, the sample was washed with pure water, further washed with acetone, and dried. After drying, the sample was observed with an optical microscope at 50x magnification. The crystal structure is shown by the micrograph of FIG. FIG. 8 shows the condition before placing above the KOH melt (K
It is a microscope picture figure which shows the crystal structure of the same sample (before OH etching). Comparing FIG. 7 and FIG. 8, the anti-phase defects, which did not appear in the photograph of FIG. 8 and had a non-uniform atomic arrangement of silicon atoms and carbon atoms, were clearly seen in the photograph of FIG. Was observed.

[0015]

As described above, according to the invention of claim 1, the crystal defects of the single crystal film epitaxially grown on the single crystal semiconductor substrate are distributed over the entire surface of the substrate to the same extent as the crystal defects of the bulk crystal. Evaluation such as measuring the distribution of defect density can be performed. According to the invention of claim 2, the sample is appropriately spaced from the liquid surface of the KOH melt, and the temperature of the KOH melt is appropriately maintained.
Further, by exposing the sample to KOH vapor for an appropriate time, the crystal defects can be observed even in the epitaxial crystal film having an extremely high etching rate. According to the invention of claim 3, when the single crystal film is a heteroepitaxial crystal film, the KOH vapor mainly contacts the single crystal film, and the semiconductor single crystal substrate located on the back surface of the single crystal film is substantially affected. Therefore, even a semiconductor single crystal substrate having a high dissolution rate with respect to this single crystal film has an advantage of not dissolving the substrate.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an etching apparatus for a single crystal film epitaxially grown on a semiconductor single crystal substrate of the present invention.

FIG. 2 is a configuration diagram of another etching apparatus of the present invention.

FIG. 3 is a gap between the surface of the KOH melt and the sample and GaA.
The figure which shows the relationship of the etching rate of s (100).

FIG. 4 G grown epitaxially on a GaAs wafer
G after etching the aAs film by the method of Example 1
The microscope picture figure which shows the crystal structure of an aAs film.

FIG. 5 is a micrograph showing a crystal structure of a GaAs film epitaxially grown before etching for comparison.

FIG. 6 is a micrograph showing a crystal structure of a GaAs wafer surface after etching a GaAs wafer before a GaAs film is epitaxially grown by a conventional method for comparison.

FIG. 7: S epitaxially grown on a silicon wafer
Si after etching the iC film by the method of Example 2
The microscope picture figure which shows the crystal structure of C film.

FIG. 8 is a micrograph showing the crystal structure of an epitaxially grown SiC film before etching for comparison.

FIG. 9 is a diagram showing a relationship between a melt temperature and an etching rate when GaAs is etched with a KOH melt.

[Explanation of symbols]

10 semiconductor single crystal substrate 11 epitaxially grown semiconductor single crystal film 12 KOH melt 13 crucibles 15a, 15b, 17 sample holders h ₁ , h ₂ , h ₃ predetermined intervals

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] January 22, 1996

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Fig. 4

[Correction method] Change

[Correction contents]

FIG. 4

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] Fig. 5

[Correction method] Change

[Correction contents]

[Figure 5]

[Procedure 3]

[Document name to be amended] Drawing

[Correction target item name] Fig. 6

[Correction method] Change

[Correction contents]

FIG. 6

[Procedure amendment 4]

[Document name to be amended] Drawing

[Name of item to be corrected] Figure 7

[Correction method] Change

[Correction contents]

FIG. 7

[Procedure Amendment 5]

[Document name to be amended] Drawing

[Correction target item name] Fig. 8

[Correction method] Change

[Correction contents]

[Figure 8] ─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] February 16, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction contents]

[0005]

However, the above-mentioned molten KO
As shown in Table 1 below, the method of immersing a silicon wafer having a heteroepitaxially grown SiC semiconductor single crystal film in H is because the etching rate of the silicon wafer is extremely higher than the etching rate of SiC. That is, the silicon wafer is preferentially dissolved in the etching solution, or the SiC film is peeled off from the substrate, which makes handling thereafter difficult. Therefore, the melting K
The OH dipping method was also unsuitable for evaluating crystal defects in the epitaxially grown semiconductor single crystal film.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction contents]

[0013]

Next, embodiments of the present invention will be described. The present invention is not limited to this embodiment. <Example 1> A semiconductor substrate obtained by epitaxially growing a GaAs single crystal film on a GaAs wafer was used as a sample. The GaAs film had a thickness of about 10 μm and its crystal orientation was (100). As shown in Figure 1, 420 ℃
Above the KOH melt maintained at
This sample was placed horizontally with the GaAs film facing downward with a gap of cm. After exposing the GaAs film of the sample to KOH vapor for 20 minutes, the sample is washed with pure water,
Further washed with acetone and dried. After drying, sample 5
It was observed with an optical microscope at a magnification of 00 times. Its crystal table
The surface is shown by the micrograph of FIG. FIG. 5 shows the Ga before the etching after the epitaxial growth of the GaAs film.
It is a microscope picture figure which shows the state of the surface of an As wafer .
Against photograph of FIG. 5, the etch pits of the epitaxial crystals was clearly observed in the photograph of FIG. In order to compare the etching rates, based on the conventional method, the GaAs wafer before epitaxial growth was immersed in the KOH melt maintained at 420 ° C. for 20 minutes as above, then pulled up, washed with water and washed with acetone. This sample is also 5
It was observed with a 0 × optical microscope. Figure 6 shows the crystal surface .
Shown in Etch pit according to the method of Example 1 (FIG. 4)
DOO density was small Ri by etch pit density by the conventional method (FIG. 6), but it was found that KOH etching process of Example 1 is a reasonable approach.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction contents]

<Embodiment 2> SiC on a silicon wafer
The sample was a semiconductor substrate obtained by epitaxially growing the single crystal film of. The SiC film was a very thin epitaxial crystal film having a thickness of about 1 μm, and its crystal orientation was (100). KO maintained at 420 ° C. as in Example 1
The sample was placed horizontally above the H melt with the SiC film facing downward with a gap of about 1 cm from the liquid surface of the melt. After exposing the SiC film of the sample to the vapor of KOH for 30 minutes, the sample was washed with pure water, further washed with acetone, and dried. After drying, the sample was observed with an optical microscope at a magnification of 1000 times. The crystal surface is shown by the micrograph of FIG. FIG. 8 is a micrograph showing the surface condition of the same sample before being placed above the KOH melt (before KOH etching). Comparing FIG. 7 and FIG.
In the photograph of FIG. 7, a large number of island-shaped anti-phase defects, which did not appear in the photograph of FIG. 7, and in which the atomic arrangements of silicon atoms and carbon atoms were not uniform were clearly observed.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction contents]

[0015]

As described above, according to the invention of claim 1, the crystal defects of the single crystal film epitaxially grown on the single crystal semiconductor substrate are distributed over the entire surface of the substrate to the same extent as the crystal defects of the bulk crystal. Evaluation such as measuring the distribution of defect density can be performed. According to the invention of claim 2, the sample is appropriately spaced from the liquid surface of the KOH melt, and the temperature of the KOH melt is appropriately maintained.
Moreover, by exposing the sample to KOH vapor for an appropriate time, the crystal defects can be observed even in the epitaxial crystal film having an etching rate different from that of the substrate . Further, according to the invention of claim 3, when the single crystal film is a heteroepitaxial single crystal film, KOH vapor mainly contacts the single crystal film, and the semiconductor single crystal substrate located on the back surface of the single crystal film is Since it is not substantially touched, even a semiconductor single crystal substrate having a high dissolution rate with respect to this single crystal film has an advantage of not dissolving the substrate.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] Fig. 4

[Correction method] Change

[Correction contents]

FIG. 4 G grown epitaxially on a GaAs wafer
G after etching the aAs film by the method of Example 1
The microscope picture figure which shows the crystal surface of an aAs film.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] Fig. 5

[Correction method] Change

[Correction contents]

FIG. 5 is a micrograph showing a surface condition of an epitaxially grown GaAs film before etching for comparison.

[Procedure amendment 7]

[Document name to be amended] Statement

[Correction target item name] Fig. 6

[Correction method] Change

[Correction contents]

FIG. 6 is a micrograph showing a crystal surface of a GaAs wafer surface after etching a GaAs wafer before a GaAs film is epitaxially grown by a conventional method for comparison.

[Procedure amendment 8]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 7

[Correction method] Change

[Correction contents]

FIG. 7: S epitaxially grown on a silicon wafer
Si after etching the iC film by the method of Example 2
The microscope picture figure which shows the crystal surface of C film.

[Procedure amendment 9]

[Document name to be amended] Statement

[Correction target item name] Fig. 8

[Correction method] Change

[Correction contents]

FIG. 8 is a micrograph showing a surface condition of an epitaxially grown SiC film before etching for comparison.

Claims (3)

[Claims] 1. A semiconductor single crystal substrate having a predetermined gap (h ₁ , h ₂ , h ₃ ) from the liquid surface of the melt (12) above the KOH melt (12).
(10) A semiconductor for evaluating crystal defects of the single crystal film (11) by selectively etching the semiconductor single crystal film (11) epitaxially grown on the single crystal film (11) with the surface of the single crystal film (11) facing downward. Method for evaluating crystal defects in single crystal film. 2. The predetermined gap (h ₁ , h ₂ , h ₃ ) is at most 3 cm, and the temperature of the KOH melt (12) is 450 ° C. or lower,
The method for evaluating a crystal defect of a semiconductor single crystal film according to claim 1, wherein the disposition time of the epitaxially grown semiconductor single crystal film (11) is 20 to 30 minutes. 3. The semiconductor single crystal film (11) is a semiconductor single crystal substrate.
(10) The method for evaluating crystal defects of a semiconductor single crystal film according to claim 1 or 2, which is a film grown by heteroepitaxial growth on the film.