JP2723734B2 - Single crystal for collimator - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single crystal for collimator for X-ray diffraction with few crystal defects.

[0002]

2. Description of the Related Art A two-crystal method or a three-crystal method is usually used for X-ray diffraction for high-performance detection of crystal defects.
In order to suppress the angular spread of the incident X-ray, one or two single crystals for collimator are used.

As those single crystals, those of the same quality as the sample single crystal are used, which is called a (+n, -n) arrangement.
Also, there is a method called (+n1, +n2, -n3) arrangement in which a material different from the sample single crystal can be used. These methods are shown in FIGS. 1 and 2.

Here, n represents the index of the diffraction grating surface, and the sample crystal is generally arranged at the final stage. The latter method (Fig. 2) can use a single crystal for collimator which is different from the sample because the wavelength dispersion of X-rays can be suppressed ("X-ray diffraction", p.179, Shizuo Miyake, Showa Showa). Four
4 years, published by Asakura Shoten).

Single crystal 1 or 2 for such a collimator
If asymmetric reflection is used for the angle divergence, the angle divergence becomes extremely small and the diffraction from the sample crystal 3 can be accurately measured. Here, the asymmetric reflection is cut out by inclining the angle between the diffractive surface hkl to be used and the collimator single crystal surface, and from the angle y of the incident X-ray and the diffracted ray with respect to the collimator single crystal surface, the asymmetry factor b=sin( x)/sin(y) and b
It is achieved in a geometric relation such that <<1.

The angular dispersion of the diffracted X-ray from the collimator single crystal is proportional to b ^m when the collimator single crystal is successively reflected m times. That is, if b<1,
The angular dispersion of the incident X-ray is reduced by b times after diffraction. Specifically, the incident X-ray may be incident just on the surface. This relationship is shown in FIG.

A well-known technique is a diffraction microscopic method in which the intensity of the diffracted X-rays from the sample is detected by the photographic plate 4 as shown in FIG. 1 to detect the lattice distortion in the sample crystal in such a diffraction arrangement. Is. Generally, by using this type of device, lattice strain can be detected with high sensitivity of 10 ^-7 .

However, b cannot be infinitely close to zero. This is because when X-rays are incident on the surface of the single crystal for a collimator, optical total reflection occurs and diffraction does not occur. The critical angle θc at this time is expressed by θc≈√(2δ) from the refractive index δ of the X-ray to the surface (“X-ray diffraction”, p. 7, Shizuo Miyake, 1969,
Published by Asakura Shoten, see). Therefore, the lower limit of x is θc, and b is also b>sin(θc)/sin(y). Generally, θc is about 10 minutes.

As described above, this type of device is characterized in that it detects the lattice strain in the sample single crystal with high sensitivity. As a problem here, regarding the single crystal for collimator,
The point is that perfection is required rather than the sample single crystal to be measured.

Generally, a silicon single crystal is used as a single crystal for a collimator, but a silicon single crystal is used as a sample, and its integrity is examined. For a collimator having a higher completeness than a silicon single crystal of a sample. Single crystals are needed.

Recently, the perfection of a silicon single crystal has been required for the production of a VLSI such as 16MDRAM. Conventionally, a single crystal for a collimator has been used as a silicon single crystal for the VLSI. The quality of the single crystal for collimator itself is becoming a problem when using a silicon single crystal ingot of the same level as a sample.

[0012]

DISCLOSURE OF THE INVENTION The inventors of the present invention have conducted extensive research on such a single crystal for collimators in order to obtain a single crystal that is more complete than a single crystal for VLSI and does not contain lattice defects. is there.

In connection with the present invention, the present inventor has conducted various researches on incomplete lattice defects in VLSI single crystals. As a result, it was found that such lattice defects can be observed under an optical microscope by leaving them in a mixed solution of dichromic acid and hydrofluoric acid for 30 minutes [Reference, H. Yamagi
shi et al: DRIP 41991 Engla
nd paper N 14].

Further, it has been found that such lattice defects are relatively proportional to the number of etch pits generated when repeatedly washed in a mixed solution of ammonia solution and hydrogen peroxide [reference document, Izumi Fusegawa et al.: 38th Spring Association of Japan paper No. 28p-ZL-3].

Based on such knowledge, the present inventor discovered that a thin epitaxial film was grown on the surface of a silicon single crystal by a CVD process and that the lattice defects caused by the substrate silicon single crystal did not penetrate into the epi film, and the above-mentioned was described above. The present invention has been completed by solving the conventional problems. The present invention is
An object of the present invention is to provide a single crystal for a collimator, which has a small number of crystal defects and which can detect lattice strain in a sample single crystal with high sensitivity.

[0016]

[In the above formula (1), x is an incident angle on the surface of the single crystal, y is a diffraction angle, and the black diffraction angle θb has a relationship of x+y=2θb. ]

The minimum value of the incident angle x is selected so as to be larger than the critical angle θc at which the incident X-ray causes total reflection, and b>
Use diffractive surface so that sin(θc)/sin(y)
A substrate a single crystal having a surface inclined from preferably has a single-crystal thin film made of a substrate a single crystal single crystal of the same quality of the material grown on the surface of the. Further, it is preferable that the substrate single crystal is a silicon single crystal, and a single crystal thin film is grown on the silicon single crystal by epitaxial growth.

[0018]

Further, the point of the present invention is that in X-ray diffraction, a technique for growing an epitaxial film on the surface of a silicon single crystal by CVD can be applied to the above-mentioned asymmetric reflection in which the surface of the silicon single crystal and the diffraction surface used are inclined. I have done so.

Conventionally, a technique for growing an epitaxial film on the surface of a silicon single crystal has been known. However, such a technology has a silicon wafer surface index of (100) or (1
10) or (111) etc.
Or publicly known literature (CE Drum; Journal)
of Electrochemical Societ
y 115 (1968), 664), the surface is inclined by about 3° from that surface.

The present invention overcomes these fixed ideas in the conventional epitaxial growth technique, and forms an epitaxial film such that the asymmetry factor b in asymmetric reflection in X-ray diffraction is smaller than 1 and the surface and the diffractive surface are largely inclined. It was created and used as a single crystal for a collimator.

[0021]

EXAMPLES The present invention will be described more specifically with reference to examples of the present invention. Of course, the present invention is not limited to the description of this embodiment. Manufacture example 1 After the polysilicon raw material was filled in a quartz crucible by the Czochralski method, a diameter of 6" having a growth orientation <100> after melting
Of silicon single crystal rods were grown. At this time, since the growth was performed without adding the dopant impurities, the resistivity of the single crystal rod after the growth was 2000 ohm·cm.

A silicon single crystal for a collimator was cut from the single crystal rod. X-ray diffraction was taken into consideration when processing. X-ray wavelength used for X-ray diffraction λ
Was set as CuKα1 and the Bragg diffraction angle θb due to 422 reflection of silicon was calculated. The above calculation is "X-ray diffraction principle"
(Written by Curity, published by Agne Publishing Co. in 1972).

It was found that the diffraction angle at this time was 44.040°. Therefore, from the (211) plane to the surface 4
It was tilted at 3.540° and cut from the previously grown silicon single crystal ingot. At this time, the incident angle x and the diffraction angle y of the X-ray with respect to the silicon single crystal surface are 0.5 and 0.5, respectively.
And 87.580°, and the asymmetry factor b=0.008
It became 7.

The thickness of the cut out silicon single crystal was 2 mm, and a plurality (a) of which an epitaxial film was grown on such a wafer (Example 1) and a sample (c) of Comparative Example 1 (Comparative Example 1) were prepared. The epitaxial growth was performed at 1100° C. for 2 hours while flowing a mixed gas of trichlorosilane and hydrogen.

Measurement Example 1 The thickness of the epitaxial film of the collimator single crystal a (Example 1) at this time was measured by an ellipsometer and found to be 30 μm. Since the so-called extinction distance of X-rays penetrating from the surface of the sample single crystal into the inside of the crystal is at most several micrometers, the thickness of the epitaxial film to be grown can be considered on the basis of this extinction distance.

In addition, for a (Example 1) and c (Comparative Example 1), 5 in a mixed solution of the above-mentioned ammonia solution and hydrogen peroxide (abbreviated as ammonia-hydrogen peroxide in Table 1).
The cleaning was repeated 20 minutes each, and the density of the generated etch pits was measured with a laser particle counter.

The measurement principle at this time is that the scattering of the irradiation laser light from the generated etch pit is measured. The number of counts at this time is shown in Table 1 and is 1/surface for a (Example 1) and c (Comparative Example 1), respectively.
It was expected that the number of crystal defects would be less in the case where the number was 52/surface and the epitaxial film was grown.

When such a crystal was used as a single crystal for a collimator, it was checked whether an abnormal image due to lattice defects appeared. The arrangement at this time is shown in FIG. 1 (+n,
-N) configuration and checked by X-ray microscopy.
The crystals of a and c were arranged in pairs in the first crystal and the second crystal. That is, a combination of aa (Example 1) and cc (Comparative Example 1) was used.

As the X-ray source, CuKα1 ray generated from a Cu target by the rotating anticathode rotation method was used. The slit 5 made a line width of 100 μm, and the light was made incident on the first crystal. X
The distance from the radiation source to the first crystal was 1 m, the distance between the first crystal and the second crystal was 10 cm, and the distance between the second crystal and the X-ray imaging film was 2 cm.

A nuclear dry plate was used as a film for X-ray imaging, and the developed film was magnified 20 times under a microscope and the number of blackened portions was counted. At this time, the procedure for photographing the X-ray topography was performed as follows.

The second crystal was rotated in 0.1 second steps about the vertical direction perpendicular to the beam as an axis, and the X-ray diffraction intensity was measured by a counter installed behind the X-ray imaging film. This is generally called a rocking curve.

By the way, if the lattice is distorted in the portion where the lattice defect exists in the crystal and the interplanar spacing d changes by Δd, the rotation angle of the second crystal with respect to the vertical direction is Δθ=-ta.
It is known to deviate from the Bragg angle by n(θb)·Δd/d.

Therefore, in order to detect the lattice defect in the crystal by the above method, it is sufficient to hold the rotation angle of the second crystal outside the peak of the rocking curve. In the present measurement example, after the rocking curve measurement, an X-ray topograph was photographed every 0.3 seconds from the angular position showing the peak to the minus direction to the plus direction, and the maximum value of the blackened image was measured. The absolute value of the angle deviation at this time was 1.2 seconds.

The results are shown in Table 1. Since the density of black dots became almost 0 in the combination of aa, the effectiveness in the present invention was proved.

[0035]

[Table 1]

[0036]

As described above, the single crystal for collimator of the present invention has few crystal defects and enables the lattice strain in the sample single crystal to be detected with high sensitivity.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an X-ray two-crystal diffraction microscopy (+n, −n) arrangement.

FIG. 2 is an explanatory diagram showing an X-ray three-crystal diffraction method (+n, +n, −n) arrangement.

FIG. 3 is an explanatory diagram showing a geometrical arrangement in a single crystal for a collimator.

[Explanation of symbols]

1,2 Collimator single crystal 3 Sample single crystal 4 Nuclear dry plate 5 X-ray source 6,7 Slit x Incident angle y Diffraction angle θb Bragg angle

Claims (3)

(57) [Claims] 1. A collimator for single crystal X-ray diffraction, and the substrate a single crystal having a surface asymmetric factor b represented by the following formula (1) is tilted from the use diffraction plane so that less than 1 , a single crystal for collimator and having a single-crystal thin film made of a single crystal of the same quality of the material grown on the surface of the substrate single crystal. b=sin(x)/sin(y) (1) [In the above formula (1), x is the angle of incidence on the single crystal surface,
y is a diffraction angle, and black diffraction angle θb is x+y=2
There is a relationship of θb. ] 2. A minimum value of the incident angle x is selected so as to be larger than a critical angle θc at which the incident X-ray causes total reflection, and b
Diffraction used so that >sin(θc)/sin(y)
A substrate a single crystal having a surface inclined from the surface, for collimator according to claim 1, characterized in that it has a single-crystal thin film made of a substrate a single crystal single crystal of the same quality of the material grown on the surface of Single crystal. 3. The single crystal for a collimator according to claim 1, wherein the substrate single crystal is a silicon single crystal, and a single crystal thin film is grown on the surface of the silicon single crystal by epitaxial growth.