JP2967609B2 - Total reflection X-ray diffraction microscopy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-sensitive total reflection X-ray diffraction microscopic method for detecting minute crystal defects very near the surface of a Si wafer.

[0002]

2. Description of the Related Art Crystal defects (for example, vacancies, interstitial atoms, dislocations, stacking faults, precipitation, segregation, surface polishing distortion, etc.) existing in a Si wafer adversely affect semiconductor device characteristics. In particular, semiconductor devices typified by recent super-integrated circuits are becoming highly integrated and multilayered, and are likely to have new crystal defects easily generated on Si wafers due to external factors such as stress concentration, ion implantation, and dry etching. It is in. These crystal defects tend to form deep levels in the forbidden body in the band structure of the semiconductor, and can be generation and recombination centers of carriers. Conventionally, X-ray diffraction microscopy methods using various X-ray diffraction phenomena have been proposed in order to observe the pattern of the spatial distribution of crystal defects in a Si wafer. However, there is no method suitable for observing a crystal defect having a strain field sufficiently smaller than the extinction distance of the X-ray in the vicinity of the surface.

[0003]

In a conventional X-ray diffraction microscope, the depth of penetration into an X-ray Si wafer is as large as about several μm, and only average information in the depth direction can be obtained. In recent years, in a shallow junction, there has been a defect that it is impossible to obtain information on crystal defects very near the surface required by a semiconductor device. In addition, the obtained diffraction image is based on a dynamic diffraction effect obtained in the case of having high perfect crystallinity, and it is impossible to observe a crystal defect having a minute strain field. there were. An object of the present invention is to provide a method for observing minute crystal defects very near the surface by X-ray diffraction microscopy while eliminating such conventional defects.

[0004]

According to the total reflection X-ray diffraction microscopy of the present invention, a silicon crystal to be measured is made monochromatic.
Irradiation with synchrotron radiation under total internal reflection conditions
After obtaining the irradiated diffraction line, the peak of the intensity of the diffraction line
It is characterized by taking diffraction images at deviated angular positions
You.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Synchrotron radiation has a strong continuous wavelength and is very useful as an X-ray source for crystal defect evaluation using diffraction phenomena. The present invention makes effective use of the features of the synchrotron radiation light.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a total reflection X according to the present invention.
It is a figure which shows one Example of a line diffraction microscopy apparatus. Code 11
Is synchrotron radiation, which is continuous light. This synchrotron radiation light 11 is shaped into an X-ray beam by a slit 12 and then monochromatized by a two-crystal spectroscope 13 provided with a crystal having a Si (111) plane. This monochromatic X-ray 14 is shaped into a beam size by a slit 15 and then installed on the head of a goniometer 16 rotatable by ω-2θ (100) Si.
The light enters the wafer 17. (100) Si wafer 17
Diffraction from uses a 422 asymmetric reflection, which is a grating plane tilted 35.26 ° relative to the (100) surface. For example, 2
An X-ray 14 having a wavelength λ = 1.29 A is selected from the synchrotron radiation 11 by a crystal spectroscope 13, and ω−2θ
The rotatable goniometer 16 provides (100) Si
When the wafer 17 is set so as to have an incident angle (θ _B −α) with respect to the X-ray 14, the diffraction line 18 due to the 422 asymmetric reflection of the (100) Si wafer 17 can be obtained. Here, θ _B is a diffraction angle having 35.58 °, and α is an angle formed between the (100) surface and the (422) plane, and has the above-mentioned value of 35.26 °. The incident angle of the X-rays 14 on the (100) Si wafer 17 is 0.3
2 °. At this time, as shown by the penetration depth curve 21 calculated in FIG. 2, the penetration depth of the X-ray 14 into the (100) Si wafer 17 is about several thousand A. When the wavelength of the X-rays 14 selected by the two-crystal spectroscope 13 is slightly shortened by sequentially rotating the two-crystal spectroscope 13 toward the low-angle side with respect to the synchrotron radiation 11, diffraction by the 422 asymmetric reflection surface is performed. The angle θ _B decreases accordingly. As a result, the incident angle of the X-rays 14 on the (100) Si wafer 17 is reduced without losing the diffraction line 18 from the (100) Si wafer 17 and finally becomes smaller than the critical angle θ _C that causes total reflection. It is possible to This makes effective use of the wavelength continuity of synchrotron radiation and asymmetrical reflection from a Si crystal. When this operation is performed until the wavelength of the X-rays 14 becomes close to λ = 1.284 A, the incident angle of the X-rays 14 on the (100) Si wafer 17 becomes 0.13 °, and the critical angle θ _C = 0.18. °. At this time, the reflectivity of the X-ray 14 on the (100) Si wafer is close to 1 as indicated by the reflectivity curve 22, and the intensity of the X-ray field is also changed as indicated by the X-ray field intensity curve 23. Big enough. Further, as shown by the penetration depth curve 21, the penetration depth of the X-rays 14 into the (100) Si wafer 18 is about several tens of amperes, and information near the surface can be obtained. As described above, the diffraction line 18 from the (100) Si wafer 17 can be obtained under the condition that the total reflection occurs on the surface of the (100) Si wafer 17. here,
(10) by the goniometer 16 rotatable by ω-2θ
0) The Si wafer 17 is set at an angular position at the foot of the peak of the diffraction line 18. In this configuration, the dynamic diffraction intensity from the highly intact bulk crystal is extremely suppressed,
The kinematic diffraction intensity generated by minute crystal defects existing very near the surface is relatively increasing.
Under such conditions, the (100) Si wafer 17
Line 18 due to 422 asymmetric reflection of photographic film 1
Observe microscopically at 9.

[0007] The present invention relates to 25.
A similar effect can be obtained by using 311 asymmetric reflection, which is a lattice plane inclined by 24 °. When the wavelength near 1.404 A is finally selected from the synchrotron radiation 11 using the above-described procedure, the (100) Si wafer 1
7 was 0.15 °, and the critical angle was 0.20 °
Smaller. As a result, the (100) Si wafer 1
A diffraction line 18 from a (100) Si wafer 17 can be obtained under the condition that total reflection occurs on the surface 7. Here, (1)
00) If the Si wafer 17 is set at an angle position at the foot of the peak of the diffraction line 18 and photographed by diffraction microscopy with the photographic film 19, minute crystal defects existing very near the surface can be observed. .

According to the present invention, the (1)
A similar effect is exerted on a Si epitaxial crystal having a surface inclined by 4 ° in the <00> direction. In this case, it is effective to use asymmetrical reflection by the 084 plane perpendicular to the <100> direction inclined by 4 °. Using the procedure described above, finally, from the synchrotron radiation 11,
A wavelength near 1.086 A is selected, the incident angle of the X-rays 14 on the Si epitaxial crystal is reduced to a critical angle of 0.156 ° or less, and imaging is performed by diffraction microscopy at the angular position at the foot of the peak of the diffraction line 18. For example, minute crystal defects existing very close to the surface can be observed.

[0009]

As described above, according to the present invention, it is possible to observe, by X-ray microscopy, minute crystal defects existing in the vicinity of several tens of amperes from the surface. This has an effective effect on the comparison with the characteristic deterioration.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a calculation result under conditions according to the present invention.

Claims (1)

(57) [Claims] 1. A monochromatization of a silicon crystal to be measured.
Irradiated with synchrotron radiation under total internal reflection conditions
After obtaining the reflected diffraction line, the peak of the intensity of the diffraction line is obtained.
Total reflection X-ray diffraction microscopy , wherein a diffraction image is taken at an angular position deviated from the angle .