JPS6259253B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an X-ray diffraction apparatus. With the advancement of electronics technology, high quality crystals for electronic devices have become required. In particular, research on lattice distortion or warpage in epitaxial films on semiconductor silicon substrates, etc., has been actively conducted, and X-ray diffraction is generally used as a method for evaluating them. This method uses a diffraction intensity curve called a rocking curve. For example, by drawing the diffraction intensity curves of the substrate, epitaxial film, and diffusion layer, and knowing the relative difference in the diffraction angles between them, This is a method to obtain relative lattice strain. In this method, only one X-ray beam is irradiated onto the measurement sample, and it is possible to obtain information such as the relative lattice strain between the substrate and the epitaxial film formed on it at one irradiated location. It will be done.

Currently, wafer warpage and relative lattice strain at different locations on the crystal surface are measured using diffraction intensity curves, but
Since there is only one ray beam (irradiation X-ray beam),
To obtain X-ray diffraction at different locations, it is necessary to move the sample in parallel to change the location where the X-rays are irradiated, and measure the diffraction intensity curve each time the location is changed. Parallel movement of the sample is usually done mechanically, so it is extremely difficult to move the sample in parallel with an accuracy of less than 1 second, and therefore it is virtually impossible to determine minute differences in diffraction angles between different locations. It was impossible.

When determining the difference in diffraction angles, for example, it is necessary to always find a position on two diffraction intensity curves where the absolute values of the diffraction angles are the same. Generally, when measuring diffraction intensity curves, it is easy to determine the difference in relative diffraction angles, but it is not easy to reproducibly set the absolute value of the rotation angle of the sample to a certain value in separate measurements. .

In contrast, in the present invention, by using two or more irradiating X-ray beams, diffraction intensity curves at two or more different locations can be obtained in one measurement simply by rotating the sample. Relative differences in diffraction angles can be easily read, and measurement errors are small.

Next, details of the present invention will be explained based on the drawings.
An example of the measurement system in the X-ray diffraction apparatus of the present invention is shown in FIG. The X-ray beam generated by the X-ray source 1 is divided into parallel X-ray beams with a certain width by the first slit 2.
It becomes a line beam. This width is for example 0.2mm to 1.0mm
That's about it. The primary X-ray beam 3 passing through the first slit 2 is diffracted by the first monochrome collimator 4 and becomes a secondary X-ray beam 6 with excellent parallelism and monochromaticity. A dislocation-free silicon crystal is used as the first monochromatic collimator, and for example, (111) is used as the crystal surface and (511) is used as the diffraction surface. In this diffraction, the width of the secondary X-ray beam 6 diffracted by the monochrome collimator 4 becomes larger because the first-order X-ray beam 3 barely enters the crystal surface of the monochrome collimator. For example, when the angle between the primary X-ray beam 3 and the crystal surface is 6°, the X-ray beam width becomes approximately one order of magnitude larger. The secondary X-ray beam 6 is diffracted again by the second monochromatic collimator 5, and the width of the X-ray beam is further expanded, similar to the first diffraction.

There is an X-ray diffraction method called the two-crystal method, but this uses a single monochromatic collimator, and with this method, it is difficult to spread a well-paralleled X-ray beam to a width of, for example, 3 inches. . An X-ray beam of this width can be easily obtained by using two or more monochrome collimators. Furthermore, the greater the number of monochrome collimators, the better the monochromaticity of X-rays. This expanded tertiary X-ray beam 7 enters a second slit (slit system) 8. This slit type 8
has two slits, each of which can be opened and closed independently, and by opening two slits, two X-ray beams can be irradiated to different locations on the sample surface at the same time.

For example, the width of each slit in a slit system is
It is about 0.2mm to 0.5mm. These two irradiation X-ray beams 9 and 10 are irradiated onto the measurement sample 12.
If the rotation angle of the sample with respect to the incident direction is θ, if the lattice constants on the sample surface irradiated with the irradiated X-ray beams 9 and 10 are different, the rotation when the irradiated X-ray beams 9 and 10 are diffracted on the sample surface The angles θ are different from each other. Note that the measurement sample 12 is rotated around an axis included in the diffraction surface within the measurement sample, as in the conventional case.

In the figure, the irradiated X-ray beam 9 is diffracted by the sample 12, and the diffracted X-ray beam is indicated at 11.
Further, the irradiated X-ray beam 10 is diffracted in the state of the sample 16 in which the sample 12 is rotated by Δθ, and the diffracted X-ray beam is indicated by 17. Diffraction X-ray beam 1
1 is detected by a scintillation counter 13, passes through an amplifier 14, and is transmitted to an XY recorder 15.
is recorded as a diffraction intensity curve 18.

In the figure, two silicon crystals are shown as monochrome collimators, but there is no problem even if there are two or more silicon crystals. Further, the number of slits in the second slits (slit system) 8 does not need to match the number of monochrome collimators, and may be provided as many as the number of points on the sample that are desired to be measured.

By using the device of the present invention in this way,
Differences in diffraction angles at different locations on the crystal surface are represented in one diffraction intensity curve, and the differences in diffraction angles are easily obtained.

Next, a specific example using the present invention will be described. Sample 12 in Figure 1 is a silicon wafer (111) that is sufficiently thick that warpage is almost negligible.
A material partially subjected to antimony diffusion treatment was used. As X-ray source 1, CuKa ₁ ray, intensity 50KV.
80mA was used. The first slit makes the beam width 0.8 mm, and the two monochromatic collimators use dislocation-free silicon crystals as the diffraction surface (511).
was used. The crystal surface is oriented so as to form an angle of about 6° with the incident beam, and the slit system has two rectangular slits with a width of 0.2 mm and a length of 5 mm, and the slit interval is 9.
10 was selected so that the diffusion area and other areas were irradiated. Open both of these slits,
The diffraction intensity curve was measured by simultaneously irradiating the diffusion region and other regions with the irradiation X-ray beam. Note that (511) is used as the diffraction surface of the sample here. As a result, two diffraction peaks separated by about 2 seconds were obtained, and knowledge regarding the relative lattice strain in these two regions was obtained.

In this embodiment, the relative lattice strain at different locations has been described, but by using the apparatus of the present invention, it is possible to obtain knowledge regarding wafer warpage in addition to such lattice strain.

As described above, the present invention is different from the conventional one.
Unlike devices that measure diffraction intensity curves using a single irradiated X-ray beam, by using two or more irradiated X-ray beams, differences in diffraction angles at different locations can be drawn in one diffraction intensity curve. By using the device of the present invention, relative lattice strain at different locations on the wafer surface, warpage of the wafer, etc. can be controlled by rotating the sample instead of translating it as in the conventional method. The diffraction intensity curve can be determined easily and accurately by just one measurement.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the present invention. 1... X-ray source, 2... First slit, 3... Primary X-ray beam, 4... First monochrome collimator, 5... Second
Monochrome collimator, 6...secondary X-ray beam, 7...
Tertiary X-ray beam, 8... Second slit (slit system), 9, 10... Irradiation X-ray beam, 11, 17...
Diffraction X-ray beam, 12, 16...Measurement sample, 13...
Scintillation counter, 14...Amplifier, 1
5...X-Y recorder, 18... Diffraction intensity curve.

Claims (1)

[Claims] 1. In an X-ray diffraction apparatus that uses X-ray diffraction to detect lattice strain on the surface of a crystal wafer or warpage of the wafer, a first monochromatic collimator made of silicon crystal that diffracts X-rays from an X-ray source; Diffraction X from the monochrome collimator
It has at least two collimators, including a second monochrome collimator made of silicon crystal that diffracts the line beam again, and a single diffracted X-ray emitted from the last monochrome collimator placed between the last monochrome collimator and the measurement sample. A slit system having a plurality of slits that divides the beam into a plurality of desired X-ray beams and simultaneously irradiates the measurement sample surface with the plurality of X-ray beams, and an axis included in the diffraction surface within the measurement sample. A sample rotation mechanism that rotates the measurement sample around the center, and a diffraction An X-ray diffraction apparatus comprising a detection/recording mechanism for continuously recording the rotation angle of the sample.