JP6032404B2 - X-ray crystal analysis method - Google Patents

Description

  The present invention relates to an X-ray crystal analysis method.

  In current advanced devices, not only inorganic semiconductors such as silicon and gallium nitride, but also organic substances such as functional polymers and organometallic complexes are used.

  In general, the former is a material close to a single crystal, and even when formed as a thin film, the crystal can be grown in an epitaxial state, and the crystallinity is very good. On the other hand, the latter has low crystallinity. In device development using such materials, not only the crystallinity and crystal orientation of the material, but also the amount of crystals and the distribution in the depth direction of the crystals have a great influence on the electrical characteristics and stress characteristics of the device. A typical method for evaluating a crystal of a material is an X-ray diffraction method.

  In the crystal analysis method using the X-ray diffraction method, there is a small angle incident X-ray diffraction method as a method for evaluating the structure near the surface of the sample and in the depth direction from the surface of the sample. The small-angle incident X-ray diffraction method is a method for sensitively measuring diffracted X-rays from a thin film by making X-rays incident on a sample at a shallow angle and suppressing the penetration depth of the X-rays into the sample.

  When the X-ray incident angle is smaller than the total reflection critical angle of the sample, the X-ray penetration depth is on the order of several nm. By increasing the incident angle of X-rays beyond the total reflection critical angle, the penetration depth of X-rays can be changed from 100 nm to several μm. Conventionally, by utilizing this phenomenon and controlling the X-ray incident angle near the total reflection critical angle, X-ray diffraction from the sample region corresponding to the penetration depth of the X-ray is obtained, and the thin film and the surface vicinity. I got information about the crystals.

Zeit fur Kristallography Vol.213 (1998) pp. 319-336

In the above method of controlling the incident angle of X-rays near the total reflection critical angle, it is possible to detect the presence or absence of crystals in a region corresponding to the penetration depth of X-rays. However, even if the angle is slightly increased near the total reflection critical angle, the X-ray penetration depth changes abruptly by about two orders of magnitude, making it difficult to determine the crystal distribution in the depth direction with high accuracy.

  An object of the present invention is to provide an X-ray crystal analysis method for measuring the crystal distribution in the depth direction from the surface of a sample having a crystal and a structural order with higher accuracy than before.

According to one aspect of the present embodiment, X-rays are incident on a set point on the surface of a sample having a crystal and a structural order at an incident angle in a set range with reference to the total reflection critical angle, and from the sample. The intensity of the diffracted X-ray diffracted at a desired diffraction angle is measured, a measured X-ray diffraction intensity profile indicating a change in the intensity of the diffracted X-ray with respect to the incident angle is obtained, and the incident angle at the set location of the sample By measuring the reflection intensity of the X-rays that are totally reflected in the set range, obtaining an X-ray reflection intensity profile indicating the relationship between the incident angle and the X-ray reflection intensity, and analyzing the X-ray reflection intensity profile The density distribution in the depth direction in the sample is determined, the refractive index for the X-ray in the sample is obtained, and the electric field strength showing the relationship between the electric field intensity due to the X-ray formed in the sample and the incident angle Total distribution Assuming a depth distribution of the amount of crystals in the sample, the multiplication result obtained by multiplying the electric field intensity distribution by using the depth distribution of the amount of crystals as a weighting factor is a thickness with respect to the depth of the sample. To obtain a calculated X-ray diffraction intensity profile by calculating the relationship between the incident angle and the X-ray diffraction intensity of the set range, and the previously calculated X-ray diffraction intensity profile is the measured X-ray diffraction intensity. The depth distribution of the crystal amount is changed so as to match the profile, parameter fitting is performed, and the depth distribution of the crystal that the X-ray diffraction intensity profile calculated earlier matches the measured X-ray diffraction intensity profile is changed. An X-ray crystal analysis method is provided that includes a process for determining a final crystal content distribution in the depth direction of a sample.
The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention.

  According to the present embodiment, the distribution of crystals in the depth direction from the surface of the organic substance can be determined by using data obtained by X-ray irradiation. It is also possible to determine the depth distribution of crystals having different crystal orientations.

FIG. 1 is a perspective view showing an example of a test apparatus for performing the X-ray crystal analysis method according to the embodiment. FIG. 2 is a cross-sectional view showing an example of a layer structure of a sample to be analyzed by the X-ray crystal analysis method according to the embodiment. FIG. 3 is a flowchart showing an example of the X-ray crystal analysis method according to the embodiment. FIG. 4 is a diagram illustrating an example of an X-ray diffraction intensity profile measured for a set position of a sample in the X-ray crystal analysis method according to the embodiment. FIG. 5 is a characteristic diagram illustrating the dependency of the X-ray reflection intensity on the X-ray incident angle of the set portion of the sample in the X-ray crystal analysis method according to the embodiment. FIG. 6 is a diagram illustrating a sample density distribution in the depth direction at a sample setting position in the X-ray crystal analysis method according to the embodiment. FIGS. 7A, 7 </ b> B, and 7 </ b> C are electric field intensity distribution diagrams illustrating the relationship between the X-ray incident angle and the electric field intensity at a set position of the sample in the X-ray crystal analysis method according to the embodiment. FIG. 8 is a diagram illustrating an example of a crystal amount distribution assumed in the depth direction at a set position of a sample in the X-ray crystal analysis method according to the embodiment. FIG. 9 is an X-ray diffraction intensity profile obtained by calculation of the relationship between the X-ray diffraction intensity and the incident angle at a set position of the sample in the X-ray crystal analysis method according to the embodiment. FIG. 10 is an X-ray diffraction intensity profile showing an example of fitting the X-ray diffraction intensity profile shown in FIG. 8 to the X-ray diffraction intensity profile shown in FIG. FIG. 11 is a diagram illustrating an example of a test result of a crystal amount distribution at a selected portion of a sample in the X-ray crystal analysis method according to the embodiment.

  Embodiments will be described below with reference to the drawings. In the drawings, similar components are given the same reference numerals. FIG. 1 is a perspective view showing an example of a test apparatus for performing the X-ray crystal analysis method according to the embodiment.

  In FIG. 1, an X-ray source 1 has a structure in which X-rays are emitted in the form of a beam onto the surface of a sample 10 placed in front of the X-ray source 1 and the emission angle θ relative to the surface can be adjusted. On the side opposite to the X-ray source 1 with respect to the sample 10, an X-ray detector 3 including an X-ray detection element array such as a CCD array is arranged in a direction to receive X-rays reflected from the sample 10. . A calculation unit 4 for obtaining a crystal distribution in the sample 10 based on the emission angle θ of the X-ray light source 1 and the detection value of the X-ray detector 3 is connected to the X-ray source 1 and the X-ray detector 3. . In FIG. 1, the horizontal line of the alternate long and short dash line shown in the X-ray detector 3 indicates the position in the plane on the extension of the upper surface of the sample 10, and the area above it indicates the area outside the plane.

When there are a plurality of microcrystals in the sample 10, a part of the X-rays irradiated to the sample 10 is emitted to the outside of the sample 10 as diffracted X-rays. Angle of incidence of X-rays in the sample 10 theta is the case close to the total reflection critical angle at the surface of the sample 10, from the sample 10 in addition to the diffracted X-rays, there is component X ₀ specularly reflected by the sample 10 surface. The specular reflection is applied to a position indicated by a chain line of the X-ray detector 3 shown in FIG. Further, as the X-ray irradiation angle θ is increased from 0 °, the X-ray incident depth in the sample 10 becomes deeper.

As a sample 10, a structure as illustrated in FIG. 2, that is, an indium tin oxide (ITO) transparent conductive layer 12, a molybdenum oxide (MoO ₃ ) layer 13, and an organic material layer 14 are formed in this order on a glass substrate 11. Use a laminated structure. This laminated structure is used for an organic thin film solar cell, for example. As the organic material layer 14, a layer having crystal and structural order, for example, PCDTBT that is a polycarbazole conjugated polymer or PCBM that is a fullerene derivative is formed.

  Next, the X-ray crystal analysis method will be described according to the flowchart shown in FIG. The flow may be executed by the calculation unit 4 shown in FIG. For example, a program for executing the flow shown in FIG. 3 may be stored in a storage unit of a computer and executed by a CPU or the like.

  An X-ray beam having a wavelength of 0.14 nm is irradiated at an incident angle θ in the vicinity of the total reflection critical angle θc (S1 and S2 in FIG. 3) on a set portion of the sample 10 having the above structure. Then, the relationship between the intensity of the diffracted X-rays from the crystal in the sample 10 appearing at a diffraction angle of 17 ° indicated by the dashed semicircle of the X-ray detector 3 in FIG. 1 and the emission angle θ is measured, and is shown in FIG. An X-ray diffraction intensity profile is acquired (S3 in FIG. 3). In FIG. 4, the incident angle θ is set in the vicinity of the total reflection critical angle θc as a reference, for example, a range of about 0.04 ° to 0.30 °. In this case, the total reflection critical angle θc is 0.16 °. The incident angle of the X-ray on the sample 10 with respect to the surface of the sample 10 is the same as the emission angle from the X-ray source 1.

  The horizontal axis of FIG. 4 indicates the magnitude of the incident angle θ of the X-ray with respect to the surface of the sample 10, and the vertical axis indicates the intensity of the standardized diffraction X-ray. When the incident angle θ is in the range from 0.00 ° to about 0.14 °, the intensity of the diffracted X-ray at the diffraction angle of 17 ° is almost zero. Further, the incident angle θ has a peak depending on the transparent conductive layer 12 below from about 0.15 ° to about 0.18 °, and the diffracted X-ray intensity from about 0.18 ° to about 0.25 °. Decreases while vibrating. Further, the constant strength is substantially maintained at about 0.25 ° or more. The diffraction X intensity profile having vibration reflects the existence of a crystal distribution in the depth direction of the sample 10, but the distribution of the crystal amount in the depth direction (thickness direction) is unknown as it is.

  Next, when X-rays are irradiated to the portion irradiated in the measurement shown in FIG. 4 in the sample 10 and the X-ray intensity reflected specularly on the sample surface is changed by changing the incident angle θ, a profile as shown in FIG. 5 is obtained. Is obtained (S4 in FIG. 3). In FIG. 5, the specular reflection intensity of the X-ray on the vertical axis is shown on a logarithmic scale, and when the incident angle θ is larger than about 0.16 °, it has a profile that vibrates according to the laminated structure of the sample 10 and becomes larger. Decays quickly. The reflectance profile has a specific vibration structure depending on the thickness, density, and interface roughness of the material. In addition, since the incident angle θ is too small from about 0.02 ° to about 0.16 °, the X-ray reflection reflectivity cannot be measured accurately, and logically the same intensity as in the case of about 0.16 °. Become.

  Therefore, when the density distribution and thickness in the depth direction of the sample 10 in which the X-ray reflection intensity profile shown in FIG. 5 appears are obtained by fitting, the distribution shown in FIG. 6 is obtained (S5 in FIG. 3). In the horizontal axis shown in FIG. 6, the upper surface of the glass substrate 1 of the sample 10 is shown as thickness reference 0, and the same applies to FIGS. 7, 8, and 11 described later.

According to FIG. 6, the density of the ITO transparent conductive film 12 is the highest in the sample 10, and the densities of the MoO ₃ layer 13 and the organic layer 14 on the ITO transparent conductive film 12 change in the depth direction. A method for determining the density of a sample from an X-ray reflection intensity profile is a known analysis technique, for example, an X-ray reflectivity method. In the X-ray reflectivity method, an X-ray was incident on the surface of the sample 10 at an extremely shallow angle, and an X-ray intensity profile as shown in FIG. 5 was measured based on the intensity of the X-ray reflected in the mirror surface direction with respect to the incident angle. This is a method of determining the film thickness and density of the sample by comparing the profile with the simulation result and optimizing the simulation parameters later. In this case, the crystal content distribution in the depth direction cannot be directly derived from the density analysis result in the organic layer 14 of the sample 10.

  When an X-ray reflection intensity profile is obtained by calculation based on the density distribution in FIG. 6, it is confirmed that the measured value is equal to or greater than the total reflection critical angle θc as shown by the white line in FIG. In the X-ray reflection intensity profile, since the error of the actual measurement value is large at an angle lower than the total reflection critical angle θc as described above, the calculated X-ray reflection intensity profile is used for the following calculation and the like.

  Next, a refractive index distribution for X-rays in the sample 10 is calculated based on the density distribution in the sample 10 shown in FIG. 6, and the electric field intensity distribution E by X-rays in the sample 10 is determined by defining the condition of the incident angle θ. (Z, θ) is calculated (S6 in FIG. 3). Such an electric field intensity distribution is obtained, for example, in a range from an incident angle of 0 ° to 0.3 °, and an example thereof is shown in FIGS. 7 (a), (b), and (c). 7A, 7B, and 7C show cases of 0.165 °, 0.170 °, and 0.175 ° that are larger than the total reflection critical angle θc, and an electric field is also generated on the surface of the sample 10. Appears.

  The electric field intensity distribution E (Z, θ) is calculated by a distorted wave Born approximation (DWBA) method. The DWBA method is a known method and is described, for example, in Zeit fur Kristallography Vol. 213 (1998) pp. 319-336.

  Next, the depth distribution D (Z) of the crystal amount from the surface of the sample 10 to the depth of 90 nm including the organic layer 14 is assumed as shown in FIG. 8 (S7 in FIG. 3). FIG. 8 shows an example in which the organic material layer 14 is divided into an upper layer, a middle layer, and a lower layer using a multi-slice method.

  The multi-slice method is one method for calculating the intensity of transmitted waves and diffracted waves under a crystal when an electron beam is incident on the crystal. The layer containing the crystal is regarded as a series of strips parallel to the surface and having a certain width in the depth direction, and electrons incident on this crystal are scattered by the first slice and undergo phase change until the next slice. The diffraction amplitude (intensity) on the lower surface of the crystal is calculated on the assumption that the electron beam reaches the lower surface of the crystal by propagating and repeating scattering and propagation in successive slices. In FIG. 8, it is assumed that the same crystal amount is distributed in the upper layer, the middle layer, and the lower layer, but they may be assumed to be different.

  The depth distribution function D (Z) of the crystal amount shown in FIG. 8 is used as a weighting factor to multiply the electric field intensity distribution E (Z, θ). Calculate the integral. By this calculation, as shown by the broken line, the two-dot chain line, and the one-dot chain line in FIG. 9, the calculated X-ray diffraction intensity profile for the incident angle θ is obtained for the upper layer, the middle layer, and the lower layer (S8 in FIG. 3). The sum of the calculated X-ray diffraction intensity profiles of the upper layer, middle layer, and lower layer of the sample 10 in this case is shown by the solid line in FIG.

  Next, the depth distribution D (Z) of the crystal amount is set so that the calculated X-ray diffraction intensity profile of the sum shown by the solid line in FIG. 9 matches the X-ray diffraction intensity profile of the measurement result shown in FIG. Adjust and perform parameter fitting. That is, as shown by the solid line and the dot in FIG. 10, the calculated X-ray diffraction intensity profile is matched with the measured X-ray diffraction intensity profile. According to the recalculation of the calculated X-ray diffraction intensity profiles of the upper layer, middle layer, and lower layer using the adjusted crystal depth distribution D (Z), the broken line, the two-dot chain line, and the one-dot chain line in FIG. An X-ray diffraction intensity profile as shown is determined.

  Next, the depth distribution D (Z) of the crystal amount modified and adjusted to obtain the X-ray diffraction intensity profile shown in FIG. 10 is as shown in FIG. 11, for example. According to FIG. 11, the distribution of the amount of crystal of the sample 10 that becomes the X-ray diffraction intensity profile by actual measurement shown in FIG. 4 is about 0.20 for the upper layer, about 0.35 for the middle layer, and about 1.3 for the lower layer. Thus, it can be seen that the distribution is such that the lower the layer, the greater the amount of crystals (S9 in FIG. 3). Note that when using the multi-slice method, the number of layers is not limited to three, and the details of the crystal distribution become clear as the number of layers increases.

  In the above description, first, a profile (FIG. 4) of an X-ray diffraction intensity change including a fine structure such as a peak structure and a vibration structure obtained by changing the incident angle θ of the X-ray with respect to the sample 10 is obtained. ing. Further, the density (FIG. 6) determined by the X-ray reflection intensity (FIG. 5) and the refractive index are used to calculate the X-ray electric field strength (FIG. 7) in the sample 10, and the depth in the sample 10 is also calculated. A distribution of the amount of crystals in the vertical direction (FIG. 8) is assumed. Then, the electric field intensity is multiplied by using the distribution of the crystal amount as a weighting factor, and the result is used to calculate the integral of the thickness of the organic material of the sample 10 in the depth direction, and the calculated X-ray diffraction intensity profile with respect to the incident angle θ. (FIG. 9) is obtained. Further, the distribution in the depth direction of the crystal amount in the sample 10 is changed so as to fit the calculated X-ray diffraction intensity profile to the actually measured X-ray diffraction intensity profile (FIG. 10), and the data after the change is changed to the depth direction. It is determined as the final crystal amount distribution (FIG. 11).

  This makes it possible to determine the depth distribution of crystals in a system with low crystallinity typified by organic matter or crystals scattered in the material. In particular, when the analysis target is an organic thin film, the depth distribution of the electric field strength in the thin film largely depends on the underlying layer, so when a substance having a density higher than that of the organic thin film is used as the underlying layer, for example, an ITO transparent conductive layer, The analysis effect is great.

  By the way, in the above-described embodiment, the distribution of the depth of the crystal amount may be assumed using a peak function such as a Gaussian function, a Lorentz function, or a pseudo-Fork instead of the multi-slice method. In this case, parameters, positions, widths, and areas of the peak function are determined by fitting using a plurality of peak functions.

  In addition, X-rays are irradiated to a plurality of locations to measure the intensity of diffracted X-rays having the same diffraction index, for example, 17 °, and different orientations, and the incident angle dependence of a plurality of measured X-ray diffraction intensity profiles and X-ray reflection intensity And the above calculation may be further performed to determine the final crystal content distribution at a plurality of locations. Thereby, the final crystal quantity distribution in the plane direction can be acquired for the same sample, and the variation in the crystal quantity distribution in the thickness direction on the same plane can be detected.

  The scales on the vertical axis and the horizontal axis in FIGS. 4 to 11 are proportional scales unless otherwise specified.

  All examples and conditional expressions given here are intended to help the reader understand the inventions and concepts that have contributed to the promotion of technology, such examples and It should be construed without being limited to the conditions, and the organization of such examples in the specification is not related to showing the superiority or inferiority of the present invention. Although embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions and variations can be made thereto without departing from the spirit and scope of the present invention.

DESCRIPTION OF SYMBOLS 1 X-ray source 3 X-ray detector 4 Calculation part 10 Sample 11 Glass substrate 12 Transparent conductive layer 13 MoO ₃ layer 14 Organic substance layer

Claims (4)

X-rays are incident on a set point on the surface of a sample having a crystal and structural order at an incident angle within a set range based on the total reflection critical angle, and diffracted X-rays diffracted at a desired diffraction angle from the sample. Measuring an intensity, obtaining a measured X-ray diffraction intensity profile showing a change in intensity of the diffracted X-ray with respect to the incident angle;
Measuring the reflection intensity of the X-rays that are totally reflected in the setting range of the incident angle at the setting location of the sample, obtaining an X-ray reflection intensity profile indicating the relationship between the incident angle and the X-ray reflection intensity;
By analyzing the X-ray reflection intensity profile, the density distribution in the depth direction in the sample is determined, the refractive index for the X-ray in the sample is obtained, and the electric field by the X-ray formed in the sample Calculate the electric field intensity distribution indicating the relationship between the intensity and the incident angle,
Assuming a depth distribution of the amount of crystals in the sample,
The multiplication result obtained by multiplying the electric field intensity distribution by using the depth distribution of the crystal amount as a weighting factor is executed to integrate the thickness with respect to the depth of the sample. Obtain the calculated X-ray diffraction intensity profile by calculating the relationship of X-ray diffraction intensity,
Parameter fitting is performed by changing the depth distribution of the amount of crystal so that the first-calculated X-ray diffraction intensity profile matches the measured X-ray diffraction intensity profile. An X-ray crystal analysis method including a process of determining a depth distribution of the crystal to be matched with a diffraction intensity profile as a final crystal amount distribution in a depth direction of the sample . In the sample, a high-density layer formed of a material having a higher density than the thin film is formed below the thin film having the crystal and structural order for which the final crystal amount distribution is to be determined. The X-ray crystal analysis method according to claim 1 . 3. The X-ray crystal analysis method according to claim 1, wherein, in the sample, the crystal and the thin film having a structural order on which the final crystal amount distribution is determined are formed of an organic substance. . Two or more diffracted X-ray diffracted X-rays having the same diffraction index and different orientations are acquired, and the same portion where the X-rays are irradiated to acquire the respective measured X-ray diffracted intensity profiles is obtained. The X-ray crystal analysis method according to claim 1, wherein the calculated X-ray diffraction intensity profile is acquired to determine the final crystal content distribution.

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