JP2005274536A - Method and system for evaluating crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for evaluating a crystal, which can acquire accurate information required for evaluating a crystal property or an orientation of the crystal material and can carry out its evaluation appropriately by using the acquired information. <P>SOLUTION: The method for evaluating the crystal irradiates a sample with radiation, measures diffraction radiation reflected by the sample and evaluates the sample from the measurement. In the method, a coordinate system is set, wherein total three variables which are used as mutually independent axes, are composed of one variable 2θ and two variables selected from ϕ, ψ and ω, and a diffraction image of the sample is expressed as a function having the above three variables. The variables respectively represent a rotation angle (ϕ) so defined that its axis of rotation is perpendicular to the sample plane; a tilt angle (ψ) formed in a plane perpendicular to the incidence axis of the incident radiation; an incident angle (ω) between the sample plane and the incident radiation under the condition that ψ is zero degree; and an included angle (2θ) between the incident radiation and the diffraction radiation. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a crystal evaluation method and a crystal evaluation system for evaluating crystallinity and orientation distribution of a crystal such as a thin film crystal material by utilizing a diffraction phenomenon such as X-ray.

Conventionally, as a method for evaluating this type of crystal material, the crystal structure of the crystal material is evaluated by irradiating a sample to be measured with X-rays and measuring reflected X-rays by Bragg reflection from the crystal plane. What to do is known.
That is, in this crystal material evaluation method, the incident direction of X-rays is changed little by little, and the Bragg reflected light is measured to detect reciprocal lattice points in the reciprocal space and its distribution characteristics (two-dimensional reciprocal space) It is known to create a map) and thereby evaluate the crystal structure of the crystal material.

However, in the conventional method, a two-dimensional reciprocal lattice space map is created. For this reason, for example, accurate information regarding the evaluation of crystallinity and orientation of a thin film material deposited on a crystal substrate, or lattice matching at the interface (the junction between the crystal substrate and the thin film formed thereon) is not displayed. There is a problem that it is difficult to acquire by destruction.
Conventionally, the evaluation of the interface has been performed using a cross-sectional TEM (transmission electron microscope). However, such a method has problems such as difficulty in preparing a sample and obtaining only local information.

  Therefore, an object of the present invention is to obtain accurate information necessary for evaluation of crystallinity and orientation of a crystal material, and to perform appropriate evaluation based on the acquired information, and a crystal It is to provide an evaluation system.

In order to solve the above problems and achieve the object of the present invention, each invention has the following configuration.
That is, the first invention is a crystal evaluation method in which a sample is irradiated with radiation, diffracted radiation reflected by the sample is measured, and the sample is evaluated based on the measurement. Rotation angle (φ), tilt angle (ψ) perpendicular to the incident direction of incident radiation, incident angle (ω) formed by the sample surface and incident radiation in the state of ψ = 0 °, and incidence Of the included angle (2θ) formed by radiation and diffracted radiation, using a coordinate system with all three variables consisting of two variables selected from 2θ and φ, ψ, ω as independent axes, A diffraction image from the sample was expressed as a function of the three variables.

According to a second invention, in the first invention, from the diffraction intensity distribution from the sample expressed in the space coordinates constituted by the axes composed of the three variables, the highest on the perpendicular to an arbitrary plane in the space. Data having a large value of the diffraction intensity is projected as a representative point.
According to a third invention, in the first invention, when obtaining a projection from a diffraction intensity distribution from a sample expressed in space coordinates composed of the three axes, to an arbitrary plane in the space. The diffraction intensity distribution of the cut surface that passes through the vicinity of the point having the largest intensity value in the space and is cut by a plane parallel to the plane is used as the projection value.

According to a fourth invention, in any one of the first to third inventions, the radiation is any one of an X-ray, an electron beam, and a neutron beam.
In the fifth aspect of the invention, when there is an instruction to create a map of a predetermined three-dimensional reciprocal lattice space necessary for the structural analysis of the sample, X-rays are irradiated to the sample in accordance with this instruction and reflected from the sample. X-ray diffracting means for receiving diffracted X-rays satisfying Bragg's condition and measuring diffraction intensity data thereby, and collecting diffraction intensity data measured by the X-ray diffracting means, and based on this, the three-dimensional inverse Data processing for creating a lattice space map and displaying the diffraction intensity data of reciprocal lattice points in the 3D reciprocal lattice space accumulated at the time of creating the 3D reciprocal lattice space as a three-dimensional image display At least diffraction intensity data processing means for performing, and display means for three-dimensionally displaying an image obtained by data processing of the diffraction intensity data processing means.

  In a sixth aspect based on the fifth aspect, the predetermined three-dimensional reciprocal lattice space is perpendicular to the rotation angle (φ) about the direction perpendicular to the sample surface and the incident direction of incident X-rays. The tilt angle (ψ) of the direction, the incident angle (ω) formed by the sample surface and the incident X-ray in the state of ψ = 0 °, and the included angle (2θ) formed by the incident X-ray and the diffracted X-ray Of these, a coordinate system is used in which all three variables composed of two variables selected from 2θ and φ, ψ, and ω are independent axes.

In the present invention having such a structure, the distribution of the reciprocal lattice points in the reciprocal space necessary for the analysis of the structure of the crystal material can be expressed in three dimensions, that is, a three-dimensional reciprocal lattice space map can be obtained and necessary. Depending on, the projection of the arbitrary surface can be expressed.
For this reason, according to the present invention, accurate information necessary for evaluating the crystallinity and orientation of the crystal material can be acquired, and various evaluations of the crystal material can be appropriately performed based on the acquired information. it can.

Embodiments of a crystal evaluation method and a crystal evaluation system according to the present invention will be described below with reference to the drawings.
The crystal evaluation method of the present invention creates a three-dimensional reciprocal lattice space map representing the distribution of reciprocal lattice points in a reciprocal space necessary for structural analysis of crystal materials and the like in three dimensions, and at the time of creating the map. In order to evaluate crystal materials, etc., three-dimensional image display of intensity data (diffraction intensity data) of reciprocal lattice points accumulated in the three-dimensional reciprocal lattice space or an arbitrary cross section thereof is displayed. It is designed to obtain the accurate information necessary for the operation.

Therefore, the crystal evaluation system according to this embodiment includes at least an X-ray diffractometer 1, a diffraction intensity data processor 2, a display device 3, and an input device 4, as shown in FIG. .
As will be described later, when the X-ray diffractometer 1 receives an instruction from the input device 4 to create a three-dimensional reciprocal lattice space map necessary for the structural analysis of the sample a to be measured, Then, X-rays that are radiation are irradiated, diffracted X-rays that satisfy the Bragg condition reflected from the sample a are received, and diffraction intensity data is thereby measured.

That is, as shown in FIG. 1, the X-ray diffraction apparatus 1 includes a stage 11 on which a sample a is set, an X-ray irradiation unit 12 that irradiates the sample a with X-rays, and diffraction reflected from the sample a. It includes at least a light receiving unit 13 that receives X-rays, and measures diffraction intensity data for creating a three-dimensional reciprocal lattice space map as described later.
Here, the sample a is a crystal material such as a thin film crystal material, or a film in which a film of platinum or the like is formed on the surface of a silicon substrate.

The diffraction intensity data processing device 2 is composed of a computer or the like, collects the diffraction intensity data measured by the X-ray diffraction device 1, and based on this collects the three-dimensional reciprocal lattice space as will be described later, which is necessary for the structural analysis of the sample. Create a map.
Further, the diffraction intensity data processing device 2 displays a three-dimensional image of the diffraction intensity data of reciprocal lattice points in the three-dimensional reciprocal lattice space accumulated when creating the three-dimensional reciprocal lattice space map, or an arbitrary display thereof. Data processing for displaying a cross section as an image is performed.

The display device 3 displays an image obtained based on the data processing of the diffraction intensity data processing device 2 in two-dimensional or three-dimensional color display, for example.
When the input device 4 is used in this crystal evaluation system to evaluate a crystal, the input device 4 gives various instructions such as measurement conditions to be described later to the X-ray diffraction device 1 and the diffraction intensity data processing device 2. Is what you do.

Next, a crystal evaluation method performed using the crystal evaluation system according to the embodiment having such a configuration will be described.
The three-dimensional reciprocal space map expressed by this embodiment is a reciprocal space composed of three parameters selected from 2θ, ω, φ, and ψ among the notations in the real space defined in FIG. Are displayed (drawn) as a set of X-ray diffraction (reflection) points.

Here, φ is a rotation angle with the direction perpendicular to the surface of the sample a as the rotation axis, and ψ is a tilt angle perpendicular to the incident direction of incident X-rays (incident radiation). Further, ω is an incident angle formed between the sample a surface and incident X-rays in the state of ψ = 0 °, and 2θ is an included angle formed between the incident X-rays and the diffracted X-rays.
Therefore, the three-dimensional reciprocal lattice space obtained in this way is, for example, 2 as shown in FIG.
Of the axes of θ, ω, ψ, those of the axes of 2 θ, ψ, φ as shown in FIG. 3B, and those of 2 θ, φ, ω as shown in FIG. The thing which consists of each axis is mentioned.

FIGS. 3A, 3B, and 3C are three-dimensionally enlarged views of a minute space composed of small spheres A, B, and C shown in the coordinates of the central view of FIG. Further, the planes of the kamaboko-shaped figures E and F drawn in the central coordinate system of FIG. 3 are planes from which X-rays enter and exit.
Next, the measurement performed by the X-ray diffraction apparatus 1 when creating the three-dimensional reciprocal lattice space map as described above will be described.

In this example, a case will be described in which a three-dimensional reciprocal lattice space map including respective axes as shown in FIG. 3B is created based on an operator's instruction from the input device 4.
In this case, when the sample a is set on the stage 11, the X-ray diffractometer 1 sets the included angle 2θ shown in FIG. 2 to a fixed state, which is the distance from the origin of the coordinates of the three-dimensional reciprocal lattice space. It corresponds to fixing. The X-ray diffractometer 1 measures the diffraction intensity data of the sample a by fixing the tilt angle ψ while fixing the included angle 2θ and slightly changing the incident angle ω in this state.

Thereafter, the X-ray diffractometer 1 fixes the tilt angle ψ slightly by changing the tilt angle 2θ slightly, and fixes it again. In this state, the incident angle ω is changed slightly, and the diffraction intensity data of the sample a is obtained. taking measurement.
By repeating such measurement, the diffraction intensity data processing apparatus 2 collects the above diffraction intensity data and creates an X-ray diffraction intensity distribution in a plane (layer) composed of two parameters.

Furthermore, the X-ray diffraction apparatus 1 slightly changes the included angle 2θ to be in a fixed state, changes the tilt angle ψ and the incident angle ω slightly as described above, and the diffraction intensity data of the sample a each time. Measure.
As a result of this measurement, the diffraction intensity data processing device 2 creates a three-dimensional reciprocal lattice space map in which X-ray diffraction intensity distributions in a plane are stacked at a minute interval (see FIG. 3B).

Note that when creating a three-dimensional reciprocal lattice space map consisting of the axes shown in FIG. 3A or FIG. 3C, a three-dimensional reciprocal lattice space map consisting of the axes shown in FIG. This can be realized by the same measurement as in the case of.
Next, the diffraction intensity data processing device 2 displays a three-dimensional image of diffraction intensity data of reciprocal lattice points in the three-dimensional reciprocal lattice space accumulated at the time of creating the three-dimensional reciprocal lattice space map, or Data processing for image display of an arbitrary cross section or the like is performed.

  For the data processing performed by the diffraction intensity data processing apparatus 2, a three-dimensional image processing method of acquired data used in CT (Computed Tomography) and MRI (Magnetic Resonance Imaging) image diagnosis is applied in the advanced medical field. Examples include MPR (Multi Planer Reconstruction), MIP (Maximum Intensity Projection), and VR (Volume Rendering).

Here, MPR is a method of slicing intensity data accumulated in a three-dimensional space at an arbitrary location and orientation, and displaying a cross-sectional intensity distribution in a two-dimensional plane with a color map, contour lines, and the like. The names shown in FIG. 4 are used according to the orientation of the slice plane.
MIP is a method of projecting, as a representative point, data having the highest intensity on a perpendicular to a wall surface when projecting intensity data accumulated in a three-dimensional space on an arbitrary wall surface.

VR is a method in which a surface is created using a specific intensity data value as a threshold value, and a three-dimensional sensation is drawn by adding a shadow of light to the surface. In addition to still images, moving images such as rotation can be created, and if necessary, they can be expressed in a cut model by combining them.
Next, since the three-dimensional reciprocal lattice space map was specifically created by the crystal evaluation system according to the embodiment shown in FIG. 1, it was created using the specific example and diffraction intensity data accumulated at that time. Various image display examples for crystal evaluation will be described.

In this example, the sample a is obtained by depositing Pt (platinum) on a silicon substrate. Since any Pt is almost (111) oriented, the three-dimensional reciprocal lattice space map was created by the following procedure.
First, the X-ray diffraction apparatus 1 fixes the included angle 2θ (CuKα: ˜40 °) corresponding to the interval of the Pt (111) plane, and scans the incident angle ω and the tilt angle ψ within an appropriate range. Using the diffraction intensity data collected in this way, the diffraction intensity data processing apparatus 2 creates a two-dimensional layer. Next, the X-ray diffraction apparatus 1 slightly shifts the included angle 2θ and performs ω-ψ scanning again. The diffraction intensity data processing device 2 creates a three-dimensional reciprocal lattice space map by repeating this within an appropriate range of 2θ and stacking the obtained two-dimensional layers.

Next, the diffraction intensity data processing device 2 converts the diffraction intensity data of the reciprocal lattice points in the three-dimensional reciprocal lattice space accumulated when the three-dimensional reciprocal lattice space map is created as described above into a three-dimensional image display. Or data processing for converting the arbitrary cross section into an image.
Since the display device 4 displays an image obtained based on data processing, a specific image display example will be described with reference to FIGS.

FIGS. 5A and 5B are VRs of a three-dimensional reciprocal lattice distribution in the vicinity of Pt (111) with respect to Pt made under different film forming conditions. Here, although FIG. 5 is expressed as a black and white grayscale image, it is actually expressed as a color image, and the same applies to FIGS. 6 to 8 below.
The difference between the CT and MRI intensity data and the diffraction intensity data related to this measurement is that the latter is a collection of intensity data that changes fairly continuously, so there is no clear boundary surface. Therefore, here, VR is drawn with the half-value of the maximum intensity as a threshold value.

  The difference in distribution between (a) and (b) in FIG. 5 can be visually distinguished instantaneously. The distribution of the ellipsoid in the major axis direction (ω or ψ direction or any direction in a plane including these axes) represents the distribution (disturbance) of crystal orientation. On the other hand, the distribution in the minor axis direction (2θ direction) corresponds to good or bad crystallinity (disturbance of periodicity of atomic arrangement or crystal strain distribution due to stress). Conventionally, such an evaluation could not be performed. However, in the three-dimensional display according to the present invention, it has become possible to accurately collect and visualize information related to the above-described crystal state.

In both cases, the intensity distribution near the center can be seen by using cut models.
FIG. 6 shows VR (4) with three MPRs superimposed. (1) and (2) in FIG. 6 correspond to a sagittal image and a coronal image in CT (although neither section is shown here), and (3) in FIG. 6 corresponds to an oblique image.

FIG. 7 shows MIP on three orthogonal surfaces. This image is projected from the diffraction intensity distribution from the sample expressed in the three-dimensional reciprocal space with the data having the largest value of the diffraction intensity on the perpendicular to an arbitrary plane in the space as a representative point. Is.
The projection plane can be selected in any orientation, which is very useful for evaluating the interfacial lattice matching between the substrate described later and the epitaxial film on this substrate, and is extremely important that has not been considered in the past. Provides useful information.

FIG. 8 shows a cross section obtained by slicing a Pt (111) reciprocal lattice point distribution expressed in VR with a plane inclined with respect to a measurement axis (here, 2θ, ω, ψ axes: see FIG. 3A). That is, an oblique image is shown.
FIG. 8 shows the point of the highest intensity value in the space when the projection is obtained from the diffraction intensity distribution from the sample expressed in the three-dimensional reciprocal lattice space to an arbitrary plane in the space. It is an image in which the diffraction intensity distribution of a cut surface that passes through the vicinity and is cut by a plane parallel to the plane is a projection value.

This cross-sectional intensity distribution can be used together with MIP as a probe for evaluating the interfacial lattice matching between the substrate and the epitaxial film.
Next, an application example to the interface lattice matching evaluation of the epitaxial film on the substrate will be described below.
Evaluation of interfacial lattice matching between the substrate and the epitaxial film on this substrate based on the overlap between the MIP of the 3D reciprocal lattice point intensity distribution of the crystal thin film on the reciprocal lattice plane parallel to the substrate surface and the reciprocal lattice point of the substrate can do.

Here, the three-dimensional reciprocal lattice point intensity distribution (point) of the crystal thin film uses not the reflection distribution on the symmetric surface (the small sphere A in the center diagram of FIG. 3) but the reflection distribution on the asymmetric surface (FIG. 3). Small sphere B or small sphere C in the middle figure of FIG.
Further, instead of MIP, an intensity distribution on a slice plane parallel to the substrate surface in an oblique image as shown in FIG. 8 may be used. In that case, it is desirable that the highest intensity point of the three-dimensional reciprocal lattice point intensity distribution is included in the slice plane.

  FIG. 9 shows an image diagram of the evaluation method of the present invention. FIG. 9A shows the VR of the three-dimensional reciprocal lattice point intensity distribution of the crystal thin film, and FIG. 9B shows the MIP to the Qx-Qy plane. The point G on the Qx-Qy plane is one of the reciprocal lattice points of the (single crystal) substrate. For example, it is conceivable that a quantitative evaluation is performed based on an overlap integral value of the intensities of the two and a scale for determining the degree of lattice matching is good or bad.

As described above, according to this embodiment, accurate information necessary for evaluating the crystallinity and orientation of a crystal material can be acquired, and various evaluations of the crystal material can be appropriately performed based on the acquired information. Can be done.
In the description of the above embodiment, X-rays are used for the three-dimensional reciprocal lattice space map used for sample evaluation. However, in addition to electromagnetic waves such as X-rays, particle beams such as electrons and neutrons are used. You may make it use radiation, such as.

  In the technique of the present invention, the local part in the reciprocal lattice space is enlarged and expressed in three dimensions. For this reason, for example, when several crystal systems are complicatedly mixed at the phase boundary, even a slight difference that cannot be separated conventionally can be determined with higher resolution.

It is a block diagram which shows the structural example of embodiment which concerns on the crystal evaluation system of this invention. It is explanatory drawing of each parameter defined in real space. It is a figure for demonstrating three-dimensional reciprocal lattice space. It is explanatory drawing for demonstrating MPR. It is an example of the image which shows VR of Pt (111) vicinity three-dimensional reciprocal lattice distribution with respect to Pt produced on different film-forming conditions. It is an example of an image expressed by superimposing three MPRs on VR (4). It is an example of the image which shows MIP to three orthogonal surfaces. It is an example of the image which shows the cross section which sliced the Pt (111) reciprocal lattice point distribution expressed by VR by the surface inclined with respect to the measurement axis. It is a figure which shows the image of the evaluation method which concerns on this invention.

Explanation of symbols

  a ... sample, 1 ... X-ray diffraction device, 2 ... diffraction intensity data processing device, 3 ... display device, 4 ... input device. 11... Stages 11, 12... X-ray irradiation unit, 13.

Claims (6)

In the crystal evaluation method, the sample is irradiated with radiation, the diffracted radiation reflected by the sample is measured, and the sample is evaluated based on the measurement.
The rotation angle (φ) with the direction perpendicular to the sample surface as the rotation axis, the tilt angle (ψ) perpendicular to the incident direction of the incident radiation, and the sample surface and incident radiation in the state where ψ = 0 ° Of the incident angle (ω) formed and the included angle (2θ) between the incident radiation and the diffracted radiation, all three variables consisting of two variables selected from 2θ and φ, ψ, and ω are independent of each other. A crystal evaluation method, wherein a diffraction image from the sample is expressed as a function of the three variables using a coordinate system with axes.   From the diffraction intensity distribution from the sample expressed in the spatial coordinates composed of the three axes, the data having the largest value of the diffraction intensity on the perpendicular to an arbitrary plane in the space is used as a representative point. The crystal evaluation method according to claim 1, wherein the crystal is projected.   When the projection is obtained from the diffraction intensity distribution from the sample expressed in the space coordinates composed of the three-variable axes to an arbitrary plane in the space, the point having the largest intensity value in the space 2. The crystal evaluation method according to claim 1, wherein a diffraction intensity distribution of a cut surface that is cut by a plane parallel to the plane passing through the vicinity of the plane is used as a projection value.   4. The crystal evaluation method according to claim 1, wherein the radiation is any one of an X-ray, an electron beam, and a neutron beam. When there is an instruction to create a map of a predetermined three-dimensional reciprocal lattice space necessary for the structural analysis of the sample, X-rays are applied to the sample in accordance with this instruction, and the conditions of Bragg reflected from the sample are satisfied. X-ray diffracting means that receives diffracted X-rays and thereby measures diffraction intensity data;
Diffraction intensity data measured by the X-ray diffracting means is collected, the three-dimensional reciprocal lattice space map is created based on the collected data, and the three-dimensional inverse lattice stored when the three-dimensional reciprocal lattice space map is created. Diffraction intensity data processing means for performing at least data processing for three-dimensionally displaying diffraction intensity data of reciprocal lattice points in the lattice space;
Display means for three-dimensionally displaying an image obtained by data processing of the diffraction intensity data processing means;
A crystal evaluation system comprising: The predetermined three-dimensional reciprocal lattice space is
The rotation angle (φ) with the direction perpendicular to the sample surface as the rotation axis, the tilt angle (ψ) perpendicular to the incident direction of the incident X-ray, and the sample surface and the incident X in the state where ψ = 0 ° Of the incident angle (ω) formed by the line and the included angle (2θ) formed by the incident X-ray and the diffracted X-ray, all three of two variables selected from 2θ and φ, ψ, and ω 6. The crystal evaluation system according to claim 5, comprising a coordinate system having variables as independent axes.

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