JPH04319655A - Method for analyzing and measuring rutherford back scattering - Google Patents

Abstract

PURPOSE:To remove an ion subjected to back scattering within an angle range wherein a cavity curve containing a compensation shoulder appears from measured data when a sample is measured at random while subjected to in-plane rotation. CONSTITUTION:A sample 2 is irradiated with ion beam 1 while the sample 2 is rotated so that the crystal axis of the sample 2 does not become parallel to the incident direction of the ion beam 1 and the scattering yield at each angle is measured. An angle range wherein a cavity curve containing a compensation shoulder appears is set on the basis of the measured data and, when the sample 2 is continuously measured at random while subjected to in-plane rotation, the ion subjected to back scattering within the angle range is removed from the measured data. By this method, highly accurate random measurement can be performed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Rutherford backscattering analysis method.

0002

[Prior Art] The Rutherford backscattering analysis method
Ion beams with energies ranging from eV to several MeV (
For example, there is a method in which a sample is irradiated with ions (He+, He2+, or H+) and the energy of backscattered ions is measured using a semiconductor detector.

The principle, measurement method, and application of this analytical method are described in W.-K. Chu, Mayer (J.
W. Mayer) and Nicolette (M.-A.Nic)
olet), “Backscattering Spectrometry”
ctrometry)” (Publisher Academic
Press, New York, 1978). The terminology used in the above documents will also be utilized in the following description of the invention. When a collimated ion beam is incident almost parallel to the crystal axis or crystal plane of a crystalline material, most particles do not have close collisions with crystal atoms, but continuously interact with atomic columns (coupling). The ions travel through the sample while oscillating periodically, and the proportion of backscattered ions is greatly reduced. This is called the channeling phenomenon. In particular, channeling by crystal axes is called "axial channeling," and channeling by crystal planes is called "plane channeling." By utilizing the channeling phenomenon, it is possible to evaluate crystallinity, determine the depth distribution of lattice defects, or determine the atomic positions in the lattice of impurities.

However, when analyzing the composition of a crystalline material in the depth direction using the Rutherford backscattering analysis method, as shown in FIG. Incident direction of ion beam 1 and sample 2
Sample 2 is placed on sample stand 3 so that the crystal planes are not parallel to each other.
or after mounting the sample 2 on the sample stage 3, tilt and/or rotate the sample stage 3 in the plane so that the ion beam 1
The measurement is performed in a state in which the incident direction of the sample 2 is not parallel to each crystal plane of the sample 2. This is called random measurement.

FIG. 3 shows He2+(
Acceleration energy: 2 MeV) was used as sample 2 (1
00) Mount the gallium arsenide substrate on the sample stage 3, and set the angle between the incident direction of the ion beam 1 and the in-plane rotation center axis 4 of the sample stage 3 to be 7 degrees. These are the results of measuring the scattering yield at each angle while irradiating the sample with the same amount of ion beam 1 while rotating the sample 360 degrees in 0.6 degree increments about the central axis of rotation 4. The significant decrease in scattering yield at several locations is due to channeling by crystal planes. However, even if the sample 2
As is clear from Figure 3, even if the sample stage 3 is attached, the scattering yield differs depending on the angle of the sample 2, even if statistical variations in the scattering yield are taken into consideration. With this method, it is difficult to obtain measurement results with good reproducibility.

In order to solve the above problem, as a known method, the sample 2 is mounted on the sample stage 3, and the angle between the incident direction of the ion beam 1 and the crystal axis is set to be several degrees.
A method is used in which random measurements are performed while rotating the sample stage 3 around the in-plane rotation center axis 4, and the scattering yields at each angle are averaged.

[0007]

[Problems to be Solved by the Invention] However, in the above-mentioned method of measuring while rotating the sample stage within the plane,
Data on the angle at which channeling occurs on each surface is also taken in and averaged.

[0008] FIG. 5 shows that the same amount of 1.8 MeV He ions are irradiated while the sample is rotated by small angles so as to cross the {110} plane with the {110} plane of a silicon single crystal as the center, and the backscattered This figure shows the results of measuring the scattering yield of He ions (cited reference is E. Rimin
i, E. Lugujjo, and J. W. Mayer
, Phys. Rev. B6, 718 (1972). ). This curve is called a dip curve, and the part where the scattering yield on both sides of the dip 6 is larger than 1 is called the compensation shoulder 7. According to the current theoretical interpretation, the reduced area of the dip 6 is the compensation shoulder 7 on both sides. It is believed that this will be compensated by. However, as is clear from FIG. 5, the reduced area of the recess 6 is much larger. Comparing the sum of the scattering yields at 1 degree before and after the angle at which the scattering yield of the depression 6 has the minimum value, it is about 7% lower than the completely amorphous case where the scattering yields are all 1. . Further, the reduced area of the recess 6, the area of the compensation shoulder 7, and the shape of the recess curve largely depend on the crystallinity of the sample or the parallelism of the ion beam.

[0009] Originally, random measurement is a method in which the sample is assumed to be amorphous and measured, and accurate data can be obtained by measuring while taking in data in the range where the channeling phenomenon occurs.
There was a problem that data could not be obtained.

In order to solve the above problems, the present invention provides a highly accurate random measurement method by excluding from measurement data ions that are backscattered within an angular range in which a concave curve including a compensation shoulder appears. The purpose is to provide.

[0011]

[Means for Solving the Problems] In order to achieve the above object, the present invention is directed to directing the ion beam while rotating the sample so that the crystal axis of the sample and the direction of incidence of the ion beam are not parallel to each other. The sample is irradiated, the scattering yield at each angle is measured, and from this measurement data the angle range in which the concave curve including the compensation shoulder appears is set, and then the sample is randomly measured while rotating in the plane. When carrying out this method, ions backscattered within the angular range are excluded from the measurement data.

0012

[Operation] According to the present invention, when performing random measurements of the sample while rotating in the plane, ions backscattered within the angular range where a concave curve including a compensation shoulder appears are excluded from the measurement data. By doing so, highly accurate random measurement becomes possible.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a flowchart of a measuring method according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of a Rutherford backscattering analyzer according to an embodiment of the present invention. FIG. 3 shows the measurement results of the scattering yield of a (100) gallium arsenide substrate according to an example of the present invention. FIG. 4 is a conceptual diagram of a method for setting an angular range that is not captured as measurement data in each concave curve according to an embodiment of the present invention.

A crystalline material has a plurality of crystal axes and crystal planes, and a crystalline material (for example, a gallium arsenide substrate or a silicon substrate) has a crystal axis perpendicular to the sample surface.
Among these, the case where a (100) gallium arsenide substrate is measured will be explained. (1) First, the sample 2 is mounted on the sample stage 3 having an in-plane rotation mechanism. The (100) gallium arsenide substrate has a <100> axis substantially perpendicular to the plane of the sample stage 3. (2) Tilt the sample stage 3 several degrees so that the crystal axes of ion beam 1 and sample 2 are not parallel, and rotate the sample stage 3 in the plane while irradiating sample 2 with the same amount of ion beam 1. It is rotated by small angles around the central axis 4, and the scattering yield at each angle is measured.

FIG. 3 shows a sample stage mounted with a (100) gallium arsenide substrate tilted 7 degrees and rotated 0.6 degrees at a time.
These are the results of scattering yields measured while irradiating with 2+ (acceleration energy: 2 MeV). (3) Calculate the average value (N) of scattering yield. (4) Calculate the square root (σ) of the above average value (N). (5) Calculate the judgment value. From the above average value (N),
The value obtained by subtracting three times the square root (σ) of the above average value (
N-3σ) is calculated, and this is used as the judgment value. (6) Detect the angle (ψi) at which the scattering yield is minimum in the concave curve due to channeling on each surface. first,
Compare the scattering yields at each angle and find the angle with the minimum value. Next, the magnitude of the scattering yield at the angle of the minimum value is compared with the determination value, and if it is smaller than the determination value, this angle is determined to be the angle of the minimum value of the concave curve. Next, compare the scattering yield of each angle within the angle range excluding 3 degrees before and after this minimum value angle, find the angle that has the minimum value within that angular range, and judge in the same way as above. If it is smaller than the determination value, it is set as the minimum value of the second concave curve. Such a procedure is repeated until the scattering yield at the angle having the minimum value becomes larger than the determination value, and a plurality of angles (ψi) at which the scattering yield becomes the minimum are determined in each concave curve.

(100) <100> of gallium arsenide substrate
When the scattering yield is measured with the axis tilted by about 7 degrees, surface channeling occurs at eight major surfaces. From Figure 3, the minimum angle (ψi) of each concave curve is 4.80 degrees,
52.2 degrees, 98.4 degrees, 143.4 degrees, 187.8 degrees
The values of 231.0 degrees, 274.8 degrees, and 319.2 degrees were obtained from the above judgment results. (7) Find the half width (C) of the concave curve due to channeling on each surface. First, compare the scattering yield of the large angle (ψi+1) immediately to the right of each (ψi) determined above with the value of 1/2 of the average value (1/2N), and if it is larger than 1/2N, Let the angle be A, and if it is smaller than 1/2N, then the scattering yield of the larger angle immediately to the right and 1/2N
A is obtained by repeatedly comparing the size with . Similarly, (
Compare the scattering yield of the small angle (ψi-1) immediately to the left of ψi) with 1/2N, and if it is larger than 1/2N, set that angle as B, and if it is smaller than 1/2N, then B is obtained by repeatedly comparing the scattering yield of the small angle on the left with 1/2N. Next, in each concave curve, A
The absolute value of the difference between and B is calculated, and this is taken as the half width (C) of each concave curve. (8) Centering on the angle (ψi) of each minimum value, take an angle three times the half width determined at each angle on both sides, and use this angle range (ψi±3C) as the angle range in which no measurement data is taken. Set multiple locations. (9) Within the angle range set above, random measurements were performed while rotating the sample stage 3 within the plane without taking data.

[0017] The measurement method of the present invention enables highly accurate random measurement. Note that within the angle range of the sample stage set above, it is also possible to increase the speed of in-plane rotation and shorten the measurement time.

Furthermore, the angular range in which measurement data is not taken needs only to include at least all the concave curves, so even if a wider angular range is set, there will be no problem in solving the problems of the present invention. Must not be.

Another method for setting a plurality of angular ranges from which measurement data is not taken is to display the diagram shown in FIG. The measurer reads the angle using a cursor, inputs the angle into a computer using an input device such as a mouse or keyboard, and selects several angles within several degrees before and after that as an angle range in which no measurement data is taken. It is also possible to set

Another method for setting multiple angle ranges from which measurement data is not captured is to display the diagram in FIG. A person reads the information and inputs it into the computer using an input device such as a mouse or keyboard,
It is also possible to set multiple locations.

In the embodiments of the present invention, only crystal axes that are perpendicular to the sample surface have been described, but the present invention can be similarly applied to crystal axes that are not perpendicular to the sample surface.

In addition to crystalline materials, the present invention can of course be applied to multilayer thin film samples containing at least one crystalline layer, or thin film samples fabricated on crystalline substrates. The same applies.

Note that the present invention can solve the problems of the present invention if the angle range in which the concave curve including the compensation shoulder appears on each crystal plane of the sample can be set.
The present invention is not limited to the above embodiments, and various modifications can be made based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0024] The present inventor has invented that highly accurate random measurement can be performed by the above measurement method.

[0025]

As is clear from the above description, according to the present invention, when random measurements are made on the sample while rotating in the plane, it is possible to perform a backward measurement within the angle range in which the concave curve including the compensation shoulder appears. By excluding scattered ions from the measurement data, highly accurate random measurements are now possible.

[Brief explanation of the drawing]

FIG. 1 is a flowchart of a measurement method according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a Rutherford backscattering analyzer according to an embodiment of the present invention.

FIG. 3 is a measurement result of the scattering yield of a (100) gallium arsenide substrate according to an example of the present invention.

FIG. 4: Measured data for each concave curve of the embodiment of the present invention.
FIG. 4 is a conceptual diagram of a method for setting an angular range in which no data is included.

Figure 5: {10
0} surface concavity curve measurement results.

[Explanation of symbols]

1 Ion beam 2 Sample 3 Sample stage 4 In-plane rotation center axis of the sample stage 5 Detector 6 Dent 7 Compensation shoulder

Claims (2)

[Claims] 1. The ion beam is irradiated onto the sample while rotating the sample so that the crystal axis of the sample and the direction of incidence of the ion beam are not parallel, and the scattering yield at each angle is measured. An angular range in which a concave curve including a compensation shoulder appears from the measurement data is set, and then, when performing random measurements of the sample while rotating in the plane, backscattered ions within the angular range are measured. A measurement method of Rutherford backscattering analysis characterized by excluding data from the data. 2. The Rutherford backscattering analysis measurement method according to claim 1, wherein an angular range in which a concave curve including a compensation shoulder appears is set from a half width of the concave curve.