JPH07234195A - Crystal surface analyzer - Google Patents

Abstract

PURPOSE:To quickly and accurately search the channeling axis of a crystal by changing incidence angle while applying high-energy ion beams to the surface of a sample and measuring the change in the amount of secondary electrons. CONSTITUTION:The surface of a sample S is irradiated with ion beams IB and at the same time a goniostage 2 is driven and ion incidence angel is changed, and then incidence angle scanning is performed. A multi-channel plate (MCP) 5 detects secondary electrons emitted from the surface of the sample S in response to each ion incidence angle (axial angle of the stage 2), converts 51 the current signal to a voltage signal, and then introduces it to a computer 6 for storage. In the data curve of the amount of secondary electrons, the angle (dip position) at a position corresponding to the bottom of a curve corresponds to the position where surface chattering occurs. Therefore, by obtaining a plurality of dip positions by performing scanning at each axial angle of the stage 2, the chattering axis of the sample S is obtained from the total data, thus achieving a measurement with less statistical error quickly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a high energy ion beam as a probe for RBS (Ratherford Ba-ckscatteri).
ng Spectroscopy: Rutherford backscattering spectroscopy) or PIXE (Particle Induced X-ray Emission: particle excitation X-ray spectroscopy) or the like for an analyzer for obtaining information on whether the crystallinity of the sample surface is good or not.

[0002]

2. Description of the Related Art When a high-energy ion beam is incident on a single-crystal sample, if the direction of incidence is parallel to the low-index crystal axis of the sample, most of the ions will be scattered inside the crystal except for being scattered by surface atoms. The phenomenon of penetrating deep into the channel, that is, channeling occurs. This channeling can be used for investigating the crystallinity such as the state of rearrangement of constituent atoms on the crystal surface, the relative amount of interstitial positions of diffused or doped impurity atoms, and the confirmation of the presence of defects.

As a crystal surface analyzer applying such channeling, the incidence of a high-energy ion beam on the sample surface is directed in a direction parallel to the channeling axis (channeling direction) and in a direction not parallel to the channeling axis. (Random direction), and the amount (yield) of ions backscattered from surface atoms in each incident direction is determined by RB
There is an apparatus that evaluates the quality of the crystallinity of a sample from the ratio of the ion yields of the channeling direction and the random direction, which are detected by S measurement and obtained from the detected value. In addition to RBS measurement, this type of analyzer also employs a so-called PIXE that detects X-rays excited on the sample surface due to high ion beam incidence.

[0004]

According to the above-mentioned crystal surface analysis, it is necessary to search the channeling axis of the sample before the measurement. The channeling axis search method is generally based on the phenomenon that when the incident ions on the sample are along the channeling axis, the probability that the ions are scattered back near the sample surface is low, and the backscattering To measure the amount of ions, a surface barrier type semiconductor detector used in RBS measurement when evaluating crystallinity has been conventionally used.

However, in the measurement using such a semiconductor detector, there is a problem that it takes a very long time to search the channeling axis. That is, in the channeling measurement, the channeling axis is determined by scanning the incident angle of the ions on the sample surface and measuring the amount of ions at several points to several tens of points. When a semiconductor detector is used for the measurement, it usually takes several seconds to several tens of seconds to measure one site, and thus it is necessary to obtain the measured value of the ion amount of several tens of sites. Requires a considerable amount of time.

Further, in order to perform accurate measurement, measures such as increasing the incident ion beam amount and increasing the solid angle can be considered, but the semiconductor detector cannot perform accurate counting above a certain counting rate. However, these are also limited, and therefore, when a semiconductor detector is used, it takes a lot of time to perform measurement with a small statistical error.

The present invention has been made in view of such circumstances, and an object thereof is to evaluate crystallinity of a sample surface using a high energy ion beam.
An object of the present invention is to provide an analyzer capable of accurately searching a channeling axis of a crystal (channeling measurement) in a short time.

[0008]

In order to achieve the above object, the present invention irradiates a sample surface with a high-energy ion beam, and changes the incident angle of ions to the sample to perform crystal channeling measurement. , An analyzer that obtains information for crystal evaluation in the vicinity of the sample surface by determining the ion incident angle to the sample based on the measurement information of the channeling axis and irradiating the sample with the high energy ion beam, By providing a detector that detects the amount of secondary electrons emitted from the sample surface by beam irradiation, and using the output of the detector before and after changing the ion incident angle described above as information for determining the channeling axis, Characterized.

[0009]

When the sample is irradiated with the high energy ion beam, secondary electrons are included in the charged particles emitted from the sample surface. Also, this secondary electron, like the backscattered ion,
When the incident ions on the sample are along the channeling axis,
The probability of being released from the sample surface is low. Therefore, by irradiating the sample surface with a high-energy ion beam and measuring the change in the amount of secondary electrons by changing the angle of incidence of the ions on the sample, it becomes possible to search the channeling axis from the measurement result.

Here, the number of secondary electrons emitted by irradiation with a high-energy ion beam is several orders of magnitude higher than that of ions scattered backward from the irradiation position, and therefore information for searching for channeling is obtained. By using the amount of secondary electrons as, it becomes possible to perform measurement with a small statistical error in a short time.

[0011]

1 is a block diagram of an embodiment of the present invention. An ion beam IB (for example, 3 MeV He ²⁺ ions) IB extracted from an ion source and given high energy by an accelerator (both not shown) is introduced into the vacuum chamber 1.
The incident ion beam IB is applied to the surface of the sample S placed on the goniometer stage 2 arranged inside the chamber 1.

Further, inside the vacuum chamber 1, the sample S
A semiconductor detector 3 for detecting ions scattered backward from the sample surface by irradiation of the ion beam IB, and a semiconductor detector 4 for detecting X-rays generated from the irradiation position of the ion beam IB. Each of them is arranged in a predetermined positional relationship with respect to the goniometer stage 2.

The former semiconductor detector 3 is used for RBS measurement, and its detection signal is amplified by a preamplifier 31 and an amplifier 32, converted into a digital signal by an A / D converter 33, and then MCA (multi-channel). Analyzer 34). The latter semiconductor detector 4 is P
This output signal is also used for IXE measurement, and this output signal is likewise passed through the preamplifier 41, the amplifier 42, and the A / D converter 43, and then guided to the MCA 44. Get caught.

On the other hand, the gonio stage 2 is a moving stage driven by a stepping motor or the like, and as shown in FIG. 2, the angles θx, θy, with respect to the traveling line of the ion beam IB.
At least two axes of θz can be freely changed. Here, it is assumed that θx and θy can be changed. The gonio stage 2 is drive-controlled by a signal output from the controller 21 according to an instruction from the computer 6.

The above structure is a known structure generally applied to this type of analyzer. What should be noted in the embodiment of the present invention is that an MCP (multi-channel plate) 5 is arranged inside the vacuum chamber 1 at a position facing the goniometer stage 2.

The MCP 5 is for detecting secondary electrons emitted from the sample surface by irradiation of the sample S with the ion beam IB, and is processed into a disk shape, and is coaxial with the beam axis of the ion beam IB. It is placed on top. However, a beam passing hole 5a is formed in the center of the MCP 5. The output of this MCP5, that is, the current signal is I / V
After being converted into a voltage signal by the converter 51, it is guided into the computer 6.

The power source 52 connected to the circuit system of the MCP 5 is a power source for driving the MCP 5. Also, MC
Power supply 53 connected between P5 and goniometer stage 2
Is for placing the MCP 5 at a positive potential with respect to the sample S, and the secondary electrons emitted from the surface of the sample S can be efficiently collected in the MCP 5 due to the potential difference provided by the power source 53.

Then, the computer 6 performs RBS measurement and PIXE on the basis of the outputs to the semiconductor detectors 3 and 4 described above.
In addition to performing various control and measurement operations at the time of measurement, when searching for a channeling axis to be described later, only the output of MCP5 is taken in and the detected data (secondary electron amount)
Are sequentially stored in correspondence with the drive position of the gonio stage 2, that is, the angles θx and θy.

Next, the operation of the embodiment of the present invention will be described together with the procedure for searching the channeling axis. 3 and 4 are explanatory views of the operation. First, the ion beam is applied to the surface of the sample S.
While irradiating IB, the gonio stage 2 is driven to change the ion incident angle. The angle scan at this time is performed only for the angle θx of the other axis, for example, with the angle θy of one axis of the two X-Y axes fixed.

By such a scan, data of the amount of secondary electrons with respect to the angle θx (θy is fixed) of the goniometer stage 2 as shown in FIG. 3 is obtained, and the position of the position corresponding to the valley of the data curve shown in FIG. 3 is obtained. The angle (dip position) corresponds to the position where surface channeling is occurring. Therefore, if a plurality of dip positions are obtained by appropriately scanning the angles θx and θy axes of the gonio stage 2, the channeling axis of the sample S can be obtained from all the information.

An example of a concrete method for searching the channeling axis will be described below with reference to FIG. First, with the Y-axis angle θy of the goniometer stage 2 fixed at θy1,
Scan by changing the angle θx of the X-axis, then Y
The angle of the axis is fixed at θy2 and the scan of the angle θx of the X axis is performed. Further, the angle of the T axis is fixed at θy2 and the angle θ of the X axis is set.
Perform a total of 3 scans of x.

In these scans, the dips A (θx1, θy1) and B (θx are made by the first scan SC1.
2, θy1) is obtained, dips C (θx3, θy2) and D (θx4, θy2) are obtained in the second scan SC2, and dips E (θx5, θy are obtained in the second scan SC3.
3) and F (θx6, θy3) are obtained respectively, dips A, D and F are on a straight line, the line connecting them corresponds to the surface channeling axis, and dips B, C and F are also straight lines. On the line, these also correspond to the surface channeling axes. Therefore, if such two surface channeling axes are found, the channeling axis C is calculated from the intersection point.
AX is required.

Then, based on the information of the channeling axis obtained as described above, the irradiation of the sample S with the high energy ion beam IB is performed from the direction parallel to the channeling axis and the direction not parallel to the channeling axis. The ions that are backscattered from the surface atoms of the sample S by the incident ions from the respective directions are respectively detected by the semiconductor detector (RBS).
3), and at the same time, the semiconductor detector (for PIXE) 4 detects X-rays generated from the surface of the sample S, and the detection data in each of the channel direction and the random direction is detected by a computer. 6 to obtain information for evaluating the crystallinity of the sample S.

Here, in the above-described embodiment of the present invention, when measuring in the channeling direction and the random direction, MC
If the MCP 5 applies a negative potential to the sample S by the power source 53 connected between the P5 and the gonio stage 2, the MCP 5 has energy equal to or more than the energy determined by this potential.
It becomes possible to select and detect only the secondary electrons, and from the collection amount (detection value) of secondary electrons of the specific energy, RB
In addition to S measurement and PIXE measurement, it becomes possible to obtain information that can be used for crystal evaluation.

In the above embodiment, RBS and PI are used.
Two semiconductor detectors 3 and 4 are arranged in the vacuum chamber 1 so that the XE can be measured in the channeling direction and in the random direction, but the semiconductor detector is not limited to this, and the semiconductor detector is RBS or It may be for measuring either one of the PIXEs, and the semiconductor detector may be a detector for making a measurement for another purpose.

In the above embodiment, the MCP 5 for secondary electron detection is arranged coaxially with the beam axis of the ion beam IB. However, the arrangement is not limited to this, and the arrangement site is the incident ion beam, It is arbitrary as long as it is a position where it does not interfere with the backscattered ions, X-rays, etc. and can efficiently detect secondary electrons. In this case, it is possible to omit the beam passage hole of the MCP.

Further, as the detector for detecting the secondary electrons, a ceratron or the like may be used instead of the MCP. In the present invention, if an MCP is used as a detector for detecting the amount of secondary electrons, and the MCP has a disk shape and is arranged coaxially with the beam axis of the incident ion beam, the secondary electrons emitted from the sample surface Can be detected efficiently. In addition,
In this case, a beam passage hole is provided in the center of the MCP.

In addition, MCP and sample stand (gonio stage)
When a power source is connected between and, and a potential difference that makes the MCP a positive potential is applied between the two, it is emitted from the sample surface.
Secondary electrons can be efficiently collected in the MCP.

Furthermore, if a potential that makes the MCP have a negative potential with respect to the sample is given by a power source connected between the MCP and the sample stage (gonio stage), the secondary electrons having an energy equal to or more than the energy determined by this potential are given. Since only the secondary electrons can be selected and detected, information that can be used for crystal evaluation can be obtained from the amount of secondary electrons.

[0030]

As described above, according to the crystal surface analysis apparatus of the present invention, the amount of secondary electrons emitted from the sample surface upon irradiation of the sample with the high-energy ion beam is detected. Since the channeling axis is obtained from the change in the amount of secondary electrons, it is possible to perform the measurement with a small statistical error in a short time, and thus the time required for the analysis of crystal evaluation can be significantly shortened as compared with the conventional method.

[Brief description of drawings]

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

FIG. 2 is a diagram schematically showing the operation of the goniometer stage 2 used in the embodiment of the present invention.

FIG. 3 is a diagram for explaining the operation of the embodiment of the present invention, and is a data curve showing changes in the amount of secondary electrons with respect to the angle of the goniometer stage 2.

FIG. 4 is a graph showing the coordinates of the dip position, which is also an operation explanatory diagram.

[Explanation of symbols]

 1 vacuum chamber 2 goniometer stage 21 controller 3 semiconductor detector (for RBS) 4 semiconductor detector (for PIXE) 5 MCP (micro channel plate) 51 I / V converter 6 computer S sample IB ion beam

Claims (1)

[Claims] 1. The sample surface is irradiated with a high-energy ion beam, and the incident angle of the ions to the sample is changed to perform crystal channeling measurement, and the ion incident angle to the sample is based on the measurement information of the channeling axis. In the analyzer which obtains information for crystal evaluation in the vicinity of the sample surface by determining and determining the irradiation of the high-energy ion beam, the amount of secondary electrons emitted from the sample surface by the high-energy ion beam irradiation is detected. A crystal surface analyzer, characterized in that the detector is provided, and the output of the detector before and after the ion incident angle is changed is used as information for obtaining the channeling axis.