JPS6319746A - Surface analysis device - Google Patents

Abstract

PURPOSE:To enable a scattering angle to be set nearly at 180 deg., by disposing a first deflecting magnet on the passage for both of ion beams before radiation and scattered beams from a sample, and then disposing a second deflecting magnet on the passage for scattered beams passing through the first magnet. CONSTITUTION:The first deflecting magnet 30 is disposed on the passage for both of ion beams 3 before radiation and scattered beams 4a from a sample 15, and then the second deflecting magnet 32 is disposed on the passage of scattered beams 4b passing through the first magnet, and then the radiated beams 4 are put into an instrument 20 through a deceleration tube 18, so that a surface analysis device can be composed. When deflecting angles phi1 and phi2, emission angles alpha1 and alpha2, radiuses r1 and r2 of curvature of the scattered beams having no energy loss are respectively formed in the deflecting magnets 30 and 32, the relation of phi1=phi2, alpha1=alpha2=(phi1/2)-90 deg., and r1=r2 is needed to be satisfied. Therefore, measurement can be performed with the scattering angle being nearly 180 deg., so that sharp spectra become available. 15: sample.

Description

Detailed Description of the Invention [Industrial Application Field] This invention is a surface analysis device using PELS (Proton Energy Loss Spectrum Analysis). The present invention relates to a surface analysis device that analyzes the physical properties of a sample surface by passing scattered beams from several layers through a deceleration tube to decelerate them and measuring the energy of the decelerated scattered beams.

[Conventional technology]

FIG. 5 is a schematic plan view showing a conventional surface analysis apparatus using PELS. An ion beam, such as a proton beam, extracted from the ions [2] is accelerated by an acceleration tube 6, and the accelerated ion beam is focused by a focusing system 8 as required. Thereafter, beam deflection (mass analysis) is performed using the mass analysis magnet 10. After deflection, the sample (not shown) in the scattering chamber 14 is irradiated with the ion beam. In order to irradiate a part of the sample with the ion beam, a slit of approximately 1 mm diameter (not shown) is placed on the beam line before entering the scattering chamber 14. ) is installed. Furthermore, if an ion beam such as He is used, there is a possibility that divalent ions will be scattered in addition to monovalent ions, making measurement complicated.
In reality, protons are used in which only monovalent ions exist. In the figure, 12 is a vacuum pump.

The ion beam irradiated onto the sample is scattered by several layers on the sample surface. This scattered beam generally has various energies, and in order to suppress the energy width, a slit (not shown) with a diameter of about 2 mm is installed on the beam line after scattering. After the scattered beam passing through this slit is decelerated by the deceleration tube 18, its energy spectrum is measured by the measuring device 20. The potential after deceleration in this case is determined as follows.

That is, referring also to FIG. 6, if the extraction voltage of the ion beam in the ion source 2 is the acceleration voltage in the Vex acceleration tube 6 is V, and the scattering chamber 14 is assumed to be grounded, its potential is O. , the total acceleration voltage Va of the ion beam is Va=V+Ve. If the potential Vd, which is lower than this voltage by the offset voltage Vo, is the potential of the pedestal 19 (insulated from the earth) on which the measuring device 20 is installed, then the deceleration voltage at the deceleration tube 18 is (Va - V).

), the energy of the scattered beam that is decelerated and enters the measuring device 20 is qXVo (eV) (ignoring energy loss when colliding with the sample). Here q
is the unit charge of an ion, such as a proton.

In this case, the acceleration energy of the ion beam irradiated to the sample is preferably high, for example, about 100 KeV, in order to reduce the probability of neutralization of the ion beam on the sample surface. In order to be able to measure the energy spectrum with precision, it is preferable to reduce the speed to a lower value, for example, to about IKeV or less.

By measuring the energy spectrum of the scattered beam decelerated as described above, physical properties such as the crystal structure of the surface of a solid sample can be investigated.

For example, referring to FIG. 7, if the energy loss of the ion beam 3 caused by the collision between the ion beam 3 and the sample 15 is 8E, and the energy of the scattered beam 4 incident on the measuring instrument 20 is E, then the following relational expression is obtained. holds true.

ΔE=qVo −E (1) Because the energy E of the scattered beam 4 incident on the measuring instrument 20
is expressed as follows, E-qVa-ΔE-q(Va-Vo) If this is transformed, equation (1) can be obtained.

In addition, here, as the measuring device 20, for example, an energy analyzer 21 and a detector 22 such as a channeltron are used.
If the voltage applied to the energy analyzer 21 is V E3A, the energy E can also be expressed as follows. Here k is a constant.

E"kqVEjA... (2) Therefore,
As can be seen from equations (1) and (2), the energy loss spectrum depends on whether the offset voltage Vo or the voltage Y ESA
It can be obtained by changing . for example,
Comparing the beams scattered by atoms in the first layer and atoms in the second layer, etc. on the sample surface, the scattered beam from the second layer, etc. has an energy loss ΔE because it travels a long distance within the lattice.
becomes large, and a spectrum as shown in FIG. 8, for example, is obtained.

[Problem that the invention seeks to solve]

However, in the above-mentioned apparatus, the scattering angle θ (see FIG. 7) could only be set to about 10 degrees. This is because as the scattering angle θ increases from 0 degrees, the solid angle of the scattered beam 4 becomes smaller and the beam detection efficiency decreases.
This is because if the scattering angle θ is made too large, various parts of the device will mechanically interfere. Therefore, since the scattering angle θ is such a small value, the scattered beam 4 is affected by disturbances g on the surface of the sample 15 (that is, energy straggling), resulting in a problem that the spectrum becomes broad and the analysis accuracy is not very good. Ta.

In addition, by directly inputting the ion beam 3 into the measuring device 20 without being scattered by the sample 15, the origin of energy loss (i.e., the point where the scattered beam 4 enters with energy loss ΔE = 0 in the measuring device 20) and the energy resolution of the device can be determined. When measuring , the scattering chamber 1 is set so that the scattering angle θ becomes O angle.
It is necessary to reconnect the four beam transport lines, etc., which requires a lot of effort and alignment adjustment, and there is also the problem that the reproducibility of assembly is deteriorated.

On the other hand, the inventor determined that the scattering angle θ was approximately 180 degrees by a detailed study of the relationship between the scattering angle θ and the solid angle of the scattered beam 4.
It has been found that by setting the angle at a certain degree, it is possible to obtain a sharp spectrum, and the beam detection efficiency is also significantly improved.

Therefore, the main object of the present invention is to provide a surface analysis device that can measure a scattering angle of approximately 180 degrees and also easily measure the origin of energy loss and energy resolution.

[Means for solving problems]

The surface analysis apparatus of the present invention is provided with a first deflection magnet that deflects both the ion beam before irradiating the sample and the scattered beam from the sample on the path of the ion beam, and the scattering that passes through the first deflection magnet. A second deflection magnet is provided on the beam path to deflect the scattered beam in the same direction as the first deflection magnet and enter the deceleration tube, and a deflection angle on the path side of the scattered beam in the first deflection magnet is provided. is φ1, and the exit angle is α.

, the radius of curvature of the scattered beam with zero energy loss is rl, the deflection angle at the second deflection magnet is φ2, and the incident angle is α
2. The radius of curvature of the scattered beam with zero energy loss is r2
In this case, φ, = φz1α - α2 = (φl /2)
-90C degree] and r, = rz.

[Effect]

Since the first deflection magnet separates the trajectories of the ion beam irradiated onto the sample and the scattered beam from the sample, the scattering angle can be set to approximately 180 degrees.

In that case, although the scattered beam is dispersed by the first deflecting magnet due to the difference in the degree of energy loss in the sample, this dispersed scattered beam has a structure that is almost symmetrical to that of the first deflecting magnet. By being deflected by the second deflection magnet, the light is again focused into one trajectory and enters the deceleration tube.

As a result, in the apparatus of the present invention, a sharp spectrum can be obtained and beam detection efficiency is also greatly improved. Moreover, it is also possible to accurately measure energy loss over a wide range.

In addition, by controlling the first deflection magnet, the ion beam can be directly guided to the deceleration tube without irradiating the sample. Resolution can be measured.

〔Example〕

FIG. 1 is a schematic plan view showing a surface analysis device according to an embodiment of the present invention. This device is also similar in principle to the conventional device described above. Note that parts not particularly relevant to the explanation of differences from the conventional example are omitted.

In this device, a first deflection magnet 30 made of, for example, an electromagnet and approximately T-shaped is provided in front of the scattering chamber 14, and an acceleration system for the ion beam 3 and a measurement system for the scattered beam 4 are arranged on the left and right sides of the first deflection magnet 30. This allows measurement at a scattering angle θ of 180 degrees.

That is, f! is extracted from the ion source 2. An ion beam 3, such as a proton beam, subjected to mass analysis by an analysis magnet 10 is accelerated to an energy of about 100 KeV by an acceleration tube 6 having several electrodes 7, for example, as in the conventional case, and on its path. It is deflected by a provided deflecting magnet 30 and guided into, for example, an ultra-high vacuum scattering chamber 14, where it is irradiated onto a sample 15. In this case, the sample 15 is set so that the aforementioned scattering angle θ is 180 degrees, so that the ion beam 3 is incident perpendicularly to the surface of the sample 15, and the scattered beam 4 from the sample 15 is also incident on the surface of the sample 15. go out perpendicular to the surface.

Therefore, the scattered beam 4 passes through the deflection magnet 30 by traveling along the same path as the ion beam 3 in the opposite direction, where it is deflected to the left and right opposite sides of the ion beam 3. That is, the deflection magnet 30 separates the trajectories of the ion beam 3 before irradiating the sample 15 and the scattered beam 4 from the sample 15. Incidentally, the direction of the magnetic flux of the deflecting magnet 30 in this example is upward with respect to the plane of the paper.

A Q lens (electrostatic triple quadrupole lens) 8a provided downstream of the accelerating tube 6 and a Q lens 8b provided in front of the scattering chamber 140 respectively shape the ion beam 3 or the scattered beam 4 and This is to prevent divergence (particularly divergence in the vertical direction on the paper), and although neither is essential, it is preferable to provide it as in this embodiment in order to make measurements more accurate.

On the other hand, on the path of the scattered beam 4 passing through the deflecting magnet 30, the scattered beam 4 is deflected in the same direction as the deflecting magnet 30, and the scattered beam 4 is placed near the central axis of the deceleration tube 18 having several electrodes 17. A second deflection magnet 32 is provided to make the light incident on the light beam.

This deflecting magnet 32 is also made of, for example, an electromagnet, and the direction of its magnetic flux is upward with respect to the plane of the paper.

Then, the scattered beam 4 is decelerated by the deceleration tube 18 so that its energy becomes, for example, about 1 KeV or less as in the conventional case, and the energy spectrum thereof is measured by the measuring device 20.

The reason for providing the deflection magnet 32 as described above is as follows. That is, the scattered beam 4 passing through the deflection magnet 30
For example, 42 (the energy loss ΔE=0) and 4b (the energy loss ΔE≠0) in FIG.
As schematically shown in FIG. 1, the dispersed scattered beam 4 is dispersed by the deflecting magnet 30, so that the dispersed scattered beam 4 is again collected into one orbit by the deflecting magnet 32 and made to enter the deceleration tube 18.

This is because the dispersed scattered beam 4 passes through the deceleration tube 18 and remains dispersed, or in some cases is subjected to a lens action in the deceleration tube 18 and is further dispersed before entering the measuring device 20. The efficiency of incident energy loss Δ
This is because the beam transport efficiency varies depending on E, that is, the beam transport efficiency varies depending on the energy loss ΔE, which causes a decrease in reliability, quantitative performance, etc. of measurement.

Therefore, the path side of the scattered beam 4 in the deflecting magnet 30 and the deflecting magnet 32 have a substantially symmetrical structure. That is, the deflection angle on the path side of the scattered beam 4 in the deflection magnet 30 is φ1, the exit angle is α1, the radius of curvature of the scattered beam 4a with energy loss ΔE=0 is rl, the deflection angle in the deflection magnet 32 is φ2, and the incident angle is When α2 is the radius of curvature of the scattered beam 4a, and r2 is the radius of curvature of the scattered beam 4a, the following equation is obtained. More specifically, in this example:
φ1 = φ2 = 90°, α1 = α2 = -45° (α1
, α2 are generally expressed as negative values in the case shown in the figure. ).

When the above formula (3) is satisfied, the scattered beam 4a separated from one orbit by the deflecting magnet 30 and the scattered beam 4b
are parallel to each other when they leave the deflection magnet 30, and are deflected in the deflection magnet 32 in exactly the opposite manner to that in the deflection magnet 30, and are brought together into one orbit again and exit the deflection magnet 32. Go.

As a result, regardless of the difference in energy loss ΔE, the scattered beam 4 enters the deceleration tube 18 in one central orbit, passes there and enters the measuring device 20, so the difference in energy loss ΔE There is no difference in the efficiency of incidence on the measuring device 20, and it becomes possible to accurately measure a wide range of energy loss ΔE from large to small. There is no need to make any corrections.

Incidentally, although the same applicant has separately proposed a surface analysis device in which deflection magnets 34 and 36 as shown in FIG. 2 are provided instead of the deflection magnets 30 and 32 as described above, this invention can be said to be a further improvement on that device.

That is, the apparatus shown in FIG. 2 also separates the trajectories of the ion beam 3 and the scattered beam 4 by the deflecting magnet 34 to enable measurement at a scattering angle θ of 180 degrees, and deflects the dispersed scattered beam 4 by the deflecting magnet 34. Reducer tube 1 by magnet 36
The deflection magnet 36 is focused near the central axis of the magnet 8 to eliminate the difference in the efficiency of incidence on the measuring device 20 due to the difference in energy loss E. However, as in this embodiment, the deflection magnet 36 has an energy loss This embodiment is more accurate when measuring scattered beams 4 with energy loss ΔE over a wide range, since there is no function to combine the center orbits of scattered beams 4 with different values into one at the time of emission.

Note that if the measuring device 20 is configured as shown in FIG. 3, for example, it is possible to measure energy over a wide range at once. That is, in this example, the measuring device 20 is equipped with a parallel plate analyzer 21, a microchannel plate 24, a position detector 25, etc., and the scattered beam 4 is detected on the microchannel plate 24 by the difference in energy, that is, energy loss ΔE. They are dispersed at each point, their incident positions are detected by a position detector 25 and a position calculator 26, and the counts at each position are displayed on a multi-channel analyzer 27. Therefore, according to such a measuring device 20, the amount of scattered beams from each surface layer can be measured simply by tilting the sample 15 (the angle varies depending on the sample and how many atoms are used to scatter the beam). The offset voltage Vo and the voltage V applied to the energy analyzer 21 can be measured all at once, as in the conventional case. For example, a spectrum as shown in FIG. 8 can be efficiently obtained without changing A.

Therefore, there is an advantage that the influence of state changes during spectrum analysis can be eliminated.

FIG. 4 is a diagram showing the change in the optimized solid angle with respect to the change in the scattering angle, and the vertical axis is on a logarithmic scale. As can be seen from this figure, when the scattering angle θ is set to 180 degrees, the optimized solid angle ΔΩ (str), that is, the beam detection efficiency, is several hundred times ( When the sample 15 is gold) to several thousand times better (when the sample 15 is silicon).Moreover, when the scattering angle θ is 180 degrees, the scattered beam 4 is not affected by disturbances on the surface of the sample 15. In other words, since the scattered beam 4 is influenced only by atoms on the sample surface, a sharp spectrum can be obtained, which improves the accuracy of analysis.

On the other hand, when measuring the origin of energy loss or the energy resolution of the device, by controlling the polarity and magnetic flux density of the deflecting magnet 30, the ion beam 3 incident on the deflecting magnet 3° can be directly irradiated onto the sample 15. The beam can be emitted on the same trajectory as the scattered beam 4a with energy loss ΔE=O. Therefore, there is no need to change the arrangement of the device as in the prior art, and therefore there is no need for time-consuming alignment adjustments or deterioration of assembly reproducibility.

In particular, as in this example, the above-mentioned condition φ1=φz=9
In addition to 0°, the deflection angle φ of the deflection magnet 30 on the path side of the ion beam 3. If the angle is set to 90°, when measuring the origin of energy loss or energy resolution, the deflecting magnet 30
Simply turning off the excitation of the ion beam 3 causes the ion beam 3 to travel straight through the deflection magnet 30 and exit on the same trajectory as the scattered beam 4a with energy loss ΔE=0, as shown by A in FIG. It becomes like this. Therefore, it becomes extremely easy to measure the origin of energy loss and energy resolution.

Incidentally, in the apparatus shown in Fig. 2, the ion beam 3 is largely deflected as shown by B in the figure by switching the polarity of the deflection magnet 34 and increasing the magnetic flux density, and the origin of energy loss and energy resolution can be measured. However, in the embodiment described above, it is much easier to do so because it is sufficient to simply turn off the excitation of the deflection magnet 30.

〔Effect of the invention〕

As described above, in this invention, the scattering angle is approximately 180
This allows measurements to be performed with the beam set at 100 degrees, resulting in sharp spectra and greatly improved beam detection efficiency. Furthermore, since the center orbits of the scattered beams incident on the deceleration tube can be unified regardless of their differences in energy loss, there is no change in detection efficiency due to differences in energy loss, making it possible to accurately measure a wide energy range. It can be carried out. Furthermore, the origin of energy loss and energy resolution can be easily measured without changing the arrangement of the device.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view showing a surface analysis device according to an embodiment of the present invention. FIG. 2 is a schematic plan view partially showing a prior example of the surface analysis device. FIG. 3 is a schematic diagram showing an example of the measuring device of FIG. 1. FIG. 4 is a diagram showing a change in the optimized solid angle with respect to a change in the scattering angle. FIG. 5 is a schematic plan view showing a conventional surface analysis device. FIG. 6 is a diagram showing the potential distribution of the device of FIG. 5. FIG. 7 is a diagram for explaining the principle of the apparatus shown in FIG. 5. FIG. 8 is a diagram for explaining a spectrum obtained by the apparatus of FIG. 5. 2... Ion source, 3... Ion beam, 4, 4a,
4b...Scattered beam, 15...Sample, 18...Deceleration tube, 20...Measuring instrument, 30...First deflection magnet,
32...Second deflection magnet.

Claims (1)

[Claims] (1) The sample is irradiated with an accelerated ion beam, the scattered beam from several layers on the sample surface is decelerated by passing through a deceleration tube, and the energy of the decelerated scattered beam is measured to determine the physical properties of the sample surface. In an apparatus for analyzing a sample, a first deflection magnet is provided to deflect both the ion beam and the scattered beam from the sample onto the path of the ion beam before irradiation of the sample,
and a second deflecting magnet is provided on the path of the scattered beam passing through the first deflecting magnet, and the second deflecting magnet deflects the scattered beam in the same direction as the first deflecting magnet and causes the scattered beam to enter the deceleration tube, and the first deflecting magnet The deflection angle on the path side of the scattered beam in the second deflecting magnet is φ_1, the exit angle is α_1, the radius of curvature of the scattered beam with zero energy loss is r_1, the deflection angle in the second deflecting magnet is φ_2, the incident angle is α_2, and the energy If the radius of curvature of the scattered beam with zero loss is r_2, then φ_1=
φ_2, α_1=α_2=(φ_1/2)-90 [degrees]
A surface analysis device characterized in that: and r_1=r_2.