JPS62249041A - Surface analyzing device - Google Patents

Abstract

PURPOSE:To execute a measurement at a scattering angle of about 180 deg. by making an electrostatic deflecting means active, when a sample irradiating pulse beam passes through said means, and making said means inactive, when a scattered beam passes through said means. CONSTITUTION:When a pulse beam 3P from a slit 36 passes through a deflecting electrode 38, the deflecting electrode 38 is made active. Accordingly, the pulse beam 3P is deflected electrostatically by the deflecting electrode 38, and radiated on a sample 15 in a scattering chamber. A scattering angle is set to 180 deg., the pulse beam 3P is made incident vertically on the surface of the sample 15, and also, a scattered beam 4 also goes out vertically to the surface of the sample. When the scattered beam 4 passes through the deflecting electrode 38, the deflecting electrode becomes zero, and the scattered beam 4 travels straight without being deflected at all. The scattered beam passes through a decelerating tube 18 and made incident on a measuring instrument 20, and its energy spectrum is measured.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is a surface analysis device using PELS (Proton Energy tM 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 surface layers through a deceleration tube to decelerate them and measuring the energy of the decelerated scattered beams.

[Conventional technology]

FIG. 6 is a schematic plan view showing a conventional surface analysis apparatus using PELS. An ion beam, such as a proton beam, extracted from the ion source 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, 211II
A slit (not shown) of about 11φ 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, with reference also to FIG. 7, the extraction voltage of the ion beam in the ion source 2 is Ve, the acceleration voltage in the acceleration tube 6 is V, and the potential of the scattering chamber 14 is O assuming that it is grounded. For example, the total acceleration voltage Va of the ion beam becomes Va-V+Ve. If the potential Vd, which is lowered by the offset voltage vO from this voltage, is the potential of the pedestal 19 (insulated from the ground) on which the measuring instrument 20 is installed, then the deceleration voltage at the deceleration pipe 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. For example, I
Decelerate to about KeV 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. 8, if the energy loss of the ion beam 3 caused by the collision between the ion beam 3 and the sample 15 is ΔE, and the energy of the scattered beam 4 incident on the measuring instrument 20 is E, the following relational expression is obtained. To establish.

ΔE=qVo −E (1) Because the energy E of the scattered beam 4 incident on the measuring instrument 20
is expressed as follows, EwqVa-8E-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.
The voltage applied to the energy analyzer 21 is V! If IA, the above energy E can also be expressed as follows. Here k is a constant.

E-kqVtsa... (2) Therefore,
As can be seen from equations (1) and (2), the energy loss spectrum depends on the offset voltage Vo or the voltage ■. It can be obtained by changing . For example, when comparing 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 thick, and a spectrum as shown in FIG. 9, for example, is obtained.

[Problem that the invention seeks to solve]

However, in the above-mentioned apparatus, the scattering angle θ (see FIG. 8) 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 on the surface of the sample 15 (i.e., energy straggling), resulting in a broad spectrum and a problem that the analysis accuracy is not very good. .

On the other hand, the inventors determined that the scattering angle θ was approximately 18
It has been found that by setting the angle to 0 degrees, not only can a sharp spectrum be obtained, but also the beam detection efficiency can be significantly improved.

Therefore, the main object of the present invention is to provide a surface analysis device capable of performing measurements with a scattering angle of approximately 180 degrees.

[Means for solving problems]

The surface analysis device of the present invention irradiates a sample with an accelerated ion beam, decelerates the scattered beams from several layers on the sample surface by passing through a deceleration tube, and measures the energy of the decelerated scattered beams. An apparatus for analyzing the physical properties of a sample surface by means of a pulsed beam generating means for generating the ion beam as a pulsed beam, an electrostatic deflection means for electrostatically deflecting the pulsed beam and guiding it to the sample, and a scattering beam generated from the sample. A deceleration pipe is provided on the path downstream of the electrostatic deflection means, and when the pulse beam passes through the electrostatic deflection means, the said means is activated, and the scattered beam passes through the electrostatic deflection means. The present invention is characterized in that it includes a control means for disabling the means when performing the measurement, thereby making it possible to perform measurements at a scattering angle of approximately 180 degrees.

[Effect]

The pulsed beam (ion beam) generated by the pulsed beam generation means is electrostatically deflected by the activated electrostatic deflection means and guided to the sample. The scattered beam from the sample directly passes through the inactivated electrostatic deflection means and enters the deceleration tube provided on the downstream side. That is, since the electrostatic deflection means separates the trajectory of the pulsed beam before irradiating the sample and the scattered beam from the sample, measurement at a scattering angle of approximately 180 degrees is possible. As a result, in the apparatus of the present invention, a sharp spectrum can be obtained.

〔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 embodiment, several electrodes 7 are placed on the path of the ion beam 3, such as a proton beam, extracted from the ions 82 and subjected to mass analysis by the mass spectrometer magnet 10.
a set of scanning electrodes 30 to which a scanning voltage V is supplied from a scanning power supply 32, a slit plate 34 having a slit 36, and a set of four deflection electrodes 38 to which a deflection voltage v2 is supplied from a deflection power supply 40. is provided. In this example, the scanning electrode 30, the scanning power supply 32, the slit plate 34
etc., the pulse beam generating means is connected to the deflection electrode 38.
, a deflection power source 40, etc. constitute the electrostatic deflection means. However, the pulse beam generating means does not use such a scanning electrode 30, slit plate 34, etc., but directly from the ion source 2 by controlling the extraction voltage of the ion beam 3 in the ion source 2 in a pulsed manner. It may also be one that draws out a pulsed beam 3p as described later.

A control circuit 42 is connected to the scanning power supply 32 and the deflection power supply 40 to control the scanning voltage V and the deflection voltage 2 by controlling them, and in this example, the control circuit 42 and the like control the control means. It consists of In the following, the outline of the control will be described first, and the details will be further explained with reference to FIG. 3.

The ion beam 3 from the X-quantity analysis magnet 10 is accelerated by the acceleration tube 6 to an energy of about 100 KeV, for example, as in the conventional case.

The ion beam 3 from the accelerator tube 6 has a scanning voltage ■.

is scanned by the scanning electrode 30 to which the beam is supplied, and every time it passes through the slit 36 of the slit plate 34, it is emitted from there as a pulse beam 3p with a predetermined pulse width W.

When the pulsed beam 3p from the slit 36 passes through the deflection electrode 38, the deflection voltage Vt is set to a predetermined value under the control of the control circuit 42 and the deflection electrode 38 is activated, so that the pulsed beam 3p passes through the deflection electrode 38. 3p is electrostatically deflected by the deflection electrode 38, guided into, for example, an ultra-high vacuum scattering chamber (not shown), and irradiated onto the sample 15 housed therein.

In this example, sample 15 has an abuse θ of 180 compared to 11 described above.
It is set to be 3 degrees, so vals beam 3
p enters the surface of the sample 15 perpendicularly, and the scattered beam 4 from the sample 15 also exits perpendicularly to the surface.

In that case, the scattered beam 4 will of course also be pulsed. The scattered beam 4 enters the deflection electrode 38 by traveling in the opposite direction along the same path as the pulsed beam 3p.

When the scattered beam 4 passes through the deflection electrode 38, the control circuit 42 sets the deflection voltage V2 to 0 and disables the deflection electrode 38. Therefore, the scattered beam 4 passes through the deflection electrode 38. It continues straight ahead without being deflected in any way.

Therefore, the pulse beam 3p before irradiating the sample 15 and the sample 1
The trajectories of the scattered beams 4 from 5 are separated, which makes it possible to measure scattering angles θ of approximately 180 degrees.

A deceleration tube 18 having several electrodes 17 is provided on the path of the scattered beam 4 on the downstream side of the deflection electrode 38, and the scattered beam 4 can pass through the deceleration tube 18. The energy is decelerated, for example, to about IKeV or less, as in the conventional case, and is input to the measuring device 20. Then, the measuring device 20 measures the energy spectrum.

Note that the pulsed beam 3p is near the sample 15.
For example, a detector 46 such as a channeltron is provided to detect secondary electrons 44 generated when irradiated with
The detection signal is amplified by an amplifier 48 and supplied to the control circuit 42.

In this example, the measuring device 20 is, for example, as shown in FIG.
Parallel plate analyzer 23, microchannel plate 2
4. It is equipped with a position detector 25, etc., which disperses the scattered beam 4 to each point on the microchannel plate 24 depending on its energy, that is, the difference in energy loss ΔE, and detects the incident position by the position detector 25 and a position calculator. 26, and the counts at each position are displayed on a multichannel analyzer 27.

Therefore, according to such a measuring device 20, the amount of scattered beams from each surface layer of the sample 15 can be measured all at once, and the offset voltage vO and the voltage V applied to the energy analyzer 21 can be measured at once. . For example, a spectrum as shown in FIG. 9 can be obtained without changing A. Therefore, there is an advantage that the influence of state changes during spectrum analysis can be eliminated.

FIG. 3 is a time chart showing an example of the operation of the apparatus shown in FIG. d and -d in the figure indicate normal delays in control, detection, etc. that come to the fore when dealing with fast phenomena like the present case.

When the ion beam 3 is scanned once in a predetermined direction and stopped by applying a scanning voltage 1 to the scanning electrode 30, the pulse width W determined by the scanning speed, the width of the slit 36, etc.
The pulse beam 3p is output from the slit 36. For example, let the output start time be tl. In this case, detection of the start of output of the pulse beam 3p can be performed by various methods, for example, by monitoring the scanning voltage V and detecting the above-mentioned time 1.

In this example, the control circuit 42 controls the deflection power supply 40 to raise the deflection voltage v2 in response to the start of outputting the pulse beam 3p. This deflection voltage v2 is set to a predetermined value at least by the time t2 when the head of the pulse beam 3p reaches the deflection electrode 38, and remains in that state at least until the time t when the tail of the pulse beam 3p leaves the deflection electrode 38. It is maintained. In addition, this time t! , L3 can be determined based on the energy of the pulse beam 3p and the dimensions and arrangement of the deflection electrode 38 and the like. The details will be described later.

The pulsed beam 3p is therefore deflected by the deflection electrode 38, and its head reaches the sample 15 at time t. Along with this, a pulsed scattered beam 4 is generated from the sample 15 and advances toward the deflection electrode 38.

On the other hand, secondary electrons 44 are also generated from the sample 15 by the irradiation with the pulsed beam 3p, and in this example, by detecting these with the detector 46, the sample 15 is irradiated with the pulsed beam 3p.
5 has been detected.

In this example, in response to the detection of the secondary electrons 44, the control circuit 42 controls the deflection power supply 40 to lower the deflection voltage V2. This deflection voltage V2 is brought to O by at least the time t when the head of the scattered beam 4 reaches the deflection electrode 38 and at least the time t when the tail of the scattered beam 4 leaves the deflection electrode 38.

This state will be maintained until then. The direction and the times 1S and 1b can also be determined based on the energy of the scattered beam 4 and the dimensions and arrangement of the deflection electrode 38 and the like. The details will be described later.

In the second state, the deflection voltage V2 is 0, so the scattered beam 4 travels straight through the deflection electrode 38, enters the deceleration tube 18, and is decelerated at time t? The head reaches the measuring device 20. There, the energy spectrum of the scattered beam 4 is measured.

When the above measurement is completed at time t8, the scanning voltage (1) is again applied to the scanning electrode 30 as required to scan the ion beam 3 and output the next pulsed beam 3p from the slit 36. In this case, the end of the measurement can be detected by various methods, such as by detecting that the detection output from the measuring device 20 disappears.

Thereafter, operations similar to those described above are repeated as necessary.

In addition to controlling the device described above, in addition to proceeding with the next control in response to detection at each point as in the example above, for example, the control circuit 42 may be configured to control the size and structure of the device. Various timings determined by the above may be set in advance, and the control may proceed automatically based on the timings. In this way, a detection means such as the detector 46 is not required, and the apparatus is simplified, and fast phenomena can be easily followed.

For example, by scanning the ion beam 3 at a predetermined period, the pulse beam 3p is output at a predetermined period, and by synchronizing the output of the deflection voltage 2 at a predetermined timing, the timing shown in FIG. You may try to satisfy them. Or conversely, the deflection voltage V2 side may be output at a predetermined period, and the output of the pulse beam 3p may be synchronized with it at a predetermined timing.

By the way, if the energy of the pulsed beam 3p is the mass of the E5 constituent ions as m, its speed V is...=F''
; The speed v2 of the scattered beam that has undergone energy loss ΔE is expressed as follows. Therefore, the distance between the temporary slit 34 and the deflection electrode 38 is 1-1, the length of the deflection electrode 38 is t, the distance between the deflection electrode 38 and the sample 15 is 5, and the distance between the deflection electrode 38 and the measuring device 20 is L4 and the pulse width of the pulse beam 3p is W, then each of the above-mentioned times t2 to t is as follows: t2 = CH+L+/V+ t3=t, +L, /v, +W tm "" j++ +Lz/vl -wts =tn
+Li/vz W Lb ””us +L, /v2+W t Fu − Lb +La/Vz W.

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.

Furthermore, as is clear from a comparison between FIG. 1 and FIG. 6, in the apparatus according to the present invention, the acceleration system for the ion beam 3 and the measurement system for the scattered beam 4 are connected to the sample 15 (scattering chamber 14). They also have the advantage that the device can be significantly smaller, since they can be placed on the same side and close to each other.

By the way, in order to enable measurement with a scattering angle θ of approximately 180 degrees, for example, as shown in FIG. Although there is an idea to separate the trajectories of the scattered beam 4 from the sample 15 and the scattered beam 4 from the sample 15, in order to accurately measure the energy loss ΔE over a wide range, it is believed that an apparatus like the one shown in Fig. 1 is more advantageous. I can say it. This is because the scattered beam 4 passing through the deflection magnet 50 has different degrees of energy loss ΔE in the sample 15, for example,
In the figure, 4a (its energy loss ΔEa=o), 4b
(The energy loss ΔEb>0) and 4c (The energy loss ΔEc>ΔEb) are dispersed by the deflection magnet 50 as schematically shown.

To deal with this problem, a deflection electrode 52 consisting of two sets of electrodes 54 and 56 is provided between the deflection magnet 50 and the deceleration tube 18 as shown, so that the scattered beam 4 is directed toward the center axis of the deceleration tube 18. Although it is necessary to correct the trajectory so that the scattered beam 4 passes nearby, if the range of energy loss ΔE included in the scattered beam 4 is wide, the scattering of the scattered beam 4 due to passing through the deflection magnet 50 becomes large. It doesn't go very well. This is because although the deflection electrode 52 has the effect of deflecting (correcting) the trajectory of the scattered beam 4, it has almost no effect of converging the widely dispersed scattered beam 4 (for example, see 40 in FIG. 5). Then, 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, resulting in a decrease in beam transport efficiency. In addition, the efficiency with which the energy enters the measuring device 20 varies depending on the energy loss ΔE, which causes a decrease in the reliability, quantitative nature, etc. of the measurement.

However, in the device shown in FIG.
0 is not used, the scattered beams 4 are not dispersed at all (therefore, all the scattered beams 4 can be incident parallel to the center axis of the deceleration tube 18 (that is, perpendicularly incident). Of course, There is no possibility that the scattered beam 4 will be affected by a lens effect and its trajectory will be deviated by the deceleration tube for one day.

Therefore, not only is the transport efficiency of the scattered beam 4 to the measuring device 20 good, but also the transport efficiency does not change depending on the difference in the energy loss ΔE of the beams included in the scattered beam 4, so the energy loss ΔE is wide ranging from large to small. measurement can be performed accurately.

〔Effect of the invention〕

As described above, in this invention, the scattering angle is approximately 180
It can be set to 100 degrees, which results in a sharp spectrum. Moreover, since the scattered beam is perpendicularly incident on the deceleration tube, the beam transport efficiency does not change due to energy loss, making it possible to accurately measure energy loss over a wide range. Furthermore, the size of the device is also reduced compared to conventional devices.

[Brief explanation of drawings]

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 diagram showing an example of the measuring device of FIG. 1. FIG. 3 is a time chart showing an example of the operation of the apparatus shown in FIG. 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 an example of a surface analysis device using a deflection magnet. FIG. 6 is a schematic plan view showing a conventional surface analysis device. FIG. 7 is a diagram showing the potential distribution of the device of FIG. 6. FIG. 8 is a diagram for explaining the principle of the apparatus shown in FIG. 6. FIG. 9 is a diagram for explaining the spectrum obtained by the apparatus of FIG. 6. 2...Ion source, 3...Ion beam, 3p...
Pulse beam, 4... Scattered beam, 15... Sample,
18... Reduction tube, 20... Measuring device, 30... Scanning electrode, 32... Scanning power supply, 36... Slit, 3rd... Deflection electrode, 40... Deflection power supply, 42 ...control circuit

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 ion beams, a pulsed beam generating means for generating the ion beam as a pulsed beam, an electrostatic deflecting means for electrostatically deflecting the pulsed beam and guiding it to the sample, and a device on the path of the scattered beam from the sample. A deceleration tube provided downstream of the electrostatic deflection means, which enables the means when the pulse beam passes through the electrostatic deflection means and disables the means when the scattered beam passes through the electrostatic deflection means. 1. A surface analysis device comprising: a control means for controlling the surface of the surface, thereby making it possible to perform measurements at a scattering angle of approximately 180 degrees.