JPH0622915Y2 - Surface analyzer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field The present invention relates to a surface analysis device capable of downsizing a device having high beam transportation efficiency.

The surface analysis device is a device for applying an accelerated proton beam to a sample in an ultra-high vacuum to obtain an energy spectrum of scattered protons, and then obtaining an atomic number distribution on the sample surface.

The ultrahigh vacuum is used so that the probability that protons are scattered by gas molecules is substantially zero. In the ideal case of not colliding with gas molecules, the protons are only scattered by the atoms of the sample. The energy loss due to scattering depends on the angle and the atomic mass number Γ. The more scattered by a high mass atom, the smaller the energy loss.

The larger the scattering angle, the larger the energy loss.

If only the scattered protons with a certain scattering angle are observed, the kind of atom of the scattering partner can be known due to the energy loss. By obtaining the energy loss spectrum, the abundance of the counterpart atom on the sample surface can be known.

(B) The principle of PELS This measurement method uses the Proton E method because the surface condition of the sample is examined by spectral analysis of the energy loss of protons.
It is called energy loss spectroscopy (PELS).

The kinetic energy E ₀ of a proton with an initial velocity of U and a mass of m can be non-relativistically written as E ₀ = 1 / 2mU ² (1). This is often on the order of about 100 keV.

Suppose this proton collides with an atom of mass M that was initially stationary. Let Θ be the scattering angle. Proton energy after scattering
E ₁ is E ₁ = KE ₀ (2) Γ = M / m (4) Since Γ is the atomic mass divided by the proton mass, it is almost equal to the mass number. Therefore, this is simply called the mass number.

From (3), it can be seen that the larger the scattering angle Θ, the larger the loss ΔE. The loss ΔE is ΔE = E ₀ −E ₁ (5) = (1−K) E ₀ (6).

When PELS was first developed, the small scattering angle (Θ0) region with the highest yield was used, but recently, the large scattering angle (Θ = 180 °) with the large ΔE is used. When Θ = 180 °, the reciprocating paths are the same, so the accelerating tube for accelerating protons and the decelerating tube for decelerating can be integrated into one.

When Θ = 180 °, the energy loss due to scattering is the largest. The damping constant K is Becomes

Γ is known by knowing ΔE. Since Γ is a mass number,
The atom that caused the proton scattering can be identified.
If the loss energy spectrum Y (ΔE) of scattered protons is obtained using ΔE as a variable, the distribution of atoms that cause proton scattering can be obtained.

(C) Conventional Technique A conventional surface analysis device will be described with reference to FIG.

Proton ions are produced by the ion source 1. Extraction voltage is Vex
And the charge is q. Kinetic energy is qVex.
Proton ions travel in a high vacuum.

It can be bent by the magnet 2. This has a mass spectrometric effect.

Further, the protons pass through the acceleration / deceleration tube 3 and are accelerated there. After being accelerated, pass through Orihuis 4 and Q lens 1
5, and collides with the sample 10 in the ultra-high vacuum chamber 7 via the orifice 16.

After the collision, the protons are scattered in various directions.

Of these, the protons scattered in the direction of Θ = 180 ° pass through the acceptance slit 8 in the opposite direction. Then, it is stopped down by the Q lens 15. Pass Orihuisu 4 in reverse. It is decelerated by the acceleration / deceleration pipe 3.

Furthermore, it enters the magnet 2 and draws a semi-circular orbit here. Let L be the diameter of the semi-circular orbit, Becomes Where B is the magnetic flux density of the magnet 2 and Ea is the kinetic energy of the proton. Proton energy Ea after deceleration
Differ from each other by the scattering energy loss ΔE. Therefore, L is different for protons having different ΔE.

Protons that draw a semi-circular orbit enter the position detector 9. The position detector has a large number of microchannels arranged in one dimension, and each channel has an amplification function. Since the position of the microchannel corresponds to the above L, which microchannel is incident is determined by the energy Ea.

By counting the number of incident protons for each microchannel, the spectrum Y (Ea) for the energy Ea is obtained.

(D) Problems to be solved by the device The space through which protons pass must be kept in a high vacuum state.

However, the degree of vacuum required in each space is different. Therefore,
Several independent vacuum pumps are provided in each space. In order to maintain the difference in vacuum degree, an orifice or slit is provided between the spaces.

The orifice and slit are holes made in a plate. The hole diameter is a problem. The holes must be small to maintain the vacuum differential.

However, when the hole becomes smaller, the scattered protons are less likely to pass through the hole, which reduces the transport efficiency. The number of protons entering the position detector is reduced.

If this happens, the measurement time will be long and the S / N ratio will decrease.

For this reason, setting the slit hole diameter is a fairly difficult problem.

It is better that the hole diameter is wider so that the difference in vacuum degree can be maintained and that protons can easily pass through. For this reason, in addition to a plate in which a hole is simply formed, a partition plate in which a cylinder is provided following the hole may be used. The former is called slit and the latter is called Orihuis.

As the diameter of the orifice is reduced and the length thereof is increased, the conductance is reduced, so that the pressure difference between the spaces on both sides can be maintained. However, since the proton beam is passed, the diameter cannot be made too small.

Then, there is no choice but to lengthen the orientation.

In FIG. 6, the orifice 16 between the Q lens 15 and the ultrahigh vacuum chamber 7 is, as described above, considerably long.

The ultra-high vacuum chamber should have an ultra-high vacuum of 10 ^-11 to 10 ^-10 Torr. However, the Q lens 15 may have a vacuum degree lower by one digit than that.

The Q lens 15 is for focusing the scattered proton beam.

In the conventional example, since the Q lens 15 and the orifice 16 are provided in series, there is a drawback that this portion becomes too long.

FIG. 7 shows only this portion on an enlarged scale.

Immediately before the sample 10 is the acceptance slit 8. This is a slit for cutting a proton beam with Θ ≠ 180 °.

It is for passing only Θ = 180 °. There is always a width of 180 °. Those with Θ = 180 ° ± ε pass through the acceptance slit 8. The width ε is determined by the hole diameter of the slit 8.

The scattered proton beam that has passed through the acceptance slit 8 expands. The diameter W of the diverging beam increases in proportion to the distance traveled.

As shown in FIGS. 6 and 7, since the distance S between the Q lens 15 and the acceptance slit 8 is long, the divergent beam diameter W is large.

Since the diverging beam is converged, the inner diameter of the Q lens 15 must be increased. Then, the chamber surrounding the Q lens 15 also becomes large.

The distance S is increased because the orifice 16 is interposed. The orifice 16 must be long enough to maintain the ultra high vacuum of the ultra high vacuum chamber 7.

Therefore, the distance S is long and the beam diverges.

In FIG. 7, the space between the Q lens 15 and the acceleration / deceleration tube 3 is partitioned by the slit 14.

Since the degree of vacuum is different in the space in which the Q lens 15 and the acceleration / deceleration tube 3 are located, it must be partitioned by the slit 14.

When the air diameter d of the slit 14 is reduced in order to maintain the difference in vacuum degree, the scattered beam does not pass through the holes and hits the plate surface. This is the loss of the proton beam. The signal beam is reduced. It is not desirable because it reduces the S / N ratio. The beam transportation efficiency is low.

Therefore, as shown in FIG. 8, the partition between the Q lens 15 and the acceleration / deceleration tube 3 is changed to the orifice 4. The orifice 4 can have an inner diameter D larger than the slit hole diameter d.

Since the inner diameter D becomes large, the proton beam can easily pass through.

On the other hand, however, the beam line becomes too long by using the orifice 4. Therefore, the space to be evacuated increases. This means that the amount of gas released from the wall surface will increase, so the capacity of the vacuum exhaust device must be increased.

(E) Purpose It is an object of the present invention to provide a surface analysis device which has a short proton beam line, which makes the device compact and which has high beam transport efficiency.

(F) Structure The orifice 16 was necessary to maintain the difference in vacuum degree. However, because of this, the proton beam is Q lens 15
It spreads before reaching.

In the present invention, in order to solve such a drawback, the Q lens and the orifice are integrated and provided in the same portion.

Since the Q lens can approach the ultra-high vacuum chamber, it can be converged by the Q lens while the beam divergence is small. In addition, since the space conventionally used for the Q lens can be omitted, the beam line can be shortened.

FIG. 1 is a schematic vertical sectional view of the surface analysis apparatus of the present invention.

Ion source 1, magnet 2, acceleration / deceleration tube 3, Q lens 5,
It consists of an ultra-high vacuum chamber 7 and several vacuum exhaust devices.

The ion source 1 produces a proton ion beam. The hydrogen gas sent from the hydrogen cylinder is ionized into electrons and protons by the ion source 1.

Therefore, the ion source 1 is evacuated, and the hot cathode,
Proton ions are generated by the grid electrode, the extraction electrode, and the like. If the extraction voltage is Vex, the kinetic energy Ee is Ee ＝ qVex (9). The orbit of the proton beam is bent by the magnet 2. The radius of curvature Re of this orbit is Is. After passing through the slits 31 and 32, the vehicle further proceeds straight, enters the acceleration / deceleration pipe 3, and is accelerated there. Acceleration voltage
If Vacc, the energy Eo after acceleration is Eo ＝ qVex ＋ qVacc (11). The accelerated protons pass through the orifice 4, the orifice 6, and reach the ultrahigh vacuum chamber 7.

The protons pass through the acceptance slit 8 and collide with the sample 10. The sample 10 is attached to the holder 11.
The holder 11 is held by a manipulator 12 so as to be rotatable and vertically movable.

All spaces through which protons pass must be kept in a high vacuum. Therefore, a suitable number of vacuum exhaust devices 21 to 24 are provided.

When a proton hits the sample 10, the atom is scattered by the atom on the surface of the sample. If Θ is 90 ° or less, it will get inside the sample. If the angle is 90 ° or more, it is repelled to the outside of the sample. Those with Θ of (180-ε) to 180 ° pass through the hole of the acceptance slit 8 in the opposite direction.

Letting ΔE be the energy loss due to collisions with atoms, the scattered proton energy E ₁ is E ₁ = E ₀ −ΔE (12) ΔE = (1−K) E ₀ (13). This passes through the orientation 6 and the Q lens 5 in opposite directions.

The Q lens 5 is for narrowing the scattered beam. Since it is near the acceptance slit 8, the scattered beam does not spread very much. This is easy because it is narrowed down. The Q lens inner diameter is also small.

The orifice 6 is provided to maintain the difference in vacuum degree between the ultra-high vacuum chamber 7 and the exhaust chamber 19 in the next stage. It corresponds to the orifice 16 in FIG.

The proton beam focused by the Q lens 5 passes through the acceleration / deceleration tube 3 in the opposite direction. Since the deceleration voltage is equal to the accelerating voltage Vacc, the proton energy Ea after deceleration becomes _{Ea = E 1 -qVacc (14)} = qVex-ΔE (15).

After passing through the slit 32, the proton receives the magnetic field of the magnet 2 and flies in a semicircular orbit. This is incident on one of the microchannels of the position detector 9.

The distance from the point K entering the magnet to the near end M of the position detector is 1 on the magnet side.

Let N be the incident point of the proton on the position detector. Let x be the distance from the end point M, as in the longitudinal direction of the position detector.

Which microchannel you entered, that is,
The x-coordinate of the incident point N can be known.

L = l + x (16), where L is as described above Is. From (16) and (17), the relation between energy Ea and x can be obtained.

Counting the number of protons entering each channel, as a function of x,
The yield Y (x) can be obtained. This is (16), (17)
Therefore, the yield Y (Ea) for Ea can be obtained.

Alternatively, by using (15), the energy loss spectrum Y (ΔE) with the energy loss ΔE on the horizontal axis can be obtained.

The part for obtaining the kinetic energy spectrum Y (Ea) of scattered protons is called an analyzer.

There are electric field type as well as magnetic field type as shown in the figure.

This is because a voltage is applied between two parallel electrode plates,
A position detector is provided on the bottom surface of one of the electrode plates in the longitudinal direction, and a hole is made at a point distant from the position detector of the same electrode plate.

The scattered proton beam is obliquely incident through this hole. Then, due to the action of the electric field, the proton draws a parabola between the electrodes.

The range when a parabola is drawn is detected by a position detector. Range is proportional to proton kinetic energy. Therefore, the kinetic energy spectrum Y (Ea) is obtained.

In addition to this, there are analyzers that use both magnetic and electric fields,
The present invention can be applied to any analyzer.

A feature of the present invention is that the orifice 6 and the Q lens 5 are provided at the same place.

The Q lens focuses the beam by the action of an electric field or a magnetic field.

In the case of FIG. 6, vacuum evacuation was performed at a place where the Q lens was provided, so that the magnetic field type Q lens could not be adopted.

However, in the case of the present invention, the Q lens and the vacuum exhaust device 23
A magnetic field type Q lens can also be used since it is separate from the exhaust chamber 19 connected to the same.

An example of using the magnetic field type Q lens will be described with reference to FIGS. 2 and 3.

Inside the circular iron core 34, there are four magnetic poles 35 facing inward.
Are formed. A coil 36 is wound around the magnetic pole 35. A direct current is passed through the coil 36 to magnetize the four magnetic poles 35. Among the four, the opposing magnetic poles have the same polarity, and the adjacent magnetic poles have different polarities.

Then, the magnetic field lines are generated like that in a square having four poles as vertices.

When the proton passes between the four magnetic poles, it receives a force in a certain direction to converge and a force to diverge in a direction perpendicular thereto.

Such quadrupoles are arranged in three stages in the proton beam direction. The directions of the magnetic poles of the first step and the third step are the same. However, the pole arrangement of the second stage is set to be the opposite.

In this way, the beam can be focused in either direction.

As shown in FIG. 2, the magnetic field type Q lens is provided outside the vacuum chamber. This is because the action of the magnetic field is not obstructed by the wall surface of the vacuum chamber.

The inner diameter of the Q lens can be, for example, about 20 mm. The inner diameter of the orifice 4 is, for example, about 30 mm.

The walls of the vacuum chamber must be made of non-magnetic metal. It can be made of non-magnetic stainless steel.

An example of the electric field type Q lens will be described with reference to FIGS. 4 and 5.

The wall surface of the vacuum chamber is formed by the insulator. Insulation wall 38
Then, four electrodes 39 are provided so as to correspond to the vertices of the square.

The electrode 39 is, for example, aluminum. The insulating wall 38 is, for example, a ceramic. A hole is punched in this, the electrode 39 is inserted, and it is sealed with Kovar glass, an adhesive, or the like.

Of the four electrodes, those facing each other have the same polarity. In this way, the proton receives a converging force in a certain direction and a diverging force in a direction perpendicular to it.

Three such electric quadrupoles are installed in the beam line direction. The first electrode and the third electrode have the same electrode arrangement, and the second electrode has the opposite electrode arrangement.

Thus, the proton beam will be focused by these Q lenses.

The insulating wall 38 serves as an orifice.

(G) Action The acceptance slit 8 just before the sample has a scattering angle Θ of 18
Pass only protons with 0-ε ≤ Θ ≤ 180 °. ε is determined by the hole diameter of the slit 8.

The protons that have passed through the acceptance slit 8 immediately enter between the Q lenses 5. It is still a thin beam because it enters the Q lens before it is sufficiently diffused.

With the Q lens having a small inner diameter, the proton beam can be narrowed down. For this reason, it becomes easy to pass through the hole of the orifice 4 immediately after the acceleration / deceleration pipe. Since it does not hit the plate surface of the orifice 4 and passes through the hole, the proton transport efficiency is improved.

In the end, it is significant that the Q lens could be brought closer to the sample. Even though the Q lens is brought closer, the orifice 6 can be present, so that the high vacuum of the ultra-high vacuum chamber 7 can be maintained.

Since the orifice 6 and the Q lens 5 are integrated, the beam line becomes short. If the beamline becomes shorter, the size of the device can be made shorter than before. It is significant in itself, and the load on the vacuum exhaust device can be reduced.

(H) Effect Since the acceptance slit 8 and the Q lens 5 can be brought close to each other, it is easy to narrow the scattered proton beam.
A Q lens with a small inner diameter can be used for efficient focusing.

Because it is a thin beam, it can pass through slits and orifices in the subsequent stages. Therefore, the beam transportation efficiency can be improved.

Moreover, there is an orifice between the ultra-high vacuum chamber and the exhaust chamber, so that the difference in vacuum degree between both spaces can be maintained.

The higher the beam transport efficiency, the more scattered proton beams can be made incident on the position detector. Therefore, S / N
The ratio increases, and the time required for measurement can be shortened.

A magnetic field type Q lens can be used.

Since the beam line becomes short, the device can be made more compact.

[Brief description of drawings]

FIG. 1 is a schematic overall configuration diagram of the surface analysis apparatus of the present invention. FIG. 2 is a central longitudinal sectional view in the vicinity of the Q lens when a magnetic field type Q lens is used. FIG. 3 is a sectional view taken along the line III-III in FIG. FIG. 4 is a central longitudinal sectional view in the vicinity of the Q lens when the electric field type Q lens is used. 5 is a sectional view taken along line VV of FIG. FIG. 6 is a schematic overall configuration diagram of a surface analysis apparatus according to a conventional example. FIG. 7 is a vertical cross-sectional view of the conventional device in which the Q lens and the acceleration / deceleration pipe are separated by a slit. FIG. 8 is a vertical cross-sectional view of the conventional device in which the Q lens and the acceleration / deceleration tube are partitioned by an orifice. 1 ... Ion source 2 ... Magnet 3 ... Acceleration / deceleration tube 4 ... Orifice 5 ... Q lens 6 ... Orifice 7 ... Ultra high vacuum chamber 8 ... Acceptance slit 9 ... Position detector 10 ... Specimen 11 …… Holder 12 …… Manipulator 15 …… Q lens 16 …… Olyphus 21 to 24 …… Vacuum exhaust device 31,32 …… Slit 34 …… Iron core 35 …… Magnetic pole 36 …… Coil 38 …… Insulating wall 39 …… Electrode

Claims (3)

[Scope of utility model registration request] 1. A sample by accelerating an ion source 1 for generating a proton beam in a vacuum, a magnet 2 for bending a proton beam orbit in a vacuum, and a proton passing through the magnet 2 in a vacuum. Acceleration / deceleration tube 3 for decelerating protons scattered at a scattering angle of Θ180 ° among protons scattered by the sample, Q lens 5 for narrowing the proton beam scattered in vacuum, and ultrahigh vacuum. And an ultra-high vacuum chamber 7 for holding the sample 10 therein, an acceptance slit 8 provided immediately before the sample 10 for passing an incident proton beam and a scattered beam having a scattering angle Θ within a certain range from 180 °, and acceleration / deceleration. A cylindrical orifice 6 provided between the space of the tube 3 and the ultra-high vacuum chamber 7 for maintaining the difference in vacuum degree between both spaces, and an analyzer for measuring the kinetic energy distribution of the scattered and decelerated proton beam. Surface analysis consisting of The surface analysis device is characterized in that the Q lens 5 and the orifice 6 are provided at the same position in the device. 2. The surface analysis device according to claim 1, wherein the Q lens is a magnetic field type Q lens. 3. The surface analysis device according to claim (1), wherein the Q lens is an electric field type Q lens.