JPH0622916Y2 - Surface analyzer - Google Patents

Description

[Detailed Description of the Device] (a) Technical Field This device is capable of easily measuring the proton beam current applied to the sample and is capable of adjusting the profile of the incident proton beam. Regarding the device.

The surface analyzer applies an accelerated proton beam to the sample in an ultra-high vacuum and measures the kinetic energy distribution of the protons scattered in a certain angle direction to determine the abundance of elements on the sample surface. It is a device that seeks.

When the proton hits the sample, it is inelastically scattered. This is because it collides with a stationary atom and robs it of some of its kinetic energy. The lighter the atom of the other party, the greater the energy loss of the proton.

Therefore, the amount of various atoms existing on the sample surface can be known by measuring the energy loss spectrum of protons.

Since this method analyzes the energy loss spectrum of protons, this method is called Proton Energy Loss Spectroscopy (PE
LS).

(A) Principle of PELS It is assumed that the atom of mass M is stationary. It is assumed that a proton of mass m is accelerated and has a velocity U. Kinetic energy of proton
E ₀ is E ₀ = 1/2 mU ² (1). This collides with a stationary atom, and the scattering angle Θ
Scattered in the direction of.

Let the kinetic energy after scattering be E ₁ . This is naturally less than E ₀ . The ratio of these is called the damping constant K. this is, It is given by Γ = M / m (3). The definition is E ₁ = KE ₀ (4). Energy loss ΔE is the difference between E ₀ and E ₁ .

ΔE = E ₀ −E ₁ (5) = (1−K) E ₀ (6) The scattering angle Θ can be selected in any way. First, the present inventors performed PELS measurement with a small scattering angle Θ0.

However, Θ = 180 ° is also promising. Large energy loss and high resolution. Since the protons are incident on the surface of the sample at a right angle, there is an advantage in that it is not affected by surface irregularities.

In this case, the value of K that determines the relationship between E ₁ , E ₀ and ΔE is Given by. Since Γ is the atomic mass M divided by the proton mass, it is almost equal to the mass number. Therefore, this is simply called the mass number.

E ₀ is known and constant. Then, if you measure E ₁ or ΔE, you will know the atomic mass of the other party. The element can be specified if the atomic mass is known. By counting and integrating the number of protons for ΔE, a proton number spectrum for ΔE is obtained. This corresponds to the abundance of elements on the sample surface.

PELS can determine the atomic distribution of one or two layers on the surface of the sample and the extremely surface layer.

In reality, a proton beam is created by an ion source, and this is accelerated and applied to the sample. The scattered protons are decelerated and the energy spectrum is determined by the position detector.

(C) Prior Art The present invention relates to improvement of the structure of the acceptance slit in the ultra high vacuum chamber among PELS devices.

A conventional example will be described with reference to FIGS. 6 and 7.

A sample 10 is held in an ultrahigh vacuum chamber 8 by a holder 12 and a manipulator 13 so as to be vertically rotatable.

In front of the sample 10, the acceptance slit 9 and the shutter 14 are provided. A proton beam Ψ is introduced into the ultrahigh vacuum chamber 8 from the orifice 11 located further forward.

There are two mechanisms that can be opened and closed.

The shutter 14 can be raised and lowered. When the shutter 14 is opened, the proton beam Ψ hits the sample 10 as shown in FIG.

When the shutter 14 is closed, the proton beam Ψ is blocked and does not hit the sample 10.

The shutter 14 can be raised and lowered from the outside by a feedthrough 19.

In some cases, the function of the shutter 14 is simply to open and close the proton beam towards the sample.

Going one step further, the shutter 14 on the Faraday cup 20
There is also a mechanism in which the proton beam entering the Faraday cup 20 is counted and the beam flux is measured when the shutter is attached and the shutter is closed.

It is important to monitor the intensity of the proton beam flux just before the sample.

Of course, when proton ions are generated in the ion source, the proton flux can be obtained from the value of the current. But,
Not all generated protons hit the sample. Therefore, there is some meaning in measuring the proton flux just before the sample.

As a method of measuring the proton beam flux incident on the sample, there is also a method of using a channel tron having a motion mechanism different from that of the shutter. The sample is displaced from the beam and the channel tron is moved to a fixed position on the sample. A proton beam is generated and made incident on a channel tron.

Measure the number of incident protons in a unit time with a channel nertron.

This is undesirable as it complicates the structure in the ultra high vacuum chamber. It also adds one feedthrough, making it difficult to maintain ultra-high vacuum.

Therefore, as shown in FIG. 7, the one having the function of measuring the proton beam flux in addition to the function of opening and closing the beam in the shutter has certain advantages.

The acceptance slit 9 has one or a plurality of openings 15 on the plate surface. It passes a proton beam scattered by the sample.

This device extracts only the scattering angle Θ = 180 °, but in reality, there is a finite width and 180 ° -ε ≦ Θ ≦ 18
I will take out the one at 0 °.

Although ε has a constant angle, it may be fixed at one value or may take two values. For example, ε is 0.5 ° or 1.
It may be 0 °. Since ε is a half-vertical angle when facing the opening of the acceptance slit from the point on the sample, the vertical angle is 2ε.

The diameter of the opening 15 is determined by ε.

When the distance from the sample surface to the acceptance slit is ζ, the diameter σ of the opening 15 is σ = 2ζtan ε (8).

When measuring the proton beam flux, the shutter 14 is lowered as shown in FIG. 7, and the proton beam is blocked by the protons. The intensity of the proton beam is detected by the Faraday cup 20 of the shutter 14.

When a surface of a sample is subjected to a proton beam for surface analysis, the shutter 14 is raised to position any opening 15 of the acceptance slit 9 in the path of the proton beam.

FIG. 8 shows the movement of the acceptance slit 9.

Several apertures 15 are bored, which will alternatively block the proton beam path.

The incident proton beam is sufficiently thin that it can pass through the aperture. However, since the scattered beam is divergent, only a small part of them, the scattering angle of which is limited by 180 ° -ε ≦ Θ ≦ 180 °, can pass through the aperture of the acceptance slit.

If the aperture is made larger, more of the scattered protons enter the position detector, and the yield increases.

The smaller the aperture, the narrower the proton energy width (due to the scattering angle Θ) and the higher the energy resolution.

The size of the opening is appropriately selected according to the purpose.
The opening can be selected by rotating the vacuum feedthrough 18 of the acceptance slit 9.

(D) Problems to be solved by the invention It is not desirable to have many movable mechanisms in the ultra-high vacuum chamber. It may be a serious obstacle to increase the degree of vacuum.

In order to draw the ultra-high vacuum chamber to an ultra-high vacuum of 10 ^-11 to 10 ^-10 Torr, it must be baked at about 200 ° C to release the gas from the chamber wall and the surface of the internal mechanism.

In such a high heat state, thermal distortion easily occurs in the movable part. The seal may be damaged due to distortion and deformation, and gas may leak.

For this reason, the number of internal mechanisms operated from the outside by feedthrough should be as small as possible.

It is not effective to use one port for beam shutter. It is more effective to attach other analytical equipment instead of a simple operation such as a shutter.

(E) Configuration The acceptance slit and the shutter have conventionally been independent mechanisms that are provided on the beam path and can be operated from the outside.

The purpose of the shutter is to prevent the proton beam from hitting the sample. The acceptance slit is used for the purpose of limiting the proton beam scattered by the sample to the position detector.

The roles of the shutter and the acceptance slit are completely different.
Not only that, but it is used exclusively. This is important. The shutter and the acceptance slit do not function simultaneously.

Therefore, in the present invention, the shutter is incorporated into the acceptance slit.

FIG. 3 exemplifies the acceptance slit 9 used in the present invention.

The acceptance slit 9 includes the circular plate 25 and the circular plate 2.
It is composed of a connecting rod 26 for supporting 5, a rotary shaft 27, a feedthrough 18, and the like. The arc plate 25 is provided with several operating points a, b, c, ....

Here, the operating point means that it can be located on the path of the proton beam in the ultrahigh vacuum chamber 8 by operating the feedthrough 18.

At the operating point a, a measuring device for measuring the total flux of the proton beam, for example, a Faraday cup 20, is attached to the back surface.

The other operating points b, c, ... Are simply openings 15 having different diameters.
It is said. For example, b is a 2 ° opening and c is a 1 ° opening. Here, 2 ° or 1 ° is the apex angle of the opening as seen from the proton incident point on the sample surface. The above equation, 180 ° -ε
At ≦ Θ ≦ 180 °, 2ε hits this apex angle.

In addition to this, one or two openings may be added. The number of openings is arbitrary.

That is, the arc plate 25 of the acceptance slit 9 has
One operating point for mounting the measuring instrument and an appropriate number of operating points with openings having different apex angles are provided. The former takes over the function of the shutter of the conventional device, and the latter takes the function of the acceptance slit.

The entire surface analysis apparatus will be described with reference to FIG.

The ion source 1 is a device that ionizes hydrogen gas to produce a proton beam. This extracts the proton beam at the extraction voltage Vex. The kinetic energy Ee of the proton is uniform and Ee ＝ qVex (9).

The magnet 2 redirects the protons traveling in the vacuum container by the Faraday force and performs mass spectrometry. Orbit radius
Re is Since there are slits 22 and 23 in the orbit, charged particles other than protons are completely excluded from the orbit.
B is the magnetic flux density.

This proton beam is accelerated through the acceleration / deceleration tube 3. If the acceleration voltage is Vacc, the proton energy E ₀ after acceleration is E ₀ = qVex ＋ qVacc (11). This passes through the Q lens 4, passes through the orifice 11, and enters the ultra high vacuum chamber 8.

The space in which the protons travel is maintained at high vacuum by the vacuum exhaust devices 31 to 34. This is because protons must not collide with gas molecules.

FIG. 1 shows a state in which the acceptance slit 9 corresponds to the opening 15 in the proton beam path. That is, the surface analysis is being performed.

The spread angle of the opening is predetermined, for example, 1 ° or 2 °. The entire flux of protons enters the sample 10 through the aperture.

Protons are scattered by the atoms on the sample surface. Scattered in various directions. The direction of travel changes due to scattering. With energy loss ΔE.

Of these, only a very small scattering angle of 180 ° -ε ≦ θ ≦ 180 ° passes through the opening 15 of the acceptance slit 9 in the opposite direction. The scattered protons pass through the orifice 11 and are focused by the Q lens 4.

After passing through the Q lens 4, the acceleration / deceleration tube 3 is reached. The energy E ₁ just before this is E ₁ = E ₀ −ΔE (12) = KE ₀ (13).

It is decelerated by the acceleration / deceleration pipe. Deceleration voltage is equal to the accelerating voltage, energy Ea after deceleration becomes _{Ea = E 1 -qVacc = qVex-} ΔE (14).

This proton enters under the magnetic field of the magnet 2. Draw a semi-circle orbit here. The diameter L of the semi-circular orbit is a function of Ea, Is. After drawing a semi-circular orbit, the position detector 5 is entered. This is a detector with many microchannels in one dimension. The microchannel has a high amplification factor and can generate a detection current of about PC to 100PC by the injection of one proton.

There is a one-to-one correspondence between the energy Ea and which microchannel to enter.

When the number of incident protons for each microchannel is integrated and rewritten by the energy Ea, the energy spectrum of the incident protons is obtained.

The distance from the end of the position detector to the microchannel is x. Let f (x) be the integrated value of the number of incident protons that enter the microchannel group of width dx at the point of x. energy
There is a relationship of Y (Ea) dEa = f (x) dx (16) L = L ₀ + x (17) between the yield Y (Ea) and f (x) with respect to Ea. L ₀ is the length along the magnet side from the point where the scattered proton beam enters the magnet field to the end of the position detector.

The yield Y (Ea) for Ea is obtained from (15) to (17).
By rewriting Ea by ΔE according to (14), the spectrum Y (ΔE) for ΔE can be obtained.

The structure and function of such a surface analysis device are the same as before. An analyzer is a device that obtains the proton energy distribution as a position distribution using a position detector. In addition to the one shown here, there are analyzers that bend the beam by an electric field. There is also an analyzer that combines both.

The present invention is characterized by the acceptance slit 9. The first feature is that a measuring device is provided in addition to the opening 15.

In addition to this, another example is made in this example. That is, the secondary electron collecting cylinder 28 is provided around the opening 15 through which the scattered protons pass so as to substantially surround the space between the sample 10 and the opening 15.

FIG. 5 shows an enlarged cross section of the vicinity of the secondary electron collecting cylinder 28.

The secondary electron collecting cylinder 28 is fixed to the circular arc plate 25 of the acceptance slit 9 via an insulator 29. The arc plate 25 is made of metal and is grounded. The sample 10 and the secondary electron collecting cylinder 28 are electrically connected to each other, and the ion current is measured by the ammeter A ₀ .

The electrical connections are shown schematically. Actually, sample 10
Is an ammeter A ₀ via the holder 12 and the manipulator 13.
Connected to.

The secondary electron collecting cylinder 28 and the arc plate 25 are taken out to the outside through the feedthrough 18 by independent lead wires or the like. Then, they are connected to A ₀ and ground, respectively.

The secondary electron collecting cylinder 28 is not the acceptance slit of the conventional surface analysis device.

The function of this will be described.

Proton ions hit the sample. Many protons have low-angle scattering (Θ
0) and then enter the sample. If Θ is 90 ° or less, the sample is trapped.

The protons that enter the sample lose their positive charge and become neutral hydrogen.
At this time, this charge flows from the sample to the ground. If an ammeter is installed between the sample and the ground, the intensity of the ion beam incident can be monitored.

Since this is the beam incident on the sample, it can be detected directly to the extent of a much larger nA.

Of course, protons with Θ> 90 ° are repelled, so this proton does not neutralize and does not give a charge to the sample. Of the incident beam, protons with Θ> 90 ° do not reach the above ammeter.

However, the number of protons with Θ> 90 ° is smaller than that with Θ ≦ 90 °, and there is a direct proportional relationship between them. Therefore, it is impossible to measure the charge of protons with Θ> 90 °.
It doesn't really matter.

Rather, a problem when monitoring ion beam incidence is the emission of secondary electrons.

Since high-energy (100 keV) protons are applied to the sample, they scatter the outer shell electrons of the atom. Most of these electrons return to the atomic model in a short time. However, part of it goes off the orbit and jumps out from the sample surface.

Let the amount of secondary electron emission be Ie, and let the amount of incident protons be Ip. The current flowing in the ammeter that connects the sample and the ground becomes the sum of these Ie + Ip (18). What I want to measure is Ip. Ie is noise. If you don't cut Ie, you don't know the exact Ip.

The conventional one has such drawbacks. If Ie / Ip is small, it does not matter much. However, depending on the material, this ratio can be large.

Therefore, in the present invention, the secondary electron collecting cylinder 28 is provided to collect the secondary electrons. After the rear hole 30 is the sample 10. Although the secondary electrons go forward, almost all of them hit the secondary electron collecting cylinder 28 and are absorbed by it because there is no accelerating electric field. This electron flows to ground through the ammeter A ₀ . Since the charge is negative, the resulting current is -Ie.

Since the current flowing from the sample to A ₀ is as shown in (18), A ₀ is A ₀ = (Ie + Ip) −Ie (19) = Ip (20), and Ie is canceled. In this way, only the ion current Ip due to the incident proton can be measured.

Next, as shown in FIG. 2, when the sample is not irradiated with a proton beam,
This will be described with reference to FIG.

A wide beam through hole 36 is formed in the circular arc plate 25 of the acceptance slit. A Faraday cup is placed behind this, but it has been further devised here.

To measure the amount of the incident proton beam, simply place a cup, collect the proton beam, and measure the ion current.

As shown in FIG. 4, an annular ring 38 is provided behind the beam passage hole 36 via an insulator 37. A through hole 40 is formed in the center of the ring 38. The diameter of the back through hole 40 is smaller than the diameter of the beam through hole 36.

The Faraday cup 20 is provided behind the back hole 40.

A ground plate 39 is provided between the ring 38 and the Faraday cup 20.

A parallel proton beam is incident on the Faraday cup. The incident ion current of the Faraday cup is detected by an ammeter A ₁ .

If the collimated proton beam has a divergence, some will enter the annulus 38. This can be detected by the ammeter A ₂ .

If the proton beam has a fixed distribution type, the detected value of A ₁ and A ₂ spreads the proton beam,
The strength can be calculated.

Therefore, if the value of A ₂ / A ₁ is made constant, the divergence of the beam can be made constant.

The divergence and distribution of the beam can be changed by adjusting the ion source and the Q lens.

It is important to make the beam divergence constant in order to improve the position resolution when the sample surface has variations in atomic distribution or when there is a pattern on the surface.

(F) Action The operation of the acceptance slit 9 conventionally requires two operations, a shutter operation and an acceptance slit operation, by one operation.

When the measuring instrument a is placed in the proton beam path, the beam is blocked and does not enter the sample. In other words, it becomes a shatter.
Not only that, it can measure the incident proton beam.

When the openings 15 (b, c, ...) Are located in the proton beam path, the sample is hit by the proton beam. Out of the scattered beam
The size of the aperture 15 determines what range (180 ° −ε) the scattered beam is detected. The size of the opening is appropriately set according to the purpose.

(G) Effect (1) Spread angle of scattered beam (acceptance angle)
The Faraday cup for beam measurement is attached to the acceptance slit mechanism that determines the.

By rotating one vacuum feedthrough, the divergence angle can be set and the beam current can be measured.

(2) Since the feed through for the shutter is unnecessary, other measuring instruments can be installed.

(3) During beam measurement, rotate the feedthrough so that the measuring instrument a is on the proton beam path.

Most of the beam current flows through the ammeter A ₁ , and the rest is the ammeter.
It flows to A ₂ .

Adjust the beam so that A ₂ / A ₁ is a small constant value. In this way, a predetermined beam size can be obtained on the sample surface.

(4) When performing surface analysis, operate the acceptance slits so that the openings b, c, ... Are in the proton beam path. Since the secondary electron collecting cylinder is provided on the back side of the opening so as to cancel the current due to the secondary electron, the net proton ion current can be measured.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing a state in which a proton beam is applied to a sample of the surface analysis device of the present invention. FIG. 2 is a sectional view of only the ultra-high vacuum chamber in which the proton beam amount is being measured. FIG. 3 is a front view of the acceptance slit used in the present invention. FIG. 4 is a sectional view of a beam amount measuring device portion. FIG. 5 is a cross-sectional view of the acceptance slit in the state where the sample is being measured. FIG. 6 is a cross-sectional view of an ultra-high vacuum chamber at the time of sample measurement in the conventional surface analyzer. FIG. 7 is a cross-sectional view of an ultra-high vacuum chamber when beam measurement is being performed by the conventional surface analysis device. FIG. 8 is a front view of an acceptance slot of a conventional example. 1 …… Ion source 2 …… Magnet 3 …… Acceleration / deceleration tube 4 …… Q lens 5 …… Position detector 8 …… Ultra high vacuum chamber 9 …… Acceptance slit 10 …… Sample 11 …… Olihus 12 …… Holder 13 …… Manipulator 14 …… Shutter 15 …… Opening 18 …… Feed through 19 …… Feed through 20 …… Faraday cup 22,23 …… Slit 25 …… Arc plate 26 …… Connecting rod 27 …… Rotating shaft 28 …… 2 Secondary electron collecting cylinder 29 …… Insulator 30 …… Hole 31… 34 …… Vacuum exhaust device 36 …… Beam through hole 37 …… Insulator 38 …… Circular 39 …… Grounding plate 40 …… Back hole

Claims (2)

[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 that decelerates the protons scattered at a scattering angle of 180 ° among the protons scattered by the sample, Q lens 4 that narrows the proton beam in vacuum, and ultrahigh vacuum. And the ultra-high vacuum chamber 8 that holds the sample 10 and only the proton beam that is provided immediately before the sample 10 and is scattered by the sample through the incident proton beam and has a scattering angle Θ of 180 ° -ε ≦ Θ ≦ 180 °. In a surface analysis device including an acceptance slit 9 having an appropriate number of apertures 15 through which the light passes and an analyzer that measures the kinetic energy distribution of the scattered and decelerated proton beam, the acceptance slit 9 is scattered on a rotatable circular plate 25. An opening 15 having an appropriate divergence angle 2ε for passing the beam and a measuring instrument for beam measurement are provided, and a secondary electron collecting cylinder 28 is provided on the back surface of the opening 15 via an insulator 29. A surface analysis apparatus characterized in that the ion current of the sample 10 and the secondary electron current of the secondary electron collecting cylinder 28 are added so that the current can be measured by an ammeter A ₀ . 2. A measuring instrument for beam measurement is a through hole 4 smaller than the beam through hole 36 of the acceptance slit.
A ring 38 having a hole 0, an insulator 37 connecting the ring 38 and the arc plate 25 of the acceptance slit 9, and the ring 3
The utility model registration claim characterized in that it comprises a Faraday cup 20 provided behind 8, an ammeter A ₁ for measuring the current of the Faraday cup, and an ammeter A ₂ for measuring the current of the ring 38. The surface analysis apparatus according to item (1).