JPH02126550A - Surface analysis device - Google Patents

Abstract

PURPOSE:To make it possible to analyze even light atoms which are low in mass number by tilting a specimen to proton beams in case of the light atoms in order to measure the speeds of recoil atoms, holding the specimen close to the direction normal to the proton beams in case of heavy atoms, and thereby determine the loss in energy of scattered protons by a position detector so as to obtain the spectrum of each atom. CONSTITUTION:In case of light atoms, a specimen is held obliquely to the axial line of protons so that recoil atoms go into a TOF device which is arranged obliquely. Then, when the speed is obtained by a step of measuring the time from the departure of each atom out of the specimen 4 to its arrival to a micro- channel plate 8, the kind of the atom is determined. In case of heavy atoms, the specimen 4 is held to the direction normal to the incident beam of the protons. In this case, the protons are scattered in all directions by the heavy atoms, but only the proton with H=180 deg. out of them goes into a position detector 5, the abundance of the heavy protons is thereby determined by a step of counting the protons going into the respective positions of the position detector 5. By this constitution, it is possible to make the measurement of the atoms in a wide range complementarily by a single device.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field The present invention relates to a surface analysis device capable of detecting even elements with small mass numbers.

A surface analysis device is used to determine the atomic distribution on the surface of a sample by exposing accelerated protons to the sample in a vacuum and determining the energy distribution of the bounced protons.

Since the energy loss of protons is used as a means of analysis, Pr
oton Energy Loss 5pectros
It's called copy PELS.

The surface analysis device is thus also called PELS, and the two have been equivalent until now.

However, although what we propose here is a surface analysis device, it does not fall into the PELS category. This is because the energy loss of protons is not considered.

This point must be emphasized first.

(b) PELS Explain the principle.

FIG. 5 shows a schematic diagram when a proton of mass m collides with an atom of mass M. Suppose that a proton enters at a velocity U and is scattered by an angle e due to a collision, resulting in a velocity W. Atoms fly out with velocity V in the direction of angle Φ.

Conventional PELS determines the energy loss of incident protons. If the energy of the incident proton is EO and the energy of the scattered proton is El, then there is a proportional relationship between them.

If the constant of proportionality is @, E1 = K@Eo (1) It is determined by the - group. " is M divided by m, which is approximately equal to the mass number. Energy loss ΔE is ΔE == E
o-El(4).

PELS is a method of bombarding an object with protons and examining whether the same particles bounce back.

Initially, a low scattering angle θ of 0 was proposed.

This is because the yield is high. However, as can be seen from (2), when the scattering angle is low, the energy loss of protons is small, and unless the energy resolution is very high, it is not possible to discriminate between elements with similar mass numbers.

Furthermore, if the surface is uneven, scattering may occur more than once.

In the case of a low scattering angle, the sample surface is nearly parallel to the incident proton beam, and the scattered proton beam is such that the incident beam is slightly bent.

The present invention is similar in this geometric arrangement. However, the object of measurement is different. The present invention measures the velocity of scattered atoms. PELS measures the energy of scattered protons.

(1) Prior Art Since there are other drawbacks, the low scattering angle type was eventually replaced by the high scattering angle type (e==180').

This causes the scattered protons to travel the same path as the incident protons. Energy loss ΔE is maximum.

In reality, protons are made into ions, which rise to the extraction voltage Vex and give kinetic energy of qVex. This is 5 ke
It is a low voltage of V~20 keV.

This results in a lack of energy. Therefore, an accelerating voltage Vacc is applied through an accelerating tube. In this way, the energy Eo of the incident proton is expressed as EO= q'/ax −)−qVacc
(obtained by 51. Eo is approximately 100 keV.

Figure 6 shows an overview of PELS. It consists of an ion source 1, a magnet 2, an acceleration/deceleration tube 3, a sample 4, and a position detector 5. Both are in high vacuum. Vacuum container for easy,
A vacuum evacuation device is not shown.

The energy E1 of the light scattered by the sample and reflected in the 180° direction is El = qVex -1 - qVacc - ΔE (6). The energy Ea when it passes through the acceleration/deceleration tube 3, enters the magnet 2, and enters the position detector 5 is a qVex - ΔE (7 n).

If θ−π, becomes. Lighter elements have a smaller K.

The energy loss ΔE is ΔE 1-K)E.

Therefore, lighter elements are larger.

) Problem to be solved by the invention If the detection lower limit of the position detector is Ed, then this is Q, 5
It is about keV to 1 keV. If it is not more than this, it cannot be counted.

Then, unless E, ≧ Ed (old), there will be a counting error.

Then, for light elements, ΔE becomes thicker (, Ea becomes smaller,
It cannot be measured with PELS.

q Vex ≦Ed+ΔE (1,
PELS is powerless against light elements such as 2).

FIG. 7 is a graph with the proton orbit radius R in the magnet 2 as the horizontal axis and the energy loss ΔE1 mass number I'' as the vertical axis. The parameters of the curve are the extraction energy qVe
x o Eo = 100key, θ=π.

By increasing the extraction energy qVex, it becomes possible to measure light elements (but even then, elements with mass numbers below 20 cannot be measured by PELS.q
This is because it is difficult to increase Vex to 20 keys or more.

By lowering the incident energy Eo, ΔE can be lowered.

However, if the %EO is low, protons often become neutralized on the sample surface, which is undesirable. Therefore, Eo cannot be lowered much.

When the mass number is 20 or less, H, He, LL, Be
, B, C1N, OlF, and other elements. this house,
H, C.

0 is an element that is often included in samples, and its analysis is important.

Analysis of H is particularly important in terms of surface properties.

Current PELS cannot detect many of these basic elements. This has little value as an analyzer.

00 Purpose It is an object of the present invention to provide a surface analysis device capable of analyzing even light elements with low mass numbers.

ψ) Configuration The surface analysis device of the present invention is similar to the conventional PELS for heavy elements.
In addition to the mechanism, it is equipped with a mechanism that can detect the velocity of recoil atoms and measure the distribution of light elements.

The former is well known and the latter is new.

This does not measure the energy of the scattered protons, but rather the velocity of the recoil atoms. Therefore, PELS
isn't it.

The velocity of a recoil atom tells us what this atom is. Therefore, by counting how many atoms fly at a certain speed, the atomic distribution on the sample surface can be determined.

Since the energy of an incident proton is constant, the energy of an atom that is repelled in a certain direction Φ increases as it becomes lighter. In other words, hydrogen atoms have a large recoil energy.

It is difficult to measure energy directly. If it has a charge, such as a proton beam, you can bend it with a magnet. However, recoil atoms cannot be used with magnets because they are neutral.

Instead of measuring the energy of the recoil atom, a certain − constant distance l
Measure the time T required to travel.

This is called flight time.

Since 1/T is velocity, it can also be related to energy.

However, elements can be identified only by flight time.

Lighter elements have less recoil energy and less mass, so their speed is greater. Therefore, the flight time T of lighter elements becomes shorter. If a graph is drawn with the flight time T as the horizontal axis and the number of incoming atoms as the vertical axis, this graph will express the abundance ratio of atoms.

FIG. 1 is a schematic diagram of the overall configuration of a surface analysis apparatus according to the present invention.

The ion source 1 ionizes hydrogen gas into an ion beam. The extraction voltage is Vex.

The magnet 2 bends the proton beam emitted from the ion source 1. Ions other than protons are blocked by the collimator 16 and removed.

The acceleration/deceleration tube 3 accelerates the protons coming from the ion source 1 and decelerates the protons scattered 180° by the sample. The acceleration energy is Eacc.

This corresponds to the sample 4 supported by a sample holder (not shown) or the like.

The purpose of this device is to examine the surface condition of sample 4, and there are two methods.

One is a means of investigating light elements. In this case, the sample 4 is placed at an angle with respect to the proton axis, so that recoil atoms enter the TOF device placed at an angle. The sample shown by the solid line in FIG. 1 is in such a state. It is no longer protons that fly from the sample to the TOF device 6. It is a recoil atom.

When measuring heavy elements, it is better to hold the sample 4 at right angles to the incident proton beam. This is indicated by a dashed line. In this case, protons are scattered in multiple directions due to the heavy elements.

Of these, only θ=180° passes through the acceleration/deceleration tube in the opposite direction and becomes the energy Ea shown in the force equation. This draws a semicircular arc with the magnet 2 and enters the position detector 5.

The diameter of a semicircular arc is given by. q is the electric charge, and B is the magnetic flux density of the magnet.

When scattered by atoms with large mass, Ea is large, so L is large. By counting the number of protons that have entered each position of the position detector 5, the abundance ratio of the scattered atoms can be determined. This allows us to determine the abundance of heavy atoms. What is obtained is a spectrum of energy loss ΔE as shown in FIG. 1(b). Such a mechanism already exists.

The TOF device 6 includes a microchannel plate 8, an amplifier 9, a pulse power supply γ, a trigger circuit 10, and a delay circuit 15.
, TDCli, a computer 12, an electrostatic deflector 13, a slit 14, etc.

The microchannel plate 8 is a detector in which a current flows when recoil atoms are incident at high speed. The recoil atoms are neutral, but when they hit, they release secondary electrons, which are amplified and produce a perceivable electrical current. Even a single particle can be detected.

Amplifier 9 amplifies this.

The pulse power supply 7 generates a short width pulse voltage.

A pulsed voltage is applied to the electrostatic deflector 13. A proton beam is deflected by electrostatic forces. Since there is a slit 14 in front, the deflected protons hit the wall and are removed. Therefore, the proton beam becomes pulsed.

For example, this proton beam pulse has a width of 10n se
The repetition rate can be set to 20kHz with c.

The pulsed protons hit sample 4. The recoil atoms fly in the aft direction. Since the microchannel plate 8 is provided in the direction of the recoil angle Φ, atoms flying in this direction are incident.

The time taken for these atoms to leave the sample 4 and enter the microchannel plate 8 is the flight time T.

(TOF). Knowing this, the distance l? 1-To
Divide by to find the speed.

If you know the velocity, you can tell what kind of atom it is.

The trigger circuit 10 triggers the pulse generation of the pulse power source 7. At this time, it is assumed that protons pass through the electrostatic deflector 13. The time t3 required for protons to fly from the electrostatic deflector 13 to the sample 4 is known.

The delay circuit 15 delays f: 5TART signal by t3 from the time when the trigger signal is generated in the trigger circuit 10.
Give Cl 1. The timing of the 5TART signal coincides with the time when protons hit the sample and recoil atoms fly out.

The recoil atoms then fly a distance l and enter the microchannel plate 8. Let this time be T2. At this time, the 5TOP signal is input to TDCll.

If the time when the trigger signal is generated is T3, the time T1 when the atom leaves the sample 4 is T1-T3-1-t3.

Since the flight time To of the atom is (T2 ''+), the velocity V of this atom is .This is the TOF' method (Time of Flig
ht).

This method itself is well known.

TDC11 (Time to Digital C
onverter) calculates the time difference between the start time T1 and the stop time T2, and processes the speed data by the computer 12.

Continuing such counting yields a count as a function of the flight time To.

If a graph is drawn with the flight time TOF (To) as the horizontal axis and the count number as the vertical axis, a distribution as shown in FIG. 1(C) will be obtained. A small To corresponds to a light element, and a large To corresponds to a heavy element. To can be replaced by mass number I'. In other words, from such a graph, the distribution of light (I''≦20) elements on the surface of the sample can be seen.

Instead of the flight time To, the recoil atomic energy Ere
The coil may be plotted on the horizontal axis.

Erecoil = -! ! -v'', Erecoil can be found from V of f15).

(→ The surface condition of the working sample 40 is investigated; if a heavy element is the target, the sample is made perpendicular to the proton beam and the broken line is drawn).The position detector 5 counts the number of protons for each energy. This yields a graph as shown in FIG. 1(b). The horizontal axis is the proton energy loss.

This has been attempted in the past when used as PELS.

When targeting light elements, the sample 4 is tilted, the recoil atoms are made to enter the TOF apparatus, and the number of counts is counted relative to the flight time To.

As a result, a graph as shown in FIG. 1(C) is obtained.

Alternatively, convert it into Erecoil to obtain a graph like (d).

The purpose of the present invention is to perform surface analysis using TOF of recoil atoms.

Therefore, we will give a formula that relates the recoil angle Φ, velocity V, etc. to the mass number [゛.

In FIG. 5, it is assumed that a proton of mass m travels straight on the X-axis at a velocity U, hits an atom M, and is scattered at a velocity W in the direction of θ. Suppose that the atom M recoils in the direction of Φ.

From the law of conservation of momentum, m [J = m WCO5θ + MVCO3Φ
(17) 0 = m Wsinθ−MVsinΦ(
l (To) From the law of conservation of energy, ±mU2 = ±mW2 + Sat Mv' α] Solving these and expressing Φ as an independent variable, we get (From 20, with the recoil angle Φ constant, find the speed ■ with respect to I'' I can do things.

for example, EO= If it is 100 keV, the initial velocity of the proton is U is 43 × 108cm/sec It is.

11 = 100 cm do, becomes.

At Φ=30°, TO- 133 (1'+ 1) n5ec (2(a) At Φ=60°, TO= 232 (I'+ 1) n
5ec (25) It can be seen that there is a one-to-one correspondence between the flight time and the mass number l'.

FIG. 3 shows the relationship between the flight time To and the mass number 1''.

This is EO = 100 keV, 11 = 100c
This is an example of m,, 'I' = 300.60°.

The energy of the recoil atom, Erecoil, is given by (20): EO = 100 keV,
When Φ = 30° and 60°, it becomes as follows, and it can be seen that the recoil energy is also uniquely connected to l''. Figure 2 shows the relationship between ' and Erecoil.

(ri) Effect Conventional PELS cannot be applied to elements with a mass number of 20 or less.

(1) The present invention can be used to measure the distribution of elements with small mass numbers. It provides a powerful analytical means for important elements such as C and Hlo.

(2) It can be installed in the same device as a conventional PELS device. Heavy and light elements can be measured just by rotating the sample.

A single device can perform complementary measurements on a corresponding range of elements.

(3) Analysis of light elements can be performed in real time. In other words, while monitoring the surface condition in real time,
Surface analysis is possible.

An example is shown in FIG. The Erecoix distribution for t=to is shown in (a). The distribution of Erecoil at t-tl is shown in (b). Since such a distribution can be obtained in a short time, real-time processing is possible. Rapid changes in surface conditions can be dynamically detected.

[Brief explanation of drawings]

FIG. 1(a) is an overall configuration diagram of the surface analysis apparatus of the present invention. (
b) to (d) are graphs showing measurement results. Figure 2 is a graph illustrating the relationship between mass number ■'' and recoil energy. Figure 3 is a graph illustrating the relationship between mass number F and flight time To. Figure 4 is an example of changes in surface condition. Spectrum diagram. Figure 5 is a diagram for defining variables during collisions between protons and atoms. Figure 6 is a diagram of the principle configuration of a conventional surface analysis device. Figure 7 is a diagram showing the principle configuration of a conventional surface analysis device. A graph drawn with the semicircle diameter as the horizontal axis, ΔE1 mass number [゛ as the vertical axis, and extraction energy as the parameter. ...Accelerator/deceleration tube 4...Sample 5...Position detector 6...TOF device 7...8...9... ...... 10... 11... 12... 13... 14... Pulse power supply Microchannel Brake amplifier trigger circuit DC Computer static Electric deflector slit light source Masahiko Maruki

Claims (1)

[Claims] An ion source 1 that generates a proton beam in a vacuum, a magnet 2 that bends the trajectory of the proton ions generated from the ion source 1, and a magnet 2 that accelerates the protons that have passed through the magnet 2 and hits a sample 4 where they are scattered by the sample 4. an acceleration/deceleration tube 3 that decelerates protons passing in the opposite direction, a position detector 5 that measures the energy distribution of the proton beam that is scattered by the sample 4, decelerated by the acceleration/deceleration tube 3, and bent by the magnet 2; A vacuum container surrounding the device, a vacuum evacuation device that evacuates the vacuum container to a vacuum,
The TOF device 6 is installed obliquely behind the sample when viewed from the incident line of the proton beam, and measures the velocity of recoil atoms exiting the sample surface.When measuring the surface distribution of light elements, the sample 4 is When tilting the sample 4 with respect to the beam so that the recoil atoms enter the TOF device 6, thereby obtaining the spectrum of light elements, and measuring the surface distribution of heavy elements, the sample 4 should be placed close to perpendicular to the proton beam. A surface analysis device characterized in that the energy loss of scattered protons is determined by a position detector 5 to determine the spectrum of heavy elements.