JPS61239186A - Non-contact ionic current measuring device - Google Patents

Abstract

PURPOSE:To measure exactly and easily an ionic current in no contact with an ionic beam, by supplying a neutral target atom to an ionic beam line, making an ion collide with the neutral target atom, and counting a generated secondary electron by a particle detector. CONSTITUTION:By supplying a neutral target atom 2 to an ionic beam line from a neutral target atom supply device 13, an area where an ion 1 and the neutral target atom 2 collide with each other is provided, a secondary electron 3 generated by its collision is counted by a particle detector 4, and an ionic current value is derived from its value. That is to say, a true ionic current value is measured in advance by a Faraday cup 7 which has been installed from of a secondary electron generating zone, also a secondary electron counting value corresponding to its current value is derived by the particle detector 4, and its calibration table is made beforehand. In this way, on the contrary, the ionic current can be derived from the counting value.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to an ion implantation device and a wooden accelerator, and in particular to a non-contact ion implanter suitable for measuring ion beam current without contacting the ion beam. This invention relates to a beam current measuring device.

[Background of the invention]

Ions with high kinetic energy can be obtained by ionizing various elements in a vacuum and accelerating these ions with an electric field. The main purpose of ion implantation is to irradiate the solid surface with these ions to improve the properties and impart functions to the solid surface. Ion irradiation research for scientific purposes has been conducted for a long time, but recently, ion irradiation has been actively used for engineering purposes. In particular, its application to semiconductor manufacturing as impurity injection technology has already been put into practical use, and its application to metals is increasing, such as improving corrosion resistance, synthesizing new materials, and simulating irradiation damage in nuclear reactor materials. There is a trend of expansion.

Considering the purpose of these ion implantations, in most cases they must be performed quantitatively, and for this purpose, the amount of ion irradiation must be accurately determined. In order to perform the irradiation tt measurement, it is necessary to measure the current of ions irradiated onto the target, and conventionally the following method has been adopted.

(1) By electrically insulating the target from the target, it becomes possible to measure the current of ions irradiated there.

In other words, the target is given the role of an ion current measuring device (hereinafter referred to as a 7Araday cup).

(2) The fight shown in Figure 2! By using t,
Ion current can be measured without contact. By passing ions 1 through the center of 140 ferrite rings, a magnetic field is generated around the ion beam, and a magnetic field of a certain size is generated. The current generated in the coil 16 wound around the coil 16 is measured, and the ion current is calculated from that value (Hiroo Kumagai, Accelerator J p590, Kyoritsu Shuppan).

However, each of these methods has the following problems.

In the method (1) above, since it is necessary to electrically insulate the target from other targets, it is difficult to irradiate a large or complex-shaped target that is difficult to insulate. Furthermore, due to the secondary electrons emitted when the target is irradiated, the measured ion current value is larger than the actual ion current value. A device (hereinafter referred to as a suppressor) must be installed. Therefore, targets can only be installed in locations where there is sufficient space to install a suppressor.

The method (2) above does not allow continuous measurement of ion current. This is because current is generated in the coil only when the magnetic field changes, either at the moment the irradiation starts or at the moment it ends.

In other words, the conventional ion current measurement method has significant limitations in ion implantation technology, which is expected to be used in more and more fields in the future. Therefore, there is a need to develop a new ion current measurement device that can fundamentally solve these sentinel problems.

1. [Object of the Invention] An object of the present invention is to provide an apparatus that enables accurate and easy measurement of ion current without contacting the ion beam.

[Summary of the invention]

The present invention provides a region (hereinafter referred to as a secondary electron generation zone) where ions and neutral target atoms collide by supplying neutral target atoms to an ion beam line, and electrons ( Hereinafter referred to as secondary electrons) are counted by a nucleon detector installed behind the secondary electron generation zone, and the ion current value is determined from the counted value. In other words, the true ion current value is measured in advance with a Faraday cup installed in front of the secondary electron generation zone, and the secondary electron count value corresponding to that current value is determined using a particle detector, and a calibration table is created. I'll keep it. By doing so, you can conversely calculate the ion current from the counted values.

As a result, it becomes possible to accurately and easily measure the ion current without contacting the ion beam.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail using FIGS. 1 and 3 to 5. First, the configuration of a non-contact ion beam current measurement device according to the present invention will be explained. FIG. 1 shows its configuration. This embodiment is composed of a neutral target atom supply system, a gas pressure control system, a secondary electron detection system, and an ion current value calibration system, each of which is installed along the ion beam passage path. The neutral target atom supply system supplies the neutral target atoms 2 obtained from the neutral target atom supply device 13 to the ion beam passage path.

The gas pressure control system keeps the gas pressure constant by opening and closing the needle pulp 9 while measuring the gas pressure of the neutral target atoms using the gas pressure gauge 12. The secondary electron detection system detects secondary electrons 3t-1 generated in the secondary electron generation zone 16 by a particle detector 4 installed behind the secondary electrons 3t-1. The ion current value calibration system includes a Faraday cup 7 necessary for calibrating the ion current value from the secondary electron count obtained from the particle detector.

Next, the basic principle of this embodiment will be explained.

Generally, when a charged ion A collides with an ionizing target atom B, the following reaction occurs.

Ak+B=A'″10B”+(m+n-k)e-・”-(
1) In other words, ion A undergoes electron capture and electron loss and becomes charged state m, while neutral target atom B becomes charged state n, but at that time, (m-)-n-k) electrons e − is released. In this embodiment, the t secondary electrons generated here are detected by the particle detector 2 installed behind the secondary electron generation zone, and the ion current value is derived from the counted value.

The number of secondary electrons generated in the secondary electron generation zone depends on the number of collisions between neutral target atoms and accelerated ion particles in that region. The number of collisions per unit volume in the secondary electron generation band (hereinafter referred to as collision density), n, is the neutral target atom density nos, the ion density in the ion beam nl, and the average velocity of ions vi, as follows: can be expressed.

no ”=6 (El) ” n6 @nl e V
・”・(2) σ(g) is the total ionization cross section and depends on the energy E1 of the ion.The ion current density i is expressed as i=, enloV (eU element tl ・
---(3), and assuming that the secondary electron count value N in the particle detector is approximately proportional to the collision density, the following relationship can be obtained from equation (2).

Ω is a solid angle that tilts the detection surface of the detected amount of particles when the secondary electron generation band is set as a point. In other words, equation (4) shows the following. For a certain combination of ions and neutral target atoms, if the gas pressure of the neutral target atoms and the positional relationship between the secondary electron generation band and the particle detector are held constant, one can estimate the energy of the ions E t %. This is a term that depends only on the acceleration voltage V. In this embodiment, if the human value at each acceleration voltage is determined in advance for each combination of ions and neutral target atoms, the ion current value can be calibrated from the count value of the particle detector. The calibration is performed by first accurately measuring the ion current using a Faraday cup in the ion beam calibration system, and then comparing it with the secondary electron count of the particle detector. From the results, by obtaining a calibration curve in which human values for each acceleration voltage are plotted for each ion and neutral target atom, the ion current value can be easily obtained from the secondary electron count value.

Next, it is sufficient to examine whether the ion current detection sensitivity of this embodiment is a reasonable value.

Now, the minute ion current density i = lμA/z"'t-
The gas pressure Pt of the neutral target atom required for detection is determined. First, unit area (1 cr
The number of ions passing per second, n, / is
It is calculated as follows.

nl'=-=6 (We are considering an ion with a single charge). Further, the value of the total separated cross-sectional area, which indicates the probability of collision, can be determined as follows. Now, let's take the case of hydrogen ions and hydrogen atoms as an example. Figure 4 is 300
When a hydrogen ion with an energy of KeV collides with a hydrogen atom, the double differential cross section (total ionization cross section σ(fi:I)e secondary electron emission angle and secondary electron Differentiating with the energy E, we have (,pσ(Et)/dΩ・d(E,)),
This is a plot of the emission angle of secondary electrons. From this figure, it can be seen that in order to eject a large number of secondary 'electrons, it is more advantageous to make the emission angle smaller. In particular, high-energy secondary electrons are only emitted forward. Therefore, it was decided to install the particle detector at a position of 20° with respect to the secondary electron generation band. Figure 5 shows 100-1500K
When a hydrogen ion with an energy of eV collides with a hydrogen atom, the energy of the secondary electron emitted at 200 is expressed as 2
It is plotted against the heavy differential cross section. From this figure, the differential cross section (, ) when ions accelerated at 300 kV collide and are emitted in the 20° direction dσ(El) can be determined as follows by triangular approximation.

The inequality sign here is actually the differential ionization cross section,
Although the beak becomes larger, this is because the count value of the particle detector is estimated to be a small value in order to know the detection sensitivity of this example. The ionization cross section that generates the secondary electrons with the emission angle of 20° that you want to find now by multiplying the differential ionization cross section that you just found by multiplying it by the minute solid angle dΩ that the single-particle detector makes with respect to the secondary electron generation band. σ(Hl)zel' can be obtained. In this case, the secondary electron generation band is approximated to a point, the secondary electron detection area S of the particle detector is 1 m'', and the distance to the secondary electron generation band is t.
If t-5cm, dΩ is found as follows.
Ru.

Therefore, the ionization cross section σ(HI)2o that we want to find now is the following formula.

Now, if the gas pressure of the neutral target atoms is 10''5 Torr, the density of the neutral target atoms contained therein can be determined as follows.
4 (A: Avogadro's number, 几: gas constant, T: temperature) Using equation (4), the count value in the particle detector is N
=σ (Et72o*n6 *flt'==5X10
' (flip/S). In other words, the degree of vacuum in the beam duct is t 10-? If it is TOrr, it is understood that if the vacuum e in the secondary electron generation chamber is made two orders of magnitude worse, it is possible to measure a minute current of 1 μA.

In this example, it goes without saying that a nuclide that generates a large number of secondary electrons is more advantageous as a combination of ions and neutral target atoms. Also, when an ion collides with a neutral target atom, secondary electrons and KX-rays are generated at the same time.
This causes measurement noise, so it is advantageous to use a combination of nuclides that are less likely to generate X-rays.

In this example, the beam current is measured by colliding neutral target atoms with ions, so although it cannot be said to be strictly non-contact, the ions emit secondary electrons. 41, ゎoff, 3゜UT+7)*af5
・5 Qualitative 7 Meaning 7 Non-contact''A6 ・Next, other 2 of the present invention
We will explain two embodiments”, fKff,
-J-20'kWttlL-f)bthVc 1. Electrons 19e flying from outside the secondary electron generation band can be excluded, thereby improving the measurement accuracy of the ionic current.

A third embodiment of the present invention will be described using FIG. 7. In this example, the source of neutral target atoms, ′″″
″r′4i1i (to HiL4m1231:ffl#Ll
! ``222>hlp-,'' ``It is possible to use the evaporated atoms 2 as neutral target atoms.'' If this neutral target atom supply device is used, ``the pressure of the secondary electron generation chamber can always be maintained at the same level as the type of liquid being used.'' 5yo71
It can be maintained at atmospheric pressure, and the accuracy of measuring ion current can be improved.

Note that when ions and neutral target atoms collide, characteristic X-rays are generated that cause measurement noise, but they can also be used to measure the ion current.

Finally, by providing a negative electrode in front of the particle detector as a bias, the secondary electrons are repelled and only the characteristic X-rays are detected by the particle detector, which also makes it possible to accurately measure the ionic current t. I can do it.

〔Effect of the invention〕

According to the present invention, it is possible to accurately and easily measure the ion current without contact while irradiating the target with accelerated ions, so there is no need to electrically insulate the target from others. With that in mind, by ensuring electrical insulation, restrictions on the size or shape of the target are eliminated, and there is no need to install a suppressor in front of the target, so the target installation can also eliminate restrictions on position. effective.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram illustrating an embodiment of the present invention, and FIG.
The figure shows a known example closest to the present invention, Figure 3 is a diagram explaining the basic principle of the present invention, and Figure 4 shows that when a hydrogen ion with an energy of 300 KeV collides with a hydrogen atom, The t-diagram showing the angular distribution for secondary electrons at various energies, Figure 5, shows the angle distribution for secondary electrons of various energies.
Figure 47 is a schematic diagram for explaining the third embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Ion, 2... Neutral radial atom, 3... Secondary electron, 4... Particle detector, 5... Beam duct, 6...
...Secondary electron generation chamber, 7...Faraday cup, 8...Slit, 9...Needle valve, 10
...Vacuum pump, 11...Cooling pipe for temperature adjustment,
12... Gas pressure gauge, 13... Neutral target atom supply device, 14... Ferrite ring, 15... Amplifier, 1
6... Coil, 17... Secondary electron generation band, 18...
・Secondary electron detection surface, 19...Secondary electrons generated outside the secondary electron generation zone, 20...Collimator, 21...
Neutral target atom supply chamber/bar, 22... Liquid for neutral target atom supply, 23... Cryogenic chamber, 1st♂ @ tfJ

Claims (1)

[Claims] 1. In a non-contact ion current measurement device, neutral target atoms are supplied to the ion beam line, and secondary electrons generated by collisions between ions and neutral target atoms are counted by a particle detector. A non-contact ion current measuring device characterized by measuring an ion current. 2. A non-contact ion current measuring device according to claim 1, characterized in that a collimator is provided in front of the particle detector. 3. In the non-contact ion current measuring device according to claim 1, a liquid consisting of a single nuclide is held in a cryogenic chamber, and atoms evaporated from the liquid are used as neutral target atoms. A non-contact ion current measuring device characterized by being provided with a target atom supply device.