JPS593814B2 - solid ion source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Recently, in addition to ion species based on gas components, ion species based on solid components have begun to be used in secondary ion analyzers, ion implantation, ion beam evaporation, and other fields.

As an example, considering the application to a secondary ion analyzer, conventionally, the gas component elements Ar+, 0
2+, N2+, etc. were mainly used.

The reason is that these ions do not have particular characteristics in analysis, but are easy to ionize because they are gas components.

However, elements that are electronegative as primary ions (
When using inert ions (such as Ar) or inert ions (such as Ar), the ionization rate varies from one to four digits depending on the element, and Au, As, which are considered to be particularly important elements in the semiconductor industry, It has been found that the secondary ionization rate of , Te, etc. is low, raising the analytical limit of these elements, and this has been pointed out as one of the problems of secondary ion analysis.

FIG. 1 shows the relative ionization rate of each element when an electronegative 0-ion is used as the primary ion.

The figure shows that the ionization rate varies significantly depending on the element.

That is, the ionization rate of elements that are relatively active toward oxygen, such as Al tMg and Cr tReW, is high, and S.

The ionization rate of relatively inert elements such as As y cat P t t Au is low.

On the other hand, it is known that when electropositive ions are used as primary ions, the relationship between elements and relative ionization rates exhibits a completely different tendency than when electronegative ions are used as shown in FIG.

FIG. 2 shows the relative secondary ionization rate of each element when electropositive Cs+ ions are used as primary ions.

The figure shows that S, As, which showed an extremely low ionization rate when electronegative ions (0-) were used.
.

(: The ionization rate of elements such as d, Te, and Au increases by about three orders of magnitude, and when 0-ions are used, the ionization rate of Cr
It can be seen that the values are relatively close to those of , At, Mg, Cr, etc.

On the other hand, there are no gaseous electropositive elements, and these elements form solids, making it difficult to efficiently ionize them as an ion source.

Therefore, until now, there has been no powerful and stable ion source capable of extracting electropositive ions.

As an electropositive ion source, there is a Cs ion source that has been used.
It was used because it has a low evaporation temperature and is easy to thermally ionize.

However, the problem is that it is difficult to provide a stable supply of materials, which is a problem in cases where beam stabilization is required, such as in secondary ion analyzers, and this has prevented practical application.

The present invention relates to a new solid-state ion source that eliminates the above-mentioned conventional problems.

Examples will be described below.

FIG. 3 shows the configuration of a conventional duoplasmatron ion gun.

The device is composed of a gas introduction part 1, a hollow cathode 2, a shield electrode 3, an intermediate electrode 4, a magnet 5 for supplying a magnetic field to a space consisting of the intermediate electrode 4 and an anode 6, and a secondary ion extraction electrode 8. .

Further, the driving power source 13 of the ion gun is connected to the hollow cathode 2, the intermediate electrode 4, and the anode 6 through a protective resistor 15 and a discharge stabilizing resistor 16.

Further, the secondary ion accelerating power source 14 is connected between the anode 6 and the extraction electrode 80.

The principle of operation is to first close the gas inlet 1, evacuate the entire ion gun, then introduce a gas corresponding to the required ion species, and reduce the degree of vacuum in the space created by the anode 6 or intermediate electrode 4 to 10'~ Maintain at 1O-2 Torr.

Next, the discharge power supply 13 causes the anode 6 or the intermediate electrode 4 to
A discharge is caused in the space of the hollow cathode 2 to generate an ionized state of gas, that is, plasma.

The space created by the anode 6 and the extraction electrode 8 is maintained at a vacuum of ~10-5 Torr due to the differential pumping effect of the anode hole.

In this state, plasma is blown out from the anode hole due to diffusion, and when an extraction electric field is applied, positive or negative ions are extracted.

In operation of the hollow cathode, first, strong plasma is generated in the hollow by discharge, and an electron beam is emitted toward the intermediate electrode 4.

As a result, plasma with high ionized dust is generated in the space created by the anode 6 and the intermediate electrode 4.

A magnetic field by the magnet 5 is generated in the axial direction in the space between the anode 6 and the intermediate electrode 4, and serves to increase the plasma density in this space (pinch effect).

Next, examples of the present invention will be described.

FIG. 4 shows a configuration diagram of the ion gun.

Most of the configuration is the same as the conventional method, and only new parts will be explained here.

The essential difference between the present invention and the conventional method is that a new ion source material 11 is placed in the hollow cathode 2.
In this embodiment, a mesh (gold wire) 12 is provided for holding the ion source material.

7 is an insulator, which plays the role of high-voltage insulation between the ion source and the extraction electrode.

The ion source material 11 may be NaCl depending on the purpose.

Cao 1 Cs Ot Na OHt KCtt M
gO* Cs Ct etc. are used.

FIG. 5 shows the configuration and power supply circuit of the ion source of the present invention.

The power supply circuit is completely the same as that of the conventional method, and its explanation will be omitted.

Examples will be described below. As the ion source material 11, NaCl crystal was used.

The size of the NaCt crystal used was 5 mm x 5 dishes x 10
mmt, and the support 12 of NaC1 is 0.4m.
Mφ gold wires were assembled into a mesh with a space occupation rate of 50, or a step provided in the hollow cathode 2 was used.

In both cases the samples were well supported.

The operating principle is almost the same as the conventional method; first, a Na Ct crystal is placed in the hollow cathode 2, the gas introduction section 1 is closed, the ion source is evacuated to ~1O-6T□r7, and then the Ar gas is introduced from the gas introduction part 1, the ion source chamber is maintained at 1O-1 Torr, and the discharge power source 13 is heated to about 30
A voltage of 0V is supplied to excite a hollow discharge due to Ar.

In this state, +NaCl is bombarded with ions by Ar and simultaneously receives a heating effect, is sputtered or evaporated, and is ionized in the plasma.

As a result, even if the introduction of Ar gas is cut off, ionization continues due to sputtered or evaporated particles of only NaCt.

The plasma generated in the intermediate electrode 4 and the anode space in this way is caused by the magnetic field supplied from the magnet 5.
High density, making it a more powerful ion source.

The generated plasma is released through the holes of the anode 6 by diffusion.

In this state, apply a positive or negative voltage to the acceleration power supply 14,
Extracts both positive and negative ions independently.

FIG. 6 shows one embodiment.

NaCl crystal was used as the primary ion source material 11, and a direct current of 300 V was applied as the discharge voltage to sustain the discharge.

In the initial discharge excitation, Ar gas was introduced from the gas inlet, but later the gas introduction was shut off, and the discharge caused only by the sputtered particles (or evaporated particles) of NaCl was utilized.

In this case as well, it was found that the ion source operated stably and that the mixing of excitation Ar ions could be reduced.

When using CaO or the like as the ion source material 11,
It is necessary to introduce Ar gas into the chamber during operation.

That is, introduction of Ar is essential depending on the material.

In FIG. 6, + indicates the acceleration voltage dependence of Na and Ct- ion currents, and the following became clear from this example.

(1) For both (Na+ and Ct- ions), ion currents comparable to those of conventional gas component ions, such as Ar+ and 02+ ions, are obtained.

(2Na+ ion current and Ct- ion current have similar behavior, and the amount of Ct- ions is about 4 times that of Na+ ions.

From the above results, it has become clear that solid component element ions, which were traditionally difficult to obtain, are now relatively easy to obtain, and are effective for application and performance improvement in ion implantation methods and secondary ion analyzers. Ta.

Finally, the results of studying the effects of applying the ion source of the present invention to a secondary ion analyzer will be shown.

FIG. 1 shows the results of measuring the secondary ionization rate of each element by extracting electropositive Na ions as primary ions from the ion source of the present invention and introducing electronegative 02 gas into the sample chamber.

As an effect, S and As, which had previously shown extremely low values,
The secondary ionization rate of $Au etc. has increased to 103 to 104, and At has traditionally had a high ionization rate.

It has become clear that the values are approximately the same as those of Si, Mg, etc.

This has made it possible to directly estimate quantitative analysis from the obtained mass spectral intensity, which was previously considered difficult.

[Brief explanation of drawings]

Figure 1 is a diagram showing the ionization rate of each element when O- ions are used as the primary ions, Figure 2 is a diagram showing the ionization rates of each element when Cs + ions are used as the primary ions, 3 is a block diagram of a conventional duoplasmatron ion source, FIG. 4 is an embodiment of the present invention, FIG. 5 is an embodiment of the present invention, and FIGS. 6 and 1 are diagrams of the present invention. It is a figure showing the effect of the invention.

Claims (1)

[Claims] 1. In a duoplasmatron ion gun equipped with a hollow cathode, a material serving as an ion source is placed in the hollow cathode, and the ion source material is sputtered or evaporated and ionized by operating the ion gun, A solid ion device characterized by extracting elemental or molecular ions constituting the ion source material.