JPS5836456B2 - microwave plasma ion source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in ion sources that utilize microwave discharge.

Figure 1 shows a conventional microwave discharge ion source.
1 is a discharge electrode, 2 is a gap for microwave matching necessary for microwaves to enter between the discharge electrodes, and an insulator 3 is provided here to prevent discharge from occurring within this gap. Filled.

Further, although 3' is also an insulator, it has the role of vacuum sealing and prevents discharge from spreading to this part.

4 is a sample gas introduction pipe, 5 is an ion extraction electrode, 6 is
is the lens electrode.

Note that 5 has a rectangular opening.

However, in such a conventional microwave discharge type ion source, the surface of the discharge electrode 1 is sputtered due to ion bombardment, and as this is ionized, ions of elements constituting the discharge electrode are mixed into the extracted ion beam. Otherwise, it may cover the surface of the insulating material used for introducing microwaves and hinder the introduction of microwaves.

It is an object of the present invention to eliminate these drawbacks of conventional ion sources, and to actively utilize the ion sputtering effect to efficiently obtain ions from solid substances.

FIG. 2 is a diagram explaining the principle of the ion sputter effect used in the present invention.

Although plasma T is generated between the discharge electrodes, an ion sheath 8 exists between the discharge electrode 1 and the plasma boundary 9.

The plasma has a positive potential with respect to the discharge electrode 1 by a so-called floating potential.

This floating potential is a function of plasma parameters, but typically ranges from a few volts to several tens of volts.

Therefore, the ions that have jumped out of the plasma boundary are accelerated toward the discharge electrode and collide with this electrode with energy equal to this floating potential.

At this time, the number of sputtered atoms per unit area is n(
ke/d), the following equation holds true.

However, J (A/i) is the ion current flowing out from the plasma boundary of unit area, α is the sputtering rate per ion, and the ions are assumed to be monovalent.

α is a function of the ion species, the type of solid element being sputtered, and the ion accelerating voltage.

Since the threshold voltage at which sputtering generally occurs is several volts, α takes a value other than zero under the above conditions.

For example, in the literature (M. Kamisky's Atomic
and Ionic Impact Phenomen
a or Metal Surfaces +Spr
inger-Veriag. Berlin (1
965) As shown in P151), when metallic chromium is folded with argon ions, α is approximately 0 at 40V.
．． It is 1.

Therefore, if the current density is 0. If the value IA/i is used, n will be approximately 6×1016 pieces/sec.

If the distance between atoms in a solid is several A, then approximately one layer will be sputtered per second.

FIG. 3 is a diagram showing an embodiment of the present invention.

The coating material 10 provided on the inner wall surface of the discharge space surrounded by the discharge electrode 1 and the insulators 3, 3', etc. is provided to take advantage of the above-mentioned sputtering effect.For example, when it is desired to obtain boron ions, the coating material 10 is as BC#3t B
A vapor such as Fs or B2H6 may be introduced through the gas introduction pipe 4, and boron crystals or a compound such as boron nitride may be used as the coating material 10.

This 10 is in close contact with the discharge electrode 1 and the inner wall surfaces of the insulators 3 and 3'.

Now, considering the case where BCl3 vapor is introduced, the ion species generated by microwave discharge are mainly B++++ BCII, BC/l2, Cl, and Cl2+, and the proportion of B+ in the total ions is 0.2 to 0.
．． It is 1.

Also, considering that most of the ions generated in the discharge box generally collide with the discharge electrode and the walls of the discharge box,
For a moment, when each of the above ion species collides with the boron crystal, if the sputtering efficiency α is assumed to be 0.05 to 0.1, approximately the same number of boron atoms as the number of B+ colliding with the wall will be sputtered. become.

Therefore, since the proportion of B+ occupying the plasma in the discharge box increases, the amount of B+ ions extracted also increases.

As described above, in the apparatus of the present invention, contamination of electrode constituent elements can be prevented, and target element ions can be effectively obtained by utilizing the sputter effect.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a conventional microwave discharge type ion source, FIG. 2 is a diagram explaining the ion sputtering effect used in the present invention, and FIG. 3 is a diagram showing an embodiment of the present invention. In the figure, 1...Discharge electrode, 2...Gap for microwave matching, 3...Insulating filling,
3'...Insulating plate for vacuum sealing, 4...Sample gas introduction hole, 5.Curved/ion extraction electrode, 6...
...Lens electrode, 7...Plasma, 8...
...Ion sheath, 9...Old plasma boundary, 10...
...A covering material made of a solid substance containing an element to be ionized.

Claims (1)

[Claims] 1. A microwave plasma ion source that ionizes the element to be ionized by introducing vapor containing the element to be ionized into the discharge vessel and generating microwave discharge plasma in the discharge vessel, A microwave plasma ion source characterized in that the inner wall surface of the discharge vessel is covered with a covering material made of a solid substance containing the above-mentioned element to be ionized.