JPH02112140A - Low speed ion gun - Google Patents

Abstract

PURPOSE:To exclude the limitations of beam diameter and current value by space charge effect and enable the generation of a large current and highly focusing ion beam by confining electrons in an energy region near the ion optical axis between the deceleration and focusing space of the ion beam and a sample by a magnetic field. CONSTITUTION:An ion beam 3 drawn by an electrode 2 is focused by an electrostatic lens 4, and only a desired ion spices is separated by a mass spectrometer 5, decelerated by a deceleration and focusing lens 6 and throttled by apertures 8, 9. In this case, to prevent the divergence of the beam 3 by space charge effect, the thermoelectrons emitted from an electron generating device 7 are confined near the ion optical axis by a magnet 10. The space of the drift region not conducting acceleration and deceleration of the beam 3 is filled with the electrons. At a result, the positive charge by the ions in the beam 3 and the negative charge by the electrons are well-balanced to neutralize the space charge. The beam 3 passed through a device 7 comes into a sample 11 through the aperture 9.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention decelerates ions extracted from an ion source,
This invention relates to a slow ion gun that focuses and irradiates a sample.

[Prior Art 1] Low-velocity ion beams are important as a means of low-damage etching in materials analysis and semiconductor device manufacturing. When analyzing a minute portion of a sample, it is necessary to irradiate the sample with an ion beam that is focused as narrowly as possible. In addition, when using mass-separated ions for etching, it is necessary to accelerate the ion beam, then mass-separate it using an electric or magnetic field, and then decelerate it before irradiating it onto the sample in order to increase the resolution of the mass separation. . In such cases, a method or apparatus for effectively focusing a slow ion beam is needed. Conventionally, it has been possible to easily focus a high-speed (eg, 10 KeV or higher) ion beam using, for example, an electric field, but it has been difficult to focus a low-speed ion beam.

Generally, the diameter and current value of an ion beam are greatly limited by space charge effects. In conventional ion guns, a slow ion beam is focused using an electrostatic lens.
The current value generated by the ion beam is large, and therefore, as the current density increases, the beam diameter increases due to the space charge effect. As a result, when obtaining a small beam diameter, the current value is limited. For example, 100e
In the case of an Ar ion beam of V, the beam with a current value of 50 nA or more is 5. It was difficult to converge to a diameter of QOμm or less.

[Problems to be Solved by the Invention] The conventional low-velocity ion gun described above has the disadvantage that it is not possible to obtain a beam diameter smaller than the value limited by the space charge effect or a current value larger than that.

The present invention was proposed to improve the above-mentioned drawbacks, and its purpose is to eliminate the above-mentioned limitations due to space charge effects, and to generate a low-speed ion beam with high current and high focusability. Our goal is to provide ion guns.

[Means for Solving the Problems] The low-velocity ion gun of the present invention includes electrons in an energy range with a low probability of bonding with positive ions in the space between the sample and the deceleration/focusing region that decelerates and focuses the ion beam. The apparatus includes an electron generating means for generating electrons, and a magnetic field generating means for generating a magnetic field for confining the electrons near the ion optical axis.

[Function] Therefore, the electrons generated by the electron generation means and confined around the ion optical axis do not combine with the ions, but shield each ion from the space charge, thereby reducing the space charge effect. Prevents ion beam divergence.

[Example] Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a first embodiment of the low-velocity ion gun of the present invention, and FIG. 2 is a block diagram of the electron generator 7 of FIG. 1.

The low-speed ion gun of the present invention includes a positive ion source 1 and an ion beam 3.
extraction electrode 2, electrostatic lens 4, mass spectrometer 5, deceleration/focusing lens 6, electron generator 7, aperture 8.9,
It is composed of a magnetic field generating coil 1o and power supplies 12, 13, and 14. The ion beam 3 is extracted by the extraction electrode 2 at an accelerating voltage of 1 kV, focused by the electrodes 4+ and 42, 43 of the electrostatic lens 4, and then subjected to a mass spectrometer 5 using a static magnetic field and an electrostatic field to extract desired ions. Only the seeds are separated, and the electrode 61' of the deceleration/focusing lens 6
, 62 and '6'3', the ion beam 3 is focused while being decelerated, and narrowed down by the apertures 8 and 9. At this time, in order to prevent divergence of the ion beam 3 due to the space charge effect, as will be described later, the electrons emitted from the electron generator 7 are confined near the ion optical axis by the magnet 10, and the drift region of the ion beam 3 is (
This fills the space between the deceleration/focusing lens 6 and the sample 11 (an area where acceleration/deceleration is not performed). As a result, the positive charges caused by the ions and the negative charges caused by the electrons in the ion beam 3 are balanced, and the space charges are effectively neutralized. The ion beam 3 that has passed through the electron generator 7 passes through the aperture 9 and enters the sample 11 . The ion beam 3 hits the sample 11
The energy incident on is provided by a power source 12. The ion source 1, electrostatic lens 4, deceleration and focusing lens 6, and mass spectrometer 5 are at a floating potential as shown in FIG. The coil IO is installed outside the vacuum container containing the deceleration/focusing lens 6, the electron generator 7, and the sample 11. Further, in this embodiment, the length of the coil 10 is such that it includes a part of the deceleration/focusing lens 6 and the sample 11.

As shown in FIG. 2, the electron generator 7 is provided between the apertures 8.9 in an arrangement surrounding the ion optical axis, and is composed of a filament 15 for emitting thermoelectrons, a grid 16, and a power source. has been done.

The optimum electron density for shielding the space charge effect is adjusted as follows. The filament 15 is connected to the grid 1 at ground potential.
6, it is biased to a negative potential ■f. The number of electrons injected into the drift region can be adjusted by bias voltage V and filament current It. Furthermore, the electron density near the ion optical axis in the drift region through which the ion beam 3 passes can be controlled by the thickness of the external magnetic field LX generated by the coil 10. Electrode plate 6 of deceleration/focusing lens 6
3 is positively biased, some of the electrons in the drift region are drawn inside the deceleration and focusing lens 6, reducing the space charge effect of the ion beam 3 in this region. Further, some of the electrons also flow into the sample 11 through the hole of the aperture 9, reducing the space charge effect of the ion beam 3 between the aperture 9 and the sample 11. Further, in order to prevent neutralization of the ions themselves by electrons, the bias voltage (1) of the filament 15 is set to 10 V or more. This is because the probability of an electron bonding to an ion (neutralization probability) is high when the energy of the electron is as low as several eV. However, this does not apply when an atomic beam or molecular beam in which the ion beam 3 is neutralized is required.

FIG. 3 shows the magnitude of the Ar ion beam current that passes through the aperture 9 with a diameter of 500 μm and enters the sample when the magnitude of the magnetic field Hox by the coil 10 is varied. The energy of the Ar ions is OOe V, the filament current is 50 mA, and the bias voltage is 20 V. The effect of electrons flowing into the sample is corrected. The Ar ion current value when the electron generator 7 is not used is 50n
△ and small. This is because while the ion beam 3 passes between the drift regions, the diameter of the beam increases to 500 μm or more due to the space charge effect, and the value of the ion current passing through the aperture 9 decreases. Using the electron generator 7, 1-18. As the voltage is applied, the Ar ion current value increases due to the improvement of the focusing property of the Ar ion beam. When H6X was 30 [Oe], the maximum Δr ion current of 6 μA was obtained. In this way, by correcting the space charge effect, it was possible to obtain an ion current 120 times greater.

FIG. 4 is a diagram illustrating the main parts of the second embodiment of the present invention.

In this embodiment, the coil 10 of the second embodiment is replaced with a Helmholtz coil 17, and a magnetic field HoX having a similar effect can be generated. helmholtz coil 1
7 has the advantage that other structures between the two coils, e.g.
Even if there are joints in the vacuum container, a uniform magnetic field of a desired magnitude can be generated in the drift space.

[Effects of the Invention] As explained above, the present invention is capable of confining electrons in an energy region with a low probability of bonding with ions near the ion optical axis between the ion beam deceleration/focusing space and the sample using a magnetic field. This reduces space charge effects and allows the use of slower ion beams with higher current densities, resulting in less damaging etching, which benefits materials analysis and semiconductor manufacturing.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a first embodiment of the low-speed ion gun of the present invention, FIG. 2 is a block diagram of the electron generator 7 of FIG. 1, and FIG. FIG. 4 is a diagram illustrating the main part of the second embodiment of the present invention. 1... Ion source, 2... Extraction electrode, 3...
・Ion beam, 4... Electrostatic lens, 41.42.4
3... Electrode, 5... Mass spectrometer, 6... Deceleration/focusing lens,
6□, 62; '63...electrode, 7...electron generator, 8,9...aperture, 0.
... Coil, 11...8 Omura, 2.13.14
...power supply, 5...filament, 6...grid, 17...Helmholtz coil.

Claims (1)

[Claims] 1. In a low-speed ion gun that decelerates and focuses ions extracted from a positive ion source and irradiates them onto a sample, a space between the deceleration/focusing region that decelerates and focuses the ion beam and the sample. A low-speed ion gun characterized by comprising: an electron generating means for generating electrons in an energy range where the probability of bonding with ions is low; and a magnetic field generating means for generating a magnetic field that confines the electrons near the ion optical axis.