Radiant energy – Ion generation – Field ionization type
Utility Patent
1998-09-24
2001-01-02
Anderson, Bruce C. (Department: 2881)
Radiant energy
Ion generation
Field ionization type
C250S492210
Utility Patent
active
06169288
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an ion source which utilizes laser ablation.
2. Description of the Prior Art
Various ion sources for use in the ion injection devices for introducing impurities into semiconductor substrates, direct ion deposition devices for depositing a thin film on a substrate, and other such devices have been studied and developed.
Among these is the ion source which utilizes so-called laser ablation (hereinafter referred to “laser ablation type ion source”). The term “laser ablation” refers to the phenomenon of a solid raw material whose surface is exposed to a pulse laser beam of high intensity separating and emitting constituent atoms and the like to generate a plume resembling a plasma near the surface of exposure. As disclosed in Japanese Public Disclosure Hei 5-279848, for example, laser ablation has been utilized for depositing a thin film on a substrate by disposing a solid raw material and the substrate opposite each other in a vacuum vessel, projecting a laser beam obliquely on the solid raw material, and allowing the atoms and the like emitted from the solid raw material to accumulate on the substrate.
The laser ablation type ion source is a device that utilizes laser ablation. The ion source takes advantage of the fact that the ratio of ions in the plasma-like plume rises in proportion as the intensity of the laser beam increases. It forms an ion beam by extracting these ions from the relevant electrode and accelerating the extracted ions. As in the technique mentioned above of using laser ablation to deposit a thin film, the conventional laser ablation type ion source is configured to project the laser beam onto the solid raw material in an oblique direction (typically 45 degrees) and to extract the ions emitted from the solid in the direction perpendicular to the surface of exposure. The laser ablation type ion source, unlike the ion source using plasma sputtering, does not require an operating gas but operates in a high vacuum. Emission of impurities is therefore effectively suppressed. The use of the laser ablation type ion source is therefore advantageous for attaining ion injection and thin film deposition with high purity.
However, the conventional laser ablation type ion source is practically deficient in ion emission efficiency relative to the intensity of the pulse laser beam. Another drawback is that the difference between the direction of laser beam projection and the direction of ion extraction requires the distance between the electrode and the solid raw material to made long so that the extracting electrode can be disposed without obstructing the laser beam. This enlarges the ion source size. Another disadvantage is the need to accommodate a space-consuming mass spectrograph for selection and separation of specific ions and for the convergence of ions. Still another is that the ion source is difficult to optically adjust.
The development of a laser ablation type ion source which is free of these problems is desired.
The inventors continued a study with a view to providing such an ion source and accomplished the present invention as a result.
SUMMARY OF THE INVENTION
This invention concerns a laser ablation type ion source which enables efficient extraction of ions from a solid raw material, is small in size, and is easy to adjust.
Specifically, this invention is directed to a laser ablation type ion source which comprises a vacuum chamber and a laser beam source for projecting a laser beam of high density into the vacuum chamber, the vacuum chamber being provided therein with a retaining section for retaining a solid raw material for generation of ions at a position exposed to the projected laser beam, a hole for allowing passage of the laser beam from the laser beam source and the ions generated from the solid raw material on the path of the laser beam projected into the vacuum chamber, an ion accelerating electrode and an ion extracting electrode disposed in this order from the laser beam source side, and a mass spectrograph for ion separating having a mass separation electromagnet for guiding specific ions passing through the hole in a direction deviating from the path of the laser beam in accordance with the mass of the ions.
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Chayahara Akiyoshi
Horino Yuji
Kinomura Atsushi
Mihara Toshiyuki
Tsubouchi Nobuteru
Agency of Industrial Science & Technology, Ministry of Internati
Anderson Bruce C.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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