Chemistry: electrical and wave energy – Apparatus – Coating – forming or etching by sputtering
Patent
1988-06-08
1989-10-17
Weisstuch, Aaron
Chemistry: electrical and wave energy
Apparatus
Coating, forming or etching by sputtering
C23C 1434
Patent
active
048744972
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an apparatus for forming thin films of various materials on specimen substrates, and more particularly, a novel thin film forming apparatus utilizing sputtering by high density plasma, thereby forming various thin films at a high rate and a high degree of efficiency.
BACKGROUND ART
The so-called sputtering apparatus for forming a film by sputtering a target as a thin film forming element in plasma has been used widely in various fields of forming thin films of various materials. Especially (1) a conventional diode (rf or dc) sputtering apparatus (refer to F. M. D'HEURLE: Metall. Trans., Vol 1, March, 1970, pp 725-732) in which a target 1 and a substrate 2 are disposed in opposing relationship in a vacuum chamber 4 as shown in FIG. 1; (2) a triode sputtering apparatus (refer to W. W. Y. Lee and D. Oblas: J. Appl. Phys., Vol. 46, No. 4, 1975 pp 1728-1732) in which, as shown in FIG. 2, a third electrode 3 for emitting electrons is further disposed and (3) the magnetron sputtering process (refer to R. K. Waits: J. Vac. Sci. Technol., Vol. 15, No. 2, 1978, pp 179-187) in which, as shown in FIG. 3, a suitable magnetic field is applied to a target 1 by a magnet 5 to generate high density and low-temperature plasma, thereby forming thin films at a high rate, are known in the technical field of thin film formation. Each of the above-mentioned equipment and process comprises generally a target 1 which is a thin film forming element, a substrate 2 upon which a thin film is formed, a vacuum chamber 4 in which the target 1 and the substrate 2 are enclosed and gas inlet and outlet systems, whereby plasma is generated in the vacuum chamber 4.
In case of forming a thin film at a high rate in each of the above-mentioned apparatus and process, it is essential that the density of plasma be maintained at a high level. In the case of the diode sputtering apparatus, the higher the density of plasma, the more drastically a voltage applied to the target is increased and concurrently the temperature of the substrate rapidly rises because of the bombardment of high energy particles an high-energy electrons in the plasma thereon. As a result, damage to the grown thin films is increased, so that the diode sputtering apparatus can be only used with special heat-resistive substrates, thin film materials and film compositions. In the case of the triode sputtering apparatus, even though the density of the plasma increases by the feeding of electrons from the third electrode, as in the case of the diode sputtering apparatus, the rapid temperature rise of the substrate results in damage to the thin film. As a consequence, the triode sputtering apparatus has the defect that only special film-forming materials may be used and the kinds of substrates to be used are also limited in number.
On the other hand, with the high-rate magnetron sputtering apparatus, the gamma (.gamma.-) electrons which are emitted from the target and which are needed to ionize a gas in plasma are confined over the surface of the target by the magnetic and electric field, so that it becomes possible to generate high-rate plasma at a low gas pressure. For instance, the high-speed sputtering process can be carried out at a low pressure as low as 10.sup.-3 Torr in practice, so that the magnetron sputtering process has been used widely to form various thin films at high rates. However, in this process, the film being formed is subjected to the bombardment of ions (mainly Ar.sup.+) from the plasma; high-energy neutral particles (mainly Ar reflected at the surface of the target); and negative ions. Accordingly in almost all the cases, the compositions of the films thus formed are deviated and not only the film but also the substrate are damaged. Furthermore, it is well known in the art that in the case of the formation of a ZnO film, the quality of the portion of the ZnO film immediately above the eroded or bombarded portion of the target is considerably different from the quality of the remaining portion. Thus, the magnet
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F. M. D'Heurle: Metall. Trans., vol. 1, Mar. 1970, pp. 725-732.
W. W. Y. Lee and D. Oblas: J. Appl. Phys., vol. 46, No. 4, 1975, pp. 1728-1732.
R. K. Waits; J. Vac. Sci. Technol., vol. 15, No. 2, 1978, pp. 179-187.
Ono et al., Jpn. J. Appl. Phys., vol. 23, No. 8, 1984, L534-L536.
Matsuoka Morito
Ono Ken'ichi
Nippon Telegraph and Telephone Corporation
Weisstuch Aaron
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