Chemistry: electrical and wave energy – Apparatus – Coating – forming or etching by sputtering
Reexamination Certificate
1999-12-13
2001-09-04
Nguyen, Nam (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Coating, forming or etching by sputtering
C204S298130
Reexamination Certificate
active
06284111
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a sputtering target which provides a stable film deposition rate from an initial stage of sputtering and which eliminates the need for burn-in, or pre-sputtering, which removes substantially the entire surface-deformed layer of the sputtering target to provide the surface of the sputtering target in a state suitable for sputtering. The present invention also relates to a method for manufacturing such a sputtering target.
BACKGROUND OF THE INVENTION
Heretofore, the surface of a sputtering target has been finished by machining, such as, cutting, grinding, or polishing.
Due to the characteristics of machining by forcedly processing while physically breaking metal crystal grains, a large number of strains and defects, known as a surface-deformed layer, remain on the surface of the target.
Since sputtering is a process for releasing metal atoms constituting the target by using collision energy generated by physically colliding cations, such as Ar+, to a target installed on a cathode, the ease of releasing the metal atoms themselves differs depending upon the arrangement of metal atoms in a crystal (crystal orientation).
In a sputtering target having machining-affected layers as described above still remaining on the surface of the sputtering target, a stable surface state which provides a stable film deposition rate is obtained only after the target has been used for a certain period of time.
Therefore, as long as surface-deformed layers remain on the sputtering target, the deposition rate cannot be stabilized. This in turn causes an increase in the use of integrated input electric energy which is required for pre-sputtering of the target.
In order to solve such problems, a method for removing surface-deformed layers by etching the target surface has been proposed (Japanese Patent Laid-Open No. 7-118842).
However, such a method has a problem in that the integrated input energy required for pre-sputtering cannot be significantly decreased by rigorous etching under conditions suitable for removing surface-deformed layers.
OBJECTS OF THE INVENTION
In order to solve the above-described problems, in particular to realize quick stabilization of the film deposition rate, the object of the present invention is to provide a sputtering target which has a surface in a desired state so that a stable film deposition rate is provided from the initial stage of use of the sputtering target.
Another object of the present invention is to provide a method for manufacturing such a sputtering target.
SUMMARY OF THE INVENTION
The inventors of the present invention conducted repeated examinations for solving the above-described problems and obtained the following findings.
In the state where the film deposition rate of a sputtering target is stabilized after the sputtering target has been used for a certain period of time, a microscopic crystal surface covers the target surface which is subjected to erosion and from which metal atoms are easily released by sputtering. Such a crystal surface appears one after another even after sputtering has been proceeded.
Unless the surface of the target has been covered with a crystal surface which can be readily sputtered at a stable film deposition rate, integrated input electric power cannot be decreased to zero. This is true even if the surface roughness of the target is minimized, for example, by mirror polishing, or even if the target surface is in a state where no surface-deformed layers are present. (See Comparative Example 3 which is discussed later in this application.)
If a surface-deformed layer remains on an area of the target undergoing sputtering, the film deposition rate is higher than a stabilized film deposition rate. Therefore, the surface-deformed layer must be removed to substantially zero to stabilize the film deposition rate.
Even if there is no surface-deformed layer, a target having a crystal surface that is easily sputtered cannot be obtained if the target surface is excessively rough. Such a target requires pre-sputtering to obtain a surface which is easily sputtered. (See Comparative Example 5 discussed later in this application.)
A target which consumes little integrated input electric power until the film deposition rate is stabilized can be obtained by decreasing the surface-deformed layer to substantially zero. This can be accomplished by precision machining the target in order to minimize the surface-deformed layer and then by etching the target until the surface of the target is covered with a crystal surface that is easily sputtered.
On the basis of the above described findings and according to a first aspect of the present invention, a sputtering target is provided such that it is practically free of surface-deformed layers created by machining the target surface subjected to erosion. This surface is provided with a surface roughness (Ra) in a range between about 0.1% and 10% of the mean crystal grain diameter of the material constituting the target. The surface roughness (Ra) is defined as the mean roughness on the center line of the surface which is subjected to erosion.
According to a second aspect of the present invention, the surface roughness (Ra) of the above referenced target surface is in a range between about 1% and 10% of the mean crystal grain diameter.
According to a third aspect of the present invention, a method for manufacturing a sputtering target is provided. The method comprises the steps of reducing the surface-deformed layer by precision machining the target surface and etching the target surface to make the surface roughness (Ra) of the target surface be in a range of between about 0.1% and 10% of the mean crystal grain diameter of the material constituting the target.
According to a fourth aspect of the present invention, the above described method is utilized to provide the target surface with a surface roughness (Ra) in a range of about 1% and 10% of the mean crystal grain diameter.
According to a fifth aspect of the present invention, the precision machining step of the above described method is utilized until the thickness of the surface-deformed layer is reduced to about 20 &mgr;m or less.
REFERENCES:
patent: 4663120 (1987-05-01), Parent et al.
patent: 4750932 (1988-06-01), Parent et al.
patent: 5294321 (1994-03-01), Satou et al.
patent: 5409517 (1995-04-01), Satou et al.
patent: 5418071 (1995-05-01), Satou et al.
patent: 5460793 (1995-10-01), Kano et al.
patent: 5464520 (1995-11-01), Kano et al.
patent: 5630918 (1997-05-01), Takahara et al.
patent: 6139701 (2000-10-01), Pavate et al.
patent: 6153315 (2000-11-01), Yamakoshi et al.
patent: 634498 (1995-01-01), None
patent: 902102 (1999-03-01), None
patent: 03-257158 (1991-11-01), None
patent: 07-118842 (1995-05-01), None
patent: 10 158 829 A (1998-06-01), None
patent: 10 310 470 A (1998-11-01), None
patent: 11 080 942 A (1999-03-01), None
English Abstract of the Japanese publication No. 03-257158 (Derwent).
English Abstract of the Japanese publication No. 03-257158 (Dialog).
English Abstract of the Japanese publication No. 07-118842 (Derwent).
Ishigami et al., “High Purity Ti Sputter Target for VLSIs”, Toshiba Review, No. 161, pp. 38-41, Autumn 1987.
A. Abel et al., “Preparation and Characterization of Pure Metals”, Metals Handbook, 10thEdition, vol. 2, pp. 1095-1097, 1990.
Co-pending U.S. Patent application No. 09/060,209, filed Apr. 14, 1998.
Ohhashi Tateo
Seki Kazuhiro
Takahashi Hideyuki
Cantelmo Gregg
Howson and Howson
Nguyen Nam
Nikko Materials Company Limited
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