The present invention relates to a method for recycling a tantalum coil for sputtering, wherein a coil, which is disposed so as to surround a space between a substrate and a sputtering target in a sputtering device in order to prevent the coil from becoming the cause of the generation of particles and arcing, undergoes, after the sputtering is complete, a recycling process to eliminate the sputtered grains accumulated on the surface of the spent coil, and additionally relates to a tantalum coil that is recycled thereby.
This tantalum coil for sputtering has a surface that is curved as shown in the photograph explained later, and both the inner surface and the outer surface of the coil are the object of the present invention. Accordingly, the expression “surface of the coil” refers to both the inner surface and the outer surface of the coil, and the same shall apply hereinafter.
In recent years, the sputtering method that is capable of easily controlling the film thickness and components is commonly used as one of the deposition methods of materials for use in electronic and electrical components.
With the sputtering method, a substrate as the positive electrode and a target as the negative electrode are placed opposite each other, and a high voltage is applied between the substrate and the target in an inert gas atmosphere so as to generate an electric field. Here, the ionized electrons and the inert gas collide and plasma is formed. When the positive ions in the plasma collide with the surface of the target (negative electrode), the atoms configuring the target are sputtered, and the sputtered atoms adhere to the opposing substrate surface and thereby form a film.
As recent sputtering technology, there is a technique of disposing a coil in a space between the sputtering target and the substrate to increase the density of the plasma, and to direct the scattered sputtered grains toward the substrate as much as possible. Consequently, the sputtering rate is increased, the uniformity of the film is improved, and the quality of the film that is deposited on the substrate can be comprehensively improved. There are cases where this coil is sputtered and subject to erosion, and cases where this coil is not sputtered and the sputtered grains scatter and adhere to the coil (formation of re-deposited film). This depends on the bias to the coil (refer to Patent Documents 1 and 2).
Accordingly, as the material of the coil, generally used is the same material as the target material, or the material configuring a part of constituents of the sputtered film to be deposited on the substrate. Nevertheless, there is no particular limitation so as long as the coil material does not contaminate the thin film on the substrate. Moreover, as the shape of the coil, there are circular coils and spiral coils (refer to Patent Documents 1, 2, and 3), and there are cases where these coils are disposed in multiple stages.
However, when disposing the foregoing coil between a target and a substrate so as to increase the density of the plasma and direct the scattered sputtered grains toward the substrate as much as possible, while decreasing the amount of sputtered grains that will scatter and adhere to, other than the substrate, the inner wall or the internal elements of the thin-film forming device, there is a problem in that the sputtered grains become accumulated on the coil itself.
In order to avoid this kind of problem, Patent Document 3 described above proposes grinding down the upper end of the inner surface side of the coil so as to reduce the inner peripheral thickness. Here, since the upper end of the coil is sharpened toward the upper direction, the provided explanation is that the deposited material to become accumulated at the apex of the coil slips down and will not remain thereon, and the coil is further cleansed since new sputtered grains will collide therewith.
Nevertheless, the portion where the sputtered grains will accumulate is not limited to the upper end of the coil. There is a possibility that the sputtered grains will also become accumulated on the surface of the coil; that is, on the outer surface and the inner surface of the coil. In the foregoing case, the flakes from the surface of the coil, where the sputtered grains have accumulated, become scattered and adhere directly to the substrate surface. And, it causes the generation of particles, but no measures are being taken for this problem. Based device circuit, the generation of particles from the foregoing locations will also become a major problem.
In order to resolve the foregoing problem, there has been a proposal of blasting the side surface of the target and a portion in the vicinity of the backing plate so as to increase the adhesion based on the anchor effect.
Nevertheless, in the foregoing case, there are the following problems; namely, contamination of the product caused by the residual blasting material, flaking of the adhered grains accumulated on the residual blasting material, and the flaking caused by the selective and non-uniform growth of the adhesive film, and the blasting described above is not a final solution. In particular, when the coil is made of a hard material like tantalum, it is difficult to even form irregularities by simply performing blasting, and it is not possible to effectively enhance the adhesion.
Moreover, Patent Document 4 discloses that a coil to be used for the flange, side wall, shield, covering and the like of a target is subject to knurling to form a diamond-shaped or cross-hatch (net-like) pattern thereon. Here, the depth is roughly 0.350 mm to 1.143 mm, but since the irregularities on the worked surface are of a simple shape, there is a possibility that a sufficient anchor effect cannot be obtained.
As described above, there are basically two types of spent coils, but in the case of a coil that is not subject to erosion, it is necessary to eliminate the re-deposited film therefrom. If the coil is reused without eliminating the re-deposited film, the re-deposited film will peel off and cause the generation of particles.
In the foregoing formation of a thin film based on the sputtering method, if it is possible to efficiently eliminate the re-deposited film from the spent coil after the sputtering is complete and recycle the coil, a significant cost reduction can be achieved.
Conventionally, there are several Patent Documents that are based on the foregoing perspective. Patent Document 5 proposes exposing the deposited material to at least one etching solution selected from a group consisting of H3PO4, HNO3, and HF in order to prolong the reuse life of a processing kit. Moreover, elimination of the adhered particles (re-deposited film) via etching or pickling is proposed in Patent Document 6 and Patent Document 7. These technologies need to be further improved in order to stably and efficiently eliminate the re-deposited film.    Patent Document 1: Published Japanese Translation No. 2005-538257 of PCT Application    Patent Document 2: JP2001-214264 A    Patent Document 3: Published Japanese Translation No. 2008-534777 of PCT Application    Patent Document 4: WO2009/099775 (PCT/US2009/031777)    Patent Document 5: US2007/0012658    Patent Document 6: CN101519767    Patent Document 7: CN101591767