JP6498527B2 - Sputtering target - Google Patents

Description

 The present invention relates to a sputtering target capable of improving the film formation rate in sputtering.

 The wiring of a semiconductor integrated circuit is required to be thinned with each generation, and sputtering, which is a kind of physical vapor deposition, is used to form a thin film that becomes such wiring. In recent years, in order to increase the film formation rate of sputtering, magnetron sputtering in which plasma is controlled by electromagnetic force is often used. In sputtering used in such a state-of-the-art, a stable and easily controlled target is indispensable. When stable film formation cannot be performed because the apparatus is stopped due to poor plasma ignition or voltage fluctuation occurs, not only productivity but also product quality may be deteriorated. In addition, if the control is difficult, stable film formation may not be started or maintained when the film formation conditions are changed intentionally.

 A sputtering target made of tantalum is used to form a copper wiring barrier film. Since the barrier film is also formed in a wiring hole having a high aspect ratio (ratio of step depth to opening), it is necessary to control the film formation rate to stably form an ultrathin film. On the other hand, in order to increase the throughput, it is necessary to secure a desired film thickness by sputtering with high power in a short time, and a target having a high film formation rate is also required.

 The tantalum target has a purity of 4N5 (99.995 wt%) from the viewpoint of versatility. However, in order to suppress deterioration of film adhesion due to impurities and increase in leakage current as much as possible, the tantalum target is substantially used. A product of purity 6N (99.9999 wt%) may be used. In recent years, in order to increase the degree of freedom in wiring design, the use of such ultra-high purity materials is increasing.

 The target is softened by increasing the purity, and it may be difficult to control the quality of the target, such as inhomogeneous texture orientation after plastic working and crystal coarsening during recrystallization by heat treatment. . These problems can be solved to some extent by strictly controlling the manufacturing process of the target, but even with high-quality targets manufactured in this way, the use environment of the target becomes more severe, and new problems have emerged. It may become.

 For example, when shortening the film formation time is required to improve throughput, the film formation conditions have been changed for each process. However, changing the film formation conditions impairs the stability of the process, and the film quality In addition, the development of new film formation conditions has a problem of increasing human costs.

That is, in the past, the film formation speed was adjusted by changing the film formation conditions, but in recent years, the manufacturing process has become complicated according to a wide variety of semiconductor devices. The change made it difficult to produce high-quality products stably and quickly.
In addition, although patent documents 1-4 etc. are known as a sputtering target considered to be related to this invention, all do not solve said problem.

International Publication WO2006 / 054409 JP 2003-226965 A JP 2003-27225 A JP 2004-84007 A

 The present invention has been made in view of the above circumstances, and it is an object to provide a sputtering target and a film forming apparatus capable of improving the film forming speed without changing the film forming conditions. To do.

Based on such knowledge, the present invention provides the following techniques.
1) A sputtering target characterized in that a processing groove is arranged in a flat portion of the sputtering target.
2) The sputtering target according to 1) above, wherein the area ratio of the processed grooves in the flat portion is greater than 0% and 10% or less.
3) The sputtering target according to 1) or 2) above, wherein the processed groove is formed in a concentric shape centering on the center of the target.
4) The sputtering target according to any one of 1) to 3) above, comprising tantalum having a purity of 4N5 or higher.

 Since the sputtering target of the present invention can improve the deposition rate without changing the deposition conditions, the stability of the process can be improved, and further, the development and evaluation of new deposition conditions are accompanied. The human burden can be reduced. Thereby, it can contribute to the improvement of a throughput and the improvement of cost performance.

It is an explanatory schematic diagram of the sputtering target of the present invention.

 The sputtering target of the present invention will be described below with reference to FIG. FIG. 1 (upper view) shows a sputtering surface (side) of the sputtering target, and FIG. 1 (lower view) shows a cross section of the sputtering target. Note that FIG. 1 is merely one form for easy understanding, and the present invention is not limited by this form. The present invention includes various modifications other than those described below.

 The sputtering surface (surface exposed to plasma) of the sputtering target of the present invention is composed of both the flat portion and the taper portion, or only the flat portion. The flat portion is a portion of the sputter surface that substantially contributes to film formation excluding the taper portion, and the taper portion means a chamfered portion at the outer peripheral end portion of the target sputter surface. In particular, it is a part that does not contribute to film formation or contributes little. As shown in FIG. 1, the present invention is characterized in that processed grooves are formed at a predetermined area ratio in a flat portion of a target (a surface parallel to an opposing wafer surface). Thereby, the film-forming speed | velocity by magnetron sputtering can be improved significantly.

 Although this mechanism is not necessarily clear, the leakage flux of the magnet rotating on the back side of the target is increased by the confinement effect due to the reduction of the target thickness by the groove and the inclination angle of the inner wall of the groove, and the result is that the plasma current density is improved. In particular, it is considered that the film forming speed is improved. The processed groove can be formed by mechanically processing the sputter surface of the target, and the area ratio of the projected area of the processed groove can be appropriately adjusted by changing the number and the groove width. it can.

 In the present invention, the area ratio of the processed groove means the area projected on the flat portion of the groove cut out by the processing. By setting the area ratio of the projected area (projected area of the processed groove / area of the flat part) to be larger than 0% and 10% or less, the film formation speed is improved as compared with a target having no processed groove part. be able to. On the other hand, when the area ratio of the processed groove exceeds 10%, the leakage amount of the magnetic flux changes, and the direction of the magnetic field changes, so that the effect of confining electrons by the magnetic field does not function, and as a result, the current value during sputtering is reduced. The plasma may become unstable.

 The sputtering surface of the target (surface exposed to plasma) is usually composed of a flat portion and a tapered portion. However, the taper portion is often applied mainly to the outermost periphery of the target, and the extent that the magnetic flux density of the magnet is removed from the high part or the magnetic flux leakage direction is inclined outward due to the inclination, thereby contributing to the increase of the leakage magnetic flux density. Is low. As described above, since the groove processing on the taper portion cannot obtain the intended effect, the present invention mainly forms an effect obtained by forming the processing groove on the flat portion.

 In the present invention, the shape of the processing groove can have a V-shaped, U-shaped, square-shaped cross section, and the shape can be selected or combined depending on the ease of processing and the occurrence of foreign matter. The depth of the processed groove is not related to the above-mentioned area ratio and is not particularly limited. However, since the processed groove gradually becomes shallower as the erosion progresses, the effect of improving the film formation rate is reduced. Therefore, such effect reduction can be suppressed by adjusting the depth of the processed groove. In particular, the depth is preferably 1 mm to about half the target thickness. The processed groove is formed only in the flat portion of the sputtering surface, but as described above, the groove processing in the tapered portion does not affect the film forming speed. Moreover, since the position of the processing groove may depend on the specifications of the sputtering apparatus, it may be appropriately selected according to the specifications.

  The processing groove of the present invention has a concentric circle centered on the center of the target, as shown in FIG. 1, in the flat portion of the sputtering surface of the target (however, the arc may be discontinuous). ) Can be formed. Needless to say, the optimum position (diameter of concentric circles), shape, number, etc. of the processing grooves are selected according to the specifications of the sputtering apparatus. The above-mentioned processed groove relates to the shape of the sputtering target, and has an effect of improving the film formation rate (rate) regardless of the material and composition of the target.

 The above-described processed groove relates to the shape of the sputtering target, and can improve the film formation rate regardless of the material and composition of the target. On the other hand, by using a target made of a high-purity material, for example, a tantalum target having a purity of 4N5 (99.995%) or higher, film quality deterioration caused by impurities can be suppressed. In the present invention, purity 4N5 (99.995%) means that the dissolved Ta ingot is analyzed by glow discharge mass spectrometry (GDMS), and Na, Al, Si, K, Ti, Cr, Mn, Fe, Co , Ni, Cu, Zn, Zr means that the total value is less than 50 ppm.

  Hereinafter, a description will be given based on examples. In addition, a present Example is an example for making an understanding easy to the last, and is not restrict | limited at all by this example. In other words, the present invention is limited only by the scope of the claims, and includes various modifications other than the embodiments described in the present invention.

Example 1
In a tantalum sputtering target (purity of 4N5 or more) having a diameter of 444 mm and a sputter surface diameter of 406 mm, a V-shaped cross-sectionally processed groove was formed concentrically on the flat portion of the sputter surface. The width of the groove was 3 mm, the depth was 3 mm, the length of the groove was about 522 mm on the outer periphery and about 503 mm on the inner periphery, and the area ratio of the processed groove in the flat portion was 1.2%. Next, after this target was bonded to the backing plate, sputtering was performed under the sputtering conditions described below, and the film formation rate was examined. As a result, the film formation rate increased by about 15% from 37.4 nm / min to 43.0 nm / min as compared with the same type target without processed grooves.

(Sputtering conditions)
Power supply: DC
Atmosphere: Argon gas 8sccm
Power: 15000W
Wafer bias: 400W
Deposition time: 15 sec

(Example 2)
In a tantalum sputtering target (purity of 4N5 or more) having a diameter of 444 mm and a sputter surface diameter of 406 mm, a V-shaped cross-sectionally processed groove was formed concentrically on the flat portion of the sputter surface. The groove width was 6 mm, the depth was 3 mm, the groove length was about 1212 mm for the outer circumference and about 1193 mm for the inner circumference, and the area ratio of the processed groove in the flat portion was 2.8%. Next, after this target was bonded to the backing plate, sputtering was performed under the same conditions as in Example 1 to examine the film formation rate. As a result, the film formation rate increased by about 22% from 37.4 nm / min to 45.8 nm / min, compared to the same type target without processed grooves.

(Example 3)
In a tantalum sputtering target (purity of 4N5 or more) having a diameter of 444 mm and a sputter surface diameter of 406 mm, a V-shaped cross-sectionally processed groove was formed concentrically on the flat portion of the sputter surface. The width of the groove was 6 mm, the depth was 3 mm, the length of the groove was about 1212 mm on the outer periphery and about 1175 mm on the inner periphery, and the area ratio of the processed groove in the flat portion was 5.5%. Next, after this target was bonded to the backing plate, sputtering was performed under the same conditions as in Example 1 to examine the film formation rate. As a result, the film formation rate increased by about 31% from 37.4 nm / min to 49.1 nm / min as compared with the same type target having no processed groove.

Example 4
In a tantalum sputtering target (purity of 4N5 or more) having a diameter of 444 mm and a sputter surface diameter of 406 mm, a V-shaped cross-sectionally processed groove was formed concentrically on the flat portion of the sputter surface. The groove width was 10 mm, the depth was 3 mm, the groove length was about 1256 mm for the outer circumference and about 1193 mm for the inner circumference, and the area ratio of the processed groove in the flat portion was 9.5%. Next, after this target was bonded to the backing plate, sputtering was performed under the same conditions as in Example 1 to examine the film formation rate. As a result, the film formation rate increased by approximately 52% from 37.4 nm / min to 57.1 nm / min as compared with the same type target having no processed groove.

(Example 5)
In a tantalum sputtering target (purity of 4N5 or more) having a diameter of 444 mm and a sputter surface diameter of 406 mm, eight processed grooves having a V-shaped cross section were formed at equal intervals on a concentric circle having a radius of 1190 mm in the flat portion of the sputter surface. The width of the groove was 5 mm, the length was 20 mm, the depth was 3 mm, and the area ratio of the processed groove in the flat portion was 1.2%. Next, after this target was bonded to the backing plate, sputtering was performed under the same conditions as in Example 1 to examine the film formation rate. As a result, the film formation rate increased by about 6% from 37.4 nm / min to 39.8 nm / min as compared with the same target having no processed groove.

(Comparative Example 1)
A tantalum sputtering target (purity 4N5 or more) having a diameter of 444 mm and a sputter surface diameter of 406 mm was prepared without a processing groove. After this target was bonded to the backing plate, sputtering was performed under the following film formation conditions to examine the film formation rate. As a result, the film formation rate was 37.4 nm / min.

(Comparative Example 2)
In a tantalum sputtering target (purity of 3N5 or more) having a diameter of 444 mm and a sputter surface diameter of 406 mm, a V-shaped cross-sectionally processed groove was formed concentrically on the tapered portion of the sputter surface. The groove width was 2 mm, the depth was 2 mm, the groove length was about 1294 mm on the outer periphery and about 1281 mm on the inner periphery, and the area ratio of the processed groove in the flat portion was 10.1%. Next, after this target was bonded to the backing plate, sputtering was performed under the same conditions as in Example 1 to examine the film formation rate. As a result, the film formation rate did not change much from 37.4 nm / min to 37.7 nm / min as compared with the same type target without processed grooves.

(Comparative Example 3)
In a tantalum sputtering target (purity of 3N5 or more) having a diameter of 444 mm and a sputtering surface diameter of 406 mm, a V-shaped cross-sectionally processed groove was formed concentrically on the flat portion of the sputtering surface. The groove width was 14 mm, the depth was 3 mm, the groove length was about 1250 mm on the outer periphery and about 1175 mm on the inner periphery, and the area ratio of the processed groove in the flat portion was 11.2%. Next, after this target was bonded to the backing plate, sputtering was performed under the same conditions as in Example 1. As a result, the current value during sputtering decreased, and the phenomenon that the sputtering power was unstable was observed. Canceled. The results are shown in Table 1.

 Since the sputtering target of the present invention can improve the deposition rate without changing the deposition conditions, the stability of the process can be improved, and further, the development and evaluation of new deposition conditions are accompanied. The human burden can be reduced. Thereby, it can contribute to the improvement of a throughput and the improvement of cost performance. The sputtering target of the present invention is useful for forming a thin film for electronic devices.

Claims (5)

A processed groove is disposed in the flat part of the sputtering target, the area ratio of the processed groove in the flat part is greater than 0% and 10% or less, and the processed groove has a depth of 1 to 3 mm and a width of 3 to 10 mm. The sputtering target is made of tantalum . 2. The sputtering target according to claim 1, wherein the area ratio of the processed grooves in the flat portion is 5.5% or more and 10% or less.   The sputtering target according to claim 1 or 2, wherein the processing groove is formed concentrically with the center of the target as a center.   The sputtering target according to any one of claims 1 to 3, wherein the sputtering target is made of tantalum having a purity of 4N5 or higher. The sputtering target according to any one of claims 1 to 4, wherein a cross-sectional shape of the processing groove of the flat part is V-shaped.