Method for connecting magnetic substance target to backing plate, and magnetic substance target

Abstract

A method for connecting a magnetic substance target to a backing plate with less variation in plate thickness, characterized in having the steps of connecting the magnetic substance target to an aluminum plate beforehand while maintaining the flatness, connecting the magnetic substance target connected to the aluminum plate to the backing plate while maintaining the flatness, and grinding out the aluminum plate, whereby the flatness of the magnetic substance target can be maintained until the magnetic substance target is connected to the backing plate by a relatively simple operation.

Claims

1. An assembly, comprising: a magnetic substance target, a backing plate, and an aluminum reinforcing plate, said magnetic substance target having an as-wrought structure with remnant stress sufficient to provide magnetic anisotropy necessary for enabling magnetron sputtering, wherein said magnetic substance target has a surface face, an opposite face bonded to said backing plate, and a thickness defined by a distance between said surface face and said opposite face, the thickness being 5 mm or less on average along said surface face and having a variation of 4% or less of said average thickness, wherein the surface face is bonded to the aluminum reinforcing plate such that the aluminum reinforcing plate is integral to the magnetic substance target, and wherein the opposite face is bonded to the backing plate after bonding the surface face to the reinforcing plate.

2. An assembly according to claim 1, wherein the magnetic substance target is made of a magnetic substance selected from the group consisting of iron, cobalt, nickel, platinum and alloys thereof.

3. The assembly according to claim 2, wherein the surface face is bonded to the aluminum reinforcing plate with an adhesive or brazing material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an explanatory diagram showing the cross section of a case where a high purity cobalt target is placed on a vacuum chuck while maintaining a state of flatness, and an aluminum plate being connected thereto via an adhesive material;

(2) FIG. 2 is an explanatory diagram showing the cross section of a case of connecting a copper alloy backing plate to a high purity cobalt target, wherein an aluminum plate has been connected hereto via a bonding material;

(3) FIG. 3 is a diagram showing the relation between the integral power consumption and uniformity;

(4) FIG. 4 is a diagram showing the results upon measuring the thickness of the nickel target in the case of employing an aluminum plate (reinforcing plate) at a total of 25 points for each prescribed angle () radially from the center thereof with an ultrasonic thickness indicator;

(5) FIG. 5 is a diagram showing the measurement results of the leakage flux of above;

(6) FIG. 6 is a diagram showing the results upon measuring the thickness of the nickel target in the case of not employing an aluminum plate (reinforcing plate) at a total of 25 points for each prescribed angle () radially from the center thereof with an ultrasonic thickness indicator; and

(7) FIG. 7 is a diagram showing the measurement results of the leakage flux of above.

DETAILED DESCRIPTION OF THE INVENTION

(8) In a method of forming an assembly comprising a magnetic substance target and a backing to the present invention, a magnetic substance target such as iron, cobalt, nickel, platinum or the alloys thereof (FeNi alloy, CoNi alloy, MnPt alloy, etc.) is first bonded to an aluminum plate with the explosive bonding method, diffusion bonding method, brazing method, or other bonding methods while maintaining the flatness thereof by using a vacuum chuck or the like.

(9) As the method of bonding to this aluminum plate, it will suffice so as long as the bonding strength is sufficient at 250 C., and it is important that adverse effects are not inflicted upon the target. As such a method, explosive bonding method, diffusion bonding method, brazing method, or other bonding methods (adhesive methods) may be used. There is no particular limitation on these bonding methods, adhesives, and materials used for bonding.

(10) The aluminum plate is in other words a reinforcing plate or protective plate for preventing cambering of the target plate bonded thereto. The aluminum plate used here includes an aluminum alloy plate, and an inexpensive material may be used since it will be ground off later in the process.

(11) In order to maintain the flatness of the magnetic substance target, a certain degree of strength and thickness is required in the aluminum plate. Although it is appropriate to use an aluminum plate having a thickness that is the same as or greater than the magnetic substance target, since the thickness of this aluminum plate may also be arbitrarily changed depending on the strength of amount of cambering of the magnetic substance target, there is no particular limitation on the thickness, and may be suitably selected.

(12) Next, the magnetic substance target of the present invention as-bonded to the aluminum plate is bonded to the backing plate while maintaining the flatness thereof. Here, this may be connected with conventional bonding, or connected with diffusion bonding.

(13) For example, when bonding with indium or indium alloy, a temperature of 200 to 250 C. is applied, and it is necessary to make sure that the foregoing aluminum plate or bonding material has resistance characteristics against this temperature during the connection and that cambering or the Like does not occur.

(14) Since the temperature becomes relatively high during diffusion bonding, resistance characteristics against high temperatures are required. For example, in the case of a cobalt target, since low magnetic permeability must be maintained, there is a limitation that the diffusion bonding must be conducted at a low temperature (450 C. or less), but it is still necessary to apply heat up to a temperature of several hundred degrees.

(15) Upon performing diffusion bonding, it is effective to use indium, or the alloy thereof, or other low-melting insert materials which have a certain degree of thickness. In some cases, aluminum or aluminum alloy may also be used. The function of the foregoing insert material is in that diffusion bonding is enabled at low temperatures, and that the insert material alleviates the stress generated by the difference of thermal expansion between the target and backing plate after the diffusion bonding until it is cooled to room temperature.

(16) It is preferable to use copper or copper alloy or aluminum or aluminum alloy which have stronger strength as the backing plate. For instance, in terms of a backing plate with less cambering during bonding and which does not deform even during high power sputtering, it is effective to use copper alloys such as copper chrome alloy or copper zinc alloy as the backing plate.

(17) As described above, whether in the case of bonding or diffusion bonding, since the surface of the magnetic substance is covered with an aluminum plate (reinforcing plate or protective plate) via an adhesive material, the magnetic substance may be operated without being damaged by using the above as a protective plate during bonding until the completion of the connection of the magnetic substance to the backing plate, and, this may also be pressed when necessary.

(18) After the magnetic substance target is bonded to the backing plate, the aluminum plate as the reinforcing plate and the adhesive material are ground off. Substances generated through the explosive bonding, diffusion bonding method, brazing, or other bonding or adhesive method to the aluminum plate, and that is, the bonding or adhesive material and substances left or generated at the interface between the magnetic substance target and the aluminum plate are all eliminated together with the aluminum plate.

(19) In this stage, since the magnetic substance target is connected to the backing plate formed from the likes of aluminum alloy or copper alloy having stronger strength, the flatness thereof may be maintained without change. After the grinding out of the aluminum plate and bonding material, the magnetic substance surface may be further ground.

(20) FIG. 1 is an explanatory diagram showing the cross section of a case where a high purity cobalt target 2 is placed on a vacuum chuck 1 while maintaining a state of flatness, and an aluminum plate 4 being connected thereto via an bonding material 3.

(21) FIG. 2 is an explanatory diagram showing the cross section of a case of connecting a copper alloy backing plate 5 to a high purity cobalt target 2, wherein an aluminum plate 4 has been connected thereto via a bonding material 3, with a bonding brazing material 6.

(22) As a result of employing the foregoing method for connecting a magnetic substance target to a backing plate, obtained is a magnetic substance target in which a variation in the thickness of the magnetic substance target is 4% or less of an average thickness thereof; the average leakage flux in relation to the maximum leakage flux is 80% or more, preferably 90% or more, when the maximum leakage flux of the target is 100%; and the minimum leakage flux in relation to said maximum leakage flux is 70% or more when the maximum leakage flux of the target is 100% at the respective position across the surface area of the target.

(23) This magnetic substance target may be employed as a magnetic substance of iron, cobalt, nickel, platinum or the alloys thereof.

(24) Further, the leakage flux may be measured upon using a standard gauss meter. In other words, a magnet is placed on the backing plate side, a probe is made to contact the magnetic substance side on the opposite side, and measurement is thereby made with a gauss meter. The position to be measured is performed by arbitrarily moving the probe.

EXAMPLES AND COMPARATIVE EXAMPLES

(25) The present invention is now explained in detail with reference to the Examples. These Examples are merely illustrative, and the present invention shall in no way be limited thereby. In other words, various modifications and other embodiments based on the technical spirit claimed in the claims shall be included in the present invention as a matter of course.

Example 1

(26) High purity cobalt raw material of 99.999 wt % (5N) was warm rolled at 450 C. to prepare a high purity cobalt plate having a thickness of 6 mm, and this was further machine processed to complete a discoid target having a diameter of 350 mm and a thickness of 3.5 mm.

(27) Copper chrome alloy (chrome content of 1 wt %) was used as the backing plate.

(28) While retaining the high purity cobalt plate with a vacuum chuck and maintaining the flatness, an aluminum plate of 10 mm was connected to this high purity cobalt plate with PbAgSn brazing material (97.5Pb-1Sn-1.5Ag) at 325 C. After the connection, the target side was surface ground (approximately 0.3 mm) so as to form a flat surface.

(29) Next, indium soldering was used to connect the sputtering target and the backing plate. The heating temperature was 230 C.

(30) Thereafter, the aluminum plate was removed with mechanical processing (grinding), and the cobalt was faced (approximately 0.2 mm) so as to obtain a target-backing plate assembly.

(31) Next, with the discoid cobalt target facing upward, the target thickness was measured with a supersonic thickness indicator. A total of 49 points (1 point in the center, 8 points in of the periphery, 16 points in of the periphery, and 24 points in the outer periphery) were radially measured.

(32) As a result, the maximum thickness was 3.06 mm, the minimum thickness was 2.90 mm, and the displacement from the target thickness was 0.1 mm (3.3%) at maximum. Further, the difference between the maximum thickness and minimum thickness was 0.16 mm. As described above, the thickness variation was small, the connection status was favorable, and there were no generation of abrasion marks or the like.

(33) Although cambering should occur during the connection of the target to the backing plate or during the processing thereof, this is firmly retained and protected with the aluminum plate via the brazing material. Further, grinding of aluminum and brazing material is easy, and the increase in processing steps or costs was minimal.

(34) Next, the discoid cobalt target-backing plate assembly was used to perform sputtering on a substrate, and the uniformity of the formed cobalt was observed. The results are shown in FIG. 3.

(35) Moreover, the sputtering conditions were as follows:

(36) Applied Power: 1 kw

(37) T-S: 50 mm

(38) Film Thickness: 1000

(39) Ar Pressure: 910.sup.3 Torr

(40) As shown in FIG. 3, the uniformity begins to improve from around an integral power consumption of approximately 6 kwh, this is maintained at a uniformity of 2% or less up to an integral power consumption of approximately 30 kwh, and this shows that the uniformity of the film formed with sputtering is favorable. This is considered to be a result of the variation in the target thickness being small, and the flatness being superior.

Comparative Example 1

(41) With the same method as Example 1, high purity cobalt raw material of 99.999 wt % (5N) was warm rolled at 450 C. to prepare a high purity cobalt plate having a thickness of 6 mm, and this was further machine processed to complete a discoid target having a diameter of 350 mm and a thickness of 3.0 mm. Copper chrome alloy (chrome content of 1 wt %) was used as the backing plate, and indium soldering was used to directly connect the sputtering target and backing plate. The heating temperature was 230 C.

(42) Next, similar to Example 1, with the discoid cobalt target facing upward, the warp amount was measured with a supersonic thickness indicator. A total of 49 points (1 point in the center, 8 points in of the periphery, 16 points in of the periphery, and 24 points in the outer periphery) were radially measured.

(43) As a result, the maximum thickness was 3.12 mm, the minimum thickness was 2.78 mm, and the displacement from the target thickness was 0.22 mm (7.3%) at maximum. Further, the difference between the maximum thickness and minimum thickness was 0.34 mm.

(44) As described above, the warp amount was significantly large, and there were generation of abrasion marks and the like. This is considered to be because since a reinforcing aluminum plate is not provided, significant cambering occurred during the connection of the sputtering target and backing plate, and, since grinding was conducted with the existence of such camber, the center portion became thin and the outer portion became thick (the opposite for the grinding side).

(45) Next, the discoid cobalt target-backing plate assembly was used to perform sputtering on a substrate, and the uniformity of the formed cobalt was observed. The results are similarly shown in FIG. 3 in comparison to Example 1.

(46) Incidentally, the sputtering conditions were the same as Example 1.

(47) As shown in FIG. 3, uniformity was inferior at roughly 7% even at an integral power consumption of approximately 6 kwh. And, the uniformity exceeded 2% up to an integral power consumption of approximately 30 kwh, and varied.

(48) The reason why the uniformity of the film formed upon sputtering the discoid cobalt target illustrated in the Comparative Example is considered to be because the variation in the target thickness being great, and the flatness being inferior.

Example 2

(49) High purity nickel raw material of 99.999 wt % (5N) was warm rolled at 450 C. to prepare a high purity nickel plate having a thickness of 6 mm, and this was further machine processed to complete a discoid target having a diameter of 350 mm and a thickness of 3.5 mm. Copper chrome alloy (chrome content of 1 wt %) was used as the backing plate.

(50) While retaining the high purity nickel plate with a vacuum chuck and maintaining the flatness, an aluminum plate of 10 mm was connected to this high purity nickel plate with PbAgSn brazing material (97.5Pb-1Sn-1.5Ag) at 325 C. After the connection, the target side was surface ground (approximately 0.3 mm) so as to form a flat surface.

(51) Next, indium soldering was used to connect the sputtering target and the backing plate. The heating temperature was 230 C.

(52) Thereafter, the aluminum plate was removed with mechanical processing (grinding), and the nickel was faced (approximately 0.2 mm) so as to obtain a target-backing plate assembly.

(53) Next, with the discoid nickel target facing upward, the target thickness was measured with a supersonic thickness indicator. A total of 25 points (1 point in the center, 8 points in of the periphery, and 16 points in of the periphery) were measured for each prescribed angle () radially from the center thereof. The results are shown in Table 1. Further, the graph corresponding to Table 1 is shown in FIG. 4.

(54) As a result, as shown in Table 1 and FIG. 4, the maximum thickness was 3.24 mm, the minimum thickness was 3.20 mm, and the average was 3.216 mm. The displacement from the average thickness was 0.024 mm (0.7%) at maximum. Further, the difference between the maximum thickness and minimum thickness was 0.04 mm. As described above, the thickness variation was extremely small, and, as with Example 1, the connection status was favorable, and there were no generation of abrasion marks or the like.

(55) TABLE-US-00001 TABLE 1 (deg) Center R R 0 3.21 0 3.20 45 3.20 90 3.20 135 3.20 180 3.22 225 3.21 270 3.21 315 3.21 0 3.22 22.5 3.21 45 3.21 67.5 3.21 90 3.20 112.5 3.21 135 3.23 157.5 3.22 180 3.23 202.5 3.24 225 3.22 247.5 3.22 270 3.23 292.5 3.23 315 3.22 337.5 3.23

(56) Next, the leakage flux of this discoid nickel target was measured with a gauss meter. The points measured were the same as the thickness measurement described above. Generally, the larger the leakage flux, the higher the sputtering efficiency, and this is considered to be favorable.

(57) The relative values in the respective measuring points when the strongest value of the leakage flux is 100% were measured. The result was maximum 100%, minimum 91%, and average 95%. The difference between maximum and minimum was 9%. The results are shown in Table 2 and FIG. 5.

(58) In comparison to Comparative Example 2 described later, a result was obtained in that the leakage flux will increase if the change in thickness is small. Further, in the case of nickel, it has become evident that the leakage flux will be influenced significantly due to the variation in thickness.

(59) TABLE-US-00002 TABLE 2 (deg) Center R R 0 94% 0 97% 45 98% 90 99% 135 100% 180 96% 225 93% 270 95% 315 94% 0 92% 22.5 96% 45 97% 67.5 96% 90 100% 112.5 100% 135 93% 157.5 92% 180 93% 202.5 91% 225 94% 247.5 95% 270 93% 292.5 92% 315 93% 337.5 91%

(60) The strongest value of the leakage flux is indicated as 100%.

Comparative Example 2

(61) With the same method as Example 2, high purity nickel raw material of 99.999 wt % (5N) was warm rolled at 450 C. to prepare a high purity nickel plate having a thickness of 6 mm, and this was further machine processed to complete a discoid target having a diameter of 350 mm and a thickness of 3 mm. Copper chrome alloy (chrome content of 1 wt %) was used as the backing plate, and indium soldering was used to directly connect the sputtering target and backing plate. The heating temperature was 230 C.

(62) Next, similar to Example 2, a total of 25 points (1 point in the center, 8 points in of the periphery, and 16 points in of the periphery) were measured for each prescribed angle () radially from the center thereof. The results are shown in Table 3. Further, the graph corresponding to Table 3 is shown in FIG. 6.

(63) TABLE-US-00003 TABLE 3 (deg) Center R R 0 2.95 0 3.07 45 3.10 90 3.05 135 3.11 180 3.12 225 3.08 270 3.10 315 3.12 0 3.25 22.5 3.22 45 3.21 67.5 3.21 90 3.20 112.5 3.21 135 3.31 157.5 3.29 180 3.30 202.5 3.29 225 3.27 247.5 3.25 270 3.23 292.5 3.23 315 3.22 337.5 3.19

(64) As a result, as shown in Table 3 and FIG. 6, the maximum thickness was 3.31 mm, the minimum thickness was 2.95 mm, and the average was 3.183 mm. The displacement from the average thickness was 0.233 mm (7.3%) at maximum. Further, the difference between the maximum thickness and minimum thickness was 0.36 mm.

(65) As described above, the warp amount was significantly large, and there were generation of abrasion marks and the like as with Comparative Example 1. This is considered to be because, since a reinforcing aluminum plate is not provided, significant cambering occurred during the connection of the sputtering target and backing plate, and, since grinding was conducted with the existence of such camber, the center portion became thin and the outer portion became thick (the opposite for the grinding side).

(66) Next, the leakage flux of this discoid nickel target was measured with a gauss meter. The points measured were the same as the thickness measurement described above.

(67) The relative values in the respective measuring points when the strongest value of the leakage flux is 100% were measured. The result was maximum 100% (center portion), minimum 64%, and average 79.5%. The difference between maximum and minimum was 36%. The results are shown in Table 4 and FIG. 7.

(68) In comparison to Comparative Example 2 described above, a result was obtained in that the larger the change in thickness, the faster the leakage flux decreases.

(69) TABLE-US-00004 TABLE 4 (deg) Center R R 0 100% 0 91% 45 89% 90 92% 135 89% 180 86% 225 88% 270 90% 315 88% 0 69% 22.5 75% 45 73% 67.5 72% 90 76% 112.5 77% 135 64% 157.5 67% 180 66% 202.5 70% 225 73% 247.5 75% 270 77% 292.5 78% 315 80% 337.5 83%

(70) The present invention yields a superior effect in that, upon connecting a magnetic substance target to a backing plate, the flatness of the magnetic substance target during operation can be maintained until the magnetic substance target is connected to the backing plate by a relatively simple operation, and without generating any cambering of the magnetic substance target, and the flatness can be maintained after connecting a magnetic substance target and a backing plate.