Full density Co-W magnetic sputter targets
A sputter target is provided with a first elemental phase of a first material, the first material being either cobalt or tungsten, a first intermetallic phase including the first material and a second material, the second material being either tungsten or cobalt and different from the first material, the first material in a greater atomic percentage than the second material, and a second intermetallic phase including the second material and the first material, the second material in a greater atomic percentage than the first material. The sputter target includes 20-80 at. % cobalt, and has a density greater than 99% of a theoretical maximum density thereof. The sputter target is fabricated by selecting a cobalt powder and a tungsten powder having the same particle size distribution, blending the cobalt powder and the tungsten powder to form a blended powder, canning the blended powder, hot pressing the blended powder to form a solid, and machining the solid to form a sputter target.
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Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENTNot applicable.
FIELD OF THE INVENTIONThe present invention generally relates to sputter targets and, in particular, relates to full density cobalt-tungsten sputter targets and methods for manufacturing the same.
BACKGROUND OF THE INVENTIONThe manufacture of full density cobalt-tungsten sputtering targets presents a number of challenges. Specifically, because of the difference in density between cobalt (Co) and tungsten (W), the elemental phases in a sputter target containing both tend to segregate during manufacture. Moreover, the formation of excessive intermetallic phases during manufacture can render the resultant alloy extremely hard, brittle, and prone to cracking during processing.
SUMMARY OF THE INVENTIONThe present invention solves the foregoing problems by providing fully dense cobalt-tungsten sputter targets and methods of manufacturing the same. The targets may contain between 20-80 at. % cobalt and 80-20 at. % tungsten. The targets have a substantially uniform multi-phase microstructure, and are substantially chemically homogenous both across their surface and through their thickness (i.e., along the sputter direction). The optimized volume fractions of the intermetallic phases and the elemental phase(s) allow the targets to maintain mechanical strength (e.g., resistance to cracking during hot isostatic pressing, machining, or subsequent sputtering) and machinability while achieving a density greater than about 99% of a theoretical maximum density. The micro-cracks and micro-porosities that plague other cobalt-tungsten targets have been minimized.
According to one embodiment of the present invention, a method of fabricating a sputter target comprises the steps of selecting a cobalt powder having a particle size distribution and a tungsten powder having the same particle size distribution, blending the cobalt powder and the tungsten powder to form a blended powder, canning the blended powder, hot pressing the blended powder to form a solid, and machining the solid to form a sputter target.
According to another embodiment of the present invention, a sputter target comprises a first elemental phase of a first material, the first material being either cobalt or tungsten, a first intermetallic phase including the first material and a second material, the second material being either tungsten or cobalt and different from the first material, the first material in a greater atomic percentage than the second material, and a second intermetallic phase including the second material and the first material, the second material in a greater atomic percentage than the first material. The sputter target includes 20-80 at. % cobalt, and a density of the sputter target is greater than 99% of a theoretical maximum density thereof.
It is to be understood that both the foregoing summary of the invention and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
The accompanying drawings, which are included to provide further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings:
In the following detailed description, numerous specific details are set forth to provide a full understanding of the present invention. It will be apparent, however, to one ordinarily skilled in the art that the present invention may be practiced without some of these specific details. In other instances, well-known structures and techniques have not been shown in detail to avoid unnecessarily obscuring the present invention.
One approach to fabricating fully dense cobalt-tungsten sputter targets involves increasing the hot isostatic press (“HIP”) temperature and hold time in order to reduce the occurrence of voids in tungsten-rich regions. One drawback to this approach, however, is the excessive formation of intermetallic phases, rendering the alloy too brittle and hard to machine without cracking. Another drawback to increasing the time and temperature of the HIP is the formation of Kirkendall porosities. Reducing the temperature and time of the HIP to avoid these issues, however, prevents the tungsten-rich areas of the target from consolidating, leaving voids in those regions that reduce the final density of the target, as shown in
For example,
Turning to
In accordance with one embodiment of the present invention, a cobalt-tungsten sputter target is provided which overcomes the foregoing problems.
For the purposes of this application, an “elemental phase” may be understood to be a region of the sputter target which retains its elemental character (i.e., is not an alloy), and which is a physical structure associated with one or more elemental particles that have been sintered by the fabrication process described in greater detail below with respect to
As can be seen with reference to the scale in
As will become evident when comparing
Furthermore, as can be seen with reference to
Turning to
As can be seen with reference to the scale in
Similarly, the Co—W and W—Co intermetallic phases such as phases 602 and 603 are between 10 and 100 microns in width (e.g., a dimension of these phases in cross section are between 10 and 100 microns). More specifically, in this 40Co-60W sputter target 600, many of the Co—W intermetallic phases form a layer (between about 20 and 80 microns thick) around an elemental cobalt phase. Similarly, many of the W—Co intermetallic phases form a layer (between about 20 and 60 microns thick) around an elemental tungsten phase. According to various other embodiments of the present invention, a sputter target may have intermetallic phases with a thickness of between about 20 and 50 microns, between about 50 and 100 microns, between about 40 and 80 microns, or between about 10 and 90 microns.
While the foregoing exemplary embodiments have been described as “cobalt-tungsten” sputter targets, this label is not intended to imply a greater atomic percentage of cobalt than tungsten. Rather, the term “cobalt-tungsten” as used herein encompasses all compositions including both cobalt and tungsten, with any relative percentages, including compositions in which the amount of tungsten is greater than the amount of cobalt.
While the foregoing exemplary embodiments have been described as having two elemental phases and two intermetallic phases, the scope of the present invention is not limited to such an arrangement. Rather, in embodiments of the present invention in which a sputter target has a sufficiently low atomic percentage of either cobalt or tungsten, there may be no elemental phases of the scarcer element in the sputter target. Accordingly, in various embodiments of the present invention, a sputter target may have either four phases (i.e., elemental Co, intermetallic Co—W, intermetallic W—Co and elemental W) or only three phases (i.e., intermetallic Co—W, intermetallic W—Co and either elemental Co or elemental W).
Turning to
In accordance with one embodiment of the present invention, a tumbler-type blender is used, for a time between 10 and 120 minutes. For example, the constituent powders of sputter target 400 illustrated in
The method continues in step 702, in which the blended powder from step 701 is canned and degassed. For example, the blended powder may be loaded into a steel cylinder and subjected to near-vacuum conditions to extract any atmospheric (or other) gases from the blended powder prior to heating to ensure that the final sputter target will be fully densified.
In step 703, the degassed blended powder is hot pressed (e.g., by hot isostatic pressing). The hot isostatic pressing (“HIPing”) includes heating to a first soak temperature between about 500° C. and about 1050° C., and holding at that temperature for between about 15 and 120 minutes. Then, the HIPing continues by heating to a second soak temperature between about 1050° C. and 1450° C. and pressurizing to a pressure between about 15 kilopounds per square inch (“ksi”) and about 45 ksi. This pressure and temperature is held for between about 20 and 360 minutes. Then the target is cooled at a controlled rate and unloaded from the can. Of course, additional soak times and temperatures may be used in addition to those disclosed herein.
For example, sputter target 400 illustrated in
In step 704, the dense solid formed in step 703 is machined to the desired final dimensions. Because of the careful selection of the PSD of the powders in step 701, the dense solid does not contain excessive intermetallic phases, and accordingly is not as prone to cracking during machining as other cobalt-tungsten sputter targets. This permits the dense solid to be machined to any desired shape (e.g., cylindrical, round, rectilinear, etc.).
In step 705, the sputter target is sputtered in a process well known to those of skill in the art. Because of the foregoing advantages enjoyed by the sputter targets of the various embodiments of the present invention, the uniformity and yield of a cobalt-tungsten film sputtered therefrom is greatly improved over other cobalt-tungsten sputter targets.
While the present invention has been particularly described with reference to the various figures and embodiments, it should be understood that these are for illustration purposes only and should not be taken as limiting the scope of the invention. There may be many other ways to implement the invention. Many changes and modifications may be made to the invention, by one having ordinary skill in the art, without departing from the spirit and scope of the invention.
Claims
1. A method of fabricating a sputter target, the method comprising the steps of:
- selecting a cobalt powder having a particle size distribution and a tungsten powder having the same particle size distribution;
- blending the cobalt powder and the tungsten powder to form a blended powder;
- canning the blended powder;
- hot pressing the blended powder to form a solid; and
- machining the solid to form a sputter target.
2. The method according to claim 1, wherein the solid has a density greater than 99% of a theoretical maximum density thereof.
3. The method according to claim 1, wherein the particle size distribution is between about 20 and 250 microns.
4. The method according to claim 1, wherein the particle size distribution is between about 40 and 150 microns.
5. The method according to claim 1, wherein the hot pressing is hot isostatic pressing which includes:
- heating to a first soak temperature between about 500° C. and 1050° C.,
- holding at the first soak temperature for between about 15 and 120 minutes,
- heating to a second soak temperature between about 1050° C. and 1450° C. and pressurizing to a pressure between about 15 ksi and about 45 ksi, and
- holding at the second soak temperature and at the pressure between about 15 ksi and about 45 ksi for between about 20 to 360 minutes.
6. The method according to claim 1, wherein the hot pressing is hot isostatic pressing which includes:
- heating to about 800° C. and holding at about 800° C. for about 60 minutes,
- heating to about 1050° C., pressurizing to about 29 ksi and holding at about 1050° C. and about 29 ksi for about 240 minutes, and
- heating to about 1236° C., maintaining a pressure of about 29 ksi and holding at about 1236° C. and about 29 ksi for about 60 minutes.
7. The method according to claim 6, wherein the hot isostatic pressing further includes:
- cooling from about 1236° C. to about 800° C. at a rate of about 2° C./minute,
- holding at about 800° C. for about 60 min, and
- cooling from about 800° C. to about 400° C. at a rate of about 3° C./minute.
8. The method according to claim 1, wherein the cobalt powder is a powder of elemental cobalt.
9. The method according to claim 1, wherein the tungsten powder is a powder of elemental tungsten.
10. The method according to claim 1, further comprising the step of sputtering the sputter target to form a film including cobalt and tungsten.
11. A film sputtered according to the method of claim 10.
12. A cobalt-tungsten sputter target, comprising:
- a first elemental phase of a first material, the first material being either cobalt or tungsten;
- a first intermetallic phase including the first material and a second material, the second material being either tungsten or cobalt and different from the first material, the first material in a greater atomic percentage than the second material; and
- a second intermetallic phase including the second material and the first material, the second material in a greater atomic percentage than the first material,
- wherein the sputter target includes 20-80 at. % cobalt, and
- wherein a density of the sputter target is greater than 99% of a theoretical maximum density thereof.
13. The sputter target of claim 12, wherein the first intermetallic phase is a layer surrounding the first elemental phase.
14. The sputter target of claim 12, further comprising a second elemental phase of the second material.
15. The sputter target of claim 14, wherein the second intermetallic phase is a layer surrounding the second elemental phase.
16. The sputter target of claim 14, wherein the second elemental phase has a cross-sectional dimension of between about 5 microns and about 150 microns.
17. The sputter target of claim 12, wherein the first elemental phase has a cross-sectional dimension of between about 5 microns and about 150 microns.
18. The sputter target of claim 12, wherein each of the first intermetallic phase and the second intermetallic phase has a thickness of between about 10 microns and about 100 microns.
19. The sputter target of claim 12, wherein the sputter target includes 40-60 at. % cobalt.
20. The sputter target of claim 12, wherein a cross section of the sputter target includes an average of less than 10 voids per square millimeter.
21. The sputter target of claim 20, wherein the voids have an average size of less than 5 microns.
22. The sputter target of claim 12, wherein a cross section of the sputter target includes an average of less than 20 cracks per square millimeter.
23. The sputter target of claim 22, wherein the cracks have an average length of less than 150 microns.
Type: Application
Filed: Jan 11, 2007
Publication Date: Jul 17, 2008
Applicant: Heraeus Incorporated (Chandler, AZ)
Inventors: Fenglin Yang (Gilbert, AZ), Bernd Kunkel (Phoenix, AZ), Steven Roger Kennedy (Chandler, AZ), Anirban Das (Chandler, AZ)
Application Number: 11/653,003
International Classification: B22F 3/24 (20060101); B22F 3/12 (20060101); C22C 19/07 (20060101); C22C 27/04 (20060101);