Fine grained sputtering targets of cobalt and nickel base alloys made via casting in metal molds followed by hot forging and annealing and methods of making same
Disclosed are sputtering targets and methods for making various nickel and cobalt base alloys into sputtering targets by melting the alloys in a vacuum or under a low partial pressure of inert gas and subsequent casting of the melt as round, square or rectangular plates in metal molds under vacuum or under low partial pressure of inert gas are provided. The plates are subsequently preheated and deformed between two flat dies.
This invention relates to sputter targets and methods of making same. Sputter targets made of ferromagnetic materials are critical to thin film deposition in industries such as data storage and VLSI (very large scale integration)/semiconductors. Magnetron cathode sputtering is one means of sputtering magnetic thin films.
BACKGROUND OF THE INVENTIONThe sputtering process involves argon ion bombardment of a target as a cathode in the presence of an electric field. The dislodge atoms from the target due to ion bombardment traverse the enclosure and deposit as a thin film onto a substrate or substrates maintained at or near anode potential.
In magnetron cathode sputtering, an arched magnetic field created by magnets behind the target and formed in a closed loop over the surface of the sputter target, is superimposed on the electric field. The closed-loop leakage magnetic field traps electrons and increases the plasma density adjacent to the surface of the target, thereby significantly increasing the sputtering activity.
The use of magnetron sputtering to deposit thin films of magnetic target materials is widespread in the electronics industry, particularly in the fabrication of semiconductor and data storage devices. Due to the magnetic nature of the target materials, there is considerable shunting of the applied magnetic field in the bulk of the target. Erosion of particles from the sputter target surface generally occurs in a relatively narrow ring-shaped region corresponding to the shape of the closed-loop magnetic field. Only the portion of the total target material in this erosion groove is consumed before the target must be replaced. The result is that typically only 18-25% of the target material is utilized. Thus, a considerable amount of material, which is generally very expensive, is either wasted or must be recycled. (In the present specification, all compositional percentages are weight percents unless otherwise indicated). Furthermore, a considerable amount of sputter deposition equipment “down-time” occurs due to frequent target replacement.
Several sputtering processes and apparatus with which the invention may be usable are disclosed in Bergmann, et al., U.S. Pat. Nos. 4,889,772 and 4,961,831; Shagun, et al., U.S. Pat. No. 4,961,832; Shimamura, et al., U.S. Pat. No. 4,963,239; Nobutani, et al., U.S. Pat. No. 4,964,962; Arita, U.S. Pat. No. 4,964,968; Kusakabe, et al., U.S. Pat. No. 4,964,969 and Hata, U.S. Pat. No. 4,971,674; and the references referred to therein; sputtering targets are discussed also in Fukaswawa, et al. U.S. Pat. Nos. 4,963,240 and 4,966,676; and Archut, et al., U.S. Pat. No. 4,966,676. These disclosures of sputtering processes and apparatus as well as sputtering targets are expressly incorporated herein by reference. Additional background on sputtering is presented by U.S. Pat. Nos. 6,402,912; 6,494,999, and 6,585,870 expressly incorporated herein by reference.
Thin films of a magnetic alloy such as Co—Ni—Pt, Co—Cr—Ni, Co—Cr—Ta, Co—Cr, Co—Ni—Cr—V, Co—Cr—Pt, or the like, formed via magnetron sputtering on a substrate are used as magnetic recording medium in magnetic disks, hard drives, magneto-optical disks. Recently, various ideas such as increasing the coercive force of the magnetic film or reducing a noise have been proposed for the magnetic recording medium to cope with high density recording.
The pass through flux (PTF) of a magnetic sputtering target is defined as the ratio of transmitted magnetic field to the applied magnetic field. A PTF value of 100% is indicative of a non-magnetic material where none of the applied field is shunted through the bulk of the target. The PTF of magnetic target materials is typically specified in the range of 0 to 100%, with the majority of commercially produced materials exhibiting values between 10 to 95%.
For magnetron sputtering, the magnetic leakage flux (MLF) or leakage magnetic field at the target surface must be high enough to start and sustain the plasma. Under normal sputtering conditions, such as an argon pressure of 5-10 mTorr, the minimum MLF, also known as pass through flux (PTF), is approximately 150 gauss at the sputtering surface, and preferably is about 200 gauss for high speed sputtering. The magnet strength of the cathode sputtering target in part determines the MLF. The higher the magnet strength, the higher the MLF. In the case of ferromagnetic sputter targets, however, the high intrinsic magnetic permeability of the material effectively shields or shunts the magnetic field from the magnets behind the target and hence reduces the MLF on the target surface. This leads to reduced sputtering efficiency.
Because of high permeability and thus low MLF, ferromagnetic sputter targets are generally made much thinner than non-magnetic sputter targets to allow enough magnetic field to be leaked out to the sputtering surface to sustain the sputtering plasma necessary for magnetron sputtering. With some ferromagnetic materials, particularly those with higher permeability, the targets have to be machined to 0.0625 inch thick or less to achieve an MLF at the sputtering surface of 150 gauss, and some very high permeability materials are impossible to magnetron sputter because an MLF of 150 gauss simply cannot be achieved. Thus, not only can these ferromagnetic targets not simply be made thicker so as to reduce equipment down-time, they must actually be made thinner.
In general, the higher the permeability of the ferromagnetic material, the thinner the sputter target is required to be. Such a limitation on target thickness, however, leads to a shorter target life, waste of material and a need for more frequent target replacement. Furthermore, the high permeability and low MLF of a ferromagnetic target can cause problems of high impedance, low deposition rates, narrow erosion grooves, poor film uniformity and poor film performance. It is thus desirable to provide a high MLF ferromagnetic sputter target that may be made relatively thick without sacrificing film integrity.
It is well known that reducing target material permeability or increasing the target material PTF promotes less severe erosion profile, thus enhancing target material utilization during the sputtering process. This leads to a net reduction in target material cost per unit sputter fabricated product. Furthermore, the presence of severe target erosion profiles can also lead to a point source sputtering phenomena which can result in a deposited thin film that lacks thickness uniformity. Therefore, in addition to less severe erosion profile, increasing the PTF of the target material has the added benefit of increasing the uniformity of the thickness of the deposited thin film.
Magnetic target PTF is a strong function of both target chemistry and the thermo-mechanical techniques utilized during target fabrication. For alloys that do not possess inherently high PTF as a result of their stoichiometry, i.e., PTF<85%, it is possible to increase product PTF by various thermo-mechanical manipulations during product fabrication. For example, the typical fabrication of Ni, Co and Co-alloy targets involves casting, hot-rolling and either heat treatment or cold-rolling or a combination of heat treatment followed by cold-rolling. It is known that heat treating and cold-rolling of magnetic target materials can increase product PTF. Heat treatment of Co—Cr—Ta—(Pt) alloys below 2200° F. has been shown to increase the PTF by promoting matrix crystallographic phase transformation from face centered cubic to hexagonal closed packed as discussed in Chan et al., Magnetism and Magnetic Materials, Vol. 79, pp. 95-107 (1989).
It is suggested in Weigert et al., Mat. Sci. and Eng., A 139, p.p. 359-363 (1991), that cold-rolling of an alloy comprising 62-80 atomic % Co, 18-30 atomic % Ni, and 0-8 atomic % Cr immediately after the hot-rolling step results in an increase in product PTF. A similar result is disclosed in Uchida et al., U.S. Pat. No. 5,468,305 for an alloy containing 0.1-40 atomic % Ni, 0.1-40 atomic % Pt, 4-25 atomic % Cr and the remainder Co which is cold-rolled by not more than a 10% reduction after the hot-rolling process. Uchida et al. claim that the cold-deformation induced internal strain in the alloy reduces magnetic permeability.
High PTF in the ferromagnetic sputtering targets are generally achieved by heat treatment and/or thermal-mechanical processing treatments.
Co alloy targets strongly require the lowering in permeability. The lowering in permeability is most effective to enhance the sputtering efficiency of Co alloy targets and it also greatly contributes to the reduction in cost from the viewpoint of users.
Sputtering efficiencies of targets depend on several factors such as: (a) grain size, (b) grain orientation and texture, and (c) the homogeneity of dispersion and particle size of second phase precipitates. Fine grain sizes, finely dispersed second phases in the matrix and strong texture will enhance sputtering efficiency of targets.
The effect of crystallographic orientation of a sputtering target on sputtering deposition rate and film uniformity has been described in an article by C. E. Wickersham, Jr., entitled Crystallographic Target Effects in Magnetron Sputtering in the J.Vac. Sci. Technol. A5(4), July/August 1987 publication of the American Vacuum Society.
However, there is a limit to how fine a grain size, how strong a texture, and how small a precipitate size can be achieved with conventional metal processing techniques, i.e., rolling, forging, for each metal system and alloy.
Similarly, the development of different textures and anisotropic properties by rolling is difficult. Desired plane textures and enhanced properties can be created only along the rolling direction with accompanying large reductions (see e.g., U.S. Pat. Nos. 3,954,516, 4,406,715, 4,609,408, 4,753,692 and 5,079,907). In addition, methods are not available which develop the required texture and anisotropy at a desired angle relative to the rolling direction at the rolling plane. Production of non-oriented textureless or isotropic products by rolling is also a difficult problem. Moreover, intensive rolling develops strongly laminated materials that often exhibit anisotropy of material properties which cannot be eliminated through existing technologies.
Grain size reduction in cobalt alloys can be achieved by thermo-mechanical processing such as hot rolling or hot forging followed by recrystallization. However, cobalt alloys containing multiple elements such as chromium, tantalum, nickel, platinum and boron are difficult to hot work by the conventional ingot metallurgy route due to segregated microstructures containing brittle second phases at the grain boundaries. Often the expensive powder metallurgy route is followed to fabricate these alloys with desirable fine and homogeneous microstructures.
To improve the performance of sputtering targets, manufacturers have used special casting techniques to reduce the resulting as-cast grain size. Also, hot or cold deformation followed by recrystallization has been used to reduce the grain size of the metal to be formed into a sputtering target.
Grain orientation control has also been suggested. A slow hot forging technique which produces a predominately <110> texture is described in U.S. Pat. No. 5,087,297 to Pouliquen.
Conventional casting, forming, annealing, and forging techniques have produced sputtering targets with limited minimum grain sizes. Ultra-fine grains have also been achieved with a technique known as equal channel angular extrusion (ECAE), but not in production of sputtering targets. The ECAE process has been a technical curiosity but has not been used for any known commercial purpose. It is a method which uses an extrusion die containing two transversely extending channels of substantially identical cross section. It is common, but not necessary, to use channels which are perpendicular to each other, such that a cross section of the transverse channels forms an “L” shape.
Thermo-mechanical processing (i.e., various combinations of heat treatment and mechanical working) is performed on materials to refine grains and phases, change their aspect ratios, orientation and distribution, and develop substructures. Intensive plastic deformation plays an important role in thermo-mechanical materials processing. Different deformation methods are used for material processing depending upon the shape and dimensions of the billet and the initial and final properties of the material. Hot forging of metals is an advantageous method of producing sputtering materials for PVD targets. Hot forging also tends to produce a finer metallurgical grain size. The mechanism for this improved microstructure is dynamic recrystallization.
Dynamic recrystallization is a softening process that takes place during metal deformation at elevated temperatures. This softening is observed in a large number of metals and alloys and for numerous deformation processes. Careful analyses of the deformation behavior, including microstructural investigations, have shown that there are two broad classes of dynamic softening.
The first class is described in the literature as involving the discontinuous formation of new grains within the deformed matrix. To be more specific, grains develop during deformation by nucleation and growth, so that the average dislocation density drops, leading to significant softening. This type of dynamic recrystallization is associated with low or medium stacking fault energy metals (copper, silver, nickel, the austenite phase of conventional steels, and austenitic stainless steels).
The second class of softening process is associated with materials in which dynamic recovery is rapid enough to insure slow migration of the subgrain boundaries. Such materials undergo softening by continuous fragmentation of their substructure. This fragmentation produces a fine grained microstructure, without involving any nucleation or growth mechanism. For these reasons, the first broad class is usually referred to as “discontinuous dynamic recrystallization,” while the second is designated as “continuous dynamic recrystallization.”
Traditionally, forming operations such as forging and rolling were performed on billets to develop desired physical/mechanical properties. However, in many respects, such operations are ineffective. The difficulty in achieving the high strains necessary for structure and texture formation represents the greatest limitation in these operations. In order to develop cumulative strain sufficient to provide grain refinement by recrystallization during subsequent annealing, it is necessary to apply a number of successive forging stages along the three perpendicular axes of a billet (see, e.g., U.S. Pat. Nos. 3,954,514 and 4,721,537). However, such a forging operation may be used only with billets having approximately equal dimensions along their three perpendicular axes. The treatment of plates by such a process results in a marked change of billet dimensions from a plate to a bar-shape (see, e.g., U.S. Pat. No. 4,511,409). However, conventional ingots of cobalt base alloys that are used for applications as ferromagnetic sputtering targets contain coarse, brittle intermetallic phases and hence are difficult to be deformed or strained via hot working operations.
There is a need for an improved cost effective process for making ferromagnetic sputtering targets with fine and uniform grain structure based on various cobalt and nickel based alloys suitable for high efficiency utilization in magnetron sputtering equipment.
PREFERRED OBJECTS OF THE PRESENT INVENTIONIt is a preferred object of the present invention to rapidly cast various cobalt and nickel base alloys as plates in reusable metallic molds having high melting point, high thermal conductivity and high strength under vacuum or inert gas atmosphere.
It is another preferred object of the present invention to produce fine columnar grains parallel to the thickness of the cast plates by maintaining the thickness of the castings under 2 inch.
It is another preferred object of the invention to hot forge the cast plates containing the columnar grains along the thickness direction at in successive steps.
It is another preferred object of the invention to carry out the hot forging operations at certain combinations of temperatures and strain rates depending on the alloy composition which will cause deformation of the columnar grains followed by dynamic recrystallization into fine equiaxed grains.
SUMMARY OF THE INVENTIONThe invention relates to a method for making various metallic alloys based on cobalt and nickel alloys as plates with fine grain uniform microstructures that can be machined to final net shaped sizes for applications as ferromagnetic sputtering targets with high pass through flux.
This invention relates to a method for making various metallic alloys based on cobalt and nickel as plates suitable for applications as ferromagnetic sputtering targets in magnetron sputtering equipment. The invention relates to fabrication of the sputtering targets of cobalt and nickel alloys as follows:
(a) The alloys are vacuum induction melted and cast as plates under vacuum with a maximum thickness of 2 inches in metallic molds having melting points between 2350-3000F, thermal conductivity between 300-600 Btu/Ft2/hr/in/F in the range 70-700F and room temperature tensile strength between 100-200 KSI.
(b) The cast plates are hot forged along the thickness direction under certain critical combinations of strain rate ranging between 0.1/second to 10/second and temperature ranging between 500° F. and 2200° F. and total deformation ranging between 20-80 %.
(c) The forged plates are subsequently annealed within certain ranges of temperatures between 500° F. to 2000° F.
Depending on the alloy compositions, the columnar grain structure of the cast plates undergoes dynamic recrystallization during forging and/or subsequent annealing step into fine, homogeneous equiaxed grains.
More particularly, this invention relates to the use of metallic molds such as certain grades of plain carbon steels, malleable cast irons and low alloy steels. High melting point (>2350° F.) and high thermal conductivity (300-400 Btu/Ft2/hr/in/° F. in the temperature range 70-700° F.) and high ultimate tensile strength (100-200 KSI) are some of the characteristics of the metallic materials that render them suitable for use as molds for casting cobalt and nickel base alloys of as much as 2 inch thickness with fine columnar grains along the thickness direction in accordance with the scope of the present invention.
The present invention has a number of advantages:
(1) Use of metallic molds having high melting points and high thermal conductivity leads to formation of columnar grains parallel to the thickness direction in the cobalt and nickel base alloys intended for applications as magnetic sputtering target. The columnar grain structure is critical for achieving equiaxed fine grains by high strain rate forging induced dynamic recrystallization. The fine grain structure of the forged and annealed plates of cobalt and nickel alloys are critical for improved properties and high efficiency performance of the sputtering targets compared to the sputtering targets of similar alloys produced by conventional processes.
(2) The metallic molds having high strength and high melting points can be used repeatedly many times thereby reducing significantly the cost of fabrication of the castings.
(3) The castings can be made in molds held at room or low temperatures resulting in finer grain structures and improved mechanical properties.
(4) The fine columnar grains of certain cobalt base alloys containing brittle intermetallic phases are amenable to deformation by hot forging without fracture or cracks. Large ingots produced by conventional slow cooling process contains large grains with brittle intermetallic grain boundary phases and such ingots are difficult to hot forge at high strain rate necessary to impart substantial strain energy in the alloy which triggers simultaneous grain refinement by the mechanism of dynamic recrystallization.
This invention also relates to a sputtering target made of alloys, such as various metallic alloys based on cobalt and nickel alloys, made by the method of the present invention.
This invention also relates to a nickel base alloy sputtering target or cobalt base alloy sputtering target having a percentage PTF (pass through flux) of at least 60%.
This invention also relates to a nickel base alloy sputtering target or a cobalt base alloy sputtering target having a percentage PTF (pass through flux) of at least 65%, for example 65% to 80% or 65% to 75%.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTSA. Metallic Molds
Certain grades of plain carbon steels, low alloy steels and malleable cast irons are preferred materials as the main body of the mold of the present invention for the following reasons:
The metallic alloys have high melting point between 2350° F.-3000° F. and thermal conductivity between 300-400 Btu/Ft2/hr/° F. in the temperature range 70-700° F. and ultimate tensile strength between 100-200 KSI.
Other important properties of the above material are high thermal shock, wear and chemical resistance, and minimum wetting by liquid metal.
The typical physical and mechanical properties of metallic molds suitable for casting cobalt and nickel base alloys in accordance with the present invention are given in Table 1.
The chemical compositions of the alloys listed in Table 1 are given in the CRC Handbook of Materials Science, Vol. II, edited by C. T. Lynch, CRC Press, Inc, Boca Raton, Fla., 1975.
Parameters referenced in the present specification are measured according to the following standards unless otherwise indicated.
Tensile strength is measured by ASTM E8-96
Thermal conductivity is measured according to ASTM C-714.
B. Molding
An embodiment of the present invention is a method of making an article of metallic alloy, comprising the steps of: melting the metallic alloy under vacuum or partial pressure of inert gas; pouring the metallic alloy into a mold with a cavity of uniform thickness, the metallic alloys having melting point between 2350-3000° F. and thermal conductivity between 300-400 Btu/Ft2/hr/in/° F. in the temperature range 70-700° F. and ultimate tensile strength between 100-200 KSI, solidifying the melted metallic alloy into a solid metallic body taking the shape of the mold cavity as a plate of constant thickness; preheating the solidified plate at temperature below the melting temperature of the metallic alloy; deforming the preheated plate between two flat dies with the application of pressure along the thickness direction producing a plate with reduced but constant thickness; and annealing the deformed plate at temperatures below the melting temperature of the metallic alloy.
If molds are made of metallic materials which have thermal conductivity outside the critical range i.e. <300 Btu/Ft2/hr/in/° F. and >400 Btu/Ft2/hr/in/° F. in accordance with the present invention , the properties of the sputtering targets made via casting melt in such molds followed by hot forging will be less than optimum.
At low thermal conductivity, the metallic melt cast into it will not cool fast enough to generate predominantly columnar grains perpendicular to the mold wall and will lead to formation of a mixture of columnar grains and equiaxed in the solidified casting. Under the condition, when solidification begins, the melt will solidify as columnar grains perpendicular to the wall of the mold followed by formation of equiaxed grains in the center region of the casting away from the surface. Similarly, when the thermal conductivity of a specific mold material is greater than 400 Btu/Ft2/hr/in/° F., solidification will begin with the formation of very fine equiaxed adjacent to the mold wall followed by formation of columnar grains. In either condition of thermal conductivity of the mold materials, a mixture of equiaxed and columnar grains present in the cast body will result into non-uniform distribution of strain energy in it during the subsequent high strain rate forging operation. The strain energy being stored in the material body as it gets deformed during forging has to reach a critical value to trigger the subsequent recrystallization of fine grains. The mixture of equiaxed and columnar grains in the casting will result in retained strain energy in some parts of the material body to be below the critical value necessary for dynamic recrystallization of fine grains. At the end of the forging operation, the grain structure in the final product will have, or consist of, a mixture of fine recrystallized grains and coarse unrecrystallized grains. The properties of the sputtering targets will be inferior as a consequence of uniform grain structure.
The melting point of the material below 2350° F. makes it unsuitable for use as mold in accordance with the present invention. Low melting point (<2350° F.) of a mold material will have a tendency to melt or react with the candidate cobalt and nickel base alloys having relatively high melting points (i.e. >2650° F.) when cast into such molds.
The preferred tensile strength of the metallic mold material is between 100 and 200 KSI. Some of the candidate metallic mold materials listed in Table 1 can be heat treated to achieve a certain combination of tensile strength and elongation (i.e., ductility). For example, the plain carbon and alloy steels such as AISI 1080, AISI 1095, AISI Type B 1211, AISI 4130, AISI 4330 and AISI 4340 can be heat treated to achieve ultimate tensile strength in excess of 200KSI at lower than optimum ductility. Under such conditions of mechanical properties, the mold materials when subjected to repeated cycles of thermal stress during casting operations will crack and prematurely fail. When the ultimate tensile strength is below 100 KSI, the mold material will deform due to high thermal stress leading to low mold life.
Typically the melting is done by vacuum induction melting (VIM).
Preferably the mold has a temperature in the range from 30 to 300° C. when the alloy is poured into the mold. Typically, the mold has a temperature in the range from 20 to 400° C. when the alloy is poured into the mold, or the mold has a temperature in the range from 100 to 200° C. when the alloy is poured into the mold. Typically the mold cavity is round or square or rectangular with a constant thickness in the range from 0.25 to 2 inch, or from 0.5 to 2 inch, or from 0.5 to 1 inch.
C. Preheating
Typically, after molding the solidified plate is preheated before deformation via hot forging at temperature in the range from 500 to 2200° F. or in the range from 1000 to 2200° F., or in the range from 1000 to 2000° F. or in the range from 1200 to 1800° F. or in the range from 1200 to 1600° F.
D. Hot Forging
The hot forging of plates cast in graphite molds is primarily carried out in open flat dies in accordance with the present invention. The optimum forging parameters need to be determined for each alloy before the actual forging operation is carried out.
Flow stress of an alloy at a specific temperature is a fundamental characteristic of great importance. It is the stress that must be applied to make the metal deform plastically.
The control of grain size evolving during the hot forging process for cobalt and nickel base alloys is achieved by using a specific set of thermo-mechanical processing conditions. The starting columnar grain size produced by the casting process employed in the present invention is critical. Samples machined from each cast plate are subjected to a series of hot compression tests over a range of temperatures and strain rates. Hot compression is carried out to achieve deformation in the range, 10-80% or 20-80% in a single step or a multiple steps at a given temperature.
Typically, the preheated plate is pressed between two flat dies at strain rate in the range from 0.1/second to 10/second, or in the range from 0.5/second to 10/second, or in the range from 1/second to 10/second, or in the range from 1/second to 5/second. Typically, the preheated plate is deformed between two flat dies undergoing 10-80% reduction in thickness, or 20-80% reduction in thickness, or 30-70% reduction in thickness.
E. Annealing
Following hot compressions, the samples are annealed optionally to induce dynamic recrystallization. The microstructures including grain size and grain distribution are evaluated after hot compression and annealing treatments. Based on microstructural characteristics, the hot forging parameters are determined for each alloy.
F. Alloys
The invention is suitable for fabricating various nickel and cobalt base alloys which are suitable for applications as ferromagnetic sputtering targets in magnetron sputtering systems.
1. Cobalt and Cobalt base alloys
The Co-base alloy used as targets for magnetron cathode sputtering contains further elements that produce intermetallic phases dispersed in the matrix. The typical chemistries of such alloys can be described by the following formula:
Co1-x-yMxRy
The compositions are in atom percent, wherein M is at least one of the elements chromium, platinum, nickel, palladium or similar elements and 0<=x<=0.3, and R is at least one of the elements tantalum, molybdenum, tungsten, boron, hafnium, niobium, vanadium or similar elements which promotes the tendency towards the formation of intermetallic phases and 0.015<=y<=0.20.
Depending on the manufacturing techniques employed, the grain boundaries, twin grain boundaries or slip bands of the Co based matrix are decorated with the elements forming the intermetallic phase.
Sputtering targets based on cobalt alloys such as Co—30 Ni—15 Cr (atom percent) are used for magnetic recording media production to form recording and protection films, respectively. Poor consumable volume efficiency of Co alloy targets fabricated by conventional techniques such as ingot casting and hot rolling have permeability of >200. If the microstructure of cobalt alloys can be rendered more homogeneous and fine grained, permeability can be reduced to below 50 leading to 100% increase in target life.
Cobalt-Iron-Boron is a family of ferromagnetic target alloys a containing various amounts of Iron (Fe) and Boron (B). Typically these amounts are approximately 10 at% Fe and 2-5 at% B.
Various other ternary and multi-component cobalt base alloy systems for sputtering target applications are listed below:
Cobalt-Iron
Cobalt-Iron-Boron
Cobalt-Iron-Chromium
Cobalt-Zirconium-Tantalum
Cobalt-Zirconium-Niobium
Cobalt-Zirconium-Rhodium
Cobalt-Platinum
Cobalt-Chromium-Platinum
Cobalt-Chromium-Platinum-Tantalum
Cobalt-Platinum-Boron
Cobalt-Chromium
Cobalt-Chromium-Nickel
Cobalt-Chromium-Tantalum
Cobalt- Niobium-Hafnium
Cobalt-Niobium-Titanium
Cobalt-Niobium-Iron.
Typically the metallic alloy is a cobalt base alloy having the composition in weight percent as follows:
Cobalt=Balance
Chromium=5 to 20%
Tantalum=5 to 15%
and inevitable impurity elements, wherein the impurity elements are less than 0.01% each and less than 0.05% total
Another typical metallic alloy is a cobalt base alloy having the composition in weight percent as follows:
Cobalt=Balance
Chromium=5-20%
Iron=0-15%
and inevitable impurity elements, wherein the impurity elements are less than 0.01% each and less than 0.05% total.
Another typical metallic alloy is a cobalt base alloy having the composition in weight percent as follows:
Cobalt=Balance
Chromium=5-20%
Platinum=5-15%
Boron=0-2%
and inevitable impurity elements, wherein the impurity elements are less than 0.01% each and less than 0.05% total.
Another typical metallic alloy is a cobalt base alloy having the composition in weight percent as follows:
Cobalt=Balance
Chromium=0-20%
Zirconium=0-5%
Niobium=0-5%
Tantalum=0-10%
Hafnium=0-10%
and inevitable impurity elements, wherein the impurity elements are less than 0.01% each and less than 0.05% total.
2. Nickel and Nickel Alloys
Nickel and nickel alloy targets are used in magnetron sputtering process to fabricate thin films on substrates for a variety of applications such as:
Corrosion resistant film adherence to non-metals, thin film resistors, magnetic thin films, disk drives and magnetic random access memory (MRAM), contact layers and under bond metallization, ferromagnetic films and diffusion barriers.
Various ternary and multicomponent nickel base alloy systems that are currently used as sputtering targets are listed below:
High purity nickel (3N7 purity)
Nickel-Chromium.
Nickel Chromium Iron
Nickel-Iron-Rhodium
Nickel-Tungsten
Nickel-7 weight percent Vanadium
A typical nickel base alloy has the composition in weight percent as follows:
Nickel=Balance
Chromium=0-20%
Iron=0- 10%
and inevitable impurity elements, wherein the impurity elements are less than 0.01% each and less than 0.05% total.
Another typical nickel base alloy has the composition in weight percent as follows:
Nickel=Balance
Chromium=0-20%
Rhodium=0-10%
and inevitable impurity elements, wherein the impurity elements are less than 0.01% each and less than 0.05% total.
The nickel-tungsten alloy systems, typically have, or consist of, 10 weight percent of tungsten. The tungsten is added to make the nickel non-magnetic while retaining similar properties to pure nickel as a thin film.
A typical metallic alloy is a nickel base alloy having the composition in weight percent as follows:
Nickel=Balance
Chromium=0- 20%
Tungsten=0-10%
and inevitable impurity elements, wherein the impurity elements are less than 0.01% each and less than 0.05% total.
The nickel-vanadium alloy system, the desirable compositions are composed of 93 weight % nickel and 7 weight % vanadium. The vanadium is added to make the nickel non-magnetic while retaining similar properties to pure nickel as a thin film.
A typical metallic alloy is a nickel base alloy having the composition in weight percent as follows:
Nickel=Balance
Vanadium=0-10%
and inevitable impurity elements, wherein the impurity elements are less than 0.01% each and less than 0.05% total.
Another suitable material is a nickel base alloy has a composition in weight percent as follows:
Nickel=99.95 to 99.99%.
EXAMPLES Example 1 Table 2 lists several alloy compositions which are suitable for fabrication as sputtering targets in accordance with the scope of the present invention.
An alloy having the composition of Co-16 atom % Cr alloy is cast into metallic molds of several metal alloys as listed in Table 1 according the scope of the sent invention as plates with the following dimensions: 5×5×1 inch thick plate. The following metal alloys are used as molds: AISI 1030, AISI 1095, AISI 1141, AISI 4130 and AISI 4340.
The plate are heated to 2100° F. and forged into 0.4 inch thick plates. The forged plates show fine grained microstructures with homogeneous dispersions of fine second phase precipitates throughout the primary grains of the matrix. The forged plates are machined to final thickness of about 0.315 inch and are analyzed for the percentage PTF (pass through flux). The results are shown in Table 3 below. Also listed in the same Table 3 the data obtained from sputtering targets having the similar compositions produced by the conventional process based on ingot melting, casting and hot rolling. The sputtering targets produced by the method disclosed in the present invention show higher PTF values compared to the similar targets produced by the conventional processes.
Several cobalt base alloy compositions as listed in Table 4 below are cast into PERMANICKEL alloy 300 molds according the scope of the present invention as plates having a thickness ranging between 1 to 2 inches. PERMANICKEL alloy has the following chemical composition (weight percent):
Nickel=98.5, C=0.20, Mn=0.25, Fe=0.30, Si=0.18, Cu=0.13, Ti=0.40, Mg=0.35
The plates are heated between 1200° F.-2150° F. and forged into plates at strain rates ranging between 0.1/second to 10/second with total deformation ranging between 20 to 80%. The forged plates show fine equiaxed grains with homogeneous dispersions of fine second phase precipitates throughout the primary grains of the matrix. The forged plates are machined to final thickness of 0.250 inch and are analyzed for the percentage PTF (pass through flux). The results are shown in Table 4 below.
An alloy having the composition of Co-16 atom % Cr is cast into molds made of Nitriding steel Type 135 and Nitriding steel type N according the scope of the present invention as plates with the following dimensions: 5×5×1 inch.
The plates are heated to 2100° F. and forged into 0.4 inch thick plates. The forged plate show very fine grain structures. The forged plates show PTF values in excess of 70%.
Example 5An alloy having the composition of Co-14Cr-4Ta (atom %) is cast into a mold made of Pearlitic 80002 type malleable cast iron according the scope of the present invention as plates. The plates are heated to 2100° F. and forged into 0.4 inch thick plates. The forged plate show very fine grain structures. The forged plates show PTF values in excess of 70%. The microstructure of the forged plate is found to be considerable more uniform in comparison to a sputtering target of the same alloy made by the conventional process of ingot metallurgy followed by hot rolling.
Example 6An alloy having the composition of Co-16 atom % Cr is cast into a mold made of different carbon steels as listed in Table 1 such as AISI 1118, A AISI 1030, AISI 1050, AISI 1080, AISI 1095, AISI 1141, AISI Type B 1211 and AISI type B 1212 according to the scope of the present invention as plates with the following dimensions: 5×5×1 inch. The samples from each of the cast plates are examined metallographically under an optical microscope. The microstructure of the samples from the as cast plates show fine columnar grain structure.
Example 7The alloy of Example 6 which is cast into AISI 4340 and AISI 4330 steel molds into plates having the following dimensions 5 inch×5 inch×1 inch thick. The cylindrical samples (0.625 inch diameter×1 inch long) are machined from the cast plates and are hot compressed at strain rate of 3/sec at four different temperatures 2000° F., 1800° F., 1700° F. and 1600° F. The hot compressed specimens are analyzed for microstructures. Hot compression at lower temperatures results into finer microstructures.
Example 8A nickel plate with purity of 99.95% is cast into molds made of the following cast alloy steels: Class 105,000, Class 120,000 and Class 200,000 According to the scope of the present invention with the following dimensions: 5×5×1 inch. Samples sectioned from the cast plates are hot compressed at 3/second strain rate at various temperatures ranging from 1200° F. to 1800° F.
The microstructures of the as cast plate as well as hot compressed specimens are examined. Samples hot compressed at lower temperatures (1200° F. and 1400° F.) are found to show finer grain sizes as compared to the as cast plates as well as the samples hot compressed at temperatures greater than 1400° F.
Example 9Several nickel base alloys listed in Table 2 are cast in PERMANICKEL alloy 300 molds into plates with thickness ranging between 0.5 to 2 inches. The plates are hot forged at strain rates between 0.1/second to 10/second at temperatures between 1200° F. and 2200° F. Following forging the plates are annealed at 1200° F.-2000° F. for 10 minutes to 2 hours. The microstructures of the plates following forging and annealing consist of uniform fine equiaxed grains with grain size below 50 microns as a result of dynamic recrystallization.
Example 10Several materials listed in Table 5 have been considered as potential candidates for use as mold materials in accordance with the present invention. Although the materials listed in Table 5 have desirable mechanical and physical properties, some of the properties fall outside the critical range of properties such as thermal conductivity, melting point and ultimate tensile strength of mold materials in accordance with the present invention.
Several nickel and cobalt base alloys listed in Table 2 such as Ni-7 wt % V and Co-10 wt % Cr-10 wt % Ta are melted and cast in molds made of materials listed in Table 5 as 5×5×1 inch thick plate. The plates are hot forged at strain rates between 0.1/second to 10/second at temperatures between 1200° F. and 2200° F. Following forging the plates are annealed at 1200° F.-2000° F. for 10 minutes to 2 hours. The PTF values of the plates following forging and annealing are measured to be low i.e. below 50% and hence are determined to be unsuitable for use as magnetron sputtering targets.
The chemical compositions of the alloys listed in Table 5 are given in the CRC Handbook of Materials Science, Vol. II, edited by C.T. Lynch, CRC Press, Inc, Boca Raton, Florida, 1975.
It should be apparent that in addition to the above-described embodiments, other embodiments are also encompassed by the spirit and the scope of the present invention. Thus, the present invention is not limited by the above-provided description, but rather is defined by the claims appended hereto.
Claims
1. A method of making an article of metallic alloy, comprising the steps of:
- melting the metallic alloy under vacuum or partial pressure of inert gas;
- pouring the metallic alloy into a metal mold with a cavity of uniform thickness, wherein the metal mold is made by machining or casting technique from materials having melting point in the temperature range 2350° F.-3000° F. and thermal conductivity between 300-400 Btu/Ft2/hr/in/° F. in the temperature range 70-700° F. and ultimate tensile strength betwen 100 and 200 KSI,
- solidifying the melted metallic alloy into a solid body taking the shape of the mold cavity as a plate of constant thickness;
- preheating the solidified plate at temperature below the melting temperature of the metallic alloy;
- deforming the preheated plate between two flat dies with the application of pressure along the thickness direction producing a plate with reduced but constant thickness;
- optionally annealing the deformed plate at temperatures below the melting temperature of the metallic alloy.
2. The method of claim 1, wherein the mold has a temperature in the range from 30 to 800° C. when the alloy is poured into the mold.
3. The method of claim 1, wherein the mold has a temperature in the range from 200 to 800° C. when the alloy is poured into the mold.
4. The method of claim 1, wherein the mold has a temperature in the range from 100 to 500° C. when the alloy is poured into the mold.
5. The method of claim 1, wherein the mold cavity is round or square or rectangular with a constant thickness in the range from 0.25 to 2 inch.
6. The method of claim 1, wherein the mold cavity is round or square or rectangular with a constant thickness in the range from 0.5 to 2 inch.
7. The method of claim 1, wherein the mold cavity is round or square or rectangular with a constant thickness in the range from 0.5 to 1 inch.
8. The method of claim 1, wherein the solidified plate is preheated before deformation at temperature in the range from 500 to 2200° F.
9. The method of claim 1, wherein the solidified plate is preheated before deformation at temperature in the range from 1000 to 2200° F.
10. The method of claim 1, wherein the solidified plate is preheated before deformation at temperature in the range from 1000 to 2000° F.
11. The method of claim 1, wherein the solidified plate is preheated before deformation at temperature in the range from 1200 to 1800° F.
12. The method of claim 1, wherein the solidified plate is preheated before deformation at temperatures in the range from 1200 to 1600° F.
13. The method of claim 1, wherein the preheated plate is pressed between two flat dies at strain rate in the range from 0.1/second to 10/second.
14. The method of claim 1, wherein the preheated plate is pressed between two flat dies at strain rate in the range from 0.5/second to 10/second.
15. The method of claim 1, wherein the preheated plate is pressed between two flat dies at strain rate in the range from 1/second to 10/second.
16. The method of claim 1, wherein the preheated plate is pressed between two flat dies at strain rate in the range from 1/second to 5/second.
17. The method of claim 1, wherein the preheated plate is deformed between two flat dies undergoing 10-80% reduction in thickness.
18. The method of claim 1, wherein the preheated plate is deformed between two flat dies to undergo 20-80% reduction in thickness.
19. The method of claim 1, wherein the preheated plate is deformed between two flat dies to undergo 30-70% reduction in thickness.
20. The method of claim 1, wherein the metallic alloy is a cobalt base alloy having the composition in weight percent as follows:
- Cobalt=Balance
- Chromium=5 to 20%
- Tantalum=5 to 15%
- and inevitable impurity elements, wherein the impurity elements are less than 0.01% each and less than 0.05% total
21. The method of claim 1, wherein the metallic alloy is a cobalt base alloy having the composition in weight percent as follows:
- Cobalt=Balance
- Chromium=5-20%
- Iron=0-15%
- and inevitable impurity elements, wherein the impurity elements are less than 0.01% each and less than 0.05% total.
22. The method of claim 1, wherein the metallic alloy is a cobalt base alloy having the composition in weight percent as follows:
- Cobalt=Balance
- Chromium=5-20%
- Platinum=5-15%
- Boron=0-2%
- and inevitable impurity elements, wherein the impurity elements are less than 0.01% each and less than 0.05% total.
23. The method of claim 1, wherein the metallic alloy is a cobalt base alloy having the composition in weight percent as follows:
- Cobalt=Balance
- Chromium=0-20%
- Zirconium=0-5%
- Niobium=0-5%
- Tantalum=0-10%
- Hafnium=0-10%
- and inevitable impurity elements, wherein the impurity elements are less than 0.01% each and less than 0.05% total.
24. The method of claim 1, wherein the metallic alloy is a nickel base alloy having the composition in weight percent as follows:
- Nickel=Balance
- Chromium=0-20%
- Iron=0-10%
- and inevitable impurity elements, wherein the impurity elements are less than 0.01% each and less than 0.05% total.
25. The method of claim 1, wherein the metallic alloy is a nickel base alloy having the composition in weight percent as follows:
- Nickel=Balance
- Chromium=0-20%
- Rhodium=0-10%
- and inevitable impurity elements, wherein the impurity elements are less than 0.01% each and less than 0.05% total.
26. The method of claim 1, wherein the metallic alloy is a nickel base alloy having the composition in weight percent as follows:
- Nickel=Balance
- Chromium=0-20%
- Tungsten=0-10%
- and inevitable impurity elements, wherein the impurity elements are less than 0.01% each and less than 0.05% total.
27. The method of claim 1, wherein the metallic alloy is a nickel base alloy having the composition in weight percent as follows:
- Nickel=Balance
- Vanadium=0-10%
- and inevitable impurity elements, wherein the impurity elements are less than 0.01% each and less than 0.05% total.
28. The method of claim 1, wherein the metallic alloy has the composition in weight percent as follows:
- Nickel=99.95 to 99.99%.
29. A sputtering target made by the method of claim 1.
30. The sputtering target of claim 29, wherein the sputtering target is a nickel base alloy sputtering target.
31. The sputtering target of claim 29, wherein the sputtering target is a cobalt base alloy sputtering target.
32. A nickel base or cobalt base alloy sputtering target having a percentage pass through flux of at least 60%.
33. The sputtering target of claim 32, having a percentage pass through flux of at least 65%.
34. The sputtering target of claim 32, having a percentage pass through flux of 65% to 80%.
35. The sputtering target of claim 32, having a percentage pass through flux of 65% to 75%.
36. The sputtering target of claim 32, wherein the sputtering target is a nickel base alloy sputtering target.
37. The sputtering target of claim 32, wherein the sputtering target is a cobalt base alloy sputtering target.
Type: Application
Filed: Feb 23, 2004
Publication Date: Aug 25, 2005
Inventor: Ranjan Ray (Tucson, AZ)
Application Number: 10/782,927
