Metal treatment – Stock – Nickel base
Reexamination Certificate
2001-04-25
2002-11-12
King, Roy (Department: 1742)
Metal treatment
Stock
Nickel base
C148S409000, C148S556000, C420S441000, C204S298130
Reexamination Certificate
active
06478895
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to nickel-titanium alloy sputter targets for use with magnetron sputtering systems to deposit nickel.
BACKGROUND OF THE INVENTION
With magnetron sputtering, magnets are located behind the cathode target in a manner as to cause closed magnetic field loops to cut through the cathode. A portion of the magnetic field loop is located adjacent the front face of the cathode. The combination of magnetic field and electric field causes electrons to spiral in long confined paths giving rise to a very dense plasma immediately adjacent to the face of the target material. This dense plasma facilitates an increased yield of material sputtered from the target.
One limitation to magnetron sputtering, however, is that this technique is not amenable to the deposition of ferromagnetic materials. A target of ferromagnetic material acts as a shunt and prevents magnetic field lines from cutting through the target and being located, as required, in front of the target. Therefore, materials such as iron and nickel cannot generally be magnetron sputtered. In order to light and maintain a plasma during the sputtering of ferromagnetic materials, such as pure nickel, it usually is necessary to limit the thickness of the nickel target to usually less than 3 mm. This thin target, however, provides only limited source material and thereby reduces the useful life of the target.
Some limited success in the magnetron sputtering of magnetic nickel has been achieved by using specially fabricated targets in which a thin layer of the ferromagnetic material plates onto a non-ferromagnetic base material. The layer is thin enough so as not to completely shunt the magnetic field, but again, the target is now very expensive and the source has a severely limited lifetime due to the reduced amount of source material.
The Curie temperature varies over a wide range for various materials. By properly forming an alloy of the ferromagnetic nickel with one or more other elements, the Curie temperature can be reduced from that of pure nickel to a temperature lower than the desired sputtering temperature. For example, Nanis, in U.S. Pat. No. 5,405,646, disclose binary systems of platinum, palladium, molybdenum, vanadium, silicon, titanium, chromium, aluminum, antimony, manganese and zinc. Similarly, Wilson, in U.S. Pat. No. 4,159,909, discloses the use of platinum, copper and tin to render nickel paramagnetic at room temperature. As far as known, targets manufactured from these alloys have not received widespread acceptance in the marketplace.
In addition, adding about 7 weight percent vanadium to nickel lowers the Curie temperature for obtaining paramagnetic properties at room temperature. The Curie temperature is the lowest temperature before spontaneous magnetization occurs. The Curie temperature separates the disordered paramagnetic phase from the ordered ferromagnetic phase. Stated in another way, at temperatures below a material's Curie temperature, that material is strongly magnetic or ferromagnetic. For temperatures at and above the Curie temperature, the magnetic properties disappear.
With its shift in Curie temperature, Ni-7 V (wt. %) has become the standard composition for use with direct current magnetron sputtering systems to deposit magnetic nickel. Nickel/vanadium (Ni/V) serves as a barrier/adhesion layer for under-bump metals to support flip chips, or C4 (collapsed, controlled, chip connection) assemblies. The flip chips allow high I/O counts, good speed and electrical performance, thermal management, low profile, and the use of standard surface mount and production lines for assembly. Unfortunately, Ni/V target materials are susceptible to high impurity concentrations and to cracking during fabrication of the target blanks. Moreover, Ni/V films can suffer problems during subsequent etching procedures.
Because magnetic nickel is a highly desirable thin film-for many microcircuit and semiconductor device applications, there is a need to develop a method for sputtering high purity magnetic nickel that does not suffer the above disadvantages.
SUMMARY OF THE INVENTION
The sputter target deposits nickel from a binary alloy. The binary alloy contains, by weight percent, 9 to 15 titanium and the balance nickel and incidental impurities. The binary alloy has, by weight percent, 35 to 50 TiNi
3
needle-like intermetallic phase and balance &agr;-nickel phase. The TiNi
3
needle-like intermetallic phase and &agr;-nickel phase are formed from a eutectic decomposition. The &agr;-nickel phase has a grain size between 50 and 180 &mgr;m. The binary alloy has a Curie temperature of less than or equal to a temperature of 25° C. and exhibits paramagnetic properties at temperatures of 25° C. or lower.
The method forms a binary nickel-titanium sputter target blank by first casting a binary alloy of the above composition into an ingot. The binary alloy has, by weight percent, 35 to 50 TiNi
3
intermetallic phase and balance &agr;-nickel phase. Then, dissolving the TiNi
3
intermetallic phase into a single &agr;-nickel phase at a temperature of at least 1000° C. prepares the alloy for hot working. Hot working the ingot at a temperature between 1000° C. and the ingot melting temperature forms the target blank, reduces the thickness by at least fifty percent and reduces the &agr;-nickel phase grain size to between 50 and 180 &mgr;m. Finally, cooling the target blank precipitates a needle-like TiNi
3
intermetallic phase in a &agr;-nickel phase matrix to form the final microstructure.
DETAILED DESCRIPTION
The present invention provides the specific alloying concentration for this binary alloy with a method of preparing targets that facilitates magnetron sputtering of nickel. Magnetron sputtering of nickel can be accomplished by using a binary nickel alloy target material having a properly selected titanium alloying concentration in order that the alloy has a Curie temperature at or below room temperature (25° C.), thereby making the material paramagnetic at room temperature.
A series of incremental tests determined that about 9 weight percent was the minimum amount of titanium necessary to make the alloy paramagnetic at room temperature. For purposes of this specification, all composition's units are expressed in weight percent, unless specifically noted otherwise. This alloy allows the thickness of the target to be increased significantly as compared to a pure nickel target, thereby decreasing the sputtering cost per wafer. With the lower Curie temperature, the alloy is non-ferromagnetic at the sputtering temperature, and is therefore amenable to magnetron sputtering.
Alloying about 9 to 15 weight percent titanium with the balance nickel and incidental impurities produces a sputtering target with paramagnetic properties at room temperature. Advantageously, the alloy contains about 9.5 to 12 weight percent titanium. Most advantageously, the alloy has a nominal composition of about ten weight percent. In addition, advantageously, limiting impurities to less than 0.1 percent provides commercially pure properties. Most advantageously, the target contains less than 0.01 percent impurities.
The melting of the nickel and titanium source material advantageously occurs under a vacuum or protective atmosphere. Most advantageously, a vacuum furnace, such as a semi-continuous vacuum melter (SCVM) can melt the source material in a steel, graphite or ceramic mold. Advantageously, the vacuum is about 1.0×10
−4
mTorr to about 10.0 mTorr.
Advantageously, the binary alloy casting occurs under an atmosphere pressure of less than about 5 mTorr. For example, vacuum atmospheres having a pressure of about 1 mTorr to about 5 mTorr are effective for limiting uncontrolled oxidation of the melt. In addition, pouring into molds having a low pressure protective atmosphere is another procedure for limiting oxidation. To maintain low impurities, it is important to cast the alloy under a controlled atmosphere such as under a protective argon, helium or other Group VIII gas or combination of gases. For
Gilman Paul S.
Hunt Thomas J.
Koenigsmann Holger J.
Biederman Blake T.
King Roy
Praxair S.T. Technology, Inc.
Wilkins, III Harry D
LandOfFree
Nickel-titanium sputter target alloy does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Nickel-titanium sputter target alloy, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Nickel-titanium sputter target alloy will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2919132