Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – Autogenously or by activation of dry coated particles
Reexamination Certificate
1994-08-25
2003-06-24
Lechert, Jr., Stephen J. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
Autogenously or by activation of dry coated particles
C264S109000, C425S352000, C425S812000
Reexamination Certificate
active
06582641
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the manufacture of sputtering targets, more particularly to the manufacture of sputtering targets from volatile and thermally unstable metal oxides, and even more particularly to the manufacture of indium oxide and tin oxide sputtering targets.
BACKGROUND OF THE INVENTION
Thin films are often produced using plasma sputtering techniques. Targets are used during the sputtering process as the source of material for the film being deposited onto a substrate. Targets made from volatile and thermally unstable metal oxides have been used to sputter thin films which exhibit properties useful in a variety of applications. For example, thin films of electro-optic materials, such as indium oxide and tin oxide, are known to exhibit high transmittance and low resistivity. These materials are commonly used as electro-conductive films in electroluminescence (EL) displays, liquid crystal displays, solar cells, defrost/defog heaters for airplanes and the like.
Known methods of making sputtering targets from such volatile and thermally unstable metal oxides have included consolidating, such as by hot-pressing, powders of the metal oxide target starting material, like In
2
O
3
and SnO
2
, into a target blank in an inert gas environment. Graphite or ceramic die assemblies with a die cavity typically have been used to press the powdered material. In a number of these prior processes, in particular prior processes for making indium oxide and tin oxide (ITO) targets, the metal oxide powder was loaded into the die cavity such that the powder was in direct contact with the walls of the die cavity. After consolidation, the resulting target blank was typically formed, such as by machining, grinding, polishing, etc., into a finished target. Detailed descriptions of a number of prior processes for making ITO sputtering targets may be found in U.S. Pat. Nos. 5,160,675 and 5,094,787 and in Japanese Patent Nos. 04341504, 04293769, 04154654, 04074860, 03199373 and 02043356.
The production of metal oxide targets, notably ITO targets, using graphite die assemblies have been known to exhibit a number of chronic problems associated with interaction between the powdered target starting material and the graphite material of the die assembly. The problems have included full reduction of the metal oxide to metal, at least in the form of a layer on the outer surface of the resulting target blank. Removal of this metal layer is generally necessary before the target is suitable for use. However, removal of the reduced metal, for example, a layer of indium or indium-tin alloy on an ITO target, often results in cracks in the target or fracturing of the target, which then must be scrapped. Also, the formation of cracks in the target reduces its resistance to fracturing during use. Lower pressing temperatures and/or shorter pressing times have been used in order to avoid the formation of a reduced metal layer while still using a graphite die assembly to press the powder. Pressing at lower temperatures and/or for shorter times typically results in poor consolidation of the powdered target starting material, which in turn results in targets with low density, low strength and/or a low resistance to fracturing (i.e., low toughness).
The density, strength and toughness of a target are often very important to the target's performance. Reportedly, high density ITO targets are required in order to sputter high quality ITO thin films, in particular, thin films free from particles. In addition, good strength and toughness are typically necessary to successfully form the ITO target blank into the desired final target shape. ITO targets with good toughness are also less likely to fracture during the sputtering process. Such fracturing can result in relatively large particles being deposited onto the substrate, often generating defects in the ITO film. Such defects in the ITO film can adversely affect the electro-optic properties of the film.
ITO and other such metal oxide sputtering targets produced with die assemblies made of a ceramic, such as Al
2
O
3
or ZrO
2
, are less likely to exhibit the problems noted above when graphite die assemblies are used. However, such ceramic die assemblies are generally more expensive to manufacture, less resistant to thermal shock and not as thermally conductive as comparable graphite die assemblies. Ceramic dies are thus more likely to crack during use, require longer heating and soaking times during the hot-pressing operation, and generally increase the costs of the target manufacturing process.
Therefore, there is a need for a more cost effective method and apparatus for manufacturing denser, stronger and tougher sputtering targets made from volatile and thermally unstable metal oxides.
SUMMARY OF THE INVENTION
The present invention is directed to a less expensive apparatus and process for consistently making acceptable sputtering targets by hot-pressing metal oxides that are volatile and thermally unstable at the hot-pressing temperature.
A general aspect of the present invention is directed to such an apparatus and process using a graphite die assembly.
A particular aspect of the present invention is directed to such an apparatus and process for consistently making relatively higher density, higher strength and tougher indium oxide and tin oxide (ITO) sputtering targets using a graphite die assembly.
According to the general principles of the present invention, a powder of a first material, also termed a target starting material, which includes metal oxide particles, is surrounded by a barrier material, as the first material is hot-pressed at an elevated temperature into a target blank in an oxygen-free, preferably inert, gas environment. The metal oxide particles in the powdered target starting material are volatile and thermally unstable at the elevated hot-pressing temperature. The barrier material is not in powder form, but is in the form of a solid sleeve which is thermally stable at elevated temperatures. In the present invention, first the barrier sleeve is placed in the die cavity of a graphite die assembly, followed by the target starting material. While in the die cavity encased by the barrier sleeve, the target starting material is bonded together (or sintered) by applying a sufficiently high temperature and pressure, for a long enough period of time, to produce a metal oxide sputtering target having a density, strength and toughness suitable for sputtering films of desirable quality. The barrier material sleeve is intended to substantially prevent a reducing gas from penetrating therethrough and reaching the unstable target starting material during the hot-pressing operation, thereby preventing any significant degree of full reduction of the metal oxide target material to metal. Preferably, the barrier material sleeve is also sufficient to substantially protect the graphite die assembly from attack and degradation by any dissociated components of the metal oxides during hot-pressing.
At elevated hot-pressing temperatures, the volatile and thermally unstable metal oxides break down or dissociate into oxygen gas and reduced oxides which may or may not be volatile, depending upon the temperature attained. For example, when the ITO material is subjected to hot-pressing temperatures of greater than or equal to about 850° C., the In
2
O
3
may begin to dissociate into free and reactive oxygen gas and other lower order indium oxides. Depending upon the hot-pressing temperature, some of these other indium oxides, such as In
2
O, may vaporize, while the balance of the indium oxide remains stable (i.e., in solid form). The dissociation of In
2
O
3
is evidenced by color changes in the ITO material. In
2
O
3
is yellow, while In
2
O is black. Typically, it is desirable for the target to have a uniform color which is indicative of a uniform composition. For at least some ITO targets, a uniform dark blue color is preferred. The present invention enables targets with such a uniform color to be consistently produced in a cost effective
Lo Chi-Fung
Turn John
Lechert Jr. Stephen J.
Praxair S.T. Technology, Inc.
Schwartz Turie A.
LandOfFree
Apparatus and method for making metal oxide sputtering targets does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for making metal oxide sputtering targets, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for making metal oxide sputtering targets will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3158019