Metal fusion bonding – Process – With shaping
Reexamination Certificate
1999-08-03
2001-09-04
Ryan, Patrick (Department: 1725)
Metal fusion bonding
Process
With shaping
C228S136000, C204S192380, C204S298120
Reexamination Certificate
active
06283357
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method of fabricating hollow cathode magnetron sputter targets for use in the physical vapor deposition of thin films on semiconductor devices.
BACKGROUND OF THE INVENTION
In the semiconductor industry, there is a constant need for faster and smaller integrated circuit chips to manage an ever-growing assortment of sophisticated applications. Thus, the semiconductor industry is edging toward mass production of circuit devices with sub-0.25 &mgr;m features. To produce these devices, significant changes in all aspects of manufacturing are needed, including new materials and manufacturing technologies. The sub-0.25 &mgr;m features, along with their increased aspect ratios, compared to current devices, present a significant challenge to current physical vapor deposition (PVD) and metallization technologies.
A new development in physical vapor deposition (PVD) technology that addresses the challenges of the sub-0.25 &mgr;m devices is the hollow cathode magnetron (HCM), which is a high density plasma device for use as an ionized PVD sputter target source for semiconductor device fabrication. This HCM sputtering source in an ionized PVD application is a low-cost, high-performance alternative to traditional PVD technologies.
HCM technology, when used in an ionized PVD environment, facilitates more efficient production of ions of target material that are directed at right angles to a substrate being coated for efficient via filling. This technology provides a highly directional deposition that is relatively unaffected by feature width. It offers excellent bottom coverage of high-aspect-ratio features without the use of a collimator. The HCM sputter target, as currently designed, has a cup shape. HCMs are an attractive alternative to planar cathodes because the cup design enables superior filling of high aspect ratio features. A special arrangement of oriented permanent magnets is mounted on the exterior wall of the target, which creates a high-density plasma inside the target region. This HCM design allows deposited neutrals (i.e., neutral polarity atoms) to be recycled until they are ionized by the high-density plasma. A longer target lifetime results from this recycling effect. Other HCM advantages include longer shield life, extended maintenance intervals and significantly lower cost of ownership than other sputtering technologies. This deposition technology meets and exceeds the demands of the semiconductor industry for sub-0.25 &mgr;m devices. Specifically, HCM ionized source technology enables high quality Ta, TaN, Cu, Ti, TiN, and other films to be deposited into sub-0.25 &mgr;m dual damascene structures.
HCM targets have generally been fabricated as monolithic targets by casting a billet of target material and then forming the billet into the specially designed HCM target by known metal forming techniques, such as forging or deep drawing. The formed target is then machined to final dimensions. The target materials are generally quite expensive and heavy. As target dimensions continue to increase to meet industry demands, the monolithic targets are becoming more expensive, heavier and more difficult to handle.
Furthermore, erosion of particles from the sputter target surface generally occurs in a relatively narrow ring-shaped region, called the “racetrack region.” Only the portion of the total target material in the racetrack region is consumed before the target must be replaced. For monolithic HCM sputter targets, typically only 25% or less of usable target material falls within the racetrack region and is therefore actually sputtered. The large amount of remaining expensive, usable target material is either wasted or must be recycled.
There is thus a need to develop a method for fabricating inexpensive, lightweight HCM targets to accommodate the continuing need for increased target dimensions, and further to develop such a target having a higher percentage utilization of sputter target material.
SUMMARY OF THE INVENTION
The present invention provides a clad HCM sputter target having a sheet of lightweight and/or inexpensive, low purity cladding material bonded to a plate of sputter target material, the sputter target material preferably having a fine, uniform microstructure. This clad HCM sputter target is lighter in weight and/or less expensive than monolithic HCM sputter targets and provides a greater percentage utilization of sputter target material. To this end, and in accordance with the principles of the present invention, a sputter target material is formed into a plate, such as by pressing and/or rolling, and preferably heat treated to develop a fine, uniform microstructure. This plate of target material is then bonded to a sheet of lightweight and/or inexpensive cladding material, such as by diffusion bonding, explosion bonding, friction welding, epoxy bonding, soldering or brazing, to form a clad target assembly having a lighter weight and/or costing less than monolithic sputter targets of equal dimensions. Preferably, the bonding method is one in which the microstructure of the target material is not substantially altered, such as explosion bonding.
The clad target assembly is then formed into a HCM sputter target, such as by deep drawing, forging, hydroforming, explosive forming, punching, roll forming, stretch forming or electromagnetic forming. The HCM sputter target is preferably formed by deep drawing, whereby the microstructure of the target material is not significantly altered. The total amount of sputter target material used to form the clad HCM sputter target of the present invention is less than with monolithic assemblies, yet the same amount of sputter target material is available in the racetrack region for sputtering.
A flange of relatively inexpensive, commercial grade material may then be attached to the HCM sputter target, such as by mechanical joints, E-beam welding, brazing or epoxy bonding.
There is thus provided a HCM sputter target assembly capable of meeting increased target dimension requirements without becoming prohibitively expensive or heavy. There is further provided a HCM sputter target with increased percentage utilization of sputter target material.
These and other objects and advantages of the present invention shall become more apparent from the accompanying drawings and description thereof.
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Kulkarni Shailesh
Lam Raymond K. F.
Sica Tony
Biederman Blake T.
Johnson Jonathan
Praxair S.T. Technology, Inc.
Ryan Patrick
LandOfFree
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