Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2000-03-23
2001-09-18
Nguyen, Nam (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
Reexamination Certificate
active
06290821
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for performing high-rate cathode sputtering of a target material for obtaining high purity thin film layers on substrate surfaces. More particularly, the invention relates to a method for performing high-rate sputter deposition onto static or moving substrates to obtain high purity thin film layers having desired physical, chemical, and/or mechanical properties. The invention has particular utility in the manufacture of magnetic recording media comprising a layer stack or laminate of a plurality of overlying layers.
BACKGROUND OF THE INVENTION
Magnetic recording media are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval purposes. A conventional, single-sided, longitudinal magnetic recording medium
1
in e.g., disk form, such as utilized in computer-related applications, is schematically depicted in FIG.
1
and comprises a non-magnetic substrate
10
, e.g., of glass, ceramic, glass-ceramic composite, polymer, metal, metal-ceramic composite, or metal alloy, typically an aluminum (Al)-based alloy such as aluminum-magnesium (Al—Mg), having at least one major surface
10
A on which a layer stack comprising a plurality of thin film layers constituting the medium are sequentially deposited. Such layers typically include a plating layer
11
, as of amorphous nickel-phosphorus (NiP), a polycrystalline interlayer
12
, typically of chromium (Cr) or a Cr-based alloy, a magnetic recording layer
13
, e.g., of a cobalt (Co)-based alloy, a protective overcoat layer
14
, typically containing carbon (C), e.g., a diamond-like carbon (DLC), and a lubricant topcoat layer
15
, typically of a perfluoropolyether compound.
According to conventional manufacturing methodology, a majority of the above-described layers constituting magnetic recording medium
1
are deposited by cathode sputtering, typically by means of multi-cathode and/or multi-chamber sputtering apparatus wherein a separate cathode comprising a selected target material is provided for deposition of each component layer of the stack and the sputtering conditions are optimized for the particular component layer to be formed. Each cathode comprising a selected target material can be positioned in a separate, independent process chamber, in a respective process chamber located within a larger chamber, or in one of a plurality of separate, interconnected process chambers each dedicated for deposition of a particular layer. According to such conventional manufacturing technology, media substrates, e.g., disks, are serially transported, in linear or circular fashion, depending upon the physical configuration of the particular apparatus utilized, from one sputtering target and/or process chamber to another for sputter deposition of a selected layer thereon. In some instances, again depending upon the particular apparatus utilized, sputter deposition of the selected layer commences only when the substrate (e.g., disk) deposition surface is positioned in complete opposition to the sputtering target, e.g., after the disk has fully entered the respective process chamber or area in its transit from a preceding process chamber or area, and is at rest. Stated differently, sputter deposition commences and continues for a predetermined interval only when the substrate is not in motion, i.e., deposition occurs onto static substrates. In other instances, however, substrate motion between adjoining process chambers or areas is continuous, and sputter deposition of each selected target material occurs onto moving substrates as the substrates pass by the particular cathode/target assembly.
Regardless of which type sputtering apparatus is employed for forming the thin layer stacks constituting the magnetic recording medium, it is essential for obtaining high recording density, high quality media that each of the component layers be deposited in a highly pure form. Film purity depends, inter alia, upon the purity of the atmosphere in which the film is grown; hence films are grown in as low a vacuum as is practicable. If the growth rate is maintained constant, purity can therefore be increased by more effective pumping away of contaminant gases which enter the process chamber, either by outgassing or desorption from the chamber walls and other system components, permeation into the chamber through seals such as O-rings, or as impurities in the sputter gas, e.g., argon (Ar). Alternatively, increased film purity can be obtained by increasing the rate of growth to decrease the ratio of impurity atoms in the film to those of the intended deposit.
However, practical limitations exist with respect to increasing the deposition speed obtainable with conventional sputtering apparatus and manufacturing technology, whether the deposition is performed onto static or moving substrates. For example, the available technology imposes certain limits on the output of RF and DC sputter power supplies and transport speed of the substrates from one process chamber to another (via air-locks, etc.). More specifically, available technology cannot provide more than about a ten-fold (“10×”) increase in sputtering power and more than about a three-fold (“3×”) increase in transport speed. Moreover, since in a moving substrate process/apparatus, a 10× increase in deposition rate requires a corresponding 10× in transport speed past the target sputtering surface in order to maintain the produced film thickness constant at the desired or target value, it becomes apparent that the requisite increase in transport speed becomes the limiting factor in obtaining higher deposition rates on moving substrates. Since only an about 3× increase in transport speed is practically possible, it is evident that only a modest improvement in film purity is possible by increasing the sputtering power applied to the target.
In addition to the above-described need for deposition rates of high purity layers consistent with the productivity requirements imposed by automated manufacturing technology, it is also essential that each of the deposited films exhibit respective physical, chemical, and/or mechanical properties, including, inter alia, proper crystal morphology necessary for high recording density media, e.g., polycrystallinity; good magnetic properties, e.g., coercivity and squareness ratio; chemical stability, e.g., inertness or corrosion resistance; and good tribological properties, e.g., wear resistance and low stiction/friction.
Accordingly, there exists a need for improved methodology for forming, by sputtering techniques, thin film layers of high purity and desired physical, chemical, and/or mechanical properties, which methodology provides for rapid, simple, and cost-effective formation of thin film layers suitable for use in the manufacture of magnetic recording media comprising a plurality of stacked layers deposited on a suitable substrate surface.
The present invention addresses and solves problems attendant upon the use of sputtering techniques for obtaining high purity thin film layers having requisite properties, such as are utilized, inter alia, in the manufacture of high recording density magnetic recording media, while maintaining full compatibility with all aspects of conventional automated manufacturing technology. Further, the methodology provided by the present invention enjoys diverse utility in the manufacture of a variety of devices and products requiring high purity thin film coating layers having desirable physical, chemical, and/or mechanical properties.
Disclosure of the Invention
An advantage of the present invention is an improved method for sputter depositing high purity thin film layers onto a substrate deposition surface.
Another advantage of the present invention is an improved method for sputter depositing high purity thin film layers having desired physical, chemical, and/or mechanical properties onto a substrate deposition surface.
Yet another advantage of the present invention is an improved method
McDermott & Will & Emery
Nguyen Nam
Seagate Technology LLC
VerSteeg Steven H.
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