Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2000-03-08
2001-12-11
Huff, Mark F. (Department: 1756)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192150, C204S192200, C204S298260, C204S298180, C204S298120, C204S298190, C204S298230, C204S298280, C204S298110
Reexamination Certificate
active
06328856
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for performing multilayer film deposition on a substrate surface, e.g., a disk-shaped substrate, which method and apparatus utilizes a rotating multiple magnetron cathode sputtering device. The invention has particular utility in the formation of superlattice structures, e.g., (Co/Pt)
n
and (Co/Pd)
n
superlattices, as part of automated manufacture of magnetic and magneto-optical (MO) data/information storage and retrieval media in disk form.
BACKGROUND OF THE INVENTION
Magnetic and magneto-optical 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, or metal alloy, typically an aluminum (Al)-based alloy such as aluminum-magnesium, having at least one major surface 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 underlayer
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., diamond-like carbon (DLC), and a lubricant topcoat layer
15
, typically of a perfluoropolyether compound.
Magneto-optical (MO) recording media (MO) similarly comprise a laminate of layers formed over a suitable substrate, e.g., a disk. By way of illustration, shown in
FIG. 2
is a single-sided MO medium
20
having a first surface magneto-optical (FSMO) layer configuration, wherein reference numeral
21
denotes a disk-shaped substrate formed of a material selected from, for example, aluminum (Al), plated aluminum, aluminum alloys, metals, metal alloys, glass, ceramics, and glass-ceramic composite materials. Formed on one surface
21
A of substrate
21
is a layer stack, comprising, in sequence from surface
21
A, a reflective, heat sinking layer
22
, comprising Al or an alloy thereof, e.g., AlCr, AlTi, AlCu, AlMo, etc., which layer may also serve to prevent laser beam transmission through the substrate when the latter is transparent, as in the case of glass or glass-based materials, and thus render surface
21
A opaque; a first dielectric material layer
23
, substantially transparent to the wavelength(s) of the at least one laser beam employed for writing and reading out information stored in the medium, typically selected from SiN
x
, AlN
x
, SiO
x
, and AlO
x
; a MO read-write layer
24
, for example, comprising a rare earth-transition metal thermo-magnetic (RE-TM) material having perpendicular magnetic anisotropy, large perpendicular coercivity H
c
at room temperature, and high Curie temperature T
c
, typically selected from TbFe, TbFeCo, TbDyFeCo, etc.; a second transparent dielectric material
25
typically selected from the same materials utilized for the first transparent dielectric layer
23
; a thin, amorphous, diamond-like carbon (DLC) protective overcoat layer
26
; and a lubricant topcoat layer
27
, typically comprising a fluoropolyether or perfluoropolyether material.
A promising new class of materials suitable for use as the magnetic recording layer
13
of the magnetic medium of
FIG. 1
or the MO read-write layer
24
of the magneto-optical (MO) medium of
FIG. 2
includes cobalt/platinum (Co/Pt)
n
and cobalt-palladium (Co/Pd)
n
multilayer stacks, also referred to as “superlattice” structures. As schematically illustrated in
FIG. 3
, such multilayer stacks or superlattice structures
30
comprise n pairs of alternating discrete layers of Co (designated by letter A in the drawing) and Pt or Pd (designated by letter B in the drawing), where n=an integer between about 10 and about 30. Superlattice
30
is typically formed by a suitable vapor deposition technique and can exhibit perpendicular magnetic anisotropy arising from metastable chemical modulation in the direction normal to the substrate. Compared to conventional cobalt-chromium (Co—Cr) alloys utilized in magnetic data storage/retrieval disk applications, such (Co/Pt)
n
and (Co/Pd)
n
multilayer or superlattice structures offer an economic advantage in facilitating room temperature deposition processing necessary for utilization of lower cost polymeric substrates. When utilized in MO disk-based applications, (Co/Pt)
n
and (Co/Pd)
n
superlattices offer superior corrosion resistance and blue wavelength response vis-à-vis conventional RE-TM alloys.
For example, a (Co/Pt)
n
multilayer stack or superlattice
30
suitable for use as the magnetic recording layer
13
of the magnetic recording medium of
FIG. 1
or the magneto-optical (MO) read-write layer
24
of the MO medium of
FIG. 2
can comprise a plurality of Co/Pt pairs, i.e., n=about 10 to about 30, e.g., 13, wherein each Co/Pt pair consists of a 3 Å thick Co layer adjacent to an 8 Å thick Pt layer, for a total of 26 separate or discrete layers. When utilized as a high recording density magneto-optical (HDMO) read-write layer
24
in e.g., a MO medium as illustrated in
FIG. 2
, such multilayer stacks or superlattice structures
30
are characterized by having a large perpendicular anisotropy and high coercivity, high squareness ratio (S) for a magnetic hysteresis (M-H) loop measured in the perpendicular direction, and high Kerr rotation angle for light of a particular wavelength region, e.g., blue or red light. By way of illustration, but not limitation, (Co/Pt)
n
and (Co/Pd)
n
HDMO superlattices, wherein n=about 10 to about 30 pairs of Co and Pt or Pd layers having thicknesses as indicated supra and fabricated, e.g., by means of techniques disclosed in U.S. Pat. No. 5,750,270, the entire disclosure of which is incorporated herein by reference, exhibit perpendicular anisotropy exceeding about 2×10
6
erg/cm
3
; coercivity as high as about 5,000 Oe; squareness ratio (S) of a M-H loop, measured in the perpendicular direction, of from about 0.85 to about 1.0; and carrier-to-noise ratio (CNR) of from about 30 dB to about 60 dB.
According to conventional methodologies and practices for automated manufacture of disk-shaped magnetic and MO media, when the various above-described thin film layers constituting the medium are deposited on the disk-shaped substrates, as by cathode sputtering techniques, it is generally advantageous to coat one disk at a time with the various requisite layers. However, the continuing requirement for increased storage density has increased the number of requisite layers and, as the number of requisite layers increases, it becomes impractical to build and operate multi-chamber cathode sputtering apparatus wherein each separate or discrete layer to be deposited requires a separate sputtering cathode/target assembly and associated vacuum chamber because either the system becomes unwieldy as a result of its great length in the case of linearly-arranged deposition systems, or in the case of circularly-configured systems, the diameter of the circle becomes too large.
The above-described difficulty associated with increasing numbers of requisite layers is magnified in the case of recording media comprising (Co/Pt)
n
or (Co/Pd)
n
multilayer stacks or superlattice structures where n=about 10 to about 30 layer pairs due to the very large number of individual layers required to be deposited. Currently available disk processing apparatus, whether pallet pass-by, single disk, or some variation thereof, do not have an adequate cathode count for single-pass coating of a large number of layers. Certain types of existing sputtering apparatus can be modified to perform multiple pass, back-and-forth, or up-and-down repetitive disk transport to fab
Chacko-Davis Daborah
Huff Mark F.
McDermott & Will & Emery
Seagate Technology LLC
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