Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2003-02-13
2004-12-28
Versteeg, Steven (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S298210, C204S298220, C204S298260
Reexamination Certificate
active
06835290
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the reduction of defects resulting from magnetron sputtering, and, more particularly to reducing and controlling the number of defects due to carbon inclusions on magnetic media.
2. Description of the Related Art
Computer disc drives commonly use components made out of thin films to store information. Typical disc drive thin film components include read-write head elements for reading and writing magnetic signals and magnetic media for writing magnetic signals onto. Conventional magnetic media is usually made by depositing a stack of thin film layers over each other as illustrated in FIG.
1
A.
FIG. 1A
is an illustration showing the layers of a conventional magnetic media structure including a substrate
103
, a seed layer
105
, a magnetic layer
107
, a protective layer
109
, and a lube layer
111
. The first layer of the media structure is the substrate
103
, which is typically made of nickel-phosphorous plated aluminum or glass that has been textured. The seed layer
105
, typically made of chromium, is the first thin film deposited onto the substrate
103
. The magnetic layer
107
, typically made of a magnetic alloy containing cobalt (Co), platinum (Pt) and chromium (Cr), is a thin film deposited on top of the seed layer
105
. The protective layer
109
, typically made of carbon and hydrogen, is a thin film that is deposited on top of the magnetic layer
107
. Finally the lube layer
111
, typically made of a polymer containing carbon (C ) and fluorine (F) and oxygen (O), is deposited on top of the protective layer
109
.
The durability and reliability of recording media is achieved primarily by the application of the protective layer
109
and the lube layer
111
. The protective layer
109
is typically an amorphous film called diamond like carbon (DLC), which contains carbon and hydrogen and exhibits properties between those of graphite and diamond. Thin layers of DLC can be deposited on disks using a variety of conventional thin film deposition techniques such as ion beam deposition (IBD), plasma enhanced chemical vapor deposition (PECVD), magnetron sputtering, radio frequency sputtering or chemical vapor deposition (CVD). During the deposition process, adjusting sputtering gas mixtures of argon and hydrogen varies the concentrations of hydrogen found in the DLC. Since typical thicknesses of protective layer
109
are less than 100 Angstroms, lube layer
111
is deposited on top of the protective layer
109
for added protection, lubrication and enhanced disk drive reliability. Lube layer
111
further reduces wear of the disc due to contact with the magnetic head assembly.
Although there are several techniques available for depositing DLC films as a protective layer
109
for magnetic recording media, as previously discussed, planar magnetron is the preferred method because of its wide spread use and good resultant film properties. However, there are problems associated with using planar magnetron sputtering including low yields resulting of the high number of defects found on the disk.
FIG. 1B
is an illustration showing a cross sectional side view of a conventional magnetron sputtering system including a target
110
, a target erosion zone
115
, a redeposition area
120
, a backing plate
125
, a coolant
130
, magnets
135
, a shunt
140
, a cathode
145
and a plasma
150
. Target
110
is a conventional sputtering target that is mounted to the backing plate
125
with indium. Magnets
135
are typically permanent magnets, which are used to confine plasma
150
near the surface of the target. Coolant
130
is typically water which is circulated behind backing plate
125
to cool the target while it is being sputtered. Shunt
140
diverts the magnetic field to the exterior of the target
110
causing electrons to be trapped and consequently causing sputtering of the target
110
.
The sputtering process removes target material from the target erosion zone
115
and deposits that material throughout the chamber including the substrate, chamber walls and target
110
. If reactive gases such as ethylene or methane are used then additional material other than the sputtered material is deposited throughout the chamber and substrate. The area on the target
110
where sputtered material gets redeposited and any film grows as a result of using reactive gasses is called the redeposition area
120
. This redeposited material, located in the redeposition area
120
, is sometimes ejected from the target
110
surface and bombards the substrate creating a defect, as explained in more detail below.
FIG. 1C
is a block diagram showing a front view of typical planar sputtering cathode including a target
110
, a target erosion zone
115
and a redeposition area
120
. The target erosion zone
115
, resembling a racetrack, is the area of the target
110
where material is sputtered off. The redeposition area
120
is the area on the target where carbon is redeposited during the sputtering process. Redeposition area
120
includes the rectangular area in the center of the target erosion zone
115
as well as the outer part of the target
110
between the target erosion zone
115
and the edge of the target
110
.
FIG. 1D
is an illustration showing a top view of a conventional magnetron sputtering system including a first chamber wall
155
, a second chamber wall
160
, a top view of eight planar cathode mounted sputtering targets with redeposition areas
120
, a top view of eight plasma patterns
165
and a top view of a transport mechanism
170
. First chamber wall and second chamber wall are both conventional walls of a vacuum chamber typically constructed out of stainless steel. The eight sputtering patterns represent the material sputtered from the erosion pattern
115
along with ionized sputtering gas atoms (argon). Transport mechanism
170
is a transportation device that moves disks or pallets full of disks in front of plasma
150
as further described with reference to
FIG. 1E
below.
FIG. 1E
is an illustration showing a front view of one side of a conventional magnetron sputtering system including four targets
110
with erosion zones and redeposition areas and a transport
170
located within a vacuum chamber
180
as well as disks
185
, a pallet
187
and a beam
191
. Vacuum chamber
180
is a conventional chamber, typically made of stainless steel, that houses targets
110
and transport
170
. Disks
185
are substrates
103
with seed layer
105
and magnetic layer
107
already on them and ready for depositing protective layer
109
to be deposited. Pallet
187
is typically made of aluminum and is machined to hold disks
185
in an upward position. Beam
191
is typically a stainless steel beam from which pallet
187
hangs and is transported in vacuum chamber
180
.
A significant disadvantage with conventional planar magnetron sputtering techniques, such as the one described with reference to
FIGS. 1A-1E
, is the high number of particulates that are produced on the substrate. If too many particulates are deposited on a substrate then the substrate is defective and cannot be used. Although defects resulting from excessive particulates on a substrate can occur when sputtering any material, the problem is enhanced when sputtering carbon.
Typical carbon defects include particulates containing carbon and traces of the sputtering gases used (typically argon) that range in size from sub micron to micron in diameter. These defects, which have a high content of SP2/SP3 hybridization, are often found embedded deeply into the NiP coated aluminum substrate manifesting themselves as glide height asperities and/or thermal asperities when the magneto-resistive recording head glides over them. The rate at which these defects are generated is time dependent. New or recently resurfaced targets have a low emission rate for these defects. As the targets are sputtered, the rate increases to a maximum, and then decreases over time to a stable level. For this example of planar magnetrons,
Barlow Stephen Eric
Cai Zhiwei
Reiter Jeffrey Shane
Castillo Jesus Del
Minisandram Raghunath S.
Seagate Technology LLC
Versteeg Steven
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