Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Reexamination Certificate
1998-02-06
2001-01-16
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
C428S065100, C428S690000, C428S611000, C428S336000, C428S900000, C204S192200
Reexamination Certificate
active
06174582
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the field of data storage devices such as disk drives having thin film magnetic disks. More particularly, the invention relates to methods for fabricating thin film magnetic disks from nonmetallic substrates using a seed layer.
Background of the Invention
The thin film magnetic recording disk in a conventional hard disk drive assembly typically consists of a rigid substrate, an underlayer of chromium (Cr) or a Cr-alloy, a cobalt-based magnetic alloy deposited on the underlayer, and a protective overcoat over the magnetic layer. A variety of disk substrates such as NiP-coated Al—Mg, glass, glass ceramic, glassy carbon, etc., have been used. The microstructural parameters of the magnetic layer, i.e., crystallographic preferred orientation (PO), grain size and magnetic exchange decoupling between the grains, play key roles in controlling the recording characteristics of the disk. The Cr underlayer is mainly used to control such microstructural parameters as orientation and grain size of the cobalt-based magnetic alloy. When the Cr underlayer is deposited at elevated temperature (>150° C.) on a NiP-coated Al—Mg substrate a [200] preferred orientation is usually formed. This preferred orientation promotes the epitaxial growth of [11{overscore (2)}0] PO of the cobalt (Co) alloy, thereby improving the in-plane magnetic performance of the disk.
The use of glass substrates gives improved shock resistance and allows thinner substrates to be used. However, media fabricated glass substrates may have higher noise compared with those made on NiP-coated Al—Mg substrates under identical deposition conditions. The reason is that the nucleation and growth of Cr or Cr-alloy underlayers on glass and most non-metallic substrates differ significantly from those on NiP-coated Al—Mg substrate. It is for this reason that an initial layer on the substrate called a seed layer is used. The seed layer is formed between the alternate substrate and the underlayer in order to control nucleation and growth of the Cr underlayer and, therefore, the magnetic layers. Several materials have been proposed in the prior art as candidates for seed layers such as: Al, Cr, Ti, Ni
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P, MgO, Ta, C, W, Zr, AlN and NiAl on glass and non-metallic substrates. (See for example, Seed Layer induced (002) crystallographic texture in NiAl underlayers, Lee, et al., J. Appl. Phys. 79(8), April 1996, p.4902ff).
In order to control nucleation and growth of the Cr underlayer on alternate substrates, a variety of seed layers have been reported. H. Kataoka, et al., have reported that the deposition of a tantalum seed layer on glass substrates promotes the [200] orientation in the Cr underlayer which, in turn, promotes the [11{overscore (2)}0] PO orientation in the magnetic layer. (IEEE Trans. Magnetic. 31(6), Nov. 1995, p.2734ff). They compared Cr, Ta, W and Zr for use as seed layers using a fixed underlayer and magnetic layer. The magnetic alloy used in their study was a 27 nm thick ternary CoPtCr alloy. The underlayer was CrTi and was 100 nm thick. The purpose of adding Ti was to increase the lattice spacing for optimum matching with CoCrPt.
One method for improving the recording performance of a magnetic disk medium is the use of a CrTi underlayer, which was suggested by Michaelsen, et al. in U.S. Pat. No. 4,245,008. Matsuda, et al., also reported that the addition of Ti to Cr increases the lattice parameters of the Cr to enhance the epitaxial growth of the magnetic layer. (J. Appl. Phys. 79, pp. 5351-53 (1996)). They have also reported that the grain size of CrTi underlayer decreases with increasing the Ti concentration. It should be noted that although sputtered Ti has usually a very small grain size, it is not suitable for use as an underlayer or a seed layer as it promotes the <0001> orientation in the magnetic layer, thereby making it unsuitable for longitudinal recording.
Another means of affecting the crystal lattice orientation of the magnetic layer is to alter the character of the seed layer. For example, Magnetic and Recording Characteristics of Cr, Ta, W, and Zr Precoated Glass Discs, (IEEE Transactions on Magnetics, Vol. 31 No. 6, 1995, p. 2734) discloses depositing a Cr, Ta, W, or Zr pre-coat layer or seed layer with a thickness between 10 and 100 nm on a glass discussed followed by depositing a CrTi layer and a CoCrPt magnetic layer. The article discusses coercivity, coercive squareness and signal to noise ratio with different layer compositions. The seed layer was deposited using an in-line sputtering system with DC magnetron sources.
High Coercivity and Low Noise Media Using Glass Substrate, (IEEE Transactions on Magnetics, Vol. 30, No. 6, 1994, p. 3963) discloses depositing a thin film of NiP
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, TiSi2, Cr or C as a reactive layer before depositing conventional magnetic alloys. U.S. Pat. No. 4,632,883 to Howard et al. shows depositing a NiFe layer on a substrate to provide a magnetic flux return path. An underlayer of beta-Ta is deposited on the NiFe. A cobalt chromium tantalum magnetic layer is deposited on the underlayer.
U.S. Pat. Nos. 5,221,449 and 5,281,485 to Colgan et al., although not working in the magnetic disk field, show reactive sputtering of a Ta seed layer with thickness between 16 and 500C in a nitrogen containing environment and forming layers of alpha-Ta on the seed layer. After the Ta(N) layer is deposited, an “tantalum layer is deposited on the Ta(N) layer to form the actual seed layer.
U.S. Pat. Nos. 3,847,658; 3,664,943; and 3,663,408 to Kumagia et al. also not working in the magnetic disk field, disclose forming nitrogen doped beta tantalum resistor films using plasma sputtering The deposition takes place in a mixture of nitrogen and argon. The substrate is presputtered in a gaseous mixture prior to main sputtering, during which time the substrate is heated. The resulting resistor film has a resistance which is dependent upon the substrate temperature.
SUMMARY OF THE INVENTION
The invention provides a method of fabricating a thin film magnetic disk, comprising the steps of sputtering a seed layer of a refractory metal such as tantalum and a non-inert element such as nitrogen or oxygen; depositing a nonmagnetic underlayer onto the seed layer; and depositing a magnetic layer onto the underlayer.
In accordance with a further aspect of the invention of thin film magnetic disk is provided comprising: a substrate; a seed layer comprising a refractory metal such as tantalum deposited onto the substrate, the seed layer comprising at least 1 atomic-% of a second element such as nitrogen or oxygen; an underlayer comprising chromium or an alloy of chromium deposited onto the seed layer, the underlayer having a preferred orientation of [200]; and a magnetic layer deposited onto the underlayer, the magnetic layer having a [11{overscore (2)}0] PO.
By deposition of a refractory metal seed layer and a second reactive element, a magnetic thin film disk with high coercivity and improved longitudinal performance can be manufactured.
The seed layer may be used on metallic or non metallic substrates. The use of glass substrates is desired for improved shock resistance and to allow the usage of a thinner substrates. For optimum performance of a thin film magnetic disk on a glass substrate, for example, it is necessary to deposit a proper seed layer prior to deposition of the underlayer to promote the desired nucleation and crystallographic orientation of the Cr underlayer and the magnetic layer. This invention provides a seed layer, which is a thin layer of M(x), (preferably 10-30 nm in thickness), where M is a refractory metal with a high affinity to N with a structure similar to Ta, Nb, V, W, Mo or Cr; and x is a reactive element such as nitrogen or oxygen. When the second element is available in a gas form it may be introduced into the sputtering chamber along with the working gas which is typically argon. The sensitivity of the disk characteristics to variations in sputtering equipment
Bian Xiaoping
Duan Shanlin
Li Jinshan
Mirzamaani Mohammad
International Business Machines - Corporation
Kiliman Leszek
Knight G. Marlin
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