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`
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`5,527,605
`[11] Patent Number:
`Unlted States Patent
`
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`Jun. 18, 1996
`[45] Date of Patent:
`Doessel et al.
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`[19]
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`lllllllllllllllllllllllllllIlllllllllllllllllll|||||l|l|lllllllllllllllllll
`U8005527605A
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`
`
`FOREIGN PATENT DOCUMENTS
`
`
`
`
`
`
`11/1984 European Pat. on. .
`0126589
`P t. Off. .
`0217096
`4/1987
`E
`
`
`
`
`
`10/1987 15:33:: Pit. Off. .
`0225141
`
`
`
`
`
`
`
`
`
`
`7/1987 European Pat. on. .
`0227480
`7/1987 European Pat. 011°.
`0229292
`.
`
`
`
`
`
`9/1983 Germany .
`3309483
`
`
`
`3536210
`4/1986 Germany .
`6/1988 Germany ,
`3642161
`
`
`
`
`
`£2332: 12/32; is:
`
`
`
`12/1985
`Japan.
`243840
`048148
`3/1986
`Japan .
`
`
`
`184940
`7/1988
`Japan .
`
`
`
`
`
`
`63-188843
`8/1988
`Japan.
`
`
`
`
`7/1986 United Kingdom.
`2169742
`OTHER PUBLICATIONS
`
`
`
`
`
`
`
`
`S. Takayarna, et al., “Magnetic and Magneto—Optical Prop~
`rties of Tb—Fe—Co Amorphous Films”, J. Appl. Phys. 61 (7),
`
`
`
`
`
`
`
`.
`.
`e
`.
`
`
`
`
`
`
`APE 1: 19314411153103“ Immune 01’ PhYSICS: PP- 2610—2616-
`
`
`
`
`
`
`
`S. Asari, et al. “Preparation of a Magneto—Optical Disk
`Using a Rare Earth—Transition Metal Alloy Target”, J. Vac.
`
`
`
`
`
`
`
`
`
`
`
`
`
`Sci. Technol. A5(4), Jul/Aug. 1987, pp. 1949—1951.
`
`
`
`
`
`
`E- Schultheiss, ot 81-, “Production Technology for Magno-
`
`
`
`
`
`
`tooptic Data Storage Media”, Solid State Technology/Mar.
`
`
`
`1988, pp. 107_112_
`
`
`
`(List continued on next page)
`P .
`k Kil
`E
`.
`L
`
`
`
`Anm‘z’y Xam’"”}.esze F 1 “‘SLHL d
`
`
`
`”may,
`"m— 0 By
`gen” 0’
`at “er
`
`
`
`
`
`
`
`
`
`
`A magnetooptic layer made from rare-earth metals and
`
`
`
`
`
`
`
`transition metals exhibits a gradient in the alloy composition
`
`
`
`
`
`
`
`
`
`
`over the layer depth, and has a coercive field strength of
`
`
`
`
`
`
`
`more than 8 kOe in the temperature range of AT=100° C.
`
`
`
`
`
`around the compensation temperature Tm," . The layer is
`fabricated with a dynamic sputter process}: in which the
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
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`substrates to be coated are led past one or a plurality of
`
`
`
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`
`
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`sputter targets, arranged in a common plane parallel to the
`
`
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`
`
`
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`track of the substrates. A mask is located between the sputter
`
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`targets and the substrates.
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`
`[75]
`
`
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`
`[54] MAGNETOOPTIC LAYER AND A PROCESS
`
`
`FOR ITS FABRICATION
`Inventors: Karl-Friedrich Doessel, Wiesbaden;
`
`
`
`
`
`
`Berndé‘isscher, WiesbadE-Nordenstadt;
`chlosser, Kel
`.
`Ernst
`eim;
`
`
`
`Guenther Schmidt, Niedernhausen, all
`
`
`
`of Germany
`
`
`
`
`
`
`
`
`
`[73] Assignee: Hoechst Aktiengesellschaft, Frankfurt
`
`
`
`am Mama Germany
`
`
`
`_
`
`
`
`
`[21] APPL N°-- 2241190
`.
`,
`.
`
`
`
`[22]
`Filed‘
`Apr 7 1994
`
`
`
`
`
`
`
`Related U'S' Application Data
`.
`.
`
`
`
`
`
`
`
`
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`
`
`[63] Continuation of Ser. No. 785,880, Nov. 4, 1991, abandoned,
`
`
`
`
`which is a continuation of Ser. No. 480,496, Feb. 16, 1990,
`
`abandoned.
`_
`.
`.
`.
`.
`
`
`
`
`
`
`Forflgn APP‘lcanon Priority Data
`[30]
`
`
`
`
`
`
`
`
`[DE]
`Germany .......................... 39 04 611.7
`Feb. 16, 1989
`6
`
`
`
`
`
`
`
`................................ G11B 5/66; (1331233253 151/150
`[51]
`Int. Cl.
`
`
`
`
`
`
`
`
`
`.......................... 428/332; 428/336; 428/610;
`[52] us. Cl.
`
`
`
`
`
`428/684 ML; 428/684 SC; 428/684.6 R;
`
`
`
`
`
`428/684 NF; 428/684 MM; 428/684 T;
`428/684 RF; 428/684 XS; 428/900; 428/638;
`
`
`
`
`
`
`
`
`
`
`[58] Field of Search ..................... 428/694 ML, 694 SC,
`
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`
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`
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`
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`428/694 GR, 900, 694 NF, 694 MM, 694 IS,
`
`
`
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`
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`
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`
`
`
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`
`
`332, 336, 610, 694 XS; 369/13; 204/192],
`1922, 19225
`
`
`
`
`[56]
`
`
`4,293,621
`
`4,649,519
`4,670,356
`
`4,694,358
`
`4,740,430
`
`
`
`
`.
`
`References Cited
`U S PATENT DOCUMENTS
`
`
`'
`'
`
`
`
`
`................................... 428/694
`10/1981 Togami
`
`
`
`
`
`
`365/122
`3,1987 Sun et al.
`...........
`6/1987 Sato et al.
`428/693
`
`
`
`
`
`
`
`9/1987 Muchnik et al. ............. 360/59
`
`
`
`
`
`
`4/1988 Frankenthal et al.
`................... 428/630
`
`
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`
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`
`
`
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`
`
`
`
`33 Claims, 6 Drawing Sheets
`
`
`
`3
`
`
`3
`
`/
`
`9min
`S.E /’ / \/ \/5\ \\
`S,E
`/>
`/I // \
`/
`\
`\\
`V;
`..
`
`\
`
`2
`
`\
`
`
`\
`I
`\
`
`
`I pm
`
`
`
`\L 1
`*3 $0:
`bit/x 1:;21
`
`
`
`
`: ~ _ , of‘__ , 3,
`5
`k
`
`
`
`
`1
`~ ’/ \\— (I
`I
`k3
`k2
`
`kL
`
`Page 1 of 14
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`APPLIED MATERIALS EXHIBIT 1070
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`Page 1 of 14
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`APPLIED MATERIALS EXHIBIT 1070
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`

`

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`5,527,605
`Page 2
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`
`OTHER PUBLICATIONS
`
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`
`
`Masahiko Takahash et a1., “Study on Recorded Domain
`
`
`
`
`
`Characteristics of Magneto—Optical tbFeCo Disks,” Journal
`
`
`
`
`
`
`
`
`
`
`of Applied Physics, vol. 64 (1), Jul. 1, 1988, pp. 262—269.
`
`
`
`
`
`
`
`S. Takayama et a1., “Magnetic and Magneto—Optical Prop-
`
`
`
`
`
`
`erties of Tb—Fe—Co Amorphous Films,” Journal of Applied
`
`
`
`
`
`
`
`Physics, vol. 61 (7), Apr. 1, 1987, pp. 2610—2616.
`
`
`
`
`
`
`
`
`S. Asari et 3.1., “Preparation of a Magneto—Optical Disk
`
`
`
`
`
`
`
`Using a Rare Earth—Transition Metal Alloy Target,” J. Vac.
`
`
`
`
`
`
`
`
`Sci. Technol., v01. A 5 (4), Jul./Aug. 1987, pp. 1949—1951.
`
`
`
`
`
`
`E. Schultheiss, “Production Technology for Magnetooptic
`
`
`
`
`
`
`
`
`Data Storage Media," Solid State Technology, Mar., 1988,
`
`
`pp. 107—112.
`
`
`
`
`
`
`M. H. Kryder et al., “Stability of Perpendicular Domains in
`
`
`
`
`
`Thermomagnetic Recording Materials,” pp. 236—241.
`
`Page 2 of 14
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`Page 2 of 14
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`US. Patent
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`Jun. 18, 1996
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`Sheet 1 0f 6
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`5,527,605
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`FIB.2
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`US. Patent
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`Jun. 18, 1996
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`Sheet 2 0f 6
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`5,527,605
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`*7.
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`SE
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`HM
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`SE
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`FIB.3
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`t
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`US. Patent
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`Jun. 18, 1996
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`Sheet 3 of 6
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`5,527,605
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`2
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`5d
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`2
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`Ba
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`'
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`FIG.SA
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`FIG.SB
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`2
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`6c
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`FIG.5C
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`H850
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`US. Patent
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`Jun. 18, 1996
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`Sheet 4 of 6
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`5,527,605
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`FIG.6A
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`FIG.EB
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`FIB.5C
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`FIB.BD
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`US. Patent
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`Jun. 18, 1996
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`Sheet 5 of 6
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`5,527,605
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`TWP
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`FIG]
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`WC]
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` ‘
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`"
`FIG.8
`~
`-
`Tcomp1~K__——H‘Tcnmp2
`
`TI'C]
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`US. Patent
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`Jun. 18,1996
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`Sheet 6 of 6
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`5,527,605
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`I6
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`I5
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`l3
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`l4
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`l2
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`I3
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`‘
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`FIG.9
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`Page 8 of 14
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`

`

`
`1
`MAGNETOOPTIC LAYER AND A PROCESS
`
`
`
`FOR ITS FABRICATION
`
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`5,527,605
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`2
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`To avoid or prevent this disadvantage, the addition of
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`various anticorrosive substances or elements, respecitvely,
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`to the magnetooptic allows is recommended (GB-A-2,175,
`160; EPvAl-0,229,292). The addition of such substances to
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`the entire volume of the magnetooptic recording layer
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`improves the corrosion resistance, but at the expense of
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`other desired properties, such as high Kerr angle, high
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`coercive field strength, high writing sensitivity, high signal-
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`to-noise ratio and the like. In the magnetooptic recording
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`medium according to EP-Al-0,229,292, further anticorro-
`sive substances are added to a first substance in order to
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`achieve an enrichment of the anticorrosive substances at the
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`surface of the recording medium. In this process it
`is
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`disadvantageous that the desirable magnetooptic properties
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`can be even more strongly impaired through the addition of
`further elements.
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`Thin banier layers made from anticorrosive substances
`are described in U.S. Pat. No. 4,740,430. A discrete mul-
`
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`tiple—layer structure of the magnetooptic recording medium
`
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`is produced.
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`In order to achieve a high storage density of the magne-
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`tooptic recording materials, it is necessary to produce stable
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`domains which are as small as possible in the magnetooptic
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`recording layer. A precondition for this is that the product of
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`the saturation magnetization Ms and the coercive field
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`strength HC be as large as possible (Kryder et al., SPIE
`
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`Proc., Vol. 420, page 236 (1983)). For known magnetooptic
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`recording materials, a product of the saturation magnetiza-
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`tion and coercive field strength which is as large as possible
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`is achieved only in a narrow temperature range around the
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`compensation temperature Temp.
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`More recently, magnetooptic recording materials have
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`been described that are suitable for the direct overwriting of
`information (U.S. Pat. No. 4,694,358, U.S. Pat. No. 4,649,
`
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`
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`519, EP-A2-0,225,141, EP-A2—0,227,480 and EP-A2-0,217,
`
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`096). In all cases, use is made of a construction of the
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`magnetooptic recording medium in which two separate
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`layers having different magnetic properties are stratified one
`above the other.
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`The publications EP-A2—0,217,096 and EP-A2—0,227,480
`
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`describe magnetooptic recording media in which a thermally
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`insulating interlayer is present in the construction between
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`the magnetooptic recording layer and a magnetic layer
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`which generates a polarizing field. In the remaining citations
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`from the literature mentioned above such interlayers are
`recommended because otherwise there can be dilfusion of
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`alloying components into the magnetic layer. Naturally, such
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`a difiusion of alloying components alters the properties of
`
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`the magnetooptic recording medium.
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`Another way to increase the long-term stability of a
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`magnetooptic storage device is proposed in the process
`
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`
`
`in
`according to German Offenlegungsschrift 3,642,161,
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`which, during and/or after the successive deposition of a
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`dielectric layer, a magnetooptic layer and a cover layer on a
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`substrate, a curing treatment is carried out in a virtually dry
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`atmosphere in a temperature range from room temperature
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`to just below the crystallization temperature of the magne-
`
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`tooptic layer.
`
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`There is known from Japanese Published Specification
`
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`
`
`188,843/88 a process for fabricating a photomagnetic disk,
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`in which the photomagnetic recording layer is sputtered on
`
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`in such a way that the substrate moves past three targets
`made from rare-earth metal and transition metal. The central
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`target
`is arranged parallel
`to the transport track of the
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`substrate, with a target being mounted in front of and behind
`
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`the central target in the direction of transport of the substrate
`
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`5
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`10
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`15
`
`20
`
`25
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`
`This application is a continuation of application Ser. No.
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`
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`07/785,880, filed Nov. 4, 1991, now abandoned, which is a
`continuation of Ser. No. 07/480,496, filed Feb. 16, 1990,
`
`
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`
`
`
`
`
`
`now abandoned.
`
`
`BACKGROUND OF THE INVENTION
`
`
`
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`
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`The present invention concerns a magnetooptic layer
`
`
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`
`
`made from an amorphous rare-earth/transition metal alloy
`
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`
`
`having magnetic anisotropy, the easily magnetizable axis of
`
`
`
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`which is perpendicular to the surface.
`
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`Amorphous magnetooptic materials having such a
`
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`uniaxial perpendicular anisotropy are known. The most
`
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`
`
`widespread are alloys of rare-earth metals, such as gado-
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`linium, terbium and dysprosium, with transition metals, such
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`as iron and cobalt, to which yet further components may be
`
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`added. The magnetic properties of these alloys depend very
`
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`strongly on their composition.
`
`
`
`
`
`German Olfenlegungsschrift 3,309,483 describes magne-
`
`
`
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`
`
`
`tooptic recording materials made from amorphous ternary
`
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`
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`alloys based on terbium, iron and cobalt. When the cobalt
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`components are equal to or less than forty percent of the
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`alloy there is an approximately linear relationship of both
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`the angle of the Kerr rotation and the Curie temperature
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`relative to the cobalt content of the alloys. The same holds
`
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`
`
`for the magnetooptic recording media described in German
`30
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`Offenlegungsschrift 3,536,210 and in an article in Journal of
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`Applied Physics, 64:262.
`(1988). Thus, a magnetooptic
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`recording medium made from an amorphous film composed
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`of rare—earth/transition metals and having a compensation
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`temperature of 50° to 200° C., or a compensation tempera-
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`ture of 0° C. or less, is known from German Ofl'enlegungss-
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`chrift 3,536,210. When an amorphous film of the Tb-Fe-Co
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`system is used, the compensation temperature of 50° to 200°
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`C. is achieved with a composition having 24 to 30 atom
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`percent terbium, 7 to 20 atom percent cobalt, the remainder
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`being iron, while a compensation temperature of 0° C. or
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`less is attained with a composition having 18 to 21.5 atom
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`percent
`terbium, 8 to 10 atom percent cobalt and the
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`remainder being iron. These relationships are explained in
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`detail in German Offenlegungsschrift 3,536,210.
`45
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`Starting from page 2610 of an article in Journal of
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`Applied Physics, 61 (1987) and from page 1949 of an article
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`in J. Vac. Sci. Technol. A5 (1987), it is pointed out that, for
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`example, increasing the terbium content by 1 atom percent
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`can shift the compensation temperature by up to 40° C.
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`The control of the composition of the layer is therefore
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`very important for design of the sputtering process and of a
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`corresponding production plant, as discussed in Solid State
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`Technology, March 1988, page 107.
`In general, it is indicated that the deviation of the terbium
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`concentration from the mean concentration in the layer
`volume is to amount to less than 0.5%.
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`The uniformity sought in the composition of the alloy
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`components in the depth profile of a magnetooptic recording
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`layer, together with the attempts to hold the alloy compo-
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`sition constant over the width and length of the coating
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`require a high degree of effort, e.g., the disks to be coated
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`rotate during the coating process about their own axis of
`rotation, and at the same time travel around on a sizeable
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`circuit.
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`A further disadvantage of known magnetooptic recording
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`materials is their high corrodibility.
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`Page 9 of 14
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`5,527,605
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`3
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`at a predetermined angle with respect to the central target.
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`The composition of the photomagnetic recording film thus
`obtained on the substrate is uniform.
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`SUMMARY OF THE INVENTION
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`It is therefore an object of the invention to provide a
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`magnetooptic layer, having an easily magnetizable axis
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`perpendicular to the surface of the layer, which can be
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`fabricated simply and reproducibly, has a high corrosion
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`resistance with respect to moisture and/or oxygen, makes
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`possible high storage densities, and is suitable for direct
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`overwriting.
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`It is a further object of the invention to provide a process
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`of fabrication of such a magnetooptic layer.
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`These and other objects according to the invention are
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`achieved by a magnetooptic layer comprising an amorphous
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`rare-earth/transition metal alloy having magnetic anisotropy
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`the easily magnetizable axis of which is perpendicular to the
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`surface, wherein the magnetooptic layer exhibits a gradient
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`in the concentration of the composition with depth and has
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`a coercive field strength of more than 8 kOe in the tempera-
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`ture range of AT=100° C. around the compensation tem-
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`perature Twmp.
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`Other objects, features and advantages of the present
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`invention will become apparent from the following detailed
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`the
`description. It should be understood, however,
`that
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`detailed description and the specific examples, while indi-
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`cating preferred embodiments of the invention, are given by
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`way of illustration only, since various changes and modifi-
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`cations within the spirit and scope of the invention will
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`become apparent to those skilled in the art from this detailed
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`description.
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`5
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`10
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`The invention is explained in more detail below with
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`reference to the drawings, in which:
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`FIG. 1 shows a schematic representation of the arrange-
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`ment of a target in a plane parallel
`to the track of the
`substrates to be coated;
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`FIG. 2 shows a diagrammatic arrangement of a plurality
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`of targets in a common plane parallel to the track of the
`substrates to be coated;
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`FIG. 3 shows, diagrammatically, the composition of a
`magnetooptic layer based on rare-earth metals RE and
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`transition metals TM over the depth of the layer;
`FIG. 4 shows a mask characteristic of a mask inserted
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`between target and substrate, and the sputter rates over the
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`depths of the magnetooptic layer;
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`FIGS. 5A to 5D show a top view of various masks with
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`different mask openings, which are arranged between the
`targets and the substrates;
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`FIGS. 6A to 6D show, schematically, the composition of
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`magnetooptic layers over the layer depths, which are
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`obtained with the masks according to FIGS. 5A to 5D;
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`FIG. 7 shows the relationship between the coercive field
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`strength He and the temperature T of various magnetooptic
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`layers;
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`FIG. 8 shows the relationship between the reciprocal 1/Hc
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`of the coercive field strength and the temperature T of the
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`magnetooptic layers according to FIG. 7; and
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`FIG. 9 shows a magnetooptic recording medium produced
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`according to the present invention.
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`Page 10 of 14
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`4
`DETAILED DESCRIPTION OF THE
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`PREFERRED EMBODIMENTS
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`A magnetooptic recording layer according to the present
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`invention exhibits a gradient in the concentration of the
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`composition with depth and has a coercive field strength of
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`more than about 8 kOe in the temperature range of AT=1 00°
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`C. around the compensation temperature Temp is provided.
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`In one embodiment of the present invention, the alloy
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`consists of terbium, gadolinium, dysprosium,
`iron and
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`cobalt, or of terbium, dysprosium, iron and cobalt. Further-
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`more, the alloy can consist of terbium, gadolinium, dyspro-
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`sium and cobalt, or of terbium, dysprosium and cobalt alone.
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`One of the alloys of the magnetooptic layer expediently has
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`a composition according to the formula
`(pryl—x)y (FBZCOI-z) l-y
`
`where
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`0§x§l,
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`0.15éyé030
`and
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`0.60ézél.
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`In a frnther embodiment of the invention, there is present
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`in one or both surfaces of the magnetooptic layer a concen—
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`tration of rare-earth metals which is enhanced by compari-
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`son with the average concentration of the composition, i.e.,
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`in which the concentration of rear-earth metals is greater
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`than the average concentration of rare-earth metals in the
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`composition.
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`It is likewise possible that there is present in one or both
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`surfaces of the magnetooptic layer a concentration of tran-
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`sition metals which is enhanced by comparison with the
`average concentration, i.e., in which the concentration of
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`transition metals is greater than the average concentration of
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`transition metals in the composition.
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`A magnetooptic layer according to the invention is a
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`component of a magnetooptic recording medium in which
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`the magnetooptic layer is arranged between two barrier
`layers made from SiN, SiON, SiAlON, AlN, AlON, an oxide
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`of tantalum or an oxide of niobium for protection against
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`moisture and/or oxygen. One barrier layer is covered on one
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`side by a substrate, and the other by a metallic mirror, a
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`lacquer or adhesive layer and a second substrate.
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`The process for the fabrication of a magnetooptic layer is
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`distinguished by the fact that the rare-earth/transition metal
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`alloy is sputtered on dynamically by transporting the sub-
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`strate to be coated relative to one or a plurality of sputter
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`targets which are arranged in a common plane.
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`The magnetooptic layers according to the invention pro-
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`a directly overwritable magnetooptic
`recording
`vide
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`medium, in a system in which a modulation of the magnetic
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`field or a modulation of the laser energy takes place during
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`the writing of the information.
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`Represented diagrammatically in FIG. 1 is an arrange-
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`ment for the fabrication of a magnetooptic layer on sub-
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`strates 3, 4 and 5, which are led past a sputter cathode in the
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`form of target 1 in the direction of arrow A. Located between
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`target 1 and the plane of the track of substrates, 3, 4 and 5
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`is mask 2 with opening 6 which, as will be explained later
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`in further detail, can be formed asymmetrically in relation to
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`the center of the sputter cathode or of target 1.
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`Target 1 has a composition of at least one element of the
`rare-earth metal RE and at least one transition metal TM.
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`The rare-earth metals are generally terbium, gadolinium and
`dysprosium while the transition metals are first and foremost
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`iron and cobalt. The target alloy can consist, inter alia, of
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`5
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`is
`iron and cobalt. It
`terbium, gadolinium, dysprosium,
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`possible to use a target alloy of terbium, dysprosium, iron
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`and cobalt or of terbium, gadolinium, dysprosium and
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`cobalt. A composition of terbium, dysprosium and cobalt is
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`also suitable as a ternary alloy for target 1.
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`By way of example, a quantitative composition of the
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`target alloy has the formula
`(TbeYI»x)y (Fezcol~z)1-y
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`6
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`diode sputtering process since, by comparison with diode
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`sputtering, higher sputter rates are obtained at reduced
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`power, and much less heating of the substrates occurs, since
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`only a few electrons impinge on the substrate, being instead
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`deflected by the magnetic field of the magnetron cathode.
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`Due to the different sputter lobes for rare-earth metals and
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`transition metals,
`there is present
`in the center of the
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`magnetooptic layer a concentration of transition metals
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`which is enhanced by comparison with the average concen-
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`tration. There is also present at the edges and in one or both
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`surfaces of the magnetooptic layer a concentration of rare-
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`earth metals which is enhanced by comparison with the
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`average concentration. It is clear from FIG. 3 that by suitable
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`design of the masks, sketched by way of example in FIGS.
`5A to 5D, which are mounted between the cathode and the
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`substrate, an M-shaped profile of the rare-earth concentra-
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`tion can be achieved and a A—shaped and a V—shaped profile
`of the rareAearth concentration can occur. It is likewise
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`possible to adjust the concentration distributions in the depth
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`to virtually any type by suitable series connection of coating
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`stations with overlapping sputter lobes.
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`In the embodiment of a sputtering facility shown in FIG.
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`2, sputter cathodes are arranged next to one another in
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`sputtering chamber 3 in a plane parallel to the direction of
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`the transport A of substrates 3, 4 and 5 to be coated, the
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`sputter cathodes consisting of targets 7, 1, 8 with difierent
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`alloy compositions made from rare-earth/transition metals.
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`For example, targets 7 and 8 are operated using the diode
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`sputtering process, and target 1 using the magnetron sput-
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`tering process. It is likewise possible for all three targets to
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`be operated using the diode sputtering process or using the
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`magnetron sputtering process. It is likewise possible, by
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`altering the gas flow and the sputtering power of the indi-
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`vidual cathodes, to adjust the layer thickness profiles, i.e.,
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`the distribution of the alloy components. The close spatial
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`proximity of the sputter cathodes causes a continuous tran—
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`sition of the concentrations of the alloying components.
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`Since a discontinuity in the concentration is thereby avoided
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`in the magnetooptic layer by comparison with a structure of
`discrete coats, there is a reduction in diffusion effects, which
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`can occur in the case of repeated writing and erasing of the
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`magnetooptic layer, and in changes associated therewith in
`the write/read characteristics.
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`The first target in the direction of transport of the substrate
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`exhibits, e.g., a higher transition metal content, especially a
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`higher cobalt content than the second target 1, seen in the
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`direction of the transport.
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`On the side of the magnetooptic layer facing the substrate
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`there is present, for example, an enhanced concentration of
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`transition metals, especially an enhanced cobalt concentra-
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`tion, to enhance the signal-to-noise ratio, while the concen—
`tration of rare-earth metals is enhanced on the side of the
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`magnetooptic layer away from the substrate.
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`It is also possible to use more than three sputter cathodes,
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`for example, if at least one side of the magnetooptic layer is
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`covered by a dielectric layer. Suitable, inter alia, as the
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`dielectric layer are the barrier layers against moisture and/or
`oxygen described above. The thickness of this dielectric
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`layer is chosen as approximately N4n on the side facing the
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`substrate, 7» being the wavelength of a writing laser and n the
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`refractive index of the dielectric layer. On the side of the
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`magnetooptic layer away from the substrate, the thickness of
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`the barrier layer is smaller than or equal to the thickness of
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`the barrier layer facing the substrate. The thickness of the
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`magnetooptic layer amounts to about 15 to 100 nm.
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`The barrier layer or anti—reflective layer on the side of the
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`magnetooptic layer facing the substrate has a thickness of
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`10
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`15
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`20
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`25
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`30
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`4O
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`45
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`50
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`60
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`65
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`Oéxél,
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`0.15§y§0.30
`and
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`0.60ézél.
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`When a ternary alloy containing terbium as the sole
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`element of the rare-earth metals is used as the target, a
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`preferred composition is Tbo.224128 Fe0_70_0.64 C0008-
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`Target 1 is operated, for example, as a magnetron sputter
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`cathode using a magnetron sputtering process known per se.
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`The heart of the magnetron sputter cathode is a magnet
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`system in which magnets with alternating poles are arranged
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`on a soft-iron disk. A section through such a planar magne-
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`tron MDC is represented diagrammatically in FIGS. 1 and 2.
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`The magnetron is connected electrically as the cathode, and
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`the substrate holder as the anode or to a floating potential.
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`Located between the electrodes is an ionized gas,
`for
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`example argon, which is at a specific pressure, preferably
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`3X10“3 mbar to 2X10_2 mbar. Due to the magnet arranged
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`behind the target, a nonhomogeneous magnetic field forms
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`below target 1 and leads, in combination with the electric
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`field, to a preferred sputtering of the target at sputter rifts 9,
`10 marked in FIG. 1. Moreover, the RE metals and the TM
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`are sputtered diiferently and give rise to different spatial
`35
`distributions k1, k2, k3, k4, indicated in FIG. 1, for the
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`rare~earth metals and the transition metals. These difierent
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`spatial distributions, also termed sputter lobes, of the rare-
`earth metals and the transition metals are used in order, in
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`dynamic magnetron sputtering with only one cathode or
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`only one target, to obtain a specific concentration profile for
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`the rare-earth metals over the depth of the magnetooptic
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`layer. These depth profiles of the rare-earth metals RE and
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`of the transition metals TM are represented in FIG. 3, in
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`which the depth t of the magnetooptic layer is plotted on the
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`abscissa axis, and the atomic percentages of the alloying
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`components are plotted on the ordinate axis. If, for example,
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`target 1 in FIG. 1 consists of a terbium-iron-cobalt alloy,
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`terbium is distributed in accordance with the sputter lobes k1
`and k4 in FIG. 1, and the transition metals iron and cobalt
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`are distributed in accordance with the central sputter lobes
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`k2 and k3. In this way, a magnetooptic layer is obtained
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`which contains an “M”—shaped terbium concentration profile
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`with two peaks, as may be seen from the rare-earth metal
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`profile RE in FIG. 3, while the transition metal profile TM
`55
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`exhibits a single peak which, however, is higher than the two
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`peaks of the terbium concentration profile.
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`The magnetooptic layer can, of course, also be fabricated
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`in a diode or triode sputtering facility by a direct-current
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`discharge. In such a diode sputtering facility, the substrate to
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`be coated is connected, for example, as an anode, and the
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`target forms the sputter cathode for this. B