`Doessel et al.
`
`I IIIII IIIIIIII Ill lllll lllll lllll lllll lllll lllll lllll lllll 111111111111111111
`US005527605A
`5,527,605
`[lll Patent Number:
`Jun. 18, 1996
`[45J Date of Patent:
`
`[54] MAGNETOOPTIC LAYER AND A PROCESS
`FOR ITS FABRICATION
`
`[75]
`
`Inventors: Karl-Friedrich Doessel, Wiesbaden;
`Bernd Fischer, Wiesbaden-Nordenstadt;
`Ernst G. Schlosser, Kelkheim;
`Guenther Schmidt, Niedemhausen, all
`of Germany
`
`[73] Assignee: Hoechst Aktiengesellschaft, Frankfurt
`am Main, Germany
`
`[21] Appl. No.: 224,190
`
`[22] Filed:
`
`Apr. 7, 1994
`
`Related U.S. Application Data
`
`[63] Continuation of Ser. No. 785,880, Nov. 4, 1991, abandoned,
`which is a continuation of Ser. No. 480,496, Feb. 16, 1990,
`abandoned.
`
`[30]
`
`Foreign Application Priority Data
`
`Feb. 16, 1989
`
`[DE] Germany .......................... 39 04 611.7
`
`[51]
`
`Int. Cl.6
`
`................................ GllB 5/66; B32B 5/16;
`C23C 14/00
`[52] U.S. Cl . .......................... 428/332; 428/336; 428/610;
`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;
`204/192.1; 204/192.2; 204/192.26; 363/13
`[58) Field of Search ..................... 428/694 ML, 694 SC,
`428/694 GR, 900, 694 NF, 694 MM, 694 IS,
`332, 336, 610, 694 XS; 369/13; 204/192.1,
`192.2, 192.26
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,293,621 10/1981 Togami ................................... 428/694
`4,649,519
`3/1987 Sun et al. ................................ 365/122
`6/1987 Sato et al. ............................... 428/693
`4,670,356
`9/1987 Muchnik et al. ......................... 360/59
`4,694,358
`4/1988 Frankenthal et al .................... 428/630
`4,740,430
`
`FOREIGN PATENT DOCUMENTS
`
`0126589
`0217096
`0225141
`0227480
`0229292
`3309483
`3536210
`3642161
`009855
`243844
`243840
`048148
`184940
`63-188843
`2169742
`
`11/1984
`4/1987
`10/1987
`7/1987
`7/1987
`9/1983
`4/1986
`6/1988
`1/1985
`12/1985
`12/1985
`3/1986
`7/1988
`8/1988
`7/1986
`
`European Pat. Off ..
`European Pat. Off ..
`European Pat. Off ..
`European Pat. Off ..
`European Pat. Off ..
`Germany.
`Germany.
`Germany.
`Japan.
`Japan.
`Japan.
`Japan.
`Japan.
`Japan.
`United Kingdom .
`
`OTHER PUBLICATIONS
`
`S. Takayama, et al., "Magnetic and Magneto-Optical Prop(cid:173)
`erties of Tb-Fe-Co Amorphous Films", J. Appl. Phys. 61 (7),
`Apr. 1, 1987, American Institute of 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, et al., "Production Technology for Magne(cid:173)
`tooptic Data Storage Media", Solid State Technology/Mar.
`1988, pp. 107-112.
`
`(List continued on next page.)
`
`Primary Examiner-Leszek Kilman
`Attorney, Agent, or Firm-Foley & Lardner
`
`[57]
`
`ABSTRACT
`
`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 liT=l00° C.
`around the compensation temperature T comp· The layer is
`fabricated with a dynamic sputter process, in which the
`substrates to be coated are led past one or a plurality of
`sputter targets, arranged in a common plane parallel to the
`track of the substrates. A mask is located between the sputter
`targets and the substrates.
`
`38 Claims, 6 Drawing Sheets
`
`A
`
`5
`
`Page 1 of 14
`
`APPLIED MATERIALS EXHIBIT 1070
`
`
`
`5,527,605
`Page 2
`
`OTHER PUBLICATIONS
`
`Masahiko Takahash et al., "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 al., "Magnetic and Magneto-Optical Prop(cid:173)
`erties of Tb-Fe-Co Amorphous Films," Journal of Applied
`Physics, vol. 61 (7), Apr. 1, 1987, 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., vol. 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
`
`
`
`U.S. Patent
`
`Jun. 18, 1996
`
`Sheet 1 of 6
`
`5,527,605
`
`~ ~ ~}MOC
`g~ \oSE
`. >/ ' /y"' "'v 6 \
`SE
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`_\/" 2
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`,
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`k
`'-.
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`\
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`
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`
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`
`7
`l
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`N
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`I
`
`+1
`
`V(Z)
`A ~
`
`2
`Pl/At"'
`
`> I Cs
`i) (
`
`FIG.2
`
`?
`5
`
`8
`)
`
`Page 3 of 14
`
`
`
`U.S. Patent
`US. Patent
`
`Jun. 18, 1996
`Jun. 18, 1996
`
`Sheet 2 0f 6
`Sheet 2 of 6
`
`5,527,605
`5,527,605
`
`'I.
`*7.
`
`U M
`
`SE
`
`SE
`
`FI G.3
`FIB.3
`
`,
`
`b
`
`l
`FIG.4
`
`Page 4 of 14
`
`t
`t
`
`
`
`g
`
`Page 4 of 14
`
`
`
`U.S. Patent
`
`Jun. 18, 1996
`
`Sheet 3 of 6
`
`5,527,605
`
`2
`
`I
`I
`I
`I
`
`6a
`
`FIG.SA
`
`FIG.SB
`
`---2
`
`I
`I
`1--
`I
`i
`I
`FIG.SC
`
`6c
`
`FIG.SD
`
`2
`
`6b
`
`2
`
`6d
`
`Page 5 of 14
`
`
`
`U.S. Patent
`
`Jun. 18, 1996
`
`Sheet 4 of 6
`
`5,527,605
`
`0/o
`
`/ ..
`r-UM
`
`I
`
`/
`
`t
`
`FIG.SA
`
`FIG.SB
`
`SE
`
`t
`
`O/o
`
`UM
`---------L
`SE
`
`O/o
`
`,, UM
`,' '<
`,
`
`SE
`
`t
`
`FIG.SC
`
`t
`
`FIG.60
`
`Page 6 of 14
`
`
`
`U.S. Patent
`
`Jun. 18, 1996
`
`Sheet 5 of 6
`
`5,527,605
`
`Hc[kOe 1
`8
`
`7
`
`6
`
`5
`
`4
`
`I
`I
`/
`Hcinh
`~
`I
`I
`I
`I
`I
`
`I
`
`/
`
`1
`
`11Hc
`[ 1/kOe]
`
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`
`I
`I
`
`AT~ 100°c
`
`\
`\
`\-Hcinh
`\
`\
`\
`\
`\
`
`\
`
`"
`
`Teo mp
`
`FIG.7
`
`~
`
`T(OC]
`
`Tcomp
`1
`f I G. 8
`Tc omp 1.---"\1------_...~
`lTcomp 2
`
`Page 7 of 14
`
`
`
`U.S. Patent
`US. Patent
`
`Jun. 18,1996
`Jun. 18, 1996
`
`Sheet 6 of 6
`Sheet 6 of 6
`
`5,527,605
`5,527,605
`
`..... / 16
`
`3 ~,
`~ ~, 4
`
`-I 5
`
`t'-1
`
`13
`2
`
`,
`
`..
`
`,I""
`
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`
`
`
`\.... I I
`
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`
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`13
`.._., I
`4
`--
`13
`i'-1
`5
`16
`
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`
`..
`
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`
`FIG.9
`
`Page 8 of 14
`
`Page 8 of 14
`
`
`
`5,527,605
`
`1
`MAGNETOOPTIC LAYER AND A PROCESS
`FOR ITS FABRICATION
`
`This application is a continuation of application Ser. No.
`07/785,880, filed Nov. 4, 1991, now abandoned, which is a
`continuation of Ser. No. 07/480,496, filed Feb. 16, 1990,
`now abandoned.
`
`5
`
`BACKGROUND OF THE INVENTION
`
`10
`
`The present invention concerns a magnetooptic layer
`made from an amorphous rare-earth/transition metal alloy
`having magnetic anisotropy, the easily magnetizable axis of
`which is perpendicular to the surface.
`Amorphous magnetooptic materials having such a !5
`uniaxial perpendicular anisotropy are known. The most
`widespread are alloys of rare-earth metals, such as gado(cid:173)
`linium, terbium and dysprosium, with transition metals, such
`as iron and cobalt, to which yet further components may be
`added. The magnetic properties of these alloys depend very 20
`strongly on their composition.
`German Offenlegungsschrift 3,309,483 describes magne(cid:173)
`tooptic recording materials made from amorphous ternary
`alloys based on terbium, iron and cobalt. When the cobalt
`components are equal to or less than forty percent of the 25
`alloy there is an approximately linear relationship of both
`the angle of the Kerr rotation and the Curie temperature
`relative to the cobalt content of the alloys. The same holds
`for the magnetooptic recording media described in German
`Offenlegungsschrift 3,536,210 and in an article in Journal of 30
`Applied Physics, 64:262 (1988). Thus, a magnetooptic
`recording medium made from an amorphous film composed
`of rare-earth/transition metals and having a compensation
`temperature of 50° to 200° C., or a compensation tempera(cid:173)
`ture of 0° C. or less, is known from German Offenlegungss- 35
`chrift 3,536,210. When an amorphous film of the Tb-Fe-Co
`system is used, the compensation temperature of 50° to 200°
`C. is achieved with a composition having 24 to 30 atom
`percent terbium, 7 to 20 atom percent cobalt, the remainder
`being iron, while a compensation temperature of 0° C. or 40
`less is attained with a composition having 18 to 21.5 atom
`percent terbium, 8 to 10 atom percent cobalt and the
`remainder being iron. These relationships are explained in
`detail in German Offenlegungsschrift 3,536,210.
`Starting from page 2610 of an article in Journal of 45
`Applied Physics, 61 (1987) and from page 1949 of an article
`in J. Vac. Sci. Technol. AS (1987), it is pointed out that, for
`example, increasing the terbium content by I atom percent
`can shift the compensation temperature by up to 40° C.
`The control of the composition of the layer is therefore
`very important for design of the sputtering process and of a
`corresponding production plant, as discussed in Solid State
`Technology, March 1988, page 107.
`In general, it is indicated that the deviation of the terbium 55
`concentration from the mean concentration in the layer
`volume is to amount to less than 0.5%.
`The uniformity sought in the composition of the alloy
`components in the depth profile of a magnetooptic recording
`layer, together with the attempts to hold the alloy compo- 60
`sition constant over the width and length of the coating
`require a high degree of effort, e.g., the disks to be coated
`rotate during the coating process about their own axis of
`rotation, and at the same time travel around on a sizeable
`circuit.
`A further disadvantage of known magnetooptic recording
`materials is their high corrodibility.
`
`50
`
`65
`
`2
`To avoid or prevent this disadvantage, the addition of
`various anticorrosive substances or elements, respecitvely,
`to the magnetooptic allows is recommended (GB-A-2,175,
`160; EP-Al-0,229,292). The addition of such substances to
`the entire volume of the magnetooptic recording layer
`improves the corrosion resistance, but at the expense of
`other desired properties, such as high Kerr angle, high
`coercive field strength, high writing sensitivity, high signal(cid:173)
`to-noise ratio and the like. In the magnetooptic recording
`medium according to EP-Al-0,229,292, further anticorro(cid:173)
`sive substances are added to a first substance in order to
`achieve an enrichment of the anticorrosive substances at the
`surface of the recording medium. In this process it is
`disadvantageous that the desirable magnetooptic properties
`can be even more strongly impaired through the addition of
`further elements.
`Thin barrier layers made from anticorrosive substances
`are described in U.S. Pat. No. 4,740,430. A discrete mul(cid:173)
`tiple-layer structure of the magnetooptic recording medium
`is produced.
`In order to achieve a high storage density of the magne(cid:173)
`tooptic recording materials, it is necessary to produce stable
`domains which are as small as possible in the magnetooptic
`recording layer. A precondition for this is that the product of
`the saturation magnetization Ms and the coercive field
`strength He be as large as possible (Kryder et al., SPIE
`Proc., Vol. 420, page 236 (1983)). For known magnetooptic
`recording materials, a product of the saturation magnetiza(cid:173)
`tion and coercive field strength which is as large as possible
`is achieved only in a narrow temperature range around the
`compensation temperature T comp·
`More recently, magnetooptic recording materials have
`been described that are suitable for the direct overwriting of
`information (U.S. Pat. No. 4,694,358, U.S. Pat. No. 4,649,
`519, EP-A2-0,225,141, EP-A2-0,227,480 and EP-A2-0,217,
`096). In all cases, use is made of a construction of the
`magnetooptic recording medium in which two separate
`layers having different magnetic properties are stratified one
`above the other.
`The publications EP-A2-0,217,096 and EP-A2-0,227,480
`describe magnetooptic recording media in which a thermally
`insulating interlayer is present in the construction between
`the magnetooptic recording layer and a magnetic layer
`which generates a polarizing field. In the remaining citations
`from the literature mentioned above such interlayers are
`recommended because otherwise there can be diffusion of
`alloying components into the magnetic layer. Naturally, such
`a diffusion of alloying components alters the properties of
`the magnetooptic recording medium.
`Another way to increase the long-term stability of a
`magnetooptic storage device is proposed in the process
`according to German Offenlegungsschrift 3,642,161, in
`which, during and/or after the successive deposition of a
`dielectric layer, a magnetooptic layer and a cover layer on a
`substrate, a curing treatment is carried out in a virtually dry
`atmosphere in a temperature range from room temperature
`to just below the crystallization temperature of the magne(cid:173)
`tooptic layer.
`There is known from Japanese Published Specification
`188,843/88 a process for fabricating a photomagnetic disk,
`in which the photomagnetic recording layer is sputtered on
`in such a way that the substrate moves past three targets
`made from rare-earth metal and transition metal. The central
`target is arranged parallel to the transport track of the
`substrate, with a target being mounted in front of and behind
`the central target in the direction of transport of the substrate
`
`Page 9 of 14
`
`
`
`3
`at a predetermined angle with respect to the central target.
`The composition of the photomagnetic recording film thus
`obtained on the substrate is uniform.
`
`SUMMARY OF THE INVENTION
`
`5,527,605
`
`4
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`5
`
`A magnetooptic recording layer according to the present
`invention exhibits a gradient in the concentration of the
`composition with depth and has a coercive field strength of
`more than about 8 kOe in the temperature range of ~T=l00°
`C. around the compensation temperature T comp is provided.
`In one embodiment of the present invention, the alloy
`10 consists of terbium, gadolinium, dysprosium, iron and
`cobalt, or of terbium, dysprosium, iron and cobalt. Further(cid:173)
`more, the alloy can consist of terbium, gadolinium, dyspro(cid:173)
`sium and cobalt, or of terbium, dysprosium and cobalt alone.
`One of the alloys of the magnetooptic layer expediently has
`15 a composition according to the formula
`
`(Tb.,Dy,_Jy (Fe2Co,.2l1-y
`
`It is therefore an object of the invention to provide a
`magnetooptic layer, having an easily magnetizable axis
`perpendicular to the surface of the layer, which can be
`fabricated simply and reproducibly, has a high corrosion
`resistance with respect to moisture and/or oxygen, makes
`possible high storage densities, and is suitable for direct
`overwriting.
`It is a further object of the invention to provide a process
`of fabrication of such a magnetooptic layer.
`These and other objects according to the invention are
`achieved by a magnetooptic layer comprising an amorphous
`rare-earth/transition metal alloy having magnetic anisotropy
`the easily magnetizable axis of which is perpendicular to the 20
`surface, wherein the magnetooptic layer exhibits a gradient
`in the concentration of the composition with depth and has
`a coercive field strength of more than 8 kOe in the tempera(cid:173)
`ture range of Lff=100° C. around the compensation tem(cid:173)
`perature T comp·
`Other objects, features and advantages of the present
`invention will become apparent from the following detailed
`description. It should be understood, however, that the
`detailed description and the specific examples, while indi(cid:173)
`cating preferred embodiments of the invention, are given by 30
`way of illustration only, since various changes and modifi(cid:173)
`cations within the spirit and scope of the invention will
`become apparent to those skilled in the art from this detailed
`description.
`
`25
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`35
`
`where
`o;;;x;;;l,
`0.15~y~0.30
`and
`0.60~z~l.
`In a further embodiment of the invention, there is present
`in one or both surfaces of the magnetooptic layer a concen(cid:173)
`tration of rare-earth metals which is enhanced by compari(cid:173)
`son with the average concentration of the composition, i.e.,
`in which the concentration of rear-earth metals is greater
`than the average concentration of rare-earth metals in the
`composition.
`It is likewise possible that there is present in one or both
`surfaces of the magnetooptic layer a concentration of tran(cid:173)
`sition metals which is enhanced by comparison with the
`average concentration, i.e., in which the concentration of
`transition metals is greater than the average concentration of
`transition metals in the composition.
`A magnetooptic layer according to the invention is a
`component of a magnetooptic recording medium in which
`the magnetooptic layer is arranged between two barrier
`layers made from SiN, SiON, SiAlON, AlN, Al ON, an oxide
`of tantalum or an oxide of niobium for protection against
`moisture and/or oxygen. One barrier layer is covered on one
`side by a substrate, and the other by a metallic mirror, a
`lacquer or adhesive layer and a second substrate.
`The process for the fabrication of a magnetooptic layer is
`distinguished by the fact that the rare-earth/transition metal
`alloy is sputtered on dynamically by transporting the sub(cid:173)
`strate to be coated relative to one or a plurality of sputter
`targets which are arranged in a common plane.
`The magnetooptic layers according to the invention pro(cid:173)
`vide a directly overwritable magnetooptic
`recording
`medium, in a system in which a modulation of the magnetic
`field or a modulation of the laser energy takes place during
`the writing of the information.
`Represented diagrammatically in FIG. 1 is an arrange-
`ment for the fabrication of a magnetooptic layer on sub(cid:173)
`strates 3, 4 and 5, which are led past a sputter cathode in the
`form of target 1 in the direction of arrow A. Located between
`target 1 and the plane of the track of substrates, 3, 4 and 5
`is mask 2 with opening 6 which, as will be explained later
`in further detail, can be formed asymmetrically in relation to
`the center of the sputter cathode or of target 1.
`Target 1 has a composition of at least one element of the
`rare-earth metal RE and at least one transition metal TM.
`65 The rare-earth metals are generally terbium, gadolinium and
`dysprosium while the transition metals are first and foremost
`iron and cobalt. The target alloy can consist, inter alia, of
`
`40
`
`The invention is explained in more detail below with
`reference to the drawings, in which:
`FIG. 1 shows a schematic representation of the arrange(cid:173)
`ment of a target in a plane parallel to the track of the
`substrates to be coated;
`FIG. 2 shows a diagrammatic arrangement of a plurality
`of targets in a common plane parallel to the track of the 45
`substrates to be coated;
`FIG. 3 shows, diagrammatically, the composition of a
`magnetooptic layer based on rare-earth metals RE and
`transition metals TM over the depth of the layer;
`FIG. 4 shows a mask characteristic of a mask inserted 50
`between target and substrate, and the sputter rates over the
`depths of the magnetooptic layer;
`FIGS. SA to SD show a top view of various masks with
`different mask openings, which are arranged between the
`targets and the substrates;
`FIGS. 6A to 6D show, schematically, the composition of
`magnetooptic layers over the layer depths, which are
`obtained with the masks according to FIGS. SA to SD;
`FIG. 7 shows the relationship between the coercive field
`strength He and the temperature T of various magnetooptic
`layers;
`FIG. 8 shows the relationship between the reciprocal 1/Hc
`of the coercive field strength and the temperature T of the
`magnetooptic layers according to FIG. 7; and
`FIG. 9 shows a magnetooptic recording medium produced
`according to the present invention.
`
`55
`
`60
`
`Page 10 of 14
`
`
`
`5,527,605
`
`5
`terbium, gadolinium, dysprosium, iron and cobalt. It is
`possible to use a target alloy of terbium, dysprosium; iron
`and cobalt or of terbium, gadolinium, dysprosium and
`cobalt. A composition of terbium, dysprosium and cobalt is
`also suitable as a ternary alloy for target 1.
`By way of example, a quantitative composition of the
`target alloy has the formula
`
`10
`
`6
`diode sputtering process since, by comparison with diode
`sputtering, higher sputter rates are obtained at reduced
`power, and much less heating of the substrates occurs, since
`only a few electrons impinge on the substrate, being instead
`5 deflected by the magnetic field of the magnetron cathode.
`Due to the different sputter lobes for rare-earth metals and
`transition metals, there is present in the center of the
`magnetooptic layer a concentration of transition metals
`which is enhanced by comparison with the average concen-
`tration. There is also present at the edges and in one or both
`surfaces of the magnetooptic layer a concentration of rare(cid:173)
`earth metals which is enhanced by comparison with the
`average concentration. It is clear from FIG. 3 that by suitable
`design of the masks, sketched by way of example in FIGS.
`15 SA to SD, which are mounted between the cathode and the
`substrate, an M-shaped profile of the rare-earth concentra(cid:173)
`tion can be achieved and a A-shaped and a V-shaped profile
`of the rare-earth concentration can occur. It is likewise
`possible to adjust the concentration distributions in the depth
`to virtually any type by suitable series connection of coating
`stations with overlapping sputter lobes.
`In the embodiment of a sputtering facility shown in FIG.
`2, sputter cathodes are arranged next to one another in
`sputtering chamber 3 in a plane parallel to the direction of
`the transport A of substrates 3, 4 and S to be coated, the
`sputter cathodes consisting of targets 7, 1, 8 with different
`alloy compositions made from rare-earth/transition metals.
`For example, targets 7 and 8 are operated using the diode
`sputtering process, and target 1 using the magnetron sput(cid:173)
`tering process. It is likewise possible for all three targets to
`be operated using the diode sputtering process or using the
`magnetron sputtering process. It is likewise possible, by
`altering the gas flow and the sputtering power of the indi(cid:173)
`vidual cathodes, to adjust the layer thickness profiles, i.e.,
`the distribution of the alloy components. The close spatial
`proximity of the sputter cathodes causes a continuous tran-
`sition of the concentrations of the alloying components.
`Since a discontinuity in the concentration is thereby avoided
`in the magnetooptic layer by comparison with a structure of
`discrete coats, there is a reduction in diffusion effects, which
`can occur in the case of repeated writing and erasing of the
`magnetooptic layer, and in changes associated therewith in
`the write/read characteristics.
`The first target in the direction of transport of the substrate
`exhibits, e.g., a higher transition metal content, especially a
`higher cobalt content than the second target 1, seen in the
`direction of the transport.
`On the side of the magnetooptic layer facing the substrate
`there is present, for example, an enhanced concentration of
`transition metals, especially an enhanced cobalt concentra(cid:173)
`tion, to enhance the signal-to-noise ratio, while the concen-
`tration of rare-earth metals is enhanced on the side of the
`magnetooptic layer away from the substrate.
`It is also possible to use more than three sputter cathodes,
`for example, if at least one side of the magnetooptic layer is
`covered by a dielectric layer. Suitable, inter alia, as the
`dielectric layer are the barrier layers against moisture and/or
`oxygen described above. The thickness of this dielectric
`layer is chosen as approximately A./4n on the side facing the
`substrate, A being the wavelength of a writing laser and n the
`refractive index of the dielectric layer. On the side of the
`magnetooptic layer away from the substrate, the thickness of
`the barrier layer is smaller than or equal to the thickness of
`the barrier layer facing the substrate. The thickness of the
`magnetooptic layer amounts to about 15 to 100 nm.
`The barrier layer or anti-reflective layer on the side of the
`magnetooptic layer facing the substrate has a thickness of
`
`where
`O~x~l,
`0.15~y~0.30
`and
`0.60~z~l.
`When a ternary alloy contammg terbium as the sole
`element of the rare-earth metals is used as the target, a
`preferred composition is Tb0 _22-0.zs Fe0 _7 0-0.64 Co0 _08 .
`Target 1 is operated, for example, as a magnetron sputter
`cathode using a magnetron sputtering process known per se. 20
`The heart of the magnetron sputter cathode is a magnet
`system in which magnets with alternating poles are arranged
`on a soft-iron disk. A section through such a planar magne(cid:173)
`tron MDC is represented diagrammatically in FIGS. 1 and 2.
`The magnetron is connected electrically as the cathode, and 25
`the substrate holder as the anode or to a floating potential.
`Located between the electrodes is an ionized gas, for
`example argon, which is at a specific pressure, preferably
`3x10-3 mbar to 2x10-2 mbar. Due to the magnet arranged
`behind the target, a nonhomogeneous magnetic field forms 30
`below target 1 and leads, in combination with the electric
`field, to a preferred sputtering of the target at sputter rifts 9,
`10 marked in FIG. 1. Moreover, the RE metals and the TM
`are sputtered differently and give rise to different spatial
`distributions kl, k2, k3, k4, indicated in FIG. 1, for the 35
`rare-earth metals and the transition metals. These different
`spatial distributions, also termed sputter lobes, of the rare(cid:173)
`earth metals and the transition metals are used in order, in
`dynamic magnetron sputtering with only one cathode or
`only one target, to obtain a specific concentration profile for 40
`the rare-earth metals over the depth of the magnetooptic
`layer. These depth profiles of the rare-earth metals RE and
`of the transition metals TM are represented in FIG. 3, in
`which the depth t of the magnetooptic layer is plotted on the
`abscissa axis, and the atomic percentages of the alloying 45
`components are plotted on the ordinate axis. If, for example,
`target 1 in FIG. 1 consists of a terbium-iron-cobalt alloy,
`terbium is distributed in accordance with the sputter lobes kl
`and k4 in FIG. 1, and the transition metals iron and cobalt
`are distributed in accordance with the central sputter lobes 50
`k2 and k3. In this way, a magnetooptic layer is obtained
`which contains an "M"-shaped terbium concentration profile
`with two peaks, as may be seen from the rare-earth metal
`profile RE in FIG. 3, while the transition metal profile TM
`exhibits a single peak which, however, is higher than the two 55
`peaks of the terbium concentration profile.
`The magnetooptic layer can, of course, also be fabricated
`in a diode or triode sputtering facility by a direct-current
`discharge. In such a diode sputtering facility, the substrate to
`be coated is connected, for example, as an anode, and the 60
`target forms the sputter cathode for this. By applying a
`voltage, a plasma is obtained between the two electrodes in
`a carrier gas, which is under a specific pressure. The ions of
`the carrier gas, which are accelerated in the electric field,
`knock out molecules or atoms from the target, which forms 65
`the cathode, and these are deposited on the substrate. In
`general, the magnetron sputtering process is preferred to the
`
`Page 11 of 14
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`
`
`5,527,605
`
`7
`approximately 'JJ5n, n being the refractive index of the layer,
`and A being the wavelength of the laser light. A character(cid:173)
`istic layer construction is as follows: substrate/70 nm±5
`nm(Si,N)/80 nm±5 nmTbFeCo/50 nm±5 nm(Si,N), the
`refractive index n of the silicon nitride of the first (Si,N)
`layer being 2.20±0.1 and of the second (Si,N) layer being
`2.05±0.1. The barrier layer on the side of the magnetooptic
`layer away from the substrate is, e.g., a reflective layer made
`from Ag, Cu, Au, TiN or ZrN. The following is an example
`of such a three-layer construction: substrate/70 nm±5 nm(Si, 10
`N)/25 nm±5 nmTbFeCo/50 nm±5 nm reflective layer. How(cid:173)
`ever, these three-layer constructions are less preferred than
`a four-layer construction in which a reflective layer is
`applied to a transparent barrier layer which is away from the
`substrate. Such a four-layer construction comprises, for
`example: substrate/70 nm±5 nm(Si,N)/25 nm±5 nm(Tb(cid:173)
`FeCo )/30 nm±5 nm(Si,N)/50 nm±5 nm (Al).
`If barrier layers are applied to both sides of the magne(cid:173)
`tooptic recording medium, sputtering is done from targets
`which lie ahead of target 7 or after target 8 in FIG. 2. In this
`process, the target (not shown) lying ahead of target 7
`consists, for example, of silicon, silicon-aluminium, alu(cid:173)
`minium, tantalum or niobium. The diode sputtering process,
`or preferably the magnetron sputtering process, is applied in
`an argon and oxygen and/or nitrogen atmosphere. A layer of
`SiN, SiON, SiAlON AlN, AlON, an oxide of tantalum or an
`oxide of niobium is first formed on substrate 3 as a barrier
`layer against moisture and/or oxygen.
`A further enhancement of the corrosion resistance of the
`resulting magnetooptic recording medium is obtained by
`sputtering on an anti-corrosive element in a sizable concen(cid:173)
`tration from the cathode, to be precise target 7, lying ahead
`of the magnetron sputter cathode in the direction of transport
`or in the direction of the track A of the substrates. Target 7
`can, for example, consist completely of an anticorrosive
`element, which can be titanium, chromium, aluminium,
`platinum, zirconium, vanadium, tantalum, molybdenum,
`tungsten, copper, ruthenium, rhenium, palladium, silicon,
`niobium, iridium and/or hafnium. Target 7 can also contain
`two or more of these elements in higher concentration, or
`consist entirely of two or more of these elements. Subse(cid:173)
`quent to the sputtering of this anti-corrosive layer onto the
`substrate provided with a barrier layer, the magnetooptic
`layer is sputtered on, as is described with reference to FIG.
`1. In the last process step, an anticorrosive element is 45
`sputtered on from a target 8 which may have the same
`composition as target 7. In one or both surfaces of the
`magnetooptic layer, the anticorrosive element or elements
`exhibit a higher concentration after the sputtering by com(cid:173)
`parison with the average concentration of elements.
`A magnetooptic recording medium comprising all the
`described layers is shown in FIG. 9, including substrate 11,
`inner barrier layers 12, anticorrosive layers 13, magnetoop(cid:173)
`tic layer 14, outer barrier layers 15, and reflective layers 16.
`Inner barrier layers 12 may have anti-reflective properties
`and outer barrier layers 15 may have reflective properties, as
`described above. Various combinations of these described
`layers may be used.
`Targets 7, 1, 8 in FIG. 2 have an approximate mutual
`spacing which corresponds to the spacing of the targets to
`the substrates to be coated. In this way, an overlapping of the
`sputter lobes can be achieved, and layers with any desired
`concentration distribution in the layer thickness can be
`fabricated.
`In order to obtain in the magnetooptic layer a depth profile
`of the rare-earth and transition metals which has an asym(cid:173)
`metric concentration gradient over the depth, it is possible to
`
`8
`arrange, between the plane of the substrates and the targets,
`the mask shown diagrammatically in FIG. SA or SB which
`exhibits mask opening 6a or 6b, formed asymmetrically in
`relation to the center of the sputter target or of the sputter
`5 cathode.
`FIGS. SA to SD show different embodiments of such a
`mask 2, the mask having, according to FIGS. SC and SD
`mask opening 6c or 6d extending symmetrically to the
`center line.
`The curve S above reference line gin FIG. 4 indicates the
`sputter rate for an element, for example a rare-earth metal
`RE, which is applied to the substrate without an inserted
`mask. The values rl, r2 are plotted as representatives of the
`individual local sputter rates. A sputter rate in accordance
`15 with curve C is obtained for the transition metals 1M, its
`shape being altered by comparison with the shape for the
`rare-earth metals RE.
`Target 1, from which sputtering is carried out, has width
`b perpendicular to the direction of transport A and a length
`20 1 in the direction of transport A of the substrates.
`The curves in accordance with FIGS, 6A to 6D reproduce
`the concentrations in atom % of the transition metals TM
`and of the rare-earth metals RE over the layer thickness or
`depth t of the magnetooptic laye