Electroless plating process for alternative memory disk substrates

Magnetic recording media including an alternative substrate material having a Young's Modulus greater than that of Al-based substrate materials and a preselected average surface roughness (Ra) are formed by depositing a continuous, adherent, non-magnetic, catalytically active layer on a surface of the substrate and electrolessly plating an amorphous seed layer on the catalytically active layer, the Ra of the resultant surface of the amorphous seed layer being reduced from that of the substrate, thereby providing a substantially defect-free surface for deposition thereon of magnetic recording media layers thereon. Embodiments include sputter depositing an catalytically active layer of Ni--Al or Ni--P and electrolessly plating an amorphous seed layer of Ni--P thereon.

FIELD OF THE INVENTION
 The present invention relates to a method of manufacturing a magnetic
 recording medium, such as a thin film magnetic recording disk. The
 invention has particular applicability in manufacturing low noise, high
 areal recording density magnetic recording media utilizing alternative
 substrates having a greater Young's Modulus than conventional aluminum
 (Al)-based substrates.
 BACKGROUND OF THE INVENTION
 Magnetic media are widely used in various applications, particularly in the
 computer industry. A conventional longitudinal recording disk medium 1
 used in computer-related applications is schematically depicted in FIG. 1
 and comprises a non-magnetic metal substrate 10, typically of an aluminum
 (Al) alloy, such as an aluminum-magnesium (Al--Mg) alloy having
 sequentially deposited thereon a plating layer 11, such as of amorphous
 nickel-phosphorus (Ni--P), a polycrystalline underlayer 12, typically of
 chromium (Cr) or a Cr-based alloy, a magnetic layer 13, e.g., of a cobalt
 (Co)-based alloy, and a protective overcoat layer 14, typically containing
 carbon (C). The Co-based alloy magnetic layer 13 deposited by conventional
 techniques, e.g., sputtering, normally comprises polycrystallites
 epitaxially grown on the polycrystalline Cr or Cr-based alloy underlayer
 12.
 In operation of medium 1, the magnetic layer 13 can be locally magnetized
 by a write transducer, or write head, to record and store information. The
 write transducer creates a highly concentrated magnetic field which
 alternates direction based on the bits of information being stored. When
 the local magnetic field produced by the write transducer is greater than
 the coercivity of the recording medium layer 13, then the grains of the
 polycrystalline medium at that location are magnetized. The grains retain
 their magnetization after the magnetic field produced by the write
 transducer is removed. The direction of the magnetization matches the
 direction of the applied magnetic field. The magnetization of the
 recording medium can subsequently produce an electrical response in a read
 transducer, allowing the stored information to be read.
 Thin film magnetic recording media are conventionally employed in disk form
 for use with disk drives for storing large amounts of data in magnetizable
 form. Typically, one or more disks are rotated on a central axis in
 combination with data transducer heads. In operation, a typical contact
 start/stop (CSS) method commences when the head begins to slide against
 the surface of the disk as the disk begins to rotate. Upon reaching a
 predetermined high rotational speed, the head floats in air at a
 predetermined distance from the surface of the disk due to dynamic
 pressure effects caused by air flow generated between the sliding surface
 of the head and the disk. During reading and recording operations, the
 transducer head is maintained at a controlled distance from the recording
 surface, supported on a bearing of air as the disk rotates, such that the
 head can be freely moved in both the circumferential and radial
 directions, allowing data to be recorded on and retrieved from the surface
 of the disk at a desired position. Upon terminating operation of the disk
 drive, the rotational speed of the disk decreases and the head again
 begins to slide against the surface of the disk and eventually stops in
 contact with and pressing against the disk. Thus, the transducer head
 contacts the recording surface whenever the disk is stationary,
 accelerated from the static position, and during deceleration just prior
 to completely stopping. Each time the head and disk assembly is driven,
 the sliding surface of the head repeats the cyclic sequence consisting of
 stopping, sliding against the surface of the disk, floating in the air,
 sliding against the surface of the disk, and stopping.
 It is considered desirable during reading and recording operations to
 maintain each transducer head as close to its associated recording surface
 as possible, i.e., to minimize the flying height of the head. Thus, a
 smooth recording surface is preferred, as well as a smooth opposing
 surface of the associated transducer head, thereby permitting the head and
 the disk to be positioned in close proximity, with an attendant increase
 in predictability and consistent behavior of the air bearing supporting
 the head during motion. However, if the head surface and the recording
 surface are too flat, the precision match of these surfaces gives rise to
 excessive stiction and friction during the start-up and stopping phases of
 the cyclic sequence, thereby causing wear to the head and recording
 surfaces, eventually leading to what is referred to as "head crash". Thus,
 there are competing goals of reducing head/disk friction and minimizing
 transducer flying height.
 Conventional practices for addressing these apparent competing objectives
 involve providing a magnetic disk recording medium with a toughened
 recording surface to reduce head/disk friction by techniques generally
 known as "texturing". Conventional texturing techniques involve polishing
 the surface of a disk substrate to provide a texture thereon prior to
 subsequent deposition thereon of layers, such as an underlayer, a magnetic
 layer, a protective overcoat, and a lubricant topcoat, wherein the
 textured surface of the underlying substrate is intended to be
 substantially replicated in the subsequently deposited layers.
 A variety of techniques, including laser-based techniques, have been
 developed for texturing metal-based magnetic recording medium substrates,
 e.g., the Ni--P plated Al-based substrates described supra. Such
 substrates, however, exhibit low head impact resistance due to the low
 mechanical yield strength (e.g., as reflected by Young's Modulus values
 less than about 72 Gpa), thereby limiting their utility such that they are
 not particularly desirable for use in mobile computer data storage
 applications, such as lap-top computers. As compared to conventional,
 Ni--P plated, Al-based substrates, glass, glass-ceramic, ceramic, and
 metal-ceramic substrates having greater values of Young's modulus exhibit
 superior shock resistance. Accordingly, such "alternative" substrates are
 desirable candidates for use in data storage applications, particularly
 mobile computer applications. In addition to the requirement for good
 shock resistance, the "alternatives" type substrates are required to
 provide good vibration performance, especially when utilized in high rpm
 disk drives.
 A number of advanced, high track per inch (TPI), low track misregistration
 (TMR), and non-repeatable run-out (NRRO) alternative substrates have been
 proposed for use in hard disk drive applications. However, none of the
 proposed alternative substrates has been utilized for the manufacture of
 practical disk drives, for the following reasons:
 1. Poor lapability/grindability: in general, the glass, ceramic, and
 glass-ceramic and metal-ceramic composite materials contemplated for use
 as hard disk substrates are extremely difficult to lap or grind according
 to conventional techniques. More specifically, pure ceramic materials such
 as alumina (Al.sub.2 O.sub.3) are too hard to grind, and metal-ceramic
 composites (e.g., ceramic within a metal matrix) contain at least two
 non-uniform phases, i.e., a soft phase and a hard phase, which make the
 grinding process even more difficult. Moreover, the ultimate cost for
 grinding such substrates is significantly higher than that for
 conventional Ni--P plated, Al-based substrates.
 2. Poor platability: due to the multi-phase nature and multi-crystal
 features of such alternative substrates, plating of a Ni--P seed layer for
 ensuring proper polycrystallinity of a Cr-based underlayer is necessary,
 as in the case of conventional Al-based substrates. However, the
 requirements for low TMR and high TPI require formation of Ni--P seed
 layers with defect-free surfaces after plating and/or polishing, with an
 attendant requirement for planarity which is higher than that required for
 conventional Al-based substrates. To date, none of the tested alternative
 substrates has evinced an ability to achieve a surface finish even
 approaching that of the conventional Ni--P plated, Al alloy substrates.
 3. Plating of non-conductive disks: currently available non-conductive
 substrate candidates for use as disk-type magnetic recording media include
 glass, glass-ceramics, and ceramics, none of which provide the
 catalytically active surface which is requisite for electroless plating of
 the amorphous seed layer (typically of Ni--P) thereon prior to deposition
 of the polycrystalline underlayer (typically of Cr or a Cr-based alloy).
 As a consequence, conventional processing for electroless Ni--P deposition
 on such non-conductive substrates involves a sensitization pre-treatment
 with colloidal palladium (Pd) prior to immersion in the electroless Ni--P
 plating bath, e.g., as disclosed in U.S. Pat. Nos. 3,904,792; 3,961,109;
 4,604,299; and 4,933,010, the entire disclosures of which are incorporated
 herein by reference. However, these sensitization pre-treatment procedures
 were developed mainly in the context of printed circuit board (PCB)
 manufacturing where microscopic (e.g., nanometer-dimensioned) defects in
 the produced Ni--P plating layers were not critical. Since the sensitizer,
 or activator, layer formed by such processing methodology consists
 essentially of discontinuous Pd, e.g., discrete Pd islands formed at
 spaced-apart locations on the substrate surface, it is therefore very
 difficult to obtain a fully sensitized surface (i.e., fully Pd-covered)
 required for obtaining nano-defect free Ni--P electrolessly plated layers
 thereon such as a required in the manufacture of high-density magnetic
 storage media. Additionally, the adhesion of Pd-activated electrolessly
 plated Ni--P coatings on such non-conductive substrate surfaces is
 obtained by acid etching and roughening to provide anchoring of the
 coating layer.
 Disadvantageously, however, the chemical etching process frequently results
 in the formation of surface defects, e.g., cavities and pits.
 4. Plating of metal-ceramics substrates: currently available metal-ceramics
 composites which are candidates for use as substrates in magnetic
 recording media comprise an Al or Al-alloy matrix and ceramic particles
 held within the matrix. Such metal-ceramics composites, e.g., Al-ceramics
 composites, are typically activated for Ni--P plating thereon by means of
 a zincating process. However, the inability to plate on the non-conductive
 ceramic particles within the conductive metal matrix results in the
 formation of discontinuous Zn films, i.e., spaced-apart islands, as with
 the wholly non-conductive glass, ceramic, and glass-ceramics substrates
 described above. Such discontinuous Zn film formation typically results in
 the formation of plating defects in the form of pits. As a consequence,
 the defect level of the plating layer(s) is essentially determined by the
 size and distribution of the ceramic particles within the metal matrix,
 and it is very difficult to achieve defect-free Ni--P seed layers for use
 in memory disks by the use of existing electroless process methodology.
 Accordingly, there exists a need for an improved electroless plating
 process suitable for forming defect-free plating or seed layers required
 in the manufacture of high-density magnetic recording media utilizing
 alternative substrate materials, which process provides coatings which are
 adherent to the substrate as well as to layers formed thereon. In
 addition, there exists a need for an improved electroless processing
 methodology for manufacturing alternative substrate-based high-density
 magnetic recording media which is simple, costeffective, and fully
 compatible with the productivity and throughput requirements of automated
 manufacturing technology.
 The present invention fully addresses and solves the above-described
 problems attendant upon the manufacture of high-density magnetic recording
 media and hard drives utilizing alternative-type substrates, while
 maintaining full compatibility with all mechanical aspects of conventional
 disk drive technology.
 DISCLOSURE OF THE INVENTION
 An advantage of the present invention is an improved method of
 electrolessly plating alternative-type substrates for use in high-density
 magnetic recording media.
 Another advantage of the present invention is an improved method of
 electrolessly plating a substantially defect-free amorphous seed layer on
 an alternative-type magnetic recording media substrate having a Young's
 Modulus greater than that of aluminum and its alloys.
 Yet another advantage of the present invention is an improved magnetic
 recording medium comprising an alternative-type substrate and including an
 electrolessly-plated seed layer formed according to the inventive
 methodology.
 A still another advantage of the present invention is an improved magnetic
 recording medium comprising a nonmagnetic substrate and means on the
 substrate for providing a substantially defect-free surface for formation
 of a magnetic recording layer thereon.
 Additional advantages and other features of the present invention will be
 set forth in the description which follows and in part will become
 apparent to those having ordinary skill in the art upon examination of the
 following or may be learned from practice of the present invention. The
 advantages of the present invention may be realized and obtained as
 particularly pointed out in the appended claims.
 According to one aspect of the present invention, the foregoing and other
 advantages are obtained in part by a method of fabricating a magnetic
 medium including a substrate having a Young's Modulus greater than that of
 aluminum (Al) and its alloys and a surface with a preselected average
 roughness (Ra), which method comprises the sequential steps of:
 (a) depositing a continuous, adherent, non-magnetic, catalytically active
 layer on the substrate surface; and
 (b) electrolessly plating an amorphous seed layer comprising a metal, metal
 alloy, or metal compound on the catalytically active layer, the Ra of the
 resultant surface of the amorphous seed layer being reduced from the
 preselected Ra of the substrate surface, thereby providing a substantially
 defect-free surface for deposition thereon of (a) layer(s) comprising the
 magnetic recording medium.
 According to embodiments of the present invention, the substrate comprises
 a material selected from glass, glass-ceramics, ceramics, and metal
 ceramic composites; step (a) comprises depositing, by a physical vapor
 deposition (PVD), chemical vapor deposition (CVD), or a plasma-enhanced
 chemical vapor deposition (PECVD) process, a continuous, catalytically
 active layer comprising a metal selected from the group consisting of
 nickel (Ni), palladium (Pd), titanium (Ti), aluminum (Al), zinc (Zn),
 copper (Cu), and alloys and compounds thereof with non-metals; and step
 (b) comprises electrolessly plating an amorphous seed layer comprising a
 material selected from Ni--P alloys with phosphorus (P) content in the
 range of from about 10 to about 13.5 wt. %, optionally followed by
 polishing of the Ni--P amorphous seed layer.
 According to further embodiments of the present invention, step (a)
 comprises sputter depositing a catalytically active layer of Ni-Al or
 Ni--P about 50 to about 5,000 .ANG. thick and further includes first
 depositing an adhesion layer comprising a metal, metal alloy, or ceramic
 layer on the substrate surface prior to depositing the catalytically
 active layer.
 According to a still further embodiment of the present invention, the
 method comprises the further steps of:
 (c) depositing a magnetic recording layer over the amorphous seed layer;
 and
 (d) forming a protective overcoat layer over the magnetic recording layer.
 According to another aspect of the present invention, a method of
 manufacturing a magnetic recording media comprises the sequential steps
 of:
 (a) providing a disk-shaped substrate comprising a material having a
 Young's modulus greater than that of Al and its alloys and a surface with
 a preselected Ra;
 (b) depositing a continuous, adherent, non-magnetic, catalytically active
 layer on the substrate surface by a PVD process, the catalytically active
 layer comprising a metal selected from Ni, Pd, Ti, Al, Zn, Cu, and alloys
 and compounds thereof with non-metals; and
 (c) electrolessly plating a seed layer of amorphous Ni--P on the
 catalytically active layer, the Ra of the resultant surface of the
 amorphous Ni--P seed layer being reduced from the preselected Ra of the
 substrate surface, and providing a substantially defect-free surface for
 deposition thereon of layers comprising the magnetic medium layer(s).
 According to embodiments of the present invention, step (a) comprises
 providing a substrate comprising a material selected from glass,
 glass-ceramics, ceramics, and metal-ceramics; and the method comprises the
 further steps of:
 (d) depositing a magnetic recording layer over the amorphous Ni--P seed
 layer; and
 (f) forming a protective overcoat layer over the magnetic recording layer.
 In further embodiments according to the present invention, step (a)
 comprises providing a glass-ceramic substrate having a surface Ra of about
 800 .ANG.; step (b) comprises sputter depositing a continuous,
 catalytically active layer comprising Ni--Al or Ni--P from about 50 to
 about 5,000 .ANG. thick; and step (c) comprises electrolessly plating a
 seed layer of amorphous Ni--P about 1 to about 20 .mu.m thick and having a
 resultant surface Ra of less than about 550 .ANG..
 In still further embodiments according to the present invention, step (b)
 further comprises depositing a layer of an adhesion promoting material
 selected from Cr, Ti, Cr--Ti alloys, alumina (Al.sub.2 O.sub.3), and other
 ceramics, from about 10 to about 100 .ANG. thick, on the substrate surface
 prior to depositing the catalytically active layer thereon.
 According to still another aspect of the present invention, a magnetic
 recording media comprising an alternative-type substrate and including an
 electrolessly plated seed layer formed according to the inventive
 methodology, is provided, comprising:
 a non-magnetic substrate having a Young's Modulus greater than that of Al
 and its alloys and a surface with a preselected surface roughness (Ra);
 a continuous, adherent, non-magnetic, catalytically active layer on the
 substrate surface; and
 an electrolessly plated, amorphous seed layer comprising a metal, metal
 alloy, or metal compound on the catalytically active layer, the surface of
 the amorphous seed layer being substantially defect-free and having an Ra
 less than that of the substrate surface.
 According to still another aspect of the present invention, a magnetic
 recording medium is provided, comprising:
 a non-magnetic substrate having a Young's Modulus greater than that of Al
 and a surface having a preselected average surface roughness Ra; and
 means for providing a substantially defect-free surface for formation of a
 magnetic recording layer thereover and having an Ra less than the
 preselected Ra.
 Additional advantages of the present invention will become readily apparent
 to those skilled in the art from the following detailed description,
 wherein embodiments of the invention are shown and described, simply by
 way of illustration of the best mode contemplated for practicing the
 present invention. As will be described, the present invention is capable
 of other and different embodiments, and its several details are
 susceptible of modification in various obvious respects, all without
 departing from the spirit of the present invention. Accordingly, the
 drawing and description are to be regarded as illustrative in nature, and
 not as limitative.

DESCRIPTION OF THE INVENTION
 The present invention addresses and solves problems arising from the
 inability to provide alternative-type substrates for use in magnetic
 recording media, such as hard disks, with suitable defect-free surfaces
 required for deposition of magnetic recording medium layers thereon. More
 specifically, the inventive methodology avoids the problems of poor
 lapability/grindability of glass, glass-ceramics, ceramics, and
 metal-ceramic composite alternative substrates and formation of poorly
 adherent, defect-containing amorphous seed layers thereon by conventional
 electroless plating techniques.
 According to the present invention, the above-enumerated problems and
 difficulties attendant upon the use of alternative-type substrates for the
 manufacture of magnetic recording media, such as hard disks, are
 eliminated, or at least minimized, by the inventive methodology wherein
 the conventional chemical sensitization step performed preliminary to
 electroless plating of the amorphous seed layer, which process typically
 results in formation of discontinuous catalytic metal deposits (i.e.,
 "islands") which in turn result in defects in the seed layer formed
 thereon, is replaced by a step of depositing a continuous, adherent,
 non-magnetic, catalytically active layer on the substrate surface.
 Subsequent electroless deposition of the amorphous seed layer on the
 continuous, catalytically active layer results in a smoothening effect,
 wherein the average surface roughness (Ra) of the resultant surface of the
 seed layer is lower than that of the underlying alternative-type
 substrate. The resultant surface of the seed layer, after polishing, is
 substantially defect-free with respect to the formation of the layers
 comprising the magnetic recording medium thereon. Alternatively, the
 resultant surface of the amorphous seed layer can receive a texturizing
 treatment, if desired.
 Referring now to FIG. 2, shown therein in simplified cross-sectional form,
 is an illustrative, but not limitative embodiment of the present
 invention, wherein similar reference numerals as shown in FIG. 1 are
 employed to denote similar features. As will be apparent to one of
 ordinary skill in the art, the inventive methodology is readily adapted
 for use in the manufacture of a variety of magnetic recording media, e.g.,
 magneto-optical (MO) media. It should also be recognized that the process
 steps and structures described below do not necessarily form a complete
 process flow for manufacturing such media. However, the present invention
 can be practiced in conjunction with conventional deposition techniques
 and methodologies as are currently employed in the art, and only so much
 of the commonly practiced process steps are included here as are necessary
 for providing an understanding of the present invention. Finally, the
 drawing figures each representing cross-sections of a portion of a
 magnetic recording medium are not drawn to scale, but instead are drawn as
 to best illustrate the features of the present invention.
 Referring now more particularly to FIG. 2, a longitudinal recording disk
 medium 2 according to the present invention, comprises an alternative-type
 substrate 20 comprising a material having a Young's Modulus greater than
 that of Al or Al-based alloys (e.g., Al--Mg), i.e., greater than about 72
 Gpa, and is selected from the group consisting of glass, glass-ceramics,
 ceramics, and metal-ceramic composites. The thickness of substrate 20 is
 selected to provide a desired rigidity and strength, and is in the range
 of from about 0.5 to about 1.27 mm thick, typically about 0.8 mm thick.
 According to the present invention, the substrate 20 can be utilized
 without any preliminary smoothening treatment of the upwardly facing
 surface 21, as by lapping, grinding, or polishing, providing the average
 roughness (Ra) thereof is less than about 2,000 .ANG., e.g., about 800
 .ANG.. Ready-to-use glass and glass-ceramic substrates suitable for the
 practice of the present invention and having an Ra&lt;2,000 .ANG. are
 available from inter alia, Hoya, Yamanashi, Japan; Ohara Corp., Kanagawa,
 Japan; and NGK-Locke, Inc., Sunnyvale, Calif.
 In a first step according to the present invention, a continuous, adherent,
 layer 22 from about 50 to about 5,000 .ANG. thick, typically about 100 to
 about 1,000 .ANG. thick, is deposited on the surface 21 of substrate 20,
 as by a physical vapor deposition (PVD), chemical vapor deposition (CVD),
 to plasma-enhanced chemical vapor deposition (PECVD) technique. Layer 22
 is comprised of a metal, a metal alloy, or a compound thereof with a
 non-metal and must fulfill the following requirements: (1) be
 non-magnetic; (2) be catalytically active for electroless plating thereon
 of suitable amorphous seed layer materials, e.g., Ni--P; and (3) have good
 adhesion to both the substrate and the seed layer. Suitable materials for
 catalytically active layer 22 include metals such as Ni, Pd, Ti, Al, Zn,
 Cu, and alloys (e.g., Ni--Al) and compounds thereof with non-metals, e.g.,
 NiP. In addition to the enumerated metals, a hybrid layer comprising a
 plurality of deposited metal layers can also be utilized.
 In some instances, an adhesion promoting layer 22A may be first deposited
 over substrate surface 21 prior to depositing catalytically active layer
 22 thereon. Such adhesion promoting layer 22A may be from about 10 to
 about 100 .ANG. thick, typically about 30 to about 40 .ANG. thick, and
 comprise a metal such as Cr or Ti and alloys thereof, or alumina (Al.sub.2
 O.sub.3) or other ceramic material.
 A suitable PVD technique for depositing each of the catalytically active
 and adhesion promoting layers is cathode sputtering, either DC or RF
 activated, depending upon the electrical conductivity of the sputtering
 target. By way of illustration, but not limitation, suitable continuous,
 adherent, catalytically active layers 22 comprising Ni--Al alloys or Ni--P
 (P=15-25 at %) compounds may be deposited by DC magnetron sputtering of
 similarly composed targets at a power density of about 0.5 kW/in.sup.2, an
 Ar pressure of about 10 mTorr, and a substrate temperature of about
 100.degree. C.
 In the next step according to the present invention, substrate 20 with
 continuous, catalytically active layer 22 formed on surface 21 is immersed
 in an electroless plating bath of the type conventionally utilized for
 forming amorphous plating layers on Al-based magnetic recording medium
 substrates, for forming thereon an amorphous seed layer 23 of a material
 which induces a next-deposited magnetic recording media underlayer 12,
 typically of Cr or Cr-based alloy, to exhibit polycrystallinity with a
 desired crystallographic orientation which, in turn, causes the magnetic
 alloy layer 13 deposited thereon to exhibit an optimal crystal
 microstructure for high-density recording. Suitable materials for
 amorphous seed layer 23 include Ni--P alloys with a P content of from
 about 10 to about 13.5 wt. %. According to a feature of the present
 invention, the amorphous seed layer is electrolessly plated for a
 sufficient interval under suitable conditions of temperature and solution
 replenishment such that: (1) the resultant thickness of the amorphous seed
 layer is about 1 to about 20 .mu.m, typically about 8 to about 12 .mu.m;
 and (2) the average surface roughness (Ra) of the resultant seed layer
 surface 23A is substantially less, typically at least about one-third
 less, than that of substrate surface 20A, e.g., less than about 550 .ANG..
 The resultant seed layer surface 23A provided by the inventive methodology
 is, after optional additional polishing depending upon the surface finish
 of the original substrate, substantially defectfree in relation to its
 intended use, i.e., manufacture of magnetic recording media. For example,
 if relatively rough (i.e., Ra&gt;100 .ANG.) substrate starting blanks are
 employed, post-electroless deposition polishing is required in order to
 the achieve low roughness surfaces contemplated by the present invention.
 However, according to the inventive methodology, polishing is
 advantageously performed on the softer, more friendly Ni--P amorphous seed
 layer surface rather than on the hard and/or multi-phase substrate
 surface, as in the conventional methodology. Alternatively, the need for
 polishing of the electrolessly-plated Ni--P amorphous seed layer may be
 eliminated by utilizing smooth substrate blanks (i.e., Ra&lt;100 .ANG.),
 in which case processing may proceed directly to texturing or media layer
 deposition.
 A particularly suitable material for use as amorphous seed layer 23 is
 Ni--P. Suitable baths for electroless plating of non-magnetic Ni--P layers
 are disclosed in U.S. Pat. No. 4,659,605, the entire disclosure of which
 is incorporated herein by reference. By way of illustration, but not
 limitation, a suitable electroless plating bath for deposition of
 amorphous Ni--P seed layers consistent with the requirements of the
 present invention includes a source of nickel ions (typically NiSO.sub.4),
 hypophosphite ions, a buffering agent (e.g., a carboxylic acid, boric acid
 or soluble borate, and an ester complex (e.g., an ester complex of
 glucoheptonic acid). Another suitable Ni--P electroless plating bath
 includes an unsaturated carboxylic acid, a nickel ion source, and
 hypophosphite ions. Baths of this type can provide amorphous Ni--P
 deposits with a phosphorus content within the range of from about 10 to
 about 13.5 wt. % at a high plating rate, which deposits are non-magnetic
 as provided and do not become magnetic with age. In addition to the above,
 electroless Ni--P plating baths usable in the present invention include,
 inter alia, Enthone 6450 (Enthone-OMI, New Haven, Conn.), Fidelity 4355
 (OMG Fidelity Chemical Products Corp., Newark, N.J.), and UIC SHDX
 (Uyemura Int'l Corp., Ontario, Calif.).
 Following electroless deposition of the amorphous seed layer 23 of
 sufficient thickness and reduced surface roughness (Ra) vis-a-vis the
 substrate surface 20A, magnetic underlayer 12 (typically of Cr or a
 Cr-alloy) is deposited thereon in conventional fashion without further
 surface treatment thereof other than optional polishing. Alternatively,
 the seed layer can be given a surface texturing or roughening treatment
 prior to deposition of magnetic underlayer 12 thereon, for inducing
 particular crystallographic structure of magnetic recording layer 13
 deposited thereon, as disclosed in U.S. Pat. No. 5,733,370, the entire
 disclosure of which is incorporated herein by reference. Protective
 overcoat layer 14 is then formed over magnetic recording layer 13 in
 conventional manner, as by use of materials and procedures disclosed in
 U.S. Pat. No. 5,733,370.
 EXAMPLE 1
 Glass-ceramic substrates (NGK-Locke Inc., Sunnyvale, Calif.) having an
 as-supplied surface roughness of about 800 .ANG. were sputtered with a 400
 .ANG. thick continuous, catalytically active layer and immersed in an
 Enthone 6450 (Enthone-OMI, New Haven, Conn.) electroless Ni--P plating
 bath at about 87-92.degree. C., without a conventional sensitizing
 pre-treatment step. After 2.5 hours, with bath replenishment, a uniform
 coating of Ni--P about 12.5 .mu.m thick was formed, with a reduced surface
 roughness (Ra) of about 550 .ANG..
 Similar results were obtained with the use of sputtered Ni--P continuous,
 catalytically active layers about 10 to about 1,000 .ANG. thick.
 EXAMPLE 2
 NGK glass-ceramic substrates of 800 .ANG. Ra were sputtered with a 400
 .ANG. thick adhesion layer of Cr, followed by a 200 .ANG. thick sputtered
 Ni--Al continuous, catalytically active layer. An about 12.5 .mu.m thick
 amorphous Ni--P layer was electrolessly plated thereon from a Fidelity
 4355 bath (Fidelity Chemical Products Corp., Newark, N.J.). The Ra of the
 Ni--P layer was about 550 .ANG..
 Thus, in view of the foregoing, the present invention provides a number of
 advantages over the conventional Pd-based chemical sensitization
 processing for activation of non-conductive, or partially non-conductive
 alternative hard drive substrates for electroless plating thereon as part
 of a manufacturing process for magnetic recording media. More
 specifically, the inventive methodology is cleaner and simpler in that a
 reduced amount of mechanical polishing of the softer Ni--P surface is
 required. Plating defects due to acid etching and non-uniform coverage by
 the Pd sensitizer layer are eliminated. Re-mounting of disk mandrels and
 fixtures as are required by conventional Pd-based sensitization processing
 are not necessary, and less waste is generated.
 In addition to the above, as compared to direct media processing of
 alternative-type substrates without a Ni--P seed layer, the present
 invention eliminates the requirement for preliminary
 grinding/lapping/polishing of the substrate prior to layer deposition
 thereon.
 In the previous description, numerous specific details are set forth, such
 as specific materials, structures, reactants, processes, etc., in order to
 provide a better understanding of the present invention. However, the
 present invention can be practiced without resorting to the details
 specifically set forth. In other instances, well known processing
 materials and techniques have not been described in detail in order not to
 unnecessarily obscure the present invention.
 Only the preferred embodiments of the present invention and but a few
 examples of its versatility are shown and described in the present
 disclosure. It is to be understood that the present invention is capable
 of use in various other combinations and environments and is susceptible
 of changes and/or modifications within the scope of the inventive concept
 as expressed herein.