Magnetic recording disk having pre-patterned surface features and planarized surface

A magnetic recording disk with pre-patterned surface features of elevated lands and recessed grooves or trenches, like a discrete-track media (DTM) or bit-patterned media (BPM) disk, has a planarized surface. A multilayered disk overcoat is used to protect the recording layer, and at least one of the overcoat layers functions as a stop layer for terminating a chemical-mechanical polishing (CMP) process that substantially planarizes the disk. All of the layers of the multilayered overcoat are located above the lands, but none of the overcoat layers, or a number of layers less than the number of layers over the lands, is located above the recesses.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a magnetic recording disk with pre-patterned surface features of elevated lands and recessed grooves or trenches, and more particularly to such a disk with a planarized surface.

2. Description of the Related Art

Conventional magnetic recording hard disk drives use either horizontal recording wherein the magnetized regions that define the magnetically recorded data bits are oriented in the plane of the recording layer on the hard disks, or perpendicular recording wherein the magnetized regions are oriented perpendicular to the plane of the recording layer. The conventional disk is a “continuous-media” (CM) disk wherein the recording layer is a continuous layer of magnetic material that becomes formed into concentric data tracks containing the magnetically recorded data bits when the write head writes on the magnetic material. The recording layer also includes a pre-recorded pattern of servo sectors that are used to position the read/write heads to the desired data tracks and maintain the heads on the data tracks during reading and writing. The conventional CM disk has a protective overcoat, typically formed of amorphous carbon, like diamond-like carbon (DLC), that covers the recording layer and provides a generally smooth planar surface. The read/write heads are located on air-bearing sliders that are supported above the smooth disk surface on a thin film of air or “air-bearing” as the disk rotates.

A variation of a CM disk is a “discrete-track media” (DTM) disk, meaning that the concentric data tracks of continuous magnetic material are radially separated from one another by concentric nonmagnetic guard bands. DTM disks are known in the art, as described for example in U.S. Pat. No. 4,912,585. In a DTM disk, the data tracks are typically elevated lands that contain magnetic material and the nonmagnetic guard bands are trenches or grooves that are recessed below the elevated lands. The nonmagnetic guard bands are either formed of nonmagnetic material or contain magnetic material but are recessed far enough below the elevated data tracks to not adversely the readback signals from the data tracks.

In addition to CM disks and DTM disks, magnetic recording disks with “bit-patterned media” (BPM) have been proposed to increase the data density. In BPM disks, the magnetizable material on the disk is patterned into small isolated data islands such that there is a single magnetic domain in each island or “bit”. The single magnetic domains can be a single grain or consist of a few strongly coupled grains that switch magnetic states in concert as a single magnetic volume. This is in contrast to conventional CM disks wherein a single “bit” may have multiple magnetic domains separated by domain walls. To produce the required magnetic isolation of the patterned islands, the magnetic moment of the spaces between the islands must be destroyed or substantially reduced so as to render these spaces essentially nonmagnetic. In one type of BPM disk, the data islands are elevated, spaced-apart pillars that are separated by nonmagnetic trenches or recesses.

DTM disks and BPM disks also require servo sectors that are angularly spaced around the disk and extend generally radially across the concentric data tracks. The servo sectors are pre-recorded patterns that cannot be written over by the write heads and that are used to position the read/write heads to the desired data tracks and maintain the heads on the data tracks during reading and writing. In both DTM disks and BPM disks, the servo sectors may be pre-patterned surface features of elevated servo blocks of magnetic material separated by nonmagnetic trenches or recesses.

There are several methods for fabricating disks with surface features of elevated lands and recessed grooves. In one technique, applicable for both DTM and BPM disks, all the required layers, including the layer or layers of magnetic recording material, are deposited on the disk substrate, typically by sputter deposition. The disk is then lithographically patterned into the desired pattern of data tracks and guard bands, as well as servo sectors. A vacuum etch process, such as ion milling or reactive ion etching (RIE), then removes the exposed magnetic recording material. This results in lands of magnetic material and nonmagnetic grooves recessed from the upper surface of the lands.

In another technique, particularly applicable for BPM disks, the disks are produced by replication from a mold via nanoimprinting. The nanoimprinting process forms not only the isolated data islands in the data tracks, but also the servo blocks in the servo sectors. In nanoimprinting, a mold or template replicates a topographic pattern of surface features onto a polymeric resist coating on the disk substrate. The disk substrate may have a dielectric coating, such as a silicon nitride film. The nanoimprinted resist pattern is then used as a mask for etching the pattern into the silicon nitride film with a fluorine plasma. After etching the silicon nitride, the resist is removed. Magnetic material is then sputter deposited over the lands and grooves. The grooves may be recessed far enough from the read/write heads to not adversely affect reading or writing, or they may be “poisoned” with a dopant material to render them nonmagnetic.

For DTM disks and BPM disks there is a need to planarize the surface topography so that the slider is maintained at a relatively constant “fly height” by the air-bearing generated by the rotating disk. Planarization is especially important to reduce or eliminate slider excitations induced by transitioning from a data to servo region or from a servo to data region.

What is needed is a disk with pre-patterned surface features of elevated lands and recessed grooves or trenches that has a planarized surface.

SUMMARY OF THE INVENTION

In the disk according to this invention a multilayered disk overcoat is used, and at least one of the overcoat layers functions as a stop layer for terminating a chemical-mechanical polishing (CMP) process that substantially planarizes the disk. All of the layers of the multilayered overcoat are located above the lands, but none of the overcoat layers, or a number of layers less than the number of layers over the lands, is located above the recesses.

In a first embodiment, a first overcoat layer of a subsequent multilayered overcoat is deposited on top of the recording layer. The first overcoat layer will function as a CMP stop layer. The disk is then lithographically patterned and etched, leaving elevated lands of recording layer material and grooves or recesses. The lands have an upper surface on which the first overcoat layer is deposited and the recesses have a lower surface below the upper surface of the lands. The etching may been performed to a depth such that all of the recording layer material is removed from the regions of the recesses, or to a depth such that only a portion of the recording layer material is removed. Fill material is then deposited over the entire surface of the etched disk, and CMP is then performed. The material selected for the fill material has a CMP removal rate that is faster than the CMP removal rate for the first overcoat layer so that the first overcoat layer functions as a CMP stop layer. After CMP, a second overcoat layer is deposited, typically by sputter deposition, on the substantially planar surface of the upper surface of the first overcoat layer and the upper surface of the fill material. The second overcoat layer can be a different or a similar material to the first overcoat layer. In the first embodiment the first overcoat layer is located only on the lands and the second overcoat layer is located on both the lands and the fill material in the recesses.

In a second embodiment, both overcoat layers are located only above the lands and no overcoat layer is located above the fill material in the recesses, so that the upper surface of the second overcoat layer is substantially planar with the upper surface of the fill material in the recesses.

In a third embodiment the disk is lithographically patterned and etched before the first overcoat layer is deposited, leaving elevated lands of recording layer material and grooves or recesses. The first overcoat layer of a subsequent multilayered overcoat is then deposited over the entire surface of the etched disk to cover the top surface of the lands, the lower surface of the recesses and the sidewalls of the recesses. The first overcoat layer will function as a CMP stop layer. Fill material is then deposited over the entire surface of the disk to cover the first overcoat on the top surface of the lands and fill the recesses. CMP is then performed using the first overcoat layer as a CMP stop layer. After CMP, a second overcoat layer is deposited on the substantially planar surface of the upper surface of first overcoat layer and the upper surface of the fill material. In the third embodiment the first overcoat layer is located on the lands, in the bottom of the recesses and the sidewalls of the recesses, and the second overcoat layer is located on both the lands and the fill material in the recesses.

The fill material may be a silicon oxide (SiOx), a silicon nitride (SiN), a SiOx-metal or SiN-metal, amorphous carbon, a Ti alloy, or a metal selected from W, Ti, Ta, and Cu. The materials that may be used for the first and second overcoat layers include amorphous carbon, carbides such as silicon carbides and boron carbides, nitrides such as silicon nitrides, titanium nitrides, and boron nitrides, and metal oxides, such as TiO2, ZrO2, Al2O3, Cr2O3, Ta2O5and ZrO2—Y2O3.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1illustrates a disk drive with a rotary actuator2and a rigid magnetic recording disk10having pre-patterned surface features formed on surface11. The surface features include at least pre-patterned servo blocks in angularly-spaced servo sectors18. The disk10rotates in the direction102about a central axis100. The surface11has an annular data band12which is defined by an inside diameter (ID)14and an outside diameter (OD)16. The portions of the data band between the servo sectors18are used for the storage of user data and contain circular data tracks, with each data track being typically divided into physical data sectors. The disk10may be a DTM disk, in which case the circular data tracks are discrete radially-spaced elevated tracks separated by recessed guard bands, with the elevated tracks and recessed guard bands forming surface features in addition to the servo blocks in servo sectors18. The disk10may also be a BPM disk, in which case the circular data tracks contain discrete elevated data islands separated by recesses, with the elevated islands and recesses forming surface features in addition to the servo blocks in servo sectors18.

The rotary actuator2rotates about pivot4and supports a read/write head6at its end. As the actuator2rotates, the head6follows a generally arcuate path between ID14and OD16. The servo sectors18form a pattern of angularly spaced arcuate lines that extend generally radially from ID14to OD16. The arcuate shape of the servo sectors matches the arcuate path of head6. During operation of the disk drive, the head6reads or writes data on a selected one of a number of concentric circular data tracks located between the ID14and OD16of the annular data band12. To accurately read or write data from a selected track, the head6is required to be maintained over the centerline of the track. Accordingly, each time one of the servo sectors18passes beneath the head6, the head6detects discrete magnetized servo blocks in the position error signal (PES) field in the servo sector. A PES is generated and used by the disk drive's head positioning control system to move the head6towards the track centerline. Thus, during a complete rotation of the disk10, the head6is continually maintained over the track centerline by servo information from the servo blocks in successive angularly spaced servo sectors18.

FIG. 2Ais an expanded top view of disk10where the disk is a DTM disk and shows a typical servo sector18and portions of three DTM data tracks20,22,24. Three discrete elevated data tracks20,22,24and two recessed guard bands21,23are shown. All of the shaded portions of servo sector18represent discrete elevated servo blocks magnetized in the same direction. They may all be magnetized in the same direction horizontally, i.e., in the plane parallel to the plane of the paper inFIG. 2Aif the disk drive is designed for longitudinal or horizontal magnetic recording, or perpendicularly, i.e., into or out of the plane of the paper if the disk drive is for perpendicular magnetic recording. The non-shaded regions70in servo sector18, and the guard bands21,23, represent nonmagnetic regions that are recessed from the elevated servo blocks and elevated data tracks20,22,24. The term “nonmagnetic” means that the regions70between the servo blocks, and guard bands21,23between the data tracks20,22,24, are recesses or grooves that contain a nonferromagnetic material, such as a dielectric, or a material that has no substantial remanent moment in the absence of an applied magnetic field, or a ferromagnetic material that is recessed far enough below the elevated servo blocks to not adversely affect reading or writing. The nonmagnetic regions70and guard bands21,23may also be recessed grooves or trenches in the magnetic recording layer or disk substrate that contain no ferromagnetic material.

The servo blocks that make up servo sector18are arranged in fields30,40,50and60, as shown inFIG. 2A. Servo field30is an automatic gain control (AGC) field of blocks31-35that are used to measure the amplitude of the signal and adjust the gain for the subsequently read servo blocks. Servo field40is sector identification (SID) field, also called a servo timing mark or S™ field, to provide a timing mark to establish start/stop timing windows for subsequent servo blocks. Servo field50is a track identification (TID), also called the cylinder or CYL field because the tracks from all of the disk surfaces in a disk drive with a multiple stacked disks from a “cylinder” of tracks. The TID field50contains the track number, typically Gray-coded, and determines the integer part of the radial position. Servo field60is the position error signal (PES) field, which in this example contain A, B, C, D subfields of servo blocks as part of the well-known “quad-burst” PES pattern, and are used to determine the fractional part of the radial position.

FIG. 2Bis a schematic illustration of a top view of a portion of disk10where the disk is a BPM disk. The three data tracks20,22,24each contain discrete isolated data islands164and are shown with two successive servo sectors18that extend generally radially across the concentric data tracks20,22,24. The islands164are depicted as having a square shape, but the islands may be patterned in different shapes, such as circular, generally elliptical or generally rectangular. Like the servo blocks in servo sector18(FIG. 2A), each data track20,22,24contains discrete elevated spaced-apart lands that are islands164of magnetic material. The discrete islands are separated from other islands by recessed nonmagnetic regions70. The BPM disk shown inFIG. 2Bthus contains surface features of elevated lands and recessed grooves not only in the servo sectors18, but also in the data tracks20,22,24.

The planarized disk with surface features of elevated lands and recessed grooves according to the invention, and the method for planarizing the disk, will be explained withFIGS. 3A-3E, which show sectional views of a DTM disk taken along a plane perpendicular to the discrete data tracks at various stages of the method. However, the method and resulting disk planarized by the method are also fully applicable to a BPM disk. In this invention a multilayered disk overcoat is used, and at least one of the overcoat layers functions as a stop layer for terminating a chemical-mechanical polishing (CMP) process that substantially planarizes the disk. All of the layers of the multilayered overcoat are located above the lands but none of the overcoat layers, or a number of layers less than the number of layers over the lands, are located above the recesses.

FIG. 3Ais a sectional view showing the disk200prior to lithographic patterning and etching to form the DTM disk. The disk200is a substrate201having a generally planar surface202on which the representative layers are deposited, typically by sputtering. The disk200is depicted as a perpendicular magnetic recording disk with a recording layer (RL) having perpendicular (i.e., generally perpendicular to substrate surface201) magnetic anisotropy and an optional soft magnetic underlayer (SUL) below the RL. The optional SUL serves as a flux return path for the magnetic write field from the disk drive write head.

The hard disk substrate201may be any commercially available glass substrate, but may also be a conventional aluminum alloy with a NiP surface coating, or an alternative substrate, such as silicon, canasite or silicon-carbide. An adhesion layer or onset layer (OL) for the growth of the SUL may be an AlTi alloy or a similar material with a thickness of about 2-10 nm is deposited on substrate surface202.

The SUL may be formed of magnetically permeable materials such as alloys of CoNiFe, FeCoB, CoCuFe, NiFe, FeAlSi, FeTaN, FeN, FeTaC, CoTaZr, CoFeTaZr, CoFeB, and CoZrNb. The SUL may also be a laminated or multilayered SUL formed of multiple soft magnetic films separated by nonmagnetic films, such as electrically conductive films of Al or CoCr. The SUL may also be a laminated or multilayered SUL formed of multiple soft magnetic films separated by interlayer films that mediate an antiferromagnetic coupling, such as Ru, Ir, or Cr or alloys thereof. The SUL may have a thickness in the range of about 5 to 50 nm.

An exchange-break layer (EBL) is typically located on top of the SUL. It acts to break the magnetic exchange coupling between the magnetically permeable films of the SUL and the RL and also serves to facilitate epitaxial growth of the RL. The EBL may not be necessary, but if used it can be a nonmagnetic titanium (Ti) layer; a non-electrically-conducting material such as Si, Ge and SiGe alloys; a metal such as Cr, Ru, W, Zr, Nb, Mo, V and Al; a metal alloy such as amorphous CrTi and NiP; an amorphous carbon such as CNx, CHxand C; or oxides, nitrides or carbides of an element selected from the group consisting of Si, Al, Zr, Ti, and B. The EBL may have a thickness in the range of about 5 to 40 nm.

The RL may be a single layer or multiple layers of any of the known amorphous or crystalline materials and structures that exhibit perpendicular magnetic anisotropy. Thus, the RL may be a layer of granular polycrystalline cobalt alloy, such as a CoPt or CoPtCr alloy, with a suitable segregant such as oxides of one or more of Si, Ta, Ti, Nb, Cr, V and B. Also, the RL may be composed of multilayers with perpendicular magnetic anisotropy, such as Co/Pt, Co/Pd, Fe/Pt and Fe/Pd multilayers, with or without a suitable segregant such as those mentioned above. In addition, perpendicular magnetic layers containing rare earth elements are useable for the RL, such as CoSm, TbFe, TbFeCo, GdFe alloys. The RL may also be formed of chemically ordered CoPt, CoPd, FePt or FePd. These chemically ordered alloys, in their bulk form, are known as face-centered tetragonal (FCT) L10-ordered phase materials (also called CuAu materials). The c-axis of the L10phase is the easy axis of magnetization and is oriented perpendicular to the substrate. Like the Co/Pt and Co/Pd multilayers, these layers exhibit very strong perpendicular magnetic anisotropy. The total thickness of the RL is typically in the range of about 5 to 25 nm.

A first overcoat layer210of a subsequent multilayered overcoat is deposited on top of the RL. The first overcoat layer210will function as a CMP stop layer and is preferably a layer of amorphous carbon like diamond-like carbon (DLC), or a silicon nitride (SiN) such as predominantly Si3N4, sputter deposited to a thickness of about 1 to 3 nm. The amorphous carbon CMP stop layer may contain elements such as hydrogen or nitrogen.

FIG. 3Bis a sectional view of the disk200after lithographic patterning and etching. The etching may be a vacuum etching process like ion milling or reactive ion etching (RIE). After etching, elevated lands220of RL material and grooves or recesses230are formed above the substrate surface202. The lands220have an upper surface221on which the first overcoat layer210is deposited. The recesses230have a lower surface231below the upper surface221of the lands220. In the example shown inFIG. 3B, the etching has been performed to a depth such that all of the RL material and a portion of the EBL material has been removed from the regions of the recesses230. However, alternatively the etching can be performed to a depth such that only a portion of the RL material is removed. In that case, there would be a layer of RL material below the lower surface231of the recesses230.

FIG. 3Cis a sectional view of the disk200after deposition of fill material240. The fill material240is preferably a silicon oxide (SiOx), such as predominantly SiO2, that is sputter deposited. Other materials that may be used for the fill material240include a silicon nitride (SiN) such as predominantly Si3N4; SiOx-metal or SiN-metal where the metal can be Ti, Ta, Al Cr or Pt; amorphous DLC including hydrogenated or nitrogenated amorphous DLC; Ti alloys; and a metal selected from W, Ti, Ta, and Cu. The fill material may be sputter deposited as a single continuous layer or in multiple layers, as would be the case if the sputter deposition is done in multiple steps, such as in sequential sputter deposition stations. Also, it possible that the fill material can be formed of multiple layers of different materials, such as a layer of SiOx and a layer of SiN. Other materials may be alloys or mixtures of the above materials. The material selected for the fill material240should have a CMP removal rate that is faster than the CMP removal rate for the first overcoat layer210so that the first overcoat layer210functions as the CMP stop layer.

FIG. 3Dis a sectional view of the disk200after CMP has removed the fill material240down to the stop layer (first overcoat layer210). The first overcoat layer210may be made thinner than originally deposited due to either the CMP step or by a subsequent process step such as a plasma etch. The fill material240now remains in the recesses on top of lower recess surface231. The upper surface241of the fill material in the recesses may experience a very slight recession following CMP, as depicted inFIG. 3D. However, the upper surface241of the recesses and the upper surface of first overcoat layer210together form a substantially planar surface. As used herein, “substantially planar” means that the recession of upper surface241of the fill material in the recesses is less than about 5 nm from the upper surface of first overcoat layer210and not sticking above the upper surface of first overcoat layer210by more than about 1 nm. CMP is a well-known process widely used in semiconductor manufacturing and thin-film magnetic recording head manufacturing. The CMP slurry may include a liquid that softens the fill material and a particle that helps cut through the softened fill material to remove it. CMP slurries with different chemical properties are commercially available and are selected based on the material to be removed. Also various CMP endpoint detection systems and techniques are known. For example, measurement of platen and carrier motor current and measurement of platen temperature by infrared (IR) sensor can be used to determine when the CMP process has reached the stop layer.

FIG. 3Eis a sectional view of the disk200after deposition of the second overcoat layer212and lubricant layer250, and thus depicts the completed disk structure according to one embodiment of the invention. The second overcoat layer212is deposited, typically by sputter deposition, on the substantially planar surface of the upper surface of first overcoat layer210and the upper surface241of the fill material240. The second overcoat layer212is preferably a different material from the first overcoat layer210. Preferably the second overcoat layer212is amorphous carbon, like DLC, which may also be hydrogenated or nitrogenated, and is sputter deposited to a thickness between about 1-2 nm. The materials that may be used for the first and second overcoat layers include amorphous carbon such as DLC; carbides such as silicon carbides and boron carbides; nitrides such as silicon nitrides, titanium nitrides, and boron nitrides; ametal oxides, such as TiO2, ZrO2, Al2O3, Cr2O3, Ta2O5and ZrO2—Y2O3; and mixtures of these materials Also, while only two overcoat layers are depicted and described, the multilayered overcoat may have three or more layers. Thus, in the embodiment ofFIGS. 3A-3Ethe first overcoat layer210is located only on the lands220and the second overcoat layer212is located on both the lands220and the fill material240in recesses230.

The lubricant layer250may be a conventional disk lubricant, like a perfluorinated polyether (PFPE) polymer, that is either bonded or unbounded to the second overcoat layer212. The lubricant is typically applied by dipping the disk into a solution of the PFPE in a suitable solvent and then evaporating the solvent.

FIG. 4is a sectional view of a disk200′ according to a second embodiment of the invention. In this embodiment both overcoat layers210,212form a multilayered overcoat and are located only above the lands220with the upper surface of second overcoat layer214being substantially planar with the upper surface241of the fill material240in the recesses. The disk200′ is made in a process similar to that shown inFIGS. 3A-3E, except that inFIG. 3A, the second overcoat layer212is sputter deposited on top of the first overcoat layer210. The remaining process steps are like those shown inFIGS. 3B-3D, after which the lubricant layer is applied, resulting in the disk200′ shown inFIG. 4. The first and second overcoat layers are different materials, preferably a SiN or amorphous carbon, and the fill material is preferably a silicon oxide. In this embodiment the second overcoat layer212functions as the CMP stop layer.

FIGS. 5A-5Dshow an embodiment of the method for planarizing the disk, and the resulting planarized disk, according to a third embodiment of the invention.

FIG. 5Ais a sectional view showing the disk200″ prior to lithographic patterning and etching to form the DTM disk. The disk200″ is like that shown inFIG. 3Aexcept there is no first overcoat layer, so that the upper surface of the disk is the upper surface of the RL.

FIG. 5Bis a sectional view of the disk200″ after lithographic patterning and etching. The etching may be a vacuum etching process like ion milling or reactive ion etching (RIE). After etching, elevated lands220of RL material and grooves or recesses230are formed above the substrate surface202. The lands220have an upper surface221. The recesses230have a lower surface231below the upper surface221of the lands220. In the example shown inFIG. 5B, the etching has been performed to a depth such that all of the RL material and a portion of the EBL material has been removed from the regions of the recesses230. However, alternatively the etching can be performed to a depth such that only a portion of the RL material is removed. In that case, there would be a layer of RL material below the lower surface231of the recesses230. Also, alternatively the etching can be performed to a depth such that substantially all the of the RL is removed and essentially none of the EBL is removed.

FIG. 5Cis a sectional view of the disk200″ after deposition of first overcoat layer210. The first overcoat layer210of a subsequent multilayered overcoat is deposited on the top surface221of the lands220and into the recesses230. This results in the first overcoat layer210being located on the lower surface231of the recesses and on the sidewalls of the recesses. The first overcoat layer210will function as a CMP stop layer and is preferably a layer of amorphous carbon, DLC or a silicon nitride (SiN) sputter deposited to a thickness of about 1-3 nm. Next, fill material is deposited, like inFIG. 3C, and then the fill material is removed down to the stop layer (first overcoat layer210) by the CMP process, like inFIG. 3D.

FIG. 5Dis a sectional view of the disk200″ after deposition of the second overcoat layer212and lubricant layer250, and thus depicts the completed disk structure according to the third embodiment of the invention. The disk200″ inFIG. 5Dis thus like the disk200inFIG. 3E, except that the first overcoat layer210is also located on the lower surface231of the recesses and the sidewalls of the recesses.