US20050264949A1 - Recessed SiO2 or Si3N4 overcoat for GMR head in magnetic disk drive - Google Patents
Recessed SiO2 or Si3N4 overcoat for GMR head in magnetic disk drive Download PDFInfo
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- US20050264949A1 US20050264949A1 US10/857,036 US85703604A US2005264949A1 US 20050264949 A1 US20050264949 A1 US 20050264949A1 US 85703604 A US85703604 A US 85703604A US 2005264949 A1 US2005264949 A1 US 2005264949A1
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- overcoat layer
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/127—Structure or manufacture of heads, e.g. inductive
- G11B5/31—Structure or manufacture of heads, e.g. inductive using thin films
- G11B5/3109—Details
- G11B5/313—Disposition of layers
- G11B5/3133—Disposition of layers including layers not usually being a part of the electromagnetic transducer structure and providing additional features, e.g. for improving heat radiation, reduction of power dissipation, adaptations for measurement or indication of gap depth or other properties of the structure
- G11B5/3136—Disposition of layers including layers not usually being a part of the electromagnetic transducer structure and providing additional features, e.g. for improving heat radiation, reduction of power dissipation, adaptations for measurement or indication of gap depth or other properties of the structure for reducing the pole-tip-protrusion at the head transducing surface, e.g. caused by thermal expansion of dissimilar materials
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/127—Structure or manufacture of heads, e.g. inductive
- G11B5/31—Structure or manufacture of heads, e.g. inductive using thin films
- G11B5/3103—Structure or manufacture of integrated heads or heads mechanically assembled and electrically connected to a support or housing
- G11B5/3106—Structure or manufacture of integrated heads or heads mechanically assembled and electrically connected to a support or housing where the integrated or assembled structure comprises means for conditioning against physical detrimental influence, e.g. wear, contamination
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/127—Structure or manufacture of heads, e.g. inductive
- G11B5/31—Structure or manufacture of heads, e.g. inductive using thin films
- G11B5/3109—Details
- G11B5/313—Disposition of layers
- G11B5/3133—Disposition of layers including layers not usually being a part of the electromagnetic transducer structure and providing additional features, e.g. for improving heat radiation, reduction of power dissipation, adaptations for measurement or indication of gap depth or other properties of the structure
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/127—Structure or manufacture of heads, e.g. inductive
- G11B5/31—Structure or manufacture of heads, e.g. inductive using thin films
- G11B5/3163—Fabrication methods or processes specially adapted for a particular head structure, e.g. using base layers for electroplating, using functional layers for masking, using energy or particle beams for shaping the structure or modifying the properties of the basic layers
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49002—Electrical device making
- Y10T29/4902—Electromagnet, transformer or inductor
- Y10T29/49021—Magnetic recording reproducing transducer [e.g., tape head, core, etc.]
- Y10T29/49032—Fabricating head structure or component thereof
- Y10T29/49036—Fabricating head structure or component thereof including measuring or testing
- Y10T29/49043—Depositing magnetic layer or coating
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49002—Electrical device making
- Y10T29/4902—Electromagnet, transformer or inductor
- Y10T29/49021—Magnetic recording reproducing transducer [e.g., tape head, core, etc.]
- Y10T29/49032—Fabricating head structure or component thereof
- Y10T29/49036—Fabricating head structure or component thereof including measuring or testing
- Y10T29/49043—Depositing magnetic layer or coating
- Y10T29/49044—Plural magnetic deposition layers
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49002—Electrical device making
- Y10T29/4902—Electromagnet, transformer or inductor
- Y10T29/49021—Magnetic recording reproducing transducer [e.g., tape head, core, etc.]
- Y10T29/49032—Fabricating head structure or component thereof
- Y10T29/49036—Fabricating head structure or component thereof including measuring or testing
- Y10T29/49043—Depositing magnetic layer or coating
- Y10T29/49046—Depositing magnetic layer or coating with etching or machining of magnetic material
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49002—Electrical device making
- Y10T29/4902—Electromagnet, transformer or inductor
- Y10T29/49021—Magnetic recording reproducing transducer [e.g., tape head, core, etc.]
- Y10T29/49032—Fabricating head structure or component thereof
- Y10T29/49048—Machining magnetic material [e.g., grinding, etching, polishing]
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49002—Electrical device making
- Y10T29/4902—Electromagnet, transformer or inductor
- Y10T29/49021—Magnetic recording reproducing transducer [e.g., tape head, core, etc.]
- Y10T29/49032—Fabricating head structure or component thereof
- Y10T29/49048—Machining magnetic material [e.g., grinding, etching, polishing]
- Y10T29/49052—Machining magnetic material [e.g., grinding, etching, polishing] by etching
Definitions
- a moving magnetic storage medium typically a disk
- the changing magnetic flux from magnetized regions in the moving storage disk induces a changing magnetic flux in the pole-tips and the gap between them.
- the magnetic flux is carried through the pole-tips and yoke-shaped core and around spiral conductor coil winding turns located between the yoke arms.
- the changing magnetic flux induces an electrical voltage across the conductor coil.
- the electrical voltage is representative of the magnetic pattern stored on the moving magnetic storage disk.
- an electrical current is caused to flow through the conductor coil.
- the current in the coil induces a magnetic field across the gap between the pole-tips.
- a fringe field extends into the nearby moving magnetic storage disk, inducing (or writing) a magnetic domain in the magnetic storage disk. Impressing current pulses of alternating polarity across the coil causes the writing of magnetic domains of alternating polarity in the storage disk.
- the GMR head is normally attached to a substrate, the head and substrate together forming a slider.
- the substrate includes aerodynamic surfaces that cause the slider to “fly” over the moving disk.
- the “flying height” of the GMR heads has become lower.
- the reduced flying height is necessary to enable the head to read the data bits stored on the disk effectively and without interference or crosstalk from adjacent data bits.
- the top layer in the head is a relatively thick “overcoat layer” that is formed of alumina (Al 2 O 3 ).
- alumina Al 2 O 3
- CTE coefficient of thermal expansion
- ABS air-bearing surface
- Other materials with lower CTEs might be desirable as substitutes for alumina in the overcoat layer, but in many cases these other materials present manufacturability problems.
- the recess is formed by a process that includes: depositing (e.g., plating) a seed layer on the surface of the overcoat layer, depositing a mask layer over the seed layer, the mask layer having an opening where the recess is to be located thereby exposing a section of the seed layer, wet-etching the exposed section of the seed layer through the opening in the mask layer, removing any remaining portions of the exposed section of the seed layer by a reactive ion etch (ion milling), and etching the recess in the overcoat layer through the opening in the mask layer by reactive ion etching.
- depositing e.g., plating
- a plurality of heads are formed on a single wafer, and the process described above is used to form a rectilinear lattice of trenches that separate the individual heads.
- the recess is located on one side of each head. Therefore, the dicing saw that is used to separate the heads cuts a path that abuts three sides of each head and is separated from the fourth side of each head by a distance that is substantially equal to the width of the recess.
- FIG. 1 is a side view of a conventional slider containing a GMR head.
- FIG. 3 is a detailed cross-sectional view of a GMR head in accordance with the invention.
- FIGS. 5A and 5B are top views of a portion of a wafer containing GMR heads prior to dicing.
- FIG. 6A is a cross-sectional view of a portion of the wafer before the GMR heads are separated.
- FIG. 8 is a graph showing the size of the temperature-induced protrusion generated by a silicon dioxide overcoat layer as a function of the width of the recess.
- FIG. 10 is a graph showing the rise time of the magnetic flux in a head containing a recessed overcoat as compared with the rise time of the magnetic flux in a head containing a non-recessed overcoat.
- Overcoat layer 106 is customarily made of alumina.
- Alumina has a relatively high coefficient of thermal expansion (CTE) of 6 ⁇ m/m/° C. It would be preferable to use a material such as silicon dioxide, which has a CTE of 2 ⁇ mlm/° C., or silicon nitride, which has a CTE of 3 ⁇ m/m/° C.
- CTE coefficient of thermal expansion
- silicon dioxide which has a CTE of 2 ⁇ mlm/° C.
- silicon nitride which has a CTE of 3 ⁇ m/m/° C.
- a 30-50% reduction in the size of the temperature-induced protrusion can be achieved by forming the overcoat layer of silicon dioxide or silicon nitride.
- FIGS. 4A-4H illustrate a cross-sectional view of two GMR heads 260 and 262 in a wafer 250 .
- the details of GMR heads 260 and 262 have been omitted. Only the contour of the yoke is shown.
- FIGS. 4A-4H will be used to explain the process of forming recesses 208 .
- seed layer materials listed in Table 1 are illustrative only and not limiting. Other conductive metals can be used as the seed layer.
- the HCl/ferrous sulfate etchant will etch a CoFe/CoFeN seed layer without etching plated NiFe, even after etching over 6 minutes.
- a typical etch for a 1500 ⁇ seed layer may last 1 to 3 minutes.
- the NaH 4 OH/ammonium persulfate etchant will also attack NiFe, but at a different rate than Cu. Typically, 15 to 45 seconds are required to etch a 1500 ⁇ Cu seed layer.
- Overcoat layer 206 is etched using a reactive ion etch (RIE) process.
- RIE reactive ion etch
- a Unaxis etcher may be used.
- the RIE may be CF 4 based, with the RF power at 100-300 W.
- the silicon dioxide or silicon nitride etchs at a rate of 4000 ⁇ /min. If overcoat layer 206 is formed of silicon nitride, 20-100 sccm of CHF 3 are added to the RIE.
- trenches 278 because of the formation of trenches 278 , the dicing saw does not need to cut into overcoat layer 206 which, being made of silicon dioxide and silicon nitride, is prone to chipping and cracking. Moreover, as described above, certain of the trenches 278 are used to form recesses 208 .
- FIG. 6B shows head 260 after it has been separated from the surrounding heads, with trench 278 forming recess 208 .
- FIG. 8 is a graph showing the temperature-induced protrusion of a silicon dioxide overcoat layer as a function of the width of the recess (measured from the ABS). As indicated, the temperature-induced protrusion increases as the width of the recess increases. It has been found that a recess having a width of 3 ⁇ 2 ⁇ m is desirable to maintain a relatively low and stable pole-top recess (PTR).
- PTR pole-top recess
- FIG. 9 is a graph showing the relative change in the temperature-induced protrusion of four of the layers in a GMR head as the temperature increases from 25° C. to 75° C.
- the four layers are the undercoat layer (UC), the pole layers P 1 and P 2 , and the silicon dioxide overcoat layer (OC). Note that the PTR of the silicon dioxide overcoat layer has been reduced about 3 nm as the temperature increases from 25° C. to 75° C.
- FIGS. 10 and 11 this change significantly improves the magnetic performance of the head.
- FIG. 10 shows that the magnetic flux rise time (t r ) of a head having a recessed overcoat is significantly less than the rise time of a non-recessed overcoat head.
- FIG. 11 indicates that the write current required to saturate a recessed overcoat head is significantly less than the write current required to saturate a non-recessed overcoat head
- this invention permits the use of silicon dioxide or silicon nitride as an overcoat layer in a GMR head, with the consequent reduction in CTE and temperature-induced protrusion, without creating any fabrication problems and without sacrificing the electromagnetic performance of the head.
Abstract
A giant magnetoresistive (GMR) head contains an overcoat layer consisting of silicon dioxide or silicon nitride. These materials have a coefficient of thermal expansion (CTE) that is less than alumina, which is conventionally used for the overcoat layer. As a result, the overcoat layer exhibits a smaller temperature-induced protrusion when the head heats up from friction with the passing air stream. The process of forming the head includes forming a recess in the overcoat layer that reduces the stress on the poles and improves the performance of the head. The process includes depositing a seed layer over the overcoat layer in preparation to plating a metal mask layer with an opening where the recess is to be formed, wet chemical etching the seed layer through the opening in the mask layer and performing an ion milling process to remove any remaining traces of the seed layer. With the seed layer completely removed, a trench having smooth sidewalls and bottom can be etched in the overcoat layer by a reactive ion etch (RIE) process. The saw that is used to separate the head elements in the wafer can be passed through the clean trench without contacting the overcoat layer, thereby avoiding the chipping and cracking that might otherwise result from the use of a silicon dioxide or silicon nitride overcoat layer.
Description
- This invention relates to giant magnetoresistive (GMR) heads for recording and reading magnetic transitions on a moving magnetic medium. In particular, this invention relates to the problems created by the thermal expansion of the layers in such GMR heads.
- In the operation of a typical GMR head device, a moving magnetic storage medium, typically a disk, is placed near the pole-tips of the GMR head. During the read operation, the changing magnetic flux from magnetized regions in the moving storage disk induces a changing magnetic flux in the pole-tips and the gap between them. The magnetic flux is carried through the pole-tips and yoke-shaped core and around spiral conductor coil winding turns located between the yoke arms. The changing magnetic flux induces an electrical voltage across the conductor coil. The electrical voltage is representative of the magnetic pattern stored on the moving magnetic storage disk. During the write operation, an electrical current is caused to flow through the conductor coil. The current in the coil induces a magnetic field across the gap between the pole-tips. A fringe field extends into the nearby moving magnetic storage disk, inducing (or writing) a magnetic domain in the magnetic storage disk. Impressing current pulses of alternating polarity across the coil causes the writing of magnetic domains of alternating polarity in the storage disk.
- The GMR head is normally attached to a substrate, the head and substrate together forming a slider. The substrate includes aerodynamic surfaces that cause the slider to “fly” over the moving disk.
- As the recording density of the magnetic domains in the magnetic disks increases, the “flying height” of the GMR heads has become lower. The reduced flying height is necessary to enable the head to read the data bits stored on the disk effectively and without interference or crosstalk from adjacent data bits.
- The lessening in the flying height has created a number of problems in the fabrication of the GMR heads. One of these problems relates to the thermal properties of the layers that together make up the head. In particular, the head tends to heat up by friction with the supporting layer of air as the head “flies” over the disk, and the constituent layers expand as this happens. This expansion increases the risk that the head will contact or “crash into” the disk, thereby damaging the head, the disk, or both, and that stresses will be created between the layers in the head.
- Typically, the top layer in the head is a relatively thick “overcoat layer” that is formed of alumina (Al2O3). One problem with alumina is that its coefficient of thermal expansion (CTE) of 6 μm/m/° C. is relatively high, which creates a temperature-induced protrusion at the air-bearing surface (ABS) when the head heats up. Other materials with lower CTEs might be desirable as substitutes for alumina in the overcoat layer, but in many cases these other materials present manufacturability problems.
- U.S. Pat. No. 5,643,259 to Sone et al. describes the formation of a recess in the overcoat layer at the trailing edge of the slider, which, it claims, prevents the temperature-induced protrusion from extending “above a predetermined level of the surface facing the disk” (col. 2, lines 50-51). Alumina is used for the overcoat layer, however, so Sone et al. are limited to the relatively high CTE of alumina. Published European Patent Application No. 0627732 A1 teaches an overcoat layer made of silicon dioxide or silicon nitride, both of which have a CTE less than alumina, but it fails to teach a technique for overcoming the fabrication problems presented by the use of these materials, namely, that they tend to chip or crack when the GMR head elements in a wafer are separated from each another by sawing.
- Accordingly, what is needed is a material for use in the overcoat layer that has a CTE lower than alumina and yet can readily accommodate to the fabrication process.
- In accordance with an embodiment of this invention, silicon dioxide (SiO2) or silicon nitride (Si3N4) is used as an overcoat layer in a giant magnetoresistive (GMR) head, and a recess is formed in the silicon dioxide or silicon nitride overcoat layer to prevent the overcoat layer from chipping during the separation (sawing) of the wafer into individual heads and to relieve stress on the other layers of the head during operation. The recess is formed by a process that includes: depositing (e.g., plating) a seed layer on the surface of the overcoat layer, depositing a mask layer over the seed layer, the mask layer having an opening where the recess is to be located thereby exposing a section of the seed layer, wet-etching the exposed section of the seed layer through the opening in the mask layer, removing any remaining portions of the exposed section of the seed layer by a reactive ion etch (ion milling), and etching the recess in the overcoat layer through the opening in the mask layer by reactive ion etching. By this process, essentially all of the exposed section of the seed layer is removed, and this yields a recess having a smooth floor and sidewall.
- Typically, a plurality of heads are formed on a single wafer, and the process described above is used to form a rectilinear lattice of trenches that separate the individual heads. In the finished heads, the recess is located on one side of each head. Therefore, the dicing saw that is used to separate the heads cuts a path that abuts three sides of each head and is separated from the fourth side of each head by a distance that is substantially equal to the width of the recess. After the heads have been diced, the section of the wafer than remains attached to the head becomes the substrate, and the head and substrate together form the slider.
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FIG. 1 is a side view of a conventional slider containing a GMR head. -
FIG. 2 is a side view of a slider containing a GMR head with a silicon dioxide or silicon nitride overcoat layer and a recessed overcoat layer. -
FIG. 3 is a detailed cross-sectional view of a GMR head in accordance with the invention. -
FIGS. 4A-4H illustrate a process for fabricating a GMR head according to the invention. -
FIGS. 5A and 5B are top views of a portion of a wafer containing GMR heads prior to dicing. -
FIG. 6A is a cross-sectional view of a portion of the wafer before the GMR heads are separated. -
FIG. 6B is a cross-sectional view of a single GMR head after it has been separated from other heads in the wafer. -
FIG. 7 is a graph showing a comparison of the temperature-induced protrusion generated by alumina and silicon dioxide overcoat layers, respectively, as a function of the thickness of the overcoat layer. -
FIG. 8 is a graph showing the size of the temperature-induced protrusion generated by a silicon dioxide overcoat layer as a function of the width of the recess. -
FIG. 9 is a graph showing the relative change in the temperature-induced protrusion of various layers in GMR heads containing an alumina and a silicon dioxide overcoat layer, respectively, as the temperature increases from 25° C. to 75° C. -
FIG. 10 is a graph showing the rise time of the magnetic flux in a head containing a recessed overcoat as compared with the rise time of the magnetic flux in a head containing a non-recessed overcoat. -
FIG. 11 is a graph showing the write current required to saturate a head containing a recessed overcoat as compared with the write current required to saturate a head containing a non-recessed overcoat. -
FIG. 1 shows a side view of aslider 10 and amagnetic storage disk 12.Slider 10 includes asubstrate 100, which has a leadingedge 102, and a giant magnetoresistive (GMR)head 104. Asdisk 12 moves in the direction indicated by the arrow, air strikes the leadingedge 102 and causesslider 10 to “float” at a flying height H abovedisk 12. - As indicated above and as described further below, GMR
head 104 includes a number of layers of insulating and magnetic materials. One of the thickest layers is the overcoat layer, indicated at 106. As the air passes beneathassembly 10, friction between the moving air andassembly 10 causesassembly 10 to heat up, for example, to a temperature of 50° to 75° C. This in turn causes the layers inGMR head 104 to expand and can create a temperature-induced protrusion, represented by the dashed line inFIG. 1 . If the temperature-induced protrusion becomes too large, contact may occur betweenGMR head 104 anddisk 12. Such contact, usually referred to a “crash,” can damageGMR head 104,disk 12, or both. - Overcoat
layer 106 is customarily made of alumina. Alumina has a relatively high coefficient of thermal expansion (CTE) of 6 μm/m/° C. It would be preferable to use a material such as silicon dioxide, which has a CTE of 2 μmlm/° C., or silicon nitride, which has a CTE of 3 μm/m/° C. A 30-50% reduction in the size of the temperature-induced protrusion can be achieved by forming the overcoat layer of silicon dioxide or silicon nitride. -
FIG. 2 shows a similar cross-sectional view of aslider 20, which contains aGMR head 204 in accordance with the invention. Anovercoat layer 206 inGMR head 204 is made of silicon dioxide or silicon nitride, and arecess 208 has been formed inovercoat layer 206 at the trailing edge ofslider 20. -
FIG. 3 is a detailed cross-sectional view ofGMR head 204, showing its constituent layers. A portion ofsubstrate 200 is also shown. Note that, inFIG. 3 ,GMR head 204 has been rotated 90° as compared withFIG. 2 , so thatrecess 208 is at the upper right hand corner andsubstrate 200 is located underGMR head 204. - The structure of
GMR head 204 will now be described. Starting at the bottom, in direct contact withsubstrate 200 is anundercoat layer 210, which is typically made of alumina.Layer 212 is an optional layer that may contain magneto-resistive (MR) head. In some embodiments,layer 212 is omitted. Abovelayer 212 are twolayers GMR head 204. A plurality of coil windings C1 are formed in an opening inlayer 216, separated fromlayer 214 by an insulatinglayer 218.Layers Layer 222, normally referred to as the yoke, is curved, and a plurality of coil windings C2 are formed in the space created by the curve inlayer 222. Poles P1 and P2 are separated by an insulatinglayer 224 which forms agap 226 at the air-bearing surface ABS. To write data, a current is applied through terminals (not shown) that connect to coil windings C1 and C2. This current induces a magnetic field across thegap 226, which writes data onto a magnetic data storage disk. - An
alumina layer 228 coversmagnetic layer 222, andovercoat layer 206 is formed overalumina layer 228.Alumina layer 228 may be 1-5 μm thick, for example.Overcoat layer 206 may be about 20 μm thick as measured from the top of alumina layer 228 (T) and about 30 μm thick as measured from thegap 226. As noted above,overcoat layer 206 is made of silicon dioxide or silicon nitride to take advantage of the lower CTE of these materials as compared with alumina.Recess 208, having a width Wr and a depth Dr, is shown at the upper right hand corner of the figure. Wr may be equal to 3 μm±2 μm, for example. - Methods of fabricating poles P1 and P2, coil windings C1 and C2 and the intervening insulating layers are well known in the art and will not be described here.
- It is important that
recess 208 be perfectly vertical and have smooth side walls and bottom, free of any spikes or projections of silicon dioxide or silicon nitride. Otherwise, during the dicing process (described below), these brittle spikes or projections will tend to break off and fragment, causing crack/chip defects and reducing product yield. Furthermore, the brittle spikes may break of inside the disk drive, causing it to fail. - As noted above, typically a plurality of GMR heads are fabricated simultaneously on a wafer, and then the wafer is diced (sawed) to separate the heads from each other.
FIGS. 4A-4H illustrate a cross-sectional view of two GMR heads 260 and 262 in awafer 250. For the sake of clarity, the details of GMR heads 260 and 262 have been omitted. Only the contour of the yoke is shown.FIGS. 4A-4H will be used to explain the process of formingrecesses 208. - As shown in
FIG. 4A , the process starts withovercoat layer 208 having been deposited over the top surface of thewafer 250. The thickness ofovercoat layer 208 may vary from 15 μm to 45 μm, for example.Overcoat layer 208 is made of silicon dioxide or silicon nitride and may be deposited by a conventional physical vapor deposition (PVD) or plasma-enhanced chemical vapor deposition (PECVD) process. Afterovercoat layer 208 has been deposited, its top surface may be lapped or chemical-mechanical polished to planarize it, remove any irregularities and expose the copper connections. - Next, as shown in
FIG. 4B , aseed layer 270 is deposited on the surface ofovercoat layer 208 to form a base for the metal mask layer that will be deposited later (see below).Seed layer 270 is typically deposited by evaporation or PVD and may be 800 Å thick in one embodiment. The composition ofseed layer 270 depends on the composition of the metal mask layer that will later be deposited. Table 1 shows the composition ofseed layer 270 for several types of metal mask layer.TABLE 1 Metal Mask Layer Seed Layer NiFe Ta/Cu/NiFe, CoFe, CoFeN, NiCr CoFe NiCr CoNiFe NiCr Cu AuCr, Cu, NiFe/Cu - It should be understood that the seed layer materials listed in Table 1 are illustrative only and not limiting. Other conductive metals can be used as the seed layer.
- After
seed layer 270 has been deposited, aphotoresist layer 272 is formed onseed layer 270 and patterned as shown inFIG. 4C . The sections ofphotoresist layer 272 that remain after patterning cover the areas whererecesses 208 are to be formed. As shown inFIG. 3 , recesses 208 include the plane defined by the ABS and extend back a distance Wr from the ABS. - As shown in
FIG. 4D , ametal mask layer 274 is deposited in the areas not covered byphotoresist layer 272.Metal mask layer 274 may be deposited by plating or physical vapor deposition (sputtering) and may be 1-2 μm thick, for example.Metal mask layer 274 may consist of any of the materials listed in Table 1. Aftermetal mask layer 274 has been deposited, the remaining portions ofphotoresist layer 272 are removed, yielding the structure shown inFIG. 4E , withopenings 276 formed inmetal mask layer 274 whererecesses 208 will be located. - As
FIG. 4E indicates, the formation ofopenings 276 inmetal mask layer 274 exposes areas ofseed layer 270 which must be removed beforeovercoat layer 206 can be etched. It is highly important that all of the areas ofseed layer 270 that lie beneathopenings 276 be removed while doing minimal damage to the vertical surfaces ofmetal mask layer 274 that surroundopenings 276. Known processes of removingseed layer 270, which use a wet-chemical etch, leave traces ofseed layer 270 in theopenings 276. These traces act as “micromasks” during the etching ofovercoat layer 206, creating a jagged surface which is replicated as the etching ofovercoat layer 206 continues down to the etch-stop layer (e.g. alumina layer 228 inFIG. 3 ). The resulting spikes and other irregularities inovercoat layer 206 can break off or fracture during the dicing ofwafer 250. - To insure that all of the
seed layer 270 that is exposed byopenings 276 is removed, a combination wet/dry etch process is used. First,seed layer 270 is exposed to a wet chemical etch. The chemicals and temperature of the etch process depend on the composition ofseed layer 270 and are shown in Table 2.TABLE 2 Seed Layer Etchants Temperature CoFe or CoFeN 30-50% HCl and Ferrous Sulfate 20-35° C. NiFe H2SO4 and Ferric Ammonium Sulfate 20-35° C. Cu 25-45% NaH4OH and Ammonium 15-35° C. Persulfate - The HCl/ferrous sulfate etchant will etch a CoFe/CoFeN seed layer without etching plated NiFe, even after etching over 6 minutes. A typical etch for a 1500 Å seed layer may last 1 to 3 minutes.
- The H2SO4/ferric ammonium sulfate etchant will attack the NiFe seed as well as plated NiFe. It will attack Cu at a different rate. Therefore, Cu should be used as the metal mask layer. Typically, 30 seconds to 1 minute is required to etch a 1500 Å seed layer.
- The NaH4OH/ammonium persulfate etchant will also attack NiFe, but at a different rate than Cu. Typically, 15 to 45 seconds are required to etch a 1500 Å Cu seed layer.
- The wet-chemical etch is followed by a low-rate ion milling process, which cleans the interface between
seed layer 270 andovercoat layer 206. The angle of the ion beam with respect to the normal of the surface ofovercoat layer 206 is set from −10° to −70°. The ion milling process can be performed for 5 to 10 minutes. - With all traces of
seed layer 270 removed from the surface ofovercoat layer 206, the etching ofovercoat layer 206 thoughopenings 276 inmetal mask layer 274 can begin.Overcoat layer 206 is etched using a reactive ion etch (RIE) process. A Unaxis etcher may be used. The RIE may be CF4 based, with the RF power at 100-300 W. Under these process conditions, the silicon dioxide or silicon nitride etchs at a rate of 4000 Å/min. Ifovercoat layer 206 is formed of silicon nitride, 20-100 sccm of CHF3 are added to the RIE. - A CF4-based RIE process provides a vertical 90-degree profile. The unique wet/dry seed layer removal ensures a smooth sidewall. The wet chemical etch removes the seed layer with minimal damage to the mask layer, while the subsequent low rate ion milling process removes any remaining trace of the seed layer. The resulting sidewall of the SiO2 or Si3N4 overcoat layer is much smoother than can be obtained using a conventional seed layer removal process.
- At the completion of the RIE process,
trenches 278 have been formed inovercoat layer 206, as shown inFIG. 4G .Trenches 278 could be 30-120 μm wide and 5-45 μm deep, for example.Metal mask layer 274 andseed layer 270 are then removed, leaving the structure shown inFIG. 4H . -
FIG. 5A is a top view ofwafer 250, showing the rectilinear lattice oftrenches 278 surrounding GMR heads 260 and 262. The upper coil C2 and ABS of each head are shown, as well asterminals 290, which are connected to coils C1 and C2 via connectors (not shown). The dashed lines inFIG. 5B show thepaths wafer 250 on the sides adjacent the air bearing surfaces (ABS). Sawpaths FIG. 3 ). -
FIG. 6 is a cross-sectional view ofsaw paths head 260. - Thus, because of the formation of
trenches 278, the dicing saw does not need to cut intoovercoat layer 206 which, being made of silicon dioxide and silicon nitride, is prone to chipping and cracking. Moreover, as described above, certain of thetrenches 278 are used to form recesses 208.FIG. 6B showshead 260 after it has been separated from the surrounding heads, withtrench 278 formingrecess 208. - As indicated above, the use of a silicon dioxide or silicon nitride overcoat layer reduces the temperature-induced protrusion of the overcoat layer, as compared with an overcoat layer made of alumina.
FIG. 7 is a graph showing the temperature-induced protrusion of silicon dioxide and alumina layers as a function of the thickness of the overcoat layer. It indicates that the advantages of using silicon dioxide increase as the thickness of the overcoat layer increases. For example, at a thickness of 20 μm the temperature-induced protrusion of a silicon dioxide overcoat layer is less than 1.0 nm for silicon dioxide versus almost 2.0 nm for alumina. -
FIG. 8 is a graph showing the temperature-induced protrusion of a silicon dioxide overcoat layer as a function of the width of the recess (measured from the ABS). As indicated, the temperature-induced protrusion increases as the width of the recess increases. It has been found that a recess having a width of 3±2 μm is desirable to maintain a relatively low and stable pole-top recess (PTR). -
FIG. 9 is a graph showing the relative change in the temperature-induced protrusion of four of the layers in a GMR head as the temperature increases from 25° C. to 75° C. The four layers are the undercoat layer (UC), the pole layers P1 and P2, and the silicon dioxide overcoat layer (OC). Note that the PTR of the silicon dioxide overcoat layer has been reduced about 3 nm as the temperature increases from 25° C. to 75° C. - This invention allows GMR head designers to obtain the reduced temperature-induced protrusion of a silicon dioxide or silicon nitride layer without sacrificing the advantages of having a recess in the overcoat layer. The formation of a recess reduces the stress to which the upper pole-tip P2/P3 is exposed. The overcoat layer is generally deposited under a compressive stress. Therefore, with no recess the pole-tip P2/P3 experiences a tensile stress. Computer modeling studies indicate that the pole-tip sees a stress that is equal to approximately one-half of the stress in the overcoat layer.
- When a recess is formed in the overcoat layer, the pole-tips experience a compressive stress that is equal to about one-half of the stress in the overcoat layer. Thus the net change in the stress experienced by the pole-tips from the addition of the recess is approximately equal to the stress in the overcoat layer.
- As shown in
FIGS. 10 and 11 , this change significantly improves the magnetic performance of the head.FIG. 10 shows that the magnetic flux rise time (tr) of a head having a recessed overcoat is significantly less than the rise time of a non-recessed overcoat head.FIG. 11 indicates that the write current required to saturate a recessed overcoat head is significantly less than the write current required to saturate a non-recessed overcoat head - In summary, this invention permits the use of silicon dioxide or silicon nitride as an overcoat layer in a GMR head, with the consequent reduction in CTE and temperature-induced protrusion, without creating any fabrication problems and without sacrificing the electromagnetic performance of the head.
Claims (31)
1. A GMR head comprising:
a substrate;
a bottom magnetic pole disposed on said substrate and including a bottom pole-tip;
a top magnetic pole disposed over said bottom magnetic pole and including a top pole-tip, said bottom and top pole-tips being separated by a non-magnetic gap layer;
a coil positioned such that a current through said coil induces a magnetic field between said pole-tips;
an overcoat layer overlying said top pole, said overcoat layer being formed of a material selected from the group consisting of silicon dioxide and silicon nitride, a recess being formed in said overcoat layer, said recess having a bottom and a sidewall that are substantially smooth and devoid of spikes or projections.
2. The GMR head of claim 1 wherein overcoat layer has a thickness in the range of 15 μm to 45 μm.
3. The GMR head of claim 2 wherein said recess has a width of from 1 μm to 5 μm.
4. A method of fabricating a GMR head comprising:
providing a wafer element comprising a plurality of GMR head elements, each of said GMR head elements comprising a pair of magnetic pole-tips and a coil;
forming an overcoat layer over said GMR head elements;
forming a seed layer on said overcoat layer;
forming a mask layer on said seed layer, said mask layer having an opening at a location where a trench is to be formed in said overcoat layer, said opening exposing an exposed section of said seed layer;
etching said exposed section of said seed layer through said opening in said mask layer using a wet chemical;
directing an ion milling beam into said opening in said mask layer to remove remaining portions of said exposed section of said seed layer; and
etching said overcoat layer through said opening in said mask layer to create a trench in said overcoat layer.
5. The method of claim 4 wherein said opening in said mask layer is configured such that etching said overcoat layer creates a rectilinear lattice of trenches in said overcoat layer.
6. The method of claim 5 wherein said plurality of GMR head elements are separated from each other by said rectilinear lattice of trenches.
7. The method of claim 6 comprising separating said GMR head elements.
8. The method of claim 7 wherein separating said GMR head elements comprises running a dicing saw blade over a plurality of linear saw paths, each of said linear paths lying within said trenches.
9. The method of claim 8 wherein said saw blade makes no substantial contact with said overcoat layer.
10. The method of claim 4 wherein etching said overcoat layer comprises reactive ion etching.
11. The method of claim 4 wherein forming an overcoat layer comprises forming a layer comprising a material selected from the group consisting of silicon dioxide and silicon nitride.
12. The method of claim 11 wherein forming a mask layer comprises:
depositing a photoresist layer on said seed layer;
patterning said photoresist layer so as to leave sections of said photoresist layer remaining;
depositing said mask layer between said sections of said photoresist layer; and
removing said sections of said photoresist layer so as to form said opening.
13. The method of claim 12 wherein depositing said mask layer comprises plating.
14. The method of claim 12 wherein depositing said mask layer comprises physical vapor deposition.
15. The method of claim 11 wherein forming said mask layer comprises forming a NiFe layer.
16. The method of claim 15 wherein forming said seed layer comprises evaporation or physical vapor deposition.
17. The method of claim 16 wherein forming said seed layer comprises forming a layer comprising a material selected from the group consisting of Ta/Cu/NiFe, CoFe, CoFeN and NiCr.
18. The method of claim 17 wherein said wet chemical comprises a mixture of H2SO4 and ammonium sulfate.
19. The method of claim 18 wherein said ion milling process is performed for 5 to 10 minutes.
20. The method of claim 19 wherein said ion milling process is performed with an ion beam set at an angle of from −10° to −70° with respect to normal of the surface of said overcoat layer.
21. The method of claim 11 wherein forming said mask layer comprises forming a layer comprising a material selected from the group consisting of CoFe and CoNiFe.
22. The method of claim 21 wherein forming said seed layer comprises evaporation or physical vapor deposition.
23. The method of claim 22 wherein forming said seed layer comprises forming a layer comprising NiCr.
24. The method of claim 23 wherein said ion milling process is performed for 5 to 10 minutes.
25. The method of claim 24 wherein said ion milling process is performed with an ion beam set at an angle of from −10° to −70° with respect to normal of the surface of said overcoat layer.
26. The method of claim 11 wherein forming said mask layer comprises forming a Cu layer.
27. The method of claim 26 wherein forming said seed layer comprises evaporation or physical vapor deposition.
28. The method of claim 27 wherein forming said seed layer comprises forming a layer comprising a material selected from the group consisting of AuCr, Cu and NiFe/Cu.
29. The method of claim 28 wherein said wet chemical comprises a mixture of NaH4OH and ammonium persulfate.
30. The method of claim 29 wherein said ion milling process is performed for 5 to 10 minutes.
31. The method of claim 30 wherein said ion milling process is performed with an ion beam set at an angle of from −10° to −70° with respect to normal of the surface of said overcoat layer.
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US10/857,036 US20050264949A1 (en) | 2004-05-28 | 2004-05-28 | Recessed SiO2 or Si3N4 overcoat for GMR head in magnetic disk drive |
US11/809,184 US7520048B2 (en) | 2004-05-28 | 2007-05-31 | Method of fabricating a GMR head |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US10/857,036 US20050264949A1 (en) | 2004-05-28 | 2004-05-28 | Recessed SiO2 or Si3N4 overcoat for GMR head in magnetic disk drive |
Related Child Applications (1)
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US11/809,184 Division US7520048B2 (en) | 2004-05-28 | 2007-05-31 | Method of fabricating a GMR head |
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US20050264949A1 true US20050264949A1 (en) | 2005-12-01 |
Family
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US10/857,036 Abandoned US20050264949A1 (en) | 2004-05-28 | 2004-05-28 | Recessed SiO2 or Si3N4 overcoat for GMR head in magnetic disk drive |
US11/809,184 Expired - Fee Related US7520048B2 (en) | 2004-05-28 | 2007-05-31 | Method of fabricating a GMR head |
Family Applications After (1)
Application Number | Title | Priority Date | Filing Date |
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US11/809,184 Expired - Fee Related US7520048B2 (en) | 2004-05-28 | 2007-05-31 | Method of fabricating a GMR head |
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US20070008657A1 (en) * | 2005-06-07 | 2007-01-11 | Fujitsu Limited | Magnetic head including read head element and inductive write head element |
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US8607438B1 (en) | 2011-12-01 | 2013-12-17 | Western Digital (Fremont), Llc | Method for fabricating a read sensor for a read transducer |
US8670214B1 (en) | 2011-12-20 | 2014-03-11 | Western Digital (Fremont), Llc | Method and system for providing enhanced thermal expansion for hard disk drives |
US8749920B1 (en) | 2011-12-16 | 2014-06-10 | Western Digital (Fremont), Llc | Magnetic recording head with dynamic fly height heating and having thermally controlled pole tip protrusion to control and protect reader element |
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US20120134045A1 (en) * | 2010-11-30 | 2012-05-31 | Kabushiki Kaisha Toshiba | Magnetic head and disk drive with the same |
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US7520048B2 (en) | 2009-04-21 |
US20070242393A1 (en) | 2007-10-18 |
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