U.S. patent application number 10/857036 was filed with the patent office on 2005-12-01 for recessed sio2 or si3n4 overcoat for gmr head in magnetic disk drive.
This patent application is currently assigned to Hitachi Global Storage Technologies Netherlands, B.V.. Invention is credited to Gao, Yunxiao, Pentek, Aron, Tam, Alan J., Zhang, Sue Siyang.
Application Number | 20050264949 10/857036 |
Document ID | / |
Family ID | 35424915 |
Filed Date | 2005-12-01 |
United States Patent
Application |
20050264949 |
Kind Code |
A1 |
Gao, Yunxiao ; et
al. |
December 1, 2005 |
Recessed SiO2 or Si3N4 overcoat for GMR head in magnetic disk
drive
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.
Inventors: |
Gao, Yunxiao; (Sunnyvale,
CA) ; Pentek, Aron; (San Jose, CA) ; Tam, Alan
J.; (San Jose, CA) ; Zhang, Sue Siyang;
(Saratoga, CA) |
Correspondence
Address: |
SILICON VALLEY PATENT GROUP LLP
2350 MISSION COLLEGE BOULEVARD
SUITE 360
SANTA CLARA
CA
95054
US
|
Assignee: |
Hitachi Global Storage Technologies
Netherlands, B.V.
|
Family ID: |
35424915 |
Appl. No.: |
10/857036 |
Filed: |
May 28, 2004 |
Current U.S.
Class: |
360/324 ;
360/320; G9B/5.079; G9B/5.087; G9B/5.094 |
Current CPC
Class: |
G11B 5/3133 20130101;
Y10T 29/49052 20150115; Y10T 29/49046 20150115; Y10T 29/49043
20150115; G11B 5/3136 20130101; G11B 5/3106 20130101; G11B 5/3163
20130101; Y10T 29/49048 20150115; Y10T 29/49044 20150115 |
Class at
Publication: |
360/324 ;
360/320 |
International
Class: |
G11B 005/33; G11B
005/127 |
Claims
What is claimed is:
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 .mu.m to 45 .mu.m.
3. The GMR head of claim 2 wherein said recess has a width of from
1 .mu.m to 5 .mu.m.
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 H.sub.2SO.sub.4 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.degree. to
-70.degree. 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.degree. to
-70.degree. 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 NaH.sub.4OH 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.degree. to
-70.degree. with respect to normal of the surface of said overcoat
layer.
Description
FIELD OF THE INVENTION
[0001] 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.
BACKGROUND
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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.
[0006] Typically, the top layer in the head is a relatively thick
"overcoat layer" that is formed of alumina (Al.sub.2O.sub.3). One
problem with alumina is that its coefficient of thermal expansion
(CTE) of 6 .mu.m/m/.degree. 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.
[0007] 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.
[0008] 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.
SUMMARY
[0009] In accordance with an embodiment of this invention, silicon
dioxide (SiO.sub.2) or silicon nitride (Si.sub.3N.sub.4) 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.
[0010] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a side view of a conventional slider containing a
GMR head.
[0012] 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.
[0013] FIG. 3 is a detailed cross-sectional view of a GMR head in
accordance with the invention.
[0014] FIGS. 4A-4H illustrate a process for fabricating a GMR head
according to the invention.
[0015] FIGS. 5A and 5B are top views of a portion of a wafer
containing GMR heads prior to dicing.
[0016] FIG. 6A is a cross-sectional view of a portion of the wafer
before the GMR heads are separated.
[0017] FIG. 6B is a cross-sectional view of a single GMR head after
it has been separated from other heads in the wafer.
[0018] 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.
[0019] 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.
[0020] 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.degree. C. to
75.degree. C.
[0021] 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.
[0022] 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.
DETAILED DESCRIPTION
[0023] FIG. 1 shows a side view of a slider 10 and a magnetic
storage disk 12. Slider 10 includes a substrate 100, which has a
leading edge 102, and a giant magnetoresistive (GMR) head 104. As
disk 12 moves in the direction indicated by the arrow, air strikes
the leading edge 102 and causes slider 10 to "float" at a flying
height H above disk 12.
[0024] 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 beneath assembly 10, friction
between the moving air and assembly 10 causes assembly 10 to heat
up, for example, to a temperature of 50.degree. to 75.degree. C.
This in turn causes the layers in GMR head 104 to expand and can
create a temperature-induced protrusion, represented by the dashed
line in FIG. 1. If the temperature-induced protrusion becomes too
large, contact may occur between GMR head 104 and disk 12. Such
contact, usually referred to a "crash," can damage GMR head 104,
disk 12, or both.
[0025] Overcoat layer 106 is customarily made of alumina. Alumina
has a relatively high coefficient of thermal expansion (CTE) of 6
.mu.m/m/.degree. C. It would be preferable to use a material such
as silicon dioxide, which has a CTE of 2 .mu.mlm/.degree. C., or
silicon nitride, which has a CTE of 3 .mu.m/m/.degree. 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.
[0026] FIG. 2 shows a similar cross-sectional view of a slider 20,
which contains a GMR head 204 in accordance with the invention. An
overcoat layer 206 in GMR head 204 is made of silicon dioxide or
silicon nitride, and a recess 208 has been formed in overcoat layer
206 at the trailing edge of slider 20.
[0027] FIG. 3 is a detailed cross-sectional view of GMR head 204,
showing its constituent layers. A portion of substrate 200 is also
shown. Note that, in FIG. 3, GMR head 204 has been rotated
90.degree. as compared with FIG. 2, so that recess 208 is at the
upper right hand corner and substrate 200 is located under GMR head
204.
[0028] The structure of GMR head 204 will now be described.
Starting at the bottom, in direct contact with substrate 200 is an
undercoat 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. Above layer 212 are two
layers 214 and 216 of a magnetic material such as NiFe that
together form the bottom pole P1 of GMR head 204. A plurality of
coil windings C1 are formed in an opening in layer 216, separated
from layer 214 by an insulating layer 218. Layers 220 and 222 are
magnetic layers of a magnetic material such as NiFe that together
form a top pole P2. 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 in layer 222. Poles P1 and P2 are separated by
an insulating layer 224 which forms a gap 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 the gap 226, which writes data onto
a magnetic data storage disk.
[0029] An alumina layer 228 covers magnetic layer 222, and overcoat
layer 206 is formed over alumina layer 228. Alumina layer 228 may
be 1-5 .mu.m thick, for example. Overcoat layer 206 may be about 20
.mu.m thick as measured from the top of alumina layer 228 (T) and
about 30 .mu.m thick as measured from the gap 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 W.sub.r and a depth Dr, is
shown at the upper right hand corner of the figure. W.sub.r may be
equal to 3 .mu.m.+-.2 .mu.m, for example.
[0030] 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.
[0031] 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.
[0032] 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 a
wafer 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 forming recesses
208.
[0033] As shown in FIG. 4A, the process starts with overcoat layer
208 having been deposited over the top surface of the wafer 250.
The thickness of overcoat layer 208 may vary from 15 .mu.m to 45
.mu.m, 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. After overcoat 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.
[0034] Next, as shown in FIG. 4B, a seed layer 270 is deposited on
the surface of overcoat 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 .ANG.
thick in one embodiment. The composition of seed layer 270 depends
on the composition of the metal mask layer that will later be
deposited. Table 1 shows the composition of seed layer 270 for
several types of metal mask layer.
1 TABLE 1 Metal Mask Layer Seed Layer NiFe Ta/Cu/NiFe, CoFe, CoFeN,
NiCr CoFe NiCr CoNiFe NiCr Cu AuCr, Cu, NiFe/Cu
[0035] 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.
[0036] After seed layer 270 has been deposited, a photoresist layer
272 is formed on seed layer 270 and patterned as shown in FIG. 4C.
The sections of photoresist layer 272 that remain after patterning
cover the areas where recesses 208 are to be formed. As shown in
FIG. 3, recesses 208 include the plane defined by the ABS and
extend back a distance W.sub.r from the ABS.
[0037] As shown in FIG. 4D, a metal mask layer 274 is deposited in
the areas not covered by photoresist layer 272. Metal mask layer
274 may be deposited by plating or physical vapor deposition
(sputtering) and may be 1-2 .mu.m thick, for example. Metal mask
layer 274 may consist of any of the materials listed in Table 1.
After metal mask layer 274 has been deposited, the remaining
portions of photoresist layer 272 are removed, yielding the
structure shown in FIG. 4E, with openings 276 formed in metal mask
layer 274 where recesses 208 will be located.
[0038] As FIG. 4E indicates, the formation of openings 276 in metal
mask layer 274 exposes areas of seed layer 270 which must be
removed before overcoat layer 206 can be etched. It is highly
important that all of the areas of seed layer 270 that lie beneath
openings 276 be removed while doing minimal damage to the vertical
surfaces of metal mask layer 274 that surround openings 276. Known
processes of removing seed layer 270, which use a wet-chemical
etch, leave traces of seed layer 270 in the openings 276. These
traces act as "micromasks" during the etching of overcoat layer
206, creating a jagged surface which is replicated as the etching
of overcoat layer 206 continues down to the etch-stop layer (e.g.
alumina layer 228 in FIG. 3). The resulting spikes and other
irregularities in overcoat layer 206 can break off or fracture
during the dicing of wafer 250.
[0039] To insure that all of the seed layer 270 that is exposed by
openings 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 of seed layer 270 and are shown in Table 2.
2TABLE 2 Seed Layer Etchants Temperature CoFe or CoFeN 30-50% HCl
and Ferrous Sulfate 20-35.degree. C. NiFe H.sub.2SO.sub.4 and
Ferric Ammonium Sulfate 20-35.degree. C. Cu 25-45% NaH.sub.4OH and
Ammonium 15-35.degree. C. Persulfate
[0040] 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 .ANG. seed layer may last 1 to 3
minutes.
[0041] The H.sub.2SO.sub.4/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
.ANG. seed layer.
[0042] The NaH.sub.4OH/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 .ANG. Cu seed layer.
[0043] The wet-chemical etch is followed by a low-rate ion milling
process, which cleans the interface between seed layer 270 and
overcoat layer 206. The angle of the ion beam with respect to the
normal of the surface of overcoat layer 206 is set from -10.degree.
to -70.degree.. The ion milling process can be performed for 5 to
10 minutes.
[0044] With all traces of seed layer 270 removed from the surface
of overcoat layer 206, the etching of overcoat layer 206 though
openings 276 in metal 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 CF.sub.4 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 .ANG./min. If overcoat
layer 206 is formed of silicon nitride, 20-100 sccm of CHF.sub.3
are added to the RIE.
[0045] A CF.sub.4-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 SiO.sub.2 or Si.sub.3N.sub.4 overcoat
layer is much smoother than can be obtained using a conventional
seed layer removal process.
[0046] At the completion of the RIE process, trenches 278 have been
formed in overcoat layer 206, as shown in FIG. 4G. Trenches 278
could be 30-120 .mu.m wide and 5-45 .mu.m deep, for example. Metal
mask layer 274 and seed layer 270 are then removed, leaving the
structure shown in FIG. 4H.
[0047] FIG. 5A is a top view of wafer 250, showing the rectilinear
lattice of trenches 278 surrounding GMR heads 260 and 262. The
upper coil C2 and ABS of each head are shown, as well as terminals
290, which are connected to coils C1 and C2 via connectors (not
shown). The dashed lines in FIG. 5B show the paths 292, 294, 296 of
the dicing saw blade that is used to separate the heads in wafer
250 on the sides adjacent the air bearing surfaces (ABS). Saw paths
298, 300 separate the heads on the sides perpendicular to the ABS.
After the heads are separated by sawing, the edges are lapped as
necessary to provide the desired width of recesses 208 (the
dimension W.sub.r in FIG. 3).
[0048] FIG. 6 is a cross-sectional view of saw paths 292 and 298,
showing how they run along the sides of head 260.
[0049] Thus, 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.
[0050] 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
.mu.m 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.
[0051] 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
.mu.m is desirable to maintain a relatively low and stable pole-top
recess (PTR).
[0052] 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.degree. C. to 75.degree. 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.degree. C. to 75.degree.
C.
[0053] 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.
[0054] 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.
[0055] 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 (t.sub.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
[0056] 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.
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