U.S. patent application number 10/217236 was filed with the patent office on 2003-02-27 for enhanced ion beam etch selectivity of magnetic thin films using carbon-based gases.
This patent application is currently assigned to Seagate Technology LLC. Invention is credited to Covington, Mark William, Minor, Michael Kevin, Seigler, Michael Allen, Singleton, Eric Walter.
Application Number | 20030038106 10/217236 |
Document ID | / |
Family ID | 23217747 |
Filed Date | 2003-02-27 |
United States Patent
Application |
20030038106 |
Kind Code |
A1 |
Covington, Mark William ; et
al. |
February 27, 2003 |
Enhanced ion beam etch selectivity of magnetic thin films using
carbon-based gases
Abstract
A method of etching a structure including a magnetic material,
the method includes providing a structure including a magnetic
material, applying a mask material to at least a portion of the
structure, and reactive ion beam etching the magnetic material
using an etch process including a carbon based compound, wherein
the mask material forms a material which etches slower than the
magnetic material. The etch process can further include argon ions.
The carbon based compound can be a compound selected from the group
of C.sub.2H.sub.2, CHF.sub.3, and CO.sub.2. The etch process can
alternatively include argon ions, oxygen and either C.sub.2H.sub.2
or CHF.sub.3. The magnetic material can comprise a compound
including a material selected from the group of Fe, Ni, and Co. The
mask material can comprise a layer of Ta, W, Mo, Si, Ti or a
photoresist. Magnetic heads made using the process, and disc drives
including such magnetic heads are also included.
Inventors: |
Covington, Mark William;
(Pittsburgh, PA) ; Seigler, Michael Allen;
(Pittsburgh, PA) ; Singleton, Eric Walter; (Maple
Plain, MN) ; Minor, Michael Kevin; (Gibsonia,
PA) |
Correspondence
Address: |
Robert P. Lenart
Pietragallo, Bosick & Gordon
One Oxford Centre, 38th Floor
301 Grant Street
Pittsburgh
PA
15219
US
|
Assignee: |
Seagate Technology LLC
Scotts Valley
CA
|
Family ID: |
23217747 |
Appl. No.: |
10/217236 |
Filed: |
August 12, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60313919 |
Aug 21, 2001 |
|
|
|
Current U.S.
Class: |
216/2 ;
G9B/5.082; G9B/5.094 |
Current CPC
Class: |
G11B 5/3163 20130101;
H01F 41/308 20130101; B82Y 25/00 20130101; G11B 5/3116 20130101;
H01J 2237/31713 20130101; B82Y 40/00 20130101; H01F 41/18
20130101 |
Class at
Publication: |
216/2 |
International
Class: |
C23F 001/00 |
Claims
What is claimed is:
1. A method of etching a structure including a magnetic material,
the method comprising: providing a structure including a magnetic
material; applying a mask material to at least a portion of the
structure; and reactive ion beam etching the magnetic material
using an etch process including a carbon based compound, wherein
the mask material forms a material which etches slower than the
magnetic material.
2. The method of claim 1, wherein the etch process further includes
argon ions.
3. The method of claim 2, wherein the carbon based compound
comprises a compound selected from the group of: C.sub.2H.sub.2,
CHF.sub.3, and CO.sub.2.
4. The method of claim 2, wherein the etch process further includes
oxygen and either C.sub.2H.sub.2 or CHF.sub.3.
5. The method of claim 1, wherein the carbon based compound
comprises a compound selected from the group of: C.sub.2H.sub.2,
CHF.sub.3, and CO.sub.2.
6. The method of claim 1, wherein the magnetic material comprises
an alloy including a material selected from the group of: Fe, Ni,
and Co.
7. The method of claim 6, wherein the mask material comprises a
material selected from the group of: Ta, W, Mo, Si, Ti and a
photoresist.
8. The method of claim 1, wherein the mask material forms an etch
stop.
9. The method of claim 1, wherein the mask material is applied to
at least a portion of a surface of the magnetic material.
10. The method of claim 1, wherein the structure comprises: a
portion of a write pole; an etch stop layer supported by the
portion of the write pole, wherein the etch stop layer supports the
magnetic material; a cap layer supported by the magnetic material,
wherein the cap layer supports the mask material; a layer of
reactive ion etch mask supported by the mask material; and a resist
supported by the reactive ion etch mask.
11. The method of claim 10, wherein the structure further
comprises: a buffer layer between the etch stop layer and the
magnetic material.
12. The method of claim 1, wherein the magnetic material forms a
layer in a magneto-resistive stack.
13. The method of claim 1, wherein the magnetic material forms a
write pole.
14. The method of claim 1, wherein the material which etches slower
than the magnetic material comprises a carbide.
15. A magnetic head made using the process of claim 1.
16. A disc drive comprising: a magnetic head made using the process
of claim 1; means for rotating a magnetic storage medium; and means
for positioning the magnetic head adjacent to a surface of the
magnetic storage medium.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application Serial No. 60/313,919, filed Aug. 21, 2001.
FIELD OF THE INVENTION
[0002] This invention relates to ion beam etching processes, and
more particularly to the use of such processes in the manufacture
of magnetic recording heads.
BACKGROUND OF THE INVENTION
[0003] Many disc drives use a recording head including two
elements. The first element is a write head that is used for
writing data to the surface of a magnetic disc. The second element
is a read head including a magneto-resistive element or giant
magneto-resistive element ("MR element") that is used to read data
from the surface of the disc. The resistance of the MR element
changes in the presence of a magnetic field so the MR element is
used to sense magnetic transitions on the disc that have been
previously written by the write element. The recording head is
typically housed within a small ceramic block called a slider. The
slider is positioned near the rotating disc and separated from the
surface of the disc by an air bearing.
[0004] Many processes in recording head fabrication use sputtered
thin films. The most critical elements of the reader are fabricated
exclusively from sputtered films and it is expected that sputtering
will soon replace plating as the preferred deposition technique for
the writer. Anisotropic dry etch processes are a key enabling
technology for sputtered films. Device structures need to be
fabricated with nanometer-scale accuracy and precision, and with
thickness-to-width aspect ratios that are sometimes greater than
one. The data storage industry currently relies on argon ion beam
etching (IBE) to define the sputtered magnetic materials in
recording heads. Since Ni, Fe, and Co alloys tend to be physically
hard materials that etch slowly, it is difficult to preferentially
etch them with IBE One consequence is that masking material must be
made very thick because few materials etch more slowly than these
alloys. Furthermore, the IBE process must allow for a lot of
over-etching into underlying material in order to fully define the
magnetic structures.
[0005] An alternative approach is to exploit chemical selectivity
and use reactive ion etching (RIE) to preferentially etch certain
materials over others. RIE forms volatile reaction products on the
exposed wafer surface. Once formed, these reaction products desorb
from the wafer surface and are pumped away. Unfortunately, it is
challenging to form volatile compounds from Ni, Fe, and Co at
conventional wafer processing temperatures, which are on the order
of 300.degree. C. and below. Hence, these materials and their
associated alloys are difficult to RIE. Past attempts at reactive
etching have typically used either CO or Cl. Researchers have tried
to form volatile Ni-, Fe-, and Co-carbonyls by using CO in either
chemically assisted IBE or RIE processes. However, to date, there
are no data that conclusively prove that carbonyls do indeed form.
In contrast, a few research groups have achieved limited success
using Cl-based RIE to etch NiFe and spin-valves, although the etch
selectivity with respect to other materials is poor. It is well
known that the introduction of reactive gases in an ion mill can
reduce the etch rate of certain materials, an example of which is
oxygen reactive ion beam etching (RIBE). In fact, this type of
approach has been used to preferentially etch FeAlN over Ti by
adding N.sub.2 into an ion mill.
[0006] Reactive etch processes for writer processing have been
disclosed for etching the gap of a longitudinal writer in a notched
pole process. Those reactive processes relate to CF.sub.4- or
CHF.sub.3-based RIBE of an Al.sub.2O.sub.3 gap, which is well
known. The enhanced etching of various non-magnetic transition
metal gap materials using noble metal gases that are different than
Ar, such as Kr or Xe, has also been proposed.
[0007] The data storage industry presently has few options to dry
etch magnetic materials and those that are available suffer from
poor selectivity. There is a need to develop a portfolio of
anisotropic dry etch processes that preferentially etch magnetic
materials.
SUMMARY OF THE INVENTION
[0008] A method of etching a structure including a magnetic
material, the method includes providing a structure including a
magnetic material, applying a mask material to at least a portion
of the structure, and reactive ion beam etching the magnetic
material using an etch process including a carbon based compound,
wherein the mask material forms a material which etches slower than
the magnetic material. The etch process can further include argon
ions. The carbon based compound can be a compound selected from the
group of C.sub.2H.sub.2, CHF.sub.3, and CO.sub.2. The etch process
can alternatively include argon ions, oxygen and either
C.sub.2H.sub.2 or CHF.sub.3. The magnetic material can comprise a
compound including a material selected from the group of Fe, Ni,
and Co. The mask material can comprise a layer of Ta, W, Mo, Si, Ti
or a photoresist. Magnetic heads made using the process, and disc
drives including such magnetic heads are also included.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a pictorial representation of a magnetic disc
drive that can include magnetic heads constructed in accordance
with this invention;
[0010] FIG. 2 is a graph showing the etch rates for various
materials using argon and acetylene reactive ion beam etching;
[0011] FIG. 3 is a graph showing the relative etch selectivity for
various materials using argon and acetylene reactive ion beam
etching;
[0012] FIG. 4 is a graph showing the etch rates for various
materials using argon and CHF.sub.3 reactive ion beam etching;
[0013] FIG. 5 is a graph showing the relative etch selectivity for
various materials using argon and CHF.sub.3 reactive ion beam
etching;
[0014] FIG. 6 is an air bearing surface view of an intermediate
structure formed during the manufacture of a magnetic write
head;
[0015] FIG. 7 is an air bearing surface view of another
intermediate structure formed during the manufacture of a magnetic
write head;
[0016] FIG. 8 is an air bearing surface view of another
intermediate structure formed during the manufacture of a magnetic
write head;
[0017] FIG. 9 is an air bearing surface view of another
intermediate structure formed during the manufacture of a magnetic
write head;
[0018] FIG. 10 is an air bearing surface view of an intermediate
structure formed during the manufacture of a magnetic read
head,
[0019] FIG. 11 is an air bearing surface view of another
intermediate structure formed during the manufacture of a magnetic
read head;
[0020] FIG. 12 is an air bearing surface view of another
intermediate structure formed during the manufacture of a magnetic
read head;
[0021] FIG. 13 is an air bearing surface view of another
intermediate structure formed during the manufacture of a magnetic
read head;
[0022] FIG. 14 is a graph showing the etch rates for various
materials using argon and CO.sub.2 reactive ion beam etching;
and
[0023] FIG. 15 is a graph showing the relative etch selectivity for
various materials using argon and CO.sub.2 reactive ion beam
etching;
DETAILED DESCRIPTION OF THE INVENTION
[0024] The process of this invention includes the combination of
(1) carbon-based gases in an ion mill and (2) appropriate materials
for hard masks and etch stops. For example, an ion mill with
carbon-based gases in combination with Ta (and other materials) can
be used to selectively etch Ni-, Fe-, and Co-alloys. The reactive
IBE process proposed in this application is a physical etch
process, rather than a predominantly chemically driven process like
RIE. No volatile compounds are formed. The invention modifies the
physical etch rates of various materials to permit preferential
etching of one material with respect to another.
[0025] This invention encompasses processes that can be used in the
manufacture of magnetic heads for use with magnetic recording
media, as well as magnetic recording heads made by the processes
and disc drives that include the heads. FIG. 1 is a pictorial
representation of a disc drive 10 that can utilize magnetic heads
constructed in accordance with this invention. The disc drive
includes a housing 12 (with the upper portion removed and the lower
portion visible in this view) sized and configured to contain the
various components of the disc drive. The disc drive includes a
spindle motor 14 for rotating at least one magnetic storage medium
16 within the housing, in this case a magnetic disc. At least one
arm 18 is contained within the housing 12, with each arm 18 having
a first end 20 with a recording and/or reading head or slider 22,
and a second end 24 pivotally mounted on a shaft by a bearing 26.
An actuator motor 28 is located at the arm's second end 24, for
pivoting the arm 18 to position the head 22 over a desired sector
of the disc 16. The actuator motor 28 is regulated by a controller
that is not shown in this view and is well known in the art.
[0026] This invention provides anisotropic dry etch processes that
can preferentially etch materials and can be used in the
manufacture of magnetic recording heads. In one example, the
invention provides a reactive ion beam etch (RIBE) process that
uses carbon-containing gases. The invention seeks to achieve the
highest possible etch selectivity of common magnetic materials and
alloys by introducing reactive gases into an ion mill to form hard
surface layers on potential masking materials. This is accomplished
by using materials that form carbides that etch more slowly than
Ni, Fe, Co, and their respective carbides. The likelihood of
forming volatile compounds with this approach is remote, but this
is of secondary importance since the ion mill can remove
redeposited material from sidewalls by etching at an oblique
angle.
[0027] This invention encompasses various processing schemes, which
use a combination of a reactive etch gas and selected materials for
hard masks and etch stops. The reactive gases can be introduced
into the Kaufman source of a standard ion mill, which creates ions
in an inductively coupled plasma and accelerates them through a set
of voltage-biased grids.
[0028] In one example, the process uses a mixture of acetylene
(C.sub.2H.sub.2) and Ar in a RIBE process. Experimental data for
the absolute etch rate of several materials as a function of the
relative C.sub.2H.sub.2 flow rate are shown in FIG. 2. For the sake
of clarity, only etch rate data for FeCoB, Ta, and AZ1505
photoresist are shown. The data for other materials follow roughly
the same trend, but have been omitted from the figure. The total
flow rate was 14, 15, and 17 SCCM for the relative flow rates of
0.714, 0.8, and 0.882, respectively. The "medium" ion beam
parameters used an acceleration voltage of 600 V, beam current of
300 mA, RF power of .about.400 W, and a suppressor voltage of 400
V. In FIG. 2, line 40 represents the etch rate for FeCoB, line 42
represents the etch rate for Ta, and line 44 represents the etch
rate for AZ1505 photoresist. FIG. 2 illustrates the etch rate for a
fixture angle of 45.degree. but these data reflect the behavior
observed for all fixture angles. The data in FIG. 2 are
representative of the overall trend we have observed in that the
etch rate decreases as the relative amount of C.sub.2H.sub.2
increases. Despite the overall decrease in the etch rate of FeCoB,
the etch rates for Ta and photoresist decrease even faster.
[0029] FIG. 3 shows the etch selectivity of FeCoB with respect to
Ta and AZ1505 photoresist, which is defined as the quotient of the
etch rates of FeCoB and either Ta or photoresist. The dashed line
46 indicates the best selectivity we have achieved using
conventional Ar IBE and either W or high-quality Al.sub.2O.sub.3.
In FIG. 3, line 48 represents the selectivity for FeCoB/Ta, and
curve 50 represents the selectivity for FeCoB/AZ1505. For the
highest relative C.sub.2H.sub.2 flow rates studied, we observe a
remarkable etch selectivity of almost nine-to-one. Note that the
highest relative flow rate caused severe degradation in the
photoresist that is reminiscent of when resist overheats and
consequently "burns".
[0030] Another example process combines CHF.sub.3 and Ar, and the
data for the absolute etch rate and selectivity are shown in FIGS.
4 and 5, respectively. The parameters used to generate the data in
FIG. 4 are the same as those used to generate the data of FIG. 2
except that CHF.sub.3 has been used in place of acetylene. In FIG.
4, curve 52 represents the etch rate for FeCoB, curve 54 represents
the etch rate for NiFeCr, curve 56 represents the etch rate for W,
and curve 58 represents the etch rate for AZ1505 photoresist.
[0031] FIG. 5 shows etch selectivity as a function of relative
CHF.sub.3 flow rate. The dashed line 46 in FIG. 5 is the same as in
FIG. 3. In FIG. 5, curve 60 represents the relative etch rate for
FeCoB:W, curve 62 represents the selectivity for NiFeCr:W, curve 64
represents the relative etch rate for FeCoB:AZ1505, and curve 66
represents the relative etch rate for NiFeCr:AZ1505. For this
process, we observed an improvement when using W and a relative
CHF.sub.3 flow rate of 0.357, in which case the selectivity is
approximately 45% better than Ar IBE with W or Al.sub.2O.sub.3.
Photoresist AZ1505 also exhibits improved selectivity by adding
CHF.sub.3, although its selectivity remains below the best Ar IBE
performance. For this process, there is a small "window" of
CHF.sub.3 flow rate in which the selectivity improves. The relative
flow rate of the CHF.sub.3 to (CHF.sub.3+Ar) is preferably between
0.27 and 0.43, and more preferably between 0.3 and 0.4. While these
data indicate that there is little latitude for process variations,
it nevertheless illustrates that the process allows the use of
different materials. This can be useful if, for example, W is a
better choice than Ta as a mask or etch stop.
[0032] Both of these processes improve upon the best selectivity
performance we have achieved using standard Ar IBE. Using FeCoB as
a benchmark magnetic material, the best selectivity with Ar IBE at
a 45.degree. fixture angle is achieved by using either W or
high-quality Al.sub.2O.sub.3 as masking material. This selectivity
is indicated by curve 46 in FIGS. 3 and 5. For the C.sub.2H.sub.2
RIBE process, we observe significantly better selectivity using
either Ta or photoresist. Other non-magnetic materials, such as W,
Al.sub.2O.sub.3, and SiO.sub.2, show either no change or worse
selectivity with increasing C.sub.2H.sub.2 flow rate. For the
CHF.sub.3 RIBE process, we observe better selectivity using W or
AZ1505 photoresist. In contrast, Ta shows no improvement and the
selectivity of Al.sub.2O.sub.3 and SiO.sub.2 gets worse with
increasing CHF.sub.3 flow rate.
[0033] We have also evaluated the performance of these two
processes with other technologically important materials, such as
NiFe and a top spin valve structure [for example,
55NiFeCr/50CoFe/30Cu/30CoFe/4Ru/25CoFe/70Ir- Mn/60Ru, where the
numbers indicate the layer thicknesses in .ANG.]. We observed an
improvement in selectivity that is comparable to that observed with
the benchmark performance of FeCoB, shown in FIGS. 2-5.
Furthermore, we have also measured the selectivity using higher
voltage beam parameters that etch more quickly. For the
C.sub.2H.sub.2 RIBE process with the highest C.sub.2H.sub.2 flow
rate, we have observed a selectivity of approximately
four-to-one.
[0034] The diametric performance of Ta and W, and their dependence
on the type of reactive gas used, suggest that there are subtle
details in how carbides form on the surface. In addition,
previously published data show that carbides will form when using
C-based etch gases and TaC and WC would be expected to etch more
slowly than Ta and W.
[0035] Although we have primarily investigated Ta and W as hard
mask materials, the C-based RIBE processes included in this
invention are not limited to these materials alone. Carbon-based
RIBE can also be extended to a wider range of materials that form
slower etching carbides, such as Mo, Si, and Ti.
[0036] Finally, one benefit of using C.sub.2H.sub.2 or CHF.sub.3 in
a reactive etch is that they are safer than other reactive gases,
such as CO, CH.sub.4, and Cl, and thus arc more consistent with the
desire to eliminate hazardous materials from disk drive production.
There are no safety provisions required for CHF.sub.3. Acetylene is
flammable but not toxic and, therefore, only requires a gas
cabinet. Unlike a toxic gas, there is no need for expensive
double-walled plumbing and gas monitors. Furthermore, the reactive
by-products we form on the wafer surface are presumably carbides,
which are much safer than carbonyls and corrosive Cl by-products.
Hence, there are no special safety provisions required for the ion
mill exhaust.
[0037] We now illustrate the applicability of these RIBE processes
by outlining two processes for defining a sputtered top pole in a
magnetic write head, and the track width of a
current-perpendicular-to-the-plane (CPP) giant magneto-resistance
(GMR) reader. The C-based RIBE can be applied to many processes
other than the ones described here. For example, two other
applications include the definition of a current-in-plane (CIP) GMR
reader and a tunnel junction read head.
[0038] A process using this invention to define a sputtered top
pole of a magnetic write head is illustrated schematically in FIGS.
6-9. FIGS. 6-9 show the application of carbon-based RIBE to writer
fabrication. The figures are schematics showing the air bearing
surface (ABS) view for a fabrication sequence to build a top pole
in a perpendicular writer. FIG. 6 is a cross-section of the thin
film multilayer with lithographically defined resist. An Ar IBE
process defines the resist pattern into the RIE mask (not shown). A
thin film multilayer structure 70 is deposited onto a planarized
surface 72 in which a fraction of the surface contains an exposed
portion of a write yoke. All of the material and structures
fabricated before this top pole step lie below surface 72 and they
are represented by layer 74. The roles of each layer in the
structure 70 are as follows. A bottom layer 76 of Ta or W will
serve as an etch stop. A buffer layer 78 is optional but can be
included if it promotes good magnetics in the high-moment material
and if it can serve as a sacrificial layer that helps to eliminate
"feet" in the high-moment layer during the RIBE process. A high
moment magnetic layer 80 is positioned on the buffer layer. Cap
layer 82 is positioned on the high moment magnetic layer. A hard
mask layer 84 of Ta, or W is positioned on the cap layer. A
reactive ion etch mask 86 is positioned on hard layer. A resist 88
is positioned on reactive ion etch mask
[0039] At one point in the process, it is desirable to open a via
through layers 76 and 78 of FIG. 6 down to the yoke so that the
high-moment layer in this example will be exchange-coupled to the
rest of the yoke. The high-moment layer will form the top pole of a
perpendicular writer. We use the example of FeCoB but other
high-moment materials can be used. The cap layer is a non-magnetic
material that protects the trailing edge of the write pole. This
layer is both resistant to F-based RIE and readily etches with
C-based RIBE, an example of such material is non-magnetic NiFeCr.
The top Ta or W layer will act as a hard mask for the high-moment
layer. Finally, the RIE mask is used to define the top pole
structure into the Ta or W during the first RIE step.
[0040] FIG. 7 shows the definition of the device pattern into a Ta
or W hard mask by F-based RIE. The top pole structure is
transferred from the resist to the RIE mask by a standard Ar IBE
step. We note that the RIE mask can also be defined in a lift-off
process where some material that is resistant to F-based RIE, such
as NiFe or Al, is deposited through resist with a directional
technique, like evaporation or ion beam deposition. Once the RIE
mask is defined, the pattern can be transferred to the Ta or W
layer by F-based RIE. This will then serve as the top pole mask
during the C-based RIBE of the high-moment layer. FIG. 8 shows that
a Ta or W hard mask is then used to define the device structure
during the C-based RIBE of the high-moment top pole, which is FeCoB
for this example. FIG. 9 shows the final step of using a second
F-based RIE to remove the Ta or W etch stop layer. The last step,
illustrated in FIG. 9, is a clean-up process that removes the Ta or
W etch stop layer from the field.
[0041] The process can also be applied to the manufacture of CPP
readers as shown in FIGS. 10-13. These figures show an ABS view for
a proposed process for track width definition of a CPP reader. FIG.
10 is a cross-sectional view of the thin film multilayer with
lithographically defined resist. A thin film multilayer structure
100 is deposited onto a planarized surface 102 of a Cu lead or NiFe
shield 104. The roles of each layer in the structure 100 are as
follows. A bottom layer 106 of Ta or W will serve as an etch stop.
A buffer layer 108 is optional but can be included if it promotes
good magnetics in the GMR stack and if it can serve as a
sacrificial layer that helps to eliminate "feet" in the GMR stack
during the RIBE process. A GMR stack 110 is positioned on the
buffer layer. Cap layer 112 is positioned on the GMR stack. A
resist 114 is positioned on cap layer.
[0042] C-based RIBE then defines the track width of the CPP sensor
by removing portions of the cap layer, GMR stack and bottom layer
is not protected by the resist, as shown in FIG. 11. An insulator
116 is then deposited on the structure using a directional
deposition process as shown in FIG. 12. The insulator and resist
are then lifted off to leave the structure shown in FIG. 13.
[0043] The methodology of the process shown in FIGS. 10-13 is very
similar to that described for the writer. In this case, we used a
resist to define the track width rather than a metal hard mask so
that one can use lift-off to remove the insulator. One important
difference from the writer process is the constraint on the
resistivity of the Ta or W etch stop layer. Stray resistance from
leads and other miscellaneous layers in the CPP stack must be
minimized. This is potentially a problem since Ta typically forms a
body centered tetragonal phase that has very high resistivity of
.about.180 .mu..OMEGA.-cm. It is possible to form the low
resistivity body centered cubic phase of Ta that has a resistivity
of around 20 .mu..OMEGA.-cm, but this is not guaranteed to occur.
In contrast, W thin films typically have a resistivity of around 20
.mu..OMEGA.-cm and may be a better choice for the CPP reader
application.
[0044] Whether one chooses to use resist or a metal hard mask, the
C-based RIBE process will help to relax the constraints on the dry
etch process. The enhanced selectivity can allow thicker layers to
be etched for the same thickness of resist or hard mask.
Conversely, the same thickness can be etched with a thinner mask.
C-based RIBE, when incorporated into the writer process described
above, can substantially improve upon our current sputtered top
pole etch process. Finally, another key benefit of using Ta and W
as masks is the fact that both materials can be readily etched with
F-based RIE.
[0045] This invention provides a new C-based RIBE process for
selective etching of Ni, Fe, and Co alloys used in recording heads.
This process is a substantial improvement over standard Ar IBE and
is a potentially better alternative than Cl-based RIE for dry
etching magnetic materials. While we present data for just two sets
of ion beam parameters, the principle behind this disclosure can be
extended to any set of beam parameters, if necessary.
[0046] Data have been presented for the field etch rates of various
materials when subjected to reactive ion beam etch (RIBE) processes
that use either C.sub.2H.sub.2 or CHF.sub.3. Two examples are given
to illustrate the application of these processes during recording
head fabrication.
[0047] The accumulation of the carbon-rich material during the
carbon-based etch can be prevented by including elements or
compounds in the gas mixture that readily react with carbon to form
fast-etching compounds that may or may not be volatile. One way to
accomplish this is to incorporate oxygen into the gas mixture used
during carbon-based RIBE. The oxygen in the ion beam will then form
carbon monoxide or carbon dioxide from the residual carbon that
accumulates on the sidewalls. In general, molecular oxygen can be
mixed with carbon-containing gases that do not contain oxygen, such
as acetylene and methane. Another approach is to use a gas that has
both carbon and oxygen. Since carbon monoxide is flammable and
toxic, we chose carbon dioxide.
[0048] FIG. 14 shows measured field etch rates for various
materials used in recording head fabrication as a function of the
relative flow rate of CO.sub.2. The combined flow rates of Ar and
CO.sub.2 vary from 10 to 16 SCCM. The measured values are the
absolute etch rates. FIG. 15 shows the etch selectivity of NiFe and
FeCo with respect to various materials. The selectivity is computed
from the data in FIG. 14. Pure CO.sub.2 RIBE yields a selectivity
of NiFe and FeCo that is approximately 6 to 7 times higher than
that for pure Ar IBE. This carbon-based etch process leads to
structures with clean sidewalls that are free of the carbon-rich
build-up.
[0049] The data in FIGS. 14 and 15, show the measured field etch
rates as a function of the relative amount of CO.sub.2 mixed with
Ar. The absolute etch rates of most materials exhibit an overall
gradual decline with increasing concentration of CO.sub.2, but the
etch selectivity of NiFe and FeCo with respect to Ta exhibits a
remarkable enhancement. This behavior is similar to that observed
with C.sub.2H.sub.2 RIBE. Pure CO.sub.2 RIBE produces an etch
selectivity of the benchmark materials NiFe and FeCo that is six to
seven times larger than that for pure Ar IBE. This is a significant
enhancement and comes with only a small compromise in absolute etch
rate, which is about 2.3 times smaller than that for pure Ar
IBE.
[0050] The key test of CO.sub.2 RIBE is whether it can eliminate
the accumulation of carbon-rich material. Patterned structures have
been constructed in which the magnetic material in the surrounding
field has been etched solely by CO.sub.2 RIBE. The structures
exhibit clean sidewalls.
[0051] Overall, CO.sub.2 RIBE is able to match the etch selectivity
produced by C.sub.2H.sub.2 RIBE. Furthermore, CO.sub.2 RIBE is able
to do so while at the same time offering several improvements and
advantages. In particular, CO.sub.2 and C.sub.2H.sub.2 are both
non-toxic. However, CO.sub.2 is even safer because it is
non-flammable, which means that no gas cabinet is required. Pure
CO.sub.2 can be run through the ion beam source. This is in
contrast to the behavior observed with C.sub.2H.sub.2 RIBE, in
which a finite amount of Ar is required in order for the ion beam
source to generate the required currents. CO.sub.2 leads to less
carbon build-up in the vacuum chamber and in the turbo pump. Thus,
running CO.sub.2 will lead to fewer maintenance issues than when
using C.sub.2H.sub.2. CO.sub.2 can be used beyond just a clean-up
step because it leads to clean sidewalls.
[0052] The addition of oxygen helps keep sidewalls clean when using
a carbon-based RIBE process. We have accomplished this by using
CO.sub.2, but other ways of achieving the same results are through
the use of CO or using a mixture of O.sub.2 with carbon-containing
gases that do not have oxygen, such as C.sub.2H.sub.2 and CH.sub.4.
The selectivity of magnetic materials to photoresist goes down with
increasing relative CO.sub.2 flow rate. This is in contrast to
C.sub.2H.sub.2 RIBE in which the relative etch rate of photoresist
with respect to magnetic alloys goes down with increasing relative
C.sub.2H.sub.2 flow. This can be compensated for by adding a gas,
such as CHF.sub.3 or C.sub.2H.sub.2, to CO.sub.2 that induces
slower etch rates for photoresist.
[0053] The etch selectivity is a function of the ion energy, where
the selectivity increases with decreasing beam voltage. This can be
exploited to minimize the amount of over-etching into underlying
material by employing a multi-step CO.sub.2 RIBE process. In such a
process, higher beam energies are used to clear material from the
field for the first step. Then, a second step that employs lower
beam energies can be used for the over-etching necessary to clean
up corners and straighten sidewalls. CO.sub.2 RIBE in combination
with a Ta etch stop layer can also be used as a clean-up or via
opening step in a manner similar to that described above for
C.sub.2H.sub.2 RIBE.
[0054] While the present invention has been described in terms of
several examples, it will be apparent to those skilled in the art
that various changes can be made to the disclosed examples without
departing from the scope of the invention as defined by the
following claims.
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