U.S. patent application number 09/992517 was filed with the patent office on 2003-05-15 for a process for manufacturing a flat coil.
This patent application is currently assigned to Headway Technologies, Inc.. Invention is credited to Chang, Jei-Wei, Ju, Kochan.
Application Number | 20030088970 09/992517 |
Document ID | / |
Family ID | 25538424 |
Filed Date | 2003-05-15 |
United States Patent
Application |
20030088970 |
Kind Code |
A1 |
Chang, Jei-Wei ; et
al. |
May 15, 2003 |
A PROCESS FOR MANUFACTURING A FLAT COIL
Abstract
A process for manufacturing a flat coil for use as the write
head in a magnetic disk system is disclosed. The process starts
with a blanket seed layer which is coated with a photoresist frame
that defines the shape of the coil. The latter is then
electroformed from the seed layer within the confines of said
frame. Key features of the invention include capping the coil with
a layer of gold to protect it during the removal of copper that is
exposed after photoresist removal, using reactive ion etching to
convert the exposed copper to the chloride (which is then easily
rinsed away), and then removing all last traces of chlorides
through an ashing process.
Inventors: |
Chang, Jei-Wei; (Cupertino,
CA) ; Ju, Kochan; (Fremont, CA) |
Correspondence
Address: |
GEORGE O. SAILE & ASSOCIATES
28 DAVIS AVENUE
POUGHKEEPSIE
NY
12603
US
|
Assignee: |
Headway Technologies, Inc.
|
Family ID: |
25538424 |
Appl. No.: |
09/992517 |
Filed: |
November 14, 2001 |
Current U.S.
Class: |
29/603.07 ;
29/606; 29/846; 29/847 |
Current CPC
Class: |
H05K 2203/095 20130101;
H05K 3/388 20130101; H05K 2203/0361 20130101; H05K 2203/1142
20130101; H05K 3/108 20130101; H05K 2203/0315 20130101; Y10T
29/49069 20150115; Y10T 29/49071 20150115; H05K 3/062 20130101;
Y10T 29/49156 20150115; H01F 17/0006 20130101; H01F 41/043
20130101; Y10T 29/49165 20150115; H05K 1/165 20130101; Y10T
29/49032 20150115; Y10T 29/49073 20150115; Y10T 29/49155
20150115 |
Class at
Publication: |
29/603.07 ;
29/846; 29/847; 29/606 |
International
Class: |
H05K 003/10; H04R
031/00 |
Claims
What is claimed is:
1. A process for manufacturing a flat coil, comprising the
sequential steps of: providing a substrate; on said substrate,
depositing a layer of titanium and then a seed layer of copper;
coating the copper layer with photoresist and then patterning and
developing the photoresist to form a frame that defines the shape
of a coil; by means of electroplating, depositing additional copper
on all exposed copper surfaces, said electroplated copper having an
upper surface and a thickness; by means of electroplating,
depositing a layer of gold on said upper surface; removing all
photoresist; by means of reactive ion etching in a gaseous mixture,
converting all copper in said seed layer to copper chloride;
removing the copper chloride by rinsing in very dilute hydrochloric
acid, thereby forming the flat coil and exposing said titanium
layer; and exposing the coil and the titanium to an oxygen plasma
thereby removing any remaining copper chloride and converting all
titanium to titanium oxide.
2. The process of claim 1 wherein the titanium layer is deposited
to a thickness that is between about 10 and 200 Angstroms.
3. The process of claim 1 wherein the copper seed layer is
deposited to a thickness between about 300 and 2,000 Angstroms.
4. The process of claim 1 wherein the thickness of the copper coil
is between about 0.5 and 2.5 microns.
5. The process of claim 1 wherein the gold layer is deposited to a
thickness between about 0.05 and 0.3 microns.
6. The process of claim 1 wherein said very dilute solution has a
hydrochloric acid concentration between about 0.01 and 0.1 molar %
and a pH that is less than 1.
7. The process of claim 1 wherein the step of exposing the coil and
the titanium to an oxygen plasma further comprises using an oxygen
plasma at a temperature that is 5-10.degree. C. above room
temperature, at a flow rate from 10-200 SCCM, for 0.5 to 10
minutes.
8. The process of claim 1 wherein the step of reactive ion etching
in a gaseous mixture further comprises using RF to excite a plasma
in chlorine gas whose flow rate is between 2 and 20 SCCM, at a
pressure between 0.5 and 0.2 Pa, and a substrate temperature below
100.degree. C., thereby achieving etch rates between 100 to 3,000
Angstroms per minute.
9. The process of claim 1 wherein the titanium and copper seed
layers are deposited by physical vapor deposition.
10. The process of claim 1 wherein the substrate is selected fro
the group consisting of hard-baked photoresist, aluminum oxide, and
silicon oxide.
11. A process for manufacturing a flat coil, comprising the
sequential steps of: providing a substrate; on said substrate,
depositing a layer of titanium and then a seed layer of copper;
coating the copper layer with photoresist and then patterning and
developing the photoresist to form a frame that defines the shape
of a coil; by means of electroplating, depositing additional copper
on all exposed copper surfaces, said electroplated copper having an
upper surface and a thickness; by means of electroless plating,
depositing a layer of gold on said upper surface; removing all
photoresist; by means of reactive ion etching in a gaseous mixture,
converting all copper in said seed layer to copper chloride;
removing the copper chloride by rinsing in very dilute hydrochloric
acid, thereby forming the flat coil and exposing said titanium
layer; and exposing the coil and the titanium to an oxygen plasma
thereby removing any remaining copper chloride and converting all
titanium to titanium oxide.
12. The process of claim 11 wherein the titanium layer is deposited
to a thickness that is between about 10 and 200 Angstroms.
13. The process of claim 11 wherein the copper seed layer is
deposited to a thickness between about 300 and 2,000 Angstroms.
14. The process of claim 11 wherein the thickness of the copper
coil is between about 0.5 and 2.5 microns.
15. The process of claim 11 wherein the gold layer is deposited to
a thickness between about 0.05 and 0.3 microns.
16. The process of claim 11 wherein said very dilute solution has a
hydrochloric acid concentration between about 0.01 and 0.1 molar %
and a pH that is less than 1.
17. The process of claim 11 wherein the step of exposing the coil
and the titanium to an oxygen plasma further comprises using an
oxygen plasma at a temperature that is 5-10.degree. C. above room
temperature, at a flow rate from 10-200 SCCM, for 0.5 to 10
minutes.
18. The process of claim 11 wherein the step of reactive ion
etching in a gaseous mixture further comprises using RF to excite a
plasma in chlorine gas whose flow rate is between 2 and 20 SCCM, at
a pressure between 0.5 and 0.2 Pa, and a substrate temperature
below 100.degree. C., thereby achieving etch rates between 100 to
3,000 Angstroms per minute.
19. The process of claim 11 wherein the titanium and copper seed
layers are deposited by physical vapor deposition.
20. The process of claim 11 wherein the substrate is selected fro
the group consisting of hard-baked photoresist, aluminum oxide, and
silicon oxide.
21. A process for manufacturing a flat coil, comprising the
sequential steps of: providing a substrate; on said substrate,
depositing a layer of chromium and then a seed layer of copper;
coating the copper layer with photoresist and then patterning and
developing the photoresist to form a frame that defines the shape
of a coil; by means of electroplating, depositing additional copper
on all exposed copper surfaces, said electroplated copper having an
upper surface and a thickness; by means of electroplating,
depositing a layer of gold on said upper surface; removing all
photoresist; by means of reactive ion etching in a gaseous mixture,
converting all copper in said seed layer to copper chloride;
removing the copper chloride by rinsing in very dilute hydrochloric
acid, thereby forming the flat coil and exposing said chromium
layer; and exposing the coil and the chromium to an oxygen plasma
thereby removing any remaining copper chloride and converting all
chromium to chromium oxide.
22. The process of claim 21 wherein the chromium layer is deposited
to a thickness that is between about 10 and 200 Angstroms.
23. The process of claim 21 wherein the chromium and copper seed
layers are deposited by physical vapor deposition.
24. A process for manufacturing a flat coil, comprising the
sequential steps of: providing a substrate; on said substrate,
depositing a layer of chromium and then a seed layer of copper;
coating the copper layer with photoresist and then patterning and
developing the photoresist to form a frame that defines the shape
of a coil; by means of electroplating, depositing additional copper
on all exposed copper surfaces, said electroplated copper having an
upper surface and a thickness; by means of electroless plating,
depositing a layer of gold on said upper surface; removing all
photoresist; by means of reactive ion etching in a gaseous mixture,
converting all copper in said seed layer to copper chloride;
removing the copper chloride by rinsing in very dilute hydrochloric
acid, thereby forming the flat coil and exposing said chromium
layer; and exposing the coil and the chromium to an oxygen plasma
thereby removing any remaining copper chloride and converting all
chromium to chromium oxide.
25. The process of claim 24 wherein the chromium layer is deposited
to a thickness that is between about 10 and 200 Angstroms.
26. The process of claim 24 wherein the chromium and copper seed
layers are deposited by physical vapor deposition.
27. A process for manufacturing a flat coil, comprising the
sequential steps of: providing a substrate; on said substrate,
depositing a layer of tantalum and then a seed layer of copper;
coating the copper layer with photoresist and then patterning and
developing the photoresist to form a frame that defines the shape
of a coil; by means of electroplating, depositing additional copper
on all exposed copper surfaces, said electroplated copper having an
upper surface and a thickness; by means of electroplating,
depositing a layer of gold on said upper surface; removing all
photoresist; by means of reactive ion etching in a gaseous mixture,
converting all copper in said seed layer to copper chloride;
removing the copper chloride by rinsing in very dilute hydrochloric
acid, thereby forming the flat coil and exposing said tantalum
layer; and exposing the coil and the tantalum to an oxygen plasma
thereby removing any remaining copper chloride and converting all
tantalum to tantalum oxide.
28. The process of claim 27 wherein the tantalum layer is deposited
to a thickness that is between about 10 and 200 Angstroms.
29. A process for manufacturing a flat coil, comprising the
sequential steps of: providing a substrate; on said substrate,
depositing a layer of tantalum and then a seed layer of copper;
coating the copper layer with photoresist and then patterning and
developing the photoresist to form a frame that defines the shape
of a coil; by means of electroplating, depositing additional copper
on all exposed copper surfaces, said electroplated copper having an
upper surface and a thickness; by means of electroless plating,
depositing a layer of gold on said upper surface; removing all
photoresist; by means of reactive ion etching in a gaseous mixture,
converting all copper in said seed layer to copper chloride;
removing the copper chloride by rinsing in very dilute hydrochloric
acid, thereby forming the flat coil and exposing said tantalum
layer; and exposing the coil and the tantalum to an oxygen plasma
thereby removing any remaining copper chloride and converting all
tantalum to tantalum oxide.
30. The process of claim 29 wherein the tantalum layer is deposited
to a thickness that is between about 10 and 200 Angstroms.
Description
FIELD OF THE INVENTION
[0001] The invention relates to the general field of magnetic disks
with particular reference to fabricating miniaturized write coils
having high aspect ratios.
BACKGROUND OF THE INVENTION
[0002] Referring to FIG. 1, we show, in schematic representation, a
cross-sectional view of a write head for a magnetic disk system.
The magnetic field needed to perform the write operation is
generated by flat coil 16 made up of a number of turns, with 13
being an example of one side of a single turn. Surrounding the flat
coil is magnetic material comprising upper and lower pole pieces 12
and 11 respectively. These pole pieces are joined at one end (on
the left in this figure) and are separated by small gap 14 at the
other end. The magnetic field that is generated by flat coil 16
ends up being concentrated at gap 14. It is sufficiently powerful
that the fringing field that extends outwards away from gap 14 is
capable of magnetizing the magnetic storage medium over whose
surface 15 the head `flies`. The distance between gap 14 and
surface 15 is typically between about 0.005 and 0.075 microns.
[0003] As write heads continue to develop, a need has arisen for
coils that are both more compact as well as having greater current
carrying capability. This implies coils that have of the order of
3-20 turns made up of wires whose widths are less than about 0.5
microns and that are separated from one another by less than about
0.5 microns. Thus, to retain adequate cross-sectional area, it is
necessary for coils to be at least about 1 microns thick.
[0004] Manufacturing coils whose windings have the required high
aspect ratios have presented the industry with formidable
challenges. Two requirements, inter alia, have to be met. The first
is that the material for the coils have little or no built-in
stress. The second is that a method other than subtractive (i.e.
post deposition) etching be used. Electroplating meets both these
requirements. Once a seed layer (almost always of copper) which can
be connected to a source of electrical power is available on a
substrate, it becomes possible to place a non-conductive mask on
the seed layer and to then build up the uncovered areas through
electroplating.
[0005] Once the coil has been electroformed, it is still necessary
to remove all seed layer material that is not directly beneath the
coil. This is a particularly difficult problem for copper when such
high aspect ratios and narrow separations between windings are
involved. Since both the seed layer and the coil are made of
copper, a highly anisotropic etching process must be used to ensure
that no vertical surfaces (such as the sides of the copper coil)
are attacked, etching being limited to horizontal surfaces. This
means that reactive ion etching (RIE), or similar process, must be
used. RIE, in turn, depends on the generation of gaseous reaction
products, which is not the case for copper.
[0006] Until recently this problem has precluded routine use of RIE
for copper etching. However, a method for overcoming this was
recently proposed by Yue Kuo and S. Lee in "A new copper reactive
ion etching process" in the Proceedings of the '99 Joint
International Meeting of the ECS, ECSJPN, and JPN SAP (Nov. 1,
1999). Their method relies on the formation of copper chloride
which can later be selectively removed using a liquid etchant.
Although this represents an improvement over earlier practices,
problems still remain. In particular, some of the copper coil
itself is also converted to copper chloride, thereby reducing the
coil thickness, and a certain amount of copper chloride remains
behind despite the use of the liquid etchant. The present invention
provides solutions to both these problems.
[0007] An alternative approach to the blanket seed layer method
described above is the damascene method in which the photoresist
frame is formed before deposition of the seed layer. For a
comparison of the blanket seed and damascene methods we refer now
to FIGS. 2a and 2b. Seen in both figures is substrate 21 and
photoresist frame 23. However, in FIG. 2a the frame sits over the
seed layer 22a while in FIG. 2b the seed layer 22b has been
deposited over the frame. FIGS. 3a and 3b show the electroplated
layers 31a and 31b respectively. 31a is required to end slightly
below the top of frame 23 while 31b must be thick enough to fully
fill the frame, causing its thickness to be about twice that of
31a.
[0008] FIG. 4a shows the structure after removal of the photoresist
and all seed layer not under coil fragment 31a. In FIG. 4b the
structure is seen after the surface has been planarized and
polished down (generally using chemical mechanical polishing, or
CMP) until the top surface of photoresist 23 is exposed, thereby
allowing it to be removed, leaving behind the desired coil.
[0009] Although the damascene approach solves the problem of how to
remove unplated areas of seed layer, it is actually subject to
severe limitations. As the aspect ratio of the windings increases
and their separation decreases, there is a growing danger of
forming voids in the separation area between coils because of
loading effects that cause copper on opposing top surfaces to meet
before the separation area is fully filled in. Additionally, it is
clear that the damascene approach sets limits on the thickness of
the seed layer, particularly if it is preceded by a `glue` layer to
improve adhesion of the copper to the substrate. Again, the problem
of the formation of `keyhole` voids when filling spaces of high
aspect ratio is well known. It is thus clear that flat coils having
high aspect ratio and narrow separation between coils will need to
be fabricated using the blanket seed approach.
[0010] Finally, we note that attempts to remove the seed layer by
ion beam milling after formation of the coil, using the coil as its
own mask, have been unsuccessful. This is because of shadowing
effects--the high aspect ratio of the coil makes it very difficult
for ions to reach the seed layer without first glancing off the
side-walls of the coils which causes the removal of substantial
amounts of material therefrom.
[0011] A routine search for prior art was performed. Although
several references of interest were found none describe the exact
process that constitutes the present invention. Thus, for example,
in U.S. Pat. No. 5,926,349, Krounbi et al. teach a plate-up coil
process. Coil manufacturing processes based on electroplating are
disclosed in U.S. Pat. No. 5,777,824 (Gray) and U.S. Pat. No.
5,684,660 (Gray et al.), while other plating processes are taught
in U.S. Pat. No. 5,875,080 (Seagle) and U.S. Pat. No. 5,751,522
(Yamada et al.).
SUMMARY OF THE INVENTION
[0012] It has been an object of the present invention to provide a
process for manufacturing a flat coil for use in the write head of
a magnetic disk system.
[0013] Another object of the invention has been to be able to
manufacture flat coils having very high aspect ratios and very
small separation between windings.
[0014] A further object of the invention has been to manufacture a
flat coil that is protected against corrosion failure during its
life.
[0015] These objects have been achieved by using the blanket seed
layer process wherein the coil is electroformed from the seed layer
within the confines of a photoresist frame. Key features of the
invention include capping the coil with a layer of gold to protect
it during the removal of copper that is exposed after photoresist
removal, using RIE to convert the exposed copper to the chloride
(which is then easily rinsed away), and then removing all last
traces of said chlorides through an ashing process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic cross-section of a write head for a
magnetic disk system.
[0017] FIGS. 2a and b through 4a and b compare the blanket seed
layer process with the damascene process for forming a flat
coil.
[0018] FIG. 5 shows the starting point for the process of the
present invention, including a photoresist frame that defines the
shape of the coil.
[0019] FIG. 6 shows the coil after it has been electroformed within
the frame.
[0020] FIG. 7 shows the coil after a protective gold layer has been
added.
[0021] FIG. 8 shows the structure after photoresist stripping.
[0022] FIG. 9 shows the structure after the exposed seed layer has
been converted to copper chloride.
[0023] FIG. 10 shows the end product of the process.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] Referring now to FIG. 5, we show there a schematic
representation of the starting point of the process of the present
invention. Substrate 21 (of a non-conductive material such as
hard-baked photoresist, aluminum oxide, or silicon oxide) has been
coated with a `glue` layer 21 of titanium which is between about 10
and 200 Angstroms thick, with a preferred thickness of about 100
Angstroms. Note that, although we will continue our description in
terms of titanium, chromium or tantalum could have been used in
place of titanium. This is followed by the deposition of copper
seed layer 22a (between about 300 and 2,000 Angstroms thick with
about 600 Angstroms being preferred). The titanium and copper seed
layers are deposited by either physical deposition or CVD (chemical
vapor deposition), with former being preferred.
[0025] Copper layer 22a is then coated with photoresist, the latter
being patterned and developed to form photoresist frame 23 that
defines the shape of a coil. Then, as seen in FIG. 6, additional
copper layer 61 is grown on all exposed copper surfaces by means of
electroplating. The thickness of the copper coil at the conclusion
of electroplating is between about 0.5 and 2.5 microns.
[0026] The next step, illustrated in FIG. 7, is a key feature of
the invention. It is the deposition of gold layer 71 on the surface
of copper layer 61. We have found two different ways of depositing
this layer to be equally effective.
[0027] In a first embodiment of the invention, gold layer 71 is
deposited by means of electroplating while in a second embodiment
it is deposited by means of electroless plating. For both
embodiments our preferred thickness for gold layer 71 has been
about 0.1 microns although any thickness between about 0.05 and 0.3
microns would still work. The purpose of the gold layer is to
protect the top surface of copper coil 61 during the etching and
rinsing steps that follow. This allows the height of the coil to be
limited only by the dimensions of the photoresist frame. Gold layer
71 also serves to protect the coil from atmospheric corrosion
during its life.
[0028] After the removal of all photoresist, the structure has the
appearance illustrated in FIG. 8. However, although layer 61 has
the shape of a coil, it is still shorted out by (newly exposed)
seed layer 22a as well as by titanium glue layer 52. Reactive ion
etching is used to effect the removal of seed layer 22a. This is
accomplished by immersing the structure in a gaseous mixture that
has been electrically excited to form a plasma. The effect of this
is to convert all horizontal surfaces of copper to copper chloride.
As noted above, the process is highly anisotropic so vertical
surfaces (in particular the side-walls of the coil) are not
attacked. Details of the process are as follows:
[0029] Using RF, a plasma is excited in chlorine gas whose flow
rate is between 2 nad 20 SCCM, with pressure being adjusted to
between 0.5 and 0.2 Pa. Etch rates ranged from 100 to 3,000
Angstroms per minute. Substrate temperature was kept below
100.degree. C.
[0030] Since copper chloride is not volatile, it remains on the
surface within the coil. This is shown as layer 91 in FIG. 9. Note
that, because of the presence of gold layer 71, no copper chloride
has formed on the top surface of the coil. Once all exposed copper
horizontal surfaces have been converted to copper chloride it is
necessary to remove the latter. This is accomplished by rinsing in
a very dilute solution of hydrochloric acid (concentration between
about 0.01 and 0.1 molar %) and a pH that is less than 1, giving
the structure the appearance illustrated in FIG. 10.
[0031] As noted earlier, the rinsing process cannot be relied upon
to fully remove all last traces of copper chloride. Additionally,
at this stage partial titanium layer 52 still remains in place
which means that the coil is still being shorted out. Therefore, in
another key feature of the invention, the process concludes with an
ashing step. This involves exposing the coil and the titanium to an
oxygen plasma, thereby removing any remaining copper chloride and
converting all remaining titanium to titanium oxide. Details of the
ashing procedure include using an oxygen plasma at a temperature
that is 5-10.degree. C. above room temperature. Oxygen flow rate
was from 10-200 SCCM and oxidation times ranged from 0.5 to 10
minutes.
[0032] While the invention has been particularly shown and
described with reference to the preferred embodiments thereof, it
will be understood by those skilled in the art that various changes
in form and details may be made without departing from the spirit
and scope of the invention.
* * * * *