U.S. patent application number 10/155755 was filed with the patent office on 2002-09-26 for etched substrate.
Invention is credited to Gray, G. Robert, Jordan, Stephen G., Malhotra, Arun.
Application Number | 20020137344 10/155755 |
Document ID | / |
Family ID | 24508231 |
Filed Date | 2002-09-26 |
United States Patent
Application |
20020137344 |
Kind Code |
A1 |
Jordan, Stephen G. ; et
al. |
September 26, 2002 |
Etched substrate
Abstract
Etched substrate produced by chemical-mechanical processing of a
patterned substrate which selectively etches patterned portions of
the substrate surface, producing deep narrow features with a rapid
etch rate. This chemical-mechanical processing is termed
chemical-mechanical etching and produces a result that is
substantially the opposite of the planarization that is achieved by
conventional chemical-mechanical polishing (CMP). A
chemical-mechanical polishing (CMP) technique which is widely used
for planarization of surfaces is converted for usage as an etching
technique, a chemical-mechanical etching (CME) technique, by
forming a patterned mask on the substrate surface prior to
mechanical polishing. The usage of chemical-mechanical polishing
techniques in this manner yields an etching method with properties
including a rapid etch rate, a highly controllable etch rate, a
highly controllable etch depth, and a greatly selective etch
directionality. A coating that inhibits the removal of the
substrate material protects selectively patterned areas of a
substrate, thereby creating a recess in substrate areas that are
not protected by the coating.
Inventors: |
Jordan, Stephen G.;
(Fremont, CA) ; Gray, G. Robert; (Fremont, CA)
; Malhotra, Arun; (San Jose, CA) |
Correspondence
Address: |
David W. Heid
Skjerven Morrill LLP
Suite 700
25 Metro Drive
San Jose
CA
95110
US
|
Family ID: |
24508231 |
Appl. No.: |
10/155755 |
Filed: |
May 24, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10155755 |
May 24, 2002 |
|
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|
09625932 |
Jul 26, 2000 |
|
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6417109 |
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Current U.S.
Class: |
438/689 ;
257/E21.23; 257/E21.232 |
Current CPC
Class: |
H01L 21/30625 20130101;
H01L 21/3081 20130101 |
Class at
Publication: |
438/689 |
International
Class: |
H01L 021/302; H01L
021/461 |
Claims
What is claimed is:
1. An etched substrate comprising: a glass substrate wafer having a
substantially uniform surface; and a plurality of elevated
structures on the surface of the glass substrate wafer, the
elevated structures having side walls substantially perpendicular
to the substantially uniform surface of the glass substrate
wafer.
2. An etched substrate comprising: an alumina substrate wafer
having a substantially uniform surface; and a plurality of elevated
structures on the surface of the alumina substrate wafer, the
elevated structures having side walls substantially perpendicular
to the substantially uniform surface of the alumina substrate
wafer.
3. An etched substrate comprising: a substrate wafer selected from
the group consisting of silicon, silicon dioxide, silicon nitride,
gallium arsenide, polyimide, photoresist, aluminum, tungsten,
molybdenum, and titanium having a substantially uniform surface;
and a plurality of elevated structures on the surface of the
substrate wafer, the elevated structures having sidewalls
substantially perpendicular to the substantially uniform surface of
the substrate wafer.
4. An etched substrate fabricated by a process comprising: forming
a patterned protective layer composed of a hard material on a
surface of a substrate; and chemical-mechanical etching (CME) the
substrate using a chemical-mechanical polishing technique to form
an etched substrate structure having elevated structures in regions
of the substrate that are protected by the patterned protective
layer and having trenches in regions of the substrate that are not
protected by the patterned protective layer.
5. The etched substrate of claim 4, wherein: the forming step
includes the step of forming a patterned protective layer composed
of a hard material is composed of diamond-like carbon (DLC).
6. The etched substrate of claim 5, wherein: the forming step
includes the step of forming the diamond-like carbon (DLC)
patterned protective layer with a Knoop hardness in a range from
approximately 700 to approximately 2000.
7. The etched substrate of claim 4, wherein: chemical-mechanical
etching (CME) the substrate so that the elevated structures have
substantially vertical side walls.
8. The etched substrate of claim 4, wherein the process further
comprises: chemical-mechanical etching (CME) the substrate so that
the trench structures have a substantially uniform depth.
9. The etched substrate of claim 4, wherein the process further
comprises: providing a glass substrate; wherein the forming step
includes the step of forming, a patterned protective layer composed
of a hard material is composed of diamond-like carbon (DLC).
10. The etched substrate of claim 4, wherein the process further
comprises: providing The alumina substrate; wherein the forming
step includes the step of forming a patterned protective layer
composed of a hard material is composed of diamond-like carbon
(DLC).
11. The etched substrate of claim 4, wherein the process further
comprises: providing a substrate selected from the group consisting
of silicon, silicon dioxide, silicon nitride, gallium arsenide,
polyimide, photoresist, aluminum, tungsten, molybdenum, and
titanium; wherein the forming step includes the step of forming a
patterned protective layer composed of a hard material is composed
of diamond-like carbon (DLC).
12. The etched substrate of claim 4, wherein the forming step
includes: depositing a silicon adhesion layer on a surface of the
substrate; and depositing a patterned protective layer composed of
diamond-like carbon (DLC).
13. The etched substrate of claim 4, wherein: the CME step includes
the step of contouring the thin film substrate using a orbital,
planetary motion.
14. The etched substrate of claim 4, wherein: the CME step includes
the step of contouring the thin film substrate using a rectilinear
motion.
15. The etched substrate of claim 4, wherein the process further
comprises: patterning the patterned protective layer using a
reactive ion etch process.
16. An etched substrate fabricated by a process comprising:
providing a substrate wafer having a surface; forming a hard
patterned protective layer on a surface of a substrate to form
protected regions and unprotected regions of the substrate surface;
and chemical-mechanical polishing (CMP) the substrate, the
chemical-mechanical polishing step etching the substrate in
unprotected regions to form trenches adjacent to the protected
regions of the substrate surface.
17. The etched substrate according to claim 16, wherein: the
elevated structures have substantially vertical side walls.
18. The etched substrate according to claim 16, wherein: the trench
structures have a substantially uniform depth.
19. The etched substrate according to claim 16, wherein: the
forming step includes the step of forming a patterned protective
layer composed of a hard material is composed of diamond-like
carbon (DLC).
20. The etched substrate according to claim 19, wherein: the
forming step includes the step of forming the diamond-like carbon
(DLC) patterned protective layer with a Knoop hardness in a range
from approximately 700 to approximately 2000.
21. The etched substrate according to claim 16, wherein the
substrate is fabricated by the process further comprising:
providing a glass substrate; and wherein the forming step includes
the step of forming a patterned protective layer composed of a hard
material is composed of diamond-like carbon (DLC).
22. The etched substrate according to claim 16, wherein the
substrate is fabricated by the process further comprising:
providing an alumina substrate; and wherein the forming step
includes the step of forming a patterned protective layer composed
of a hard material is composed of diamond-like carbon (DLC).
23. The etched substrate according to claim 16, wherein the
substrate is fabricated by the process further comprising:
providing a substrate selected from the group consisting of
silicon, silicon dioxide, silicon nitride, gallium arsenide,
polyimide, photoresist, aluminum, tungsten, molybdenum, and
titanium; wherein the forming step includes the step of forming a
patterned protective layer composed of a hard material is composed
of diamond-like carbon (DLC).
24. The etched substrate according to claim 16, where the forming
step includes: depositing a silicon adhesion layer on a surface of
the substrate; and depositing a patterned protective layer composed
of diamond-like carbon (DLC).
25. The etched substrate according to claim 4, wherein the
patterned protective layer is patterned using a reactive ion etch
process.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a division of and claims priority from
U.S. patent application Ser. No. 09/625,932, filed Jul. 26, 2000,
entitled, "Chemical-Mechanical Etch (CME) Method For Patterned
Etching Of A Substrate Surface"
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention generally relates to a substrate wafer
having a substantially uniform surface and a plurality of elevated
structures on the surface of the substrate.
[0004] 2. Description of the Related Art
[0005] Various etching techniques are used in the fabrication of
various microminiature structures and devices to form patterns in a
substrate for many applications. An etching technique which is
suitable for a particular purpose etches selected layers in a
structure without damaging other layers and forms structures with a
sufficient etch rate, etch rate selectivity and directional
selectivity that a specified end product is produced
efficiently.
[0006] A wet etching technique employs liquid chemicals, such as
acids or corrosive materials, as an etching agent. The etching
process proceeds through chemical reactions at the surface of the
etched material and is limited by the rate of chemical reactions
and the rate of removal of products of the chemical reaction. In
some applications the wet etching process is electrically aided by
connecting the structure to be etched either an anode or a cathode
of an electrolytic cell. Unfortunately, wet etching has several
disadvantages. Direction etch selectivity is typically very poor
for wet etchants. One result of this poor direction etch
sensitivity is a large line-width loss that precludes the usage of
wet etching to form narrow lines that are common in many
applications. Furthermore, the etch rate is only marginally
controllable for many wet etchants. A further disadvantage is that
wet etching requires the handling, use and disposal of highly toxic
and corrosive chemicals, raising cost and safety concerns.
[0007] An alternative type of etching is dry etching, or
plasma-assisted etching, which uses either chemical or physical
reactions between a low-pressure plasma or glow discharge and the
surface to be etched in a gas phase. Dry etching is a complex
process with results that are greatly affected by small variations
in process parameters. Dry etching typically is used to pattern
smaller geometries than wet etching and has lateral etch rates that
are small so that the etched pattern is highly controllable and
smooth edge profiles are produced. Advantages of dry etching are a
highly directional etch anisotropy and a facility to penetrate
small photoresist apertures for etching small and intricate
geometries.
[0008] Plasma etching is a process in which a plasma generates
reactive species that chemically etch material in direct proximity
with the plasma. Plasma etching is typically used to etch
photoresists, silicon dioxide (SiO.sub.2), silicon nitride
(Si.sub.3N.sub.4), aluminum, polysilicon and metal silicides. If
the chemical reactions are enhanced by the kinetic energy of the
ions in the plasma, the process is a kinetically-assisted chemical
reaction. Reactive ion etching is similar to plasma etching but
only uses kinetically-assisted chemical etching. Reactive ion beam
etching separates the wafers from the plasma by a grid that
accelerates the ions created in the plasma towards the wafer,
raising the ion energy so that some etching is caused by physical
reactions.
[0009] Sputter etching uses energetic ions from the plasma to
physically wrench (sputter) atoms from the substrate surface
without assistance by chemical reactions.
[0010] Ion milling is a purely mechanical etching method that uses
a roughly collimated beam of energetic ions to erode a surface by
bombardment. Ion milling advantageously can be applied at angles
other than an angle perpendicular to the substrate wafer.
[0011] The etch rate achieved by the various etching techniques is
widely variable depending on the characteristics of the material to
be etched and etchant characteristics such as the selected chemical
for chemical etching methods and the ion, energy and density of the
etching ions for ion etching methods. Typical etch rates are in the
range of 100 to 3000 .ANG./min for most materials.
[0012] Some materials are not easily etched in a desired pattern
using conventional etching methods. For example, various substrates
resist etching using conventional patterned etching methods such as
plasma etching. Chemical etching is not easily performed due to the
usage of toxic chemicals and the poor directional selectivity of
chemical etchants.
[0013] What is needed is a technique for etching hard materials
that yields a rapid but controllable etch rate and directionality.
What is also needed is an etching technique for hard materials that
has high direction selectivity.
SUMMARY OF THE INVENTION
[0014] It has been discovered that chemical-mechanical processing
of a patterned substrate is highly effective for selectively
etching patterned portions of the substrate surface, producing deep
narrow features with a rapid etch rate. This chemical-mechanical
processing is termed chemical-mechanical etching and produces a
result that is substantially the opposite of the planarization that
is achieved by conventional chemical-mechanical polishing (CMP).
Chemical-mechanical etching is useful for patterned etching of
substrate materials including, for example, silicon, silicon
dioxide, silicon nitride, gallium arsenide, polyimide, photoresist,
aluminum, tungsten, molybdenum, titanium, glass, and the like.
[0015] In accordance with the present invention, an etched
substrate provided, the etched substrate being fabricated by a
chemical-mechanical etching (CME) technique, by forming a patterned
mask on the substrate surface prior to mechanical polishing. The
usage of chemical-mechanical polishing techniques in this manner
yields a surprisingly effective etching method with highly
desirable properties including a rapid etch rate, a highly
controllable etch rate, a highly controllable etch depth, and a
greatly selective etch directionality.
[0016] In accordance with an embodiment of the present invention,
an etched substrate is provided by a process in which a coating
inhibits the removal of the substrate in selectively patterned
areas of a substrate, thereby creating a recess in substrate areas
that are not protected by the coating.
[0017] In accordance with a specific embodiment of the present
invention, an etched substrate is provided by a process in which
the substrate is patterned with a diamond-like carbon (DLC) coating
and etched using a chemical-mechanical etch (CME) process. The CME
process forms deep narrow features having an angle essentially
normal to the plane of the substrate surface.
[0018] Many advantages are achieved using the disclosed
chemical-mechanical etch (CME) process. One advantage is that the
CME process performs a highly anisotropic etch that forms sidewalls
of an etched cut that are essentially vertical. Another advantage
is that the CME process forms a highly controllable structure with
substantially no undercutting of the mask. It is advantageous that
the etch rate is relatively rapid (for example, approximately 1
.mu.m per minute) so that processing throughput is facilitated, but
also sufficiently linear and restrained so that precise control of
the etch depth is facilitated.
[0019] Another advantage is that the usage of toxic and dangerous
chemicals is avoided, thereby lowering processing costs and
improving safety.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The features of the invention believed to be novel are
specifically set forth in the appended claims. However, the
invention itself, both as to its structure and method of operation,
may best be understood by referring to the following description
and accompanying drawings.
[0021] FIGS. 1A through 1D are a sequence of cross-sectional views
of a substrate workpiece depicting steps of a method of etching the
substrate workpiece using a chemical-mechanical etch process in
accordance with an embodiment of the present invention.
[0022] FIG. 2A is a two-dimensional top view of the substrate
workpiece subsequent to the chemical-mechanical etch process
described in FIGS. 1A through 1C.
[0023] FIG. 2B is a three-dimensional scanning interferometric
microscope image of the substrate workpiece following application
of the chemical-mechanical etch process described in FIGS. 1A
through 1C.
[0024] FIG. 2C is a profile plot of the substrate workpiece
subsequent to chemical-mechanical etch process described in FIGS.
1A through 1C.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Referring to FIGS. 1A through 1D, a sequence of
cross-sectional views of a substrate workpiece 100 depict steps of
a method of etching the substrate workpiece 100 using a
chemical-mechanical etch process. FIG. 1A illustrates a substrate
wafer 102 prior to processing. The substrate wafer 102 has an outer
surface 104. The substrate wafer 102 is to be etched to form a
recessed surface 106 of the substrate wafer 102 with one or more
structures 108 extending essentially to the outer surface 104. The
dimensions of the structures 108 are selected according to the
intended application of the processed substrate workpiece 100. For
example, in some embodiments, the structures 108 may take the form
of lenses, pads, rails, pillars, slider arms, support structures or
many other various structures. The substrate wafer 102 is composed
of various substrate materials including, for example, silicon,
silicon dioxide, silicon nitride, gallium arsenide, polyimide,
photoresist, aluminum, tungsten, molybdenum, titanium, glass, and
other suitable materials.
[0026] Referring to FIG. 1B, a protective layer 110 is formed
overlying the outer surface 104 of the substrate workpiece 100. In
one example, the protective layer 110 is deposited using
plasma-enhanced chemical vapor deposition (PECVD) to deposit a
silicon intermediate adhesion layer 114 overlying the substrate
workpiece 100. A hard layer, for example a layer of diamond-like
carbon (DLC) 116, is deposited on the substrate workpiece 100
overlying the silicon adhesion layer 114. The DLC layer 116
typically has a Knoop hardness ranging from approximately 700 Knoop
to 2000 Knoop. In alternative embodiments, hard materials other
than diamond-like carbon may be used which have a Knoop hardness in
the range from approximately 700 Knoop to 3000 Knoop or more.
[0027] The DLC layer 116 is deposited via a chemical vapor
deposition (CVD) process and patterned. More specifically, the DLC
layer 116 and the silicon adhesion layer 114 are reactive ion
etched.
[0028] The silicon adhesion layer 114 is sputter deposited on an
exposed surface of the substrate wafer 102. The silicon adhesion
layer 114 enables the DLC layer 116 to adhere to the substrate
wafer 102. The silicon adhesion layer 114 typically has a thickness
in a range from approximately 400 .ANG. to approximately 1000
.ANG.. A suitable thickness is about 600 .ANG..
[0029] The silicon adhesion layer 114 is sputter-cleaned prior to
deposition of the DLC layer 116. During sputter cleaning,
approximately 200 .ANG. of the 600 .ANG. silicon adhesion layer 114
is removed. In one embodiment, the silicon adhesion layer 114 is
sputter-cleaned using a SAMCO plasma machine, Model No. PD-200D
(Plasma Enhanced CVD System for DLC Deposition and Etching), called
a "plasma machine". Sputter cleaning is performed with Argon in a
plasma within the plasma machine vessel at a pressure of 70 mTorr
with 180 watts RF input power at a frequency of 13.56 MHz. The flow
rate of Argon is approximately 100 sccm. The substrate workpiece
100 is sputter-cleaned on a 6 inch diameter cathode (i.e. the
energized electrode) of the SAMCO plasma machine, Model PD-200D,
for approximately 3 to approximately 4 minutes.
[0030] Following Argon plasma cleaning (sputter etching), input
power to the plasma machine is reduced to 110-150 Watts to the same
6 inch cathode electrode. The Argon source is terminated and a
source of liquid hydrocarbon DLC source material is accessed. For
example, one DLC source material that may be used is Part No. S-12
available from SAMCO, Sunnyvale, Calif. The pressure within the
vessel ranges from approximately 20 mTorr to approximately 25 mTorr
at a flow rate of source material of approximately 25 cm.sup.3/min.
Although the temperature is not specifically controlled during the
process, the substrate wafer 102 is held on a water-cooled cathode
while in the plasma machine. Under these conditions, a DLC
deposition rate of approximately 1000 .ANG./min is obtained and
maintained until the desired DLC thickness of approximately 5.mu.
is attained.
[0031] The resulting DLC layer 116 has a Knoop hardness of
approximately 800. A DLC layer Knoop hardness of greater than 700
up to approximately 2000 Knoop produces an acceptably hard
protective layer 110 for chemical-mechanical etching. The DLC layer
116 is then reactive ion etched.
[0032] Prior to exposing the substrate workpiece 100 to the
reactive ion etch, the substrate workpiece 100 is covered with a
layer of photoresist (not shown). The photoresist layer is
patterned to include unprotected open regions overlying portions of
the substrate wafer 102 that are to be etched. In this manner, when
the substrate workpiece is subjected to the reactive ion etch, the
portions of DLC layer 116 overlying portions of the substrate wafer
102 to be etched are removed and the remaining portions of the DLC
layer 116 are protected and remains as DLC layer 116.
[0033] An alternative method to the above described photoresist
masking approach to patterning the protective layer 110 is to cover
the substrate wafer 102 with a metal layer constructed from a metal
such as chromium. For example, a relatively thin (for example, 500
.ANG. in thickness) photomask layer (not shown) of chromium is
sputtered over the DLC layer 116. The metal photomask layer is
photo-patterned and etched to expose DLC areas which are to be
excavated by reactive ion etching. The DLC layer is then reactive
ion etched to the desired DLC structure.
[0034] DLC is advantageously used as a protective barrier in the
protective layer 110 since DLC bonds well with various substrates,
including examples of aluminum oxide (alumina), silicon dioxide,
and glass, etch well in oxygen for removal of the DLC layer
subsequent to etching. In other embodiments, hard materials other
than DLC may be used as the protective barrier of the protective
layer 110.
[0035] Referring to FIG. 1C, a chemical-mechanical processing step
is applied to the outer surface 104 of the substrate workpiece 100
to selectively etch the portions of the substrate workpiece 100
that are not protected by the protective layer 110.
Chemical-mechanical etching (CME) utilizes application of polishing
pad in a typically orbital or planetary motion to a stationary thin
film substrate. The orbital or planetary motion is applied to the
thin film substrate by a lapping surface of the polishing pad to
etch the areas of the substrate wafer 102 that are not covered by
the protective layer 110.
[0036] CME processing involves application of a chemical slurry to
the polishing pad and the thin film substrate workpiece to generate
a chemical etching while the workpiece is mechanically contoured.
The slurry is a mixture of a chemical etchant and an abrasive
compound. As the slurry and polishing motion of the polishing pad
are applied to the thin film substrate workpiece, the workpiece is
lapped by a lapping surface of the polishing pad. Typically, the
slurry contains chemical etchants that are nontoxic and benign so
that disposal is inexpensive in contrast to conventional chemical
etchants such as hydrochloric acid, which are unsafe and expensive
to remove.
[0037] Referring to FIG. 1D, following etching of the substrate
wafer 102 the protective layer 110 is removed by applying an
etchant that preferentially etches the hard protective layer 110.
In some embodiments, the entire protective layer 110 is removed
including the silicon layer 112, the intermediate adhesion layer
114, and the diamond-like carbon (DLC) layer 116. In other
embodiments, the DLC layer 116 alone may be removed. An oxygen-rich
liquid, such as hydrogen peroxide (H.sub.2O.sub.2), preferentially
etches DLC. In other embodiments, other oxygen-rich etchants may be
used including HOC1, KOC1, KMgO.sub.4, and CH.sub.3COOH.
[0038] Referring again to FIGS. 1A through 1D, a more specific
embodiment of the method of etching the substrate workpiece 100
using a chemical-mechanical etch process is described. In the
specific embodiment, the substrate wafer 102 is most commonly a
substrate such as alumina or glass. In other examples, the
substrate wafer 102 is selected from among silicon, silicon
dioxide, silicon nitride, gallium arsenide, polyimide, photoresist,
aluminum, tungsten, molybdenum, titanium, and other suitable
materials. Protective layer 110 shown in FIG. 1B is deposited
including the DLC layer 116 having a thickness of approximately 3.5
.mu.m. The chemical-mechanical etch process is performed using an
eighteen inch "soft" polishing pad and disk which is rotated at a
rate of about 60 rpm. The pressure applied to the substrate wafer
102 by the polishing pad is approximately 2.5 psi. The soft
polishing pad is flooded, or saturated, with Rodel R-94 slurry. One
example of a soft polishing pad is a Model 205 pad from Rodel
Products Corp. of Scottsdale, Ariz.
[0039] The polishing pad and the slurry are selected to achieve a
desired etching performance. In general, a soft polishing pad forms
a deeper trench and a harder polishing pad forms a more shallow
trench.
[0040] The substrate workpiece 100 is chemical-mechanical etched
for a suitable time to etch a desired depth into the substrate
wafer 102. In the illustrative example, the substrate wafer 102 is
chemical-mechanical etched at a substantially linear rate of
approximately 1 .mu.m per minute.
[0041] FIGS. 2A, 2B, and 2C are depictions of a substrate workpiece
200, in particular a magnetic recording head slider, subsequent to
CME processing respectively represented by a two-dimensional top
view of the substrate workpiece 100 (FIG. 2A), a three-dimensional
scanning electron micrograph (SEM) image (FIG. 2B), and a profile
plot (FIG. 2C). The substrate workpiece 200 is etched following
application of a pattern defining two slider rails 202 and 204
arranged in substantially parallel lines and a pad 206 having a
rectangular shape when viewed from the top view of the substrate
workpiece 200. The pad 206 is positioned substantially along a
center line equidistant between the two slider rails 202 and 204.
The pad 206 and the two slider rails 202 and 204 are protected from
etching by the protective layer 110 during etching so that trenches
having a depth of approximately 15 .mu.m are formed surrounding the
pad 206 and two slider rails 202 and 204. At an etch rate of
approximately 1 .mu.m per minute, a trench is formed in
approximately 15 minutes. At a top surface 208 of the substrate
workpiece 200, the pad 206 and the two slider rails 202 and 204
form a coplanar surface. Side walls 210 of the pad 206 and the two
slider rails 202 and 204 are substantially vertical and a trench
212 that is formed using the CME processing has a highly uniform
depth with the floor 214 of the trench 212 forming essentially a 90
degree angle with the side walls 210 of the pad 206 and the two
slider rails 202 and 204. The slope of the side walls 210 and the
uniformity of the trench depth are dependent upon characteristics
of the CME operation including the type of slurry and hardness of
the polishing pad.
[0042] The three-dimensional interferometric microscope image shown
in FIG. 2B illustrates the highly advantageous structure that is
produced using the CME process. Essentially no undercutting of the
DLC mask takes place. Thus the CME process forms a highly
anisotropic etch so that the walls of an etched cut are
substantially vertical.
[0043] In a conventional chemical etching process, a substrate may
have a crystal axis with a defined orientation so that etching
occurs preferentially depending on the orientation of the crystal.
Properly orienting of the substrate is generally difficult or
impossible. Chemical-mechanical etching (CME) etches the substrate
according to the arrangement of the DLC mask regardless of the
orientation of the substrate crystal axis.
[0044] Chemical-mechanical etching (CME) is a process that is
similar to conventional chemical-mechanical polishing (CMP) except
that the CME process uses a patterned protective mask layer at the
surface of the substrate to selectively protect regions of the
substrate that are protected from etching. The result of the CME
process is nearly the opposite of the result of CMP with the CME
process forming a structure with high topographical variability and
the CMP process forming a planar surface.
[0045] Conventional chemical-mechanical polishing (CMP) is a known
technique for planarizing various structures on a thin film
substrate. CMP is conventionally used to create a smooth, planar
surface for intermediate processing steps of a thin film
fabrication process. Specifically, various layers such as
metallization layers are deposited and etched during the
fabrication of thin film devices on a substrate. These layers are
commonly subjected to CMP so that planar deposition of additional
layers is achieved. CMP processing not only is used to planarize
protruding surfaces, but also to remove undesirable residues that
remain from other substrate processing steps.
[0046] CMP involves simultaneous chemically etching and mechanical
polishing or grinding of a surface so that a combined chemical
reaction and mechanical polishing removes a desired material from
the substrate surface in a controlled manner. The resulting
structure is a planarized substrate surface with protruding surface
topography leveled. CMP is typically performed by polishing a
substrate surface against a polishing pad that is wetted with a
slurry including an acidic or basic solution, an abrasive agent and
a suspension fluid.
[0047] The special CME processing that is used to precisely etch a
substrate is different from a conventional CMP process on the basis
that the CME process includes the formation of a patterned hard
mask layer, such as a patterned DLC layer, on the surface of a
substrate and the hard mask layer serves to protect patterned
regions of the substrate while unprotected regions are etched. Once
the hard mask layer is formed on the substrate, the CME process is
substantially the same as conventional CMP processing techniques
that are otherwise used to planarize surface structures in
intermediate steps of integrated circuit fabrication. CME
processing is selectively performed using a wide range of
mechanical polishing techniques employing polishing pads ranging
from hard pads to soft pads, various slurry materials, polishing
speeds throughout the range of CMP processes, for example a speed
of 50 or more revolutions per minute (rpm), corresponding to a
linear speed of 25 inches per second (ips), or faster. CME
mechanical polishing is applied at a conventional range of
pressures from a relatively high pressure to a relatively low
pressure. In one example, the procedure involves a mechanical
polishing using a hard polishing pad applied at a high speed and
low pressure of about 2 psi or less. A typical speed and pressure
of a conventional process is 60 rpm and 8 psi. A hard polishing pad
typically has a compressibility of less than about ten or twelve
percent. Conventional CMP processing procedure typically uses a
slurry with an etchant that achieves etching through either
chemical or physical reactions taking place between a plasma and
the surface to be etched.
[0048] In one example, the special CME processing for etching an
alumina or glass substrate using a DLC mask employs a compliant, or
soft, polishing pad which develops an advantageous etch shape with
substantially vertical structure walls and a substantially uniform
trench depth. One example of a soft polishing pad is a Model 205
pad from Rodel Products Corp. of Scottsdale, Ariz. This soft
polishing pad is constructed from napped poromeric synthetics and
has a compressibility of from 20 to 38 percent. In contrast, a
typical hard polishing pad is constructed from polyurethane
impregnated polyester felts. The mechanical etching of the special
CME process also employs a soft polishing pad applied at a
relatively low speed and a relatively high pressure to the thin
film substrate surface. The softness of the polishing pad is
selected to determine the shape and contour of the etched substrate
surface, specifically to achieve substantially vertical structure
walls and a uniform trench depth. The low speed of the special CME
processing is typically on the order of 1/3 the speed of a
conventional CMP process. For example, a typical low processing
speed is approximately 10 RPM to 40 RPM, corresponding to a linear
speed of 5 ips to 20 ips. The relatively high pressure of the
special CME processing is typically on the order of two to three
times the pressure of a conventional CMP procedure. For example, a
typical high processing pressure is approximately 2 psi to 10 psi.
The special CME processing employs either conventional orbital
motion of the polishing pad or a rectilinear motion between the
thin film substrate and the polishing pad table. Slurry may be
applied either lightly for heavily in the special CME
processing.
[0049] The CME process utilizes a mechanical action, which is
generated by movement on a suitable surface, or "lap". The surface
of a thin film substrate to be etched using CME is substantially
saturated with a slurry that contains a chemical etchant. The
mechanical action etches the unprotected regions of the substrate
while the protected regions remain, producing a structure with
substantially vertical side walls and a highly uniform trench
depth.
[0050] While the invention has been described with reference to
various embodiments, it will be understood that these embodiments
are illustrative and that the scope of the invention is not limited
to them. Many variations, modifications, additions and improvements
of the embodiments described are possible. For example, although
the material which is etched using the CME process is an alumina or
glass material, other materials may be etched using the described
CME process including silicon, silicon dioxide, silicon nitride,
gallium arsenide, polyimide, photoresist, aluminum, tungsten,
molybdenum, titanium, glass, and other suitable materials. Also,
although a protective structure of the mask material is described
as being a diamond-like carbon (DLC) structure, other types of
protective materials may be used. Furthermore, the CME process is
described using a polishing pad that is saturated with slurry. In
other embodiments, various other amounts of slurry may be utilized
including small amounts of slurry. In addition, various hardnesses
of polishing pads may be used ranging from hard pads to soft
pads.
[0051] Although the illustrative method is shown applied to the
fabrication of a magnetic thin film head slider structure, the
method may be applied to a wide variety of structures. One example
is the fabrication of air bearings on an aluminum substrate.
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