U.S. patent application number 15/947234 was filed with the patent office on 2019-07-11 for techniques for improved removal of sacrificial mask.
This patent application is currently assigned to Varian Semiconductor Equipment Associates, Inc.. The applicant listed for this patent is Varian Semiconductor Equipment Associates, Inc.. Invention is credited to Eric J. Bergman, James Cournoyer, John Lee Klocke, Kwangduk Lee, Terrance Lee, Tzu-Yu Liu, Rajesh Prasad, Kyu-Ha Shim, Harry S. Whitesell, Ning Zhan.
Application Number | 20190214255 15/947234 |
Document ID | / |
Family ID | 67144324 |
Filed Date | 2019-07-11 |
United States Patent
Application |
20190214255 |
Kind Code |
A1 |
Prasad; Rajesh ; et
al. |
July 11, 2019 |
TECHNIQUES FOR IMPROVED REMOVAL OF SACRIFICIAL MASK
Abstract
A method may include forming a sacrificial mask on a device
structure, the sacrificial mask comprising a carbon-based material.
The method may further include etching memory structures in exposed
regions of the sacrificial mask, implanting an etch-enhancing
species into the sacrificial mask, and performing a wet etch to
selectively remove the sacrificial mask at etch temperature, less
than 350.degree. C.
Inventors: |
Prasad; Rajesh; (Lexington,
MA) ; Zhan; Ning; (Scarsdale, NY) ; Liu;
Tzu-Yu; (Somerville, MA) ; Cournoyer; James;
(Rockport, MA) ; Shim; Kyu-Ha; (Andover, MA)
; Lee; Kwangduk; (Redwood City, CA) ; Klocke; John
Lee; (Kalispell, MT) ; Bergman; Eric J.;
(Kalispell, MT) ; Lee; Terrance; (Oakland, CA)
; Whitesell; Harry S.; (Sunnyvale, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Varian Semiconductor Equipment Associates, Inc. |
Gloucester |
MA |
US |
|
|
Assignee: |
Varian Semiconductor Equipment
Associates, Inc.
Gloucester
MA
|
Family ID: |
67144324 |
Appl. No.: |
15/947234 |
Filed: |
April 6, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62614943 |
Jan 8, 2018 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 21/31155 20130101;
H01L 21/0337 20130101; H01L 21/31111 20130101 |
International
Class: |
H01L 21/033 20060101
H01L021/033; H01L 21/311 20060101 H01L021/311; H01L 21/3115
20060101 H01L021/3115 |
Claims
1. A method, comprising: forming a sacrificial mask on device
structure, the sacrificial mask comprising a carbon-based material;
etching memory structures in exposed regions of the sacrificial
mask; implanting an etch-enhancing species into the sacrificial
mask; and performing a wet etch to selectively remove the
sacrificial mask at an etch temperature, less than 350.degree.
C.
2. The method of claim 1, the etch-enhancing species comprising
hydrogen.
3. The method of claim 1, the wet etch comprising a sulfuric
acid/hydrogen peroxide mixture.
4. The method of claim 1, the implanting comprising implanting a
dose of hydrogen ions of between 4 E13/cm.sup.2 and
1E15/cm.sup.2.
5. The method of claim 4, the implanting comprising implanting the
dose of hydrogen ions in a plurality of implant procedures, wherein
a first implant procedure comprises a first ion energy, and a
second implant procedure comprises a second ion energy, lower than
the first ion energy.
6. The method of claim 1, wherein the sacrificial mask comprises an
initial thickness of 1000 nm to 1500 nm.
7. The method of claim 1, wherein the etch temperature is between
250.degree. C. and 300.degree. C.
8. The method of claim 1, wherein the sacrificial mask comprises a
carbon/boron mixture having a molar ratio of 90% carbon/10% boron
to 30% carbon/70% boron.
9. The method of claim 8, wherein the sacrificial mask further
comprises hydrogen.
10. The method of claim 1, wherein the implanting comprising
implanting at least one dose of hydrogen ions at an ion energy
between 30 keV and 170 keV.
11. A method, comprising: forming a sacrificial mask on device
structure, the sacrificial mask comprising a carbon-based material;
etching memory structures in exposed regions of the sacrificial
mask; performing a first wet etch to selectively remove a first
portion of the sacrificial mask at a first etch temperature, the
first etch temperature being 350.degree. C. or less, wherein a
second portion of sacrificial mask remains; implanting an
etch-enhancing species into a remaining portion of the sacrificial
mask; and performing a second wet etch to selectively remove the
remaining portion of the sacrificial mask at a second etch
temperature, the second etch temperature being less than
350.degree. C.
12. The method of claim 11, the second temperature being between
250.degree. C. and 300.degree. C.
13. The method of claim 11, wherein the sacrificial mask comprises
a carbon/boron mixture having a molar ratio of 90% carbon/10% boron
to 30% carbon/70% boron.
14. The method of claim 11, wherein the sacrificial mask further
comprises hydrogen.
15. The method of claim 11, wherein the first portion of the
sacrificial mask comprises 40%-80% of an initial thickness of the
sacrificial mask.
16. A method, comprising: forming a sacrificial mask on device
structure, the sacrificial mask comprising a carbon-based material;
etching memory structures in exposed regions of the sacrificial
mask; performing an implant procedure to implant an etch-enhancing
species into the sacrificial mask, the implant procedure
comprising: performing a first implant at a first ion energy; and
performing a second implant at a second ion energy, greater than
the first ion energy, wherein the first ion energy and second ion
energy are in a range of 30 keV to 170 keV; and performing a wet
etch to selectively remove the sacrificial mask at an etch
temperature, the etch temperature being less than 350.degree.
C.
17. The method of claim 16, wherein the sacrificial mask comprises
an initial thickness of 1000 nm to 1500 nm.
18. The method of claim 16, wherein the implant procedure comprises
a total ion dose of between 5 E13/cm.sup.2 and 1E16/cm.sup.2.
Description
RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
application 62/614,943, filed Jan. 8, 2018, entitled TECHNIQUES FOR
IMPROVED REMOVAL OF SACRIFICIAL MASK, and incorporated by reference
herein in its entirety.
FIELD
[0002] The present embodiments relate to device processing, and
more particularly, to removal of sacrificial masks during device
processing.
BACKGROUND
[0003] In the present day, device fabrication, such as
semiconductor device fabrication, may the use of one or multiple
sacrificial mask layers, or sacrificial masks, including so-called
hard masks. During removal of a mask such as a hard mask, portions
of a device may be exposed to a harsh etchant used for mask
removal. As an example, during three dimensional NAND memory device
(3D NAND) fabrication, a memory array may be exposed to the etchant
used to remove hard mask material. While the etchant may be
designed to remove the hard mask at a target etch rate using a
target recipe, the target recipe may also attack the memory array,
resulting in degraded performance of yield. For example, the target
recipe may entail high temperature etching effective to remove a
carbon-based hard mask. By reducing the etch temperature, attack of
the memory by the etchant may be reduced or prevented, while the
resulting etch rate of the hardmask may also be reduced below the
target etch rate.
[0004] With respect to these and other considerations the present
disclosure is provided.
BRIEF SUMMARY
[0005] In one embodiment, a method may include forming a
sacrificial mask on device structure, the sacrificial mask
comprising a carbon-based material, etching memory structures in
exposed regions of the sacrificial mask, and implanting an
etch-enhancing species into the sacrificial mask. The method may
further include performing a wet etch to selectively remove the
sacrificial mask at an etch temperature, less than 350.degree.
C.
[0006] In another embodiment, a method may include forming a
sacrificial mask on device structure, the sacrificial mask
comprising a carbon-based material, and etching memory structures
in exposed regions of the sacrificial mask. The method may further
include performing a first wet etch to selectively remove a first
portion of the sacrificial mask at a first etch temperature, the
first etch temperature being 350.degree. C. or less, wherein a
second portion of sacrificial mask remains. The method may also
include implanting an etch-enhancing species into a remaining
portion of the sacrificial mask; and performing a second wet etch
to selectively remove the remaining portion of the sacrificial mask
at a second etch temperature, the second etch temperature being
less than 350.degree. C.
[0007] In a further embodiment, a method may include forming a
sacrificial mask on device structure, the sacrificial mask
comprising a carbon-based material, and etching memory structures
in exposed regions of the sacrificial mask. The method may include
performing an implant procedure to implant an etch-enhancing
species into the sacrificial mask. The implant procedure may
involve performing a first implant at a first ion energy;
performing a second implant at a second ion energy, greater than
the first ion energy, wherein the first ion energy and second ion
energy are in the range of 30 keV to 170 keV. The method may also
include performing a wet etch to selectively remove the sacrificial
mask at an etch temperature, the etch temperature being less than
350.degree. C.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 shows a device arrangement, according to embodiments
of the disclosure;
[0009] FIG. 2 presents an exemplary process flow, according to
embodiments of the disclosure;
[0010] FIG. 3 presents another exemplary process flow, according to
further embodiments of the disclosure;
[0011] FIG. 4A presents a graph depicting hydrogen implant depth as
a function of ion energy for implantation into a carbon-boron
layer;
[0012] FIG. 4B presents a graph depicting hydrogen implant profiles
for four different implant ion energies for implantation into a
carbon-boron layer;
[0013] FIG. 4C presents a graph depicting a composite hydrogen
implant profile based upon a sum of the implant profiles of FIG.
4B;
[0014] FIG. 4D presents a graph depicting a composite hydrogen
implant profile based upon a sum of three implant profiles for
three different ion energies;
[0015] FIG. 4E presents a graph depicting a composite hydrogen
implant profile based upon a sum of two implant profiles for two
different ion energies;
[0016] FIG. 5 presents the etch rate of singly-implanted
carbon-boron samples as a function of ion dose for different
procedures, according to embodiments of the disclosure;
[0017] FIG. 6A, FIG. 6B, FIG. 6C, and FIG. 6D present the results
of etch rate enhancement of an implanted carbon-boron layer as a
function of ion energy for different ion doses, in accordance with
embodiments of the disclosure;
[0018] FIG. 7 presents the etch rate of multiply-implanted
carbon-boron samples as a function of ion dose for different
procedures, according to embodiments of the disclosure; and
[0019] FIG. 8 shows an exemplary process flow according to
embodiments of the disclosure.
[0020] The drawings are not necessarily to scale. The drawings are
merely representations, not intended to portray specific parameters
of the disclosure. The drawings are intended to depict exemplary
embodiments of the disclosure, and therefore are not be considered
as limiting in scope. In the drawings, like numbering represents
like elements.
[0021] Furthermore, certain elements in some of the figures may be
omitted, or illustrated not-to-scale, for illustrative clarity. The
cross-sectional views may be in the form of "slices", or
"near-sighted" cross-sectional views, omitting certain background
lines otherwise visible in a "true" cross-sectional view, for
illustrative clarity. Furthermore, for clarity, some reference
numbers may be omitted in certain drawings.
DETAILED DESCRIPTION
[0022] The present embodiments will now be described more fully
hereinafter with reference to the accompanying drawings, where some
embodiments are shown. The subject matter of the present disclosure
may be embodied in many different forms and are not to be construed
as limited to the embodiments set forth herein. These embodiments
are provided so this disclosure will be thorough and complete, and
will fully convey the scope of the subject matter to those skilled
in the art. In the drawings, like numbers refer to like elements
throughout.
[0023] In accordance with some embodiments, a novel processing
technique entails providing a carbon-based hardmask on a memory
structure and implanting the hardmask with etch-enhancing species.
The process further involves stripping the hardmask using a dry
etchant or wet etchant. In accordance with various embodiments the
hardmask may be a boron-carbon material, while the etch-enhancing
species include oxygen or hydrogen.
[0024] In some embodiments, a carbon-based hardmask is composed of
a carbon-boron mixture. In embodiments employing a wet etchant to
selectively remove the hardmask, the wet etch chemistry may involve
a mixture of sulfuric acid and hydrogen peroxide. Exemplary etch
temperatures employing the wet etchant range from 200.degree. C. to
400.degree. C. The embodiments are not limited in this context. In
some embodiments, the etch temperature may be between 250.degree.
C. and 350.degree. C.
[0025] Turning now to FIG. 1, there is shown a device arrangement
100, according to embodiments of the disclosure. The device
arrangement 100 may represent a memory device, including a memory
area 104 and processor region 106, formed in a substrate 102, such
as a silicon substrate. The device arrangement 100 shows a device
at a stage of fabrication where openings 110 have been etched into
the memory area 104. As such, formation of the openings 110 may
take place while the processor region 106 is covered with mask 108.
The mask 108 may be a carbon-based hardmask, such as a carbon-boron
mixture, to be used as a sacrificial mask, and may be patterned to
protect the processor region 106 while the openings 110 are being
etched. In the instance depicted in FIG. 1, ions 120 are directed
to the substrate 102 and impinge upon the mask 108. In accordance
with various embodiments the ions 120 implant into the mask 108,
where the ions 120 may represent etch-enhancing species, where such
species to enhance the etchability of the mask 108. In particular
embodiments, the ions 120 may be oxygen ions or hydrogen ions.
After implantation of the ions 120 is complete, the mask 108 may be
removed using a suitable etchant, including a wet etchant. By
tailoring the conditions of implantation of ions 120, the etching
of the mask 108 may be modified to allow selective removal of the
mask 108, at a target etch rate, while not damaging the memory area
104.
[0026] Turning now to FIG. 2, there is shown a process flow 200,
according to embodiments of the disclosure. At block 202, a
sacrificial mask is formed on a device structure, where the
sacrificial mask is a carbon-based material. In some examples, the
mask may be patterned on the device structure, wherein a plurality
of openings are formed on the device structure. In particular
embodiments, the plurality of openings may be formed to define
exposed regions of the device structure, corresponding to a memory
area. Examples of a carbon-based material suitable for the
sacrificial mask include a carbon-boron mixture. In some examples,
the carbon-boron mixture may have a relative carbon/boron
composition (molar ratio) in the range of 90% carbon/10% boron to
30% carbon/70% boron, while the density of the sacrificial mask may
be between 1.5-2.2 g/cm.sup.3. In some embodiments, the
carbon-boron material of the sacrificial mask may additionally
include hydrogen. As such, a carbon-boron-hydrogen material used as
the sacrificial mask may be in amorphous form according to some
embodiments. In some embodiments, the carbon-boron material of the
sacrificial mask may additionally include nitrogen. In various
embodiments, the sacrificial mask may be formed by a suitable
deposition process, such as chemical vapor deposition, plasma
enhanced chemical vapor deposition, physical vapor deposition, or
other deposition process. The embodiments are not limited in this
context. According to various embodiments, the thickness of the
sacrificial mask may range between 500 nm and 2000 nm. The
embodiments are not limited in this context.
[0027] At block 204, a plurality of memory structures are etched
into the exposed regions, defined by the openings of the
sacrificial mask. The memory structures may be formed by etching
holes such as vias or trenches, such as in known memory arrays
including NAND structures, such as VNAND. As such, regions of the
device structure covered by the sacrificial mask may be protected
from the etchant used to etch the memory structures.
[0028] At block 206, etch-enhancing species are implanted into the
sacrificial mask. Examples of suitable species for etch-enhancing
include hydrogen or oxygen ions. The implantation recipe of the
etch-enhancing species into the sacrificial mask may be tailored
according to the material and the thickness of the sacrificial
mask, as well as the etchant recipe to be used for etching the
sacrificial mask. Examples of parameters of the implantation recipe
include ion species, ion energy, ion dose, and number of
implantation procedures to be performed, among other factors.
[0029] At block 208, a wet etch is performed to selectively remove
the sacrificial mask, such as a sulfuric acid/hydrogen peroxide
etch. The etch temperature of the wet etch may be below 350.degree.
C., such as down to temperatures as low as 200.degree. C. in some
embodiments. The wet etch may be arranged to etch the sacrificial
mask at a target etch rate, such as 500 nm/min to 1000 nm/min. The
embodiments are not limited in this context. Advantageously, the
wet etch rate may be designed to etch the sacrificial mask at a
commercially useful etch rate, while not generating defects in the
exposed regions of the device structure, such as in a memory area
exposed to the wet etch during removal of the sacrificial mask
[0030] Turning now to FIG. 3, there is shown a process flow 300,
according to further embodiments of the disclosure. At block 302, a
sacrificial mask is formed on a device structure, where the
sacrificial mask is a carbon-based material, as detailed for block
202 above.
[0031] At block 304, a plurality of memory structures are etched
into the exposed regions, defined by the openings of the
sacrificial mask, as described for block 204 above.
[0032] At block 306, a first wet etch is performed to selectively
remove a first portion of the sacrificial mask, such as sulfuric
acid/hydrogen peroxide etch. The etch temperature of the first wet
etch may be at 350.degree. C. or below, such as down to
temperatures as low as 200.degree. C. in some embodiments. The wet
etch may be arranged to etch the first portion of the sacrificial
mask at a target etch rate, such as 500 nm/min to 1000 nm/min. The
embodiments are not limited in this context. The first portion of
the sacrificial mask may represent 40%-80% of the thickness of the
sacrificial mask in some embodiments. In one embodiment where the
sacrificial mask has an initial thickness of 1500 nm, the first
portion may represent a thickness of 700 nm to 1200 nm. The
remaining portion may represent a thickness of 300 nm to 800 nm.
The embodiments are not limited in this context.
[0033] At block 308, etch-enhancing species are implanted into the
second portion of the sacrificial mask. Examples of suitable
species for etch-enhancing include hydrogen or oxygen ions. The
implantation recipe of the etch-enhancing species into the
sacrificial mask may be tailored according to the material and the
thickness of the second portion of the sacrificial mask, as well as
the etchant recipe to be used for etching the sacrificial mask.
Examples of parameters of the implantation recipe include ion
species, ion energy, ion dose, and number of implantation
procedures to be performed, among other factors. For example,
because the second portion of the sacrificial mask is less than the
initial thickness, the ion energy, ion dose, or the two parameters
may be reduced in comparison to embodiments where etch-enhancing
species are implanted into a sacrificial mask having the initial
thickness. This approach may serve to lower implantation costs and
overall process cost.
[0034] At block 310, a second wet etch is performed to selectively
remove the second portion of the sacrificial mask, such as sulfuric
acid/hydrogen peroxide etch. The etch temperature of the wet etch
may be below 350.degree. C., such as down to temperatures as low as
200.degree. C. in some embodiments. The second wet etch may be
arranged to etch the sacrificial mask at a target etch rate, such
as 500 nm/min to 1000 nm/min. The embodiments are not limited in
this context. Advantageously, the first wet and second wet etch may
be designed to generate an overall etch rate to etch the
sacrificial mask at a commercially useful etch rate, while not
generating defects in the exposed regions of the device structure,
such as a memory area.
[0035] FIG. 4A presents a graph depicting hydrogen implant depth as
a function of ion energy for implantation into a carbon-boron layer
having a carbon/boron ratio of 40%/60% and a density of 2.1
g/cm.sup.3. As illustrated, as implant energy increases to 170 keV,
the range increases up to approximately 12000 A (1200 nm), while
the straggle (multiplied by 3) increases up to approximately 14500
A. Based upon this behavior a series of implantation procedures
were performed for increasing etch rate in a carbon-boron layer
using hydrogen ion implantation.
[0036] FIG. 4B presents a graph depicting hydrogen implant profiles
for four different implant ion energies for implantation into a
carbon-boron layer. The implant profiles all show a peak and a
distribution of hydrogen concentration as a function of depth,
where the peak increases in depth with increasing ion energy, as
shown also in FIG. 4A. FIG. 4C presents a graph depicting a
composite hydrogen implant profile based upon a sum of the implant
profiles of FIG. 4B. For the four different implant energies shown
(35 keV, 60 keV, 110 keV, and 170 keV), the composite implant
profile exhibits four distinct peaks in concentration. FIG. 4D
presents a graph depicting a composite hydrogen implant profile
based upon a sum of the three implant profiles of FIG. 4B. For the
three different implant energies shown (35 keV, 60 keV, and 110
keV), the composite implant profile exhibits three distinct peaks
in concentration. FIG. 4E presents a graph depicting a composite
hydrogen implant profile based upon a sum of the two implant
profiles of FIG. 4B. Likewise, for the two different implant
energies shown (35 keV, and 110 keV), the composite implant profile
exhibits two distinct peaks in concentration.
[0037] In one series of etch rate experiments, multiple
implantation procedures were performed where a dose of hydrogen
ions was implanted into a single 1.5 .mu.m thick carbon-boron layer
at energies of 65 keV, 80 keV, 110 keV, and 170 keV in separate
implants. Ion dose was 5 E14/cm.sup.2 for each implantation
procedure. Plasma etching was conducted after implantation to
remove a portion of the implanted layer. As compared to an
unimplanted layer, the etch rate increased by 44%.
[0038] In additional experiments, ion implantation was used to
enhance the wet etch rate of a carbon-boron layer. For the data
presented in FIGS. 5A-5D, 6, and 7, the etching of the carbon-boron
layers proceeded generally as follows: In various experiments,
after ion implantation, a boron carbon film of approximately 60%
boron, 40% carbon was etched using a solution of 50% (volume) 96%
(weight) sulfuric acid and 50% (volume) 30% (weight) hydrogen
peroxide. Volumetric flow rate was .about.60 ml/min and delivery
was in an aerosol form. In particular, a boron-carbon coated
silicon wafer was rotated while being heated using UV lamps, to an
approximate temperature in the range of 250.degree. C. to
300.degree. C. The time for the chemical delivery, while
accompanied by heat, was 150 seconds. This time is the time frame
of maximum etching, as no etching will occur in the absence of the
chemical etchant, and minimal etching will occur until the wafer
supporting the boron-carbon film and chemical have achieved a
temperature in excess of 200.degree. C.
[0039] In one series of procedures, a single implantation was
performed where hydrogen ions were implanted into a 1.5 .mu.m thick
40% carbon-60% boron layer at energies of 65 keV, 80 keV, 110 keV,
and 170 keV. Ion dose was varied between 3 E14/cm.sup.2 to
1E16/cm.sup.2. FIG. 5 shows the results of the effect of ion
implantation dose on wet etch rate, where wet etching was conducted
after implantation to remove approximately 700 nm-1000 nm of the
implanted layer. The data (and the data of FIGS. 5A-6) is based
upon SEM measurements and is plotted as etch rate enhancement (etch
rate increase with respect to an unimplanted layer) as a function
of ion dose on a semilog scale. As compared to an unimplanted
layer, the etch rate increased in the range of 10% to 50%. For ion
dose in the range of 2E14/cm.sup.2 to 5 E14/cm.sup.2 an etch rate
enhancement was observed of approximately 10% to 35%, with no clear
energy dependence of etch rate. For 80 keV ion implantation, ion
dose was varied between 1 E15/cm.sup.2 and 1E16/cm.sup.2, yielding
increases post-implantation etch rate of 35% up to 50%, the latter
result for 1E16/cm.sup.2 dose.
[0040] FIG. 6A, FIG. 6B, FIG. 6C, and FIG. 6D present the results
of wet etch rate enhancement (etch rate increase with respect to
unimplanted carbon-boron layers) as a function of ion energy for
different ion doses for a 40% carbon/60% boron layer. The key for
the experimental conditions used to produce the sample data for
these figures is shown in table I. In FIG. 6A for a given implant,
the ion dose is 5 E13/cm.sup.2, in FIG. 6B the ion dose is
1E14/cm.sup.2, in FIG. 6C the ion dose is 2E14/cm.sup.2, and in
FIG. 6D the ion dose is 5E14/cm.sup.2. In many of the samples,
multiple implants were performed, as listed in table I. The data in
FIGS. 6A-6D is plotted for the highest energy implant used to
implant a given sample. For example, sample A of FIG. 6A is
implanted twice at 5 E13/cm.sup.2 for a given implant, where one
implant energy is 30 keV, while the highest implant energy (for the
other implant) is 110 keV, for a total implant dose of 1
E14/cm.sup.2. In FIG. 6B, for sample A, three different implants
are performed, where a given implant introduces an ion dose of 1
E14/cm.sup.2 for a total ion dose of 3 E14/cm.sup.2, where the
highest implant energy is 110 keV. The sample B for FIG. 6B uses
the same implants as sample A, with an additional implant at 170
keV, for a total dose of 4 E14/cm.sup.2. In FIG. 6C, the samples
were implanted with just one implant, save for sample B, where
three different implants, at 2 E14/cm.sup.2 ion dose in a given
implant, were performed. The samples in FIG. 6D were implanted with
just one dose at 1 E14/cm.sup.2 for the given ion energies
shown.
[0041] While much of the data of FIGS. 6A-6C presents the results
of multiple implants, some general trends may be discerned. At
relatively lower single of total implant dose values, the etch rate
increases after ion implantation, with etch rate enhancement
generally increasing with increasing ion energy up to 170 keV.
Notably, as shown in FIG. 6D, at 5E14/cm.sup.2 ion dose, implanted
in just one implant, the etch rate enhancement with respect to
unimplanted samples decreases with increasing ion energy up to 170
keV. Accordingly, from the results of FIGS. 6A-6D, a combination of
implants at different ion energies may be useful to enhance the
etch rate of an implanted carbon-boron layer. The etch rate is
stated as a percentage change of the etch rate of the implanted
sample relative to an unimplanted sample.
TABLE-US-00001 TABLE I Key to sample conditions in FIGS. 6A-6D etch
rate enhancement energy dose (%) FIG. 6A samples A 30,110 each at
5e13 -3 B 30,65,110 each at 5e13 2 C 30,65,110,170 each at 5e13 14
FIG. 6B samples A 30,65,110 each at 1e14 5 B 30,65,110,170 each at
1e14 24 FIG. 6C samples A 65 each at 2e14 4 B 30,65,110 each at
2e14 8 C 110 each at 2e14 20 D 170 each at 2e14 13 FIG. 6D samples
A 65 5.00E+14 15 B 110 5.00E+14 10 C 170 5.00E+14 2
[0042] In another series of examples, multiple hydrogen
implantations were performed for a given carbon-boron layer sample,
where the ion energy was varied between implantations into the
given sample. The ion energy for a given implantation was 30 keV,
65 keV, 110 keV, or 170 keV. For example, a two-implantation
procedure involved implantation at 30 keV and 110 keV, a
three-implantation procedure involved implantation at 30 keV, 65
keV, and 110 keV, while a four-implantation procedure involved
implantation at 30 keV, 65 keV, and 110 keV, and 170 keV.
[0043] After the multiple implantations were performed into a given
carbon-boron sample, a wet etch was performed using a sulfuric
acid/hydrogen peroxide mixture as described above at 250.degree.
C.-300.degree. C. FIG. 7 is a graph presenting the etch rate of
multiply-implanted 40% carbon-60% boron samples as a function of
ion dose (on a semilog scale) for different procedures. The etch
rate is expressed as a relative increase in etch rate with respect
to an unimplanted carbon-boron sample. The x-axis plots ion dose
per implant procedure, where a given ion dose is repeatedly
implanted at different ion energies, described in the preceding
paragraph. Thus, total ion dose may be determined by multiplying
the value on the x-axis by the number of implants (energies) for a
given data point. As shown, the etch rate is substantially
increased in all implanted samples, while generally increasing with
ion dose up to the highest dose measured, 4 E14/cm.sup.2. As an
example, for a two-implantation procedure, at 4 e14/cm.sup.2 dose
(for each of two different procedures, meaning a total dose of 8 e
14/cm.sup.2), the relative etch rate is increased 45% with respect
to an unimplanted sample. In this particular example, one
implantation was performed at 30 keV and ion dose of 4e14/cm.sup.2
and another implantation was performed at 110 keV with ion dose
also at 4e14/cm.sup.2.
[0044] In summary, implantation of a sacrificial mask, such as a
carbon-boron mask, using an appropriate ion, may yield an increase
in etch rate of the sacrificial mask in the range of 30%-50% for
etchants including plasma etching, as well as wet etchants. As an
example, these results enable an effective sacrificial mask etch
rate in the range of 800 nm/min to 1000 nm/min for sulfuric
acid/hydrogen peroxide mixture at etch temperatures of 350.degree.
C. or less, wherein damage to exposed regions of a device, such as
memory areas, is prevented or reduced during removal of the
sacrificial mask.
[0045] FIG. 8 presents an exemplary process flow 800 according to
embodiments of the disclosure. At block 802, a sacrificial mask is
formed on a device structure, where the sacrificial mask is a
carbon-based material.
[0046] At block 804, etching of memory structures in exposed
regions of the sacrificial mask is performed.
[0047] At block 806, an etch-enhancing species is implanted into
the sacrificial mask, in a plurality of implantation procedures.
Examples of suitable species for etch-enhancing include hydrogen or
oxygen ions. The implantation recipe of the etch-enhancing species
into the sacrificial mask may be tailored according to the material
and the thickness of the sacrificial mask, as well as the etchant
recipe to be used for etching the sacrificial mask. Examples of
parameters of the implantation recipe include ion species, ion
energy, ion dose, and number of implantation procedures to be
performed, among other factors. For example, the ion energy may be
varied between different implantation procedures, to generate an
implant profile to optimize etch rate enhancement for removing the
sacrificial mask.
[0048] At block 808 a wet etch is performed to selectively remove
the sacrificial mask at an etch temperature, less than 350.degree.
C.
[0049] In sum, the present embodiments provide the advantages of
the ability to reduce damage to exposed regions of a device during
removal of a sacrificial mask, while providing the additional
advantage of achieving a target etch rate using commercially viable
processes, such as wet etching. Another advantage provided by the
present embodiments is the ability to substantially increase etch
rate of a sacrificial mask while maintaining ion dose at an
adequately low dose to achieving a low-cost implantation process
per substrate.
[0050] The present disclosure is not to be limited in scope by the
specific embodiments described herein. Indeed, other various
embodiments of and modifications to the present disclosure, in
addition to those described herein, will be apparent to those of
ordinary skill in the art from the foregoing description and
accompanying drawings. Thus, such other embodiments and
modifications are intended to fall within the scope of the present
disclosure. Furthermore, the present disclosure has been described
herein in the context of a particular implementation in a
particular environment for a particular purpose. Those of ordinary
skill in the art will recognize the usefulness is not limited
thereto and the present disclosure may be beneficially implemented
in any number of environments for any number of purposes. Thus, the
claims set forth below are to be construed in view of the full
breadth and spirit of the present disclosure as described
herein.
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