U.S. patent application number 13/902795 was filed with the patent office on 2014-11-27 for method for making a chemical contrast pattern using block copolymers and sequential infiltration synthesis.
The applicant listed for this patent is HGST Netherlands B.V.. Invention is credited to Yves-Andre Chapuis, Ricardo Ruiz, Lei Wan.
Application Number | 20140346142 13/902795 |
Document ID | / |
Family ID | 51934679 |
Filed Date | 2014-11-27 |
United States Patent
Application |
20140346142 |
Kind Code |
A1 |
Chapuis; Yves-Andre ; et
al. |
November 27, 2014 |
METHOD FOR MAKING A CHEMICAL CONTRAST PATTERN USING BLOCK
COPOLYMERS AND SEQUENTIAL INFILTRATION SYNTHESIS
Abstract
A method for making a chemical contrast pattern uses directed
self-assembly of block copolymers (BCPs) and sequential
infiltration synthesis (SIS) of an inorganic material. For an
example with poly(styrene-block-methyl methacrylate) (PS-b-PMMA) as
the BCP and alumina as the inorganic material, the PS and PMMA
self-assemble on a suitable substrate. The PMMA is removed and the
PS is oxidized. A surface modification polymer (SMP) is deposited
on the oxidized PS and the exposed substrate and the SMP not bound
to the substrate is removed. The structure is placed in an atomic
layer deposition chamber. Alumina precursors reactive with the
oxidized PS are introduced and infuse by SIS into the oxidized PS,
thereby forming on the substrate a chemical contrast pattern of SMP
and alumina. The resulting chemical contrast pattern can be used
for lithographic masks, for example to etch the underlying
substrate to make an imprint template.
Inventors: |
Chapuis; Yves-Andre; (San
Francisco, CA) ; Ruiz; Ricardo; (Santa Clara, CA)
; Wan; Lei; (San Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HGST Netherlands B.V. |
Amsterdam |
|
NL |
|
|
Family ID: |
51934679 |
Appl. No.: |
13/902795 |
Filed: |
May 25, 2013 |
Current U.S.
Class: |
216/51 ;
216/62 |
Current CPC
Class: |
G03F 7/0002 20130101;
C08J 7/02 20130101 |
Class at
Publication: |
216/51 ;
216/62 |
International
Class: |
C08J 7/02 20060101
C08J007/02 |
Claims
1. A method using a block copolymer (BCP) for making a chemical
contrast pattern on a substrate comprising: providing a substrate;
depositing on the substrate a sublayer for the BCP; patterning the
sublayer; forming on the patterned sublayer a BCP, the BCP material
being directed by the patterned sublayer to self-assemble into
first and second components of the BCP; removing the second
component and underlying sublayer to expose regions of the
underlying substrate, leaving the first component on the substrate;
depositing on the first component and the exposed substrate regions
a surface modification polymer having functional end groups;
removing portions of the surface modification polymer not bound to
the substrate; placing the substrate with the bound surface
modification polymer and first component in an atomic layer
deposition (ALD) chamber; introducing into the ALD chamber a first
precursor for an inorganic material, said first precursor being
non-reactive with the surface modification polymer and reactive
with the first component; and introducing into the ALD chamber a
second precursor for said inorganic material, said second precursor
being non-reactive with the surface modification polymer and
reactive with said first precursor to form said inorganic material
in the first component, thereby forming on the substrate a chemical
contrast pattern of surface modification polymer and inorganic
material.
2. The method of claim 1 wherein the BCP is a copolymer of
polystyrene (PS) as said first component and poly(methyl
methacrylate) (PMMA) as said second component.
3. The method of claim 2 wherein the PS and PMMA self-assemble as
lamellae perpendicular to the substrate.
4. The method of claim 2 wherein removing the second component
comprises removing the PMMA by reactive ion etching (RIE) in an
oxygen plasma, the oxygen plasma oxidizing the PS second
component.
5. The method of claim 1 wherein said inorganic material is
selected from an aluminum oxide, a titanium oxide, SiO.sub.2, ZnO,
and W.
6. The method of claim 1 wherein said first precursor is
trimethylaluminum (TMA), said second precursor is water vapor, and
said inorganic material is an aluminum oxide.
7. The method of claim 1 wherein the substrate comprises a silicon
oxide and wherein the functional end group of the surface
modification polymer is an OH group for binding to the silicon
oxide.
8. The method of claim 1 further comprising, after said inorganic
material is formed in said first component, continuing the
introduction of said first and second precursors while heating the
substrate to form a film of said inorganic material on said first
component.
9. The method of claim 1 further comprising: after said inorganic
material is formed in the first component, removing the surface
modification polymer bound to the substrate; etching the substrate,
using said inorganic material as an etch mask; and thereafter
removing said inorganic material and first component, leaving the
etched substrate.
10. The method of claim 1 further comprising: forming on said
chemical contrast pattern of surface modification polymer and
inorganic material additional BCP, the additional BCP being
directed by the chemical contrast pattern to self assemble with the
second component of the additional BCP on the inorganic material
and the first component of the additional BCP on the surface
modification polymer.
11. The method of claim 10 further comprising: after the additional
BCP components have self assembled, removing the BCP components and
surface modification polymer, leaving a pattern of inorganic
material on the substrate; and etching the substrate using the
inorganic material as an etch mask.
12. The method of claim 10 wherein the additional BCP has the same
components as the BCP formed on said patterned sublayer.
13. The method of claim 10 wherein the additional BCP has a natural
pitch that is an integer fraction of the natural pitch of the BCP
formed on said patterned sublayer.
14. A method using a block copolymer (BCP) for making a chemical
contrast pattern on a substrate comprising: providing a substrate;
forming on the substrate a block copolymer of polystyrene (PS) and
poly(methyl methacrylate) (PMMA) self-assembled into a pattern of
PS and PMMA; removing the PMMA to expose regions of the underlying
substrate, leaving the PS on the substrate; oxidizing the PS;
depositing on the PS and the exposed substrate regions a surface
modification polymer having functional end groups; removing
portions of the surface modification polymer not bound to the
substrate; placing the substrate with the bound surface
modification polymer and oxidized PS in an atomic layer deposition
(ALD) chamber; introducing into the ALD chamber a first precursor
for an inorganic material, said first precursor being non-reactive
with the surface modification polymer and reactive with the
oxidized PS; and introducing into the ALD chamber a second
precursor for said inorganic material, said second precursor being
non-reactive with the surface modification polymer and reactive
with said first precursor to form said inorganic material in the
oxidized PS, thereby forming on the substrate a chemical contrast
pattern of surface modification polymer and inorganic material.
15. The method of claim 14 wherein the PS and PMMA are
self-assembled as lamellae perpendicular to the substrate.
16. The method of claim 14 wherein the steps of removing the PMMA
to expose regions of the underlying substrate and oxidizing the PS
comprise reactive ion etching (RIE) in an oxygen plasma to
simultaneously remove the PMMA and oxidize the PS.
17. The method of claim 14 wherein said inorganic material is
selected from an aluminum oxide, a titanium oxide, SiO.sub.2, ZnO,
and W.
18. The method of claim 14 wherein said first precursor is
trimethylaluminum (TMA), said second precursor is water vapor, and
said inorganic material is an aluminum oxide.
19. The method of claim 14 wherein the substrate comprises a
silicon oxide and wherein the functional end group of the surface
modification polymer is an OH group for binding to the silicon
oxide.
20. The method of claim 14 further comprising, after said inorganic
material is formed in the PS, continuing the introduction of said
first and second precursors while heating the substrate to form a
film of said inorganic material on the PS.
21. The method of claim 14 further comprising: after said inorganic
material is formed in the PS, removing the surface modification
polymer bound to the substrate; etching the substrate, using said
inorganic material as an etch mask; and thereafter removing said
inorganic material and PS, leaving the etched substrate.
22. The method of claim 14 wherein the self-assembled pattern of PS
and PMMA on the substrate is a first layer and further comprising:
forming on said chemical contrast pattern of surface modification
polymer and inorganic material a second layer of additional PMMA
and PS, the additional PMMA and PS being directed by the chemical
contrast pattern to self assemble with the additional PMMA on the
inorganic material and the additional PS on the surface
modification polymer; removing the PS in the first layer and the
surface modification polymer and the PMMA and PS in the second
layer, leaving a pattern of inorganic material on the substrate;
and etching the substrate using the inorganic material as an etch
mask.
23. The method of claim 22 wherein the second layer of additional
PMMA and PS has a natural pitch that is an integer fraction of the
natural pitch of said first layer of PS and PMMA.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates generally to the use of block
copolymers (BCPs) to make a chemical contrast pattern, and more
particularly to the use of the chemical contrast pattern as an etch
mask for pattern transfer into a substrate.
[0003] 2. Description of the Related Art
[0004] Directed self-assembly (DSA) of block copolymers (BCPs) has
been proposed for making imprint templates. Imprint templates have
application in making patterned-media magnetic recording disks and
in semiconductor manufacturing, for example, for patterning
parallel generally straight lines in MPU, DRAM and NAND flash
devices. DSA of BCPs by use of a patterned sublayer for the BCP
film is well-known. After the BCP components self-assemble on the
patterned sublayer, one of the components is selectively removed,
leaving the other component with the desired pattern, which can be
used as an etch mask to transfer the pattern into an underlying
substrate. The etched substrate can be used as an imprint
template.
[0005] More recently a method termed "sequential infiltration
synthesis" (SIS) uses a BCP and atomic layer deposition (ALD) to
selectively grow nanometer scale patterns of inorganic material
inside BCP. In SIS, a BCP film is deposited onto a substrate and
annealed to form a self-assembled pattern of the two BCP
components. In one example, the BCP is poly(styrene-block-methyl
methacrylate) (PS-b-PMMA). A first precursor for the inorganic
material is introduced into the ALD and infiltrates the PMMA but
does not react with the PS. A second precursor for the inorganic
material is then introduced to finish the reaction, forming the
inorganic material, for example alumina (Al.sub.2O.sub.3), in the
locations in the PMMA where the first precursor attached. The PS
and PMMA are removed, leaving a pattern that generally replicates
the original pattern of PS and PMMA but that is now made of the
inorganic material synthesized by the ALD precursors. This pattern
of inorganic material can then be used as an etch mask to etch the
substrate.
[0006] While the conventional SIS method provides a way to use the
distinct chemistries of the constituent components of a BCP film to
grow materials by ALD on specific locations, the density of active
sites where the ALD precursor can bind is extremely low, especially
when using the method to achieve dimensions down to a few
nanometers. It has been found that after removal of all of the
polymer material (the PS and PMMA in the above example), the amount
of inorganic material (alumina in the above example) is not
sufficient to make a robust etch mask. This is because the
remaining features may be discontinuous or may have shifted as the
PS and PMMA is removed, thus degrading the image quality of the
original pattern.
[0007] What is needed is a method for making a chemical contrast
pattern with BCPs that uses SIS but that does not result in a
pattern with discontinuous or shifted features.
SUMMARY OF THE INVENTION
[0008] Embodiments of the invention relate to methods that use DSA
of BCPs and take advantage of SIS to make a chemical contrast
pattern. For the example with PS and PMMA as the BCP components, in
contrast to the conventional SIS method, embodiments of the
invention remove the PMMA prior to the ALD and makes the PS the
active material for the ALD. The inorganic material grown by ALD in
the active PS replicates the original pattern without major image
quality distortions.
[0009] In an example of the method that uses PS-b-PMMA as the BCP
and alumina as the inorganic material, the PS and PMMA
self-assemble on a patterned sublayer formed on a suitable
substrate. The PMMA is removed to expose regions of the underlying
substrate, leaving the PS on the substrate, after which the PS is
oxidized. A surface modification polymer (SMP) having functional
end groups is deposited on the oxidized PS and the exposed
substrate regions and the SMP not bound to the substrate is
removed. The substrate with the bound SMP and oxidized PS is then
placed in an atomic layer deposition (ALD) chamber and the alumina
precursors are introduced. The precursors are non-reactive with the
SMP but reactive with the oxidized PS, so that alumina is formed in
the oxidized PS, thereby forming on the substrate a chemical
contrast pattern of SMP and alumina. The resulting chemical
contrast pattern can be used for lithographic masks, for example to
etch the underlying substrate to make an imprint template.
[0010] The chemical contrast pattern can also be used as a pattern
for DSA of additional BCP that results in a more robust pattern for
pattern transfer into a substrate, as compared to the conventional
SIS method. For the example where alumina is the inorganic
material, the pattern of SMP and PS with alumina directs the
self-assembly of a second upper BCP film. If the second BCP is also
PS-b-PMMA, then the SMP bound to the substrate is preferentially
wet by the PS of the second BCP, whereas the alumina on the first
PS is preferentially wet by the second PMMA. In this case, the
second upper BCP components replicate the pattern of the original
underlying first BCP components, but with a "phase shift", i.e., in
those regions where originally there was PS, now there is a PMMA,
and vice versa. Upon annealing, the chemical contrast pattern of
the underlying SMP and PS with alumina directs the self assembly of
the additional upper PMMA and PS components into a periodic pattern
that replicates the underlying chemical contrast pattern. The
structure is then placed in an ALD and exposed to the alumina
precursors. The alumina now becomes infused into the second upper
PMMA. As a result there is an upper pattern of PMMA with infused
alumina directly above a lower pattern of PS with infused alumina.
The PS and PMMA are removed, for example by reactive ion etching
(RIE), condensing the infused alumina in the upper PMMA on top of
the previously infused alumina in the lower PS. The resulting
chemical contrast pattern can be used for lithographic masks, for
example to etch the underlying substrate to make an imprint
template.
[0011] For a fuller understanding of the nature and advantages of
the present invention, reference should be made to the following
detailed description taken together with the accompanying
figures.
BRIEF DESCRIPTION OF THE DRAWING
[0012] FIGS. 1A-1D are view illustrating the prior art method for
making an imprint template using directed self-assembly (DSA) of
block copolymers (BCPs).
[0013] FIGS. 2A-2F are side sectional views illustrating the prior
art sequential infiltration synthesis (SIS) method using atomic
layer deposition (ALD) and a BCP film.
[0014] FIGS. 3A-3E are side sectional views illustrating
embodiments of the invention to make a chemical contrast pattern
using BCPs and SIS.
[0015] FIGS. 4A-4C are side sectional views illustrating use of the
chemical contrast pattern made according to embodiments of the
invention as an etch mask for pattern transfer into a
substrate.
[0016] FIGS. 5A-5E are side sectional views illustrating use of the
chemical contrast pattern made according to embodiments of the
invention as a pattern for DSA of an additional BCP to create a
more robust pattern as an etch mask for pattern transfer into a
substrate.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Self-assembling block copolymers (BCPs) have been proposed
for creating periodic nanometer (nm) scale features.
Self-assembling BCPs typically contain two or more different
polymeric block components, for example components A and B, that
are immiscible with one another. Under suitable conditions, the two
or more immiscible polymeric block components separate into two or
more different phases or microdomains on a nanometer scale and
thereby form ordered patterns of isolated nano-sized structural
units. There are many types of BCPs that can be used for forming
the self-assembled periodic patterns. If one of the components A or
B is selectively removable without having to remove the other, then
an orderly arranged structural units of the un-removed component
can be formed.
[0018] Specific examples of suitable BCPs that can be used for
forming the self-assembled periodic patterns include, but are not
limited to: poly(styrene-block-methyl methacrylate) (PS-b-PMMA),
poly(ethylene oxide-block-isoprene) (PEO-b-PI), poly(ethylene
oxide-block-butadiene) (PEO-b-PBD), poly(ethylene
oxide-block-styrene) (PEO-b-PS), poly(ethylene
oxide-block-methylmethacrylate) (PEO-b-PMMA),
poly(ethyleneoxide-block-ethylethylene) (PEO-b-PEE),
poly(styrene-block-vinylpyridine) (PS-b-PVP),
poly(styrene-block-isoprene) (PS-b-PI),
poly(styrene-block-butadiene) (PS-b-PBD),
poly(styrene-block-ferrocenyldimethylsilane) (PS-b-PFS),
poly(butadiene-block-vinylpyridine) (PBD-b-PVP),
poly(isoprene-block-methyl methacrylate) (PI-b-PMMA),
poly(styrene-block-lactic acid) (PS-b-PLA) and
poly(styrene-block-dymethylsiloxane) (PS-b-PDMS).
[0019] The specific self-assembled periodic patterns formed by the
BCP are determined by the molecular volume ratio between the first
and second polymeric block components A and B. When the ratio of
the molecular volume of the second polymeric block component B over
the molecular volume of the first polymeric block component A is
less than about 80:20 but greater than about 60:40, the BCP will
form an ordered array of cylinders composed of the first polymeric
block component A in a matrix composed of the second polymeric
block component B. When the ratio of the molecular volume of the
first polymeric block component A over the molecular volume of the
second polymeric block component B is less than about 60:40 but is
greater than about 40:60, the BCP will form alternating lamellae
composed of the first and second polymeric block components A and
B. The un-removed component is used as an etch mask to etch the
underlying template substrate. When the ratio of B over A is
greater than about 80:20 the BCP will form an ordered array of
spheres in a matrix of the second component. For lamellar or
cylinder forming BCPs, the orientation of the lamellae or the
cylinders with respect to the substrate depends on the interfacial
energies (wetting properties) of the block copolymer components at
both the substrate interface and at the top interface. When one of
the block components preferentially wets the substrate (or the top
free interface) the block copolymers form layers parallel to the
substrate. When the wetting properties at the interface are neutral
to either block, then both block components can be in contact with
the interface, facilitating the formation of block copolymer
domains with perpendicular orientation. In practice, the wetting
properties of the substrate are engineered by coating the substrate
with "surface modification layers" that tune the wetting properties
at the interface. Surface modification layers are usually made of
polymer brushes or mats typically (but not necessarily) composed of
a mixture of the constituent block materials of the BCP to be
used.
[0020] The periodicity or natural pitch (L.sub.0) of the repeating
structural units in the periodic pattern is determined by intrinsic
polymeric properties such as the degree of polymerization N and the
Flory-Huggins interaction parameter .chi.. L.sub.0 scales with the
degree of polymerization N, which in turn correlates with the
molecular weight M. Therefore, by adjusting the total molecular
weight of the BCP, the natural pitch (L.sub.0) of the repeating
structural units can be selected.
[0021] To form the self-assembled periodic patterns, the BCP is
first dissolved in a suitable solvent system to form a BCP
solution, which is then applied onto a surface to form a thin BCP
layer, followed by annealing of the thin BCP layer, which causes
phase separation between the different polymeric block components
contained in the BCP. The solvent system used for dissolving the
BCP and forming the BCP solution may comprise any suitable
non-polar solvent, including, but not limited to: toluene,
propylene glycol monomethyl ether acetate (PGMEA), propylene glycol
monomethyl ether (PGME), and acetone. The BCP solution can be
applied to the substrate surface by any suitable techniques,
including, but not limited to: spin casting, coating, spraying, ink
coating, dip coating, etc. Preferably, the BCP solution is spin
cast onto the substrate surface to form a thin BCP layer. After
application of the thin BCP layer onto the substrate surface, the
entire substrate is annealed to effectuate microphase segregation
of the different block components contained by the BCP, thereby
forming the periodic patterns with repeating structural units.
[0022] The BCP films in the above-described techniques
self-assemble without any direction or guidance. This undirected
self-assembly results in patterns with defects so it is not
practical for applications that require long-range ordering, such
as for making imprint templates. However, directed self-assembly
(DSA) of block copolymers (BCPs) has been proposed for making
imprint templates. DSA of BCPs by use of a patterned sublayer for
the BCP film is well-known, as described for example in U.S. Pat.
No. 7,976,715; U.S. Pat. No. 8,059,350; and U.S. Pat. No.
8,119,017. Pending application Ser. No. 13/627,492, filed Sep. 26,
2012 and assigned to the same assignee as this application,
describes the use DSA of BCPs to make two submaster imprint
templates, one with a pattern of generally radial lines, and the
other with generally concentric rings, to make a master imprint
template, which is then used to imprint patterned-media magnetic
recording disks. Imprint templates made with DSA of BCPs have also
been proposed for use in semiconductor manufacturing, for example,
for patterning parallel generally straight lines in MPU, DRAM and
NAND flash devices.
[0023] The prior art method for making an imprint template using
DSA of BCPs will be described in general terms with FIGS. 1A-1D for
an example where the template 50 will become an imprint template
with protrusions 51 in a pattern of parallel bars. FIG. 1A is a
side sectional view showing a patterned sublayer 105 on the surface
of template 50. Alternating A component (polystyrene--PS) parallel
lines 112 and B component (PMMA) parallel lines 115 are formed on a
sublayer 105 and regions 106. The regions 106 can be exposed
portions of the template 50 not covered by sublayer 105 or regions
covered by a different sublayer. The sublayer 105 has been
patterned to direct the self-assembly of the BCP A and B components
with a natural pitch of L.sub.0. In FIG. 1B, the portions of
parallel lines 115, the B component (PMMA), are then selectively
removed by a wet etch or a dry etch process. This leaves generally
parallel lines 112 of the A component (PS) on the template 50.
Then, a dry etch process is used to etch the template 50 to form
recesses 52 using the parallel lines 112 as the etch mask. The
material of parallel lines 112 and the remaining underlying
sublayer 105 is then removed, leaving recesses 52 in template 50.
This leaves the structure as shown in FIG. 1C, with a pattern of
protrusions formed as parallel bars 51 and recesses formed as
parallel bars 52. FIG. 1D is a side sectional view of the resulting
imprint template.
[0024] More recently a method termed "sequential infiltration
synthesis" (SIS) uses BCP films and atomic layer deposition (ALD)
to selectively grow nanometer scale patterns of inorganic material
inside BCP films. (See Peng et al., "A Route to Nanoscopic
Materials via Sequential Infiltration Synthesis on Block Copolymer
Templates", ACS Nano, VOL. 5, NO. 6, 4600-4606, 2011). This process
is depicted in FIGS. 2A-2F. In SIS, a BCP film is deposited onto a
substrate and annealed to form a self-assembled pattern, for
example PS and PMMA (FIG. 1A). The sample is then placed in an ALD
chamber, such as those available from Cambridge Nanotech Inc. of
Cambridge, Mass. ALD is known as a process for forming very thin
films on a substrate. ALD involves deposition of gas phase
precursor molecules. Most ALD processes are based on binary
reaction sequences where two surface reactions occur and deposit a
binary compound film, such as the use of trimethylaluminum (TMA)
and H.sub.2O to form alumina (Al.sub.2O.sub.3). An overview of ALD
is presented by George, "Atomic Layer Deposition: An Overview",
Chemical Review, 2010, Vol. 110, No. 1, 111-131. In SIS, the BCP
has been chosen so that one component, for example PS, is inert to
the ALD precursors while the other component, PMMA, reacts with the
precursor. A first precursor, for example TMA, is introduced into
the ALD chamber (FIG. 2B). PMMA contains carbonyl groups that react
with the TMA, causing the TMA to infiltrate the PMMA. The
controlled interaction of TMA with carbonyl groups in the PMMA
generates Al--CH.sub.3/Al--OH sites inside the PMMA. A second
precursor, for example water vapor, is then introduced to finish
the reaction, forming alumina in the locations in the PMMA where
the TMA attached (FIG. 2C). The processes may be repeated a number
of cycles to increase the amount of infiltrated alumina. For
lithographic applications, the PS component, which is inert to the
ALD precursors, and the PMMA material is then removed by oxygen
plasma to leave a pattern that mimics the original pattern of PS
and PMMA but that is now made of the alumina synthesized by the ALD
precursors (FIG. 2D). This pattern of alumina can then be used as
an etch mask to reactively ion etch (RIE) the substrate (FIG. 2E),
after which the alumina is removed, leaving the etched substrate
(FIG. 2F).
[0025] While the conventional SIS method provides a way to use the
distinct chemistries of the constituent components of a BCP film to
grow materials by ALD on specific locations, the density of active
sites where the ALD precursor can bind is extremely low, especially
when using the method to achieve dimensions down to a few
nanometers. It has been found that after removal of all of the
polymer material (the PS and PMMA in the above example), the amount
of inorganic material (alumina in the above example) is not
sufficient to make a robust etch mask. This is because the
remaining features may be discontinuous or may have shifted as the
PS and PMMA is removed, thus degrading the image quality of the
original pattern. This is described by R. Ruiz, et al., Journal of
Vacuum Science & Technology B: Microelectronics and Nanometer
Structures, 2012, 30, (6).
[0026] Embodiments of the invention use DSA of BCPs and take
advantage of SIS to make a chemical contrast pattern. For the
example with PS and PMMA as the BCP components, in contrast to the
conventional SIS method, an embodiment of the invention removes the
PMMA prior to the ALD and makes the PS the active material for the
ALD. The inorganic material grown by ALD in the active PS
replicates the original pattern without major image quality
distortions. The resulting chemical contrast pattern can be used
for lithographic masks, for example to etch the underlying
substrate to make an imprint template, or as a chemical contrast
pattern to guide the growth of other materials, such as in DSA.
[0027] An embodiment of the invention is illustrated in FIGS.
3A-3E. FIG. 3A is a cross-sectional view of a BCP film that has
been directed to self-assemble into PMMA and PS by a patterned
sublayer on a suitable substrate, in this example a silicon (Si)
substrate that may have a silicon oxide surface. The substrate may
be formed of any suitable material, such as, but not limited to,
single-crystal Si, amorphous Si, silica, fused quartz, silicon
nitride, carbon, tantalum, molybdenum, chromium, alumina and
sapphire. The sublayer may be a nearly neutral layer of a material
that does not show a strong wetting affinity by one of the polymer
blocks over the other. The neutral layer can be, but is not
restricted to, a functionalized polymer brush like
carboxyl-terminated or hydroxyl-terminated brush, a cross-linkable
polymer, a functionalized polymer "A" or "B" or a functionalized
random copolymer "A-r-B". The functional group may be, for example,
a hydroxyl (OH) group. In the present example, the substrate has a
silicon oxide surface film and the neutral layer is a
hydroxyl-terminated poly(styrene-r-methyl methacrylate) brush
containing .about.67% styrene. Alternatively, the sublayer may be a
material known as a polymer "mat" layer that shows strong wetting
affinity by one of the polymer blocks over the other. The material
of mat layer can be, but is not limited to, a cross-linkable
polymer "A" or "B" like a crosslinkable polystyrene (XPS mat). The
sublayer material may be spin-coated on the substrate to a
thickness of about 1-10 nm. The sublayer is annealed for the
end-groups to graft to the oxidized substrate surface in the case
of an end-functionalized material or for the cross linking units to
carry the cross-linking in the case of polymer "mats". After
annealing, any ungrafted sublayer material is rinsed away in a
suitable solvent (toluene, PGMA, NMP, etc). The purpose of the
sublayer is to tune the surface energy adequately to promote the
desired domain orientation (for example, perpendicular lamellae of
the BCP components).
[0028] For DSA, additional steps are required to create a chemical
pattern in the sublayer. These steps may include e-beam
lithography, photolithography or nanoimprint lithography and
potentially a combination of polymer mats and brushes. For example,
a resist layer can be patterned by e-beam, followed by deposition
of the sublayer material and removal of the resist. Alternatively,
the chemical structure of exposed portions of a neutral sublayer
can be chemically damaged or altered (by oxygen plasma etching or
other process such as RIE, neutral atom (such as Ar) or molecule
milling, ion bombardment and photodegradation) so that the exposed
portions of the neutral sublayer have a preferred affinity (or
repulsion) for one of the BCP components.
[0029] The resulting pattern of the sublayer directs the BCP
components to self-assemble according to the pattern. The BCP is
chosen to form either lamellae, cylinders or spheres with a
characteristic center-to-center distance or "natural pitch" L.sub.0
in the range of 5-50 nm. FIG. 3A shows an example of
lamellae-forming poly(styrene-block-methyl methacrylate)
(PS-b-PMMA) BCP for which the OH-terminated brush neutral layer was
chosen as the sublayer to promote perpendicular orientation of the
lamellar domains.
[0030] In FIG. 3B one of the two BCP components is selectively
removed, for example by reactive ion etching (RIE), wet etching, or
ion milling. In the example of FIG. 3B, the PMMA and the underlying
sublayer regions have been removed by oxygen plasma RIE. The
remaining component, in this example the PS, needs to be chemically
active to react with the ALD precursors. The remaining component
material may naturally contain active groups, such as carbonyl or
hydroxyl groups, or it's chemistry may be altered, for example by
an oxygen plasma and/or UV radiation, to render the material active
for reaction with the ALD precursors. In the example of FIG. 3B,
the PMMA component is removed by RIE with an oxygen plasma. The
oxygen plasma also simultaneously oxidizes the remaining PS,
creating active groups, including carbonyl groups, that can react
with the ALD precursors. An additional UV curing step may be
applied to further harden the remaining PS material.
[0031] Next, in FIG. 3C, a layer of a surface modification polymer
(SMP) with functionalized groups is applied onto the substrate with
the PS and annealed. The SMP is chosen from a material that is
generally inert to the ALD precursors. The functionalized groups of
the SMP are chosen to chemically bind with the exposed portions of
the substrate, but not with the remaining BCP component. In the
example of FIG. 3C, where the substrate is a Si substrate with a
native SiO.sub.x surface, the SMP is a PS--OH brush for which the
OH functional groups bind to the SiO.sub.x surface after thermal
annealing. After annealing, the excess brush material that is not
bound to the substrate can be rinsed away. The resulting pattern
consists of features that are chemically prone to react with the
ALD precursors (in this example, the PS modified by the oxygen
plasma) and features that are chemically inert to the ALD
precursors (the SMP bound to the substrate).
[0032] In FIG. 3D the structure of FIG. 3C is placed in an ALD
chamber and exposed to chemical precursors that react only with one
material in the pattern (in this example the oxidized PS). For
example, if the chemical precursors are a sequence of trimethyl
aluminum, TMA and water, the TMA will react with the carbonyl
groups in the oxidized PS and become infused into the PS material.
The second water precursor reacts with the TMA to form an aluminum
oxide (AlO.sub.x), which is predominately alumina, in the PS. The
ALD process can be repeated a number of cycles to form the desired
amount of alumina film in the PS. It is possible to first run the
ALD tool in "static mode", also called as "sequential infiltration
synthesis" (SIS), depicted in FIG. 3D, to infuse the TMA inside the
oxidized PS, and then switch to conventional thermal ALD, wherein
the substrate is heated, to increase the growth rate and to grow
alumina films on top of the targeted PS, as depicted in FIG. 3E.
The resulting chemical contrast pattern in FIGS. 3D and 3E mimics
the original PS/PMMA pattern (FIG. 3A) with higher fidelity and
higher continuity than the conventional SIS method. In conventional
SIS, the features of alumina infiltrated in the PMMA (FIG. 1D) can
be discontinuous after the removal of the PS/PMMA polymer matrix.
In FIG. 3D, the thickness of the PS has been reduced during the
oxygen plasma RIE that oxidizes the PS, as shown by the reduced
height of the PS from FIG. 3A to FIG. 3B. This places the alumina
closer to the substrate than conventional SIS, making it less prone
to mechanical deformations when the PMMA is removed. In the
conventional SIS method, because the alumina is infiltrated over
the entire thickness of the PMMA in a rather low density matrix,
the alumina is prone to deformation upon removal of the PMMA and
PS. The aspect ratio (thickness to width) of the PMMA with infused
alumina in conventional SIS is fairly large, around 2:1, whereas
the aspect ratio for the PS with infused alumina may be less than
1.
[0033] The chemical contrast pattern depicted in FIG. 3D or 3E can
be used as an etch mask for pattern transfer. FIGS. 4A-4C
illustrate the additional steps. In FIG. 4A, the SMP bound to the
substrate (shown in FIGS. 3D and 3E), i.e., the PS--OH brush layer
material in the regions between the PS with alumina that did not
react with the ALD precursors, is selectively removed by RIE in an
oxygen plasma. In FIG. 4B, a second RIE can be used to etch into
the substrate, using the PS with alumina as an etch mask. In the
example with a Si substrate and alumina on the PS, a fluorine etch
can be used to etch features into the Si substrate. In FIG. 4C, the
remaining alumina and underlying PS material can be removed by RIE
or a wet etch. Alternatively, the substrate could have suitable
transfer layers, like a hard mask, between the substrate and the PS
with alumina, to aid in transferring the chemical contrast pattern
into the substrate. The resulting substrate with the etched pattern
can be used as an imprint template.
[0034] The chemical contrast pattern can be also used as a pattern
for DSA of the same BCP that results in a more robust pattern for
pattern transfer into a substrate, as compared to the conventional
SIS method. The process is shown in FIGS. 5A-5E. This process
starts from the chemical contrast pattern depicted either in FIG.
3D or 3E. The pattern of SMP and PS with alumina direct the
self-assembly of a second BCP film. In FIG. 5A a thin film of a
second BCP is spin coated on top of the chemical contrast pattern
of the SMP and PS with alumina. The second BCP can have the same or
different components as the first BCP, but should have the same
natural pitch (L.sub.0) as the first BCP (like the example of FIG.
5A) or a natural pitch that is an integer fraction, for example
1/2, the natural pitch of the first BCP. In the example shown in
FIG. 5A, the PS--OH brush (the SMP) bound to the substrate is
preferentially wet by the PS of the second additional PS-b-PMMA
BCP, whereas the alumina on the PS is preferentially wet by the
additional PMMA. This is because PMMA, being a more polar molecule,
preferentially wets the oxide interface, while PS preferentially
wets the PS in the SMP. In this case, the second BCP components
replicate the pattern of the original underlying BCP components,
but with a "phase shift". In those regions where originally there
was PS, now there is a PMMA, and vice versa. Upon annealing, the
chemical contrast pattern of the underlying SMP and PS with alumina
directs the self assembly of the additional PMMA and PS components
into a periodic pattern that replicates the underlying chemical
contrast pattern. In FIG. 5B, the structure is now exposed to ALD
precursors for SIS. The TMA precursor selectively attaches to the
carbonyl groups in the PMMA and is infused in the PMMA. A second
precursor, for example water vapor, is introduced which completes
the reaction, converting the TMA into alumina in the PMMA. The ALD
cycle can be repeated a number of times to increase the amount of
infused alumina. As a result there is an upper pattern of PMMA with
infused alumina directly above a lower pattern of PS with infused
alumina. In FIG. 5C the PS and PMMA is removed with RIE, condensing
the infused alumina in the upper PMMA on top of the previously
infused alumina in the lower PS. In conventional SIS it is common
that the alumina features (or other inorganic features) remaining
after RIE are not continuous, resulting in broken features or
broken lines. The structure of FIG. 5C has an important advantage
over conventional SIS in that the second or upper alumina is
deposited on top of the previously infused lower alumina. Thus even
if the upper film of alumina is broken in certain sections, the
lower alumina adds additional material to prevent a broken feature.
In FIG. 5D, a second RIE can be used to etch into the substrate,
using the alumina film as an etch mask. In the example with a Si
substrate and alumina film as the inorganic material, a fluorine
etch can be used to etch features into the Si substrate. In FIG.
5E, the remaining alumina and underlying sublayer material can be
removed by RIE or a wet etch. Alternatively, the substrate could
have suitable transfer layers, like a hard mask, between the
substrate and the alumina film, to aid in transferring the chemical
contrast pattern into the substrate. The resulting substrate with
the etched pattern can be used as an imprint template.
[0035] In the example of FIGS. 5A-5E, the second BCP has the same
natural pitch (L.sub.0) as the first BCP. However, density
multiplication of the pattern can be achieved by use of a second
BCP that has a natural pitch that is an integer fraction, for
example 1/2, the natural pitch of the first BCP. In such an
embodiment to double the density, the PS in the lower layer would
have a width one-half that shown in FIG. 5A. This would be achieved
by continuing the O.sub.2 RIE shown in FIG. 3B to remove additional
PS material until the width of the PS features is reduced by
one-half. With this pattern of reduced-width PS and SMP as the
lower layer in FIG. 5A, the second BCP components would be directed
to self-assemble with one PMMA feature on each reduced-width PS
feature. This would cause alternating PS/PMMA/PS features to
self-assemble on each lower SMP feature. The resulting chemical
contrast pattern would look like that of FIG. 5C, but with double
the density of AlOx features.
[0036] The ALD precursors are selected to infiltrate the inorganic
material into one of the BCP components and to be non-reactive with
the other BCP component. In the examples above the inorganic
material is alumina and the precursors are TMA, which is reactive
with the carbonyl groups in PMMA and non-reactive with PS, and
water vapor. However, other inorganic materials with suitable
precursors may be formed by ALD. For example, if the inorganic
material is to be a titanium oxide (TiOx), the precursors may be
tetrakis(dimethylamido)titanium (TDMAT) and water vapor.
Alternatively, other titanium containing precursors could be used
in conjunction with water, such as titanium tetrachloride
(TiCl.sub.4) and titanium butoxide (Ti(OBu).sub.4). If the
inorganic material is to be ZnO then the precursors may be diethyl
zinc and water. If the inorganic material is to be SiO.sub.2 then
the precursors may be tris(tert-pentoxy)silanol and water. If the
inorganic material is to be tungsten (W), then the precursors may
be tungsten hexafluoride and disilane. In some of these examples,
if the first precursor for the desired inorganic material does not
readily react with the BCP component, a first TMA/H.sub.2O cycle
may be used to grow a first film of alumina and then the alumina
film is used to grow the film of the desired inorganic material in
subsequent cycles.
[0037] While the present invention has been particularly shown and
described with reference to the preferred embodiments, it will be
understood by those skilled in the art that various changes in form
and detail may be made without departing from the spirit and scope
of the invention. Accordingly, the disclosed invention is to be
considered merely as illustrative and limited in scope only as
specified in the appended claims.
* * * * *