U.S. patent application number 14/605276 was filed with the patent office on 2015-05-21 for polymeric materials in self-assembled arrays and semiconductor structures and methods comprising such polymeric materials.
The applicant listed for this patent is MICRON TECHNOLOGY, INC.. Invention is credited to Dan B. Millward, Donald L. Westmoreland.
Application Number | 20150137331 14/605276 |
Document ID | / |
Family ID | 41255682 |
Filed Date | 2015-05-21 |
United States Patent
Application |
20150137331 |
Kind Code |
A1 |
Millward; Dan B. ; et
al. |
May 21, 2015 |
POLYMERIC MATERIALS IN SELF-ASSEMBLED ARRAYS AND SEMICONDUCTOR
STRUCTURES AND METHODS COMPRISING SUCH POLYMERIC MATERIALS
Abstract
Methods for fabricating sublithographic, nanoscale
microstructures in line arrays utilizing self-assembling block
copolymers, and films and devices formed from these methods are
provided. Semiconductor structures may include self-assembled block
copolymer materials in the form of lines of half-cylinders of a
minority block matrix of a majority block of the block copolymer.
The lines of half-cylinders may be within trenches in the
semiconductor structures.
Inventors: |
Millward; Dan B.; (Boise,
ID) ; Westmoreland; Donald L.; (Boise, ID) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MICRON TECHNOLOGY, INC. |
Boise |
ID |
US |
|
|
Family ID: |
41255682 |
Appl. No.: |
14/605276 |
Filed: |
January 26, 2015 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13928746 |
Jun 27, 2013 |
8993088 |
|
|
14605276 |
|
|
|
|
13396039 |
Feb 14, 2012 |
8518275 |
|
|
13928746 |
|
|
|
|
12114173 |
May 2, 2008 |
8114301 |
|
|
13396039 |
|
|
|
|
Current U.S.
Class: |
257/622 ;
428/173; 438/763 |
Current CPC
Class: |
H01L 29/0657 20130101;
Y10S 438/947 20130101; Y10T 428/249921 20150401; B82Y 30/00
20130101; H01L 21/02118 20130101; B81C 1/00031 20130101; Y10T
428/24521 20150115; B81C 2201/0149 20130101; H01L 29/06 20130101;
H01L 21/0223 20130101; Y10S 977/895 20130101; Y10S 977/888
20130101; Y10S 977/90 20130101; B81C 2201/0198 20130101; Y10T
428/2462 20150115; Y10T 428/24182 20150115; G03F 7/0002
20130101 |
Class at
Publication: |
257/622 ;
428/173; 438/763 |
International
Class: |
H01L 29/06 20060101
H01L029/06; H01L 21/02 20060101 H01L021/02 |
Claims
1. A semiconductor structure, comprising: a material over a
substrate, the material defining a first trench and a second trench
therein, the first trench having a width of at least two times a
width of the second trench; a neutral wetting material on a floor
of each of the first trench and the second trench; and at least one
line of half-cylinders of polymeric material within each of the
first trench and the second trench.
2. The semiconductor structure of claim 1, wherein the at least one
line of half-cylinders of polymeric material within each of the
first trench and the second trench is disposed over the neutral
wetting material.
3. The semiconductor structure of claim 1, wherein the at least one
line of half-cylinders of polymeric material within each of the
first trench and the second trench comprises at least two parallel
lines of half-cylinders of polymeric material within the first
trench.
4. The semiconductor of structure claim 1, wherein the at least one
line of half-cylinders of polymeric material within each of the
first trench and the second trench comprises a single line of
half-cylinders of polymeric material within the second trench.
5. The semiconductor structure of claim 1, wherein the at least one
line of half-cylinders of polymeric material within each of the
first trench and the second trench comprises a block copolymer
material comprising a major domain and a minor domain.
6. The semiconductor structure of claim 5, wherein the at least one
line of half cylinders of polymeric material within each of the
first trench and the second trench further comprises an inorganic
component.
7. The semiconductor structure of claim 1, further comprising a
matrix of another polymeric material at least partially surrounding
the at least one line of half-cylinders of polymeric material
within each of the first trench and the second trench.
8. The semiconductor structure of claim 1, further comprising a
portion of the polymeric material over the material defining the
first trench and the second trench.
9. The semiconductor structure of claim 1, wherein the at least one
line of half-cylinders of polymeric material within each of the
first trench and the second trench comprises at least one
crosslinked polymer domain.
10. A polymeric material, comprising: at least one self-assembled
line of half-cylinders of polymeric material over a neutral wetting
material on a floor of each of a first trench and a second trench
over a substrate, the first trench having a width of at least two
times a width of the second trench.
11. The polymeric material of claim 10, further comprising another
polymeric material in contact with the half-cylinders of polymeric
material, wherein the another polymeric material comprises a
majority block of a block copolymer, and wherein the half-cylinders
of polymeric material comprise a minority block of the block
copolymer.
12. The polymeric material of claim 11, wherein the block copolymer
comprises a material selected from the group consisting of
poly(styrene)-b-poly(vinylpyridine) (PS-b-PVP),
poly(styrene)-b-poly(methylmethacrylate) (PS-b-PMMA),
poly(styrene)-b-poly(lactide) (PS-b-PLA),
poly(styrene)-b-poly(tert-butyl acrylate) (PS-b-PtBA),
poly(styrene)-b-poly(ethylene-co-butylene) (PS-b-(PE-co-PB)),
poly(styrene)-b-poly(ethylene oxide) (PS-b-PEO),
polybutadiene-b-poly(vinylpyridine) (PB-b-PVP), and
poly(ethylene-alt-propylene)-b-poly(vinylpyridine) (PEP-b-PVP).
13. The polymeric material of claim 10, wherein the at least one
self-assembled line of half-cylinders is oriented parallel to the
floor of the first trench or the second trench, and wherein the at
least one self-assembled line of half-cylinders extends along a
length of the first trench or the second trench, the half-cylinders
having a face oriented toward and wetting the floor of the first
trench or the second trench.
14. The polymeric material of claim 10, wherein the at least one
self-assembled line of half-cylinders of polymeric material
comprises at least two self-assembled lines of half-cylinders of
polymeric material within the first trench.
15. The polymeric material of claim 10, wherein the at least one
self-assembled line of half-cylinders of polymeric material
comprises a metal.
16. The polymeric material of claim 15, wherein the metal comprises
at least one material selected from the group consisting of a metal
salt, a metal oxide gel, a metal alkoxide polymer, a metal oxide
precursor, a metal nitride precursor, and metal fine particles.
17. A method of forming a semiconductor structure, comprising:
forming a material over a substrate, the material defining a first
trench and a second trench therein, the first trench having a width
of at least two times a width of the second trench; forming a
neutral wetting material on a floor of each of the first trench and
the second trench; and forming at least one line of half-cylinders
of polymeric material within each of the first trench and the
second trench.
18. The method of claim 17, wherein forming at least one line of
half-cylinders of polymeric material within each of the first
trench and the second trench comprises forming at least two lines
of half-cylinder of polymeric material within the first trench.
19. The method of claim 17, wherein forming at least one line of
half-cylinders of polymeric material within each of the first
trench and the second trench comprises forming a block copolymer
material comprising a major domain and a minor domain within each
of the first trench and the second trench.
20. The method of claim 17, wherein forming at least one line of
half-cylinders of polymeric material within each of the first
trench and the second trench comprises forming an inorganic species
within at least one of the first trench and the second trench, and
further comprising oxidizing at least a portion of the polymeric
material to convert the inorganic species to a non-volatile
inorganic oxide.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 13/928,746, filed Jun. 27, 2013, which application is a
divisional of U.S. patent application Ser. No. 13/396,039, filed
Feb. 14, 2012, now U.S. Pat. No. 8,518,275, issued Aug. 27, 2013,
which application is a divisional of U.S. patent application Ser.
No. 12/114,173, filed May 2, 2008, now U.S. Pat. No. 8,114,301,
issued Feb. 14, 2012, the disclosure of each of which is hereby
incorporated herein in its entirety by this reference.
FIELD
[0002] Embodiments of the invention relate to methods of
fabricating thin films of self-assembling block copolymers, and
devices resulting from those methods.
BACKGROUND
[0003] As the development of nanoscale mechanical, electrical,
chemical and biological devices and systems increases, new
processes and materials are needed to fabricate nanoscale devices
and components. Making electrical contacts to conductive lines has
become a significant challenge as the dimensions of semiconductor
features shrink to sizes that are not easily accessible by
conventional lithography. Optical lithographic processing methods
have difficulty fabricating structures and features at the sub-60
nanometer level. The use of self-assembling diblock copolymers
presents another route to patterning at nanoscale dimensions.
Diblock copolymer films spontaneously assemble into periodic
structures by microphase separation of the constituent polymer
blocks after annealing, for example, by thermal annealing above the
glass transition temperature of the polymer or by solvent
annealing, forming ordered domains at nanometer-scale
dimensions.
[0004] The film morphology, including the size and shape of the
microphase-separated domains, can be controlled by the molecular
weight and volume fraction of the AB blocks of a diblock copolymer
to produce lamellar, cylindrical, or spherical morphologies, among
others. For example, for volume fractions at ratios greater than
about 80:20 of the two blocks (AB) of a diblock polymer, a block
copolymer film will microphase separate and self-assemble into
periodic spherical domains with spheres of polymer B surrounded by
a matrix of polymer A. For ratios of the two blocks between about
60:40 and 80:20, the diblock copolymer assembles into a periodic
hexagonal close-packed or honeycomb array of cylinders of polymer B
within a matrix of polymer A. For ratios between about 50:50 and
60:40, lamellar domains or alternating stripes of the blocks are
formed. Domain size typically ranges from 5 nm to 50 nm.
[0005] A lamellar-phase block copolymer material has been used for
making line features on a substrate. However, cylinders
self-assemble more rapidly and correct defects faster than
lamellae. Researchers have reported producing lines of
upward-facing, half-cylinders of a minority block of a block
copolymer in a matrix of the majority block through self-assembly
of a cylindrical-phase morphology block copolymer on a chemically
neutral surface. After removal of the matrix material, the
half-cylinders form a masking structure over the underlying
substrate. However, subsequent etching tends to undercut and
isotropically etch the matrix material that remains under the
half-cylinder lines, which will negatively affect etch resolution
of the substrate. Applications for forming structures in an
underlying substrate for semiconductor systems require a complex
layout of elements for forming contacts, conductive lines and/or
other elements, such as DRAM (dynamic random-access memory)
capacitors.
[0006] It would be useful to provide methods of fabricating films
of line arrays of ordered nanostructures that overcome these
problems.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Embodiments of the invention are described below with
reference to the following accompanying drawings, which are for
illustrative purposes only. Throughout the following views,
reference numerals are used in the drawings, and the same reference
numerals are used throughout the several views and in the
description to indicate same or like parts.
[0008] FIG. 1 illustrates a diagrammatic top plan view of a portion
of a substrate at a preliminary processing stage according to an
embodiment of the present disclosure, showing the substrate with a
neutral wetting material thereon. FIGS. 1A and 1B are elevational,
cross-sectional views of the substrate depicted in FIG. 1 taken
along lines 1A-1A and 1B-1B, respectively.
[0009] FIG. 2 illustrates a diagrammatic top plan view of the
substrate of FIG. 1 at a subsequent stage showing the formation of
trenches in a material layer formed on the neutral wetting
material. FIGS. 2A and 2B illustrate elevational, cross-sectional
views of a portion of the substrate depicted in FIG. 2 taken,
respectively, along lines 2A-2A and 2B-2B.
[0010] FIG. 3 illustrates a side elevational view of a portion of a
substrate at a preliminary processing stage according to another
embodiment of the disclosure, showing the substrate with trenches
in a material layer formed on the substrate.
[0011] FIG. 4 illustrates a side elevational view of the substrate
of FIG. 3 at a subsequent stage showing the formation of a neutral
wetting material within the trenches.
[0012] FIG. 5 is a diagrammatic top plan view of the substrate of
FIG. 2 at a subsequent stage in the fabrication of a
self-assembled, cylindrical phase, block copolymer film within the
trenches according to an embodiment of the disclosure. FIGS. 5A and
5B illustrate elevational, cross-sectional views of a portion of
the substrate depicted in FIG. 5 taken along lines 5A-5A and 5B-5B,
respectively.
[0013] FIG. 6 is a view of the substrate depicted in FIG. 5B at a
subsequent stage showing positioning of a preferential wetting
material over the block copolymer material within the trenches.
[0014] FIG. 7 is a top plan view of the substrate shown in FIG. 6
at a subsequent stage, showing a cutaway of the preferential
wetting material over the surface of the self-assembled block
copolymer material within the trenches. FIGS. 7A and 7B illustrate
cross-sectional views of the substrate depicted in FIG. 7, taken
along lines 7A-7A and 7B-7B, respectively. FIG. 7C is a top plan
view of a cross-section of the substrate shown in FIG. 7A taken
along lines 7C-7C, showing the self-assembled half-cylinder lines
within a polymer matrix within the trenches.
[0015] FIG. 8 is a view of the substrate depicted in FIG. 7B at a
subsequent stage showing removal of the preferential wetting
material from the surface of the self-assembled block copolymer
material according to an embodiment of the disclosure.
[0016] FIG. 9 is a top plan view of the substrate shown in FIG. 7
at a subsequent stage, showing the removal of one of the polymer
domains of the self-assembled block copolymer material within the
trenches. FIGS. 9A and 9B illustrate cross-sectional views of the
substrate depicted in FIG. 9, taken along lines 9A-9A and 9B-9B,
respectively.
[0017] FIGS. 10 and 11 are top plan views of the substrate of FIG.
9 at subsequent stages, illustrating an embodiment of the use of
the self-assembled block copolymer film after removal of one of the
polymer blocks, as a mask to etch the substrate and filling of the
etched openings. FIGS. 10A and 11A illustrate elevational,
cross-sectional views of a portion of the substrate depicted in
FIGS. 10 and 11 taken along lines 10A-10A and 11A-11A,
respectively. FIGS. 10B and 11B are cross-sectional views of the
substrate depicted in FIGS. 10 and 11 taken along lines 10B-10B and
11B-11B, respectively.
[0018] FIG. 12 is a view of the substrate depicted in FIG. 5A at a
subsequent stage showing application of a preferential wetting
atmosphere over the block copolymer material within the trenches
according to another embodiment of the invention.
[0019] FIG. 13 is a top plan view of the substrate shown in FIG. 12
at a subsequent stage, showing a preferential wetting brush layer
over the surface of the self-assembled block copolymer material
within the trenches. FIGS. 13A and 13B illustrate cross-sectional
views of the substrate depicted in FIG. 13, taken along lines
13A-13A and 13B-13B, respectively.
DETAILED DESCRIPTION
[0020] The following description with reference to the drawings
provides illustrative examples of devices and methods according to
embodiments of the invention. Such description is for illustrative
purposes only and not for purposes of limiting the same.
[0021] In the context of the current application, the terms
"semiconductor substrate," "semiconductive substrate,"
"semiconductive wafer fragment," "wafer fragment," or "wafer" mean
any construction comprising semiconductor material including, but
not limited to, bulk semiconductive materials such as a
semiconductor wafer (either alone or in assemblies comprising other
materials thereon), and semiconductive material layers (either
alone or in assemblies comprising other materials). The term
"substrate" refers to any supporting structure including, but not
limited to, the semiconductive substrates, wafer fragments or
wafers described above.
[0022] "L.sub.o" as used herein is the inherent periodicity or
pitch value (bulk period or repeat unit) of structures that
self-assemble upon annealing from a self-assembling (SA) block
copolymer. "L.sub.B" as used herein is the periodicity or pitch
value of a blend of a block copolymer with one or more of its
constituent homopolymers. "L" is used herein to indicate the
center-to-center cylinder pitch or spacing of cylinders of the
block copolymer or blend, and is equivalent to "L.sub.o" for a pure
block copolymer and "L.sub.B" for a copolymer blend.
[0023] In embodiments of the invention, a polymer material (e.g.,
film, layer) is prepared by guided self-assembly of block
copolymers, with both polymer domains wetting the interface with
the trench floor. Block copolymer materials spontaneously assemble
into periodic structures by microphase separation of the
constituent polymer blocks after annealing, forming ordered domains
at nanometer-scale dimensions. In embodiments of the invention, one
or more rows or lines of parallel-oriented half-cylinders are
formed within a trench, with the face of the half-cylinder lines
wetting a chemically neutral trench floor. Following self-assembly,
the parallel-oriented line(s) formed on the substrate can then be
used, for example, as an etch mask for patterning nanometer-scale
line openings into the underlying substrate through selective
removal of one block of the self-assembled block copolymer. Since
the domain sizes and periods (L) involved in this method are
determined by the chain length of a block copolymer (MW),
resolution can exceed other techniques such as conventional
photolithography. Processing costs using the technique are
significantly less than extreme ultraviolet (EUV) photolithography,
which has comparable resolution.
[0024] A method for fabricating a self-assembled block copolymer
material that defines an array of nanometer-scale,
parallel-oriented, downward facing half-cylinder lines according to
an embodiment of the invention is illustrated in FIGS. 1-9.
[0025] The described embodiment involves an anneal of a
cylindrical-phase block copolymer in combination with a
graphoepitaxy technique that utilizes a lithographically defined
trench as a guide with a floor composed of a material that is
neutral wetting to both polymer blocks and sidewalls and ends that
are preferential wetting to one polymer block and function as
constraints to induce self-assembly of the block copolymer
material. In some embodiments, an overlying material layer that is
preferential wetting is placed over the block copolymer material in
the trench. In other embodiments, an air interface can selectively
wet the desired block. Upon annealing, the block copolymer material
will self-assemble into one or more rows or lines of half-cylinders
in a polymer matrix and registered to the trench sidewalls, with
the face of the half-cylinders oriented downward and wetting the
trench floor. In some embodiments, an ordered array of two or more
rows of half-cylinders can be formed in each trench.
[0026] As depicted in FIGS. 1-1B, a substrate 10 is provided, which
can be silicon, silicon oxide, silicon nitride, silicon oxynitride,
silicon oxycarbide, among other materials.
[0027] In the illustrated embodiment, a neutral wetting material 12
(e.g., random copolymer, blend of functionalized homopolymers,
etc.) has been formed over the substrate 10. A material layer 14
(or one or more material layers) can then be formed over the
neutral wetting material and etched to form trenches 16, 16a, as
shown in FIGS. 2-2B. Portions of the material layer 14 form a
spacer 18 outside and between the trenches 16, 16a. The trenches
16, 16a are structured with opposing sidewalls 20, opposing ends
22, a floor 24, a width (w.sub.t, w.sub.t2), a length (l.sub.t) and
a depth (D.sub.t).
[0028] In another embodiment illustrated in FIGS. 3 and 4, the
material layer 14' can be formed on the substrate 10', etched to
form the trenches 16', 16a', and a neutral wetting material 12' can
then be formed on the trench floors 24'. For example, a random
copolymer material can be deposited into the trenches 16', 16a' and
crosslinked or grafted to form the neutral wetting material layer
12'. Material on surfaces outside the trenches 16', 16a', such as
on spacers 18' (e.g., non-crosslinked random copolymer) can be
subsequently removed.
[0029] Single or multiple trenches 16, 16a (as shown) can be formed
using a lithographic tool having an exposure system capable of
patterning at the scale of L (10 to 100 nm). Such exposure systems
include, for example, extreme ultraviolet (EUV) lithography,
proximity X-rays and electron beam (e-beam) lithography, as known
and used in the art. Conventional photolithography can attain (at
smallest) about 58 nm features.
[0030] A method called "pitch doubling" or "pitch multiplication"
can also be used for extending the capabilities of
photolithographic techniques beyond their minimum pitch, as
described, for example, in U.S. Pat. No. 5,328,810 (Lowrey et al.),
U.S. Pat. No. 7,115,525 (Abatchev et al.), U.S. Patent Publication
No. 2006/0281266 (Wells) and U.S. Patent Publication No.
2007/0023805 (Wells). Briefly, a pattern of lines is
photolithographically formed in a photoresist material overlying a
layer of an expendable material, which in turn overlies a
substrate, the expendable material layer is etched to form
placeholders or mandrels, the photoresist is stripped, spacers are
formed on the sides of the mandrels, and the mandrels are then
removed leaving behind the spacers as a mask for patterning the
substrate. Thus, where the initial photolithography formed a
pattern defining one feature and one space, the same width now
defines two features and two spaces, with the spaces defined by the
spacers. As a result, the smallest feature size possible with a
photolithographic technique is effectively decreased down to about
30 nm or less.
[0031] Factors in forming a single line or multiple lines of
parallel-oriented half-cylinders within the trenches include the
width (w.sub.t) of the trench, the formulation of the block
copolymer or blend to achieve the desired pitch (L), and the
thickness (t) of the block copolymer material.
[0032] There is a shift from two lines to one line of the
half-cylinder lines as the width of the trench is decreased (e.g.,
from width w.sub.12 to width w.sub.t) and/or the periodicity (L
value) of the block copolymer is increased, for example, by forming
a ternary blend by the addition of both constituent homopolymers.
The boundary conditions of the trench sidewalls 20 in both the x-
and y-axis impose a structure wherein each trench contains "n"
number of features (e.g., n lines of half-cylinders).
[0033] In the illustrated embodiment shown in FIGS. 2-2B, trenches
16 are constructed with a width (w.sub.t) of about 1.5 to 2 times L
(or 1.5-2.times. the pitch value) of the block copolymer material
26 such that a cast block copolymer material (or blend) of about L
will self-assemble upon annealing into a single parallel-oriented,
downward-facing half-cylinder line (line width at or about 0.5
times L) that is aligned with the sidewalls 20 down the center of
each trench 16. A relatively wider trench 16a has been formed with
a width (w.sub.t2) of (n+1)*L such that the block copolymer
material 26 (or blend) of about L will self-assemble into n lines
of downward-facing half-cylinders (line width about 0.5 times L) at
a center-to-center pitch distance (p) of adjacent lines at or about
the L value of the block copolymer material 26. For example, the
width (w.sub.t2) of a wider trench 16a can be about 3 to 65 times L
to result in the formation of 2 to 64 rows, respectively, of the
downward-facing half-cylinders.
[0034] For example, in using a cylindrical-phase block copolymer
with an about 50 nm pitch value or L, in trenches 16 with a width
(w.sub.t) of about 1.5 to 2 times 50 nm or about 75 to 100 nm, the
block copolymer material will form a single downward-facing
half-cylinder having a line width of about 25 nm. In trench 16a
with a width (w.sub.t2), for example, of about 3 times L or about 3
times 50 nm (or about 150 nm), the block copolymer material will
form two rows of the half-cylinder structures (line width of about
25 nm) at a center-to-center pitch distance (p) of adjacent
half-cylinder lines of about the L value (about 50 nm).
[0035] In another example, with a cylindrical-phase block copolymer
or blend having a pitch or L value of 35 nm, a single line of about
17.5 nm wide (about 0.5 times L) of a downward facing half-cylinder
will form in trench 16 having a width (w.sub.t) of about 1.5 to 2
times L or about 52.5 to 70 nm wide, and two parallel lines of
half-cylinders (each about 17.5 nm wide) at a center-to-center
pitch distance (p) of about 35 nm will form in trench 16a having a
width (w.sub.t2) of about 3 times L or about 3 times 35 nm (or
about 105 nm).
[0036] The length (l.sub.t) of the trenches 16, 16a is according to
the desired length of the half-cylinder line(s).
[0037] The depth (D.sub.t) of the trenches 16, 16a is effective to
direct lateral ordering of the block copolymer material during the
anneal. In embodiments of the invention, the trench depth can be at
or less than the final thickness (t.sub.2) of the block copolymer
material (D.sub.t.ltoreq.t.sub.2), which minimizes the formation of
a meniscus and variability in the thickness of the block copolymer
material across the trench width. In some embodiments, the trench
depth is at about two-thirds (2/3) to about three-fourths (3/4), or
about 67% to 75% less than the final thickness (t.sub.2) of the
block copolymer material within the trench.
[0038] In some embodiments, the dimensions of the trenches 16, 16a
are a width of about 20 nm to 100 nm (trench 16, w.sub.t) and about
20 nm to 3200 nm (trench 16a, w.sub.t2), a length (l.sub.t) of
about 100 .mu.m to 25,000 .mu.m, and a depth (D.sub.t) of about 10
nm to 100 nm.
[0039] As depicted in FIGS. 5-5B, a self-assembling,
cylindrical-phase block copolymer material 26 having an inherent
pitch at or about L.sub.o (or a ternary blend of block copolymer
and homopolymers blended to have a pitch at or about L.sub.B) is
deposited into the trenches 16, 16a. A thin layer or film 26a of
the block copolymer material 26 can be deposited onto the material
layer 14 outside the trenches 16, 16a, e.g., on the spacers 18.
[0040] The block copolymer material 26 or blend is constructed such
that all of the polymer blocks will have equal preference for a
neutral wetting material on the trench floor 24. In some
embodiments of the invention, the block copolymer or blend is
constructed such that the major domain can be selectively removed.
In other embodiments, the minor domain polymer block can be
selectively doped or structured to incorporate an inorganic
component or species (e.g., a filler component) during annealing
into microphase domains, which will remain on the substrate 10 as
an etch resistant material (e.g., mask) upon selective removal of
the majority polymer domain or, in some embodiments, both the
majority and minority polymer domains. Suitable inorganic
precursors are thermally stable and do not volatilize at the anneal
temperature.
[0041] Block copolymers that incorporate an inorganic species can
be prepared by techniques known in the art, for example, by a
direct synthesis technique, or by incorporating atoms of an
inorganic species by complexation or coordination with a reactive
group of one of the polymer blocks.
[0042] For example, as described in U.S. Pat. No. 6,565,763
(Asakawa et al.), the block copolymer can be blended with an
inorganic heat resistant material or precursor thereof, which will
segregate to one polymer phase, for example, a metal salt, a metal
oxide gel, a metal alkoxide polymer, a metal oxide precursor, a
metal nitride precursor, or metal fine particles. Examples of the
metal include silicon (Si), chromium (Cr), titanium (Ti), aluminum
(Al), molybdenum (Mo), gold (Au), platinum (Pt), ruthenium (Ru),
zirconium (Zr), tungsten (W), vanadium (V), lead (Pb), and zinc
(Zn), among others.
[0043] Examples of metal alkoxides include alkoxysilanes such as
tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane,
tetraisopropoxyaluminum and tetraisopropoxytitanium, and
alkylalkoxysilanes such as butyltriethoxysilane and
propyltriethoxyaluminum. An example of the metal alkoxide polymer
is polydiethoxysiloxane.
[0044] Examples of a metal oxide precursor or metal nitride
precursor include polysilsesquioxane (e.g.,
polymethylsilsesquioxane, polymethylhydroxyl silsesquioxane,
polyphenylsilsesquioxane, etc.), polyhedral oligomeric
silsesquioxane (POSS), and polysilazane.
[0045] In some embodiments, a solution of a block copolymer can be
combined with an additive such as an organic metal salt that has a
high affinity to one of the polymer chains of the block copolymer
and will segregate during an anneal to one of the polymer phases.
For example, the block copolymer can be mixed with a metal salt
combined with an organic compound. Examples of such organic metal
salts include lithium 2,4-pentanedionate, lithium
tetramethylpentanedionate, ruthenium 2,4-pentanedionate, magnesium
2,4-pentanedionate, magnesium hexafluoropentanedionate, magnesium
trifuoropentanedionate, manganese(II) 2,4-pentanedionate,
molybdenum(V) ethoxide, molybdenum(VI) oxide
bis(2,4-pentanedionate), neodymium
6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate, neodymium
hexafluoropentanedionate, neodymium(III) 2,4-pentanedionate,
nickel(II) 2,4-pentanedionate, niobium(V) n-butoxide, niobium(V)
n-ethoxide, palladium hexafluoropentanedionate, palladium
2,4-pentanedionate, platinum hexafluoropentanedionate, platinum
2,4-pentanedionate, rhodium trifuoropentanedionate, ruthenium(III)
2,4-pentanedionate, tetrabutylammonium hexachloroplatinate(IV),
tetrabromoaurate(III) cetylpyridinium salt, among others.
[0046] As described in U.S. Patent Publication No. 2007/0222995 and
U.S. Patent Publication No. 2007/0289943 (Lu; Agilent Technologies
Inc.), atoms of an inorganic species such as a metal (e.g., iron,
cobalt, molybdenum, etc.) can be incorporated into one block of a
diblock copolymer by complexation of the atoms of the inorganic
species with the pyridine units of
poly(styrene)-b-poly(vinylpyridine) (PS-b-PVP), where the pyridine
group forms a coordination bond with the inorganic species, e.g.,
iron (Fe), etc., or forms as an acid-base conjugate. As an example
of an acid-base conjugate, a solution of the PS-b-PVP block
copolymer can be combined with dihydrogen hexachloroplatinate
(H.sub.2PtCl.sub.6) wherein a single Pt atom can be complexed with
each pyridine group (at maximum loading).
[0047] As also described in U.S. Patent Publication No.
2007/0222995, block copolymers that incorporate an inorganic
species can also be prepared by a direct synthesis technique. For
example, a sequential living polymerization of a
nonmetal-containing monomer (e.g., styrene monomer) followed by an
inorganic species-containing monomer (e.g.,
ferrocenylethylmethylsilane monomer) can be used to synthesize an
inorganic species-containing block copolymer (e.g.,
poly(styrene)-b-poly(ferrocenylmethylethylsilane) (PS-b-PFEMS).
[0048] Examples of diblock copolymers include, for example,
poly(styrene)-b-poly(vinylpyridine) (PS-b-PVP),
poly(styrene)-b-poly(methylmethacrylate) (PS-b-PMMA) or other
PS-b-poly(acrylate) or PS-b-poly(methacrylate),
poly(styrene)-b-poly(lactide) (PS-b-PLA),
poly(styrene)-b-poly(tert-butyl acrylate) (PS-b-PtBA), and
poly(styrene)-b-poly(ethylene-co-butylene (PS-b-(PE-co-PB)), and
poly(styrene)-b-poly(ethylene oxide) (PS-b-PEO),
polybutadiene-b-poly(vinylpyridine) (PB-b-PVP),
poly(ethylene-alt-propylene)-b-poly(vinylpyridine) (PEP-b-PVP),
among others, with PS-b-PVP diblock copolymers used in the
illustrated embodiment. Other types of block copolymers (i.e.,
triblock or multiblock copolymers) can be used. Examples of
triblock copolymers include ABC copolymers such as
poly(styrene-b-methylmethacrylate-b-ethylene oxide)
(PS-b-PMMA-b-PEO), and ABA copolymers such as PS-PMMA-PS,
PMMA-PS-PMMA, and PS-b-PI-b-PS, among others.
[0049] Examples of diblock copolymers that incorporate an inorganic
species include poly(styrene)-b-poly(dimethylsiloxane) (PS-b-PDMS),
poly(isoprene)-b-poly(dimethylsiloxane) (PI-b-PDMS), PS-b-PFEMS,
poly(isoprene)-b-poly(ferrocenylmethylethylsilane) (PI-b-PFEMS),
poly(styrene)-b-poly(vinylmethylsiloxane) (PS-b-PVMS),
poly(styrene)-b-poly(butadiene) (PS-b-PB) where the polybutadiene
(PB) is stained by osmium tetroxide (OSO.sub.4), and
poly(styrene)-b-poly(vinylpyridine) (PS-b-PVP) where the pyridine
group forms a coordination bond with an inorganic species, among
others. After annealing and self-assembly of the polymer blocks
into the half-cylinders and matrix, an oxidation process (e.g.,
ultraviolet (UV)-ozonation or oxygen plasma etching) can be
performed to remove the organic components of the block copolymer
domains and convert the inorganic species to form a non-volatile
inorganic oxide, which remains on the substrate and can be used as
a mask in a subsequent etch process. For example, the inorganic
species of the PDMS and PFEM block copolymers are silicon and iron,
which, upon oxidation, will form non-volatile oxides, e.g., silicon
oxide (SiO.sub.x) and iron oxide (Fe.sub.xO.sub.y).
[0050] The L value of the block copolymer can be modified, for
example, by adjusting the molecular weight of the block copolymer.
The block copolymer material can also be formulated as a binary or
ternary blend comprising a block copolymer and one or more
homopolymers (HPs) of the same type of polymers as the polymer
blocks in the block copolymer, to produce a blend that will swell
the size of the polymer domains and increase the L value. The
concentration of homopolymers in a blend can range from 0 wt % to
about 60 wt %. Generally, when added to a polymer material, both
homopolymers are added to the blend in about the same ratio or
amount. An example of a ternary diblock copolymer blend is a
PS-b-PVP/PS/PVP blend, for example, 60 wt % of 32.5K/12K PS-b-PVP,
20 wt % of 10K PS, and 20 wt % of 10K PVP. Another example of a
ternary diblock copolymer blend is a PS-b-PMMA/PS/PMMA blend, for
example, 60 wt % of 46K/21K PS-b-PMMA, 20 wt % of 20K polystyrene
and 20 wt % of 20K poly(methylmethacrylate). Yet another example is
a blend of 60:20:20 (wt %) of PS-b-PEO/PS/PEO, or a blend of about
85 to 90 wt % PS-b-PEO and up to 10 to 15 wt % PEO homopolymer.
[0051] The film morphology, including the domain sizes and periods
(L.sub.o) of the microphase-separated domains, can be controlled by
chain length of a block copolymer (molecular weight, MW) and volume
fraction of the AB blocks of a diblock copolymer to produce
cylindrical morphologies (among others). For example, for volume
fractions at ratios of the two blocks generally between about 60:40
and 80:20, the diblock copolymer will microphase separate and
self-assemble into periodic half-cylindrical domains of polymer B
within a matrix of polymer A. An example of a cylinder-forming
PS-b-PVP copolymer material (L.sub.o.about.35 nm) to form about 20
nm wide half-cylindrical PVP domains in a matrix of PS is composed
of about 70 wt % PS and 30 wt % PVP with a total molecular weight
(M.sub.n) of 44.5 kg/mol.
[0052] Referring to FIGS. 5-5B, the cylindrical-phase block
copolymer material 26 can be cast or deposited into the trenches
16, 16a to an initial thickness (t.sub.1) at or about the L value
of the block copolymer material 26 (e.g., about .+-.20% of L) such
that the thickness (t.sub.2) after annealing will be at or below
the L value and the block copolymer material 26 will self-assemble
to form a single layer of downwardly facing half-cylinders
registered parallel to the sidewalls 20 and extending the length
(l.sub.t) of each of the trenches 16, 16a (e.g., as in FIGS. 7A and
7B). The thickness of the block copolymer material 26 can be
measured, for example, by ellipsometry techniques.
[0053] The block copolymer material 26 can be deposited by
spin-casting (spin-coating) from a dilute solution (e.g., about
0.25 wt % to 2 wt % solution) of the copolymer in an organic
solvent such as dichloroethane (CH.sub.2Cl.sub.2) or toluene, for
example. Capillary forces pull excess block copolymer material 26
(e.g., greater than a monolayer) into the trenches 16, 16a. As
shown, a thin layer or film 26a of the block copolymer material 26
can be deposited onto the material layer 14 outside the trenches
16, 16a, e.g., on the spacers 18. Upon annealing, the thin film 26a
will flow into the trenches 16, 16a leaving a structureless brush
layer on the material layer 14 from a top-down perspective.
[0054] In the present embodiment shown in FIGS. 5-5B, the trench
floors 24 are structured to be neutral wetting (equal affinity for
both blocks of the copolymer) to induce formation of half-cylinder
polymer domains that are oriented facing downward on the trench
floors 24, and the trench sidewalls 20 and the ends 22 are
structured to be preferential wetting by one block of the block
copolymer to induce registration of the half-cylinders to the
sidewalls 20 as the polymer blocks self-assemble. Entropic forces
drive the wetting of a neutral wetting surface by both blocks, and
enthalpic forces drive the wetting of a preferential-wetting
surface by the preferred block (e.g., the minority block).
[0055] A chemically neutral wetting trench floor 24 allows both
blocks of the copolymer material to wet the floor 24 of the
trenches 16, 16a and provides for the formation of the
half-cylinder line layout of the disclosure. The use of a neutral
wetting trench floor in embodiments of the invention expands the
number of block copolymer materials that can be utilized to produce
self-assembled films having a series of parallel lines formed on a
substrate surface that can be readily used as a mask for etching
the underlying substrate to form a multiple line layout on a
nanoscale level.
[0056] A neutral wetting material 12 can be provided, for example,
by applying a neutral wetting polymer (e.g., a neutral wetting
random copolymer) onto the substrate 10, then forming an overlying
material layer 14 and etching the trenches 16, 16a to expose the
underlying neutral wetting material, as illustrated in FIGS.
2-2B.
[0057] In another embodiment illustrated in FIGS. 3 and 4, a
neutral wetting random copolymer material can be applied after
forming the trenches 16', 16a', for example, as a blanket coat by
casting or spin-coating into the trenches 16', 16a' as depicted in
FIG. 4. The random copolymer material can then be thermally
processed to flow the material into the bottom of the trenches 16',
16a' by capillary action, which results in a layer (mat) 12'
composed of the crosslinked, neutral wetting random copolymer. In
another embodiment, the random copolymer material within the
trenches 16', 16a' can be photo-exposed (e.g., through a mask or
reticle) to crosslink the random copolymer within the trenches 16',
16a' to form the neutral wetting material 12'. Non-crosslinked
random copolymer material outside the trenches 16', 16a' (e.g., on
the spacers 18') can be subsequently removed.
[0058] Neutral wetting surfaces can be specifically prepared by the
application of random copolymers composed of monomers identical to
those in the block copolymer and tailored such that the mole
fraction of each monomer is appropriate to form a neutral wetting
surface. For example, in the use of a PS-b-PVP block copolymer, a
neutral wetting material 12 can be formed from a thin film of a
photo-crosslinkable random PS-r-PVP copolymer that exhibits
non-preferential or neutral wetting toward PS and PVP, which can be
cast onto the substrate 10 (e.g., by spin coating). The random
copolymer material can be fixed in place by chemical grafting (on
an oxide substrate) or by thermally or photolytically crosslinking
(any surface) to form a mat that is neutral wetting to PS and PVP
and insoluble when the block copolymer material is cast onto it,
due to the crosslinking.
[0059] In another embodiment, a blend of hydroxyl-terminated
homopolymers and a corresponding low molecular weight block
copolymer can be grafted (covalently bonded) to the substrate to
form a neutral wetting interface layer (e.g., about 4 nm to 5 nm)
for PS-b-PMMA and PS-b-P2VP, among other block copolymers. The
block copolymer can function to emulsify the homopolymer blend
before grafting. For example, an about 1 wt % solution (e.g., in
toluene) of a blend of about 20 wt % to 50 wt % (or about 30 wt %
to 40 wt %) OH-terminated homopolymers (e.g., M.sub.n=6K) and an
about 80 wt % to 50 wt % (or about 70 wt % to 60 wt %) of a low
molecular weight block copolymer (e.g., 5K-5K) can be spin-coated
onto a substrate 10 (e.g., SiO.sub.2), heated (baked) (e.g., at
160.degree. C.), and the non-grafted (unbonded) polymer material
may be removed, for example, by a solvent rinse (e.g., toluene).
For example, the neutral wetting material can be prepared from a
blend of about 30 wt % PS--OH (M.sub.n=6K) and PMMA-OH (M.sub.n=6K)
(weight ratio of 4:6) and about 70 wt % PS-b-PMMA (5K-5K), or a
ternary blend of PS--OH (6K), P2VP--OH (6K) and PS-b-2PVP (8K-8K),
etc.
[0060] In embodiments in which the substrate 10 is silicon (with
native oxide), a neutral wetting surface for PS-b-PMMA can be
provided by hydrogen-terminated silicon. The floors 24 of the
trenches 16, 16a can be etched, for example, with a hydrogen
plasma, to remove the oxide material and form hydrogen-terminated
silicon, which is neutral wetting with equal affinity for both
blocks of a block copolymer material. H-terminated silicon can be
prepared by a conventional process, for example, by a fluoride ion
etch of a silicon substrate (with native oxide present, about 12
.ANG. to 15 .ANG.) by exposure to an aqueous solution of hydrogen
fluoride (HF) and buffered HF or ammonium fluoride (NH.sub.4F), by
HF vapor treatment, or by a hydrogen plasma treatment (e.g., atomic
hydrogen).
[0061] An H-terminated silicon substrate can be further processed
by grafting a random copolymer such as PS-r-PVP, PS-r-PMMA, etc.,
selectively onto the substrate 10, resulting in a neutral wetting
surface for the corresponding block copolymer (e.g., PS-b-PVP,
PS-b-PMMA, etc.). For example, a neutral wetting layer of a
PS-r-PMMA random copolymer can be provided by an in situ free
radical polymerization of styrene and methylmethacrylate using a
di-olefinic linker such as divinyl benzene, which links the
copolymer to an H-terminated silicon surface to produce about a
10-nm to 15-nm thick film.
[0062] Referring again to FIGS. 3 and 4, in another embodiment, a
neutral wetting random copolymer material 12' can be applied after
formation of the material layer 14' and trenches 16', 16a', which
reacts selectively with the trench floor 24' (composed of the
substrate 10' material) and not the trench sidewalls 20' or ends
22' (composed of the material layer 14'). For example, a random
copolymer (or appropriate blend of homopolymers with a block
copolymer surfactant) containing epoxide groups will react
selectively to terminal amine functional groups (e.g., --NH-- and
--NH.sub.2) on silicon nitride and silicon oxynitride surfaces
relative to silicon oxide or silicon. In another example in which
the trench floor 24' is silicon or polysilicon and the sidewalls
20' are a material such as an oxide (e.g., SiO.sub.x), the floor
24' can be treated to form H-terminated silicon and a random
copolymer material (e.g., PS-r-PVP, PS-r-PMMA, etc.) can be formed
by in situ polymerization only at the floor surface.
[0063] In yet another embodiment, a neutral wetting surface (e.g.,
for PS-b-PMMA and PS-b-PEO) can be provided by grafting a
self-assembled monolayer (SAM) of a trichlorosilane-base SAM such
as 3-(para-methoxyphenyl)propyltrichorosilane grafted to oxide
(e.g., SiO.sub.2) as described, for example, by D. H. Park,
Nanotechnology 18 (2007), p. 355304.
[0064] A surface that is neutral wetting to PS-b-PMMA can also be
prepared by spin-coating a blanket layer of a photo- or thermally
crosslinkable random copolymer such as a benzocyclobutene- or
azidomethylstyrene-functionalized random copolymer of styrene and
methylmethacrylate (e.g.,
poly(styrene-r-benzocyclobutene-r-methylmethacrylate
(PS-r-PMMA-r-BCB)). For example, such a random copolymer can
comprise about 42 wt % PMMA, about (58-x) wt % PS and x wt % (e.g.,
about 2 wt % to 3 wt %) of either polybenzocyclobutene or
poly(para-azidomethylstyrene)). An
azidomethylstyrene-functionalized random copolymer can be UV
photo-crosslinked (e.g., 1 MW/cm.sup.2 to 5 MW/cm.sup.2 exposure
for about 15 seconds to about 30 minutes) or thermally crosslinked
(e.g., at about 170.degree. C. for about four hours) to form a
crosslinked polymer mat as a neutral wetting layer. A
benzocyclobutene-functionalized random copolymer can be thermally
crosslinked (e.g., at about 200.degree. C. for about four hours or
at about 250.degree. C. for about ten minutes).
[0065] In another embodiment, a neutral wetting random copolymer of
polystyrene (PS), polymethacrylate (PMMA) with hydroxyl group(s)
(e.g., 2-hydroxyethyl methacrylate (P(S-r-MMA-r-HEMA)) (e.g., about
58 wt % PS) can be can be selectively grafted to a substrate 10
(e.g., an oxide) as a neutral wetting layer about 5 nm to 10 nm
thick by heating at about 160.degree. C. for about 48 hours. See,
for example, In et al., Langmuir, 2006, 22, 7855-7860.
[0066] To provide preferential wetting trench sidewalls 20, for
example, in the use of a PS-b-PVP block copolymer, the material
layer 14 can be composed of silicon (with native oxide), oxide
(e.g., silicon oxide, SiO.sub.x), silicon nitride, silicon
oxycarbide, indium tin oxide (ITO), silicon oxynitride, and resist
materials such as methacrylate-based resists and polydimethyl
glutarimide resists, among other materials, which exhibit
preferential wetting toward the preferred block (e.g., the minority
block), which is the PVP block in the illustrated embodiment. Upon
annealing and self-assembly of the block copolymer material 26, the
preferred block (e.g., the PVP block) will form a thin interface
layer along the preferential wetting sidewalls 20 and ends 22 of
the trenches 16, 16a.
[0067] In other embodiments utilizing PS-b-PMMA, a preferential
wetting material such as a polymethylmethacrylate (PMMA) polymer
modified with an --OH containing moiety (e.g.,
hydroxyethylmethacrylate) can be selectively applied onto the
sidewalls of the trenches in embodiments where a neutral wetting
material 12, 12', is in place on the trench floor 24, 24' (as in
FIGS. 2-2B and FIG. 4). For example, a neutral wetting layer can be
formed on the trench floor 24, 24' (e.g., depicted in FIG. 4 as a
layer) by an in situ polymerization of a random copolymer on
H-terminated silicon in the presence of SiO.sub.x sidewalls, and
OH-modified PMMA then grafted to the sidewalls. An OH-modified PMMA
can be applied, for example, by spin coating and then heating
(e.g., to about 170.degree. C.) to allow the terminal OH groups to
selectively end-graft to the sidewalls 20 and ends 22 (e.g., of
oxide) of the trenches 16, 16a, 16', 16a'. Non-grafted material can
be removed by rinsing with an appropriate solvent (e.g., toluene).
See, for example, Mansky et al., Science, 1997, 275, 1458-1460, and
In et al., Langmuir, 2006, 22, 7855-7860.
[0068] Referring to FIG. 6, a surface 28 of the block copolymer
material 26 in the trenches 16, 16a (see FIGS. 5A and 5B) is then
contacted by a material 30 that will preferentially wet one of the
blocks of the copolymer material 26, which is the minority block in
the illustrated embodiment.
[0069] In an embodiment of the invention, the preferential wetting
material 30 is composed of a solid material that is placed onto the
surface of the block copolymer material 26. For example, the
preferential wetting material 30 can be composed of a soft,
flexible or rubbery solid material such as a crosslinked
poly(dimethylsiloxane) (PDMS) elastomer (e.g., Sylgard 184 by Dow
Corning Corp., Midland, Mich.) or other elastomeric polymer
material (e.g., silicones, polyurethanes, etc.).
[0070] A crosslinked, solid PDMS material 30 provides an external
surface that is hydrophobic, which can be altered, for example, by
a plasma oxidation to add silanol (SiOH) groups to the surface to
render the PDMS surface hydrophilic. For example, in using a
PS-b-PVP (70:30) block copolymer, a PDMS material 30 having a
hydrophobic surface placed into contact with the PS-b-PVP block
copolymer material 26 will be preferentially wetted by the PS
block, while a PDMS material 30 modified with a hydrophilic surface
will be preferentially wetted by the PVP block. After annealing, a
PDMS material 30 can be removed, for example, by lifting or peeling
the material 30 from the surface 28 of the block copolymer material
26, which can include applying a solvent such as water, alcohols,
etc. (e.g., by soaking), to permeate and swell the PDMS material 30
to enhance physical removal, and which is compatible with and does
not dissolve the block copolymer. A dilute fluoride solution (e.g.,
NH.sub.4F, HF, NaF, etc.) can also be applied to etch and dissolve
away a PDMS material.
[0071] In another embodiment, the preferential wetting material 30
can be formed as an inorganic film on the surface 28 of the block
copolymer material 26. For example, a layer of a spin-on dielectric
(SOD) material can be formed by applying, for example, a spin-on
liquid silicon-containing polymer, removing the solvent (e.g., by
heating), and then oxidizing the polymer layer (e.g., oxygen
atmosphere, steam-oxidation process, wet chemical oxidation, etc.)
to form a hard silicon dioxide (SiO.sub.2) layer, a hydrophilic
surface that will be preferentially wetted by the PVP (minority)
block. In embodiments of the method, the oxidation can be conducted
simultaneously with a thermal anneal of the block copolymer
material 26. Examples of silicon-containing polymers include
silicates, siloxanes (e.g., hydrogen silsesquioxane (HSQ),
hexamethyldisiloxane, octamethyltrisiloxane, etc.), silazanes
(e.g., polysilazanes such as hexamethyldisilazane (HMDS),
tetramethyldisilazane, octamethylcyclotetrasilazine,
hexamethylcyclotrisilazine, diethylaminotrimethylsilane,
dimethylaminotrimethylsilane, etc.) and silisesquioxanes (e.g.,
hydrogen silsesquioxane (HSQ). The spin-on polymer material can be
applied, for example, by casting, spin applying, flow coating or a
spray coating technique. The solvent of the spin-on polymer
material is compatible with and does not dissolve the block
copolymer, for example, water or an alcohol. After annealing, a
layer of dielectric preferential wetting material 30 can be removed
using a controlled etch back process, for example, by applying a
fluoride-based etchant whereby the dielectric material is etched at
a low etch rate (e.g., less than about 200 .ANG./minute).
[0072] With the preferential wetting material 30 in contact with
the surface 28 of the block copolymer material 26, an annealing
process is conducted (arrows , FIG. 6) to cause the polymer blocks
to phase separate in response to the preferential and neutral
wetting of the trench surfaces and the preferential wetting of the
overlying material 30, and form a self-assembled polymer material
32 as illustrated in FIGS. 7-7C.
[0073] Thermal annealing can be conducted at above the glass
transition temperature of the component blocks of the copolymer
material 26 (see FIG. 6). For example, a PS-b-PVP copolymer
material can be globally annealed at a temperature of about
150.degree. C. to 275.degree. C. in a vacuum oven for about 1 to 24
hours to achieve the self-assembled morphology. The resulting
morphology of the annealed copolymer material 32 (e.g., parallel
orientation of the half-cylinder lines) can be examined, for
example, using atomic force microscopy (AFM), transmission electron
microscopy (TEM), scanning electron microscopy (SEM).
[0074] The block copolymer material 26 can be globally heated or,
in other embodiments, a zone or localized thermal anneal can be
applied to portions or sections of the block copolymer material 26.
For example, the substrate 10 can be moved across a hot-to-cold
temperature gradient 34 (FIG. 6) positioned above (as shown) or
underneath the substrate 10 (or the thermal source can be moved
relative to the substrate 10, e.g., arrow .fwdarw.) such that the
block copolymer material 26 self-assembles upon cooling after
passing through the heat source. Only those portions of the block
copolymer material 26 that are heated above the glass transition
temperature of the component polymer blocks will self-assemble, and
areas of the material that were not sufficiently heated remain
disordered and unassembled. "Pulling" the heated zone across the
substrate 10 can result in faster processing and better ordered
structures relative to a global thermal anneal.
[0075] Upon annealing, the cylindrical-phase block copolymer
material 26 will self-assemble into a polymer material 32 (e.g., a
film), as depicted in FIGS. 7-7C. In response to the character of
the cylinder-phase block copolymer composition (e.g., 70:30
PS-b-PVP having an inherent pitch at or about L) combined with the
boundary conditions, including the constraints provided by the
width (w.sub.t) of the trenches 16 and the wetting properties of
the trench surfaces (i.e., a trench floor 24 that exhibits neutral
or non-preferential wetting toward both polymer blocks, e.g., a
random graft copolymer, and trench sidewalls 20 and an overlying
material 30 that are preferential wetting to the minority block),
the minority (preferred) block (e.g., PVP) will self-assemble to
form parallel-oriented, downward-facing, half-cylinder domain
(line) 36 on the non-preferential (neutral) wetting material 12 on
the trench floor, which is parallel to the trench floor 24 and
registered to the sidewalls 20 for the length (l.sub.t) of trenches
16, 16a. Within the trenches, a matrix 38 of the majority polymer
block (e.g., PS) overlies and surrounds the half-cylinder(s) 36.
Generally, the lines of the half-cylinder 36 (both blocks
considered) will have a width (w.sub.c) at or about 0.5 times
L.
[0076] In addition, the minority (preferred) block (e.g., PVP) will
segregate to and wet the preferential wetting sidewalls 20 and ends
22 of the trenches 16, 16a to form a thin interface or wetting
(brush) layer 36a, and will segregate to and wet the overlying
preferential wetting material layer 30 to form an overlying thin
wetting layer 36a.sub.s. The thickness of the wetting layers 36a,
36a.sub.s (both blocks considered) is generally about 0.5 times L,
which includes <0.25 times L of the minority block and about
0.25 times L of the majority block. For example, a <0.25 times L
thick layer of the PVP block will wet oxide interfaces with
attached PS domains (about 0.25 times L thick) directed outward
from the oxide material.
[0077] In embodiments of the invention, the self-assembled polymer
material 32 has a post-anneal thickness (t.sub.2) at or below the L
value, or t.sub.2=b+(0.5*L) (where b is the thickness of the
overlying wetting layer 36a.sub.s, both blocks considered), or
t.sub.2=[(.ltoreq.0.5*L)+(0.5*L)], or t.sub.2.ltoreq.L.
[0078] In embodiments in which the block copolymer material 26
includes an inorganic species such as a metal (e.g., Si, Fe, etc.),
the inorganic species will segregate to one polymer phase upon
annealing. For example, with a PS-b-PVP copolymer combined with a
silicon- and/or iron-containing additive where the pyridine group
selectively solvates the Si and Fe species, during the anneal, the
Si and Fe species will segregate to the PVP half-cylinders 36 (and
wetting layers 36a). Suitable inorganic precursors are thermally
stable and will not volatilize at the anneal temperature.
[0079] In the illustrated embodiment, the width (w.sub.t) of
trenches 16 are about 1.5 to 2 times L (or 1.5 to 2.times. the
pitch value) of the block copolymer 26, resulting in the formation
of a single half-cylinder down the center of the trench 16 from a
block copolymer having a pitch value of about L. As depicted in
FIGS. 7A and 7C, within a wider trench 16a having a width
(w.sub.t2) of about (n+1)*L (or (n+1).times. the pitch value), the
block copolymer material will self-assemble to form multiple (n)
lines of half-cylinders 36 (shown as two lines) with a
center-to-center pitch distance (p) of adjacent lines at or about
the pitch distance or L value of the block copolymer material. The
number (n) of half-cylinder lines 36 within a trench can be varied,
for example, according to the width of the trench and/or the pitch
distance (p) or L value of the block copolymer material.
[0080] After the block copolymer material is annealed and ordered,
the preferential wetting material 30 can be removed from contact
with the assembled block copolymer material 32, as shown in FIG.
8.
[0081] For example, in the use of a solid, elastomeric material 30
such as PDMS, the material can be lifted or peeled from the surface
of the block copolymer material 32. To facilitate removal, a
solvent that is compatible with and does not dissolve or etch the
assembled polymer domains such as water, alcohol, etc. can be
applied (e.g., by spraying, soaking the material) to permeate and
swell the material and enhance removal without altering or damaging
the assembled polymer structure. A dilute fluoride solution (e.g.,
NH.sub.4F, HF, NaF, etc.) can also be applied to mediate the
removal and decomposition of a PDMS material.
[0082] In embodiments of the invention in which the preferential
wetting material 30 is composed of an inorganic material such as a
spin-on dielectric (SOD), the material 30 can be removed by a
controlled etch back process, for example, by applying a
fluoride-based etchant whereby the dielectric material is etched at
a low etch rate (e.g., less than about 200 .ANG./minute) without
altering or damaging the assembled polymer structure.
[0083] In embodiments in which an elastomeric material 30 is used
with a block copolymer material that includes an inorganic species
(e.g., Si, Fe, etc.), a process that dissolves or etches the
polymer components but not the inorganic species can be used to
selectively remove the organic components of the block copolymer
domains, leaving the inorganic species on the substrate to form a
mask material. For example, an oxygen plasma etch will remove the
carbonaceous major domains, leaving inorganic material (e.g., Si,
Fe, etc.) as lines on the substrate surface.
[0084] Generally, a block copolymer thin film 26a outside the
trenches (e.g., on spacers 18) will not be not thick enough to
result in self-assembly. Optionally, the unstructured thin film 26a
can be removed, for example, by an etch technique or a
planarization process to provide an about uniformly flat
surface.
[0085] Optionally, the copolymer material can be treated to
crosslink one of the polymer domains (e.g., the PVP half-cylinders)
to fix and enhance the strength of the polymer blocks. For example,
one of the polymer blocks can be structured to inherently crosslink
(e.g., upon exposure to ultraviolet (UV) radiation, including deep
ultraviolet (DUV) radiation), or the polymer block can be
formulated to contain a crosslinking agent. For example, the trench
regions can be selectively exposed through a reticle (not shown) to
crosslink only the self-assembled polymer material 32 within the
trenches 16, 16a and a wash can then be applied with an appropriate
solvent (e.g., toluene) to remove the non-crosslinked portions of
the block copolymer material 26a, leaving the registered
self-assembled polymer material 32 within the trench and exposing
the surface of the material layer 14 above/outside the trenches. In
another embodiment, the annealed polymer material 32 can be
crosslinked globally, a photoresist material can be applied to
pattern and expose the areas of the polymer material 26a outside
the trench regions, and the exposed portions of the polymer
material 26a can be removed, for example by an oxygen (O.sub.2)
plasma treatment.
[0086] An embodiment of the application of the self-assembled
polymer material 30 is as an etch mask to form openings in the
substrate 10. After annealing and self-assembly of the polymer
blocks into the half-cylinders 36 and matrix 38, and removal of the
preferential wetting material 30, the assembled polymer material 32
can be processed to form a structure that can be used as an etch
mask to form openings in the substrate 10.
[0087] In some embodiments of the invention, the surface wetting
layer 36a.sub.s (FIGS. 7A, 7C) composed of the minority block
(e.g., PVP) can be selectively removed to expose the matrix 38 of
the self-assembled polymer material 32. For example, a surface
wetting layer 36a.sub.s of PVP can be removed by an RIE process
using an oxygen, fluorocarbon, or argon plasma, for example.
[0088] In embodiments of the invention in which one of the polymer
domains includes an inorganic species (e.g., Si, Fe, etc.), an
oxidation process such as a UV-ozonation or oxygen plasma etching,
can be performed to remove the organic material (i.e., the polymer
domains) and convert the inorganic species to a non-volatile
inorganic oxide, e.g., silicon oxide (SiO.sub.x), iron oxide
(Fe.sub.xO.sub.y), etc., which remains on the substrate and can be
used as a mask in a subsequent etch process.
[0089] For example, as depicted in FIGS. 9-9B, in the illustrated
embodiment in which the block copolymer material (26) is composed
of PS-b-PVP combined (e.g., doped) with an Si- and/or Fe-containing
additive, and the Si and/or Fe species are segregated to the PVP
half-cylinders 36 and wetting layers 36a. An oxidation process
(arrows ) can be performed to remove both the PS matrix 38 and PVP
polymer component of the half-cylinders 36 (and neutral wetting
layer 12) and convert the Si and/or Fe species within the
half-cylinders to inorganic oxide, e.g., SiO.sub.x and/or
Fe.sub.xO.sub.y, resulting in non-volatile, inorganic oxide lines
40 on the substrate 10.
[0090] In other embodiments, the matrix domain 38 of the
self-assembled polymer material 32 can be selectively removed
relative to the half-cylinder lines 36, which can be used as a mask
to etch the exposed substrate 10 at the trench floor 24. For
example, in using a PS-b-PMMA block copolymer, PMMA domains can be
selectively removed by UV exposure/acetic acid development or by
selective reactive ion etching (RIE), and the remaining PS domains
can then be used as a mask to etch the substrate 10.
[0091] The oxide lines 40 can then be used as a mask to etch line
openings 42 (e.g., trenches) in the substrate 10, as depicted in
FIGS. 10 and 10B, for example, using an anisotropic, selective
reactive ion etch (RIE) process.
[0092] Further processing can then be performed as desired. For
example, as depicted in FIGS. 11 and 11B, the residual oxide lines
40 can be removed, for example, using a fluoride-based etchant, and
the substrate openings 42 can be filled with a material 44 such as
a metal or metal alloy such as Cu, Al, W, Si, and Ti.sub.3 N.sub.4,
among others, to form arrays of conductive lines, or with an
insulating material such as SiO.sub.2, Al.sub.2O.sub.3, HfO.sub.2,
ZrO.sub.2, SrTiO.sub.3, and the like.
[0093] Referring now to FIG. 12, in another embodiment of the
invention, an atmosphere 46' can be applied to form an air
interface at the surface 28' of the block copolymer material 26' in
the trenches that is preferentially wetting to one of the blocks of
the copolymer material 26'.
[0094] In some embodiments, a preferentially wetting atmosphere can
be composed of clean, dry air to preferentially wet the polymer
block having the lower surface tension. For example, in the use of
PS-b-PVP and PS-b-PEO, the PS block has a relatively lower surface
tension and will preferentially wet a clean dry air atmosphere. In
the use of PS-b-PDMS, the PDMS block has a lower surface tension
and will preferentially wet a clean dry air atmosphere. In other
embodiments, a humid atmosphere (air) can be applied to
preferentially wet PEO over PS (e.g., using PS-b-PEO), or a
near-saturated solvent atmosphere (e.g., ethanol, dimethylformamide
(DMF), and the like) can be applied as a vapor phase to
preferentially wet PVP over the PS block (e.g., using
PS-b-PVP).
[0095] An anneal of the block copolymer material 26' in the
presence of the preferentially wetting atmosphere 46' can then be
conducted such that the polymer blocks phase separate in response
to the preferential and neutral wetting of the trench surfaces and
the preferential wetting of the overlying atmosphere 46' at the
air-interface to form a self-assembled polymer material 32' as
illustrated in FIGS. 13-13B. In response to the constraints
provided by the width (w.sub.t) of the trenches 16', 16a', a floor
24' that is neutral wetting to both polymer blocks, and sidewalls
20' and an air interface that are preferential wetting to the
minority block, a cylinder-phase block copolymer composition (e.g.,
70:30 PS-b-PVP (inherent pitch L) will self-assemble such that the
minority (preferred) block (e.g., PVP) will form parallel-oriented,
downward-facing, half-cylinder domains 36' on the neutral wetting
material 12' on the trench floors surrounded by an overlying matrix
38' of the majority polymer block (e.g., PS). In addition, the
minority (preferred) block (e.g., PVP) will segregate to and wet
the sidewalls 20' and ends 22' of the trenches 16', 16a' and the
air interface (e.g., using a near-saturated solvent atmosphere),
which are preferential wetting to the minority block, to form an
thin interface or wetting layer 36a' (on the sidewalls) and
36a'.sub.s (at the air interface) (e.g., at a thickness of about
0.25 times L). As another example, in the use of a
cylindrical-phase PS-b-PDMS, PDMS half-cylinders 36' would assemble
on the neutral wetting material 12' within an overlying PS matrix
38', and PDMS would form a brush layer 26a' on the trench sidewalls
20' and ends 22' and a brush layer 26a.sub.s' at the interface with
a clean, dry air atmosphere that would preferentially wet PDMS.
[0096] Following the anneal, the polymer material 32' can be
optionally crosslinked as previously described. In some
embodiments, the surface wetting layer 36a'.sub.s at the air
interface (e.g., the minority block, PVP) can be selectively
removed to expose the underlying matrix 38', e.g., by an RIE
process. The self-assembled polymer material can then be processed
as desired, for example, to form a masking material to etch the
underlying substrate 10'.
[0097] Embodiments of the invention provide methods of forming
structures of parallel lines that assemble via graphoepitaxy
rapidly and defect-free over large areas in wide trenches. The
structures formed from cylinder-forming block copolymers can be
produced considerably faster than for lamellar-forming block
copolymers, and have improved pattern transfer to an underlying
substrate when used as an etch mask compared to arrays of minority
block cylinders fully suspended in a majority block matrix due to
undercutting of the matrix underneath the cylinders during etching.
The methods also provide ordered and registered elements on a
nanometer scale that can be prepared more inexpensively than by
electron beam lithography, EUV photolithography or conventional
photolithography. The feature sizes produced and accessible by this
invention cannot be easily prepared by conventional
photolithography. The described methods and systems can be readily
employed and incorporated into existing semiconductor manufacturing
process flows and provide a low cost, high-throughput technique for
fabricating small structures.
[0098] Although specific embodiments have been illustrated and
described herein, it will be appreciated by those of ordinary skill
in the art that any arrangement calculated to achieve the same
purpose may be substituted for the specific embodiments shown. This
application is intended to cover any adaptations or variations that
operate according to the principles of the invention as described.
Therefore, it is intended that this invention be limited only by
the claims and the equivalents thereof. The disclosures of patents,
references and publications cited in the application are
incorporated by reference herein.
* * * * *