U.S. patent application number 14/636433 was filed with the patent office on 2015-06-18 for block co-polymer photoresist.
The applicant listed for this patent is Pixelligent Technologies, LLC. Invention is credited to Gregory D. COOPER, Brian L. WEHRENBERG.
Application Number | 20150168842 14/636433 |
Document ID | / |
Family ID | 48944938 |
Filed Date | 2015-06-18 |
United States Patent
Application |
20150168842 |
Kind Code |
A1 |
COOPER; Gregory D. ; et
al. |
June 18, 2015 |
BLOCK CO-POLYMER PHOTORESIST
Abstract
An integrated circuit is made by depositing a pinning layer on a
substrate. A block copolymer photoresist is formed on the pinning
layer. The block copolymer has two blocks A and B that do not
self-assemble under at least some annealing conditions. The exposed
block copolymer photoresist is processed to cleave at least some
block copolymer bonds in the exposed selected regions. The exposed
pinning layer is processed to create a chemical epitaxial pattern
to direct the local self assembly of the block copolymer.
Inventors: |
COOPER; Gregory D.; (Fulton,
MD) ; WEHRENBERG; Brian L.; (Baltimore, MD) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Pixelligent Technologies, LLC |
Baltimore |
MD |
US |
|
|
Family ID: |
48944938 |
Appl. No.: |
14/636433 |
Filed: |
March 3, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13764514 |
Feb 11, 2013 |
8993221 |
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14636433 |
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61597526 |
Feb 10, 2012 |
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61597544 |
Feb 10, 2012 |
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Current U.S.
Class: |
257/499 ;
430/319 |
Current CPC
Class: |
H01L 21/0274 20130101;
G03F 7/004 20130101; G03F 7/20 20130101; H01L 21/0271 20130101;
G03F 7/0002 20130101; H01L 21/82 20130101; B82Y 10/00 20130101;
H01L 29/06 20130101; B82Y 40/00 20130101; H01L 27/04 20130101; H01L
21/324 20130101; G03F 7/039 20130101; B81C 2201/0149 20130101; B81C
1/00031 20130101; G03F 7/38 20130101 |
International
Class: |
G03F 7/38 20060101
G03F007/38; H01L 27/04 20060101 H01L027/04; H01L 21/82 20060101
H01L021/82; H01L 21/324 20060101 H01L021/324; H01L 21/027 20060101
H01L021/027 |
Claims
1. A method of making an integrated circuit comprising: depositing
a pinning layer on a substrate; forming a block copolymer
photoresist on the pinning layer; wherein the block copolymer has
two blocks A and B that do not self-assemble under at least some
annealing conditions; exposing selected regions of the block
copolymer photoresist and the pinning layer; processing the exposed
block copolymer photoresist to cleave at least some block copolymer
bonds in the exposed selected regions; processing the expose
pinning layer to create a chemical epitaxial pattern to direct the
local self assembly of the block copolymer; processing further
includes changing A to A' such that A' and B self-assemble under
said at least some annealing conditions; annealing the wafer under
said at least some annealing conditions; developing the block
copolymer photoresist; and further processing said substrate to
make an integrated circuit.
2. An integrated circuit device made by a method including:
depositing a pinning layer on a substrate; forming a block
copolymer photoresist on the pinning layer; wherein the block
copolymer has two blocks A and B that do not self-assemble under at
least some annealing conditions; exposing selected regions of the
block copolymer photoresist and the pinning layer; processing the
exposed block copolymer photoresist to cleave at least some block
copolymer bonds in the exposed selected regions; processing the
expose pinning layer to create a chemical epitaxial pattern to
direct the local self assembly of the block copolymer; processing
further includes changing A to A' such that A' and B self-assemble
under said at least some annealing conditions; annealing the wafer
under said at least some annealing conditions; developing the block
copolymer photoresist; and further processing said substrate to
form integrated circuitry thereon.
3. A method of making an integrated circuit comprising: forming a
block copolymer photoresist on a substrate; wherein the block
copolymer has three blocks A, B, and C with block B in the middle
and A and C at the ends; wherein the block copolymer would self
assemble under a certain set of annealing condition with A and B in
one phase and C in the other phase; exposing selected regions of
the block copolymer photoresist; processing the exposed block
copolymer photoresist to cleave at least some block copolymer bonds
in the exposed selected regions; processing further includes
changing B to B' such that that the block copolymer would self
assemble under a certain set of annealing condition with A in one
phase and B and C in the other phase; developing the block
copolymer photoresist; and further processing said substrate to
make an integrated circuit.
4. An integrated circuit device made by a method including: forming
a block copolymer photoresist on a substrate; wherein the block
copolymer has three blocks A, B, and C with block B in the middle
and A and C at the ends; wherein the block copolymer would self
assemble under a certain set of annealing condition with A and B in
one phase and C in the other phase; exposing selected regions of
the block copolymer photoresist; processing the exposed block
copolymer photoresist to cleave at least some block copolymer bonds
in the exposed selected regions; processing further includes
changing B to B' such that that the block copolymer would self
assemble under a certain set of annealing condition with A in one
phase and B and C in the other phase; developing the block
copolymer photoresist; and further processing said substrate to
form integrated circuitry thereon.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The following are incorporated herein by reference: U.S.
patent application Ser. No. 13/764,514 filed Feb. 11, 2013, which
claims the benefit of U.S. Provisional Application Nos. 61/597,526
and 61/597,544 filed Feb. 10, 2012; U.S. patent application Ser.
No. 11/774,171 filed Jul. 6, 2001; which claims the benefit of U.S.
Provisional Application No. 60/806,877 filed Jul. 10, 2006, and
U.S. Provisional Application No. 60/870,795 filed Dec. 19, 2006;
application Ser. No. 13/189,143 filed Jul. 22, 2011; which is a
divisional application of U.S. patent application Ser. No.
12/415,013 filed Mar. 31, 2009; which is a divisional of U.S.
patent application Ser. No. 10/792,377 filed Mar. 4, 2004, now U.S.
Pat. No. 7,524,616 issued 28 Apr. 2009; which claims the benefit of
U.S. Provisional Application No. 60/451,240 filed Mar. 4, 2003.
FIELD
[0002] This patent application relates to advanced materials for
lithographic patterning, and more particularly to photoresist
materials for use in lithography, and more particularly to
photoresists which make use of the self-assembly of block copolymer
materials and to methods for using said materials to form patterns
on semiconductor substrates.
BACKGROUND AND SUMMARY
Photoresists in Lithography
[0003] Lithography, in general terms, is the process of printing or
transferring a pattern onto a surface. Optical lithography plays an
important role in the production of semiconductor devices, among
other things. In semiconductor lithography patterns of conductors
and insulators are written onto a semiconductor substrate. One
technologically important use of semiconductor lithography is in
the production of an integrated circuit (IC). In an IC, lithography
is typically used to write patterns of insulators, conductors,
doped regions, etc. onto a semiconductor substrate, usually a
silicon wafer. These patterns, once written, are then used to
control the electric fields and electric currents within the IC.
Advances in semiconductor lithography are important for the
industry since lithography often tends to be the technical limiter
for further advances in transistor size reduction.
[0004] A simplified view of a generic optical lithographic process
is as follows. Photoresist material is deposited onto the substrate
or an intermediate layer which is to be patterned by means of a
deposition process, such as, but not limited to spin casting,
drop-casting, or spray-casting. Photoresist (or resist), is a
polymeric material which undergoes a chemical reaction, or series
of chemical reactions, upon exposure to light. Then light from a
light source is passed through a photomask, which lies between the
light source and said substrate and serves to introduce a pattern
into the light, also known as the aerial image. The patterned light
impinges upon the photoresist layer where it exposes the resist.
There are a variety of methods for exposing the resist including,
but not limited to contact lithography, proximity lithography,
projection lithography and immersion lithography. Upon exposure,
the exposed area of the resist undergoes a chemical change,
creating what is known as a latent image in the resist. This light
induced chemical change usually leads, either directly or
indirectly, to a change in the solubility of the resist. The resist
is then developed, a step which translates the chemical changes in
the resist into a change in the coverage of the resist on the
substrate by removing selected areas of the resist. The physical
pattern in the resist is then transferred to the underlying
substrate by various means, including, but not limited to: etching
of the substrate, deposition of conductors or semiconductors, and
ion implantation. Methods of etching the substrate include, but are
not limited to: wet etch, plasma etch, and reactive ion etch (RIE).
In this manner a pattern can be transferred onto the semiconductor
substrate. In order to create more complex structures on the
semiconductor substrate, the light exposure and physical pattern
transfer steps (deposition/etch/ion implantation/etc.) may be
repeated a number of times, with the same or different light mask
patterns, with each subsequent pattern being aligned with the
previously transferred pattern on the wafer.
[0005] The light driven chemical reactions which occur in the
photoresist are most often utilized to selectively change the
solubility of the light exposed regions of the polymer, allowing
the selective removal during later processing. The ranges of the
electromagnetic spectrum from the light source which are used to
expose the resist in optical lithography, may be chosen from a wide
variety of ranges, including, but not limited to: visible light,
ultraviolet (UV) light, extreme ultraviolet (EUV) light, electron
beams, ion beams and x-rays. The light sources may be relatively
more monochromatic or polychromatic in nature. Also within these
different light ranges, a variety of wavelengths may be chosen.
Wavelengths for optical lithography include, but are not limited
to: 435 nm, 365 nm, 248 nm, 193 nm, and 157 nm. For the case of
positive resists, the resist become more soluble in developer upon
exposure, and thus the exposed areas may be selectively removed
during development. The opposite is true for negative resists,
where the resist becomes less soluble upon exposure. A wide variety
of different chemical mechanisms have been exploited for both
positive and negative. Two broad classes of resists are the
conventional resists and the chemically amplified resists. In both
classes of resist, the structure and etch resistance of the films
are provided by the polymeric resin.
[0006] In conventional resists, mainly exposed with 436 nm and 365
nm light, the absorption of light by a photoactive compound (PAC)
leads directly to a change in the solubility of the resist. Common
examples of conventional resists include the diazonaphthoquinone
(DNQ)/novolac family of resists. These positive resists are
composed of DNQ, a PAC, mixed with a novolac resin. DNQ inhibits
the dissolution of the novolac resin by the developer solution.
Upon absorption of a photon the DNQ is converted to a carboxylic
acid. The presence of the carboxylic acid acts to increase the
solubility of the resin in the developer, leading to the efficient
removal of the exposed areas of the resist during development.
[0007] In chemically amplified resists, by way of contrast with
conventional resists, the product of the photochemical reaction
does not appreciably change the solubility of the resist resin
directly. Instead, in a chemically amplified resist the light is
absorbed by a chemical species which as a result of the absorption
process generates another active chemical species which then in
turn can catalyze reactions in the resin to change the resin's
solubility. One group of such photochemical generators, which are
widely utilized in chemically amplified resists are photoacid
generators (PAGs). As a result of the absorption of a photon the
PAG generates an acid. During a post exposure bake (PEB), the resin
then undergoes thermally induced reactions catalyzed by the
photogenerated acid, resulting in a change in solubility for the
resist. One non-limiting example of a thermally induced reaction
which may take place in a positive tone chemically amplified
resist, is the acid catalyzed deblocking of the resin. The
deblocked resin can be much more soluble in the developer solution
and thus be removed. A non-limiting example of a thermally induced
reaction which may be exploited for a negative tone resist, is the
acid catalyzed activation of a cross linking agent. The
cross-linked, and thus effectively higher molecular weight resin,
may be significantly less soluble in the developer solution and
thus selectively remain behind during the development stage. In
addition to photoacid generators, there are also other
photochemical generators, such as photobase generators and
photoradical generators, which generate bases and radicals
respectively upon the absorption of light, which may be utilized in
chemically amplified resists. Recently there has been exploration
of negative tone development. In negative tone development, a
traditional chemically amplified resist, which are currently being
used in leading edge lithography production as positive resists, is
used but the developer is replaced with an organic solvent that
dissolves the blocked portion of the resin.
[0008] The smallest feature size that can be printed by an optical
lithography system, also referred to as the resolution of the
system, is determined by two main factors. These are the smallest
image features that can be projected onto the substrate and the
ability of the photoresist to resolve the image and translate that
image into a latent chemical image. The first factor is mainly
determined by the feature size of the mask, the wavelength of light
used to create the aerial image and the numerical aperture, in the
case of projection optical lithography. The resolving power of the
photoresist depends on the type of resist, i.e. conventional or
chemically amplified, and the specifics of the resist. In
chemically amplified resists there is a relationship between the
resolution, line-edge roughness, and sensitivity of the
photoresist, known as the RLS triangle. In simple terms it states
that only two of the three properties can be optimized in the
formulation of the resist. For example, a high resolution resist
which can produce features with low line-edge roughness, will,
according to this relationship suffer from low sensitivity. The
ability to produce a photoresist which can combine all three
desirable properties may enable new technologies.
Block Copolymers
[0009] Polymers are macromolecules which are composed of smaller
repeating structural units, often referred to as monomers,
chemically bound to each other. Homopolymers are polymers in which
the constituent monomers are chemically identical. Copolymers are a
class of polymers which are composed of at least two different
monomeric species. Block copolymers are copolymers in which the
different monomeric species are segregated into homopolymer
subunits or blocks which are covalently bonded to each other. At
the juncture of the homopolymer blocks there may also be an
intermediate subunit added for the sake of chemical compatibility.
In conceptual terms then, a block copolymer can be thought of as
two or more discrete homopolymers linked covalently end to end.
Block copolymers composed of two and three homopolymer blocks are
known as diblock copolymers and triblock copolymers, respectively.
Block copolymers with even more blocks are also known.
[0010] The different blocks, may have properties which make it
energetically unfavorable for them to mix with each other at a
molecular scale, thus resulting in the phase separation of the
different blocks. One example may be the case of amphiphilic block
copolymers, where one block is lipophilic and the other block is
hydrophilic. The resulting copolymer chain therefore is a single
molecule which will mix with other copolymer chains in a way to
create a polymeric material which can have chemically distinct
periodic domains created by the phase separation of the different
polymeric blocks. Bulk or macroscopic phase separation cannot
result because the blocks are bound to each other in a single
polymer chain. The result is that the blocks within the block
copolymer self-assemble into repeating patterns (or arrays) of
small domains.
[0011] The domains created by the phase separation of the block
copolymers can be made to have a variety of sizes and shapes and
geometries depending upon several factors but mostly due to the
relative lengths of the homopolymer blocks. The sizes of the block
copolymer domains may vary a good deal depending upon the exact
makeup of the copolymer, but sizes usually vary in the range of 5
to 50 nm. The natural period of the block copolymer is often used
when describing the size of the domains in the block copolymer. The
natural period, L.sub.0, is the defined as twice the length of the
block copolymer in its ordered state (H. Kim, W. D. Hinsberg, J.
Vac. Sci. Technol. A 22(6), 2008, 1369). For the case of an ideal
diblock copolymer the geometry or morphology of the resulting
domains changes as a function of the relative chain lengths of the
homopolymer blocks and thus by extension the volume fraction of a
given block. For example, for a diblock copolymer with a low volume
fraction of one block, the minority blocks form spherical domains
arrayed within the bulk of the majority polymer. At higher
fractional volumes of one block, the minority blocks form
cylindrical domains which are arrayed in a hexagonal fashion within
the bulk of the majority polymeric block. For an ideal diblock
copolymer where the relative amount of one block is about the same
as the other domain, the two blocks create parallel lamellar
domains.
[0012] The thickness of a block copolymer film can also strongly
influence the phase separated block domain structure or morphology.
This is mainly due to the way in which changing the thickness of
the film changes the relative important of the interactions of the
copolymer at the block copolymer/air and block copolymer/substrate
interface. For films thinner than the natural period of the block
copolymer, L.sub.0, the formation of equilibrium type domains may
be frustrated by the increased importance of the block copolymer
interfaces. This usually results in the formation of complex
morphologies. For the formation of patterns which are more
typically of interest to lithography, the desired film thickness is
on the order of the natural period of the block copolymer, L.sub.0.
In this range the effect of the interfaces usually has more
influences over the long range ordering or directionality of the
domains rather than the shape of the domains. The domain shapes and
sizes for films in this thickness range are typically closer to
those for bulk block copolymers where the effects of the interfaces
are minimized.
[0013] Deposition of block copolymer films can be performed by a
variety of methods, including, but not limited to drop-casting,
spin-casting, dip-coating, or spray-casting. After being deposited,
the block copolymers are usually not in an equilibrium or
near-equilibrium state, i.e. they have not formed the morphology of
the phase separated domains which would minimize the energy of the
film. An anneal step, or series of annealing steps, are then used
to drive the morphology in the direction of equilibrium or near
equilibrium structures and create a film with the desired
self-assembled domains made up of the blocks of the copolymer.
These thermal annealing step usually raise the temperature of the
block copolymers above the glass transition temperatures of the
constituent blocks.
Lithographic Patterning with Block Copolymers
[0014] For years the ability of block copolymers to create patterns
on the nanoscale has been well known. There have already been
examples of copolymer thin films being used for in the creation of
etching masks for the transference of patterns to a substrate as
well as further promise of creating patterns where the domain sizes
are in the range of interest for current and future lithographic
features. Early work demonstrating the use of the phase separated
domains in block copolymers to pattern a substrate date back to
over 20 years. Thin films of block copolymers may be formed on a
substrate and various processing methods, such as selectively
etching one block of the copolymer, may then be used to transfer
the pattern to the substrate. The resulting patterns may be smaller
than what can be easily achieved by purely optical methods. The
patterning of block copolymers can potentially supplement optical
lithography in making certain patterns with feature sizes that are
comparable to or smaller than what is achievable with more
conventional means and often in a simpler or cheaper manner.
[0015] While the range of domain geometries fall loosely within the
three listed above (lamellar, cylindrical, and spherical) these
geometries can be used to create at least two important
lithographic patterns. For example, thin films of block copolymers
with spherical domains or cylindrical domains orientated
perpendicular to the substrate may be used to make via or point
contact patterns. In a similar fashion, both lamellar and
cylindrical domains orientated parallel to the substrate may be
used to create line-space patterns.
[0016] Since the size of the pattern features given by block
copolymer domains and their sharpness directly relate to the size
and chemistry of the blocks which make up the copolymer, the
control of the dimensions of the repeating domains and their short
range ordering can be quite robust. However, the use of block
copolymers to generate lithographic patterns can often be limited
by a relative lack of longer range order. Long range order is
defined as length scales of several natural periods of the block
copolymer, compared to localized or short range order, which would
be in the range of one to two natural periods. For example, if a
line-space pattern with equal-lined, equal-spaced distances is
desired, a block copolymer may be composed and spin cast onto a
substrate in such a way as to create a lamellar structure with
lines and spaces determined by the respective and absolute sizes of
the various blocks, among other factors. The pattern created by the
block copolymer may have very good short term order, i.e. the
dimension of the domains which will make up the spaces and the
lines may be as desired and the lines and spaces may be parallel,
but simply drop casting the film of block copolymers may not create
long range order, i.e. with all the lines and spaces running
straight from one end of the substrate to the other and oriented in
the correct manner.
[0017] There are many ways to maximize, or at least to increase,
the long range order of the block copolymers, including, but not
limited to: increased film annealing times in the presence of
solvent vapor, directional solvent vapor evaporation techniques,
the introduction of shear forces, the use of a temperature
gradient, and directed self-assembly. From a lithographic
standpoint, the most useful methods for introducing more long range
control over the alignment and orientation of the domains within
the block copolymer are the methods of directed self-assembly. In
these methods the long range order is transferred to the block
copolymer from patterns previously written into the substrate. The
use of these methods may often require the use of complementary
lithographic techniques. Two of these methods to help introduce
long term order into patterns of are known as chemical epitaxy and
graphoepitaxy. In both of these methods, the substrate or a thin
film deposited on the substrate has a background pattern already
written into it. The features of this pattern are usually larger
than the desired feature size for the block copolymer and the main
purpose is to create a long term ordering which the self-assembled
pattern of the blocks of the copolymer can build upon. One example
of this might be to use optical lithography to create a line and
space pattern in a resist, hardmask, or substrate, with a
relatively large feature size and then use the self-assembly of the
block copolymers to perform a pitch division. Deposition of the
block copolymer, previously optimized to create a lamellar type
geometry, onto the coarsely patterned surface may then, with the
aid of further processing, write finer lines and spaces aligned
within these coarse features. In this example the coarse features
written by the optical lithography would define the directionality
and alignment of the finer domain features. In graphoepitaxy the
chemistry of the walls and floors of the spaces can strongly effect
the ordering of the phase separated block domains. For example, if
features that are perpendicular to the substrate are desired, often
the case for efficient pattern transfer of both lamellar and column
type features, the "floor" of the space (substrate, hardmask,
underlayer, etc.) should be neutral with respect to wetting by the
two blocks of the block copolymer. If instead one block
preferentially wets the surface, the pattern will tend to have
components which may vary with the depth of the feature, which is
significantly less desirable. The chemistry of the walls of the
space can also play an important role in the final morphology and
long range ordering of the block copolymer film.
[0018] For the case of chemical epitaxy, chemical differentiation
on a flat surface is used to direct the self-assembly process,
inducing long range order. These sparse patterns of chemical
differentiation can be written by various techniques involving a
variety of lithographic technologies, including optical and e-beam
lithography. The chemistry which interacts with the blocks of the
copolymer and directs the self-assembly are usually of a pinning or
preferential wetting type. Features written with chemical
differentiation potentially have better resolution (smaller
line-edge roughness, etc.) than graphoepitaxy, but it is usually
harder to write these chemical patterns.
Cleavable Block Copolymers
[0019] Recently there has been an interest in the development of
cleavable block copolymer for a variety of uses including drug
delivery and the production of nanoporous surfaces. Cleavable block
copolymers are copolymers which can undergo a reaction to break the
linkage between two of the blocks of the copolymer. This is usually
achieved by placing a reactive chemical unit or linker between the
neighboring blocks of a block copolymer. Under exposure to a
specific stimulus the linker undergoes a chemical reaction, the end
result of which being the breaking of the chemical bonds within the
linker or between the linker unit and one or both of the blocks of
the copolymer to which it is attached. Thus the block copolymer can
be split into two separate segments along the juncture of two
blocks. In the case of a block copolymer, the result would be to
break the copolymer into two separate segments each containing only
the one block and possibly fragments of the linker molecule.
Several different linker groups with a variety of driving stimuli
(photons, acid exposure, etc.) have been developed to this end. A
non-exhaustive list of examples of photocleavable block copolymers
(block copolymers which can be cleaved by exposure to light)
include: block copolymers in which the linker is an
ortho-nitrobenzyl group {Synthesis of Photocleavable
Poly(styrene-block-ethylene oxide) and its Self-Assembly into
Nanoporous Thin Films} or an anthracene photodimer {J. T. Goldbach,
K. A. Lavery, J. Penelle, T. P. Russell Macromolecules 2004, 37,
9639.}, both of which can be cleaved by exposure to UV light. There
are also examples of block copolymers which can be cleaved by
exposure to an acid. Examples of this include block copolymers with
a triphenylmethyl (trityl) ether linkage {M. Zhang, L. yang, S.
Yurt, M. J. Misner, J. Chen, E. B. Coughlin, D. Venkataraman, T. P.
Russell, "Highly Ordered Nanopourous Thing Films from Cleavable
Polystyrene-block-pol(ethylene oxide)" Adv. Mater. 2007, 19,
1571.}, a tert-butyl carbamate linker {M. A. DeWit, E. R. Gillies,
"A cascade Biodegradable Polymer Based on Alternating Cyclization
and Elimination Reactions" J. Am. Chem. Soc. 2009, 131, 18327.}, a
diphenyl methyl ether linkage {S. K. Varshney, J. Zhang, J. Ahmend,
Z. Song, V. Klep, I. Luzinov, "Synthesis of
poly(styrene-block-ethylene oxide) copolymers by anionic
polymerization and acid cleavage into its constituent homopolymers
for the formation of ordered nanoporous thing films" e-Polymers
2008, 94.}
SUMMARY
[0020] Herein we describe a new photoresist, which we shall refer
to as a block copolymer photoresist (BCP) which combines some of
the patterning attributes and capabilities of a directed
self-assembled block copolymer with a conventional photoresist.
Herein we also describe several methods for patterning with this
advanced resist and methods for making integrated circuits and
small features. In a conventional photoresist the location, size,
and line edge roughness of the features are defined (at least in
significant part) by the pattern of the actinic radiation. This can
limit the resolution of the final features to be written as well as
increasing the complexity of the exposure and subsequent processing
steps necessary for writing certain patterns lithographically. In a
BCP the size, shape, and line edge roughness of the features to be
written are determined by the block copolymer. This may allow the
lithographic performance of BCPs to break free from the RLS
triangle. The exact location of the feature(s) to be written
depends on a combination of the directed self-assembly of the block
copolymer and the patterning of the actinic radiation used to
expose the photoresist. The block copolymer photoresist will be
designed to lay out a pattern of phase separated domains onto the
substrate after deposition and annealing. There are a variety of
different domain morphologies for the block copolymer photoresists
that may be desirable, including, but not limited to, lamellar
domain morphologies for the creation of line and space patterns on
the substrate and columnar block morphologies set perpendicular to
the substrate for the creation of contact hole patterns. The
location of these phase separated domains on the substrate may be
directed by a variety of means including, but not limited to
graphoepitaxy and chemical epitaxy. Actinic radiation will then be
used to expose chosen domains of the block copolymer. This
selective exposure to actinic radiation will cause a chemical
reaction or series of chemical reactions which will ultimately
allow for the selective removal of chosen domains of the block
copolymer upon further processing. BCPs may be used with
conventional optical lithography, (including exposure at the g, h,
i lines or 248 nm, 193 nm, 157 nm), EUV lithography, or charged
particle lithography.
[0021] As an illustrative non-limiting example, the use of BCPs may
allow for a lithography process to create small dense features with
low line edge roughness at relatively low doses compared to a
conventional resist. BCPs may also be designed to be more absorbing
than a conventional resist. In current photoresists, the resist
must be transparent enough to the exposure radiation to ensure that
the exposure dose for the top of the resist is similar to the
exposure dose at the bottom of the resist. This will help ensure
the sidewalls of the features are approximately perpendicular to
the substrate. This constraint may be relaxed for BCPs. This is due
to the fact that the geometry of the sidewalls will be determined
by the interface between the block domains of the block copolymer
and not by exposure. A more absorbing resist may be advantageous
since it can make more efficient use of the exposing actinic
radiation. For example the BCP could absorb more than 99%, 98%,
97%, 96%, 95%, 90%, 85%, 80%, 75%, 70%, 65%, 60%, 55%, 50%, 45%,
40%, 35%, 30%, or 25% of the incident light.
[0022] As an illustrative non-limiting example, BCPs may also take
advantage of more chemical amplification than a conventional
resist. While chemical amplification increases the sensitivity of
the resist, in a traditional resist it reduces resolution and line
edge roughness. In a BCP an acid could catalyze more than 100, 200,
300, 400, 500, 750, 1000, 1500, 2000, 2500, 4000, or 5000 chemical
reactions
[0023] As an illustrative non-limiting example, BCPs may be
utilized in both single and multiple exposure patterning and may be
used alone as a patterning layer or as part of a multilayer stack.
The block copolymer photoresist may also be used with functional
topcoats, such as contrast enhanment layers, which may allow for
the printing of even smaller, denser patterns than without the
enhancement layer. Also BCPs with non-linear absorption processes
to drive the selective removal of part of the block copolymer
photoresist may also increase the performance of this
technology.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 A Scheme for use of positive tone BCP.
[0025] FIG. 2 A Scheme for use of negative tone BCP.
[0026] FIG. 3 A double exposure scheme for use of positive tone
BCP.
[0027] FIG. 4 A block flow diagram showing the use of BCP for
patterning a substrate.
[0028] FIG. 5 A Scheme for use of a pinning layer with a locally
self assembling BCP.
DETAILED DESCRIPTION OF PRESENTLY PREFERRED EXAMPLE ILLUSTRATIVE
NON-LIMITING EMBODIMENTS
Materials
[0029] One preferred exemplary illustrative non-limiting embodiment
provides for a block copolymer photoresist that is a cleavable
block copolymer, which can undergo self-assembly to create a
pattern of phase separated domains on a substrate. The
self-assembly process may be directed by graphoepitaxy or chemical
epitaxy. The linker group, at which the cleavage of the block
copolymer will take place may be a variety of chemical units
including, but not limited to: an ortho-nitrobenzyl group,an
anthracene photodimer, triphenylmethyl (trityl) ether group, a
tert-butyl carbamate group, a diphenyl methyl ether group, or any
other groups that may be used to link two blocks of a block
copolymer together and allow cleavage when exposed to various
stimuli, including but not limited to: exposure to acid, base, or
any other chemical agents as well as exposure to actinic radiation,
etc. This linker group may be a molecule or may be a polymeric or
oligomeric block itself, separating the blocks to be cleaved. There
may be one or possibly more linker groups in the block copolymer,
linking the different blocks to each other. The exact mechanism(s)
used for the cleavage of the block copolymer may vary, but the
cleavage will be initiated by exposure to actinic radiation. Some
non-limiting examples include: the direct cleavage of bonds after
the absorption of a photon by the linker group or bond breakage as
the result of exposure to an acid generated by a photoacid
generator (PAG). It is important to note that for these cleavable
block copolymer types of resists in this exemplary non-limiting
embodiment, the solubility altering reactions may take place at the
interface domain interfaces, where the reactive inter-block linker
groups are located as opposed to traditional resists where the
solubility altering reactions take place in the bulk of the
material. Therefore in a BCP, it is at this interface where the
absorption of the photon must happen, in the case of a photo-driven
process, or to which the acid or other reacting molecule must
travel in order to promote cleavage. After the exposure of the BCP
and subsequent cleavage reactions the original block copolymer
resin may now exist in one of three chemically distinct forms: the
intact original block copolymer, one segment of the block copolymer
which contains at least one whole block of the original block
copolymer, a second segment of the block copolymer which contains
at least one whole block of the original block copolymer. The
solubility of each of the two segments of the block copolymer may
now be determined by the chemistry of the segment itself rather
than the whole block copolymer. The blocks of the copolymer may be
designed so that upon cleavage, at least one of the polymeric
segments will be soluble in developer, while at least one of the
polymeric segments will be insoluble in developer. This may allow
for the selective removal of certain domains of the block copolymer
as the result of exposure to actinic radiation. The remaining
domains of the block copolymer can then be used to transfer the
pattern to an underlying substrate by a variety of means including,
but not limited to: etching, deposition, or ion implantation.
[0030] One preferred exemplary illustrative non-limiting embodiment
provides for a positive tone BCP. The main constituent of the BCP
is a block copolymer that is not soluble in the developer and when
cleaved, one fragment is soluble and the other fragment is
insoluble in the developer. The self-assembly of the BCP may be
directed by graphoepitaxy or chemical epitaxy. FIG. 1 illustrates a
generic patterning scheme using a positive tone BCP made from a
cleavable diblock copolymer followed by reactive ion etching. 1A
shows the periodic pattern of the BCP created by self-assembly of
the film on the substrate. The dark and light shadings of the film
on the substrate reflect the different chemistries of the blocks
which make up the phase separated domains of the self-assembled
block copolymer. In this illustration the phase separated blocks in
the BCP have a lamellar-type domain morphology after annealing.
Selective exposure of the BCP to actinic radiation is then shown in
1B followed by the development of the BCP in FIG. 1C and
transferring of the BCP pattern in 1D by means of etching. The
selective exposure areas are indicated by the arrows in FIG. 1B.
Also shown above the blocks in 1B is the spatial intensity
distribution of the exposure light, for this case it is illustrated
as a diffraction limited pattern. The pattern of exposure needs to
correspond only loosely to the desired final pattern, since the
final shape of the feature sidewalls will reflect the location of
the chemical transition between the block domains, rather than just
the dosing location. In the figure light is shown impinging the
domains immediately next to the domain desired, but having no
effect on the final image quality. In this positive tone BCP, the
blocks in which the domain interfaces directly surrounding it have
undergone cleavage, either by direct illumination or by reaction
with the photo-created reagents, such as photogenerated acid, will
have solubility that is directed by the block or block segments
within that now segmented domain, while the intact (uncleaved)
block copolymers will retain their insolubility in the developer
solution. Therefore the segments and blocks which are soluble will
be selectively removed during the development step(s). The pattern
of the remaining BCP can then be transferred to the substrate below
by further processing and pattern transfer steps, including, but
not limited to: etching, ion implantation, and deposition.
[0031] Another preferred exemplary illustrative non-limiting
embodiment provides for a negative tone BCP. In a negative tone
BCP, the block copolymer itself is soluble in the developer and
upon cleavage one fragment is soluble, while the other fragment is
insoluble. The self-assembly of the negative tone BCP may be
directed by graphoepitaxy or chemical epitaxy. Negative tone BCPs
may allow for the creation of patterns not available to positive
tone BCPs or the use of negative tone BCPs may make it simpler to
fabricate these features. An example of a generic negative tone BCP
is shown in FIG. 2. In negative tone BCPs, the constituents resins
in the domains filled with block copolymer segments which have
undergone cleavage reactions, either by direct illumination or by
reaction with the photo-created reagents, such as photogenerated
acid, will have solubility that is controlled by the block or block
segments within that cleaved domain, while the intact (uncleaved)
block copolymers will retain their solubility in the developer
solution. Therefore both the intact block copolymers and the
selectively segmented blocks which are now soluble will be
selectively removed during the development step(s). The pattern of
the remaining BCP can then be transferred to the substrate below by
further processing and pattern transfer steps, including, but not
limited to: etching, ion implantation, and deposition.
[0032] Another preferred exemplary illustrative non-limiting
embodiment is a positive tone BCP, where the block copolymer used
as the main component of the resist in addition to being cleavable
may also undergo chemistry changes as a direct or indirect
consequence to the exposure to actinic radiation which may change
the solubility of one or both of the cleaved segments. These blocks
may be designed to exploit mechanisms currently in use for
conventional or chemically amplified photoresists to change
solubility, including, but not limited to chain scission,
deblocking of functional groups, and crosslinking of the polymeric
chains. In the case of chemically amplified photoresists PAG may be
included in the block copolymer dispersion as it is deposited or it
may be bound to the block copolymer itself. The change in
solubility of one or more of the cleaved blocks of the block
copolymer may allow for easier selective removal of the desired
blocks during the development of the resist due to the increased
dispersibility contrast between the blocks. This may improve the
functionality or performance of the simple cleavage resists
described above in a variety of ways. For example, it may be
desirable for the areas just adjacent to the domains to be removed
to become cross-linked by the exposure, in order to limit any
defects or line edge roughness that may otherwise be formed during
the removal of the cleaved polymer sections during development.
Another useful example may be the inclusion of chemistry within the
area to be removed by subsequent development which would make it
even more dispersible in the developer solution, say by chain
scission reactions or deblocking of functional groups which would
make it soluble in the developer.
[0033] Another preferred exemplary illustrative embodiment is a
negative tone BCP, where the block copolymer used as the main
component of the resist in addition to being cleavable may also
undergo chemistry changes as a direct or indirect consequence to
the exposure to actinic radiation which may change the solubility
of one or both of the cleaved segments. These blocks may be
designed to exploit mechanisms currently in use for conventional or
chemically amplified photoresists to change solubility, including,
but not limited to chain scission, deblocking of functional groups,
and crosslinking of the polymeric chains. In the case of chemically
amplified photoresists PAG may be included in the block copolymer
dispersion as it is deposited or it may be bound to the block
copolymer itself The change in solubility of one or more of the
cleaved blocks of the block copolymer may allow for easier
selective removal of the desired blocks during the development of
the resist due to the increased dispersibility contrast between the
blocks. This may improve the functionality or performance of the
simple cleavage resists described above in various ways. As a
non-limiting example, for the case of a negative BCP, it may be
desirable in this case to have the fragments which have been
exposed and are desired to stay on the substrate made even more
insoluble in the resist upon exposure, say by a mechanism such as
cross-linking. During development this may result in more of the
block domain which is desired to not be removed, to be left intact,
thus increasing the fidelity of the pattern.
[0034] Another preferred exemplary illustrative non-limiting
embodiment is for a BCP, which is not composed of a cleavable block
copolymer, but instead is composed of a block copolymer in which
one or more blocks of the copolymer are removed by other methods as
a result of exposure to actinic radiation. The self-assembly of
this type of BCP may be directed by graphoepitaxy or chemical
epitaxy. One non-limiting example of this, is having a block or
blocks which undergo chain scission or some other kind of
degradation due either to direct exposure to light or as a result
of exposure to a reagent generated by exposure of the BCP to
actinic radiation, such as photoacid generated by PAG. PMMA is one
non-limiting example of a block which can form block domains as
part of a block copolymer and can be directly decomposed by
exposure to deep ultraviolet radiation and can subsequently be
removed by further processing, i.e. washing with acetic acid. {T.
Thurn-Albrecht, J. Schotter, G. A. Kastle, N. Embley, T. Shibauchi,
L. Krustin-Elbaum, K. Guarini, C. T. Black, M. T. Tuominen, T. P.
Russell "Ultrahigh-Density Nanowire Arrays Grown in Self-Assembled
Diblock Copolymer Templates" Science 2000, 290, 2126.}
[0035] Another preferred exemplary illustrative non-limiting
embodiment is for a block copolymer photoresist in which the
chemistries of the constituent blocks are designed to allow for
selectivity in the mobility of photogenerated chemical species in
the deposited film of the BCP. These photogenerated chemical
species may include, but are not limited to: photoacid generated by
the absorption of actinic radiation by a photoacid generator,
photobase generated by the absorption of actinic radiation by a
photobase generator, and photoradicals generated by the absorption
of actinic radiation by a photoradical generator. The chemistry of
the blocks may be such that the chemical species generated by a
photogenerator would have significantly enhanced mobility in the
areas where it is desired for the block copolymer to undergo the
reactions which are catalyzed by the photogenerated species. One
example would be the enhanced mobility of the photoacid in the
block domains composed of the blocks which are designed to be
soluble upon scission in a cleavable positive tone resist. The
enhanced mobility of the acid within these blocks when compared to
the other blocks would allow for a very sensitive resist, where
relatively low levels of light may be necessary to fully exposure
the domains or where PAG concentration can be enhanced without
having the generated acid move to other domains of the same type
due to the slowed mobility in the contrasting domains. This
enhanced mobility may be understood to apply to any chemical
species which are photogenerated and which either catalyze or act
as a reagent in chemical reactions which results in the cleavage of
the block copolymer or in other manners induce chemical changes
which ultimately result in the change in solubility of components
of the BCP.
[0036] Another exemplary non-limiting illustrative embodiment
provides for a BCP which is composed of more than one species of
block copolymer or a blend of block copolymers. One or more of the
block copolymers may be sensitive to actinic radiation and undergo
cleavage or changes in solubility as a result of the exposure. The
relative volume ratio(s) of the different block copolymers may take
on a wide variety of values depending on the final pattern
desired.
[0037] Another exemplary non-limiting illustrative embodiment
provides for a BCP which is composed of one or more homopolymers
added to the block copolymer or blend of block copolymers. One or
more of the block copolymers or homopolymers may be sensitive to
actinic radiation and undergo cleavage or changes in solubility as
a result of the exposure The relative amounts of the homopolymer(s)
to the block copolymer(s) may take on a variety of values.
[0038] Another exemplary non-limiting illustrative embodiment
provides for a BCP in which the self-assembled domains of the BCP
have been designed to have contrasting values for the index of
refraction. This may allow for light to be "focused" into the phase
separated domains with the higher value for the index of
refraction, effectively increasing the sensitivity of the
photoresist. It may prove beneficial to have the effectively
increased light doses due to this focusing in areas which may
contain the PAGs or the other photoactive compounds which absorb
the light which initiates the reactions which ultimately result in
the change in the solubility of selected domains of the block
copolymer photoresist. The methods employed to create the index of
refraction contrast between the domains may include, but are not
limited to, the use of blocks to make up a block copolymer which
natively have a relatively large difference in the index of
refraction and the selective inclusion of high index filler
materials into one or more of the domains of the BCP.
[0039] Another exemplary non-limiting illustrative embodiment
provides for a BCP in which the self-assembled domains of the BCP
have been designed to have contrasting values of light absorption
at the wavelength or range of wavelengths used for the exposure of
the BCP. This may allow for light to be "focused" into the phase
separated domains with the higher absorptivity, effectively
increasing the sensitivity of the photoresist. It may prove
beneficial to have the effectively increased light doses due to
this focusing in areas which may contain the PAGs or the other
photoactive compounds which absorb the light which initiates the
reactions which ultimately result in the change in the solubility
of selected domains of the block copolymer photoresist. The methods
employed to create the absorptivity contrast between the domains
may include, but are not limited to, the use of blocks to make up a
block copolymer which natively have relatively large differences in
absorptivity, the modification of blocks within the block copolymer
which add absorptivity to the blocks, and the selective inclusion
of highly absorbing compounds into one or more of the domains of
the BCP. In one exemplary non-limiting embodiment, the insensitive
area of the resist could be more absorbing than the sensitive area.
This would serve to help focus the light into the sensitive
area.
[0040] Another exemplary non-limiting illustrative embodiment
provides for a BCP in which the block copolymer that would not self
assemble until it was exposed to actinic light. The light would
initiate a change the chemical properties of one of the blocks such
that the block copolymer would then self assemble. The layer below
the block copolymer photoresist would be a pinning layer, that
would be chemically changed by the actinic radiation to pin one of
the phases. After the exposure of the pattern, the actinic light
would initiate chemical reactions in one phase of the block
copolymer to allow the block copolymer to locally self assemble.
The actinic light would also chemically change the pinning layer to
provide either a graphoepitaxial or preferably a chemical epitaxial
pattern to direct the local self assembly of the pattern. The
location of the pinning areas and the chemically altered block
copolymer would be self aligned but the pinning layer would serve
to prevent the block copolymer from moving around during subsequent
processing. Both the block copolymer and the pinning layer may be
designed to exploit mechanisms currently in use for conventional or
chemically amplified photoresists to either initiate a local self
assembly in the case of block copolymer or to initiate a chemical
epitaxy pattern in the case of the pinning layer. For example both
could use chemical amplification and or deblocking of functional
groups. After the exposure, the wafer could be processed to allow
completion of any chemical reaction initiated by the actinic light.
In the case of chemical amplification and deblocking this could be
a post exposure bake. Next the block copolymer would be annealed to
allow the local self assembly directed by the light pattern. This
step could occur simultaneously with the post exposure bake. If it
occurs after the post exposure base it may be necessary to
deactivate the photogenerated catalyst (e.g. photoacid, photobase,
or photoradical) to control the amount of chemical amplification.
This would allow arbitrary placement of features, they would not
need to be aligned to a pre-existing pattern and would not need to
be on a pre-determined pitch. The size of the feature would be
determined by the length of the block that undergoes chemical
changes and the space between the features would be determined by
the length of the other block. The edges would be determined by the
transition between the phases of the polymer. This would again
allow us to have significant improvements of the existing RLS
tradeoffs. This would also allow for different kinds of features in
the same layer. The block copolymer would need to be sufficiently
transparent to allow the light through to the pinning layer. Also
the pinning layer could use non-linear processes to initiate the
chemical epitaxy pattern. These non-linear processes would allow
the pinning layer to have smaller patterns that could be placed
closer together allowing for more precise placement of the desired
features. This process could be used with multiple exposures to
print features beyond the diffraction limit. The block copolymer
could also use non-linear processes to initiate the chemical change
to allow for self assembly.
[0041] Another exemplary non-limiting illustrative embodiment
provides for a tri Block Copolymer Photoresist (triBCP) with three
units A, B, and C. The B block would be in the middle of the
triBCP, with Blocks A and C on the end. Blocks A and B would be
chemically similar (for example A and B could have a low .chi.
(Flory-Huggins Interaction parameter)) while block C would be
chemically different (for example C could have a high .chi. with
both A and B). The triBCP would self assemble under a certain set
of annealing condition with A and B in one phase and C in the other
phase. Upon exposure to actinic light, block B would undergo a
chemical change to become B', which is chemically similar to block
C and not to block A (for example B' and C could have a low .chi.,
while B' and A could have a high .chi., and A and C could still
have a high .chi.). The actinic radiation could induce a change
from B to B' in a number of ways. B could have protection groups
and a photoacid could be used in a chemical amplification process
to de-protect B and change its chemical properties. The exposed
triBCP would self assemble under a certain set of annealing
conditions with A in one phase and B' and C in the other phase. The
exposure would change the relative volume of the two phase and
could result in either a change in feature size or a change the
structures that formed (for example a change from cylinders to
lamellae or vice versa). This change would be determined by the
relative volume of block B.
Methods
[0042] One preferred exemplary illustrative non-limiting embodiment
provides for a block copolymer photoresist which can be used alone
to transfer a pattern to the underlying substrate. The pattern to
be written to the substrate is a result of the combination of the
pattern of the block domains made after deposition and any
annealing or aligning steps that may be necessary and a pattern of
actinic radiation. The actinic radiation may act to "turn on" or
"turn off" certain domains are regions of domains in the block
copolymer pattern in order to create the pattern that is to be
written to the underlying substrate. The annealing and alignment
steps used to aid in the creation the pattern of block domains
within the block copolymer photoresist may include, but are not
limited to: external electric fields, temperature gradients,
solvent annealing, etc. {S. H. Kim, M. J. Misner, T. Xu, M. Kimur,
T. P Russell "Highly Oriented and ordered arrays from Block
Copolymers via Solvent Evaporation", Adv. Mater. 2004, 16(3), 226.}
As an example PS-b-PEO block copolymers, with a PS weight fraction
of 0.75, have been deposited as films and solvent-annealed in
benzene to produce a phase separated block morphology of
horizontally ordered arrayed cylinders of PEO in a PS matrix which
are oriented perpendicular to the substrate on which they are
grown. {S. H. Kim, M. J. Misner, T. Xu, M. Kimur, T. P Russell
"Highly Oriented and ordered arrays from Block Copolymers via
Solvent Evaporation", Adv. Mater. 2004, 16(3), 226.} Furthermore,
PS-b-PEO block copolymers with a photo-cleavable linkage
ortho-nitrobenxyl (ONB) group between the PS and PEO have been
synthesized and self-assembled into films. {Synthesis of
Photocleavable Poly(styrene-block-ethylene oxide) and its
Self-Assembly into Nanoporous Thin Films} A cleavable block
copolymer such as mentioned in the above reference would be
deposited onto a substrate, such as a silicon wafer, by a process
such as spin-casting. Subsequent solvent-annealing in the presence
of benzene solvent vapor, as prescribed in the above reference,
would create the desired morphology of the block copolymer domains,
namely PEO cylinders arrayed regularly in a PS matrix, with the PEO
cylinders oriented perpendicular to the substrate. Exposure to
patterned actinic radiation would then selectively cleave the block
copolymers which have linkers within the irradiation zone. Upon
exposure to developer, for example an aqueous solution of TMAH, the
PEO segments of the cleaved block copolymer would be removed,
leaving behind a pattern which may be used as a mask to transfer
the pattern to the underlying substrate by a variety of methods
including, but not limited to etching of ion implantation.
[0043] In another preferred exemplary illustrative embodiment, the
BCP may be utilized to print features beyond the diffraction limit
of the light used to create the aerial image. The block copolymer
photoresist is used to create a periodic pattern of phase separated
domains on the surface to be patterned. The morphologies of the
domains may take on a variety of shapes including but not limited
to: an array of spherical domains dispersed regularly in a matrix,
an array of column shaped domains arranged perpendicular or
parallel to the substrate, or a series of lamellar domains. The
location and alignment of the domains may be directed by either
graphoepitaxy or chemical epitaxy. The size and shape of the
features to be written onto the substrate are controlled by the by
the size and shape of phase-separated domains of the block
copolymer. The line edge roughness of the features depends on the
sharpness of the interface between the block domains. The aerial
image, which may be diffraction limited, serves only to choose
which of the phase-separated domains are transferred to the
substrate as features, by initiating reactions which ultimately
result in a pattern of phase separated domains which may be
selectively removed by development. The patterns of the remaining
domains of the block copolymer, which may contain features smaller
than allowed by the diffraction limit, may then be transferred to
the underlying layers or substrate by a variety of methods
including but not limited to: deposition, etching, and ion
implantation.
[0044] In another preferred exemplary illustrative embodiment, the
BCP may be used as a component in a multilayer stack. For example,
the BCP may be sandwiched between an underlying hardmask and/or
spin on carbon layers and conventional topcoat layers. The
underlayers may provide increased etch resistance for pattern
transfer to the substrate while the topcoat may provide
anti-reflective properties or may be utilized as a protecting layer
for the BCP, say during immersion lithography.
[0045] In another preferred exemplary illustrative embodiment, the
BCP may be used in conjunction with a topcoat which is block
copolymer. The block copolymer topcoat would be deposited onto the
BCP layer after the self-assembly of the BCP. The self-assembly of
the block copolymer topcoat may be directed by the pattern of the
BCP layer. The block copolymer topcoat may be designed to have
phase separated domains which have contrasting values for the index
of refraction. This may allow for light to be "focused" by the
topcoat domains with higher value for the index of refraction into
selective underlying domains in the BCP layer. It may prove
beneficial to have the effectively increased light doses due to
this focusing in areas of the BCP which may contain the PAGs or the
other photoactive compounds in the BCP layer.
[0046] In another preferred exemplary illustrative embodiment, the
BCP may be used in conjunction with a topcoat which is block
copolymer. The block copolymer topcoat would be deposited onto the
BCP layer after the self-assembly of the BCP. The self-assembly of
the block copolymer topcoat may be directed by the pattern of the
BCP layer. The block copolymer topcoat may be designed to have
phase separated domains which have contrasting absorptivity values
at the wavelength or in the wavelength range used for exposure of
the BCP. This may allow for further modification of the aerial
image before it reaches the BCP since light of the same intensity
that passes through topcoat domains with higher absorptivity will
have lower intensity once they reach the BCP layer with respect to
light that has passed through the topcoat domains with lower
absorptivity. This may allow for the printing of patterns which are
otherwise unobtainable or it may make the printing of these
features more easily accomplished than by other means. It may also
prove beneficial to have increased light doses in areas of the BCP
which may contain the PAGs or the other photoactive compounds in
the BCP layer as opposed to other regions of the BCP.
[0047] In one exemplary non-limiting embodiment, the block
copolymer resist could be coated with a functional topcoat. One
non-limiting potential functional topcoat could be a contrast
enhancement layer (CEL) or a reversible CEL (RCEL). A CEL or RCEL
topcoat may allow for the printing of features smaller than
possible without the contrast enhancement. As example, take the
case of a positive tone cleavable block copolymer photoresist.
Without a contrast enhancement layer, for good image transfer it is
important that only the interfaces directly surrounding the
phase-separated blocks to be removed be given a sufficient dose to
encourage significant bond cleavage, otherwise blocks other than
those desired may be at least partially removed during development.
The image contrast enhancement layer could help to print smaller
features by effectively cutting off the low intensity light at the
edges of the light pattern before the light can impinge the
resist.
[0048] In another preferred exemplary illustrative embodiment, the
use of non-linear absorption processes to drive the cleavage of the
block copolymer photoresist and also potentially the chemical
changes to the fragments of the block copolymer photoresist may
also increase the resolution of printable features. As non-limiting
examples, the cleavage may be driven by a non-linear optical
absorption process, where the reaction probability does not depend
linearly on the intensity of the light, but superlinearly, or where
the cleavage or deprotection of one of the blocks is driven by an
acid or base catalyzed reaction, the generation of the acid may be
driven in a nonlinear fashion as well. Similar to the case of the
BCP with a contrast enhancement layer, this would mean that low
intensity light at the edges of the spatial distribution would not
be sufficient to drive the reactions, in this case because of the
superlinear dependence on intensity rather than for the case of the
CEL where the low intensity light is absorbed before reaching the
BCP.
* * * * *