U.S. patent application number 13/586475 was filed with the patent office on 2012-12-06 for radiation sensitive self-assembled monolayers and uses thereof.
This patent application is currently assigned to International Business Machines Corporation. Invention is credited to Ali Afzali-Ardakani, Cherie R. Kagan, Laura L. Kosbar, Charan Srinivasan, Sally A. Swanson.
Application Number | 20120308933 13/586475 |
Document ID | / |
Family ID | 38788877 |
Filed Date | 2012-12-06 |
United States Patent
Application |
20120308933 |
Kind Code |
A1 |
Afzali-Ardakani; Ali ; et
al. |
December 6, 2012 |
RADIATION SENSITIVE SELF-ASSEMBLED MONOLAYERS AND USES THEREOF
Abstract
The invention is directed to a radiation sensitive compound
comprising a surface binding group proximate to one end of the
compound for attachment to a substrate, and a metal binding group
proximate to an opposite end of the compound. The metal binding
group is not radiation sensitive. The radiation sensitive compound
also includes a body portion disposed between the surface binding
group and the metal binding group, and a radiation sensitive group
positioned in the body portion or adjacent to the metal binding
group. The surface binding group is capable of attaching to a
substrate selected from a metal, a metal oxide, or a semiconductor
material.
Inventors: |
Afzali-Ardakani; Ali;
(Ossining, NY) ; Kagan; Cherie R.; (Ossining,
NY) ; Kosbar; Laura L.; (Mohegan Lake, NY) ;
Swanson; Sally A.; (San Jose, CA) ; Srinivasan;
Charan; (State College, PA) |
Assignee: |
International Business Machines
Corporation
Armonk
NY
|
Family ID: |
38788877 |
Appl. No.: |
13/586475 |
Filed: |
August 15, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12199607 |
Aug 27, 2008 |
8273886 |
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13586475 |
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11445326 |
Jun 2, 2006 |
7531293 |
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12199607 |
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Current U.S.
Class: |
430/296 ;
430/322; 430/323 |
Current CPC
Class: |
C23C 22/02 20130101;
G03F 7/165 20130101; B82Y 10/00 20130101; G03F 7/405 20130101 |
Class at
Publication: |
430/296 ;
430/322; 430/323 |
International
Class: |
G03F 7/20 20060101
G03F007/20 |
Goverment Interests
GOVERNMENT RIGHTS
[0002] The U.S. government may have rights in this invention due to
funding from the Defense Advanced Research Projects Agency (DARPA)
under Contract N66001-00-C-8083.
Claims
1. A lithographic process for patterning a substrate comprising:
providing a substrate and attaching a plurality of radiation
sensitive compounds to the substrate, wherein the radiation
sensitive compounds include a surface binding group for attachment
to the substrate and a metal binding group; exposing the surface
attached radiation sensitive compounds to UV or e-beam radiation;
and complexing the metal binding group of the radiation sensitive
compounds with a metal species selected from a metal cation, metal
compound, or metal or metal-oxide nanoparticle to form metallized
radiation sensitive compounds in a predetermined pattern on the
substrate.
2. The process of claim 1 further comprising attaching a connecting
ligand to the metallized radiation sensitive compounds followed by
complexing a second metal species to the connecting ligand.
3. The process of claim 1 further comprising transferring the
pattern to the underlying substrate by dry etching.
4. The process of claim 1 wherein the surface binding group is
capable of attaching to a substrate selected from a metal, a metal
oxide, or a semiconductor material.
5. The process of claim 1 wherein the radiation sensitive group is
adjacent to the metal binding group and is displaced from the metal
binding group upon exposure to said UV or e-beam radiation, thereby
activating the metal binding group to interact with a metal
species.
6. The process of claim 1 wherein the surface binding group is
selected from the group consisting of thiols, selenols,
isocyanides, chloro silanes, alkoxy silanes, phosphonic acids,
hydroxamic acids, aldehydes and carboxylic acids.
7. The process of claim 1 wherein the metal binding group is
selected from the group consisting of a nitrogen heterocycle,
phosphonic acids, sulfonic acids and isocyanides.
8. The process of claim 1 wherein the radiation sensitive group is
selected from the group consisting of nitrobenzyl, benzyl ether,
succinimidyl sulfonic acids, thiols and disulfides.
9. The process of claim 1 wherein the radiation sensitive compound
is represented by formula I SB-BP-MB-RS I wherein SB is a surface
binding group; BP is a body portion; MB is a metal binding group;
and RS is a radiation sensitive group, wherein the radiation
sensitive group is displaced from the metal binding group upon
exposure to UV or e-beam radiation, thereby activating the metal
binding group to interact with a metal species.
10. The process of claim 9 wherein the surface binding group is
selected from the group consisting of thiols, selenols,
isocyanides, chloro silanes, alkoxy silanes, phosphonic acids,
hydroxamic acids, aldehydes and carboxylic acids.
11. The process of claim 10 wherein the radiation sensitive group
is selected from the group consisting of nitrobenzyl, benzyl ether,
succinimidyl sulfonic acids, thiols and disulfides.
12. The process of claim 1 wherein the radiation sensitive compound
is represented by formula II SB-RSBP-MB II wherein SB is a surface
binding group; MB is a metal binding group; and RSBP is a body
portion that includes a radiation sensitive group that causes the
displacement of the metal binding group from the compound upon
exposure to UV or e-beam radiation, wherein the radiation sensitive
group in the body portion is not an amine.
13. The process of claim 12 wherein the surface binding group is
selected from the group consisting of thiols, selenols,
isocyanides, chloro silanes, alkoxy silanes, phosphonic acids,
hydroxamic acids, aldehydes and carboxylic acids.
14. The process of claim 13 wherein the radiation sensitive group
is selected from the group consisting of nitrobenzyl, benzyl ether,
succinimidyl sulfonic acids, thiols and disulfides.
15. The process of claim 1 wherein the radiation sensitive compound
is represented by formula I or formula II SB-BP-MB-RS I wherein in
formula I, SB is a surface binding group; BP is a body portion; MB
is a metal binding group; and RS is a radiation sensitive group,
wherein the radiation sensitive group is displaced from the metal
binding group upon exposure to UV or e-beam radiation, thereby
activating the metal binding group to interact with a metal
species; SB-RSBP-MB II wherein in formula II, SB is a surface
binding group; MB is a metal binding group; and RSBP is a body
portion that includes a radiation sensitive group that causes the
displacement of the metal binding group from the compound upon
exposure to UV or e-beam radiation, wherein the radiation sensitive
group in the body portion is not an amine; and wherein in formula I
and in formula II, the metal binding group is selected from the
group consisting of pyridine, dipyridine, terpyridine, phosphonic
acids, sulfonic acids and isocyanides.
16. The process of claim 1 wherein the radiation compound is
selected from the group consisting of the compounds represented by
the following formulae: ##STR00003##
17. The process of claim 15 wherein the surface binding group is
selected from the group consisting of thiols, selenols,
isocyanides, chloro silanes, alkoxy silanes, phosphonic acids,
hydroxamic acids, aldehydes and carboxylic acids.
18. The process of claim 17 wherein the radiation sensitive group
is selected from the group consisting of nitrobenzyl, benzyl ether,
succinimidyl sulfonic acids, thiols and disulfides.
19. The process of claim 15 wherein the radiation sensitive group
is selected from the group consisting of nitrobenzyl, benzyl ether,
succinimidyl sulfonic acids, thiols and disulfides.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of co-pending application
Ser. No. 12/199,607 filed on Aug. 27, 2008, which is a continuation
of co-pending application Ser. No. 11/445,326 filed on Jun. 2,
2006; the contents of all are hereby incorporation by
reference.
FIELD OF THE INVENTION
[0003] The invention relates to multi-functional compounds used to
form molecular assemblies and the use of the molecular assemblies
as thin-film resists in lithographic applications.
BACKGROUND OF THE INVENTION
[0004] The fabrication of small patterned features with a desired
functionality is important in a wide variety of fields and
applications. Improvements in lithographic techniques to decrease
image dimensions have allowed the microelectronics industry to
fabricate denser and faster microelectronics chips. Traditional
resist technology, however, is rapidly reaching the limits of
achievable dimension reductions. Consistent production of sub-60 nm
linewidths will require advances beyond the current approaches.
[0005] As the size of microelectronic devices shrink, it becomes
necessary to define ever smaller features--current manufacturing
lines produce sub 70 nm features. Resolving features in this size
range requires the use of 193 or 157 nm optical exposures, or
electron beam (e-beam) radiation and very thin resist films.
Traditional resist films contained phenolic resins that had a
moderate resistance to "dry" transfer methods such as reactive ion
etching (RIE). Due to the high absorbance of phenolic moieties at
wavelengths below 200 nm, resists for deep UV exposure must be
primarily aliphatic or cycloaliphatic. The aliphatic polymers used
as resist films in the deep UV regime are less etch resistant than
traditional phenolic resins. To achieve high resolution, the aspect
ratio of the resist thickness to the width of the features must be
kept comparable, so it may not be possible to increase the
thickness of the resist to compensate for its poorer etch
performance.
[0006] In addition, the use of high numerical aperture lenses to
increase the resolution of optical exposures is reducing the depth
of focus of the tools, which also pushes towards the use of very
thin resist films. Another problem that occurs when creating fine
lithographic features is collapse of resist lines. Even for
relatively thin resists (0.1-0.3 um) the wet development step often
causes line collapse due to surface tension effects of the aqueous
developers and rinses on features with high aspect ratios (Jung,
M-H, et al., Proceedings SPIE, Vol. 5039, 1298, 2003).
[0007] Line edge roughness is another significant concern in the
sub-100 nm feature regime. Traditional resists are composed of
polymer chains with "protected" side groups that can react with
acids. Photoacid generators produce acids when exposed to light,
which then diffuse in the film and catalyze the deprotection of the
polymer chain, allowing it to become soluble in the basic
developer. The roughness of lithographic features defined by this
process can be related to both the size of the polymer chains
dissolving out of the film and by the diffusion length of the
photoacids (Yoshimura, T., et al., Japan. J. Appl. Phys., Vol. 32,
6065, 1993). For features in the sub-100 nm regime, both of these
sources of line edge roughness are important.
[0008] Self-assembled monolayers (SAMs). It is well known that
organic molecules containing certain terminal head groups will self
assemble from solution to form monolayers on specific surfaces
(Ulman, A., An Introduction to Ultrathin Organic Films, Academic
Press, Chap. 3, 1991). The most common monolayers are formed from
organic thiols which attach to gold substrates, organic alkoxy or
chloro silanes which react with silicon dioxide, or phosphonic
acids, hydroxamic acids, or carboxylic acids which react with metal
oxides (Taylor, C. et al., Langmuir, Vol. 19, 2665, 2003). The
monolayers are stabilized by the chemisorption of the head group to
the surface and the formation of covalent bonds (in the case of
silanes or thiols) or ionic bonding (in the case of acids) of the
terminal head group with the surface, as well as intermolecular
interactions between the molecules such as van der Waals forces,
pi-pi interactions or hydrogen bonding.
[0009] Self-assembled monolayers are prepared by placing substrates
in a solution containing from 0.1 mM to about 1% of the molecules
forming the monolayer in a non-reactive, low boiling solvent. The
self-assembly process may take from a few minutes up to a day or
more to form complete, dense monolayers (Ulman, A., An Introduction
to Ultrathin Organic Films, Academic Press, Chap. 3, 1991).
[0010] There are various examples of monolayers with terminal tail
groups that can bind to metal ions or metal complexes, including
phosphonic acids which bind to Zr or Hf (Fang, M., et al., J. Am.
Chem. Soc., Vol. 119, 12184, 1997), pyridine which binds to metals
or metal complexes such as Rh complexes (Lin, C. et al., J. Am.
Chem. Soc., Vol. 125, 336, 2003) or Zr complexes (Hatzor, A. et
al., Langmuir, Vol. 16, 4420, 2000), or terpyridine which is
capable of binding to a variety of metal ions (Hofineier, H., et
al., Chem. Soc. Rev., Vol. 33, 373, 2004; Maskus, M., et al.,
Langmuir, Vol. 12, 4455, 1996) The metal/monolayer complexes will
self assemble in solution through the chelation of the metal
ions/complexes by the tail group of the monolayer.
[0011] The initial metal/monolayer complexes may in some cases be
extended into multilayer structures through the use of difunctional
"linking ligands", such as diphosphonic acids, dipyridines,
diisocyanides or diterpyridines. By sequential exposure to the
linking ligand and the metal species, layers may be built up on the
original monolayer/metal complex. Films with at least 30
ligand/metal bilayers have been assembled in this fashion (Lin, C.
et al., J. Am. Chem. Soc., Vol. 125, 336, 2003).
[0012] The concept of using monolayers as ultrathin resists had
been proposed and explored by others. Long chain alkyl thiols or
silanes have been patterned using UV light or e-beam radiation
(Smith, R., et.al., Prog. Surf. Sci., Vol. 75, 1, 2004; Ryan, D.,
et.al., Langmuir, Vol. 20, 9080, 2004; Zharnikov, M., et.al., J.
Vac. Sci. Technol. B, Vol. 20, 1793, 2002; Calvert, J. Vac. Sci.
Technol. B, Vol. 11, 2155, 1993). However, the monolayer films that
have been proposed to date do not have sufficient RIE etch
resistance to transfer images using standard dry etching
techniques.
SUMMARY OF THE INVENTION
[0013] The invention is directed to a radiation sensitive compound
comprising a surface binding group proximate to one end of the
compound for attachment to a substrate, and a metal binding group
proximate to an opposite end of the compound. The metal binding
group is not radiation sensitive. The radiation sensitive compound
also includes a body portion disposed between the surface binding
group and the metal binding group, and a radiation sensitive group
positioned in the body portion or adjacent to the metal binding
group. The surface binding group is capable of attaching to a
substrate selected from a metal, a metal oxide, or a semiconductor
material.
[0014] In one embodiment, the invention is directed to a radiation
sensitive compound of formula I
SB-BP-MB-RS I
[0015] wherein SB is a surface binding group; BP is a body portion;
MB is a metal binding group; and RS is a radiation sensitive group.
The radiation sensitive group is displaced from the metal binding
group upon exposure to UV or e-beam radiation, thereby activating
the metal binding group to interact with a metal species.
[0016] In another embodiment, the invention is directed to a
radiation sensitive compound of formula II
SB-RSBP-MB II
[0017] wherein SB is a surface binding group; MB is a metal binding
group; and RSBP is a body portion that includes a radiation
sensitive group. Upon exposure to UV or e-beam radiation the metal
binding group is displaced from the compound. The radiation
sensitive group in the body portion is not an amine.
[0018] The invention is also directed to a lithographic process for
patterning a substrate comprising: providing a substrate and
attaching a plurality of radiation sensitive compounds to the
substrate, wherein the radiation sensitive compounds include a
surface binding group for attachment to the substrate and a metal
binding group; exposing the surface attached radiation sensitive
compounds to UV or e-beam radiation; and complexing the metal
binding group of the radiation sensitive compounds with a metal
species selected from a metal cation, metal compound, or metal or
metal-oxide nanoparticle to form metallized radiation sensitive
compounds in a predetermined pattern on the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] These and other features of the present invention will
become apparent upon consideration of the following description of
the invention when read in conjunction with the drawings, in
which:
[0020] FIG. 1(a)-1(g) is a schematic representation of a process of
the invention related to the forming of a "positive tone" resist
film;
[0021] FIG. 2(a)-2(g) is a schematic representation of a process of
the invention related to the forming of a "negative tone" resist
film.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The present invention is directed to radiation sensitive
compounds comprising: a surface binding group proximate to one end
of the compound for attachment to a substrate; a metal binding
group proximate to an opposite end of the compound (NOTE: it may
not be at the opposite end of the molecule if the radiation
sensitive group is the terminal group); a body portion disposed
between the surface binding and the metal binding groups; and a
radiation sensitive group positioned in the body portion or
adjacent to the metal binding group. The body portion provides a
sufficient intermolecular interaction with neighboring molecules
attached to the substrate to form a monolayer on the substrate. The
radiation sensitive group controls the ability of the monolayer to
coordinate metals, either by cleaving the metal binding group from
the monolayer upon irradiation in the case of "positive tone"
monolayers, or by cleaving from the metal binding group and
allowing it to coordinate metals in the case of "negative tone"
monolayers. Also, the metal binding group of the radiation
sensitive compounds are not radiation sensitive.
[0023] The term "radiation sensitive" refers to the breakage of
covalent chemical bonds in a particular position of the compound
upon exposure to ultraviolet (UV) or electron beam (e-beam)
radiation under lithographic conditions. A metal binding group is
not radiation sensitive if the metal binding group attached to the
body portion of the compound retains the capability of interacting
with a metal species following exposure to UV or e-beam radiation.
A metal binding group that is activated towards metal species
interactions by displacement of a radiation sensitive group
adjacent to the metal binding group is not itself radiation
sensitive. An amine group is one example of a radiation sensitive
metal binding group.
[0024] The radiation sensitive compounds can function as negative
or positive thin-film resists for use in lithography depending upon
the position of the radiation sensitive group in the compound. In
particular, the radiation sensitive compounds are designed for high
resolution (sub-100 nm) lithography that utilizes UV and e-beam
radiation.
[0025] In one embodiment, the exposure of the radiation sensitive
group to radiation results in the cleaving of the metal binding
group from the body portion of the compound. Consequently, the
exposed compound can no longer bind metals, and thereby functions
as a positive tone resist.
[0026] In another embodiment, the exposure of the radiation
sensitive group to radiation results in the cleaving of the
radiation sensitive group from the compound at a position adjacent
to the metal binding group, and thereby activates the metal binding
group to complex with a metal species. Consequently, the metal
binding group of the exposed molecular precursor is activated
toward metallization, thereby functioning as a negative tone
resist.
[0027] It is to be understood that one of ordinary skill in the art
can design any number of radiation sensitive compounds with each
compound having a surface binding group, a metal binding group, a
body portion and a radiation sensitive group. In one embodiment,
the invention is directed to a radiation sensitive compound of
formula I
SB-BP-MB-RS I
[0028] SB is a surface binding group, BP is a body portion, MB is a
metal binding group and RS is a radiation sensitive group. The
radiation sensitive group is displaced from the metal binding group
upon exposure to UV or e-beam radiation, thereby activating the
metal binding group to interact with a metal species.
[0029] In another embodiment, the invention is directed to a
radiation sensitive compound of formula II
SB-RSBP-MB II
[0030] Again, SB is a surface binding group and MB is a metal
binding group. However, the radiation sensitive group is positioned
in the body portion of the compound and identified as RSBP. The
radiation sensitive group in the body portion is not an amine. In
this case, the radiation sensitive group can cause cleavage of the
metal binding group from the compound upon exposure to UV or e-beam
radiation.
[0031] Examples of surface binding groups that can be incorporated
into the compounds for interacting with or binding to a particular
substrate surface with chemical specificity include one or more of
the functional groups selected from a phosphine, phosphonic acid,
carboxylic acid, thiol, epoxide, amine, imine, hydroxamic acid,
phosphine oxide, phosphite, phosphate, phosphazine, phosphonic
acid, azide, hydrazine, sulfonic acid, sulfide, disulfide,
aldehyde, ketone, resorsinol, silane, germane, arsine, nitrile,
isocyanide, isocyanate, thiocyanate, isothiocyanate, amide,
alcohol, selenol, nitro, boronic acid, ether, thioether, carbamate,
thiocarbamate, dithiocarbamate, dithlocarboxylate, xanthate,
thioxanthate, alkylthiophosphate, dialkyldithiophosphate or any
combination thereof.
[0032] Some of the more preferred surface binding groups
include:
[0033] a. thiols that bind to metal and semiconductor surfaces
(e.g. Au, Pd, Pt, AuPd, Si, Ge, GaAs, Cu);
[0034] b. Selenols that bind to a similar group of metals and
semiconductors as thiols
[0035] c. isocyanides that bind to metal surfaces;
[0036] d. phosphonic acids, hydroxamic acids, carboxylic acids,
suflonic acids or resorsinols that to bind to metal oxide surfaces
(e.g. aluminum oxides, zirconium oxides and hafnium oxides);
[0037] e. hydroxamic or carboxylic acids--which bind to metals and
metal oxides
[0038] f. chloro and alkoxy silanes that bind to silicon oxide
surfaces; and
[0039] g. dienes alcohols, and aldehydes that bind to silicon
surfaces.
[0040] Examples of metal binding groups that can be incorporated
into the compounds include:
[0041] a. nitrogen heterocycles such as pyridine, dipyridine or
terpyridine. These sigma donating nitrogen ligands can bind to a
variety of metals at different oxidation states across the periodic
table such as those of Group IV (Ti, Zr and Hf), Group V (Nb and
Ta), Group V (Cr, Mo and W), Group VI (Mn and Re) and Group VIII
metals (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and Pt);
[0042] b. phosphonic acids that selectively bind to metal ions
including Zr and Hf;
[0043] c. sulfonic acids that selectively bind to metal ions
including Fe; and
[0044] d. isocyanides that selectively bind to Group VIII metals as
well as some early transition metals.
[0045] Examples of radiation sensitive groups that can be
incorporated into the compounds include:
[0046] a. nitrobenzyl groups;
[0047] b. benzyl ether groups;
[0048] c. succinimidyl sulfonic acid groups; and
[0049] d. alkyl thiols or disulfides.
[0050] Compounds A, B, C and D are some examples of radiation
sensitive compounds of the invention, and thus, compounds that can
be used in photolithography to pattern a substrate. Each of the
compounds have a surface binding group (SB); A,
Si(OCH.sub.3).sub.3; B, PO(OH).sub.2; C, thiol; and D, hydroxamic
acid. Each of the compounds have a metal binding group (MB); A,
PO(OH).sub.2; B, pyridine; C, terpyridine; and D, S(O).sub.2OH.
Each of the compounds have a radiation sensitive group (RS); A,
nitrobenzyl; B, benzyl ether; C, carbon-sulfur bond; and D,
succinimidyl. Compounds B and C have radiation sensitive groups
positioned in the body portion, and therefore, the metal binding
group is displaced upon exposure of the compounds to radiation.
Compounds A and D have radiation sensitive groups adjacent to the
metal binding group, and therefore, the metal binding group is
activated upon exposure. Again, compounds A to D are only
exemplary, and thus, the invention is not restricted to these four
compounds. For example, a particular radiation sensitive compound
can be designed according to the device application and the type of
radiation used for exposure.
##STR00001##
[0051] The radiation sensitive compounds can be used to provide
ultra-thin (monolayer or multilayer) self-assembled films that can
be patterned by standard lithographic exposure techniques such as
e-beam or deep UV optical exposure systems. The radiation sensitive
compounds of the invention are designed to form self-assembled
films, and then selectively complex with metal species, e.g., metal
ions or metal nanoparticles, that will improve the etch resistance
of the films in plasma or reactive ion etching environments.
Patterned images can then be transferred into oxide, metal,
semiconductor, or hardmask layers beneath the self-assembled
films.
[0052] FIG. 1(a) is a schematic representation depicting the
radiation sensitive compounds in the form of an assembled monolayer
on a substrate. As shown, the radiation sensitive compounds include
a surface binding group 10 attached to the substrate 13, a metal
binding group 11 and a radiation sensitive group 12 positioned in
the body portion. FIG. 1(b) depicts the exposing of the monolayer
of FIG. 1(a) with UV radiation 14 through an opening in mask 15 or
by patterned e-beam radiation which does not require the use of a
mask. FIG. 1(c) depicts the developed pattern following exposure.
As shown, the radiation sensitive portion of the compounds exposed
to the radiation have been displaced in-part from the monolayer
leaving a predetermined pattern. Depending upon the radiation
sensitive moiety, those compounds exposed can form small molecule
residues that will either vaporize or can be rinsed from the
surface by common solvents. The surface of the monolayer now
contains regions with and without terminal metal binding
capabilities. The monolayer is then contacted with a metal species
16, e.g., metal ions and the metal species will complex with the
metal binding groups of the unexposed compounds, FIG. 1(d).
[0053] In some applications, one can rely on the metal film of the
patterned monolayer to pattern the substrate. However, for many
other applications the monolayer is insufficient, and a thicker
film is needed with a greater density of metal species in the film.
The build-up of the monolayer can continue by contacting the
complexed metal species with a connecting ligand 17, FIG. 1(e). The
process of contacting the connecting ligand with metal species and
the complexed metal species with a subsequent connecting ligand can
proceed any number of times until the desired thickness of the film
and density of metal species is sufficient to provide a certain
degree of etch selectivity, FIG. 1(f). Once the desired film
thickness is obtained, the exposed portions of the substrate 13 can
be etched resulting in a patterned substrate, FIG. 1(g).
[0054] FIG. 2(a) is a schematic representation depicting the
radiation sensitive compounds in the form of an assembled monolayer
on a substrate. As shown, the radiation sensitive compounds include
a surface binding group 10 attached to the substrate 13, a metal
binding group 11 and a radiation sensitive group 12 adjacent to the
metal binding group. The body portion of the radiation sensitive
compounds that make up the monolayer is not shown, but it is
disposed between the surface binding group 10 and the metal binding
group 11. FIG. 2(b) depicts the exposing of the monolayer of FIG.
2(a) with UV or e-beam radiation 14 through an opening in mask 15
or through the use of patterned e-beam radiation. FIG. 2(c) depicts
the developed monolayer following exposure. As shown, the radiation
sensitive groups exposed to the radiation have been displaced from
the metal binding groups in the monolayer leaving a predetermined
pattern. The exposed portion of the monolayer is now available to
complex with a metal species 16, e.g., metal ions, as the metal
binding groups of the compounds have been activated toward
complexation, FIG. 1(d).
[0055] In some applications, one can rely on the metal film of the
patterned monolayer to pattern the substrate. However, for many
other applications the monolayer is insufficient, and a thicker
film is needed with a greater density of metal species in the film.
The build-up of the monolayer can continue by contacting the
complexed metal species with a connecting ligand 17, FIG. 2(e). The
process of contacting the connecting ligand with metal species and
the complexed metal species with a subsequent connecting ligand can
proceed any number of times until the desired thickness of the film
and density of metal species is sufficient to provide a certain
degree of etch selectivity, FIG. 2(f). Once the desired film
thickness is obtained, the unexposed portions of the substrate 13
can be etched resulting in a patterned substrate, FIG. 2(g).
[0056] As described, the monolayer comprising the radiation
sensitive compounds can provide the foundation upon which
subsequent layers containing various metal species can be
constructed. These subsequent layers are constructed using
connecting ligands and subsequent attachment of the metal species.
The radiation sensitivity of the assembled monolayer allows
lithographic definition of regions of the substrate where
layer-by-layer structures may or may not be fabricated. The
incorporation of metal species into the ultra-thin resist layer
increases its resistance to dry (reactive ion) etching techniques.
The invention uses these metal-organic layers to create patterned
features on surfaces that are of potential importance to a wide
range of fields including silicon technology, carbon nanotube
fabrication, nanoelectronics, electroless plating, sensors,
biotechnology, and non-linear optics.
[0057] Some of the process advantages of the invention include:
[0058] 1. the use of ultra-thin resist films will minimize the
impact of a reduced depth of focus for many of the high energy
optical exposure systems;
[0059] 2. the use of ultra-thin resist films will minimize line
collapse of fine features, which can result from surface tension
effects on thick resist images;
[0060] 3. the minimization of line edge roughness through the use
of individual radiation sensitive compounds rather than large
polymeric molecules and photoacid generators that can diffuse
outside the exposed region;
[0061] 4. to provide a site selective patterned substrate for
applications such as carbon nanotube (CNT) and nanowire growth or
electroless plating, fabrication of field effect transistor (FET)
device components including, but not limited to, contact or gate
structures; and
[0062] 5. to provide device structures for chemical or biological
sensors, and non-linear optics.
[0063] In addition to use in traditional lithographic applications,
the ability to selectively localize metal atoms on a range of
surfaces may be useful in a wide range of applications. A technique
that allows site specific deposition of selected metal ions or
nanoparticles would permit molecules or supramolecular structures
to be formed specifically where they are needed. This invention may
allow the synthesis of nanotubes or nanowires at the site of use by
patterning the required metal catalyst allowing nanotubes/wires to
only form is specified areas, as described in U.S. patent
application entitled "Spatially selective growth of carbon
nanotubes and semiconductor nanowires using molecular assemblies",
and assigned to International Business Machines Corporation.
[0064] The process of the invention can also be used to
lithographically define very fine metal containing features where
the metal acts as the seed layer or catalyst for electroless
plating. It combines the resist and seed layers into one ultra-thin
layer with the potential for very high resolution.
[0065] The patterned organic/metal assembly layers of the invention
can be used in the fabrication of nanoscale FET or memory devices.
The electrical properties of such devices can be controlled through
the choice of the organic layer and metal species, e.g., select
metal ions. Charge storage behavior, potentially useful in memory
devices, has been demonstrated using iron/terpyridine complexes
(Li, C., et al., J. Am. Chem. Soc., Vol. 126, 7750, 2004).
Layer-by-layer organic/metal structures have also displayed
non-linear optical properties (Katz, H. et al., Science, Vol. 254,
1485, 1991) as well as electrochemical and electrogenerated
chemiluminescence (Guo, A., et al. Anal. Chem., Vol. 76, 184,
2004). The process of the invention allows lithographic definition
of features with the specified functionality directly on the
substrate of interest.
[0066] A monolayer comprising the radiation sensitive compounds of
the invention can be formed by exposing an appropriate substrate to
a dilute solution containing the compounds. For example, the
substrate can be a top insulating layer such as an oxide or a top
metal (metal alloy) layer deposited on another material such as
silicon. Base metal, metal alloy and semiconductor substrates (Si,
SiGe, GaAs) can also be used. Typical solutions contain 1 mM to 1%
of the radiation sensitive compound in a non-interacting, low
boiling solvent, and typical immersion times range from 20 minutes
to overnight. An assembled radiation sensitive monolayer with a
terminal metal binding group is depicted in FIG. 1(a), and one with
a terminal radiation sensitive group is depicted in FIG. 2(a).
[0067] The metal species that can be used to complex with the metal
binding groups include metal ions, metal complexes, or metal
nanoparticles. The substrate containing the patterned monolayer
with the terminal metal binding groups is placed in contact with a
dilute solution of the appropriate metal species. The metals will
tend to assemble on the metal binding groups, as depicted in FIGS.
1(d) and 2(d). Exemplary metal species include solutions of metal
halides in alcohol or aqueous solutions, metal/organic complexes
such as di-rhodium complexes in toluene solutions, or metal
nanoparticles stabilized with alkylcarboxylic acids in solution in
hexane or other nonpolar solvents.
[0068] As described, once the assembled monolayer includes the
complexed metal species additional layers can be constructed on the
monolayer using a connecting ligand. Again, the metal terminated
assembly is placed in contact with solutions containing the
connecting ligands to produce layered assemblies like those
depicted in FIGS. 1(e) and 2(e). Exemplary connecting ligands
include diterpyridines such as tetra-2-pyridinylpyrazine,
dipyridines, such as dipyridinyl ethylene, or di-phosphonic,
sulfonic, or carboxylic acids. Typical ligand concentrations will
be between 0.1-10 mM in appropriate solvents. The assembly of
layer-by-layer structures can be constructed by alternate contact
of the assembly layer(s) to metal-containing solutions and
connecting ligand containing solutions until the film has attained
the desired thickness.
[0069] Layer-by-layer films containing a significant content of
metals may then be used as a barrier for dry or wet etching of the
substrate, as depicted in FIGS. 2g and 3g. The etch resistance of
the film may also be increased through the use of aromatic organic
or highly fluorinated organic molecules as the linking ligands. It
is also possible to grow patterned layer-by-layer films on thin,
sacrificial etch barriers, such as hardmasks, initially
transferring the image into the hardmask and using the patterned
hardmask to transfer the image into the underlying structure.
[0070] The invention herein disclosed reduces or eliminates several
problems with current lithographic resists for creating sub-100 nm
features. The ultra-thin radiation sensitive monolayers (.about.10
to 20 .ANG.) allow the possibility of true "top surface" imaging to
optimize resolution and alleviate issues with depth of focus of
advanced optical exposure systems. The films will not be subject to
absorption concerns faced by thicker resist films in the deep UV.
Due to their thickness and the aspect ratio of the features, these
will not be subject to the surface tension effects which lead to
collapse in thicker films. Edge roughness should also be minimized
due to the use of individual radiation sensitive molecules rather
than larger polymer chains with multiple reactive sites and
photoacid generators that diffuse through the film.
[0071] A wide range of additional applications of the materials
defined in this invention are also possible. Some of these
applications may not require an extended or multilayer assembly
structure. Films that are just prepared through step d) in FIG. 1
or 2 will have patterned regions containing a uniform layer of
metal atoms. The appropriate selection of metal species can also be
used as the seed or catalytic layer for patterned electroless
plating. The plated features defined by this process could have
much smaller dimensions than those formed through conventional
lithographic definition of catalytic layers. Patterned metal
containing regions could also be used as the catalyst for the
site-specific synthesis of organic molecules for applications in
molecular recognition such as the selective binding of biomolecules
or in the creation chemical sensors. The patterning capabilities of
metal/catalyst containing molecules described herein would allow
for the fabrication of dense sensor arrays.
Example 1
[0072] Mercaptophenylterpyridine (MPTP) which contains thiol,
surface binding groups and terpyridine, metal binding groups was
prepared (Auditore, A, et.al, Chem. Comm. 2494, 2003). An assembled
monolayer comprising MPTP was prepared by immersing O.sub.2 plasma
cleaned gold substrates into a 1 mM solution of MPTP in 3:1
toluene:ethanol overnight. The presence of the MPTP monolayer was
confirmed by both UV and FTIR spectroscopy.
[0073] The monolayer of MPTP was then exposed to 1-10 mM solutions
of various metal halides in alcohol or water for 10 minutes
including RuCl.sub.3, IrBr.sub.3, RhCl.sub.3, TiCl.sub.3,
SnCl.sub.4, ZrCl.sub.4, WCl.sub.4, and Cucl.sub.2. Again,
spectroscopic evidence (UV and FTIR) indicated the complexation of
the metal ions to the MPTP. The substrates were then immersed in a
1 mM solution of tetra-2-pyridylpyrazine, a connecting ligand, in
1:1 ethanol:toluene solution for 10 minutes. The substrates were
then cycled between immersion in the metal halide and the
connecting ligand solutions to construct assembled multilayered
films. The UV spectra of the films were recorded after each
immersion and demonstrated relatively linear increases in
absorbance consistent with uniform layered growth. In some cases,
an assembled film with up to 20 bilayers of metal ions and
connecting ligand were prepared. AFM measurements also indicated
increasing film thicknesses that were consistent with the film
thickness predicted from molecular modeling.
Example 2
[0074] A monolayer of MPTP was exposed to 193 nm UV light (7.5
J/cm.sup.2) and no residual absorbance in either UV or FTIR scans
was observed, thus indicating complete reaction of the
sulfur-carbon bond and removal of the portion of the molecule
containing terpyridine. The exposed monolayer was also cycled
through the solutions of metal halide and connecting ligand, and
these did not demonstrate the increase in absorbance and film
thickness as did the unexposed substrates of Example 1.
Example 3
[0075] 4-[N-(3-triethoxysilyl)propyl]-carbamoyl-2-nitrobenzyl
isonicotinate (TCNI) which binds to silicon dioxide through the
ethoxysilyl groups, and has a pyridine metal binding group and a
nitrobenzyl radiation sensitive group was prepared according to the
synthetic procedure represented in Scheme 2.
4-Bromomethyl-3-nitrobenzoic acid (A) was refluxed overnight with
sodium carbonate in acetone/water (1:1). After cooling to room
temperature, the reaction mixture was made acidic with 1 N
hydrochloric acid and the product was extracted into ethyl acetate,
dried over magnesium sulfate and rotary evaporated to yield
4-hydroxymethyl-3-nitrobenzoic acid. The
4-hydroxymethyl-3-nitrobenzoic acid (B) was dissolved in pyridine
and reacted with isonicotinoyl chloride hydrochloride at room
temperature for 2 days. The resultant solution was poured onto ice,
stirred overnight at room temperature and extracted with ethyl
acetate. The organics were dried over magnesium sulfate and rotary
evaporated to remove the solvents. Residual pyridine was removed by
the addition of toluene followed by rotary evaporation. The
resultant solid was slurried in ethanol at room temperature and the
product, 4-carboxy-2-nitrobenzyl isonicotinate, was isolated by
filtration and dried under vacuum.
[0076] The 4-carboxy-2-nitrobenzyl isonicotinate (C) was treated
with excess thionyl chloride and a few drops of dimethylformamide
at room temperature for 45 minutes, followed by rotary evaporation
to remove thionyl chloride and azeotropic removal of thionyl
chloride by 3 additions of toluene followed by rotary evaporation
to give 4-chlorocarbonyl-2-nitrobenzyl isonicotinate hydrochloride
(D). The 4-chlorocarbonyl-2-nitrobenzyl isonicotinate hydrochloride
(D) and excess triethylamine were dissolved in chloroform and
cooled in an ice/acetone bath. A chloroform solution of
3-aminopropyltriethoxysilane was added dropwise and the reaction
was allowed to warm to room temperature and stirred for 4 hours.
The solvents were removed by rotary evaporation. The resultant
mixture was treated with ether and filtered to remove salts. The
filtrate was rotary evaporated and purified by flash chromatography
on silica gel using ethyl acetate as the eluent to yield
4-[N-(3-triethoxysilyl)propyl]carbamoyl-2-nitrobenzyl
isonicotinate.
##STR00002##
[0077] Monolayers of TCNI were prepared by immersing O.sub.2 RIE
cleaned silicon chips with 5000 .ANG. of thermal oxide into a 1 mM
solution of TCNI in dry toluene overnight. Upon removal from the
solution the chips were rinsed in clean solvent and baked at 120 C
for 10 minutes. Ten layers of metal ions and connecting ligands
were built up on top of a TCNI monolayer as described in Example 1.
Samples with R.sup.3+, R.sup.3+, and Ir.sup.3+ were prepared. All
samples, along with uncoated control chips, were etched in a RIE
tool using CHF.sub.3 and O.sub.2 at a pressure of 50 mTorr and a
power of 150 watts for 3.5 minutes.
[0078] The etch was designed to completely remove the film such
that the maximum resistance of the film to RIE could be determined
by the decrease in the loss of SiO.sub.2 relative to the control
samples. The chips with ten layers of Ir.sup.3+ lost an average of
750 .ANG. less oxide, the R.sup.3+ layers lost an average of 500
.ANG. less oxide, and the Rh.sup.3+ lost 380 .ANG. less oxide than
the control samples. The predicted film thickness for a 10 layer
film is about 90 .ANG., so all of the LBL films demonstrate etch
resistances far greater than 1:1 (which is typical for organic
resist films).
* * * * *