U.S. patent application number 11/180787 was filed with the patent office on 2007-01-18 for process of making a lithographic structure using antireflective materials.
This patent application is currently assigned to International Business Machines Corporation. Invention is credited to Marie Angelopoulos, Katherina E. Babich, Sean D. Burns, Allen H. Gabor, Scott D. Halle, Arpan P. Mahorowala, Dirk Pfeiffer.
Application Number | 20070015082 11/180787 |
Document ID | / |
Family ID | 37662015 |
Filed Date | 2007-01-18 |
United States Patent
Application |
20070015082 |
Kind Code |
A1 |
Angelopoulos; Marie ; et
al. |
January 18, 2007 |
Process of making a lithographic structure using antireflective
materials
Abstract
A lithographic structure comprising: an organic antireflective
material disposed on a substrate; and a silicon antireflective
material disposed on the organic antireflective material. The
silicon antireflective material comprises a crosslinked polymer
with a SiO.sub.x backbone, a chromophore, and a transparent organic
group that is substantially transparent to 193 nm or 157 nm
radiation. In combination, the organic antireflective material and
the silicon antireflective material provide an antireflective
material suitable for deep ultraviolet lithography. The invention
is also directed to a process of making the lithographic
structure.
Inventors: |
Angelopoulos; Marie;
(Cortlandt Manor, NY) ; Babich; Katherina E.;
(Chappaqua, NY) ; Burns; Sean D.; (Hopewell
Junction, NY) ; Gabor; Allen H.; (Katonah, NY)
; Halle; Scott D.; (Hopewell Junction, NY) ;
Mahorowala; Arpan P.; (Bronxville, NY) ; Pfeiffer;
Dirk; (Dobbs Ferry, NY) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ LLP
P.O. BOX 2207
WILMINGTON
DE
19899-2207
US
|
Assignee: |
International Business Machines
Corporation
Armonk
NY
|
Family ID: |
37662015 |
Appl. No.: |
11/180787 |
Filed: |
July 14, 2005 |
Current U.S.
Class: |
430/270.1 ;
430/311; 430/313; 430/9; 430/950 |
Current CPC
Class: |
G03F 7/091 20130101;
G03F 7/0757 20130101; Y10T 428/31663 20150401; Y10T 428/24942
20150115 |
Class at
Publication: |
430/270.1 ;
430/009; 430/311; 430/313 |
International
Class: |
G03F 7/26 20070101
G03F007/26; G03C 5/00 20060101 G03C005/00 |
Claims
1. A lithographic structure comprising: an organic antireflective
material disposed on a substrate; and a silicon antireflective
material disposed on the organic antireflective material, wherein
the silicon antireflective material comprises a crosslinked polymer
with a SiO.sub.x backbone, a chromophore attached to the SiO.sub.x
backbone, and a transparent organic group that is substantially
transparent to 193 nm or 157 nm radiation.
2. The lithographic structure of claim 1 wherein the chromophore
provides the site for crosslinking.
3. The lithographic structure of claim 1 wherein the chromophore is
selected from the group consisting of phenyl, phenol, naphthalene,
and an unsaturated organic group.
4. The lithographic structure of claim 1 wherein the crosslinked
polymer further comprises a reaction product resulting from the
reaction of a thermal acid generator.
5. The lithographic structure of claim 1 wherein the transparent
organic group that is substantially transparent provides the site
of crosslinking.
6. The lithographic structure of claim 1 wherein the transparent
organic group is a hydrofluorocarbon or perfluorocarbon.
7. The lithographic structure of claim 5 wherein the transparent
organic group includes one or more organic functional group
selected from an epoxide, alcohol, acetoxy, ester or ether.
8. The lithographic structure of claim 5 wherein the transparent
organic group is a cycloaliphatic epoxide.
9. The lithographic structure of claim 1 wherein the crosslinked
polymer comprises units of a glycoluril compound.
10. The lithographic structure of claim 1 wherein the organic
antireflective material comprises a polymer with crosslinked
phenolic sites, and a number average molecular weight of about
2,000 to about 10,000.
11. The lithographic structure of claim 1 further comprising a
photoresist on the silicon antireflective material.
12. The lithographic structure of claim 1 wherein the organic
antireflective material has an index of refraction (n) of 1.3-2.0
and an extinction coefficient (k) of 0.4-0.9, at 193 nm radiation,
and the silicon antireflective material has an index of refraction
(n) of 1.5-2.2 and an extinction coefficient (k) of 0.1-0.8 at 193
nm radiation.
13. The lithographic structure of claim 1 wherein the silicon
antireflective material and the organic antireflective material
together provide a reflectivity below 0.5% up to numerical aperture
(NA) of 1.4.
14. The lithographic structure of claim 4 wherein the silicon
antireflective material and the organic antireflective material
together provide a reflectivity below 0.5% up to numerical aperture
(NA) of 1.4.
15. The lithographic structure of claim 7 wherein the silicon
antireflective material and the organic antireflective material
together provide a reflectivity below 0.5% up to numerical aperture
(NA) of 1.4.
16. The lithographic structure of claim 1 wherein the silicon
antireflective material has a thickness of T.sub.k and the organic
antireflective material has a thickness of about 2T.sub.k to about
12T.sub.k, wherein the thickness T.sub.k is in nanometers.
17. An antireflective material comprising an organic antireflective
material and a silicon antireflective material disposed on the
organic antireflective material, wherein the silicon antireflective
material comprises: a crosslinked polymer with a SiO.sub.x
backbone; a chromophore attached to the SiO.sub.x backbone; and a
transparent organic group that is substantially transparent to 193
nm or 157 nm radiation.
18. The antireflective material of claim 17 wherein the silicon
antireflective material further comprises a reaction product
resulting from the reaction of a thermal acid generator.
19. The antireflective material of claim 17 wherein the transparent
organic group provides the site of crosslinking, and is one or more
organic functional groups selected from an epoxide, alcohol,
acetoxy, ester or ether.
20. The antireflective material 19 wherein the transparent organic
group is a cycloaliphatic epoxide.
21. The antireflective material of claim 17 wherein the organic
antireflective material has an index of refraction (n) of 1.3-2.0
and an extinction coefficient (k) of 0.4-0.9, at 193 nm radiation,
and the silicon antireflective material has an index of refraction
(n) of 1.5-2.2 and an extinction coefficient (k) of 0.1-0.8 at 193
nm radiation, and the silicon antireflective material and the
organic antireflective material together provide a reflectivity
below 0.5% up to numerical aperture (NA) of 1.4.
22. The antireflective material of claim 17 wherein the silicon
antireflective material has a thickness of T.sub.k and the organic
antireflective material has a thickness of about 2T.sub.k to about
12T.sub.k, wherein the thickness T.sub.k is in nanometers.
23. A process of making a lithographic structure comprising:
providing a substrate; providing an organic antireflective material
on the substrate; providing a silicon antireflective material on
the organic antireflective material, wherein the silicon
antireflective material comprises a crosslinked polymer with a
SiO.sub.x backbone, a chromophore attached to the SiO.sub.x
backbone; and a transparent organic group that is substantially
transparent to 193 nm or 157 nm radiation, depositing a photoresist
on the silicon antireflective material, pattern expose the
photoresist to radiation, and remove portions of the photoresist to
expose the silicon antireflective material, removing portions of
the silicon antireflective material to expose the organic
antireflective material; removing portions of the organic
antireflective material to expose portions of the substrate; and
removing portions of the substrate.
24. The process of claim 23 wherein removing portions of the
silicon antireflective material, and the organic antireflective
material is accomplished by reactive ion etching in a plasma.
25. The process of claim 23 wherein the deposited silicon
antireflective material has a thickness T.sub.k and the organic
antireflective material has a thickness of about 2T.sub.k to about
12T.sub.k, wherein the thickness T.sub.k is in nanometers.
26. The process of claim 23 wherein the deposited silicon
antireflective material and the deposited organic antireflective
material together provide a reflectivity below 0.5% up to numerical
aperture (NA) of 1.4.
27. The process of claim 24 wherein the silicon antireflective
material further comprises a reaction product resulting from the
reaction of a thermal acid generator.
28. The process of claim 24 wherein the removing portions of the
organic antireflective material includes introducing a taper.
29. A process of claim 23 wherein the silicon antireflective
material comprises the silicon backbone of ##STR7## which is
crosslinked with a crosslinking agent of formula ##STR8## and
prepared in the presence of an acid generator of formula ##STR9##
wherein A is S or I, and x is 0 to 7.
Description
FIELD OF INVENTION
[0001] The invention relates to a process of making a lithographic
structure using antireflective materials. In particular, the
invention relates to a process of making a lithographic structure
using a silicon antireflective material and an organic
antireflective material.
BACKGROUND OF THE INVENTION
[0002] In the process of making semiconductor devices a photoresist
and an antireflective material are applied to a substrate.
Photoresists are photosensitive films used to transfer an image to
a substrate. A photoresist is formed on a substrate and then
exposed to a radiation source through a photomask (reticle).
Exposure to the radiation provides a photochemical transformation
of the photoresist, thus transferring the pattern of the photomask
to the photoresist. The photoresist is then developed to provide a
relief image that permits selective processing of the
substrate.
[0003] Photoresists are typically used in the manufacture of
semiconductors to create features such as vias, trenches or
combination of the two, in a dielectric material. In such a
process, the reflection of radiation during exposure of the
photoresist can limit the resolution of the image patterned in the
photoresist due to reflections from the material beneath the
photoresist. Reflection of radiation from the substrate/photoresist
interface can also produce variations in the radiation intensity
during exposure, resulting in non-uniform linewidths. Reflections
also result in unwanted scattering of radiation exposing regions of
the photoresist not intended, which again results in linewidth
variation. The amount of scattering and reflection will vary from
one region of the substrate to another resulting in further
non-uniform linewidths.
[0004] With recent trends towards high-density semiconductor
devices, there is a movement in the industry to use low wavelength
radiation sources into the deep ultraviolet (DUV) light (300 nm or
less) for imaging a photoresist, e.g., KrF excimer laser light (248
nm), ArF excimer laser light (193 nm), electron beams and soft
x-rays. However, the use of low wavelength radiation often results
in increased reflections from the upper resist surface as well as
the surface of the underlying substrate.
[0005] Substrate reflections at ultraviolet and deep ultraviolet
wavelengths are notorious for producing standing wave effects and
resist notching which severely limit critical dimension (CD)
control. Notching results from substrate topography and non-uniform
substrate reflectivity which causes local variations in exposure
energy on the resist. Standing waves are thin film interference or
periodic variations of light intensity through the resist
thickness. These light variations are introduced because
planarization of the resist presents a different thickness through
the underlying topography. Thin film interference plays a dominant
role in CD control of single material photoresist processes,
causing large changes in the effective exposure dose due to a tiny
change in the optical phase. Thin film interference effects are
described in "Optimization of optical properties of resist
processes" (T. Brunner, SPIE 10 Proceedings Vol. 1466, 1991,
297).
[0006] Bottom anti-reflective coatings (BARCs) have been used with
single material resist systems to reduce thin film interference
with some success. However, BARCs do not provide control of
topographic variations and do not address the differences in resist
thickness. BARCs such as silicon nitride or silicon oxide typically
follow the already existing topography, and thus, the BARC exhibits
nearly the same thickness non-uniformity as the underlying
material. Consequently, the BARC alone will generally not planarize
topographic variations resulting from underlying device features.
As a result, there will be a variation in exposure energy over the
resist. Current trends to provide uniform topography via
chemical/mechanical polishing still leaves significant variations
in film thickness.
[0007] Variations in substrate topography also limits resolution
and can affect the uniformity of photoresist development because
the impinging radiation scatters or reflects in uncontrollable
directions. As substrate topography becomes more complex with more
complex circuit designs, the effects of reflected radiation becomes
even more critical. For example, metal interconnects used on many
microelectronic substrates are particularly problematic due to
their topography and regions of high reflectivity.
[0008] One approach to variations in substrate topography is
described in U.S. Pat. No. 4,557,797 (Fuller et al.). Another
approach used to address variations in substrate topography is
described in Adams et al., Planarizing AR for DUV Lithography,
Microlithography 1999: Advances in Resist Technology and Processing
XVI, Proceedings of SPIE, vol. 3678, part 2, pp 849-856, 1999,
which discloses the use of a planarizing antireflective
coating.
[0009] Although multimaterial patterning schemes exist in the prior
art (see, U.S. Pat. No. 6,140,226; and R. D. Goldblett, et al.
Proceedings of the IEEE 2000 International Technology Conference, p
261-263), there remains the need for new antireflective materials.
Many of the prior antireflective materials contain silicon based
intermediate materials that do not act as antireflective coatings,
e.g. silicon oxide like materials require the use of an additional
antireflective coating because they cannot be optically tuned to
control reflections.
[0010] The present trend to 248 nm and 193 nm lithography and the
demand for sub 200 nm features requires that new processing schemes
be developed. To accomplish this, tools with higher numerical
aperture (NA) are emerging. The higher NA allows for improved
resolution but reduces the depth of focus of aerial images
projected onto the resist. Because of the reduced depth of focus, a
thinner resist is typically required. However, as the thickness of
the resist is decreased, the resist becomes less effective as a
mask for subsequent dry etch image transfer to the underlying
substrate. Without significant improvement in the etch resistance
exhibited by current single material resists, these systems cannot
provide the necessary etch characteristics for high resolution
lithography.
SUMMARY OF THE INVENTION
[0011] The invention is directed to a lithographic structure
comprising: an organic antireflective material disposed on a
substrate; and a silicon antireflective material disposed on the
organic antireflective material. The silicon antireflective
material comprises a crosslinked polymer with a SiO.sub.x backbone,
a chromophore, and a transparent organic group that is
substantially transparent to 193 nm or 157 nm radiation. In many
instances, the silicon antireflective material will further
comprise a reaction product resulting from the reaction of a
thermal acid generator.
[0012] In combination, the organic antireflective material and the
silicon antireflective material provide an antireflective material
suitable for deep ultraviolet lithography. The lithographic
structure is then used to pattern a substrate. The invention is
also directed to a process of making a lithographic structure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] This invention will be better understood by reference to the
Detailed Description of the Invention when taken together with the
attached drawings, wherein:
[0014] FIG. 1 is a simulated plot of reflectivity for an
antireflective material in the art and for a silicon antireflective
material disposed on an organic antireflective material according
to the invention; and
[0015] FIG. 2 is a schematic representation for the patterning of a
substrate according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0016] To address many of the lithographic processing issues
summarized in the "Background of the Invention", applicants have
developed a lithographic structure that includes a silicon
antireflective material in combination with an organic
antireflective material. The use of two antireflective materials
provides the engineer with the process control and flexibility
required for high resolution (low wavelength) lithography. For
example, the engineer can selectively etch the organic
antireflective material relative to the silicon antireflective
material. As a result, once the silicon antireflective material is
patterned, the underlying organic antireflective material can be
etched with minimal removal of the silicon antireflective
material.
[0017] For many lithographic imaging processes, the resists used do
not provide sufficient resistance to subsequent etching steps to
enable effective transfer of the resist pattern to a material
underlying the resist. The resist typically gets consumed after
transferring the pattern into the underlying BARC and substrates.
In addition, the trend to smaller sub 90 nm node feature sizes
requires the use of an ultra thin resist (>200 nm) to avoid
image collapse. In many instances, if a substantial etching depth
is required, or if it is desired to use certain etchants for a
given underlying material, the resist thickness is now insufficient
to complete the etch process.
[0018] Applicants' lithographic structure and process addresses
many of the above issues by initially transferring the pattern onto
a silicon antireflective material which then serves as an etch mask
to continue transferring the pattern into a relatively thick
organic antireflective material.
[0019] The invention also provides the process engineer with the
optical tunability or flexibility to control the antireflective
properties of the lithographic structure, if needed. Through the
specific selection of silicon and organic antireflective materials
a lithographic structure with the desired optical characteristics
for high resolution, deep ultraviolet imaging is possible. Proper
selection of optical constants for the silicon and organic
antireflective materials can suppress the undesired reflectivity
from the polarization nodes TE and TM (x and y polarization states)
at high NA lithography.
[0020] The invention is directed to a lithographic structure
comprising: an organic antireflective material disposed on a
substrate; and a silicon antireflective material disposed on the
organic antireflective material. The silicon antireflective
material comprises a crosslinked polymer with a SiO.sub.x backbone
and a chromophore attached to the SiO.sub.x backbone. The
crosslinked, silicon oxide polymer also includes a transparent
organic group that is substantially transparent to 193 nm or 157 nm
radiation. In many instances, the silicon antireflective material
will further comprise a reaction product resulting from the
reaction of a thermal acid generator. The lithographic structures
provides the needed optical and mechanical properties as well as
etch selectivity.
[0021] The polymer is crosslinked through reactive sites on the
polymer with an external crosslinking agent. Typically, the
reactive site is a functional group, e.g., hydroxyl, on the
chromophore or the organic transparent group. Alternatively, the
polymer can include internal crosslinking groups, i.e., attached to
one of the organic groups of the polymer, e.g., the chromophore or
the organic transparent group.
[0022] The organic antireflective material is a crosslinked polymer
with little, if any, silicon. The organic antireflective material
can be formed by spin coating followed by crosslinking. Organic
antireflective materials and the processes by which they are made
are well known to those in the art of semiconductor processing.
[0023] The silicon antireflective material is optically tuned by
careful selection of the chromophore, or the organic transparent
group of the polymer. The degree of oxygen in the SiO.sub.x polymer
also can be used to optically tune the silicon antireflective
material. In addition, the selection of an organic antireflective
material with the appropriate optical constants in combination with
a selected silicon antireflective material can provide a
semiconductor structure with excellent antireflective properties at
193 nm radiation, in particular at high NA lithography.
[0024] The silicon oxide polymer used to form the silicon
antireflective material is preferably an organosiloxane, more
preferably an organosilsesquioxane. Examples of suitable silicon
oxide polymers of the silsesquioxane-type (ladder or network) have
structures I to III below: ##STR1##
[0025] where R.sub.1 comprises a chromophore, R.sup.2 comprises an
organic group transparent to 193 nm radiation, and R.sup.3
comprises a reactive site available for crosslinking.
[0026] Examples of suitable silicon oxide polymers of the
organosiloxane-type have structures IV to VI below: ##STR2##
[0027] where R.sup.1, R.sup.2 and R.sup.3 are as described above.
The silicon oxide polymer can also contain various combinations of
structures I to VI such that the average silicon oxide structure
with a chromophore R.sup.1 is represented as structure (VII) below
and the average structure with a reactive site R.sup.2 is
represented by structure (VIII) below, and the average structure
with a reactive site R.sup.3 is represented by structure (IX)
below. ##STR3##
[0028] where x is from about 1 to about 1.5.
[0029] The silsesquioxane-type polymers (I to III) will often have
superior etch resistance. Still, if the organosiloxane-type
polymers are used (IV to VI), the degree of crosslinking is
generally increased compared to formulations based on
silsesquioxanes. In many cases, the silicon oxide polymer will have
solution and film-forming characteristics conducive to forming a
layered material by conventional spin-coating.
[0030] Exemplary silicon oxide polymer compositions used to provide
the silicon antireflective material of the invention and methods of
depositing such a material is described in U.S. Pat. Nos. 6,420,088
and 6,730,454, assigned to International Business Machines, the
entire disclosures of which are incorporated herein by reference. A
select listing of silicon oxide polymers that can be used are
lisyed on column 4, line 45 to column 5 line 8 of U.S. Pat. No.
6,420,088.
[0031] Alternatively, the polymer compositions described in
Japanese patent application 2004-158639, Japanese patent
application 2003-157808 or Japanese patent application 2004-172222,
the entire disclosures of which are incorporated herein by
reference, can be used to provide the silicon antireflective
material of the invention.
[0032] The following silicon oxide polymer depicted below provides
a silicon antireflective material with optimal characteristics and
performance. ##STR4##
[0033] The chromophore-containing groups R.sup.1 may contain any
suitable chromophore which (i) can be grafted onto the silicon
polymer (ii) has suitable radiation absorption characteristics, and
(iii) does not adversely affect the performance of the material or
any overlying photoresist material. Preferred chromophore moieties
include chrysenes, pyrenes, fluoranthrenes, anthrones,
benzophenones, thioxanthones, and anthracenes. Anthracene
derivatives, such as those described in U.S. Pat. No. 4,371,605 can
also be used. The chromophore 9-anthracene methanol is a preferred
chromophore for 248 nm lithography.
[0034] Other chromophores suitable for this invention are described
in U.S. Pat. No. 6,730,454; Japanese patent application
2004-158639; and Japanese patent application 2004-172222, the
disclosures of which is incorporated herein by reference. An
exemplary list include chromophores selected from the group
consisting of phenyl, phenol, naphthalene, and an unsaturated
organic group. The use of a phenyl chromophore for 193 nm
lithography exhibits certain advantages over some of the other
chromophores listed. Also, for 193 nm lithography, non-aromatic
compounds with one or more unsaturated carbon-carbon bonds can be
used.
[0035] The chromophore can be chemically attached to the silicon
polymer by acid-catalyzed O-alkylation or C-alkylation such as by
Friedel-Crafts alkylation. Alternatively, the chromophore can be
chemically attached by esterification. For example, the chromophore
can be attached via a hydroxyl-substituted aromatic group such as a
hydroxybenzyl or hydroxymethylbenzyl group.
[0036] The selection of the transparent organic groups R.sup.2 used
will depend on the wavelength or character of the imaging
radiation. In the case of 193 nm imaging radiation, the transparent
organic groups are preferably bulky (C.sub.2 or higher) organic
radicals substantially free of unsaturated carbon-carbon bands.
Organic transparent groups such as epoxides are particularly suited
for 193 nm lithography. A cycloaliphatic epoxide exhibits
exceptional characteristics for 193 nm lithography. Other
functional groups such as an alcohol, acetoxy, ester and/or ether
based transparent groups can also be used.
[0037] Organic transparent groups that can be used in the silicon
antireflective materials are described in U.S. Pat. No. 6,730,454;
Japanese patent application 2004-158639; and Japanese patent
application 2004-172222. In many instances, the amount of
transparent organic groups is preferably balanced with the amount
of chromophore to provide a desired combination of energy
absorption and antireflection character in the silicon
antireflective material.
[0038] In the case of 157 nm imaging radiation, the organic
transparent groups are preferably fluorine-containing groups such
as a trifluoromethyl group or a perfluoroalkyl. Again, the amount
of transparent organic groups is preferably balanced with the
amount of chromophore to provide a desired combination of energy
absorption and antireflection character in the silicon
antireflective material.
[0039] The reactive site R.sup.3 comprises alcohols, more
preferably aromatic alcohols (e.g., hydroxybenzyl, phenol,
hydroxymethylbenzyl, etc.) or cycloaliphatic alcohols (e.g.,
cyclohexanoyl). Alternatively, non-cyclic alcohols such as
fluorocarbon alcohols, aliphatic alcohols, amino groups, vinyl
ethers, and epoxides can be used.
[0040] The external crosslinking agent used to form the silicon
antireflective material can be one that reacts with the silicon
polymer and is catalyzed by an acid and/or by heat. Generally, the
crosslinking agent can be any suitable crosslinking agent known in
the negative photoresist art which is otherwise compatible with the
other selected components of the polymer composition. Preferred
crosslinking agents are glycoluril compounds such as
tetramethoxymethyl glycoluril, methylpropyltetramethoxymethyl
glycoluril, and methylphenyltetramethoxymethyl glycoluril,
available as POWDERLINK.RTM. from Cytec Industries.
[0041] Other possible crosslinking agents include:
2,6-bis(hydroxymethyl)-p-cresol compounds such as those found in
Japanese Laid-Open Patent Application (Kokai) No. 1-293339,
etherified amino resins, for example methylated or butylated
melamine resins (N-methoxymethyl- or N-butoxymethyl-melamine
respectively), and methylated/butylated glycolurils, as can be
found in Canadian Patent No. 1 204 547. Other crosslinking agents
such as bis-epoxies or bis-phenols (e.g., bisphenol-A) can also be
used. Combinations of two or more crosslinking agents can also be
used.
[0042] The following crosslinker depicted below provides a silicon
antireflective material with optimal characteristics and
performance. ##STR5##
[0043] The silicon oxide polymer compositions used to form the
silicon antireflective material will likely contain an acid
generator, which is used to catalyze the crosslinking of the
polymer. The acid generator can be a compound that liberates acid
upon thermal treatment. A listing of known thermal acid generators
include 2,4,4,6-tetrabromocyclohexadienone, benzoin tosylate,
2-nitrobenzyl tosylate and other alkyl esters of organic sulfonic
acids. Compounds that generate a sulfonic acid upon activation are
generally suitable. Other suitable thermally activated, acid
generators are described in U.S. Pat. Nos. 5,886,102 and 5,939,236;
the disclosures of these two patents as related to the thermally
activated, acid generating compounds are incorporated herein by
reference.
[0044] If desired, a radiation-sensitive acid generator can be used
as an alternative to a thermally activated acid generator or in
combination with a thermally activated acid generator. Examples of
suitable radiation-sensitive acid generators are described in U.S.
Pat. Nos. 5,886,102 and 5,939,236, the disclosures of these two
patents as related to radiation sensitive, acid generating
compounds are incorporated herein by reference. Other
radiation-sensitive acid generators known in the resist art can be
used as long as they are compatible with the other components of
the polymer composition.
[0045] The following acid generator depicted below provides a
silicon antireflective material with optimal characteristics and
performance. ##STR6##
[0046] wherein A is S or I, and x is 0 to 7.
[0047] The silicon oxide polymer compositions can contain (on a
solids basis) (i) about 50-98 wt. % of the silicon polymer, more
preferably about 70-80 wt. %, (ii) about 1-50 wt. % of crosslinking
agent, more preferably about 3-25% wt. %, and (iii) about 1-20 wt.
% acid generator, more preferably about 1-15 wt. %.
[0048] The silicon oxide polymer compositions will generally
contain a solvent. The solvent may be any solvent conventionally
used with resists which otherwise does not have any excessively
adverse impact on the performance of the antireflective
composition. Exemplary solvents include propylene glycol monomethyl
ether acetate, cyclohexanone, and ethyl lactate. The compositions
can also contain small amounts of auxiliary components (e.g., base
additives, etc.) known in the art.
[0049] The silicon oxide polymer compositions can be prepared by
combining the silicon oxide polymer, crosslinking component and
acid generator, and any other desired ingredients (e.g., solvent)
using conventional methods. The silicon polymer compositions can be
deposited on the organic antireflective material by spin-coating
followed by heating to achieve crosslinking and solvent removal.
The heating is preferably conducted at about 250.degree. C. or
less, more preferably about 150.degree. C. to 220.degree. C. The
heating time will depend on the material thickness and
temperature.
[0050] The organic antireflective material used in the lithographic
structure can be any polymer containing the elements of carbon,
hydrogen, oxygen and nitrogen and mixtures thereof, that can be
spin applied and crosslinked with a heat treatment. Typical organic
polymer compositions suitable for this invention are being used in
lithographic applications such as organic BARCs or as planarizing
undermaterials in bimaterial or other multimaterial lithographic
schemes. The choice of the appropriate organic polymer composition
will depend upon the optical constants as described in the section
below. Examples of suitable organic polymer compositions are
described in U.S. Pat. Nos. 6,503,689; 6,410,209; 6,686,124; and
U.S. published application 20020058204A1, the entire disclosures of
which are incorporated herein by reference.
[0051] The selection of which organic antireflective polymer
composition to use will depend on several characteristics such as
solubility, optical properties, thermal properties, mechanical
properties, etch selectivity, and film forming ability. The
resulting organic antireflective material will be suitable for
low-wavelength radiation. Like the silicon oxide polymer described
above, the organic polymer can have a plurality of different
chemical groups each having a specific function in the overall
performance of the material. Optical properties, mode of
insolubilization, solubility enhancement, and etch resistance are
among the properties that can be tailored by a judicious selection
of the chemical groups.
[0052] Examples of suitable organic polymers that can be used
include poly(4-hydroxystyrene), copolymers of 4-hydroxystyrene such
as with up to 40 weight % of an alkyl methacrylate, alkylacrylate
and/or styrene; novolac resins, acrylate polymers, methacrylate
polymers, fluorocarbon polymers, and cycloaliphatic polymers such
as norbornene-based and maleic anhydride polymers. Some examples of
specific polymers include poly(3-hydroxystyrene), poly(acrylic
acid), poly(norbonene carboxylic acid), copolymer of
(4-hydroxystyrene and styrene), copolymer of 4-hydroxystyrene and
acrylic acid, copolymer of styrene and acrylic acid, and copolymer
of norbonene and maleic anhydride.
[0053] The lithographic structures comprising the silicon and
organic antireflective materials will likely exhibit excellent
reflectivity control in particular at 193 nm lithography with a
numerical aperture greater than 0.75 NA. Reflectivity control is
accomplished by providing the appropriate optical properties for
each of the silicon and the organic antireflective materials. The
chromophore and organic transparent groups are optimized to achieve
the appropriate index of refraction (both real and imaginary; n and
k respectively) at 193 nm or 157 nm wavelengths.
[0054] FIG. 1 shows a reflectivity simulation (software "Prolith"
from KLA, Inc.) for a traditional, single antireflective material
and for a lithographic structure with an antireflective material
that comprises a silicon antireflective material and an organic
antireflective material. The substrate reflectivity of 193 nm
radiation is plotted against the incident angle of the light. The
angle is expressed as n*sin(.theta.), where .theta. is the incident
angle and n is the index of refraction of the imaging medium. This
value is also known as the numerical aperture of the imaging
system. In this case, the imaging medium is considered to have an
index of refraction of 1.43, which is the index of refraction of
water at 193 nm. This value is chosen to be consistent with the
industry's choice of water as the imaging medium for immersion
lithography, but the invention is not specific to any particular
imaging medium.
[0055] In general, the organic antireflective material will have an
index of refraction (n) of 1.3-2.0 and an extinction coefficient
(k) of 0.4-0.9, at 193 nm radiation, and the silicon antireflective
material will have an index of refraction (n) of 1.5-2.2 and an
extinction coefficient (k) of 0.1-0.8, at 193 nm radiation.
Ideally, the antireflective materials of the invention provide a
semiconductor structure with a reflectivity below 0.5% up to
NA=1.4, thus demonstrating excellent reflectivity control for a
high NA lithography imaging process.
[0056] The optical constants and thickness used for the traditional
antireflective material are n=1.8 and k=0.5 and a thickness of 30
nm. The optical constants and thickness used for the silicon and
organic antireflective materials are n=1.75, k=0.2, thickness=35 nm
and n=1.7, k=0.5, and thickness 200 nm, respectively. As shown, the
traditional material reflectivity at low NA is adequate if below
1%. In general, it is desired to have an antireflective material
structure that results in reflectivity below 1% of the incident
light. However, at high NA (NA>1) the reflectivity increases
sharply to values as high as 3-5%, which is typically considered
unacceptable for a lithographic process. In comparison, applicants'
lithographic structure provides a reflectivity below 0.5% up to
NA=1.4, thus demonstrating excellent reflectivity control for a
high NA lithography imaging process. It is to be understood,
however, that it is not necessary to have the exact optical
constants and thickness values shown in this example in order to
attain low reflectivity, and in fact these values will vary
depending upon the underlying film stack.
[0057] Table 1 provides a range of optical properties and thickness
that may result in low reflectivity control depending upon the
underlying film stack. TABLE-US-00001 TABLE 1 structure material
thickness (nm) n k photoresist n/a 1.6-2.3 0-0.05 silicon 10-150
1.3-2.2 0-0.5 organic 20-500 1.3-2.2 0.2-1.0
[0058] The thickness of the silicon and organic antireflective
materials depends upon the desired function. For most applications,
the thickness of the silicon antireflective material is typically
about 20 nm to 100 nm. To achieve complete planarization the
desired film thickness of the organic antireflective material is
typically about 100 nm to 500 nm. Generally, the silicon
antireflective material will have a thickness of T.sub.k (in
nanometers) and the organic antireflective material will have a
thickness of about 2T.sub.k to about 12T.sub.k. In many instances,
the organic antireflective material will have a thickness of about
2T.sub.k to about 6T.sub.k.
[0059] The silicon and organic antireflective material is
especially advantageous for lithographic processes used in the
manufacture of integrated circuits on semiconductor substrates. The
lithographic structure is especially advantageous for lithographic
processes using 193 nm, 157 nm, x-ray, e-beam or other imaging
radiation. The composition is also especially useful for 193 nm
high NA lithography with a numerical aperture (NA) ranging from
0.5-1.4.
[0060] The silicon and organic antireflective material can be used
in combination with any desired photoresist material in the
formation of a lithographic semiconductor structure. Preferably,
the photoresist can be imaged with low wavelength radiation or with
electron beam radiation. Examples of suitable resist materials are
U.S. Pat. No. 6,037,097, the disclosure of which is incorporated
herein by reference.
[0061] The invention is also directed to a process of making a
semiconductor structure comprising:
[0062] providing a substrate;
[0063] providing an organic antireflective material on the
substrate;
[0064] providing a silicon antireflective material on the organic
antireflective material, wherein the silicon antireflective
material comprises a crosslinked polymer with a SiO.sub.x backbone,
a chromophore attached to the SiO.sub.x backbone; and an organic
group that is substantially transparent to 193 nm or 157 nm
radiation, [0065] depositing a photoresist on the silicon
antireflective material, pattern expose the photoresist to
radiation, and remove portions of the photoresist to expose the
silicon antireflective material, [0066] removing portions of the
silicon antireflective material to expose the organic
antireflective material; [0067] removing portions of the organic
antireflective material to expose portions of the substrate; and
[0068] removing portions of the substrate Any remaining portions of
the photoresist, the silicon antireflective material, and the
organic antireflective material are then removed to provide a
patterned substrate.
[0069] An organic antireflective composition is applied, preferably
by spin-coating, to a substrate, e.g., a dielectric or metal
material, to be patterned. The deposited organic, polymer
composition is then heated to remove solvent and cure (crosslink)
the composition. The silicon polymer composition is then applied to
the organic antireflective material by spin coating and cured. A
radiation-sensitive resist material can then be applied (directly
or indirectly) on the silicon antireflective material.
[0070] Typically, the solvent-containing resist composition is
applied using spin coating or another technique. The photoresist
coating is then typically heated (pre-exposure baked) to remove the
solvent and improve the coherence of the photoresist material. The
pre-exposure bake temperature may vary depending on the glass
transition temperature of the photoresist. The thickness of the
photoresist is preferably designed as thin as possible with the
provisos that the thickness is substantially uniform and that the
photoresist material be sufficient to withstand subsequent
processing (typically reactive ion etching) to transfer the
lithographic pattern.
[0071] After solvent removal, the resist material is then
patternwise-exposed to the desired radiation (e.g. 193 nm
ultraviolet radiation). Where scanning particle beams such as
electron beam are used, patternwise exposure can be achieved by
scanning the beam across the substrate and selectively applying the
beam in the desired pattern. If ultraviolet radiation is used, the
patternwise exposure is conducted through a mask which is placed
over the resist material. For 193 nm UV radiation, the total
exposure energy is about 100 millijoules/cm.sup.2 or less, or about
50 millijoules/cm.sup.2 or less (e.g. 15-30
millijoules/cm.sup.2).
[0072] After the desired patternwise exposure, the resist material
is typically baked to further complete the acid-catalyzed reaction
and to enhance the contrast of the exposed pattern. The
post-exposure bake is preferably conducted at about 60.degree.
C.-175.degree. C., more preferably about 90.degree. C.-160.degree.
C. The post-exposure bake is preferably conducted for about 30
seconds to 5 minutes. After post-exposure bake, the photoresist
with the desired pattern is developed by contacting the resist
material with an alkaline solution which selectively dissolves the
areas of the resist which were exposed to the radiation. Preferred
alkaline solutions (developers) are aqueous solutions of
tetramethyl ammonium hydroxide. The resulting lithographic
structure on the substrate is then typically dried to remove any
remaining developer solvent.
[0073] In some cases it maybe desirable to remove the resist
selectively to the silicon antireflective material as part of a
rework process in case of missprocessing of the resist during the
lithographic process. The removal of the resist can be accomplished
by dissolving the resist in an organic solvent, followed by baking
to remove the solvent and the resist. Any solvent dissolving a
photoresist is suitable. In some cases it is desirable to use
solvents containing bases such as tetramethyl ammonium hydroxide or
aqueous based solutions containing ammonium hydroxide. In some
cases it is desirable to remove the silicon antireflective material
and the photoresist selectively to the organic antireflective
material. In this case the solution for removal of the photoresist
can contain fluorine. Alternatively, it is possible to etch the
resist and/or the silicon antireflective material by a dry strip
using a plasma containing fluorine, carbon, hydrogen, chlorine,
oxygen, bromine, nitrogen, sulfur and/or mixtures thereof. Of
course, a combination of two described methods can also be
used.
[0074] On advantage provided by the silicon and organic
antireflective material is that by optimizing the RIE condition
using a reactive ion plasma consisting of C, F, H, N, S O and
mixtures thereof, excellent selectivity between the silicon and
organic antireflective materials can ensure good pattern transfer.
Once the organic antireflective material is patterned, the
selective removal of the underlying substrate, e.g., a dielectric,
can continue since there is sufficient organic material left for
all subsequent etch steps.
[0075] In one embodiment, the proper pattern transfer based on the
etch selectivity between photoresist, silicon antireflective
material and organic antireflective material is exemplified in FIG.
2. By using a fluorocarbon plasma, e.g., CF.sub.4/O.sub.2, a
reactive ion etch (RIE) process, pattern transfer from the
photoresist 10 into the silicon antireflective material 12 is
established without consuming much of the photoresist. The high
etch selectivity in combination with choosing the appropriate
thickness for the silicon antireflective material enables the use
of relatively thin photoresists. The pattern is then transferred
into the underlying organic antireflective material 14. By using a
non-fluorocarbon plasma based RIE process good selectivity between
the silicon antireflective material and organic antireflective
material is established as well as consumption of the photo resist.
Once the organic antireflective material is patterned, the pattern
is then transferred to the substrate 16. If the substrate is a
dielectric material such as an oxide or low k silicon based
dielectrics, then a fluorocarbon based RIE process will likely
ensure consumption of the silicon antireflective material as well
as good selectivity between the organic material and the
dielectric. The remaining organic antireflective material is then
removed by methods known to those in the art.
[0076] The lithographic structure can also be used to introduce a
taper during the etch of the organic antireflective material, which
effectively leads to reduction in bottom critical dimension
compared to the bottom critical dimension after lithography of
contact hole patterning. Introducing a taper during etch of contact
holes using the antireflective structure provides an effective
shrink method especially for contact hole pattern. Ion sputtering
can be used to taper the corner edges of the organic antireflective
material.
[0077] The lithographic structure can be used to create patterned
material structures such as metal wiring lines, holes for contacts
or vies, insulation sections (e.g., damascene trenches or shallow
trench isolation), trenches for capacitor structures, etc, as might
be used in the design of integrated circuit devices. The
lithographic structure is especially useful in the context of
creating patterned materials of substrates such as oxides, nitrides
or polysilicon.
[0078] Examples of general lithographic processes where the
lithographic structure can be useful are disclosed in U.S. Pat.
Nos. 4,855,017; 5,362,663; 5,429,710; 5,552,801; 5,618,751;
5,744,376; 5,801,094; 5,821,469 and 5,948,570. Other examples of
pattern transfer processes are described in Chapters 12 and 25 of
"Semiconductor Lithography, Principles, Practices, and Materials"
by Wayne Moreau, Plenum Press, (1988), the disclosure of which is
incorporated herein by reference. It should be understood that the
invention is not limited to any specific lithographic technique or
device structure.
EXAMPLE 1
Silicon and Organic Antireflective Materials Deposited by Spin
Coating
[0079] The organic polymer composition, NFC-1400, commercially
available from JSR Microelectronics was spin coated onto an oxide
wafer at 3995 rpm and baked at 170.degree. C. for 60 sec providing
an organic antireflective material of a thickness of 200 nm and the
optical constants of n=1.7 and k=0.8 k (193 nm). The silicon
polymer composition, SHBA470, available from Shin-Etsu Chemical,
was spin coated onto the organic antireflective material at 3000
rpm and baked at 200.degree. C. for 120 sec providing a silicon
antireflective material with a thickness of 20 to 35 nm and optical
constants of n=1.85 and k=0.2 (193 nm).
EXAMPLE 2
193 nm Lithography and Etching the Antireflective Materials
[0080] The antireflective materials were formed as described in
Example 1. A material of acrylic-based photoresist (available from
JSR Microelectronics and Shin-Etsu) was spin-coated over the
silicon antireflective material to a thickness of about 250 nm. The
photoresist was baked at 130.degree. C. for 60 sec. The photoresist
was imaged using a 0.75 NA ASML Stepper with conventional and
annular illumination using a APSM reticle. After patternwise
exposure, the photoresist was baked at 130.degree. C. for 60 sec.
The image was then developed using commercial developer (0.26M
TMAH). The resulting pattern showed 90 nm lines with different
pitches as well as isolated and nested 120 nm contact holes.
EXAMPLE 3
[0081] The photoresist of Example 2 was selectively removed to SHB
A470 on top of NFC-1400 (Example 1) by applying a solvent mixture
of y-butyrolactone and butylacetate after patterning. Then the
photoresist was reapplied (the wafer was spun at 3000 rpm for 30
sec followed by a bake of 130.degree. C. for 30 sec) and exposed as
described in Example 2 to give lines and spaces pattern that were
in size and profile identical to the patterns obtained on SHBA470
and NFC 1400 (Example 1) without solvent rinse
[0082] The pattern (lines and spaces as well as contact holes) were
then transferred into the silicon material (Example 1) by a
fluorocarbon plasma using a LAM RIE tool. The etch selectivity
between the photoresist and the silicon antireflective material
exceeded 3:1 demonstrating that little consumption of photoresist
is lost during the silicon antireflective material open etch. The
pattern was transferred by a nitrogen hydrogen based etch into the
organic antireflective material. During this step the photoresist
was almost completely consumed, however, the silicon antireflective
material showed no significant degradation. The pattern was
transferred into a material of 300 nm oxide by a fluorocarbon
plasma RIE process, which completely consumes the silicon
antireflective material. The remaining organic antireflective
material was stripped by a nitrogen, hydrogen etch.
EXAMPLE 4
Shrink by Etch
[0083] After etching through the antireflective materials (Example
1, SHBA470 and NFC1400) using CF based RIE chemistry for the
silicon antireflective material and nitrogen hydrogen based RIE
chemistry for the organic antireflective material, a reduction of
bottom critical dimension of 15-20 nm was observed in the contact
hole patterned in Example 2 indicating that the antireflective
structure can be used as an effective contact shrink method via
RIE.
* * * * *