Note: Descriptions are shown in the official language in which they were submitted.
e~
NEW CLi'~SS OF X-RAY RE:SISTS BI~SED ~N DONOR
POLYMER--DOPEI:) HALOCARBON ~CCEPTOR
TRANSFER COMPLEXES
Bl~CKGROUND OF T~IE INVE:NTION
Field of the Inve~ntion
The invention Lies in the field of X-ray resist
compositions and the production of patterned thin
film layers thereErom.
. Prior Art
The prior a.rt is replete with radiation sensitive
materials as resists and with their use in
pattern formation in the fabrication of micro-
electronic (1evices. In tllc prior ~rt, pattcrn
formation in these materials is dependent upon
differential solubility between irradiated and
unirradiated regions. These solubility changes
are produce~ by either bondbreaking, (chain
scission) or bond formation (chain crosslinking~
in polymeric systems. This occurs in the presence
of actinic radiation, E-beam radiation or X-ray
radiation.
YO979 040
1 Several prior art resists have included in them halogen
containing organic compounds or halocarbons. These
halocarbons are generally present to enhance the sensi-
tivity of the resist. Several such resists are dis-
cussed and reviewed in U.S. Patents 3,752~669; 3,7~9,023;
3,820,993; 3,895,954; 3,988,152 and 3,316,036. The
resists disclosed in the above references are sensitive
to either actinic or electron beam radiation. ~he prime
need for the halocarbon in these resists are for the
generation of free radicals to initiate polymerization.
More recently there has been developed a new class of
E-beam resist materials based Oll donor-charge transfer
salts. These resist materials are described in Canadian
patent application 354,062, filed June 16, 1980, by E.M.
Engler et al and assigned to the assignee of the present
application and is entitled "Class Of E-Beam Resists
Based Qn Conducting Organic Charge Transfer Salts".
These materials are different and distinct from the pre-
sent compositions in that they are crystalline saltsthat are coated onto a substrate by evaporation or sub-
limination, wherein the present compositions are amor-
phous polymeric materials which are cast from a solu-
tion. The present resist compositions are two compo-
nent systems in which differential solubility is gener-
ated via salt formation as opposed to the one compo-
nent system of the above-mentioned application in
which a neutral substance is produced. Additionally,
the materials used in the present invention are in-
sulating while the aforementioned are conductive.
The prior art materials have several drawbacks amongwhich is the difficulty of obtaining sharp images of
high resolution, particularly in negative resists.
This is due to the swelling of the polymeric material
during solvent development.
YO9-79-040
SUMMARY OF THE INVENTIO~
What has been discovered here are novel X-ray negative
resists which can be broadly classified as donor
polymer-doped halocarbon charge transfer complexes. More
specifically, the materials comprise a polymer bac]cbone or
skeleton having bonded thereto electroactive molecules.
These electroactive polymer species are doped with a
halocarbon.
BRIEF DESCRIPTION OF THE DRA~7INGS
FIG. 1 shows graphically the relationship between the
exposure dose and the normalized thickness of the exposed
resist.
~IG. 2 and FIG. 3 show X-ray exposed patterns via scanning
electron microscopy.
DESCRIPTION OF THE INVENTION
The present invention teaches novel X-ray resist materials
which can be used to provide a negative resist image.
Principally, the materials are comprised of electroactive
polymers and a halocarbon. The resist includes a donor
polymer-doped halocarbon charge transfer complex.
Preferably, the electroactive polymer consists of a polymer
backbone and an electroactive molecule bonded thereto.
Several of -the electroactive polymers of the type
anticipated for use in this invention are described in U.S~
Patent No. 4,142,783 and in the IBM* Technical Disclosure
Bulletin, Vol. 20, #7, December 1977.
The polymeric backbone can be selected from several known
homopolymer and copolymer compositions having skeletal
functional groups or side chains having functional groups
capable of reacting with the functional groups of donor
molecules. Polymers which can be used, include polystyrene,
a copolymer o~ polystyrene and chloromethylated styrene,
e.g.,
*Registered Trade Mark Of International Business Machines
Corporation
YO9-79-040
CH2C~
~(CH2-CH)x (CH2-CH)I-~ ]n
where the value of X is varied (O<x<l), so that the
number of donor molecules per chain and their distance
apart can be varied. The desired lithographic
properties are thus varied as a function of X;
Typically, other polymer backbones can be selected
from the following:
polyglutamic acid
1I H
~C--CH-N~n
~CH2)2
COOH
polyvinyl chloL-ide
~; [-CH2-CH
CQ
polyepichlorohydrin
[(-C~2-CH-O~]
~2
C~
Y0979-040
poly(~halophosphazenes~
r X Rl
_ - N - P t
R Xln
poly(acrylic chLoride) ~CH -CH ~n
' COOC~
and the like.
The donor molecules that can be used in this
invention are those which can be char~cterizcd as
having the following specific molecular properties:
(a) Those that are capable of electron oxidation to
a cation.
~b) Have an oxidation potential of from about O.lV
to about lV measured against a standard calomel
electrode;
(c) those that photoionize in the presence of a
halocarbon; and
lS (d) which have a functional group whlch when reacted
with a polymer support will be bond~d thereto.
Functlonal groups contemplated by the present
invention include hydroxyl, phenoxy, carboxyl, amino
~- groups and the like.
20- A wide variety of ~ donor molecules are expected
to be active in polymeric form as negative resist
materials.
YO979-040
This invention may be effected by using donors
of the empirical formula C6H4X4R~ and having the
structural formula
F?l~¢X~ (X~ R 3
R2 X X R4
where X=O, S, Se and Te or any combination thereof.
T~e R groups may be of any organic substituent
including alkyls, such as methyl and ethyl, phenyls,
substituted phenyls, -SCH3, -CO2ME, halogen, fused
cyclics in which the substituent effectively
connec-ts Rl with R2 and R3 with R4, e.g. Some
specific fulvalene compositions include
tetrathiaulva1ene (TTF), its derlvatives and Se
analogs (TSeF) and its derivatives. For example,
tetrathiafulv~lenecarboxylic acid (l'l~O?II),
tetraselenafulvalenecarboxylic, ~hydroxyrnethyl)-
tetrathiafulvalene (TTFC1l2O~I), hydroxymethyl-
tetraselenafulvalene (TSeFC~l2O~I), (p-hydroxyphenyl)-
tetrathiafulvalene (TTFC6~l4O~I), (p hydroxyphenyl)-
tetrasclcnilEI~l.val.etlc (TSeF(:GII~OII), (p~ llin~ llcny1)-
tetra~llia~ulvalcne (TTFC6ll4Nll2), (p-carboxyphc!nyl)-
tetrathiafulvalene (TTFC6ll4CO2ll), phenoxy (TTF).
Qf~x~
The followi.ny fuscd rings, such ~.s cyclo~)cntene,
cyclohexene, benzene, furan, thiophene, clihydrofuran
and dihydrothiophene, and derivatives ttlereof can
be used. In addition, tctr~thiatctraccrle com~ounds,
e.g.
S~ S
C~
S--S
YO979-0~0
and their derivatives are also suitable for the
purpose of this invention. In general, organic
~-electron donors havinq low ionization potentials
(<7.5eV)2 can be used.
Additionally, the following compositions are
contemplated by this invention;
A~ines
R-NH2j R=Alkyl, Aryl
Pyrazolines
1 0 qS 5 ~N
I
\~3
~ Pyrazolines of particular importance include
; 1,3-di-(p-met}loxy~henyl)-5-(y-hydroxypllellyl)-~2-
pyrazoline,
1, 5-di-(p-methoxyphenyl)-3-(p-hydroxyphenyl)-A2-
pyrazoline,
3, 5-di-(p-methoxyphenyl)-1-(p-hydroxyphenyl)-~2_
pyrazoline,
1, 3-di-lp-methoxyphenyl)-5-(p-carboxypllcnyl)-A2-
pyrazoline;
1, 5-di-(p-methoxyphenyl)-3-(p-carboxyphenyl)_Q2_
pyrazoline,
3, 5-di-~p-methoxyphenyl)-1-(p-carboxyphenyl)-~2-
pyrazoline,
1, 3~di-(p-methoxypheny13-5-(p-aminophenyl)-Q2-
: 25 pyrazoline,
1, 5-di(phctlyl)-3-(p-aminophellyl)-A2-~)yra%olinc,
l-(p hydroxyphenyl)-3-(p-methoxystyryl)-5-
(p-methoxyphenyl)-~2-pyrazoline,
l-(p-hydroxyphenyl)-3-(p-diethylaminostyryl) 5-
(p-diethylaminophenyl)-~2-pyrazoline,
YO979-0~0
1 Ferrocene
<~
m
~ ~ m = Fe, etc.
~'
Phenothiazine
~ 10 ~1 -
lS [(~ -C5H5)Fe(CO)]4
Dithiadiselenafulvalene and its derivatives may also be used
as donor molecules.
The acceptor molecules that can be used in this invention
are those which can be characterized as having the following
specific molecular properties:
a) Contains one or more halogen atoms.
(b) Has high electron affinity to accept electron from
donor species (0-2eV)O
(c) Forms anionic species.
~30
Typical halocarbon acceptors which can be used are selected
from CC14, CBr4, CI4, C2 C16' C2 C12 4' 3 4 4
2 2 4' 2 2C14~ C2Br6~ ~3C18~ Cl C C13l CHBr , CHCl
CH2C12 and the like.
The halocarbon agent may be present in amounts ranging from
0.01 to 10 times the concentration of the donor moiety.
YO9-79-040
~'
There are two basic kinds of synthetic procedures
for covalently attaching the donor molecules to
the polymer resin. In equation (1~,
~ ~ ~ CH2x~ D- y ~ ~3 ~
where ~is a polymer, x is a halogen, D is a donor
molecule, and y is a functional group capable of
coupling D to the benzene ring. In this procedure,
preformed and appropriately functionalized donor
molecules tD-Y~ are reacted in single-step
coupling procedures with the polymer resin. In
this approach, the groups -x and -y are chosen
so as to lead to coupled products. Bonding to the
polymer matrix is accomplished in one step. In
an altern~te method, ti.e. reactions 2-4), the desired
electroactlve molecule is synthesi.zetl ~rom
polymer precursors directly on the resin.
; Thus, functionalized electroactive species
are not required; however, multiple polymer
reactions become necessary.
' O
C ¢S ~, ~ C l l z o--C ¢ 5~
~ ¢ ~ ~ C H2 -C--TT F
Y0979-040
1 The specific steps of the synthesis of the contemplated
compositions can be found in aforementioned U.S. Patent
No. 4,142,783.
The solvents whieh ean be used for film eoating are
toluene, chloroform, methylene chloride, eyclopentanone,
tetrahydrofuran, methyl ethyl ketone etc.
In the present invention resist compositions are exposed
to x-ray radiation.
Exposures were performed in a 10 6 torr. vaeuum, using a
vacuum generator 1 ReV electron gun (model ~VGl), with
7 KV gun voltage and 40 ma gun current. The x-rays having
an energy of about 1.34 KeV are generated with an Al tar-
get (8.3A) and x-ray spot of 1-2mm size. A gold (6000A)
mask on a polyimide substrate is coated with 500A of Al
to prevent optical exposure of the resist. The mask-wafer
separation used is 4~m, and the copy is obtained at a
gun-wafer separation of 18cm. Under these conditions
the copy time for a 100 mj/cm2 dose is about three hours.
X-ray exposures involve doses of 25-100 mj/cm .
More specifically, this invention concerns new compositions
of matter which function in a novel resist process when
irradiated by X-rays. For example, films of a polymerie
TTF materials can be spin east from a solution eontain-
ing a haloearbon aeeeptor, sueh as CBr4~ Under these
eonditions the resulting polymer film eontains CBr4 and
becomes sensitive to radiation. When X-rays are used
to irradiate these films through appropriate masks, only
the unexposed
YO9-79-040
li
areas can be removed from the underlylng substrate
by washinc3 with a non-polar solveht. This
negative resist process is a novel one and unrelated
; to those suggested earlier for polymers whose
solubility decreases upon exposure to radlation
because of radiation induced crosslinkin~ reactions.
It is suggested that these resists operate by means
.the radiation-induced formation of a salt
according to Reaction 1 where the
Poly (TTF) + CBr4 ~ poly (TTF.~ ~Br ) (1)
The neutral polymer is soluble in non-polar
solvents while the salt produced is insoluble. This
reaction is known to occur in monomeric TT~
in solution U. S. Patent No. 4 036 648
where the halide salt produced is insolu~le in
non-polar solvents. This new mechanlsm for
lithographic action has been established in the
following ways.
Using visible-rlca~ ir spcctropllotometry thc TTF
ions postulated in the above reactiorl have been
detected. By irradiating poly~TTF) doped
halocarbon films that were spun onto transparent
substrates. It has been observed that the films
spectrum changes during irradiation to give new
absorptions at 600nm and at 800nm previously
identified as characteristic of TTF ion and
aggregates thereof. (See the publication to
J. B. Torrancc ct al entitlcd oEtic l rropcrties of
the Radical Cation Tetrathiafulvalenium in its
Mixed-Valence and ~lonovalence ~alide Salts
Phys. Rev. B 19 730 (1979)). ~dditional
predictions of the suggested mechanism have also
.
YO979-040
1 been observed. For instance, it would be expected
tha-t polymer films containing no halocarbon present
would be much less sensitive to incident radiation.
Confirming this point, it has been ohserved that
irradiation of the undoped TTF polymer films have no
lithographic images when subjected to the same
incident radiation as in the case of doped films.
.
Another facet of this mechanism is that reversing of
the charge transfer in Reaction 1, see Reaction 2
below, could be expected to lead to a change in the
solubility properties, whereby, the irradiation
poly(TTF ) (X ) -~ poly TTF (2)
process would be nullified and removal of the polymer
(now in its neutral state) could take place. This
effect has been demonstrated in the following way.
An exposed film was found to be insoluble in the
organic solvent dimethylformamide (D~F). ~owever,
when the chemical reducing agent hydrazine is added
to the DMF solution, it was ohserved that the exposed
polymer fi]m was readily removed leaving a clean Si
substrate. In this process, hydrazine reduces the
oxidized TTF back to its neutral form TTF and the
neutral polymer, thus formed can he readily dissolved
in the organic solvent.
The third ramification of the postulated mechanism is
that other ~-donor polymers should be
lithographically active in the presence of halocarbon
dopants. As alluded to previously, ~-donor
sensitivity to radiation with halocarbons present has
been ohserved for a large number of donors in fluid
solution. If the postulated
Y09~79 040
1 mechanism is correct it would be expected that the
same variety of donor halocarbon ionization found in
solution would also be observed in the polymeric
solid state. Similar lithographic differential
solubility with donors such as pyrazoline,
; dimethylphenylenediamine, and ferrocene bound to
polymeric backbones and prepared as halocarbon doped
films, has in fact been observed.
A prime disadvantage of previous negative resist
materials are the inherently low resolution of the
patterns obtainable. As discussed earlier, negative
resists typically operate by means of a
- radiation-induced cross~linking process. Although
the cross-lin]ced polymer that remains cannot be
dissolved in a developer solvent, penetration of the
solvent into the polymer causes swelling of the
polymer chains since many of the development
solvents are thermodynamically good solvents for the
unexposed non-crosslinked polymer. The swelling
process grossly distorts the lithographic pattern
and attempts to alleviate this problem by use of
mixed solvents or thermal treatments have largely
been unsuccessful.
For the present resist process, however, the
lithographic patterns obtained showed no evidence
:
for solvent induced distortions or loss of
resolution. It is suggested that solvent
penetration of the polymer followed by swelling is
prevented in the system described herein, by the
presence of ions which act to repel the non-polar
solvent ~rom the polymer matrix. Thus solvent
cannot penetrate into the exposed polymer mass and
cause swelling.
~09-79-0~0
14
1 EXAMPLES
The following examples are given solely for purposes of
illustration and are not to be construed as limitations
on the inventions, many variations of which are possible
without departing from the spirit c~r scope thereof.
EXAMPLE 1
Poly (vinylcarboxytetrathiafulvalene)
Poly(vinylbenzylchloride), prepared from the monomer vin~l-
benzylchloride, 0.275g, and the cesium salt of tetrathia-
fulvalene carboxylic acid, 0.750mg, is added to 75 ml of
a DMF solvent and stirred at 75C for 24 hours. The solu-
tion is concentrated and the resultant polymer is isol~ted
by precipitation into a rapidly stirred H2O solution. Re-
peated precipitations from T~IF/H2O gave a dark brown solid.
Anal. calc'd for C15 1 Hll.6S3.5 1.7 C 0.13
9 9 ( 7 4 3O2)0.87(Cl~0.l3] C=53.81, S=33.0g~ cl=o.l4.
Found C,53.74; S,32.96; Cl,0.23.
Polymer films are prepared by mixing 4.7mg of the polymer
with l mg of C2Br2C14 which is added to 20~1 of cyclopen-
tanone. The films are spin coated at 2500 RPM on a photo-
; resist spinner. No baking is required in order to obtain
good images. Solvents used as developers include tetra-
hydrofuran, cyclopentanone, diglyme, methylene chloride,
chloroform and mixtures thereof.
Several poly (TTF) films are prepared in this manner. To
determine the sensiti~ity of this resist, these films
were exposed to X-rays at energies ranging
YO9-79-0~0
1 from 15-100 mj/cm2. The films were developed in (THF),
and then the thickness of the remaining resist was deter-
mined. From the resulting plot of normalized thickness
remaining vs. dose rate, see FIG. 1, it can be seen that
the sensitivity of the material for 50~ thickness remain-
ing is ~ 44mj/cm2. From data on other resist materials
(Table I), it can be seen that the present material is
one of the most sensitive resists known.
Determination of Resolution of Resist:
An X-ray exposed pattern was studied via scanning electron
microscopy (see FIG. 2). These photographs shown no evi
dence for the classical negative resist swelling behaviour.
All of the patterns are extremely well formed, with parallel
vertical walls and showiny no signs of pattern distortion.
From the indicated scale, it is estimated that the present
resist has a resolution of better than 2000A.
EX~MPLE 2
Poly (vinylcarboxyferrocene)
Poly (vinylben~ylchloride), (150mg) is reacted with the
360 mg of ceslum salt of ferrocene carboxylic acid, (as
prepared below) in 65ml DMF solvent. The solution is
heated to 75C, and stirred for 24 hours. The volume
of the solution is reduced and the polymer is precipi-
tated into H2O. Repeated precipitations (THF/H2O) gave
a light yellow solid. Anal. calc'd for CgHg(C7 5H5 ~l 4
FeO 7) (Clo 3) C,69.9; Fe,13.4; Cl,4. Found C,67.62;
Fe 12.11; Cl,4.61.
YO9-79-040
s
16
1 Cesium salt of carboxyferrocene. Monocarboxyferrocene
230 mg, is dissolved in ethanol. To this solution is
added 5ml of H2O which contained 250 mg CsHCO3. Using
slight heating, and high vacuum, the solution was taken
to dryness to produce the desired salt.
About 5.2 mg of -the so prepared polymer and about lmg
of C2Br2C14, the acceptor compound are added to 261ll of
THF solvent and films are spun at 2500 RPM on a photo-
resist spinner. The films are exposed to X-rays having
energies in the range 10-lOOmj/cm2. Patterns are developed
by one of the following solvents or mixtures thereof:
toluene, chloroform, methylene chloride, cyclopentanone,
THE.
No pre- or post-exposure baking is required to obtain
good images.
EXAMPLE 3
Poly (vlnylphenoxy-1,3-(p methoxyphenyl)-5-
,~
(p-hydr~oxyphenyl)-~-pyraæoline):
The potassium salt of the pyrazoline is prepared by add-
ing 374mg pyrazoline to 40 mg KH in dry THF. After stirring
for 30 minutes, 152mg of polyvinylbenzylchloride is added
to this solution. After refluxing for 4 days, the solvent
volume was reduced and the polymer isolated following
multiple reprecipitations from 50:50 MeOH/H2O. About 4.6mg
of the polymer (4.6mg) and lmg of the C2Br2C14 acceptor,
are added to 32~1 of THF. Films were spun at 2500 RPM on
a photoresist spinner. After x-ray exposures as in the
above examples, good images were obtained by developing
YO9-79-040
17
1 in toluene: THF mixtures. No pre- or post-exposure
baking was required to obtain good images
EXAMPLE 4
Poly[p-N,N-dimethylamino)-N-~-D-glutamanilide)
Poly(D-glutamic acid) (Miles-Yeda Ltd. mol wt 12400),
0.5g is dissolved in 50 mL of dry DMF and 2g of freshly
distilled N, N-dimethyl-p-phenylenediamine is then addedO
The solution is cooled to 0C and lg of DCC is added
with stirring. Stirring is continued at 0C for lh and
at room temperature for an additional 24 h. One milliter
of dry methanol is added and stirring is continued for
an additional h. The precipitate is filtered off and
the filtrate is evaporated to dryness at 35C (0.01 mm)
(bath temperature). The residue is dissolved in THF
and filtered in a drybox under nitrogen. Diethyl ether
is added to the solution and the precipitate is filtered
and collected under nitrogen. The collected solid is fur~
ther purified by precipitation from THF with diethyl ether.
Anal. Calcd for (C13H17N3O2)n
Found: C,62.69; H,7.64; N,14.54.
About 15mg of the abo~e prepared polymer (5.Omg) and the
C2Br2C14 acceptor, lmg, are added to 29~1 THF and films
are spun (2500 RPM) on a photoresist spinner. After ex-
posure to X-rays as in the above examples, good images
are obtained by use of methyl ethyl ketone developer sol-
vent. No bakiny was required.
YO9-79-040
18
1 EXAMPLE 5
Polyphenoxytetrathiafulvalene
About 15 mg of polyphenoxytetrathiafulvalene and 1.0 mg
of C2Br2C14 are added to 29~1 THF and films are spun
(2500 RPM) on a photoresist spinner. After exposure
to X-rays as in the above examples, good images are
obtained by use of methyl ethyl ketone developer sol-
vent. No baking was required.
TABLE I
AlK~ X-Ray
Resist Sensitivity (mj/cm ) Resolution
PMMA** 1000 .02
POSITIVE PBS** 80 <1
RESISTS FBM** 30 <1
Methyl 20 >1~*
Acrylate
NEGATIVE PGMA-EA** 5 >1~*
RESISTS Polysty- 40 ~0.2
rene-TTF**
*Materials are severely limited by swelling.
** PMMA - Poly(methyl methacrylate)
PBS - Poly ~butene-l-sulfone)
FBM - Poly (fluoro butyl methacrylate)
PGMA-EA - Poly (glycidyl methacrylate ethyl acrylate
copolymer)
After X-ray exposure the polymer Eilms are readily removed
by washing with a DMF solution which contained a few drops
of the reducing agent hydrazine. Because
YO9-79-0~0
19
this works by reducing the oxidized films, it
is likely that other reducing agents (and solvents)
can similarly be used.
Other functionalized polymers, e.g.,
poly~epichlorohydrin), poly(halophosphazenes),
poly(acrylic chloride) and copolymers of the same
were reacted with donors listed above. The
resultant electroactive polymers were treated
as in Examples 1-5 above and provided gooa images
when exposed to X-ray radiation.
Y0979-040
