Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-05-02
2004-12-07
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S356000
Reexamination Certificate
active
06828388
ABSTRACT:
The present invention relates to amorphous perfluorinated or fluorinated polymers substantially unstable ionic end group free, in particular COF, COOH or their corresponding esters, or salts or said end groups being undetectable by the method reported hereunder.
More specifically the present invention relates to amorphous (per)fluorinated polymers containing cyclic perfluorinated structures.
Said polymers are characterized by a high transparency at wave lengths from 150 to 250 nm. Therefore said polymers are usable for achieving protective films in the production of semiconductors by means of microlithographic techniques at 248 nm, 193 nm and 157 nm.
It is known that amorphous fluorinated polymers when used for microlithographic applications must show the lowest possible absorption with respect to the wave lengths of the incident light. In this application fluoropolymers are required having transparency at lower and lower wave lengths, from 248 nm to 193 nm and preferably even to 157 nm, to have smaller and smaller and quicker and quicker chips.
The amorphous fluorinated polymers are characterized by a high transparency in a wide range of wave lengths, however at wave lengths lower than 250 nm the transparency is not high. This is mainly due to the fact that the amorphous polymers, obtained by the known conventional syntheses of the prior art, contain unstable polar ionic end groups, mainly of the COF, COOH type, which absorb at wave lengths lower than 250 nm, reducing the film transparency of the amorphous (per)fluorinated polymer to said wave length ranges.
Various processes to decrease or neutralize the residual amounts of said polar end groups are known in the prior art, however the known methods do not allow to lead to a substantial elimination of ionic end groups, in particular the COF and COOH end groups.
One of the methods used to neutralize the acid end groups in polymers is by fluorination: the fluorinating agent is generally elementary fluorine, but also other fluorinating agents are used.
The polymer can be fluorinated under solid form as described in U.S. Pat. No. 4,743,658, or dissolved in solvents which are stable to fluorination, as described in EP 919,060. Both treatments are carried out at high temperatures, particularly of the order of 200° C., with fluorine diluted with inert gas. Or, before fluorination a pre-treatment of the end groups can be carried out with tertiary amines or alcohols to favour the subsequent fluorination reaction. The temperatures are in the range 75° C.-200° C. and must be lower than the polymer Tg. See patent application WO 89/12,240 and U.S. Pat. No. 4,966,435.
By said methods of the prior art a reduction of the polar end groups is obtained but not their substantially complete elimination. Besides, in some cases during the process other polar end groups such as for example COF are formed. See the comparative Examples.
The residual presence of polar end groups in amorphous (per) fluorinated polymers, as said, worsens their optical properties and compromises the use thereof in the microlithography field, in particular at wave lengths lower than 200 nm, more particularly lower than 180 nm.
The Applicant has unexpectedly and surprisingly found perfluorinated or fluorinated amorphous polymers substantially unstable ionic end group free, in particular COF, COOH, or their esters, or salts, on the basis of the analysis method reported hereunder. An object of the present invention are amorphous perfiuorinated or fluorinated polymers substantially unstable ionic end group free, in particular COF, COOH or their esters or salts, said end groups being undetectable by the method reported below, i.e. each end group being in a total amount lower than 0.05 mmoles/Kg polymer; the determination method of acid end groups being the Fourier transform IR spectroscopy by Nicolet® Nexus FT-IR equipment (256 scannings, resolution 2 cm
−1
), wherein on a sintered polymer powder pellet having a 5 mm diameter and thickness from 50 to 300 microns (1.75-10.5 mg of polymer) a scanning between 4,000 cm
−1
and 400 cm
−1
is initially carried out, the pellet being then kept for 12 hours in an environment saturated with ammonia vapours, and finally recording the IR spectrum under the same conditions of the initial IR spectrum; elaborating the two spectra by subtracting from the signals of the spectrum relating to the untreated sample (initial spectrum) the corresponding ones of the specimen spectrum after exposure to ammonia vapours, obtaining the udifferencen spectrum, which is normalized by the following equation:
“
Difference
spectrum
”
[
pellet
weight
(
g
)
/
pellet
area
(
cm
2
)
]
The optical densities related to the end groups which have reacted with the ammonia vapours are determined; said end groups being the COOH and COF end groups, that with ammonia vapours give rise to detectable peaks; the optical densities are converted in mmoles/kg polymer using the extinction coefficients reported in Table 1, page 73 of the paper by M. Pianca et Al. “End groups in fluoropolymers”, J. Fluorine Chem. 95 (1999), 71-84 (herein incorporated by reference); the found values express the concentrations of the residual polar end groups as mmoles of polar end groups/kg of polymer: in the spectrum of the amorphous (per)fluorinated polymers bands related to COOH groups (3,600-3,500, 1,820-1,770 cm
−1
) and/or COF groups (1,900-1,830 cm
−1
) are not detectable, the method detectability limit being 0.05 mmoles/Kg polymer.
More particularly the present invention relates to amorphous (per) fluorinated polymers containing cyclic perfluorinated structures.
With amorphous polymers according to the present invention, besides the properly said amorphous polymers, also semicrystalline polymers are meant, provided that they are soluble in perfluorinated solvents for at least 1% by weight at temperatures in the range 0° C.-100° C., preferably 20° C.-50° C. The completely amorphous polymers show only glass transition temperatures but not melting temperatures; semicrystalline polymers show one glass transition temperature and melting temperatures.
As perfluorinated solvents, perfluoroalkanes, perfluoropolyethers, preferably having boiling point lower than 200° C., such as for example Galden® LS165, tertiary perfluoroamines, etc., can for example be mentioned.
The amorphous polymers according to the present invention contain one or more of the following fluorinated comonomers:
C
2
-C
8
perfluoroolefins, such as tetrafluoroethylene (TFE) hexafluoropropene (HFP);
C
2
-C
8
chloro-fluoroolefins, such as chlorotrifluoroethylene (CTFE);
CF
2
=CFOR
f
(per)fluoroalkylvinylethers (PAVE), wherein R
f
is a C
1
-C
6
(per)fluoroalkyl, for example CF
3
, C
2
F
5
, C
3
F
7
;
CF
2
=CFOX (per)fluoro-oxyalkylvinylethers, wherein X is: a C
1
-C
12
alkyl, or a C
1
-C
12
oxyalkyl, or a C
1
-C
12
(per) fluoro-oxyalkyl having one or more ether groups, for example perfluoro-2-propoxy-propyl;
fluorosulphonic monomers, preferably selected from the following:
F
2
C=CF—O—CF
2
-CF
2
—SO
2
F;
F
2
C=CF—O—[CF
2
—CXF—O]
n
—CF
2
—CF
2
—SO
2
F wherein X=Cl, F or CF
3
; n=1-10
F
2
C=CF—O—CF
2
—CF
2
—CF
2
—SF;
fluorodioxoles, preferably perfluorodioxoles;
non conjugated dienes of the type:
CF
2
=CFOCF
2
CF
2
CF=CF
2
,
CFX
1
=CX
2
OCX
3
X
4
OCX
2
=CX
1
F
wherein X
1
and X
2
, equal to or different from each other, are F, Cl or H; X
3
and X
4
, equal to or different from each other, are F or CF
3
, which during the polymerization cyclopolymerize.
Among fluorodioxoles the ones of formula:
can be mentioned, wherein R′
F
is equal to F, R
F
or OR
F
wherein R
F
is a linear or branched when possible perfluoroalkyl radical having 1-5 carbon atoms; X
1
and X
2
eual to or different from each other being F or CF
3
.
Preferably in formula (IA) R′
F
=OR
F
, R
F
prefer
Calini Pierangelo
Tortelli Vito
Arent Fox
Lipman Bernard
Solvay Solexis S.p.A.
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