Sulfonium salt and use thereof

Details Sulfonium salt and use thereof Sulfonium salt and use thereof

2002-11-27

2004-11-16

Ashton, Rosemary (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Imaging affecting physical property of radiation sensitive...

Radiation sensitive composition or product or process of making

C430S905000, C430S921000, C522S031000

Reexamination Certificate

active

06818379

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a novel sulfonium salt, a chemical amplifying type resist composition for use in semiconductor microfabrication, and a polymerization initiator composition.
Semiconductor microfabrication employs a lithography process using a resist composition. In lithography, theoretically, the shorter the exposure wavelength becomes, the higher the resolution can be made, as expressed by Rayleigh's diffraction limit formula. The wavelength of an exposure light source for lithography used in the manufacture of semiconductor devices has been shortened year by year as g line having a wavelength of 436 nm, i line having a wavelength of 365 nm, KrF excimer laser having a wavelength of 248 nm and ArF excimer laser having a wavelength of 193 nm. F
2
excimer laser having a wavelength of 157 nm seems to be promising as the next-generation exposure light source. Further, as the exposure light source of the subsequent generation, extreme ultraviolet (EUV) ray having a wavelength of 13 nm has been proposed as the exposure light source following the 157 nm-wavelength F
2
excimer laser.
Since light sources having shorter wavelength than that of g line and i line, such as excimer laser and the like have low illumination, it is necessary to enhance the sensitivity of a resist. Consequently, there are used so-called chemical amplification type resists utilizing the catalytic action of an acid produced from a sulfonium salt by exposure and containing a resin having a group being dissociated by this acid.
However, conventionally known sulfonium salts disclosed in, for example, WO96/27584 or Research Disclosure Vol. 437 September, 1568 (2000), involve the problem that those of the type having high sensitivity provide an unsatisfactory cross-sectional view of resist particularly with a rounded head, while, conversely, those of the type capable of providing a good cross-section view of resist have low sensitivity.
The object of the present invention is to provide a novel sulfonium salt as well as to provide a chemical amplifying type positive resist composition comprising the sulfonium salt and a resin component, which resist composition is suitable for lithography employing ArF or KrF excimer laser for example and has sensitivity in good balance with a cross-sectional view of resist.
As a result of intensive study made by the inventors of the present invention, they have found that use of a specific sulfonium salt makes it possible to resolve the foregoing problem, and have completed the present invention.
SUMMARY OF THE INVENTION
That is, the present invention is directed to:
(1) A sulfonium salt represented by the following formula (I) (hereinafter referred to as “the present sulfonium salt”)
wherein Q
1
, Q
2
and Q
3
each independently represent hydrogen, hydroxy, alkyl having 1 to 6 carbon atoms, or alkoxy having 1 to 6 carbon atoms, but all of Q
1
, Q
2
and Q
3
are not the same; and Q
4
and Q
5
each independently represent perfluoroalkyl having 1 to 8 carbon atoms.
(2) The sulfonium salt according to (1), wherein in the formula (I), one of Q
1
, Q
2
and Q
3
is methyl and each of the other two is hydrogen.
(3) The sulfonium salt according to (1), wherein in the formula (I), one of Q
1
, Q
2
and Q
3
is tert-butyl and each of the other two is hydrogen.
The present invention is also directed to:
(4) A chemical amplifying type positive resist composition comprising: a resin which contains a structural unit having a group that is unstable to acid and which is insoluble or slightly soluble by itself in an aqueous alkali, but becomes soluble in the aqueous alkali by an action of acid; and the present sulfonium salt (hereinafter referred to as “the present resist composition”).
(5) The chemical amplifying type positive resist composition according to (4), further comprising an acid generator comprising at least one onium salt selected from the group consisting of;
a triphenylsulfonium salt represented by the following formula (IIa)
wherein P
1
, P
2
and P
3
each independently represent hydrogen, hydroxy, alkyl having 1 to 6 carbon atoms, or alkoxy having 1 to 6 carbon atoms and P
4
SO
3
−
represents an organic sulfonate ion;
a diphenyliodonium salt represented by the following formula (IIb)
wherein P
5
and P
6
each independently represent hydrogen, hydroxy, alkyl having 1 to 6 carbon atoms, or alkoxy having 1 to 6 carbon atoms and P
7
SO
3
−
represents an organic sulfonate ion; and
a sulfonium salt represented by the following formula (IIc)
wherein P
8
and P
9
each independently represent alkyl having 1 to 6 carbon atoms or cycloalkyl having 3 to 10 carbon atoms, or when P
8
and P
9
are combined with S
+
to form a ring, P
8
and P
9
together with S
+
represent an alicyclic hydrocarbon group having 3 to 7 carbon atoms; at least one —CH
2
— group of the alicyclic hydrocarbon group may be substituted with a —CO— group and at least one —CH
2
— group of the alicyclic hydrocarbon group may be substituted with oxygen or sulfur; P
10
represents a hydrogen and P
11
represents alkyl having 1 to 6 carbon atoms, cycloalkyl having 3 to 10 carbon atoms, or an aromatic ring group which may be substituted, or when P
10
and P
11
are combined with an adjacent CHC(O) group to form a ring, P
10
and P
11
together with the CHC(O) group represent 2-oxocycloalkyl; and P
12
SO
3
−
represents an organic sulfonate ion.
(6) The composition according to (5), wherein Q
5
and Q
6
in the formula (I) each independently represent perfluoroalkyl having 1 to 8 carbon atoms; and p
4
in the formula (IIa), P
7
in the formula (IIb) and P
12
in the formula (IIc) each independently represent perfluoroalkyl having 1 to 8 carbon atoms, alkyl having 1 to 8 carbon atoms, an aromatic group having 6 to 12 carbon atoms, or a camphor group.
(7) The composition according to (5) or (6), wherein the weight ratio of the sulfonium salt represented by the formula (I) to the at least one onium salt selected from the group consisting of the triphenylsulfonium salt represented by the formula (IIa), the diphenyliodonium salt represented by the formula (IIb) and the sulfonium salt represented by the formula (IIc) is 9:1 to 1:9.
(8) The composition according to any one of (4) to (7), wherein the content of the structural unit having a group that is unstable to acid in the resin is 10 to 80 mol %.
(9) The composition according to any one of (4) to (8), wherein the structural unit having a group that is unstable to acid in the resin is 2-alkyl-2-adamantyl (meth)acrylate or 1-(1-adamantyl)-1-alkylalkyl (meth)acrylate.
(10) The composition according to (9), wherein the resin further comprises at least one structural unit selected from the group consisting of: a structural unit derived from p-hydroxystyrene; a structural unit derived from m-hydroxystyrene; a structural unit derived from 3-hydroxy-1-adamantyl (meth)acrylate; a structural unit derived from 3,5-dihydroxy-1-adamantyl (meth)acrylate; a structural unit derived from (meth)acryloyloxy-&ggr;-butyrolactone wherein at least one hydrogen on the lactone ring may be substituted by alkyl; and a structural unit represented by the following formulae (IIIa) and (IIIb)
wherein R
1
and R
2
each independently represent hydrogen, methyl, or trifluoromethyl and n represents an integer from 1 to 3.
(11) The composition according to (9) to (10), wherein the resin further comprises a structural unit derived from 2-norbornene and a structural unit derived from aliphatic unsaturated dicarboxylic anhydride.
(12) The composition according to any one of (4) to (11), further comprising an amine as a quencher.
(13) The composition according to any one of (4), further comprising a surfactant.
Further, the present invention is directed to: (14) A polymerization initiator composition comprising the present sulfonium salt and a sensitizer (hereinafter referred to as “the present polymerization initiator composition”).
DESCRIPTION OF EMBODIMENT
In the present sulfonium salt, Q
1
, Q
2
and Q
3
each independently r

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