JPH0725846A - Alkylsulfonium salt - Google Patents

Abstract

PURPOSE:To obtain a new alkylsulfonium salt for photosensitive agent, etc., of photoresist for far-ultraviolet rays, having a 2-oxocyclic alkyl group, having high transparency to far-ultraviolet ray area and capable of effectively generating hydracid by radiation such as far-ultraviolet rays. CONSTITUTION:A sulfide derivative expressed by the formula R<3>-S-R<1> (R<1> is 1-8C alkyl; R<3> is 5-7C 2-oxo-cyclic alkyl) or the formula R<2>-S-R<3> (R<2> is 5-7C cyclic alkyl) [e.g. 2-(cyclohexylmercapto)cyclohexanone] is dissolved in a solvent such as nitromethane and the solution is made to react with a halogenated hydrocarbon (e.g. methyl iodide) expressed by the formula R<2>-W (W is halogen) or the formula R<1>-W in the presence of a compound (e.g. silver trifluoromethanesulfonate) expressed by the formula M<+>Y<-> (M<+> is K<+>, Na<+> or Ag<+>; Y<-> is counter ion) to provide the objective compound salt for photosensitive agent, etc., of photoresist for far-ultraviolet rays, expressed by the formula, having high transparency to far-ultraviolet ray area and capable of generating hydracid by far-ultraviolet rays.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkylsulfonium salt compound which absorbs far-ultraviolet light having a wavelength of 220 nm or less and efficiently generates an acid.

[0002]

2. Description of the Related Art In recent years, in the field of various electronic devices such as semiconductor devices that require fine processing, there is an increasing demand for high density and high integration of devices.
In order to meet this demand, the miniaturization of patterns has become essential.

One of the methods for reducing the size of a pattern is to shorten the wavelength of exposure light used when forming a photoresist pattern.

Generally, the resolution RS of an optical system is RS = k
Λ / NA (where λ is the wavelength of the exposure light source, NA is the numerical aperture of the lens, and k is the process factor). From this equation, it can be seen that the wavelength λ of the exposure light in lithography should be shortened in order to obtain a higher resolution, that is, the value of RS.

Currently, for example, DRA with an integration degree of up to 64M
A minimum pattern size of 0.35 μm line and space resolution is required for manufacturing M, and the g-line (4
38 nm) and i-line (365 nm) have been used as a light source, but finer processing technology (processing size is 0.25μ
DR with a degree of integration of 256M or more
Excimer laser (KrF: 248n) is used for manufacturing AM.
_{m, ArF: 193nm, F 2} : 157nm) shorter wavelength light, such as (deep UV light, it is believed that the use of deep ultraviolet light) is effective, particularly KrF excimer laser lithography is actively studied recently ing.

As a method other than this, a method of high integration by using a multi-layer (two-layer or three-layer) resist instead of the conventional single-layer resist is being studied. As a two-layer resist, for example, Sharnal of Vacuum
Science and Technology (Journal
of Vacuum Science and Tec
hology) B3, 306-309 (198)
Wilkins (5 years)
s) et al. (two-layer resist using a silylated novolak resin as the upper layer).

Further, in resist materials used for microfabrication, there is an increasing demand for high sensitivity in addition to high resolution corresponding to miniaturization of processing dimensions. This is because the use of an expensive excimer laser as the light source requires improvement in cost performance. The use of a chemical amplification system using a photo-acid generator as a method for increasing the sensitivity of resists has been studied in detail for resists for KrF excimer lasers (eg Hiroshiito, C. Grant Wilson, American Chemical Society Symposium).・ Series (American Chemica
l Society Symposium Series
s) 242, pp. 11-23 (1984)). The characteristic of the chemically amplified resist is that a protonic acid generated by exposing a photosensitizer (generally called a photoacid generator) is moved in the solid phase of the resist by a heat treatment after the exposure and catalyzed by the acid. This is to amplify the chemical change of the resist resin or the like catalytically by several hundred times to several thousand times. In this way, the photosensitivity (reaction per one photon) is dramatically higher than that of the conventional resist having a photoreaction efficiency of less than 1. Examples of photo-acid generators currently used include, for example, The Journal of Organic Chemistry (The Journal of Organic Chemistry).
Chemistry) Volume 43, No. 15, pp. 3055-3
058 (1978). V. The triphenylsulfonium salt derivative of JV Crivello et al. Is known.

[0008]

However, when a resist (including the above-mentioned chemical amplification type) which is widely used at present is used and an exposure light of a shorter wavelength is used for pattern miniaturization, the exposure light by the resist is used. It is generally very strong in absorption. Therefore, the transparency of the resist is lowered, and as a result, the ratio of exposure to light in the depth direction of the resist changes (that is, most of the light is absorbed near the resist surface on the exposure light incident side, and the resist near the substrate is absorbed). It is difficult for light to reach the part), which causes a problem that the resolution is reduced. As one means for solving this problem, there is the adoption of a multilayer resist process. This is because the multi-layer resist method applies a thinner resist than the single-layer resist method, so that the influence of absorption can be suppressed and a desired pattern can be obtained. However, the multi-layer resist process has a drawback that the number of steps required for pattern formation is significantly increased as compared with the conventional single-layer resist, resulting in an increase in cost. In addition, since the triphenylsulfonium salt derivative of Krivero et al. Strongly absorbs light of 220 nm or less, a photosensitizer (photoacid generator) for a single-layer resist that uses light having a wavelength of 220 nm or less, which is expected to have higher resolution, as exposure light. Not available as).

One of the current technical problems in this field is
This is a development of a photo-acid generator having low absorption for far-ultraviolet light of 220 nm or less and high photoreaction efficiency (photo-acid generation efficiency).

[0010]

As a result of earnest research, the inventors have found that the above technical problems can be solved by an alkylsulfonium salt compound disclosed below, and completed the present invention.

The alkylsulfonium salt compound of the present invention is represented by the following general formula (I).

[0012]

[Chemical 2]

However, in the general formula (I), R ¹ is a linear, branched, or cyclic alkyl group having 1 to 8 carbon atoms (more specifically, R ¹ is a methyl group, an ethyl group, n −
Propyl group, isopropyl group, n-butyl group, sec-
It represents a butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopropylmethyl group, a 4-methylcyclohexyl group or a cyclohexylmethyl group. ), R ² has 5 to 7 carbon atoms
(More specifically, R ² represents a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a 4-methylcyclohexyl group, a cyclohexylmethyl group, etc.), and R ³ represents 2-oxo having 5 to 7 carbon atoms. Cyclic alkyl group (more specifically, R ³ is more preferably a 2-oxocyclopentyl group, a 2-oxocyclohexyl group or a 2-oxocycloheptyl group because of the availability of raw materials or the cost thereof), Y ⁻ Represents a counter ion.

As the counter ion represented by Y ⁻ , BF ₄
^- (Tetrafluoroborate ion), AsF
₆ ^- (hexafluoroarsenate ion), SbF
₆ ^- (hexafluoroantimonate ion), PF
₆ ^- (hexafluorophosphate ion), CF ₃ S
O ₃ ^- (trifluoromethanesulfonate ion),
CH ₃ SO ₃ ^- (methanesulfonate ion), Cl
O ₄ ^- (perchlorate ion), Br ^- (bromine ion), C
l ⁻ (chlorine ion), I ⁻ (iodine ion), and the like (suppression of contamination of impurity ions during the manufacture of integrated circuits, or post-exposure bake (post exp) applied in the resist pattern manufacturing process.
Osure bake) from the viewpoint of the scattering-loss suppression of resist protonic acid in the heat treatment, among these counter ions BF ₄ ^- (tetrafluoroborate ion), AsF ₆ ^- (hexafluoroarsenate ions), SbF ₆ ⁻ (hexafluoroantimonate ion), PF ₆ ⁻ (hexafluorophosphate ion), and CF ₃ SO ₃ ⁻ (trifluoromethanesulfonate ion) are more preferable).

The alkylsulfonium salt derivative of the present invention can be used, for example, in the Journal of the American Chemical Society (Journal of the A).
(merchanical Chemical Society)
108 (7), pp. 1579-1585 (1986)
The method of D.N.Kevill et al. For sulfonium salts described in (1) can be applied. That is, the general formula (II) or (II
An excess amount of the alkyl halide represented by the general formula (IV) or (V) is added to, for example, a nitromethane solution of the sulfide derivative represented by I) (2 to 100 times mol (more preferably 5 to 20 times) the sulfide derivative). Double mole))
In addition, the reaction is carried out at room temperature for 0.5 to 5 hours (preferably 1 to 2 hours). Then, after adding a solution prepared by dissolving an organic acid metal salt represented by the general formula (VI) in nitromethane in an equimolar amount to the sulfide derivative, the solution is further added at room temperature to 50 ° C. for 3 to
Allow to react for 24 hours. After that, unnecessary metal salts are filtered off,
After the filtrate is concentrated, it is poured into a large amount of a poor solvent such as diethyl ether and reprecipitated. The target alkylsulfonium salt derivative (general formula (I)) is obtained by recrystallizing the obtained precipitate from a suitable solvent (ethyl cellosolve acetate etc.).

R ³ —S—R ¹ (II) (wherein R ¹ and R ³ are the same as above) R ³ —S—R ² (III) (wherein R ² and R ³ are the same as above) R ² -W (IV) (wherein R ² is as defined above, W is iodine, halogen atom such as bromine) R ¹ -W (V) (wherein R ^1, W is the same) M ⁺ Y ^- ( VI) (wherein, M ⁺ is K ⁺ , Na ⁺ , or Ag ⁺ , Y ⁻ is the same as described above) known photoacid generator (triphenylsulfonium trifluoromethanesulfonate (hereinafter TPS) described in Klibero et al., Supra). Abbreviated as))), the novel compound obtained in the present invention has a feature that the light absorption in the far ultraviolet region of 190 to 220 nm is extremely small.

It was also confirmed that when these alkylsulfonium salts were irradiated with radiation such as far-ultraviolet light or excimer laser, a protonic acid was generated.

The alkylsulfonium salt derivative obtained in the present invention can be used as an initiator for photocationic polymerization utilizing short-wavelength light or a photosensitizer for photoresist.

In the present invention, the carbon number of R ¹ is 1 to
Although the carbon number of 8, R ² and R ³ is 5 to 7, this is the most practically practical value, and even if the carbon number of R ¹ is 9 or more, the carbon number of R ² and R ³ is Even if the numbers are 3 to 4 and 8 or more, almost the same effect can be obtained.

[0020]

The present invention will be described in more detail by way of examples, which should not be construed as limiting the invention thereto.

Example 1 Synthesis of cyclohexylmethyl (2-oxocyclohexyl) sulfonium trifluoromethanesulfonate

[0022]

[Chemical 3]

The following synthesis operation was carried out under a yellow lamp.

2 in an eggplant-shaped flask (for 300 ml)
-(Cyclohexylmercapto) cyclohexanone 1
0.0 g (41.1 mmol) of nitromethane 30 ml
And was stirred with a Teflon stirrer / magnetic stirrer. 54 g of methyl iodide (380 mmo)
1) was added using a dropping funnel, and after dropping, the mixture was stirred at room temperature for 1 hour. Next, 12.3 g of silver trifluoromethanesulfonate
What melt | dissolved (41.1 mmol) in nitromethane 200 ml was dripped gradually using the dropping funnel. After stirring for 15 hours, the precipitated silver iodide was filtered off and the nitromethane solution was concentrated to 20 ml. Diethyl ether 20
Add in 0 ml. The precipitated crystals were washed several times with diethyl ether, and the residue was recrystallized from ethyl cellosolve acetate to obtain 11.2 g of the desired product (yield 6
3%). The structure of the target substance was confirmed by ¹ H-NMR measurement (AMX-400 type NMR apparatus manufactured by Bruker), IR measurement (IR-470 manufactured by Shimadzu Corporation), elemental analysis and the like. Thermal analysis is performed by Thermal Analysis System.
001 (manufactured by Mac Science Co.) was used.

Melting point: 91-93 ° C. ¹ H-NMR (CDCl ₃ , internal standard substance: tetramethylsilane): δ (ppm) 1.22-1.35 (m, 1H), 1.40-1.78
(M, 6H), 1.84-2.27 (m, 8H), 2.
54-2.64 (m, 2H), 2.70-2.80
(M, 1H), 2.81 (s, 1.5H), 2.92
(S, 1.5H), 3.62 (tt, 0.5H), 3.
73 (tt, 0.5H), 5.17 (t, 0.5H),
5.18 (t, 0.5H) IR (KBr tablet, cm ^-1 ) 2950, 2870 (ν
^C-H ), 1710 ((ν _{C = O} ) 1450
(Ν ^{C -H} ), 1276, 1256 (ν _{C -F} ), 11
48, 1034 (ν ^{SO 3} ) Elemental analysis C H S Measured value (wt%) 44.43 6.38 16.84 Theoretical value (wt%) 44.67 6.16 17.03 (However, the theoretical value is C _{1 4} H _{2 3} O ₄ S ₂ F ₃ (MW 3
Calculated value for 76.4485) Thermal decomposition initiation temperature: 142 ° C. (Example 2) Synthesis of dicyclohexyl (2-oxocyclohexyl) sulfonium trifluoromethanesulfonate

[0026]

[Chemical 4]

Synthesis was performed in the same manner as in Example 1 except that cyclohexyl iodide was used instead of methyl iodide (yield 16%).

Melting point: 172-174 ° C. ¹ H-NMR (CDCl ₃ , internal standard substance: tetramethylsilane): δ (ppm) 0.97-2.3 (m, 24H), 2.33-2.80
(M, 4H), 3.97-4.47 (m, 2H), 5.
20-5.35 (m, 1H) IR (KBr tablet, cm ^-1 ) 2932, 2860 (ν
^C-H ), 1700 ((ν ^{C = O} ), 1444 (ν
^C-H ), 1276, 1256 (ν ^C-F ), 116
8, 1050 (ν ^{SO 3} ) Elemental analysis C H S Measured value (wt%) 51.58 6.75 14.74 Theoretical value (wt%) 51.33 7.03 14.42 (However, the theoretical value is C _{1 9} H _{3 1} O ₄ S ₂ F ₃ (MW44
Calculated value for 4.5667) Pyrolysis initiation temperature: 185 ° C (Example 3) Synthesis of cyclopentylmethyl (2-oxocyclohexyl) sulfonium trifluoromethanesulfonate

[0029]

[Chemical 5]

Same as Example 1, except that 2- (cyclohexylmercapto) cyclohexanone is replaced by 2-
It was synthesized using (cyclopentylmercapto) cyclohexanone (yield 93%, oil).

¹ H-NMR (CDCl ₃ , internal standard substance: tetramethylsilane): δ (ppm) 1.50-2.50 (m, 14H), 2.51-2.8
0 (m, 2H), 2.85 (s, 1.5H), 2.95
(S, 1.5H), 3.67-4.23 (m, 1H),
4.87-5.37 (m, 1H) IR (KBr tablet, cm ^-1 ) 2950, 2880 (ν
^C-H ), 1710 ((ν ^{C = O} ) 1448, 1424
(Ν ^{C -H} ), 1264 (ν ^{C -F} ), 1156, 10
30 (ν ^{SO 3} ) Elemental analysis C H Actual measurement value (% by weight) 43.02 5.65 Theoretical value (% by weight) 43.08 5.84 (However, the theoretical value is C _{1 3} H _{2 1} O ₄ S ₂ F ₃ (MW36
Calculated value for 2.4217) (Example 4) Synthesis of cycloheptylmethyl (2-oxocyclopentyl) sulfonium trifluoromethanesulfonate

[0032]

[Chemical 6]

Similar to Example 1, except that 2- (cyclohexylmercapto) cyclohexanone was replaced by 2-
It was synthesized using (cycloheptylmercapto) cyclopentanone (yield 20%).

Melting point: 97-99 ° C. Elemental analysis C H actual measurement value (wt%) 44.20 6.21 theoretical value (wt%) 44.67 6.16 (however, the theoretical value is C ₁₄ H _{2 3} O ₄ S ₂ F ₃ (MW37
(Calculated value for 6.4485) (Example 5) Measurement of transmittance of resin film containing alkylsulfonium salt 6 g of ethyl cellosolve acetate and poly (methyl methacrylate) (manufactured by Aldrich Chemical Company, average molecular weight 12000, hereinafter PMMA) Abbreviated) 1.
5 g and 0.079 g of the alkyl sulfonium salt obtained in Example 1 or Example 2 (5 wt% of the alkyl sulfonium salt with respect to PMMA) were dissolved, and the pore size was 0.2.
After filtering with a membrane filter of μm, the obtained filtrate is spin-coated on a quartz substrate and then 100 on a hot plate.
It was baked at 120 ° C. for 120 seconds. By this operation the film thickness is about 1μ
A thin film of m was obtained. The wavelength dependence of the transmittance of the obtained film was measured using a UV-365 type UV-visible spectrophotometer manufactured by Shimadzu Corporation. The results are shown in Fig. 1. As a comparative example, PMM
The measurement spectra under the same conditions when TPS, which is a known compound, is used instead of the film of A alone and the alkylsulfonium salt are also shown.

From the results of this example, PMMA containing TPS was obtained.
In the film, the transmittance is extremely reduced in the wavelength range of 220 nm or less, but the alkylsulfonium salt of the present invention retains a high transmittance, and the compound of the present invention has an exposure wavelength of 220 nm.
It has been shown to be effective for sub-nm lithography. (Example 6) The photoacid generation of an alkylsulfonium salt in acetonitrile and its efficiency when irradiated with ArF excimer laser light (193 nm) were measured.

The acetonitrile solution of alkyl sulfonium salt of Example ^{1 (1 × 10 - 2 mol} · 1 - 1) 0.3
A synthetic quartz cell (cell length: 1 mm, manufactured by GL Sciences Co., Ltd.) containing ml was irradiated with an ArF excimer laser (ArF excimer laser generator manufactured by Lumonix Co., Ltd.) at room temperature (exposure area: 3 cm ² ). Then, the solution was added to an acetonitrile solution containing a sodium salt of tetrabromophenol boule and a visible absorption spectrum was measured (the amount of the generated acid was determined by Analytical Chemistry Vol. 48 (No. 2), pp. 450-451 ( 1976) and determined from the change in absorbance at 619 nm) The results are shown in Table 1. As a comparative example, the results under the same TPS conditions are also shown.

[0037]

[Table 1]

From the above results, it was shown that the alkylsulfonium salt of the present invention is effective as a photoacid generator.

(Example 7) Similar to Example 5, except that a silicon wafer was used as the substrate instead of the quartz substrate and the PM containing the alkylsulfonium salt synthesized in Example 1 was used.
An MA thin film (film thickness 1.0 μm) was created. This thin film was irradiated with ArF excimer laser light (193 nm) in the same manner as in Example 4, and the photoacid generation and its efficiency were measured. Exposure amount: 40mJ · cm ^{- 2,} exposure area: 20cm ^2. After irradiation, the thin film was dissolved in acetonitrile, the solution was added to an acetonitrile solution containing sodium salt of tetrabromophenol boule, and the visible absorption spectrum was measured in the same manner as in Example 6 to quantify the generated acid amount. The amount of protic acid produced was 14 nmol.

Reference Example 1 Similar to Example 7, except that the alkylsulfonium salt synthesized in Example 1 was replaced by dicyclohexylmethylsulfonium trifluoromethanesulfonate (melting point: 52-54 ° C., thermal decomposition starting temperature:
164 ° C.) was used to measure the acid yield. The amount of protonic acid produced was 1 nmol, which was as low as 1/14 of the amount of acid produced in the case of the compound of Example 1 under the same conditions.

From the comparison between Example 7 and this reference example, the photoacid generation of the ketone group (2-oxocycloalkyl group) structure of the alkylsulfonium salt compound by far ultraviolet light (ArF excimer laser light (193 nm) in this case) was generated. It is clear that they are increasing the efficiency of.

[0042]

As described above, the alkylsulfonium salt of the present invention has high transparency in the far ultraviolet region of 220 nm or less, and effectively generates a protonic acid by radiation such as far ultraviolet light. Therefore, it was found that the compound is useful as a photosensitizer (photoacid generator) of a photoresist for deep ultraviolet light (especially short wavelength light of 220 nm or less).

[Brief description of drawings]

FIG. 1 is a diagram showing the transmittance of a PMMA film containing a sulfonium salt.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Etsuo Hasegawa 5-7-1, Shiba, Minato-ku, Tokyo Inside NEC Corporation

Claims (2)

[Claims] 1. An alkylsulfonium salt represented by the following general formula (I). [Chemical 1] (However, R ¹ is a linear, branched, or cyclic alkyl group having 1 to 8 carbon atoms, R ² is a cyclic alkyl group having 5 to 7 carbon atoms, and R ³ is a 2-oxo cyclic group having 5 to 7 carbon atoms. alkyl group, Y ^- represents a counter ion). 2. The counter ion represented by Y ⁻ is BF ₄ ⁻ , A
_{^{sF 6 -, SbF 6 -,}} PF 6 -, or CF ₃ SO ₃
^- alkyl sulfonium salt according to claim 1, wherein the a.