JP2006222186A - Liquid for immersion exposure and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid for immersion exposure which has a refractive index larger than that of pure water, has a superior permeability and can prevent the elution and dissolution of a photoresist film or its upper layer film component (especially, a hydrophilic component), never corrodes a lens and can therefore suppress the defects at the time of forming a resist pattern, never causes defects arising from the bubbles inside the liquid when the liquid is used as a liquid for immersion, and can form a pattern having a superior resolution and depth of focus. <P>SOLUTION: This liquid is used for an immersion exposure apparatus and immersion exposure method wherein exposure is conducted via a liquid which fills a space between a lens of a projection optical system and a substrate. The liquid is in a state of liquid in the operating temperature of the immersion exposure apparatus, and can be obtained by refining a chain saturated hydrocarbon compound having 6-13 carbons and has a transmissivity of 90% or above with respect to the radiation having a wavelength of 193 nm at the optical path length of 1 mm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid for immersion exposure and a method for producing the same.

Stepper-type or step-and-scan projection exposure that transfers a reticle pattern as a photomask to each shot area on a photoresist-coated wafer via a projection optical system when manufacturing semiconductor elements, etc. The device is in use.
The theoretical limit value of the resolution of the projection optical system provided in the projection exposure apparatus becomes higher as the exposure wavelength used is shorter and the numerical aperture of the projection optical system is larger. For this reason, with the miniaturization of integrated circuits, the exposure wavelength, which is the wavelength of radiation used in the projection exposure apparatus, has become shorter year by year, and the numerical aperture of the projection optical system has also increased.
Further, when performing exposure, the depth of focus is important as well as the resolution. The theoretical limit values of the resolution R and the depth of focus δ are respectively expressed by the following mathematical formulas.

R = k1 · λ / NA (i)
δ = k2 · λ / NA ² (ii)

Where λ is the exposure wavelength, k1 and k2 are process coefficients, NA is the numerical aperture of the projection optical system, and the refractive index of air is 1, and is defined by the following equation (ii ′). That is, when the same resolution R is obtained, a greater depth of focus δ can be obtained by using radiation having a short wavelength.

NA = sin θ (θ = maximum incident angle of exposure light on resist surface) (ii ′)

As described above, so far, the demand for miniaturization of integrated circuits has been met by shortening the wavelength of the exposure light source and increasing the numerical aperture, and now an ArF excimer laser (wavelength: 193 nm) is used as the exposure light source. Mass production of 1L1S (1: 1 line and space) half pitch 90 nm nodes is under study. However, it is said that it is difficult to achieve the next generation half pitch 65 nm node or 45 nm node, which is further miniaturized, only by using an ArF excimer laser. Thus, for these next-generation technologies, the use of short-wavelength light sources such as F ₂ excimer laser (wavelength 157 nm), EUV (wavelength 13 nm), etc. is being studied. However, the use of these light sources is technically difficult and is still difficult to use.

In the above exposure technique, a photoresist film is formed on the exposed wafer surface, and a pattern is transferred to the photoresist film. In a conventional projection exposure apparatus, a space in which a wafer is placed is filled with air or nitrogen having a refractive index of 1. At this time, when the space between the wafer and the lens of the projection exposure apparatus is filled with a medium having a refractive index n, it is reported that the theoretical limit values of the resolution R and the depth of focus δ are expressed by the following formulas. Yes.

R = k1 · (λ / n) / NA (iii)
δ = k2 · nλ / NA ² (iv)

Here, NA is not the actual numerical aperture of the projection optical system, but means a constant defined by the above formula (ii ′) (exactly, the numerical aperture NA ′ of the projection optical system is NA ′ = n sin θ (n is (Same definition as above))
The above formula fills the liquid of refractive index n between the lens of the projection exposure apparatus and the wafer, and sets an appropriate optical system, thereby reducing the resolution limit value and the depth of focus to 1 / n and n times, respectively. It means that it is theoretically possible to do. For example, when water is used as the medium in the ArF process, since the refractive index n of light having a wavelength of 193 nm in water is n = 1.44, the resolution R is compared with that in exposure using air or nitrogen as a medium. It is theoretically possible to design an optical system with 69.4% (R = k1 · (λ / 1.44) / NA) and a focal depth of 144% (δ = k2 · 1.44λ / NA ² ).
A projection exposure method that can reduce the effective wavelength of radiation for exposure in this way and transfer a finer pattern is called immersion exposure, and in future lithography miniaturization, especially lithography in units of several tens of nm, It is considered an essential technique, and its projection exposure apparatus is also known (see Patent Document 1).

Conventionally, in the immersion exposure method, the liquid filled between the lens of the projection optical system and the substrate is pure water in the ArF excimer laser and fluorine because of high transparency at 157 nm in the F ₂ excimer laser. The use of system inert liquids has been studied.
Pure water is easy to obtain in semiconductor manufacturing factories and has no environmental problems. In addition, it is used as an immersion liquid for ArF (see Patent Document 2) because it can easily adjust the temperature and prevent thermal expansion of the substrate due to heat generated during exposure (see Patent Document 2). Adoption to mass production is certain.
On the other hand, a liquid to which methyl alcohol or the like is added as an additive for reducing the surface tension of pure water and increasing the surface activity is also known (see Patent Document 3).
However, when pure water is used, water may penetrate into the photoresist film, resulting in a shape deterioration in which the cross-sectional shape of the photoresist pattern becomes a T-top shape, and resolution may be reduced. In addition, water-soluble components such as photoacid generators, basic additives, and acids generated by exposure to the photo-resist elute into water, resulting in shape deterioration such as T-top shape, resolution, depth of focus, etc. Reduction, bridging defects, defects in patterns after development, and lens surfaces may be contaminated.
For this reason, there is a method of forming an upper layer film on the photoresist film for the purpose of blocking the photoresist film and water, but there are cases where sufficient transparency to exposure and intermixing with the photoresist film are not sufficient. There is also a problem that man-hours become complicated. Furthermore, it has been reported that CaF ₂ conventionally used as a lens material is eroded by water (Non-Patent Document 1), and thus a problem arises that a coating material for coating the lens surface is required. Yes.
On the other hand, since the resolution limit is about 1.44 times that of ArF dry exposure as shown in the above formula (iii), its use is particularly advanced in the next generation technology where the half pitch is 45 nm or less. It is expected to be difficult.

As described above, in the next-generation immersion exposure method in which miniaturization is progressing, a liquid having a refractive index larger than that of pure water at an exposure wavelength (for example, a wavelength of 193 nm) and having a high transmittance with respect to light of these wavelengths is required. It has been. At the same time, the liquid is required to be a liquid that does not adversely affect the photoresist film, such as elution of additives from the photoresist film, dissolution of the resist film, and pattern deterioration, and does not erode the lens. At the same time, with the increase in NA due to the introduction of immersion exposure, the introduction of polarized light as exposure light is being studied, and the liquid is a liquid that does not bend the direction of polarized light due to properties such as optical rotation other than the above requirements. Is expected.
As a method for achieving this object, for example, attempts have been made to increase the refractive index by dissolving various salts in water (Non-Patent Document 2). However, this approach is difficult to control the concentration of salt, and also has problems such as development defects due to elution of water-soluble components as well as water, lens contamination, and the like.
On the other hand, fluorine-based inert liquids such as perfluoropolyether that are being studied for F ₂ exposure are difficult to use at this wavelength because of their low refractive index at, for example, 193 nm. In addition, organic bromides and iodides, which are conventionally known as immersion exposure liquids for microscopes because of their high refractive index at a wavelength of 589 nm, have poor transparency at, for example, 193 nm and are stable against photoresist films. Inferior.
Japanese Patent Laid-Open No. 11-176727 International Publication No. WO99 / 49504 JP-A-10-303114 NIKKEI MICRODEVICE April, 2004 issue p77 Proc. SPIE Vol. 5377 (2004) p. 273

In the immersion exposure method, the inventors of the present invention have a refractive index greater than that of pure water and excellent transparency, and prevent elution and dissolution of the photoresist film or its upper layer film component (especially hydrophilic component), For the purpose of providing a liquid for immersion exposure that can form a pattern with better resolution and depth of focus when used as an immersion liquid, which can suppress defects during resist pattern generation without eroding the lens. As a result of examining various compounds, it was found that an alicyclic saturated hydrocarbon compound having a small absorption in the far ultraviolet region and having a high refractive index is suitable as a liquid for immersion exposure (for example, Japanese Patent Application No. 2004). -151711).
However, since the saturated hydrocarbon compound having an alicyclic skeleton has a rigid skeleton, gas solubility is low and bubbles are likely to be generated in some cases. In addition, these compounds generally have a high viscosity, and there is a problem that the lifetime of generated bubbles is prolonged. In addition, due to the high viscosity, there is a drawback in that the required film thickness for creating a laminar flow at the time of scanning exposure is increased. On the other hand, a chain saturated hydrocarbon compound synthesized by a known method or a commercially available saturated hydrocarbon compound, even if it is a chain saturated hydrocarbon compound having a generally low viscosity alicyclic skeleton, In general, the chain saturated hydrocarbon compound is used as an immersion exposure liquid even when the liquid film has an impurity having a large absorption in the far-ultraviolet region, and the liquid film thickness is reduced due to low viscosity. In this case, due to insufficient transmittance, the throughput decreases due to a decrease in sensitivity, and the resolution and pattern shape due to optical image defocusing, distortion, or optical image defocusing caused by refractive index fluctuations due to heat generation of the liquid due to liquid light absorption. In some cases, there was a problem such as deterioration. Also, when the above liquid is used as an immersion exposure liquid, there may be problems such as defocus due to variations in optical characteristics due to variations in purity between production lots, and a reduction in exposure margin (EL) due to variations in exposure dose. was there.

  The present invention has been made to cope with such a problem.In the immersion exposure method, the refractive index is larger than that of pure water and has excellent transparency, and a photoresist film or its upper layer film component (especially, (Hydrophilic component) can be prevented from elution and dissolution, and the defects at the time of resist pattern generation can be suppressed without eroding the lens, and when used as an immersion liquid, defects caused by bubbles in the liquid are generated. An object of the present invention is to provide a liquid for immersion exposure that can form a pattern with higher resolution and depth of focus and a method for producing the liquid.

In order to solve the above problems, by using a chain saturated hydrocarbon compound that does not have a rigid skeleton in the molecule, the transparency at 193 nm, the refractive index, and the viscosity are compatible, and the liquid is used as an immersion liquid. In this case, elution and dissolution of the photoresist film or its upper layer film component (especially hydrophilic component) is prevented, and further, problems such as defects at the time of resist pattern generation and lens erosion are solved, and more excellent resolution and depth of focus. The inventors have found that a pattern can be formed.
In addition, impurities in the chain saturated hydrocarbon compound, in particular, aromatic rings and unsaturated hydrocarbon compounds contained in the compound are efficiently removed, and a chain with less variation in purity and optical characteristics between production lots. It was necessary to develop a purification method for gaseous saturated hydrocarbon compounds. As a result of various studies on this problem, the inventors of the present application have found that a method of purifying by sulfuric acid washing that is effective in removing aromatic components or a method of performing distillation purification after sulfuric acid washing is suitable for the above-mentioned purpose. When the refined chain saturated hydrocarbon compound is used as a liquid for immersion exposure, a pattern with excellent sensitivity, resolution, and shape can be formed, and reproducibility between lots for each production of the liquid for immersion exposure. As a result, the present invention was completed.

  The immersion exposure liquid according to the present invention is a liquid used in an immersion exposure apparatus or an immersion exposure method in which exposure is performed via a liquid filled between a lens of a projection optical system and a substrate. The radiation transmittance at a wavelength of 193 nm at an optical path length of 1 mm obtained by purifying a chain saturated hydrocarbon compound having 6 to 13 carbon atoms is 90% or more in a temperature range where the immersion exposure apparatus operates. It is characterized by that.

The method for producing a liquid for immersion exposure according to the present invention comprises a liquid for immersion exposure used in an immersion exposure apparatus or an immersion exposure method for exposing via a liquid filled between a lens of a projection optical system and a substrate. A method of containing a C6-C13 chain saturated hydrocarbon compound, which is a raw material of the immersion exposure liquid, in a container, and a step of washing the hydrocarbon compound with sulfuric acid. The radiation transmittance at a wavelength of 193 nm at an optical path length of 1 mm is 90% or more.
The method for producing a liquid for immersion exposure includes a step of distillation purification after the step of washing with sulfuric acid.

  The liquid for immersion exposure and the method for producing the same according to the present invention include, as the liquid for immersion exposure, a saturated hydrocarbon compound having a high hydrophobicity, a high refractive index, and a high transmittance and having no C6-C13 cyclic structure. Since a purified liquid is used, it is possible to form a pattern with excellent resolution and depth of focus without causing shape deterioration due to elution of the photoresist component, development defects, sensitivity changes due to fluctuations in liquid transmittance, and the like.

The C6-C13 chain saturated hydrocarbon compound that can be used as a liquid for immersion exposure is a saturated hydrocarbon compound that does not contain a cyclic structure in the molecule.
Examples of the chain saturated hydrocarbon compound include linear saturated hydrocarbon compounds and branched saturated hydrocarbon compounds.
Examples of the linear saturated hydrocarbon compound include compounds such as n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane, n-dodecane and n-tridecane.
Specific examples of the branched saturated hydrocarbon compound include isohexane and isodecane, which are structural isomers of the above-mentioned linear saturated hydrocarbon compound.
Among these chain saturated hydrocarbon compounds, a compound having a straight chain structure is preferable because of its high resistance to oxidation reaction caused by oxygen and ozone generated under exposure conditions.

In the method for producing a liquid for immersion exposure according to the present invention, as the chain saturated hydrocarbon compound having 6 to 13 carbon atoms, a commercially available material can be used as a reagent or an industrial product. Moreover, it can synthesize | combine by a well-known method by using commercially available material as a raw material.
The compound used as a raw material can be obtained as a commercially available compound, or can be manufactured from the raw material which can be obtained by the existing various synthetic methods.
For example, these compounds are generally obtained as components when refining petroleum components such as gasoline and naphtha, and are inexpensively available as industrial raw materials.
Since these compounds are chemically inert and have relatively low toxicity, for example, correction fluids, paints, adhesives, inks, reaction solvents (polymerization solvents), extraction solvents, cleaning agents, various industrial uses Used in various applications such as raw materials and pharmaceuticals.

However, when these available compounds are commercial products, it is generally reported that the transmittance at 193 nm is low (see UV-VIS Atlas). When used as a liquid for immersion exposure, the temperature fluctuates due to the energy generated by light absorption being converted into heat, resulting in refractive index fluctuations that cause the exposure light to defocus and the pattern not be faithfully transferred, etc. In addition to the above problem, a decrease in the dose accompanying the light absorption of the liquid causes a significant decrease in throughput.
On the other hand, as the cause of absorption of these compounds, although the absorption of the compounds themselves is important, for example, compounds having a carbon-carbon unsaturated bond or an aromatic ring known to have extremely strong absorption at 193 nm In the case where a compound having a functional group such as a carbonyl group or a sulfide group is present as an impurity, it is expected that the transmittance will be greatly affected even if the amount is very small. For this reason, the transmittance | permeability improvement of 193 nm can be achieved by removing these compounds effectively.
Methods for removing these compounds include, for example, purification by distillation, washing with concentrated sulfuric acid, distillation after washing with concentrated sulfuric acid, neutralization after washing with concentrated sulfuric acid, washing with water, washing with chlorosulfuric acid. The method of passing through a column of diatomaceous earth mixed with concentrated sulfuric acid, the method of treating with alkaline potassium permanganate, and the like are effective.
Among the above methods, the method of washing with concentrated sulfuric acid, the method of neutralizing after washing with concentrated sulfuric acid, the method of performing washing with water, and the method of distilling after washing with concentrated sulfuric acid are effective in improving the transmittance of 193 nm and are carried out on an industrial scale. In this case, it is preferable for reasons such as excellent economy.

In order to purify the chain saturated hydrocarbon compound having 6 to 13 carbon atoms, the above raw materials are accommodated in a reaction vessel. The reaction vessel is preferably a member of the vessel or a material from which additives such as a plasticizer contained in the member are not extracted, and is preferably a material that has high acid resistance and is not affected by the chain saturated hydrocarbon compound. Preferred reaction containers include fluororesins such as polytetrafluoroethylene and glass containers.
These containers are preferably washed with deionized water and a transparent solvent such as a saturated hydrocarbon compound or acetonitrile before the reaction.

  Next, it is mixed with sulfuric acid and washed with sulfuric acid under a predetermined temperature condition. Commercially available sulfuric acid can be used. As the sulfuric acid, fuming sulfuric acid, concentrated sulfuric acid, and sulfuric acid having a concentration of 80% by weight or more can be used. Concentrated sulfuric acid having a concentration of 95% by weight or more is preferable. If the sulfuric acid concentration is less than 80% by weight, it becomes difficult to remove impurities by washing with sulfuric acid. Further, since sulfuric acid absorbs moisture and deteriorates when left in the air, it is preferably stored in a dry atmosphere or a nitrogen atmosphere.

The sulfuric acid washing is performed by mixing the chain saturated hydrocarbon compound as a raw material with sulfuric acid. Examples of the mixing method include a stirring method using a stirring spring and the like. Stirring is preferably a method in which the mixing efficiency is increased by increasing the contact area between the raw material and sulfuric acid, and mechanical stirring using a stirring spring is preferred. If the mixing efficiency decreases, the removal of impurities by sulfuric acid treatment becomes insufficient.
The sulfuric acid treatment is preferably performed in an inert gas atmosphere such as nitrogen. When the sulfuric acid treatment reaction is performed in the air, the purification efficiency decreases because the oxidation by oxygen in the air and the sulfuric acid absorb water.
Examples of the inert gas include nitrogen and argon. Nitrogen is preferable because of its low cost and easy availability.
The sulfuric acid washing is preferably carried out under suitable temperature conditions depending on the chain saturated hydrocarbon compound to be purified. A preferable washing temperature is 5 ° C to 80 ° C, more preferably 5 ° C to 30 ° C. When the temperature is less than 5 ° C, the mixing efficiency decreases. When the temperature exceeds 80 ° C, the mixing efficiency increases, but a side reaction easily occurs.
The amount of sulfuric acid used for the sulfuric acid washing is 0.01 to 1.0 equivalent, preferably 0.02 to 0.5 equivalent, more preferably 0.02 equivalent to the chain saturated hydrocarbon compound. 0.2 equivalents. When the amount exceeds 1.0 equivalent, a large amount of unreacted concentrated sulfuric acid is generated, which is not preferable. When the amount is less than 0.01 equivalent, purification efficiency decreases.

After the sulfuric acid washing, it is preferable to carry out alkali neutralization and water washing as necessary. When neutralization with an alkali is performed, for example, a sulfonic acid component generated by a reaction between concentrated sulfuric acid and an aromatic hydrocarbon compound present as an impurity can be efficiently removed.
As the alkali to be used, various alkali metal salts such as sodium hydrogen carbonate, sodium carbonate, potassium hydroxide, sodium hydroxide and the like are preferable. Alkali metal salts are preferred because they are rarely dissolved as impurities in chain saturated hydrocarbon compounds.
After the alkali cleaning, it is preferable to perform cleaning with deionized water. By washing, impurities such as metal ions contained in the alkali can be removed.

The sulfuric acid treatment, alkali neutralization, and water washing are preferably carried out an appropriate number of times depending on the purity and properties of the compound to be purified.
The sulfuric acid treatment is preferably performed 2 to 10 times, more preferably 3 to 10 times. Although the purification efficiency increases as the number of treatments increases, the manufacturing process becomes complicated and the manufacturing cost increases.
About neutralization and washing with water, purification efficiency can be improved by carrying out each treatment with sulfuric acid. For example, neutralization and washing with water are performed 1 to 5 times, preferably 1 to 2 times per sulfuric acid treatment.
The neutralization and water washing may be performed only after the sulfuric acid treatment is performed an appropriate number of times and finally. In this case, neutralization and washing with water are performed 1 to 5 times, preferably 1 to 2 times. The washing with water is preferably performed until the liquidity of the washed water becomes neutral.

By performing distillation purification after the step of washing with sulfuric acid, the transmittance can be further reduced. In this case, the distillation temperature is preferably adjusted to an appropriate range. The distillation temperature is selected according to the type of the chain saturated hydrocarbon compound, but is preferably 20 ° C to 90 ° C, more preferably 20 ° C to 60 ° C.
When the distillation temperature exceeds 90 ° C., the reaction product of impurities and sulfuric acid, or the oxidation product produced by the reaction of the raw chain saturated hydrocarbon compound and sulfuric acid is decomposed, and unsaturated compounds such as unsaturated hydrocarbon compounds And the transmittance is reduced.
Distillation is preferably performed under reduced pressure to an appropriate pressure according to the boiling point of the chain saturated hydrocarbon compound and the distillation temperature. A preferable pressure is 1 mmHg to 30 mmHg, more preferably 1 mmHg to 10 mmHg.
The distillation can be carried out in an air atmosphere. However, saturated hydrocarbon compounds and trace impurities, which are the main components of these liquids, tend to be oxidized by heating in the presence of oxygen, and the oxidation products are reduced. If it occurs, the transmittance will decrease. For this reason, it is preferable to perform this distillation in a suitable inert gas atmosphere. Examples of the inert gas include nitrogen, argon, helium, and the like. Nitrogen is preferable because it is easily available and inexpensive.
When distillation under reduced pressure is performed, it is preferable to return to normal pressure with a suitable inert gas after distillation and store it as it is. Thereby, air oxidation during storage can be prevented.
As for the number of distillation stages, it is preferable to carry out distillation in a distillation column having an appropriate number of stages according to the difference in boiling point between the impurities and the chain saturated hydrocarbon compound.
Distillation is also effective for metal removal.
The member of the distillation vessel is preferably a member in which the member is not attacked by a chain saturated hydrocarbon compound liquid such as stainless steel (SUS), glass, or a fluororesin typified by polytetrafluoroethylene, and the plasticizer does not flow out.
The distillation column is preferably washed with a hydrocarbon, an organic solvent such as acetonitrile, or water before distillation. Washing with an organic solvent is effective for removing organic components, and water washing is effective for removing metal components.

The above compound is preferably a liquid at a temperature at which the immersion exposure apparatus operates, and the refractive index is higher than that of pure water for the reasons of the above formulas (iii) and (iv).
Specifically, it is desirable that the refractive index is a value between water and the resist film before exposure (or an upper layer film for immersion), and a higher value than water, and the refractive index is 193 nm. The refractive index is 1.45 to 1.8, preferably 1.5 to 1.7, more preferably 1.52 to 1.65, and the refractive index at a wavelength of 248 nm is 1.38 to 1.65, preferably Is in the range of 1.45 to 1.60. Moreover, at 25 degreeC, the refractive index in D line | wire (wavelength 589nm) is 1.35 or more, Preferably it is 1.37-2.0, More preferably, it is the range of 1.40-1.55.

In addition, since the refractive index change due to the change in the use environment causes defocusing, it is desirable that the present compound is a compound in which the refractive index is hardly affected by temperature, pressure and the like. In particular, since the temperature is assumed to change during use due to heat generated by light absorption of the lens and resist material, it is desirable that the temperature dependence of the refractive index is low. Specifically, the absolute value of the rate of change dn / dT depending on the temperature (T) of the refractive index (n) is preferably 5.0 × 10 ⁻³ (° C. ⁻¹ ), more preferably 7.0 × 10 ^−. Within ⁴ (℃ ^-1 ).
From this viewpoint, the specific heat of the present compound is preferably a large value. Specifically, the specific heat value is preferably 0.1 cal / g · ° C. or more, more preferably 0.30 cal / g · It is above ℃.
Moreover, it is preferable that the refractive index of the compound is not easily affected by chromatic aberration, and it is preferable that the wavelength dependence of the refractive index around the exposure wavelength is small.

Other properties include high transparency in the far ultraviolet region, viscosity, solubility of gases such as oxygen and nitrogen, contact angle with lens and resist (or resist upper layer), surface tension, flash point, etc. In addition to the desirable range described below, it is desirable that the chemical interaction with the lens and resist material be small. Hereinafter, these characteristics will be specifically described.
The transmittance at 193 nm is 90% or more when the optical path length is 1 mm. In this case, if the transmittance is less than 90%, heat generation due to energy generated by light absorption of the liquid is likely to occur, and defocusing of the optical image due to a change in the refractive index due to temperature rise is likely to occur. In addition, the amount of light reaching the resist film is reduced due to the absorption of the liquid, which causes a significant decrease in throughput.

The viscosity at 20 ° C. is 0.5 Pa · s or less, particularly when used in an environment where the gap between the wafer and the lens material is 1 mm or less, preferably 0.01 Pa · s or less, particularly preferably 0.005 Pa · s. s or less. When the viscosity coefficient exceeds 0.5 Pa · s, it is difficult for liquid to enter the gap between the resist film (or the upper film for immersion) and the lens material, or as a liquid supply method for immersion, a local immersion method, As the exposure method, by moving the stage on which the wafer is placed, a temperature rise due to friction tends to occur when the step-and-scan method in which the entire surface of the wafer is exposed is used. In particular, when the gap between the wafer and the lens material is 1 mm or less, the viscosity coefficient is desirably 0.01 Pa · s or less for the former reason. In this case, the gap distance (the thickness of the liquid film) By reducing the above, it is preferable that the transmittance of the liquid for immersion exposure can be increased and the liquid can be hardly affected by the absorption of the liquid.
Moreover, when the viscosity coefficient becomes large, bubbles (nanobubbles, microbubbles) in the liquid are likely to be generated, and the lifetime of the bubbles becomes long.

Since the immersion exposure liquid according to the present invention has a chain saturated hydrocarbon structure having no cyclic skeleton, the solubility of gases such as oxygen and nitrogen is high. For example, the solubility of oxygen in hexane and heptane is about 147 ppm and 133 ppm, respectively, which is more than 10 times the solubility in water (8 ppm). These dissolved oxygens have a great influence on the transmittance of the liquid because oxygen itself, or in particular, ozone generated when oxygen is irradiated with 193 nm light strongly absorbs 193 nm light. That is, the liquid of the present invention is more susceptible to fluctuations in permeability due to dissolved oxygen than water. Therefore, it is necessary to strictly control the amount of dissolved oxygen when used as a liquid for immersion exposure.
The above-mentioned absorption derived from dissolved oxygen can be solved by deaeration or deoxygenation by an appropriate method before use.
However, in addition to the above, after purification, contact with oxygen for a long time during storage causes alteration due to liquid oxidation or the like. From the viewpoint of preventing this alteration, the liquid needs to be stored in an atmosphere substituted with an inert gas after purification. Examples of the inert gas include nitrogen, argon, helium, and the like. Nitrogen is preferable from the viewpoint of availability and low cost. In this case, the dissolved oxygen concentration is stored at 10 ppm or less, preferably 1 ppm or less.

The contact angle between the immersion exposure liquid according to the present invention and the resist (or the upper layer film for immersion) is preferably 20 ° to 90 °, more preferably 50 ° to 80 °. The contact angle with a lens material such as CaF ₂ is preferably 90 ° or less, and preferably 80 ° or less. If the contact angle between the immersion exposure liquid of the present invention and the resist before exposure (or the immersion upper layer film) is 20 ° or less, the liquid is less likely to enter the gap. When the combination of the dipping method and the step-and-scan method is used, the liquid is easily scattered in the film. On the other hand, when the contact angle between the immersion exposure liquid of the present invention and the resist (or immersion upper layer film) before exposure is 90 ° or more, it becomes easier to take in gas at the uneven resist (or upper layer film) interface, Air bubbles are likely to be generated. Such a phenomenon is described in Immersion Lithography Modeling 2003 Year-End Report (International SEMATECH).
Further, when the contact angle between the immersion exposure liquid of the present invention and the lens material exceeds 90 °, bubbles tend to be generated between the lens surface and the liquid.
Also, especially when used in a step-and-scan type exposure machine with immersion using the local immersion method, which is the same as that currently used in immersion exposure of water, liquid scattering during scanning becomes a problem. The immersion exposure liquid of the present invention preferably has a high surface tension. Specifically, the surface tension at 20 ° C. is preferably 5 dyn / cm to 90 dyn / cm, more preferably 20 dyn / cm to 80 dyn / cm.
When the contact angle between the immersion exposure liquid of the present invention and the resist surface is not suitable, the contact angle can be improved by using a suitable immersion upper layer film. In particular, since the immersion exposure liquid of the present invention has a low polarity, the contact angle can be increased by using a high-polarity upper layer film.

  The immersion exposure liquid of the present invention preferably has low toxicity to the human body and the environment. Specifically, it has low acute toxicity with respect to harm to the human body, and is carcinogenic, mutagenic, teratogenic, reproductive. Non-toxic compounds are preferred. Specifically, for example, an acceptable concentration is preferably 30 ppm or more, more preferably 70 ppm or more, and a liquid whose result of the Ames test is negative is desirable. For environmental hazards, compounds with no persistence or bioaccumulation are desirable.

The immersion exposure liquid of the present invention preferably has a purity measured by gas chromatography of 95.0% or more, particularly preferably 99.0% or more, and more preferably 99.9% or more. It is.
In particular, the ratio of a compound containing an olefin having a large absorbance at an exposure wavelength such as 193 nm, a compound containing an aromatic ring, sulfur (sulfide, sulfoxide, sulfone structure), halogen, carbonyl group, ether group, etc. Is preferably less than 0.01% by weight, particularly preferably less than 0.001% by weight.
In addition, since the liquid comprising this compound is used in the process of manufacturing a semiconductor integrated circuit, the metal or metal salt content is preferably low, specifically, the metal content is preferably 100 ppb or less, more preferably 1.0 ppb or less.
Further, the liquid for immersion exposure is preferably a liquid that does not have optical rotatory power because, when performing polarized light exposure, if it has optical rotatory power, it causes a decrease in optical contrast. Specifically, the compound constituting the liquid is preferably a compound having no optical rotatory power (not optically active), and in the case where the liquid constituting compound is a compound having optical rotatory power (optically active), etc. It is preferable that the compound contains an optical isomer in an amount (present as a racemate) and does not have optical activity as a whole immersion exposure liquid.

Hereinafter, the immersion exposure method using the immersion exposure liquid according to the present invention will be described.
As described above, it is desirable to store the immersion exposure liquid in an inert gas. However, as the container at that time, a container component or a component of the container lid (for example, a plasticizer blended in plastic) is used. It is desirable to store in a container that does not elute. Examples of preferable containers include containers made of glass, metal (eg, SUS), and earthenware. Particularly preferable are glass containers.
Examples of preferable container lids include, for example, a lid made of polyethylene and containing no plasticizer, and a lid made of glass, metal (eg, SUS) or earthenware.
Moreover, it is desirable that the pipe used for feeding the liquid from the container to the exposure machine is a pipe that does not cause elution as described above, and preferable materials for the pipe include glass, metal, ceramics, and the like.
When the immersion exposure liquid is used for immersion exposure, fine particles and bubbles (microbubbles) cause pattern defects and so on, so that the removal of dissolved gas that causes fine particles and bubbles is performed before exposure. It is preferable to keep.
Examples of the method for removing the fine particles include a method of filtering using a suitable filter. As the filter, a filter using a material that has good removal efficiency of fine particles and does not change in absorption at the exposure wavelength due to elution during filtration is preferable. Preferred filter materials include, for example, glass, metal (for example, SUS, silver), and metal oxide.
Examples of the method for removing dissolved gas include a vacuum degassing method, an ultrasonic degassing method, a degassing method using a gas permeable membrane, and a degassing method using various degassers.
Since the liquid for immersion exposure becomes a part of the optical system at the time of exposure, it is desirable to use it in an environment that is not affected by changes in optical properties such as the refractive index of the liquid. For example, it is desirable to use it in an environment where the temperature, pressure, etc. that affect the optical properties of the liquid are constant. For example, the temperature is preferably controlled within a range of ± 0.1 ° C., more preferably ± 0.01 ° C.
In addition, immersion exposure using the immersion exposure liquid of the present invention can be performed in the atmosphere, but as described above, the solubility of oxygen in the immersion exposure liquid is high and the exposure wavelength is low. Since it may affect the absorption characteristics, it is desirable to perform exposure in an inert gas that has little absorption at the exposure wavelength and does not cause a chemical reaction with the liquid. Preferred examples of the inert gas include nitrogen and argon. It is also preferable to expose the liquid in an inert gas atmosphere from the viewpoint of preventing the liquid from being ignited or ignited.
Moreover, it is preferable to manage the organic component density | concentration in use atmosphere below a fixed level from a viewpoint of preventing the change of the absorption characteristic in the exposure wavelength of the liquid by the contamination by the organic component in the air. Examples of the management method of the organic component concentration include a method using a filter for adsorbing an organic component, various gas purification pipes (apparatus), etc. in addition to using a high-purity inert gas atmosphere. For concentration management, it is preferable to periodically analyze the ambient atmosphere. For this purpose, for example, various analysis methods using gas chromatography can be used.

As a liquid supply method for immersion area exposure, a moving pool method, a semming stage method, and a local fill method (local immersion method) are known (special seminar immersion exposure technology (held on May 27, 2004). ) Refer to seminar text), and the local immersion method is preferable because the amount of immersion exposure liquid used is small.
As the final (objective) lens material for immersion exposure using the liquid for immersion exposure, current CaF ₂ or fused silica is preferable from its optical characteristics. Other preferable lens materials include, for example, a fluorine salt of a high-period alkaline earth metal M and a salt represented by the general formula Ca _x M _1-x F ₂ , and when this material is used, CaF ₂ (n @ 193nm = 1.50) and fused silica (n@193nm=1.56), because the refractive index of the lens is higher, especially when designing and processing a high NA lens with a numerical aperture exceeding 1.5 Is preferable.

The immersion exposure liquid of the present invention can be reused after use. When a resist (or resist upper layer film) in which the influence of elution from the resist film at the time of exposure is negligible is used, the immersion exposure liquid of the present invention can be reused without being purified. It is preferably reused after processing such as filtration. These treatments are preferably performed inline from the viewpoint of simplifying the process.
In addition, even if elution from the resist film is negligible in one use during use, if the number of use exceeds a certain number, the physical properties of the liquid change due to the effect of accumulated impurities. Therefore, it is preferable to recover and purify after a certain number of uses.
Examples of the purification method include water washing treatment, acid washing, alkali washing, precision distillation, purification using an appropriate filter (packed column), filtration, etc., and the above-described immersion exposure liquid of the present invention. Examples thereof include a purification method or a method using a combination of these purification methods. Among these, it is preferable to carry out purification by water washing treatment, alkali washing, acid washing, precision distillation or a combination of these purification methods.
The above alkali cleaning removes the acid generated by the exposure eluted in the immersion exposure liquid, the acid cleaning removes the basic components in the resist eluted in the immersion exposure liquid, and the water washing process elutes in the immersion exposure liquid. It is effective for removal of a photoacid generator, a basic additive, and an eluate such as an acid generated during exposure in the resist film.
The precision distillation is effective for removing low-volatile compounds among the above-mentioned additives and is effective for removing hydrophobic components generated by the decomposition of protecting groups in the resist during exposure.

The immersion exposure liquid of the present invention can be used alone or in a mixture. A preferred example is when used alone. By using it alone, it becomes easy to set immersion exposure conditions.
Further, the liquid for immersion exposure according to the present invention can be used by mixing with a liquid other than the present invention as required, and by doing so, for example, optical property values such as refractive index and transmittance, contact angle, Physical properties such as specific heat and expansion coefficient can be set to desired values.
As the liquid other than the present invention used for this purpose, other defoamable solvents, various antifoaming agents, surfactants, and the like can be used. Reduction of bubbles and control of surface tension It is effective for.

Immersion exposure is performed using the liquid for immersion exposure.
A photoresist film is formed by applying a photoresist on the substrate. As the substrate, for example, a silicon wafer, a wafer coated with aluminum, or the like can be used. In order to maximize the potential of the resist film, an organic or inorganic antireflection film is formed on the substrate to be used, as disclosed in, for example, Japanese Patent Publication No. 6-12452. I can leave.
The photoresist used is not particularly limited, and can be selected in a timely manner according to the purpose of use of the resist. Examples of the resin component of the photoresist include a polymer containing an acid dissociable group. The acid-dissociable group is preferably not decomposed by exposure, and in particular, the product after decomposition is preferably volatilized under the exposure conditions and does not elute into the immersion exposure liquid of the present invention. Examples of these polymers include resins containing alicyclic groups, lactone groups and derivatives thereof in the polymer side chain, resins containing hydroxystyrene derivatives, and the like.
In particular, a photoresist using a resin containing an alicyclic group, a lactone group and derivatives thereof in the polymer side chain is preferable. Since these photoresists contain a chemical structure similar to an alicyclic hydrocarbon compound or a cyclic hydrocarbon compound containing a silicon atom in the ring structure, they have excellent affinity with the immersion exposure liquid of the present invention. Also, the photoresist film is not eluted or dissolved.

Examples of the photoresist include a chemically amplified positive or negative resist containing a polymer containing an acid dissociable group as a resin component, an acid generator, and an additive such as an acid diffusion controller. Can do.
When the immersion exposure liquid of the present invention is used, a positive resist is particularly preferable. In a chemically amplified positive resist, an acid-dissociable organic group in the polymer is dissociated by the action of an acid generated from an acid generator by exposure to generate, for example, a carboxyl group. The solubility in an alkali developer is increased, and the exposed portion is dissolved and removed by the alkali developer to obtain a positive resist pattern.

The photoresist film is prepared by dissolving a resin composition for forming a photoresist film in a suitable solvent at a solid content concentration of, for example, 0.1 to 20% by weight, and then filtering with a filter having a pore diameter of, for example, about 30 nm. A solution is prepared, and this resist solution is applied onto a substrate by an appropriate application method such as spin coating, cast coating, roll coating, and the like, and pre-baked (hereinafter referred to as “PB”) to volatilize the solvent. To form. In this case, a commercially available resist solution can be used as it is. The photoresist film preferably has a higher refractive index than the immersion upper layer film and the immersion liquid. Specifically, the refractive index n _{RES of the} photoresist film is in the range of 1.65 or more. preferable. In particular, when NA is 1.3 or more, n _RES is preferably larger than 1.75. In this case, it is possible to prevent a decrease in contrast of exposure light accompanying an increase in NA.
In the immersion exposure method, an upper layer film for immersion can be further formed on the photoresist film.

As the upper layer film for immersion, a protective film can be formed on the photoresist film without causing sufficient transparency with respect to the wavelength of the exposure light and intermixing with the photoresist film. Any film can be used as long as it can maintain a stable film without eluting into a liquid and can be peeled off before development. In this case, it is desirable that the upper layer film is a film that can be easily dissolved in an alkaline solution as a developer because it is peeled off during development. The upper layer film for immersion preferably has a function of preventing multiple interference at the same time. In this case, the refractive index n _OC of the upper layer film for immersion is preferably a mathematical formula shown below.

n _OC = (n _lq × n _RES ) ^0.5

Here, n _lq represents the refractive index of the immersion liquid, and n _RES represents the refractive index of the resist film.
Specifically, n _OC is preferably in the range of 1.6 to 1.9.
The immersion upper film is formed by dissolving the resin composition for an immersion upper film on a resist film in a solvent that does not intermix with the resist film at a solid concentration of 0.01 to 10%, and then at the time of forming the photoresist film. It can be formed by applying and pre-baking in the same manner.
The photoresist film or the photoresist film on which the immersion upper layer film is formed is irradiated with radiation through a mask having a predetermined pattern, using the immersion exposure liquid of the present invention as a medium, and then developed, whereby a resist is obtained. Form a pattern. In this step, immersion exposure is performed, baking is performed at a predetermined temperature, and development is performed.

The liquid is inserted between an optical element such as a lens or a reticle and the substrate surface to perform immersion exposure. Specifically, for example, an illuminating unit that illuminates an original (reticle or mask) and a holding unit that holds the substrate on a stage, a tip portion of an optical element on the substrate side of the projection optical unit, and a surface of the substrate And immersion exposure using the projection exposure apparatus filled with the liquid of the present invention.
The substrate refers to a silicon wafer on which a resist or a resist upper layer protective film is formed. Further, the exposure light (light source) for illuminating the original plate is not limited, and an ArF excimer laser (193 nm), a KrF excimer laser (248 nm), an F ₂ excimer laser (157 nm), or the like can be used. Since this liquid can be used suitably and a fine pattern can be formed, it is preferable.
The immersion exposure apparatus that can be used in the present invention may be, for example, a step-and-repeat type reduction projection type exposure apparatus, or a step-and-scan type projection exposure apparatus that performs exposure by synchronously scanning a reticle and a wafer. However, the latter is preferable from the viewpoint of throughput.
The exposure apparatus is provided with a liquid supply unit, and the liquid is inserted into the exposure area to perform exposure. If air is dissolved in the liquid, foaming is caused. If bubbles are generated in the liquid, the exposure light is scattered and the pattern of the original is not correctly transferred. In particular, when oxygen is dissolved, not only does the transmittance change due to absorption by oxygen or ozone, but also the liquid is oxidized by ozone, causing the liquid to be altered. For this reason, the liquid needs to be deaerated before being supplied. Examples of the deaeration means include a method using heating, a method using reduced pressure, and a method using a gas permeable membrane.

  In addition, when fine particles other than bubbles are present, the pattern of the original plate may not be correctly transferred for the same reason as described above. In order to remove these fine particles, it is necessary to filter the liquid before supply. When an organic material such as a resin is used as a filter medium for this filtration, the resin or the plasticizer contained in the resin may elute and the liquid permeability may decrease. It is necessary to appropriately select the material of the members of the other parts and to clean them by an appropriate method. Polyolefin resin such as polyethylene resin (PE) and polypropylene resin (PP), vinyl chloride resin (PVC), etc. as materials are greatly affected by elution of resin or plasticizer, and fluorine resin (PTFE, PFA, etc.), stainless steel (SUS) and a glass filter are preferable. Examples of the cleaning method for the member include ultrapure water cleaning, cleaning using the liquid of the present invention, and cleaning with an organic liquid having a small absorption at 193 nm, such as acetonitrile.

Further, when the liquid comes into contact with the resist or the outside air at the time of exposure, there is a possibility that the gas is dissolved or fine particles are mixed and deteriorated. Therefore, it is preferable to provide the liquid supply unit with an exhaust port as well as a supply port, and use it while flowing at a constant flow rate. Thereby, for example, it is possible to solve problems such as a change in refractive index due to temperature fluctuation due to the liquid being exposed for a long period of time.
When making a laminar flow of liquid, it is preferable that the liquid has a low viscosity, but the liquid of the present invention has a low viscosity and is suitable for this purpose.
In addition, an appropriate liquid film thickness is set in consideration of the liquid transmittance. The smaller the thickness of the liquid film, the higher the transmittance and the various effects due to absorption can be ignored. However, in order to create a laminar flow, a certain thickness of the liquid film is required. Specifically, the film thickness is set to about 0.5 mm to 10 mm, preferably about 0.5 mm to 3 mm.

Various known resist materials can be used as the resist material on the substrate. For example, a resin containing an acid-dissociable group that is hardly soluble or insoluble in a developer, a photoacid generator that generates an acid upon exposure, an organic An acid diffusion inhibitor such as a base is an essential component, and the acid-dissociable group is eliminated by the acid generated by exposure, so that the exposed area becomes soluble in the developer. Resin, photoacid generator that generates acid upon exposure, acid diffusion preventive agent such as organic base, and crosslinking agent as essential components. Resin soluble in developer and crosslinking agent react with acid generated by exposure. A material such as a chemically amplified negative resist in which the exposed portion is hardly soluble or insoluble in the developer is preferable because high resolution can be obtained. Many materials have been reported as these chemically amplified resist materials, and these known materials can be used.
For example, when using an ArF excimer laser as an exposure light source, an acid dissociable protecting group having a alicyclic skeleton and a lactone side chain, which are widely used, have high resolution and high dry etching resistance. A resist material containing a (meth) acrylic acid ester copolymer resin can be used.
The resist materials typified above can be used alone, but if necessary, an antireflection film is formed between the silicon wafer and the resist material.

It is also possible to use an upper protective film formed on the resist film for the purpose of preventing elution of the resist component from the resist to the liquid and adjusting the contact angle between the liquid and the substrate. The upper protective film is required to be excellent in resistance to immersion liquid (low solubility) and easy to peel off. However, a developer peeling type protective film proposed in water immersion is not suitable. Is preferred.
When exposure is performed using the immersion liquid according to the present invention, a liquid having a higher refractive index than water in the exposure light source is used, so that light having a larger incident angle in the lens can pass through the resist film. High NA exposure is possible, and a fine pattern can be formed. In addition, in the case of the same NA, the incident angle of light to the upper layer on the resist becomes small, so that the depth of focus can be increased.
It is possible to use natural light as the exposure light. However, when performing high NA exposure, if the imaging angle in the resist becomes large, p-polarized light (TM polarized light) has a contrast depending on the imaging angle. Therefore, polarized light exposure using s polarized light (TE polarized light) is preferable.
The photoresist film or the photoresist film on which the immersion upper layer film is formed is irradiated with radiation through an original having a predetermined pattern using the immersion exposure liquid of the present invention as a medium, and is baked at a predetermined temperature. After the development, development is performed to form a desired resist pattern. The baking temperature is appropriately adjusted depending on the resist used, but is usually about 30 to 200 ° C, preferably 50 to 150 ° C.

  In order to evaluate the immersion exposure liquid of the present invention, a resist film was formed using the radiation sensitive resin composition shown below. Moreover, the upper layer film for immersion shown below was formed in a part thereof. Using this evaluation resist film, the characteristics (elution test, film solubility test, patterning evaluation) as an immersion exposure liquid were measured.

化合物（Ｓ１−１）５３．９２ｇ（５０モル％）、化合物（Ｓ１−２）１０．６９ｇ（１０モル％）、化合物（Ｓ１−３）３５．３８ｇ（４０モル％）を２−ブタノン１８７ｇに溶解した単量体溶液（１）、ジメチル２，２'−アゾビス（２−メチルプロピオネート）３．３７ｇを２−ブタノン６４ｇに溶解した溶液（２）を準備し、更に２−ブタノンを１５ｇ投入した１０００ｍｌの三つ口フラスコに前に準備した単量体溶液（１）２８．７７ｇ、溶液（２）４．２３ｇを投入し、その後減圧置換法にて窒素パージする。窒素パージの後、反応釜を攪拌しながら８０℃に加熱し、１５分後、単量体溶液（１）２５８．９８ｇ、溶液（２）２４．６４ｇを送液ポンプを用いて３時間かけて滴下した。滴下終了後更に４時間攪拌した。重合終了後、重合溶液は放冷することにより３０℃以下に冷却した。反応終了後、溶液は放冷し３０℃以下に冷却し、４０００ｇのイソプロピルアルコールへ投入し、析出した白色粉末をろ別する。ろ別された白色粉末を２度２０００ｇのイソプロピルアルコールにてスラリー上で洗浄した後、ろ別し、６０℃にて１７時間乾燥し、白色粉末の重合体を得た（８５ｇ、収率８５重量％）。この重合体はＭｗが７，６００であり、¹³Ｃ−ＮＭＲ分析の結果、化合物（Ｓ１−１）、化合物（Ｓ１−２）、化合物（Ｓ１−３）で表される繰り返し単位、各繰り返し単位の含有率が５３．１：８．５：３８．４（モル％）の共重合体であった。この重合体を樹脂（Ａ−１）とする。 Reference example 1
Resin used for a radiation sensitive resin composition was obtained by the following method.

Compound (S1-1) 53.92 g (50 mol%), compound (S1-2) 10.69 g (10 mol%), compound (S1-3) 35.38 g (40 mol%) into 2-butanone 187 g A dissolved monomer solution (1) and a solution (2) in which 3.37 g of dimethyl 2,2′-azobis (2-methylpropionate) was dissolved in 64 g of 2-butanone were prepared, and further 15 g of 2-butanone was prepared. The previously prepared monomer solution (1) 28.77 g and solution (2) 4.23 g are charged into the charged 1000 ml three-necked flask, and then purged with nitrogen by the vacuum replacement method. After purging with nitrogen, the reaction kettle was heated to 80 ° C. with stirring. After 15 minutes, 258.98 g of monomer solution (1) and 24.64 g of solution (2) were added over 3 hours using a liquid feed pump. It was dripped. After completion of the dropwise addition, the mixture was further stirred for 4 hours. After completion of the polymerization, the polymerization solution was allowed to cool and then cooled to 30 ° C. or lower. After completion of the reaction, the solution is allowed to cool, cooled to 30 ° C. or lower, poured into 4000 g of isopropyl alcohol, and the precipitated white powder is filtered off. The filtered white powder was washed twice with 2000 g of isopropyl alcohol on the slurry, filtered, and dried at 60 ° C. for 17 hours to obtain a white powder polymer (85 g, yield 85 wt. %). This polymer has Mw of 7,600, and as a result of ¹³ C-NMR analysis, the repeating unit represented by compound (S1-1), compound (S1-2), compound (S1-3), and each repeating unit Was a copolymer having a content ratio of 53.1: 8.5: 38.4 (mol%). This polymer is referred to as “resin (A-1)”.

化合物（Ｓ２−１）５０ｇ、化合物（Ｓ２−２）５ｇ、化合物（Ｓ２−３）２５ｇ、化合物（Ｓ２−４）２０ｇ、およびアゾビスイソ吉草酸メチル６．００ｇをメチルエチルケトン２００ｇに溶解し、均一溶液としたモノマー溶液を準備した。そして、メチルエチルケトン１００ｇを投入した１０００ｍｌの三口フラスコを３０分窒素パージした。窒素パージ後、フラスコ内を攪拌しながら８０℃に加熱し、事前に調製した上記モノマー溶液を滴下漏斗を用いて、１０ｍｌ／５分の速度で滴下した。滴下開始時を重合開始時点として、重合を５時間実施した。重合終了後、反応溶液を３０℃以下に冷却し、次いで該反応溶液をヘプタン２０００ｇ中へ投入し、析出した白色粉末をろ別した。ろ別した白色粉末をヘプタン４００ｇと混合してスラリーとして攪拌する操作を２回繰り返して洗浄した後、ろ別し、５０℃にて１７時間乾燥して、白色粉末の樹脂（Ｅ−１）を得た（８９ｇ、収率８９重量％）。樹脂（Ｅ−１）は、Ｍｗが７，３００であった。 Reference example 2
A resin for forming an upper film for immersion was obtained by the following method.

50 g of compound (S2-1), 5 g of compound (S2-2), 25 g of compound (S2-3), 20 g of compound (S2-4), and 6.00 g of methyl azobisisovalerate are dissolved in 200 g of methyl ethyl ketone to obtain a homogeneous solution. A monomer solution was prepared. Then, a 1000 ml three-necked flask charged with 100 g of methyl ethyl ketone was purged with nitrogen for 30 minutes. After purging with nitrogen, the inside of the flask was heated to 80 ° C. with stirring, and the monomer solution prepared in advance was added dropwise at a rate of 10 ml / 5 minutes using a dropping funnel. The polymerization was carried out for 5 hours with the start of dropping as the start of polymerization. After completion of the polymerization, the reaction solution was cooled to 30 ° C. or lower, and then the reaction solution was put into 2000 g of heptane, and the precipitated white powder was filtered off. The operation of mixing the filtered white powder with 400 g of heptane and stirring as a slurry was repeated twice, washed, filtered and dried at 50 ° C. for 17 hours to obtain a white powder resin (E-1). Obtained (89 g, 89 wt% yield). Resin (E-1) had Mw of 7,300.

Reference example 3
A radiation sensitive resin composition was obtained by the following method.
The resin, acid generator, acid diffusion controller and solvent shown in Table 1 were mixed to form a uniform solution, and then filtered through a membrane filter having a pore size of 200 nm to prepare a radiation sensitive resin composition (F2 and F3). . In Table 1, parts are by weight.
The acid generator (B), acid diffusion controller (C), and solvent (D) used are shown below.
Acid generator (B)
B-1: 4-Nonafluoro-n-butylsulfonyloxyphenyl diphenylsulfonium nonafluoro-n-butanesulfonate,
B-2: Triphenylsulfonium nonafluoro-n-butanesulfonate acid diffusion controller (C)
C-1: 2-Phenylbenzimidazole solvent (D)
D-1: Propylene glycol monomethyl ether acetate

Reference example 4
An upper layer film composition for immersion was obtained by the following method.
The resin and solvent shown in Table 2 were mixed to obtain a uniform solution, and then filtered through a membrane filter having a pore diameter of 200 nm to prepare an upper film composition (G1) for immersion. In Table 2, n-BuOH represents normal butanol, and parts are based on weight.

Reference Example 5
Evaluation resist films (H-1 to H-3) were obtained by the following method.
On the 8-inch silicon wafer, spin coating, PB (90 ° C., 60 seconds) is applied to the lower antireflection film ARC29 (Bluwa Science Co., Ltd.) to form a 77 nm-thickness coating film, under the same conditions. Resist films (thickness 205 nm) were formed using the radiation-sensitive resin composition shown in Table 7 (H-1 to H-2).
Moreover, after forming a resist film (film thickness 205 nm) using the radiation-sensitive resin composition by the same method as described above, an upper film composition for immersion shown in Table 3 is spin-coated on this resist film, An upper film of 32 nm thickness was formed by PB (130 ° C., 90 seconds) (H-3).

Example 1
A liquid for immersion exposure was obtained by purifying commercially available n-decane by the following method.
A magnetic stirrer coated with 100 ml of n-decane (manufactured by Tokyo Kasei Kogyo Co., Ltd.) and 10 ml of concentrated sulfuric acid and a 300 ml three-necked flask equipped with a nitrogen inlet and an exhaust port were charged into the flask at 20 ° C. under a nitrogen stream. After stirring for 30 minutes, the mixed liquid was transferred to a 300 ml separatory funnel, and sulfuric acid was separated by decantation. The above-described liquid was washed with sulfuric acid and the series of operations for separating sulfuric acid by decantation was repeated 8 times. Then, this liquid was mixed and washed with a separating funnel twice with 20 ml of a saturated aqueous sodium hydrogen carbonate solution and 10 times with 20 ml of deionized water. After washing, the liquid was distilled under reduced pressure, and nitrogen was saturated by returning to normal pressure using nitrogen. The liquid was purged with nitrogen in advance, introduced into a nitrogen glove bag whose oxygen concentration was confirmed to be 0.1% or less, and sampled in a quartz cell with a polytetrafluoroethylene stopper. When the transmittance at 193 nm of the liquid in the cell was measured with an ultraviolet-visible spectrophotometer (manufactured by JASCO), the transmittance was 96.1%. Moreover, when dissolved oxygen was measured using the gas chromatography, it was 1 ppm or less. The recovered amount of the liquid after distillation was 85 ml.

Example 2
Commercially available isooctane was purified by the same method as above to obtain 87 ml of a liquid having a transmittance of 95.7% at 193 nm and a dissolved oxygen concentration of 1 ppm or less.
Example 3
Commercially available n-heptane was purified in the same manner as described above to obtain 88 ml of a liquid having a transmittance of 97.1% at 193 nm and a dissolved oxygen concentration of 1 ppm or less.

Examples 4 to 8 and Comparative Example 1
Using the evaluation resist film, the immersion exposure liquid of the present invention was evaluated by an elution test and patterning evaluation (immersion patterning evaluation, immersion exposure evaluation using a two-speed interference exposure machine). The results are shown in Tables 4 and 5.

(1) Dissolution test After the wafer coated with the above-described evaluation resist film was immersed in 300 ml of immersion exposure liquid shown in Table 4, the wafer was taken out, and impurities in the remaining immersion exposure liquid were removed. Presence or absence of HPLC (Shimadzu Corporation, column Inertsil ODS-3 (inner diameter 10 mm × length 25
0 mm), developing solvent: acetonitrile / water = 80/20, detector: UV @ 205 nm, 220 nm, 254 nm, sample injection amount 4 μm). At this time, when impurities exceeding the detection limit were confirmed with any one detector, the dissolution test result x, and when impurities above the detection limit were not confirmed, the dissolution test result ○.
(2) Patterning evaluation test The ArF projection exposure apparatus S306C (
Nikon Co., Ltd.) with NA: 0.78, Sigma: 0.85, 2/3 Ann optical exposure (exposure 30 mJ / cm ² ), and then on CLEAN TRACK ACT8 hot plate PEB (130 ° C., 90 seconds), paddle development with the LD nozzle of the CLEAN TRACK ACT8 (60 seconds), rinsing with ultrapure water, and then spin drying at 4000 rpm for 15 seconds (post-development substrate A) . Thereafter, the post-development substrate A exposed by the same method as described above is immersed in the immersion exposure liquid shown in Table 4 for 30 seconds, and then PEB, development and rinsing are performed by the same method as described above, and the post-development substrate B Got. Further, after development, the substrate B was immersed in a liquid for immersion exposure shown in Table 4 for 30 seconds, and then PEB, development and rinsing were performed in the same manner as above to obtain a post-development substrate C.
Substrate A and C after development were observed with a scanning electron microscope (manufactured by Hitachi Instruments Co., Ltd.) S-9360 for a pattern corresponding to a mask pattern of 90 nm line and 90 nm space. At this time, when the resist pattern having the same rectangular shape was obtained with respect to the substrates A and C after development with the naked eye, “◯”, and when the resist pattern became a T-top shape and a good pattern was not obtained, “×” (T-top shape) ”.
(3) Exposure experiment using two-beam interference On a wafer coated with an evaluation resist film made in the same manner as the resist film H2, except that the thickness of the lower antireflection film is 29 nm and the resist film thickness is 60 nm. On the other hand, a simple exposure apparatus for two-beam interference type ArF immersion (Nikon Co., Ltd., for 35 nm 1L / 1S, using TE-polarized exposure), and between the wafers (gap 0.7 mm) for the above-mentioned post-purification immersion Insert the liquid, perform exposure, and then remove the wafer by immersion liquid air drying. Perform PEB (115 ° C, 90 seconds) on the CLEAN TRACKACT8 hotplate, and use the CLEAN TRACKACT8 LD nozzle. Development with paddle (60 seconds), rinse with ultrapure water, and the developed substrate is patterned with a scanning electron microscope (manufactured by Hitachi Instruments Co., Ltd.) S-9360 Guessed it was. At this time, the case where a resist pattern having a desired dimension L / S (1L / 1S) is obtained is obtained, and the case where the resist pattern is not resolved is not resolved. The results are shown in Table 5.

  As shown in Table 4, since the immersion exposure liquid of the present invention is a chain saturated hydrocarbon compound, the resist film alone or the upper film forming resist film is dissolved, the film components are eluted, Do not deform the resist pattern shape.

  Since the liquid for immersion exposure of the present invention is a chain saturated hydrocarbon compound, it does not dissolve the photoresist film at the time of immersion exposure, and can form a resist pattern excellent in resolution, developability, etc. It can be used very suitably for the manufacture of semiconductor devices that are expected to be further miniaturized in the future.

Claims (3)

  A liquid used in an immersion exposure apparatus or an immersion exposure method in which exposure is performed through a liquid filled between a lens of a projection optical system and a substrate, and the liquid is a temperature at which the immersion exposure apparatus operates. For immersion exposure, characterized by having a radiation transmittance of 90% or more at a wavelength of 193 nm at an optical path length of 1 mm obtained by purifying a chain saturated hydrocarbon compound having 6 to 13 carbon atoms, which is liquid in the region liquid. A method for producing an immersion exposure liquid used in an immersion exposure apparatus or an immersion exposure method for exposing via a liquid filled between a lens of a projection optical system and a substrate,
Containing a C6-C13 chain saturated hydrocarbon compound as a raw material for the immersion exposure liquid in a container;
And a step of washing the hydrocarbon compound with sulfuric acid. A method for producing a liquid for immersion exposure wherein the radiation transmittance at a wavelength of 193 nm at an optical path length of 1 mm is 90% or more.   3. The method for producing an immersion exposure liquid according to claim 2, further comprising a distillation purification step after the sulfuric acid washing step.