JP2005129810A - Optical element, and immersion type projection aligner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a protective film having high liquid resistance and high laser resistance whereby an optical element can be protected from liquid, in an aligner whereto an immersion method is applied. <P>SOLUTION: In an optical element 13 wherein the protective film 12 is formed on the surface of an optical substrate 11, the difference between each protruding portion and each recessed portion of irregular shapes is so reduced by applying uniformly constant pressure to the surface of the protective film 12 during a predetermined time, and by polishing the protruding portions of the irregular shapes of its surface as to flatten the surface of the optical element. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical element having a protective film formed on the surface of an optical substrate, and an immersion type projection exposure apparatus provided with the optical element.

  In an immersion type projection exposure apparatus that is a next-generation stepper, the optical element is likely to be deteriorated due to liquid penetration at the interface between the liquid and the optical element. Therefore, a protective film for protecting the optical element from the liquid is required. Further, since the immersion type projection exposure apparatus uses a high-power laser such as an ArF (excimer) laser as a light source, the protective film is also required to be an optical thin film having high laser resistance.

  Conventionally, a film material with high laser resistance that is transparent in the ultraviolet region has been used for an optical thin film for a stepper. In particular, a dense film such as DLC (Diamond Like Carbon) is used for an optical element that requires water resistance.

  However, although a DLC film or the like is dense, absorption in the ultraviolet region is large, and it is difficult to use it as a protective film for an optical element in an immersion projection exposure apparatus using an ArF (excimer) laser.

Thus, it is conceivable to use magnesium fluoride (MgF ₂ ) or the like as a protective film by forming a film on the outermost surface of the optical element.

  However, the surface state on which magnesium fluoride or the like is formed has irregularities and lacks flatness compared to the DLC film. Therefore, the film strength is inferior, and there is a problem with respect to resistance to liquids and lasers.

  In view of the above, the present invention has an object to provide an optical element having a protective film highly resistant to liquid and laser and an immersion type projection exposure apparatus provided with the optical element.

  According to the first aspect of the present invention, in the optical element in which a protective film is formed on the surface of the optical substrate, the surface of the protective film is uniformly applied with a constant pressure for a predetermined time to polish the convex and concave portions on the surface. By doing so, the difference between the convex and concave portions of the concavo-convex shape is reduced to flatten the surface.

  According to a second aspect of the present invention, in the optical element in which a protective film is formed on the surface of the optical substrate, a particulate substance is applied to the surface of the protective film, and the particulate substance is formed in the concave and convex portions on the surface The surface is flattened by reducing the difference between the convex and concave portions of the concavo-convex shape.

  According to a third aspect of the present invention, in addition to the structure of the second aspect, the particulate material is the same material as the protective film.

  According to a fourth aspect of the invention, in addition to the configuration of the second or third aspect, the protective film is made of magnesium fluoride, and the particulate substance is made of magnesium fluoride which is the same substance as the protective film. It is characterized by.

  According to a fifth aspect of the present invention, in addition to the structure of the first or second aspect, the protective film is characterized in that a difference in unevenness on the surface of the protective film is 10 mm or less.

  According to a sixth aspect of the present invention, the optical element according to any one of the first to fifth aspects is disposed at a position facing the exposure object, and a liquid is provided between the optical element and the exposure object. It is characterized by satisfying.

  According to the first aspect of the present invention, in the optical element in which a protective film is formed on the surface of the optical substrate, the surface of the protective film is uniformly applied with a constant pressure for a predetermined period of time, so that the convex and concave portions on the surface are formed. Since the surface is flattened by reducing the difference between the convex and concave portions of the concavo-convex shape by reducing the surface area, reducing the surface area of the protective film reduces the probability of changes in physical properties at the interface contacting the liquid Therefore, the film strength increases. Therefore, it is possible to obtain a protective film having high resistance to liquid and laser. Furthermore, in an optical device having an interface between a liquid and an optical element, it is possible to reduce deterioration of the optical element due to liquid penetration.

  According to the second aspect of the present invention, in the optical element in which the protective film is formed on the surface of the optical substrate, the particulate material is applied to the surface of the protective film, and the particulates are formed in the concave and convex portions on the surface. Since the surface is flattened by reducing the difference between the convex and concave portions of the concavo-convex shape by entering the material, the probability that a change in physical properties at the interface in contact with the liquid will occur by reducing the surface area of the protective film Increases the film strength. Therefore, it is possible to obtain a protective film having high resistance to liquid and laser. Furthermore, in an optical device having an interface between a liquid and an optical element, it is possible to reduce deterioration of the optical element due to liquid penetration.

  According to the third aspect of the present invention, in addition to the configuration of the second aspect, the particulate substance is the same substance as the protective film, and therefore, the particulate substance is applied by a relatively simple method. Thus, the surface of the protective film can be flattened.

  According to the invention described in claim 4, in addition to the configuration of claim 2 or 3, the protective film is made of magnesium fluoride, and the particulate substance is made of magnesium fluoride which is the same substance as the protective film. Thus, the protective film can be made of a substance having high resistance to liquid.

  According to the fifth aspect of the invention, in addition to the configuration of the first or second aspect, the protective film is more resistant to liquids and lasers because the difference in irregularities on the surface of the protective film is 10 mm or less. A high protective film can be provided.

  According to invention of Claim 6, the optical element as described in any one of Claims 1 thru | or 5 is arrange | positioned in the position which faces an exposure target object, Between the said optical element and the said exposure target object. Since it is filled with liquid, it is possible to provide an immersion type projection exposure apparatus having high resistance to liquid and laser.

Embodiments of the present invention will be described below.
Embodiment 1 of the Invention

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 and 2.

  FIG. 1 is a conceptual diagram of an optical element according to Embodiment 1 of the present invention and an enlarged conceptual diagram of the surface of a protective film. This optical element 13 is a protective film for protecting the surface of an optical substrate 11 from a liquid 17. 12 is formed and formed.

  The surface of the protective film 12 is flattened by uniformly applying a constant pressure to the surface for a predetermined period of time to polish the concave and convex portions on the surface, thereby reducing the difference d between the convex and concave portions on the surface. It has become.

  FIG. 2 is a schematic view of a liquid contact portion of the immersion type projection exposure apparatus according to the first embodiment of the present invention.

  The immersion type projection exposure apparatus 1 includes an optical element 13, a projection optical system 14, a stage 15, an illumination optical system (not shown), and a light source (not shown). The laser light emitted from the light source projects a mask pattern from the illumination optical system through the mask, and then is reduced by the optical element 13 through the projection optical system 14 and is applied to an exposure object such as a silicon wafer 16 placed on the stage 15. Projection exposure. The optical element 13 and the silicon wafer 16 are exposed while being filled with the liquid 17. Since the liquid 17 has a higher refractive index than that of the atmosphere, exposure with high resolution can be performed.

As described above, in the immersion type projection exposure apparatus 1, exposure is performed by emitting a laser from a light source in a state where the space between the optical element 13 and the silicon wafer 16 is filled with the predetermined liquid 17. The protective film 12 increases the strength of the protective film 12 by flattening the surface of the protective film 12, and is highly resistant to the liquid 17 and the laser.
[Embodiment 2 of the Invention]

Hereinafter, Embodiment 2 of the present invention will be described with reference to FIG.
FIG. 3 is a conceptual diagram of an optical element according to Embodiment 2 of the present invention and an enlarged conceptual diagram of the surface of the protective film. This optical element 13 is formed by applying a particulate material 18 to the surface of the protective film 12. By allowing the particulate matter 18 to enter the concave and convex portions, the difference d between the concave and convex portions and the concave portions is reduced to flatten the surface.

  Since other configurations and operations are the same as those of the first embodiment of the present invention, the same components are denoted by the same reference numerals and description thereof is omitted.

Embodiments of the present invention will be described below using examples.
[Example 1]

  A method for polishing the film surface after film formation according to Embodiment 1 of the present invention will be described below as Example 1.

  Fluorite is used for the optical substrate 11 of the optical element 13, and magnesium fluoride is used as the material for the protective film 12. As a polishing method, rubbing with a wiping cloth (trade name BEMCOT: manufactured by Asahi Kasei) is performed.

  A protective film 12 made of magnesium fluoride is formed on a fluorite parallel plate optical substrate 11 having a diameter of 30 mm and a thickness of 3 mm by a vacuum evaporation method.

  Thereafter, the sample is placed on a flat plate, and the coated surface is rubbed with BEMOT impregnated with methanol as a lubricant. The rubbing is performed for 1 minute at a pressure of about 5 kgw.

  The surface roughness (difference d between the convex portion and the concave portion) (Å) of the surface roughness of the sample without rubbing and the sample with rubbing was measured using an AFM (Atomic Force Microscope). Table 1 shows the root mean square (RMS) of the surface roughness.

  As shown in Table 1, in the film formation by vacuum deposition, the surface roughness becomes an tens of thousands as the RMS value as described above. In comparison, the RMS value of the surface roughness of the rubbed sample was less than half.

  This sample was irradiated with laser, and the change in transmittance before and after irradiation was measured. A sample holder for laser irradiation used for the measurement is shown in FIG. The optical element 13 and the uncoated quartz substrate 22 produced by the above-described method as a sample for evaluation are set in a sample holder 21 made of stainless steel, and the holder is filled with pure water 17. At this time, the coated surface of the evaluation sample is placed in contact with the pure water 17. Table 2 shows the transmittance change before and after the laser irradiation.

  Here, as a laser irradiation condition, the wavelength is set to 193. nm, fluence was 5 mJ / cm 2, the number of shots was 10E7 shots, and the oscillation frequency was 500 Hz.

As shown in Table 2, almost no decrease in transmittance was observed in the sample with rubbing. This is because the surface roughness of the coated surface is reduced, and even when a laser is irradiated during contact with the pure water 17, the strength of the protective film 12 is high, so that the deterioration of the protective film 12 is reduced.
[Example 2]

  A method for applying nanoparticles to the film surface after film formation according to Embodiment 2 of the present invention will be described below as Example 2.

  Magnesium fluoride film is applied to the optical substrate 11 by fluorite, magnesium fluoride as a material of the protective film 12, and a nanoparticle method (a kind of Sol-gel method) as a coating method.

  Similarly to Example 1, 1000 of magnesium fluoride is formed on the fluorite substrate 11 as the protective film 12. Hereinafter, a method for producing a magnesium fluoride film based on the nanoparticle method on the optical substrate 11 will be described.

  A methanol dilution of hydrofluoric acid was added to a methanol solution of magnesium acetate with sufficient stirring so that the magnesium fluoride concentration of the resulting liquid was 1.0%. This liquid was put into a cell made of polytetrafluoroethylene (PTFE), and further put into a stainless steel pressure vessel, and heated and pressurized at 135 ° C. for 24 hours. After cooling, the liquid was taken out and concentrated to 3.0 wt% with an evaporator to obtain a coating liquid. Next, the optical substrate 11 was set on a spin coater, and after applying the coating liquid onto a disk-shaped substrate having a diameter of 80 mm and a thickness of 4 mm, 1500 r. p. The film was rotated at m to apply a magnesium fluoride film. Thereafter, annealing was performed at 150 ° C. for 2 hours. The annealing temperature may be 100 ° C. to 200 ° C., and the annealing time may be 1 to 3 hours.

  By using this method, there is an effect of reducing the surface area by applying magnesium fluoride particles 18 to the level difference of the surface of the magnesium fluoride film formed by vacuum deposition.

  The surface roughness (difference d between the convex part and the concave part) (Å) of the uncoated sample and the coated sample was measured by AFM. The RMS value of the surface roughness is calculated and shown in Table 3.

  As shown in Table 3, the RMS value of the surface roughness of the sample with rubbing was less than half that of the sample without rubbing.

  Laser irradiation is performed on this sample, and the change in transmittance before and after irradiation is measured. For the measurement, the sample holder shown in FIG. Table 4 shows the change in transmittance before and after laser irradiation.

  The laser irradiation conditions are the same as those in Example 1.

  As shown in Table 4, almost no decrease in transmittance was observed in the coated sample. It can be presumed that this is because the surface roughness of the coated surface is reduced, and the change in the film and the influence on the substrate due to the laser irradiation to the contact with water are reduced.

  In the present invention, the method of polishing the protective film 12 is described as Example 1, and the method of applying the particulate matter 18 on the protective film 12 is described as Example 2. However, the method described in Example 2 is used. After the particulate matter 18 is applied on the protective film 12 and annealed, the protective film 12 may be polished by the method described in the first embodiment. In that case, the surface of the protective film 12 is flattened more than in the case where Example 1 or Example 2 is performed alone.

  In the above-described embodiment, an immersion type projection exposure apparatus that locally fills the space between the projection optical system 14 and the silicon wafer 16 with the liquid 17 is disclosed in JP-A-6-124873. An immersion type projection exposure apparatus that moves a stage holding a substrate to be exposed in a liquid tank, or a liquid having a predetermined depth on a stage as disclosed in JP-A-10-303114. The present invention can also be applied to an immersion type projection exposure apparatus that forms a bath and holds a substrate therein.

  Further, according to the present invention, as disclosed in JP-A-10-163099, JP-A-10-214783, JP-T 2000-505958, etc., substrates to be processed such as wafers are separately placed. The present invention can also be applied to a twin-stage type immersion projection exposure apparatus having two stages that can move independently in the XY directions.

It is the conceptual diagram of the optical element which concerns on Embodiment 1 of this invention, and the expansion conceptual diagram of the surface of a protective film. 1 is an immersion type projection exposure apparatus according to the first embodiment. It is the conceptual diagram of the optical element which concerns on Embodiment 2 of this invention, and the expansion conceptual diagram of the surface of a protective film. It is a conceptual diagram of the sample holder for laser irradiation used for a measurement.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Optical substrate 12 Protective film 13 Optical element 14 Projection optical system 15 Stage 16 Silicon wafer 17 Liquid (pure water)
18 Particulate matter 21 Sample holder 22 Uncoated quartz substrate

Claims (6)

In an optical element in which a protective film is formed on the surface of the optical substrate, the concave and convex portions on the surface are polished by uniformly applying a constant pressure to the surface of the protective film for a predetermined time to polish the concave and convex portions on the surface. An optical element characterized in that the surface is flattened by reducing the difference between the portion and the concave portion. In the optical element in which a protective film is formed on the surface of the optical substrate, the concavo-convex shape is obtained by applying a particulate substance on the surface of the protective film and allowing the particulate substance to enter the concave-convex concave portion on the surface. An optical element characterized in that the surface is flattened by reducing the difference between the convex portion and the concave portion. The optical element according to claim 2, wherein the particulate substance is the same substance as the protective film. 4. The optical element according to claim 2, wherein the protective film is made of magnesium fluoride, and the particulate substance is made of magnesium fluoride which is the same material as the protective film. 3. The optical element according to claim 1, wherein the protective film has a surface roughness difference of 10 mm or less. An optical element according to any one of claims 1 to 5, wherein the optical element is disposed at a position facing an exposure object, and a liquid is filled between the optical element and the exposure object. Type projection exposure apparatus.

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