JP2005114400A - Method for measuring optical characteristic, antireflection film, optical system, and projection aligner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control a refractive index value which meets requests for precise measurements, when measuring optical characteristics of a set of quasi-parallel flat plates by using an antireflection film as a measurement auxiliary means, and to enable the antireflection film to be removed after completing the measurement, without changing surface states of an object to be measured. <P>SOLUTION: The antireflection film 12 which has an antireflective function corresponding to the wavelength of incident light 13 used for measuring the object to be measured, and which can be removed without grinding the surface of the object to be measured, is formed on the object to be measured, and then the optical characteristics of the object to be measured is measured. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a measurement method implemented using an antireflection film used as an auxiliary means for interferometer measurement, an antireflection film for preventing reflection of optical components, a lens, a prism, a reflector, and the like measured by this measurement method. The present invention relates to an optical system including an optical element and a projection exposure apparatus including the optical system.

  Optical parts are generally processed by grinding or pressing into a desired shape, and used after confirming that the shape is within the design accuracy. In particular, in the case of an optical component used in a precision optical system, the accuracy of measurement accuracy affects the performance of the optical system as much as the processing technology. Therefore, as shown in Patent Document 1, a measurement technology with higher accuracy is required. I came.

  However, when evaluating an object to be measured such as a quasi-parallel flat plate, it is necessary for the observation image of the interferometer due to multiple reflections in which light is repeatedly reflected between the light incident surface and the light exit surface. There was a problem that fringes other than unnecessary information were generated. The term “quasi-parallel plate” as used herein means an optical substrate having a parallel plane shape including a subtle power on both or one of the two optical polishing surfaces. Hereinafter, it is abbreviated as a PP plate (Plane Parallel).

  FIG. 7 is a conceptual diagram at the time of reflected wavefront measurement. Hereinafter, a case where the substrate surface 10a is installed on the reference surface 11a side will be described as an example. As shown in FIG. 7, when the PP plate 10 is observed with an interferometer, the multiple reflected light 23 reaches the reference surface 11a in addition to the reflected light 22 from the substrate surface 10a of the PP plate 10 and the reflected light 22 from the back surface 10b. To do. Therefore, various interference fringes appear.

  Such interference fringes due to the multiple reflected light 23 and the like overlap with information to be originally measured and thus become noise, which has been a major obstacle to the measurement evaluation of the PP plate 10 so far. In order to avoid this problem, for example, the influence of multiple interference has been removed by estimation, for example, by visual evaluation. However, it is difficult to completely separate necessary information and noise. It was virtually impossible to perform highly accurate measurements.

  FIG. 8 is a conceptual diagram at the time of transmitted wavefront measurement. As shown in FIG. 8, in the transmitted wavefront measurement, it is necessary to obtain only the wavefront of the light that has been transmitted by the reflection mirror 14 from the transmitted light 21 that has passed through the substrate. However, actually, the reflected light 22 on the substrate surface 10a and the reflected light 22 on the back surface 10b of the PP plate 10, and the multiple reflected light 23 between the substrate surface 10a, the back surface 10b, and the reflecting mirror 14 are also formed on the reference surface 11a. To reach.

  Among these, the reflected light 22 on the substrate surface 10a of the PP plate 10 and the reflected light 22 on the back surface 10b are measured by tilting the PP plate 10 at a slight angle to avoid interference measurement on the reference surface 11a. Can be considered. That is, when the PP plate 10 is tilted at an angle of 1 ° or less, the reflected light 22 on the substrate surface 10a and the reflected light 22 on the back surface 10b exceed the resolution of the interferometer. Noise can be ignored. It is conceivable to eliminate the influence of the reflected light 22 by this prescription.

  However, the multiple reflected light 23 cannot be ignored simply by tilting the PP plate 10 as described above. For this reason, the information of the multiple reflected light 23 overlaps the measurement data, and accurate wavefront measurement cannot be performed. Therefore, as described in the reflected wavefront measurement, it is necessary to measure the transmitted light 21a by reducing the multiple reflected light 23 to a level that does not cause a problem in the measurement using an antireflection film.

  By the way, if the film thickness and refractive index uniformity of the antireflection film are good, even if the antireflection film exists on the surface of the object to be measured, the measurement result is not affected during the transmission wavefront measurement. Specifically, if the transmittance of the double-sided coat is 98% or more, it can be used for measurement.

  However, the antireflection film formed by the conventional vapor deposition method or sputtering method needs to be re-polished after the measurement to remove the film from the object to be measured, and the surface shape of the object to be measured is changed after the measurement. Will end up. In this case, since there is no meaning of carrying out the measurement, the antireflection film for measurement is required to be removable without changing the shape or optical characteristics of the measurement object. Furthermore, even if the film can be easily removed, if the antireflection film is a single layer film, the residual reflection cannot be reduced to nearly 0% simply by setting the film thickness to ¼ of the target wavelength λ.

In general, assuming that the refractive index of a single layer _film is n _film , the refractive index of a medium is n, and the refractive index of an object to be measured is n _sub , the refractive index at 0% reflection is expressed by the following relationship.

n _film ² = n × n _sub (1)

When the medium is air, in order for the residual reflection of the direct incident light 13 to be 0% in the single layer film, it is necessary that the refractive index n _{film of the film} satisfies the following conditions.

n _film ≈ (n _sub ) ^1/2 (2)

  Since the typical value of the refractive index of many optical substrates is 1.4 to 1.5, the refractive index of a single layer film is 1.25 or less. However, the refractive index of a generally known optical thin film is 1.35 or more in the visible region, and it is very difficult to obtain a film that satisfies the requirements for the single-layer film.

  There is a sol-gel method in which a material such as a gel, glass, ceramics, an organic-inorganic composite material, or a nanocomposite is synthesized based on a solution-sol-gel change starting from a solution. Products manufactured by the sol-gel method are diverse, including bulk, powder, and thin film. Among these, for the thin film, the sol-gel method is used as a method for forming a film over a large area at a low temperature at a low cost.

  Another feature of the thin film formed by the sol-gel method is that the refractive index can be arbitrarily changed by controlling the fine structure. The inventors have already reported a method for producing an ultra-low refractive index thin film and a high-performance antireflection film using the same in Patent Document 2 and Patent Document 3. The fact that the refractive index of the thin film can be changed is based on the following principle.

  In general, a thin film can be modeled as a structure in which a plurality of micropores are separated by a solid substance, so that the relationship between the packing density and the refractive index of the thin film is described in Non-Patent Document 1 and Non-Patent Document 2. Can be expressed as follows.

n _f ² = p (n ₀ ² −1) +1 (3)
Here, n _f is the apparent refractive index (depending on the packing density) of the thin film, n ₀ is the refractive index of the solid substance constituting the thin film layer, and p is the space filling ratio of the thin film. Furthermore, the space filling factor is defined as follows.

p = (volume of solid part of membrane) / (total volume of membrane) (4)
Here, the total volume of the membrane is the sum of the volume of the solid portion of the membrane and the volume of the micropores of the membrane. From the formulas (3) and (4), the space filling factor p can be changed by changing the fine structure of the film, and therefore the refractive index of the film can be controlled.
JP 2000-356508 A JP 2002-523646 A JP 2001-823914 A Satoshi Kanehara, Hideo Fujiwara: Thin film (Applied physics book, Hanakabo P.199) Yasutaka Takahashi, et al .: Thin film coating by sol-gel method (Technical Information Association p.327)

  An object of the present invention is to form an optical thin film having an antireflection effect at the wavelength of light used for measurement on the light incident surface and / or the back surface of the object to be measured.

  As a result, there is provided a method of providing an antireflection film on the measurement surface of the object to be measured, in which the reflection at the optical substrate / medium interface causing multiple reflections is almost eliminated and the multiple reflections can be reduced to a level that does not cause a problem in measurement. The task is to do.

  That is, the present invention controls the refractive index value that satisfies the requirements for high-precision measurement and changes the surface state of the measurement object in measuring the optical characteristics of the measurement object using an antireflection film as an auxiliary means for measurement. It is an object of the present invention to provide an optical property measurement method using an antireflection film that can remove the antireflection film after measurement.

  The invention according to claim 1 is an antireflection film having an antireflection function with respect to the wavelength of measurement light used for measurement of an object to be measured and capable of being removed without polishing the surface of the object to be measured. Is formed on the surface of the object to be measured, and then optical characteristics of the object to be measured are measured.

  According to a second aspect of the present invention, in addition to the configuration of the first aspect, the antireflection film is formed by a sol-gel method.

  The invention according to claim 3 is characterized in that, in addition to the structure of claim 1 or 2, the antireflection film is composed of fluoride particles having a particle diameter of 100 nm or less.

  According to a fourth aspect of the invention, in addition to any one of the first to third aspects, the antireflection film can be removed by physical means such as wiping.

  According to a fifth aspect of the present invention, in addition to the structure of any one of the first to third aspects, the antireflection film is an antireflection film that can be removed by chemical means such as cleaning with a solvent. It is characterized by that.

  According to a sixth aspect of the present invention, in addition to the configuration of any one of the first to fifth aspects, a reference surface serving as a reference when measuring the optical characteristics of the measurement object is one side of the measurement object. The antireflection film is formed on one side of the object to be measured, and the reflected wavefront of the object to be measured is measured by causing the measurement light to enter the object to be measured from the reference surface side. It is characterized by doing.

  According to a seventh aspect of the present invention, in addition to the configuration of any one of the first to fifth aspects, a reflection mirror is provided on one side of the object to be measured, and the reference surface is the other side of the object to be measured. Measuring the transmitted wavefront of the object to be measured by allowing the measurement light to enter the object to be measured from the reference surface side. Features.

  According to an eighth aspect of the present invention, in addition to the configuration according to any one of the first to seventh aspects, the object to be measured is a quasi-parallel plate having a thickness of 1 cm or less in a direction in which the measurement light is transmitted, and the reflection The transmittance of the prevention film is 98% or more, and the refractive index is 1.40 or less.

  The invention according to claim 9 is formed by applying a preparation solution prepared by a sol-gel method using a fluoride solution to an object and then drying, and has an antireflection function for a predetermined wavelength of light. In addition, the surface of the object can be removed without polishing.

  The invention according to claim 10 is characterized by comprising at least two or more optical elements evaluated by the measurement method according to any one of claims 1 to 8 and having an accuracy of a predetermined value or more. To do.

  According to an eleventh aspect of the present invention, in addition to the configuration of the tenth aspect, the optical element includes an N.P. A. > 0.80.

  The invention described in claim 12 is an apparatus for projecting and exposing a pattern image of a mask onto a substrate using a projection optical system, and an illumination optical system that illuminates the mask using ultraviolet light as exposure light, and claim 10 or 11 And a projection optical system for forming a pattern image of the mask on a substrate.

  According to the first aspect of the present invention, the reflection having an antireflection function with respect to the wavelength of the measurement light used for measurement of the object to be measured, and removable without polishing the surface of the object to be measured. After the prevention film is formed on the surface of the object to be measured, the optical characteristics of the object to be measured are measured. Therefore, since the surface state of the object to be measured is not changed after the antireflection film is removed, highly reliable and highly accurate optical measurement can be performed.

  According to the second aspect of the invention, in addition to the effect of the first aspect, since the antireflection film is formed by a sol-gel method, the refractive index can be controlled and a high-quality antireflection film can be provided.

  According to the invention of claim 3, in addition to the effect of claim 1 or 2, the antireflection film is composed of fluoride particles having a particle size of 100 nm or less, so that scattering loss can be suppressed, Highly accurate measurement can be performed.

  In addition to the effect of any one of claims 1 to 3, the antireflection film is removed by physical means such as wiping or chemical means such as cleaning with a solvent. Therefore, the antireflection film can be easily removed from the measurement object without damaging the surface state of the measurement object after measurement.

  According to the sixth aspect of the present invention, in addition to the effect of any one of the first to fifth aspects, a reference surface serving as a reference when measuring the optical characteristics of the measured object is one of the measured objects. The antireflection film is formed on one side of the object to be measured, and the measurement light is incident on the object to be measured from the reference surface side. Therefore, the reflected wavefront measurement with high reliability can be performed.

  According to the seventh aspect of the present invention, in addition to the effect of any one of the first to fifth aspects, a reflection mirror is provided on one side of the object to be measured, and the reference surface of the object to be measured is provided. Provided on the other side, the antireflection film is formed on the reflection mirror side, and the measurement wave is incident on the object to be measured from the reference surface side, thereby measuring the transmitted wavefront of the object to be measured. Therefore, it is possible to perform transmission wavefront measurement with high reliability.

  According to the invention described in claim 8, in addition to the effect of any one of claims 1 to 7, the object to be measured is a quasi-parallel plate having a thickness of 1 cm or less in a direction in which the measurement light is transmitted. Since the transmittance of the antireflection film is 98% or more and the refractive index is 1.40 or less, the refractive index of the antireflection film can be controlled. Therefore, the antireflection film has a high transmittance and, therefore, a high quality antireflection film. Can provide. Furthermore, by using a porous film formed by the sol-gel method as an auxiliary means for measurement, even for a substrate where the measurement surface that could not be measured conventionally and the back surface facing it are almost parallel, Measurement with an interferometer is possible.

  According to the ninth aspect of the present invention, the film is formed by applying a preparation solution prepared by a sol-gel method using a fluoride solution to an object and then drying, and has an antireflection function for a predetermined wavelength of light. In addition, since the surface of the object can be removed without polishing, the antireflection film can be easily removed from the object to be measured without damaging the surface state of the object to be measured after measurement.

  According to the invention described in claim 10, since the optical element evaluated by the measurement method according to any one of claims 1 to 8 and having an accuracy of a predetermined value or more is provided, it is incorporated in the optical system. Elements with poor performance can be eliminated in advance, preventing the trouble of having to re-create another optical element due to the failure of the optical system performance after the optical system has been assembled. The manufacturing cost of the optical system product can be suppressed.

  According to the eleventh aspect of the present invention, in addition to the configuration of the tenth aspect, the optical element includes N.P. A. Since> 0.80, high resolution imaging is possible.

  According to a twelfth aspect of the present invention, there is provided an apparatus for projecting and exposing a pattern image of a mask onto a substrate using a projection optical system, the illumination optical system illuminating the mask using ultraviolet light as exposure light, and tenth aspect. Or a projection optical system that includes the optical system described in claim 11 and that forms a pattern image of the mask on a substrate. Therefore, before assembling as a projection exposure apparatus, an illumination optical system or projection optical system having poor performance is assembled in advance. Therefore, after the assembly of the illumination optical system or the projection optical system in the projection exposure apparatus, after the performance evaluation of the illumination optical system or the projection optical system, if another performance is not achieved, another illumination optical system or projection optical system is connected again. The trouble of assembling can be prevented, and the manufacturing cost of the projection exposure apparatus can be reduced.

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

  Hereinafter, Embodiment 1 of the present invention will be described with reference to FIGS. 1 and 9.

  FIG. 1 is a conceptual diagram when measuring a reflected wavefront of a substrate surface of a PP plate using an antireflection film according to Embodiment 1 of the present invention.

  First, the configuration will be described. The PP plate 10 to be measured is provided so that a reference surface 11a serving as a reference for measuring optical characteristics is located on the substrate surface 10a side of the PP plate 10, and an antireflection film 12 is provided on the back surface 10b of the PP plate 10. It is formed into a film.

  As shown in FIG. 1, when incident light 13 for measurement is incident on the PP plate 10 from the reference surface 11a side, the reflected light 22 reflected by the substrate surface 10a causes interference with the reference light 11 on the reference surface 11a. It becomes possible to measure as interference fringes. On the other hand, the incident light 13 that has reached the back surface 10 b is prevented from being reflected by the antireflection film 12 and transmitted as transmitted light 21. Accordingly, the reflected light 22 and the multiple reflected light 23 from the back surface 10b of the PP plate 10 shown in FIG. 7 can be eliminated, and the reflected wavefront measurement of the substrate surface 10a of the PP plate 10 can be performed with high accuracy. .

  FIG. 9 is a schematic diagram showing the overall configuration of the projection exposure apparatus according to Embodiment 1 of the present invention. As shown in the figure, the projection exposure apparatus 1 includes a light source 2, an illumination optical system 3, a mask unit 4, a projection optical system 6, and a wafer unit 7. The PP plate 10 evaluated with the antireflection film 12 is used as an optical element by being incorporated in the entire optical system, or in the illumination optical system 3 and the projection optical system 6.

  Next, since it was found that the sol-gel method is suitable as a method of forming the antireflection film 12 having a refractive index of about 1.25 and can be removed without changing the surface state after film formation measurement on the PP plate 10, Explained.

Hereinafter, the measuring method according to the present invention will be disclosed in Examples. These examples are described by way of illustration, but the invention is not limited thereto.
[Example 1]

  An example in which Embodiment 1 of the present invention is implemented is shown below as Example 1.

  Here, an example in which a synthetic quartz glass substrate is used as the PP plate 10 and the reflected wavefront measurement is performed on the substrate surface 10a is shown.

  First, a method for producing the antireflection film 12 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 substrate of the object to be measured was set on a spin coater, and after applying the coating liquid onto the back surface 10b of the disk-shaped substrate having a diameter of 80 mm and a thickness of 4 mm, 1500 r. p. m. Was rotated to form a film. The obtained film had a refractive index of 1.290 and a transmittance of 99.98% at 633 nm.

  Next, an example in which reflected wave measurement is performed on the substrate surface 10a will be described.

  An antireflection film 12 is formed on the back surface 10b. Next, as shown in FIG. 1, the substrate surface 10a is installed substantially parallel to the reference surface 11a so that the substrate surface 10a comes to the reference surface 11a side. Then, the reflected light 22 of the substrate surface 10a is measured with the substrate surface 10a aligned with the reference surface 11a. Finally, the antireflection film 12 is removed by wiping or cleaning.

Since the sol-gel film of the present invention is not subjected to heat treatment (baking), the film strength is low. Therefore, the sol-gel film was used as an auxiliary means for measurement without increasing the film strength, and when it became unnecessary, it was considered to remove the film by a simple method. Since the film satisfying the refractive index requirement is porous, the film strength is originally low, and is rather suitable for removal later. The measuring means according to the present invention also has the advantage that a new investment in the measuring apparatus itself is not required because an interferometer that has been conventionally used for measuring a lens or the like can be used as it is.
[Comparative Example 1]

  As Comparative Example 1, FIG. 2a is an interference fringe diagram at the time of reflected wavefront measurement when the antireflection film shown in FIG. 1 is used according to Embodiment 1 of the present invention, and FIG. 2b is shown in FIG. The interference fringe figure at the time of reflected wavefront measurement in the case of no antireflection film is shown.

  As shown in FIG. 2b, when the antireflection film 12 is not formed, the reflected light 22 from both the substrate surface 10a and the back surface 10b reaches the reference surface 11a, resulting in a concentric multiple interference fringe at the center. On the other hand, as shown in FIG. 2 a, the measurement light reaching the back surface 10 b is transmitted by the function of the antireflection film 12 by the antireflection film 12. As a result, since the reflected light 22 and the multiple reflected light 23 from the back surface 10b do not reach the reference surface 11a, only interference fringes from the substrate surface 10a are obtained.

Since the transmittance of the antireflection film 12 produced this time was 99.98%, reflection occurs at a rate of 0.02%, but the value exceeds the resolution at the reference surface 11a. And only interference fringes due to the reflected wave from the substrate surface 10a and the reference light 11 are obtained.
[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 at the time of measurement of the reflected wavefront of the back surface of the PP plate using the antireflection film according to Embodiment 2 of the present invention.

  First, the configuration will be described. The PP plate 10 to be measured is provided such that the reference surface 11a is positioned on the substrate surface 10a side of the PP plate 10, and the antireflection film 12 is formed on the substrate surface 10a of the PP plate 10.

  As shown in FIG. 3, when incident light 13 for measurement is incident on the PP plate 10 from the reference surface 11a side, the reflected light 22 reflected by the back surface 10b causes interference with the reference light 11 on the reference surface 11a. Measurement is possible as interference fringes. On the other hand, the incident light 13 that has reached the substrate surface 10 a is prevented from being reflected by the antireflection film 12 and transmitted as transmitted light 21. Therefore, the reflected light 22 from the substrate surface 10a of the PP plate 10 shown in FIG. 7 can be eliminated, and the reflected wavefront measurement of the substrate surface 10a of the PP plate 10 can be performed with high accuracy.

  As shown in FIG. 1, when incident light 13 for measurement is incident on the PP plate 10 from the reference surface 11a side, the reflected light 22 reflected by the substrate surface 10a causes interference with the reference light 11 on the reference surface 11a. It becomes possible to measure as interference fringes. On the other hand, the incident light 13 that has reached the back surface 10 b is prevented from being reflected by the antireflection film 12 and transmitted as transmitted light 21. Accordingly, the reflected light 22 and the multiple reflected light 23 from the back surface 10b of the PP plate 10 shown in FIG. 7 can be eliminated, and the reflected wavefront measurement of the substrate surface 10a of the PP plate 10 can be performed with high accuracy. .

In addition, since the same structure and effect | action are the same as that of Embodiment 1 of this invention, the same code | symbol is attached | subjected to the same structure and the description is abbreviate | omitted.
[Example 2]

  An example in which Embodiment 2 of the present invention is implemented is shown below as Example 2.

  Here, a synthetic glass substrate is used as the PP plate 10 in the same manner as in Example 1, and the reflected wavefront measurement is performed on the back surface 10b of the substrate.

  An antireflection liquid is prepared by the same method as that described in Example 1. Next, after dropping the coating solution onto the disc-shaped synthetic quartz glass substrate surface 10a having a diameter of 80 mm and a thickness of 4 mm, 1500 r. p. m. Was rotated to form a film on the substrate surface 10a.

  Next, an example in which reflected wave measurement is performed on the substrate surface 10a will be described.

FIG. 3 is a conceptual diagram when measuring the reflected wavefront of the back surface 10b of the PP plate using the antireflection film according to Embodiment 1 of the present invention. As shown in FIG. 3, the substrate surface 10a is installed substantially parallel to the reference surface 11a so that the substrate surface 10a comes to the reference surface 11a side. The antireflection film 12 is formed on the substrate surface 10a side. Further, the reflected light 22 of the back surface 10b is measured with the substrate surface 10a aligned with the reference surface 11a. Finally, the antireflection film 12 is removed. The removal method of the antireflection film 12 is the same as that of the first embodiment.
Embodiment 3 of the Invention

  Hereinafter, Embodiment 3 of the present invention will be described with reference to FIGS. 4a, 4b and 5. FIG.

  FIG. 4a is a conceptual diagram at the time of transmission wavefront measurement in the case where an antireflection film is formed on both surfaces of a PP plate when the antireflection film is uniformly formed according to Embodiment 3 of the present invention. . FIG. 4 b corresponds to a conceptual diagram at the time of transmission wavefront measurement when film thickness unevenness is generated in the antireflection film.

  FIG. 5 is a conceptual diagram at the time of transmission wavefront measurement when an antireflection film is formed on the back surface of the PP plate according to Embodiment 3 of the present invention.

  Hereinafter, the configuration will be described with reference to FIGS. 4A and 5.

  In FIG. 4a, the reflection mirror 14 is installed so that the reflection mirror 14 and the reference surface 11a face each other with the PP plate 10 in between. The reference surface 11 a is provided on the substrate surface 10 a side of the PP plate 10, and antireflection films 12 are formed on both the substrate surface 10 a and the back surface 10 b of the PP plate 10.

  In FIG. 5, the antireflection film 12 on the substrate surface 10a of the PP plate 10 shown in FIG. 4a is removed, and the antireflection film 12 is formed only on the back surface 10b.

  4 and 5, the PP plate 10 is installed with an inclination of 1 ° with respect to the reference surface 11a. Thereby, in FIG. 5, the reflected light 22 (not shown) from the substrate surface 10a can be eliminated. Further, since verification is performed using the configuration of FIGS. 4 and 5, it is necessary to make the same conditions as FIG.

  When incident light 13 for measurement is incident on the PP plate 10 from the reference surface 11a side, the light reaching the back surface 10b is prevented from being reflected by the antireflection film 12 as transmitted light 21 as shown in FIG. The light passes through the opposite side of the reference surface 11a. Thereafter, the transmitted light 21 is reflected by the reflection mirror 14, passes through the antireflection film 12 again, and reaches the reference surface 11a as transmitted light 21a. Thus, interference fringes between the transmitted light 21a of the PP plate 10 and the reference light 11 can be obtained on the reference surface 11a.

  On the other hand, as shown in FIG. 4b, when the antireflection film 12 itself has the light 24 generated by the film thickness H and the refractive index unevenness, they are reflected on the wavefront, and as a result, the measurement wavefront is biased. Therefore, by confirming that the deviation is sufficiently small, it is necessary to confirm whether the antireflection film 12 has a function as the antireflection film 12 without causing unevenness in film thickness and refractive index.

  As shown in FIG. 5, it is necessary to confirm whether or not multiple reflections can be completely removed by forming the antireflection film 12 only on the back surface 10b.

Below, the result of having verified the certainty of the transmitted wavefront measurement simultaneously with the example of performing the transmitted wavefront measurement according to the present invention is shown. If transmitted wavefront measurement can be performed without changing the surface shape of the PP plate 10 by other measurement methods, the reliability of the method according to the present invention can be confirmed by comparing the result with the method according to the present invention. Since there is no highly reliable measuring means other than the method of the invention, the following inference was performed.
(inference)

  1. The multiple reflection should disappear if the reflection on the surface of the PP plate 10 is eliminated.

  2. In the transmitted wavefront measurement, multiple reflections should be less when the antireflection film 12 is formed on both surfaces than when the antireflection film 12 is formed only on the back surface 10b.

  3. The effect of multiple reflection when there is no antireflection film 12 is sufficiently large, and the effect of multiple reflection when the antireflection film 12 is formed only on the back surface 10b is the case where the antireflection film 12 is formed on both sides. If the antireflection film 12 is formed on both surfaces, the measurement of the effect of multiple reflection is sufficiently small, and the measurement is derived from the antireflection film 12 included in the measurement result of the transmitted wavefront. It should be said that the error of is small.

  Inferences 1 and 2 are apparent from the principle, but it can be said that the inferences 1 and 2 are sufficiently probable by comparing the measurement results with and without the antireflection film 12 shown in FIG.

Regarding reasoning 3, in other words, the degree of the value of the difference between the influence of multiple reflection when the antireflection film 12 is not present and the influence of multiple reflection due to film thickness unevenness of the antireflection film 12 only on one side is the antireflection film 12. Compared to the influence of multiple reflection due to film thickness unevenness etc. of the double-sided antireflection coating 12, the difference between the influence of the reflection film formed on both sides and the effect of the reflection film only on one side is large Is almost zero. Therefore, in order to confirm that this inference is correct, a verification experiment as shown in Example 3 was performed.
[Example 3]

  An example in which Embodiment 3 of the present invention is implemented is shown below as Example 3.

  Using a procedure similar to that shown in Example 1, an antireflection film is prepared by a sol-gel method using a fluoride solution.

  First, as shown in FIG. 4, an antireflection film 12 is formed on both the substrate surface 10a and the back surface 10b, and the transmitted wavefront is measured. Next, as shown in FIG. 5, the one-side antireflection film 12 is removed, and the transmitted wavefront is measured again. Finally, the difference between the two transmitted wavefront data is obtained. If this difference is sufficiently small, it is verified that there is no other than the multiple reflection described above, and that the film thickness unevenness and refractive index unevenness of the antireflection film 12 itself are small.

  FIG. 6 shows the result of the verification experiment at the time of transmission wavefront measurement. In FIG. 6, the horizontal axis represents the fitting component when the measurement result is fitted with a Zernike polynomial, and the vertical axis represents the fitted measurement result as a root mean square (RMS). . The fitting by the Zernike polynomial is a method that is often used to express the lens surface shape and the transmitted wavefront result. It is possible to fit a loose component (low order) to (medium order) to a fine component (high order) between a rotationally symmetric component term (0θ) and a rotationally asymmetric component term (EVEN, ODD). It is expressed by dividing it into very fine components (residues) that did not exist.

  The mark “♦” indicates the difference between the transmission wavefront measurement result performed without film formation on the PP plate 10 and the transmission wavefront measurement result performed with film formation only on one side of the PP plate 10. A square indicates a difference between a transmission wavefront measurement result performed without film formation on the PP plate 10 and a transmission wavefront measurement result performed with film formation on both surfaces of the PP plate 10. As shown in FIG. 6, it can be seen that there is a significant value of the RMS values of the ♦ and □ marks. Moreover, when both values in each component term are compared, they are hardly changed. Therefore, it can be seen that the measurement when the antireflection film 12 is formed on both sides has a sufficiently small influence of the multiple reflection, and the error derived from the antireflection film 12 included in the measurement result of the transmitted wavefront is also small.

  The Δ mark indicates the difference between the transmission wavefront measurement result obtained by forming the antireflection film 12 on both surfaces and the transmission wavefront measurement result carried out after removing the one-side antireflection film 12. As shown in FIG. 6, it can be seen that the RMS value is very small. Therefore, from these results, it is estimated that the influence due to the film thickness unevenness and the refractive index unevenness is sufficiently reduced, and the error due to the antireflection film 12 itself is sufficiently small.

  A cross indicates a difference between a transmission wavefront measurement result performed before film formation and a measurement result when the film is removed after film formation. As shown in FIG. 6, it can be seen that both the wavefront and the transmittance are at the level of measurement reproducibility and do not affect the optical performance.

  From these results, it is possible to perform highly accurate measurement by using the antireflection film 12 according to the present invention in transmitted wavefront measurement.

  For the reasons described above, by using a porous film formed by the sol-gel method according to the present invention as an auxiliary means for measurement, a measurement surface that could not be measured conventionally and a back surface 10b facing it are substantially parallel to each other. However, measurement with a conventional interferometer is possible.

  Furthermore, since the surface state of the object to be measured is not changed after the antireflection film 12 is removed, highly reliable optical measurement with high reliability can be performed.

  Furthermore, since the antireflection film 12 is formed by a sol-gel method, the refractive index can be controlled and a high quality antireflection film 12 can be provided. Moreover, since it is comprised with the fluoride particle | grains with a particle size of 100 nm or less, a scattering loss can be suppressed and a highly accurate measurement can be performed.

  Furthermore, since the antireflection film 12 that can be removed by physical means such as wiping or chemical means such as cleaning with a solvent is used, the surface state of the object to be measured can be easily removed from the object to be measured after measurement. The antireflection film 12 can be removed.

  Furthermore, for optical products having optical elements that are evaluated by the measurement method of the present invention and have an accuracy of a predetermined value or higher, elements with poor performance can be eliminated in advance before being incorporated into the optical system. It is possible to eliminate in advance elements that have poor performance before installation, and after assembling the optical system, the optical system has failed to achieve the performance of the optical system, so another optical element has to be produced again. This can prevent the manufacturing cost of the optical system product.

  The optical system is N.I. A. Since> 0.80, high-resolution imaging is possible.

  Furthermore, according to the present invention, the illumination optical system 3 having poor performance can be eliminated in advance before the projection exposure apparatus 1 is assembled. Therefore, the illumination optical system 3 and the projection optical system 6 are assembled in the projection exposure apparatus 1 after the assembly process. After the performance evaluation of the system 3 and the projection optical system 6, it is possible to prevent the trouble of reassembling another illumination optical system 3 and the projection optical system 6 when the performance is not achieved, and the production cost of the projection exposure apparatus 1 can be reduced. Can be suppressed.

It is a conceptual diagram at the time of the reflected wavefront measurement of the board | substrate surface of PP board using the antireflection film which concerns on Embodiment 1 of this invention. It is an interference fringe figure at the time of reflected wavefront measurement at the time of using the anti-reflective film shown in FIG. It is an interference fringe figure at the time of reflected wavefront measurement in the case of no antireflection film shown in FIG. It is a conceptual diagram at the time of the reflected wavefront measurement of the back surface of PP board using the antireflection film which concerns on form 2 of this invention. It is a conceptual diagram at the time of transmission wavefront measurement at the time of forming an antireflection film on both surfaces of a PP plate when an antireflection film is uniformly formed according to Embodiment 3 of the present invention. It is a conceptual diagram at the time of transmission wavefront measurement when film thickness nonuniformity has been made in the antireflection film. It is a conceptual diagram at the time of the transmission wavefront measurement at the time of forming the back surface anti-reflective film which concerns on the same Embodiment 3. FIG. It is a figure which shows the result of the verification experiment at the time of the transmitted wavefront measurement which concerns on the same Embodiment 3. It is a conceptual diagram at the time of the conventional reflected wavefront measurement. It is a conceptual diagram at the time of the conventional transmitted wavefront measurement. It is a conceptual diagram of a projection exposure apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 PP board 10a Substrate surface 10b Back surface 11 Reference light 11a Reference surface 12 Antireflection film 13 Incident light 14 Reflection mirror 21, 21a Transmitted light 22 Reflected light 23 Multiple reflected light 24 Light 24 generated by uneven refractive index
H film thickness

Claims (12)

An antireflection film having an antireflection function with respect to the wavelength of measurement light used for measurement of the object to be measured and removable without polishing the surface of the object to be measured is provided on the surface of the object to be measured. An optical property measuring method, comprising: measuring an optical property of the object to be measured after film formation. The optical property measuring method according to claim 1, wherein the antireflection film is formed by a sol-gel method. The optical property measuring method according to claim 1, wherein the antireflection film is made of fluoride particles having a particle diameter of 100 nm or less. 4. The optical property measuring method according to claim 1, wherein the antireflection film can be removed by physical means such as wiping. 4. The optical property measuring method according to claim 1, wherein the antireflection film can be removed by chemical means such as cleaning with a solvent. A reference surface serving as a reference when measuring the optical characteristics of the measurement object is provided on one side of the measurement object,
The antireflection film is formed on one side of the object to be measured,
By making the measurement light incident on the object to be measured from the reference surface side,
6. The optical property measuring method according to claim 1, wherein a reflected wavefront of the object to be measured is measured. A reflection mirror is provided on one side of the object to be measured;
The reference surface is provided on the other side of the object to be measured;
The antireflection film is formed on the reflection mirror side,
By making the measurement light incident on the object to be measured from the reference surface side,
6. The optical property measuring method according to claim 1, wherein a transmitted wavefront of the object to be measured is measured. The object to be measured is a quasi-parallel plate having a thickness of 1 cm or less in a direction in which measurement light is transmitted, and the transmittance of the antireflection film is 98% or more and the refractive index is 1.40 or less. The method for measuring optical characteristics according to claim 1. It is formed into a film by applying a preparation prepared by a sol-gel method using a fluoride solution to an object and then drying, and has an antireflection function for a predetermined wavelength of light, and the surface of the object is An antireflection film, which can be removed without polishing. An optical system comprising an optical element evaluated by the measurement method according to any one of claims 1 to 8 and having an accuracy equal to or higher than a predetermined value. The optical element includes N.I. A. The optical system according to claim 10, wherein> 0.80. An apparatus for projecting and exposing a pattern image of a mask onto a substrate using a projection optical system, comprising: an illumination optical system that illuminates the mask using ultraviolet light as exposure light; and the optical system according to claim 10 or 11, A projection exposure apparatus comprising: a projection optical system that forms a pattern image of a mask on a substrate.