JP2006220577A - Measuring method of interference - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a measuring method of interference for accurately measuring wavefront aberrations. <P>SOLUTION: The interference measuring method for measuring the wavefront aberrations of an optical member by an interference includes processes of: disposing the optical member between first and second parallel planar members; filling a gap between the optical member and the first parallel planar member and a gap between the optical member and the second parallel planar member with an oil having the approximately same refraction index as the optical member and forming an oil layer; irradiating the first parallel planar member with a measurement beam; a process of partially reflecting the measurement beam on an incident plane of the first parallel planar member and forming a first reflection beam; making the beam enter the second parallel planar member, after the beam passes through the first parallel planar member, the oil layer and the optical member; a process of reflecting the beam on a face opposite to the incident plane of the second parallel planar member and forming a second reflection beam; making the first reflection beam interfere with the second reflection beam and forming an interference beam; and analyzing an interference pattern in the interference beam. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for performing interference measurement of a wavefront of an optical member with high accuracy, and is particularly useful for interference measurement of an optical member for use in a semiconductor exposure apparatus or semiconductor measurement apparatus.

  In recent years, as the density of semiconductors has increased, there has been a significant demand for higher accuracy of exposure apparatuses and measurement apparatuses used in the manufacture thereof. In order to realize high accuracy of these devices, it is necessary to manufacture the optical system with high accuracy. For that purpose, it is necessary to measure the refractive index homogeneity of the optical member which is the source of the optical components constituting the optical system with high accuracy. The refractive index homogeneity can accurately measure the wavefront aberration of the optical member by interference measurement.

  A typical Fizeau interferometer is shown in FIG. 5 as an interference measurement apparatus for performing interference measurement of optical members. 5A shows a state where the optical member is set, and FIG. 5B shows a state where the optical member is not set. In (a) and (b) of FIG. 5, 1 is an optical member that is an object to be measured, 3 and 4 are transmissive parallel plate members, 2 is oil having substantially the same refractive index as that of the optical member, and 6 is transmissive. Reference numeral 7 denotes a reflection member, and reference numeral 5 denotes a measurement beam of coherent light.

  The measurement is performed as follows. First, the optical member is not set, and the two parallel plate members 3 and 4 are brought close to each other so that the gap between them is filled with the oil 2. The refractive index of the oil is almost the same value as that of the optical member 1. This situation is shown in FIG. In this state, the measurement beam 5 is incident on the transmissive member 6. A part of the incident measurement beam 5 is reflected by the first surface 6a of the transmissive member 6 to become a reflected beam 5a. The measurement beam 5 that has passed through the transmissive member 6 passes through the parallel plate member 3, the oil 2, and the parallel plate member 4 in this order, and is reflected by the first surface 7a of the reflection member 7 to become a reflected beam 5b. The reflected beam 5b is again transmitted in the order of the parallel plate member 4, the oil 2, the parallel plate member 3, and the transmissive member 6, and is combined with the reflected beam 5a to interfere with each other to become an interference beam. The first wavefront aberration in a state where the optical member 1 is not set is measured by making the interference beam incident on the imaging device and imaging, and analyzing the state of the interference fringes.

  Next, the optical member 1 is set between the two parallel plate members 3 and 4, and the gap between the optical member 1 and the parallel plate member 3 and the gap between the optical member 1 and the parallel plate member 4 are filled with oil 2. To form an oil layer. The reason why the oil layer is formed is to remove the influence of the surface state of the optical member. This situation is shown in FIG. In this state, the measurement beam 5 is incident on the transmissive member 6. A part of the incident measurement beam 5 is reflected by the first surface 6a of the transmissive member 6 to become a reflected beam 5a. The measurement beam 5 transmitted through the transmissive member 6 is transmitted in the order of the parallel plate member 3, the oil 2, the optical member 1, the oil 2, and the parallel plate member 4, and is reflected by the first surface 7a of the reflection member 7 and reflected beam 5b. Become. The reflected beam 5b again passes through the parallel plate member 4, the oil 2, the optical member 1, the oil 2, the parallel plate member 3, and the transmissive member 6 in this order, and interferes with the reflected beam 5a to form an interference beam. The second wavefront aberration in the state where the optical member 1 is set is measured by causing the interference beam to enter the imaging device and imaging and analyzing the state of the interference fringes.

  Next, the first wavefront aberration data is subtracted from the second wavefront aberration data. As a result, the wavefront aberration depending on the internal homogeneity of the optical member can be derived by removing the influence of the interferometer and oil.

  In the above description, the measurement beam 5 is reflected on the first surface 6a of the transmissive member 6 to form the reflected beam 5a. However, the measurement beam 5 is reflected on the second surface 6b of the transmissive member 6. There is also a configuration in which the reflected beam 5a is formed.

  By the way, the measurement accuracy of wavefront aberration due to interference decreases as the interference optical path length increases. In the case of the interference measurement method shown in FIG. 5, the interference optical path length is defined as the distance between the first surface 6 a of the transmissive member 6 and the first surface 7 a of the reflecting member 7. Conventionally, the wavefront aberration of the optical member has been performed by the interference measurement method shown in FIG. 5, but it has been difficult to satisfy the demand for higher measurement accuracy.

  An object of the present invention is to solve the above problems and provide an interference measurement method capable of measuring wavefront aberration with higher accuracy.

  As a result of studies conducted by the present inventors in order to solve the above-mentioned problems, the interference optical path length can be shortened by adopting a configuration in which the optical member is sandwiched between parallel plate members and the measurement beam is irradiated from one side. As a result, it has been found that interference measurement can be performed with high accuracy, and the present invention has been achieved.

  Accordingly, the present invention is first an interference measurement method for measuring the wavefront aberration of an optical member by interference, the step of disposing the optical member between a first parallel plate member and a second parallel plate member; Filling the gap between the optical member and the first parallel plate member and the gap between the optical member and the second parallel plate member with oil having a refractive index substantially equal to that of the optical member to form an oil layer; A step of irradiating the first parallel plate member; a step of partially reflecting the measurement beam on an incident surface of the first parallel plate member to form a first reflected beam; and a first parallel plate member A beam transmitted through the optical member and incident on the second parallel plate member through the optical member, and a second reflected beam is formed by reflecting the beam on a surface opposite to the incident surface of the second parallel plate member. A process, a first reflected beam and a second reaction And having the steps of the interfering beams by interfering the beam, the step of analyzing the interference fringes of the interference beam, a.

  The present invention is secondly an interference measurement method for measuring wavefront aberration of an optical member by interference, the step of disposing the optical member between a first parallel plate member and a second parallel plate member; The step of disposing the reflecting member on the opposite side of the first parallel plate member facing the second parallel plate member, the gap between the optical member and the first parallel plate member, and the optical member and the second Filling the gap between the parallel plate members with oil having a refractive index substantially equal to that of the optical member to form an oil layer, irradiating the measurement beam toward the first parallel plate member, and Reflecting the incident surface of the reflecting member to form a first reflected beam, allowing the beam transmitted through the first parallel plate member to enter the second parallel plate member through the optical member, Beam on the opposite side of the plane of incidence of the parallel plate member Projecting to form a second reflected beam, causing the first reflected beam and the second reflected beam to interfere with each other to form an interference beam, and analyzing the interference fringes of the interference beam. It is characterized by.

  Thirdly, the present invention is an interference measurement method for measuring wavefront aberration of an optical member by interference, the step of disposing the optical member between a first parallel plate member and a second parallel plate member; The step of disposing a transmissive member facing the first parallel plate member on the side opposite to the second parallel plate member, the gap between the optical member and the first parallel plate member, and the optical member and the first Filling a gap between two parallel plate members with oil having a refractive index substantially equal to that of the optical member to form an oil layer, irradiating a measurement beam toward the transmissive member, and transmitting the measurement beam through the transmission beam. Forming a first reflected beam by reflecting on the incident surface of the transmissive member, and causing the beam transmitted through the transmissive member to enter the second parallel plate member through the first parallel plate member and the optical member. And the incident surface of the second parallel plate member Reflecting the beam on the opposite surface to form a second reflected beam; causing the first reflected beam and the second reflected beam to interfere to form an interference beam; and interference fringes of the interference beam And a step of analyzing.

With these configurations, the interference optical path length can be shortened, and as a result, interference measurement can be performed with high accuracy.
According to a fourth aspect of the present invention, in the interference measuring method according to claim 1, 2 or 3, the thickness of the oil layer is 0.05 mm or more.

With such a configuration, it is possible to prevent the optical member or the parallel plate member from being bent due to the surface tension of the oil, thereby reducing the accuracy of interference measurement.
According to a fifth aspect of the present invention, in the interference measurement method according to claim 1, 2 or 3, the first parallel plate member and the second parallel plate member are connected to the first parallel plate member and the first parallel plate member by the holding member. It is characterized in that the positional relationship between the two parallel plate members is fixed so as to be maintained or adjustable.

  With such a configuration, the thickness of the oil layer can be easily adjusted.

  According to the present invention, since the interference optical path length can be shortened as compared with the conventional interference measurement method, the interference measurement of the wavefront aberration of the optical member can be performed with higher accuracy.

The interference measurement method of the present invention will be described below, but the present invention is not limited to the best mode for carrying out the present invention.
An interference measurement method according to the present invention will be described with reference to FIG. In FIG. 1, (a) shows a state where the optical member is set, and (b) shows a state where the optical member is not set. 1 (a) and 1 (b), 1 is an optical member that is the object to be measured, 3 and 4 are light transmissive parallel plate members, 2 is oil having substantially the same refractive index as that of the optical member, and 5 is coherent. 1 shows a measurement beam of light.

  The interference measurement of the present invention is performed as follows. First, the optical member is not set, and the gap between the two parallel plate members 3 and 4 is filled with the oil 2. In this state, the measurement beam 5 is incident on the parallel plate member 3. This is shown in FIG. A part of the incident measurement beam 5 is reflected by the first surface 3a of the parallel plate member 3 to become a reflected beam 5a. The measurement beam 5 transmitted through the parallel plate member 3 proceeds in the order of the parallel plate member 3, the oil 2, and the parallel plate member 4, and is reflected by the second surface 4a of the parallel plate member 4 to become a reflected beam 5b. The reflected beam 5b again proceeds in the order of the parallel plate member 4, the oil 2, and the parallel plate member 3, and is combined with the reflected beam 5a to interfere with it to become an interference beam. The first wavefront aberration in the state where the optical member 1 is not present is measured by causing the interference beam to enter the imaging device and imaging, and analyzing the state of the interference fringes.

  Next, the optical member 1 is set between the two parallel plate members 3 and 4, and the gap between the optical member 1 and the parallel plate member 3 and the gap between the optical member 1 and the parallel plate member 4 are filled with oil 2. . In this state, the measurement beam 5 is incident on the parallel plate member 3. This is shown in FIG. A part of the incident measurement beam 5 is reflected by the first surface 3a of the parallel plate member 3 to become a reflected beam 5a. The measurement beam 5 transmitted through the parallel plate member 3 proceeds in the order of oil 2, optical member 1, oil 2 and parallel plate member 4, and is reflected by the second surface 4a of the parallel plate member 4 to become a reflected beam 5b. The reflected beam 5b again proceeds in the order of the parallel plate member 4, the oil 2, the optical member 1, the oil 2, and the parallel plate member 3, and is combined with the reflected beam 5a to interfere and become an interference beam. The interference wave is incident on the image sensor to pick up an image, and the state of the interference fringes is analyzed, whereby the second wavefront aberration in the state where the optical member 1 is set is measured.

  Next, the first wavefront aberration data is subtracted from the second wavefront aberration data. As a result, the wavefront aberration depending on the homogeneity inside the optical member can be derived by removing the influence of the interferometer and oil.

  As can be seen from FIG. 1, the interference optical path length in the interference measuring method of the present invention corresponds to the distance between the first surface 3 a of the parallel plate member 3 and the second surface 4 a of the parallel plate member 4. This is much shorter than the interference measurement distance of the conventional interference measurement method shown in FIG. In the conventional interference measuring method shown in FIG. 5, the measurement beam is reflected by the transmissive member 6 and the light reflecting member 7, so that the interference optical path length is long, whereas the present invention shown in FIG. In the interference measurement method, a transmission member and a light reflection member are not required, and the measurement beam is reflected by the parallel plate member, so that the interference optical path length can be short. As already explained, in the measurement of wavefront aberration due to interference, the shorter the interference optical path length, the higher the measurement accuracy, and it can be seen that the interference measurement method of the present invention is more accurate than the conventional interference measurement method.

  Next, another embodiment of the present invention will be described with reference to FIG. In FIG. 2, the parallel plate members 3 and 4 are held by the holding member 8. As a result, the distance between the parallel flat plate members 3 and 4 and the positional relationship of the parallelism can be fixed.

  The distance between the parallel plate members 3 and 4 is preferably maintained such that the gap between the optical member 1 and the parallel plate member 3 and the gap between the optical member 1 and the parallel plate member 4 are not less than 0.05 mm. . This is because if the gap becomes smaller than this, the optical member or the parallel plate member bends due to the effect of the surface tension of the oil, and the accuracy of the interference measurement decreases. On the other hand, if the gap is too large, a large amount of oil is required, and the refractive index variation due to temperature change or the like adversely affects the interference measurement accuracy. Therefore, it is preferable that the thickness of the oil is set to an appropriate thickness larger than 0.05 mm. By using the holding adjustment means 8, it is possible to easily adjust to such a thickness.

3 and 4 show another embodiment of the present invention. In these aspects, compared to the configuration shown in FIG. 1, a reflecting member and a transmissive member are added, respectively. Even in these configurations, the interference optical path length can be shortened as compared with the prior art, and as a result, interference measurement can be performed with higher accuracy.
(Example)
The wavefront aberration of the optical members for 10 sets of the projection optical system was measured by the interference measurement method shown in FIG. After classifying according to the measured degree of wavefront aberration, these were processed into a lens shape and 10 sets of projection lenses were assembled. Next, when the Strehl value of these projection optical systems was measured, the Strehl value and the class of wavefront aberration showed a correlation. That is, it can be seen that there is a strong correlation between the interference measurement result of the optical member according to the present invention and the optical performance of the optical system constituted by these optical members. That is, it can be seen that according to the interference measurement method of the present invention, the optical member can be subjected to interference measurement with high accuracy.
(Comparative example)
The wavefront aberration of the optical members for 10 sets of the projection optical system was measured by the interference measurement method shown in FIG. Next, after classifying according to the degree of wavefront aberration, these were processed into a lens shape, and 10 sets of projection lenses were assembled. Next, when the Strehl values of these projection optical systems were measured, the Strehl value and the wavefront aberration class showed a correlation, but the correlation coefficient was considerably smaller than that in the example.
That is, it can be seen that the correlation between the interference measurement results of the conventional optical members and the optical performance of the optical system constituted by these optical members is smaller than when the interference measurement method of the present invention is used. That is, it can be seen that the conventional interference measurement method cannot measure the optical member with higher accuracy than the present invention.

  From the above results, according to the interference measurement method of the present invention, it is possible to perform interference measurement with higher accuracy.

  It is possible to perform interference measurement of the wavefront aberration of an optical device requiring high accuracy, in particular, an optical component of an exposure apparatus for photolithography with high accuracy.

It is a conceptual diagram which shows the interference measuring method of this invention. It is a conceptual diagram which shows another aspect of the interference measuring method of this invention. It is a conceptual diagram which shows another aspect of the interference measuring method of this invention. It is a conceptual diagram which shows another aspect of the interference measuring method of this invention. It is a conceptual diagram which shows the conventional interference measuring method.

  It is a conceptual diagram explaining the fringe scan of an interference measuring device.

Explanation of symbols

1 Optical components
2 Oil
3 Parallel plate member
4 parallel plate members
5 measuring beam
6 permeable member
7 Reflective member
8 Holding adjustment means

Claims (5)

An interference measurement method for measuring wavefront aberration of an optical member by interference, the step of disposing the optical member between a first parallel plate member and a second parallel plate member;
An oil layer is formed by filling the gap between the optical member and the first parallel plate member and the gap between the optical member and the second parallel plate member with oil having a refractive index substantially equal to that of the optical member. And a process of
Irradiating a measurement beam toward the first parallel plate member;
Partially reflecting the measurement beam on the incident surface of the first parallel plate member to form a first reflected beam;
Allowing the beam transmitted through the first parallel plate member to enter the second parallel plate member through the optical member;
Reflecting the beam on a surface opposite to the incident surface of the second parallel plate member to form a second reflected beam;
Interfering the first reflected beam and the second reflected beam into an interference beam;
Analyzing the interference fringes of the interference beam;
An interference measurement method characterized by comprising: An interference measurement method for measuring wavefront aberration of an optical member by interference, the step of disposing the optical member between a first parallel plate member and a second parallel plate member;
A step of facing the second parallel plate member and disposing a reflection member on the side opposite to the first parallel plate member;
An oil layer is formed by filling the gap between the optical member and the first parallel plate member and the gap between the optical member and the second parallel plate member with oil having a refractive index substantially equal to that of the optical member. And a process of
Irradiating a measurement beam toward the first parallel plate member;
Reflecting the measurement beam at an incident surface of the reflecting member to form a first reflected beam;
Allowing the beam transmitted through the first parallel plate member to enter the second parallel plate member through the optical member;
Reflecting the beam on a surface opposite to the incident surface of the second parallel plate member to form a second reflected beam;
Interfering the first reflected beam and the second reflected beam into an interference beam;
Analyzing the interference fringes of the interference beam;
An interference measurement method characterized by comprising: An interference measurement method for measuring wavefront aberration of an optical member by interference, the step of disposing the optical member between a first parallel plate member and a second parallel plate member;
Facing the first parallel plate member and disposing a transmissive member on the opposite side of the second parallel plate member;
An oil layer is formed by filling the gap between the optical member and the first parallel plate member and the gap between the optical member and the second parallel plate member with oil having a refractive index substantially equal to that of the optical member. And a process of
Irradiating a measurement beam toward the transparent member;
Reflecting the measurement beam at an incident surface of the transmissive member to form a first reflected beam;
Allowing the beam transmitted through the transmissive member to enter the second parallel plate member through the first parallel plate member and the optical member;
Reflecting the beam on a surface opposite to the incident surface of the second parallel plate member to form a second reflected beam;
Interfering the first reflected beam and the second reflected beam into an interference beam;
Analyzing the interference fringes of the interference beam;
An interference measurement method characterized by comprising: The interference measurement method according to claim 1, 2 or 3,
The method for measuring interference, wherein the oil layer has a thickness of 0.05 mm or more. The interference measurement method according to claim 1, 2 or 3,
The first parallel plate member and the second parallel plate member are fixed by a holding member so that the positional relationship between the first parallel plate member and the second parallel plate member can be held or adjusted. A characteristic interference measurement method.