JP4590124B2 - measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present inventionmeasuring deviceTherefore, the object corresponds to a wide range of surface shapes ranging from spherical to aspherical surfaces, and is suitable for measuring the surface shape of the object with high accuracy.
[0002]
In addition, the present invention transfers the pattern on the mask onto a photosensitive substrate, and the spherical surface of each optical element (lens, filter, etc.) constituting the projection optical system used in a lithography process such as manufacturing a semiconductor element. This is suitable for measuring a surface shape such as an aspherical surface with high accuracy.
[0003]
[Prior art]
Innovations in optical systems are always brought about by the introduction of new optical elements or degrees of freedom. Among them, the improvement of optical performance through the introduction of aspherical surfaces is one of the items that have been pursued since the long time ago of astronomical telescopes. It was in the place where it was introduced into the semiconductor exposure apparatus for the company.
[0004]
There are roughly three effects of the aspherical surface in the semiconductor exposure apparatus. The first effect is a reduction in the number of optical elements. With the shortening of the wavelength, it has become necessary to use expensive materials such as quartz and fluorite for the optical system of the semiconductor exposure apparatus. The reduction in the number of optical elements due to the aspherical effect is very effective in terms of production and cost. The second effect is downsizing. As an aspherical effect, the optical system can be miniaturized, and the influence on production and cost is still so great that it cannot be ignored. The third effect is higher performance. The role of an aspherical surface is very important as a means to achieve the performance of an optical system that is required to have higher accuracy due to higher NA and lower aberration.
[0005]
Recently, with the acceleration of pattern miniaturization, a method using EUV is regarded as the most important exposure method for the next generation. In EUV (Extreme Ultra Violet), light on a short wavelength of 13.4 nm, which is 1/10 or less of the wavelength of light used in conventional light exposure, is applied to the wafer on the reticle by a reflection imaging optical system. Transcript. Since the wavelength is too short in the EUV region, there is no optical member (transmitting material) that transmits light, and the optical system has only a mirror that does not use lenses. However, the reflective material is also limited in the EUV region, and the reflectivity of the mirror per surface is only 70%. Therefore, it is impossible to construct an optical system with more than 20 optical systems like an optical system using a conventional lens from the viewpoint of light utilization efficiency, and an imaging optical system that satisfies a predetermined performance with as few sheets as possible is constructed. Must.
[0006]
Currently, the EUV experimental machine uses a three- or four-mirror system with an NA of around 0.1, but in the future it will start with an NA of 0.25 with a six-mirror system. The target system is around 0.30. As a means to realize such a high-performance optical system with a small number of sheets, in order to break through the barriers of the prior art to actually process and measure a highly accurate aspherical surface and obtain an optical element of a predetermined surface shape It has become an essential technology.
[0007]
[Problems to be solved by the invention]
However, even if a design value that provides high performance is obtained, conventional aspherical processing has a limit in the accuracy of measurement of the aspherical surface, and there is a problem that a surface having an aspherical amount greater than a predetermined value cannot be processed. there were. The predetermined value is determined by a range that can be measured with a desired accuracy. As is well known, measurement and processing are integrated, and it is impossible to perform precise processing without good measurement accuracy.
[0008]
Since the spherical shape measurement technique is the most commonly used technique for measuring optical elements, general-purpose devices exist as products, and the accuracy is greatly improved by continuous efforts to improve accuracy. However, when the amount of aspherical surface is larger than 10 times the measurement wavelength, the distance between the interference fringes becomes too fine, making it difficult to obtain the same measurement accuracy as the spherical measurement. Usually, a method for measuring the surface of an aspheric surface using a mechanical or optical probe is known as a method for measuring a large aspheric surface. However, although the probe method has the flexibility to cope with aspherical surfaces of various shapes, there are problems with the measurement limit of the probe itself and the stability of probe position measurement, etc., and the accuracy is as high as the interference measurement method. Is difficult.
[0009]
  The present invention can measure the surface shape of an aspheric surface with the same accuracy as a spherical surface, and can appropriately cope with the measurement of various surface shapes.measuring deviceThe purpose is to provide.
[0010]
[Means for Solving the Problems]
  The measuring device of the invention of claim 1 comprises:
  The interference between the reference light and the light from the test surface is used toAsphericalIn a measuring device that measures the shape,
  A reference wavefront generating unit for generating a wavefront having spherical aberration;
  An optical member that generates the reference light and has a deformable reference surface, and a deformable reference surfaceStandardAn optical member,Deforming the shape of the reference surface to match the shape of the reference surface;Detecting light in which light from the reference surface interferes with light from the reference surfaceAfter deformationInterferometer for measuring the shape of the reference surfaceWhenHave
  Deforming the reference surface so that the wavefront of the reference light is aspheric,
  Reference light from the reference surface andPass through the reference wavefront generating unitThe test surfaceReflectedIt is characterized in that the shape of the test surface is measured by detecting the light that interferes with the light.
[0011]
  The invention of claim 2 is the invention of claim 1,
  The interferometer is
  A detector that detects light in which light from the reference surface interferes with light from the reference surface;
  And adjusting means for adjusting the shape of the reference surface or the reference surface based on the detection result by the detector.
[0012]
  The invention of claim 3 is the invention of claim 1,
  Reference surface deformation means for deforming the reference surface;
  Reference surface deformation means for deforming the reference surface,
  The reference surface deformation means or the reference surface deformation means is controlled based on a detection result of light in which light from the reference surface interferes with light from the reference surface.
[0013]
  The invention of claim 4 is the invention of any one of claims 1 to 3,
  SaidThe wavelength of light forming an interference fringe between the light from the reference surface and the light from the reference surface is different from the wavelength of the light used for measuring the shape of the test surface.
[0014]
  The invention of claim 5 is the invention of any one of claims 1 to 3,
  SaidIt is characterized in that the wavelength of light forming an interference fringe between the light from the reference surface and the light from the reference surface is the same as the wavelength of the light used for measuring the shape of the test surface.
[0015]
  The invention of claim 6 is the invention of any one of claims 1 to 5,
  Having a prototype arranged to be interchangeable with the reference optical member;
  It is characterized by detecting light in which light from the master and light from the reference surface interfere.
[0016]
  The invention of claim 7 is the invention of claim 6,
A plurality of the original devices are provided, and one original device selected from the plurality of original devices is arranged in the optical path.
[0017]
  The invention of claim 8 claims4In the invention of
  A reference wavefront generating unit for generating a reference wavefront having spherical aberration,
  The wavelength of light incident on the test surface is shorter than the wavelength of light that forms interference fringes between light from the reference surface and light from the reference surface.It is characterized by that.
[0018]
  The invention of claim 9 claims1 to8Any one ofIn the invention of
  The order of the radial radius of the wavefront generated by the reference wavefront generating unit is different from the order of the radial radius of the wavefront from the reference plane.
[0019]
  The invention of claim 10 claims9In the invention of
  The wavefront generated by the reference wavefront generating unit includes only a fourth-order component or more of a radius vector, and the wavefront from the reference surface includes only a sixth- or higher-order component of a radius vector.
[0020]
  The invention of claim 11 claims1 to8Any one ofIn the invention of
  The reference wavefront generation unit includes a plurality of lenses,
  Adjusting means for adjusting the distance between two of the plurality of lenses;
  The spherical aberration is generated by the adjustment by the adjusting means.
[0021]
  The invention of claim 12 claims1 to8Any one ofIn the invention of
  The reference wavefront generating unit has an Alvarez lens.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Conventional interferometers that measure a spherical surface have made great strides in accuracy and measurement reproducibility. Recently, it has become possible to show an accuracy of approaching 0.1 nm in measurement reproducibility, and has reached a level that can be used as a measurement apparatus in the EUV era.
[0034]
On the other hand, the measurement of the aspherical surface shape has a demand for the aspheric surface itself, but there are many error factors, so the accuracy does not satisfy the requirement. The embodiment of the present invention is characterized by eliminating the difference between the spherical surface and the aspherical surface. For this reason, in the embodiment of the present invention, a configuration for measuring an aspherical surface based on an optical arrangement for spherical measurement is used with the goal of achieving a spherical wave as the accuracy achievement value.
[0035]
In the present invention, an aspherical surface means not a spherical surface or a flat surface.
[0036]
  In the embodiment of the present invention, an aspheric wavefront is accurately synthesized from a wavefront of reference light and a wavefront of object light. At this time, the wavefront of the reference light is an elastically deforming mirror.(Reference plane)The wavefront of the object light is generated based on the aberration of the optical system.
[0037]
On the reference light side, a desired wavefront is created by freely creating a shape using two elastically deformable mirrors and a calibration master.
[0038]
Various methods can be used to create the reference wavefront on the object light side, but a highly versatile system can be constructed by generating aberrations in the optical system based on the following idea.
[0039]
Realization of high-precision driving in recent semiconductor manufacturing equipment and development of computers, if the aberration of the reference position is clear, accurately know the aberration generated after driving each element in an open loop from the reference position Is possible. In consideration of this point, the present invention considers the aspheric surface as an aberration as long as the aspheric surface is defined as a deviation from the spherical surface, and generates the aberration amount by the aberration generation optical system (reference wavefront generation unit). As a result, a wavefront having a desired aspherical shape is generated.
[0040]
In the present embodiment, an aspherical surface having an arbitrary shape can be detected on a general purpose without providing a dedicated element.
[0041]
In the present embodiment, in order to deform the wavefront on the reference light side, two elastically deformable mirrors or further a master is provided, and a desired reference surface wavefront is created by deforming the shape of both surfaces. As shown in FIG. 1, the two elastic deformation mirrors are arranged at the reference surface position and the reference surface position, and have both interferometers (elastic deformation amount monitor interferometers) to control the elastic deformation amount. ing. That is, the deformation amount of the two elastic deformation mirrors is grasped by the elastic deformation amount monitor interferometer, and the two reference deformation amounts are controlled alternately within the accuracy of the interferometer, so that the desired reference surface shape is finally obtained. Have created.
[0042]
Furthermore, various aspherical measurements are performed by using the wavefront generated by controlling the elastic deformation mirror on the reference light side and the reference wavefront generated on the object light side.
[0043]
  The two elastic deformation mirrors 21 and 23 used on the reference light side are, for example, thin glass plates made of an actuator or a piezoReference surface deformation means such asBy controlling with, the mirror shape (surface shape) can be changed freelyDeformableIt has a configuration. By using this elastic deformation mirror as a reference surface, a desired reference wavefront is created.
[0044]
In order to control the deformation amount of the elastic deformation mirror as the reference surface, first, the original device 22 whose shape is known in advance is arranged at the reference surface position. Then, by using an interferometer (elastic deformation monitor interferometer 101) between the elastic deformation mirror 21 disposed on the reference surface and the original device 22 disposed on the reference surface position, the elastic deformation mirror 21 on the reference surface is The shape is the same as the original device 22.
[0045]
  After calibrating the original device and the elastic deformation mirror 21, the original device 22 arranged at the reference plane position is changed to the elastic deformation mirror 23.In other words, it can be replaced with a reference optical member,The shape of the two elastic deformation mirrors 21 and 23 is grasped by an interferometer. Then, the surface shapes of both are alternately changed within a range that can be measured by the interferometer, so that the elastic deformation mirror 21 of the reference light can finally create a desired wavefront.
[0046]
The wavelength used for this elastic deformation monitor interferometer is different from the wavelength for measuring the aspherical surface shape. This makes it possible to measure an aspherical shape while monitoring the amount of elastic deformation.
[0047]
In addition, you may use the light of the same wavelength as a measurement wavelength with the monitor of the surface shape of an elastic deformation mirror.
[0048]
In this way, by using two elastically deforming mirrors on the reference light side and continuing the deformation alternately, a desired wavefront can be freely created even when the deviation from the spherical surface is large.
[0049]
  On the other hand, on the object light side, a wavefront serving as a reference for aspheric measurement is created. This reference wavefront is a reference wavefront creation unit for aberrations of the optical system.(Reference wavefront generation unit)Created by controlling by.
[0050]
Next, a case where the reference wavefront is created by the aberration of the optical system on the object light side will be described. In the reference wavefront creation unit, each order of the aspherical shape characterizing the aspherical surface is independently controlled by the generation of spherical aberration or the combination of Alvarez lenses.
[0051]
Since the target optical system is often coaxial, the optical element often has rotational symmetry. Therefore, the deviation from the spherical surface is usually represented by an even term that is the fourth power or more of the radius R, where R is the distance (radius) from the optical axis. What is particularly important is the fourth power term of the radius vector R. The fourth power term corresponds to spherical aberration in terms of aberration. Therefore, the reference wavefront creation unit intentionally generates a desired value of spherical aberration to form a wavefront corresponding to the component of the aspherical shape. However, in general, an aspherical surface cannot often be expressed only by the fourth power of the radius vector R. Therefore, an aberration that can be controlled by using an Alvarez lens for each order is generated for higher-order terms of the fourth power or higher. Thus, it is possible to synthesize wavefronts constituting a desired aspherical surface, and all the wavefronts of the fourth order or higher are generated by the Alvarez lens.
[0052]
In the present embodiment, an aspheric wavefront is created on each of the reference light side and the object light side, and an arbitrary aspherical shape can be measured by causing the wavefront to interfere with the observation surface based on this wavefront. Therefore, it is possible to create a desired wavefront by alternately deforming the wavefront of the reference light by two elastic deformation mirrors, and to monitor the amount of deformation with high accuracy. It is characterized by comprising a “reference wavefront generating unit” for creating a reference wavefront for shape measurement.
[0053]
As described above, in the present embodiment, by using two elastic deformation mirrors on the reference light side and a reference wavefront generating unit on the object light side, both wavefronts are adjusted and synthesized. Creating. Therefore, since various aspherical surfaces can be measured on the basis of the apparatus itself, an extremely versatile apparatus is configured. In addition, despite the versatility of the interferometry method, the same accuracy as measuring a spherical surface can be achieved, making it difficult to measure the aspherical surface shape with higher accuracy than before. The surface shape of the spherical surface can be measured with high accuracy.
[0054]
Next, embodiments of the present invention will be described with reference to the drawings.
[0055]
  [Embodiment 1]
  FIG. 1 is a schematic view of the essential parts of Embodiment 1 of the present invention. FIG. 1 shows a method for measuring the surface shape of an aspheric surface as a test surface. In the first embodiment, two elastic deformation mirrors 21 and 23 are used on the reference light side, the reference wavefront generating unit 3 is used on the object light side, and both aspherical wavefronts are used to form the aspherical shape of the test surface 5. Is to measure. In particular, in the elastic deformation mirrors 21 and 23 on the reference light side, the higher order of the aspherical surface (the wavefront radius R of the sixth power or moreThat is, 6th or higher), And the reference wavefront generating unit 3 on the object light surface side generates spherical aberration to generate a reference wavefront having a radius R of the fourth power or higher.
[0056]
The interferometer shown in FIG. 1 normally has a so-called Twiman Green interferometer. The figure starts from where collimated light (parallel light) from the laser light source 1 enters the interferometer. As the laser light source 1, a known laser such as a harmonic of HeNe, Ar, HeCd, or YAG can be used.
[0057]
The collimated light La is first split in wavefront by the beam splitter 11 and split into a reference optical path to the elastic deformation mirror 21 that forms a reference plane as reference light and an object optical path with the test surface 5. Thereafter, the reference light and the object light are combined by the beam splitter 11 to form interference information on the image pickup means 71 such as a CCD via the lens 61, and the surface shape of the test surface 5 is measured therefrom. .
[0058]
First, the optical path on the reference light side, which is the most characteristic feature of this embodiment, will be described.
[0059]
The most characteristic feature of the present embodiment is that a desired wavefront is created by alternately adjusting and deforming the elastic deformation mirrors 21 and 23 using the reference original 22 and the two elastic deformation mirrors 21 and 23. That is where it will be.
[0060]
The light in the reference optical path passes through the beam splitter 12, is reflected by the elastic deformation mirror (reference mirror) 21, and returns to the beam splitter 11 again. In order to obtain high-precision measurement accuracy, it is essential to perform phase measurement, so a technique called PMI (Phase Measuring Interferometer) is applied. For example, the configuration of FIG. 1 shows an example in which the reference mirror 21 is finely driven with a wavelength order.
[0061]
  As shown in FIG. 2, the elastic deformation mirrors 21 and 23 are, for example, a thin glass plate 21a and a driving member 21b such as an actuator or a piezo.(Reference surface deformation means and reference surface deformation means)By controlling at 21c, the mirror shape (reflecting surface shape) can be freely changed and a desired aspherical wavefront can be created.
[0062]
  In order to control the elastic deformation mirror 21 used as the reference surface to a desired shape, it is necessary to monitor the deformation amount with high accuracy. In consideration of the case where the measurement accuracy is insufficient with the accuracy of the piezo and the actuator, this system has another interferometer (deformation amount monitor interferometer) for monitoring the deformation amount of the reference surface as shown in FIG. ) 101 on the reference surface side. Then, the surface shape of the elastic deformation mirror 21 is controlled by the interference between the light beam from the elastic deformation mirror 21 and the light beam from the original device 22 or the elastic deformation mirror 23. FIG. 3 is an explanatory diagram of an elastic deformation monitor interferometer. As shown in FIG. 3, the reference plane position has a flat mirror 22 and an elastically deforming mirror as a prototype.(Reference optical member)23 is exchangePossibleIt is like that.
[0063]
In order to monitor the deformation amount of the elastic deformation mirror 21 on the reference surface as needed while measuring the aspheric shape of the test surface 5, it is necessary to use a wavelength different from the measurement wavelength of the aspheric surface.
[0064]
  Comparing the measurement accuracy of the aspherical shape and the amount of elastic deformation, the aspherical shape requires higher accuracy. In general, the shorter the wavelength, the better the measurementLightFIG. 1 shows a case where the source 1 uses a laser light source having a shorter wavelength than the light source 2 on the deformation monitor interferometer 101 side.
[0065]
Further, since different wavelengths can be used for aspherical measurement and deformation amount monitoring, it is possible to measure in real time, so there is an advantage that unstable components of the piezo and actuator can always be detected and fed back.
[0066]
When it is not necessary to monitor at any time, the wavelengths of the light beams from the light source 1 and the light source 2 may be the same.
[0067]
The elastic deformation amount monitor interferometer shown in FIG. 3 will be described below. After collimating the light La2 from the laser light source 2 and reflecting it with the beam splitter 13, the other beam splitter 12 uses the elastic deformation mirror 21 side where the wavefront is placed at the reference plane position, the reference plane position 22 side, Divide into The light from the elastic deformation mirror 21 returns to the beam splitter 12 and is reflected again, and the light reflected from the reference plane position 22 passes through the beam splitter 12. The two wavefronts are caused to interfere with each other, the interference information is detected by the CCD 72 via the beam splitter 13 and the lens 62, and the elastic deformation amount of the elastic deformation mirror 21 is monitored by the surface deformation amount monitoring means 103. The beam splitter 12 used here divides the wavefront of the light beam from the light source 2 used for monitoring the amount of elastic deformation into two, and transmits the wavelength of the light beam from the light source 1 used for aspherical measurement.
[0068]
Next, a procedure for changing the elastic deformation mirror 21 used as the reference surface into a desired surface shape will be described with reference to FIG.
[0069]
First, the elastic deformation mirror 21 is disposed at the reference surface position 21a, and the master 22 having a known shape is disposed at the reference surface position 22a. Here, a case where a plane mirror is used as an example of the original device 22 is shown, but it is of course possible to use a spherical surface or an aspheric surface whose shape is known in advance as the original device.
[0070]
Then, by using an interferometer (elastic deformation monitor interferometer 101) capable of monitoring both shapes, the shape of the elastic deformation mirror 21 on the reference surface is made to match that of the original device 22, so that the elastic deformation mirror 21 Perform calibration.
[0071]
After calibrating the surface shape of the elastic deformation mirror 21, the original device 22 arranged at the reference surface position 22a is replaced with the elastic deformation mirror 23, and the shapes of the two elastic deformation mirrors 21 and 23 are interferometers. To grasp. Then, the surface shape of the elastic deformation mirror 23 at the reference surface position 22a is controlled so as to coincide with the surface shape of the elastic deformation mirror 21 at the reference surface position that has been calibrated with the original device 22 earlier.
[0072]
As a result, both the surface shapes of the elastic deformation mirrors 21 and 23 are equal to those of the original device 22.
[0073]
Next, the surface shape is deformed by controlling the actuator so that the elastic deformation mirror 21 at the reference surface position 21a is brought close to a desired aspheric wavefront. This amount of deformation can be monitored by interference between the reference surface and the reference surface (elastic deformation amount monitor interferometer 101), and the amount of deformation that can be controlled is within a range that can be measured by the interferometer between the reference surface and the reference surface.
[0074]
  Further, the surface shape of the elastic deformation mirror 23 at the reference surface position 22a is changed.With reference wavefront deformation meansThe surface shape is the same as that of the elastic deformation mirror 21 at the reference surface position 21a.
[0075]
Similarly, the surface shape of the elastic deformation mirror 21 at the reference surface position 21a is controlled to be close to a desired aspheric wavefront, and then the surface shape of the elastic deformation mirror 23 at the reference surface position 22a is the same surface as the elastic deformation mirror 21. The control is repeated alternately to form the shape.
[0076]
Then, the deformation is continued alternately as described above until the surface shape of the elastic deformation mirror 21 finally arranged at the reference surface position 21a becomes a desired aspheric wavefront.
[0077]
By alternately deforming the surface shapes of the two elastic deformation mirrors 21 and 23 in this way, even if the wavefront is largely deviated from the spherical surface, it can be deformed with high accuracy using an interferometer. The desired wavefront is created.
[0078]
The deformation method of the two elastic deformation mirrors 21 and 23 is not limited to that shown in FIG. 4. When the two elastic deformation mirrors 21 and 23 are alternately deformed, the amount of deformation and the number of repetitions differ depending on the aspherical shape.
[0079]
The wavelength of the light beam from the light source 2 used for the elastic deformation amount monitor interferometer 101 for monitoring the deformation amounts of the surface shapes of the two elastic deformation mirrors 21 and 23 is from the light source 1 for measuring the aspheric surface shape. When the wavelength of the light beam is different from that of the first light beam, it is possible to monitor the amount of elastic deformation and control the amount of deformation on the reference light side and to measure the surface shape of the test surface 5 simultaneously. Comparing the measurement accuracy of the aspherical shape and the amount of elastic deformation, the aspherical shape requires higher accuracy. In general, it is preferable to use a laser light source whose wavelength from the light source 1 is shorter than that from the light source 2 because a shorter wavelength can be measured with higher accuracy. The light beam from the light source 1 and the light beam from the light source 2 may have the same wavelength.
[0080]
  In the present embodiment, a case where a plane mirror is used as the original device 22 has been described. However, it takes a long time to create a desired aspheric wavefront from a plane because the amount of deformation is too large. This original device is not limited to a flat mirror, but may be any material such as a spherical mirror or an aspherical mirror as long as the shape can be grasped. Therefore, as shown in FIG.And HaraVesselHave multipleMake the system so that it can be placed at the reference plane position 22a, and finally select one prototype according to the wavefront you want to create.And placed in the optical pathIt is also possible to do.
[0081]
For example, a plurality of spherical prototypes may be prepared, a prototype corresponding to the radius of curvature of the spherical surface to be measured may be selected, and a desired aspheric waveform may be created based on the spherical surface.
[0082]
In this system, the surface shape of the original device 22 and the elastic deformation mirrors 21 and 23 are matched at the time of the first calibration. Therefore, by using the prototype with the closest shape, the amount of deformation for deforming to the desired shape can be reduced, and the number of times to control the two elastically deforming mirrors is reduced, which makes it easier A desired reference wavefront can be formed.
[0083]
Thus, by determining the surface shape of the elastic deformation mirror 21 arranged at the reference surface position from the interference based on the light beams from the two elastic deformation mirrors and the original device, a desired reference wavefront is freely created. .
[0084]
Next, the optical path on the object light side in FIG. 1 will be described.
[0085]
The wavefront is divided by the beam splitter 11, and the light divided into the object optical path is incident on the reference wavefront generation unit 3. Various configurations of the reference wavefront generating unit 3 are conceivable. In the configuration of FIG. 1, the wavefront corresponding mainly to the fourth power of the radius R of the wavefront is positioned in the optical axis direction of the optical system in the reference wavefront generating unit 3. Is adjusted to generate spherical aberration.
[0086]
Here, a method for generating spherical aberration will be described first. In FIG. 1, reference numeral 32 denotes a first lens 33, which is a second lens. In the configuration of FIG. 1, the lens 32 functions to form parallel light incident from the beam splitter 11 at a point A. Since the lens 32 only needs to correct aberrations in a very small range near the axis, the amount of aberration can be kept extremely small. Even if the aberration of the lens 32 is very small, it can be canceled by offset processing because it is a very small amount. In the following description, it is assumed that the aberration of the lens 32 can be ignored.
[0087]
The lens 33 is a lens in which aberration is corrected with respect to a finite object point. For example, it is an objective lens of a microscope, and aberrations are well corrected with a predetermined object image positional relationship. Therefore, the imaging of the lens 33 generates a lot of aberrations when the position is set out of the predetermined relationship. Since the optical arrangement of the interferometer is used only on the axis, the aberration generated by deviating from the predetermined relationship is a rotationally symmetric aberration with respect to the optical axis, that is, a spherical aberration. Therefore, if the position of the image formation point A formed by the lens 32 coincides with the position of the object point on which the aberration of the lens 33 is to be corrected, the aberration at the image formation position formed after passing through the lens 33 is extremely good. It has been corrected.
[0088]
A point indicated by B in the figure is a position where the aberration of the subsequent collimator 4 is best corrected. When the position of the point B coincides with the image formation position by the lens 33 of the point A, all the optical elements constituting FIG. 1 are arranged with the smallest aberration. When the lenses 32 and 33 and the collimator 4 are in a state in which the aberration is best corrected as described above, the interferometer of FIG. 1 is defined to be arranged in the “reference state”.
[0089]
When the description of the reference state is advanced, the light imaged at the point B by the lens 33 is then incident on the collimator 4, and the divergent wave is converted into a convergent wave by the collimator 4 and travels toward the object 5 to be examined. Since the collimator 4 is an optical system in which aberration correction is performed with respect to the image forming point B, the convergent wave becomes a wavefront having no aberration (very little aberration) and travels toward the test object 5. That is, the reference state is an arrangement suitable for measuring a spherical surface. If a reference spherical surface whose characteristics are known in advance as a test object in the reference state, the aberration offset of the measurement optical system from the lens 32 to the collimator 4 can be obtained. That is, the reference state is a state suitable for measuring a spherical surface as a test surface, and plays a role of taking an offset of the measurement system. In addition, since it is detailed in "Optical Shop Testing" (Malacara edition) etc. about how to take an offset, it does not elaborate here.
[0090]
Next, measurement of an aspheric surface will be described. When the present inventor analyzed the shape of the aspherical surface to be measured, the aspherical shape is the fourth, sixth, eighth, tenth,... It was found that it is efficient to perform approximation from the lower order in the order of. Therefore, when creating the wavefront by the reference wavefront on the object beam side and the elastic mirror on the reference beam side, the radial radius R decreases to the fourth, sixth, eighth, tenth,... The wavefront is synthesized from the next.
[0091]
In the first embodiment shown in FIG. 1, spherical aberration is intentionally generated by the reference wavefront generating unit 3 on the object beam side, and a term of the fourth power of the radius vector R of the aspherical surface is generated (exactly the radius vector). (Not only the fourth power of R but also the fourth power or more of the radial radius R), a higher-order higher than the sixth radius of the radial radius R is generated using an elastic deformation mirror on the reference light side, The spherical wavefront can be created.
[0092]
Here, generation of spherical aberration by the reference wavefront generating unit 3 on the object light side is performed in the following procedure. As described above, the lens 33 corrects the aberration at the point B only when the image forming point A of the lens 32 reaches a predetermined object point position. Therefore, when the lens 32 is moved in the optical axis direction and the position of the point A is shifted from the position where the aberration of the lens 33 can be taken, the position of the imaging point is shifted from the point B, and spherical aberration is generated.
[0093]
FIG. 6 shows the situation during this time. FIG. 6A shows a lens arrangement in which the aberration of the lens 33 is well corrected. The imaging position point A formed by the lens 32 forms an image at a point 33p where the aberration of the lens 33 is removed, and is connected to the point 33q. I image. In the reference state, the point 33q coincides with the object position B where the aberration of the collimator 4 is corrected.
[0094]
Next, as shown in FIG. 6B, the imaging position A is shifted to the position of the point 33p1 by moving the lens 32 to the right. As a result of shifting, the imaging position by the lens 33 moves to the point 33q1. Since the point 33p1 and the point 33q1 are deviated from the relationship in which the aberration is taken, spherical aberration is generated. In this embodiment, this spherical aberration is used for an aspheric reference wavefront. If the lens 32 and the lens 33 are moved together to the left from the relationship with the collimator 4, the image forming position by the lens 33 can be made coincident with the point B while maintaining the state in which the spherical aberration is generated. The reason why the light beam can move as a whole is that the light beam incident on the lens 32 is a parallel light beam.
[0095]
The amount of spherical aberration generated by the reference wavefront generating unit 3 can control both the amount of movement of the imaging point of the lens 32 and the amount and sign in the direction of movement. Therefore, the fourth power term of the radius vector R can be treated as a variable amount. One of the objects in the present embodiment is high-accuracy measurement capable of measuring accuracy up to angstrom order. Strictly speaking, the aberration caused by the position adjustment of the lenses 32 and 33 is not only the fourth power term of the radius vector R, but if the positions of the lenses 32 and 33 are known precisely, the value is calculated by a computer. Thus, it is possible to calculate the aberration that occurs accurately up to the higher order term. The calculated value is used as the value of the reference wavefront, including higher order terms.
[0096]
Therefore, the reference light side creates an aspherical wavefront by changing the surface shape of the elastic deformation mirror 21 as desired from the two elastic deformation mirrors 21 and 23 and the original device 22, and the object light side has a lens. Spherical aberration is generated by adjusting the positions of 32 and 33, and the wavefronts from the lower order in the order of the fourth, sixth, eighth, tenth,... Radial radius R until the aspherical shape falls within the measurable range. By combining them, a desired aspheric wavefront is created, and by adjusting the wavefronts on the reference light side and the object light side, various aspheric shapes can be measured.
[0097]
In the first embodiment shown in FIG. 1, a laser interferometer (position information monitoring means) 102 that monitors the position of the lens barrel of the lens 32 is used to detect the position of the lens 32. Specifically, the light beam 32-2 from the laser interferometer 102 that monitors the position is incident on the mechanical component 32-1 that moves the lens barrel of the lens 32. It is also possible to use a position detection element such as a magnescale or an encoder instead of the laser interferometer, and the amount of aberration generated by calculating with the calculation means 104 using the monitor function can be accurately known.
[0098]
On the other hand, since what can be monitored by the laser interferometer 102 is only a relative displacement, it is necessary to separately determine a reference position. In order to determine a reference position, the above-described “reference state” is used. The optical system is placed in a reference state, and a reference spherical surface having a known feature is placed at the object position. In this state, the lenses 32 and 33, the collimator 4, Adjust the position of the reference sphere. The adjustment of the lenses 32 and 33 and the collimator 4 is finished in a state where the value is within a certain allowable value after the adjustment. This position becomes the reference position of the position detection element (laser interferometer 102). The amount of aberration generated by the drive amount from the reference position can be accurately calculated with an accuracy determined from the measurement accuracy of the drive amount. If the laser interferometer 102 is used, the driving accuracy can be in the order of nanometers, so that the accuracy is sufficient to know the value of the generated aberration.
[0099]
In FIG. 1, the position detection element is shown only for the lens 32, but the position detection elements are similarly arranged in the other optical elements 33, 4, and 21.
[0100]
Furthermore, in the first embodiment, the case where the reference wavefront is created by generating spherical aberration by adjusting the positions of the lenses 32 and 33 on the object light side has been described. The method for generating spherical aberration is not limited to this, and a method as shown in FIG. 7 as an example may be used. In the present embodiment, the lens 133 in the reference wavefront generating unit 3 has a function of generating aberration with respect to parallel light incidence.
[0101]
FIG. 7A shows a system in which the amount of spherical aberration generated is controlled by controlling the distance d between the two lenses 133 a and 133 b constituting the lens 133. The change in the imaging position accompanying the change in the distance d is adjusted by moving the entire lens 133. The reference position of the interval d is determined by obtaining a similar reference state using the lens 133, the collimator 4 and the reference spherical surface as in the previous embodiment.
[0102]
FIG. 7B shows an example in which two wedge-shaped prism members 134 and 135, which are parallel plates as a whole and whose thickness can be continuously changed, are inserted at the rear side of the lens 133. In order to make the thickness of the parallel plate variable, the object can be achieved by combining two wedges 134 and 135 having the same angle and moving them in a direction perpendicular to the optical axis 0a. The adjustment of the reference position in this case can also be obtained by once achieving the reference state as in the previous embodiment.
[0103]
FIG. 7C shows an example in which spherical aberration is controlled by discretely changing a plurality of parallel plates having different thicknesses. In this case, the generated spherical aberration can be obtained by accurately measuring the thickness of the parallel plate.
[0104]
In the present embodiment, with the above configuration, the wavefront to be detected (which passes through the reference wavefront via the elastic deformation mirror 21, the reference wavefront generating unit 3, the collimator 4, is reflected by the surface 5 to be tested, and returns to the original optical path ( The signal wavefront) is synthesized by the beam splitter 11, an interference wavefront is formed on the imaging means 71 such as a CCD by the lens 61, and the surface shape of the test surface 5 (the interference signal) is generated by the signal (interference signal) from the imaging means 71. Surface information).
[0105]
[Embodiment 2]
FIG. 8 is a schematic view of the essential portions of Embodiment 2 of the present invention.
[0106]
This embodiment shows a method for measuring an aspheric surface. In the second embodiment, two elastically deformable mirrors 21 and 23 and the original device 22 are used on the reference light side, and the reference wavefront generating unit 3 is used on the object light side. The spherical shape is measured, and the basic configuration is the same as that of the first embodiment.
[0107]
This embodiment is different from the first embodiment in that spherical aberration is generated in the reference wavefront creation unit 3 on the object light side so that the radial radius R is the fourth power or higher, and further, the radial radius R is used to the sixth power of the radial radius R 31. This is to create a higher-order wavefront of the radius R of the eighth power or more in the elastic deformation mirror 21 on the reference light side.
[0108]
In the first embodiment, a case has been described in which spherical aberration, which is mainly the aberration of the fourth power term of the radius vector R, is generated by adjusting the position of the lens in the reference wavefront creation unit 3 on the object light side. However, an actual aspherical surface cannot be represented by only the fourth power term of the radius vector R, and it may be necessary to introduce a higher order term. In some cases, it is difficult to freely control higher-order aberrations greater than or equal to the sixth power of the radius R by simply adjusting the position of the lens 32 to obtain an aspheric reference wavefront.
[0109]
Therefore, in the second embodiment, the Alvarez lens 31 is used to generate aberrations having higher-order shapes that are present on an actual aspheric surface.
[0110]
The Alvarez lens 31 will be described below.
[0111]
As shown in FIG. 9, the Alvarez lens 31 is a pair of lenses 31a1 and 32a2 having the same shape, and the aspherical surfaces indicated by f (x, y) are arranged in close proximity to each other. It is. When the relative deviation between the two lenses 31a1 and 32a2 is zero, the Alvarez lens 31 functions in the same manner as a parallel plate. If the shape of f (x, y) is appropriately selected, one of the two lenses 31a1 and 32a2 is driven in the y direction perpendicular to the direction of the optical axis 0a and the other is driven by -Δ, thereby freeing high-order aberrations. Can be generated. For example, the shape f (x, y) of the Alvarez lens that shifts in the y direction to produce the sixth power is
f (x, y) = a (x⁶y + y⁷/ 7)
Then, the transmitted wavefronts W (x, y) of the Alvarez lenses that are shifted from each other by ± Δ in the y direction are expressed as follows:
W (x, y) ≈2aΔ (n−1) (x⁶+ Y⁶)
Thus, a wavefront proportional to the shift amount Δ can be formed. If the shift amount Δ is configured symmetrically between plus and minus, the even-order term of the shift amount Δ disappears, and the nonlinear effect of the shift amount Δ can be suppressed. The amount of generated aberration can be adjusted by controlling the shift amount Δ.
[0112]
Since it is difficult to ideally create the aspherical shape f (x, y) that characterizes the Alvarez lens 31, it is necessary to calibrate the manufacturing error. At the time of calibration, as in the case of spherical aberration, measurement is performed using a reference surface whose reference state and feature are known, and an offset amount is calculated. The offset amount is corrected including an error of f (x, y), a non-linear effect generated from the shift amount Δ, and the like. The position of the Alvarez lens is detected by attaching a position detection element to each Alvarez lens.
[0113]
What has been described here is the explanation of the sixth power term of the radial radius R of the wavefront, but the eighth power term and the tenth power term can also be controlled by inserting another Alvarez lens. The number of Alvarez lenses to be inserted depends on the shape of the target aspheric surface. In FIG. 9, 31 corresponds to an Alvarez lens that generates a sixth power term of the radius R.
[0114]
As described above, according to the second embodiment, the elastic deformation mirror 21 is used on the reference light side, the reference wavefront generating unit 3 is used on the object light side, and the non-spherical wavefronts of both are adjusted, so The spherical shape is measured. In particular, the reference wavefront generating unit 3 on the object beam side mainly generates the spherical aberration, thereby mainly generating the fourth power of the radius R (more precisely, higher order), and further, Alvarz. Various aspherical measurements can be performed by creating a sixth-order wavefront of the radius R using the lens 31 and creating a higher-order (more than the eighth power of the radius R) wavefront in the elastic deformation mirror 21 on the reference light side. Can be made possible.
[0115]
On the reference light side, when creating a higher-order wavefront (the radial radius R to the eighth power or more) with the elastic deformation mirror 21, as in the first embodiment, the master 22 and the elastic deformation mirror arranged at the reference plane position are used. 23, the two elastic deformation mirrors 21 and 23 are alternately deformed to finally create a desired wavefront from the elastic deformation mirror 21.
[0116]
[Embodiment 3]
FIG. 10 is a schematic view of the essential portions of Embodiment 3 of the present invention.
[0117]
The basic configuration of this embodiment is the same as that of the first and second embodiments. The elastic deformation mirror 21 is used on the reference light side, the standard wavefront generating unit 3 is used on the object light side, and an aspheric wavefront created by both is used. Thus, the aspherical shape of the test surface 5 is measured. In particular, the third embodiment is characterized in that two Alvarez lenses 31a and 31b are used on the object light side. As in Example 2, the number of Alvarez lenses to be inserted varies depending on the target aspheric shape.
[0118]
In the present embodiment, spherical aberration is generated by the reference wavefront creation unit 3 to control the amount of spherical aberration that is mainly proportional to the fourth power of the radial radius R, and the Alvarz lens 31a has a radial radius R of 6. An aberration proportional to the power, and another Alvart lens 31b creates a wavefront proportional to the eighth power of the radius R, and the elastic deformation mirror 21 on the reference light side generates a higher-order wavefront greater than the tenth power of the radius R. By making it, various aspherical measurements are possible. The reference positions of the Alvarez lenses 31a and 31b are the same as in the first embodiment, using the lenses 32 and 33, the collimator 4, and the reference spherical surface, and after realizing the same reference state, insert the Alvarez lens and set the offset. Can be sought.
[0119]
On this reference light side, when creating a higher-order wavefront (radial radius R to the 10th power or more) with the elastic deformation mirror 21, as in the first embodiment, the original device 22 and the elastic deformation mirror arranged at the reference surface position are used. 23, the two elastic deformation mirrors 21 and 23 are alternately deformed to finally create a desired wavefront from the elastic deformation mirror 21.
[0120]
[Embodiment 4]
FIG. 11 is a schematic view of the essential portions of Embodiment 4 of the present invention.
[0121]
The basic configuration of the present embodiment is the same as that of the first and second embodiments. The elastic deformation mirror 21 is used on the reference light side, the standard wavefront generating unit 3 is used on the object light side, and both aspheric wavefronts are used. The aspherical shape of the test surface 5 is measured. In the present embodiment, the Alvarez lens 31a on the object light side is burdened with the fourth-order aberration of the radius R.
[0122]
In the present embodiment, the lens 33 has a function of forming an image of parallel light without aberration. In the figure, the Alvarez lens 31a controls the amount of spherical aberration that is proportional to the fourth power of the radius R. The reference position of the Alvarez lens is obtained by using the lenses 32 and 33, the collimator 4, and the reference spherical surface as in the first embodiment to realize the same reference state and inserting the Alvarez lens 31a to obtain the offset. Can do.
[0123]
Then, by using the elastic deformation mirror 21 disposed on the reference light side, an aberration proportional to a higher-order term of the radius R of the sixth power or higher that does not occur in the Alvarez lens 31a on the object light side is generated.
[0124]
On the reference light side, when creating a higher-order wavefront (the radius of the radius of curvature R 6 or more) with the elastic deformation mirror 21, as in the first embodiment, the master 22 and the elastic deformation mirror arranged at the reference plane position are used. 23, the two elastic deformation mirrors 21 and 23 are alternately deformed to finally create a desired wavefront from the elastic deformation mirror 21.
[0125]
Exposure is performed by forming an image formed on the first object (reticle) on the second object (wafer) with the optical element created by using one of the interferometers of the above embodiments. It is used for a projection optical system in a projection exposure apparatus.
[0126]
This facilitates the production of a projection optical system with high optical performance.
[0127]
As described above, according to the present embodiment, the original device and the two elastic deformation mirrors are arranged on the reference light side, the reference wavefront generating unit on the object light side is arranged, and the wavefront is adjusted and synthesized by both. Therefore, various reference wavefronts can be created.
[0128]
Moreover, since the apparatus itself is a reference, the apparatus can be used as a master. Furthermore, since the wavefront generated as a reference can be variably controlled with high accuracy in this embodiment, various aspheric surfaces can be used for measurement, and the versatility is extremely high. In spite of its versatility, it is an interferometric method, so it can measure aspherical surfaces with the same accuracy as measuring spherical surfaces.
[0129]
According to this embodiment, an aspherical optical element that exists as a conventional design value but is actually difficult to process can be manufactured. In addition, it is an optical system with a high accuracy such as EUV and a limited number of sheets that can be used. Conventionally, an aspheric surface in a range that could not be applied from the viewpoint of processing measurement in the past. The optical element can be used, and there is a great merit in the device configuration.
[0130]
Further, according to the present embodiment, the present invention can be applied not only to EUV but also to an aspherical surface in a conventional UV, DUV, and VUV exposure apparatus. The use of the aspherical surface increases the flexibility of the optical system, which can have a great effect on the semiconductor exposure apparatus.
[0131]
The application of the aspherical surface according to the present embodiment can be applied not only to the semiconductor exposure apparatus but also to other optical apparatuses.
[0132]
【The invention's effect】
According to the present invention, an interferometer that can measure the surface shape of an aspheric surface with the same accuracy as a spherical surface and can appropriately cope with the measurement of various surface shapes, and a semiconductor exposure apparatus using an optical element using the interferometer Can be achieved.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a main part of an aspherical measurement interferometer according to a first embodiment of the present invention.
FIG. 2 is a schematic diagram of the deformable mirror of FIG.
FIG. 3 is an explanatory diagram of a partial elastic deformation monitor interferometer of FIG.
FIG. 4 is an explanatory diagram of shape control of an elastic deformation mirror which is a reference surface of FIG.
FIG. 5 is an explanatory diagram when selecting from a plurality of prototypes at the reference plane position in FIG. 1;
FIG. 6 is an explanatory diagram showing the occurrence of spherical aberration in FIG.
FIG. 7 is an explanatory diagram for generating various spherical aberrations in FIG. 1;
FIG. 8 is an explanatory diagram of Embodiment 2 of the aspherical measurement interferometer of the present invention.
9 is a diagram illustrating the principle of the Alvarez lens shown in FIG.
FIG. 10 is a schematic view of the main part of an aspherical measurement interferometer according to a third embodiment of the present invention.
FIG. 11 is a schematic view of the essential portions of Embodiment 4 of an aspherical measurement interferometer according to the present invention.
[Explanation of symbols]
11, 12, 13 Beam splitter
21 Elastic deformation mirror at reference plane position
22 Master of reference plane position
23 Elastic deformation mirror at the reference plane position
3 Reference wavefront generation unit
32, 33 lenses
4 Collimator
5 Test object
61, 62 Imaging lens
71,72 CCD
31a, 31b Alvarez lenses

Claims (17)

In the measuring apparatus for measuring the aspherical shape of the test surface using interference between the reference light and the light from the test surface,
A reference wavefront generating unit for generating a wavefront having spherical aberration;
An optical member that generates the reference light and has a deformable reference surface and a reference optical member that has a deformable reference surface, and deforms the shape of the reference surface to match the shape of the reference surface , and a interferometer for the light from the light and the reference surface to measure the shape of the reference surface after deformation by detecting the light interference from the reference surface,
Deforming the reference surface so that the wavefront of the reference light is aspheric,
A measuring apparatus for measuring the shape of the test surface by detecting light in which the reference light from the reference surface interferes with light that has passed through the reference wavefront generation unit and reflected from the test surface . The interferometer is
A detector that detects light in which light from the reference surface interferes with light from the reference surface;
The measuring apparatus according to claim 1, further comprising an adjusting unit that adjusts a shape of the reference surface or the reference surface based on a detection result by the detector. Reference surface deformation means for deforming the reference surface;
Reference surface deformation means for deforming the reference surface,
2. The measurement according to claim 1, wherein the reference surface deformation unit or the reference surface deformation unit is controlled based on a detection result of light in which light from the reference surface interferes with light from the reference surface. apparatus. To claim 1, wherein different from the light and wavelength measurements of light used in the form of wavelength and the test surface of the light forming the interference fringes between the light from the reference surface from the reference surface 4. The measuring device according to any one of 3 above. Claims, characterized in that the light wavelength of light used for measurement of the shape of the wavelength and the test surface of the light forming the interference fringes between the light from the reference surface from the reference surface is the same The measuring apparatus according to any one of 1 to 3. Having a prototype arranged to be interchangeable with the reference optical member;
The measuring apparatus according to claim 1, wherein light that interferes with light from the original device and light from the reference surface is detected.   The measuring apparatus according to claim 6, wherein a plurality of the original devices are provided, and one original device selected from the plurality of original devices is arranged in the optical path. 5. The measurement according to claim 4, wherein a wavelength of light incident on the test surface is shorter than a wavelength of light forming an interference fringe between the light from the reference surface and the light from the reference surface. apparatus. Measurement apparatus according to any one of claims 1 to 8, wherein different from the order of the radius of the wave front from the order and the reference surface of the moving radius of the wavefront the reference wavefront generation unit generates. Wavefront the reference wavefront generation unit generates contains only 4 or higher order components of the radius vector, the wavefront from the reference surface according to claim 9, characterized in that it comprises only 6 or higher order components of the radius vector Measuring device. The reference wavefront generation unit includes a plurality of lenses,
Adjusting means for adjusting the distance between two of the plurality of lenses;
Measurement apparatus according to any one of claims 1 to 8, characterized in that it generates the spherical aberration by the adjustment by the adjustment means. The reference wavefront generation unit measuring apparatus according to any one of claims 1 to 8, characterized in that it has a Alvarez lens.   The measuring apparatus according to claim 12, wherein the wavefront generated by the Alvarez lens includes only a sixth-order component or more of a moving radius.   The measurement apparatus according to claim 12, wherein the reference wavefront generation unit includes a plurality of the Alvarez lenses, and the wavefronts generated by the Alvarez lenses are different from each other.   The measuring apparatus according to claim 12, wherein the wavefront generated by the Alvarez lens includes only a fourth-order component or more of a moving radius. The adjusting means includes
Moving means for moving the lens;
The measuring apparatus according to claim 11, further comprising position information monitoring means for monitoring position information of the lens.   The measuring apparatus according to claim 16, further comprising a calculation unit that calculates a wavefront generated by the reference wavefront generation unit based on a moving amount of the lens.

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