JP2005522026A - Condensing unit comprising a reflective element for an illumination optical system using a wavelength of 193 nm or less - Google Patents

Abstract

The present invention relates to a condensing unit for an illumination optical system using wavelengths of 193 nm, preferably in the extreme short ultraviolet (EUV) region. This condensing unit comprises at least one reflector shell having an optical action. The light beam strikes the surface tangent to the reflector shell at an angle of less than 20 °. A periodic structure having at least one diffraction grating period is provided on at least a part of the reflector shell. The plurality of reflecting mirror shells provided to be rotationally symmetric with respect to the rotation axis are provided in a nested manner around the common rotation axis.

Description

  The present invention relates to a condensing unit for an illumination optical system using a wavelength of 193 nm or less, preferably 126 nm or less, particularly in the extreme short ultraviolet (EUV) region. This condensing unit has at least one reflecting mirror shell (saddle-shaped reflecting mirror) that receives a light beam of a light beam emitted from an object and has an optical action on the light beam of such a light beam.

  It is preferable that the light beam strikes the surface tangent to the reflector shell at an angle of less than 20 °.

  The present invention also provides an illumination optical system including such a condenser, a projection exposure apparatus including the illumination optical system according to the present invention, and a method for exposing a fine structure.

  Nested concentrators for wavelengths below 193 nm, in particular in the X-ray region, are well known from many documents.

  For example, US Pat. No. 5,768,339 (Patent Document 1) describes a collimator for X-rays, and this collimator has a large number of nested parabolic reflectors. The collimator described in US Pat. No. 5,768,339 is for making a light beam emitted isotropically from an X-ray light source into a parallel light beam.

  From US Pat. No. 1,865,441 (Patent Document 2) a nested concentrator for X-rays is known which is similar to the device described in US Pat. No. 5,768,339. In addition, it is used to collimate X-rays emitted isotropically from a light source into parallel light beams.

  U.S. Pat. No. 5,763,930 discloses a nested concentrator for a pinch plasma light source that collects light emitted from the light source into a waveguide. It is for bundling.

  US Pat. No. 5,745,547 (Patent Document 4) discloses many configurations of a multi-channel optical system. These focus light rays from the light source, particularly X-rays, at one point by multiple reflection.

  The invention disclosed in US Pat. No. 5,745,547 proposes an ellipsoidal reflector in order to achieve particularly high transmission efficiency.

  From German Patent No. 3001059 (Patent Document 5), a configuration for use in a lithography system using X-rays is known. This is a parabolic telescopic reflector provided between an X-ray light source and a mask. These reflecting mirrors are arranged so that the diverging X-rays become parallel outgoing light beams.

  The invention described in DE 3001059 is also used only for good collimation of light rays in X-ray lithography.

  The telescopic reflector described in WO99 / 27542 (Patent Document 6) is used to refocus light from a light source and form a virtual light source in an X-ray proximity lithography apparatus. . The telescopic shell can be elliptical.

  US Pat. No. 6,064,072 discloses a telescopic reflector for a high energy photon source. This apparatus is for making divergent X-rays into parallel light beams.

  WO 00/63922 pamphlet (Patent Document 8) discloses a telescope for collimating neutron beams.

From WO 01/08162 pamphlet (patent document 9), one nested concentrator for X-rays is known. This concentrator is characterized in that the surface roughness of the reflecting surface inside each reflector shell is less than 12 Årms. The concentrator described in WO 01/08162 also comprises an optical system using multiple reflections, in particular a Wolter optical system, and is characterized by a high resolution as required, for example, in X-ray lithography. In the illumination optical system using a wavelength of 100 nm or less, a further problem along with focusing the light emitted from the light source is that the light emitted from the light source of such an illumination optical system is provided on the wafer surface of the projection exposure apparatus. Wavelengths that may cause undesired exposure to photosensitive objects are also included. For example, optical elements of an exposure apparatus such as a multilayer reflector are excessively heated by such light rays, and deterioration is accelerated. In order to filter out such undesirable light, for example, a transmission filter made of zircon is used, but this type of filter has a disadvantage that the loss of light amount is large. In addition, these filters may be easily destroyed when subjected to a heat load. A further problem of the illumination optical system for EUV lithography is that the loss of light quantity increases as the number of optical elements increases.
US Pat. No. 5,768,339 US Pat. No. 1,865,441 US Pat. No. 5,763,930 US Pat. No. 5,745,547 German Patent Invention No. 3001059 WO99 / 27542 pamphlet US Pat. No. 6,640,072 International Publication No. 00/63922 Pamphlet International Publication No. 01/08162 Pamphlet

  In view of the above, the object of the present invention is to satisfy the requirements for uniformity and telecentricity required for an illumination optical system, and at the same time, enable effective wavelength spectroscopy, and 193 nm or less, preferably 126 nm or less, particularly extremely short. An object of the present invention is to provide a condensing unit for an illumination optical system using a wavelength in the ultraviolet (EUV) region. What must be avoided in particular is that light having a wavelength other than the effective wavelength reaches the illumination optical system. In addition, the structural member must be compact, and when used in an EUV illumination optical system, the loss of light quantity generated in the illumination optical system must be minimized.

  According to the present invention, there is provided a light collecting unit comprising at least one reflecting mirror shell (a bowl-shaped reflecting mirror) according to the present invention. This is solved by a light collecting unit characterized in that a periodic structure having at least one diffraction grating period (grating period) is formed on a part of the surface. By providing the periodic structure in the reflector shell, the light beam impinging on the reflector shell is diffracted. The focal points of different diffraction orders are located on different planes. If a stop or the like is provided on the surface where one diffraction order is focused, the other diffraction orders cannot be passed through this stop because they are deflected toward other solid angle elements, and therefore the illumination optical system is provided downstream. Cannot reach. In this way, for example, an effective ray existing at 13.5 nm and other rays, particularly rays with a wavelength of 100 nm or more (these rays are present in the zeroth diffraction order) are separated. You do n’t have to. Furthermore, with such a configuration, it is possible to prevent particles coming from the light source from entering the illumination optical system provided downstream.

  A further advantage of the concentrator according to the present invention is that there is an effective exit space for the diffracted beam compared to an optical system in which a nested concentrator and a planar grating are provided as two separate components. That is longer. This feature has many advantages. First, if the dispersion is the same as in an optical system with a nested concentrator and a separately formed flat grating element, a smaller bandwidth is achieved while at the same time a nested collection. The separation of the different diffraction orders is greater than in the case of an optical system having an optical device and a separately formed flat diffraction grating element. If the linear density is comparable to that of a flat diffraction grating element when used in an illumination optical system, the distance in the optical path from the light source to the collector is shortened, so the illumination optical system is very compact. can do.

  In the component according to the present invention, by combining the light collecting characteristic of the condenser and the filtering characteristic of the spectral filter, one optical element can be omitted in the illumination optical system, and the transmittance of the illumination optical system is approximately 30. % Increase.

  In order to achieve particularly high diffraction efficiency, in a preferred embodiment the diffraction grating is formed as a blazed grating having a blaze angle ε.

  A configuration in which the condensing unit has a large number of reflecting mirror shells provided in rotational symmetry with respect to the rotation axis is particularly suitable. In that case, each reflecting mirror shell is provided with an annular opening element corresponding to the opening on the object side.

  Concentrators that are configured rotationally symmetrical have additional advantages. When the concentrator is configured to be rotationally symmetric with respect to the rotation axis, the uniformity of illumination on one surface and the shape of the pupil to be illuminated are compared with, for example, an illumination optical system having a flat diffraction grating element. Can be adjusted even better. In addition, when such rotationally symmetric components are used in the illumination optical system, it is advantageous to adjust the individual components to each other. Furthermore, it is also advantageous that symmetrical properties are seen, for example when heated.

  The region illuminated by the light collecting unit is, for example, present on one surface and composed of a plurality of annular elements (components), and preferably, each of the annular elements is associated with an annular aperture element. Is provided. In a preferred embodiment, the annular opening element and the corresponding annular element do not overlap, and the annular elements touch each other substantially continuously in the plane.

  With the nested concentrator according to the present invention, substantially uniform illumination in one plane can be realized. As in the present application, by combining the optical action (for example, collecting action) of the collector with respect to the light emitted from the light source and the filter action of the effective wavelength in a single component, the transmittance in the illumination optical system is increased. By increasing the length, the construction length of the illumination optical system can be greatly shortened.

  The reflector shell is preferably an elliptical, parabolic or hyperbolic ring segment. Since a light beam completely parallel to the paraboloid is obtained, a light source existing at an infinite position can be obtained.

  When the shell is part of an ellipsoid, a convergent light beam is formed. In the case of a collector having a shell that is part of a hyperboloid, the light beam will diverge.

  In order to obtain substantially uniform illumination or uniform illumination, the concentrator preferably has as many shells as possible. In the concentrator according to the present invention, preferably four or more reflectors, particularly preferably seven or more reflectors, and more preferably ten or more reflectors are provided in a shell-shaped configuration. A further advantage is that as the number of reflector shells increases, the divergence of the partial luminous flux (part of the luminous flux) of each reflector shell that is diffracted into the diaphragm surface decreases, so that at the diaphragm surface Different diffraction orders can be better separated.

It is preferable that a large number of reflector shells arranged around a common axis of rotation be configured so that multiple reflections occur for one reflector shell.
Multiple reflection occurs for one reflector shell, so that the reflection angle is kept small. In particular, in an optical system in which an even number of reflections occur, adjustment is lost, and in particular, the optical system (in the case of a rotationally symmetric optical system, the rotation axis is the optical axis) becomes stronger and is not affected.

  For reflection under conditions of grazing with respect to the surface tangent at an incident angle smaller than 20 °, the reflectivity is incident on the surface tangent for materials such as ruthenium, rhodium, palladium, silver, carbon or gold. In order to show a substantially linear behavior with the corner, for example, the reflection loss in the case of a single reflection at 16 ° or the reflection loss in the case of a double reflection at 8 ° is substantially equal. Nonetheless, it is preferred to use more than one reflection in order to maximize the aperture of the collector.

  An optical system with two reflections is particularly preferred. A concentrator with two reflections is, for example, a volter in which the first segment of the reflector shell forms a hyperboloid ring-shaped part and the second segment of the reflector shell forms an elliptical ring-shaped part. It can be formed as an optical system.

  Wolter optics are well known from literature such as Wolter, Annalen der Physik 10, 94-114, 1952. A Wolter optical system having a real vertex focal length, that is, a real intermediate image of a light source, is formed by combining a hyperboloid and an ellipsoid, as described in J. Optics, Vol. 15, 270-280. , 1984.

The Wolter optical system is particularly advantageous in a Wolter optical system having two reflections whose incident angle with respect to the surface tangent is smaller than 20 °. The condensing aperture is, for example, NA _max ˜0.985 corresponding to an aperture angle of 80 °. It is to be able to choose. Still, it is in the highly reflective area under oblique incidence conditions where the reflectivity is greater than 70%.

  In a preferred embodiment of the invention, a periodic grating is provided on the second segment of the shell of the Wolter optics.

  In such a case, the first segment is preferably part of a hyperboloid having an imaginary focus. The second segment is formed to have a focusing action. The focusing action of the second segment is realized by a concavely curved surface of the second segment in the meridional section in the case of a linear lattice having a constant linear density. In the present application, the meridional section means a section including the optical axis. The focusing action on the surface of the second segment can also be realized by changing the linear density. In this case, the surface of the second segment in the meridional section may be flat or convex. When the surface is flat in the meridional section, the second segment rotationally symmetric around the optical axis has a truncated cone shape.

  Alternatively, the grid may be on the first segment or on both segments. When it is desired to increase the spectroscopic purity, it is preferable to provide a grating in both segments. The grating is provided in the first segment, for example, in the case where it is necessary to prevent the 0th-order light from coming out of the collector, and instead it is absorbed by the back surface of the adjacent reflector shell. This is the case. At this time, an aperture for blocking unused light of the order is not necessary.

  The periodic structure on the second segment is preferably a blazed grating having a blaze depth B or a blaze angle ε, which structure is formed by diamond turning on the core for electroplating of the individual reflector shells. Alternatively, it can be formed by a method in which a groove of a grating is formed in a coating (for example, a gold coating) attached on the reflector shell.

  When the condensing unit is formed such that light of the diffraction order that is not used exits the unit, the intensity of the light of the diffraction order that exits is distributed to the annular element compared to a flat grating element. is there. This significantly reduces the thermal load on the diaphragm element compared to conventional flat grid elements.

  In addition to the light collecting unit, the present invention also provides an illumination optical system including such a light collecting unit. The illumination optical system includes a first optical element having a first raster element (mesh element) and a second raster element having a second raster element as disclosed in US Pat. No. 6,198,793. It is preferable that the illumination optical system has a facet surface at two locations. The contents disclosed in this document are comprehensively incorporated in the present application.

  The first raster element and / or the second raster element are flat facets or facets having a function of focusing or scattering light.

  The illumination optical system having the condenser according to the present invention is preferably used in a projection exposure apparatus for microlithography. This type of projection exposure apparatus is disclosed in International Patent Application No. PCT / EP00 / 07258. The disclosure of this document is comprehensively incorporated herein. The projection exposure apparatus has a projection optical system provided downstream of the illumination apparatus, for example, a projection optical system composed of four reflecting mirrors described in US Pat. No. 6,244,717. It is incorporated comprehensively in this application.

  Hereinafter, the present invention will be described with reference to the drawings.

  FIG. 1 shows, by way of example, two reflector shells in a meridional section of a telescope according to the invention. Each reflector shell 100, 102 includes a first ring-shaped segment 100.1, 102.1 having a first optical surface 100.2, 102.2 and a second optical surface 100.4, 102.4. And a second ring-shaped segment 100.3, 102.3. The individual reflector shells 100 and 102 are provided rotationally symmetrically around the x axis or the optical axis HA. As can be seen from FIG. 1, the annular aperture elements 110, 112, which correspond to the individual reflector shells 100, 102, respectively, are almost in contact with each other. That is, the object-side opening of the concentrator shown in FIG. 1 shows only the gaps determined by the finite thickness of the reflector shell between the individual annular opening elements. The annular aperture elements of the individual reflector shells receive a part of the light beam (partial light beam) emitted from the light source 105, for example a laser plasma light source. By suitably selecting the parameters of the periodic structures provided in the second segments 100.3 and 102.3, that is, the diffraction grating elements, the following becomes possible. That is, for all reflector shells, regardless of the received annular aperture element as well as the reflector shell, the partial luminous flux of the different reflector shells is limited by the diaphragm surface for a specific diffraction order, in this case the + 1st order diffraction order 129. Diffracted to 125 identical focal points 127.

  In the embodiment shown in FIG. 1, the first optical surfaces 100.2 and 102.2 and the second optical surfaces 100.4 and 102.4 are also in direct contact with each other without a gap.

  As another method, the first optical surfaces 100.2 and 102.2 and the second optical surfaces 100.4 and 102.4 may be provided without being in direct contact with each other. In that case, a gap or an unused area is provided between the optical surfaces. And in the area | region which is not used, the cooling device etc. for cooling a reflective mirror shell can be provided.

Furthermore, in the concentrator shown in FIG. 1, it turns out that the aperture_diaphragm | restriction 130 is provided inside the innermost reflector mirror shell. The concentrator provided with the telescopic reflector has a finite reflector shell, so the central part must be shaded. That is, the light beam from the light source cannot be received below a certain aperture angle NA _min . The stop 130 prevents light that passes through the central reflector shell as it is and reaches the illumination optical system provided downstream as stray light.

  FIG. 1 also shows the diffraction orders that are not focused on the diaphragm surface 125, that is, the zero-order diffraction order 131 and the + second-order diffraction order 133 for the diffraction grating provided on the second segment of the second reflector shell 102. It is shown.

  In FIG. 2, illumination on the diaphragm surface 125 by the collector according to the present application is shown in the case of a single reflector shell (in this figure, the second reflector shell 102).

The diaphragm surface 125 is defined by the z-axis and the y-axis of the coordinate system, and the origin of the coordinate system coincides with the actual light source 105. This coordinate system is shown in FIG.
As is apparent from FIG. 2, the + first-order light 129 is focused on the diaphragm surface 125 (which is a paper surface in the present drawing) and has a diameter ΔR ₁ . Orders other than the +1 order, such as the + 2nd order or the 0th order, appear as rings on the diaphragm surface. This is because the optical path is focused, so that these orders are defocused with respect to the stop surface. This can be seen very well in FIG. The zeroth-order focal point 150 is on the upstream side of the diaphragm surface 125 in the x direction, and the + secondary focal point 151 is on the downstream side of the diaphragm surface 125 in the x direction. The width of the zero-order light circular illumination is ΔR ₀ , and the width of the + second-order light circular illumination is ΔR ₂ . The average distance that each diffraction order has with respect to the optical axis is R ₂ or R ₀ .

By providing the circular diaphragm 154 having the radius R ₃ , the zero-order light or the + second-order light is shielded at the diaphragm surface 125. By such a method, wavelengths included in other orders can be completely blocked, and these wavelengths can be prevented from entering an illumination optical system provided downstream of the collector according to the present application.

FIG. 3 again shows one reflector shell of a telescopic collector according to the invention comprising two segments 102.1, 102.3. The first segment 102.1 having the first optical surface is a hyperboloid and receives light from the light source 105. The light source is also provided with the origin of a reference coordinate system used for the following derivation. Those projected on the x-axis the distance from the coordinate origin to the center point 170.1 of the first segment 102.1 in the meridional cross section is expressed as _{x 1.} A distance from the center point 170.1 of the first segment 102.1 to the imaginary focal point 172 on the meridional section is projected on the x-axis and is represented as x ₁ ′. Since the first segment 102.1 is formed as a hyperboloid, the hyperboloid has an imaginary focal point 172 and images the real light source 105 onto the imaginary light source. The imaginary light source is imaged again on the aperture plane 125 with respect to the + 1st order diffraction order 129 by the second segment 102.3 having a second optical surface with a diffraction grating element on the surface. FIG. 3 also shows the 0th diffraction order 131 and the + 2nd diffraction order 133. From the imaginary light source located at the focal 172 of the imaginary, representing the projection of the distance to the center point 170.3 of the second segment 102.3 in the meridional cross section in the x-axis and _{x 2.} A distance from the center point 170.3 of the second segment to the focal point 127 of the + 1st order diffraction order is projected on the x-axis and expressed as x ₂ ′.

  In the following, an embodiment of a nested concentrator in which a number of reflector shells having two segments are provided rotationally symmetrically around a common axis HA will be described. In the present embodiment, a lattice structure is formed in the second reflection region, that is, the second optical surface of the second segment. In this way, for example, broadband ultrashort ultraviolet (EUV) emitted from a plasma light source is filtered. Table 1 lists characteristic values of the optical system, that is, initial values for performing the following calculation.

  In the case of an optical system having two segments, the light source is imaged on the stop in two stages. The first optical reflecting surface of the first segment 102.1 is formed as a hyperboloid to create an imaginary focal point 172 for the second optical reflecting surface of the second segment 102.3. In the second segment, a lattice structure for spectrally decomposing light is formed. Here, the surface of the second reflector segment 102.3 is curved in a toroidal (doughnut) shape. That is, the outer contour line is circular, and the toroid surface (annular surface) has a curve or a radius in the meridional section. The lattice line density and the radius of the toroid surface are calculated so that the focus of the + 1st order diffraction order is on the diaphragm surface. All other diffraction orders as well as the 0th diffraction order appear as concentric rings around the focus of the + 1st diffraction order on the stop surface and are blocked by the stop. In order to achieve maximum diffraction efficiency, the grating is preferably formed as a blazed grating. The grating line density of the grating is selected so that the diffraction orders are sufficiently separated in order to obtain a good filtering effect. Furthermore, the shape of the grating must be chosen so that aberrations are minimized as much as possible.

  Equations that give the lattice constant, blaze angle, radius of the toroidal surface of the second segment in the meridional section, and parameters of the hyperboloid will be derived below.

First, a basic shape is determined by giving main dimensions. The lattice plane and hyperboloid are then determined by their parameters. Finally, the size (expansion) of the surface is determined so that the opening moves as much as possible without gaps.
The distance between the light source, the first image and the second image is determined as described below. All the values described in the equations derived below are shown in FIGS. 3, 4a and 4b.

  FIG. 3 shows a reflector shell having a first segment 102.1 and a second segment 102.3. FIG. 4a shows in more detail the second segment 102.3 of the reflector shell with the values necessary to derive the equation, and FIG. 4b shows the reflector shell with the values necessary to derive the equation. The first segment 102.1 is shown.

If the distance between the focal point 127 at the aperture plane 125 and the light source 105 projected onto the x-axis is _xg , the imaging is divided into two substantially equal stages. This prevents the incident angle from becoming excessively large for any reflection.

An axial object distance x ₁ and an image distance x ₁ ′ are defined for the first imaging stage, and an object distance x ₂ and an image distance x ₂ ′ are defined for the second imaging stage. These distances are obtained by projecting the apex focal length onto the optical axis as described in FIG. The following equations hold for these distances.
x _{g =} x ₁ + x ′ ₁ + x ₂ + x ′ ₂
The magnification of each imaging stage is expressed by the following equation.
M ₁ = −x ′ ₁ / x ₁ ; M ₂ = x ′ ₂ / x ₂
The entire imaging is as follows.
M _g = M ₁ M ₂

  Finally, the diameter must be determined for each of the second reflector segments 102.3. For this purpose, a radius r at the center point 170.3 of the second reflector segment 102.3 is defined. The center point 170.3 of the second reflector segment 102.3 is defined in FIG. The radius r is a radial distance from the optical axis HA of the center point 170.3.

From the distances x ₂ , x ₂ ′ and r, the distance (expressed as s ₂ ) between the imaging light source point (imaginary focal point 172 in this case) and the center point 170.3, and the center point 170 .3 and the image point (in this case, the focal point 127 of the primary light on the stop surface 125) (expressed as s ₂ ') is obtained. The following equation holds.

s ₂ and s ₂ ′ represent unprojected distances.

  The grating line density n is obtained from a request to separate the 0th-order diffraction order from the primary light on the diaphragm surface 125 at a sufficient distance g. The distance g from the central ray 174.1 of the first-order diffracted partial beam and the central ray 174.0 of the zero-order diffracted partial beam is shown in FIG. 4a.

If the size of the light source is assumed and the magnification is considered, the size of the image of the light source at the focal point 127 of the first diffraction order in the area of the diaphragm surface 125 is obtained. At this time, it is important that the 0th diffraction order is separated from the image by many times. At this time, for example, when the distance is 10 times f, it can be assumed that separation between the effective wavelength and other light is obtained,
g = f · d ″
It becomes. D ″ is the diameter of the image of the light source 105 on the diaphragm surface 125. The diameter D of the light source 105 is listed in Table 1.

  Thus, from such a condition for separating the 0th and 1st diffraction orders, ie the condition for the distance g, the required diffraction angles α and β with respect to the normal 180 at the center point 170.3 of the second segment The slope γ with respect to the y-axis of the normal 180 at the center point 170.3 is determined. For this purpose, the angle δ between the central rays 174.1 and 174.0 of the 0th order and the 1st order diffraction order is first calculated. This angle depends on the distance g required on the diaphragm surface 125 as shown below. There is a correlation.

  Furthermore, angles α ′ and β ′ formed by the incident and outgoing primary partial light beams with respect to the y-axis are obtained.

Thus, the desired angle is determined.
α = (α′−β′−δ) / 2
γ = α−α ′
β = β'-γ
Diffraction formula,
sinα + sinβ = n ・ k ・ λ
Can be used to calculate the linear density n for the effective wavelength for the + 1st diffraction order where k = 1. Furthermore, the blaze angle can be expressed as the following equation.
ε = (│α│-│β│) / 2

The radius RM of the second reflecting mirror segment in the meridional section, that is, the curvature of the surface provided in rotational symmetry about the optical axis HA is determined by the focusing condition in the toroidal grating. The focusing condition is F ₂₀ = 0. This condition is described in “Handbook on Synchrotron Radiation, Vol. 2, Kap. 4“ Diffraction grating optics ”, edited by GV Marr, page 69 of Elsevier Science.

From the condition of F ₂₀ = 0, the radius RM of the toroid surface in the meridional section is as follows.

  Having calculated the characteristic quantities for the second reflector segment holding the grating, the next step is to derive the characteristic quantities for the first reflector segment 170.1 having a hyperbolic surface 200 in the meridional section. To. Please refer to FIG. 4b for the drawing. A general expression representing a meridional section, that is, a hyperbola in an xy plane having an apex at the origin of the coordinate system as shown in FIG.

  On the other hand, the hyperboloid surface is obtained from the condition that the origin and the imaginary focus 172 of the light source 105 coincide with the focus of the hyperbola. This condition is satisfied when the distance between the focal points of the hyperbola is exactly 2c. On the other hand, for each point of the hyperbola, it can be said that the difference in distance to the focal point is exactly 2a. Eventually, the following relation holds for the hyperbola.

The hyperbolic constant can be determined from the above equation. First, 2c = x ₁ + x ₁ ′ is calculated. Then, assuming the end points of the lattice plane to which the hyperbola is to be connected, then a and b with it are obtained.

  For the principle of diffraction in gratings, see Handbook on Synchrotron Radiation, Vol. 2, Kap. 4 “Diffraction grating optics”, edited by G.V. Marr, Elsevier Science.

  Table 2 shows a concentrator according to the present invention which is composed of six reflecting mirror shells and is provided in a rotational manner around the main axis HA in a nested manner. Each shell has a first segment and a second segment each having a first optical surface and a second optical surface. Here, the first optical surface and the second optical surface coincide with the segments. The first segment is a hyperboloid surface, and a periodic lattice structure is formed on the second segment.

  All amounts used in Table 2 are predefined. The origin (0, 0, 0) of the selected reference coordinate system is at the position of the light source 105.

It is expressed as follows.
x ₁ : distance in the x-axis direction from the light source 105 to the center point 170.1 of the first reflector segment x ₁ ′: x-axis from the imaginary focal point 172 to the center point 170.1 of the first reflector segment Directional distance x ₂ : x-axis direction distance x ₂ ′ from the imaginary focal point 172 to the center point 170.3 of the second reflector segment: From the primary focal point 127 to the center point of the second reflector segment Distance x _{g in} the x-axis direction: x ₁ : distance in the x-axis direction from the light source 105 to the focal point 127 of the first-order diffraction order M ₁ : first imaging magnification M ₂ : second imaging magnification M _g : Overall imaging magnification x _1a : x coordinate x _1e of the start point of the first segment: x coordinate y _1a of the end point of the first segment: y coordinate y _1e of the start point of the first segment: Y coordinate a, b of end point: hyperbolic parameter x _2a : X coordinate x _2e of the start point of the second segment: x coordinate y _2a of the end point of the second segment: y coordinate y _2e of the start point of the second segment RM: y coordinate RM of the end point of the second segment RM: first in the meridional plane 2 segment radius n: grating linear density α: angle the incident central ray forms with respect to the normal at the center point of the second reflector shell β: the central ray diffracted to the first order is the second Angle ε formed with respect to the normal line at the center point of the reflector shell of λ: Blaze angle λ _min : Minimum wavelength that passes through the stop λ _max : Maximum wavelength that passes through the stop

  FIG. 5 shows a blazed grating in which the groove shape is approximately triangular. Reference numeral 201 is a light beam that strikes a blazed grating having a diffraction grating period P, 202 is a light beam that is reflected by the zeroth order in the grating, 204 is a light beam that is diffracted to the + 1st order, 206 is a light beam that is diffracted to the −1st order, Reference numeral 208 denotes a normal line of the grating, α denotes an angle formed by an incident light beam with respect to the normal line 208, and β denotes an angle of a light beam diffracted by the + 1st order. Regarding the blaze angle, the following equation is established depending on the above amount.

When the blaze angle ε and the linear density n are set, the blaze depth B is given by the following equation.
B = ntanε
Here, a light beam 201 incident at an angle α with respect to the normal 208 of the grating forms an angle β with respect to the normal 208 of the grating with a blaze efficiency corresponding to the blaze angle ε. Diffracted in the + 1st order direction.

  FIG. 6 shows the optical components of a projection exposure apparatus having a telescope according to the present invention and the paths of several rays.

  The concentrator according to the present invention has a periodic lattice structure in the second segment. Together with the stop 1202 provided in the vicinity of the light source intermediate image Z at the + 1st order diffraction order, an undesirable wavelength (13.5 nm in this embodiment) is provided downstream of the stop 1202 by this grating structure. Entering the illumination optical system is prevented.

  The diaphragm 1202 also has a role of spatially and pressure-separating the room 1204 including the light source 1000 and the telescope 1003 from the illumination optical system 1206 provided downstream. Separation in terms of space or pressure prevents contamination caused by the light source from entering the illumination optical system provided downstream of the diaphragm 1202.

  The illumination optical system shown in FIG. 6 has a nested condenser 1003 according to the present invention. The first optical element 1102 has 122 grid elements (raster elements) each having a spread of 54 mm × 2.75 mm. The second optical element 1104 has 122 second grid elements each having a diameter of 10 mm and corresponding to the first grid elements.

  The main function of the optical elements 1106, 1108, 1110 is to form a field (irradiation field) on the object plane 1114. The reticle provided on the object surface is a reflective mask. The reticle is movable in the direction 1116 shown in the figure within an ultra-short ultraviolet (EUV) projection optical system configured as a scanning system. The exit pupil of the illumination optical system is illuminated almost uniformly. This exit pupil coincides with the entrance pupil of the projection optical system provided downstream. The entrance pupil of the projection optical system is not shown. The entrance pupil of the projection optical system is provided at the position of the intersection between the principal ray reflected by the reticle and the optical axis of the projection optical system.

  For example, the projection optical system described in US patent application Ser. No. 09 / 503,640 having six reflecting mirrors 118.1, 1128.2, 1128.3, 1128.4, 1128.5, and 1128.6. 1126 forms an image of the reticle on the object 1124 to be exposed.

It is the schematic of the collector with which the grating | lattice (diffraction grating) was provided in the 2nd reflective mirror shell. It is a figure which shows the illumination in the aperture stop surface provided in the downstream of the collector, when the reflective mirror shell of a collector is one, and illumination of a different diffraction order. It is a figure which shows the reflector shell which has the 1st segment made into the segment of a ring-shaped hyperbola, and the 2nd segment in which the grating | lattice is provided and whose outline is a circle in a meridional cross section. FIG. 4 is a diagram showing, in a meridional section, the second segment of the shell surface shown in FIG. 3 provided with a lattice in a state in which an angle for deriving the linear density of the lattice is written. FIG. 4 is a diagram showing, in a meridional section, a first segment of the shell surface shown in FIG. 3 for deriving a hyperboloid radius or curvature. It is a fragmentary figure of a blazed grating. It is a figure which shows the extreme short ultraviolet-ray (EUV) projection exposure apparatus which has a nesting type concentrator which concerns on this application.

Explanation of symbols

100, 102 Reflector shell 100.1, 102.1 First ring-shaped segment 100.2, 102.2 First optical surface 100.3, 102.3 Second ring-shaped segment 100.4, 102. 4 Second optical surface 105 Light source 110, 112 Annular aperture element 125 Diaphragm surface 127 Focus

Claims (17)

A condensing unit for an illumination optical system using a wavelength of 193 nm or less, preferably 126 nm or less, particularly in the EUV region. ,
In a light collecting unit having at least one reflector shell that receives a light beam of a light beam emitted from the object and has an optical function,
A condensing unit, wherein a periodic structure having at least one diffraction grating period is formed on at least a part of the reflector shell.   The condensing unit according to claim 1, wherein the light beam of the light beam strikes the surface tangent of the reflector shell at an angle of 20 ° or less.   The light collecting unit according to claim 1, wherein the reflecting mirror shell is provided rotationally symmetrical with respect to a rotation axis.   The condensing unit according to claim 3, wherein the light collecting unit includes a plurality of reflecting mirror shells provided in a rotationally symmetrical manner, and the reflecting shells are provided so as to be nested around a common rotation axis.   Each of the reflecting mirror shells is provided so as to correspond to one annular opening element of an object-side opening that receives light emitted from a light source provided on the object surface, and the annular opening elements do not overlap each other. The light collecting unit according to claim 4.   The light collecting unit according to claim 1, wherein the reflector shell is an aspherical ring-shaped segment.   The light collecting unit according to claim 6, wherein the reflector shell is an elliptical, parabolic, hyperboloid, ring-shaped segment.   8. The at least one reflector shell has a first segment with a first optical surface and a second segment with a second optical surface. The light collecting unit according to item 1.   The light collecting unit according to claim 8, wherein the periodic structure is provided in the second segment.   The light collecting unit according to claim 8, wherein the periodic structure is provided in the first segment or in the first segment and the second segment.   The condensing unit according to claim 8, wherein the first ring-shaped segment is a part of a hyperboloid.   The condensing unit according to any one of claims 1 to 11, wherein the periodic structure is a blazed grating having a blaze angle ε.   The size of the reflector shell is different in the direction of the rotation axis, and the size of the reflector shell is such that zero-order light that is not diffracted by the grating is absorbed by the back surface of the adjacent reflector shell. The light collecting unit according to any one of claims 1 to 12, wherein any light of the light is selected so as not to come out of the light collecting unit. An illumination optical system using a wavelength of 193 nm or less, preferably 126 nm or less, particularly in the EUV region,
A light source;
At least one light collecting unit;
In an illumination optical system having a surface to be illuminated,
The illumination optical system according to claim 1, wherein the light collection unit is the light collection unit according to claim 1.   The illumination optical system has a surface conjugate to the light source between the light collecting unit and the surface to be illuminated, and is configured such that an intermediate image of the light source is formed on the surface. The illumination optical system according to claim 14.   The illumination optical system according to claim 14 or 15, wherein a wavelength of 193 nm or less is used, wherein a stop is provided in the intermediate image or in the vicinity of the intermediate image. The illumination optical system according to any one of claims 13 to 16,
A mask illuminated by the illumination optical system;
A projection optical system for imaging the mask on a photosensitive object;
An EUV projection exposure apparatus having

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