JP2008158211A - Projection optical system and exposure apparatus using the same - Google Patents

Abstract

Provided is a projection optical system for EUV light that can achieve high NA and can keep the incident angle on each reflecting surface relatively small.
A coaxial projection optical system that reflects a light beam from a pattern on an object surface with first to sixth reflecting surfaces of concave and convex portions, and connects a reduced projection image of the pattern onto an image surface. An intermediate image of the pattern is formed between the fourth reflecting surface and the fifth reflecting surface, and an optical axis of the projection optical system at a position of the intermediate image of a principal ray emitted from the center of the pattern; Θ, the image height at the position where the center of the pattern forms an image on the image plane, I, the radius of curvature of the fourth reflecting surface, and the effective diameter are R4 and D4, respectively, and the curvature of the sixth reflecting surface. When the radius and the effective diameter are R6 and D6, respectively, a predetermined conditional expression is satisfied.
[Selection] Figure 1

Description

  The present invention relates to a projection optical system that uses ultraviolet rays or extreme ultraviolet (EUV) light to reduce and project an image on an object plane onto an image plane. In particular, the present invention relates to a projection optical system, an exposure apparatus, and a device manufacturing method for projecting and exposing a target object such as a single crystal substrate for a semiconductor wafer and a glass substrate for a liquid crystal display using a pattern on a mask.

  Due to the recent demand for smaller and thinner electronic devices, there is an increasing demand for miniaturization of semiconductor elements mounted on electronic devices. For example, the design rule for the mask pattern is required to form a wide range of dimensional images of line and space (L & S) 0.1 μm or less, and in the future, it is expected to shift to circuit pattern formation of 40 nm or less. . L & S is an image projected on the wafer in the state in which the width of the line and the space is equal in the exposure, and is a scale indicating the resolution of the exposure.

  2. Description of the Related Art A projection exposure apparatus, which is a typical exposure apparatus for manufacturing semiconductors, is a projection optical that projects and exposes a pattern drawn on a mask or a reticle (in the present application, these terms are used interchangeably) onto a wafer. Has a system. The resolution (minimum dimension that can be accurately transferred) R of the projection exposure apparatus is given by the following equation using the wavelength λ of the light source and the numerical aperture (NA) of the projection optical system.

R = k1 × λ / NA
Therefore, the shorter the wavelength and the higher the NA, the better the resolution. In recent years, resolution is required to be smaller, and increasing the NA is the limit to satisfying this requirement, and the resolution is expected to be improved by shortening the wavelength. At present, the exposure light source has shifted from a KrF excimer laser (wavelength of about 248 nm) and an ArF excimer laser (wavelength of about 193 nm) to an F2 laser (wavelength of about 157 nm). Now, EUV (extreme ultraviolet) light is being put to practical use.

  However, since the glass material through which light passes is limited as the wavelength of light advances, it is difficult to use a large number of refractive elements, that is, lenses, and it is advantageous to include a reflecting element, that is, a mirror in the projection optical system. become. Furthermore, when the exposure light becomes EUV light, there is no glass material that can be used, and it becomes impossible to include a lens in the projection optical system. In view of this, a reflection type projection optical system in which the projection optical system is constituted only by a mirror (for example, a multilayer mirror) has been proposed.

  In a reflective projection optical system, a multilayer film is formed on the mirror so that the reflected light is strengthened to increase the reflectivity of the mirror, but in order to increase the reflectivity of the entire optical system, the number of sheets is as small as possible. It is desirable to configure. In order to prevent mechanical interference between the mask and the wafer, it is desirable that the number of mirrors constituting the projection optical system is an even number so that the mask and the wafer are positioned on the opposite side via the pupil. Furthermore, since the line width (resolution) required for the EUV exposure apparatus has become smaller than the conventional value, it is necessary to increase the NA (for example, NA 0.2 at a wavelength of 13.5 nm). With a mirror, it is difficult to reduce wavefront aberration. Therefore, in order to increase the degree of freedom of wavefront aberration correction, it has become necessary to reduce the number of mirrors to about six (hereinafter, in the present application, such an optical system may be expressed as a six-mirror system).

  Patent Document 1 shows a projection optical system including six reflecting mirrors in FIG. 2 as an example, and achieves a high NA of 0.45. In this configuration, incident light from the object surface is received, and an intermediate image is formed by the convex first reflecting surface, the concave second reflecting surface, the convex third reflecting surface, and the concave fourth reflecting surface, Further, the image is re-imaged on the image plane via the convex fifth reflecting surface and the concave sixth reflecting surface.

Further, Patent Document 2 shows a projection optical system composed of six reflecting mirrors in FIG. 2 as an example, and achieves a high NA of 0.55. In this configuration, incident light from the object surface is received, and an intermediate image is formed by the concave first reflecting surface, the convex second reflecting surface, the concave third reflecting surface, and the concave fourth reflecting surface, Further, the image is re-imaged on the image plane via the convex fifth reflecting surface and the concave sixth reflecting surface.
US Pat. No. 5,686,728 US Pat. No. 5,815,310

  However, in the configuration described in Patent Document 1, the curvature of each reflection surface is tight, and the incident angle of the light beam with respect to the reflection surface (the angle formed between the light beam and the normal line of the reflection surface) is large. As a result, the reflectance at the reflecting surface is lowered, the amount of light flux from the mask to the wafer is reduced, and the throughput may be reduced. Further, in the configuration of Patent Document 1, since the image surface side is not telecentric, there is a possibility that the positional deviation of the pattern image on the wafer may occur.

  Further, even in the configuration described in Patent Document 2, the incident angle of the light beam with respect to the reflecting surface is large, and sufficient reflectance is not obtained. Moreover, in the structure of this patent document 2, since the 3rd reflective surface and the 4th reflective surface are arrange | positioned in the position which remove | deviated largely from the optical axis, it was difficult to manufacture a reflective surface with high performance.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a projection optical system that is configured with a reflecting surface and has an NA of 0.3 or more and an incident angle with respect to the reflecting surface is kept relatively small.

  In order to solve the above problems, a projection optical system according to the present invention is configured to convert a light beam from a pattern on an object surface into a first reflecting surface having a concave shape, a second reflecting surface having a convex shape, a third reflecting surface having a convex shape, This is a coaxial projection optical system that reflects in the order of a concave fourth reflecting surface, a convex fifth reflecting surface, and a concave sixth reflecting surface, and connects a reduced projection image of the pattern on the image plane. And an intermediate image of the pattern is formed between the fourth reflecting surface and the fifth reflecting surface on the optical path of the light beam, and the principal ray emitted from the center of the pattern at the position of the intermediate image. The angle formed by the optical axis of the projection optical system is θ, the image height at the position where the center of the pattern is imaged on the image plane is I, the radius of curvature and the effective diameter of the fourth reflecting surface are R4 and D4, respectively. When the radius of curvature and effective diameter of the sixth reflecting surface are R6 and D6, respectively, To satisfy the condition.

Projection optical system characterized by satisfying

  According to the present invention, a projection optical system configured with a reflective surface applicable to EUV lithography, which has a high NA (an optical system having an NA of 0.3 or more) and an incident angle on the reflective surface. A relatively small projection optical system can be provided.

  The reflective projection optical system 100 of the present invention (collectively referring to 100A to 100F) reduces and projects a pattern on an object plane (for example, a mask surface) MS onto an image plane (for example, a surface of an object to be processed such as a substrate) W. This is a reflection type projection optical system (connecting reduced projection images). This reflective projection optical system is an optical system particularly suitable for EUV light (for example, a wavelength of 10 nm to 15 nm, more preferably a wavelength of 13.4 nm to 13.5 nm). The reflective projection optical system of the present invention is configured to have six reflecting surfaces from the object plane to the image plane as described in the following embodiments. However, the number is not necessarily six, and may have six or more reflective surfaces, for example, eight reflective surfaces.

  The embodiment of the present invention will be described based on the above assumptions. First, features common to all the embodiments of the present invention will be described in detail.

  The projection optical system of the present embodiment reflects the light from the pattern on the object plane in the order of the first, second, third, fourth, fifth and sixth reflecting surfaces, so that a quarter of the pattern on the image plane. This is a projection optical system that projects a double (or 1/5) image onto the image plane. This projection optical system is arranged so that the center of curvature of the above-described six reflecting surfaces is substantially aligned on a predetermined optical axis, and an intermediate image of the pattern (light light from the pattern) It is formed between the fourth reflection surface and the fifth reflection surface (on the road). Here, I is the image height (height from the optical axis) at a position where a certain point in the pattern (the center of the pattern) forms an image on the image plane, and an intermediate image of the principal ray from a certain point in the pattern The inclination with respect to the above-mentioned optical axis at the position is denoted by θ. Further, when the effective radius of the fourth reflecting surface is D4, the radius of curvature of the fourth reflecting surface is R4, the effective radius of the sixth reflecting surface is D6, and the radius of curvature R6 of the sixth reflecting surface is (Equation 1) (Equation 2) is satisfied.

  Here, the chief ray is a ray passing from the pattern to the image plane, a ray passing through the center of the stop arranged in the projection optical system, or an optical path from the pattern to the image plane as described above. Are rays that can exist in the same plane.

  The center of the pattern, as shown in FIG. 10, is the center of the illumination area having an arc slit shape (a shape in which both ends in the width direction are arcs and the arcs are connected by a straight line) on the object plane (mask). That is. This will be described in detail as follows. The axis of symmetry of the arc-shaped slit illumination area on the object plane (on the mask) (area that emits light toward the projection optical system) (the symmetry axis of the mask pattern, the central axis of symmetry) crosses the illumination area on the mask. ing. When the length of the symmetry axis passing through the illumination area on the mask is Ls (slit width of the illumination area on the mask), the center point of the length Ls is the center of the mask pattern.

  However, it is not always necessary to use the chief ray from the center of the illumination area of the mask when θ is determined in the above (Formula 2). It is only necessary that the principal ray emitted from any point in the illumination area of the mask satisfies the above-described (Expression 2). Preferably, the chief rays from all points in the illumination area of the mask satisfy the above-described (Equation 2).

  By satisfying (Equation 1) as described above, the incident angles on the fourth reflecting surface and the sixth reflecting surface can be kept low. If the lower limit of (Equation 1) is exceeded, it will be difficult to eliminate vignetting on the fifth reflecting surface and the sixth reflecting surface, and if the upper limit is exceeded, the entire optical system will be enlarged and the reflective surface will be damaged. Increasing the incident angle.

  By satisfying (Equation 2) as described above, the incident angle can be suppressed with a high NA. Specifically, when the angle of the chief ray of the intermediate image is smaller than the lower limit of (Expression 2), NA becomes too small, and when it is larger than the upper limit of (Expression 2), the reflection surface is moved to. The incident angle becomes too large.

  Here, it is more preferable to satisfy the following (Formula 1a) and / or (Formula 2a).

  This embodiment can solve the problems of the invention as long as it has features such as (Equation 1) and (Equation 2) described above. In addition, if one or more of (a), (b), (c), (d), and (e) described below are satisfied, a more preferable effect can be obtained. In addition, what is described in (a) to (e) is an additional feature in the present embodiment, or an effect (or an adverse effect by not satisfying it) in the present embodiment. 1) The effect obtained by (Expression 2) is not impaired.

  (A) With respect to the fourth reflecting surface and the sixth reflecting surface, if the following (Expression 3) is satisfied, a more preferable effect can be obtained.

  Here, when the ratio of the curvature radius of the fourth surface to the curvature radius of the sixth surface exceeds the upper limit of (Equation 3), the effective diameter of the fourth reflection surface becomes too large, which is not preferable. On the other hand, if the lower limit is not reached, the effective diameter of the fourth reflecting surface becomes small, so that the separation of light rays becomes severe, or the aberration cannot be corrected sufficiently.

  Here, it is more preferable to satisfy the following (Formula 3a).

  (A) Further, the focal length F1 of the first imaging system that forms an intermediate image of the pattern with the light flux from the pattern on the mask, and the second imaging system that connects the image on the image plane with the light flux from the intermediate image. The focal length F2 preferably satisfies (Equation 4).

  This is not preferable when the lower limit of (Expression 4) is not reached because the effective diameter of the fourth reflecting surface becomes too large. If the upper limit is exceeded, the effective diameter of the fourth reflecting surface becomes too small, so there is no room between the sixth reflecting surface and the light beam, and the aberration cannot be corrected sufficiently. This is because

  Here, it is more preferable to satisfy the following (Formula 4a).

  (C) On the optical path of the principal ray described above, when the optical path length between the fourth reflecting surface and the fifth reflecting surface is L, and the distance between the fourth reflecting surface and the intermediate image is Lm, the following (formula It is still more preferable to satisfy 5).

  Here, when the value exceeds the upper limit value of (Expression 5), the position of the intermediate image is too close to the fifth reflecting surface, and when the value is lower than the lower limit value, the position is too close to the fourth reflecting surface. This is because if the intermediate image is close to the reflecting surface, the reflecting surface cannot be used widely, so that it is easily affected by heat and it is difficult to correct aberrations.

  Here, it is more preferable to satisfy the following expression 5a.

The upper and lower limits were reduced by 10%. (D) Also, an intermediate image is formed between the fourth reflecting surface and the fifth reflecting surface, and if the above (Formula 5) is satisfied, As the NA increases, the effective diameter of the sixth reflecting surface increases, but it is easy to prevent vignetting on the sixth reflecting surface (the back surface thereof).

Further, it is desirable that the distance L ₄₆ between the fourth reflection surface curvature center O4 and the sixth reflection surface curvature center O6 satisfies Expression 6 when the total length is L _MW, and the fourth reflection surface curvature center O4 is desirably located closer to the object plane MS than the center of curvature O6 of the sixth reflecting surface. And it is desirable for these L46 and LMW to satisfy the following (Formula 6).

  Here, by moving the position of the intermediate image IM away from the fourth reflecting surface and the fifth reflecting surface, the fourth reflecting surface and the fifth reflecting surface are efficiently corrected for aberrations using the spread of the light flux. Can be used. Here, when the value exceeds the upper limit value, the incident angle on the fifth reflecting surface becomes too large, and when the value falls below the lower limit value, it is difficult to prevent vignetting on the sixth reflecting surface. Here, more preferably, the following (formula 6a) is satisfied.

  (E) The first to sixth reflecting surfaces of the reflective projection optical system of the present embodiment are concave (the reflecting surface is concave), convex (the reflecting surface is convex), convex, concave, convex, and concave. It is desirable.

  With this configuration, it is easy to form an image with a large NA and a back focus. In addition, light separation is easy even when the NA is high (interference between a light beam and a mirror is unlikely to occur). Further, it is easy to guide the light flux from the fourth reflecting mirror M4 to the fifth reflecting mirror M5 close to the optical axis, avoiding the sixth reflecting mirror M6 having a large effective diameter.

  Furthermore, if the diaphragm is disposed between the first reflecting surface and the second reflecting surface, or a diaphragm member is disposed on the second reflecting surface (or the second reflecting surface also serves as the diaphragm), the height is high. Even if the NA is used, the optical performance is not reduced so much.

  Further, when the curvature radii of the first reflecting mirror M1 to the sixth reflecting mirror M6 are R1 to R6 (the concave surface is positive and the convex surface is negative), the sum of Petzval terms as shown in the following equations 7 and 7a is obtained. Preferably it is zero or nearly zero.

  However, when trying to achieve the high NA of the subject of the present application, the radius of curvature of each reflecting surface tends to be small, and the number of reflecting surfaces is as small as six, so the number of reflecting surfaces is the same as the number of concave and convex surfaces. It is preferable that If the number is not the same, the Petzval sum cannot be reduced unless the curvature of the smaller one of the concave and convex surfaces is reduced, and aberration correction becomes difficult. Therefore, as described above, it is desirable that the number of concave surfaces and convex surfaces be the same.

  The reflective projection optical system 100 includes six reflecting surfaces, and the six reflecting surfaces are arranged so that the centers of curvature are substantially aligned on a predetermined optical axis, at least one of which is EUV. An aspherical mirror having a multilayer film that reflects light is desirable. The shape of the aspherical surface is expressed by a general aspherical equation shown in the following Equation 8. In Equation 8, Z is the coordinate in the optical axis direction, c is the curvature (the reciprocal of the radius of curvature r), h is the height from the optical axis, k is the cone coefficient, A, B, C, D, E, F, G , H, J,... Are aspherical coefficients of 4th order, 6th order, 8th order, 10th order, 12th order, 14th order, 16th order, 18th order, 20th order,.

  In addition, the centers of curvature of the six reflecting mirrors are not necessarily arranged in a straight line, and the center of curvature of a predetermined reflecting mirror is slightly deviated from the optical axis AX for the purpose of aberration correction (for example, the curvature of the reflecting mirror). 1% or less of the radius, preferably 0.3% or less). The center of curvature of the reflecting mirror means the center of curvature of the spherical surface serving as the base of the aspherical surface when the reflecting mirror is not a spherical surface but an aspherical surface. Similarly, the radius of curvature of the reflecting mirror means the radius of curvature of the spherical surface serving as the base of the aspherical surface. Further, it is desirable that the surface shape of the aspherical surface has no inflection point at the effective effective portion.

  In addition, a multilayer film that reflects EUV light is provided on the surfaces of the first reflecting mirror M1 to the sixth reflecting mirror M6, and the multilayer films exert an action of strengthening the light. The multilayer film capable of reflecting EUV light having a wavelength of 20 nm or less is, for example, a Mo / Si multilayer film in which molybdenum (Mo) layers and silicon (Si) layers are alternately stacked, or a Mo layer and beryllium (Be) layer. A Mo / Be multilayer film or the like in which are stacked alternately can be considered. Of course, an optimal material may be selected as appropriate depending on the wavelength region (wavelength) to be used. However, the multilayer film of the present invention is not limited to the above-described materials, and a multilayer film having the same functions and effects can be applied. In general, in order to obtain high reflectivity from the characteristics of the multilayer film, when the maximum value of the incident angle is large, the width of the incident angle must be relatively small, and the maximum value of the incident angle is small. In this case, the width of the incident angle may be relatively large.

  In the reflective projection optical system 100, it is desirable that the object plane MS side is non-telecentric and the image plane W side is telecentric. For example, in order to illuminate a mask arranged on the object plane MS by an illumination optical system, and to form an image of a pattern on the mask on the object to be processed, which is the image plane W, using a light beam reflected by the mask Is preferably non-telecentric on the object plane MS side of the projection optical system. On the other hand, it is desirable that the image plane W side be telecentric, for example, in order to reduce a change in magnification even when a wafer arranged on the image plane W moves in the optical axis direction.

  Further, the present embodiment is not limited to the projection optical system, but can be applied to an exposure apparatus and a device manufacturing method. The exposure apparatus of the present embodiment has an illumination optical system that illuminates a pattern on an object surface with an illumination light beam from a light source, and a projection optical system as described above that forms a reduced image on the image plane. It is said. In addition, the device manufacturing method of the present embodiment is characterized by having a step of exposing the object to be exposed using the above-described exposure apparatus and a step of developing the exposed object to be exposed.

  Hereinafter, a reflective projection optical system, an exposure apparatus, and a device manufacturing method using the exposure apparatus described in each embodiment of the present invention will be described in detail with reference to the drawings. Here, in each figure, the same reference number is attached | subjected about the same member, and the overlapping description is abbreviate | omitted.

  Hereinafter, the projection optical system of Example 1 will be described in detail with reference to FIG. 1 and Table 1.

  FIG. 1 is a schematic diagram of a main part of a first embodiment of the present invention. Table 1 shows numerical examples of the first embodiment, that is, masks, wafers, and reflection surfaces in the projection optical system of the first embodiment. The distance, the radius of curvature of each reflecting surface, the aspheric coefficient of each aspheric surface, and the like are shown.

  In this figure, 100A (in the other embodiments, 100B to 100F) is a reflective projection optical system, MS is a mask (object plane), W is a wafer (image plane), AS is an aperture stop, AX is an optical axis, and IM Is an intermediate image. M1 is a first reflecting mirror, M2 is a second reflecting mirror, M3 is a third reflecting mirror, M4 is a fourth reflecting mirror, M5 is a fifth reflecting mirror, and M6 is a sixth reflecting mirror. is there.

  In the projection optical system of Example 1, the numerical aperture NA on the image side is 0.35, the projection magnification is 1/4, and the object height is 132 to 136 mm. The NA stop coincides with the second reflection surface (the NA stop also serves as the second reflection surface). The intermediate image is formed between the fourth reflecting surface and the fifth reflecting surface in the vicinity of the sixth reflecting surface as a spatial position. In addition, the telecentricity on the image plane side is suppressed to 1 mrad or less.

  Further, the incident angle to the fourth reflecting surface and the sixth reflecting surface is 6.2 degrees or less, and the maximum effective diameter among the six reflecting surfaces is suppressed to 320 mm.

  The second embodiment of the present invention will be described in detail with reference to FIG. 2 of the schematic diagram of the main part of the second embodiment and Table 2 showing a numerical embodiment of the second embodiment. Portions that are not particularly described are the same as those in the first embodiment.

  In the projection optical system of Example 2, the numerical aperture NA on the image side is 0.35, the projection magnification is 1/4, and the object height is 126 to 130 mm. Further, the NA stop is arranged between the first reflecting surface and the second reflecting surface. The intermediate image is formed between the fourth reflecting surface and the fifth reflecting surface and in the vicinity of the sixth reflecting surface as a spatial position. In addition, the telecentricity on the image plane side is suppressed to 1 mrad or less.

  Further, the incident angle to the fourth reflecting surface and the sixth reflecting surface is 9.4 degrees or less, and the maximum effective diameter of the six reflecting surfaces is suppressed to a small value of 294 mm.

  The third embodiment of the present invention will be described in detail with reference to FIG. 3 of the schematic diagram of the main part of the third embodiment and Table 3 showing a numerical example of the third embodiment. Portions that are not particularly described are the same as those in the first embodiment.

  In the projection optical system of Example 3, the numerical aperture NA on the image side is 0.30, the projection magnification is 1/4, and the object height is 122 to 130 mm. The NA stop coincides with the second reflection surface (the NA stop also serves as the second reflection surface). The intermediate image is formed between the fourth reflecting surface and the fifth reflecting surface and in the vicinity of the sixth reflecting surface as a spatial position. In addition, the telecentricity on the image plane side is suppressed to 1 mrad or less.

  Further, the incident angle to the fourth reflecting surface and the sixth reflecting surface is 6.0 degrees or less, and the maximum effective diameter of the six reflecting surfaces is suppressed to be as small as 309 mm.

  The fourth embodiment of the present invention will be described in detail with reference to FIG. 4 of the schematic diagram of the main part of the fourth embodiment and Table 4 showing numerical examples of the fourth embodiment. Parts not specifically described are the same as those in the fourth embodiment.

  In the projection optical system of Example 4, the numerical aperture NA on the image side is 0.38, the projection magnification is 1/4, and the object height is 135.5 to 137.5 mm. Further, the NA stop is arranged between the first reflecting surface and the second reflecting surface. The intermediate image is formed between the fourth reflecting surface and the fifth reflecting surface and in the vicinity of the sixth reflecting surface as a spatial position. In addition, the telecentricity on the image plane side is suppressed to 1 mrad or less.

  Further, the incident angle to the fourth reflecting surface and the sixth reflecting surface is 9.8 degrees or less, and the maximum effective diameter of the six reflecting surfaces is suppressed to be as small as 308 mm.

  Example 5 of the present invention will be described in detail with reference to FIG. 5 of a schematic diagram of the main part of Example 5 and Table 5 showing numerical examples of Example 5. Parts not specifically mentioned are the same as those in the fifth embodiment.

  In the projection optical system of Example 5, the numerical aperture NA on the image side is 0.34, the projection magnification is 1/4, and the object height is 132 to 136 mm. The NA stop coincides with the second reflection surface (the NA stop also serves as the second reflection surface). The intermediate image is formed between the fourth reflecting surface and the fifth reflecting surface and in the vicinity of the sixth reflecting surface as a spatial position. In addition, the telecentricity on the image plane side is suppressed to 1 mrad or less.

  Further, the incident angle to the fourth reflecting surface and the sixth reflecting surface is 7.1 degrees or less, and the maximum effective diameter of the six reflecting surfaces is suppressed to 268 mm.

  Example 6 of the present invention will be described in detail with reference to FIG. 6 of a schematic diagram of the main part of Example 6 and Table 6 showing numerical examples of Example 6. Parts not specifically described are the same as those in the sixth embodiment.

  In the projection optical system of Example 6, the numerical aperture NA on the image side is 0.34, the projection magnification is 1/4, and the object height is 128 to 132 mm. Further, the NA stop is arranged between the first reflecting surface and the second reflecting surface. The intermediate image is formed between the fourth reflecting surface and the fifth reflecting surface and in the vicinity of the sixth reflecting surface as a spatial position. In addition, the telecentricity on the image plane side is suppressed to 1 mrad or less.

  Further, the incident angle to the fourth reflecting surface and the sixth reflecting surface is 9.8 degrees or less, and the maximum effective diameter of the six reflecting surfaces is suppressed to be as small as 306 mm.

  Here, Table 7 shows values of Formulas 1 to 4 in Examples 1 to 6.

  Hereinafter, an exposure apparatus 200 to which the reflective projection optical systems 100, 100A, 100B, 100C, 100D, and 100E of the present invention are applied will be described with reference to FIG. FIG. 7 is a schematic sectional view showing the arrangement of an exposure apparatus 200 as one aspect of the present invention.

  The exposure apparatus 200 of the present invention uses EUV light as exposure illumination light, and applies a circuit pattern formed on the mask 220 to the object 240 by, for example, a step-and-scan method or a step-and-repeat method. A projection exposure apparatus that performs exposure. Such an exposure apparatus is suitable for a lithography process of sub-micron or quarter micron or less, and in the present embodiment, a step-and-scan type exposure apparatus (also referred to as “scanner”) will be described as an example. Here, the “step and scan method” means that the wafer is continuously scanned (scanned) with respect to the mask to expose the mask pattern onto the wafer, and the wafer is stepped after the exposure of one shot is completed. The exposure method moves to the next exposure area. The “step-and-repeat method” is an exposure method in which the wafer is stepped and moved to the exposure area of the next shot for every batch exposure of the wafer.

  Referring to FIG. 7, an exposure apparatus 200 includes an illumination apparatus 210, a mask stage 225 on which a mask 220 is placed, a reflective projection optical system (projection optical system) 100, and a wafer on which an object 240 is placed. Stage 245. Furthermore, it has the alignment detection mechanism 250 which performs position alignment with a mask and to-be-processed object, the focus position detection mechanism 260, and the control part which is not shown in figure for controlling them.

  Further, as shown in FIG. 7, EUV light has a low transmittance to the atmosphere and generates contamination due to a reaction with a residual gas (polymer organic gas or the like) component, so at least in the optical path through which EUV light passes. (That is, the entire optical system) is in a vacuum atmosphere VC.

  The illumination device 210 is an illumination device that illuminates the mask 220 with an arcuate EUV light (for example, a wavelength of 13.4 nm) with respect to the arcuate field of view of the reflective projection optical system 100. The illumination device 210 includes an EUV light source 212 and an illumination optical system. 214.

  As the EUV light source 212, for example, a laser plasma light source is used. In this method, a target material in a vacuum vessel is irradiated with high-intensity pulsed laser light to generate high-temperature plasma, and EUV light having a wavelength of, for example, about 13 nm is emitted from the target material. As the target material, a metal film, a gas jet, a droplet, or the like is used. In order to increase the average intensity of the emitted EUV light, the repetition frequency of the pulse laser should be high, and it is usually operated at a repetition frequency of several kHz.

  The illumination optical system 214 includes a condensing mirror 214a and an optical integrator 214b. The condensing mirror 214a serves to collect EUV light emitted from the laser plasma almost isotropically. The optical integrator 214b has a role of uniformly illuminating the mask 220 with a predetermined numerical aperture. In addition, the illumination optical system 214 is provided with an aperture 214 c for limiting the illumination area of the mask 220 to an arc shape at a position conjugate with the mask 220.

  The mask 220 is a reflective mask, on which a circuit pattern (or image) to be transferred is formed, and is supported and driven by a mask stage 225. Diffracted light emitted from the mask 220 is reflected by the reflective projection optical system 100 and projected onto the object 240. The mask 220 and the workpiece 240 are arranged in an optically conjugate relationship. Since the exposure apparatus 200 is a step-and-scan exposure apparatus, the pattern of the mask 220 is reduced and projected onto the object 240 by scanning the mask 220 and the object 240.

  The mask stage 225 supports the mask 220 and is connected to a moving mechanism (not shown). Any structure known in the art can be applied to the mask stage 225. A moving mechanism (not shown) is constituted by a linear motor or the like, and can move the mask 220 by driving the mask stage 225 at least in the X direction. The exposure apparatus 200 scans the mask 220 and the object to be processed 240 in a synchronized state.

  The reflection type projection optical system 100 is a reflection type projection optical system that projects a pattern on the mask 220 surface onto the object 240 to be reduced. In FIG. 7, the reflection type projection optical system 100 is illustrated as having four reflection mirrors (reflection surfaces) in order to simplify the drawing, but the reflection mirror of the reflection type projection optical system 100 is implemented. As described in Examples 1 and 2, the number is preferably 6. Of course, it goes without saying that the number of sheets may be changed within a range where the gist of the present invention does not change. In order to realize a wide exposure area with a small number of mirrors, the mask 220 and the workpiece 240 are simultaneously scanned using only a thin arc-shaped area (ring field) separated from the optical axis by a certain distance. Transfer the area. The numerical aperture (NA) of the projection optical system 230 is about 0.3 to 0.4.

  The processing body 240 is a wafer in this embodiment, but widely includes liquid crystal substrates and other objects to be processed. A photoresist is applied to the object to be processed 240.

  The wafer stage 245 supports the object 240 by the wafer chuck 245a. For example, the wafer stage 245 moves the object 240 in the XYZ directions using a linear motor. The mask 220 and the workpiece 240 are scanned synchronously. Further, the position of the mask stage 225 and the position of the wafer stage 245 are monitored by a laser interferometer, for example, and both are driven at a constant speed ratio.

  The alignment detection mechanism 250 measures the positional relationship between the position of the mask 220 and the optical axis of the reflective projection optical system 100, and the positional relationship between the position of the object 240 and the optical axis of the reflective projection optical system 100. . In addition, the positions and angles of the mask stage 225 and the wafer stage 245 are set so that the projected image of the mask 220 matches a predetermined position of the object 240 to be processed.

  The focus position detection mechanism 260 measures the focus position on the surface of the object 240 to be processed and controls the position and angle of the wafer stage 245 so that the surface of the object 240 is always imaged by the projection optical system 230 during exposure. Keep on.

  A control unit (not shown) includes, for example, a CPU and a memory, and controls the operation of the exposure apparatus 200. The control unit is electrically connected to the illumination device 210, the mask stage 220 (ie, a moving mechanism (not shown) of the mask stage 225), and the wafer stage 245 (ie, a moving mechanism (not shown) of the wafer stage 245). The CPU includes any processor of any name such as MPU and controls the operation of each unit. The memory is composed of a ROM and a RAM, and stores firmware that operates the exposure apparatus 200.

  In exposure, the EUV light emitted from the illumination device 210 illuminates the mask 220 and forms a pattern on the surface of the mask 220 on the surface of the object 240 to be processed. In the present embodiment, the image surface is an arc-shaped (ring-shaped) image surface, and the entire surface of the mask 220 is exposed by scanning the mask 220 and the workpiece 240 at a speed ratio of the reduction ratio.

  Next, an embodiment of a device manufacturing method using the above-described exposure apparatus 200 will be described with reference to FIGS. FIG. 8 is a flowchart for explaining how to fabricate devices (ie, semiconductor chips such as IC and LSI, LCDs, CCDs, and the like). In the present embodiment, the manufacture of a semiconductor chip will be described as an example. In step 1 (circuit design), a device circuit is designed. In step 2 (mask production), a mask on which the designed circuit pattern is formed is produced. In step 3 (wafer manufacture), a wafer is manufactured using a material such as silicon. Step 4 (wafer process) is called a pre-process, and an actual circuit is formed on the wafer by lithography using the mask and the wafer. Step 5 (assembly) is called a post-process, and is a process for forming a semiconductor chip using the wafer created in step 4. The assembly process (dicing, bonding), packaging process (chip encapsulation), and the like are performed. Including. In step 6 (inspection), inspections such as an operation confirmation test and a durability test of the semiconductor device created in step 5 are performed. Through these steps, a semiconductor device is completed and shipped (step 7).

  FIG. 9 is a detailed flowchart of the wafer process in Step 4. In step 11 (oxidation), the surface of the wafer is oxidized. In step 12 (CVD), an insulating film is formed on the surface of the wafer. In step 13 (electrode formation), an electrode is formed on the wafer by vapor deposition or the like. Step 14 (ion implantation) implants ions into the wafer. In step 15 (resist process), a photosensitive agent is applied to the wafer. Step 16 (exposure) uses the exposure apparatus 200 to expose a circuit pattern on the mask onto the wafer. In step 17 (development), the exposed wafer is developed. In step 18 (etching), portions other than the developed resist image are removed. In step 19 (resist stripping), the resist that has become unnecessary after the etching is removed. By repeatedly performing these steps, multiple circuit patterns are formed on the wafer. According to the device manufacturing method of the present embodiment, it is possible to manufacture a higher quality device than before. Thus, the device manufacturing method using the exposure apparatus 200 and the resulting device also constitute one aspect of the present invention.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist. For example, the present invention can be used as a reflection type projection optical system for ultraviolet rays having a wavelength of 200 nm or less other than EUV light such as ArF excimer laser and F2 laser, and exposure that does not scan even an exposure apparatus that scans a large screen. The present invention can also be applied to an exposure apparatus.

FIG. 3 is a schematic diagram of a main part of the projection optical system according to the first embodiment. FIG. 6 is a schematic diagram of a main part of a projection optical system according to a second embodiment. FIG. 6 is a schematic diagram of a main part of a projection optical system according to a third embodiment. FIG. 6 is a schematic diagram of a main part of a projection optical system according to a fourth embodiment. FIG. 10 is a schematic diagram of a main part of a projection optical system of Example 5. FIG. 10 is a schematic diagram of a main part of a projection optical system of Example 6. It is a schematic sectional drawing of the exposure apparatus of a present Example. It is a flowchart for demonstrating manufacture of devices (semiconductor chips, such as IC and LSI, LCD, CCD, etc.). 9 is a detailed flowchart of the wafer process in Step 4 shown in FIG. 8. It is explanatory drawing for demonstrating the center of a pattern.

Explanation of symbols

100, 100A to 100F Reflective projection optical system M1 First reflecting mirror M2 Second reflecting mirror M3 Third reflecting mirror M4 Fourth reflecting mirror M5 Fifth reflecting mirror M6 Sixth reflecting mirror MS Mask (object surface)
W wafer (image plane)
AS Aperture stop AX Optical axis IM Intermediate image 200 Exposure apparatus

Claims (7)

A light beam from a pattern on the object surface is converted into a concave first reflecting surface, a convex second reflecting surface, a convex third reflecting surface, a concave fourth reflecting surface, a convex fifth reflecting surface, A coaxial projection optical system that reflects in the order of the concave sixth reflecting surface and connects the reduced projection image of the pattern on the image plane,
An intermediate image of the pattern is formed between the fourth reflecting surface and the fifth reflecting surface on the optical path of the light flux,
The angle formed by the principal ray emitted from the center of the pattern and the optical axis of the projection optical system at the position of the intermediate image is θ,
The image height of the position where the center of the pattern forms an image on the image plane is I,
The radius of curvature and the effective diameter of the fourth reflecting surface are R4, D4,
The radius of curvature and effective diameter of the sixth reflecting surface are R6, D6,
And when

Projection optical system characterized by satisfying

The projection optical system according to claim 1, wherein: When the focal length of the first imaging system composed of the first, second, third, and fourth reflecting surfaces is F1, and the focal length of the second imaging system composed of the fifth and sixth reflecting surfaces is F2. ,

The projection optical system according to claim 1, wherein: On the optical path of the principal ray, an optical path length between the fourth reflecting surface and the fifth reflecting surface is L,
On the optical path of the chief ray, when the distance between the fourth reflecting surface and the intermediate image is Lm,

The projection optical system according to claim 1, wherein:   The projection optical system according to claim 1, wherein a diaphragm of the projection optical system is disposed on the second reflecting surface. An illumination optical system that illuminates a pattern on the object surface with an illumination light beam from a light source;
An exposure apparatus comprising: the projection optical system according to claim 1, wherein the pattern forms a reduced image on the image plane. Exposing the object to be exposed using the exposure apparatus according to claim 6;
And a step of developing the exposed object to be exposed.

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