JP2008066578A - Design method for imaging optical system, imaging optical system, exposure apparatus, and device manufacturing method - Google Patents

Abstract

An imaging optical system design method capable of reducing a change in optical performance with respect to an environmental change is provided.
An image of a pattern on an object plane is formed on an image plane having a first lens group having a first focal length f1 and a second lens group having a second focal length f2. When the environment in which the imaging optical system is arranged changes from a vacuum atmosphere to an air atmosphere or from an air atmosphere to a vacuum atmosphere, the first focal length f1 and the second focal length f1 When the focus position difference Δd1 generated according to the ratio f1 / f2 to the focal length f2 is defined as Δd1 = a1 · (f1 / f2) + b1 with a1 and b1 as constants, a step of obtaining constants a1 and b1; The allowable focus position difference due to environmental change is Δd _T1 , and the ratio f1 / f2 between the first focal length f1 and the second focal length f2 is based on f1 / f2 = (Δd _T1− b1) / a1. Step to determine To provide a design wherein the.
[Selection] Figure 1

Description

  The present invention generally relates to an optical system, and more particularly to an optical system disposed in a vacuum atmosphere in an exposure apparatus that exposes an object to be processed such as a wafer for a semiconductor device or a glass plate for a liquid crystal display element. The present invention is suitable for a detection optical system used in an exposure apparatus that uses ultraviolet light or extreme ultraviolet (EUV) light as exposure light.

  2. Description of the Related Art Conventionally, a projection exposure apparatus for transferring a circuit pattern by projecting a pattern drawn on a mask (reticle) onto a wafer or the like by a projection optical system when manufacturing a fine semiconductor element using photolithography (baking) technology in use.

  The minimum dimension (resolution) that can be transferred by the projection exposure apparatus is proportional to the wavelength of light used for exposure and inversely proportional to the numerical aperture (NA) of the projection optical system. Therefore, the shorter the wavelength, the better the resolution. For this reason, the wavelength of exposure light has been shortened in accordance with the recent demand for miniaturization of semiconductor elements. For example, the wavelength of ultraviolet light used as an ultra-high pressure mercury lamp (i-line (wavelength: about 365 nm)), KrF excimer laser (wavelength: about 248 nm), and ArF excimer laser (wavelength: about 193 nm) has become shorter.

  However, semiconductor elements are rapidly miniaturized, and there is a limit in lithography using ultraviolet light. Therefore, in order to efficiently transfer a very fine circuit pattern of 42 nm or less, a projection exposure apparatus using EUV light having a wavelength shorter than that of ultraviolet light and having a wavelength of about 10 nm to 15 nm (hereinafter referred to as “EUV exposure apparatus”). Has been developed.

  When the wavelength of exposure light is shortened, the absorption of light by the substance becomes very large. Therefore, it is difficult to use a refraction element utilizing refraction of light such as that used in visible light or ultraviolet light, that is, a lens. Further, there is no glass material that can be used in the wavelength region of EUV light, and a reflective element that utilizes light reflection, that is, a reflective optical system that constitutes an optical system only with a mirror is used.

  Moreover, since EUV light is easily absorbed and attenuated in the air atmosphere, it is essential to use it in a vacuum atmosphere. Therefore, the EUV exposure apparatus accommodates at least an optical path (such as an illumination optical system and a projection optical system) through which EUV light passes in a vacuum chamber that maintains a vacuum atmosphere, and uses the EUV light without attenuation.

  However, in the alignment optical system and the focus position detection system that do not use EUV light, a part of the components can be arranged in the air atmosphere through glass (viewing window) that separates the vacuum atmosphere from the air atmosphere. (For example, refer to Patent Document 1). In Patent Document 1, components (such as a measurement light source, an image sensor, and an electric circuit) that cannot be placed in a vacuum atmosphere due to operation failure or generation of contaminants in a vacuum atmosphere are placed in an air atmosphere. is doing.

  On the other hand, all or a part of the optical system of the alignment detection system and the focus position detection system is disposed in a vacuum atmosphere. These optical systems have a problem that when the environment changes from an air atmosphere to a vacuum atmosphere, the refractive index also changes according to the change in the environment, so that the optical performance changes. For example, when the refractive index in a vacuum atmosphere is 1.00000 for light having a wavelength of 820 nm, the refractive index in an air atmosphere is 1.00027. Such a change in refractive index affects the change in the optical performance of the optical system. Here, the optical performance is a focus position, an imaging magnification, and a wavefront aberration.

An optical system disposed in a vacuum atmosphere is generally assembled and adjusted in an air atmosphere. Specifically, a change in optical performance due to an environmental change, for example, a change amount of the imaging position is obtained in advance, and the adjustment is performed in the air atmosphere in consideration of the change. However, the imaging position changes by a predetermined amount of change due to the effects of errors in assembly and adjustment of the optical system or processing errors in the optical member (lens curvature radius, thickness, glass optical constant variation), etc. Not always. Therefore, there is a concern that the optical performance of the alignment detection system or the focus position detection system in a vacuum environment is significantly deteriorated. In other words, high-precision detection cannot be performed if the optical performance changes greatly according to environmental changes. In view of this, an optical system has been proposed in which there is little change in optical performance (amount of change in imaging position) due to environmental changes (for example, see Patent Document 2).
JP 2001-217191 A JP-A-11-271604

  However, Patent Document 2 discloses an optical system with little change in optical performance with respect to environmental changes, but only discloses an optical system with an infinite object distance. (Disposition) is not disclosed. For example, an optical system that is not easily affected by environmental changes is configured using the optical system disclosed in Patent Document 2, and an object image at a finite distance is formed. In this case, it is necessary to prepare two sets of the optical system of Patent Document 2 and arrange the infinite object side of each optical system facing each other. Furthermore, it is necessary to design each optical system so as not to be affected by environmental changes. In addition, the total length of the optical system is increased and the number of lenses is increased.

  It is also conceivable to provide a vacuum chamber for adjusting the optical system, measure a change in optical performance (change in image forming position) in a vacuum atmosphere, and adjust in an air atmosphere based on the measurement result. However, in addition to the time and cost, there is a problem that the equipment for adjustment becomes complicated.

  Accordingly, an object of the present invention is to provide an imaging optical system design method capable of reducing a change in optical performance with respect to an environmental change while having a simple configuration.

In order to achieve the above object, a design method according to one aspect of the present invention includes a first lens group having a first focal length f1 and a second lens group having a second focal length f2. An image forming optical system design method for forming an image of an object plane pattern on an image plane, wherein the environment in which the image forming optical system is disposed is changed from a vacuum atmosphere to an air atmosphere or an air atmosphere. When the environment changes from the first to the vacuum atmosphere, the focus position difference Δd1 generated according to the ratio f1 / f2 between the first focal length f1 and the second focal length f2 is set to Δd1 = a1 with a1 and b1 as constants. When defining as (f1 / f2) + b1, the step of obtaining the constants a1 and b1, and the allowable focal position difference due to the environmental change as Δd _T1 , the first focal length f1 and the second Ratio f1 to focal length f2 Determining / f2 based on f1 / f2 = (Δd _T1 −b1) / a1.

A design method as another aspect of the present invention has a first focal length f1, a first lens group made of a glass material having a first refractive index n1, a second focal length f2, and a first focal length f1. And a second lens group made of a glass material having a refractive index of n2, and a method for designing an imaging optical system that forms an image of an object surface pattern on an image plane, the imaging optical system comprising: When the environment to be arranged changes from a vacuum atmosphere to an air atmosphere, or from an air atmosphere to a vacuum atmosphere, the environment is changed according to a difference Δn between the first refractive index n1 and the second refractive index n2. When the focus position difference Δd2 is defined as Δd2 = a2 · Δn + b2 where a2 and b2 are constants, the constants a2 and b2 are obtained, and the tolerance of the focus position difference due to the environmental change is Δd _T2 , Glass with refractive index n1 of 1 And the glass material of the second refractive index n2, and having a determining based on _{Δn = (Δd T2 -b2) /} a2.

An imaging optical system as still another aspect of the present invention is an imaging optical system that forms an image of an object plane pattern on an image plane, and a first lens group having a first focal length f1. And the second lens group having the second focal length f2, and the environment in which the imaging optical system is arranged has changed from a vacuum atmosphere to an air atmosphere or from an air atmosphere to a vacuum atmosphere. In this case, the focus position difference Δd1 generated according to the ratio f1 / f2 between the first focal length f1 and the second focal length f2 is set to Δd1 = a1 · (f1 / f2) + b1 with a1 and b1 as constants. is defined as the ratio f1 / f2 of the first focal length f1 and the second focal length f2 is the tolerance of the focus position difference by the environmental change When _{Δd T1, f1 / f2 = (} Δd T1 -B1) to be determined based on / a1 And butterflies.

An imaging optical system according to still another aspect of the present invention is an imaging optical system that forms an image of an object plane pattern on an image plane, has a first focal length f1, A first lens group made of a glass material having a refractive index n1, and a second lens group made of a glass material having a second refractive index n2 and having a second focal length f2, the imaging optical system comprising: When the environment to be arranged changes from a vacuum atmosphere to an air atmosphere, or from an air atmosphere to a vacuum atmosphere, the environment is changed according to a difference Δn between the first refractive index n1 and the second refractive index n2. The focus position difference Δd2 is defined as Δd2 = a2 · Δn + b2 where a2 and b2 are constants. The glass material having the first refractive index n1 and the glass material having the second refractive index n2 have a focus position difference due to the environmental change. When the allowable value is Δd _T2 , Δn = (Δd _T2 -B2) / a2 is satisfied.

  An imaging optical system as still another aspect of the present invention is characterized by being designed by the above design method.

  An exposure apparatus according to still another aspect of the present invention is an exposure apparatus that illuminates a mask using light from a light source and exposes a pattern of the mask onto an object to be processed, the focus position of the object to be processed being set. It has a detection optical system to detect, and the detection optical system includes the above-mentioned imaging optical system.

  An exposure apparatus according to still another aspect of the present invention is an exposure apparatus that illuminates a mask using light from a light source and exposes a pattern of the mask onto an object to be processed, the mask, the object to be processed, And a detection optical system that detects the relative position of the imaging optical system. The detection optical system includes the imaging optical system described above.

  An exposure apparatus according to still another aspect of the present invention is an exposure apparatus that illuminates a mask using light from a light source and exposes a pattern of the mask onto an object to be processed, the focus position of the object to be processed being set. A first detection optical system for detecting; and a second detection optical system for detecting a relative position between the mask and the object to be processed. The first detection optical system and the second detection optical system. At least one of them includes the above-described imaging optical system.

  According to still another aspect of the present invention, there is provided a device manufacturing method comprising: exposing a target object using the above-described exposure apparatus; and developing the exposed target object.

  Further objects and other features of the present invention will become apparent from the preferred embodiments described below with reference to the accompanying drawings.

  According to the present invention, it is possible to provide an imaging optical system design method capable of reducing a change in optical performance with respect to an environmental change while having a simple configuration.

  Hereinafter, an imaging optical system that forms an image of a pattern on an object on an image plane as one aspect of the present invention and a method for designing such an imaging optical system will be described with reference to the accompanying drawings. In addition, in each figure, the same reference number is attached | subjected about the same member and the overlapping description is abbreviate | omitted. In the present application, the “lens group” includes not only a plurality of lenses but also a single lens.

  First, with reference to FIG. 12, the change in the imaging position when the environment in which the imaging optical system 1000 is arranged is changed from the air atmosphere to the vacuum atmosphere or from the vacuum atmosphere to the air atmosphere will be described. Hereinafter, a case where the environment in which the optical system is arranged changes from an air atmosphere to a vacuum atmosphere or from a vacuum atmosphere to an air atmosphere is referred to as an environmental change. Here, FIG. 12 is a diagram for explaining the change of the imaging position with respect to the environmental change of the imaging optical system 1000. FIG. 12A shows the imaging relationship in a vacuum atmosphere, and FIG. ) Shows an imaging relationship in an air atmosphere.

The refractive index n _air in the air atmosphere of the space portion (that is, the space where the lens group does not exist) in the imaging optical system 1000 is 1.00027 when the refractive index n _vac in the vacuum atmosphere is 1.00000. The imaging optical system 1000 includes a lens group 1100 having a focal length f as shown in FIG.

  When the environment in which the imaging optical system 1000 is arranged changes from a vacuum atmosphere to an air atmosphere or from an air atmosphere to a vacuum atmosphere (that is, when an environmental change occurs), as described above, the imaging optical system The refractive index of the space portion of 1000 changes. Accordingly, the position of the final imaging plane of the imaging optical system 1000 changes between the vacuum atmosphere and the air atmosphere (that is, a change amount (focus position difference) d3 is generated).

  On the other hand, as shown in FIG. 1, the imaging optical system 100 of the present invention can suppress the change d3 of the position of the final imaging plane with respect to the environmental change to an extremely small value (or 0). FIG. 1 is a schematic cross-sectional view showing the configuration of the imaging optical system 100 of the present invention. In FIG. 1, the optical path in a vacuum atmosphere is indicated by a solid line, and the optical path in an air atmosphere is indicated by a broken line. Further, the imaging optical system 100 focuses light from the object plane OS (that is, an image of the pattern of the object plane OS) on the image plane IS.

Here, the reason why the imaging optical system 100 can suppress the change amount (focus position difference) d3 to an extremely small value will be described. The refractive index n _air in the air atmosphere of the space portion (that is, the space where the lens group does not exist) in the imaging optical system 100 is 1.00027 when the refractive index n _vac in the vacuum atmosphere is 1.00000. As shown in FIG. 1, the imaging optical system 100 is arranged at a position close to the image plane IS and a first lens group 110 having a first focal length f1 arranged at a position close to the object plane OS. And a second lens group 120 having a second focal length f2. The first lens group 110 and the second lens group 120 are arranged with a principal point distance e between both lens groups, and the focal length f of the imaging optical system 100 is expressed by the following Equation 1. The

  In the imaging optical system 100, the image of the pattern of the object plane OS is relayed by the first lens group 110 and the second lens group 120 (see Expressions 2 and 3 below), and finally connected to the image plane IS. Imaged. First, considering the existence of only the first lens group 110, an image of the pattern of the object plane OS is formed at a position P1, as shown in FIG. Then, the image formed at the position P1 is formed on the image plane IS by the second lens image 120 as shown in FIG. FIG. 2 is a diagram for explaining the change of the imaging position with respect to the environmental change of the imaging optical system 100. Here, the imaging formula by the first lens group 110 is expressed by the following formula 2, and the imaging formula by the second lens group 120 is expressed by the following formula 3. However, the distance from the object plane OS to the first lens group 110 is a, and the distance from the first lens group 110 to the position P1 is b. Further, the distance from the second lens group 120 to the image plane IS is c, and the distance between the first lens group 110 and the second lens group 120 (main point interval distance) is e.

  When the image formation position (position P1) by the first lens group 110 or the image formation position (image plane IS) by the second lens group 120 changes due to an environmental change, Expressions 2 and 3 are expressed by Expression 4 below. And 5.

  In Equations 4 and 5, f1 ', f2', b ', c', and e 'are a focal length, an object distance, an image distance, and a principal point interval distance that have changed due to environmental changes.

  When the environment changes, the imaging optical system 100 detects the focus position difference ΔP1 at the imaging position (position P1) by the first lens group 110 and the imaging position (image plane IS) by the second lens group 120. ) With the focus position difference d3 in FIG. Further, the imaging optical system 100 includes a first lens group 110 and a second lens group 120 that are different from each other in the direction of the imaging position that changes due to environmental changes. In other words, the imaging optical system 100 has a direction in which the focus (image formation) position by the first lens group 110 is shifted and a direction in which the focus (image formation) position by the second lens group 120 is shifted when an environmental change occurs. Are configured to cancel each other. In addition, the imaging optical system 100 has the first focal length f1 of the first lens group 110 and the second lens group 120 so that the focus position difference d3 finally becomes a very small value (or 0). The second focal length f2 is optimized.

  FIG. 3 shows the optimization of the first focal length f1 of the first lens group 110 and the second focal length f2 of the second lens group 120 (changes in the imaging position due to environmental changes are extremely small values (or It is a schematic sectional drawing which shows the optical system defined in order to explain to (0).

  The optical system shown in FIG. 3 includes a convex lens 110A having a first focal length f1 as the first lens group 110 and a concave lens 120A having a second focal length f2 as the second lens group 120. The The convex lens 110A and the concave lens 120A are ideal lenses (lens without aberration), and the principal point distance is e.

  In the optical system shown in FIG. 3, the refractive index (first refractive index) n1 of the glass material of the convex lens 110A is 1.8901, and the refractive index (second refractive index) of the glass material of the concave lens 120A is 1.4351. Are calculated from the following formulas 7 and 8. The refractive indexes n1 and n2 are values for light with a wavelength of 820 nm. N ′ represents a refractive index of 1.00000 in a vacuum atmosphere.

Further, the lens data of the convex lens 110A and the concave lens 120A was input to the optical simulator CODEV (ORA), and the focus position difference before and after the environmental change was obtained. Here, in the optical system shown in FIG. 3, the distance from the lens surface closest to the image plane IS to the imaging position in the vacuum atmosphere is d _vac , and the imaging position in the atmospheric atmosphere from the lens surface closest to the image plane IS. The distance to is _dair . Then, the shift amount of the imaging position due to the environmental change (focus position difference d3) is defined as d3 = d _vac −d _air .

  Hereinafter, a method for designing an optical system (that is, the imaging optical system 100) in which the change of the imaging position due to the environmental change is extremely small will be described with reference to FIGS. FIG. 4 is a flowchart for explaining a method for designing an imaging optical system as one aspect of the present invention. In this embodiment, as an example of the optical system shown in FIG. 3, a design of an imaging optical system having a focal length f of 100 mm and an imaging magnification of 16 will be described.

  In the optical system shown in FIG. 3, the first focal length f1 of the convex lens 110A (first lens group 110) is fixed. First, the focus ratio (ratio between the first focal distance f1 and the second focal distance f2) f1 / varies depending on the principal point distance e and the second focal distance f2 of the concave lens 120A (second lens group 120). The relationship between f2 and the focus position difference due to environmental change is obtained (step 1002). The relationship between the focus ratio f1 / f2 and the focus position difference due to environmental changes can be obtained using an optical simulator, and an example of such a simulation result is shown in FIG. FIG. 5 is a graph showing the relationship between the focus ratio of the optical system (imaging optical system) shown in FIG. 3 and the focus position difference due to environmental changes, with the horizontal axis representing the focus ratio and the vertical axis representing the focus position difference. To do. FIG. 5 shows simulation results for a plurality of imaging magnifications.

Next, in the imaging optical system (that is, the designed imaging optical system) having an imaging magnification of 16 times, an allowable focus position difference Δd _T1 due to environmental changes is set (step 1004). In the present embodiment, the allowable value Δd _T1 of the focus position difference due to the environmental change is set to −1 mm ≦ Δd _T1 ≦ 1 mm.

Next, in the graph shown in FIG. 5, the allowable values Δd _T1 = + 1 and −1 are substituted into an approximate expression (see Expression 9) representing the result of the imaging optical system with the imaging magnification of 16 times, and the focus ratio f1 The range of / f2 is determined (step 1006). In the present embodiment, the range of the focus ratio f1 / f2 is −0.833 ≦ f1 / f2 ≦ −0.782.

  Then, an optical system (imaging optical system) having a focus ratio that satisfies the range of the focus ratio f1 / f2 determined in step 1006 is designed (step 1008). Thereby, it is possible to design an optical system (imaging optical system) in which the change of the imaging position due to the environmental change is extremely small (the focus position difference d3 becomes a very small value (or 0)). Moreover, the design method of the present invention is effective not only for the optical specifications (focal length, imaging magnification, etc.) described above but also for other optical specifications.

The focus position difference allowable value Δd _T1 due to environmental change can be changed according to the required optical performance. For example, when the depth of focus (DOF) is DOF = 2 · λ · F _NO ² , the tolerance value Δd _T1 of the focus position difference due to environmental change is set between ± DOF and ± DOF / 10 with reference to such DOF. May be.

  Each coefficient of the relational expression shown in the graph of FIG. 5 is not limited to these values, and the refractive index n1 of the convex lens 110A (first lens group 110) and the concave lens 120A (second lens group 120). It changes depending on optical parameters such as the refractive index n2 or the principal point distance e. Accordingly, a relational expression may be appropriately obtained by an optical simulator, and the relational expression may be used.

Until now, in order to make the focus position difference of the imaging optical system 100 due to environmental changes extremely small (or 0), or within the tolerance Δd _T1 of the focus position difference due to environmental changes, A method for optimizing the focus ratio (f1 / f2) has been described. However, even if the refractive index n1 of the glass material of the first lens group 110 and the refractive index n2 of the second lens group 120 constituting the imaging optical system 100 are optimized, the focus position difference is extremely small (or 0). ) Or within the tolerance Δd _T1 of the focus position difference.

  Hereinafter, optimization of the refractive index n1 of the glass material of the first lens group 110 and the refractive index n2 of the second lens group 120 constituting the imaging optical system 100 (changes in imaging position due to environmental changes are extremely small values ( Or, 0)) will be described. In the present embodiment, as an optical system shown in FIG. 3, an imaging optical system having a focal distance f of 60 mm, a principal point distance e of 3 mm, and an imaging magnification of 16 will be described as an example.

  6 shows a difference in refractive index Δn (Δn = | n1−n2 |) between the first lens group 110 and the second lens group 120 of the optical system shown in FIG. 3 (that is, the imaging optical system described above). It is a graph which shows the relationship with the focus position difference by an environmental change. FIG. 6 employs the refractive index difference Δn on the horizontal axis and the focus position difference on the vertical axis. In the graph shown in FIG. 6, each of the plurality of straight lines represents the first focal length f <b> 1 of the first lens group 110 and the second focal length of the second lens group 120 constituting the imaging optical system 100. The difference of the ratio (focus ratio) f1 / f2 with f2 is shown.

For example, consider a case where the focal length ratio f1 / f2 between the first lens group 110 and the second lens group 120 is f1 / f2 = −0.8. In this case, in an imaging optical system with an imaging magnification of 16 times, if the focus position difference allowable value Δd _T2 is set to −1 mm ≦ Δd _T2 ≦ 1 mm, an approximate expression for the focus ratio f1 / f2 in the graph shown in FIG. The allowable value Δd _T2 = 1 and −1 are substituted into (Expression 10). Thereby, the range of the refractive index difference Δn of the glass material of the first lens group 110 and the second lens group 120 constituting the imaging optical system 100 constituting the imaging optical system is 0.468 ≦ | Δn | ≦ It is limited (determined) to 0.505.

  If a glass material is selected within the determined refractive index difference range, an optical system that can keep the value of the focus position difference due to environmental changes within an allowable value can be designed.

In this embodiment, the glass material (refractive index difference) for the imaging optical system having an imaging magnification of 16 is described. However, in the case of other imaging magnifications, a relational expression corresponding to the imaging magnification is given. It is possible to select an optimal glass material. Further, the focus position difference allowable value Δd _T2 due to the environmental change may be set based on the depth of focus (DOF) as described above. Further, the coefficients of the relational expression shown in the graph of FIG. 6 are not limited to these values, but optical parameters such as the first focal length f1, the second focal length f2, or the principal point spacing distance e. It depends on. Accordingly, a relational expression may be appropriately obtained by an optical simulator, and the relational expression may be used.

  In addition, the focal length f of the entire optical system is 19.32 mm, the first focal length is 22 mm, the second focal length is 100 mm, the principal point distance e is 8.1 mm, and the imaging magnification is 16 times. Consider a case in which a focus position difference of −3.1 mm occurs in the optical system. In this case, if the focal length of the imaging optical system is reduced by scaling, the focus position difference changes. Specifically, there is a directly proportional relationship between the focal length f of the entire optical system and the focus position difference. Accordingly, when designing an optical system with a limited total length of the optical system and a small focus position difference while maintaining the imaging magnification, if the focal point value is reduced and the principal point position is optimized, An optical system with a high magnification and a small focus position difference can be designed.

As described above, according to the imaging optical system design method of the present invention, it is possible to design an imaging optical system that can reduce a change in optical performance with respect to an environmental change while having a simple configuration. The imaging optical system design method according to one aspect of the present invention is characterized by conceptually having the following two steps. First, the focus position difference Δd1 generated according to the ratio f1 / f2 between the first focal length f1 and the second focal length f2 is defined as Δd1 = a1 · (f1 / f2) + b1 with a1 and b1 as constants. Constants a1 and b1 are obtained. Next, assuming that the allowable value of the focus position difference due to environmental change is Δd _T1 , the ratio f1 / f2 between the first focal length f1 and the second focal length f2 is f1 / f2 = (Δd _T1− b1) / a1. Determine based on. In addition, the imaging optical system design method according to another aspect of the present invention conceptually includes the following two steps. First, when the focus position difference Δd2 generated according to the difference Δn between the first refractive index n1 and the second refractive index n2 is defined as Δd2 = a2 · Δn + b2 where a2 and b2 are constants, the constant a2 and b2 is obtained. Next, the tolerance value of the focus position difference due to the environmental change is set as Δd _T2 , and the glass material having the first refractive index n1 and the glass material having the second refractive index n2 are determined based on Δn = (Δd _T2− b2) / a2. To do.

  Hereinafter, an exposure apparatus 300 to which the imaging optical system 100 of the present invention is applied will be described with reference to FIG. FIG. 7 is a schematic sectional view showing the arrangement of an exposure apparatus 300 as one aspect of the present invention.

  The exposure apparatus 300 of the present invention is a projection exposure apparatus that uses EUV light (for example, a wavelength of 13.4 nm) as exposure illumination light. The exposure apparatus 300 is, for example, on an object to be processed (wafer) 340 (on the image plane) on which the circuit pattern formed on the mask 320 is arranged at the image plane position by the step-and-scan method or the step-and-repeat method. To expose. 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” is a method in which a wafer is exposed to a reticle pattern by continuously scanning the wafer with respect to the reticle. In the “step-and-scan method”, the wafer is stepped after the exposure of one shot is completed, and is moved to the next exposure area. The “step-and-repeat method” is a method in which the wafer is moved stepwise for each batch exposure of the wafer and moved to the exposure area of the next shot.

  Referring to FIG. 7, an exposure apparatus 300 includes an illumination device 310, a mask stage 325 on which a mask 320 is placed, a projection optical system 330, a wafer stage 345 on which an object to be processed 340 is placed, and an alignment detection system. 350 and a focus position detection system 360.

Further, as shown in FIG. 6, 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. Therefore, at least in the optical path through which the EUV light passes. (That is, the entire optical system) is in a vacuum atmosphere VC. In the present embodiment, the vacuum degree of the vacuum atmosphere VC is about 10 ⁻⁵ Pa to 10 ⁻⁴ Pa.

  The illumination device 310 is an illumination device that illuminates the mask 320 with arc-shaped EUV light (for example, wavelength 13.4 nm) with respect to the arc-shaped field of the projection optical system 330. The illumination device 310 includes an EUV light source 312, an illumination optical system 314, and the like. Have

  As the EUV light source 312, for example, a laser plasma light source is used. The laser plasma light source irradiates a target material in a vacuum vessel with high-intensity pulsed laser light, generates high-temperature plasma, and uses, for example, EUV light with a wavelength of about 13 nm emitted from the plasma. 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 312 includes a condenser mirror 312a and an optical integrator 312b. The condensing mirror 312a has a function of collecting EUV light emitted approximately isotropically from the laser plasma. The optical integrator 312b has a function of uniformly illuminating the mask 320 with a predetermined numerical aperture. The illumination optical system 312 has an aperture 312c for limiting the illumination area of the mask 320 to an arc shape at a position conjugate with the mask 320.

  The mask 320 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 325. The diffracted light emitted from the mask 320 is reflected by the projection optical system 330 and projected onto the object to be processed 340. The mask 320 and the object to be processed 340 are arranged in an optically conjugate relationship. Since the exposure apparatus 300 is a step-and-scan exposure apparatus, the mask 320 and the object to be processed 340 are scanned to reduce and project the pattern of the mask 320 onto the object to be processed 340.

  The mask stage 325 supports the mask 320 via the mask chuck 325a and is connected to a moving mechanism (not shown). The mask stage 325 can employ any structure known in the art. A moving mechanism (not shown) is constituted by a linear motor or the like, and can move the mask 320 by driving the mask stage 325 at least in the X direction. The exposure apparatus 300 scans the mask 320 and the object to be processed 340 in a synchronized state. Here, the scanning direction in the mask 320 or the object to be processed 340 is X, the direction perpendicular to the scanning direction is Y, and the direction perpendicular to the mask 320 or the object to be processed 340 is Z.

  The projection optical system 330 projects the pattern on the mask 320 surface onto the object to be processed 340, which is an image plane, using a plurality of reflection mirrors (that is, multilayer mirrors) 330a. The number of multilayer mirrors 330a is about 4 to 6. The shape of the reflecting surface of the multilayer mirror 330a is a convex or concave spherical or aspherical surface. In order to realize a wide exposure area with a small number of mirrors, the mask 320 and the object to be processed 340 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 330 is about 0.1 to 0.3.

  The object to be processed 340 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 340.

  The wafer stage 345 supports the workpiece 345 by the wafer chuck 345a. The wafer stage 345 moves the workpiece 340 in the XYZ directions using, for example, a linear motor. The mask 320 and the workpiece 340 are scanned synchronously. Further, the position of the mask stage 325 and the position of the wafer stage 345 are monitored by, for example, a laser interferometer or the like, and both are driven at a constant speed ratio.

  The alignment detection system (first detection optical system) 350 includes, for example, an off-axis type bright-field illumination image processing detection system, and performs wafer alignment while having a predetermined baseline amount. Here, the wafer alignment is a positional relationship (relative position) between the position of the mask 320 and the optical axis of the projection optical system 330 and a positional relationship (relative position) between the position of the object 340 and the optical axis of the projection optical system 330. Position). The alignment detection system 350 is disposed in the vacuum atmosphere VC and the air atmosphere via a viewing window VW that separates the vacuum atmosphere VC and the air atmosphere. The imaging optical system 100 of the present invention can be applied to an optical system that constitutes the alignment detection system 350 and is disposed in the vacuum atmosphere VC. Thereby, the alignment detection system 350 can reduce the change in the optical performance of the optical system due to the environmental change, and can perform highly accurate detection. Note that the configuration in which the imaging optical system 100 is specifically applied to the alignment detection system 350 is the same as a focus position detection system described later, and thus detailed description thereof is omitted.

  The focus position detection system (second detection optical system) 360 measures the focus position in the Z direction on the surface of the object to be processed 340, and controls the position and angle of the wafer stage 345, so that the object to be processed is always during exposure. The 340 plane is maintained at the image formation position by the projection optical system 330. Similarly to the alignment detection system 350, the focus position detection system 360 is disposed in the vacuum atmosphere VC and the air atmosphere via the viewing window VW. The imaging optical system 100 of the present invention can be applied to the optical system that constitutes the focus position detection system 360. As a result, the optical system is assembled and adjusted in an air atmosphere and placed in the exposure apparatus 300. After that, the optical performance does not change even if the placed atmosphere changes to a vacuum atmosphere. Detection can be performed by optical performance.

  Here, a specific configuration in which the imaging optical system 100 of the present invention is applied to the focus position detection system 360 will be described. FIG. 8 is a schematic cross-sectional view showing the configuration of the focus position detection system 360. The focus position detection system 360 includes an LED light source 361, a mark 362, a projection unit 363, a detection unit 364, and a CCD 365. Note that the projection 363 and the detection unit 364 are arranged in a vacuum atmosphere VC.

  Referring to FIG. 8, the illumination light from the LED light source 361 illuminates the mark 362, and an image of the mark 362 is projected onto the object to be processed 340 via the projection unit 363. The reflected light from the object 340 is imaged on the CCD 365 via the detection unit 354. In the present embodiment, it is assumed that the imaging optical system 100 is applied to the detection unit 354. However, if the imaging magnification of the imaging optical system 100 is optimized, it can be applied to the projection unit 363.

  In exposure, the EUV light emitted from the illumination device 310 illuminates the mask 320 and forms an image of the pattern on the surface of the mask 320 on the surface of the object to be processed 340. In this embodiment, the image surface is an arc-shaped (ring-shaped) image surface, and the entire surface of the mask 320 is exposed by scanning the mask 320 and the object to be processed 340 at a speed ratio of the reduction ratio. In the exposure apparatus 300, the imaging optical system 100 is applied to the alignment detection system 350 and the focus position detection system 360, so that wafer alignment and focus position detection can be performed with an accuracy equivalent to that in the atmospheric air. As a result, the exposure apparatus 300 can provide a high-quality device (semiconductor element, LCD element, imaging element (CCD, etc.), thin film magnetic head, etc.) with high throughput and high economic efficiency.

  In the present embodiment, the alignment detection system 350 and the focus position detection system 360 are arranged in a vacuum atmosphere VC and an air atmosphere. However, as shown in FIG. 9, even if the entire alignment detection system 350 and focus position detection system 360 are arranged in a vacuum atmosphere VC, the same effect can be obtained. Here, FIG. 9 is a schematic cross-sectional view showing another configuration of the exposure apparatus 300 as one aspect of the present invention.

  Next, an embodiment of a device manufacturing method using the exposure apparatus 300 will be described with reference to FIGS. FIG. 10 is a flowchart for explaining how to fabricate devices (ie, semiconductor chips such as IC and LSI, LCDs, CCDs, and the like). Here, 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, the semiconductor device is completed and shipped (step 7).

  FIG. 11 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 300 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 repeating these steps, multiple circuit patterns are formed on the wafer. According to this device manufacturing method, it is possible to manufacture a higher quality device than before. Thus, the device manufacturing method using the exposure apparatus 300 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 applied not only to an EUV exposure apparatus but also to other optical systems used in a vacuum atmosphere.

It is a schematic sectional drawing which shows the structure of the imaging optical system as one side of this invention. It is a figure for demonstrating the change of the imaging position with respect to the environmental change of the imaging optical system shown in FIG. The optimization of the first focal length of the first lens group and the second focal length of the second lens group (the change in the imaging position due to the environmental change is set to a very small value (or 0)) will be described. It is a schematic sectional drawing which shows the optical system defined for it. 4 is a flowchart for explaining a method for designing an imaging optical system as one aspect of the present invention. It is a graph which shows the relationship between the focus ratio of the optical system (imaging optical system) shown in FIG. 3, and the focus position difference by an environmental change. It is a graph which shows the relationship between the refractive index difference of the optical system (imaging optical system) shown in FIG. 3, and the focus position difference by an environmental change. It is a schematic sectional drawing which shows the structure of the exposure apparatus as one side surface of this invention. It is a schematic sectional drawing which shows the structure of the focus position detection system of the exposure apparatus shown in FIG. It is a schematic sectional drawing which shows another structure of the exposure apparatus as one side surface of this invention. It is a flowchart for demonstrating manufacture of devices (semiconductor chips, such as IC and LSI, LCD, CCD, etc.). 11 is a detailed flowchart of the wafer process in Step 4 shown in FIG. 10. It is a figure for demonstrating the change of the imaging position with respect to the environmental change of an imaging optical system.

Explanation of symbols

100 imaging optical system 110 first lens group 110A convex lens 120 second lens group 120A concave lens OS object plane IS imaging plane 300 exposure apparatus 350 alignment detection system 360 focus position detection system 361 LED light source 362 mark 363 projection unit 364 detection Unit 365 CCD
VC vacuum atmosphere

Claims (10)

Imaging optics that has a first lens group having a first focal length f1 and a second lens group having a second focal length f2, and forms an image of an object plane pattern on the image plane A system design method,
In the case where the environment in which the imaging optical system is arranged changes from a vacuum atmosphere to an air atmosphere, or from an air atmosphere to a vacuum atmosphere,
The focus position difference Δd1 generated according to the ratio f1 / f2 between the first focal length f1 and the second focal length f2 is defined as Δd1 = a1 · (f1 / f2) + b1 with a1 and b1 as constants. Sometimes determining the constants a1 and b1;
When an allowable value of the focus position difference due to the environmental change is Δd _T1 , a ratio f1 / f2 between the first focal length f1 and the second focal length f2 is f1 / f2 = (Δd _T1− b1) / a1. And determining based on the design method. A first lens group having a first focal length f1 and made of a glass material having a first refractive index n1, and a second lens group having a second focal length f2 and made of a glass material having a second refractive index n2. And a lens group, and a design method of an imaging optical system that forms an image of an object plane pattern on the image plane,
In the case where the environment in which the imaging optical system is arranged changes from a vacuum atmosphere to an air atmosphere, or from an air atmosphere to a vacuum atmosphere,
When the focus position difference Δd2 generated according to the difference Δn between the first refractive index n1 and the second refractive index n2 is defined as Δd2 = a2 · Δn + b2 where a2 and b2 are constants, the constant a2 and determining b2;
The tolerance value of the focus position difference due to the environmental change is set to Δd _T2 , and the glass material having the first refractive index n1 and the glass material having the second refractive index n2 are determined based on Δn = (Δd _T2− b2) / a2. A design method comprising the steps of: An imaging optical system that forms an image of an object plane pattern on an image plane,
A first lens group having a first focal length f1,
A second lens group having a second focal length f2,
In the case where the environment in which the imaging optical system is arranged changes from a vacuum atmosphere to an air atmosphere, or from an air atmosphere to a vacuum atmosphere,
The focus position difference Δd1 generated according to the ratio f1 / f2 between the first focal length f1 and the second focal length f2 is defined as Δd1 = a1 · (f1 / f2) + b1 with a1 and b1 as constants. ,
The ratio f1 / f2 between the first focal length f1 and the second focal length f2 is f1 / f2 = (Δd _T1− b1) /, where Δd _T1 is an allowable focus position difference due to the environmental change. An imaging optical system that is determined based on a1. An imaging optical system that forms an image of an object plane pattern on an image plane,
A first lens group having a first focal length f1 and made of a glass material having a first refractive index n1,
Having a second focal length f2 and a second lens group made of a glass material having a second refractive index n2,
In the case where the environment in which the imaging optical system is arranged changes from a vacuum atmosphere to an air atmosphere, or from an air atmosphere to a vacuum atmosphere,
The focus position difference Δd2 generated according to the difference Δn between the first refractive index n1 and the second refractive index n2 is defined as Δd2 = a2 · Δn + b2 with a2 and b2 as constants,
The glass material having the first refractive index n1 and the glass material having the second refractive index n2 satisfies Δn = (Δd _T2− b2) / a2 where Δd _T2 is an allowable focus position difference due to the environmental change. Characteristic imaging optical system.   An imaging optical system designed by the design method according to claim 1. An exposure apparatus that illuminates a mask using light from a light source and exposes a pattern of the mask onto an object to be processed,
A detection optical system for detecting a focus position of the object to be processed;
6. The exposure apparatus according to claim 3, wherein the detection optical system includes the imaging optical system according to any one of claims 3 to 5. An exposure apparatus that illuminates a mask using light from a light source and exposes a pattern of the mask onto an object to be processed,
A detection optical system for detecting a relative position between the mask and the object to be processed;
6. The exposure apparatus according to claim 3, wherein the detection optical system includes the imaging optical system according to any one of claims 3 to 5. An exposure apparatus that illuminates a mask using light from a light source and exposes a pattern of the mask onto an object to be processed,
A first detection optical system for detecting a focus position of the object to be processed;
A second detection optical system for detecting a relative position between the mask and the object to be processed;
An exposure apparatus, wherein at least one of the first detection optical system and the second detection optical system includes the imaging optical system according to any one of claims 3 to 5.   The exposure apparatus according to claim 6, wherein the light is EUV light having a wavelength of 20 nm or less. Exposing the object to be processed using the exposure apparatus according to any one of claims 6 to 9,
And developing the exposed object to be processed.