JP3958261B2 - Optical system adjustment method - Google Patents

Description

  The present invention relates to an adjustment method and apparatus for adjusting an exposure apparatus that exposes an object to be processed such as a single crystal substrate for a semiconductor wafer and a glass substrate for a liquid crystal display (LCD). The present invention is particularly suitable for an exposure apparatus that performs exposure using ultraviolet rays or soft X-rays (EUV: extreme ultraviolet light) as an exposure light source.

  When manufacturing fine semiconductor elements such as semiconductor memories and logic circuits using photolithography technology, a circuit pattern formed on a mask (reticle) is projected onto a wafer or the like by a projection optical system. A reduction projection exposure apparatus for transferring is conventionally used.

  The minimum dimension (resolution) that can be transferred by the reduction 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, with the recent demand for miniaturization of semiconductor elements, the wavelength has been shortened, and an ultra-high pressure mercury lamp (i-line (wavelength: about 365 nm)), KrF excimer laser (wavelength: about 248 nm), ArF excimer laser (wavelength). The wavelength of the ultraviolet light used is about 193 nm.

  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 0.1 μm or less, a reduction projection optical system using soft X-rays (EUV light) having a wavelength shorter than that of ultraviolet light and a wavelength of about 10 nm to 15 nm. Has been developed (see, for example, Patent Document 1).

  In the wavelength region of EUV light, light absorption by a substance becomes very large. Therefore, a refraction type optical system using light refraction as used in visible light or ultraviolet light is not practical, and EUV light is used. In the exposure apparatus, a reflection type optical system using reflection of light is used. In this case, a reflective mask in which a pattern to be transferred by an absorber is formed on a reflecting mirror is also used.

  As a reflective optical element that constitutes an exposure apparatus using EUV light, a multilayer film reflector in which two types of substances having different optical constants are alternately stacked is used. For example, a molybdenum (Mo) layer and a silicon (Si: silicon) layer are alternately stacked on the surface of a glass substrate polished into a precise shape. For example, the thickness of the layer is about 2 nm for the molybdenum layer and about 5 nm for the silicon layer. In general, the sum of the thicknesses of two kinds of substances is called a film period, and in the above example, the film period is 7 nm.

  When EUV light is incident on such a multilayer mirror, EUV light having a specific wavelength is reflected. Assuming that the incident angle is θ, the wavelength of the EUV light is λ, and the film period is d, only EUV light having a narrow bandwidth centering on the wavelength λ satisfying the relationship of the following formula 1 is approximated. Reflected efficiently. The bandwidth at this time is about 0.6 nm to 1.0 nm.

  The reflectivity of the reflected EUV light is about 0.7 at maximum, and the EUV light that is not reflected is absorbed in the multilayer film or the substrate, and most of the energy becomes heat. Therefore, it is necessary to minimize the number of multilayer mirrors in order to increase the reflectivity of the entire optical system.

Therefore, the projection optical system used for EUV light is composed of about 4 to 6 multilayer reflectors, and the reflective surface of the multilayer reflector is a planar, convex or concave spherical or aspherical surface shape. Have
Japanese Patent Laid-Open No. 10-70058

  However, the surface shape of the multilayer mirror of the projection optical system is required to have very high accuracy. For example, if the number of multilayer film reflecting mirrors constituting the projection optical system is n and the wavelength of the EUV light is λ, the allowable shape error σ (rms value) is given by the Marechal equation shown in Equation 2.

  For example, when four multilayer mirrors constituting the projection optical system and the wavelength of EUV light are 13 nm, the shape error σ is 0.23 nm. When pattern transfer with a resolution of 30 nm is performed, the amount of wavefront aberration allowed for the entire projection optical system is about 0.4 nm.

  It is difficult to keep the shape error within the above tolerance by polishing, and even when the multilayer mirror is polished with sufficient accuracy, it occurs due to deformation due to its own weight or when combining multiple multilayer mirrors. Errors caused by alignment are inevitable. For example, “At Wavelength Testing L of B, L”, published by “2nd International Workshop on EUV Lithography Source Oct. 17-19”, “At Wavelength Testing of L. In addition, a wavefront aberration of about 1 nm remains throughout the entire projection optical system even after repeated alignment. In other words, the wavefront on the surface of the object to be processed (for example, a wafer) is calculated due to the surface shape error, alignment error of the multilayer mirror (substrate) that constitutes the projection optical system, and the self-weight deformation of the multilayer mirror. Deviation from the ideal wavefront determined by the above, so-called wavefront aberration. As a result, the imaging performance of the projection optical system cannot be fully exerted, and resolution and contrast are lowered, so that a fine pattern cannot be transferred.

  Accordingly, an object of the present invention is to provide an optical system adjustment method and apparatus, and an exposure apparatus that can stably transfer a fine pattern even when EUV light is used.

An adjustment method according to one aspect of the present invention is a method for adjusting an optical system that includes EUV light including a multilayer mirror on which a multilayer film is formed. The wavefront aberration of the optical system using the EUV light A first measurement step for measuring the wavefront aberration, a second measurement step for measuring the wavefront aberration of the optical system using light having a non-exposure wavelength different from the EUV light, and the first measurement step. Based on the removal condition determination step for determining a removal condition for removing a part of the multilayer film of the multilayer mirror so as to reduce the wavefront aberration, and the removal condition determined in the removal condition determination step, the multilayer A removal step of removing a part of the multilayer film of the film mirror, and a multilayer mirror from which a part of the multilayer film has been removed in the removal step is incorporated in the optical system, and the multilayer film among the multilayer film mirrors Excluding A measurement result of the wavefront aberration of the optical system by the second measurement step, and a third measurement step of measuring the wavefront aberration of the optical system using light of the non-exposure wavelength, An adjustment step of adjusting the optical system based on the measurement result of the wavefront aberration of the optical system in the third measurement step.

An optical system manufacturing method according to another aspect of the present invention is an optical system manufacturing method using EUV light, comprising: polishing a mirror substrate; and forming a multilayer film on the polished mirror substrate. Creating a multilayer mirror, assembling the optical system including the multilayer mirror, a first measurement step of measuring wavefront aberration of the optical system using the EUV light, and the EUV light The second measurement step of measuring the wavefront aberration of the optical system using light of different non-exposure wavelengths, and the multilayer mirror such that the wavefront aberration measured in the first measurement step is reduced. A removal condition determination step for determining a removal condition for removing a part of the multilayer film, and a removal for removing a part of the multilayer film of the multilayer mirror based on the removal condition determined in the removal condition determination step. The optical system in which a multilayer mirror from which a part of the multilayer film has been removed in the removal step and the removal step is incorporated in the optical system, and a region where the multilayer film is removed from the multilayer mirror is removed The measurement of the wavefront aberration of the optical system by using the light of the non-exposure wavelength, the measurement result of the wavefront aberration of the optical system by the second measurement step, and the optical by the third measurement step And an adjustment step for adjusting the optical system based on the measurement result of the wavefront aberration of the system .

According to still another aspect of the present invention, there is provided an exposure apparatus manufacturing method comprising: a projection optical system using EUV light, comprising: a step of polishing a mirror substrate; and a multilayer on the polished mirror substrate. Forming a multilayer mirror by forming a film; assembling the projection optical system including the multilayer mirror; and measuring a wavefront aberration of the projection optical system using the EUV light. The wavefront aberration measured in the measurement step, the second measurement step of measuring the wavefront aberration of the projection optical system using light having a non-exposure wavelength different from the EUV light, and the wavefront aberration measured in the first measurement step is reduced. Based on the removal condition determination step for determining a removal condition for removing a part of the multilayer film of the multilayer mirror, and the removal condition determined in the removal condition determination step, A removal step of removing a part of the multilayer film of the multilayer mirror, and a multilayer mirror from which a part of the multilayer film has been removed in the removal step is incorporated in the projection optical system, A third measurement step of measuring the wavefront aberration of the projection optical system using the light of the non-exposure wavelength, excluding the region where the multilayer film is removed, and the projection optical system according to the second measurement step. An adjustment step for adjusting the projection optical system based on a measurement result of the wavefront aberration and a measurement result of the wavefront aberration of the projection optical system in the third measurement step; and a step of incorporating the projection optical system in an exposure apparatus; , characterized in that it have a.

A device manufacturing method as still another aspect of the present invention includes a step of polishing a mirror substrate, a step of forming a multilayer film on the polished mirror substrate to create a multilayer mirror, and the multilayer mirror A step of assembling the projection optical system; a first measurement step of measuring wavefront aberration of the projection optical system using EUV light; and the projection optical system using light of a non-exposure wavelength different from the EUV light. A second measurement step for measuring the wavefront aberration of the system, and a removal condition for removing a part of the multilayer film of the multilayer mirror so as to reduce the wavefront aberration measured in the first measurement step. A removal condition determining step; a removal step of removing a part of the multilayer film of the multilayer mirror based on the removal condition determined in the removal condition determination step; and Measurement of the wavefront aberration of the projection optical system by incorporating a multilayer film mirror from which a part of the layer film has been removed into the projection optical system and excluding the area of the multilayer film from which the multilayer film has been removed. , A third measurement step using light of the non-exposure wavelength, a measurement result of the wavefront aberration of the projection optical system in the second measurement step, and a wavefront aberration of the projection optical system in the third measurement step An adjustment step of adjusting the projection optical system based on the measurement result of the step, a step of incorporating the projection optical system into an exposure apparatus, a step of exposing a workpiece using the exposure apparatus, and the exposed and having the steps of: performing a predetermined process to an object to be processed.

  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 adjustment method and apparatus of the present invention, the wavefront aberration is reduced by removing a part of the multilayer mirror based on the entire wavefront aberration generated in the optical system having the multilayer mirror, and the EUV light. It is possible to provide an optical system capable of stably transferring a fine pattern even in the case of using the above. Therefore, an exposure apparatus using such an optical system can provide a high-quality device with good exposure performance.

  Hereinafter, an optical system adjustment apparatus and adjustment method which are exemplary embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to these examples, and each constituent element may be alternatively substituted as long as the object of the present invention is achieved. Here, FIG. 2 is a schematic block diagram of the adjusting device 100 of the present invention.

  The adjusting device 100 adjusts an optical system having a multilayer mirror by using a coating milling technique. Coating Milling is a method for correcting the substrate surface shape of individual multilayer mirrors as “SUB-nm Figure Error Correction of a Multilayer Mirror by It's Surface Milling”. (Maki Yamamoto (2001) pp. 1282-1285). Hereinafter, coating milling will be described with reference to FIGS. 3 to 8.

  As shown in FIG. 3A, when the parallel light A having the same phase is incident on the multilayer mirror 300 in which the multilayer film 320 is uniformly formed on the flat mirror substrate 310, the phase shown in FIG. As shown, the reflected light B having a completely aligned phase (that is, a reflected wavefront) is obtained. However, as shown in FIG. 4A, when comparing with the wavefront B ′ of the reflected light from the portion 320a in which the number of layers of the multilayer film 320 is further different, as shown in FIG. A phase difference occurs in the wavefront B ′ of light. Here, FIG. 3 is a schematic diagram showing the relationship between incident light and reflected wavefront in a multilayer film having a uniform number of films, and FIG. 4 shows the relationship between incident light and reflected wavefront in a multilayer film having a different number of films. It is a schematic diagram.

  On the other hand, the reflectance of the multilayer mirror depends on the number of periods of the multilayer film. FIG. 5 shows the reflectance characteristics of the multilayer mirror. In this figure, the horizontal axis uses the number of periods of the multilayer film, and the vertical axis uses the reflectance normalized by the maximum value. Referring to FIG. 5, the reflectance increases greatly as the number of periods of the multilayer film increases up to about 40 layer pairs. However, the reflectance is almost saturated at 40 layer pairs or more. That is, after the reflectance is saturated, if a sufficient number of multilayer film cycles are stacked, for example, if about 60 pairs of layers are stacked, the phenomenon caused by the difference in the multilayer film cycle is only the difference in wavefront It is.

  In the following, a case will be considered in which when the EUV light of 13.5 nm is incident on the MoSi multilayer mirror at an incident angle of 10 °, the multilayer film on the top layer is used as the origin and the multilayer film is cut from the top layer. The amount by which the multilayer film is cut is called the removal amount. FIG. 6A is a graph of the removal amount and reflectance of the multilayer film when 13.5 nm EUV light is incident on the Mo / Si multilayer mirror at an incident angle of 10 °. The quantity graph is shown in FIG. In general, the Mo / Si multilayer mirror takes the influence of oxidation of Mo into consideration so that the Si layer is the uppermost layer. Therefore, in this embodiment, the calculation was performed with the Si layer as the uppermost layer. Referring to FIGS. 6A and 6B, it can be seen that the wavefront of the reflected light moves about 0.025 wavelength by removing one layer pair (6.99 nm) from the multilayer film. Moreover, the graph which converted the deviation | shift amount of the wave front into the deviation | shift of the spatial reflection position is shown in FIG.6 (c). Here, assuming that the wavelength of the incident light is λ and the wavefront deviation amount is W, the spatial reflection position deviation L is given by the following Equation 3.

  In the present embodiment, referring to FIG. 6C, removing one layer pair (6.99 nm) from the multilayer film is equivalent to moving the reflection position by about 0.2 nm. As can be seen from FIG. 6A, when the coating milling is performed, the reflectance and wavefront change greatly in the Mo layer compared to the Si layer due to the refractive index. As described above, if about 60 layers are stacked, the reflectance is saturated with respect to the cycle of the multilayer film. Therefore, if one cycle film thickness is removed, the reflectance does not change and only the wavefront changes.

  If the relationship described with reference to FIGS. 3 to 6 is used, correction of the substrate surface shape of the multilayer mirror to about 0.2 nm can be easily achieved by removing one pair (6.99 nm) of multilayer films. be able to.

  For example, consider the case of a multilayer mirror 400 in which a uniform multilayer film 420 is formed on a distorted mirror substrate 410 as shown in FIG. Since coating milling is a method of delaying the phase, coating milling is performed with the point A of the multilayer mirror 400 having the most delayed phase as the origin. As shown in FIG. 6, the wavefront changes little in the Si layer and the wavefront changes greatly in the Mo layer. However, as described above, the Mo layer is vulnerable to oxidation. For this reason, when a special coating is not used, it is not desirable to finish the coating milling in the middle of the Mo layer and continuously adjust the wavefront. Accordingly, as shown in FIG. 7B, the wave front is adjusted discontinuously by removing the layer of Mo and Si one by one. Since the Si layer is not easily oxidized and does not significantly affect the wavefront, the coating milling may be finished in the middle of the Si layer. As described above, when EUV light of 13.5 nm is incident at an incident angle of 10 °, a spatial reflection position, that is, a mirror, is obtained in increments of 0.2 nm by removing the multilayer film one layer at a time (6.99 nm). The shape error of the substrate can be corrected. Here, FIG. 7 is a schematic cross-sectional view of a multilayer mirror 400 in which a uniform multilayer film 420 is formed on a distorted mirror substrate 410, and FIG. 7A shows the multilayer film before coating milling. Mirror 400, FIG. 7 (b) shows the multilayer mirror 400 after coating milling.

  7A and 7B, the shape of the mirror substrate 410 at the point B has a shape error of 0.4 nm when viewed from the point A, and the point C has a shape error of 0.2 nm. In this case, the wavefront aberration due to the shape error of the mirror substrate 410 can be corrected by removing two pairs of the multilayer film 420 at the point B and further removing one pair of the multilayer film 420 at the point C.

  Similarly, for example, as shown in FIG. 8A, a case of a multilayer mirror 500 in which a uniform multilayer film 520 is formed on a mirror substrate 510 whose center F point is raised compared to the end E point. Think. Here, since the phase of point E of multilayer mirror 500 is relatively delayed, coating milling is performed with point E as the origin. Referring to FIGS. 8A and 8B, when the shape error of the mirror substrate 510 between the end E point and the center F point is about 0.4 nm and the distance between them continuously changes. Two layers of the multilayer film 520 at the center F point are removed. Furthermore, by removing one layer pair on both sides, wavefront aberration due to substrate shape error can be corrected. In any of the examples, it is preferable to stack a sufficient number of films for coating milling so that the reflectance does not decrease even when the number of multilayer films is decreased. Here, FIG. 8 is a schematic cross-sectional view of a multilayer mirror 500 in which a uniform multilayer film 520 is formed on the mirror substrate 510 whose center portion F is raised compared to the end E point. FIG. 8A shows the multilayer mirror 500 before coating milling, and FIG. 8B shows the multilayer mirror 500 after coating milling.

  The adjustment apparatus 100 includes a measurement unit 110, a removal unit 120, and a control unit 130, as well shown in FIG.

  The measurement unit 110 measures the wavefront aberration of the entire optical system, and is configured by, for example, a wavefront aberration measurement device (PDI: Point Diffraction Interferometer) such as a point diffraction interferometer. Hereinafter, PDI will be described based on an example in which the projection optical system of the exposure apparatus is an optical system. A pinhole is placed on the surface corresponding to the mask surface of the exposure apparatus, and spherical waves of light (soft X-rays, ultraviolet rays, visible light, infrared rays, etc.) are generated from the pinholes. The beam is divided into two by a diffraction grating located downstream of the pinhole, one of which passes through the projection optical system and is guided to the detector at the wafer surface position, and the other is guided to the detector as a reference wavefront.

  The wavefront aberration generated by the projection optical system is observed by causing the two wavefronts to interfere on the detector surface. With the above method, the observation of the wavefront aberration for a certain point on the wafer surface is completed. The position of the pinhole on the mask equivalent surface is moved to observe the wavefront aberration over the entire illumination area of the mask, and the entire wavefront aberration of the projection optical system is measured.

  The removing unit 120 removes a part of the multilayer film by, for example, sputtering or ion beam milling. In sputtering, accelerated ions are incident on the surface of the multilayer mirror (ie, the multilayer film), and atoms are stripped off to remove the multilayer film. In ion beam milling, an ion source is kept in a positive potential state, plasma is generated using an inert gas, inert gas ions are extracted from the ion source, and are irradiated to the multilayer mirror for etching.

  The control unit 130 is connected to the measurement unit 110 and the removal unit 120, and determines and determines the conditions for removing the multilayer film (that is, the removal region and the removal amount) based on the wavefront aberration measured by the measurement unit 110. The removal unit 120 is controlled to remove a part of the multilayer mirror according to the conditions. Further, the control unit 130 calculates the adjustment amount (that is, position and angle) of the multilayer mirror based on the wavefront aberration measured by the measurement unit 110.

  Hereinafter, with reference to FIG. 1, an adjustment method 1000 of the present invention using the above-described adjustment device 100 as the first embodiment will be described. FIG. 1 is a flowchart for explaining the adjustment method of the present invention. Here, the adjustment of the projection optical system of the exposure apparatus composed of a Mo / Si multilayer mirror will be described as an example.

  First, as shown by the Marechal equation, the surface accuracy of the mirror substrate of each Mo / Si multilayer mirror of the projection optical system is polished with sufficient accuracy (step 1002). Mo and Si are alternately laminated on a mirror substrate that has been polished with sufficient accuracy to form a multilayer film (step 1004). For example, a multilayer film having a Mo layer thickness of 2 nm and a Si layer thickness of about 5 nm is formed on all mirrors.

  Next, the multilayer mirror on which the multilayer film is formed is incorporated in the lens barrel of the projection optical system (step 1006). Then, the wavefront aberration through the projection optical system is measured on the wafer surface by the measurement unit 110 (step 1008). When such a projection optical system is used in the wavelength region of EUV light, wavefront aberration is measured using the same EUV light as the wavelength used.

  The measured aberration wavefront is compared with the allowable amount (step 1010), and when the wavefront aberration is within the allowable range, for example, when transferring with a resolution of 30 nm, if the wavelength is 0.4 nm or less, the assembling work into the lens barrel is completed. To do. If the wavefront aberration is more than the allowable amount, the number of adjustments of the mirror position is compared with the specified number of times (step 1012). If the number is within the specified number of times, the control unit 130 determines the mirror alignment adjustment amount (from the measured wavefront aberration result). That is, the mirror position and / or angle is calculated (step 1014). The control unit 130 may indicate a change in wavefront generated by rotation and movement of each mirror in advance as a change table, and use the change table.

  The control unit 130 performs mirror adjustment of the projection optical system based on the calculated alignment adjustment amount (step 1016). After performing the calculated amount of mirror adjustment, the wavefront aberration is measured by the measurement unit 110 (step 1008). If the wavefront aberration is less than the allowable value (step 1010), the assembling work is completed. If the wavefront aberration is greater than the allowable value (step 1010), the measurement unit 110 measures the wavefront aberration (step 1008) and adjusts the mirror (step 1016). Repeat the above steps. Alignment is performed so that wavefront aberration generated in the projection optical system is minimized. However, since it is difficult to remove all the wavefront aberrations caused by the surface shape error of the mirror substrate and the deflection due to the weight of the mirror by adjusting the mirror position, a predetermined number of times for adjusting the mirror position is determined.

  If the amount of wavefront aberration is equal to or greater than the allowable value even after the specified number of mirror position adjustments has been reached (step 1012), the above-described coating milling is performed.

  The wave aberration measured on the wafer surface by the measurement unit 110 is a wave aberration relating to the entire projection optical system. There is no need to perform coating milling for individual mirrors, and a predetermined mirror is selected and coating milling is performed on the mirror to correct wavefront aberration of the entire projection optical system. The predetermined mirror is not limited to one but may be a plurality. The controller 130 determines a condition (that is, a correction amount and a correction location) for removing a part of the multilayer film of the mirror from the measurement result of the wavefront aberration (step 1018). The mirror for coating milling is taken out from the lens barrel, and the multilayer film at a desired location is removed from the mirror by the removing unit 120 (step 1020).

  The mirror subjected to coating milling is incorporated into the lens barrel (step 1006), and the procedure from the measurement of wavefront aberration (step 1008) to the mirror adjustment (step 1016) by the measurement unit 110 is repeated. If the wavefront aberration does not fall below the allowable value, correction is further performed by coating milling, and the same steps are repeated.

  The procedure from Step 1008 to Step 1020 is repeated, and the adjustment of the optical system is completed when the wavefront aberration of the entire system becomes less than the allowable amount.

  After this, the wavefront aberration of the projection optical system is measured with light (ultraviolet light, visible light, infrared light) having a different wavelength from the exposure wavelength to obtain mirror information (information on the mirror angle and position). Based on the information, the projection optical system is incorporated into the exposure apparatus while measuring the wavefront aberration with a wavefront aberration measurement apparatus that uses light different from the exposure light mounted on the exposure apparatus itself described later, and the position and angle of the multilayer mirror are adjusted. You may do it.

  When measuring the wavefront aberration of a projection optical system using ultraviolet light, visible light, or infrared light, measure the wavefront of the area milled with those light (ultraviolet light, visible light, infrared light) after coating milling once. It is difficult. In the area where the coating milling is performed, a step is formed in the multilayer film, and when the wavefront is observed with ultraviolet rays, visible light, and infrared rays, the wavefront is observed to be greatly shifted, and is observed differently from the wavefront aberration of the EUV wavelength. Therefore, when wavefront aberration is measured by ultraviolet rays, visible light, and infrared rays, it is difficult to repeat the procedure from step 1006 to step 1020 and perform milling a plurality of times as described above.

  Therefore, the optical system may be adjusted by the following method, and the optical system adjustment process when the wavefront aberration is measured by the ultraviolet rays, visible light, and infrared rays will be described with reference to FIG. The procedure up to step 1016 is the same as the case where wavefront aberration is measured using the EUV light described with reference to FIG. 1, and in step 1008, optical wavefront aberration measurement at the exposure wavelength is performed.

  Also in FIG. 12, the coating milling described above is performed if the amount of wavefront aberration is equal to or greater than the allowable value even when the specified number of mirror position adjustments has been reached (step 1012). Here, before performing coating milling, the wavefront aberration measurement device using light other than the exposure wavelength is used to measure the wavefront of the optical system and acquire mirror information (information about the angle and position of the mirror). (Step 1017). In the subsequent steps 1020 and 1022, the mirror is taken out from the lens barrel, coating milling is performed, and it is incorporated into the lens barrel again at the end of the milling. In this case, the information is used to reproduce the mirror position and the like. Although an interferometer using light other than the exposure wavelength is used here, the present invention is not limited to this means as long as the position of the mirror can be reproduced. The light other than the exposure wavelength is, for example, ultraviolet light, visible light, or infrared light.

  The wavefront aberration is measured by the measurement unit 110, and the control unit 130 determines a condition for removing a part of the multilayer film of the mirror from the measurement result (step 1018). The mirror for coating milling is taken out from the lens barrel, and the multilayer film at a desired location is removed from the mirror by the removing unit 120 (step 1020).

  Further, a mirror is incorporated into the optical system (step 1022), and wavefront aberration is measured with light other than the exposure wavelength (step 1024). Here, the wavefront measured after the coating milling as described above is observed with a large deviation from the wavefront measured in step 1017.

  Therefore, the area subjected to coating milling is removed and the wavefront aberration is measured. As a method for removing the coating milling region, a mask for shielding light incident or reflected on the coating mirror milling region of the multilayer mirror may be provided, or coating milling is performed in the wavefront measurement data. The data corresponding to the wavefront from the region may be removed during data processing.

  The measured wavefront aberration is compared with an allowable value (step 1026), and if it is less than the allowable value, the adjustment of the optical system is completed. If it is greater than or equal to the allowable value, the number of adjustments of the mirror position is compared with the specified number (step 1028). If it is within the specified number of times, the alignment adjustment (steps 1022 to 1032) is repeated. The allowable value is determined based on the mirror information obtained in step 1017.

  If the amount of wavefront aberration is equal to or greater than the allowable value even after the specified number of mirror position adjustments has been reached (step 1028), the procedure from the optical element polishing (1002) is performed again.

  By using such an adjustment method, a projection optical system in which wavefront aberration is corrected is realized.

  In Examples 1 and 2, wavefront aberration measurement was performed at the exposure wavelength, that is, EUV light in Step 1008. Wavefront measurement at the exposure wavelength may require a large facility such as a synchroton light source. However, if the relationship between the wavefront measured by light other than the exposure wavelength (ultraviolet light, visible light, infrared light, etc.) and the wavefront measured at the exposure wavelength is known, only wavefront measurement using light other than the exposure wavelength Thus, information on the wavefront in the case of the exposure wavelength can be obtained, and such a large facility is not required.

  The relationship between the wavefront measured by light other than the exposure wavelength and the wavefront measured at the exposure wavelength can be obtained by simulation or the like. For example, an optical system having ideal imaging performance with EUV light is assumed. Next, in the optical system, wavefront aberrations on the image plane when using visible light are calculated by simulation. Then, by taking the sum of squares of the difference between the wavefront aberration actually measured using visible light and the wavefront aberration in the above simulation, the wavefront aberration when converted to EUV light is minimized. Reduced.

  Further, a conversion formula from wavefront aberration measured using light other than the exposure wavelength to wavefront aberration measured at the exposure wavelength may be obtained experimentally. For example, a reference lens barrel is prepared, wavefront aberration is measured using EUV light, and the wavefront aberration is reduced to an accuracy sufficient for exposure. Next, for example, the wavefront aberration of the lens barrel serving as a reference is measured using visible light. The wavefront aberration on the EUV and visible light imaging plane is developed into a Zernike polynomial, and the difference is obtained.

  During adjustment, the wavefront aberration is measured with visible light, the wavefront aberration is developed into a Zernike polynomial, and a known difference is added to obtain the wavefront aberration with EUV light.

  In any case, the wavefront information at the exposure wavelength can be obtained from the wavefront measurement using light (ultraviolet light, visible light, infrared light, etc.) other than the exposure wavelength.

  FIG. 14 shows an optical system adjustment process in the third embodiment. The procedure up to assembly of the optical system in step 1006 is the same as the adjustment process in the first embodiment and the modification. The wavefront measurement in step 1008 is performed with light other than the exposure wavelength. In step 1009, the measured wavefront is converted into a wavefront measured at the exposure wavelength by the method described above. Adjustment is performed so that the converted wavefront aberration amount is equal to or less than an allowable value.

  The following adjustment process is the same as the adjustment process in the first embodiment shown in FIG. 12, but the wavefront measurement step 1017 other than the exposure wavelength in FIG. 14 can be replaced by the wavefront measurement in step 1008 in FIG. So you can omit it.

  In the present embodiment, once the relationship between the wavefront aberration between visible light and EUV light is obtained, an optical system in which the wavefront aberration of EUV light is reduced can be obtained only by measuring the wavefront with visible light. Therefore, a large-scale facility such as a synchrotron light source is not required at the time of production, and an exposure apparatus having high imaging performance can be realized with only a simple apparatus.

  In the above first to third embodiments, the wavefront aberration measurement (steps 1008 and 1024) for the optical system assembly (steps 1006 and 1022) is performed by the adjustment device 100. However, in that case, after the projection optical system is finally adjusted by the adjustment apparatus 100, a process of incorporating the projection optical system into the exposure apparatus becomes necessary. Accordingly, at that time, aberration may occur in the projection optical system.

  Therefore, the above-described PDI may be mounted on the exposure apparatus itself to execute optical system assembly and wavefront aberration measurement.

  In this case, a specific method for measuring wavefront aberration will be described with reference to the exposure apparatus 700 in FIG.

  First, a mirror is incorporated in the projection optical system 730 of the exposure apparatus (step 1006, step 1022).

  Next, the wafer stage 745 and the mask stage 725 are driven, and the PS / PDI mask 778 on the wafer stage and the pinhole 776 on the mask stage are arranged in the exposure region. Each corresponds to one point of the mask position and wafer position during exposure.

  Then, the light from the light source 770 that generates light (ultraviolet light, visible light, infrared light, etc.) having a wavelength different from that of the exposure light is guided to the pinhole 776 provided in the mask stage 725 by the fiber 772, and a spherical wave is generated from the pinhole. Let Further, the spherical wave is divided into two by a diffraction grating 774 mounted on a grating stage (not shown), and detection means (through a projection optical system 730 and a PS / PDI mask 780 shown in FIG. The wavefront aberration of the projection optical system 730 can be measured on the exposure apparatus by detecting each of the divided lights with a CCD or the like) (steps 1008 and 1024). Here, FIG. 13 is a view showing a PS / PDI mask 780 provided on the wafer stage 745, and reference numeral 781 denotes an opening. Even when EUV light is used to measure wavefront aberration for coating milling, wavefront aberration measurement using light other than the exposure wavelength mounted in the exposure apparatus in this way for subsequent optical system assembly and wavefront aberration measurement It can be performed by the device.

  When measuring the wavefront aberration using the exposure light (step 1008 in FIGS. 1 and 12), a pinhole plate is placed on the mask stage instead of the mask 720, and the wavefront aberration is measured in the same manner. It is possible.

  Hereinafter, an exemplary exposure apparatus 700 of the present invention will be described with reference to FIG. Here, FIG. 9 is a schematic block diagram of an exemplary exposure apparatus 700 of the present invention. The exposure apparatus 200 of the present invention is a projection exposure apparatus that performs step-and-scan exposure using EUV light (for example, wavelength 13.4 nm) as exposure illumination light.

  Referring to FIG. 9, an exposure apparatus 700 includes an illumination apparatus 710, a mask (reticle) 720, a mask stage 725 on which the mask 720 is placed, a projection optical system 730, an object to be processed 740, and an object to be processed. A wafer stage 745 on which W is placed, an alignment detection mechanism 750, and a focus position detection mechanism 760 are provided.

  Further, as shown in FIG. 9, since EUV light has a low transmittance to the atmosphere, it is preferable that at least an optical path through which the EUV light passes is a vacuum atmosphere A.

  The illumination device 710 is an illumination device that illuminates the mask 720 with an arc-shaped EUV light (for example, a wavelength of 13.4 nm) corresponding to the arc-shaped field of view of the projection optical system 730. The illumination device 710 includes an EUV light source 712 and an illumination optical system. 714.

  As the EUV light source 712, 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 rate of several kHz.

  The illumination optical system 714 includes a condenser mirror, an optical integrator, and the like. The collector mirror serves to collect EUV light emitted from the laser plasma almost isotropically. The optical integrator has a role of uniformly illuminating the mask with a predetermined numerical aperture. In addition, an aperture for limiting the illumination area of the mask to an arc shape is provided.

  The mask 720 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 725. The diffracted light emitted from the mask 720 is reflected by the projection optical system 730 and projected onto the object to be processed 740. The mask 720 and the object to be processed 740 are arranged in an optically conjugate relationship. Since the exposure apparatus 700 is a step-and-scan exposure apparatus, the pattern of the mask 720 is reduced and projected onto the object 740 by scanning the mask 720 and the object 740.

  The mask stage 725 supports the mask 720 and is connected to a moving mechanism (not shown). Any configuration known in the art can be applied to the mask stage 725. A moving mechanism (not shown) is constituted by a linear motor or the like, and can move the mask 720 by driving the mask stage at least in the X direction. The exposure apparatus 700 scans the mask 720 and the workpiece 740 in a synchronized state. Here, the scanning direction in the mask 720 or the object to be processed 740 is X, the direction perpendicular to the scanning direction is Y, and the direction perpendicular to the mask 720 or the object to be processed 740 is Z.

  The projection optical system 730 uses a plurality of reflection mirrors (that is, multilayer mirrors) to reduce and project the pattern on the mask 720 onto the image plane. The number of mirrors is about 4 to 6. In order to realize a wide exposure area with a small number of mirrors, the mask 720 and the object to be processed 740 are simultaneously scanned using only a thin arc-shaped area (ring field) separated from the optical axis by a wide distance. Transfer the area. The numerical aperture NA of the projection optical system 730 is about 0.1 to 0.3. The adjustment apparatus 100 and the adjustment method 1000 of the present invention described above can be applied to the adjustment of the multilayer mirror that constitutes the projection optical system 730, the wavefront aberration is reduced, and excellent imaging performance is exhibited.

  The object to be processed 740 is a wafer in this embodiment, but widely includes spherical semiconductors, liquid crystal substrates, and other objects to be processed. A photoresist is applied to the object to be processed 740. The photoresist coating process includes a pretreatment, an adhesion improver coating process, a photoresist coating process, and a prebaking process. Pretreatment includes washing, drying and the like. The adhesion improver coating process is a surface modification process for improving the adhesion between the photoresist and the base (that is, a hydrophobic process by application of a surfactant), and an organic film such as HMDS (Hexmethyl-disilazane) is used. Coat or steam. Pre-baking is a baking (baking) step, but is softer than that after development, and removes the solvent.

  Wafer stage 745 supports object 740 to be processed by a wafer chuck. For example, the wafer stage 745 moves the object 740 in the XYZ directions using a linear motor. The mask 720 and the object 740 are scanned synchronously. Further, the positions of the mask stage 725 and the wafer stage 745 are monitored by a laser interferometer, for example, and both are driven at a constant speed ratio.

The alignment detection mechanism 750 measures the positional relationship between the position of the mask 720 and the optical axis of the projection optical system 730 , and the positional relationship between the position of the object 740 and the optical axis of the projection optical system 730 , and the projected image of the mask 720. The positions and angles of the mask stage 725 and the wafer stage 745 are set so as to coincide with a predetermined position of the object 740 to be processed.

  The focus position detection mechanism 760 measures the focus position in the Z direction on the surface of the object to be processed 740 and controls the position and angle of the wafer stage 745 so that the surface of the object to be processed 740 is always projected onto the projection optical system 730 during exposure. Keep the imaging position by.

  In exposure, the EUV light emitted from the illumination device 710 illuminates the mask 720 and forms an image of the pattern on the mask 720 surface on the surface of the object to be processed 740. In this embodiment, the image plane is an arc-shaped (ring-shaped) image plane, and the entire surface of the mask 720 is exposed by scanning the mask 720 and the object 740 at a speed ratio of the reduction ratio.

  Next, an embodiment of a device manufacturing method using the above-described exposure apparatus 700 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, a 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 700 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.

  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 to an optical system having a multilayer mirror and other optical elements (lens, diffraction grating, etc.). Further, for example, the present invention can be applied to a projection optical system for ultraviolet rays having a wavelength of 200 nm or less, such as an ArF excimer laser or F2 laser, and an exposure apparatus that performs exposure without scanning even an exposure apparatus that scans and exposes a large screen. It is also applicable to.

It is a flowchart for demonstrating the adjustment method of this invention. It is a schematic block diagram of the adjustment apparatus of this invention. It is sectional drawing which shows typically the relationship between the incident light and reflected wavefront in the multilayer film with a uniform film number. It is sectional drawing which shows typically the relationship between the incident light and reflected wavefront in the multilayer film from which a film number differs one layer. It is a graph which shows the reflectance characteristic of a multilayer film mirror. It is a graph which shows the effect at the time of removing a part of multilayer film of a multilayer film mirror. FIG. 3 is a schematic cross-sectional view of a multilayer mirror in which a uniform multilayer film is formed on a distorted mirror substrate. FIG. 5 is a schematic cross-sectional view of a multilayer mirror in which a uniform multilayer film is formed on a mirror substrate whose center is raised compared to an end. It is a schematic sectional drawing which shows the structure of the exemplary exposure apparatus of this invention. It is a flowchart for demonstrating the device manufacturing method which has the exposure apparatus of this invention. 11 is a detailed flowchart of the wafer process in Step 4 shown in FIG. 10. It is a flowchart for demonstrating the adjustment method of this invention. It is a schematic plan view showing a PS / PDI mask. It is a flowchart for demonstrating the adjustment method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Adjustment apparatus 110 Measuring part 120 Removal part 130 Control part 700 Exposure apparatus 710 Illumination apparatus 720 Mask 730 Projection optical system 740 Object 750 Alignment detection mechanism 760 Focus position detection mechanism

Claims (10)

A method of adjusting an optical system that includes EUV light including a multilayer mirror on which a multilayer film is formed,
A first measurement step of measuring the wavefront aberration of the optical system using the EUV light;
A second measurement step of measuring the wavefront aberration of the optical system using light of a non-exposure wavelength different from the EUV light;
A removal condition determining step for determining a removal condition for removing a part of the multilayer film of the multilayer mirror such that the wavefront aberration measured in the first measurement step is reduced;
Based on the removal condition determined in the removal condition determination step, a removal step of removing a part of the multilayer film of the multilayer mirror;
Incorporating a multilayer mirror from which a part of the multilayer film has been removed in the removal step into the optical system, and removing a region of the multilayer mirror from which the multilayer film has been removed, the wavefront aberration of the optical system A third measurement step in which measurement is performed using light of the non-exposure wavelength;
An adjustment step for adjusting the optical system based on the measurement result of the wavefront aberration of the optical system in the second measurement step and the measurement result of the wavefront aberration of the optical system in the third measurement step. An adjustment method characterized by.   The adjustment method according to claim 1, wherein the condition is a removal region for removing a part of the multilayer film of the multilayer mirror.   3. The adjustment method according to claim 1, wherein the condition is a removal amount for removing a part of the multilayer film of the multilayer mirror.   4. The adjustment method according to claim 1, wherein, in the second and third measurement steps, the wavefront aberration of the optical system is measured by visible light or infrared light. 5.   5. The adjustment method according to claim 1, wherein, in the third measurement step, light incident on a region of the multilayer mirror from which the multilayer film has been removed is shielded. 6.   6. The adjustment method according to claim 1, wherein, in the third measurement step, light reflected from a region of the multilayer mirror from which the multilayer film has been removed is shielded.   The data corresponding to the wavefront of the region of the multilayer mirror from which the multilayer film has been removed is removed from the data obtained by measuring the wavefront aberration of the optical system in the third measurement step. The adjustment method as described in any one of thru | or 6. A method for manufacturing an optical system using EUV light,
Polishing the mirror substrate;
Forming a multilayer film on the polished mirror substrate to form a multilayer mirror;
Assembling the optical system including the multilayer mirror;
A first measurement step of measuring the wavefront aberration of the optical system using the EUV light;
A second measurement step of measuring the wavefront aberration of the optical system using light having a non-exposure wavelength different from the EUV light;
A removal condition determining step for determining a removal condition for removing a part of the multilayer film of the multilayer mirror such that the wavefront aberration measured in the first measurement step is reduced;
Based on the removal condition determined in the removal condition determination step, a removal step of removing a part of the multilayer film of the multilayer mirror;
Incorporating a multilayer mirror from which a part of the multilayer film has been removed in the removal step into the optical system, and removing a region of the multilayer mirror from which the multilayer film has been removed, the wavefront aberration of the optical system A third measurement step in which measurement is performed using light of the non-exposure wavelength;
An adjustment step for adjusting the optical system based on the measurement result of the wavefront aberration of the optical system in the second measurement step and the measurement result of the wavefront aberration of the optical system in the third measurement step. An optical system manufacturing method characterized by the above. A method for manufacturing an exposure apparatus including a projection optical system using EUV light,
Polishing the mirror substrate;
Forming a multilayer film on the polished mirror substrate to form a multilayer mirror;
Assembling the projection optical system including the multilayer mirror;
A first measurement step of measuring the wavefront aberration of the projection optical system using the EUV light;
A second measurement step of measuring wavefront aberration of the projection optical system using light having a non-exposure wavelength different from the EUV light;
A removal condition determining step for determining a removal condition for removing a part of the multilayer film of the multilayer mirror such that the wavefront aberration measured in the first measurement step is reduced;
Based on the removal condition determined in the removal condition determination step, a removal step of removing a part of the multilayer film of the multilayer mirror;
A wavefront of the projection optical system in which a multilayer mirror from which a part of the multilayer film has been removed in the removing step is incorporated in the projection optical system, and a region where the multilayer film is removed from the multilayer mirror is removed. A third measurement step of measuring aberration using light of the non-exposure wavelength;
An adjustment step for adjusting the projection optical system based on the measurement result of the wavefront aberration of the projection optical system in the second measurement step and the measurement result of the wavefront aberration of the projection optical system in the third measurement step; ,
Incorporating the projection optical system into an exposure apparatus;
Manufacturing method for an exposure apparatus, characterized by have a. A device manufacturing method comprising:
Polishing the mirror substrate;
Forming a multilayer film on the polished mirror substrate to form a multilayer mirror;
Assembling the projection optical system including the multilayer mirror;
A first measurement step of measuring the wavefront aberration of the projection optical system using EUV light;
A second measurement step of measuring wavefront aberration of the projection optical system using light having a non-exposure wavelength different from the EUV light;
A removal condition determining step for determining a removal condition for removing a part of the multilayer film of the multilayer mirror such that the wavefront aberration measured in the first measurement step is reduced;
Based on the removal condition determined in the removal condition determination step, a removal step of removing a part of the multilayer film of the multilayer mirror;
A wavefront of the projection optical system in which a multilayer mirror from which a part of the multilayer film has been removed in the removing step is incorporated in the projection optical system, and a region where the multilayer film is removed from the multilayer mirror is removed. A third measurement step of measuring aberration using light of the non-exposure wavelength;
An adjustment step for adjusting the projection optical system based on the measurement result of the wavefront aberration of the projection optical system in the second measurement step and the measurement result of the wavefront aberration of the projection optical system in the third measurement step; ,
Incorporating the projection optical system into an exposure apparatus;
Comprising the steps of exposing an object using the exposure apparatus,
Device manufacturing method characterized by having a step of performing a predetermined process on the target object that has been exposed.

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