JP2004080021A - Method and apparatus for adjusting optical system, exposure apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adjustment method and apparatus of an optical system capable of transferring a fine pattern stably even when EUV light is used, and an exposure apparatus.
A method of adjusting an optical system having a multilayer mirror, comprising: a first measurement step of measuring wavefront aberration of the optical system using light having a wavelength used by the optical system; A second measurement step of measuring the wavefront aberration of the optical system using light of different wavelengths, and a step of removing a part of a multilayer film of a multilayer mirror based on the first measurement result; Adjusting the multilayer mirror based on the second measurement result after the removing step.
[Selection diagram] FIG.

Description

The present invention relates to an adjustment method and apparatus for adjusting an exposure apparatus for exposing 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 light or soft X-rays (EUV: extreme @ ultraviolet) as an exposure light source.

When manufacturing microscopic semiconductor devices such as semiconductor memories and logic circuits using photolithography (baking) technology, the circuit pattern formed on a mask (reticle) is projected onto a wafer or the like by a projection optical system to form the circuit pattern. 2. Related Art A reduction projection exposure apparatus for transferring has been 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)), a KrF excimer laser (wavelength: about 248 nm), an ArF excimer laser (wavelength: (Approximately 193 nm) and the wavelength of the ultraviolet light used 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 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 having a wavelength of about 10 nm to 15 nm. Has been developed (for example, see Patent Document 1).

In the wavelength region of EUV light, the absorption of light by a substance becomes extremely large, so that a refraction type optical system using refraction of light such as that used in visible light or ultraviolet light is not practical, and EUV light is used. In the exposure apparatus, a reflection type optical system utilizing light reflection 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 used as the mask.

(4) As a reflection type optical element constituting an exposure apparatus using EUV light, a multilayer film reflection mirror in which two kinds of substances having different optical constants are alternately laminated 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 to a precise shape. As for the thickness of such a layer, for example, the thickness of the molybdenum layer is about 2 nm, and the thickness of the silicon layer is about 5 nm. In general, the sum of the thicknesses of the layers of the two kinds of substances is called a film period, and in the above example, the film period is 7 nm.

(4) When EUV light is incident on such a multilayer reflector, EUV light of 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, approximately only EUV light having a narrow bandwidth centered on the wavelength λ that satisfies the relationship of the following formula 1 is approximately obtained. It is reflected efficiently. The bandwidth at this time is about 0.6 nm to 1.0 nm.

(4) The reflectance of the reflected EUV light is about 0.7 at the 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 four to six multilayer film reflecting mirrors, and the reflecting surface of the multilayer film reflecting mirror has a flat, convex or concave spherical or aspherical surface shape. Having.
JP-A-10-70058

However, the surface shape of the multilayer reflector in the projection optical system is required to be very high precision. For example, assuming that the number of multilayer mirrors constituting the projection optical system is n and the wavelength of EUV light is λ, an allowable shape error σ (rms value) is given by the Marechal equation shown in Equation 2.

For example, when the projection optical system has four multilayer film reflecting mirrors and the wavelength of EUV light is 13 nm, the shape error σ is 0.23 nm. When performing pattern transfer with a resolution of 30 nm, the amount of wavefront aberration allowed in 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 if the multilayer reflector is polished with sufficient accuracy, it may be deformed by its own weight or when combining multiple multilayer reflectors. Errors due to misalignment are inevitable. For example, "2nd International Workshop on EUV Lithography Source October 17-19" was published in "At Wavelength Testing of an EUVL Four Mirror Ring Field System" (Goldberg, et al, LLBL, UC Berkeley, LLNL) to see the contents of the Even after the repeated alignment, a wavefront aberration of about 1 nm remains throughout the entire projection optical system. That is, the wavefront on the surface of the object to be processed (for example, a wafer or the like) is calculated due to a surface shape error of the multilayer mirror (substrate) constituting the projection optical system, an alignment error, and the own-weight deformation of the multilayer mirror. Has a so-called wavefront aberration. As a result, the imaging performance of the projection optical system cannot be sufficiently exhibited, and the resolution and the contrast are lowered, so that a fine pattern cannot be transferred.

Accordingly, it is an exemplary object of the present invention to provide a method and an apparatus for adjusting an optical system and an exposure apparatus capable of stably transferring a fine pattern even when EUV light is used.

In order to achieve the above object, an adjustment method according to one aspect of the present invention is an adjustment method of an optical system having a multilayer mirror, wherein light having a wavelength used by the optical system is used to adjust a wavefront of the optical system. A first measurement step of measuring aberration, a second measurement step of measuring wavefront aberration of the optical system using light having a wavelength different from the used wavelength, and a multi-layer based on the first measurement result. The method includes a step of removing a part of the multilayer film of the film mirror, and a step of adjusting the multilayer film mirror based on the second measurement result after the removing step.

An adjustment method according to another aspect of the present invention is an adjustment method for an optical system having a multilayer mirror, wherein the step of adjusting the multilayer mirror and the step of obtaining information of the multilayer mirror after the adjusting step are performed. And removing a part of the multilayer film of the multilayer mirror so as to reduce the wavefront aberration of the optical system at the used wavelength, and after the removing step, based on the information, the multilayer film Adjusting the mirror.

An adjustment method according to still another aspect of the present invention is an adjustment method for an optical system having a multilayer mirror, wherein the wavefront aberration of the optical system is measured using light having a wavelength different from the wavelength used by the optical system. And a step of removing a part of the multilayer film of the multilayer mirror based on the wavefront aberration measured in the measurement step.

An adjusting device according to still another aspect of the present invention is an adjusting device for an optical system having a multilayer mirror, wherein the wavefront aberration of the optical system is measured using light having a wavelength different from the wavelength used by the optical system. A measuring unit, a removing unit that removes a part of the multilayer film of the multilayer mirror, and a part of the multilayer film of the multilayer mirror based on the wavefront aberration measured by the measuring unit. A control unit for controlling the removal unit.

光学 An optical system according to still another aspect of the present invention is characterized in that the optical system is adjusted using the above-described adjustment method.

露 光 An exposure apparatus as still another aspect of the present invention includes the above-described adjustment apparatus.

露 光 An exposure apparatus according to still another aspect of the present invention is characterized in that light from a light source is guided to a target object through the above-described optical system to expose the target object.

An exposure apparatus as still another aspect of the present invention is an exposure apparatus having an illumination optical system for illuminating a mask with light from a light source, and a projection optical system for projecting a pattern of the mask onto an object to be processed. It is characterized in that it has a measuring unit for measuring the wavefront aberration of the projection optical system having a multilayer mirror using light having a wavelength different from the wavelength of the exposure light.

A device manufacturing method according to still another aspect of the present invention includes a step of exposing an object to be processed using the above-described exposure apparatus, and a step of performing a predetermined process on the exposed object to be processed. And

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

ADVANTAGE OF THE INVENTION According to the adjustment method and apparatus of this invention, based on the wavefront aberration of the whole system which arises in the optical system which has a multilayer mirror, wavefront aberration is reduced by removing a part of such multilayer mirror, and EUV light It is possible to provide an optical system capable of stably transferring a fine pattern even when the optical system is used. 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 an adjustment method according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to these embodiments, and each component may be replaced 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.

Adjusting device 100 adjusts an optical system having a multilayer mirror using a coating milling technique. Coating milling is a method of correcting the substrate surface shape of each multilayer film mirror, as described in "SUB-nm {Figure} Correction \ of \ a \ Multilayer \ mirror \ by \ Its \ Surface \ M \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\. (2001) pp. 1282-1285). Hereinafter, the coating milling will be described with reference to FIGS.

As shown in FIG. 3A, when parallel light A having a uniform phase is incident on a multilayer mirror 300 in which a multilayer film 320 is uniformly formed on a flat mirror substrate 310, the light becomes as shown in FIG. As shown in the figure, reflected light B having a completely uniform phase (that is, a uniform 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 different from that of the multilayer film 320, 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 a reflected wavefront in a multilayer film having a uniform number of films, and FIG. 4 shows the relationship between incident light and a reflected wavefront in a multilayer film having a different number of films. It is a schematic diagram.

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

Hereinafter, a case will be considered in which, when EUV light of 13.5 nm is incident on the MoSi multilayer film mirror at an incident angle of 10 °, the multilayer film of the uppermost layer is set as the origin and the multilayer film is cut from the uppermost layer. The removal amount of the multilayer film is referred to as a removal amount. FIG. 6A is a graph of the removal amount of the multilayer film and the reflectance when the EUV light of 13.5 nm is incident on the Mo / Si multilayer film mirror at an incident angle of 10 °. A graph of the amount is shown in FIG. In general, in the Mo / Si multilayer mirror, the calculation was performed with the Si layer as the uppermost layer also in the present embodiment in order to consider the influence of Mo oxidation in order to make the Si layer the uppermost layer. Referring to FIG. 6A and FIG. 6B, it can be seen that the wavefront of the reflected light moves by about 0.025 wavelength by removing one layer pair (6.99 nm) of the multilayer film. FIG. 6C shows a graph in which the shift amount of the wavefront is converted into the shift of the spatial reflection position. Here, assuming that the wavelength of the incident light is λ and the shift amount of the wavefront is W, the shift L of the spatial reflection position is given by the following Equation 3.

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

Using the relationship described with reference to FIGS. 3 to 6, the correction of the substrate surface shape of the multilayer mirror by about 0.2 nm can be easily achieved by removing one pair (6.99 nm) of the multilayer film. 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 the coating milling is a method of delaying the phase, the 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 change in the wavefront is small in the Si layer, and the wavefront changes largely in the Mo layer, but the Mo layer is vulnerable to oxidation as described above. Therefore, when no special coating is performed, it is not desirable to continuously adjust the wavefront after finishing the coating milling in the middle of the Mo layer. Therefore, as shown in FIG. 7B, the layer in which Mo and Si are combined is removed one by one to adjust the wavefront discontinuously. Since the Si layer is hardly oxidized and does not significantly affect the wavefront, the coating milling may be completed 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 °, the multilayer film is removed by one layer pair (6.99 nm), and the spatial reflection position, that is, the mirror, is removed at intervals of 0.2 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 a multilayer film before coating milling is performed. Mirror 400, FIG. 7 (b), shows multilayer mirror 400 after coating milling.

Referring to FIGS. 7A and 7B, the shape of the mirror substrate 410 at the point B has a shape error of 0.4 nm as viewed from the point A, and the shape of the point C has a shape error of 0.2 nm. In this case, the wavefront aberration caused by the shape error of the mirror substrate 410 can be corrected by removing the pair of multilayer films 420 at the point B and removing the pair of multilayer films 420 at the point C.

Similarly, for example, as shown in FIG. 8A, the case of a multilayer mirror 500 in which a uniform multilayer film 520 is formed on a mirror substrate 510 in which a point F at the center is raised from a point E at the end. Think. Here, since the phase of point E of the multilayer mirror 500 is relatively late, coating milling is performed with the point E as the origin. Referring to FIG. 8A and FIG. 8B, when the shape error of the mirror substrate 510 between the end point E and the center point F is about 0.4 nm and the distance between the points changes continuously. The two layers of the multilayer film 520 at the central point F are removed. Furthermore, by removing one layer pair on both sides, the wavefront aberration caused by the shape error of the substrate can be corrected. In any case, in order to perform coating milling, it is preferable to stack a sufficient number of films so that the reflectance does not decrease even if the number of multilayer films is reduced. Here, FIG. 8 is a schematic cross-sectional view of a multilayer mirror 500 in which a uniform multilayer film 520 is formed on a mirror substrate 510 in which a central point F is raised as compared with an 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 device 100 includes a measurement unit 110, a removal unit 120, and a control unit 130, as is often shown in FIG.

The measurement unit 110 measures the entire wavefront aberration of the 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 a surface corresponding to a mask surface of an exposure apparatus, and a spherical wave of light (soft X-ray, ultraviolet light, visible light, infrared light, or the like) is generated from the pinhole. The beam is split into two by a diffraction grating located downstream of the pinhole, one of which is passed through a projection optical system and guided to a detector at a wafer surface position, and the other is guided to a detector as a reference wavefront.

波 Observe the wavefront aberration caused by the projection optical system by making the two wavefronts interfere on the detector surface. With the above method, the observation of the wavefront aberration at a certain point on the wafer surface ends. 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 wavefront aberration of the entire projection optical system is measured.

The removing unit 120 removes a part of the multilayer film by, for example, sputtering or ion beam milling. Sputtering removes the multilayer film by causing accelerated ions to enter the surface of the multilayer mirror (ie, the multilayer film) and strip off the atoms. In ion beam milling, an ion source is maintained at a positive potential, plasma is generated using an inert gas, and inert gas ions are extracted from the ion source and irradiated to a multilayer mirror to perform 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 area and the removal amount) based on the wavefront aberration measured by the measurement unit 110. The removing unit 120 is controlled to remove a part of the multilayer mirror according to the conditions. Further, the control unit 130 calculates an adjustment amount (that is, a position and an angle) of the multilayer mirror based on the wavefront aberration measured by the measurement unit 110.

Hereinafter, an adjusting method 1000 of the present invention using the above-described adjusting device 100 as the first embodiment will be described with reference to FIG. 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 including the 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 stacked on a mirror substrate which has been polished with sufficient accuracy to form a multilayer film (step 1004). For example, a multilayer film having a Mo layer thickness of about 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 into the lens barrel of the projection optical system (step 1006). Then, the measurement unit 110 measures the wavefront aberration through the projection optical system on the wafer surface (step 1008). When such a projection optical system is used in the wavelength region of EUV light, wavefront aberration is measured using EUV light having the same wavelength as that used.

The measured aberration wavefront is compared with the permissible amount (step 1010), and when the wavefront aberration is within the permissible range, for example, when transferring at a resolution of 30 nm, if the wavefront aberration is 0.4 nm or less, the incorporation work into the lens barrel is completed. I do. If the wavefront aberration is equal to or more than the allowable amount, the number of adjustments of the mirror position is compared with the specified number of times (step 1012). That is, the position and / or angle of the mirror are calculated (step 1014). The control unit 130 may show in advance a change in the wavefront caused by the rotation and movement of each mirror as a change table by calculation, 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 mirror adjustment of the calculated amount, the wavefront aberration is measured by the measurement unit 110 (step 1008). If the wavefront aberration is equal to or smaller than the allowable value (step 1010), the assembling work is completed. If the wavefront aberration is equal to or larger than the allowable value (step 1010), the mirror is adjusted (step 1016) from the measurement of the wavefront aberration by the measuring unit 110 (step 1008). Repeat steps up to. The alignment is performed so that the wavefront aberration generated in the projection optical system is minimized. However, it is difficult to remove all the wavefront aberrations caused by the surface shape error of the mirror substrate and the deflection caused by the weight of the mirror by adjusting the mirror position. Therefore, the specified number of times of the mirror position adjustment is determined and performed.

(4) If the amount of wavefront aberration is equal to or more 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 wavefront aberration measured on the wafer surface by the measuring unit 110 is a wavefront aberration for the entire projection optical system. It is not necessary to perform coating milling for each mirror, and a predetermined mirror is selected and coating mirroring is performed on the mirror to correct the wavefront aberration of the entire projection optical system. The number of the predetermined mirror is not limited to one, but may be plural. The control unit 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 performing the coating milling is taken out of the lens barrel, and the multilayer film at a desired location is removed from the mirror by the removing unit 120 (step 1020).

(4) The mirror that has been subjected to the coating milling is assembled into a lens barrel (Step 1006), and the procedure from the measurement of the wavefront aberration by the measuring unit 110 (Step 1008) to the mirror adjustment (Step 1016) 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.

手 順 The procedure from step 1008 to step 1020 is repeated, and the adjustment of the optical system ends when the wavefront aberration of the entire system becomes equal to or less than the allowable amount.

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

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

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

Also, in FIG. 12, if the amount of the wavefront aberration is equal to or more than the allowable value even after the specified number of mirror position adjustments is reached (step 1012), the above-described coating milling is performed. Here, before performing the coating milling, the wavefront measurement of the optical system is performed by the above-described wavefront aberration measuring device using light other than the exposure wavelength to acquire mirror information (information on the angle and position of the mirror). (Step 1017). In subsequent steps 1020 and 1022, the mirror is taken out of the lens barrel and coating milling is performed. When the milling is completed, the mirror is incorporated into the lens barrel again. At that time, the information is used to reproduce the mirror position and the like. Here, an interferometer using light other than the exposure wavelength is used, but the present invention is not limited to this means as long as the position of the mirror can be reproduced. 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 conditions for removing a part of the mirror multilayer film from the measurement result (step 1018). The mirror for performing the coating milling is taken out of the lens barrel, and the multilayer film at a desired location is removed from the mirror by the removing unit 120 (step 1020).

Furthermore, a mirror is incorporated into the optical system (Step 1022), and the wavefront aberration is measured with light other than the exposure wavelength (Step 1024). Here, the wavefront measured after performing the coating milling as described above is observed with a great 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 of removing the area subjected to the coating milling, a mask may be provided to block light incident or reflected on the area of the multilayer mirror subjected to the coating milling, or the coating milling may be performed among the wavefront measurement data. The data corresponding to the wavefront from the region may be removed at the time of data processing.

(4) The measured wavefront aberration is compared with the allowable value (step 1026). If the measured value is equal to or smaller than the allowable value, the adjustment of the optical system ends. If the number is equal to or larger than the allowable value, the number of adjustments of the mirror position is compared with the specified number (step 1028). If the number is within the specified number, the adjustment by alignment (steps 1022 to 1032) is repeated. Note that the allowable value is determined based on the mirror information obtained in step 1017.

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

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

In the first and second embodiments, in step 1008, the wavefront aberration was measured at the exposure wavelength, that is, EUV light. Wavefront measurement at the exposure wavelength may require large equipment, such as a synchrotron light source. However, if the relationship between the wavefront measured with light other than the exposure wavelength (ultraviolet light, visible light, infrared light, etc.) and the wavefront measured at the exposure wavelength is known, only the wavefront measurement with light other than the exposure wavelength is performed. Thus, information on the wavefront at the exposure wavelength can be obtained, and such a large facility is not required.

関係 The relationship between the wavefront measured by light other than the exposure wavelength and the wavefront measured by 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, the wavefront aberration on the imaging plane when visible light is used is 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, and minimizing the sum, the wavefront aberration when converted to EUV light is obtained. Reduced.

Alternatively, a conversion equation for converting the wavefront aberration measured using light other than the exposure wavelength to the wavefront aberration measured at the exposure wavelength may be experimentally obtained. For example, a reference lens barrel is prepared, the wavefront aberration is measured using EUV light, and the wavefront aberration is reduced to an accuracy sufficient for exposure. Next, the wavefront aberration of the reference lens barrel is measured using, for example, visible light. The wavefront aberration on the image plane of EUV and visible light is developed into a Zernike polynomial, and the difference is obtained in advance.

At the time of adjustment, the wavefront aberration is measured with visible light, the wavefront aberration is developed into a Zernike polynomial, and the wavefront aberration in EUV light can be obtained by adding a known difference.

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

FIG. 14 shows an optical system adjustment process in the third embodiment. The procedure up to the 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 using 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 becomes 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 aberrations of the visible light and the EUV light is determined, an optical system in which the wavefront aberration of the EUV light is reduced can be obtained only by measuring the wavefront with the 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 only with a simple apparatus.

In the first to third embodiments, the measurement of the wavefront aberration (steps 1008 and 1024) for assembling the optical system (steps 1006 and 1022) is performed by the adjustment device 100. However, in this case, after the adjustment of the projection optical system by the adjustment device 100, a step of further incorporating the projection optical system into the exposure apparatus is required. Therefore, at that time, an aberration may occur in the projection optical system.

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

{In this case, a specific method of measuring the wavefront aberration will be described based on the exposure apparatus 700 in FIG. 9 described in detail later.

First, a mirror is incorporated in the projection optical system 730 of the exposure device (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 respectively arranged in the exposure area. Each corresponds to one point of the mask position and the wafer position at the time of exposure.

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

When the wavefront aberration is measured using the above-described 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 similarly. 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 configuration 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, a wavelength of 13.4 nm) as illumination light for exposure.

Referring to FIG. 9, an exposure apparatus 700 includes an illumination device 710, a mask (reticle) 720, a mask stage 725 on which the mask 720 is mounted, a projection optical system 730, a processing target 740, and a processing target. It has a wafer stage 745 on which W is placed, an alignment detection mechanism 750, and a focus position detection mechanism 760.

As shown in FIG. 9, the transmittance of EUV light to the atmosphere is low, so that at least the optical path through which EUV light passes is preferably a vacuum atmosphere A.

The illumination device 710 illuminates the mask 720 with 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, and includes an EUV light source 712 and an illumination optical system. 714.

(4) As the EUV light source 712, for example, a laser plasma light source is used. In this method, a high-intensity pulsed laser beam is irradiated to a target material in a vacuum vessel to generate high-temperature plasma, and EUV light having a wavelength of, for example, about 13 nm emitted from the plasma is used. 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 is preferably high, and the operation is usually performed at a repetition rate of several kHz.

The illumination optical system 714 includes a condenser mirror, an optical integrator, and the like. The collecting mirror plays a role in collecting EUV light emitted almost isotropically from the laser plasma. The optical integrator has a role of illuminating the mask uniformly with a predetermined numerical aperture. Further, 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 the mask stage 725. The diffracted light emitted from the mask 720 is reflected by the projection optical system 730 and projected on the target object 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, it scans the mask 720 and the object 740 to reduce and project the pattern of the mask 720 onto the object 740.

The mask stage 725 supports the mask 720 and is connected to a moving mechanism (not shown). As the mask stage 725, any structure known in the art can be applied. A moving mechanism (not shown) is configured 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 object 740 in synchronization. Here, the scanning direction within the mask 720 or the object 740 is X, the direction perpendicular thereto is Y, and the direction perpendicular to the mask 720 or the object 740 is Z.

The projection optical system 730 uses a plurality of reflection mirrors (that is, a multilayer mirror) to reduce and project the pattern on the mask 720 onto the image plane. The number of mirrors is about four to six. 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 and widened using only a thin arc-shaped area (ring field) separated by a certain distance from the optical axis. Transfer 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 constituting the projection optical system 730, and the wavefront aberration is reduced and excellent imaging performance is exhibited.

The processing object 740 is a wafer in the present embodiment, but includes a spherical semiconductor, a liquid crystal substrate, and other processing objects. A photoresist is applied to the object to be processed 740. The photoresist application step includes a pretreatment, an adhesion improver application process, a photoresist application process, and a pre-bake process. The pretreatment includes washing, drying, and the like. The adhesion improver application treatment is a surface modification treatment (that is, a hydrophobic treatment by applying a surfactant) for increasing the adhesion between the photoresist and the base, and the organic film such as HMDS (Hexamethyl-disilazane) is treated. Coat or steam. Prebaking is a baking (firing) step, but is softer than that after development, and removes the solvent.

The wafer stage 745 supports the object to be processed 740 by a wafer chuck. The wafer stage 745 moves the object 740 in the XYZ directions using, for example, 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, for example, a laser interferometer or the like, 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 processing target 740 and the optical axis of the projection optical system 300, and the projected image of the mask 720 is measured. The position and angle of the mask stage 725 and the wafer stage 745 are set so that the target position coincides with a predetermined position of the processing target 740.

Further, the focus position in the Z direction is measured on the surface of the object 740 by the focus position detection mechanism 760, and the position and angle of the wafer stage 745 are controlled so that the surface of the object 740 is constantly exposed during the exposure. To maintain the imaging position.

In the exposure, the EUV light emitted from the illumination device 710 illuminates the mask 720 and forms a pattern on the mask 720 on the object 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 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 the manufacture of devices (semiconductor chips such as ICs and LSIs, LCDs, CCDs, and the like). Here, the manufacture of a semiconductor chip will be described as an example. In step 1 (circuit design), the circuit of the device is designed. Step 2 (mask fabrication) forms a mask on which the designed circuit pattern is formed. In step 3 (wafer manufacturing), a wafer is manufactured using a material such as silicon. Step 4 (wafer process) is referred to as a preprocess, 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 of forming a semiconductor chip using the wafer created in step 4, and includes processes such as an assembly process (dicing and bonding) and a packaging process (chip encapsulation). Including. In step 6 (inspection), inspections such as an operation check 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. Step 11 (oxidation) oxidizes the wafer's surface. Step 12 (CVD) forms an insulating film on the surface of the wafer. Step 13 (electrode formation) forms electrodes on the wafer by vapor deposition or the like. Step 14 (ion implantation) implants ions into the wafer. In step 15 (resist processing), 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. Step 17 (development) develops the exposed wafer. Step 18 (etching) removes portions other than the developed resist image. Step 19 (resist stripping) removes unnecessary resist after etching. By repeating 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.

Although the preferred embodiments of the present invention have been described above, it goes without saying that the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the invention. For example, the present invention can be applied to an optical system having a multilayer mirror and other optical elements (such as a lens and a diffraction grating). 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 an F2 laser, and an exposure apparatus that performs scanning exposure on a large screen and an exposure apparatus that does not scan. Is also applicable.

5 is a flowchart illustrating an adjustment method according to the present invention. It is a schematic block diagram of the adjustment device of the present invention. FIG. 4 is a cross-sectional view schematically illustrating a relationship between incident light and a reflected wavefront in a multilayer film having a uniform number of films. FIG. 4 is a cross-sectional view schematically illustrating a relationship between incident light and a reflected wavefront in a multilayer film having a different number of films. 5 is a graph showing the reflectance characteristics of a multilayer mirror. 9 is a graph showing an effect when a part of the multilayer film of the multilayer mirror is removed. FIG. 3 is a schematic sectional view of a multilayer mirror in which a uniform multilayer film is formed on a distorted mirror substrate. FIG. 3 is a schematic cross-sectional view of a multilayer mirror in which a uniform multilayer film is formed on a mirror substrate whose central portion is higher than an end portion. FIG. 1 is a schematic cross-sectional view illustrating a configuration of an exemplary exposure apparatus of the present invention. 5 is a flowchart for explaining a device manufacturing method having the exposure apparatus of the present invention. 11 is a detailed flowchart of a wafer process in Step 4 shown in FIG. 5 is a flowchart illustrating an adjustment method according to the present invention. FIG. 3 is a schematic plan view illustrating a PS / PDI mask. 5 is a flowchart illustrating an adjustment method according to the present invention.

Explanation of reference numerals

REFERENCE SIGNS LIST 100 adjustment device 110 measuring unit 120 removing unit 130 control unit 700 exposure device 710 illumination device 720 mask 730 projection optical system 740 workpiece 750 alignment detection mechanism 760 focus position detection mechanism

Claims (18)

An adjustment method of an optical system having a multilayer mirror,
A first measurement step of measuring wavefront aberration of the optical system using light having a wavelength used by the optical system;
A second measurement step of measuring wavefront aberration of the optical system using light having a wavelength different from the used wavelength;
Removing a part of the multilayer film of the multilayer mirror based on the first measurement result;
Adjusting the multilayer mirror based on the second measurement result after the removing step. An adjustment method of an optical system having a multilayer mirror,
Adjusting the multilayer mirror;
Obtaining the information of the multilayer mirror after the adjusting step;
Removing a part of the multilayer film of the multilayer mirror so that the wavefront aberration of the optical system at the used wavelength is reduced,
Adjusting the multilayer mirror based on the information after the removing step. An adjustment method of an optical system having a multilayer mirror,
Measuring the wavefront aberration of the optical system using light having a wavelength different from the wavelength used by the optical system,
Removing a part of the multilayer film of the multilayer mirror based on the wavefront aberration measured in the measurement step. The removing step converts the wavefront aberration measured in the measuring step into a wavefront aberration at the working wavelength of the optical system, and reduces one of the multilayer films of the multilayer mirror so that the converted wavefront aberration is reduced. 4. The adjustment method according to claim 3, wherein the portion is removed. The removing step is based on a relationship between a wavefront aberration of the optical system at a wavelength different from the working wavelength and a wavefront aberration of the optical system at the working wavelength obtained in advance by experiment or simulation. 4. The adjustment method according to claim 3, wherein a part of the multilayer film is removed. 3. The adjustment method according to claim 1, further comprising, after the removing step, a re-measurement step of measuring the wavefront aberration of the optical system using light other than the used wavelength. After the removing step, a re-measurement step of measuring the wavefront aberration of the optical system using light other than the used wavelength,
4. The adjusting method according to claim 3, further comprising: adjusting the multilayer mirror based on a measurement result of the re-measurement step. After the removing step, the method further includes a re-measurement step of measuring the wavefront aberration of the optical system except for a region where a part of the multilayer film of the multilayer mirror is removed by using light other than the wavelength used. The adjustment method according to any one of claims 1 to 3, wherein 9. The adjustment method according to claim 8, wherein in the re-measurement step, the measurement is performed by masking an area of the multilayer mirror where a part of the multilayer film is removed. 9. The adjustment method according to claim 8, wherein in the re-measurement step, data corresponding to a region where a part of the multilayer film of the multilayer mirror has been removed from the measurement data is excluded during data processing. 4. The adjustment method according to claim 1, wherein the light having a wavelength different from the used wavelength is ultraviolet light, visible light, or infrared light. 3. The adjusting method according to claim 1, wherein in the step of adjusting the multilayer mirror, a position or an angle of the multilayer mirror is adjusted. An optical system adjustment device having a multilayer mirror,
A measurement unit that measures the wavefront aberration of the optical system using light having a wavelength different from the wavelength used by the optical system,
A removing unit that removes a part of the multilayer film of the multilayer mirror;
A controller configured to control the removing unit so as to remove a part of the multilayer film of the multilayer mirror based on the wavefront aberration measured by the measuring unit. An exposure apparatus comprising the adjustment device according to claim 13. An optical system adjusted using the adjustment method according to any one of claims 1 to 12. An exposure apparatus that guides light from a light source to an object to be processed through the optical system according to claim 15, and exposes the object to be processed. In an exposure apparatus having an illumination optical system that illuminates a mask with light from a light source, and a projection optical system that projects a pattern of the mask onto an object to be processed,
An exposure apparatus, comprising: a measurement unit that measures a wavefront aberration of the projection optical system having a plurality of multilayer mirrors using light having a wavelength different from the wavelength of exposure light. Exposing the object to be processed using the exposure apparatus according to claim 16 or 17,
Performing a predetermined process on the exposed object to be processed.

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