Microlithographic projection exposure method and projection exposure apparatus

Abstract

In a projection exposure method for exposing a substrate arranged in the region of an image plane of a projection lens with at least one image of a pattern arranged in the region of an object plane of the projection lens with radiation from a wavelength range around a design wavelength of < 260 nm, use is made of a projection lens (PO) which is optically corrected in such a manner that, at the design wavelength, a focus is produced in a design focus position (FOC0) and, for other wavelengths from the wavelength range, offset focus positions are generated from an axially extended focus region (ΔFOC) around the design focus position (FOC0). The projection lens has a wavefront manipulation system (WFM) for controllably influencing the wavefront of the projection radiation travelling from the object plane to the image plane, wherein the wavefront manipulation system (WFM) has at least one manipulator which, in response to control signals from a control unit, passes through manipulated value changes within a usable manipulated value range, which lead to changes in the wavefront. The method comprises the following steps of: coating the substrate (SUB) with a radiation-sensitive photoresist layer (RS) having a layer thickness (SD); exposing the substrate coated with the photoresist layer with the image of the pattern using radiation which, under the control of a control unit, according to a predefined temporal profile, has different wavelengths from a wavelength range with a spectral bandwidth around the design wavelength; synchronizing control of the wavefront manipulation system (WFM) with the temporal sequence of radiation of different wavelengths in such a way that a lateral chromatic aberration caused by switching between different wavelengths is at least partly compensated for.

Description

[0001] Microlithographic projection exposure method and projection exposure apparatus

[0002] The following disclosure is based on German patent application 102024111453.3 filed on April 24, 2024, which is incorporated into this application by reference.

[0003] FIELD OF APPLICATION AND PRIOR ART

[0004] The invention relates to a projection exposure method for exposing a substrate arranged in the region of an image plane of a projection lens with at least one image of a pattern of a mask arranged in the region of an object plane of the projection lens, and to a projection exposure apparatus suitable for carrying out the method.

[0005] Microlithographic projection exposure methods are predominantly used nowadays for producing semiconductor components and other finely structured components, such as, for example, structured components for microsystems engineering. Highly integrated semiconductor components typically comprise a plurality of layers, of which only some layers are structured very finely, e.g. on the scale of a few dozen nanometres, while other layers have significantly coarser structures. The former layers realize in particular the actual main function of the semiconductor component, such as e.g. calculations and storage of data, while the latter layers serve e.g. for addressing and power supply. Structures having relatively coarse typical dimensions are also found in the field of microsystems engineering, such as e.g. in microelectromechanical systems (MEMS) or in microoptoelectromechanical systems (MOEMS). Semiconductor components are typically produced from a substrate of a semiconductor, while other substrate materials, in particular metals and vitreous substances, are also used in microsystems engineering.

[0006] Microlithographic projection exposure generally involves the use of masks (reticles) bearing the pattern of a structure to be imaged, e.g. a line pattern of a layer of a semiconductor component. A mask is positioned in a projection exposure apparatus between an illumination system and a projection lens in the region of the object plane of the projection lens and is illuminated with an illumination radiation provided by the illumination system. The radiation altered by the mask and the pattern passes as projection radiation through the projection lens, which images the pattern of the mask onto the substrate to be exposed. The substrate can be e.g. a semiconductor wafer. The substrate to be exposed bears a radiation-sensitive (i.e. photosensitive) layer composed of photoresist material on its side to be structured. Said layer is also referred to as a resist layer. One of the aims in the development of projection exposure apparatuses is to produce lithographically structures with smaller and smaller dimensions on the substrate. In the case of semiconductor components for example, smaller structures lead to higher integration densities, which generally has a beneficial effect on the performance of the microstructured components produced. The size of the structures that can be produced depends crucially on the resolving power of the utilized projection lens, and the latter can be increased, firstly, by reducing the wavelength of the projection radiation used for the projection and, secondly, by increasing the image-side numerical aperture NA of the projection lens used in the process.

[0007] These days, high-resolution projection lenses operate at design wavelengths of less than 260 nm in the deep ultraviolet (DUV) range or in the extreme ultraviolet (EUV) range. The projection lenses are optically corrected for the design wavelength and produce a focus in a design focus position at the design wavelength. In the event of deviations from the design wavelength, axially offset focus positions are generated from a focus region around the design focus position.

[0008] In order that an image of the pattern that is as faithful to the original as possible is transferred to the substrate during the exposure process, the radiation-sensitive layer on the substrate surface should lie in the image-side focus region of the projection lens during the exposure time interval. In particular, the layer arranged on the substrate surface should lie in the region of the depth of focus (DOF) of the projection lens.

[0009] According to one common definition, the depth of focus specifies the distance relative to the plane of best focus for which the intensity of a point image is at least 80% of the intensity in the plane of best focus. This is equivalent to the condition that the diameter of the point image maximally doubles. The depth of focus amounts to half of the Rayleigh unit Rll, which is defined as Rll = X / NA2, wherein X is the operating wavelength of the projection exposure apparatus and NA is the image-side numerical aperture of the projection lens; the region in which the depth of focus condition is met accordingly has a total thickness equal to the Rayleigh unit Rll. In general, the depth of focus becomes smaller, the higher the resolving power of the projection lens.

[0010] Further miniaturization of the feature sizes on computer chips is becoming more and more difficult technically and physically. The associated costs are making further miniaturization of the feature sizes less and less attractive in some cases. As an alternative to better utilization of the wafer area, it is possible to utilize the third dimension by producing structures not just on or at the surface of the wafer but into the wafer in the depth direction. The third dimension is used, for example, to create a three-dimensional stacking of flash memory structures, e.g. in the production of 3D NAND flash memories. 3D NAND is a type of non-volatile flash memory in which the memory cells are stacked vertically in multiple layers. When producing 3D NAN Ds, very thick resist layers have to be exposed. The depth of focus of customary standard scanners is generally not sufficient for this purpose.

[0011] For the exposure of relatively thick photoresist layers, in the field of 193 nm immersion lithography it is known to use so-called “Focus Drilling”.

[0012] The application US 2007 / 0013889 A1 describes a projection exposure apparatus having an illumination system for generating a beam, an arrangement of individually controllable elements which serve to impart a pattern to the beam in its cross section, a substrate table for supporting a substrate, and a projection system for projecting the patterned beam onto a target portion of the substrate. The beam comprises a plurality of beam components. These include a first beam component having a first frequency spectrum around a first frequency and at least a second beam component having a second frequency spectrum around a second frequency. The second frequency is different from the first frequency. The projection system focuses the first and second beam components at different heights relative to the substrate table.

[0013] In the projection exposure method and the projection exposure apparatus in US 4,937,619 A, a substrate is exposed with illumination light of different wavelengths, wherein the longitudinal chromatic aberration of the projection lens changes the position of the focus surface relative to the substrate surface with the wavelength.

[0014] In the projection exposure method and the projection exposure apparatus in US 5,303,002, a substrate is exposed simultaneously with narrowband pulses of closely adjacent different wavelengths. On account of the longitudinal chromatic aberration of the projection lens, an effective magnification of the depth of focus is attained.

[0015] PROBLEM AND SOLUTION

[0016] One problem addressed by the invention is that of providing a projection exposure method which allows the exposure of a relatively thick radiation-sensitive layer on a substrate to be exposed such that an exposed volume having sharp contours positioned correctly is producible over the entire thickness of the layer. A further problem is that of providing a projection exposure apparatus suitable for carrying out the method. In order to solve this problem, the invention provides a projection exposure method having the features of Claim 1. Furthermore, a projection exposure apparatus suitable for carrying out the projection exposure method and having the features of Claim 12 is provided. Advantageous developments are specified in the dependent claims. The wording of all the claims is incorporated by reference in the content of the description.

[0017] In the projection exposure method, a substrate arranged in the region of the image plane of a projection lens is exposed with at least one image of a pattern arranged in the region of the object plane of the projection lens, the object plane being optically conjugate to the image plane. Radiation from a wavelength range around a design wavelength of less than 260 nm (nanometres) is used for this purpose. A mask (reticle) bearing the pattern is generally used. It is also possible to use a controllable pattern producing device to produce the pattern to be imaged.

[0018] The projection lens used is optically corrected in such a way that, at the design wavelength, a focus is produced in a design focus position that lies in a design focal plane. For other wavelengths from the wavelength range, offset focus positions are generated from an axially extended focus region around the design focus position. The focal planes of the wavelengthdependent focus positions are offset with respect to one another in the axial direction, i.e. in the direction parallel to the optical axis of the projection lens.

[0019] The projection lens is equipped with a wavefront manipulation system that can be used to specifically influence or change the wavefront of the projection radiation travelling from the object plane to the image plane in response to control signals from a control unit. For this purpose, the wavefront manipulation system has at least one manipulator which, in response to control signals from the control unit, passes through manipulated value changes within a usable manipulated value range, which lead to changes in the wavefront. The usable manipulated value range is generally also referred to as the "range" of the manipulator. In this case, the term “manipulator” denotes, inter alia, optomechanical or optoelectronic devices configured, on the basis of corresponding control signals from an operating control system, to actively influence individual optical elements or groups of optical elements in order to change the optical effect thereof, e.g. change it in such a way that an undesirable aberration is at least partly compensated for.

[0020] In order to carry out the method, the substrate is coated with a radiation-sensitive photoresist layer (resist layer), the layer thickness of which may be relatively thick, if necessary.

[0021] The substrate coated with the photoresist layer is exposed with an image of the pattern. In order to expose the substrate coated with the photoresist layer with the image of the pattern, use is made of radiation which, under the control of a control unit, according to a predefined temporal profile, has different wavelengths from a wavelength range with a spectral bandwidth around the design wavelength.

[0022] Preferably, use is made of pulsed radiation which, under the control of the control unit, emits pulses of different wavelengths from the wavelength range around the design wavelength in a predefined temporal sequence. Due to the design of the projection lens, this results in the projection radiation associated with the pulses being at different axial focus positions within the focus region. The spectral bandwidth of the wavelength range over which the wavelength is varied is at least an order of magnitude (factor of 10) greater than the spectral bandwidth of the individual pulses. The spectral bandwidth of a pulse is given by the full width at half maximum (FWHM) of the intensity distribution around the centroid wavelength of a pulse.

[0023] What arises as a desired effect as a result is a magnification of the effectively used focus region, which corresponds to a magnification of the effective depth of focus (DOF). As a result, it becomes possible to expose even relatively thick photoresist layers over their entire depth with sufficiently focused radiation.

[0024] Within the wavelength range, there can be very many pulses of different centroid wavelengths, e.g. five or more or ten or more or 50 or more, which allows a smooth focal profile to be achieved in depth. Directly successive pulses can be spectrally separated (distance between the centroid wavelengths of greater than the FWHM), but they can also spectrally overlap (distance between the centroid wavelengths of less than the FWHM).

[0025] In this case, use is therefore made of the fact that the projection lens has a chromatic aberration which causes a wavelength-dependent focus position. An existing longitudinal chromatic aberration (axial colour) is used as the desired "vehicle" to increase the effective depth of focus.

[0026] However, projection lenses generally also have chromatic aberrations which are manifested in a lateral offset of the focus position, i.e. an offset transverse to the optical axis. This lateral offset is described by the lateral chromatic aberration (lateral colour). It has been recognized that this undesirable effect can severely affect the imaging quality if the wavelength is varied relatively greatly for the purpose of achieving a large effective depth of focus, e.g. over a wavelength range whose spectral bandwidth is at least ten times the spectral bandwidth of the pulses.

[0027] In the photolithographic process, this mainly causes the so-called "overlay" or the overlay error (OVL). The overlay is an important characteristic variable in the design of photolithographic processes. For example, the overlay accuracy of structures from different manufacturing steps of a photolithographic process is usually referred to by the term "overlay". High demands on the overlay accuracy or the overlay must also be complied with in multiple exposure methods.

[0028] In the claimed projection exposure method, the use of radiation or pulses of different wavelengths leads to a lateral chromatic aberration, which could lead to an overlay error. According to the claimed invention, this undesirable side effect is avoided or limited to sufficiently small orders of magnitude by synchronizing the control of the wavefront manipulation system with the temporal sequence of pulses of different wavelengths in such a way that a lateral chromatic aberration caused by switching between different wavelengths is at least partly compensated for. This means that the desired effect of increasing the depth of focus becomes predominantly takes effect in the process, while the undesirable side effect (overlay-like errors due to the lateral chromatic aberration) does not or does not significantly affect the imaging quality.

[0029] According to one development, the temporal sequence and the wavelengths of the radiation, in particular of the pulses, of different wavelengths are controlled in such a way that the wavelength of the radiation or of the pulses varies according to a periodic time function with a wavelength alternating frequency between a first limit wavelength and a second limit wavelength of the wavelength range, wherein manipulated value changes of the manipulator are adapted to the periodic time function in such a way that a manipulator varies periodically with the wavelength alternating frequency between a first limit manipulated value and a second limit manipulated value within a manipulated value range used. Periodic changes, to which a frequency can be assigned, can generally be generated particularly reliably both on the side of the light source and on the side of the manipulator.

[0030] In preferred method variants, provision is made for the wavelength alternating frequency to be at least an order of magnitude less than a pulse frequency of the pulsed radiation. This means that an averaging between different wavelengths is achieved substantially for each location of the exposed substrate in such a way that, on average, each point of the exposed field is exposed to similar components of the different wavelengths from the wavelength range. In this respect, relatively uniform illumination of the region to be exposed on the substrate in an operation can thus be achieved.

[0031] However, a lower limit for the wavelength alternating frequency should not be undershot either if possible. If the wavelength alternating frequency becomes too low, the extent of induced overlay errors tends to increase. In preferred embodiments, provision is made for the wavelength alternating frequency to be in a range of 50 Hz to 500 Hz, wherein the wavelength alternating frequency is preferably in a range of 100 Hz to 300 Hz. This generally makes it possible to achieve a good compromise between sufficiently strong compensation for overlay errors and not too much contrast loss.

[0032] In preferred embodiments, the time function, which describes the wavelength change, is a sine function. Such periodic changes in the wavelengths of successive pulses can be achieved particularly easily with high precision with appropriate devices in the region of the light source of the projection exposure apparatus.

[0033] In preferred embodiments, the periodic time function, which is followed by the manipulated value changes of the manipulator, is a sine function. This makes it possible to achieve a jerk-free movement of the manipulator element between the limit values of the required manipulated values. Such sinusoidal oscillation movements can often be achieved with conventional manipulators even if the moving mass of the manipulator is relatively large. If the manipulator is a system that is capable of vibration and can be characterized by a natural frequency, the alternating frequency can be optimized with regard to the natural frequency of the manipulator.

[0034] The spectral bandwidth of the wavelength range, within which the wavelengths for the different pulses lie, is preferably designed for many of the processes addressed here such that the wavelength range has a spectral bandwidth of at least 20 pm (picometres). The spectral bandwidth can also be 30 pm or more, for example between 30 pm and 50 pm. If necessary, the bandwidth can also be greater, e.g. up to 100 pm, but at least well below one nanometre. This makes it possible to meet many of today's process requirements. The spectral bandwidth here refers to the wavelength difference between an upper and a lower limit wavelength of the spectrum available for the wavelengths of the pulses.

[0035] For example, a tunable pulsed laser can be used as the light source, i.e. a laser whose pulse wavelength can be varied largely continuously within a certain range.

[0036] In some embodiments, a wavelength selection or wavelength change is achieved by mounting a rotatable grating or etalon in the resonator of the laser or by varying the resonator length. As a result, only light in a narrow frequency range can be reflected back into the resonator and contribute to the induced emission. Light of other wavelengths is reflected out of the resonator. As a result of rotation of the grating or etalon, different frequencies are successively fed back, and the colour of the laser light can be tuned. The degree of the axial extent of the effective focus region desired for a particular process can be optimized depending on the process. In some embodiments, the focus region is extended in an axial direction of the projection lens over at least 5 pm, preferably over a focus region of 10 pm or more. This means that even the relatively thick photoresist layers, which are used nowadays in the photolithographic production of three-dimensional flat memory structures, can be exposed at full depth. The focus region should not be much larger than 15 pm or 20 pm, since, with an increasing extent of the desired focus region, the undesirable side effects (overlay errors induced by lateral chromatic aberrations) also take on an extent that can be corrected only with difficulty.

[0037] It is therefore possible to achieve a good adaptation to advantageous processes in which the photoresist layer is applied with a layer thickness of the order of magnitude of 10 pm, wherein the layer thickness is preferably in the range of 5 pm to 20 pm. Layer thicknesses may possibly also be greater than 20 pm and / or less than 5 pm.

[0038] In order to compensate for the lateral chromatic aberration or the overlay error induced by the lateral chromatic aberration, use is preferably made of at least one manipulator of the wavefront manipulation system that has an optical element with refractive power arranged in the beam path of the projection lens and an actuator system for moving the optical element within the usable manipulated value range, wherein the optical element can be moved by means of the actuator system with a movement component parallel to an axial direction of the projection lens and is also moved in the method for the purpose of compensation. Such a manipulator is also referred to in this application as a Z manipulator, since the axial direction in projection lenses is usually also referred to as the Z-direction.

[0039] A single Z manipulator of this type can be used; if necessary, two or more Z manipulators can also be activated at the same time in order to cumulatively achieve the desired compensation effect. This solution has the advantage, inter alia, that most high-performance projection lenses nowadays have wavefront manipulation systems with Z manipulators. Z manipulators affect different aberrations that exhibit rotational symmetry with respect to the optical axis. For example, a Z manipulator may have a lens element that can be shifted axially (parallel to the optical axis) or an axially shiftable mirror. A Z manipulator can be used, inter alia, to change the imaging scale or the magnification of the projection lens. A change in the magnification corresponds to a lateral shift of pixels in the image plane and thus corresponds to the overlay error which can be at least partly compensated for by means of changes in the imaging scale. If the projection lens is an optically rotationally symmetric system in which the effective object field and the effective image field are centred with respect to the optical axis (on-axis systems), manipulator movements parallel to the optical axis of the projection lens can be sufficient to adequately compensate for the overlay errors induced by wavelength changes.

[0040] In some embodiments, use is made of projection lenses in which the effective object field and the effective image field optically conjugate thereto are outside the optical axis (off-axis field). This is the case, for example, with certain catadioptric projection lenses with one concave mirror or multiple concave mirrors. Due to the off-axis position of the effective fields, additional contributions can be generated for deviations of the pixel position from the desired pixel position during scanning. These contributions can be at least partly compensated for if, in addition to the axisparallel movement, the optical element of the manipulator is also tilted about a tilt axis oriented perpendicular to the axial direction.

[0041] The invention also relates to a projection exposure apparatus configured to carry out the method, and to a projection lens usable therein.

[0042] The light source is configured as a wavelength-variable light source such that, under the control of a control unit of the projection exposure apparatus, it can emit radiation, in particular in the form of pulses, of different wavelengths from a wavelength range of at least ± 20 pm (picometres) or more around its design operating wavelength (for example approximately 248 nm or approximately 193 nm). In the case of pulsed radiation, the spectral bandwidth of the individual pulses is relatively narrow compared to the spectral width of the wavelength range; it can be approximately 1 pm or less, e.g. in the range of 0.2 to 0.5 pm. The temporal profile of the change in the range between the limit wavelengths of the wavelength range can be variably specified. For example, the wavelength can change periodically, e.g. according to a sinusoidal time function. The wavelength alternating frequency is preferably continuously variable or adjustable in stages, e.g. in the range of 0 Hz (no change in the wavelength over time) up to approximately 500 Hz or more.

[0043] BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Further advantages and aspects of the invention are evident from the claims and from the description of exemplary embodiments of the invention, which will be explained below with reference to the figures. Fig. 1 shows a microlithographic projection exposure apparatus according to one exemplary embodiment of the invention;

[0045] Figs. 2A and 2B show, in 2A, a wavelength-time diagram (X / t diagram) with a temporal sequence of individual pulses whose centroid wavelengths vary substantially according to a sinusoidal time function, and, in 2B, a schematic illustration of manipulated value of a manipulator as a function of the time t with respect to the same time axis as Fig. 2A;

[0046] Fig. 3 shows the effect of a moving-average (MA) filter using the example of a periodic focus variation;

[0047] Fig. 4 shows a diagram of the field profile of Z2 using the curve OVL1 (without compensation) and OVL2 (with compensation by means of manipulator movement);

[0048] Fig. 5 shows a schematic diagram with typical profiles of overlay errors (curve MA) and contrast loss (curve MSD) as a function of frequency;

[0049] Fig. 6 shows a first exemplary embodiment of a projection lens;

[0050] Fig. 7 shows a second exemplary embodiment of a projection lens;

[0051] Figs. 8 and 9 show residual aberrations of the first exemplary embodiment;

[0052] Fig. 10 shows residual aberrations of the second exemplary embodiment.

[0053] DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0054] Figure 1 shows an example of a microlithographic projection exposure apparatus WSC which is usable in the production of semiconductor components and other finely structured components and which operates with light or electromagnetic radiation from the deep ultraviolet (DUV) range in order to obtain resolutions down to fractions of micrometres.

[0055] As light source LS, use is made of a tunable KrF excimer laser having a main operating wavelength of approximately 248 nm. Other UV laser light sources or operating wavelengths are also possible. The light source LS operates in pulsed operation and emits pulsed radiation during operation, i.e. a temporal sequence of pulses PS (see detail I), with a pulse frequency in the kilohertz range (i.e. at at least one kHz, e.g. at approximately 6 kHz). Each pulse can be characterized by its centroid wavelength and its spectral bandwidth or spectral pulse width. The centroid wavelength is that wavelength which is present with maximum intensity in the pulse. The spectral bandwidth of a pulse is given by the full width at half maximum (FWHM) of the intensity distribution around the centroid wavelength of the pulse.

[0056] Here the term “light source” is intended to encompass not only the primary light source that emits light, but also devices possibly present, such as filters, stops, bandwidth narrowing modules, wavelength varying modules or the like, which serve to alter the characteristic of the light emitted by the primary light source before said light enters the illumination system.

[0057] The light source can emit pulses of different wavelengths from a wavelength range WLB of at least ± 20 pm (picometres) around its main operating wavelength. For this purpose, the light source LS has a resonator and adjustable devices which alter optical properties of the resonator. A wavelength setting can be achieved e.g. by virtue of a rotatable grating or etalon being mounted in the resonator and / or the resonator length being varied. As a result, only light in a narrow frequency range can be reflected back into the resonator and contribute to the induced emission. Light of other wavelengths is reflected out of the resonator. As a result of rotation of the grating or etalon, different frequencies are successively fed back, and the wavelength (centroid wavelength) of the pulses of the laser light can be tuned.

[0058] The change between different centroid wavelengths within the wavelength range can take place relatively rapidly, such that ten or more pulses, possibly even one hundred or more pulses, of different centroid wavelengths from the wavelength range can be emitted within a fraction of a second.

[0059] At its exit surface ES, an illumination system ILL disposed downstream of the light source LS generates a large, sharply delimited and substantially homogeneously illuminated illumination field, which is adapted to the requirements of telecentricity of the projection lens PO arranged downstream thereof in the light path. The illumination system ILL has devices for setting different illumination modes (illumination settings) and, for example, can be switched between conventional on-axis illumination with different degrees of coherence c and off-axis illumination. By way of example, the off-axis illumination modes comprise annular illumination or dipole illumination or quadrupole illumination or any other multi-polar illumination.

[0060] Those optical components which receive the light from the light source LS and shape illumination radiation from this light, which illumination radiation is directed to the illumination field lying in the exit plane ES or to the reticle M, are part of the illumination system ILL of the projection exposure apparatus.

[0061] Arranged downstream of the illumination system is a device RS for holding and manipulating the mask M (reticle) in such a way that the pattern PAT arranged at the reticle lies in the region of the object plane OS of the projection lens PO, which coincides with the exit plane ES of the illumination system and which is also referred to here as reticle plane OS. For the purposes of scanner operation, the mask is movable parallel to this plane in a scanning direction (y-direction) perpendicular to the optical axis OA (z-direction) with the aid of a scanning drive.

[0062] The device RS comprises an integrated lifting device for linearly displacing the mask in relation to the object plane in the z-direction, i.e. perpendicular to the object plane, and an integrated tilting device for tilting the mask about a tilt axis extending in the x-direction.

[0063] Following downstream of the reticle plane OS is the projection lens PO, which acts as a reduction lens and images an image of the pattern arranged at the mask M with a reduced scale, for example with the scale of 1 :4 (|P| = 0.25) or 1 :5 (|P| = 0.20), onto a substrate W coated with a photoresist layer, the light-sensitive substrate surface SS of which lies in the region of the image plane IS of the projection lens PO.

[0064] The substrate to be exposed, which is a semiconductor wafer W in the exemplary case, is held by a device WS, which comprises a scanner drive in order to move the wafer synchronously with the reticle M perpendicular to the optical axis OA in a scanning direction (y-direction).

[0065] The device WS furthermore comprises a lifting device for linearly displacing the substrate in relation to the image plane in the z-direction and a tilting device for tilting the substrate about a tilt axis extending in the x-direction.

[0066] The device WS, which is also referred to as "wafer stage", and the device RS, which is also referred to as "reticle stage", are constituent parts of a scanner device which is controlled by way of a scan control device which, in the embodiment, is integrated in the central control device CU of the projection exposure apparatus.

[0067] The illumination field generated by the illumination system ILL defines the effective object field OF used during the projection exposure. In the exemplary case, the latter is rectangular, it has a height A* measured parallel to the scanning direction (y-direction) and it has a width B* > A* measured perpendicular thereto (in the x-direction). In general, the aspect ratio AR =B* / A* lies between 2 and 10, in particular between 3 and 6. The effective object field lies at a distance next to the optical axis in the y-direction (off-axis field). The effective image field in the image surface IS, which is optically conjugate to the effective object field, likewise is an off-axis field and it has the same shape and the same aspect ratio between the height B and width A as the effective object field, but the absolute field dimension is reduced by the imaging scale p of the projection lens,

[0068] If the projection lens is designed and operated as an immersion lens, then radiation is transmitted through a thin layer of an immersion liquid IL during the operation of the projection lens, which thin layer is situated between the exit surface of the projection lens and the image plane IS. Imageside numerical apertures NA > 1 are possible during the immersion operation. A configuration as a dry lens is also possible; in this case, the image-side numerical aperture is restricted to values NA < 1.

[0069] Exemplary embodiments of suitable projection lenses are described in connection with Figs. 8 and 9.

[0070] The projection exposure apparatus WSC comprises an operation control system configured to undertake a near-instantaneous fine optimization of imaging-relevant properties of the projection exposure apparatus in response to environmental influences and other disturbances and / or on the basis of stored control data. To this end, the operation control system comprises a multiplicity of manipulators which permit a targeted intervention in the projection behaviour of the projection exposure apparatus. An actively actuatable manipulator contains one or more actuating elements (or one or more actuators), the current manipulated value of which can be changed on the basis of control signals from the operation control system by virtue of defined manipulated value changes being undertaken. Integrated sensors detect the manipulated value changes, generate corresponding feedback signals and thus serve to control the manipulator settings.

[0071] The projection lens or the projection exposure apparatus is equipped with, inter alia, a wavefront manipulation system WFM which is configured to modify the wavefront of the projection radiation travelling from the object plane OS to the image plane IS in a controllable manner in the sense that the optical effect of the wavefront manipulation system can be variably adjusted by way of control signals from an operation control system.

[0072] The wavefront manipulation system WFM has, inter alia, a group of multiple Z manipulators which is designed to simultaneously influence certain aberrations which have rotational symmetry with respect to the optical axis OA (rotational symmetry aberrations). Each Z manipulator includes a pre-selected optical element in the form of a lens element which can be shifted individually parallel to the optical axis OA by means of an associated actuating device of the Z manipulator (see detail II which shows a periodic movement of a manipulable lens element in the z-direction). Schematic Fig. 1 illustrates, by way of example, two Z manipulators ZMAN1 , ZMAN2 with axially shiftably mounted manipulable lens elements ML1 , ML2 and associated actuating devices DR1 , DR2. Typically, there are more than two Z manipulators, for example three or four Z manipulators. The shape of the shiftable lens elements, their arrangement in the projection beam path (e.g. optical proximity or distance to the nearest field plane or pupil plane) and in relation to adjacent lens elements as well as the extent of the axial shift influence the optical effect of the respective Z manipulator.

[0073] A Z manipulator may have additional degrees of freedom of movement. In some or all Z manipulators, the actuator system is designed in such a way that the optical element can also be tilted about a tilt axis oriented perpendicular to the axial direction and to the scan direction, which corresponds to a rotation about an axis parallel to the x-axis.

[0074] In addition to the Z manipulators, the wavefront manipulation system of the exemplary embodiment has a deformation manipulator DMAN having a deformable manipulator element ME1 which, in the example of Fig. 1 , is arranged in the projection beam path in the immediate vicinity of the object plane OS of the projection lens and has two manipulator surfaces MS which are arranged in the projection beam path and the surface form of which can be reversibly modified with the aid of an actuating device DR.

[0075] The manipulators are fast or dynamically adjustable manipulators that can implement manipulated value changes in rapid succession within their usable manipulated value ranges, e.g. with frequencies of up to approximately 300 Hz or more.

[0076] The projection exposure apparatus is configured to perform a projection exposure method in which an effective depth of focus of the order of magnitude of 10 pm can be achieved by varying the wavelength used via an axial variation of the focus positions in order to produce a three- dimensional stack of flat memory structures on the substrate. The longitudinal dependence of the focus position on the wavelength, which is also referred to as axial chromatic aberration or longitudinal chromatic aberration, is intended to be used for this purpose. This causes the projection lens to produce a focus in a design focus position at the design wavelength (approximately 248 nm) and offset focus positions from an axially extended focus region around the design focus position for other wavelengths from the wavelength range. However, the projection lens not only produces the desired axial variation of the focus position, but also so-called lateral chromatic aberrations. The lateral chromatic aberration is manifested in the dependence of the image size or the image height of an off-axis object point on the wavelength. The lateral chromatic aberration thus results in a dependence of the imaging scale on the wavelength. This is also referred to as the chromatic difference of magnification (CHV) or as a wavelength-dependent distortion. This is an undesirable effect because it leads to overlay errors (OVL errors) in the process.

[0077] An example is used below to explain how the desired effect (increase in the effective DOF) can be achieved without having to accept significant disadvantages with respect to the overlay error.

[0078] For an exemplary estimation of the orders of magnitude, a substrate having approximately 170 layers with 60 nm per layer is assumed below. This results in a value of approximately 10 pm for the order of magnitude of the desired axial extent AFOC of the focus region.

[0079] The light source equipped with a laser operates at a pulse frequency of 6 kHz. In scanner operation, a scanning speed of the order of magnitude of 800 mm / sec scanning speed is intended to be achieved. This corresponds to a scan time of approximately 7 msec (milliseconds) for each point in the exposed unit for currently common sizes of units (dies) to be exposed.

[0080] The desired axial extent of the focus region (AFOC of approximately 10 pm) may be achieved with the projection lens by virtue of the fact that the wavelength used for the exposure varies within a wavelength range with a spectral bandwidth of approximately 35 pm around the design wavelength Xo. (AX = 35 pm).

[0081] In order to estimate the effects on the lithographic process, the process characteristic variables of overlay (OVL) and fading or contrast loss are considered, in particular. These are decisive from the user's point of view. The user would like the different layers of a multilayer structure of a chip to lie exactly enough on top of each other and the sharpness of the structures to be imaged to correspond to the specifications. The measure of the (local) lateral deviation of the position of a subsequent layer from the previous one is called overlay (OVL). The measure of the contrast loss caused by motion blur of the image is also referred to as “fading”. When considering the process dynamics, i.e. in the time domain, the overlay error can be described as the moving average (MA) of an image oscillation averaged over the scan time, and the fading error can be described as the moving standard deviation (MSD). An estimation of the overlay error induced by a wavelength variation of AX = 35 pm results, for conventional projection lenses considered here, in an order of magnitude of approximately 200 nm or a lateral image deviation of approximately ± 100 nm from the position of a pixel at the design wavelength. This is unacceptable for most processes.

[0082] An exemplary embodiment is used below to describe a possible way of using the claimed invention to achieve an effective increase in the depth of focus by varying the wavelength without resulting in a disruptive amount of overlay errors. For this purpose, the light source LS is controlled in such a way that it emits pulses of different wavelengths in a predefined temporal sequence, wherein the wavelengths originate from a wavelength range WLB around the design wavelength Xo. The wavelength range has a spectral bandwidth AA which is the difference between an upper limit wavelength Aoand a lower limit wavelength Au. The spectral bandwidth AA is significantly greater than the spectral bandwidth AAPof the individual pulses, e.g. by a factor of 10 or more, possibly even by a factor of 50 or more or by a factor of 100 or more. The spectral bandwidth of the pulses can be given, for example, by the full width at half maximum of the laser lines.

[0083] The control is used to synchronize the wavefront manipulation system with the temporal sequence of pulses of different wavelengths in such a way that a lateral chromatic aberration caused by the switch between different wavelengths is at least partly compensated for. This also allows the induced overlay error to be reduced accordingly to an uncritical level.

[0084] The processes in an exemplary embodiment are explained with reference to Figs. 2A and 2B. Fig. 2A shows, in a wavelength-time diagram (X / t diagram), the temporal sequence of the individual pulses, represented by vertical double-T lines. The centroid wavelengths of the individual pulses vary substantially according to a sinusoidal time function. In accordance with the pulse frequency fPof the laser, there is a pulse spacing 1 / fPbetween directly successive pulses. The spectral bandwidth of the pulses is approximately 0.35 nm and is represented more than proportionally by the line length. The spectral bandwidth AA of the wavelength range WLB in which the pulse wavelengths vary is approximately 35 pm and is thus greater than the spectral pulse width by two orders of magnitude. The spectral bandwidth AA corresponds to the amplitude of the illustrated sine function. The wavelengths of the pulses vary periodically with a wavelength alternating frequency fww, the reciprocal value 1 / fww of which corresponds to the period length of the sine function on the time axis.

[0085] It is immediately apparent that the extent of the induced lateral chromatic aberration and of the overlay error induced thereby fluctuates to the same extent when the projection lens is operated without changing its imaging properties, in particular without actuating manipulators. According to the exemplary embodiment, however, manipulated value changes of manipulators of the wavefront manipulation system are synchronized with the temporal characteristic of the wavelength change in such a way that the induced lateral chromatic aberration is at least partly compensated for. In this respect, Fig. 2B shows a schematic illustration of the manipulated value SWMAN of a manipulator or a group of manipulators as a function of the time t with respect to the same time axis as Fig. 2A. The vertical distance between the upper and lower delimiting dashed lines corresponds to the manipulated value range SWB used for the manipulator movement or the amplitude of the manipulator movement. The reciprocal value of the periodicity length of the sine function corresponds to the manipulator alternating frequency fMAN-

[0086] In the exemplary case, only Z manipulators are dynamically varied between certain manipulated value limits within their manipulated value range used according to a sine function, wherein these manipulated value limits lie within a larger possible manipulated value range of the respective manipulators. A sinusoidal change in the manipulated values of a Z manipulator thus corresponds to an axially oscillating movement of an optical element, for example a lens element, in the projection beam path.

[0087] When considering the dynamics of the process, it is expedient, inter alia, to investigate the frequencies at which the wavelength change and the corresponding manipulator movement should be expediently operated in order to achieve a sufficiently strong effect within the dynamic range of the manipulators. It should also be taken into account that, within a period (1 / fA) of the wavelength change, many light pulses of different wavelengths should be incident on each point of the exposed part of the substrate in order to achieve a sufficient depth of focus effect. The following considerations are used to estimate suitable frequency ranges.

[0088] The periodic change of the effective wavelengths within the wavelength range leads to a sinusoidal axial shift of the aerial image. The lateral chromatic aberration leads to an associated fluctuation in the imaging scale. Filter functions use averaging effects to convert the amplitude of the fluctuation in the aerial image and the imaging scale into corresponding values for the overlay (corresponding to MA) and for the contrast loss (corresponding to MSD). This takes into account the effect of the scanning movement, which causes each point to be exposed only relatively briefly during the overflow of the illuminated scanning slot.

[0089] Fig. 3 shows, by way of example, the effect of an MA filter using the example of a periodic focus variation. The three diagrams on the top line represent focus variations with alternating frequencies of 10 Hz (on the left), 75 Hz (in the centre) and 150 Hz (on the right). The time t [msec] is respectively plotted on the x-axis; the y-axis corresponds to the normalized focus position FOC. On the time axis, the narrow rectangular vertical strips have a width corresponding to the exposure time of a point in the field during scanning. For a scanning speed of 800 mm / sec and a slot width of 5.5 mm, each point on the wafer is exposed for approximately 7 msec. The diagram on the bottom line shows associated MA filter values as a function of the wavelength alternating frequency fww- Values close to 1 correspond to a large overlay error, while the overlay error disappears at a value of zero.

[0090] At the slowest alternating frequency (10 Hz), a first point P1 on the wafer "sees" an average focus value of 0.99, while a laterally offset, second point P2 "sees" an average focus value of -0.99 within its exposure time. This shows that almost the complete amplitude of the focus variation becomes effective as a corresponding overlay error on the exposed substrate when the period of wavelength change becomes large in comparison with the exposure time achievable by scanning. In the MA filter diagram on the bottom line, this situation corresponds to an MA filter value of virtually 1 , which corresponds to a virtually maximum overlay error on the normalized scale.

[0091] At the higher wavelength alternating frequency of 75 Hz, the corresponding first point P1 on the wafer "sees" an average focus value of 0.62, while the second point P2 "sees" an average focus value of -0.62. The difference between the focus values is significantly smaller than with the slower wavelength fluctuation, and so the averaging results in a smaller overlay error which is expressed by an MA filter value of approximately 0.6.

[0092] The diagram on the right for a wavelength alternating frequency of 150 Hz represents an almost ideal operating point with regard to the other boundary conditions of this example. At the first point P1 on the wafer, an average focus value of 0.03 takes effect, and, at the second point P2, an average focus value of -0.03 takes effect. These values are very close to each other, and so the temporal averaging results in virtually no more overlay errors. This is becomes noticeable in the MA filter diagram by a value close to zero at the frequency of 150 Hz.

[0093] Therefore, if the exposure time is short in comparison with the oscillation period, large overlay errors will result. If, on the other hand, the exposure time is long in comparison with the oscillation period, averaging over many aerial images occurs. This shows that the overlay error can be relatively small depending on the choice of the wavelength alternating frequency. However, this then results in a relatively strong contrast loss ("fading").

[0094] Thus, no critical overlay error is generated if the wavelength alternating frequency is high enough, but a strong contrast loss becomes apparent. In the assumed example, the MSD value representing the contrast loss is approximately 10 times higher than acceptable for the intended application.

[0095] There may be applications in which the loss of contrast is acceptable as long as the OVL error is kept small.

[0096] In the present exemplary embodiment, however, the temporally averaged OVL error is at least partly compensated for by compensation movements of Z manipulators, with the result that there is a process-compatible compromise between overlay error and contrast loss. According to the experience of the inventors, the overlay error can best be described by a linear combination of Zernike coefficients, in particular a combination of Z2, Z7, Z22. The main driver is the contribution of Z2, which represents the tilting of the wavefront about the y-axis.

[0097] In practice, it is therefore appropriate to examine and interpret the compensation measures essentially with regard to their effect on Z2. In other words, an overlay error can be identified or compensated for relatively effectively by reducing the contribution of Z2 to the wavefront aberration.

[0098] The diagram in Fig. 4 shows the field profile of the Zernike coefficient Z2 using the curve OVL1. This represents the major part of the overlay error caused by a wavelength variation of 35 pm.

[0099] In order to determine which manipulator movements counteract this error and can at least partly compensate for the overlay error, the original OVL error was thus translated into the Z2 error. This Z2 component was then fed into a so-called lens model (Driver Lens Model, DLM), and it was determined which of the Z manipulators must be moved and how in order to counteract the overlay error.

[0100] A total of six Z manipulators ZMAN1 to ZMAN6 were taken into account in the simulations. These were taken into account with different amplitudes of the actuating movements. The Z manipulators taken into account in the simulation also offer further manipulation degrees of freedom, including tilting about the x-axis and tilting about the y-axis at appropriate angles. A need for these compensation measures arises in the specific simulated example from the fact that the effective object field and the effective image field are not centred with respect to the optical axis ("on-axis field"), but lie outside the optical axis ("off-axis field").

[0101] In the case of on-axis fields, actuating movements parallel to the z-direction are sufficient; tilting components would not be required. In order to simulate the real process in a scanner system, the dynamics of the process must be taken into account. An MA filter and an MSD filter are used for this purpose, where the MA filter represents the overlay error and the MSD filter represents the contrast loss. The filter functions transfer the amplitude of a sinusoidal movement of the aerial image parallel to the x-direction to corresponding values for overlay (MA) and contrast loss (MSD). Scan weightings are taken into account.

[0102] The schematic diagram in Fig. 5 represents typical profiles of overlay errors (curve MA) and contrast loss (curve MSD) as a function of the wavelength alternating frequency fww plotted on the x-axis. The y-axis indicates the normalized extent of the respective error, where the value 1 corresponds to the maximum value.

[0103] In a first scenario, only the wavelength of the primary radiation fluctuates sinusoidally over its wavelength range, while no compensation using manipulator movements is carried out.

[0104] In a second scenario, the wavelength and the manipulated values of the Z manipulators vary synchronously according to a sinusoidal time function (cf. Figs. 2A and 2B).

[0105] Two exemplary embodiments of projection lenses are described below with reference to Figs. 6 and 7, which have an uncorrected chromatic magnification aberration CHV (or lateral colour LAT) and can be used within the scope of the invention claimed here to enable Multi-Focal Imaging (MFI). In MFI, by way of wavelength shifting, the longitudinal chromatic aberration of projection systems is used to shift the best setting plane through a “thick” photoresist layer during exposure by detuning the laser wavelength. The change in the imaging scale with the wavelength is intended to be compensated for with an additional manipulator system. In particular, the following scenarios are considered in this case: (i) movement of individual lens elements or groups of lens elements along the z-axis (optical axis) of the system, and (ii) additional support by shifting reticles and / or wafers in the z-direction.

[0106] In the following description of projection lenses, the term "optical axis" denotes a straight line through the centres of curvature of the curved lens element surfaces. In the examples, the object is a mask (reticle) with the pattern of an integrated circuit; it may also be a different pattern, for example of a grating. In the examples, the image is projected onto a wafer which is provided with a photoresist layer and acts as a substrate. Other substrates are also possible, for example elements for liquid crystal displays or substrates for optical gratings. The specifications of the projection lenses shown in the figures of the drawing are indicated in the tables compiled at the end of the description, the numbering of which tables respectively corresponds to the numbering of the corresponding figure of the drawing.

[0107] Tables 6, 6A and 7, 7A summarize the specification of the respective design in tabular form. The "SURF" column indicates the number of a refractive surface or surface with a different characteristic, the "RADIUS" column indicates the radius r of the surface (in mm), the "THICKNESS" column indicates the distance d, referred to as the thickness, between the surface and the following surface (in mm), and the "MATERIAL" column indicates the material of the optical components. The "INDEX1 ," INDEX2" and "INDEX3" columns indicate the refractive index of the material at the wavelengths of 248.413 nm (INDEX1), 247.413 nm (INDEX2) and 249.413 nm (INDEX3) (first exemplary embodiment) and 193, 192 and 194 (second exemplary embodiment). The "SEMIDIAM" column indicates the usable free radii or the free optical semidiameters of the lens elements (in mm) or of the optical elements. The radius r=0 (in the "RADIUS" column) corresponds to a plane surface. Some optical surfaces are aspherical. Tables with the suffix "A" indicate the corresponding aspherical data, wherein the aspherical surfaces are calculated according to the following rule: p(h)=[((1 / r)h2) / (1+SQRT(1-(1+K)(1 / r)2h2))]+C1*h4+C2*h6+....

[0108] The reciprocal value (1 / r) of the radius indicates the surface curvature, and h indicates the distance of a surface point from the optical axis (i.e. the ray height). Thus, p(h) indicates the sagittal height, i.e. the distance of the surface point from the surface vertex in the z-direction (direction of the optical axis). The coefficients K, C1 , C2, ... are shown in the tables with the suffix "A."

[0109] In the following description of exemplary embodiments, the same reference signs are used in all figures for the same or corresponding features. Lens elements are numbered in their sequence from the object plane to the image plane, and so, for example, the lens element L1 is the first lens element immediately following the object plane. Not all lens elements are provided with reference signs for reasons of clarity.

[0110] Fig. 6 shows a schematic meridional lens element sectional view of a first exemplary embodiment of a dioptric projection lens PO-1 (designation N822) with selected beams for elucidating the imaging beam path or the projection beam path of the projection radiation passing through the projection lens during operation. The projection lens is provided as an imaging system with a reducing effect, for imaging a pattern of a mask arranged in its object plane OS onto its image plane IS oriented parallel to the object plane directly, that is to say without producing an intermediate image, and on a reduced scale, specifically on the scale of -1 :4 (imaging scale p = -0.25).

[0111] Between the object plane and the image plane, the only pupil plane of the imaging system lies where the chief ray CR of the optical imaging intersects the optical axis OA. The aperture stop AS of the system is mounted in the region of the pupil plane. Therefore, the position suitable for mounting the aperture stop is also referred to as stop position BP here.

[0112] A stop region extends around the stop position, the condition |CRH / MRH| < 1 applying to a ray height ratio between the chief ray height CRH and the marginal ray height MRH of the imaging in said stop region. Thus, the marginal ray height here is greater than the chief ray height. The optical set-up can be characterized as follows.

[0113] A first lens element group LG1 with negative refractive power, formed by two lens elements L1 and L2 in the example, directly follows the object plane OS. Lens element L1 is a biconcave negative lens element and L2 is a negative meniscus lens element with a concave entrance surface and convex exit surface. By increasing the divergence, the first lens element group prepares the formation of a convexity in the subsequent beam path. Such a negative group in the immediate vicinity of the object plane enables the formation of a subsequent convexity at an axially short length, and is consequently conducive to a compact structural shape.

[0114] A second lens element group LG2 with positive refractive power directly follows the first lens element group LG1. This second lens element group comprises the five lens elements L3 to L7 which, apart from L7, have positive refractive power. The second lens element group collects the rays coming from the first lens element group and, as a result, forms, at least approximately, a convexity in the projection beam path.

[0115] A third lens element group LG3 with negative refractive power directly follows the second lens element group LG2. This third lens element group comprises the three lens elements L8 to L10 and produces a waist around a local minimum of the marginal ray height between the object plane OS and the image plane IS in the projection beam path. For this purpose, each of the three biconcave negative lens elements has negative refractive power.

[0116] A fourth lens element group LG4 with positive refractive power and a total of four lens elements L11 to L14 immediately follows the third lens element group LG3. The lens elements of the fourth lens element group are arranged between the third lens element group LG3 and the stop position suitable for mounting an aperture stop AS. They comprise three positive lens elements (L11 , L13 and L14) and a lens element L11 with weak refractive power.

[0117] A fifth lens element group LG5 with positive refractive power overall is situated between the stop position and the image plane IS. The fifth lens element group comprises three lens elements L15 to L17 with refractive power. A plane parallel plate PL without refractive power is provided, as an optical and mechanical termination of the projection lens, between the last lens element with refractive power (positive lens element L17) and the image plane.

[0118] Consequently, the projection lens is characterized by the refractive power sequence N-P-N-P-P, where "P" represents a lens element group with positive refractive power and "N" represents a lens element group with negative refractive power. There is only a single pronounced waist in the region of the third negative lens element group LG3 between an object-near convexity (at LG2) and an image-near convexity (at LG4 and LG5). This design as a single-waist system contributes to the Petzval correction.

[0119] All the lens elements consist of fused silica (SiO2), and so a single-material system is present.

[0120] The projection lens contains aspherical rotationally symmetric lens element surfaces (aspheres), namely the lens element surfaces SRF 2, 5, 20, 21 , 25, 33 and 35.

[0121] In all the exemplary embodiments, a photoresist layer composed of a resist material with the hypothetical refractive index n = 1.70 is present in the image plane. According to an exemplary consideration, the image then arises at a depth of 500 nm in this material and the defocus of ± 500 nm takes place exclusively in this material. This is important in particular in order to be able to correctly assess the spherical aberration that arises at the defocus. For greater layer thicknesses, the depth and defocus variation values would be greater by corresponding factors.

[0122] First exemplary embodiment (N822; 2248 nm):

[0123] The first exemplary embodiment (Fig. 6) represents a projection lens at 248 nm and with a numerical aperture of NA=0.80. It has been trimmed for compactness, i.e. the lens element diameters are very small with 240 mm (optically free diameter). The maximum diameters in the first and second convexities of the system are practically the same. In particular, the condition

[0124] D2

[0125] 0.95 < — < 1.05 applies, where D2 is a maximum optically free lens element diameter of the second lens element group LG2 and D4 / 5 is a maximum optically free lens element diameter of the fourth and fifth lens element groups LG4 and LG5.

[0126] The image is produced at the depth of 500 nm in a photoresist layer (i.e. a lacquer) with the hypothetical refractive index of n = 1.70. nm

[0127] The chromatic longitudinal aberration in the lacquer is CHL « 260“ nm

[0128] The chromatic transverse aberration is CHV « 4.8“ at an image height of 13.6 mm.

[0129] At a defocus of 500 nm in the lacquer, a field-constant aberration of Z4 « 50 nm, Z9 « 1 nm is produced in the original setting plane for the present numerical aperture of NA=0.80.

[0130] In order to be able to shift the image ±500 nm through the lacquer, the wavelength would have to be detuned by approximately 1 .8 pm. This will inevitably result in an offset of the image structures nm at the edge of the field of 1.8 pm ■ 4.1“ « 8 nm. For greater shifts (for greater layer thicknesses), the values would be linearly higher.

[0131] Fig. 8 illustrates these residual aberrations when the image is defocused solely by detuning the wavelength by 0.5 pm. In addition to somewhat spherical aberration (Z9) and astigmatism (Z5 / 6), a severe scale error of more than 7 nm (Z2 / 3) occurs. This scale variation is a consequence of the existing CHV. From Z2 and Z3, the transverse aberration q can be calculated as q = IZ2 / NAI, where NA is the numerical aperture. Then Z2 = 7 results in q = ~ 8 nm.

[0132] If the shift of the focus by changing the wavelength is supported by a Z manipulator (L16; illustrated using hatching in the lens element sectional view), the resulting scale error can be corrected virtually completely.

[0133] Fig. 9 illustrates the residual aberrations when the wavelength is detuned by 0.4 pm and the Z manipulator with L16 is shifted axially by 1.01 pm. It can be seen that the effect of the manipulator combination of wavelength and Z manipulator almost perfectly compensates for the effect of the CHV. Dominant residual errors are astigmatism as well as mild coma and spherical aberration. However, the aberrations are each less than 1 nm Zernike.

[0134] Second exemplary embodiment (N823, Z193 nm) The second exemplary embodiment (lens element sectional view in Fig. 7) is intended to be used to show, by way of example, the principle even at the wavelength A = 193 nm.

[0135] The exemplary embodiment N823 in Fig. 7 involves a projection lens with the same field size (26x8 mm2on the wafer) as in the first exemplary embodiment, but at the wavelength of 193 nm and with a numerical aperture of 0.85. Due to the larger numerical aperture, the aberration Z4 « 57 nm, Z9 « 1.35 nm is produced at a defocus of 500 nm in the lacquer.

[0136] For the MFI, the same principle as in the first exemplary embodiment has been used, i.e. the defocus is achieved by detuning the wavelength by 0.1 pm and by means of an additional Z manipulator (L16) which is shifted 0.73 pm along the optical axis.

[0137] The lens element diameters have again been kept very compact, namely at roughly 250 mm, e.g. for L5 (251 mm) and L14 (251 mm). The maximum diameters in the first and second convexities of the system are practically the same. In particular, condition 0.95<D2 / (D4_5 )<1.05 also applies nm here. This results in a chromatic transverse aberration of CHV « 20— at the image height of 13.6 nm mm. The chromatic longitudinal aberration is approximately CHL « 650— in the lacquer. The values differ greatly from the first exemplary embodiment due to the larger dispersion of the glass at 193 nm compared to 248 nm.

[0138] The residual aberrations (Fig. 10) are dominated by slight astigmatism, spherical higher-order aberration (Z16) and a small residual error in the focus, but again all individual Zernike aberrations remain well below 1 nm.

[0139] Table 6 (N822) Table 6A

[0140] Table 7A Table 7 (N823)

Claims

Patent claims1 . Projection exposure method for exposing a substrate arranged in the region of an image plane of a projection lens with at least one image of a pattern of a mask arranged in the region of an object plane of the projection lens with radiation from a wavelength range around a design wavelength of < 260 nm by means of a projection lens (PO) which is optically corrected in such a manner that, at the design wavelength, a focus is produced in a design focus position (FOC0) and, for other wavelengths from the wavelength range, offset focus positionsare generated from an axially extended focus region (AFOC) around the design focus position (FOC0), wherein the projection lens has a wavefront manipulation system (WFM) for controllably influencing the wavefront of the projection radiation travelling from the object plane to the image plane, wherein the wavefront manipulation system (WFM) has at least one manipulator which, in response to control signals from a control unit, passes through manipulated value changes within a usable manipulated value range, which lead to changes in the wavefront, the method having the following steps of: coating the substrate (SUB) with a radiation-sensitive photoresist layer (RS) having a layer thickness (SD); exposing the substrate coated with the photoresist layer with the image of the pattern using radiation which, under the control of a control unit, according to a predefined temporal profile, has different wavelengths from a wavelength range with a spectral bandwidth around the design wavelength; synchronizing control of the wavefront manipulation system (WFM) with the temporal profile of the radiation of different wavelengths in such a way that a lateral chromatic aberration caused by switching between different wavelengths is at least partly compensated for.

2. Projection exposure method according to Claim 1 , characterized in that, for exposure, use is made of pulsed radiation which, under the control of the control unit, has pulses of different wavelengths from the wavelength range around the design wavelength in a predefined temporal sequence, wherein the spectral bandwidth of the wavelength range is at least an order of magnitude greater than the spectral bandwidth of the pulses.

3. Projection exposure method according to Claim 1 or 2, characterized in that the wavelengths, in particular the wavelengths of the pulses, vary according to a periodic time function with a wavelength alternating frequency between a first limit wavelength (minimum wavelength) and a second limit wavelength (maximum wavelength) of the wavelength range, whereinmanipulated value changes of the manipulator are adapted to the periodic time function in such a way that a manipulator varies periodically with the wavelength alternating frequency between a first limit manipulated value and a second limit manipulated value within a manipulated value range used.

4. Projection exposure method according to Claim 2 or 3, characterized in that the wavelength alternating frequency is at least an order of magnitude less than a pulse frequency of the pulsed radiation, wherein the wavelength alternating frequency is preferably in a range of 50 Hz or more, wherein the wavelength alternating frequency is preferably 100 Hz or more or 150 Hz or more and / or no more than 250 Hz.

5. Projection exposure method according to one of the preceding claims, characterized in that the time function, which describes the wavelength change, is a sine function, and / or in that the periodic time function, which is followed by the manipulated value changes of the manipulator, is a sine function.

6. Projection exposure method according to one of the preceding claims, characterized in that the wavelength range has a spectral bandwidth of at least 20 pm between an upper and a lower limit wavelength, wherein the spectral bandwidth is preferably in the range of 30 pm or more.

7. Projection exposure method according to one of the preceding claims, characterized in that the focus region is extended in an axial direction of the projection lens over at least 5 pm, preferably over 10 pm or more.

8. Projection exposure method according to one of the preceding claims, characterized in that the photoresist layer is applied with a layer thickness of the order of magnitude of 10 pm, wherein the layer thickness is preferably in the range of 5 pm to 20 pm.

9. Projection exposure method according to one of the preceding claims, characterized in that the manipulator has an optical element with refractive power arranged in the beam path of the projection lens and an actuator system for moving the optical element, wherein the optical element is moved by means of the actuator system with a movement component parallel to an axial direction of the projection lens, wherein the actuator system is preferably designed in such a manner that the optical element can also be tilted about a tilt axis oriented perpendicular to the axial direction.

10. Projection exposure method according to one of Claims 3 to 9, characterized in that manipulated value changes of the manipulator are adapted to the periodic time function in such a way that the manipulator varies periodically with the wavelength alternating frequency between a first limit manipulated value and a second limit threshold value within a manipulated value range used, wherein the manipulator preferably passes through a first extreme value of a manipulated value range used when pulses are emitted with the maximum wavelength and passes through a second extreme value of the manipulated value range used when pulses are emitted with the minimum wavelength, and / or wherein manipulated values are changed according to the time function in such a way that the manipulator element of the manipulator performs a jerk-free movement.

11. Projection exposure method according to one of the preceding claims, characterized in that a wavelength difference between the first limit wavelength (minimum wavelength) and the second limit wavelength (maximum wavelength) of the wavelength range is at least 20 pm (picometres).

12. Projection exposure apparatus for exposing a substrate arranged in the region of an image plane of a projection lens with at least one image of a pattern of a mask arranged in the region of an object plane of the projection lens with radiation from a wavelength range around a design wavelength of < 260 nm, comprising: a wavelength-variable light source (LS) for emitting radiation, in particular a sequence of pulses, of different wavelengths from the wavelength range around the design wavelength; an illumination system (ILL) for receiving the radiation and for generating an illumination radiation directed onto the mask (M); a projection lens (PO) for generating an image of the pattern in the region of the image surface (IS) of the projection lens, wherein the projection lens (PO) is optically corrected in such a manner that, at the design wavelength, a focus is produced in a design focus position (FOCO) and, for other wavelengths from the wavelength range, offset focus positions are generated from an axially extended focus region (AFOC) around the design focus position (FOCO), and wherein the projection lens has a wavefront manipulation system (WFM) for controllably influencing the wavefront of the projection radiation travelling from the object plane to the image plane, wherein the wavefront manipulation system (WFM) has at least one manipulator which, in response to control signals from a control unit, passes through manipulated value changes within a usable manipulated value range, which lead to changes in the wavefront, characterized in that the control unit in at least one operating mode is configured to synchronize control of the wavefront manipulation system (WFM) with the temporal sequence of pulses ofdifferent wavelengths in such a way that a lateral chromatic aberration caused by switching between different wavelengths is at least partly compensated for.

13. Projection exposure apparatus according to Claim 12, characterized in that the projection lens (PO) comprises five lens element groups (LG1 to LG5) between the object plane and the image plane, wherein a first lens element group (LG1) immediately following the object plane has a negative refractive power and comprises at least two lens elements (L1 , L2); a second lens element group (LG2) immediately following the first lens element group has a positive refractive power; a third lens element group (LG3) immediately following the second lens element group has a negative refractive power; a fourth lens element group (LG4) immediately following the third lens element group has a positive refractive power; a fifth lens element group (LG5) immediately following the fourth lens element group has a positive refractive power; the aperture stop is mounted between the fourth and fifth lens element groups; and the conditionD20.95 < — - < 1.05 D45applies, where D2 is a maximum optically free lens element diameter of the second lens element group (LG2) and D4 / 5 is a maximum optically free lens element diameter of the fourth and fifth lens element groups (LG4 and LG5).

14. Projection exposure apparatus according to Claim 13, characterized in that the projection lens has a wavefront manipulation system (WFM) for controllably influencing the wavefront of the projection radiation travelling from the object plane to the image plane, wherein the wavefront manipulation system (WFM) has at least one manipulator which, in response to control signals from a control unit, passes through manipulated value changes within a usable manipulated value range, which lead to changes in the wavefront, wherein the manipulator has at least one of the lens elements arranged in the beam path of the projection lens and an actuator system for moving the lens element, wherein the optical element can be moved by means of the actuator system with a movement component parallel to an axial direction of the projection lens, wherein the actuator system is preferably designed in such a way that the lens element can also be tilted around a tilt axis oriented perpendicular to the axial direction.

15. Projection exposure apparatus according to Claim 12, 13 or 14, characterized in that it is configured to carry out the projection exposure method according to one of Claims 1 to 11.

Images