Projection exposure process and projection exposure system for microlithography

Abstract

In a projection exposure method for exposing a substrate arranged in the area of ​​an image plane of a projection lens with at least one image of a pattern arranged in the area of ​​an object plane of the projection lens with radiation from a wavelength range around a design wavelength < 260 nm, a projection lens (PO) is used which is optically corrected such that at the design wavelength a focus is generated in a design focus position (FOC0) and for other wavelengths from the wavelength range offset focus positions are generated from an axially extended focus area (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 extending 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 within a usable setpoint range, undergoes setpoint changes that lead to changes in the wavefront. The method comprises the following steps: . Coating the substrate (SUB) with a radiation-sensitive photoresist layer (RS) having a layer thickness (SD); exposing the photoresist-coated substrate with the image of the pattern using radiation that, under the control of a control unit, has different wavelengths from a wavelength range with a spectral bandwidth around the design wavelength according to a predetermined temporal sequence; synchronizing a wavefront manipulation system (WFM) control with the temporal sequence of radiation of different wavelengths such that a lateral chromatic aberration caused by switching between different wavelengths is at least partially compensated.

Description

SCOPE OF APPLICATION AND STATE OF THE ART

[0001] The invention relates to a projection exposure method for exposing a substrate arranged in the area of ​​an image plane of a projection lens with at least one image of a pattern of a mask arranged in the area of ​​an object plane of the projection lens, and to a projection exposure system suitable for carrying out the method.

[0002] Microlithographic projection exposure processes are predominantly used today for the fabrication of semiconductor devices and other finely structured components, such as structured components for microsystems technology. Highly integrated semiconductor devices typically have multiple layers, of which only a few are very finely structured, e.g., on the scale of a few dozen nanometers, while other layers have significantly coarser structures. The former layers primarily perform the main functions of the semiconductor device, such as computations and data storage, while the latter layers serve purposes such as addressing and power supply. Structures with relatively coarse typical dimensions also exist in the field of microsystems technology, such as in microelectromechanical systems (MEMS) or micro-optoelectromechanical systems (MOEMS).Semiconductor devices are typically manufactured from a semiconductor substrate, while in microsystems technology other substrate materials, especially metals and glass-like materials, are also used.

[0003] In microlithographic projection exposure, masks (reticules) are typically used that carry the pattern of a structure to be imaged, e.g., a line pattern of a layer in a semiconductor device. A mask is positioned in a projection exposure unit between an illumination system and a projection lens, within the object plane of the projection lens, and illuminated by light supplied by the illumination system. The light, modified by the mask and the pattern, passes through the projection lens as projection radiation, which projects the mask pattern onto the substrate to be exposed. The substrate can be, for example, a semiconductor wafer. On the side of the substrate to be patterned, it has a radiation-sensitive (i.e., photosensitive) layer of photoresist material. This layer is also called the resist layer.

[0004] One of the goals in the development of projection exposure systems is to lithographically produce structures with increasingly smaller dimensions on the substrate. Smaller structures lead to higher integration densities, for example in semiconductor devices, which generally has a positive effect on the performance of the fabricated microstructured devices. The size of the structures that can be produced depends significantly on the resolving power of the projection lens used and can be increased both by reducing the wavelength of the projection radiation used and by increasing the image-side numerical aperture (NA) of the projection lens used in the process.

[0005] High-resolution projection lenses today operate at design wavelengths of less than 260 nm in the deep ultraviolet (DUV) or extreme ultraviolet (EUV) range. These projection lenses are optically corrected for the design wavelength and produce a focus at a specific design focus position. For deviations from the design wavelength, axially offset focus positions are generated from a focus area around the design focus position.

[0006] To ensure that the exposure process transfers the most faithful possible image of the pattern onto the substrate, the radiation-sensitive layer on the substrate surface should be located within the image-side focus area of ​​the projection lens during the exposure time interval. In particular, the layer on the substrate surface should lie within the depth of focus (DOF) of the projection lens.

[0007] According to a common definition, depth of field indicates the distance relative to the plane of best focus at which the intensity of a point image is at least 80% of the intensity at the plane of best focus. This is equivalent to the condition that the diameter of the point image is at most doubled. The depth of field is half the Rayleigh unit RU, which is expressed as RU = λ / NA. 2 is defined where λ is the working wavelength of the projection exposure system and NA is the image-side numerical aperture of the projection lens; the area in which the depth-of-field condition is satisfied accordingly has a total thickness equal to the Rayleigh unit RU. In general, the depth of field decreases as the resolving power of the projection lens increases.

[0008] Further miniaturization of feature sizes on computer chips is becoming increasingly difficult from a technical and physical perspective. The associated costs make further reductions in feature size less attractive in some cases. As an alternative to better utilizing the wafer area, the third dimension can be exploited by creating structures not only on or near the surface of the wafer, but also extending deeper into the wafer.

[0009] The third dimension is used, for example, to create three-dimensional stacking of flash memory structures, such as in the production of 3D NAND flash memory. 3D NAND is a type of non-volatile flash memory in which the memory cells are stacked vertically in multiple layers. Manufacturing 3D NAND requires the exposure of very thick resist layers. The depth of field of standard scanners is generally insufficient for this.

[0010] For the exposure of relatively thick photoresist layers, the use of so-called "focus drilling" is known in the field of 193 nm immersion lithography.

[0011] Application US 2007 / 0013889 A1 describes a projection exposure system comprising an illumination system for generating a beam of light, an arrangement of individually controllable elements for imparting 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 section of the substrate. The beam comprises a multitude of beam components. These include a first beam component with a first frequency spectrum around a first frequency and at least one second beam component with a second frequency spectrum around a second frequency. The second frequency differs from the first frequency. The projection system focuses the first and second beam components at different heights relative to the substrate table.

[0012] In the projection exposure process and projection exposure system of US Patent 4,937,619 A, a substrate is exposed to illumination light of different wavelengths, whereby the position of the focal area relative to the substrate surface changes with the wavelength due to the chromatic longitudinal aberration of the projection lens.

[0013] In the projection exposure process and the projection exposure system of US 5,303,002, a substrate is simultaneously exposed with narrowband pulses of closely adjacent, different wavelengths. Due to the longitudinal chromatic aberration of the projection lens, an effective increase in depth of field is achieved. TASK AND SOLUTION

[0014] It is an object of the invention to provide a projection exposure method that allows a relatively thick radiation-sensitive layer on a substrate to be exposed in such a way that an exposed volume with correctly oriented, sharp contours can be produced over the entire thickness of the layer. It is a further object to provide a projection exposure system suitable for carrying out the method.

[0015] To solve this problem, the invention provides a projection exposure method with the features of claim 1. Furthermore, a projection exposure system suitable for carrying out the projection exposure method with the features of claim 12 is provided. Advantageous embodiments are specified in the dependent claims. The wording of all claims is made clear by reference to the content of the description.

[0016] In the projection exposure process, a substrate positioned in the image plane of a projection lens is exposed with at least one image of a pattern located in the object plane of the projection lens that is optically conjugate to the image plane. Radiation from a wavelength range around a design wavelength of less than 260 nm (nanometers) is used for this purpose. Typically, a mask (reticle) is used to carry the pattern. It is also possible to use a controllable pattern generation device to create the pattern to be imaged.

[0017] The projection lens used is optically corrected such that, at the design wavelength, a focus is generated in a design focus position that lies within a design focus plane. For other wavelengths within the wavelength range, offset focus positions are generated from an axially extended focus area around the design focus position. The focus planes of the wavelength-dependent focus positions are offset from each other in the axial direction, i.e., in the direction parallel to the optical axis of the projection lens.

[0018] The projection lens is equipped with a wavefront manipulation system that allows the wavefront of the projection radiation, which travels from the object plane to the image plane, to be selectively influenced or modified in response to control signals from a control unit. For this purpose, the wavefront manipulation system includes at least one manipulator that, in response to control signals from the control unit, undergoes changes in its setpoint within a usable range, resulting in changes to the wavefront. The usable setpoint range is generally also referred to as the "range" of the manipulator. The term "manipulator" here refers, among other things, to optomechanical or optoelectronic devices designed to actively influence individual optical elements or groups of optical elements in response to corresponding control signals from an operating control system, in order to modify their optical effect, e.g.,to modify it in such a way that an unwanted aberration is at least partially compensated.

[0019] To carry out the process, the substrate is coated with a radiation-sensitive photoresist layer, the thickness of which may be relatively thick.

[0020] The substrate coated with the photoresist layer is exposed to an image of the pattern. Radiation is used to expose the photoresist-coated substrate with the image of the pattern. This radiation, controlled by a control unit, exhibits different wavelengths from a wavelength range with a spectral bandwidth around the design wavelength according to a predetermined time profile.

[0021] Preferably, pulsed radiation is used, which, under the control of the control unit, emits pulses of different wavelengths from the wavelength range around the design wavelength in a predetermined temporal sequence. Due to the design of the projection lens, this results in the projection radiation corresponding to the pulses lying at different axial focus positions within the focus range. The spectral bandwidth of the wavelength range over which the wavelength is varied is at least one order of magnitude (a factor of 10) larger 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 center-of-mass wavelength of that pulse.

[0022] The desired effect is an increase in the effectively used focus area, which corresponds to an increase in the effective depth of field (DOF). This makes it possible to expose even relatively thick photoresist layers with sufficiently focused radiation across their entire depth.

[0023] Within the wavelength range, a very large number of pulses with different center-of-mass wavelengths can be present, e.g., five or more, ten or more, or 50 or more, thus achieving a smooth focus gradient into the depth. Immediately successive pulses can be spectrally separated (distance between center-of-mass wavelengths greater than FWHM), but they can also spectrally overlap (distance between center-of-mass wavelengths less than FWHM).

[0024] This technique takes advantage of the fact that the projection lens exhibits chromatic aberration, which causes a wavelength-dependent focus position. An existing axial color error is used as a desired "vehicle" to increase the effective depth of field.

[0025] However, projection lenses typically also exhibit chromatic aberrations, which manifest as a lateral shift in focus, i.e., a shift perpendicular to the optical axis. This lateral shift is described by lateral color aberration. It has been recognized that this undesirable effect can severely impair image quality if, in order to achieve a large effective depth of field, the wavelength is varied relatively widely, for example, over a wavelength range whose spectral bandwidth is at least ten times greater than the spectral bandwidth of the pulses.

[0026] In the photolithographic process, this primarily causes the so-called "overlay" or overlay error (OVL). The overlay is a crucial parameter in the design of photolithographic processes. For example, the overlap accuracy of structures from different manufacturing steps of a photolithographic process is commonly referred to as the "overlay." High demands on overlap accuracy, or overlay, must also be met in multiple exposure processes.

[0027] In the claimed projection exposure method, the use of radiation or pulses of different wavelengths leads to a lateral chromatic aberration, which could result in an overlay error. According to the claimed invention, this undesirable side effect is avoided or limited to sufficiently small magnitudes 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 partially compensated. This ensures that the desired effect of increasing the depth of field is predominantly achieved in the process, while the undesirable side effect (overlay-like errors due to the lateral chromatic aberration) does not, or only minimally, impair the image quality.

[0028] According to a further development process, the temporal sequence and wavelengths of the radiation, particularly the pulses, of different wavelengths are controlled such that the wavelength of the radiation or the pulses varies according to a periodic time function with a wavelength switching frequency between a first and a second cutoff wavelength of the wavelength range. Changes in the manipulator's control value are adapted to this periodic time function such that, within a used control value range, the manipulator periodically varies with the wavelength switching frequency between a first and a second cutoff value. Periodic changes to which a frequency can be assigned can generally be generated with high reliability on both the light source and the manipulator.

[0029] In preferred method variants, the wavelength switching frequency is at least one order of magnitude lower than the pulse frequency of the pulsed radiation. This ensures that, essentially for every location on the exposed substrate, an averaging of different wavelengths is achieved such that, on average, each point in the exposed field is exposed to similar proportions of the different wavelengths from the wavelength range. Thus, a relatively uniform illumination of the area to be exposed on the substrate in a single operation can be achieved.

[0030] However, a lower limit for the wavelength switching frequency should ideally not be undercut. If the wavelength switching frequency becomes too low, the extent of induced overlay errors tends to increase.

[0031] In preferred embodiments, the wavelength switching frequency is provided to be in the range of 50 Hz to 500 Hz, with the wavelength switching frequency preferably being in the range of 100 Hz to 300 Hz. This generally allows a good compromise to be achieved between sufficiently strong compensation of overlay errors and not excessive loss of contrast.

[0032] In preferred embodiments, the time function describing the wavelength change is a sine function. Such periodic changes in the wavelengths of successive pulses can be implemented particularly easily and with high precision using appropriate devices in the area of ​​the light source of the projection exposure system.

[0033] In preferred embodiments, the periodic time function followed by the manipulator's control value changes is a sine function. This allows for smooth movement of the manipulator element between the limits of the required control values. Such sinusoidal oscillatory movements can often be achieved with conventional manipulators even when the moving mass of the manipulator is relatively large. If the manipulator is an oscillating system characterized by a natural frequency, then the reversing frequency can be optimized with respect to the manipulator's natural frequency.

[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 (picometers). 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 larger, e.g., up to 100 pm, but in any case, significantly less than one nanometer. This allows many of today's process requirements to be met. Here, spectral bandwidth is defined as the wavelength difference between an upper and a lower cutoff wavelength of the spectrum available for the pulse wavelengths.

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

[0036] In some embodiments, wavelength selection or modification is achieved by placing a rotatable grating or etalon in the laser resonator or by varying the resonator length. This allows only light within a narrow frequency range to be reflected back into the resonator and contribute to induced emission. Light of other wavelengths is reflected out of the resonator. By rotating the grating or etalon, different frequencies are successively fed back into the resonator, and the color of the laser light can be tuned.

[0037] The desired axial extent of the effective focus area for a specific process can be optimized depending on the process. In some embodiments, the focus area extends at least 5 µm in an axial direction of the projection lens, preferably over a focus area of ​​10 µm or more. This allows even the relatively thick photoresist layers used today in the photolithographic fabrication of three-dimensional flat storage structures to be exposed to their full depth. The focus area should not be significantly larger than 15 µm or 20 µm, as undesirable side effects (overlay errors induced by lateral chromatic aberrations) become increasingly pronounced and difficult to correct as the desired focus area expands.

[0038] This allows for good adaptation to advantageous processes in which the photoresist layer is applied with a thickness on the order of 10 µm, preferably in the range of 5 µm to 20 µm. Layer thicknesses can also be greater than 20 µm and / or less than 5 µm if necessary.

[0039] For the compensation of the lateral chromatic aberration or the overlay error induced by the lateral chromatic aberration, preferably at least one manipulator of the wavefront manipulation system is used, which comprises 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 setpoint 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 during 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 of projection lenses is usually also referred to as the Z-direction.

[0040] A single Z-manipulator can be used, or two or more can be activated simultaneously to cumulatively achieve the desired compensation effect. This solution has the advantage that most high-performance projection lenses today incorporate wavefront manipulation systems with Z-manipulators. Z-manipulators influence various aberrations that exhibit rotational symmetry with respect to the optical axis. A Z-manipulator can, for example, consist of a lens or mirror that is axially (parallel to the optical axis) movable. Among other things, a Z-manipulator can be used to change the image scale or magnification of the projection lens.A change in magnification corresponds to a lateral shift of pixels in the image plane and thus corresponds to the overlay error, which can be at least partially compensated by changes in the image scale.

[0041] If the projection lens is an optically rotationally symmetric system in which the effective object field and the effective image field are centered on the optical axis (on-axis systems), then manipulator movements parallel to the optical axis of the projection lens may be sufficient to adequately compensate for the overlay errors induced by wavelength changes.

[0042] In some designs, projection lenses are used in which the effective object field and the optically conjugate effective image field lie off-axis (off-axis field). This is the case, for example, with certain catadioptric projection lenses with one or more concave mirrors. The off-axis position of the effective fields can generate additional contributions to deviations of the image point position from the desired position during scanning. These contributions can be at least partially compensated if the optical element of the manipulator is tilted not only parallel to the axis but also about a tilting axis oriented perpendicular to the axial direction.

[0043] The invention also relates to a projection exposure system configured to carry out the method and a projection lens usable therein.

[0044] The light source is configured as a wavelength-variable light source such that, under the control of a control unit of the projection exposure system, it can emit radiation, particularly in the form of pulses, of different wavelengths from a wavelength range of at least ± 20 pm (picometers) or more around its design operating wavelength (e.g., approximately 248 nm or approximately 193 nm). With pulsed radiation, the spectral bandwidth of the individual pulses is relatively narrow compared to the spectral width of the wavelength range; it can be, for example, approximately 1 pm or below, e.g., in the range of 0.2 to 0.5 pm. The temporal progression of the transitions between the cutoff wavelengths of the wavelength range can be variably predefined. The wavelength can, for example, change periodically, e.g., according to a sinusoidal time function. The wavelength change frequency is preferably continuously adjustable or adjustable in steps, e.g.,in the range from 0Hz (no change in wavelength over time) up to approximately 500 Hz or more. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Further advantages and aspects of the invention will become apparent from the claims and from the description of exemplary embodiments of the invention, which are explained below with reference to the figures. Fig. Figure 1 shows a microlithography projection exposure system according to an embodiment of the invention; Fig. 2A and Fig. Figure 2B shows in 2A a wavelength-time diagram (λ / t diagram) with a temporal sequence of individual pulses whose center-of-mass wavelengths vary essentially according to a sinusoidal time function, and in 2B a schematic representation of the setpoint of a manipulator as a function of time t with respect to the same time axis as Fig. 2A; Fig. Figure 3 shows the effect of a moving average (MA) filter using the example of a periodic focus variation; Fig. Figure 4 shows a diagram of the field profile of Z2 based on the curve OVL1 (without compensation) and OVL2 (with compensation by manipulator movement); Fig. Figure 5 shows a schematic diagram with typical curves of overlay errors (curve MA) and contrast loss (curve MSD) as a function of frequency; Fig. Figure 6 shows a first embodiment of a projection lens; Fig. Figure 7 shows a second embodiment of a projection lens, Fig. 8 and Fig. Figure 9 shows residual aberrations of the first embodiment; Fig. Figure 10 shows residual aberrations of the second embodiment. DETAILED DESCRIPTION OF THE EXECUTION EXAMPLES

[0046] In Fig. Figure 1 shows an example of a WSC microlithography projection exposure system, which can be used in the production of semiconductor devices and other finely structured components and works with light or electromagnetic radiation from the deep ultraviolet (DUV) range to achieve resolutions down to fractions of micrometers.

[0047] The light source LS is a tunable KrF excimer laser with a primary operating wavelength of approximately 248 nm. Other UV laser light sources and operating wavelengths are also possible. The light source LS operates in pulsed mode and emits pulsed radiation, i.e., a temporal sequence of pulses PS (see Detail I), with a pulse frequency in the kilohertz range (i.e., at least 1 kHz, e.g., approximately 6 kHz). Each pulse can be characterized by its center-of-mass wavelength and its spectral bandwidth or spectral pulse width. The center-of-mass wavelength is the wavelength present in the pulse with maximum intensity. The spectral bandwidth of a pulse is given by the full width at half maximum (FWHM) of the intensity distribution around the center-of-mass wavelength of the pulse.

[0048] The term "light source" here is intended to include not only the primary light source from which light is emitted, but also any devices such as filters, apertures, bandwidth reduction modules, wavelength modification modules or the like, which serve to change the characteristics of the light emitted by the primary light source before it enters the lighting system.

[0049] The light source can emit pulses of different wavelengths from a wavelength range (WLB) of at least ±20 pm (picometers) around its main operating wavelength. For this purpose, the light source (LS) has a resonator and adjustable devices that modify the resonator's optical properties. Wavelength tuning can be achieved, for example, by installing a rotatable grating or etalon in the resonator and / or varying the resonator length. This allows only light within a narrow frequency range to be reflected back into the resonator and contribute to induced emission. Light of other wavelengths is reflected out of the resonator. By rotating the grating or etalon, different frequencies are successively fed back into the resonator, and the wavelength (center wavelength) of the laser light pulses can be precisely tuned.

[0050] The switching between different center-of-mass wavelengths within the wavelength range can occur relatively quickly, so that within a fraction of a second ten or more pulses, possibly even one hundred or more pulses of different center-of-mass wavelengths can be emitted from the wavelength range.

[0051] An illumination system ILL, located downstream of the light source LS, produces a large, sharply defined, and essentially homogeneously illuminated field at its exit surface ES. This field is adapted to the telecentricity requirements of the projection lens PO positioned downstream in the light path. The illumination system ILL has features for setting different illumination modes (illumination settings) and can be switched, for example, between conventional on-axis illumination with varying degrees of coherence σ and off-axis illumination. Off-axis illumination modes include, for example, annular illumination, dipole illumination, quadrupole illumination, or other multipolar illumination configurations.

[0052] Those optical components that receive the light from the light source LS and form illuminating radiation from the light, which is directed towards the illumination field lying in the exit plane ES or towards the reticle M, belong to the illumination system ILL of the projection exposure system.

[0053] Behind the illumination system, a device RS for holding and manipulating the mask M (reticule) is arranged such that the pattern PAT arranged on the reticule lies in the area of ​​the object plane OS of the projection lens PO, which coincides with the exit plane ES of the illumination system and is also referred to here as the reticule plane OS. The mask can be moved parallel to this plane in a scan direction (y-direction) perpendicular to the optical axis OA (z-direction) by means of a scan drive for scanner operation.

[0054] The RS device includes an integrated lifting device to move the mask linearly in the z-direction with respect to the object plane, i.e. perpendicular to the object plane, as well as an integrated tilting device to tilt the mask about a tilting axis running in the x-direction.

[0055] Behind the reticle plane OS follows the projection lens PO, which acts as a reduction lens and projects an image of the pattern arranged on the mask M at a reduced scale, for example at a scale of 1:4 (|β|= 0.25) or 1:5 (|β| = 0.20), onto a substrate W coated with a photoresist layer or photolac layer, whose light-sensitive substrate surface SS lies in the area of ​​the image plane IS of the projection lens PO.

[0056] The substrate to be exposed, which in this example is a semiconductor wafer W, is held by a device WS which includes a scanner drive to move the wafer synchronously with the reticule M perpendicular to the optical axis OA in a scan direction (y-direction).

[0057] The WS device also includes a lifting device to move the substrate linearly in the z-direction with respect to the image plane, and a tilting device to tilt the substrate about a tilting axis extending in the x-direction.

[0058] The WS device, also known as the "wafer stage", and the RS device, also known as the "reticule stage", are part of a scanner device that is controlled by a scan control unit, which in this embodiment is integrated into the central control unit CU of the projection exposure system.

[0059] The illumination field generated by the ILL illumination system defines the effective object field OF used in the projection exposure. In this example, it is rectangular, has a height A* measured parallel to the scan direction (y-direction), and a width B* > A* measured perpendicular to it (in the x-direction). The aspect ratio AR = B* / A* is typically between 2 and 10, particularly between 3 and 6. The effective object field is located at a distance in the y-direction to the side of the optical axis (off-axis field). The effective image field in the image area IS, which is optically conjugate to the effective object field, is also an off-axis field and has the same shape and the same aspect ratio between height B and width A as the effective object field. However, the absolute field size is reduced by the magnification β of the projection lens, i.e., A = |β| A* and B = |β| B*.

[0060] When the projection lens is designed and operated as an immersion lens, a thin layer of immersion fluid (IL) is irradiated during operation. This fluid is located between the exit surface of the projection lens and the image plane (IS). In immersion mode, image-side numerical apertures (NA) > 1 are possible. A dry lens configuration is also possible, in which case the image-side numerical aperture is limited to values ​​NA < 1.

[0061] In connection with the Fig. 8 and Fig. Section 9 describes examples of suitable projection lenses.

[0062] The WSC projection system features an operating control system configured to perform timely fine-tuning of its image-relevant properties in response to environmental influences and other disturbances, and / or based on stored control data. This operating control system incorporates a variety of manipulators that allow for targeted intervention in the projection behavior of the system. An actively controllable manipulator contains one or more actuators whose current setpoint can be modified based on control signals from the operating control system by making defined changes to the setpoint. Integrated sensors detect these changes, generate corresponding feedback signals, and thus regulate the manipulator settings.

[0063] The projection lens or projection exposure system is equipped, among other things, with a wavefront manipulation system (WFM) which is configured to controllably change the wavefront of the projection radiation running from the object plane (OS) to the image plane (IS) in such a way that the optical effect of the wavefront manipulation system can be variably adjusted via control signals from an operating control system.

[0064] The wavefront manipulation system (WFM) includes, among other things, a group of several Z-manipulators designed to simultaneously influence certain aberrations that exhibit 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, which can be individually moved parallel to the optical axis OA by means of an associated positioning device of the Z-manipulator (see Detail II, which shows a periodic movement of a manipulable lens in the z-direction). In the schematic Fig. Figure 1 shows two Z-manipulators ZMAN1 and ZMAN2 as examples, each with axially displaceable manipulable lenses ML1 and ML2 and associated adjustment devices DR1 and DR2. Typically, more than two Z-manipulators are present, for example, three or four. The shape of the displaceable lenses, their arrangement in the projection beam path (e.g., optical proximity to or distance from the nearest field plane or pupil plane) and in relation to adjacent lenses, as well as the extent of the axial displacement, influence the optical effect of the respective Z-manipulator.

[0065] A Z-manipulator can have additional degrees of freedom. In some or all Z-manipulators, the actuator system is designed such that the optical element can be tilted about a tilting axis oriented perpendicular to the axial direction and the scan direction, which corresponds to a rotation about an axis parallel to the x-axis.

[0066] In addition to the Z-manipulators, the wavefront manipulation system of the exemplary embodiment includes a deformation manipulator DMAN, which has a deformable manipulator element ME1, as in the example of Fig. 1 is arranged in the immediate vicinity of the object plane OS of the projection lens in the projection beam path and has two manipulator surfaces arranged in the projection beam path, the surface shape of which can be reversibly changed by means of an actuating device DR.

[0067] The manipulators are fast or dynamically adjustable manipulators that can implement changes in position values ​​rapidly within their usable setpoint ranges, e.g. with frequencies of up to approximately 300 Hz or more.

[0068] The projection exposure system is configured to perform a projection exposure process in which an effective depth of field on the order of 10 µm can be achieved by varying the wavelength used and thus by axially varying the focus positions. This allows for the creation of a three-dimensional stacking of flat-plate storage structures on the substrate. The longitudinal dependence of the focus position on the wavelength, also known as axial chromatic aberration or longitudinal color error, is used for this purpose. This causes the projection lens to produce a focus at the design wavelength (approx. 248 nm) in a specific design focus position, and for other wavelengths outside this range, to produce focus positions from an axially extended focus area around the design focus position.

[0069] The projection lens not only produces the desired axial variation of the focus position, but also so-called lateral chromatic aberration. This lateral chromatic aberration manifests itself as the dependence of the image size, or image height, of an off-axis object point on the wavelength. Thus, the lateral chromatic aberration leads to a dependence of the image scale on the wavelength. This is also referred to as chromatic aberration (CHV) or wavelength-dependent distortion. This is an undesirable effect, as it leads to overlay errors (OVL errors) in the process.

[0070] The following example explains how the desired effect (increase in effective DOF) can be achieved without having to accept significant disadvantages regarding overlay error.

[0071] For an exemplary estimate of the magnitudes, a substrate with approximately 170 layers, each 60 nm thick, is assumed. This results in a value of approximately 10 µm for the desired axial extent ΔFOC of the focus area.

[0072] The laser-equipped light source operates at a pulse frequency of 6 kHz. In scanner mode, a scan speed of approximately 800 mm / sec is targeted. For currently typical die sizes, this corresponds to a scan time of approximately 7 msec (milliseconds) for each point within the exposed unit.

[0073] The desired axial extent of the focus area (ΔFOC approx. 10 µm) is achieved in the projection lens by varying the wavelength used for exposure within a wavelength range with a spectral bandwidth of approximately 35 pm around the design wavelength λ0 (Δλ = 35 pm).

[0074] To assess the impact on the lithographic process, the process parameters overlay (OVL) and fading, or contrast loss, are primarily considered. These are crucial from the user's perspective. The user wants the various layers of a multilayer chip structure to be precisely aligned and for the sharpness of the imaged structures to meet 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 contrast loss resulting from motion blur in 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 as the moving standard deviation (MSD).

[0075] An estimate for the overlay error induced by a wavelength variation Δλ = 35 pm yields, for conventional projection lenses considered here, an order of magnitude of approximately 200 nm, or a lateral image displacement of approximately ± 100 nm from the position of a pixel at the design wavelength. This is unacceptable for most processes.

[0076] The following describes, using an exemplary embodiment, a method for achieving an effective increase in depth of field by varying the wavelength, without resulting in significant overlay errors, using the claimed invention. For this purpose, the light source LS is controlled to emit pulses of different wavelengths in a predetermined temporal sequence, the wavelengths being drawn from a wavelength range WLB around the design wavelength λ0. This wavelength range has a spectral bandwidth Δλ, which is defined as the difference between an upper cutoff wavelength λ0 and a lower cutoff wavelength λ. U This results in a spectral bandwidth Δλ that is significantly larger than the spectral bandwidth Δλ. PThe individual pulses can be multiplied, for example, 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 (FWHM) of the laser lines.

[0077] The control system synchronizes 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 switching between different wavelengths is at least partially compensated. This also allows the induced overlay error to be reduced to a non-critical level.

[0078] The processes in one exemplary implementation are described using the following examples: Fig. 2A and Fig. 2B explained. Fig. Figure 2A shows the temporal sequence of the individual pulses in a wavelength-time diagram (λ / t diagram), which are represented by vertical double-T lines. The center wavelengths of the individual pulses vary essentially according to a sinusoidal time function. This corresponds to the pulse frequency f. P The laser has a pulse interval of 1 / f between immediately successive pulses. P The spectral bandwidth of the pulses is approximately 0.35 nm and is represented disproportionately by the line length. The spectral bandwidth Δλ of the wavelength range WLB, in which the pulse wavelengths vary, is approximately 35 pm and is thus two orders of magnitude larger than the spectral pulse width. The spectral bandwidth Δλ corresponds to the amplitude of the depicted sine function. The pulse wavelengths vary periodically with a wavelength switching frequency f. WW, whose reciprocal value 1 / f WWcorresponds to the period length of the sine function on the time axis.

[0079] It is immediately apparent that the extent of the induced lateral chromatic aberration and the resulting induced overlay aberration fluctuates equally when the projection lens is operated without changing its imaging properties, in particular without operating any manipulators.

[0080] However, according to the embodiment, changes in the setpoint of manipulators of the wavefront manipulation system are synchronized with the temporal characteristic of the wavelength change in such a way that at least partial compensation of the induced lateral chromatic aberration results. Fig. Figure 2B shows a schematic representation of the setpoint SW. MAN of a manipulator or a group of manipulators as a function of time t with respect to the same time axis as Fig. 2A. The vertical distance between the upper and lower bounding dashed lines corresponds to the used control range SWB of the manipulator movement or the amplitude of the manipulator movement. The reciprocal of the periodicity of the sine function corresponds to the manipulator switching frequency f. MAN .

[0081] In this example, only Z-manipulators are dynamically varied within their used setpoint range according to a sinusoidal function between certain setpoint limits, which lie within a larger possible setpoint range of the respective manipulators. A sinusoidal change in the setpoint of a Z-manipulator thus corresponds to an axially oscillating movement of an optical element, for example a lens, in the projection beam path.

[0082] When considering the dynamics of the process, it is useful to investigate, among other things, at which frequencies the wavelength change and the corresponding manipulator movement should be operated to achieve a sufficiently strong effect within the dynamic range of the manipulators. It is also important to consider that within one period (1 / fλ) of the wavelength change, many light pulses of different wavelengths should strike every point of the exposed part of the substrate to achieve a sufficient depth of field effect. The following considerations serve to estimate suitable frequency ranges.

[0083] 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 results in a concomitant fluctuation of the image scale. Filter functions convert the amplitude of the fluctuation of the aerial image and the image scale into corresponding values ​​for the overlay (corresponding to MA) and for the contrast loss (corresponding to MSD) via averaging effects. This takes into account the effect of the scan movement, which means that each point is only exposed for a relatively short time during the overflow of the illuminated scan slit.

[0084] Fig. Figure 3 illustrates the effect of a MA filter using the example of periodic focus variation. The three diagrams in the top row represent focus variations with switching frequencies of 10 Hz (left), 75 Hz (center), and 150 Hz (right). The x-axis represents time t [msec], and the y-axis corresponds to the normalized focus position FOC. The narrow rectangular vertical stripes on the time axis have a width corresponding to the exposure time of a point in the field during scanning. For a scan speed of 800 mm / sec and a slit width of 5.5 mm, each point on the wafer is exposed for approximately 7 msec. The diagram in the bottom row shows corresponding MA filter values ​​as a function of the wavelength switching frequency f. WW Values ​​close to 1 correspond to a large overlay error; at a value of zero, the overlay error disappears.

[0085] At the slowest switching frequency (10 Hz), a first point P1 on the wafer "sees" an average focus value of 0.99, while a second point P2, offset laterally, "sees" an average focus value of -0.99 within its exposure time. This shows that almost the entire amplitude of the focus variation becomes effective as a corresponding overlay error on the exposed substrate when the period of the wavelength change is large compared to the exposure time achievable by scanning. In the MA filter diagram in the bottom row, this situation corresponds to an MA filter value of almost 1, which, on the normalized scale, represents a near-maximum overlay error.

[0086] At the higher wavelength switching 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 in focus values ​​is significantly smaller than with the slower wavelength fluctuation, so that averaging results in a lower overlay error, which is expressed by an MA filter value of approximately 0.6.

[0087] The right-hand diagram for a wavelength switching frequency of 150 Hz represents a nearly 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 is effective, and at the second point P2, an average focus value of -0.03. These values ​​are very close to each other, so that practically no overlay error results from the time averaging. This is reflected in the MA filter diagram by a value close to zero at the frequency of 150 Hz.

[0088] Therefore, if the exposure time is short compared to the oscillation period, large overlay errors result. Conversely, if the exposure time is long compared to the oscillation period, averaging over many aerial images occurs. This shows that, depending on the chosen wavelength switching frequency, the overlay error can be relatively small. However, this then leads to a relatively strong loss of contrast ("fading").

[0089] Therefore, no critical overlay error is generated if the wavelength switching frequency is high enough, but a significant loss of contrast is observed. In the assumed example, the MSD value, which represents the contrast loss, is approximately ten times higher than acceptable for the intended application.

[0090] There may be applications where the loss of contrast is acceptable as long as the OVL error is kept small.

[0091] In the present embodiment, however, the time-averaged OVL error is at least partially compensated by compensating movements of Z-manipulators, resulting in a process-compatible compromise between overlay error and contrast loss. According to the inventors' experience, the overlay error can best be described by a linear combination of Zernike coefficients, in particular a combination of Z2, Z7, and Z22. The main driver is the contribution of Z2, which represents the tilting of the wavefront around the y-axis.

[0092] In practice, it is therefore advisable to review and design compensation measures primarily with regard to their impact on Z2. In other words, reducing the contribution of Z2 to the wavefront aberration can relatively effectively highlight or compensate for an overlay error.

[0093] The diagram in Fig. Figure 4 shows the field profile of the Zernike coefficient Z2 based on the curve OVL1. This represents the main part of the overlay error caused by a wavelength variation of 35 pm.

[0094] To determine which manipulator movements can counteract this error and at least partially compensate for the overlay error, the original OVL error was 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 needed to be moved, and in what way, to counteract the overlay error.

[0095] The simulations considered a total of six Z-manipulators, ZMAN1 to ZMAN6. These were simulated with varying amplitudes of their positioning movements. The Z-manipulators included in the simulation also offer additional degrees of freedom, including tilting around the x-axis and tilting around the y-axis at appropriate angles. In the specific simulated example, these compensatory measures are necessary because the effective object field and the effective image field are not centered on the optical axis ("on-axis field"), but rather lie off-axis.

[0096] For on-axis fields, positioning movements parallel to the z-direction are sufficient; tilting components would not be necessary.

[0097] To simulate the actual process in a scanner system, the dynamics of the process must be taken into account. This is achieved using a MA filter and an MSD filter, where the MA filter represents the overlay error and the MSD filter the contrast loss. The filter functions translate the amplitude of a sinusoidal displacement of the aerial image parallel to the x-direction into corresponding values ​​for overlay (MA) and contrast loss (MSD). Scan weightings are also considered.

[0098] The schematic diagram in Fig. Figure 5 represents typical curves of overlay errors (curve MA) and contrast loss (curve MSD) as a function of the wavelength switching frequency f plotted on the x-axis. WW The y-axis indicates the normalized magnitude of the respective error, where the value 1 corresponds to the maximum value.

[0099] In a first scenario, only the wavelength of the primary radiation fluctuates sinusoidally across its wavelength range, while no compensation is made via manipulator movements.

[0100] In a second scenario, the wavelength and the setpoints of the Z-manipulators vary synchronously according to a sinusoidal time function (see...). Fig. 2A and Fig. 2B).

[0101] The following will be based on the Fig. 6 and Fig. Figure 7 shows two embodiments of projection lenses exhibiting uncorrected chromatic aberration (CHV or lateral color LAT) that can be used within the scope of the claimed invention to enable multifocal magnification (MFI). In wavelength-shifted MFI, the longitudinal chromatic aberration of projection systems is exploited to shift the optimal focusing plane through a thick photoresist layer during exposure by detuning the laser wavelength. The change in magnification with wavelength is to be compensated for by additional manipulation. In particular, the following scenarios are considered: (i) moving individual lenses or lens groups along the z-axis (optical axis) of the system and (ii) additional support by z-shifting reticles and / or wafers.

[0102] In the following description of projection lenses, the term "optical axis" refers to a straight line through the centers of curvature of the curved lens surfaces. In the examples, the object is a mask (reticule) with the pattern of an integrated circuit; it could also be another pattern, such as a grating. The image is projected in the examples onto a wafer coated with a photoresist layer, which serves as the substrate. Other substrates are also possible, such as elements for liquid crystal displays or substrates for optical gratings.

[0103] The specifications of the projection lenses shown in the drawing figures are given in the tables compiled at the end of the description, the numbering of which corresponds to the numbering of the respective drawing figure.

[0104] Tables 6, 6A and 7, 7A summarize the specifications of each design in tabular form. The "SURF" column indicates the number of a refracting or otherwise distinguished surface, the "RADIUS" column the radius r of the surface (in mm), the "THICKNESS" column the distance d from the surface to the next surface (in mm), and the "MATERIAL" column the material of the optical components. The "INDEX1", "INDEX2", and "INDEX3" columns indicate the refractive index of the material at wavelengths of 248.413 nm (INDEX1), 247.413 nm (INDEX2), and 249.413 nm (INDEX3) (first embodiment) or 193, 192, and 194 nm (second embodiment). The "SEMIDIAM" column specifies the usable free radii or half the free optical diameters of the lenses (in mm) or optical elements. A radius of r=0 (in the "RADIUS" column) corresponds to a flat surface. Some optical surfaces are aspherical.Tables with the suffix "A" indicate the corresponding aspheric data, whereby the aspheric areas are calculated according to the following rule: p(h)=[((1 / r)h2) / (1+SQRT(1−(1+K)(1 / r)2h2))]+C1*h4+C2*h6+…

[0105] The reciprocal (1 / r) of the radius gives the surface curvature, and h gives the distance of a surface point from the optical axis (i.e., the ray height). Thus, p(h) gives the ray 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 given in the tables with the suffix "A".

[0106] In the following description of exemplary embodiments, the same reference numerals are used for identical or corresponding features in all figures. Lenses are numbered sequentially from the object plane to the image plane, so that, for example, lens L1 is the first lens immediately following the object plane. For the sake of clarity, not all lenses are labeled with reference numerals.

[0107] Fig. Figure 6 shows a schematic meridional lens section of a first embodiment of a dioptric projection lens PO-1 (designation N822) with selected beams to illustrate the imaging beam path or projection beam path of the projection radiation passing through the projection lens during operation.

[0108] The projection lens is designed as a reducing imaging system to directly map a pattern of a mask arranged in its object plane OS onto its image plane IS, which is aligned parallel to the object plane, at a reduced scale, namely at a scale of -1:4 (image scale β= -0.25), without generating an intermediate image.

[0109] The only pupil plane of the imaging system lies between the object plane and the image plane, at the point where the principal ray CR of the optical imaging intersects the optical axis OA. The aperture diaphragm AS of the system is located in the region of the pupil plane. The position suitable for mounting the aperture diaphragm is therefore also referred to here as the diaphragm position BP.

[0110] Around the aperture position, there is an aperture region in which the condition |CRH / MRH| < 1 holds for a beam height ratio between the principal beam height CRH and the marginal beam height MRH of the image. The marginal beam height is therefore greater than the principal beam height. The optical setup can be characterized as follows.

[0111] Immediately following the object plane OS is a first lens group LG1 with negative refractive power, which in this example is formed by two lenses L1 and L2. Lens L1 is a biconcave negative lens, and L2 is a negative meniscus lens with a concave entrance surface and a convex exit surface. The first lens group prepares the way for the formation of an antinode in the subsequent beam path by increasing divergence. Such a negative group in close proximity to the object plane allows the formation of a subsequent antinode over a short axial length and is therefore conducive to a compact design.

[0112] Immediately following the first lens group LG1 is a second lens group LG2 with positive refractive power. This second lens group comprises the five lenses L3 to L7, all of which, except for L7, have positive refractive power. The second lens group focuses the rays coming from the first lens group, thereby forming at least an approximate antinode in the projection beam path.

[0113] Immediately following the second lens group LG2 is a third lens group LG3 with negative refractive power. This third lens group comprises the three lenses L8 to L10 and creates a waist in the projection beam path around a local minimum of the marginal beam height between the object plane OS and the image plane IS. Each of the three biconcave negative lenses also has negative refractive power.

[0114] Immediately following the third lens group LG3 is a fourth lens group LG4 with positive refractive power, comprising a total of four lenses L11 to L14. The lenses of the fourth lens group are positioned between the third lens group LG3 and the aperture position suitable for attaching an aperture diaphragm AS. They include three positive lenses (L11, L13, and L14) and one low-power lens L11.

[0115] Between the aperture position and the image plane IS is a fifth lens group LG5 with an overall positive refractive power. This fifth lens group comprises three refractive lenses, L15 to L17. Between the last refractive lens (positive lens L17) and the image plane, a non-refractive, plane-parallel plate PL serves as the optical and mechanical seal of the projection lens.

[0116] The projection lens is thus characterized by the refractive power sequence NPNPP, where "P" stands for a lens group with positive refractive power and "N" for a lens group with negative refractive power. Between an object-proximal bulge (at LG2) and an image-proximal bulge (at LG4 and LG5), there is only one pronounced waist in the region of the negative third lens group, LG3. This design as a single-waisted system contributes to Petzval correction.

[0117] All lenses are made of quartz glass (SiO2), so it is a single-material system.

[0118] The projection lens contains aspherical rotationally symmetric lens surfaces (aspheres), namely lens surfaces SRF 2, 5, 20, 21, 25, 33 and 35.

[0119] In all embodiments, a photoresist layer made of a resist material with a hypothetical refractive index n = 1.70 is present in the image plane. According to an exemplary analysis, the image is then formed at a depth of 500 nm within this material, and the defocus of ± 500 nm occurs exclusively within this material. This is particularly important for correctly evaluating the spherical aberration that arises during defocus. With greater layer thicknesses, the values ​​for depth and defocus variation would be correspondingly larger. First embodiment (N822; λ248nm):

[0120] The first embodiment ( Fig. Figure 6) represents a projection lens at 248 nm and a numerical aperture of NA = 0.80. It has been optimized for compactness, meaning the lens diameters are very small at 240 mm (optically clear diameter). The maximum diameters in the first and second bulges of the system are practically the same. In particular, the following condition holds: 0.95 <D2D45<1.05, where D2 is a maximum optically free lens diameter of the second lens group LG2 and D4 / 5 is a maximum optically free lens diameter of the fourth and fifth lens groups LG4 and LG5.

[0121] The image is formed at a depth of 500 nm in a photoresist layer (i.e., a varnish) with a hypothetical refractive index of n = 1.70.

[0122] The chromatic longitudinal aberration in the paint is CHL≈260nmpm

[0123] The chromatic cross-aberration is CHV≈4.8nmpm at an image height of 13.6 mm

[0124] With a defocus of 500 nm in the varnish, a field constant aberration of Z4 ≈ 50 nm, Z9 ≈ 1 nm occurs in the original focusing plane at the given numerical aperture of NA=0.80.

[0125] To shift the image ±500 nm through the varnish, the wavelength would have to be detuned by approximately 1.8 pm. This inevitably leads to a displacement of the image structures at the field edge of 1.8pm⋅4.1nmpm≈8nm This would lead to larger shifts (for larger layer thicknesses, the values ​​would be linearly higher).

[0126] In Fig. Figure 8 shows these residual aberrations when the image is defocused solely by a wavelength shift of 0.5 µm. Besides some spherical aberration (Z9) and astigmatism (Z5 / 6), a significant scale error of over 7 nm (Z2 / 3) occurs. This scale variation is a consequence of the existing chromatic aberration. From Z2 and Z3, the transverse aberration q can be calculated as q = |Z2 / NA|, where NA is the numerical aperture. Then, with Z2 = 7 nm, we arrive at q = ∼ 8 nm.

[0127] If the shift of the focus by changing the wavelength is supported by a Z-manipulator (L16; shown hatched in the lens section), the resulting scale error can be almost completely corrected.

[0128] In Fig. Figure 9 shows the residual aberrations when the wavelength is detuned by 0.4 pm and the Z-manipulator with L16 is axially shifted by 1.01 µm. It can be seen that the effect of the manipulator combination (wavelength and Z-manipulator) almost perfectly compensates for the effect of the CHV (composite wavelength variation). The dominant residual errors are astigmatism, slight coma, and spherical aberration. However, these aberrations are all below 1 nm Zernike. Second embodiment (N823, λ193nm)

[0129] With the second embodiment (lens cut in Fig. 7) The principle will be demonstrated again using the wavelength λ = 193 nm as an example.

[0130] In the embodiment N823 in Fig. 7 is a projection lens with the same field size (26×8 mm). 2(on the wafer) as in the first embodiment, but at a wavelength of 193 nm and a numerical aperture of 0.85. Due to the larger numerical aperture, with a defocus of 500 nm in the resist, the aberration Z4 ≈ 57 nm, Z9 ≈ 1.35 nm occurs.

[0131] The same principle as in the first embodiment has been used for the MFI, i.e. the defocus is achieved by a detuning of the wavelength by 0.1 pm and an additional Z-manipulator (L16) which is shifted 0.73 µm along the optical axis.

[0132] The lens diameters have again been kept very compact, roughly 250 mm, for example at L5 (251 mm) and L14 (251 mm). The maximum diameters in the first and second bulges of the system are practically the same. In particular, the condition 0.95 also applies here. <D2 / (D4_5)<1.05. Es stellt sich damit eine chromatische Queraberration von CHV≈20nmpm The image height is 13.6 mm. The longitudinal chromatic aberration is approximately... CHL≈650nmpm in the paint. The values ​​differ significantly from the first embodiment due to the greater dispersion of the glass at 193nm compared to 248nm.

[0133] The remaining aberrations ( Fig. 10) are dominated by slight astigmatism, higher order spherical aberration (Z16) and a small residual error at focus, but again all individual Zernike aberrations remain well below 1 nm. Table 6 (N822) SURF RADIUS THICKNESS MATERIAL INDEX1 INDEX2 INDEX3 SEMIDIAM. 0 0,000000 48,071042 1 -38104,873853 10,000000 SILUV 1,508427 1,508989 1,507873 64,7 2 156,028923 47,028234 67,7 3 -99,193438 25,000032 SILUV 1,508427 1,508989 1,507873 70,2 4 -181,120995 1,831891 87,8 5 -813,838021 45,970111 SILUV 1,508427 1,508989 1,507873 97,2 6 -181,238112 0,999911 105,7 7 1091,788108 45,062492 SILUV 1,508427 1,508989 1,507873 118,2 8 -283,491552 15,164141 120,0 9 421,025866 40,510461 SILUV 1,508427 1,508989 1,507873 120,0 10 -644,411830 0,999332 118,8 11 173,590280 43,531567 SILUV 1,508427 1,508989 1,507873 106,4 12 1057,932434 0,999942 101,4 13 182,074321 39,070605 SILUV 1,508427 1,508989 1,507873 89,3 14 110,304069 33,715225 66,5 15 -284,868464 10,000000 SILUV 1,508427 1,508989 1,507873 64,4 16 107,698328 31,937920 56,9 17 -333,471435 10,000000 SILUV 1,508427 1,508989 1,507873 56,5 18 670,978752 52,388628 57,1 19 -85,692191 10,000000 SILUV 1,508427 1,508989 1,507873 59,6 20 238,785672 18,976940 75,5 21 915,111577 39,719643 SILUV 1,508427 1,508989 1,507873 86,4 22 -186,989511 0,999873 91,8 23 0,000000 10,000000 SILUV 1,508427 1,508989 1,507873 102,0 24 0,000000 13,267940 104,5 25 -1001,596523 42,202483 SILUV 1,508427 1,508989 1,507873 106,1 26 -173,999771 0,999780 110,4 27 301,492525 41,794911 SILUV 1,508427 1,508989 1,507873 120,0 28 -1461,329440 0,999938 119,4 29 0,000000 104,052268 118,8 30 309,415769 39,737149 SILUV 1,508427 1,508989 1,507873 120,0 31 -1993,385861 0,999816 118,4 32 149,619644 55,538749 SILUV 1,508427 1,508989 1,507873 106,8 33 1001,469119 0,999627 98,4 34 113,434437 76,803904 SILUV 1,508427 1,508989 1,507873 81,3 35 313,220683 5,517327 47,4 36 0,000000 23,108094 SILUV 1,508427 1,508989 1,507873 44,7 37 0,000000 11,999500 30,0 38 0,000000 0,000500 RESIST 1,700000 1,700000 1,700000 13,6 39 0,000000 0,000000 13,6 Table 6A SRF 2 5 20 21 25 K 0 0 0 0 0 C1 -2,227721E-07 -2,372728E-08 -4,422822E-08 -8,182041E-09 -2,708270E-08 C2 8,930794E-12 1,404533E-13 -2,393782E-12 -5,828366E-13 1,408456E-13 C3 -5,599264E-16 -2,402642E-18 3,730046E-16 1,335208E-16 -1,882969E-17 C4 3,725392E-20 9,702042E-23 -3,504214E-20 -1,105026E-20 -1,960111E-22 C5 -2,012841E-24 -8,592941E-27 1,500282E-24 7,013196E-25 -1,332026E-26 C6 1,260310E-28 1,125399E-30 -4,317693E-29 -4,191333E-29 -1,331319E-30 SRF 33 35 K 0 0 C1 1,760499E-08 7,743672E-09 C2 8,444146E-13 -7,038618E-12 C3 -2,022481E-17 -2,525678E-15 C4 2,348987E-21 5,597113E-19 C5 -1,345537E-25 -2,232000E-22 C6 8,809295E-30 4,000943E-26 Table 7A SRF 2 4 17 19 24 K 0 0 0 0 0 C1 -2,775038E-07 5,634465E-08 -1,982431E-08 1,624808E-07 5,390577E-08 C2 1,331594E-11 4,500897E-13 -1,296630E-11 2,425336E-11 1,977684E-12 C3 -8,496888E-16 -7,473988E-17 5,145394E-15 -2,098907E-15 1,354725E-17 C4 8,471001E-20 -3,985253E-21 1,156135E-19 -2,717518E-19 -1,591000E-21 C5 -5,690978E-24 3,486817E-25 -3,750094E-24 5,969521E-23 -1,977699E-25 C6 3,665060E-28 -6,803070E-30 4,876018E-27 -3,060363E-27 9,300112E-30 SRF 33 35 K 0 0 C1 1,424455E-08 -1,729355E-09 C2 1,794522E-12 2,235100E-12 C3 -1,481813E-16 4,892786E-16 C4 1,425754E-20 -1,039971E-19 C5 -7,137143E-25 3,303483E-24 C6 2,202694E-29 -4,060497E-29 Table 7(N823) SURF RADIUS THICKNESS MATERIAL INDEX1 INDEX2 INDEX3 SEMIDIAM. 0 0,000000 41,240370 1 690,569667 10,000000 SILUV 1,560970 1,562593 1,559387 64,6 2 147,341213 54,047599 66,6 3 -117,219967 24,935414 SILUV 1,560970 1,562593 1,559387 72,7 4 -425,515120 3,114271 94,3 5 -876,643815 34,096760 SILUV 1,560970 1,562593 1,559387 97,7 6 -208,879859 1,000012 103,9 7 -2810,897481 51,463574 SILUV 1,560970 1,562593 1,559387 116,7 8 -193,074996 7,001656 120,4 9 372,521573 50,506148 SILUV 1,560970 1,562593 1,559387 125,4 10 -463,195745 0,999781 124,4 11 134,937852 56,381112 SILUV 1,560970 1,562593 1,559387 103,6 12 650,062644 4,443561 95,1 13 640,605075 19,913438 SILUV 1,560970 1,562593 1,559387 91,3 14 128,897084 17,756468 71,3 15 312,240086 10,000000 SILUV 1,560970 1,562593 1,559387 69,3 16 96,684137 58,947481 59,9 17 -86,357880 10,000000 SILUV 1,560970 1,562593 1,559387 56,1 18 157,099506 19,308606 63,4 19 -1138,123504 43,652370 SILUV 1,560970 1,562593 1,559387 69,7 20 -106,646070 9,480018 72,8 21 -95,983669 10,000000 SILUV 1,560970 1,562593 1,559387 72,4 22 457,679514 22,521782 88,9 23 575,451595 37,349439 SILUV 1,560970 1,562593 1,559387 107,6 24 -243,673939 0,999918 111,4 25 -1502,637104 56,314125 SILUV 1,560970 1,562593 1,559387 117,4 26 -180,853762 1,000123 121,9 27 440,549056 30,422683 SILUV 1,560970 1,562593 1,559387 125,7 28 42039,810332 10,397564 124,9 29 0,000000 89,047491 123,8 30 1885,806986 41,763558 SILUV 1,560970 1,562593 1,559387 125,7 31 -363,305377 0,999893 125,5 32 134,843615 58,932811 SILUV 1,560970 1,562593 1,559387 107,2 33 811,746618 0,999758 99,3 34 137,840504 34,778541 SILUV 1,560970 1,562593 1,559387 83,6 35 228,239876 8,703784 70,0 36 410,681205 55,479901 SILUV 1,560970 1,562593 1,559387 66,8 37 0,000000 11,999500 34,0 38 0,000000 0,000500 RESIST 1,700000 1,700000 1,700000 14,3 39 0,000000 0,000000 14,3 QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 4,937,619 A

[0012] US 5,303,002

[0013]

Claims

[1] Projection exposure method for exposing a substrate arranged in the area of ​​an image plane of a projection lens with at least one image of a pattern of a mask arranged in the area of ​​an object plane of the projection lens with radiation from a wavelength range around a design wavelength < 260 nm, by means of a projection lens (PO) which is optically corrected such that at the design wavelength a focus is generated in a design focus position (FOC0) and for other wavelengths from the wavelength range offset focus positions are generated from an axially extended focus area (ΔFOC) around the design focus position (FOC0), wherein the projection lens has a wavefront manipulation system (WFM) for controllable influencing of the wavefront of the projection radiation extending 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 within a usable setpoint range, undergoes setpoint changes that lead to changes in the wavefront, the procedure with the following steps: Coating the substrate (SUB) with a radiation-sensitive photoresist layer (RS) having a layer thickness (SD); Exposure of the substrate coated with the photoresist layer with the image of the pattern using radiation which, under the control of a control unit, has different wavelengths from a wavelength range with a spectral bandwidth around the design wavelength according to a predetermined time course; Synchronizing the control of the wavefront manipulation system (WFM) with the temporal evolution of radiation of different wavelengths in such a way that a lateral chromatic aberration caused by switching between different wavelengths is at least partially compensated. [2] Projection exposure method according to claim 1, characterized by , that pulsed radiation is used for exposure, which, under control of the control unit, has pulses of different wavelengths from the wavelength range around the design wavelength in a predetermined temporal sequence, wherein the spectral bandwidth of the wavelength range is at least one order of magnitude larger than the spectral bandwidth of the pulses. [3] Projection exposure method according to claim 1 or 2, characterized by, that the wavelengths, in particular the wavelengths of the pulses, vary according to a periodic time function with a wavelength change frequency between a first limit wavelength (minimum wavelength) and a second limit wavelength (maximum wavelength) of the wavelength range, wherein changes in the setpoint of the manipulator are adapted to the periodic time function such that a manipulator within a used setpoint range varies periodically with the wavelength change frequency between a first limit setpoint and a second limit setpoint. [4] Projection exposure method according to claim 2 or 3, characterized bythat the wavelength switching frequency is at least one order of magnitude lower than a pulse frequency of the pulsed radiation, wherein preferably the wavelength switching frequency is in a range of 50 Hz or more, wherein the wavelength switching frequency is preferably at 100 Hz or more or at 150 Hz or more and / or at no more than 250 Hz. [5] Projection exposure method according to any of the preceding claims, characterized by , that the time function describing the wavelength change is a sine function and / or that the periodic time function followed by the manipulator's control value changes is a sine function. [6] Projection exposure method according to one of the preceding claims, characterized bythat the wavelength range has a spectral bandwidth of at least 20 pm between an upper and a lower cutoff 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 by that the focus area in an axial direction of the projection lens extends over at least 5µm, preferably over 10µm or more. [8] Projection exposure method according to one of the preceding claims, characterized by , that the photoresist layer is applied with a layer thickness on the order of 10 µm, wherein the layer thickness is preferably in the range of 5µm to 20 µm. [9] Projection exposure method according to any of the preceding claims, characterized by, that the manipulator comprises 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 preferably the actuator system is designed such that the optical element can additionally be tilted about a tilting axis oriented perpendicular to the axial direction. [10] Projection exposure method according to any one of claims 3 to 9, characterized bythat the manipulator's control value changes are adapted to the periodic time function such that the manipulator, within a used control value range, periodically varies with the wavelength change frequency between a first limit control value and a second limit threshold, wherein preferably the manipulator passes through a first extreme value of a used control value range when pulses with the maximum wavelength are emitted and passes through a second extreme value of the used control value range when pulses with the minimum wavelength are emitted and / or wherein control values ​​are changed according to the time function such that the manipulator element of the manipulator performs a jerk-free movement. [11] Projection exposure method according to any of the preceding claims, characterized by, that the wavelength difference between the first cutoff wavelength (minimum wavelength) and the second cutoff wavelength (maximum wavelength) of the wavelength range is at least 20 pm (picometers). [12] Projection exposure system for exposing a substrate arranged in the area of ​​an image plane of a projection lens with at least one image of a pattern of a mask arranged in the area of ​​an object plane of the projection lens with radiation from a wavelength range around a design wavelength < 260 nm: 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; a lighting system (ILL) for receiving the radiation and generating lighting radiation directed at the mask (M); a projection lens (PO) for generating an image of the pattern in the area of ​​the image surface (IS) of the projection lens, wherein the projection lens (PO) is optically corrected such that at the design wavelength a focus is generated in a design focus position (FOC0) and for other wavelengths from the wavelength range offset focus positions are generated from an axially extended focus area (ΔFOC) around the design focus position (FOC0), and wherein the projection lens has a wavefront manipulation system (WFM) for controllable influencing of the wavefront of the projection radiation extending 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 within a usable setpoint range, undergoes setpoint changes that lead to changes in the wavefront, characterized by, that the control unit is configured in at least one operating mode to synchronize control of the wavefront manipulation system (WFM) 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 partially compensated. [13] Projection exposure system according to claim 12, characterized by , that the projection lens (PO) between the object plane and the image plane comprises five lens groups (LG1 to LG5), wherein a first lens group (LG1) immediately following the object plane has a negative refractive power and comprises at least two lenses (L1, L2); a second lens group (LG2) immediately following the first lens group has a positive refractive power; a third lens group (LG3) immediately following the second lens group has a negative refractive power; A fourth lens group (LG4) immediately following the third lens group has a positive refractive power; a fifth lens group (LG5) immediately following the fourth lens group has a positive refractive power; The aperture diaphragm is located between the fourth and fifth lens groups; and the condition 0.95 <D2D45<1.05 applies, where D2 is a maximum optically free lens diameter of the second lens group (LG2) and D4 / 5 is a maximum optically free lens diameter of the fourth and fifth lens groups (LG4 and LG5). [14] Projection exposure system according to claim 13, characterized bythat the projection lens has a wavefront manipulation system (WFM) for controllably influencing the wavefront of the projection radiation extending 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, undergoes changes in the setpoint within a usable setpoint range, which lead to changes in the wavefront, wherein the manipulator has at least one of the lenses arranged in the beam path of the projection lens and an actuator system for moving the lens, 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 preferably the actuator system is designed such that the lens can additionally be tilted about a tilting axis oriented perpendicular to the axial direction. [15] Projection exposure system according to claim 12, 13 or 14, characterized by that it is configured to carry out the projection exposure method according to one of claims 1 to 11.

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