WO2008009356A1

WO2008009356A1 - Microlithographic projection exposure apparatus and method for correcting imaging aberrations

Info

Publication number: WO2008009356A1
Application number: PCT/EP2007/005986
Authority: WO
Inventors: Toralf Gruner; Claus Zahlten; Jörg TSCHISCHGALE
Original assignee: Carl Zeiss Smt Ag
Priority date: 2006-07-15
Filing date: 2007-07-06
Publication date: 2008-01-24
Also published as: DE102006032877A1

Abstract

A microlithographic projection exposure apparatus has a projection objective (20; 120), containing a plurality of optical elements (56; 156), and also a device (58; 116, 155, 162a, 162b), in which a device parameter can be called up. The device parameter relates to an ambient condition or a state variable of at least one of the optical elements. The device parameter can also relate to an actuating variable of an actuation element that can be used to vary the effect of at least one component (116) of the projection exposure apparatus. The temperature of a liquid (38; 138) which is arranged within or outside the projection objective and through which projection light (13; 113) passes can be set to a desired value by means of a temperature regulating device (44; 144). A control unit (48; 148) determines the desired value for the temperature of the liquid depending on the device parameter.

Description

MICROLITHOGRAPHIC PROJECTION EXPOSURE PLANT AND METHOD FOR CORRECTION OF IMAGING ERRORS

BACKGROUND OF THE INVENTION

1. Field of the invention

The invention relates to microlithographic projection exposure systems, as used for producing highly integrated circuits and other microstructured

Components are used. In particular, the invention relates to the correction of optical aberrations in projection objectives of such projection exposure apparatuses.

2. Description of the Related Art

Integrated electrical circuits and other microstructured devices are typically fabricated by applying a plurality of patterned layers to a suitable substrate, which may be a silicon wafer, for example. To structure the layers, they are first covered with a photoresist which is sensitive to light of a specific wavelength range, for example light in the deep ultraviolet spectral range (DUV, deep ultraviolet). Subsequently, the thus coated wafer is exposed in a projection exposure apparatus. This is a Pattern of structures, which is on a mask, imaged on the photoresist using a projection lens. Since the magnification is generally less than 1, such projection lenses are often referred to as reduction lenses.

After developing the photoresist, the wafer is subjected to an etching process, whereby the layer is patterned according to the pattern on the mask. The remaining photoresist is then removed from the remaining parts of the layer. This process is repeated until all layers are applied to the wafer.

Projection exposure systems have other important components in addition to the projection lens. One of them is the lighting system, which illuminates the mask with the structures to be projected. Furthermore, very precise working traversing tables must be present, with which the mask and the wafer can be moved and exactly positioned.

One of the key goals in the development of projection exposure equipment is to be able to lithographically produce structures of increasingly smaller dimensions on the wafer. Small structures lead to high integration densities, which generally has a favorable effect on the performance of the microstructured components produced by means of such systems. The size of the structures that can be generated mainly depends on the resolution of the projection lens used. Since the resolution of the projection lenses is proportional to the wavelength of the projection light, one approach to increasing the resolution is to use projection light with ever shorter wavelengths. The shortest wavelengths currently used are in the ultraviolet spectral range and are 248 nm, 193 nm or 157 nm.

Another approach to increasing resolution is based on the idea of introducing a high refractive index immersion liquid into an immersion space left between a last lens of the projection lens and the photoresist or other photosensitive layer to be exposed. Projection objectives which are designed for immersion operation and therefore also referred to as immersion objectives may have numerical apertures of more than 1, e.g. 1.3 or 1.4.

With a high resolution, however, high integration densities can only be achieved if aberrations in the projection objective are sufficiently corrected. The causes of aberrations in projection lenses are manifold. Often difficult to correct are aberrations that are due to material or manufacturing defects. The same applies to aberrations that only occur during operation. tende changes caused by the optical lens contained in the projection lens. These may be, for example, temporary changes in shape that result from local heating by the high-energy projection light. The projection light can also interact directly with the material of which the optical elements consist, and cause, for example, permanent changes in the refractive index.

Another cause of aberrations are changes in certain environmental conditions which have an influence on the imaging properties. These environmental conditions include, in particular, the pressure and the temperature of gases which are passed by projection light. The refraction at an interface between a gas and a solid medium, eg quartz glass or a crystalline material such as CaF ₂ , depends on the refractive index of the gas and on the refractive index of the solid medium. If the pressure and / or the temperature of the gas changes, so does the density and thus also the refractive index of the gas. According to the ideal gas equation, for example, pressure fluctuations at a constant temperature have a linear effect on the density. Since the design of the projection lens is based on specific refractive indices of the gases and the solid media, the optical properties of the projection lens deteriorate as the pressure and / or the temperature and thus the refractive index of the gases adjacent to the refractive interfaces change. The causes of pressure changes of gases are manifold. In addition to the altitude above sea level, weather-related fluctuations in the barometric external pressure also affect the refractive index of the gases.

For correcting aberrations caused by changes in the gas pressure, it is known to change the wavelength of the projection light that passes through the projection lens after diffraction on the mask. The fact is exploited that, especially for liquid and solid media, the refractive index depends relatively strongly on the wavelength of the projection light. In common lens materials for projection lenses, such as quartz glass or CaF ₂ , this dependence called dispersion at a wavelength of 193 nm is so large that you can achieve a noticeable change in the refractive index in the solid media even by small changes in wavelength. This makes it possible to keep the refractive index quotient which is decisive for the refraction at the interface between gaseous and solid media constant even when the refractive index of the gaseous medium changes. The change in the wavelength of the projection light is in this case generally brought about by adjusting the resonator of a laser used as the light source.

However, a correction of aberrations caused by pressure fluctuations of surrounding gases in this way succeeds only very much good if all solid refractive media in the projection lens are made of the same material, eg quartz glass. If different materials, eg CaF ₂ , BaF ₂ or lutetium garnet (LuAG) in addition to quartz glass, are used, then the refractive index quotient can no longer be kept constant for all refractive surfaces if the gas pressure changes, since the materials generally have a different dispersion ,

WO 2004/053596 A2 discloses a microlithographic projection exposure apparatus in which the temperature of an immersion liquid is adjusted in a targeted manner for the purpose of correcting imaging aberrations, in particular the spherical aberration. There, the aberrations in an image plane of the projection lens are first measured and from this the desired temperature of the immersion liquid is derived.

SUMMARY OF THE INVENTION

The object of the invention is to specify a microlithographic projection exposure apparatus with which time-varying aberrations can be better corrected.

This problem is solved by a microlithographic projection exposure apparatus with: a) a projection lens containing a plurality of optical elements,

b) a device on which a device parameter can be called up, wherein the device parameter relates to an ambient condition or a state variable of at least one of the optical elements or to a manipulated variable of an actuating element, by which the effect of at least one component of the projection exposure system can be changed is

c) a tempering device, with which the temperature of a liquid arranged inside or outside the projection lens and passing through projection light can be set to a target value,

d) a control unit which determines the setpoint for the temperature of the liquid as a function of the device parameter.

According to the invention it has been recognized that by a change in temperature of a liquid certain imaging errors, such as those that compensate for a change in the refractive index quotient at interfaces between a gas and a solid or liquid optical material, very largely. Here, the fact is exploited that for short-wave light transparent liquids have a refractive index, the relatively strong (in the Order of magnitude of about -0,0001 / K) depends on the temperature. Because of this temperature dependence, the temperature of liquids used as optical media must anyway be set very accurately to a target value estimated in the design of the projection lens. If this setpoint is slightly changed, it can be corrected very well with the help of the liquid aberrations caused by various causes, such as variations in pressure or the temperature of a gas.

The invention is also based on the recognition that it is not absolutely necessary to measure the aberrations themselves for an effective correction of aberrations with the aid of a temperature change of the liquid, as is known per se in the prior art. Rather, it is sufficient in many cases, if one makes the specification of the temperature of the immersion liquid of easily detectable device parameters. The dependence of the temperature of the liquid of one or more device parameters can be determined for example by calibration, so that you can read the desired value of the temperature of the liquid, for example, simply from a table in which the setpoint values for the temperature for different device parameters are stored. However, dependencies determined by simulation or calibration can also be stored as functions. By resorting to easily determinable device parameters, the relatively complex measurement of imaging properties, which is usually carried out in the image plane of the projection lens, is eliminated. Such measurements interrupt the operation of the projection exposure system and thus cause production losses. By contrast, the device parameters considered here can also be determined continuously during the operation of the projection exposure apparatus, so that the correction of the aberrations with the aid of the temperature setting of the liquid is continuous or intermittent, but at least during the operation of the projection exposure apparatus, for example during a short period which is already required Interruptions between exposures, can be performed.

The liquid may be located, for example, in a cavity of the projection lens whose boundary surfaces are flat or curved. In the latter case, the liquid forms a liquid lens, as has already been proposed for projection lenses for other reasons. However, such a liquid lens may also be provided specifically for the purpose of enabling the correction of aberrations described here.

In the case of immersion objectives, a liquid outside the projection objective is available with the immersion liquid, the temperature of which can be selectively changed in order to compensate for temporally variable aberrations. rigieren. The immersion liquid can adjoin the object side to a plane or to a curved refractive surface.

In the device where one or more device parameters are retrievable, it may be e.g. to be a barometer to measure the pressure or a thermometer to measure the temperature of a gas.

As a barometer for measuring the pressure of the gas, any device can be considered with which the gas pressure can be determined directly or indirectly. The easiest way is the use of barometers of conventional design, whose measurement signal directly indicates the gas pressure. By indirect measurement is meant that the gas pressure can be derived at least in principle from the measured size. The determination of the temperature setpoint as a function of the measured gas pressure is therefore the same if the desired value is determined as a function of another variable, but which is indirectly correlated with the gas pressure. As a barometer in this sense, therefore, e.g. Also called a device that measures the refractive index of the gas.

In projection lenses with a pressure-tight housing in which the space between lenses is flushed by a purge gas, the pressure within the housing is generally controlled in response to the external pressure, that the pressure difference not changed. In this way, deformation of the housing can be avoided. However, even such projection lenses have at least on the light entry side an optical surface adjacent to a surrounding gas. Although this gas is purified in clean rooms, the pressure of the gas still depends on the height of the clean room above sea level and generally also on the barometric external pressure outside the clean room. Depending on the prevailing conditions, the barometer is therefore to be arranged within the projection objective or outside the projection objective, but preferably in the vicinity of the relevant refractive surfaces. Under certain circumstances, it may also be expedient to provide a plurality of barometers if, for example, different gas pressures prevail at different locations due to a temperature gradient.

Corresponding considerations also apply to the already mentioned thermometer.

As already mentioned, the device parameter can also refer to a state variable of an optical element. These are to be understood here as quantities which refer to the position, the shape or another property of the optical element, for example its refractive index. These variables can change as a result of external influences, eg heating, but also due to the targeted action of manipulators. The device is in this case a measuring device or sensor with which the relevant state variable can be measured directly.

Furthermore, the device parameter can relate to a manipulated variable of an actuating element, by means of which the effect of at least one component of the projection exposure apparatus can be changed. Considered as devices here come e.g. the above-mentioned manipulators, by means of which the position and / or shape of the respective optical elements are highly accurately changeable. Instead of directly measuring a state variable on an optical element, it is often sufficient to know only the manipulated variable of the manipulator, which changes the relevant state variable.

Another example of such a device is a device with which different illumination angle distributions of projection light are adjustable, which falls on a mask to be imaged. This is based on the consideration that the illumination angle distribution set by such a device has an effect on the temperature distribution of the optical elements contained in the projection objective. The temperature distribution in the optical elements in turn affects the optical imaging properties of the projection lens. The specific properties of a mask, to which the adjusted illumination angle distribution is adapted, may be neglected under certain circumstances. If the illumination angle distribution is changed with the aid of the device, then the temperature be adapted to the liquid accordingly. Preferably, the "history" of the projection operation over a certain period of time is taken into account, since this also affects the temperature distribution in the optical elements.

It has been found that aberrations caused by variations in gas pressure or temperature, even without tuning the wavelength, i. Only by changing the temperature of the liquid, can be corrected very effectively. It is best, however, if both measures are combined. A wavelength manipulator is then provided with which the wavelength of the projection light entering the projection lens can be set to a desired value. The control unit determines the setpoint value for the wavelength as a function of the device parameter.

If a wavelength manipulator is present, the nominal values for the temperature of the liquid and the nominal values for the wavelength of the projection light can be stored in a data memory or can be calculated according to a predetermined functional relationship in the control unit for different values of the manipulated variable.

Because of the linearity of the relevant physical relationships in this context, the control The setpoint values for the temperature of the liquid and the setpoint values for the wavelength of the projection light are determined in a fixed ratio such that the ratio of the temperature change of the liquid and the wavelength change of the projection light remains constant for all values of the device parameter.

A further improved correction of the aberrations considered here is possible if one or more manipulators are provided with which the mask and / or the photosensitive layer and / or an optical element of the projection lens can be moved along an optical axis of the projection objective.

As example calculations show, by combining a wavelength manipulator and a tempering device for the temperature control of the liquid, it is possible to achieve such a good correction that it is possible to very effectively correct aberrations which are due to fluctuations in the gas pressure but also to other causes. The control unit is then preferably designed to collectively determine the setpoint wavelength of the projection light and the setpoint temperature of the liquid such that the imaging properties of the projection lens are within predetermined specifications. These specifications can be much narrower than those that can be achieved so far, if you only use the wavelength of the project Onslichts or alternatively only the temperature of the liquid changed.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will become apparent from the following description of exemplary embodiments with reference to the drawings. Show:

FIG. 1 shows a microlithographic projection exposure apparatus according to a first exemplary embodiment in a schematic meridional section;

FIG. 2 shows a microlithographic projection exposure apparatus according to a second exemplary embodiment in a representation similar to FIG.

DESCRIPTION OF PREFERRED EMBODIMENTS

A generally designated 10 microlithographic projection exposure exposure system has an illumination system 12 for generating projection light 13. The illumination system 12 includes a light source 14, an illumination optics schematically indicated by two lenses 16, 17, and a field stop 18. The light source 14 is designed in the illustrated embodiment as an ArF laser, the projection light 13 emits at a wavelength of about 193 nm. By adjusting the laser resonator, it is possible to continuously detune the wavelength of the projection light 13 within a predetermined wavelength range. The devices provided for detuning the laser resonator form a wavelength manipulator 19.

To Proj tion exposure system 10 also includes a

Projection objective 20 with which a mask 24 which can be arranged in its object plane 22 can be imaged in a reduced manner onto a photosensitive layer 26. The photosensitive layer 26 is located in an image plane 28 of the projection objective 20. The projection objective 20 contains a multiplicity of optical elements, only a few of which are indicated in FIG. 1 as lenses. In addition to lenses, e.g. Planar or curved mirrors and other optical elements such as diaphragms or polarization-influencing elements may also be included in the projection objective 20.

The photosensitive layer 26 may be, for example, a photoresist which is applied to a carrier 30, for example a silicon wafer. The support 30 is fixed in the illustrated embodiment at the bottom of a trough-like, upwardly open container 32, which by means of a designated 36 designated - li ^¬

Moving device is parallel to the image plane 28 and perpendicular to it. The container 32 is filled with an immersion liquid 38 so far that a gap 40 between the photosensitive layer 26 and one of these layer 26 facing the image side last optical surface 42 of the projection lens 20 at least partially, but preferably completely filled with the immersion liquid 38. It is understood that the immersion liquid 38 may be held in the space 40 other than the container 32, as is well known in the art.

In the container 32, a tempering device 44 is also arranged, which can be designed as a pure heater, but also as a combined heating / cooling device. With the aid of the tempering device 44, it is possible to keep the immersion liquid 38 located in the intermediate space 40 very precisely at a predetermined desired temperature. The tempering device 44 is indicated only schematically in FIG. Possible details and variants for a suitable tempering device can be found in WO 2005/071491 A2, the disclosure content of which is fully incorporated in the content of the present application. The tempering 44 may also be part of a cycle in which the

Immersion liquid 38 is circulated, cleaned and brought to the target temperature. Such a tempering direction is described for example in US 4,346,164.

The projection exposure apparatus 10 also has a temperature sensor 46, which measures the temperature of the immersion liquid 38 with high accuracy.

The temperature control unit 44 and the temperature sensor 46 are connected via signal lines to a control unit 48, with which a target temperature of the immersion liquid 38 can be adjusted via a control loop. The control unit 48 is further connected to the first traversing device 36 and to a second traversing device 52, which makes it possible to move the mask 24 not only parallel to the object plane 22 but also perpendicular to it with high accuracy. The first and / or the second traversing device 36 or 52 may be formed so that tilting of the mask 24 or the photosensitive layer 26 can be generated about an axis perpendicular to an optical axis 50 axis. This is particularly advantageous when the mask 24 is illuminated with an off-axis field.

A z-manipulator indicated by 54 is likewise connected to the control unit 48 and makes it possible to move a lens 56 contained in the projection objective 20 along the optical axis 50. In addition, the projection exposure apparatus 10 has a barometer 58, indicated as a measuring instrument, which is likewise connected to the control unit 48. The barometer 58 makes it possible to measure the pressure of the gas surrounding the projection objective 20. If the interspaces between the optical elements of the projection objective 20 are purged with a chemically inert purging gas, the barometer can alternatively also be arranged in one (or even several barometers in separate regions) intermediate spaces. Since most of the pressure in the spaces is adapted to the external pressure, but in many cases, a barometer that measures the external pressure can be sufficient.

The wavelength manipulator 19, the first traversing device 36, the second traversing device 52, the z-manipulator 54 and the barometer 58 together with the control unit 48 form a correction device with which aberrations of the projection lens 10 can be corrected.

The correction device works as follows:

The design of the projection objective 20 is based on certain refractive indices of the refractive optical elements passing through the projection light 13 and the surrounding gases. The refraction at the interfaces between the optical elements and the gases is thereby determined by the refractive index quotient of the adjacent media at the interface.

The refractive index of the gases surrounding the refractive optical elements depends primarily on their density. This is u.a. determined at what level above the sea level, the projection exposure system 10 is located. In addition, variations in the barometric external pressure or heating of the gases may cause their pressure to change.

As a result of the pressure change, the refractive index quotient also changes at the refractive interfaces between the gases and the refractive optical elements. If the refractive index quotient differs noticeably from that which was used in the design of the projection objective 20, this leads to aberrations.

In the projection exposure apparatus 10, the pressure of the gases is measured before or during the operation of the projection exposure apparatus 10 by means of the barometer 58. The control unit 48 determines on the basis of the measured pressure setpoints for the with the

Control unit 48 connected manipulators. In detail, these are a desired value for the temperature of the immersion liquid 38, a desired value for the wavelength of the projection light 13, and values for the respective position of the lens 56, the mask 24 and the photosensitive layer 26 along the optical axis 50.

Table 1: Imaging error with pressure change of 25 mbar

Table 1 shows for a concrete projection objective 20 how a pressure difference of 25 mbar affects a number of different aberrations, which are indicated in the table 1 by Zernike polynomials indicating abbreviations. The numerical values indicated in the line below show how the aberrations caused by the pressure change can be corrected if only the wavelength of the projection light 13 with the wavelength manipulator 19 and the position of the mask 24 and the photosensitive layer 26 along the optical axis 50 is changed appropriately. The line below indicates how the errors thus achieved can be considerably reduced again if, in addition, the temperature of the immersion liquid 38 is changed in a suitable manner. In the assumed example, a temperature change of 0.056 k is sufficient a reference temperature at normal pressure to cause the significant reduction of aberrations.

Table 1 thus clearly shows how the additional change in the temperature of the immersion liquid 38 can achieve a significant improvement in the correction of such aberrations caused by changes in the pressure of the surrounding gases.

In order to be able to find optimum setpoint values for the wavelength of the projection light 13, the temperature of the immersion liquid 38 and the position along the optical axis 50 of the mask 24 and the photosensitive layer 26 for each pressure value measured by the barometer 58 the control unit 48 includes a memory with a table stored therein containing these setpoints. In order to determine the desired values, it is possible either to carry out corresponding tests in advance in which the imaging errors are determined by measurement as a function of the gas pressure. By means of simulation or tests, combinations of the specified values can then be determined for a large number of printed values, which bring about an optimal correction of the imaging errors.

Alternatively, it is also possible, for example, to detect the dependence of the individual desired values on the measured gas pressure in the form of functional relationships that the control unit 48 can calculate the corresponding setpoints themselves at each gas pressure.

It has also been found that a good correction of aberrations caused by pressure fluctuations, can be brought about alone with a change in temperature of the immersion liquid 38. Since the temperature of the immersion liquid 38 has to be determined very precisely anyway, then the expense which is necessary for the other manipulators may be eliminated. In particular, the first and second ^{traversing devices} 36 and 52 are mechanically relatively auf ^¬ agile and therefore expensive. If slightly larger aberrations can be tolerated, then such a variant, in which only the temperature of the immersion liquid 38 is changed to correct the aberrations, is an interesting and cost-effective alternative.

Furthermore, it has been shown that it is very effective with a combination of a wavelength manipulator 19 and the temperature of the immersion liquid 38 can also correct those aberrations that are not caused by pressure fluctuations.

FIG. 2 shows, in a representation similar to FIG. 1, a meridional section through a micro-lithographic projection exposure apparatus according to another exemplary embodiment of the invention. Parts of the The projection exposure apparatus designated overall by 110, which correspond to parts of the projection exposure exposure apparatus 10 shown in FIG. 1, are designated by reference numerals increased by 100 and will in some cases not be described again in detail.

The projection exposure apparatus 110 differs from the projection exposure apparatus 10 shown in FIG. 1, inter alia, in that the projection objective 120 is subdivided by a barrier 159 into two sections 160a, 160b which are separated from one another in a gastight manner. In sections 160a, 160b, a first thermometer 162a and a second thermometer 162b, respectively, are arranged. The purpose of the thermometers 162a, 162b is to measure the temperature of a purge gas which flushes through the gaps between the optical elements disposed in the respective sections 160a and 160b. The thermometers 162a, 162b are connected to the control unit 148 via signal lines.

Furthermore, a device of the illumination optics designated by 116 in the illumination system 112 is designed such that the illumination angle distribution of the projection light 113 incident on the mask 124 can be changed. The device 116 of the illumination optics may for this purpose contain, for example, exchangeable or adjustable optical components, eg diffractive optical elements, a zoom objective, axicon elements or diaphragms. In addition, an arrangement of a plurality of pressure actuators 155 is provided as a further correction mechanism, with which the lens 156 can be deformed rotationally asymmetric. With such deformations, it is possible in particular to reduce those aberrations which are caused by a likewise rotationally asymmetric heating of optical elements.

The projection exposure apparatus 110 operates as follows:

The device 116 transmits to the control unit 148 the information as to which illumination angle distribution is set. The illumination angle distribution generally has an effect on the path which takes the projection light 113 diffracted by the mask 124 in the projection lens 120. The light path of the projection light 113, in turn, influences the temperature distribution that occurs in the optical elements of the projection lens 120 by partial absorption of the projection light 113. By changing the temperature distribution in lenses and other optical elements also change their optical properties, which leads to aberrations. The aberrations can be so great that corrective action must be taken.

To correct these aberrations, the control unit 148 causes a suitable rotationally asymmetric deformation of the lens 156 and a change in the Temperature of immersion liquid 138. The change in the temperature of immersion liquid 138 can thereby correct rotationally symmetric components of the aberrations, and / or rotationally symmetric aberrations that are introduced by the deformation of lens 156 are corrected.

When ascertaining control signals for the pressure actuators 155 and the tempering device 144 for controlling the temperature of the immersion liquid 138, it is possible to resort to different methods:

Basically, it is possible, with knowledge of the mask 124 to be projected, the illumination angle distribution set in the illumination system 112, and the design data of the projection lens 120 to predict which path the diffracted projection light 113 in the projection lens 120 will take and how the optical elements exposed to the projection light 120 will heat up. Furthermore, it can be determined by simulation how the heating of the optical elements affects the optical imaging properties of the projection lens 120 and what measures are to be taken to reduce aberrations caused by the heating.

When calculating the temperature distribution, the aberrations and the required corrective measures, the dynamic behavior must also be taken into account in general. So it makes a difference whether a project Formation of the mask 124 takes place after the projection exposure apparatus 110 was previously not operated for several days, whether another mask was previously projected with a different illumination angle distribution or whether the same mask was already projected for several days, so that in the meantime a stationary state has set.

Since the calculations explained above are relatively complicated, simplified methods can also be resorted to. Particularly suitable are calibration methods in which calibration measurements have previously been used to determine once, for certain illumination angle distributions, that the imaging properties of the projection lens 120 change and which corrective measures achieve the best correction effect. It can be exploited that the illumination angle distribution is generally adapted to certain types of mask, so that it no longer depends on the specific properties of the specifically to be projected mask 124.

In a table, for example, for different illumination angle distributions, the optimal correction measures can be stored in this simplified procedure, as they have previously been determined by appropriate calibration. Preferably, the mentioned dynamic behavior is taken into account, so that, for example, after the first recording of a projection operation the corrective measures are changed again and again until finally a stationary state has set. The dependency on formerly used lighting settings can also be determined during the calibration preliminary tests.

For the control unit 148, this means that it should to a certain extent capture and store the history of the projection operation and, in particular, the respectively set illumination setting over a certain period of time. The optimal control signals for the pressure actuators 155 and the tempering device 144 can then be read from the stored calibration data.

If a different mask with a different illumination angle distribution is to be projected, the control unit 148 reads out from the calibration data other control signals for the pressure actuators 155 and the tempering device 144.

In the embodiment described here, during the operation of the projection exposure apparatus 110, the thermometers 162a, 162b measure the temperature in the sections 160a or 160b and forward the measured values to the control unit 148. It is assumed that the temperature of the purge gases is adjusted by purging devices for the circulation of the purge gases in the sections 160a, 160b to a target value from the outside of the projection lens 120 prevailing outside temperature depends. The target temperature of the purge gases is determined so that the projection lens 120 deforms minimally with changes in the outside temperature.

If the purging devices keep the pressure of the purging gases constant in order, for example, to maintain a predetermined ratio to the external pressure prevailing outside the projection objective 120, a change in the temperature of the purging gases also causes a change in their density. As has already been explained above, this in turn has an effect on their refractive indices and thus also on the optical properties of the projection lens 120.

The control unit 148 now determines appropriate corrective actions based on the measured temperatures in the sections 160a, 160b to reduce imaging errors caused by changes in the refractive index of the purge gases. In particular, a change in the temperature of the immersion liquid 138 and a change in the wavelength of the projection light 113 come into consideration.

The control unit 148 preferably coordinates the two above-described corrective measures, which are caused by changes in the illumination angle distribution on the one hand, and by changes in the temperature of the purge gases, on the other hand. So For example, the values stored in a calibration table for control signals as a function of the set illumination angle distribution can be further dependent on the temperatures in the sections 160a, 160b.

In a modified embodiment 155 sensors are integrated in the pressure actuators, which detect the deformation of the lens 156. The control unit 148 then controls the temperature of the irrigation liquid 138 immediately in response to signals generated by the sensors which are a measure of the actual deformation of the lens 156.

It is understood that the embodiments described above are merely exemplary in character. In particular, the measurements and corrective measures described in the exemplary embodiments can be combined as desired.

Claims

1. Microlithographic projection exposure apparatus, with:

a) a projection objective (20; 120) containing a plurality of optical elements (56; 156),

b) a device (58; 116, 155, 162a, 162b) to which a device parameter is retrievable, the device parameter being based on an environmental condition or a state size of at least one of the optical elements (56; 156) or a manipulated variable of an actuator by which the effect of at least one component (116) of the projection exposure apparatus is variable,

c) a tempering device (44, 144), with which the temperature of a liquid (38, 138) arranged inside or outside the projection objective (20, 120) and passing through the projection light (13, 113) can be set to a desired value,

d) a control unit (48, 148), which the

Setpoint for the temperature of the liquid determined depending on the device parameter.

2. A projection exposure apparatus according to claim 1, wherein the apparatus is a barometer (58) for measuring the pressure of a gas.

A projection exposure apparatus according to claim 1, wherein the apparatus is a thermometer (162a, 162b) for measuring the temperature of a gas.

4. A projection exposure apparatus according to claim 1, wherein the apparatus is a manipulator (54; 155) with which the spatial arrangement or shape of at least one optical element (56; 156) of the projection lens is changeable.

5. The projection exposure apparatus according to claim 1, wherein the apparatus is a device (116) capable of adjusting different illumination angle distributions of projection light (113) incident on a mask (124) to be imaged.

6. Projection exposure system according to one of the preceding claims, wherein the projection lens

(20; 120) contains at least two solid refractive optical elements whose refractive index is voneinan ^¬ the distinguished.

7. A projection exposure apparatus according to any one of the preceding claims, comprising a wavelength manipulator (19; 119) with which the wavelength of the projection light (13; 113) entering the projection objective (20; 120) can be set to a desired value, the Control unit (48; 148) determines the setpoint value for the wavelength as a function of the device parameter.

8. A projection exposure apparatus according to claim 7, wherein in the control unit (48; 148) the setpoint values for the temperature of the liquid (38; 138) and the setpoint values for the wavelength of the projection light (13; 113) are stored in a data memory for different values of the device parameter or can be calculated according to a given functional relationship.

A projection exposure apparatus according to claim 7 or 8, wherein the control unit (48; 148) determines the set values for the temperature of the liquid and the set values for the wavelength of the projection light (13; 113) in a fixed ratio such that for all values of the device parameter the ratio of temperature change of the liquid and wavelength change of the projection light remains constant.

10. Microlithographic projection exposure apparatus, with:

a) an illumination system (12; 112) for generating projection light (13; 113),

b) a projection lens (20, 120) and

c) a correction device for correcting aberrations of the projection lens, comprising:

a tempering device (44; 144) with which the temperature of a liquid (38; 138) arranged inside or outside the projection lens and passing through projection light can be set to a desired value,

a wavelength manipulator (19; 119) with which the wavelength of the projection light entering the projection lens can be set to a nominal value, and

a control unit (48, 148), which sets the setpoint for the temperature of Liquid and the setpoint for the wavelength determined.

11 ^'projection exposure apparatus according to claim 10, wherein the control unit sets the target value for the WEI lenlänge of the projection light and the target value for the temperature of the liquid determined together such that the imaging properties of the projection objective are within predetermined specifications.

12. A projection exposure apparatus according to claim 10 or 11, wherein said correction means further comprises a barometer (58) for measuring the pressure of a gas which will pass from projection light.

13. A projection exposure apparatus according to any one of claims 10 to 12, wherein the correction means further comprises at least one manipulator (52, 36, 54, 152, 136) for moving the mask, the photosensitive layer or an optical element of the projection lens along an optical axis of the projection lens Projection lens has.

14. A method for correcting aberrations in a microlithographic projection exposure apparatus, with which a mask (24, 124) can be imaged onto a photosensitive layer (26, 126), comprising the following steps: a) providing a projection lens (20; 120) containing a plurality of optical elements (56; 156);

b) providing a liquid (38; 138) which will pass through projection light (13; 113);

c) determining a device parameter relating to an environmental condition or state quantity of at least one of the optical elements (56; 156) or to a manipulated variable of an actuating element by which the action of at least one component (116) of the projection exposure apparatus can be changed;

d) changing the temperature of the liquid (38; 138) in dependence on the device parameter determined in step c).

15. The method of claim 14, wherein the device parameter is the pressure reading of a gas detected by a barometer (58) that will pass through projection light (13; 113).

16. A method for correcting aberrations in a microlithographic projection exposure apparatus, with which a mask (24, 124) on a photosensitive layer (26; 126) can be imaged, with the following steps:

a) providing a projection lens (20; 120);

c) changing the wavelength of the projection light entering the projection lens and the temperature of the liquid such that the imaging properties of the projection lens are within predetermined specifications.

17. Method for producing microstructured components, comprising the following steps:

a) providing a microlithographic projection exposure apparatus according to one of claims 1 to 13 and

b) projecting the mask onto the photosensitive layer.