DE102011006189A1 - Method for exposing photosensitive layer for projection exposure system, involves supplementary-exposing photosensitive layer with supplementary exposure radiation with wavelength for producing intensity distribution on photosensitive layer - Google Patents

Abstract

The method involves exposing a photosensitive layer (112a) with exposure radiation (106) with a wavelength by imaging a structure (111a) on the photosensitive layer by an extreme UV (EUV)-lithography apparatus (101). The photosensitive layer is supplementary-exposed with supplementary exposure radiation with another wavelength for producing intensity distribution of the supplementary exposure radiation on the photosensitive layer, where the intensity distribution is independent from the structure and the latter wavelength is different from the former wavelength. An independent claim is also included for a device for exposing a photosensitive layer.

Description

Background of the invention

The invention relates to a method for exposing a photosensitive layer and an associated device.

In particular, projection exposure apparatuses for microlithography serve as devices for the exposure of a photosensitive layer. Such exposure systems generally consist of a light source, a light emitted by the light source to illumination light processing illumination system, an object, generally called reticle or mask, with the structure to be imaged, a projection system, which images an object field on a frame, and a another object with the photosensitive layer (photoresist or resist), on which the structure is imaged, generally called wafer or substrate. The mask or at least a part of the mask is located in the object field, and the wafer or at least a part of the wafer is located in the image field of the projection system.

If the mask is located completely in the region of the object field and the wafer is exposed without a relative movement of the wafer and the image field, the lithography system is generally referred to as a wafer stepper. If only a part of the mask is located in the region of the object field and the wafer is exposed during a relative movement of the wafer and the image field, the lithography system is generally referred to as a wafer scanner. The spatial dimension defined by the relative movement of reticle and wafer is generally referred to as scan direction.

When imaging the structure formed on the mask onto the photosensitive layer of the wafer, the problem may arise that the transmission properties of the projection system and / or the illumination system vary depending on location, in particular transversely to the scan direction, so that - regardless of the structure to be imaged - in the aerial image of the projection system Areas with larger and smaller intensity arise. This leads to an undesired inhomogeneous exposure of the photosensitive layer, in which structures with different line widths are produced from structures to be imaged with identical line widths on the mask after the development of the photoresist.

To compensate for location-dependent variations in the transmission of the projection system and / or the illumination system, it is known to use filters with location-dependent variable transmission. However, in addition to a homogenization, this also leads to a reduction of the light intensity striking the photosensitive layer and, as a result, typically a reduction in the throughput during the exposure. Furthermore, the achievable spatial resolution of the filter is often limiting the achievable uniformity of light intensity.

Object of the invention

The object of the invention is to improve conventional methods and devices for exposing a photosensitive layer, in particular with regard to uniformity and / or throughput.

Subject of the invention

This object is achieved by a method for exposing a photosensitive layer, comprising exposing the photosensitive layer to exposure radiation at a first wavelength by imaging a structure onto the photosensitive layer by means of a lithography apparatus, and additionally exposing the photosensitive layer to additional exposure radiation, especially at at least one second, different from the first wavelength, for generating an independent of the structure to be imaged intensity distribution of the additional exposure radiation on the photosensitive layer.

In particular, when using EUV radiation for exposure, the material serving as a photosensitive layer often can not simultaneously meet the requirements for resolution, sensitivity and the so-called line-edge roughness (LER). The inventors have found that it may be advantageous in this case if the photosensitive layer (resist) is additionally exposed to radiation of a different wavelength, since this can positively influence the properties of the photosensitive layer. It is exploited here that the resist material is generally not only sensitive to radiation at the first (EUV) wavelength, but also to radiation at other wavelengths, possibly over a broad spectral range. It is understood that the first and second wavelengths or the second wavelengths are matched to the resist material used.

It is also advantageous if the additional exposure radiation used for the additional exposure does not pass through the projection system for imaging the structure onto the photosensitive layer. In this way, the intensity distribution of the additional exposure radiation on the photosensitive layer can be adjusted independently of the properties of the projection system.

The additional exposure radiation can also pass through the projection system, however, the intensity of the additional exposure radiation should not depend on the structure (mask) to be imaged, so that the coupling of the additional exposure radiation into the beam path of the exposure radiation should take place after the mask, ie the additional exposure radiation should not hit the mask. When coupling the additional exposure radiation into the projection system, however, the problem may arise that the phase space available for this purpose is already completely filled by the exposure radiation, so that the additional exposure radiation is advantageously coupled in after the projection system.

In one variant, the time profile of the additional exposure and / or the dose of the additional exposure radiation is selected as a function of the material of the photosensitive layer. In particular, the dose, i. H. the intensity of the additional exposure radiation integrated over the period of time is adjusted as a function of the resist threshold of the resist. If a dose set by the lacquer threshold is exceeded, the resist is developed through, ie. H. the areas where the paint threshold is exceeded remain as structured areas after developing and washing away the resist in the substrate (wafer). Also, for a given dose, the time course of the additional exposure, in particular its duration, and the intensity of the additional exposure radiation can be adapted to the resist used.

In an advantageous variant, the intensity of the additional exposure radiation is selected as a function of a location-dependent transmission of the lithography system, depending on location. In this case, the intensity distribution of the additional exposure radiation can be chosen such that the additional exposure radiation has a non-zero intensity only in those areas in which the transmission of the projection system and / or the illumination system is reduced. By the superimposition or addition of the intensity of the additional exposure radiation in the areas of reduced transmission to the exposure radiation, a homogenization of the light distribution in the aerial image or a desired location-dependent intensity distribution on the photosensitive layer can be achieved, without requiring a reduction of the intensity in areas with high transmission is required, as would be the case with the use of a (field) filter.

In typical illumination systems for EUV radiation, the light mixture is not ideal, i. h., the illumination of the object field is not independent of the light source used. If the light source is unstable or if a light source other than that for which the illumination system is designed is used, the illumination of the object field is inhomogeneous. This inhomogeneity corresponds to a (fictitious) location-dependent transmission of the lithography system, operated with the light source used for the design. In the following, this contribution, which is dependent on the light source, will also be subsumed under the location-dependent transmission of the lithography system, since its effects are equivalent to the contributions of the projection system and the illumination system.

By using the additional exposure radiation, the throughput during exposure is not reduced or may be slightly reduced. Although the solution described above reduces the so-called "normalized image log slope" (NILS), which represents a measure of the contrast of the aerial image, such a reduction of the NILS (and thus of the process window) lies with the typically present location-dependent transmission variations of the projection optics of z. B. less than 5% also less than 5% and thus in a tolerable range. When using a filter, on the other hand, the throughput would be reduced by 5%, which is much more problematic for the exposure process.

In a further variant, a homogeneous intensity of the additional exposure radiation is generated on the photosensitive layer. In this variant, an additional, homogeneous exposure of the photosensitive layer takes place in order to increase the radiation dose on the photosensitive layer and thus the throughput during the exposure. This procedure is favorable if the exposure process has a process window which allows deterioration of the NILS, i. H. in exposure processes, which have a larger process window than would actually be necessary given the process variations.

Although a resist could be used instead of the additional exposure, which requires a lower radiation dose until the paint threshold is reached. However, in this case it would be necessary to work with several different resist materials in the production plant. However, the complexity of the chemical processes in the handling of a single resist already problematic, so that an additional homogeneous exposure using only a resist material is quite advantageous.

It is understood that a homogeneous additional exposure can also be combined with a correction of the uniformity of the exposure as described above. This can be the homogeneous Exposure and the correction of uniformity take place separately in time, for example, first a homogeneous (pre-) exposure and followed by a further additional exposure correction of uniformity. A temporal separation is particularly favorable if only one additional light source is used to generate the additional exposure radiation, which does not allow a continuous variation of the intensity, but can only be switched between a switched on and a switched off state. It is understood, however, that an additional homogeneous exposure can be combined with an additional exposure to correct the uniformity. When using a single tunable in intensity light source z. B. be added to the required for the correction of uniformity location-dependent intensity distribution, a constant offset of the intensity.

In one variant, the first wavelength selected is an EUV wavelength, in particular a wavelength of 13.5 nm. The first wavelength corresponds to the operating wavelength of the projection system or the projection exposure apparatus. As shown above, it is favorable if this is within the EUV range; In particular, there are a variety of resist materials for exposure to EUV radiation, which are also sensitive to radiation at other wavelengths, cf. for example, the article "Sensitivity of EUV resists to out-of-band radiation" by Jeanette M. Roberts et al., Proc. of SPIE Vol. 7273, 72731W-13 (2009) , Of course, the first wavelength can also be used in another wavelength range, eg. B. in the UV range (eg., Below 200 nm).

The second wavelength can be chosen larger than 200 nm and z. B. in the visible wavelength range or in the near infrared range. In these wavelength ranges, the additional exposure radiation z. B. with the help of commercially available LEDs as light sources and thus are produced particularly cost.

In a variant, at least part of the additional exposure of the photosensitive layer to the additional exposure radiation takes place during the imaging of the structure onto the photosensitive layer with the exposure radiation. In this variant, the two exposure processes are at least partially parallel, so that the throughput does not decrease or only slightly during the exposure. In particular, an additional light source can be provided in a projection exposure apparatus for the simultaneous additional exposure, as will be explained in more detail below. It goes without saying that the additional exposure can possibly also take place completely independently of the imaging exposure, ie. H. the additional exposure can be in a spatially separated from the projection exposure system or z. B. take place to this adjacent device. A further aspect of the invention is realized in an apparatus for exposing a photosensitive layer, comprising: a light source for generating exposure radiation having a first wavelength, an illumination system for illuminating a structure on a mask with the exposure radiation, a projection system for imaging the structure onto the photosensitive layer, and an additional light source for generating additional exposure radiation, in particular with a second wavelength different from the exposure radiation of the light source, for generating an independent of the structure to be imaged intensity distribution of the additional exposure radiation on the photosensitive layer.

Due to the additional light source, the imaging exposure and the additional exposure can be performed at least partially overlapping in time, so that the throughput during exposure is only marginally reduced by the additional exposure. As described above, it is favorable, in particular when using exposure radiation having a wavelength in the EUV wavelength range, to use additional exposure radiation having a wavelength which is not in the EUV wavelength range (up to approximately 20 nm).

In one embodiment, the additional light source is disposed at an exit end of the projection system, i. H. the additional exposure radiation does not pass through the projection system and the intensity distribution of the additional exposure radiation on the photosensitive layer can therefore be adjusted independently of the properties of the projection system.

In one embodiment, the additional light source extends over the entire length of a particular rectangular exit window of the projection system. A device with such a rectangular exit window of the projection system is typically a wafer scanner whose scanning direction runs along the narrow side of the rectangular exit window. The additional light source is in this case generally planar and extends along the long side of the rectangular exit window, ie transversely to the scanning direction. Since the substrate with the photosensitive layer is moved along the scan direction during the exposure, it is not necessary for the light source to extend over the entire width (short side) of the exit window (scanner slit). It is understood that the additional light source is preferred for generating a location-dependent variable intensity distribution over the entire length of the exit window is designed. For this purpose, the additional light source may comprise a plurality of individually switchable and substantially punctiform light sources arranged in a row. When imaging the structure on the mask by a scanning process, this structure is imaged onto a generally square or possibly rectangular portion of the photosensitive layer, which is also referred to as "die".

The additional light source may be arranged adjacent to the exit opening in the scanning direction in order to allow additional exposure of the respective subarea during the imaging exposure.

Alternatively, a distance between the additional light source and the (rectangular) exit window of the projection system in a scanning direction may be at least as long as the length of an exposed portion of the photosensitive layer in the scanning direction. In this case, during the exposure of one partial area or "this", the additional exposure of a further, adjacent partial area can take place simultaneously. In particular, the distance between exit window and additional light source can approximately correspond to the length of the exposed subarea, so that a simultaneous exposure of immediately adjacent subareas can take place. This has control-technical advantages, since the typically meander-shaped movement in the successive exposure of several partial areas of the photosensitive substrate 1: 1 can be converted into a movement of the additional light source.

The additional light source may in this case be attached, in particular, to the projection system at its end facing the wafer and be aligned such that the additional exposure radiation is substantially perpendicular to the image plane and strikes the wafer approximately perpendicularly to the surface of the photosensitive layer. Alternatively, the additional light source may also be aligned at an angle (different from 90 °) to the photosensitive layer.

In a further embodiment, the additional light source is designed to generate additional exposure radiation having a wavelength of more than 200 nm. The use of such wavelengths makes it possible to construct the additional light source from a plurality of conventional light emitting diodes having a wavelength of 248 nm or even 1048 nm, i. H. as a light-emitting diode array. Light-emitting diodes here are understood to be both LEDs and laser diodes. It goes without saying that the additional light source does not necessarily have to generate only additional exposure radiation for a single wavelength, but optionally also an additional light source can be used to generate radiation whose wavelengths extend over a predetermined, broad wavelength range.

In a further embodiment, the additional light source is designed to generate a location-dependent intensity of the additional exposure radiation with a spatial resolution of 0.5 mm, preferably of 0.2 mm or less. Such a resolution can be achieved in particular with light-emitting diode arrays. For example, with laser diodes, the length of the active (radiating) surface is in the range of a few micrometers.

In a further embodiment, the device is designed to set the location-dependent intensity of the additional exposure radiation as a function of a location-dependent transmission of the device for the exposure radiation. As has been shown above, the location-dependent transmission of the projection system, the illumination system and the influence of the light source on the illumination of the object field can be taken into account.

Further features and advantages of the invention will become apparent from the following description of embodiments of the invention, with reference to the figures of the drawing, which show details essential to the invention, and from the claims. The individual features can be realized individually for themselves or for several in any combination in a variant of the invention.

drawing

Embodiments are illustrated in the schematic drawing and will be explained in the following description. It shows

1 a schematic representation of an EUV lithography system,

2 a schematic representation of an aerial photograph of the EUV lithography of 1 with spatially homogeneous transmission curve,

3a , b schematic representations of a location-dependent varying transmission curve ( 3a ) and an intensity distribution of a resulting aerial image ( 3b )

4a , b schematic representations of the aerial image of 3a after filtering for homogenization ( 4a ) and after additional reduction of the scan speed ( 4b )

5 a schematic representation of an aerial image after homogenization with additional exposure radiation,

6 a plan view of a rectangular exit window of a projection system and on a light-emitting diode array as an additional light source,

7 the exit window and the light emitting diode array of 6 together with a wafer underneath, as well

8th a light-emitting diode array as an additional light source, which is arranged at an angle to a wafer.

In 1 is schematically an EUV lithography system 101 shown. This has a beam shaping system 102 , a lighting system 103 and a projection system 104 housed in separate vacuum housings and consecutively in the beam path of exposure radiation 106 arranged by an EUV light source 105 of the beam-forming system 102 emanates. As an EUV light source 105 For example, a plasma source or a synchrotron can serve. The escaping EUV radiation in the wavelength range between about 5 nm and about 20 nm is initially in a collimator 107 bundled. With the help of a subsequent monochromator 108 is filtered out by varying the angle of incidence, as indicated by a double arrow, the desired operating wavelength, which in the present example at λ ₀ = 13.5 nm.

In the aforementioned wavelength range are the collimator 107 and the monochromator 108 usually formed as reflective optical elements.

The in the beam-forming system 102 Exposure radiation treated in terms of wavelength and spatial distribution is introduced into the illumination system 103 introduced, which a first and second reflective optical element 109 . 110 having. The two reflective optical elements 109 . 110 direct the radiation onto a photomask 111 as a further reflective optical element having a structure to be imaged 111 having, by means of the projection system 104 on a smaller scale, z. B. 1: 4, on a substrate 112 (Wafer) is imaged. These are in the projection system 104 a third and fourth reflective optical element 113 . 114 intended. The reflective optical elements 109 . 110 . 111 . 112 . 113 . 114 each have an optical surface 109a . 110a . 111 . 112a . 113a . 114a on, in the beam path of the exposure radiation 106 the EUV lithography system 101 is arranged. On the substrate 112 , which is in the region of an image plane of the projection system 104 is arranged, is a photosensitive layer (resist or photoresist) 112a attached, that of the exposure radiation 106 is taken.

The EUV lithography system 101 is designed as a wafer scanner, ie during the exposure of the photosensitive layer 112a become the mask 111 and the wafer 112 by means (not shown) linear displacement devices parallel to each other, possibly opposite, along a scan direction which forms the Y-direction of an XYZ coordinate system.

2 shows a location-dependent intensity distribution I (x) of an aerial image when imaging a structure 111 in the form of a grid on the image plane of the projection system 104 , wherein the location coordinate (X-direction) shown transversely to the in 1 shown scan direction Y runs. Due to the low-pass effect of the projection system 104 arises from a rectangular intensity distribution of the lattice structure 111 on the mask 111 in the 2 shown sinusoidal intensity distribution I (x).

Will be like in 1 shown the wafer 112 into the image plane of the projection system 104 incorporated, the photosensitive layer 112a (Photoresist) durchverdelt at a certain dose of radiation, so that after washing the photosensitive layer 112a in 2 shown structured areas 115 in the substrate 112 be formed. The areas 115 show at the in 2 shown idealized example, in which by a spatially constant transmission T (x) of the EUV lithography system 101 is assumed, a constant line width.

Due to system-related changes in the optical components of the EUV lithography system 101 z. For example, during prolonged operation, the transmission T (x) of the EUV lithography system 101 change so that it is no longer constant over the exposed field, as in 3a is shown. Particularly problematic here is the in 3a shown average field range, in which the transmission T (x) is significantly reduced (by about 20%). An aerial view taken from an EUV lithography plant 101 is generated with such a transmission curve T (x) is in 3b shown. It can be clearly seen that in the middle field region in which the transmission T (x) is reduced, the line widths of the structured regions 115 opposite the desired line widths of 2 are significantly reduced.

In order to remedy this problem, a filtering can be carried out which also reduces the intensity I (x) in the other exposed field regions, such that the line widths of the structured regions 115 be homogenized, cf. this in 4a shown aerial view, but the line widths of the structured areas 115 towards those of 2 are significantly reduced. The filtering can be carried out, for example, by attaching a plurality of fingers displaceable in the scanning direction in the illumination system in the vicinity of a field plane, which fingers are arranged next to one another in a direction transverse to the scanning direction and partly overlap. The controlled shifting of the fingers in the scanning direction allows the intensity distribution of the illumination radiation to be set transversely to the scanning direction. Due to the extension of the fingers in the scanning direction, which is usually several millimeters, such an adjustment is possible only with a low spatial resolution.

To return the line widths to the in 2 can increase either the radiant power of the EUV light source 105 be increased, but this is problematic, since this works at the exposure anyway with maximum radiant power, or the speed of scanning must be reduced, ie the throughput of the EUV lithography system 101 decreases. Effectively, this leads to a change in the paint threshold and thus the width of the structured areas 115 expressed in the intensity I (x) of the aerial image, cf. 4b , It is understood that the paint threshold of the photosensitive layer 112a expressed by the radiation dose depends only on the resist material used and thus remains unchanged.

In the 4a , Homogenization of the intensity distribution described thus leads to a reduction of the throughput. To obtain a homogeneous and sufficiently large line width (as in 2 ) without achieving a (significant) reduction of the throughput, is at an in 5 shown alternative possibility for homogenization additional exposure radiation 116 to that of the EUV light source 105 generated exposure radiation 106 added. The intensity distribution of the additional exposure radiation 106 This is chosen so that this in 3a compensated transmission loss, cf. the aerial view in 5 above.

The intensity distribution I (x) required for the homogenization of the additional illumination radiation 116 In the aerial image is an offset, which typically does not depend on the structure being imaged 111 depends, ie there is no information about the mask used for each exposure 111 necessary to carry out the homogenization by means of the additional exposure.

This can be explained as follows: Assuming that the aerial image intensities I (x) due to system faults on the lithographic system 101 lead to a transmission loss by a factor a (x) (a (x) <1), field regions which have an intensity I ₀ without the system disturbances have the lacquer threshold of the photosensitive layer 112a corresponds to the system disturbances only an intensity of a (x) I ₀ on. Will now be using the additional exposure radiation 116 introduced a location-dependent varying additional intensity of (1 - a (x)) I ₀ , then those field points that have the intensity I ₀ without the system disturbances, now again the desired intensity I ₀ in the aerial image.

As based on a comparison between the intensity distributions I (x) of 5 and from 2 can be found, the solution described leads to a slight reduction of the so-called "normalized image log-slope" (NILS), which is a measure of the contrast of the aerial image. The solution described here, however, reduces in contrast to that based on 4a Solution shown b the throughput during exposure not or only slightly and has therefore proved to be particularly advantageous.

To the in 5 shown location-dependent varying intensity distribution I (x) of the additional illumination radiation 116 To realize, there are various possibilities, two of which are based on 6 to 8th being represented. These two solutions exploit the fact that the photosensitive layer 112a typically not only for the exposure radiation 106 at a wavelength of λ ₀ = 13.5 nm but also sensitive to other wavelengths, so that the additional exposure radiation 116 may have different wavelengths from the EUV wavelength range, which may be in the visible or even in the near infrared range, so that in particular light-emitting diodes may be used as additional light sources for generating the additional exposure radiation.

6 shows an additional light source in the form of a light-emitting diode array 117 which has a plurality of light-emitting diodes arranged side by side in the X-direction, ie transversely to the scanning direction (Y-direction) 118 having. The light-emitting diodes 118 can z. B. be designed to generate additional exposure radiation at a wavelength λ of 248 nm or 1048 nm. By the plurality of light emitting diodes 118 allows the light-emitting diode array 117 the generation of a location-dependent varying intensity distribution I (x) in the X direction, as for example in 5 is shown. In particular, when using the light-emitting diode array 117 an intensity distribution of the additional exposure radiation 116 are generated with a spatial resolution of less than 0.5 mm, preferably less than 0.2 mm, ie with a comparison with the above-described filtering significantly better spatial resolution, taking into account that at a typical reduction scale of the projection system 104 of 1: 4 a light-emitting diode array a factor 4 must be finer than the filtering described above.

The light-emitting diode array 117 is parallel to the long side of a rectangular exit window 119 (Scanner slot) of the projection system 104 from 1 arranged and extends over its entire length L, which z. B. may be about 26 mm. In this way, the intensity distribution I (x) across the scanning direction Y along the entire length L of the exit window corresponding to the exposed field area 119 be set. The spatial extent of the light-emitting diode array 117 in the scanning direction, however, may be smaller than the extension of the exit window 119 in this direction, since the photosensitive layer 112a is moved along the scan direction lying field direction (Y direction).

It is understood that the light emitting diode array 117 unlike in 6 also shown in the scan direction leading to the exit window 117 can be arranged. A distance d1 between the light emitting diode array 117 and the exit window 119 at the in 6 shown example smaller than the length L of the exit window 117 , In this example, the additional exposure becomes coincident with the imaging exposure at one and the same square portion of the photosensitive layer 112a carried out whose dimensions in the longitudinal and transverse directions of the length L of the exit window 119 correspond. It is understood that the portion is not necessarily square, but may also be rectangular.

Alternatively, a distance d2 between the exit window 119 and the light emitting diode array 117 be selected in the scanning direction Y, which is at least as large as the length L in the scanning direction Y of a respective exposed portion 120 in the scanning direction. In this case, when exposing a first section 120 the photosensitive layer 112a at the same time an additional exposure to a second, adjacent subarea 120 be performed as in 7 is shown. It is understood that alternatively the light emitting diode array 117 even at an even greater distance from the exit window 119 can be arranged so that on two not directly adjacent subareas 120 Synchronous both an imaging exposure and an additional exposure can take place.

To everyone in 7 shown portions of the photosensitive layer 112a to expose, becomes the substrate 112 , which is arranged on a (not shown) wafer stage, meandering moves. It is important to ensure that each of the subsections 120 both from the exit window 119 exiting exposure radiation 106 as well as the additional exposure radiation 116 of the light-emitting diode array 117 is suspended. In particular, if the exposure and the additional exposure to adjacent sub-areas 120 be carried out, the control considerably simplifies the meandering movement. In any case, the throughput of the EUV lithography system is largely due to the additional exposure taking place parallel to the imaging exposure 101 not or only slightly reduced.

While in 6 and 7 the additional exposure radiation 116 (substantially) perpendicular to the photosensitive layer 112a or to the image plane, is in the in 8th illustrated embodiment, the light emitting diode array 117 at an angle α of z. B. 30 ° to the photosensitive layer 112a aligned. Alternatively to the arrangement of the additional light source at the outlet of the projection system 104 It is also possible to use the additional light source in the beam path after the mask 111 in the area of entry into the projection system 104 to install. For example, the additional light source in front of the first reflective optical element 113 of the projection system 104 to be ordered. Because in the area of the mask 111 between projection system 104 and lighting system 103 little space is available, an arrangement of the additional light source is oblique next to the mask 111 advantageous. Since the deflection angle of the exposure radiation 106 on the mask 111 at least twice the numerical aperture and the additional light source corresponds to the beam path of the exposure radiation 106 is not allowed to shade, such an arrangement is particularly in the in 1 illustrated EUV lithography system 101 low, since these types of projection systems usually have a low numerical aperture. In addition to or as an alternative to the above-described application, where the additional light source is used to compensate for variations in uniformity, it is also possible to use the additional light source 117 to control the generation of a homogeneous over the exposed field area intensity distribution, so that over the entire length L of the exit window 119 Background radiation of constant intensity on the photosensitive layer 112a meets. In this way, the throughput can be increased at the expense of the process window (reduction of the NILS), which is particularly favorable in exposure processes that have a larger process window than is necessary by the actual process fluctuations. It is understood that the homogeneous additional exposure can also be combined with the correction of uniformity.

Although the additional exposure in the above-described examples was carried out in an exposure apparatus, more specifically in an EUV lithography apparatus, the additional exposure (also with a certain time interval) in another, specially designed for this purpose unit. It is understood that the procedure described above also in other imaging systems, eg. As in projection exposure systems, which are operated with exposure radiation in the UV wavelength range, in particular at 193 nm, can be used advantageously.

Also, in addition to the applications described above, ie the homogeneous additional exposure and the additional exposure to compensate for transmission variations, additional exposure can also be made to the properties of the photosensitive substrate 112a due to the use of wavelengths outside the EUV wavelength range positively influence. In this case, both the temporal and the local course of the additional exposure can be suitably adjusted (depending on the selected photoresist), wherein, in particular, the dose of the additional exposure radiation to the material of the photosensitive layer 112a can be adjusted.

To make this adjustment is in the EUV lithography system 101 from 1 a control device 121 provided which the additional light source 117 suitable controls. The control device 121 This may possibly be based on measured data z. B. with respect to the location-dependent transmission of the EUV lithography system 101 which are provided, for example, by sensors (not shown) so that an intensity distribution I (x) suitable for homogenization of the additional exposure radiation 116 can be adjusted. It is understood that the procedure described above is not limited to wafer scanner, but z. B. can also be used in wafer steppers, in which case, if necessary, in two spatial directions varying intensity distribution I (x, y) can be generated by the additional light source.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• "Sensitivity of EUV resists to out-of-band radiation" by Jeanette M. Roberts et al., Proc. of SPIE Vol. 7273, 72731W-13 (2009) [0018]

Claims (17)

Method for exposing a photosensitive layer ( 112a ), comprising: exposing the photosensitive layer ( 112a ) with exposure radiation ( 106 ) at a first wavelength (λ ₀ ) by imaging a structure ( 111 ) on the photosensitive layer ( 112a ) by means of a lithography system ( 101 ), and additional exposure of the photosensitive layer ( 112a ) with additional exposure radiation ( 116 ), in particular at least a second, different from the first wavelength (λ), for generating a structure to be imaged by the ( 111 ) independent intensity distribution (I (x)) of the additional exposure radiation ( 116 ) on the photosensitive layer ( 112a ). Method according to Claim 1, in which the time profile and / or the dose of the additional exposure radiation ( 116 ) depending on the material of the photosensitive layer ( 112a ) is selected. Method according to Claim 1 or 2, in which the location-dependent intensity (I (x)) of the additional exposure radiation ( 116 ) as a function of a location-dependent transmission (T (x)) of the lithographic system ( 101 ) is selected. Method according to one of the preceding claims, in which a homogeneous intensity (I (x)) of the additional exposure radiation ( 116 ) on the photosensitive layer ( 112a ) is set. Method according to one of the preceding claims, in which the first wavelength (λ ₀ ) is an EUV wavelength, in particular a wavelength of 13.5 nm. Method according to one of the preceding claims, in which the second wavelength (λ) is chosen greater than 200 nm. Method according to one of the preceding claims, in which at least part of the additional exposure of the photosensitive layer ( 112a ) with the additional exposure radiation ( 116 ) during imaging of the structure ( 111 ) on the photosensitive layer ( 112a ) with the exposure radiation ( 106 ) he follows. Contraption ( 101 ) for exposing a photosensitive layer ( 112a ) comprising: a light source ( 105 ) for generating exposure radiation ( 106 ) having a first wavelength (λ ₀ ), an illumination system ( 103 ) for illuminating a structure ( 111 ) on a mask ( 111 ) with the exposure radiation ( 106 ), a projection system ( 104 ) for mapping the structure ( 111 ) on the photosensitive layer ( 112a ), as well as an additional light source ( 117 ) for generating additional exposure radiation ( 116 ), in particular with at least one of the first wavelength (λ ₀ ) different second wavelength (λ), for generating a structure to be imaged by the ( 111 ) independent intensity distribution (I (x)) of the additional exposure radiation ( 116 ) on the photosensitive layer ( 112a ). Device according to Claim 8, in which the additional light source ( 117 ) at an exit end of the projection system ( 104 ) is arranged. Device according to Claim 9, in which the additional light source ( 117 ) over the entire length (L) of a particular rectangular exit window ( 119 ) of the projection system ( 104 ). Apparatus according to claim 9 or 10, wherein a distance (d2) between the additional light source ( 117 ) and the exit window ( 119 ) of the projection system ( 104 ) in a scanning direction (Y) is at least as large as the length (L) of an exposed subregion ( 120 ) in the scanning direction (Y). Device according to one of Claims 8 to 11, in which the additional light source ( 117 ) at an angle (α) to the photosensitive layer ( 111 ) is aligned. Device according to one of Claims 8 to 12, in which the light source ( 105 ) is designed to generate radiation having a first wavelength (λ ₀ ) in the EUV wavelength range. Device according to one of claims 8 to 13, wherein the additional light source ( 117 ) for generating additional exposure radiation ( 116 ) is formed with a second wavelength (λ) of more than 200 nm. Apparatus according to any one of claims 8 to 14, wherein the additional light source comprises a light emitting diode array ( 117 ). Device according to one of Claims 8 to 15, in which the additional light source ( 117 ), a location-dependent intensity of the additional exposure radiation ( 116 ) with a spatial resolution of 0.5 mm, preferably 0.2 mm or less. Device according to one of claims 8 to 16, which is designed, the location-dependent intensity (I (x)) of the additional exposure radiation ( 116 ) depending on a location-dependent transmission (T (x)) of the device ( 101 ) for the exposure radiation ( 106 ).

Images