DE102015224521B4 - Microlithographic projection system and method for operating such a system - Google Patents

Abstract

A method of operating a microlithographic projection apparatus (10), comprising the steps of: a) providing a mask (14) containing a first mask pattern (72) and a second mask pattern (78), the first mask pattern bouncing incident projection light more than that b) providing an illumination system (12) having an optical axis (OA1) and adapted to illuminate the mask with projection light (30); c) providing a projection lens (20) adapted to illuminate a mask d) illuminating the mask with projection light, which in a pupil plane (56) of the illumination system has a first region (A, B) and a second region (C , C ') which does not overlap with the first area; e) placing a diaphragm (92) in a pupil plane (90) of the projection lens such that s at least partially transmits the aperture projection light (A, A, B, B-) which has passed through the first area (A, B) in the pupil plane (56) of the illumination system and has been diffracted by the first mask pattern (72), Projection light (C, C, C, C; C ', C', C'-, C'-) at least partially transmitting, which in the pupil plane (56) of the illumination system has passed through the second region (C, C ') and has been diffracted by the second mask pattern (78), and - At least partially dimming projection light (C; C ') which has passed through the second region (C, C') in the pupil plane (56) of the illumination system and has been diffracted by the first mask pattern (72); Projection light illuminated part (16) of the mask on the photosensitive layer.

Description

BACKGROUND OF THE INVENTION

Field of the invention

The invention relates to microlithographic projection systems, with which a mask with a pattern of fine structures is imaged onto a photosensitive surface. The surface is typically a photoresist in the case of a projection exposure apparatus and an electronic photodetector in the case of a mask inspection system. In particular, the invention relates to problems in mapping masks containing overlay markers.

Description of the Prior Art

Integrated electrical circuits and other microstructured devices are typically fabricated by attaching to a suitable substrate, e.g. To act on a silicon wafer, several structured layers can be applied. To structure the layers, they are first covered with a resist which is sensitive to light of a specific wavelength range, eg. Deep ultraviolet (DUV), vacuum ultraviolet (VUV) or extreme ultraviolet (EUV, extreme ultraviolet) spectral regions. Subsequently, the thus coated wafer is exposed in a projection exposure apparatus. In this case, a mask with a pattern of structures is illuminated by a lighting system and imaged onto the photoresist with the aid of a projection objective. In general, since the magnification amount is smaller than 1, such projection lenses are sometimes 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.

In order to be able to image the pattern on the mask optimally on the photoresist, the mask is usually illuminated with a specially adapted to the pattern illumination angle distribution. The term "illumination angle distribution" refers to the distribution of the directions of the light rays as they strike the mask.

The illumination angle distribution in the mask plane corresponds to a spatial distribution in a pupil plane of the illumination system which is in a Fourier relationship with the mask plane. For describing the illumination angle distribution in the mask plane, therefore, the corresponding spatial distribution in the pupil plane is frequently used. In an annular illumination setting, for example, an annular area is illuminated in the pupil plane. For the illumination angle distribution, this means that the projection light impinges on the individual field points exclusively obliquely. The angles occurring are defined by the inner and outer radii of the illuminated in the pupil ring. In multipole illumination, only individual poles separated from each other are illuminated in the pupil plane of the illumination system. In this case, the projection light assigned to a pole strikes the mask at comparatively large angles, which differ only slightly from one another.

A difficulty in the lithographic production of microstructured components is to align the structures of adjacent layers exactly to each other. Similar problems arise when the structures are generated within a single layer by multiple exposure. Then, the structures defined by a first exposure step must be very closely aligned with the structures defined by a second exposure step.

The overlay offset (overlay) is a measure of how exactly the structures created with different masks can be arranged within a component. Especially in the case of multiple exposure methods, which have become common practice, the tolerable overlay offset has been greatly reduced in recent years.

In order to be able to better align the structures produced in several exposure steps on the wafer, overlay markers are frequently produced on the wafer. The overlay markers are usually located outside the actual components and usually consist of arrangements of comparatively coarse line structures. Usually, the overlay markers generated in one exposure step are generated directly on the overlay markers that were generated in a previous exposure step with another mask. From a measurement of the relative position of the overlay markers taking place after the exposure, it can be determined whether the overlay is so small that the wafer can be further processed, or if the permissible tolerances are exceeded, which can occasionally be corrected by readjustments in the subsequent process steps , To create the overlay markers, the mask contains corresponding overlay patterns that are imaged onto the wafer. The width of the structures of the overlay pattern is typically at wavelengths in the DUV and VUV spectral range in the order of 1 micron.

Problems can arise when imaging the overlay pattern onto the photosensitive layer, however, because the lines that make up the overlay pattern usually have a significantly larger line width than the lines of the mask structures that define a structural plane of the component to be produced , As already mentioned above, the mask structures can only be imaged optimally if they are illuminated with light having an illumination angle distribution adapted to the mask structures. This also applies to the relatively coarse meshes of the overlay patterns; they are often optimally imaged when illuminated with a conventional lighting setting where the light hits the overlay pattern at small angles from all sides. In the pupil then a central disc is illuminated. By contrast, very narrow parallel lines, as often occur in the mask structures, often require a dipole illumination setting in which the light only strikes the mask from two opposite sides at relatively large angles of incidence.

If the coarse grid of the overlay pattern is illuminated with a dipole setting, this results in a very shallow depth of field when mapping the overlay pattern. The reason for this is that because of the large line widths, the diffraction angles that occur are small. As a result, the projection light incident obliquely in a dipole illumination setting is hardly deflected. Each illumination pole therefore produces an extremely non-telecentric image, i. the bundles of rays impinging on the photosensitive layer are not parallel to the axis, but are highly inclined with respect to the optical axis. The depth of field is correspondingly low, so that the smallest axial displacements of the photosensitive layer lead to a significant lateral offset of the image of the overlay markers relative to the fine mask structures.

Another problem with mapping overlay patterns is that aberrations of the projection lens have different effects on the mapping of the coarser lines of the overlay patterns on the one hand and the finer lines of the actual mask structure on the other hand.

Both effects lead to the fact that the position of the mask structures can no longer be precisely determined by the position of the overlay markers.

So it would be ideal if you could illuminate the overlay patterns with a different lighting setting, which is better adapted to the overlay pattern. In conventional lighting systems, however, the projection light has the same illumination angle distribution at all locations in the illumination field. However, lighting systems have already been proposed in which the illumination angle distribution varies within certain limits depending on the field, i. depending on the location in the lighting field.

So is out of the US 2013/0114060 A1 an illumination system in which an optical integrator generates a plurality of secondary light sources, which together illuminate a field plane in which an adjustable field stop is arranged. This field level is mapped to the mask by a field stop lens. Images of the entrance facets of the optical integrator are superimposed in the field plane and thus also on the mask. As a result, a very uniform illumination of the mask is achieved. In order to be able to set the illumination angle distribution field-dependently, a large number of small optical modulators are located in a field plane in front of the optical integrator with which the distribution of the projection light on the entrance facets of the optical integrator can be changed without loss. Since each entrance facet illuminates the mask from a different direction, in this way the illumination angle distribution on the mask can be adjusted field-dependently.

An even more flexible approach is made possible by the lighting system that comes out of the WO 2015/074746 A1 is known. In order to be able to better influence the light distribution on the entrance facets of the optical integrator, micromirrors of a digital mirror array (DMD, Digital Micromirror Device) are imaged there on the entrance facets. As a result, virtually any field dependencies of the illumination angle distribution can be adjusted - although at the expense of low light losses.

Both approaches have in common that the entrance facets of the optical integrator must be high-resolution and variably illuminated. Since the entrance facets are very small, it is technologically demanding to produce there with the required precision variable intensity distributions.

Furthermore, from the US5552856A and the US2001 / 0026448A1 in each case a microlithographic projection exposure apparatus is known, which has both in a pupil plane of the illumination optics and in a pupil plane of the projection optics in each case a diaphragm which has both for illumination light permeable and impermeable areas. The diaphragms within the projection optics each have annular annular shape. The translucent areas of the aperture in the illumination optics according to the US5552856A can be designed differently, for. B. circular, annular or quadrupole, while the translucent areas of the aperture in the illumination optics according to US2001 / 0026448A1 consist of a central circular area with an annular annular area surrounded.

SUMMARY OF THE INVENTION

Object of the present invention is to provide a microlithographic projection system and a method for operating such a system, with which or with the simple means overlay pattern or other relatively coarse structures can better map.

In operation, a mask is arranged between the illumination optics and the projection optics, acted upon by the illumination optics with light and imaged by means of the projection optics onto a wafer arranged in the image plane of the projection optics.

1. a) Bereitstellen einer Maske, die ein erstes Maskenmuster (engl. mask pattern) und ein zweites Maskenmuster enthält, wobei das erste Maskenmuster auftreffendes Projektionslicht stärker beugt als das zweite Maskenmuster;
2. b) Bereitstellen eines Beleuchtungssystems, das eine optische Achse hat und dazu eingerichtet ist, die Maske mit Projektionslicht zu beleuchten;
3. c) Bereitstellen eines Projektionsobjektivs, das dazu eingerichtet ist, einen von dem Projektionslicht beleuchteten Teil der Maske auf eine lichtempfindliche Schicht abzubilden;
4. d) Beleuchten der Maske mit Projektionslicht, das in einer Pupillenebene des Beleuchtungssystems einen ersten Bereich und einen zweiten Bereich durchtreten hat, der sich nicht mit dem ersten Bereich überlappt;
5. e) Anordnen einer Blende in einer Pupillenebene des Projektionsobjektivs derart, dass die Blende
   • - Projektionslicht zumindest teilweise durchlässt, das in der Pupillenebene des Beleuchtungssystems den ersten Bereich durchtreten hat und von dem ersten Maskenmuster gebeugt wurde,
   • - Projektionslicht zumindest teilweise durchlässt, das in der Pupillenebene des Beleuchtungssystems den zweiten Bereich durchtreten hat und von dem zweiten Maskenmuster gebeugt wurde, und
   • - Projektionslicht zumindest teilweise abblendet, das in der Pupillenebene des Beleuchtungssystems den zweiten Bereich durchtreten hat und von dem ersten Maskenmuster gebeugt wurde;
6. f) Abbilden der des von dem Projektionslicht beleuchteten Teils der Maske auf die lichtempfindliche Schicht.

With regard to the method, this object is achieved according to the invention by a method comprising the following steps:

1. a) providing a mask containing a first mask pattern and a second mask pattern, wherein the first mask pattern diffracts incident projection light more than the second mask pattern;
2. b) providing an illumination system having an optical axis and adapted to illuminate the mask with projection light;
3. c) providing a projection lens which is adapted to image a part of the mask illuminated by the projection light onto a photosensitive layer;
4. d) illuminating the mask with projection light that has penetrated in a pupil plane of the illumination system a first region and a second region that does not overlap with the first region;
5. e) arranging a diaphragm in a pupil plane of the projection lens such that the diaphragm
   • At least partially transmitting projection light which has passed through the first region in the pupil plane of the illumination system and has been diffracted by the first mask pattern,
   • At least partially transmitting projection light which has passed through the second region in the pupil plane of the illumination system and has been diffracted by the second mask pattern, and
   • At least partially dimming projection light which has passed through the second region in the pupil plane of the illumination system and has been diffracted by the first mask pattern;
6. f) imaging the portion of the mask illuminated by the projection light onto the photosensitive layer.

The invention is based on the consideration that projection light incident on an overlay pattern or other less diffractive second mask pattern bends the incident projection light less than the first mask pattern. Therefore, in a pupil plane of the projection lens, this projection light basically passes through regions other than projection light incident on the first mask pattern.

This opens up the possibility of illuminating the second mask pattern with projection light which has an illumination angle distribution specially adapted to the second mask pattern in the mask plane and therefore also passes through other regions in a pupil plane of the illumination system. However, since this projection light also falls on the first mask pattern and would disturb its imaging, the proportion of this projection light diffracted by the first mask pattern is removed from the beam path by means of a diaphragm, preferably completely or at least partially. As a result, the second mask pattern is illuminated with an illumination angle distribution which is optimally adapted thereto, without disturbing the image of the first mask pattern.

In particular, because of the illumination angle distribution optimally adapted to the second mask pattern, it is possible to image the second mask pattern telecentrically on the photosensitive layer. This greatly reduces the sensitivity of the image to axial displacements of the photosensitive layer, as is characteristic of non-telecentric imaging.

At the same time, the device-related expense for carrying out the method is very low since only one diaphragm has to be provided in the pupil plane of the projection objective. Since this diaphragm only fades off a very small part of the projection light, the associated losses in the throughput of the projection system are correspondingly low and can be further reduced by measures explained below.

The first mask pattern may be associated with structures of a device that are formed on a substrate of the photosensitive layer. The second mask pattern can be associated with a marker which serves to align layers of structures of the device during its manufacture to one another. Such markers, also referred to as overlay markers, often include arrangements of parallel lines extending along one or two orthogonal directions. The overlay patterns on the mask used to create the overlay markers can often be particularly well reproduced with small conventional illumination settings where the projection light falls approximately perpendicular to the second mask pattern.

The overlay patterns are only for the production of auxiliary structures on the carrier, which later are not part of the device to be manufactured. However, there are also components which comprise both very fine and very coarse structures (eg connections for electrical contacting of the components). The invention is thus applicable not only for improved imaging of overlay patterns, but generally when a first mask pattern diffracts the incident projection light significantly more than a second mask pattern.

The first more diffractive mask pattern is often imaged particularly well on the photosensitive layer when illuminated with a non-conventional illumination setting. In this case, the incident projection light falls obliquely on the first mask pattern. This projection light then passes through the pupil plane of the illumination system in a first area, which is located outside the optical axis of the illumination system. In the case of a dipole illumination setting, the first region has, for example, two poles that are equidistant from the optical axis of the illumination system. In the case of a quadrupole illumination setting, two such pairs of poles are offset by 90 ° from one another.

In one embodiment, the first region is out of the optical axis of the illumination system while the second region is on the optical axis and thus intersects it. In addition, an optical axis of the projection lens intersects an opaque region of the diaphragm provided according to the invention. It is exploited here that projection light which passes through the second axial region in the pupil plane of the illumination system and falls onto the first mask pattern is diffracted so strongly that in the pupil plane of the projection objective the higher diffraction orders lie outside the numerical aperture. In order to prevent interference by this proportion of light, it is sufficient to dim an area covering the optical axis, so that the zeroth diffraction order of this projection light can not propagate to the photosensitive layer. Although this opaque portion of the diaphragm covers also projection light, which has also pass through the second area in the pupil plane of the illumination system and then dropped onto the second mask pattern. Since the latter, however, diffracts the incident projection light weaker, at least some of the higher diffraction orders are then within the numerical aperture. These higher diffraction orders are sufficient to be able to image the second mask pattern exactly on the photosensitive layer.

In another embodiment, the second region is outside the optical axis of the illumination system. Correspondingly, an opaque region of the diaphragm is then located outside an optical axis of the projection lens such that the optical axis itself remains translucent. Such an off-axis arrangement of the second area is expedient for certain second mask patterns which can not be optimally imaged with a conventional illumination setting. However, such an off-axis arrangement of the second region can also be favorable if a central zone of the pupil plane of the projection objective is illuminated by diffraction orders which have been generated by the first mask pattern.

Similarly to the first region, the second region may then also have two separate poles that are equidistant from the optical axis of the illumination system. To diminish unwanted diffraction orders of projection light that has passed through the second region in the pupil plane of the illumination system and has been diffracted by the first mask pattern, an opaque part of the iris can be formed by a socket of an optical element of the projection objective. Such diffraction orders are thus outside the numerical aperture of the projection lens.

In another embodiment, the second region has a periodic light pattern of partial regions. The diaphragm has a periodic pattern of opaque diaphragm structures, which is adapted to the light pattern of partial areas. Such a determination of the light distribution in the pupil plane of the illumination system and an appropriately adapted aperture is particularly advantageous if the second mask pattern diffracts the incident projection light so weakly that the diffraction orders lie very close to each other in the pupil plane of the projection lens. By a suitable choice of the period can then be achieved that the opaque aperture structures only dimming the unwanted projection light and transmitting the desired projection light.

In particular, a zeroth diffraction order of the projection light, which has only passed through the second region in the pupil plane of the illumination system and has been diffracted by the first mask patterns, can be dimmed by the opaque diaphragm structures. At least two higher diffraction orders of the projection light, which has passed through the second region in the pupil plane of the illumination system and has been diffracted by the second mask pattern, can then at least partially pass through gaps between the opaque diaphragm structures.

In order to minimize light losses through the diaphragm, the projection exposure apparatus can be controlled in such a way that only projection light passes through the second region in the pupil plane of the illumination system when projection light strikes the second mask pattern. During the rest of the time, the second area in the pupil plane of the illumination system is not illuminated, since then no second mask pattern has to be imaged.

When the mask moves along a scanning direction at a scanning speed while imaging the part of the mask illuminated by the projection light onto the photosensitive layer, the scanning speed can be reduced as long as the second mask pattern is in the part of the mask illuminated by the projection light , In this way, it is ensured that all structures on the mask can always be transmitted with the same radiation dose, regardless of whether or not the second area in the pupil plane of the illumination system is briefly illuminated and at the same time a small part of the projection light is dimmed ,

The invention can be used regardless of which wavelength the projection light used has. The illumination system and the projection objective can therefore be made dioptric, catoptric or catadioptric.

1. a) eine Maske, die ein erstes Maskenmuster (engl. mask pattern) und ein zweites Maskenmuster enthält, wobei das erste Maskenmuster auftreffendes Projektionslicht stärker beugt als das zweite Maskenmuster;
2. b) ein Beleuchtungssystem, das eine optische Achse hat und dazu eingerichtet ist, die Maske mit Projektionslicht zu beleuchten;
3. c) ein Projektionsobjektiv, das dazu eingerichtet ist, einen von dem Projektionslicht beleuchteten Teil der Maske auf eine lichtempfindliche Schicht abzubilden;
4. d) eine Blende, die in einer Pupillenebene des Projektionsobjektivs derart angeordnet ist, dass die Blende
   • - Projektionslicht zumindest teilweise durchlässt, das in der Pupillenebene des Beleuchtungssystems einen ersten Bereich durchtreten hat und von dem ersten Maskenmuster gebeugt wurde,
   • - Projektionslicht zumindest teilweise durchlässt, das in der Pupillenebene des Beleuchtungssystems einen zweiten Bereich, der sich nicht mit dem ersten Bereich überlappt, durchtreten hat und von dem zweiten Maskenmuster gebeugt wurde, und
   • - Projektionslicht zumindest teilweise abblendet, das in der Pupillenebene des Beleuchtungssystems den zweiten Bereich durchtreten hat und von dem ersten Maskenmuster gebeugt wurde.

With regard to the device, the object stated at the beginning is solved by a microlithographic projection exposure apparatus, which comprises:

1. a) a mask containing a first mask pattern and a second mask pattern, wherein the first mask pattern diffracts incident projection light more than the second mask pattern;
2. b) an illumination system having an optical axis and adapted to illuminate the mask with projection light;
3. c) a projection lens configured to image a portion of the mask illuminated by the projection light onto a photosensitive layer;
4. d) a diaphragm which is arranged in a pupil plane of the projection lens such that the diaphragm
   • At least partially transmitting projection light which has passed through a first region in the pupil plane of the illumination system and has been diffracted by the first mask pattern,
   • At least partially transmitting projection light, which in the pupil plane of the illumination system has passed through a second region, which does not overlap with the first region, and has been diffracted by the second mask pattern, and
   • At least partially dimming projection light which has passed through the second region in the pupil plane of the illumination system and has been diffracted by the first mask pattern.

The considerations mentioned above for the procedure apply here accordingly.

DEFINITIONS

The term "light" includes electromagnetic radiation of any kind, in particular visible light, UV, DUV, VUV and EUV light and X-radiation.

The term "light beam" refers to light whose propagation path can be described by a line.

The term "light bundle" refers to a plurality of light rays having a common origin in a field plane.

The term "field plane" designates the image plane of the projection objective in which structures of the mask to be imaged during operation of the projection apparatus are arranged, as well as each plane which is optically conjugated.

The term "conjugate levels" refers to levels between which an imaging relationship exists. A light beam emanating from a point in one of the two planes therefore converges at a point in the plane conjugate thereto.

The term "pupil plane" denotes a plane that is at least substantially in a Fourier relation to a field plane. Light rays which in a field plane parallel to each other pass through, meet in the pupil plane therefore in one point. If the light rays pass through the field plane parallel to the axis, this point lies on the optical axis. A "pupil plane" does not have to be perfectly flat in the mathematical sense, but may also be slightly curved, so that the pupil plane would have to be correctly designated as a pupil surface. If an optical system has several pupil planes, these are also optically conjugate with each other.

The term "field dependence" denotes any functional dependence of a physical quantity on the location in a field level.

The term "illumination angle distribution" describes how the intensity of a light beam is distributed among the different directions of the light beams that make up the light beam. Usually, the illumination angle distribution can be described by a function I (α, β), where α, β are angular coordinates indicating the direction of the light beams. If the illumination angle distribution has a field dependence, the intensity I also additionally depends on the field coordinates.

The term "surface" refers to any plane or curved surface in three-dimensional space. The surface can be part of or detached from a body.

As used herein, the term "aperture" refers to an optical element that contains an accumulation of solid, liquid or gaseous matter that at least 75% absorbs or scatters or reflects incident light of the operating wavelength used so that the scattered or reflected light is no longer in the Nutzlichtstrahlengang can enter. A panel always has at least one arbitrarily shaped opening in which the expansion of the light is not hindered.

list of figures

• 1 eine stark vereinfachte perspektivische Darstellung einer erfindungsgemäßen mikrolithographischen Projektionsbelichtungsanlage;
• 2 einen schematischen Meridionalschnitt durch ein Beleuchtungssystem der in der 1 gezeigten Anlage;
• 3 eine Draufsicht auf ein in der 2 gezeigtes Mikrolinsen-Array;
• 4 eine perspektivische vereinfachte Darstellung auf ein in der 2 gezeigtes Mikrospiegel-Array;
• 5 eine perspektivische Darstellung der Maske und dreier Lichtbündel, die auf Maskenstrukturen beziehungsweise ein Overlay Muster gerichtet sind;
• 6 einen schematischen Meridionalschnitt durch ein Projektionsobjektiv der in der 1 gezeigten Anlage;
• 7 eine Draufsicht auf eine Blende, das in dem Projektionsobjektiv gemäß der 6 angeordnet ist;
• 8 eine schematische Darstellung der Beugungsordnungen in einer Objektivpupille, wenn Bauelement-Strukturen mit einem Dipol-Beleuchtungssetting beleuchtet werden;
• 9 eine schematische Darstellung der Beugungsordnungen in einer Objektivpupille, wenn Overlay-Strukturen mit einem Dipol-Beleuchtungssetting beleuchtet werden;
• 10 eine schematische Darstellung der Beugungsordnungen in einer Objektivpupille, wenn Bauelement-Strukturen mit einem Dipol-Beleuchtungssetting beleuchtet werden, das gemäß einem ersten Ausführungsbeispiel der Erfindung modifiziert wurde;
• 11 eine schematische Darstellung der Beugungsordnungen in einer Objektivpupille, wenn Overlay-Strukturen mit einem Dipol-Beleuchtungssetting beleuchtet werden, das gemäß dem ersten Ausführungsbeispiel der Erfindung modifiziert wurde;
• 12 eine schematische Darstellung der Beugungsordnungen in einer Objektivpupille, wenn Bauelement-Strukturen mit einem Dipol-Beleuchtungssetting beleuchtet werden, das gemäß einem zweiten Ausführungsbeispiel der Erfindung modifiziert wurde;
• 13 eine schematische Darstellung der Beugungsordnungen in einer Objektivpupille, wenn Overlay-Strukturen mit einem Dipol-Beleuchtungssetting beleuchtet werden, das gemäß dem zweiten Ausführungsbeispiel der Erfindung modifiziert wurde;
• 14 eine schematische Darstellung der Beugungsordnungen in einer Objektivpupille, wenn Bauelement-Strukturen mit einem Dipol-Beleuchtungssetting beleuchtet werden, das gemäß einem dritten Ausführungsbeispiel der Erfindung modifiziert wurde;
• 15 eine schematische Darstellung der Beugungsordnungen in einer Objektivpupille, wenn Overlay-Strukturen mit einem Dipol-Beleuchtungssetting beleuchtet werden, das gemäß dem dritten Ausführungsbeispiel der Erfindung modifiziert wurde;
• 16 ein Flussdiagramm, in dem wichtige Schritte des erfindungsgemäßen Verfahrens dargestellt sind.

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

• 1 a greatly simplified perspective view of a microlithographic projection exposure apparatus according to the invention;
• 2 a schematic meridional section through a lighting system in the 1 shown plant;
• 3 a top view of a in the 2 shown microlens array;
• 4 a simplified perspective view of a in the 2 shown micromirror array;
• 5 a perspective view of the mask and three light beams, which are directed to mask structures or an overlay pattern;
• 6 a schematic meridional section through a projection lens in the 1 shown plant;
• 7 a plan view of a diaphragm, which in the projection lens according to the 6 is arranged;
• 8th a schematic representation of the diffraction orders in a lens pupil when device structures are illuminated with a dipole illumination setting;
• 9 a schematic representation of the diffraction orders in an objective pupil when overlay structures are illuminated with a dipole illumination setting;
• 10 a schematic representation of the diffraction orders in an objective pupil when illuminating device structures with a dipole illumination set, which has been modified according to a first embodiment of the invention;
• 11 a schematic representation of the diffraction orders in an objective pupil, when overlay structures are illuminated with a dipole illumination set, which has been modified according to the first embodiment of the invention;
• 12 a schematic representation of the diffraction orders in an objective pupil when illuminating device structures with a dipole illumination set, which has been modified according to a second embodiment of the invention;
• 13 a schematic representation of the diffraction orders in an objective pupil, when overlay structures are illuminated with a dipole illumination set, which has been modified according to the second embodiment of the invention;
• 14 a schematic representation of the diffraction orders in an objective pupil, when illuminating device structures with a dipole illumination set, which has been modified according to a third embodiment of the invention;
• 15 a schematic representation of the diffraction orders in a lens pupil when overlay structures are illuminated with a dipole illumination setting, according to the third embodiment of the invention has been modified;
• 16 a flowchart in which important steps of the inventive method are shown.

DESCRIPTION OF PREFERRED EMBODIMENTS

Basic structure of the projection exposure machine

The 1 shows a highly schematic perspective view of a projection exposure system 10 , which is suitable for the lithographic production of microstructured components. The projection exposure machine 10 contains a lighting system 12 on a mask 14 a narrow, in the illustrated embodiment ring segment-shaped illumination field 16 illuminates. Other illumination field shapes, e.g. As rectangles, of course, also come into consideration.

Inside the lighting field 16 underlying structures 18 on the mask 14 be using a projection lens 20 that has several lenses 21 and optionally further optical elements, on a photosensitive layer 22 displayed. The photosensitive layer 22 , which may be, for example, a photoresist, is on a wafer 24 or another suitable substrate and is located in the image plane of the projection lens 20 , Because the projection lens 20 has a magnification β for which | β | <1, those within the illumination field 16 lying structures 18 reduced to a projection field 16 ' displayed.

In the illustrated projection exposure system 10 become the mask 14 and the wafer 24 travels along a scan direction designated Y during projection. The ratio of the travel speeds is equal to the magnification β of the projection lens 20 , If the projection lens 20 the image inverted (ie β <0), the traversing movements of the mask run 14 and the wafer 24 in reverse, as in the 1 is indicated by arrows A1 and A2. In this way, the illumination field passes over 16 scanner-like the moving mask 14 , allowing even larger structured areas contiguous to the photosensitive layer 22 can be projected.

lighting system

The 2 shows the lighting system 12 in a meridional section. The lighting system 12 becomes linearly polarized projection light 30 from a light source 31 fed outside a housing 32 arranged and thus not part of the lighting system 12 is. The projection light generated by the light source 30 has a wavelength of λ = 193 nm in the illustrated embodiment; other wavelengths such as 248 nm or 157 nm are also possible in this embodiment.

Between the light source 31 and the lighting system 12 can the projection light 30 be guided over deflecting mirrors in tubes (not shown), which form a beam transmission device (English beam delivery).

In the lighting system 12 On the input side is a beam expander 33 arranged, which the projection light 30 widens and two lenses in the illustrated embodiment 34 . 35 includes. In the beam path behind it is a Strahlhomogenisierer 36 comprising a first honeycomb panel W1 and a second honeycomb panel W2, and the projection light 30 mixed.

On the jet homogenizer 36 followed by a first condenser 38 , In the light path behind the condenser 38 is a microlens array 40 arranged, whose structure in the 3 is shown in a plan view. The microlens array 40 comprises a plurality of spherical microlenses ML with square peripheral surfaces, so that the microlens array 40 the incident projection light 30 divided into a plurality of individual converging beams, one of which in the 2 designated LB1.

In the light path behind the microlens array 39 a pupil-shaping device PFE is arranged, which comprises a micromirror micromirror array MMA 42 includes. The 4 shows in a simplified perspective view a plan view of the micromirror array MMA. Depending on the position of the micromirrors 42 incident light beams LB1, LB2 are deflected in different directions. The micromirrors 42 thus represent light deflecting elements whose deflection angle can be varied individually and continuously. For this purpose, the micromirror array MMA with a control device 43 connected, in turn, with a parent central control 45 the projection exposure system 10 communicated.

The pupil shaper PFE further includes a prism 46 with two inclined surfaces 48a . 48b at which the projection light entering the prism 30 is reflected by total reflection. The prism 46 has the task, the projection light 30 on the micromirror array MMA and reflected light back into the beam path.

The second condenser 50 on which the projection light 30 falls, causes the distribution of deflection angles generated by the micromirror array MMA in a spatial distribution on the entrance surface of an optical integrator 52 is converted. The optical integrator 52 comprises - similar to the beam homogenizer 34 - two plates 54a . 54b with fly eye lenses 55 wherein each pair of facing fly-eye lenses 55 defines an optical channel that generates a secondary light source. The secondary light sources are in a pupil plane 56 of the lighting system 12 connected to a front focal plane of a fourth condenser 58 coincides. In a rear focal plane of the fourth condenser 58 there is a field level 60 in which an adjustable field stop 62 is arranged. The field level 60 is using a field stop lens 64 , the lenses 65a . 65b includes, mapped to a plane in which the mask 14 is arranged and therefore the following as mask level 66 referred to as.

Like the one in the 2 shows the optical path shown sets the local intensity distribution in the pupil plane 56 the illumination angle distribution of the projection light 30 in the field level 60 and in the optically conjugate mask plane 66 firmly. Because each light spot on the entrance surface of the optical integrator 52 to a corresponding intensity distribution in the pupil plane 56 leads, the illumination angle distribution of the first projection light can be 301 in the mask level 66 by changing the from the micromirrors 42 vary generated deflection angle.

The angular distribution of the pupil plane 56 generated secondary light sources, however, sets the intensity distribution of the first projection light in the field level 60 and thus the maximum dimensions of the in 1 recognizable lighting field 16 along the X and Y directions. In the XZ plane (ie the paper plane of the 2 Therefore, the secondary light sources have a large numerical aperture, while in the YZ plane parallel to the scanning direction, the secondary light sources have a much smaller numerical aperture. In this way, the slot shape of the illumination field arises 16 in the mask level 66 ,

Illumination of overlay patterns

The 5 shows the mask 14 from the 1 in an enlarged view. The mask 14 contains an arrangement of several rectangular fields 70 that later dies on the wafer 24 correspond. The fields 70 contain a first mask pattern, which in the illustrated embodiment for all fields 70 is identical. Each first mask pattern consists of an array of parallel structures aligned along the Y direction and corresponds to a pattern of structure (or a portion thereof) formed in a layer of the device using the projection exposure equipment 10 is to be prepared lithographically. Therefore, the first mask pattern will be briefly referred to as a device pattern in the following 72 and the structures contained within 18 referred to as component structures 74. Because the pitch of the device structures 74 is on the order of the wavelength of the projection light, incident projection light from the device pattern 72 strongly bent.

The fields 70 with the device patterns 72 are through gaps 76 separated from each other, which correspond to the later scribe lines on the wafer, along which the dies are separated. For clarity, the spaces are 76 reproduced particularly broad in the illustrated embodiment; Usually the spaces are 76 as narrow as possible to as many components on the wafer 24 to be able to produce.

In the intervals 76 between the fields 70 are overlay patterns 78 so distributed that between adjacent fields 70 exactly one overlay pattern 78 is arranged. Every overlay pattern 78 represents a second mask pattern of parallel structures 18 which are also aligned along the Y direction and will be referred to as overlay structures 80 below. The overlay structures 80 are wider and spaced at a coarser pitch than the device structures 74 , This will bend the overlay structures 80 incident projection light less than the finer component structures 74 ,

The pictures of the overlay pattern 78 on the photosensitive layer 22 Define the later overlay markers on the wafer, whose positions are precisely measured with the aid of measuring instruments. In this way it is possible to check whether the layers produced on the wafer are correctly aligned with each other.

At larger dies this covers a field 70 practically the entire mask 14 , In such cases, the overlay patterns are located 78 on special islands within the fields.

The different dimensions and pitches of the component structures 74 one hand, and the overlay structures 80 On the other hand, for optimal mapping of the structures 74 . 80 on the photosensitive layer 22 different lighting settings are needed. The fine parallel component structures 74 Best with a dipole lighting setting pictured like this in the 5 is illustrated for a field point P1. On the field point P1 converges a light beam, consisting of two partial light bundles 82a . 82b consists. These are arranged inclined to the optical axis OA1 of the illumination system 12, so that the projection light impinges only obliquely on the field point P1. In the exit pupil indicated by a circle 84 which is assigned to the light beam, therefore become two poles 86a . 86b illuminated, the X-direction diametrically opposite each other. In order to illuminate the field point P1 with such a dipole illumination setting, must also in the pupil plane 56 in the 2 shown illumination system 12 be illuminated in the corresponding places two poles.

The overlay pattern 78 however, it is best to use a conventional illumination setting on the photosensitive layer 22 displayed. In the 5 this is with a bundle of light 88 indicated on a field point P2 in the region of an overlay pattern 78 falls and in the associated exit pupil 89 a central pole 90 illuminates. The projection light thus falls parallel to the axis or at small angles to the field point P2.

Illuminated the overlay pattern 78 with only a dipole illumination setting, because of the weak diffraction effect of the overlay structures 80 non-telecentric beams on the photosensitive surface 22 the image of the overlay pattern 78 produce. For non-telecentric radiation beams, the direction of the light energy flux as a whole is not parallel to the optical axis. Is the photosensitive surface 22 during the exposure is not exactly in the image plane, this leads to a lateral shift of the images of the overlay pattern 78 , which gives the image the overlay pattern 78 is recorded.

Ideally, for optimal mapping, the device patterns 72 with a dipole illumination setting and the overlay patterns become 78 mapped with a conventional lighting setting, as shown in the 5 is illustrated. So as not in different places on the mask 14 Having to create different lighting settings, according to the invention all locations on the mask 14 illuminated with the same lighting setting as in the 5 (only) is illustrated for a third field point P3, which for the sake of clarity outside the illumination field 16 located. This illumination setting represents an additive combination of the two illumination settings shown for the field points P1 and P2. Consequently, the exit pupil associated with the third field point P3 contains three poles 90 . 86a and 86b , Even so, the component patterns become 72 and the overlay patterns 78 shown with different lighting settings. In the following, it is explained how this is achieved according to the invention with the aid of a diaphragm arranged in a pupil plane of the projection objective.

Aperture in the projection lens

The 6 shows the projection lens 20 from the 1 in an enlarged view. The projection lens 20 contains a pupil plane 90 in which a replaceable aperture 92 is arranged. The aperture 92 consists in the illustrated embodiment of a disc-shaped glass plate 93 partially covered with chrome or another opaque material 94 is coated. The apertures of the aperture that are transparent to the projection light 92 are thus through the spaces between the opaque material 94 established. About one with a lock 96 closable opening in a housing 98 of the projection lens 20 can the aperture 92 against another panel 92 ' be replaced, in which the opaque material 94 ' other areas on the glass plate 93 ' covered. In the 6 is such an exchange process indicated by a double arrow.

Because the aperture 92 in a pupil plane of the projection lens 20 is located, meets axis-parallel light, that of the mask 14 goes out, on the middle of the aperture 92 , ie the location where the optical axis OA2 of the projection lens 20 the aperture 92 interspersed. The larger the angles to the optical axis OA2 of the projection lens 20 below which the projection light is the mask plane 66 leaves, the farther from the optical axis OA2 hits the projection light on the aperture 92 ,

The 7 shows a plan view of the in the beam path of the projection lens 20 arranged aperture 92 , You can see that the glass plate 93 in a circular central area 98 and an outer ring area 100 with the opaque material 94 is coated, with both areas 98 . 100 are arranged concentrically to the optical axis OA2. The aperture is therefore annular in this embodiment. Like in the 6 is recognizable, is thereby projection light, which is the mask level 66 leaves axially parallel, from the absorbing central area 98 the aperture 92 absorbed. The same applies to projection light, which is the mask layer 66 leaves at very large angles to the optical axis OA2 and on the absorbent ring area 100 the aperture 92 meets.

function

The following describes how to use the aperture 92 is achieved that the overlay pattern 78 with a conventional one Lighting settings can be mapped without this affecting the figure of the component structures 74 disturbs.

introduction

In the 8th schematically illustrates at which locations projection light the pupil plane 90 of the projection lens 20 interspersed when the finer component structures 74 illuminated with a dipole lighting setting. Top left in the 8th is the intensity distribution in the pupil plane 56 of the lighting system 12 illustrated when adjusting a dipole illumination setting by means of the pupil shaping unit PFE. Illuminated there are two poles A and B, which are hatched differently for better distinctness. During operation of the projection exposure apparatus, light with an illumination angle distribution corresponding to this dipole illumination setting falls onto the mask 74 and thus also on the finer component structures 74 ,

In the middle part of the 8th is at 90 the pupil plane of the projection lens 20 indicated briefly below as "objective pupil". Projection light, which is in the pupil plane 56 of the illumination system (hereinafter referred to as "illumination pupil" for short) illuminates the pole A, is of the finer device structures 74 strongly diffracted into several diffraction orders A ₀ , A ₊₁ , A _-1 , A _{+ 2} , A _-2 ....

The diffraction angles are greater, the smaller the period of the diffractive structures. This connection is in the lower part of the 8th schematically for the device structures 74 and the overlay structures 80 Illuminated with obliquely incident light. Because of the large diffraction angles, the diffraction orders A ₀ , A ₊₁ , A _-1 , A _{+ 2} , A _-2 ... Associated with the pole A lie in the objective pupil 90 relatively far apart. One recognizes in the middle part of the 8th in that, of the three diffraction orders A ₀ , A ₊₁ and A _-1, only the zeroth diffraction order A ₀ and the +1. Diffraction order A ₊₁ within the numerical aperture of the projection objective 20 are located. The 1. Diffraction order A _-1 corresponds to such large angles that the projection light falling into this diffraction order is no longer dependent on the numerical aperture of the projection objective 20 can be included. The +1. and the -1. Diffraction order A ₊₁ and A _-1 behave differently because the pole A is arranged off-axis and therefore also the undiffracted light of the zeroth diffraction order A ₀ obliquely into the projection lens 20 entry.

Corresponding considerations also apply to the projection light which is assigned to the second pole B. Again, only two diffraction orders, namely the zeroth diffraction order B ₀ and the -1. Diffraction order B _-1 , from the projection lens 20 so that they finally hit the photosensitive layer 22 can reach. The +1. Diffraction order B ₊₁ and all higher orders of diffraction, however, are through the projection lens 20 filtered out.

So on the photosensitive layer 22 an image may arise, always at least two diffraction orders, which are assigned to one of the poles A or B, in the image plane of the projection lens 20 can interfere. The projection light A illuminating the pole A is not coherent with the projection light illuminating the pole B, so that in the image plane of the projection lens 20 no interference between light of poles A and B is possible. Thus, for the pole A, the diffraction orders A ₀ and A ₊₁ and for the pole B the diffraction orders B ₀ and B _-1 on the photosensitive layer interfere 22 , The superimposition of these diffraction orders is in the objective pupil 90 indicated by a crossed hatching.

Since, for each of the two poles A, B, the projection light emanating therefrom symmetrically from both sides of the photosensitive layer 22 falls, the picture is telecentric. The energetic center of gravity of the diffraction orders A ₀ and A _{+ 1} associated light beam is therefore exactly on the optical axis OA2 of the projection lens 20 ; this also applies to the diffraction orders B ₀ and B _-1 . Will the photosensitive surface 22 axially from the image plane of the projection lens 20 led out, the resulting image is indeed low-contrast, but does not shift in a lateral direction. Some loss of contrast can generally be tolerated because of the sharp exposure threshold of the photoresist.

The 9 shows the relationships, if not the device structures 74 but the coarser overlay structures 80 with the in the 8th illuminated dipole illumination set are illuminated.

Because the division of the coarser overlay structures 80 is significantly larger, the diffraction angles are correspondingly smaller, as is the lower part of the 8th shows. Within the numerical aperture of the projection lens 20 Therefore, there are significantly more diffraction orders that are assigned to the two poles A and B. In the lower part of the 9 are the diffraction orders generated by the pole A with A ₀ , A ₊₁ , A _-1 , A ₊₂ and A _-2 and the diffraction orders generated by the pole B with B ₀ , B ₊₁ , B _-1 , B ₊₂ and B. _-2 designates.

In the 9 can be seen in the lower part that, to image the overlay structures 80, the diffraction orders A ₀ , A ₊₁ and A ₊₂ on the photosensitive layer 22 overlap. The energetic focus of these diffraction orders is, however, off-axis, ie the projection light illuminating the pole A falls obliquely and thus not telecentrically on the photosensitive layer 22 , The same applies to the projection light which is assigned to the second pole B. As a result of this non-telecentric imaging, the image produced by one of the poles A, B shifts on the photosensitive layer 22 if it is arranged in the axial direction defocused.

Become both the finer component structures at the same time 74 and the coarser overlay structures 80 Illuminated with the dipole illumination setting, so arise in the lens pupil 90 both in the middle part of the 8th as well as the bottom of the 9 represented poles, the different diffraction orders and the different structures 74 . 80 assigned. One recognizes in the 9 in that the diffraction orders A ₊₁ and A ₊₂ as well as B _-1 and B _{-2 are different} from the overlay structures 86 be generated areas of the lens pupil 90 enforce that meets no projection light, that of the component structures 74 was bent. That of the coarser overlay structures 80 diffracted projection light thus passes through at least pupil-like optical elements of the projection lens at locations other than the projection light, which is used to image the finer component structures 74 contributes. Therefore, this is for mapping the overlay structures 80 contributing projection light to other aberrations of the projection lens 20 exposed. Thus, for example, corrective actions such as deformation or displacement of lenses are effective 21 in the projection lens 20 , possibly different on the image of the component structures 74 and the overlay structures 80 out. Also, therefore, make the coarser and therefore actually easier to map overlay structures 74 when imaging in the projection exposure machine 10 considerable difficulties.

First embodiment

The present invention solves these problems by a surprisingly simple approach in which the lighting setting is created by generating additional, overlay structures 74 adjusted illumination angle is modified. As a result, diffraction orders resulting from the imaging of the device structures 74 are disrupted by the absorbent material 94 the aperture 92 in the pupil plane 90 of the projection lens removed from the beam path. This approach is explained below with reference to the 10 and 11 illustrated first embodiment.

The 10 shows in a to the 8th ajar representation, as the finer component structures 74 illuminated with a dipole lighting setting. In the illumination pupil 56, however, using the pupil-shaping unit PFE, with which virtually any intensity distributions are made in the illumination pupil 56 can generate, not only the off-axis poles A and B, but also an axial pole C illuminated.

In the middle of 10 it can be seen that from the poles A and B in the objective pupil 90 the same diffraction orders A ₀ , A ₊₁ and A _-1 and B ₀ , B ₊₁ and B _{-1 are} generated, as described above with reference to FIGS 8th was explained. Added are the diffraction orders C ₀ , C ₊₁ and C _-1 , which were generated by the central pole C. Due to the large diffraction angle are the +1. and the -1. Diffraction orders C ₊₁ and C _-1 outside the numerical aperture of the projection lens 20 and thus do not contribute to the picture. Only the projection light falling in the zeroth diffraction order C ₀ is applied to the photosensitive layer 22 directed. However, this light can not produce an image since two different orders of diffraction must interfere with each other. Therefore, the projection light falling in the zeroth diffraction order C ₀ merely causes the photosensitive layer 22 is uniformly illuminated with projection light, which reduces the contrast of the images, which are generated by the diffraction orders A ₀ , A ₊₁ on the one hand and B ₀ and B _-1 on the other hand.

To prevent this, the diameter of the central absorbent area 98 the aperture 92 such that the central area 98 through the zeroth diffraction order C ₀ in the objective pupil 90 completely created covered axial pole. The projection light associated with the central pole C thus does not affect the imaging of the finer device structures 74 ,

The 11 shows in a to the 9 ajar representation of the relationships, as in the mapping of coarser overlay structures 90 prevail with the inventively modified lighting setting.

As in the middle of 11 can be seen, are the diffraction orders C ₀ , C ₊₁ , C _-1 , C ₊₂ and C _-2 generated by the central pole C because of the now very small diffraction angles close to each other; the in the 9 shown diffraction orders, which are generated by the poles A and B, are for clarity in the 11 not shown. In the lower part of the 11 is seen through the absorbent central area 98 the aperture 92 is again dimmed zeroth order of diffraction C ₀ , since the place where the zeroth diffraction order C ₀ the objective pupil 90 interspersed, not by the size or division of the diffractive structures on the mask 14 being affected.

The other diffraction orders C ₊₁ , C _-1 , C ₊₂ and C _-2 within the numerical aperture, on the other hand, contribute to the mapping of the overlay structures 90 at and are arranged symmetrically to the optical axis, resulting in a telecentric beam path. This creates a high-contrast image of the overlay structures 90 on the photosensitive layer 22 , because of the telecentric beam path largely insensitive to axial displacements of the photosensitive layer 22 is. Simulations have shown that the diffraction orders assigned to poles A and B do not significantly affect this figure.

By removing the zeroth diffraction order C ₀ , the aerial image of the overlay pattern 78 is significantly changed, since it leads to a frequency doubling in the periodic spatial distribution in the image plane of the projection lens 20 comes. However, this effect can be easily predicted and in the design of the overlay structures 80 be kept.

Second embodiment

As is clear from the above explanation of 10 and 11 has emerged, the aperture must 92 in the objective pupil 90 fulfill several requirements. On the one hand, it has to transmit projection light completely or at least to a large extent, that in the pupil plane 56 of the lighting system 12 the poles A and B has passed through and from the component structures 74 that the component pattern 72 form, was bent.

In addition, the aperture must 92 Let projection light through at least partially, that in the pupil plane 56 of the lighting system 12 has passed through the pole C and from the overlay structures 80 which the overlay pattern 78 was bent, because this part of the projection light causes the telecentric imaging of the overlay pattern 78 ,

The aperture 92 but the projection light must be at the pupil level 56 of the lighting system 12 the pole C has passed through and of the device structures 74 was diffracted, completely or at least partially dimming, since this projection light is the image of the device structures 74 disturbs.

At certain divisions of the device structures 74 and the overlay structures 80 However, it can be difficult, an aperture 92 find that meets all the above requirements. Especially when the divisions of the device structures 74 and the overlay structures 80 do not differ as clearly from each other, as was assumed in the above-described embodiment, the diffraction orders generated by the poles A, B and C in the objective pupil 90 overlap.

For example, if the in 11 In the situation shown, the diffraction orders C ₀ , C ₊₁ , C _-1 , C ₊₂ and C _-2 overlap, it would be tolerable that the central area 98 the diaphragm 92 not only the zeroth diffraction order C ₀ , but also the +1. and the -1. Diffraction order C ₊₁ and C _-1 covered. On the photosensitive layer 22 Then the diffraction orders C _{+ 2} and C _-2 and possibly further higher diffraction orders could overlap and a high-contrast image of the overlay structures 80 produce.

If the zeroth diffraction order C ₀ overlaps one of the diffraction orders A ₊₁ and B _-1 , it may be necessary for the absorbing material 94 the aperture 92 covering a small part of the diffraction orders A ₊₁ and B _-1 . If intolerable is that the aperture 92 attenuates a part of the diffraction orders A ₊₁ and B _-1 , so may alternatively the aperture 92 only part of the zeroth diffraction order C ₀ at the further propagation in the projection lens 20 prevent.

In order to avoid such compromises are in the in the 12 and 13 illustrated second embodiment in the illumination pupil 56 not a single central pole C, but two poles C, C 'eccentrically generated in the manner of a dipole arrangement by means of the pupil forming unit PFE.

The 12 illustrates the position of the diffraction orders in the objective pupil 90 that of the component structures 74 be generated. It is assumed here that the component structures 74 have a greater division and therefore the diffraction orders are closer together.

Due to the eccentric arrangement of the poles C, C 'in the illumination pupil 56 lie in the objective pupil 90 the poles of the +1. and the -1. Diffraction order C ₊₁ , C _-1 and C ' ₊₁ , C' _-1 outside the numerical aperture and therefore need not be dimmed by additional absorbing areas. The aperture 92 Therefore, only the zeroth diffraction orders C ₀ and C ' _{0 must} prevent further propagation. For this purpose, the aperture 92 in this embodiment no absorbing central area 98 but two absorbing and diametrically opposed areas 106 . 106 ' on, the zeroth Diffraction order C ₀ and the C ' ₀ absorb. In this way, in this embodiment, the additional wear in the illumination pupil 56 generated poles C, C 'not for imaging the device structures 74 at. At the same time, however, remains in the objective pupil 90 the designated 104 and in the 12 marked by a hatching area for the diffraction orders generated by the poles A and B.

With only a single central pole C, as in the case of 10 illustrated embodiment, would be in the here assumed weaker diffractive component structures 74 the 1. Diffraction order C _-1 and the +1. Diffraction order C ₊₁ overlap with the zeroth diffraction orders A ₀ and B ₀ , respectively, generated by the poles A and B and for the imaging of the device structures 74 needed. In order to suppress the disturbing diffraction orders C _-1 and C ₊₁ , a part of the zeroth diffraction orders A ₀ and B ₀ generated by the poles A and B would also have to be absorbed, which adversely affects the imaging of the component structures 74 effect.

The 13 illustrates, as in this embodiment, the overlay structures 80 with the in the 12 shown illumination setting can be mapped. Similar to the one in the 11 As shown, the pole C is generated in the illumination pupil 56 by diffraction at the overlay structures 80 in the objective pupil 90 a plurality of densely spaced diffraction orders C ₀ , C ₊₁ , C _-1 , C _{+ 2} and C _-2 , while the pole C 'diffraction orders C' ₀ , C ' ₊₁ , C' _-1 , C ' ₊₂ and C '- ₂ generated. The absorbent areas 106 . 106 ' The aperture 92 also cover here the zeroth diffraction orders C ₀ , C ' ₀ , but let pass the other diffraction orders, so that they are used to image the overlay structures 80 can contribute.

Third embodiment

In the two embodiments described above, the higher diffraction orders are from the central pole C or from the diametrically opposite poles C, C 'in the objective pupil 90 are so far apart that when dimming the zeroth diffraction order C ₀ , or C ' _0, the adjacent diffraction orders are not dimmed simultaneously with. For even coarser overlay structures 80 The case may occur in the lens pupil 90 the diffraction orders generated by the additional poles overlap. The distance between the lenses in the pupil 90 diffraction orders generated by an additional pole C, C 'is then smaller than the size of the poles in the objective pupil 90 be illuminated by these diffraction orders.

It has already been pointed out above that, in such a case, it is possible to consider, with a diaphragm, not only the zeroth diffraction order C ₀ , which is the image of the component structures 74 disturbs, but also at least partially cover some of the adjacent diffraction orders. This, however, projection light for the mapping of the overlay structures 80 lost.

In such a situation can be remedied if the addition of the pupil forming unit PFE in the illumination pupil 56 produced poles have a periodic fine structure and also the aperture 92 in the projection lens 20 has a periodic fine structure of light-absorbing material adapted thereto. This approach is described below with reference to the 14 and 15 explained.

In the 14 is in the upper partial view recognizable that the central pole C, in addition to the poles A and B in the pupil plane 56 of the lighting system 12 is illuminated, a fine structure of periodically (ie, with a constant pitch) arranged fine stripes 109 (shown here in white). This arrangement of parallel stripes is limited by a circular envelope.

In the middle of 14 is analogous to 10 shown how the component structures 74 diffract projection light, which is associated with the finely structured pole C. The zeroth diffraction order C ₀ produces a corresponding strip-like illumination in the center of the objective pupil 90 ,

The aperture 92 has a central area in the illustrated embodiment 108 comprising an array of parallel and periodically arranged absorbing strips 110 includes. The width and orientation of the stripes 110 as well as their distance from each other are chosen so that the absorbing strips 110 exactly cover the stripes, those of the zeroth diffraction order C ₀ in the middle of the objective pupil 90 be lit up. Thus, even in this embodiment, the zeroth diffraction order C _{0 is} not for imaging the device structures 74 contribute.

The 15 shows the situation when mapping the assumed coarse overlay structures 80 , Because of the large division of overlay structures 80 lie in the lens pupil 90 the diffraction orders C ₀ , C ₊₁ , C _-1 , ... generated by the pole C are so close to each other that they partially overlap. For clarity, the higher diffraction orders in the 15 not shown.

As best in the enlarged section of the lower part of the 15 recognizable, the overlapping +1. and -1. Diffraction order C ₊₁ or C _-1 of the absorbent material 94 the aperture 92 not covered, because the absorbent strips 110 the aperture 92 cover exactly those parts of the diffraction orders C ₊₁ , C _-1 , on the anyway no light falls due to the fine structuring of the central pole C. The fine structuring of the illumination pupil 56 in combination with the fine structuring of the aperture 92 Thus, even if those assigned to the central pole C and of the overlay structures 80 generated diffraction orders C ₀ , C ₊₁ , C _-1 , ... overlap, only the zeroth diffraction order C _{0 is} absorbed, which is the image of the device structures 74 otherwise it would disturb.

If the overlay structures 80 are finer and thus have a smaller pitch, the diffraction orders C ₊₁ , C _{-1 are} further apart. The fine structure of the panel 92 and thus also the pole C can then be chosen correspondingly coarser.

dose adjustment

Because the dimming of projection light through the aperture 92 inevitably leads to light losses that the throughput of the projection exposure system 10 can reduce the control of the projection exposure system 10 be set up so that one or more additional poles C, C 'in the illumination pupil 56 only during short time intervals generated in the course of a scan. Because when the lighting field 16 solely about the component structures 74 there is no need to additionally have one or more poles C, C 'in the pupil plane 56 Illuminate, as reflected in the lighting field 16 yes no overlay patterns 78 are located. Once overlay patterns 78 in the lighting field 16 reach, the additional poles C, C 'are illuminated. At the same time, the scanning speed is reduced momentarily to ensure that the component structures 74 be illuminated with a constant dose.

There - unlike in the 5 for clarity's sake - the overlay patterns 78 only a negligible proportion of the total area of the mask to be scanned 14 In short, the times with reduced scan speed are very short overall. As a result, the reduction of the throughput of the projection exposure apparatus is correspondingly low 10 ,

For the sake of simplicity, it has been assumed in the exemplary embodiments explained above that both the component structures 74 as well as the overlay structures 80 only extend parallel in one direction. Of course, the principles of the invention also apply to structures aligned along another (especially orthogonal) direction.

Also in the mapping of patterns containing orthogonal or at a different angle arranged structures, the invention can be advantageously used. To the in the 10 and 11 as well as diffraction orders 14 and 15, only further orders of diffraction are added, but these do not overlap with the diffraction orders shown in these figures ( 10 and 11 ) or in which an overlap is harmless because of the periodic fine structuring.

Important process steps

Important steps of the method according to the invention are in the flow chart of 16 shown.

In a first step S1, a mask is provided which contains a first mask pattern and a second less diffractive mask pattern.

In a second step S2, a lighting system and a projection lens are provided.

In a third step S3, the mask is illuminated with projection light, which has passed through a first region and a second region which does not overlap in an illumination pupil.

In a fourth step S4, an image of the first mask pattern is generated with light that has passed through the first region in the illumination pupil and has been diffracted by the first mask pattern.

In a fifth step S5, an image of the second mask pattern is generated with light which has passed through the second region in the illumination pupil and has been diffracted by the second mask pattern.

In a sixth step S6, light is dimmed which has passed through the second region in the illumination pupil and has been diffracted by the first mask pattern.

Claims (20)

Method for operating a microlithographic projection system (10), comprising the following steps: a) providing a mask (14) including a first mask pattern (72) and a second mask pattern (78), wherein the first mask pattern diffracts incident projection light more than the second mask pattern; b) providing an illumination system (12) having an optical axis (OA1) and adapted to illuminate the mask with projection light (30); c) providing a projection objective (20) which is adapted to image a part (16) of the mask illuminated by the projection light onto a photosensitive layer (22); d) illuminating the mask with projection light which has penetrated in a pupil plane (56) of the illumination system a first region (A, B) and a second region (C, C ') which does not overlap with the first region; e) arranging an aperture (92) in a pupil plane (90) of the projection lens such that the aperture at least partially transmits projection light (A ₀ , A _{+ 1} , B ₀ , B - ₁ ) in the pupil plane (56) of the Illumination system has passed through the first region (A, B) and has been diffracted by the first mask pattern (72), - projection light (C ₊₁ , C _{+ 2} , C _-1 , C ₂ , C ' ₊₁ , C' _{+ 2} , C'- ₁ , C'- ₂ ) passing through the second region (C, C ') in the pupil plane (56) of the illumination system and diffracted by the second mask pattern (78), and - projection light (C ₀ ; C ' ₀ ) at least partially fades, which in the pupil plane (56) of the illumination system has passed through the second region (C, C') and has been diffracted by the first mask pattern (72); f) imaging the portion of the mask (16) illuminated by the projection light onto the photosensitive layer. Method according to Claim 1 wherein the first mask pattern (72) is associated with structures (74) of a device that are formed on a support (24) of the photosensitive layer (22), and wherein the second mask pattern (78) is associated with a marker that serves to Align layers of structures of the device during its manufacture to each other. Method according to Claim 1 or 2 , wherein the first region (A, B) is located outside the optical axis (OA1) of the illumination system. Method according to Claim 3 wherein the first region has two poles (A, B) equidistant from the optical axis (OA1) of the illumination system (12). Method according to Claim 3 or 4 wherein the optical axis (OA1) of the illumination system intersects the second region (C), and wherein an optical axis (OA2) of the projection objective (20) intersects an opaque region of the aperture (92, 98). Method according to one of Claims 1 to 4 , wherein the second region (C, C ') is located outside the optical axis of the illumination system, and wherein a translucent the aperture (92, 106) on an optical axis (OA2) of the projection lens (20). Method according to Claim 6 , wherein the second region has two separate poles (C, C ') equidistant from the optical axis (OA1) of the illumination system (12). The method of any one of the preceding claims, wherein the second region comprises a periodic light pattern of portions (109), and wherein the aperture comprises a periodic pattern of opaque aperture structures (110) matched to the light pattern of the second region (78). Method according to Claim 8 in which a) a zeroth diffraction order (C ₀ ) of the projection light, which in the pupil plane of the illumination system has passed through the second region (C) and has been diffracted by the first mask pattern (72), is dimmed by the opaque aperture structures (110), and wherein b) at least two higher orders of diffraction (C ₊₁ , C _-1 ) of the projection light, which in the pupil plane of the illumination system has passed through the second region (C) and has been diffracted by the second mask pattern (78), at least partially gaps between the opaque ones Aperture structures (110) pass through. Method according to one of the preceding claims, in which only projection light passes through the second region (C) in the pupil plane of the illumination system when projection light strikes the second mask pattern (78). Method according to Claim 10 in that the mask (14) moves along a scanning direction (Y) at a scanning speed, while the part (16) of the mask illuminated by the projection light is imaged onto the photosensitive layer (22) and the scanning speed is reduced, as long as the second mask pattern (78) is in the part (16) of the mask illuminated by the projection light. A microlithographic projection apparatus (10) comprising: a) a mask (14) including a first mask pattern (72) and a second (78) mask pattern, wherein the first mask pattern diffracts incident projection light more than the second mask pattern; b) an illumination system (12) having an optical axis (OA1) and adapted to illuminate the mask (14) with projection light; c) a projection lens (20) adapted to image a portion of the mask illuminated by the projection light onto a photosensitive layer (22); d) a diaphragm (92) which is arranged in a pupil plane (90) of the projection lens in such a way that the diaphragm at least partially transmits projection light (A ₀ , A _{+ 1} , B ₀ , B _-1 ) that is in the pupil plane (90). 56) of the illumination system has passed through the first region (A, B) and has been diffracted by the first mask pattern (72), - projection light (C ₊₁ , C _{+ 2} , C- ₁ , C ₂ ; C ' ₊₁ , C' ₊₂ , C'- ₁ , C'- ₂ ), which in the pupil plane (56) of the illumination system has passed through the second region (C, C ') and has been diffracted by the second mask pattern (78), and Projection light (C ₀ ; C ' ₀ ) at least partially fades, which in the pupil plane (56) of the illumination system, the second region (C, C') has passed through and was diffracted by the first mask pattern (72). Projection system after Claim 12 wherein the first mask pattern (72) is associated with structures (74) of a device that are formed on a support (24) of the photosensitive layer, and wherein the second mask pattern (78) is associated with a marking that serves to form layers of structures align the device during its manufacture to each other. Projection system after Claim 12 or 13 , wherein the first region (A, B) is located outside the optical axis (OA1) of the illumination system. Projection system after Claim 14 wherein the first region has two poles (A, B) equidistant from the optical axis (OA1) of the illumination system (12). Projection system after Claim 14 or 15 wherein the optical axis (OA1) of the illumination system intersects the second region (C), and wherein an optical axis (OA2) of the projection objective (20) intersects an opaque region of the aperture (92, 98). Projection system according to one of Claims 12 to 15 , wherein the second region (C, C ') is located outside the optical axis of the illumination system, and wherein a translucent region of the diaphragm (92, 106) is located on an optical axis (OA2) of the projection objective (20). Projection system after Claim 17 , wherein the second region has two separate poles (C, C ') equidistant from the optical axis (OA1) of the illumination system (12). Projection system according to one of Claims 12 to 18 wherein the second region comprises a periodic pattern of light portions (109), and wherein the aperture comprises a periodic pattern of opaque aperture structures (110) matched to the light pattern of the second region (78). Projection system after Claim 19 in that the opaque diaphragm structures are designed such that a) a zero diffraction order (C ₀ ) of the projection light, which has passed through the second region (C) in the pupil plane of the illumination system and has been diffracted by the first mask pattern (72), from the diaphragm structures (110) is dimmed, and wherein b) at least two higher diffraction orders (C ₊₁ , C _-1 ) of the projection light which has passed through the second region (C) in the pupil plane of the illumination system and has been diffracted by the second mask pattern (78) at least partially pass spaces between the panel structures (110).

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