KR20180013933A - Optical system of microlithographic projection exposure apparatus - Google Patents

Abstract

The present invention relates to an optical system of a microlithographic projection exposure apparatus, wherein the projection exposure apparatus has an illumination unit and a projection lens, and the light existing in the optical tubes (205, 305) used during the operation of the projection exposure apparatus, At least one laminate arrangement (100) having at least one reflective lamina (211, 212, 311, 312, 511, 512, 611, 612), proceeding from the entrance of the projection lens through the object plane of the projection lens to the image plane of the projection lens 310, 410, 420, 430, 440, 450, 450, 440, 450, 450, , 510, 520, 610) are arranged to reflect light that is incident on and used at least regularly during the operation of the projection exposure apparatus and does not belong to the used light tubes (205, 305) toward the beam dump (250) .

Description

Optical system of microlithographic projection exposure apparatus

This application claims priority from German Patent Application DE 10 2015 210 041.3 filed on June 1, 2015. The contents of this DE application are incorporated herein by reference.

Field of invention

The present invention relates to an optical system of a microlithographic projection exposure apparatus.

Microlithography is used, for example, to fabricate microstructured components such as integrated circuits or LCDs. The microlithography process is performed in a so-called projection exposure apparatus including an illumination device and a projection lens. The image of the mask (= reticle) illuminated via the illumination device is transferred onto a substrate (e.g. a silicon wafer) coated with a photosensitive layer (photoresist), in this case to transfer the mask structure to the photosensitive coating of the substrate Is projected via the projection lens and arranged in the image plane of the projection lens.

Due to the lack of the availability of a suitable translucent material for a projection exposure apparatus designed for the EUV range, for example at a wavelength of approximately 13 nm or approximately 7 nm, for example, It is used as an optical component.

In order to generate EUV light, for example, an EUV light source in the form of a plasma light source or a free electron laser (FEL) is known. Here, in order to increase the throughput of the microlithographic projection exposure apparatus and to minimize the effect of shot noise, which is additionally undesirable (and, in principle, increasing with wavelength reduction) There is a tendency to use a high light output.

One problem that is actually associated with an increase in the light output of an EUV light source is that the blocking of a portion of the EUV light required in some areas of the projection exposure apparatus for design reasons results in an increase in the thermal power input as a function of the light output, Possibly undesirable, heat-based deformation of their retention device). These deformations then lead to impairment of the imaging characteristics of the projection exposure apparatus.

A reticle masking system and associated REMA diaphragm for use in an illumination device, and possibly also a light beam path (not shown) to affect the intensity, such as an aperture stop commonly used in projection lenses to delimit apertures, The elements introduced into it are particularly worthy of mention in this regard.

In the context of the prior art, reference is made, for example, to WO 2012/041341 A1.

It is an object of the present invention to provide an optical system of a microlithographic projection exposure apparatus capable of increasing light output while at least largely avoiding the above-described problems.

This object is achieved by an optical system according to the features of the independent patent claim 1.

The optical system of the microlithographic projection exposure apparatus according to the present invention is characterized in that the projection exposure apparatus has an illumination device and a projection lens, and the light, which is located in the used optical tube, ≪ / RTI > to the image plane of the projection lens through the object plane of

At least one lamella arrangement having at least one reflective lamella; And

- having at least one beam dump,

The lamellar arrangement is arranged to reflect, at least temporarily, light incident on the lamellar arrangement during operation of the projection exposure apparatus and not belonging to the used light tubes towards at least one beam dump.

Within the meaning of the present application, the term "used optical tube" is understood to mean the volume on which light or electromagnetic radiation travels, which may contribute appropriately to illuminate the image field in the image plane of the projection lens. If there is an adjustable or temporarily variable diaphragm, the optical tube used is also correspondingly temporally variable.

The present invention particularly relates to a microlithographic imaging process in a projection exposure apparatus which at least partially utilizes additional components in the form of a lamellar arrangement, such that the electromagnetic radiation is likewise additionally reflected towards a beam dump It is based on the concept of eliminating unavailable electromagnetic radiation. The present invention is based on the fact that, due to the appropriate design or alignment of the lamellar arrangement, at least mainly by reflection (and possibly without absorption or only some absorption) occurring on this lamellar arrangement itself, At least mainly only at a sufficient distance from the optical component - specifically only at the site of the beam dump - to generate absorption of the relevant electromagnetic radiation not used for the microlithographic imaging process.

It is ultimately possible in this way to avoid, at least in large part, the absorption-based heating of the optical components present in the projection exposure apparatus and the associated deformation and corresponding damage of the imaging characteristics of the projection exposure apparatus.

The present invention also relates to an apparatus and a method for correcting iris diaphragms as required in a projection exposure apparatus on an associated iris such that the associated iris only needs to absorb radiation not previously deflected in the direction of the beam dump by the lamella arrangement according to the invention, Includes a concept of partially alleviating the load of radiation absorption to be provided by the aperture stop of the reticle masking system or the aperture of the REMA aperture type. In other words, when the laminate arrangement according to the invention is properly arranged, the electromagnetic radiation which is located relatively farther out of the used optical tube is pre-reflected by the laminate arrangement according to the invention and is passed through the beam dump according to the invention The iris (e.g., aperture or REMA) aperture needs only to capture or absorb radiation that proceeds, for example, only slightly outside of the optical tube used.

According to an embodiment, the optical system has at least one diaphragm, and the laminate arrangement is arranged at a distance of less than 200 mm from the diaphragm.

According to an embodiment, the diaphragm is an aperture diaphragm arranged in the projection lens to delimit the numerical aperture.

According to another embodiment, the aperture is a REMA aperture of a reticle masking system (REMA) arranged in the illumination device. The REMA diaphragm of this reticle masking system is dynamically displaced in a known manner in the microlithography process to ensure that the electromagnetic radiation is incident only on a portion of the wafer that is currently being exposed. Wherein the movement of the wafer typically follows a meandering pattern wherein the REMA diaphragm of the reticle masking system is completely closed, for example, in the phase of lateral movement of the wafer. In this scenario, the aforementioned "relief" in accordance with the present invention of the load on the REMA diaphragm via the lamina array used in the concept of the present invention in combination with the beam dump, also occurs during the phase in which the REMA diaphragm is fully closed (For example, in the case of a plasma light source), the operation can be ensured (since there is no interruption). Moreover, the use of free electron lasers (FEL), as the light source is also made possible or facilitated, typically requires an uninterrupted operation, especially if a free electron laser provides illumination for more than one projection exposure apparatus do.

According to the embodiment, the thin plate arrangement according to the present invention has a plurality of reflective thin plates. This design is used outside of the optical tube used and therefore uses differently laminated foils of the lamellar arrangement to deflect, or deflect, as far as possible the beam damps coupled out, to portions of different light or radiation, , And each optimal reflection condition can be provided in accordance with the actual light distribution (minimizing undesirable absorption by each lamina). Here, each tilt of the individual thin plates with respect to the optical system axis is located at the outside of the optical tube actually used in each case and is thus maximally effective towards the beam dump according to the invention for the individual beams of radiation to be coupled out May be selected differently in an appropriate manner in order to realize reflection. Depending on the specific light distribution, the portion of the radiation that is to be coupled out, located outside the optical tube used, will deviate from the laminate arrangement and thereby affect the undesirable introduction of heat, eventually due to absorption by the optical components in the system It is possible to avoid what can happen.

According to the embodiment, the at least one reflective thin plate is arranged such that, during operation of the projection exposure apparatus, the light is at least temporally incident with respect to the surface normal at an incident angle of at least 65 [deg.]. Due to this condition corresponding to "grazing incidence ", the maximum reflection effect is intended to be achieved (with minimal undesirable absorption with respect to the laminate arrangement). The above-described conditions are preferably established for all reflective thin plates of the lamellar arrangement according to the invention.

According to an embodiment, the laminate arrangement according to the invention is arranged to be movable. This is particularly advantageous if the laminate arrangement according to the invention is arranged as described above in the area of the REMA iris of the reticle masking system - it is possible to dynamically displace the lamina arrangement during the microlithography process and thus to reduce the size of the iris Lt; RTI ID = 0.0 > of < / RTI >

According to an embodiment, the at least one lamina of the laminate arrangement according to the invention has a reflective layer made of a material layer selected from the group consisting of ruthenium, molybdenum, silicon, lanthanum, boron, boron carbide and rhodium. Platinum metals (i.e., palladium (Pd), osmium (Os), iridium (Ir) and platinum (Pt)) not listed above may also be advantageously used.

Without limiting the invention, it may be desirable to have the thin plate (s) used in accordance with the present invention be designed in the manner of custom mirrors (also referred to as GI mirrors, GI = "grazing incidence") designed for operation under tilt angle incidence It is possible. To this end, and by way of example only, each laminate may be formed from a suitable substrate (for example, silicon dioxide or a mixture thereof such as those based on a mixture of silicon and cordierite or silicon carbide, or those materials sold under the trade name ULE® or Zerodur®, For example, a 30 nm thick ruthenium layer on a substrate (made of a mirror substrate material).

It is preferred that the material of each reflective layer of the foil (s) be a layer material which exhibits the highest possible chemical and mechanical stability (in particular not degassing under vacuum conditions), where furthermore the roughness requirement to be placed on the reflective layer is relatively large (Since deflection of the radiation to be coupled out towards the beam dump needs to be performed with relatively lower angular accuracy).

According to another embodiment, the optical system is designed for operating wavelengths of less than 30 nm, in particular less than 15 nm, more preferably less than 8 nm.

The present invention also relates to a microlithographic projection exposure apparatus comprising an illumination device and a projection lens, wherein the projection exposure apparatus comprises an optical system having the features described above.

Other configurations of the present invention can be obtained from the detailed description and the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is described in more detail below on the basis of exemplary embodiments shown in the accompanying drawings.

In the drawings,
Figures 1A and 1B show schematic diagrams for illustrating possible configurations of a microlithographic projection exposure apparatus designed for operation in EUV.
2 to 6 show schematic diagrams for explaining various embodiments of the present invention.

First, FIG. 1A shows a schematic diagram of a projection exposure apparatus 10 provided as an example and designed for operation in the EUV range.

According to Fig. 1A, the illumination device in the projection exposure apparatus 10 includes a field facet mirror 3 and a pupil facet mirror 4. The light from the light source unit including, for example, the plasma light source 1 and the condenser mirror 2 is directed onto the field facet mirror 3. The first retractable mirror 5 and the second retractable mirror 6 are arranged in the optical path on the downstream side of the pupil facet mirror 4. A deflection mirror 7 is arranged on the downstream side in the optical path which directs the radiation incident thereon onto the objective field in the object plane of the projection lens comprising the six mirrors 21-26. At the location of the object field, a reflective structure support mask 31 is arranged on the mask stage 30, which is imaged in the image plane with the aid of a projection lens, which is coated with a photosensitive layer (photoresist) The substrate 41 is placed on the wafer stage 40. The structure supporting mask 31 is also referred to as a reticle. The substrate 41 is also referred to as a wafer.

The structure supporting area of the mask 31 is generally larger than the objective field of the projection lens, especially it is more expansive in one direction. For this reason, the exposure of the substrate 41 occurs via scanning, i.e. the mask stage 30 and the wafer stage 40, and thus also the mask 31 and the substrate 41, Where the ratio of the respective velocities is determined by the magnification scale of the projection lens. The displacement direction is also referred to as the scanning direction, and the size of the objective lens along the scanning direction is also referred to as the length of the scanning slit.

Structure support region of the mask 31 is transferred to the substrate 41 via a displaceable reticle masking aperture (REMA aperture) 32a, 32b when the edge of the structure support area on the mask 31 is reached during a scanning operation. It is possible to ensure that it contributes to the exposure of the exposure light.

In the projection exposure apparatus shown in FIG. 1A, electromagnetic radiation or EUV light that would cause unwanted or undesirable wafer exposure for wafer exposure is coupled out or blocked at different locations due to design out. This coupling-out is carried out in the illumination device via the REMA iris 32a, 32b of the reticle masking system 32, particularly in the immediate vicinity of the reticle 31. [ This coupling-out is also carried out in the projection lens by means of the aperture stop 27, which is present to delimit the aperture.

The volume at which the EUV radiation travels, which may be appropriately contributed to the illumination of the image field of the projection lens of the projection exposure apparatus 10 and thus of the photosensitive layer on the substrate 40, emitted by the plasma light source 1, Called optical tube. The optical tube used is in particular here formed by the stop 27, 32a, 32b of the projection exposure apparatus 10. [ If the iris is adjustable, or if the settings of these are temporarily variable, then the optical tube used is also correspondingly temporally variable.

In a projection lens composed of a spherical mirror, the aperture stop is arranged on the mirror 22, as indicated in Fig. 1A, relative to the aperture stop 27. Fig. In an aspherical design, an intermediate image is present on or between one of the other positions of the aperture diaphragm, specifically other mirrors (except mirror 26), and the optical tube used is between two mirrors without overlap, Between the mirrors 22 and 23 (as indicated in Fig. 1B for the aperture stop 27 ') is also possible.

Without additional measures, an increase in the light output of the EUV light source during the operation of the projection exposure apparatus of Figs. 1A and 1B can be achieved with respect to the impairment of the imaging results of the projection exposure apparatus, especially with the aperture stops described above (i.e., the REMA diaphragms 32a, Undesired introduction of heat energy into the optical system caused by absorption in the region of the EUV mirror (s) 32b and aperture diaphragm 27 and the associated deformation of the optical component or EUV mirror.

In order to avoid this effect, in order to allow absorption and associated conversion into the heat only at the site of the relevant beam dump, at relatively large distances only from the relevant diaphragm or optical component, A laminate arrangement having at least one reflective laminate is used in accordance with the present invention to reflect electromagnetic radiation that is not required for the microlithographic imaging process (i.e., not belonging to the used optical tube) towards the provided beam dump. The use of a beam dump can also provide the advantage that it can be particularly optimized for heat removal from the system.

2 to 4, a thin plate arrangement according to the present invention is arranged in an area of a bore stop (for example, as the bore stop 27 in the projection lens of the projection exposure apparatus of Figs. 1A and 1B) An embodiment of the present invention will be described.

Figure 2 shows only a section of the projection lens in a schematic view, in which only two EUV mirrors 220 and 240 are shown. "205 " indicates the used optical tube that contributes to the exposure of the wafer, i.e., the used optical tube, surrounding these rays of EUV light traveling from the entrance of the illumination device through the object plane to the image plane of the projection lens.

In addition to this used optical tube, additional EUV radiation is also present in the volume indicated by the dashed line in Figure 2, where aperture stop 230 (aperture stop 27 or 27 'in Figures 1a and 1b) Serves to stop down radiation components that do not belong to the optical tube used.

To reduce any heating of the aperture stop 230 caused by absorption of "extra" or unused EUV radiation that does not belong to the optical tube used (particularly in the area of one or more kilowatts, Output), a thin plate arrangement 210 having a plurality of reflective thin plates 211, 212, ... is provided according to FIG. 2, 2 - deflects the non-progressing electromagnetic radiation in the used optical tube 205 towards the remote beam dump 250. The EUV radiation that reaches the beam dump 250 via the foil arrangement 210 and is absorbed by the beam dump 250 is thus subject to any undesired heating of the aperture stop 230 For example, the coherent introduction of heat into the region of EUV mirrors 220, 240).

In the exemplary embodiment of FIG. 2 - however, the present invention is not so limited - the thin plates 211, 212, ... have different slopes with respect to the optical axis. In consideration of the light distribution occurring during the operation of the projection lens, the respective inclination angles of the individual thin plates 211, 212, ... are here to be coupled out (i. E. , The maximum possible part of the radiation (not belonging to the used optical tube) can be selected to be incident on the one reflective lamina 211, 212, ..., in each case, of the lamina array 210 under the sag angle incidence As a result, absorption by each reflective laminate, which is increasingly due to vertical incidence, is avoided or minimized.

As indicated schematically only in Figures 4a-4e, the different geometric shapes of the reflective laminae in each lamina array are, in each case, generated during the operation of the projection exposure apparatus, Wherein each slope or slope of the thin plate with respect to the optical axis can be increased or decreased in the direction of propagation of the light, wherein also (Fig. 4d) and Fig. 4 A thin plate arrangement 440 or 450 having a curvature or kink (as indicated in e) of Figure 4) is also used to reflect the light beam as many times as possible (and here, among other things, ).

FIG. 3 shows a schematic diagram for explaining another embodiment of the present invention, wherein elements similar or substantially similar to those of FIG. 2 are denoted by reference numerals increased by "100 ". In contrast to FIG. 2, aperture diaphragm 330 of the embodiment of FIG. 3 is arranged in the immediate vicinity of one of the EUV mirrors (specifically, EUV mirror 340), where also another EUV Mirror 360 is also shown in the light beam path. According to the present invention, the use of a thin plate arrangement (likewise shown in FIG. 3 and denoted by "310") is thus not limited to a specific geometric shape, but is advantageous in any desired configuration or beam path in a projection exposure apparatus Each alignment of the reflective foil 311, 312, ... of the foil arrangement 310, as described hereinabove, can be accomplished using the light tubes used in the beam dump according to the invention The most effective reflection of the electromagnetic radiation not belonging to the radiation source (not shown) is achieved and, in addition, the mechanical or design effort is kept as low as possible.

5A, 5B and 6, another embodiment of the present invention in which the thin plate array according to the present invention is used in the region of the reticle masking system in the illumination device of the projection exposure apparatus will be described below. This reticle masking system has two REMA diaphragms 531 and 532 movable in parallel with respect to the scanning direction (extending in the y-direction in the illustrated coordinate system), and two REMA diaphragms 531 and 532, Another REMA diaphragm (substantially fixed and bounding the illumination area on the reticle in the x-direction perpendicular thereto). REMA diaphragms 531 and 532 correspond to diaphragms 32a and 32b from Figs. 1A and 1B. The diaphragms 531 and 532 are independently displaceable.

The REMA diaphragms 531 and 532 of this reticle masking system are positioned in the immediate vicinity of reticle 540 (corresponding to element 31 from Figs. 1A and 1B), according to Figs. 5A and 5B, The length l of the slit can be varied by REMA diaphragms 531 and 532, as shown in Figs. 5A and 5B. In the embodiment of Figures 5A and 5B, each REMA diaphragm 531, 532 displaceable in the y-direction is moved in the direction of movement indicated by the double arrow ("P") in each case (i.e., Are assigned to a single lamina arrangement 510 or 520 having displaceable laminae 511, 512, ..., or 521, 522, ... In this way, the foils 511, 512, ..., 521, 522, ... of the foil arrangements 510, 520 can be used as the light tubes (Not shown in FIGS. 5A and 5B) to reflect the electromagnetic radiation that does not belong to REMA diaphragms 531 and 532 and to be deflected toward the beam dump of the present invention have.

The inclination of the thin plates 511, 512, ..., 521, 522, ... of the thin plate arrangement 510 or 520 is such that the angle between the normal of the reticle 540 and the thin plate is the numerical aperture NA), i.e., the light beam may be incident on both sides of the same thin plate, so that the thin plate should not be too steep. The tips of the thin plates 511, 512, ..., 521, 522 ... of the thin plate arrangements 510 and 520 are arranged such that the angle of the thin plate 511 with respect to the normal to the reticle 540 is the numerical aperture NA at the reticle. Such that the tips are at least substantially located on the same line. This allows the placement of all of the foil in the foil arrangement 510, 520 in the vicinity of the optical tube used.

The present invention is applicable to continuous continuous insertion of the foils 511, 512, ..., 521, 522, ... according to Figures 5a and 5b, or to the presence of two foil arrangements 510, It is not. In another embodiment, the insertion of two thin plate arrays or a single thin plate arrangement in the light beam path may also occur only after the REMA diaphragm of the reticle masking system is completely closed, 611, 612, ...) is also sufficient. Particularly, the above-described discontinuous insertion of a single lamellar arrangement reduces the mechatronic effort, and is particularly acceptable if the following conditions are met.

(1)

(One)

Where d represents the distance between the tip of the thin plate closest to the reticle and the reticle and l represents the length of the scanning slit in the reticle, 2 * [alpha] * d describes the magnitude of the generated half-shade.

Thus, the ease of successive insertion of the at least one foil arrangement into the light beam path is dependent on the magnitude of the half-shade produced by the foil arrangement compared to the overall size of the scanning slit. If the half-shade is fairly extensive, the insertion of the foil of the foil arrangement is also carried out in a discontinuous manner (for example, immediately after the already performed closed position of the REMA aperture), without an associated increase in absorption on the REMA diaphragm While the continuous insertion of the sheet into the light beam path may be advantageous if the size of the half-shade produced by the sheet arrangement is relatively small compared to the length of the scanning slit.

While the present invention has been described with reference to particular embodiments, numerous modifications and alternative embodiments will become apparent to those skilled in the art by way of example and / or in combination with the features of the individual embodiments. Accordingly, it is evident to those skilled in the art that these variations and alternative embodiments are included by the present invention incidentally, and that the scope of the present invention is limited only within the meaning of the appended claims and their equivalents.

Claims (12)

An optical system of a microlithographic projection exposure apparatus, the projection exposure apparatus having an illumination device and a projection lens, wherein the light located within the optical tube (205, 305) used is reflected by the projection system From the entrance through the object plane of the projection lens to the image plane of the projection lens,
- at least one foil arrangement 210, 310, 410, 420, 430, 440, 450, 510, 520, 512 with at least one reflective element 211, 212, 311, 312, 511, 512, 611, 610); And
Having at least one beam dump 250,
The thin plate arrangements 210, 310, 410, 420, 430, 440, 450, 510, 520, 610 are incident on the foil arrangement body at least temporarily during operation of the projection exposure apparatus, Are arranged to reflect light not belonging to the tubes (205, 305) toward the at least one beam dump (250). The optical system according to claim 1, further comprising at least one stop, the thin plate arrangement being arranged at a distance of less than 200 mm from the stop. 3. The optical system of claim 2, wherein the diaphragm is an aperture diaphragm (230, 330) arranged in the projection lens to delimit a numerical aperture. 3. An optical system according to claim 2, characterized in that the diaphragm is a REMA diaphragm (531, 532, 631, 632) of a reticle masking system (REMA) arranged in the illumination device. The thin plate arrangement (210, 310, 410, 420, 430, 440, 450, 510, 520, 610) according to any one of claims 1 to 4, , 312, 511, 512, 611, 612). 6. A projection exposure apparatus according to any one of claims 1 to 5, wherein at least one reflective thin plate (211, 212, 311, 312, 511, 512, 611, 612) Is arranged to be incident at least temporarily at an incident angle of less than 65 degrees with respect to the optical axis. 7. The projection exposure apparatus according to claim 5 or 6, wherein all the reflective thin plates (211, 212, 311, 312, 511, 512, 611, 612) And is arranged to be incident on the reflective thin plate at least temporarily at an incident angle. The optical system according to any one of claims 5 to 7, wherein the at least two thin plates (211, 212, 311, 312, 511, 512, 611, 612) And the optical system. 9. A method according to any one of claims 1 to 8, characterized in that the foil arrangements (210, 310, 410, 420, 430, 440, 450, 510, 520, 610) Optical system. 10. A method according to any one of claims 1 to 9, wherein the at least one lamina (211, 212, 311, 312, 511, 512, 611, 612) comprises ruthenium, molybdenum, silicon, lanthanum, boron, boron carbide And a reflective layer made of a material layer selected from the group consisting of rhodium. 11. An optical system according to any one of the preceding claims, characterized in that it is designed for an operating wavelength of less than 30 nm, in particular less than 15 nm, more preferably less than 8 nm. A microlithographic projection exposure apparatus (10) having an illumination device and a projection lens, characterized in that the projection exposure apparatus has an optical system according to any one of claims 1 to 11. A microlithographic projection exposure Device.

Images