Patent Application
20100134891
The disclosure concerns an optical system of a microlithographic projection exposure apparatus.
Microlithography is used for the production of microstructured components such as for example integrated circuits or LCDs. The microlithography process is carried out in what is referred to as a projection exposure apparatus having an illumination system and a projection objective. The image of a mask (=reticle) illuminated via the illumination system is projected via the projection objective onto a substrate (for example a silicon wafer) which is coated with a light-sensitive layer (for example photoresist) and arranged in the image plane of the projection objective in order to transfer the mask structure onto the light-sensitive coating on the substrate.
In some instances, in the illumination system and also in the projection objective, a desired intensity distribution and/or an initially set polarization state can be altered in an unwanted fashion. The influences which are responsible for that include in particular birefringence effects which are variable in respect of time such as what is referred to as polarization-induced birefringence (PIB), compacting in non-crystalline material (for example quartz glass) of optical components, degradation phenomena and thermal effects as well as birefringence which is present in anti-reflecting or highly reflecting layers on the optical components as a consequence of form birefringence or by virtue of different Fresnel reflection and transmission for orthogonal polarization states.
In some embodiments, the disclosure provides an optical system of a microlithographic projection exposure apparatus that permits comparatively flexible and fast influencing of the intensity distribution and/or the polarization state.
In certain embodiments, the disclosure provides an optical system of a microlithographic projection exposure apparatus that includes at least one layer system which is at least one-side bounded by a lens or a mirror, wherein the layer system is an interference layer system of several layers and has at least one liquid or gaseous layer portion whose maximum thickness is at a maximum 1 micrometer (μm), and a manipulator for manipulation of the thickness profile of the layer portion.
The effect achieved by the layer system with a liquid or gaseous layer portion of a maximum thickness of a maximum of 1 micrometer (μm) is to be distinguished from the action achieved in accordance with the state of the art (for example in the case of a liquid lens) of a refractive optical element. While, in the latter case, the refractive power which influences the beam path and which is dependent on the form of the refractive lens is altered the concept of the disclosure provides that the beam path as such is not influenced in a first approximation but—in a fundamentally different form of action—it can involve influencing for example phase separation by interference effects which occur between the partial waves of the light components partially reflected a plurality of times in the layer system.
In other words, in accordance with the disclosure—unlike for example a liquid lens with a liquid layer of typically a few millimeters—the system does not influence the direction of individual flat waves (or beams), but essentially only the phase position of the individual flat waves is manipulated. In contrast the interference effects utilized in accordance with the disclosure, in a conventional liquid lens with a liquid layer of typically a few millimeters, because of the limited coherence length of the light, no longer play any part as the interference effects utilized in accordance with the disclosure and thus phase influencing occur only in the thickness region which is selected in the present case and which is near the wavelength.
Partial reflection phenomena occur at the interfaces in relation to the liquid or gaseous layer portion provided in accordance with the disclosure, wherein ultimately the effect of the layer system is determined by the superimpositioning which takes place in respect of the partial waves occurring in that situation. In that respect use is made of the fact that the action of the layer stack, as an interference phenomenon, is particularly sensitively dependent on the thicknesses of the individual layers. The concept according to the disclosure of providing a liquid or gaseous layer portion, in the case of application to a multilayer system with a multiplicity of partial layers, involves modulating the thickness of one of those partial layers in its thickness configuration, whereby the interference properties are modified.
The layer system is at least one-side bounded by a lens or a mirror, i.e. the layer system is arranged adjacent, at least on one side of the layer system, to a lens or a mirror.
Basically the layer system according to the disclosure provides that, for each of the two parameters intensity I and phase φ, both the averaged value ((Is+Ip/2) and (φs+φp)/2)) as well as the separation of intensity (Is−Ip, “diattenuation”) or the phase (φs−φp) can be influenced.
In that respect the variation in thickness which is caused in the liquid layer portion, depending on the respective specific factors involved, that is to say the structure of the layer system as well as the arrangement thereof within the optical system, can have an effect either on the phase or also on the intensity, with a relatively high degree of sensitivity. In particular the layer design in the layer system according to the disclosure can be so selected that one of the foregoing four parameters (for example phase separation, i.e. the phase difference obtained for orthogonal polarizations states) is influenced in a deliberately specific fashion, with the other parameters remaining at least substantially unchanged.
In particular the layer system according to the disclosure—with the averaged intensity being influenced—can be used as a variable gray filter, for example in the projection objective, the properties of which can be manipulated on a comparatively small time scale.
In certain embodiments, the layer system is at least one-side bounded by a lens and the manipulator has an arrangement of actuators provided at the edge of the lens. In particular the liquid or gaseous layer portion can be arranged between two lenses, wherein at least one of those two lenses is actively deformable. In that case the manipulator can have for example an arrangement of actuators provided at the edge of a lens arranged in adjacent relationship with the layer portion.
In some embodiments, the layer system is at least one-side bounded by a mirror and the manipulator has an arrangement of actuators that is provided on a surface, which is not optically effective, of the mirror (for example the “rear side” of a concave mirror).
The concept according to the disclosure makes it possible to provide for deliberate targeted detuning of the layer system for the correction of a disturbance, which is present elsewhere in the optical system (for example the projection objective) in respect of the desired intensity distribution, insofar as reflection or the action in the transmission mode—depending on the respective arrangement of the layer system on a mirror or a refractive lens—is manipulated in positionally resolved fashion until the desired correction action is achieved, by deliberate targeted deformation of the deformable layer portion.
In addition a change in phase which possibly occurs in an unwanted fashion can be remedied by phase manipulators arranged elsewhere in the optical system so that intensity influencing remains as the sole nett effect. Equally polarization separation which possibly occurs in an unwanted fashion can also be compensated by suitable manipulators elsewhere in the optical system.
Phase separation can also be set as a desired effect with the layer system according to the disclosure which includes the deformable layer portion, in order for example to compensate for a disturbance, which occurs elsewhere in the optical system, in polarization distribution (for example as a consequence of holder-induced stress refraction etc.). Influencing the above-described separation parameters (that is to say transmission or phase separation) represents a particularly advantageous use of the disclosure as basically that is relatively difficult to achieve with other approaches.
In certain embodiments, the maximum thickness of the liquid or gaseous layer portion is at a maximum half a working wavelength (λ) of the optical system. Typical working wavelengths in a microlithographic projection exposure apparatus are less than 250 nm, for example about 193 nm or about 157 nm. In that respect, use is made of the fact that in the thickness range of between zero and λ/2, basically the entire range of action can be covered by setting a phase in the range of 0°-180°, which can also be covered with somewhat thicker layer systems (for example a layer of a thickness of 3λ/2).
The maximum thickness of the liquid or gaseous layer portion can be in particular in the range of between 10 and 100 nm (e.g., in the range of between 30 and 100 nm, in the range of between 50 and 100 nm).
In some embodiments, the layer system has an alternate succession of layers of a first layer material and a second layer material, wherein the first layer material has a refractive index of less than the refractive index of quart glass (SiO2) at a working wavelength and the second layer material has a refractive index of greater than the refractive index of quart glass (SiO2) at the working wavelength. In that respect in accordance with the disclosure it is possible in particular to use layer materials which admittedly are otherwise rather unusual but provide the deformable layer portion or the desired deformability, for example water with n=1.44 at λ=193 nm or also a suitable gel. It is also possible to use in a liquid layer portion for example the immersion liquids H2SO4, H3PO4 and aqueous solutions thereof, as are referred to in US 2006/0221456 A1 (with refractive indices n in the range of 1.5-1.8 at λ=193 nm and optionally with substitution of deuterium), or cyclohexane (with a refractive index n=1.556 at λ=193 nm).
In that respect, in the context of layer optimization—which as such can be implemented in conventional manner—it can be predetermined that the respectively desired layer portions including the stated deformable liquid or gaseous layer portion are included in the layer system.
In certain embodiments, a layer portion with particularly advantageous growth or adhesion conditions can be provided in the layer system as the first (growth) layer portion. Furthermore a protective layer affording a particularly good protective action in relation to environmental influences can advantageously be selected as the outermost, uppermost layer portion of the layer stack.
In some embodiments, a change in a reflection capability of the layer system of at least 0.1% (e.g., at least 1%) can be set by a variation in the thickness profile of the first layer for at least one optically useable direction of incidence of light passing through the layer system.
In certain embodiments, a change in a transmission separation of the layer system of at least 0.1% (e.g., at least 1%) can be set by a variation in the thickness profile of the first layer for at least one optically useable direction of incidence of light passing through the layer system.
In some embodiments, a change in a birefringence of the layer system of at least 0.1° (e.g., at least 1°) can be set by a variation in the thickness profile of the first layer for at least one optically useable direction of incidence of light passing through the layer system.
An optical system as set forth in claim 1, wherein a change in an absorption capability of the layer system of at least k=0.001/cm (at least k=0.01/cm) can be set by a variation in the thickness profile of the first layer for at least one optically useable direction of incidence of light passing through the layer system.
In some embodiments, a flow movement can be produced or maintained in the liquid or gaseous layer portion in operation of the optical system, whereby it is possible to counteract an unwanted rise in temperature of the respectively adjoining optical element (lens or mirror).
The concept according to the disclosure can equally well be implemented both in the illumination system and also in the projection objective.
The disclosure further concerns an optical element, a method of modifying the imaging properties in an optical system of a microlithographic projection exposure apparatus, a microlithographic projection exposure apparatus, a process for the microlithographic production of microstructured components and a microstructured component.
Further configurations of the disclosure as set forth in the description and the appendant claims.
The disclosure is described in greater detail hereinafter by way of exemplary embodiments aspects of which are illustrated in the accompanying drawings.
In the drawings:
a-b show the calculated incidence angle dependency of reflection (
In
In
It will be appreciated that the disclosure is not limited to a concave mirror so that instead thereof it is also possible to use a flat mirror for the arrangement of the layer portions on that mirror. Corresponding suitable flat mirrors are available both in the illumination system and also in various designs of projection objectives, for example in the RCR design described in fuller detail hereinafter with reference to
The actuators 105a, 105b, 105c, . . . in their totality thus form a manipulator for manipulation of the thickness profile of the liquid layer portion 123 and can be for example in the form of piezoelectric elements and/or Lorentz motors.
As is shown in
It will be appreciated that the illustration of the layer system 120 in
Suitable layer materials of the “low-refractive” layer portions are for example chiolith (refractive index n=1.38 at λ=193 nm) and magnesium fluoride (MgF2, n(193 nm)=1.42).
Suitable layer materials of the “higher-refractive” layer portions are for example sapphire (Al2O3, n(193 nm)=1.81) and lanthanum fluoride (LaF3, n(193 nm)=1.70).
A specific embodiment by way of example of a layer system according to the disclosure is set out in Table 1.
The disclosure is not limited to a liquid medium such as for example water in regard to the layer portion which can be manipulated (“tuned”) in respect of its thickness profile, but instead it is also possible to use a gaseous medium such as for example air or another gas, wherein in the case of using the disclosure in a projection objective, that gas can in particular also be a flushing gas used in the projection objective (for example a chemically inert gas such as nitrogen (N2), argon (Ar), helium (He) or mixtures thereof.
The use of a gaseous medium such as air in place of a liquid medium can be advantageous in particular in regard to service life of the adjoining optical components or layer portions. Embodiments for layer systems with such a gaseous layer portion are set forth hereinafter in Tables 2 and 3, in each of which an air layer is used in place of a water layer.
The layer system in accordance with Table 2, including the layer portion of air, can be implemented in such a way that the layer portions Nos 1-5 are vapor deposited in mutually superposed relationship on a quartz substrate, the layer portions 7-10 are similarly vapor deposited on another quartz substrate, and then the two sub-layer systems formed in that way are arranged at the spacing corresponding to the air layer to be formed, relative to each other. In the layer system of Table 3, unlike the example of Table 2, the “tunable” air layer directly adjoins a quartz substrate so that only one substrate has to be coated, unlike the situation with the example of Table 2.
It will be appreciated that the disclosure is not limited to quartz or quartz glass as a material adjoining the layer system according to the disclosure so that instead it is also possible to use other suitable lens materials such as for example calcium fluoride (CaF2), garnets, in particular lutetium aluminum garnet (Lu3Al5O12) and yttrium aluminum garnet (Y3Al5O12) or spinel, in particular magnesium spinel (MgAl2O4) as materials adjoining the layer system according to the disclosure.
The following layer systems of Tables 4 and 5 are further embodiments by way of example of layer systems with a liquid layer of water which otherwise involve a respective structure similar to Table 2 and Table 3 respectively. As can be seen from
Referring to
It will be appreciated that the disclosure is not limited to curved lens surfaces so that instead it is also possible to use plane plates for the arrangement of the layer portion according to the disclosure.
The microlithographic projection exposure apparatus has an illumination system 301 and a projection objective 302. The illumination system 301 serves for illuminating a structure-bearing mask (reticle) 303 with light from a light source unit 304 which for example includes an ArF laser for a working wavelength of 193 nm as well as a beam shaping optical mechanism for producing a parallel light beam. The parallel light beam of the light source unit 304 is firstly incident on a diffractive optical element 305 (also referred to as a “pupil defining element”) which, by way of an angle radiation characteristic defined by the respective diffracting surface structure, produces in the pupil plane P1 a desired intensity distribution (for example dipole or quadrupole distribution). Disposed downstream of the diffractive optical element 305 in the light propagation direction is an optical unit 306 including a zoom objective for producing a parallel light beam of variable diameter, and an axicon lens. Different illumination configurations are produced via the zoom objective in conjunction with the upstream-disposed diffractive optical element 305 in the pupil plane P1 depending on the respective zoom position and the position of the axicon elements. In the illustrated example the optical unit 306 further includes a deflection mirror 307. Disposed downstream of the pupil plane P1 in the light propagation direction is a light mixing device 308 disposed in the beam path and which for example in per se known manner can have an arrangement of microoptical elements that is suitable for achieving a light mixing effect. The light mixing device 308 is followed in the light propagation direction by a lens group 309, downstream of which is disposed a field plane F1 with a reticle masking system (REMA) which is projected by an REMA objective 310 following in the light propagation direction onto the structure-bearing mask (reticle) 303 arranged in the field plane F2, and thereby limits the illuminated region to the reticle. The image of the structure-bearing mask 303 is formed with the projection objective 302 which in the illustrated embodiment has two pupil planes PP1 and PP2 on a substrate 311 or a wafer provided with a light-sensitive layer.
One or more layer systems according to the disclosure can be used in the illumination system 301 and/or the projection objective 302, for example in the proximity of a pupil plane and/or a field plane of the illumination system 301 and/or the projection objective 302 respectively. Depending on the respectively desired effect the layer system according to the disclosure can be used both in field-near relationship, pupil-near relationship and also at an intermediary position. Thus for example in the case of correction to be implemented for a disturbance in intensity and/or polarization distribution, the correction action of the layer system is generally correspondingly better, the better the positioning in question of the layer system used as the correction element, in terms of its arrangement in field-near, pupil-near or intermediary relationship (that is to say for example in respect of the subaperture ratio), corresponds to the corresponding location of the disturbance to be corrected. Ideally, the arrangement of the layer system in dependence on the location to be expected for the defect to be corrected can already be taken into consideration in the design of the optical system.
Referring to
The aspheric constants are set forth in Table 7. The surfaces which are identified in
In that formula P is the camber height of the surface in question parallel to the optical axis, h is the radial spacing from the optical axis, r is the radius of curvature of the surface in question, cc is the conic constant (identified in Table 7 by K) and C1, C2, . . . are the aspheric constants set out in Table 7.
As shown in
The first optical subsystem 410 includes an arrangement of refractive lenses 411-417 and forms the image of the object plane “OP” as a first intermediate image IMI1, the approximate position of which is indicated by an arrow in
A layer system according to the disclosure can be arranged in the case of the projection objective 400 of
A layer system according to the disclosure can be arranged in the case of the projection objective 500 of
Even if the disclosure has been described by reference to specific embodiments numerous variations and alternative embodiments will be apparent to the man skilled in the art, for example by combination and/or exchange of features of individual embodiments. Accordingly it will be appreciated by the man skilled in the art that such variations and alternative embodiments are also embraced by the present disclosure and the scope of the disclosure is limited only in the sense of the accompanying claims and equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102007034641.9 | Jul 2007 | DE | national |
This application is a continuation of, and claims benefit under 35 USC 120 to, international application PCT/EP2008/059435, filed Jul. 18, 2008, which claims benefit of German Application No. 10 2007 034 641.9, filed Jul. 23, 2007 and U.S. Ser. No. 60/951,294, filed Jul. 23, 2007. International application PCT/EP2008/059435 is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60951294 | Jul 2007 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2008/059435 | Jul 2008 | US |
| Child | 12687299 | US |
