Patent Number: 
Section: description

In FIGS. 1 and 2, preferred arrangements of the five-mirror projection objectives according to the invention are shown. Each has an optical free working distance that corresponds at least to the used diameter of the mirror closest to the wafer or object to be illuminated. In all embodiments below, the same reference numbers are used for the same components with the following nomenclature employed: first mirror (S1), second mirror (S2), third mirror (S3), fourth mirror (S4), and fifth mirror (S5). In particular, FIG. 1 shows a five-mirror projection objective with a beam path from the reticle plane 2 to the wafer plane 4. The embodiment can be considered as a series circuit with (1) a three-mirror system consisting of S1, S2 and S3, that produces a real, reduced image of the object, as the intermediate-image Z and (2) a two-mirror system S4, S5, which images the intermediate image Z in the wafer plane 4 while maintaining the telecentricity requirements. The aberrations of the subsystems are balanced against one another in such a way that the total system has sufficient quality for the application. A physical aperture stop B is arranged on the first mirror S1. To block light from passing above the aperture stop B, a narrow ring is used to block the light reflected toward S2 from S1. In the embodiment shown in FIG. 1, the aperture is realized as an opening at the S1 mirror. The aperture stop can also be positioned between the mirror S1 and the mirror S2. In the system according to FIG. 1, the optical free working distance D between the mirror next to the wafer plane 4, the fourth mirror S4 in the present embodiment, and the wafer plane 4 is greater than the used diameter of mirror S4, that is, the following condition is fulfilled: optical distance from S4 to the wafer plane 4 greater than  used diameter S4. Other distance conditions are possible, for example, that the optical free working distance is greater than the sum of one-third of the used diameter of the mirror S4 nearest to the wafer plane 4 plus 20 mm or that the optical free working distance can be greater than 50 mm. In the embodiment of FIG. 1, the free optical working distance is 60 mm. Such an optical working distance guarantees sufficient free mechanical working distance, which is greater than 0, as well as the use of optical components with sufficient strength properties to be used at wavelengths  less than 100 nm and preferably of 11 or 13 nm. The optical components for a wavelength of xcex=13 nm and xcex=11 nm include, for example, Mo/Si and Mo/Be multilayer coating systems, respectively, where the typical multilayer coating systems for xcex=13 nm are 40 Mo/Si layer pairs, while the Mo/Be systems that are suitable for xcex11 nm have approximately 70 layer pairs. Reflectivities of such systems lie in the range of approximately 70%. In the multilayer coating systems, layer stresses of above 350 MPa and more may occur. Stresses of such values may induce surface deformation, especially in the edge regions of the mirror. The systems according to the invention, as shown as an example in FIG. 1, have: RES=k1xcex/NA. This results in a nominal resolution of at least 50 nm and 35 nm at a minimum numerical aperture of NA=0.15 for k1=0.57 and xcex=13 nm, and k1=0.47 and xcex=11 nm, respectively, where k1 is a parameter specific for the lithographic process. Furthermore, the beam path of the objective shown in FIG. 1 is obscuration-free. For example, in order to produce image formats of 26xc3x9734 mm2 or 26xc3x9752 mm2, the projection objectives according to the invention are preferably used in an arc-shaped field scan projection exposure apparatus, where the secant length of the scan slit is at least 26 mm. Numerous types of mask can be used in the projection exposure apparatus, including transmission masks, stencil masks, and reflection masks, and the system, which is telecentric on the image-side can be telecentric or not telecentric on the object-side. For example, to form a telecentric beam path on the object-side, when using a reflection mask, a transmission-reducing beam splitter must be employed. With a beam path not telecentric on the object-side, unevenness of the mask will not lead to scaling errors in the image. The main beam angles at the reticle plane 2 are therefore preferably less than 10xc2x0, so that the requirements for reticle evenness lie in technologically realizable range. Moreover, the system according to FIG. 1 has an image-side telecentering error on the wafer plane 4 of 3xc2x10.1 mrad at a numerical aperture of 0.15. In the embodiment shown, all mirrors S1-S5 are aspherical, and the maximum asphericity in the used area lies at 14 xcexcm. The maximum asphericity occurs on mirror S3. The low asphericity of the arrangement is advantageous from a manufacturing point of view, since the technological difficulties in producing of the surfaces of the multilayer mirror increase with the aspherical deviation and increasing gradient of the asphere. The highest angle of incidence in the arrangement according to FIG. 1 occurs at S2 and is 18.9xc2x0. The wavefront error of the arrangement is better than 0.023 xcex in the 2 mm wide arc-shaped field at xcex=13 nm. With the embodiments shown in FIGS. 1 and 2, the disadvantage of a mirror system with an odd number of mirrors, namely that a stretched structure reticle-projection optics-wafer can no longer be realized, is overcome. This disadvantage results from the fact that the reticle plane and the wafer plane were illuminated from the same direction especially in the case of systems with near normal incidence. This condition led to the reticle plane and the wafer plane lying on the same side of the objective. According to FIG. 1 or 2, the reticle plane 2 is placed within the projection system. The mirror arrangement is chosen so that, in the direction of the optical axis, the structural space provided for the reticle stage, within the projection system, is as large as possible, preferably 400 mm. In addition, the plane of the object, i.e., the reticle, has a sufficiently large distance to the light bundles traveling in the objective. This ensures that a sufficiently large object, i.e., reticle, can be scanned in an annular field scanning operation. In a preferred example, approximately 200 mm can be scanned on the reticle, corresponding to 50 mm on the wafer. In the embodiment shown in FIG. 1, the two mirrors of the two-mirror subsystem (S4, S5) have approximately the same radii R, within a few percent, and the distance between the two of the two oblate ellipsoidal mirrors is approximately R/{square root over (2)}. The three-mirror subsystem near the reticle plane 2 consists of three almost concentric mirrors (S1, S2, S3) of which the primary (S1) and the tertiary mirror (S3) have similar radii. The subsystem near the reticle plane 2 differs from a disturbed Offner system mainly by the position of the aperture stop B on the primary mirror and the non-telecentric beam path on the reticle. A real intermediate image Z is produced between the two subsystems. The chief-ray angle inclination on the reticle plane 2 permits a vignetting-free illumination of a reflection mask. Furthermore, in the embodiments according to FIGS. 1 and 2, the distances between the mirrors are chosen to have a value such that the mirrors can be sufficiently thick so that the required strength properties are still obtained at the high layer stresses that occur. The parameters of the systems shown in FIG. 1 are given in Table 1 in Code V ((trademark)) nomenclature. The objective is a 4xc3x97 system with a 26xc3x972 mm2 arc-shaped field and a numerical aperture NA of 0.15. The mean image-side radius of the system is approximately 26 mm. FIG. 2 shows an alternative embodiment of the invention of a five-mirror system in which the aperture stop B is between the first mirror and the second mirror. The same components as in FIG. 1 are assigned the same reference numbers. The optical free working distance at the wafer plane 4 is approximately 60 mm in this embodiment, and thus it is larger than the used diameter of the mirror S4, which is closest to the wafer plane 4. In contrast to the embodiment according to FIG. 1, in FIG. 2 the aperture stop B is placed physically between the first and second mirrors so that it is freely accessible. The wavefront error is 0.024 xcex, within the 1.7 mm wide arc-shaped field at xcex=13 nm. Table 2 shows the constructional data of the 4xc3x97 objective according to FIG. 2 in Code V ((trademark)) nomenclature. The mean radius of the 26xc3x971.7 mm2 is again 26 mm and the aperture NA=0.15. FIGS. 3A and 3B illustrate the meaning of the used diameter D in the present application. As an example, let the illuminated field 100 on a mirror in FIG. 3A be a rectangular field. The used diameter D is then the diameter of the envelope circle 102, which encompasses the rectangle 100, where the corners 104 of the rectangle 100 lie on the envelope circle 102. FIG. 3B shows a second example. The illuminated field 100 has a kidney shape, as expected for the useful range when using the objective according to the invention in a microlithography projection exposure apparatus. The envelope circle 102 encompasses the kidney shape fully and coincides with the edge 110 of the kidney shape at two points 106, 108. The used diameter D is then the diameter of the envelope circle 102. Thus, with the invention, a five-mirror projection objective is given for the first time, with an imaging scale of preferably 4xc3x97, 5xc3x97 as well as 6xc3x97 for preferred use in an EUV arc-shaped projection system. The projection objection has the necessary resolution for the required image field and provides conditions that make functional structural design possible, since the aspheres are sufficiently mild, the angles are sufficiently small for the layers and the structural spaces for the mirror carriers are sufficiently large.