X-ray or gamma ray systems or devices – Specific application – Lithography
Reexamination Certificate
2000-11-03
2002-06-04
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Lithography
C378S034000, C378S145000, C378S146000, C378S147000, C378S154000
Reexamination Certificate
active
06400794
ABSTRACT:
The invention concerns an illumination system according to the preamble of claim
1
as well as a projection exposure device with such an illumination system and a process for the production of microelectronic components with a projection exposure device.
BACKGROUND OF THE INVENTION
In order to still further reduce the structural widths for electronic components, particularly in the submicron range, it is necessary to reduce the wavelength of the light utilized for microlithography. Lithography with soft x-rays, so-called EUV lithography, is conceivable at wavelengths below 193 nm for example.
An illumination system suitable for EUV lithography will homogeneously, i.e., uniformly illuminate, with as few reflections as possible, a predetermined field for EUV lithography, particularly the annular field of an objective. Furthermore, the pupil of the objective should be illuminated up to a specific degree of filling, independent of the field, and the exit pupil of the illumination system should lie in the entrance pupil of the objective.
An illumination system for a lithography device, which uses EUV radiation, has been made known from U.S. Pat. No. 5,339,246. For uniform illumination in the reticle plane and filling of the pupil, U.S. Pat. No. 5,339,246 proposes a condenser, which is constructed as a collector lens, and comprises at least four pairs of mirror facets, which are arranged symmetrically. A plasma light source is used as the light source.
An illumination system with a plasma light source comprising a condenser mirror is shown in U.S. Pat. No. 5,737,137, in which an illumination of a mask or a reticle to be illuminated is achieved by means of spherical mirrors.
U.S. Pat. No. 5,361,292 shows an illumination system, in which a plasma light source is provided and the point plasma light source is imaged by means of a condenser, which has at least three aspherical mirrors arranged off-center, in a ring-shaped illuminated surface. The ring-shaped illuminated surface is then imaged in the entrance pupil by means of a special sequence of grazing-incidence mirrors.
An illumination system has been made known from U.S. Pat. No. 5,581,605, in which a photon beam is spilt into a multiple number of secondary light sources by means of a plate with raster elements. A homogeneous or uniform illumination is achieved in this way in the reticle plane. The imaging of the reticle on the wafer to be exposed is produced by means of a conventional reducing optics. A gridded mirror with equally curved elements is provided precisely in the illuminating beam path.
U.S. Pat. No. 5,677,939 shows an illumination system for EUV illumination devices, in which an annular field is homogeneously illuminated. In the EUV illumination system according to U.S. Pat. No. 5,677,939, the beams emitted from the EUV source are formed into a parallel beam of light, for example, by means of a mirror. In order to form a multiple number of secondary light sources, the parallel beam of light is guided onto a mirror with a plurality of cylinder raster elements. U.S. Pat. No. 5,677,939 also describes the use of synchrotron radiation sources, but of course, the light of the source is guided directly onto the mirror with cylinder raster elements, due to the parallel nature of the emitted synchrotron radiation, without optical elements situated therebetween. All embodiments shown in U.S. Pat. No. 5,677,939 operate in a parallel beam path. In addition, the facetted mirrors known from U.S. Pat. No. 5,677,939 contain facets with an optical effect and are arranged on a planar substrate.
From U.S. Pat. No. 5,512,759 for an arc shaped-field projection system with a synchrotron radiation source an illumination system has been made known, which comprises a condenser system with a multiple number of convergent mirrors. The mirrors collect the radiation emitted by the synchrotron radiation source, to form an annular light beam, which corresponds to the annular field to be illuminated. Therefore, the annular field is illuminated very uniformly. The synchrotron radiation source has a beam divergence >100 mrads in the beam plane.
U.S. Pat. No. 5,439,781 shows an illumination system with a synchrotron radiation source, in which the waveguide value, i.e., the Lagrange optical invariant, is adjusted by means of a scatter disk in the entrance pupil of the objective, whereby the scatter disk may have a plurality of pyramidal structures. The synchrotron radiation source in the case of U.S. Pat. No. 5,439,781 also has a beam divergence >100 mrads. The collector mirror for collecting the synchrotron radiation and bundling the same may itself be constructed with facets.
The disclosure content of all of the previously named documents:
U.S. Pat. No. 5,339,246
U.S. Pat. No. 5,737,137
U.S. Pat. No. 5,361,292
U.S. Pat. No. 5,581,605
U.S. Pat. No. 5,677,939
U.S. Pat. No. 5,512,759
U.S. Pat. No. 5,439,781
is incorporated in the present application by reference.
SUMMARY OF THE INVENTION
An object of the invention is to provide an illumination system that is constructed as simply as possible fulfilling the requirements for an exposure system for wavelengths ≦193 nm, particularly in the EUV region and a process for the design of such a system. In addition to a uniform illumination of the reticle, also the telecentric requirements of a system for wavelengths ≦193 nm particularly should be fulfilled.
Telecentricity is to be understood in the present application in that the entire system is telecentric at the wafer. This requires an adaptation of the exit pupil of the illumination system to the entrance pupil of the objective, which is finite for a reflective reticle.
In the present application, the telecentricity requirement is fulfilled, if the divergence of the principal beams of the illumination system and objective in the reticle plane does not exceed a predetermined value, for example, ±4.0 mrads, preferably ±1.0 mrad, and the principal beams impinge on the wafer telecentrically.
According to the invention, this object is achieved in that for the above-described illumination system, the light source is a light source for producing radiation with a wavelength ≦193 nm, which irradiates with a wavelength spectrum in a predetermined plane, wherein the radiation in the wavelength range that can be used for applications, particularly lithography, has a beam divergence perpendicular to the predetermined plane, which is less than 5 mrads.
Synchrotron radiation sources are used in the EUV region as preferred light sources, with a beam divergence smaller than 5 mrads in the plane perpendicular to the predetermined plane. Synchrotron radiation is emitted, if relativistic electrons are deflected in a magnetic field. The synchrotron radiation is emitted tangentially to the path of the electrons.
At the present time, one can distinguish three types of sources in the case of synchrotron radiation sources:
bending magnets
wigglers
undulators.
In bending-magnet sources, electrons are deflected by a bending magnet and photon radiation is emitted.
Wiggler sources contain a so-called wiggler for deflection of the electron or an electron beam, the wiggler comprising many pairs of magnets with alternating polarity arranged in rows. When an electron passes through a wiggler, the electron will be subjected to a periodic, vertical magnetic field; the electron oscillates accordingly in the horizontal plane. Furthermore, wigglers are characterized in that no coherence effects occur. The synchrotron radiation produced by means of a wiggler is similar to that of a bending magnet and radiates in a horizontal solid angle. In contrast to the bending magnet, it has a flux that is amplified by the number of poles of the wiggler.
There is no clear dividing line between wiggler sources and undulator sources.
In the case of undulator sources, the electrons in the undulator are subjected to a magnetic field with shorter period and a magnetic field of the deflection poles being smaller than in the case of the wiggler, so that interference effects occur in the s
Schultz Jörg
Wangler Johannes
Barber Therese
Carl-Zeiss-Stiftung
Kim Robert H.
Ohlandt Greeley Ruggiero & Perle LLP
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