Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2001-01-03
2003-06-10
Lee, John R. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S50400H, C356S051000, C359S353000, C355S066000, C355S067000
Reexamination Certificate
active
06576912
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates an extreme ultraviolet radiation transparent structure in a vacuum wall. More particularly, the invention relates to the use of the transparent structure in a lithographic projection apparatus comprising:
an illumination system constructed and arranged to supply a projection beam of radiation;
a mask table constructed to hold a mask;
a substrate table constructed to hold a substrate; and
a projection system constructed and arranged to image an irradiated portion of the mask onto a target portion of the substrate.
2. Discussion of Related Art
For the sake of simplicity, the projection system may hereinafter be referred to as the “lens”; however, this term should be broadly interpreted as encompassing various types of projection system, including refractive optics, reflective optics and catadioptric systems, for example. In addition, the first and second object tables may be referred to as the “mask table” and the “substrate table”, respectively. Further, the lithographic apparatus may be of a type having two or more mask tables and/or two or more substrate tables. In such “multiple stage” devices the additional tables may be used in parallel, or preparatory steps may be carried out on one or more stages while one or more other stages are being used for exposures. Twin stage lithographic apparatus are described in International Patent Applications WO 98/28665 and WO 98/40791, for example.
Lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, the mask (reticle) may contain a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target area (comprising one or more dies) on a substrate (silicon wafer) which has been coated with a layer of radiation-sensitive material (resist). In general, a single wafer will contain a whole network of adjacent target areas which are successively irradiated via the mask, one at a time. In one type of lithographic projection apparatus, each target area is irradiated by exposing the entire mask pattern onto the target area in one go; such an apparatus is commonly referred to as a wafer stepper. In an alternative apparatus, which is commonly referred to as a step-and-scan apparatus, each target area is irradiated by progressively scanning the mask pattern under the projection beam in a given reference direction (the “scanning” direction) while synchronously scanning the substrate table parallel or anti-parallel to this direction; since, in general, the projection system will have a magnification factor M (generally<1), the speed V at which the substrate table is scanned will be a factor M times that at which the mask table is scanned. More information with regard to lithographic devices as here described can be gleaned from International Patent Application WO 97/33205.
In a lithographic apparatus the size of features that can be imaged onto the substrate is limited by the wavelength of the projection radiation. To produce integrated circuits with a higher density of devices, and hence higher operating speeds, it is desirable to be able to image smaller features. Whilst most current lithographic projection apparatus employ ultraviolet light generated by mercury lamps or excimer lasers, it has been proposed to use shorter wavelength radiation of around 13 nm. Such radiation is termed extreme ultraviolet radiation, also referred to as XUV or EUV radiation. XUV generally refers to the wavelength range from several tenths of nanometer to several tens of nanometers, combining the soft x-ray and vacuum UV range, whereas EUV is normally used in conjunction with lithography (EUVL) and refers to a radiation band from approximately 5 to 20 nm, i.e. part of the XUV range.
Possible sources include, for instance, laser-produced plasma sources, discharge plasma sources, or synchrotron radiation from electron storage rings. An outline design of a lithographic projection apparatus using synchrotron radiation is described in “Synchrotron Radiation Sources and Condensers for Projection X-Ray Lithography”, J. B. Murphy et al, Applied Optics, Vol. 32, No. 24, pp. 6920-6929 (1993). Apparatus using discharge plasma sources are described in: W. Partlo, I. Fomenkov, R. Oliver, D. Birx, “Development of an EUV (13.5 nm) Light Source Employing a Dense Plasma Focus in Lithium Vapor”, Proc. SPIE 3997, pp. 136-156 (2000); M. W. McGeoch, “Power Scaling of a Z-pinch Extreme Ultraviolet Source”, Proc. SPIE 3997, pp. 861-866 (2000); W. T. Silfvast, M. Klosner, G. Shimkaveg, H. Bender, G. Kubiak, N. Fornaciari, “High-Power Plasma Discharge Source at 13.5 and 11.4 nm for EUV lithography”, Proc. SPIE 3676, pp. 272-275 (1999); and K. Bergmann et al., “Highly Repetitive, Extreme Ultraviolet Radiation Source Based on a Gas-Discharge Plasma”, Applied Optics, Vol. 38, pp. 5413-5417 (1999). So-called “undulators” and “wigglers” have been proposed as an alternative source of extreme ultraviolet radiation. In these devices, a beam of electrons traveling at high, usually relativistic, speeds, e.g. in a storage ring, is caused to traverse a series of regions in which magnetic fields perpendicular to the beam velocity are established. The directions of the magnetic field in adjacent regions are mutually opposite, so that the electrons follow an undulating path. The transverse accelerations of the electrons following the undulating path cause the emission of Maxwell radiation perpendicular to the direction of the accelerations, i.e. in the direction of the non-deviated path.
Radiation sources may require the use of a rather high partial pressure of a gas or vapor to emit XUV radiation, such as discharge plasma radiation sources referred to above. In a discharge plasma source a discharge is created in between electrodes, and a resulting partially ionized plasma is subsequently caused to collapse to yield a very hot plasma that emits radiation in the XUV range. The very hot plasma is quite often created in Xe, since a Xe plasma radiates in the EUV range around 13.5 nm. For an efficient EUV production, a typical pressure of 0.1 mbar is required near the electrodes of the radiation source. A drawback of having such a rather high Xe pressure is that Xe gas absorbs EUV radiation. For example, 0.1 mbar Xe transmits over 1 m only 0.3% EUV radiation having a wavelength of 13.5 nm. It is therefore required to confine the rather high Xe pressure to a limited region around the source. To reach this the source can be contained in its own vacuum chamber that is separated by a chamber wall from a subsequent vacuum chamber in which the collector mirror and illumination optics may be contained. However, an EUV radiation transparent opening is needed to pass the EUV radiation emitted by the source to the next vacuum chamber. Since a large opening in the wall, required to collect sufficient EUV radiation, would cause an elevated pressure in the next vacuum chamber, the opening might be closed off using a thin window of a few micron thickness or less, which is (partially) transparent for EUV radiation. Such a thin window will, however, not survive the heat load from the high-power EUV radiation source that is needed for EUV lithography.
SUMMARY OF THE INVENTION
It is an object of the present invention is to provide a structure in a vacuum chamber wall that is transparent for EUV radiation and further presents a gas barrier so as to be able to maintain different vacuum levels in vacuum chambers on both sides of the vacuum chamber wall.
Further objects of the invention will become apparent from the description of the invention that follows.
According to a first aspect of the present invention there is provided a lithographic projection apparatus comprising an illumination system constructed and arranged to supply a projection beam of radiation; a mask table constructed to hold a mask; a substrate table constructed to hold a substrate; and a projection system constructed and arranged to image an irradiated portion of the mask on
Banine Vadim Y.
Bisschops Theodorus H. J.
Jonkers Jeroen
Sandstrom Richard L.
Visser Hugo M.
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