X-ray or gamma ray systems or devices – Specific application – Lithography
Reexamination Certificate
2002-04-17
2004-01-27
Glick, Edward J. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Lithography
C378S035000
Reexamination Certificate
active
06683936
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an EUV-transparent interface structure for optically linking a first closed chamber and a second closed chamber whilst preventing a contaminating flow of a medium and/or particles from one chamber to the other.
The invention also relates to an EUV illuminating device comprising such an interface structure and to an EUV lithographic projection apparatus provided with such an EUV-transparent interface structure and/or illumination device. The invention further relates to a method of manufacturing devices wherein such an apparatus is used.
BACKGROUND AND SUMMARY OF THE INVENTION
A lithographic apparatus is an essential tool in the manufacture of integrated circuits (ICs) by means of masking and implantation techniques. By means of such an apparatus, a number of masks having different mask patterns are successively imaged at the same position on a semiconductor substrate.
A substrate is understood to mean a plate of material, for example silicon, in which a complete multilevel device, such as an IC, is to be formed level by level by means of a number of successive sets of processing steps. Each of these sets comprises as main processing steps: applying a radiation-sensitive (resist) layer on the substrate, aligning the substrate with a mask, imaging the pattern of this mask in the resist layer, developing the resist layer, etching the substrate via the resist layer and further cleaning and other processing steps. The term substrate covers substrates at different stages in the manufacturing process, i.e. both a substrate having no level or only one level of already configured device features and a substrate having all but one level of already configured device features, and all intermediate substrates.
The minimum size of the device structures that can be imaged with the required quality by a lithographic projection apparatus depends on the resolving power, or resolution, of the projection system of this apparatus. This resolution is proportional to &lgr;/NA, wherein &lgr; is the wavelength of the projection beam used in the apparatus and NA is the numerical aperture of the projection system. To produce devices with a higher density, and hence higher operating speeds, smaller device structures have to be imaged so that the resolution should be increased. To this end, the numerical aperture could be increased and/or the wavelength decreased. In practice, an increase of the numerical aperture, which is currently fairly large, is not very well possible because this reduces the depth of focus of the projection system, which is proportional to &lgr;/NA
2
and, moreover, it becomes too difficult to correct the projection system for the required image field. Therefore, the wavelength is reduced to decrease the minimum device feature that can still be imaged satisfactorily.
Conventional lithographic projection apparatuses employ ultraviolet (UV) radiation, which has a wavelength of 356 nm and is generated by mercury lamps, or deep UV (DUV) radiation, which has a wavelength of 248 nm or 193 nm and is generated by excimer lasers. More recently it has been proposed to use extreme UV (EUV) radiation in the projection apparatus. With such a radiation, also called soft-x ray radiation, which has a considerably smaller wavelength, considerably smaller device features can be imaged. EUV radiation is understood to mean radiation with a wavelength from a few to some tens of nm and preferably of the order of 13 nm.
Possible EUV radiation sources include, for example, laser-produced plasma sources and discharge plasma sources. A laser-produced plasma EUV source is described, for example, in the article: “High-power source and illumination system for extreme ultraviolet lithography” in: Proceedings of the SPIE Conference on EUV, X-Ray and Neutron Optics and Sources, Denver, July 1999, Vol.3767, pages 136-142. A discharge plasma source is described in, for example, the article: “Highly repetitive, extreme-ultraviolet radiation source based on gas-discharge plasma” in Applied Optics, Vol.38, No.25, Sep. 1, 1999, pages 5413-17.
EUV radiation sources, such as the discharge plasma source referred to above, require the use of a rather high partial pressure of a gas or vapor to emit EUV radiation. In a discharge plasma source, a discharge is created in between two electrodes, and ionized plasma generated is subsequently caused to collapse to yield very hot plasma that emits radiation in the EUV range. The very hot plasma is often created in xenon (Xe), since xenon 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 xenon pressure is that xenon gas absorbs EUV radiation. For example, xenon gas with a pressure of 0.1 mbar transmits over 1 m only 0.2% EUV radiation having a wavelength of 13.5 nm. It is therefore required to confine the rather high xenon pressure to a limited region around the source. To this end, the source can be embedded in its own vacuum chamber that is separated by a chamber wall from the next vacuum chamber in which at least a part of the illumination optics, comprising a collector mirror, is arranged. Said chamber wall should have an EUV-radiation transparent opening to pass the EUV radiation from the source to the subsequent chamber, whilst the different vacuum levels in the source chamber and said next chamber should be maintained.
A problem with a discharge plasma source, but also with other plasma sources like a laser-produced plasma source, is the relatively large amount of debris, e.g. contaminating particles, produced by this source. For a discharge plasma source, the debris stems mainly from erosion of the electrodes, by interaction of the plasma with these electrodes, and from erosion of the walls of the source chamber. Such an erosion of the walls, which is due to the high temperature generated in the source chamber, also occurs in a laser-produced plasma source. Moreover, the plasma, like xenon plasma, may emit high-energetic ions. The contaminating particles and ions may escape through the opening in the wall of the source chamber and reach optical components, or reflectors of the illumination system. These components, the first one of which is a collector mirror, for example a grazing-incidence mirror, are composed of a number of thin layers of, for example, silicon and molybdenum. They are very vulnerable and their reflection coefficient is easily decreased to an unacceptable level when they are hurt by such particles. As a consequence, the intensity of the EUV illumination beam would become too small.
Another problem in a lithographic projection apparatus is that debris and byproducts, in general material, may be sputtered loose from the resist layer by the EUV beam. The evacuated intervening space between the substrate and the projection system allows the released material to migrate towards the projection system without undergoing substantial scattering or deflection. In the projection system, the material is deposited on one or more mirrors, thereby forming a spurious coating, which has a roughening effect on the mirror surfaces. As a result of this, the resolution and definition of the images formed by means of the projection rapidly degenerate. Moreover, the reflection coefficient of the mirrors decreases so that less EUV radiation can reach the resist layer.
It is an object of the present invention to provide means for solving the above-mentioned problems and to improve the performance of a lithographic projection apparatus.
According to a first aspect of the invention, it provides an EUV-transparent interface structure as defined in the opening paragraph, which is characterized by an EUV-transparent member and a gas guide for injecting a flow of EUV-transparent gas in the neighborhood of the member surface facing the contaminating flow and for flushing the EUV-transparent gas in a direction opposite to the direction of the contaminating flow.
The member blocks the
Glick Edward J.
Kiknadze Irakli
Koninklijke Philips Electronics , N.V.
Waxler Aaron
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