Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
2000-06-01
2002-09-24
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S001000, C355S071000, C362S551000, C385S901000
Reexamination Certificate
active
06456362
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to integrators for use in lithographic projection apparatus comprising:
an illumination system for supplying a projection beam of electromagnetic radiation having a wavelength of less than about 50 nm;
a first object table provided with a first object holder for holding a mask;
a second object table provided with a second object holder for holding a substrate; and
a projection system for imaging an irradiated portion of said mask onto a target portion of said substrate.
More particularly, the invention relates to such a device in which the electromagnetic radiation is extreme ultra-violet light (EUV), typically with a wavelength below about 15 nm. An example of a wavelength in the EUV region which is gaining considerable interest in the lithography industry is 13.4 nm, though there are also other promising wavelengths in this region, such as 11 nm, for example.
BACKGROUND OF THE INVENTION
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. The radiation system may also include elements operating according to any of these principles for directing, shaping or controlling the projection beam, and such elements may also be referred to below, collectively or singularly, as a “lens”. 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 tables while one or more other tables are being used for exposures.
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 an exposure area (die) on a substrate (silicon wafer) which has been coated with a layer of energy-sensitive material (resist). In general, a single wafer will contain a whole network of adjacent dies which are successively irradiated via the reticle, one at a time. In one type of lithographic projection apparatus, each die is irradiated by exposing the entire reticle pattern onto the die at once; 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 die is irradiated by progressively scanning the reticle pattern under the projection beam in a given reference direction (the “scanning” direction) while synchronously scanning the wafer 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 wafer table is scanned will be a factor M times that at which the reticle table is scanned. More information with regard to lithographic devices as here described can be gleaned from International Patent Application WO97/33205, for example.
Until very recently, lithographic apparatus contained a single mask table and a single substrate table. However, machines are now becoming available in which there are at least two independently moveable substrate tables; see, for example, the multi-stage apparatus described in International Patent Applications WO98/28665 and WO98/40791. The basic operating principle behind such multi-stage apparatus is that, while a first substrate table is at the exposure position underneath the projection system for exposure of a first substrate located on that table, a second substrate table can run to a loading position, discharge a previously exposed substrate, pick up a new substrate, perform some initial measurements on the new substrate and then stand ready to transfer the new substrate to the exposure position underneath the projection system as soon as exposure of the first substrate is completed; the cycle then repeats. In this manner it is possible to increase substantially the machine throughput, which in turn improves the cost of ownership of the machine. It should be understood that the same principle could be used with just one substrate table which is moved between exposure and measurement positions.
In the case of the current invention, which encompasses electromagnetic radiation in the EUV range, the projection system will generally consist of an array of mirrors, and the mask will be reflective; see, for example, the apparatus discussed in WO 99/57596 (P-0111). The radiation in this case can be produced by various known means, such as:
by suitable laser-irradiation of a gas, liquid or solid;
on the basis of a plasma source;
with the aid of an undulator/wiggler placed around the path of an electron beam in a synchrotron or storage ring.
An example of an illuminator comprised in the illumination system and suitable for use with such radiation is described in European Patent Application no 98204237.6 (P-0122), whereas a suitable condenser for use with EUV is described in European Patent Application no 00300784.6 (P-0129).
In general, it will be desirable to incorporate an integrating element in the illumination system, which element serves to improve the intensity uniformity throughout the cross-section of the projection beam prior to the mask. In the case of UV lithography, such an integrating element (“integrator”) may comprise a so-called fly-eye lens, or a refractive bar (such as a quartz rod). However, such integrators are not suitable for use with radiation in the EUV range, and alternatives have therefore been sought. To date, the use of alternatives such as ripple plates, multilayer mirrors and wigglers has been proposed.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an alternative integrator for use with electromagnetic radiation having a wavelength of 50 nm or less, and particularly for use with EUV.
These and other objects are achieved in a lithographic projection apparatus comprising:
an illumination system for supplying a projection beam of electromagnetic radiation having a wavelength of less than about 50 nm;
a first object table provided with a first object holder for holding a mask;
a second object table provided with a second object holder for holding a substrate;
a projection system for imaging an irradiated portion of said mask onto a target portion of said substrate; and
an integrating element disposed in the path of the radiation in the illumination system, the integrating element comprising a hollow waveguide.
The inventors have demonstrated that such an integrator can have a surprisingly high efficiency and transmission, and lends itself to many varied applications. Preferential embodiments of the invention are specified further in the claims, and a number of these embodiments are elucidated below in the embodiments and figures.
The invention also relates to a method of manufacturing a device using a lithographic projection apparatus comprising:
an illumination system for supplying a projection beam of electromagnetic radiation having a wavelength of less than about 50 nm;
a first object table provided with a first object holder for holding a mask;
a second object table provided with a second object holder for holding a substrate; and
a projection system for imaging an irradiated portion of said mask onto a target portion of said substrate; the method comprising the steps of:
providing a mask bearing a pattern to said first object table;
providing a substrate having a radiation-sensitive layer to said second object table;
irradiating portions of the mask with said projection beam; and
imaging irradiated portions of the mask onto target portions of the substrate;
characterized in that, prior to being directed onto the mask, the projection beam is passed thro
Adams Russell
ASML Netherlands B.V.
Fuller R. E
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