Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2000-12-14
2002-09-17
Berman, Jack (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C378S119000
Reexamination Certificate
active
06452194
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to radiation sources, particularly discharge plasma sources emitting EUV radiation such as may be used as the radiation source of a lithographic projection apparatus comprising:
a radiation source constructed and arranged to generate extreme ultraviolet radiation;
an illumination system constructed and arranged to receive said extreme ultraviolet radiation and to supply a projection beam of said extreme ultraviolet radiation;
patterning means constructed and arranged to pattern the projection beam according to a desired pattern;
a substrate table constructed to hold a substrate; and
a projection system constructed and arranged to image the patterned beam onto target portions of the substrate.
2. Description of the Related Art
The term “patterning means” should be broadly interpreted as referring to means that can be used to endow an incoming radiation beam with a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate; the term “light valve” has also been used in this context. Generally, the said pattern will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit or other device (see below). Examples of such patterning means include:
A mask table for holding a mask. The concept of a mask is well known in lithography, and its includes mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. Placement of such a mask in the radiation beam causes selective transmission (in the case of a transmissive mask) or reflection (in the case of a reflective mask) of the radiation impinging on the mask, according to the pattern on the mask. The mask table ensures that the mask can be held at a desired position in the incoming radiation beam, and that it can be moved relative to the beam if so desired;
A programmable mirror array. An example of such a device is a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such an apparatus is that (for example) addressed areas of the reflective surface reflect incident light as diffracted light, whereas unaddressed areas reflect incident light as undiffracted light. Using an appropriate filter, the said undiffracted light can be filtered out of the reflected beam, leaving only the diffracted light behind; in this manner, the beam becomes patterned according to the addressing pattern of the matrix-adressable surface. The required matrix addressing can be performed using suitable electronic means. More information on such mirror arrays can be gleaned, for example, from U.S. Pat. Nos. 5,296,891 and 5,523,193, which are incorporated herein by reference; and
A programmable LCD array. An example of such a construction is given in U.S. Pat. No. 5,229,872, which is incorporated herein by reference. For purposes of simplicity, the rest of this text may, at certain locations, specifically direct itself to examples involving a mask table and mask; however, the general principles discussed in such instances should be seen in the broader context of the patterning means as hereabove set forth.
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. Further, the lithographic apparatus may be of a type having two or more mask tables and/or two or more substrate tables.
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 a pattern onto the target area 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 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 general, apparatus of this type contained a single mask (first object) table and a single substrate (second object) table. However, machines are 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 WO 98/28665 and WO 98/40791. The basic operating principle behind such a multi-stage apparatus is that, while a first substrate table is underneath the projection system so as to allow exposure of a first substrate located on that table, a second substrate table can run to a loading position, discharge an exposed substrate, pick up a new substrate, perform some initial metrology steps on the new substrate, and then stand by to transfer this new substrate to the exposure position underneath the projection system as soon as exposure of the first substrate is completed, whence the cycle repeats itself; in this manner, it is possible to achieve a substantially increased machine throughout, which in turn improves the cost of ownership of the machine.
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 (EUV) or soft x-ray and 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”, JB 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; and 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.
In a discharge plasma source, a partially ionized, low-density and relatively cold plasma is formed by an electrical discharge and then compressed so that it becomes highly ionized and reaches a very high temperature, causing the emission of EUV radiation. Preionization by, for instance, a source of RF power may be employed to start the discharge and to possibly create a well-defined
Banine Vadim Y.
Bartnik Andrzej
Bijkerk Frederik
de Bruijn Cornelis C.
Fiedorowicz Henryk
ASML Netherlands B.V.
Berman Jack
Pillsbury & Winthrop LLP
Smith II Johnnie L
LandOfFree
Radiation source for use in lithographic projection apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Radiation source for use in lithographic projection apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Radiation source for use in lithographic projection apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2886361