Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
2000-12-12
2003-12-30
Nguyen, Henry Hung (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S053000, C355S069000
Reexamination Certificate
active
06671035
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an illumination system for a lithography apparatus, such as may be used to produce an illumination beam of radiation and in which the intensity distribution of a beam of radiation at a plane is controlled. More particularly, the invention relates to the use of the illumination system in a lithographic projection apparatus comprising:
a radiation system comprising an illumination system, for supplying a projection beam of radiation;
patterning means, for patterning the projection beam according to a desired pattern;
a substrate table for holding a substrate; and
a projection system for imaging the patterned beam onto a target portion 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 cause 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-addressable 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.
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 the sake 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. The radiation system may also include components operating according to any of these design types for directing, shaping or controlling the projection beam of radiation, and such components may also be referred to below, collectively or singularly, as a “lens”. Further, the lithographic apparatus may be of a type having two or more substrate tables and/or two or more mask 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. Twin stage lithographic apparatus are described in for example, U.S. Pat. No. 5,969,441 and U.S. Ser. No. 09/180,011, filed Feb. 27, 1998, incorporated herein by reference.
Lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, the patterning means may generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (comprising one or more dies) on a substrate (silicon wafer) which has been coated with a layer of photosensitive material (resist). In general, a single wafer will contain a whole network of adjacent target portions which are successively irradiated via the projection system, one at a time. In current apparatus, employing patterning by a mask on a mask table, a distinction can be made between two different types of machine. In one type of lithographic projection apparatus, each target portion is irradiated by exposing the entire mask pattern onto the target portion 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 portion 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, for example, from U.S. Pat. No. 6,046,792, incorporated herein by reference.
A projection apparatus, such as used in lithography, generally includes an illumination system, referred to hereafter simply as an illuminator. The illuminator receives radiation from a source, such as a laser, and produces an illumination beam for illuminating an object, such as the patterning means (e.g. a mask on a mask table). Within a typical illuminator, the beam is shaped and controlled such that at a pupil plane the beam has a desired spatial intensity distribution. This spatial intensity distribution at the pupil plane effectively acts as a virtual radiation source for producing the illumination beam. Following the pupil plane, the radiation is substantially focussed by a lens group referred to hereafter as “coupling lens”. Said coupling lens couples the substantially focussed light into an integrator, such as a quartz rod. The function of said integrator is to improve the homogeneity of both the spatial and angular intensity distribution of the illumination beam. The spatial intensity distribution at the pupil plane is converted to an angular intensity distribution at the object being illuminated by said coupling optics, because the pupil plane substantially coincides with the front focal plane of the coupling optics. Controlling the spatial intensity distribution at the pupil plane can be done to improve the processing parameters when an image of the illuminated object is projected onto a substrate.
A known illuminator comprises an optical system referred to hereafter as “zoom-axicon”. The zoom-axicon is a means for adjusting the intensity distribution at the pupil plane. Radiation from the source passes through a first optical component, which generates an angular intensity distribution. Next, the radiation beam traverses a zoom lens. In the back focal plane of the zoom lens a spatial intensity distribution occurs that generally is suitable to serve as a secondary light source in the pupil plane. Hence, the back focal plane of the zoom lens typically substantially coincides with the pupil plane (i.e., the front focal plane of the coupling optics). The outer radial extent of the spatial intensity distribution at the pupil plane can be changed by ch
Eurlings Markus F
Krikke Jan J
ASML Netherlands B.V.
Nguyen Henry Hung
Pillsbury & Winthrop LLP
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