Photocopying – Projection printing and copying cameras – Step and repeat
Reexamination Certificate
2000-12-19
2003-02-25
Mathews, Alan A. (Department: 2851)
Photocopying
Projection printing and copying cameras
Step and repeat
C355S072000, C318S649000
Reexamination Certificate
active
06525803
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to balanced positioning systems, such as may be used to position a moveable object in at least three degrees of freedom. More particularly, the invention relates to the use of such a balanced positioning system in lithographic projection apparatus comprising:
an illumination system for supplying a projection beam of radiation;
a first object table for holding patterning means capable of patterning the projection beam according to a desired pattern;
a second object 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 held by said first object table. 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 projection 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 first object table ensures that the mask can be held at a desired position in the incoming projection beam, and that it can be moved relative to the beam if so desired.
A programmable mirror array held by a structure, which is referred to as first object table. 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, held by a structure which is referred to as first object table. 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; 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 illumination 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”. In addition, the first and second object table may be referred to as the “mask table” and the “substrate table”, respectively.
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) that has been coated with a layer of radiationsensitive material (resist). In general, a single wafer will contain a whole network of adjacent target portions that 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—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.
In general, apparatus of this type contained a single first object (mask) table and a single second object (substrate) table. However, machines are becoming available in which there are at least two independently movable substrate tables; see, for example, the multi-stage apparatus described in U.S. Pat. No. 5,969,441 and U.S. Ser. No. 09/180,011, filed Feb. 27, 1998 (WO 98/40791), incorporated herein by reference. 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 known lithographic apparatus, the drive unit of the positioning device for the substrate table comprises two linear Y-motors each of which comprises a stator extending parallel to the Y-direction and secured to a base of the positioning device, and a translator (Y-slider) movable along the stator. The base is secured to the frame of the lithographic device. The drive unit further comprises a linear X-motor that comprises a stator extending parallel to the X-direction and a translator (X-slider) which can be moved along the stator. The stator of the X-motor is mounted on an X-beam that is secured, near its respective ends, to the translators (Y-sliders) of the linear Y-motors. The arrangement is therefore H-shaped, with the two Y-motors forming the uprights and the X-motor forming the cross-piece, and this arrangement is often referred to as an H-drive.
The driven object, in this case the substrate table, can be provided with a so-called air foot. The air foot comprises a gas bearing by means of which the substrate table is guided so as to be movable over a guide surface of the base extending at right angles to the Z-direction.
In a lithographic apparatus, reactions on the machine frame to acceleration forces used to position the mask (reticle) and substrate (wafer) to nanometer accuracies are a major cause of vibration, impairing the ac
Kwan Yim Bun P.
van de Wiel Wilhelmus J. T. P.
ASML Netherlands B.V.
Mathews Alan A.
Pillsbury & Winthrop LLP
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