Radiant energy – With charged particle beam deflection or focussing – With target means
Reexamination Certificate
2001-02-07
2003-12-02
Lee, John R. (Department: 2881)
Radiant energy
With charged particle beam deflection or focussing
With target means
C250S400000, C250S492100, C250S492200, C250S492220
Reexamination Certificate
active
06657204
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to arrangements for cooling voice coil motors, and in particular to arrangements for cooling voice coil motors for use in lithographic projection apparatus comprising:
a radiation 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. Background of the Related Art
The terms “patterning means” “mask”, or “projection beam patterning structure” 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.
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, catadioptric systems, and charged particle optics, for example. The radiation system may also include elements operating according to any of these principles for directing, shaping or controlling the projection beam of radiation, 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 table” 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, for example, in U.S. Pat. No. 5,969,441 and U.S. Ser. No. 09/180,011 filed Feb. 27, 1998 (WO98/40791), incorporated herein by reference.
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 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 substrate will contain a whole network of adjacent target portions which are successively irradiated via the mask, one at a time. 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 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 U.S. Pat. No. 6,046,792, incorporated herein by reference.
In a lithographic apparatus, voice coil motors (typically Lorentz-force motors) are used, for example, for fine positioning of the substrate table and the mask table. The motors dissipate heat in operation which, if not removed in a controlled manner, would affect the thermal stability of the apparatus. In the case of the fine positioning of a substrate table, it is important that heat transfer from the motor to the substrate table is minimized. The substrate table is designed to be operated at a predetermined temperature and heat transfer to the substrate table may lead to expansion or contraction in the substrate table and/or the substrate causing an inaccuracy in the positioning of the substrate and thus of the target portion to be irradiated.
At present the coils of the motors are cooled by a thin metal cooling plate in thermal contact with the coil. Heat from the coil is removed by thermal conduction through the cooling plate to its sides which are connected to a water cooling system. Thus there is inevitably a temperature variation across the cooling plate, and heat loss by convection or radiation from the surfaces of the cooling plate can lead to a heat load on the substrate table which is too large. For example, in a typical design no more than 0.5W out of approximately 350W of heat dissipated in each voice coil motor can be allowed to escape to the surrounding components without causing a detrimental effect.
An object of the present invention is to provide an improved means of cooling the voice coil motors of lithographic apparatus which will result in a reduction in the heat loss to its surroundings.
SUMMARY OF THE INVENTION
According to the present invention there is provided a lithographic projection apparatus comprising:
a radiation system for providing a projection beam of radiation;
patterning means, for patterning the projection beam according to a desired pattern;
a substrate table for holding a substrate;
a projection system for imaging the patterned beam onto a target portion of the substrate; wherein
at least one of the patterning means and the substrate table is associated with positioning means comprising at least one voice coil motor having a coil in thermal contact with a cooling jacket; characterized in that:
the cooling jacket comprises at least one channel for circulation of a cooling fluid,
Buis Edwin J.
Gilissen Noud J.
Kwan Yim Bun P.
Schapendonk Paulus H.C.M.
ASML Netherlands B.V.
Lee John R.
Pillsbury & Winthrop LLP
Souw Bernard
LandOfFree
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