The patent's inventors are Streefkerk, Bob (
This patent was filed on
From the background information supplied by the inventors, news correspondents obtained the following quote: "A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, such as a mask, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising part of, one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the 'scanning'-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
"It has been proposed to immerse the substrate in the lithographic projection apparatus in a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the final element of the projection system and the substrate. The point of this is to enable imaging of smaller features since the exposure radiation will have a shorter wavelength in the liquid. (The effect of the liquid may also be regarded as increasing the effective NA of the system and also increasing the depth of focus.)
"However, submersing the substrate or substrate and substrate table in a bath of liquid (see for example U.S. Pat. No. 4,509,852, hereby incorporated in its entirety by reference) means that there is a large body of liquid that must be accelerated during a scanning exposure. This requires additional or more powerful motors and turbulence in the liquid may lead to undesirable and unpredictable effects.
"One of the solutions proposed is for a liquid supply system to provide liquid on only a localized area of the substrate and in between the final element of the projection system and the substrate using a liquid supply system (the substrate generally has a larger surface area than the final element of the projection system). One way which has been proposed to arrange for this is disclosed in PCT patent application publication WO 99/49504, hereby incorporated in its entirety by reference. As illustrated in FIGS. 6 and 7, liquid is supplied by at least one inlet IN onto the substrate, preferably along the direction of movement of the substrate relative to the final element, and is removed by at least one outlet OUT after having passed under the projection system. That is, as the substrate is scanned beneath the element in a -X direction, liquid is supplied at the +X side of the element and taken up at the -X side. FIG. 6 shows the arrangement schematically in which liquid is supplied via inlet IN and is taken up on the other side of the element by outlet OUT which is connected to a low pressure source. In the illustration of FIG. 6 the liquid is supplied along the direction of movement of the substrate relative to the final element, though this does not need to be the case. Various orientations and numbers of in- and out-lets positioned around the final element are possible, one example is illustrated in FIG. 7 in which four sets of an inlet with an outlet on either side are provided in a regular pattern around the final element.
"Clearly the presence of liquid in the immersion lithographic projection apparatus raises difficulties not present in conventional lithographic apparatus. For example, sensors such as interferometers for measuring the position of a substrate table which supports the substrate can be influenced by humidity present due to immersion liquid. Furthermore, not all of the solutions described herein for the liquid supply system may be perfect at containing all of the immersion liquid and some seepage or spillage may occur."
Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "Accordingly, it would be advantageous, for example, to reduce problems associated with the presence of immersion liquid in a lithographic projection apparatus.
"According to an aspect, there is provided a lithographic apparatus comprising:
"an illumination system adapted to condition a beam of radiation;
"a support structure configured to hold a patterning device, the patterning device configured to impart the beam with a pattern in its cross-section;
"a substrate table configured to hold a substrate;
"a projection system adapted to project the patterned beam onto a target portion of the substrate;
"a liquid supply system configured to at least partly fill a space between the projection system and an object on the substrate table with a liquid; and
"an active drying station configured to actively remove the liquid from the object, the substrate table, or both.
"Active removal of immersion liquid (which is, in an embodiment, accomplished without substantial heating of the substrate) may ensure that immersion liquid is in contact with the resist on the substrate (if the substrate is the object) for as short a time as possible. This is important because the immersion liquid may react with the resist so that the quality of the image on the substrate can change according to the amount of time that the resist is in contact with immersion liquid. Furthermore, if an active drying station removes liquid from a sensor the performance of that sensor may be enhanced. Removing liquid from an object and/or the substrate table may reduce contamination of the atmosphere in the apparatus with liquid vapor. This may enhance the performance of any optical sensors which may be present in the apparatus. The active removal generally takes place after the object and/or substrate table is moved from under the projection system and/or removed from the liquid supply system i.e. after the supply of liquid to the object and/or substrate table is stopped.
"In an embodiment, the substrate table transports the object to the active drying station and supports the object during active removal of liquid from the object by the active drying station. This may ensure that the active removal of liquid takes place as soon as possible after removal from under the projection system (or from the liquid supply system) thereby reducing the amount of time that liquid is exposed to the atmosphere of the apparatus and to the resist on the substrate; the substrate does not need to be removed from the substrate table before it is dried.
"The active drying station may be positioned between the projection system and a substrate post exposure processing module so that the removal of liquid can take place between the exposure position and the post exposure processing module or in the case of a substrate table mounted sensor, just before measurement using the sensor. That is the active drying station is within and/or part of the projection apparatus and not the post exposure processing module.
"In an embodiment, the drying station comprises gas flow device to provide a flow of gas over a surface of the object and/or the substrate table. In an embodiment, the gas flow device can provide a flow of gas of at least 50 liters per minute. This may ensure that the humidity inside the lithographic apparatus remains low and can help in keeping the apparatus stable in terms of temperature fluctuations, for example. The active drying station may comprise a gas inlet configured to provide gas onto a surface of the object and/or substrate table and/or a gas outlet configured to remove gas and/or liquid from the surface of the object and/or substrate table. In the case of a gas inlet, the gas inlet may comprise a gas knife or a gas shower with at least ten inlets. Both of those solutions have been found to be particularly effective at removing liquid from the surface of the object and/or the substrate table.
"The active drying station may comprise a spinner configured to spin the object and/or substrate table. The spinner makes use of centrifugal forces to remove liquid from the object and/or substrate table. This solution may be particularly suitable for when the object is the substrate in which case the substrate is spun in its major plane around its center.
"Another alternative which may be used by itself or in addition to any of the other measures discussed above, wherein the liquid between the projection system and an object on the substrate table is a first liquid, comprises a first liquid dissolving liquid supply device configured to provide a second liquid, in which the first liquid dissolves, to a surface of the object. In this way the first liquid can be dissolved in the second liquid. The second liquid itself is chosen for easy removal from the substrate. This may be effected, for example, by choosing a second liquid which has wetting properties of the surface of the object and/or substrate table which promote drying. Alternatively or additionally, the second liquid may be chosen to be more volatile than the first liquid such that it easily evaporates off of the surface of the object and/or substrate table. In an embodiment, the second liquid is a ketone or an alcohol.
"According to a further aspect, there is provided a device manufacturing method comprising:
"providing a liquid between a projection system and an object on the substrate table;
"projecting a patterned beam of radiation, through the liquid, onto a target portion of a substrate using the projection system; and
"actively removing the liquid from the object, the substrate table, or both.
"Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms 'wafer' or 'die' herein may be considered as synonymous with the more general terms 'substrate' or 'target portion', respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) or a metrology or inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.
"The terms 'radiation' and 'beam' used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelength of 365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams.
"The term 'patterning device' used herein should be broadly interpreted as referring to any device that can be used to impart a projection beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the projection beam may not exactly correspond to the desired pattern in the target portion of the substrate. Generally, the pattern imparted to the projection beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.
"A patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions; in this manner, the reflected beam is patterned. In each example of a patterning device, the support structure may be a frame or table, for example, which may be fixed or movable as required and which may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms 'reticle' or 'mask' herein may be considered synonymous with the more general term 'patterning device'.
"The term 'projection system' used herein should be broadly interpreted as encompassing various types of projection system, including refractive optical systems, reflective optical systems, and catadioptric optical systems, as appropriate for example for the exposure radiation being used, or for other factors such as the use of an immersion fluid or the use of a vacuum. Any use of the term 'projection lens' herein may be considered as synonymous with the more general term 'projection system'.
"The illumination system may also encompass various types of optical components, including refractive, reflective, and catadioptric optical components 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'.
"The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more mask tables). In such 'multiple stage' machines 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 exposure."
For the URL and additional information on this patent, see: Streefkerk, Bob; Donders,
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