Patent Application
20080137055
The present invention relates to a substrate support constructed to support a substrate for lithographic processing purposes, in particular, for immersion lithographic processing purposes.
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. 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 a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
There is an increased need to thermally stabilize a substrate, such as a substrate to be targeted with a patterned beam, due to ever more demanding requirements for image resolution, in particular in the new field of immersion lithography. For immersion, thermal stabilization is difficult, since an immersion liquid may cause thermal cooling by transitioning to a vapor phase. In addition or alternatively, in particular near an edge of the substrate, the immersion liquid may be difficult to handle, especially, since splashing or sticking may occur of the liquid near the edge of the substrate. Such may give rise to contamination and/or the occurrence of a local thermal gradient in the substrate that may need to be stabilized.
It is desirable, for example, to provide a photolithographic apparatus, wherein one or more thermal problems, such as those mentioned above, are treated and where an improved thermal stabilization of the substrate is provided, in particular, near the edge of the substrate.
According to an aspect of the invention, there is provided a substrate support constructed to support a substrate for immersion lithographic processing, the substrate support comprising:
a central part;
a peripheral part comprising an extraction duct configured to extract a liquid from a top surface of the substrate support, the extraction duct connected to an exit duct configured to duct the liquid away from the substrate support; and
a thermal stabilizer, arranged in the peripheral part, configured to thermally stabilize a central part of the substrate support relative to the peripheral part.
According to an aspect of the invention, there is provided a lithographic apparatus comprising:
an illumination system configured to condition a radiation beam;
a patterning device support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam;
a substrate support constructed to support a substrate, the substrate support comprising:
a projection system configured to project the patterned radiation beam onto a target portion of a substrate.
According to an aspect of the invention, there is provided an immersion lithographic apparatus comprising:
an illumination system configured to condition a radiation beam;
a patterning device support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam;
a substrate support constructed to support a substrate, the substrate support comprising:
a projection system configured to project the patterned radiation beam onto a target portion of the substrate,
wherein the lithographic apparatus is arranged to provide the liquid between the substrate support and the projection system to provide immersion lithography.
According to an aspect of the invention, there is provided an immersion lithographic apparatus comprising:
an illumination system configured to condition a radiation beam;
a patterning device support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam;
a substrate support constructed to support a substrate, the substrate support comprising a duct configured to duct thermally stabilizing media in the substrate support;
a projection system configured to project the patterned radiation beam onto a target portion of the substrate; and
a supply system configured to supply the thermally stabilizing media to the substrate support and comprising a temperature controller configured to control a temperature of the thermally stabilizing media to a preset temperature, the preset temperature being lower than a set average temperature of the substrate support,
wherein the lithographic apparatus is arranged to provide a liquid between the substrate support and the projection system to provide immersion lithography.
According to an aspect of the invention, there is provided a method of supplying thermally stabilizing media to a substrate support in a lithographic apparatus, the substrate support comprising an annular extraction duct, arranged in a peripheral part of the substrate support, configured to extract a liquid from the substrate support, the extraction duct being connected to an exit duct configured to duct the liquid away from the substrate support, and the substrate support comprising a thermal stabilizer, arranged in the peripheral part, configured to thermally stabilize a central part of the substrate support relative to the peripheral part, the method comprising controlling a temperature of a thermally stabilizing media to a preset temperature before supplying the media to the substrate support; the preset temperature being lower than a set average temperature of the substrate support.
Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:
an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation);
a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters;
a substrate table (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate in accordance with certain parameters; and
a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.
The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.
The support structure holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure 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 “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a radiation 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 radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.
The 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. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix.
The term “projection system” used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid 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”.
As here depicted, the apparatus is of a transmissive type (e.g. employing a transmissive mask). Alternatively, the apparatus may be of a reflective type (e.g. employing a programmable mirror array of a type as referred to above, or employing a reflective mask).
The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more support structures). In such “multiple stage” machines, the additional tables and/or support structures may be used in parallel, or preparatory steps may be carried out on one or more tables and/or support structures while one or more other tables and/or support structures are being used for exposure.
The lithographic apparatus may also be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that liquid is located between the projection system and the substrate during exposure.
Referring to
The illuminator IL may comprise an adjuster AD for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may comprise various other components, such as an integrator IN and a condenser CO. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section.
The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF (e.g. an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (which is not explicitly depicted in
The depicted apparatus could be used in at least one of the following modes:
1. In step mode, the support structure MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure.
2. In scan mode, the support structure MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion.
3. In another mode, the support structure MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above.
Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed.
The extraction duct 5 is connected to an exit channel system 7, schematically illustrated in
Accordingly, peripheral thermal loads ΔQ are kept local to the peripheral part 9 and are limited in affecting a central part 12 of the substrate table 1. In addition to the insulating piece 11, other isolating pieces may be present at a different radial distance measured from a center of the substrate table 1, such as is shown in
Accordingly, according to an embodiment of the invention, a thermal sensor arrangement is provided in or near the peripheral duct 15 for calculating the amount of energy to be applied by the heater and/or cooler 18. The thermal sensor arrangement comprises desirably at least two temperature sensors distanced from each other at predetermined locations. In the illustrated embodiment, the predetermined locations are located near an input 22 and an output 23 of the duct 15. In an embodiment, a temperature control can be provided by connecting the duct 15 and a central duct 24 that meanders through a central part of the substrate table. In the shown embodiment the central duct 24 is in thermal connection with the supply heater and/or cooler 18 to supply temperature control to the central duct 24. A supply system and reception system are not shown but implicitly present.
In this embodiment of
With the edge temperature sensor 25 provided in or near the input of the duct 15, the edge heater 16 can be controlled by temperature signals from the edge temperature sensor 25 and the output temperature sensor 20. Desirably, the temperature differences in the edge are kept minimal, therefore, the control goal will preferably be in such a way that (Tliquid,out=Tliquid,edge) to compensate global edge loads.
Although
Furthermore, conventionally, a thermally stabilizing fluid is conditioned to a preset supply temperature equal to a set temperature of the substrate support 1, in particular to about 22° C. (=the optimal system temperature, based on desired projection system temperature). Accordingly, the temperature set point of the supply fluid is conventionally not based on expected heat load towards the fluid. As a result, the temperature of the return fluid is likely to be higher than the optimal system temperature. In addition, the average tool temperature and average component temperature may vary with different modes of operation of the lithographic system. Both effects may result in machine performance loss. According to an aspect of the invention, the fluid supply temperature is at a temperature lower than a set temperature, in such a manner that the average fluid temperature (supply vs. return) will be the set temperature, in particular, of about 22° C. In this way, the effect of the heat input from (a) fluid lines and/or (b) components may be reduced or minimized. According to an aspect, two ways of implementing this principle are foreseen: 1) a fixed fluid supply temperature having a set point temperature, based on, e.g., a maximum heat load towards (part of) the fluid system so that the average temperature of supply and return fluid will be closer to the set point of 22° C.; and/or 2) the fluid supply temperature is controlled actively. In this way, variations due to varying power consumption/heat load can be dealt with.
These aspects may be combined in the embodiment depicted in
Although the illustrated embodiments refer to a substrate support to be used to hold a substrate to be targeted with a patterned beam, the structure may be very well applied to a patterning device support structure or any other support that needs thermal stabilization.
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, flat-panel displays, 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), a metrology tool and/or an 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.
Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.
The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelength of or about 365, 355, 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 “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.
While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, the invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (e.g. semiconductor memory, magnetic or optical disk) having such a computer program stored therein.
One or more embodiments of the invention may be applied to any immersion lithography apparatus, in particular, but not exclusively, those types mentioned above and whether the immersion liquid is provided in the form of a bath or only on a localized surface area of the substrate. A liquid supply system as contemplated herein should be broadly construed. In certain embodiments, it may be a mechanism or combination of structures that provides a liquid to a space between the projection system and the substrate and/or substrate table. It may comprise a combination of one or more structures, one or more liquid inlets, one or more gas inlets, one or more gas outlets, and/or one or more liquid outlets that provide liquid to the space. In an embodiment, a surface of the space may be a portion of the substrate and/or substrate table, or a surface of the space may completely cover a surface of the substrate and/or substrate table, or the space may envelop the substrate and/or substrate table. The liquid supply system may optionally further include one or more elements to control the position, quantity, quality, shape, flow rate or any other features of the liquid.
The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.
