Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/708—Construction of apparatus, e.g. environment aspects, hygiene aspects or materials
  • G03F7/70858—Environment aspects, e.g. pressure of beam-path gas, temperature
  • G03F7/70866—Environment aspects, e.g. pressure of beam-path gas, temperature of mask or workpiece
  • G03F7/70875—Temperature, e.g. temperature control of masks or workpieces via control of stage temperature
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/20—Exposure; Apparatus therefor

Definitions

• the present invention relates to a lithography system for projecting an image pattern on to a target surface such as a wafer.
• Such systems are generally known, e.g. in the form of a mask writer or in the form of a lithography application as in WO 2004038509.
• the target to be patterned is subjected to incidence of photons or charged particles such as ions and electrons. Due to the energy load of such particles or photons, inherent to the manner of extracting or emitting the same, the target is at least locally heated.
• Such heating in accordance with an insight developed as part of the invention, becomes problematic when expansion of the target under influence by it's processing exceeds a predefined value. In general it was observed that heating becomes problematic with the ever continuing, contemporary development towards high throughput.
• heat development and its removal from the target to be processed will be problematic in all sort of lithography. This may e.g. be due to ever decreasing size of nodes and/or to tighter overlay prescription, and is also problematic in contemporary emerging, vacuum types of lithography .
• Precise positioning of patterns is of significant importance given various stages in which a target is normally treated, possibly by different types of lithography apparatuses.
• a main solution in this respect is to remove heat from the wafer, thereby limiting expansion, at least controlling the magnitude of positioning error.
• Known practices of removing heat appear however to be insufficient for removing the heat that is developed in nowadays and future direct write and other litho systems, which may e.g. at maskless e-beam lithography be in the order of hundred thousands of charged particle beams per die, alternatively put per slit. Such is in particular insufficient in case throughput of the system is not to be compromised.
• a wafer clamp which is favourably used for transport of heat induced by a charged particle beam on a target.
• Clamping of a wafer on to a supporting structure is in this known device performed by applying "one or more" phase transitions to a clamping component that is applied between a wafer and a supporting structure, which phase transitions “facilitate various operations throughout the process” and “ensure that the wafer may be easily loaded and released from the structure.
• the clamping component is applied in a liquid or gaseous form, and brought into a solid state by active cooling of the support structure, so as to achieve a solid clamping of wafer to said structure.
• the present invention provides a solution to the problem of heat transfer as described earlier, i.e. within a limited amount of space, with relatively high capacity and swift transfer of heat, without unduly complicating the process of loading or locating a target to be cooled within the stage of a direct write lithography machine.
• the invention is characterised in that energy that is accumulated in a target by the projection of said image or image pattern is removed from said target in such a manner that expansion by local and overall heating of said target is limited to a relevant pre-defined value, wherein such heat removal is realised by the use of a phase transition in a heat absorbing material that is brought into thermal contact with said target.
• phase transition in itself may be effectively used for absorbing heat from a lithography target.
• temperature of the material in transition remains at least virtually constant, i.e. varies with a relatively much less extend than outside said phase transition, with sustained application of heat to said material.
• the combined material is mixed with the first material in a solution, most preferably in an emulsion.
• the combined material is a honeycomb-like structure, preferably entirely enclosing the heat absorbing material.
• the two embodiments are combined.
• Such heat conducting material may e.g. be a metal, e.g. in the form of metal particles in case of a solution.
• said phase transition should preferably take place at a temperature corresponding to the operational temperature of the lithography machine already improved in accordance with the invention, thereby also enhancing handling and functional aspects related to the overall operation of the machine.
• such phase transition is to take place at a temperature around room temperature.
• hexadecane is currently used as a heat absorbing material.
• hexadecane or any other liquid heat absorbing material because of the use of said phase transition, only a very limited amount of material is required for absorbing heat induced by the majority of types of lithography machines.
• the material may therefore in principle simply be adhered to the backside of e.g. a wafer, where a layer of very limited thickness may suffice for heat absorption without undue raise in temperature.
• the heat absorbing material is included in the litho machine in a porous structure, typically composed of the earlier mentioned heat conducting material.
• the structure is brought into thermal contact with the target, e.g. a wafer.
• the invention in principle however also relates to a target such as a wafer of which the backside is provided porous, e.g. by bore holes, e.g. realised using etching techniques. In this manner, contacting surface is strongly increased without the need of an intermediate conducting material.
• Figure 1 schematically illustrates a lithography target, here as a top view of a wafer, and the effect thereon caused by induced heating;
• Figure 2A and 2B represent a temperature characteristic of a phase transition of a material, which is favourably used in the invention
• Figure 3 represents a first embodiment of a relevant part of a lithography system, adapted for favourably removing heat from a lithography target.
• Figure 4 is alike figure 3, a schematic representation however of a second embodiment of the invention in which in this case fluid heat absorbing material is included in a framed structure that is brought into contact with the target.
• Figure 5 is a schematic top view representation of the structure of figure 4, with an exploded view of part thereof, showing the internal grid structure.
• Figure 6 is a schematic representation of a wafer and a supported by chuck as may be applied according to the invention.
• Figure 7 schematically illustrates a workout of the principle illustrated along figures 4 and 5;
• Figure 1 shows a target, here in the form of a wafer 1, which moves relative to e.g. a charged particle beam column of a litho apparatus, or other kind of beam source for lithography, according to path 4, here indicating the centre of a lens assembly or slit 2, passing over several fields 6 of the wafer.
• a target here in the form of a wafer 1
• path 4 here indicating the centre of a lens assembly or slit 2
• phase transition material - here also denoted as phase change material - that is brought into thermal contact with said target 1, e.g. as illustrated by any of the embodiments of figure 4.
• Figure 2 illustrates the principle of such phase transition, in figure 2A by the transition of a heat absorbing means from solid state Sol to liquid state Liq, and in figure 2B by the transition from liquid state Liq to gaseous state Gas:
• the temperature T of the absorbing means is set out (in degrees Kelvin) against the heat H (in Joules) induced by an impinging charged particle beam.
• H in Joules
• the temperature T does in principle not, and in practice only at a rather low rate, increase with increase of amount of heat H.
• the above described effect is according to the invention favorably used in the practice for transport and accumulation of heat from a target to the absorbing means.
• a superior coefficient of heat transport is desired between target and heat absorber.
• a material having preferably both a large coefficient of heat transport and a transition phase temperature near environmental temperature of the target in said lithography apparatus is applied. Most preferably is a phase transition temperature near room temperature.
• heat absorber features like non- toxiness and ability to withstand the vacuum in which it is to operate, and CMOS compatibility.
• the invention therefore proposes as a good and preferred material for application as a heat absorber, an emulsion comprising particles with a relatively high coefficient of heat transport such as metal or silicon.
• a material is relatively easily adhered to the bottom side of a target by adhesive force, and requires only a limited amount of space. In this respect a layer of several micrometers suffices.
• a preferred emulsion material is hexadecane.
• glycerol C 3 H 8 O 3 ; also well known as glycerin and glycerine, and less commonly as propane- 1,2,3-triol, 1,2,3-propanetriol, 1,2,3- trihydroxypropane, glyceritol, glycyl alcohol, citifluor AF 2; grocolene
• the invention addresses a finding that with a phase transition the heat transfer capacity of the heat absorbing material decreases to a minimum value. Such implies than only very thin layers of the phase change or heat absorbing material can be used. To overcome this problem the same heat absorbing material is still used, however in combination with a surface increasing measure.
• Figure 3 illustrates a first embodiment according to the invention, demonstrating a straight forward manner of putting the invented principle into practice.
• reference 1 is a cross section of a target in the form of a wafer, while 10 denotes an emulsion satisfying the needs defined in accordance with the invention.
• Figure 4 illustrates another embodiment, showing a porous carrier for said target and carrying the heat absorber in its pores. In this manner a large contacting area between heat absorber and target is created by means of said intermediate carrier.
• a porous carrier which may be either the target itself or a separate frame as in figure 4, heat by-passes heat absorbent that has fluidised in the upper zones thereof, thus guaranteeing an increased transfer of heat at any instant within the process of phase transition.
• the carrier has an improved thermal conductance relative to a fluidised part of the heat absorbent.
• a suitable heat conducting material such as metal or silicon, i.e.
• the square holes or bores may be achieved by etching, and are in the present example of a dimension of 50 by 50 ⁇ m or smaller, with wall thicknesses of 5 ⁇ m or smaller.
• Figure 5 provides sectional views of a possible hexadecane frame as illustrated by figure 4.
• the left side figure part is an overall view of e.g. a wafer like structure, while the right side figure part illustrates a section as could be applicable to the size of a die in a wafer.
• the goal of the frame is to increase the usable area of the PCM.
• Q ( k * A / 1 ) * dT, the required temperature difference dT to transport a given amount of heat Q over a distance 1, reduces with increasing surface A.
• the usable surface per area W*W is increased to h*4*W for the shown geometry.
• Corresponding calculations also apply to a preferred frame with at least predominantly rectangular bores as taken in cross section. Such is embodied with the sort side of such shape considerably smaller in width than the width of the walls shaping said rectangular structure, preferably with a ratio within the range of 5 to 15, preferably around 10, thus e.g. bores or openings of a size of 50 by 5 micrometer, without these examples limiting the principle of increasing surface area by means of relatively long stretched openings.
• the degree of possible filling said structure with heat absorbing means is thereby increased, and preferably set to a value within the range of 60% to 90% surface area, e.g. around 75%.
• Figure 6 provides a schematic representation of a wafer and a wafer chuck as may for example be applied in accordance with the invention.
• the wafer is placed on burls 13.
• burls 13 By applying burls 13, the chance that a particle will be present between the wafer 1 and a burl 13 is minimised.
• the wafer 1 is attracted on a very flat table made out of said burls.
• An electrostatic clamp 14 is applied in this respect, favourably meeting the vacuum condition of a stage.
• Other known or new type of clamps may in principle be applied as well however, an example of which is provided in the following.
• Typical values for applied attractive force are around 0.1 Bar or lower, depending on the applied manner of attraction.
• the dielectric properties of the material between wafer and clamp determine the achievable attractive force between wafer and clamp.
• the maximum allowable clamp voltage is limited by the breakthrough voltage and also depends on material and manufacturing process.
• other manners of clamping may also be applied, without diminishing the significance of the present invention.
• a fluid could be provided between the burled layer and the target, however strongly differing from the heat absorbing material, due to a desired function of improving heat conductance. In this respect the occurrence of a phase transition would for this material be highly undesired.
• the burls are preferably produced significantly smaller than conventional electrostatic clamping burls.
• the total area of the burls is made significantly larger than conventional, i.e. with a function in clamping alone, or at least than without such added function of conduction of heat.
• the total contacting surface between target and burl is within the range of 1 to 5% of the total target surface, preferably around 1%. The latter and the increased number of burls implies an increased though accepted risk of particles trapped in between burls and wafer, distorting the flatness of the latter.
• Figure 7 schematically illustrates one possible embodiment of the principle illustrated along figure 4 and 5, in which the heat conducting frame is constituted by a wafer having an upper side 15, which is etched to the effect that burls 15B are created, in casu approximately 1 micron high burls.
• the opposite side 15A of the wafer is etched to the effect that bores are created for holding the heat absorbing material.
• the bottom layer 16 represented in figure 7 represents a frame closing layer attached to the bottom of the first layer and is here embodied by a second wafer. In this manner the heat absorbing material is shielded from the vacuum in which it is as in this example, very often to function.
• the top layer 17 present on the frame represented in figure 7, is a thermally conducting, electrically insulating layer.
• Such layer is applied, e.g. by sputtering, onto the surface burls including surface.
• X micron Aluminium nitride (AIN) material is used, but such could in accordance with the invention also e.g. be Beryllium Oxide (BeO).
• FIG 7 illustrates a relatively advantageous manner of putting the principle illustrated along figure 4 into practice.
• the closing plate 16 serves to keep the phase change material in the etched frame, prevents out gassing in a vacuum environment, provides strength to the structure and serves as a flat reference plane.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Engineering & Computer Science (AREA)
• Atmospheric Sciences (AREA)
• Toxicology (AREA)
• Life Sciences & Earth Sciences (AREA)
• Environmental & Geological Engineering (AREA)
• Epidemiology (AREA)
• Public Health (AREA)
• Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)
• Container, Conveyance, Adherence, Positioning, Of Wafer (AREA)
• Exposure Of Semiconductors, Excluding Electron Or Ion Beam Exposure (AREA)

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• 2007
  • 2007-07-13 WO PCT/NL2007/000181 patent/WO2008013443A2/en not_active Ceased
  • 2007-07-13 JP JP2009521714A patent/JP5384339B2/ja active Active
  • 2007-07-13 KR KR1020097004269A patent/KR101486407B1/ko active Active
  • 2007-07-13 EP EP07793822.3A patent/EP2054771B1/en active Active
  • 2007-07-13 CN CN2007800285269A patent/CN101495922B/zh active Active
  • 2007-07-27 TW TW096127402A patent/TW200813656A/zh unknown
  • 2007-07-27 TW TW103133925A patent/TWI534560B/zh active

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