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
  • G03F7/70883—Environment aspects, e.g. pressure of beam-path gas, temperature of optical system
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B08—CLEANING
  • B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
  • B08B7/00—Cleaning by methods not provided for in a single other subclass or a single group in this subclass
  • B08B7/0035—Cleaning by methods not provided for in a single other subclass or a single group in this subclass by radiant energy, e.g. UV, laser, light beam or the like
  • B08B7/0057—Cleaning by methods not provided for in a single other subclass or a single group in this subclass by radiant energy, e.g. UV, laser, light beam or the like by ultraviolet radiation
• • 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
  • G03F7/70908—Hygiene, e.g. preventing apparatus pollution, mitigating effect of pollution or removing pollutants from apparatus
  • G03F7/70925—Cleaning, i.e. actively freeing apparatus from pollutants, e.g. using plasma cleaning

Definitions

• the present invention is directed generally to a process for mitigating degradation and contamination of surfaces caused by radiation induced breakdown of molecules and their subsequent reaction and/or deposition on these surfaces. More particularly, the process disclosed herein is directed to protection of the surfaces of components of a lithographic stepper, such as the mask and imaging optics, from the consequences of radiation induced molecular breakdown.
• Photolithography is a well-known technique for applying patterns to the surface of a workpiece, such as a circuit pattern to a semiconductor chip or wafer. This technique has the advantage of being able to faithfully reproduce small and intricate patterns.
• Traditional photolithography involves applying electromagnetic radiation to a mask having openings formed therein (transmission mask) such that the light or radiation that passes through the openings is applied to a region on the surface of the workpiece that is coated with a radiation-sensitive substance, e.g., a photoresist.
• the mask pattern is reproduced on the surface of the workpiece by removing the exposed or unexposed photoresist.
• the capabilities of conventional photolithographic techniques have been severely challenged by the need for circuitry of increasing density and higher resolution features.
• the demand for smaller feature sizes has inexorably driven the wavelength of radiation needed to produce the desired pattern to ever-shorter wavelengths.
• the wavelength of the applied radiation is made shorter the energy of the radiation becomes greater to the point where the radiation can cause the decomposition of molecules adsorbed on or proximate to a surface to produce reactive species that can attack, degrade, or otherwise contaminate the surface.
• Low energy (5-10 eV) secondary electrons are known to be very active in breaking chemical bonds by direct ionization of adsorbed molecules or by electron attachment, wherein a secondary electron binds to a molecule producing a reactive negative ion that then de-excites to a dissociated product.
• Any type of radiation photons, electrons, ions, and particles
• energies of about 4-5 eV are required.
• FIG. 1 A mechanism for the contamination of surfaces having gaseous species adsorbed thereon and exposed to an incident flux of radiation is illustrated schematically in Fig. 1.
• surface 1 10 has both hydrocarbon and water molecules adsorbed thereon.
• hydrocarbon can include any carbon containing species.
• Exposure to a radiation flux causes secondary electrons to be emitted from surface 110 that can dissociate the adsorbed hydrocarbon molecules to form reactive carbon fragments that can form a graphite layer on the surface.
• secondary electrons emitted from surface 110 in response to the radiation flux can dissociate adsorbed water molecules to form reactive oxygen species that can oxidize a surface to form an oxide film that can degrade the reflectivity of a mirror by absorption of radiation.
• reactive oxygen species can oxidize a surface to form an oxide film that can degrade the reflectivity of a mirror by absorption of radiation.
• a gas or a mixture of gases is introduced into the environment of a surface(s) to be protected.
• the choice of the gaseous species to be introduced is dependent upon the contamination as well as the ability of the gaseous species to bind to the surface to be protected. The latter criterion is invoked so that secondary electrons emitted from the surface in response to incident radiation can dissociate the adsorbed species.
• reactive species are formed that react with surface contaminants such as carbon or oxide films to form volatile products (e.g., CO, CO 2 ) which desorb from the surface.
• Figure 1 illustrates schematically a process resulting in surface contamination.
• FIG. 2 illustrates schematically an embodiment of the present invention.
• Figure 3A depicts the oxidation of a Si surface exposed to electron beam irradiation and water vapor.
• Figure 3B shows mitigation of oxidation caused by the addition of ethanol.
• Figure 4 shows the effect of water vapor and ethanol on a Si surface exposed to EUV radiation.
• Figure 5 shows the effect of molecular oxygen on carbon deposition.
• the present invention is directed to a process for mitigating or eliminating contamination and/or degradation of surfaces having common, adventitious atmospheric contaminants adsorbed thereon and exposed to energetic radiation.
• contaminants can include such species as hydrocarbons and water vapor that can be inherently present in the atmosphere of any system and generally can arise from such sources as materials of construction, vacuum pump oils and greases.
• Energetic radiation can be photons, electrons, or ions. This invention finds particular utility in those lithographic processes that employ highly energetic radiation such as extreme ultravoilet radiation and thus present a significant potential for contamination and, as a consequence, degradation of the performance of critical components.
• EUV extreme ultraviolet
• Fig. 2 shows a Si surface 210 of a Mo/Si multilayer mirror.
• water vapor will be present in any system, particularly an unbaked vacuum system.
• adventitious water vapor arises from outgassing of various system components and these water vapor molecules can be adsorbed onto any surface, such as illustrated by Fig. 2.
• Subjecting surface 210 to high energy radiation, such as by EUV radiation, can cause secondary electrons to be ejected from surface 210. As discussed above, these electrons can react with the adsorbed water molecules causing them to dissociate into reactive oxygen species that will, in turn, react with the Si surface.
• Prior to exposing surface 210 to incident radiation a small amount of a hydrocarbon gas that will also bind to surface 210 is admitted to the system. In the example illustrated by Fig.
• the hydrocarbon gas is ethanol (C 2 H5OH).
• C 2 H 5 OH molecules bound to surface 210 will also be dissociated by the secondary electrons ejected from that surface.
• Reactive carbon fragments from the dissociated C 2 H5OH can react with reactive oxygen species on surface 210 to form volatile products such as CO and CO 2 .
• reactive oxygen species that could oxidize the Si surface and degrade its reflectivity are eliminated.
• the process described above can function in the opposite manner. That is, when an environment is rich in carbon containing gases carbon contamination of surfaces can be produced by radiation exposure and the primary surface contaminant can be graphitic carbon.
• EXAMPLE 1 Initially, a Si-terminated multilayer mirror was exposed to an electron beam current density of about 5 ⁇ A/mm 2 at a beam energy of 2 keV in the presence of about 2xl0" 7 Torr of water vapor. The chemical composition of the surface of the mirror was monitored as a function of time. The Auger peak heights (which reflect the surface composition) of Si and SiO 2 are shown in Fig. 3 A. It can be seen that the composition of the surface changed rapidly from Si to Si ⁇ 2 as oxidation progressed with a corresponding degradation in reflectivity.
• hydrocarbon molecules are those that will bind to native surface constituents, for example, a polar, hydroxylated film such as can be found on the surfaces of glasses, metals, and silicon. Therefore, hydrocarbon molecules containing such polar functional groups as ketones, aldehydes, esters, alcohols, amines, thiols, and carboxylic acids that will bind well to hydroxylated surfaces are preferred.
• a Si-terminated Mo/Si mirror was exposed to 13.4 nm EUV radiation at a power level of about 7 mW/mm 2 .
• the mirror was exposed to four different exposure conditions and the secondary electron emission was plotted as a function of time in Fig. 4.
• the exposure conditions were: background pressure (about 4xl 0 -9 Torr); ethanol alone at a pressure of 4xl 0 -7 Torr; water vapor alone at a pressure of 2xl0 -7 Torr; and a mixture of ethanol (4xl 0 -7 Torr) and water vapor (2xl0 -7 Torr).
• Secondary electron emission has been shown to be a useful monitor of the surface processes because the onset of oxidation is signaled by a very rapid increase in secondary electron emission that is due to EUV absorption by oxygen with subsequent emission of secondary electrons. On the other hand, carbon deposition is signaled by a decrease in secondary electron emission due to the poor secondary electron emission characteristics of carbon.
• a 2kV electron beam at a current density of about 5 ⁇ A/mm 2 , is incident onto a Si-terminated Mo/Si multilayer mirror.
• the mirror is maintained at a vacuum of about 5xl0 - 10 Torr.
• an increase in atomic percentage of carbon on the mirror surface takes place.
• about 2xl 0 - 8 Torr of molecular oxygen is admitted to the vacuum chamber. At that time, the increase in carbon deposition stops and no measurable additional carbon deposition occurs
• the present invention provides an important advantage in this regard since, as exemplified above, the partial pressures of the various added gaseous molecular species need be only as high as necessary to affect surface chemistry.
• the use of gas pressures up to about lxl 0 -5 Torr would generally be adequate to provide a protective effect for most contamination problems while having negligible impact on lithographic throughput or uniformity.
• the transmission of EUV radiation at 13.4 nm through 2 meters of a water/ethanol gas mixture, with each component at a partial pressure of about lxlO -5 Torr would be reduced by only about 0.05%).
• the present invention provides a process for reducing or eliminating contamination and oxidation of surfaces caused by the interaction of high energy radiation on adventitious impurities.
• the process disclosed here can be used for reducing or eliminating oxide or carbon films on surfaces, such as the surface of silicon mirrors.
• the present invention provides special advantage in removing or reducing surface contamination in those components, such as masks and imaging optics, used in lithographic applications.

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• General Physics & Mathematics (AREA)
• Plasma & Fusion (AREA)
• Toxicology (AREA)
• Optics & Photonics (AREA)
• Exposure Of Semiconductors, Excluding Electron Or Ion Beam Exposure (AREA)
• Physical Or Chemical Processes And Apparatus (AREA)
• Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)
• Medicines That Contain Protein Lipid Enzymes And Other Medicines (AREA)
• Radiation-Therapy Devices (AREA)

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• 2000
  • 2000-12-21 AT AT00988384T patent/ATE460688T1/de not_active IP Right Cessation
  • 2000-12-21 JP JP2002553187A patent/JP4790970B2/ja not_active Expired - Lifetime
  • 2000-12-21 WO PCT/US2000/035394 patent/WO2002052347A1/en not_active Ceased
  • 2000-12-21 EP EP00988384A patent/EP1344110B1/en not_active Expired - Lifetime
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