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
  • G03F1/00—Originals for photomechanical production of textured or patterned surfaces, e.g., masks, photo-masks, reticles; Mask blanks or pellicles therefor; Containers specially adapted therefor; Preparation thereof
  • G03F1/68—Preparation processes not covered by groups G03F1/20 - G03F1/50
  • G03F1/82—Auxiliary processes, e.g. cleaning or inspecting
  • G03F1/84—Inspecting
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/8806—Specially adapted optical and illumination features
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/8806—Specially adapted optical and illumination features
  • G01N2021/8835—Adjustable illumination, e.g. software adjustable screen
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
  • G01N21/956—Inspecting patterns on the surface of objects
  • G01N2021/95676—Masks, reticles, shadow masks
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
  • G01N21/956—Inspecting patterns on the surface of objects
• • 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
  • G03F1/00—Originals for photomechanical production of textured or patterned surfaces, e.g., masks, photo-masks, reticles; Mask blanks or pellicles therefor; Containers specially adapted therefor; Preparation thereof
  • G03F1/68—Preparation processes not covered by groups G03F1/20 - G03F1/50
  • G03F1/72—Repair or correction of mask defects

Definitions

• the invention relates to a method and an apparatus for characterizing a microlithography mask.
• Microlithography is used for production of microstructured components, such as integrated circuits or LCDs, for example.
• the microlithography process is conducted in what is called a projection illumination apparatus, which comprises an illumination device and a projection lens.
• a projection illumination apparatus which comprises an illumination device and a projection lens.
• the practice of recording and evaluating an aerial image of a section of the mask in a mask inspection apparatus wherein, for the purposes of recording the aerial image, the structures to be measured on the mask are illuminated by a magnifying illumination optics unit and the light coming from the mask is projected on a detector unit via an imaging optical unit and detected by said detector unit.
• the invention relates to a method of characterizing a microlithography mask, wherein the mask to be characterized is illuminated with light from a light source via an illumination optics unit, said light having a wavelength of less than 30 nm; wherein light that passes in a used beam path from the light source via the mask to a sensor unit is evaluated; wherein, at least intermittently, a portion of the light emitted by the light source is outcoupled from the used beam path by means of a mirror array having a multitude of independently adjustable mirror elements; and wherein, intermittently by means of the mirror array, all light is outcoupled from the used beam path for establishment of a defined illumination time of the sensor unit.
• the outcoupled light may especially be directed to a beam trap.
• This configuration takes account of the fact that, on the one hand, the light sources available for generation of EUV light, such as, in particular, a plasma light source for instance, do not enable switch-on and switch-off on the short timescale required in the mask inspection process, but, on the other hand, the sensor arrangement used in the mask inspection process (e.g. CCD camera) requires exactly defined illumination times (typically in the order of magnitude of 200 ms).
• the sensor arrangement used in the mask inspection process e.g. CCD camera
• the invention here advantageously makes use of the fact that, as a result of the pulsed operation, the period of time remaining between successive pulses (of the order of magnitude of typically about 0.2 ms) is available for the respectively required tilting movement of the mirror elements.
• the intensity of a light component outcoupled from the used beam path by the mirror array is detected with an intensity sensor.
• the invention takes account, inter alia, of the fact that, in the case of EUV light, outcoupling cannot be effected with a partly transparent mirror as is the case for UV light or for light in the visible wavelength range, since no such thing exists for EUV.
• the invention includes the concept of outcoupling a portion of the light emitted by the at least one light source and of detecting the intensity or energy of this outcoupled portion. According to the invention, this allows the ascertainment of energy fluctuations on the part of the (at least one) light source such that the images ultimately recorded by the sensor unit can be normalized in relation to the energy of the at least one light source.
• one advantageous consequence of the configuration according to the invention is that a distinction can be made in respect of brightness variations that occur in the images recorded by the sensor unit as to whether such brightness variations are caused by the mask currently being characterized (for example as a result of defects possibly present on this mask) or whether such brightness variations are caused by energy fluctuations of the light source used. In this way, it may be possible to avoid drawing incorrect conclusions about defects perceived to be present on the mask.
• the invention can also make use of the fact that only relative variations or fluctuations over time are of interest in respect of the intensity or energy emitted by the at least one light source; in other words, in particular, there is no need for a spatially resolved quantitative intensity measurement.
• the invention can make use of the fact that only a comparatively small portion of the light emitted by the at least one light source needs to be outcoupled for said ascertainment of relative variations of the energy or intensity over time, and so the predominant portion of light by far is still available for the actual mask characterization.
• the invention particularly takes account of the circumstances that already minor variations (of the order of significantly less than one percent) are important for the reliable identification of relevant defects in the mask on account of the high demands in terms of accuracy in the microlithography application.
• the detecting of the light component outcoupled from the used beam path by the mirror array with an intensity sensor is also advantageous irrespective of the above-described functionality as high-speed shutter.
• the invention therefore also relates to a method of characterization of a microlithography mask, wherein the mask to be characterized is illuminated with light from a light source via an illumination optics unit, said light having a wavelength of less than 30 nm; wherein light that passes in a used beam path from the light source via the mask to a sensor unit is evaluated; wherein, at least intermittently, a portion of the light emitted by the light source is outcoupled from the used beam path by means of a mirror array having a multitude of independently adjustable mirror elements; and wherein, at least intermittently, the intensity of a light component outcoupled from the used beam path by the mirror array is detected with an intensity sensor.
• greyscale adjustment is achieved by actuating at least some of the mirror elements in such a way that they outcouple light from the used beam path only for some of the period of illumination of the sensor unit.
• the array according to the invention composed of independently adjustable mirror elements, is utilized for achievement of greyscale values in that the respective illumination time or the illumination dose is adjusted individually via the individual mirror elements by virtue of the relevant mirror element being "switched off” or tilted in such a way that light incident on this mirror element no longer reaches the sensor unit after the individually definable duration (which is shorter than the overall illumination duration).
• This configuration takes account of the fact that, in the inventive operation of a mask inspection system with EUV light, the array according to the invention, composed of independently adjustable mirror elements, cannot be utilized as a blazed grating (for angle-dependent establishment of greyscale values via variation of diffraction efficiency) since, on account of the shorter wavelength by a number of orders of magnitude compared to the dimensions and separations of the mirror elements, it is ultimately necessary to proceed from a geometric optics unit.
• greyscale values are achieved in accordance with the invention in spite of this fact, namely in that the respective mirror elements, even after a portion of the respective illumination time (for example after a period of time of 50 ms and hence even after a quarter of the total illumination time of, for example, 200 ms), are tilted into the position suitable for outcoupling of the light from the used beam path.
• This aspect of establishing greyscale values is advantageous even irrespective of the above-described functionalities of the replacement of a high-speed shutter or of the outcoupling to give an intensity sensor.
• the invention thus also further relates to a method of characterizing a microlithography mask, wherein the mask to be characterized is illuminated with light from a light source via an illumination optics unit, said light having a wavelength of less than 30 nm; wherein light that passes in a used beam path from the light source via the mask to a sensor unit is evaluated; wherein, at least intermittently, a portion of the light emitted by the light source is outcoupled from the used beam path by means of a mirror array having a multitude of independently adjustable mirror elements; and wherein greyscale adjustment is achieved by actuating at least some of the mirror elements in such a way that they outcouple light from the used beam path only for some of the period of illumination of the sensor unit.
• the settings of the mirror elements are chosen such that a first group of mirror elements is in an illumination beam path leading from the light source to the mask, and a second group of mirror elements is in an imaging beam path leading from the mask to the sensor unit.
• the invention then advantageously makes use of the property of the array used, composed of a multitude of independently adjustable mirror elements, that suitable adjustment of the mirror elements allows the mirror array to contribute partly to the illumination beam path (leading from the light source to the mask) and partly to the imaging beam path (leading from the mask to the sensor arrangement).
• the settings of the mirror elements are chosen such that light hits the mask at an angle based on the mask surface of at least 85°, especially at an angle of 90° (i.e. at right angles to the mask surface).
• the light from the light source has a wavelength of less than 15 nm, especially within the range between 13 nm and 14 nm.
• the invention relates to an apparatus for characterizing a mask for microlithography, comprising a light source for generating light of a wavelength of less than 30 nm; an illumination optics unit for illuminating the mask to be characterized with light from the light source; a sensor unit; an evaluation unit for evaluating the light that passes in a used beam path from the light source via the mask to the sensor unit; a mirror array composed of a multitude of independently adjustable mirror elements via which at least a portion of the light can be outcoupled from the used beam path; and an actuation unit for actuating the mirror array; wherein, by means of this actuation for establishment of a defined illumination time of the sensor unit, it is possible to intermittently outcouple all light from the used beam path by means of the mirror array.
• the apparatus has a beam trap for receiving a light component outcoupled from the used beam path by the mirror array.
• the apparatus has an intensity sensor for detecting the intensity of a light component outcoupled from the used beam path by the mirror array.
• the invention relates to an apparatus for characterizing a mask for microlithography, comprising a light source for generating light of a wavelength of less than 30 nm; an illumination optics unit for illuminating the mask to be characterized with light from the light source; a sensor unit; an evaluation unit for evaluating the light that passes in a used beam path from the light source via the mask to the sensor unit; a mirror array composed of a multitude of independently adjustable mirror elements via which at least a portion of the light can be outcoupled from the used beam path; and an intensity sensor for detecting the intensity of a light component outcoupled from the used beam path by the mirror array.
• the apparatus is configured to conduct a method having the features described above.
• Figures 1 a-1 c schematic diagrams for elucidation of the possible construction and the manner of function of an apparatus of the invention for characterization of a mask in a first embodiment
• Figure 2 a schematic diagram for elucidation of the possible construction of an apparatus of the invention in a further embodiment
• Figure 3 a schematic diagram for elucidation of the possible construction of an apparatus of the invention in a further embodiment
• FIGS 4-5 schematic diagrams for elucidation of the possible manner of function of an apparatus of the invention
• Figure 6 a schematic diagram for elucidation of the possible construction of an apparatus of the invention in a further embodiment
• FIGS. 7a-7d schematic diagrams for elucidation of construction and possible mode of function of an apparatus of the invention in a further embodiment.
• Figure 8 a schematic diagram for elucidation of the general construction of an apparatus for characterization of a mask.
• a mask inspection system 800 comprises an illumination system 801 and a projection lens 805, wherein light from a light source (not shown in Fig. 1) enters the illumination system 801 and a pencil of illumination rays 802 is directed to a mask 803 arranged in the object plane of the projection lens 805, and wherein the illuminated region of the mask 803 is imaged by means of a pencil of observation rays 804 onto a sensor arrangement 806, e.g. a CCD camera, by means of the projection lens 805.
• a sensor arrangement 806 e.g. a CCD camera
• the illumination settings used in the production illumination system or lighting device thereof in conjunction with the mask 803, i.e. including partial coherence of the illumination light hitting the mask 803 that may be associated with the illumination setting, for which it is customary in turn to use corresponding shutters (i.e., for instance, in the case of a quadrupole setting used in the later lithography process, a quadrupole shutter with four cutouts adapted to the illumination poles) in the illumination system of the mask inspection system 800, by means of which it is possible to implement partial coherent illumination in the mask inspection system.
• the projection lens 805 of the mask inspection system 800 it is possible to simulate the limitation of the beam pathway, i.e. the NA, likewise through use of a suitable mask (typically with a corresponding circular or elliptical cutout).
• a mirror array composed of a multitude of independently adjustable mirror elements is used in order to intermittently outcouple light for implementation of different functionalities from the used beam path that leads from the light source through the mask to the sensor arrangement.
• the mirror elements of the mirror array each have a coating suitable for the working wavelength of the light source (for example about 13.5 nm), for example a molybdenum (Mo)-silicon (Si) reflection layer stack.
• said EUV light from the light source passes through a shutter 110 via a mirror 120 to such a mirror array 130, whence the EUV light, according to the setting of the respective mirror elements, can be directed through the mask 140 to the sensor arrangement (likewise not shown in Fig. 1a) or else outcoupled from the used beam path.
• the light component outcoupled from said used beam path is directed here into a beam trap identified by “150”.
• a first functionality implementable with the construction of Fig. 1a it is then possible, by means of suitable actuation of the mirror elements of the mirror array 130, to establish a defined illumination time of the sensor unit, namely by outcoupling all the light from the used beam path at the respectively suitable junctures via the mirror array 130.
• said actuation of the mirror elements of the mirror array 130 makes it unnecessary to use a high-speed shutter.
• Figs 1 b and 1c show schematic diagrams for illustration of the above-described functionality of the mirror array 130.
• Fig. 1c before commencement and after the end of the respectively desired exposure time, all mirror elements of the mirror array 130 are tilted with respect to the rest position and reflect incident illuminating light from the light source in the direction of the beam trap 150.
• all mirror elements of the mirror array 130 are in rest position and reflect the incident illuminating light from the light source in the direction of the photomask. If combination of this functionality with the functionality for forming a particular illumination setting is desired, from the start to the end of the respectively desired illumination time, the mirror elements in rest position are solely those at positions where the desired illumination setting is bright. All other mirror elements, before, during and after the desired exposure time, are tilted such that they direct the light in the direction of the beam trap 150.
• Fig. 2 shows a schematic diagram for elucidation of a further embodiment of an apparatus of the invention for characterizing a mask, wherein components that are analogous or substantially functionally identical in comparison with Fig. 1a are designated by reference numerals increased by "100".
• the apparatus additionally has an intensity sensor 260 via which the intensity of a light component outcoupled from the mirror array 230 can be detected.
• the invention enables ascertainment of energy fluctuations on the part of the light source such that the images recorded by the sensor unit can be normalized to the energy of the light source.
• a distinction can be made as to whether such fluctuations in brightness in the images recorded by the sensor unit are caused by the mask 240 currently being characterized (for example by any defects present in this mask 240) or by fluctuations in energy of the light source, such that incorrect conclusions as to defects perceived to be present on the mask may be avoided.
• Fig. 4 shows an illustrative implementation, wherein, of the mirror elements of a mirror arrangement 400, the mirror elements shown in hatched form (of which, by way of example, two are identified as “402”) direct incident light to the intensity sensor, whereas the light from the other mirror elements (of which, by way of example, one is identified as “401”) hits the mask.
• the mirror elements shown in hatched form of which, by way of example, two are identified as “402”
• the light from the other mirror elements of which, by way of example, one is identified as “401”
• Fig. 5 shows a schematic diagram analogous to Fig. 4 for illustration of a further possible scenario, wherein mirror elements not shown in hatched or dotted form (of which, by way of example, one is identified as “501”) direct the respectively incident light in the direction of the mask, with the mirror elements shown in dotted form (of which, by way of example, one is identified as “502”) directing the respectively incident light in the direction of the intensity sensor for the purpose of the above-described normalization, and with the mirror elements shown in hatched form (of which, by way of example, one is identified as “503”) directing incident light in the direction of the beam trap.
• a desired illumination setting a dipole illumination in the specific working example
• Fig. 3 shows a schematic diagram for elucidation of a further embodiment of an apparatus of the invention for characterizing a mask, wherein components that are analogous or substantially functionally identical in comparison with Fig. 2 are designated by reference numerals increased by "100".
• the embodiment according to Fig. 3 differs from that from Fig. 2 in particular in the different positioning of the mirror array 330 based on the optical beam path.
• the mirror array 330 based on the optical path, is arranged upstream of the mirror 320 and upstream of the shutter 310, for the purpose of which a further mirror 325 is provided after the mirror 320 in the continuation of the beam path.
• 3 is advantageous firstly in that a restriction of the available light path between mask 340 and imaging optics or sensor unit by the mirror array 330 is avoided, and there is also an increase in the construction space available for cooling of the mirror array 330 (for example via cooling fluid connections) and for electronic and actuation components as a result of the positioning of the mirror array 330 at a greater distance from the mask 340.
• the invention includes, for implementation of greyscale values, the principle of establishing different greyscale values over the duration of the respective tilting of the mirror elements (or the ratio between this duration and the overall illumination time).
• some of the mirror elements even after a portion of the respective illumination time (for example after a period of time of 50 ms and hence a quarter of the total illumination time of, for example, 200 ms), are tilted into the position suitable for outcoupling of the light from the used beam path.
• Figs 6a-7d show schematic diagrams for elucidation of further embodiments of an apparatus according to the invention for characterization of a mask.
• the further functionality of a beam divider for separation of the imaging beam path from the illumination beam path is especially implemented for enabling a mask inspection with perpendicular incidence of light.
• the invention includes the further principle of ensuring, by suitable adjustment of the mirror elements of the mirror array, that the mirror array can ultimately contribute to the illumination beam path and to the imaging beam path.
• Figs. 6a-6b firstly show schematic diagrams for illustration of the underlying principle, wherein according to Fig. 6a, in principle, a beam divider 601 for vertical illumination of a mask 602 and enabling of imaging to give a sensor unit 603 is required.
• Fig. 6b illustrates the implementation in principle of an inventive mirror array 630, with “611” indicating the illuminating light incident on the mirror array 630 and “614” the light directed by the mirror array 630 to the imaging optics.
• “615” indicates a light component outcoupled analogously to the above- described embodiments in the direction of an additional intensity sensor.
• Fig. 7a shows a schematic diagram of the possible construction of a corresponding apparatus according to the invention, in which all of the above- described functionalities (i.e. the implementation of a high-speed shutter, the outcoupling of a light component in the direction of an intensity sensor for normalization or calibration purposes, the establishment of greyscale values and the separation of illumination beam path and imaging beam path for the purpose of characterization of the mask with perpendicular incidence of light) are implemented.
• Components analogous or substantially functionally identical in comparison with Fig. 3 are denoted here by reference numerals increased by “400”.
• Fig. 7a additionally shows the position of an (EUV) light source 705 and of a sensor unit 770 (configured, for example, as a CCD camera).
• EUV EUV
• “715”, “735”, “745” and “755” each indicate mirrors that are present for implementation of the beam path and are curved in the working example.
• “780” indicates a beam trap for receiving light which is reflected by mirror elements of the mirror array 730 in the respective rest position.
• “790” indicates a light trap for trapping imaging light which is reflected by mirror elements and is used for outcoupling of a light component in the direction of the intensity sensor 760.
• Fig. 7b shows, with reference to an enlarged detail of the mirror array 730, a scenario that occurs in operation of the apparatus when light in each case hits the mirror array 730 for the first time.
• Fig. 7b for example, half of the mirror elements are in rest position, such that they reflect the incident illuminating light in the direction of the beam trap.
• the other mirror elements of the mirror array 730 by contrast, are deflected in such a way that they reflect the incident illuminating light in the direction of the mask 740.
• Fig. 7c shows a further scenario that occurs in the operation of the apparatus when light hits the mirror array 730 for a second time.
• their mirror elements in the rest position reflect the light coming from the mask 740 in the direction of the sensor unit 770 or CCD camera, whereas the other, deflected mirror elements reflect the light incident on the mask back to the light source 705.
• Fig. 7d shows a further scenario in the operation of the apparatus, wherein two mirror elements of the mirror array 730 are tilted here such that they direct incident illuminating light in the direction of the intensity sensor 760.

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• General Health & Medical Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Health & Medical Sciences (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)
• Preparing Plates And Mask In Photomechanical Process (AREA)
• Electron Beam Exposure (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Related Child Applications (1)

Publications (1)

Family

ID=81941168

Family Applications (1)

Country Status (5)

Cited By (1)

Families Citing this family (1)

Citations (9)

Family Cites Families (13)

• 2021
  • 2021-05-27 DE DE102021113780.2A patent/DE102021113780B9/de active Active
• 2022
  • 2022-05-10 JP JP2023573235A patent/JP2024518810A/ja active Pending
  • 2022-05-10 WO PCT/EP2022/062684 patent/WO2022248216A1/en not_active Ceased
  • 2022-05-26 TW TW111119671A patent/TWI815479B/zh active
• 2023
  • 2023-10-30 US US18/385,114 patent/US20240061328A1/en active Pending

Patent Citations (9)

Also Published As

Similar Documents

Legal Events