Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J4/00—Measuring polarisation of light
  • G01J4/04—Polarimeters using electric detection means
• • 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
  • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
  • G03F7/7055—Exposure light control in all parts of the microlithographic apparatus, e.g. pulse length control or light interruption
  • G03F7/70566—Polarisation control
• • 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
  • G03F7/2002—Exposure; Apparatus therefor with visible light or UV light, through an original having an opaque pattern on a transparent support, e.g. film printing, projection printing; by reflection of visible or UV light from an original such as a printed image
  • G03F7/2004—Exposure; Apparatus therefor with visible light or UV light, through an original having an opaque pattern on a transparent support, e.g. film printing, projection printing; by reflection of visible or UV light from an original such as a printed image characterised by the use of a particular light source, e.g. fluorescent lamps or deep UV light
  • G03F7/2006—Exposure; Apparatus therefor with visible light or UV light, through an original having an opaque pattern on a transparent support, e.g. film printing, projection printing; by reflection of visible or UV light from an original such as a printed image characterised by the use of a particular light source, e.g. fluorescent lamps or deep UV light using coherent light; using polarised light
• • 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
  • G03F7/70058—Mask illumination systems
  • G03F7/70091—Illumination settings, i.e. intensity distribution in the pupil plane or angular distribution in the field plane; On-axis or off-axis settings, e.g. annular, dipole or quadrupole settings; Partial coherence control, i.e. sigma or numerical aperture [NA]
• • 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
  • G03F7/70058—Mask illumination systems
  • G03F7/70191—Optical correction elements, filters or phase plates for controlling intensity, wavelength, polarisation, phase or the like
• • 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
  • G03F7/70216—Mask projection systems
  • G03F7/70308—Optical correction elements, filters or phase plates for manipulating imaging light, e.g. intensity, wavelength, polarisation, phase or image shift
• • 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
  • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
  • G03F7/70591—Testing optical components
• • 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
  • G03F7/70691—Handling of masks or workpieces
  • G03F7/70716—Stages

Definitions

• a Passive Reticle Tool A Lithographic Apparatus And A Method Of Patterning A Device In A Lithography Tool
• the present invention relates to a lithographic apparatus, a method for determining a polarization property, a projection lens polarization sensor, a lithographic projection system, a method for determining a polarization state, an active reticle tool, a method of patterning a device, a passive reticle tool, a polarization analyzer an a polarization sensor.
• 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).
• a patterning device which is alternatively referred to as a mask or a reticle, may be used to generate a pattern of radiation corresponding to 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.
• resist radiation-sensitive material
• a single substrate will contain a network of adjacent target portions that are successively patterned.
• 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
• a known wafer scanner (EP 10371 17), hereby incorporated by reference in its entirety, comprises an illuminator and a projection lens. In operation a reticle with a circuit pattern in its cross section is positioned between illuminator and projection lens. A wafer is positioned such that an image of the circuit pattern on the reticle is formed on the surface of the wafer by radiation that passes through the illuminator, the reticle and the projection lens respectively.
• the imaging properties of the projection lens differ for different polarization status of the light.
• the imaging performance of wafer scanners with a projection lens operated with high numerical apertures (NA) depend significantly on the polarization state of the light coming out of an illuminator (in combination with the polarization dependent imaging properties of the projection lens).
• NA numerical apertures
• One effect is that where an image (formed at the wafer) of a circuit pattern on a reticle can be in focus at a distance zl between projection lens and wafer for a first polarization state, the image is in focus at a distance z2 between projection lens and wafer for a second polarization state.
• the state of polarization of the radiation impinging on the patterning device such as a reticle. It can also be desirable to know the effect on the state of polarization caused by the projection system (e.g., projection lens).
• the projection system e.g., projection lens.
• Existing radiation sensors built into lithographic apparatus are typically polarization insensitive.
• the state of polarization of the illumination radiation at the level of the patterning device cannot be easily or cost-effectively measured at the level of the substrate without knowing the effect of the projection system on the polarization.
• the polarization of the radiation when impinging on the wafer is for a part determined by the polarization of the radiation after passing the illuminator.
• a polarization analyzer In order to perform polarization measurements of the radiation at the illuminator, a polarization analyzer must be introduced between the illuminator and the projection lens.
• the polarization analyzer When field resolved polarization measurements are needed, the polarization analyzer, which is needed for every polarization measurement, must comprise a polarizing element and a motor to move that polarizing element to the field positions to be analyzed. Alternatively, it must comprise a number of polarizing elements at the different field positions to be analyzed and an equal amount of shutters to select one polarizing element. By opening the shutter at a desired field position and closing the shutters at the other positions, the polarization can be measured for that position. A motor or a combination of several polarizing elements and several shutters necessarily comprise a lot of space between the illuminator and the projection lens.
• the space between the illuminator and the projection lens is rather small and is occupied by the reticle stage compartment.
• This reticle stage compartment is the area in which the reticle stage moves. Other components may not intrude that area because of collision risks between those other components and the reticle stage.
• the wafer stage consumes the space needed by the polarization analyzer.
• the radiation received from an illuminator has a predefined and known polarization state.
• Embodiments include methods and arrangements using a polarization sensor to adjust an illuminator to improve polarization quality
• the polarization sensor globally consists of two parts: some optical elements that treat the polarization of the illuminator light (retarder, polarizer), and a detector that measures the intensity of the treated light. From the intensity measurements, the Stokes vector can be derived consisting of four parameters So to S 3 A field point is a position in a cross section perpendicular to the optical axis of the beam of radiation passing through the illuminator.
• Light at each field point can be measured using a field stop at that point through which a narrow beam of light travels.
• the light emerging from the field stop is detected by a detector, for example, a 2-d detector.
• the intensity detected by a 2-d detector comprises an array of sub-intensity measurements each collected at an individual x-y position, where the x,y position corresponds to a pupil coordinate in the illuminator. Three or more intensity measurements per field point are sufficient to define the polarization state of the light at that field point. From the three or more intensity measurements collected at each x-y point on the detector, a polarization pupil map can be constructed, which comprises a Stokes vector at each measured pupil position in the illuminator from which light travels through the field stop.
• Measured information on the polarization at a field point can be used to fine-tune polarization setting of the illuminator.
• the polarization state can be measured at different times to monitor the illuminator output over time.
• measurements can be taken at a series of field points and these measurements used to map the polarization state of radiation as a function of field point position.
• the contribution of the projection lens concerning polarization can be measured using additional optics.
• the polarization state of the light at wafer level can be monitored over time as well, taking account of for example drift effects of illuminator and/or lens.
• both illuminator and projection lens polarization sensors may include optical elements that treat and analyze a polarization state of light, as well as detectors to measure intensity of light.
• optical elements that treat and analyze a polarization state of light, as well as detectors to measure intensity of light.
• detectors to measure intensity of light.
• a lithographic apparatus comprising: an illumination system configured to condition a radiation beam; a support constructed to support a patterning device, the patterning device capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; a projection system configured to project the patterned radiation beam onto a target portion of the substrate; a detector configured to measure an intensity of the radiation after it has passed through the projection system; an adjustable polarization changing element; and a polarization analyzer, wherein the polarization changing element and the polarization analyzer are arranged in order in a path of the radiation beam at a level at which the patterning device would be supported by the support.
• a lithographic apparatus comprising: an illumination system configured to condition a radiation beam; a support constructed to support a patterning device, the patterning device capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; a projection system configured to project the patterned radiation beam onto a target portion of the substrate; and an interferometric sensor configured to measure a wavefront of the radiation beam at a level of the substrate, the interferometric sensor having a detector and operating in conjunction with a source module at a level of the patterning device to condition the radiation to overfill the pupil of the projection system; and an adjustable polarizer configured to polarize the radiation prior to the projection system.
• a method for determining a polarization property of a lithographic apparatus comprising: using a detector to take intensity measurements for a plurality of different settings of a polarization changing element of the lithographic apparatus; and determining, from the intensity measurements, information on a state of polarization of the radiation before it encounters the polarization changing element.
• a method for determining a polarization property of a lithographic apparatus comprising: using an interferometric sensor of the lithographic apparatus to measure respective wavefronts of the radiation beam at a substrate level of the apparatus for at least two different settings of an adjustable polarizer that is positioned in the lithographic apparatus prior to a projection system thereof; and determining, from the wavefront measurements, information on polarization affecting properties of the projection system.
• a projection lens polarization sensor configured to measure a polarization contribution arising from a projection lens of a lithographic apparatus, comprising: a pinhole provided in a reticle arranged to reside in a reticle stage of a lithographic apparatus, the pinhole configured to receive radiation from an illuminator, the radiation having a first polarization state and configured to transmit a first beam of radiation through a projection lens; a first optical element arranged to be located at a wafer level of the lithographic apparatus and configured to reflect the first beam of radiation to produce a second beam of radiation; a second optical element configured to direct the second beam of radiation to a further component; a polarizer arranged to polarize radiation received from the second optical element; and a detector arranged to receive polarized radiation.
• a lithographic projection system comprising an illuminator configured to provide illuminator radiation to a reticle level, the illuminator radiation having a first polarization state; a projection lens configured to project radiation having a second polarization state to wafer level; and a projection lens sensor, the projection lens sensor comprising: a pinhole provided in a reticle of a lithographic apparatus, the pinhole configured to receive from an illuminator radiation having a first polarization state and transmit a first beam radiation through a projection lens; a first optical element located at wafer level and configured to reflect the first beam of radiation to produce a second beam of radiation; a second optical element configured to direct the second beam of radiation to a further component; a polarizer arranged to polarize radiation received from the second optical element; and a detector arranged to receive polarized radiation, wherein the projection lens sensor is configured to measure a polarization contribution arising from the projection lens.
• a method of measuring a polarization state of radiation passing through a projection lens comprising determining an input polarization state of a first beam of radiation; directing the first beam of radiation in a first direction through the projection lens; reflecting, at a wafer level, the first beam of radiation as a second beam of radiation in a second direction substantially opposite to the first direction; reflecting the second beam of radiation as a third beam of radiation through a polarizer at a reticle level; and measuring an intensity of the third beam of radiation at a detector.
• an active reticle tool having a carrier configured to couple to a reticle stage of a lithographic apparatus, comprising: a pinhole configured to admit a beam of radiation received from an illuminator at a first field point, the beam having a first polarization state; a retarder rotatably coupled to the carrier and configured to retard the first polarization state of the beam of radiation having the first polarization state; and a polarizer configured to receive the retarded polarized beam and direct radiation of a predetermined polarization state toward a detector, wherein the detector is configured to perform a plurality of intensity measurements of the radiation having the predetermined polarization state.
• a lithographic apparatus comprising an illuminator configured to supply radiation towards a reticle stage; an active reticle toolhaving: a pinhole configured to admit a beam of radiation received from the illuminator at a first field point, the beam having a first polarization state; a retarder rotatably coupled to the carrier and configured to retard the first polarization state of the beam of radiation having the first polarization state; and comprising a polarizer configured to receive the retarded polarized beam and direct radiation of a predetermined polarization state toward a detector, wherein the detector is configured to perform a plurality of intensity measurements of the radiation having the predetermined polarization state.
• a method of patterning a device in a lithography tool comprising receiving in a reticle stage radiation corresponding to a first field point in an illuminator field, is characterized by applying a plurality of polarization retardation conditions to the radiation corresponding to the first field point; directing a plurality of radiation beams derived from the plurality of polarization retardation conditions toward a polarizing element configured to forward radiation having a predetermined polarization; measuring a radiation intensity of each of the plurality of radiation beams forwarded from the polarizing element; determining a polarization condition of radiation located at the first field point in the illuminator field; and adjusting an illuminator based on the determined polarization condition.
• a passive reticle tool comprising a carrier configured to reside in a reticle stage of a lithographic apparatus; and an array of polarization sensor modules associated with the carrier, wherein the array of polarization sensor modules is configured to receive illuminator radiation from an illuminator at a plurality of field points, and wherein the array of polarization sensor modules is configured to output radiation to a detector that is configured to perform a set of intensity measurements of polarized light derived from the illuminator radiation, the set of intensity measurements corresponding to a plurality of retardation conditions applied to the illumination radiation by the array of polarization sensor modules.
• a lithographic apparatus comprising an illuminator configured to supply radiation towards a reticle stage; and a passive reticle tool having a carrier disposed at a reticle stage of a lithographic apparatus; and an array of polarization sensor modules associated with the carrier, wherein the array of polarization sensor modules is configured to receive illumination radiation from an illuminator at a plurality of field points, and wherein the array of polarization sensor modules is configured to output radiation to a detector that is configured to perform a set of intensity measurements of polarized light derived from the illuminator radiation, the set of intensity measurements corresponding to a plurality of retardation conditions applied to the illuminator radiation.
• a method of patterning a device in a lithography tool comprising receiving in a reticle stage radiation corresponding to a first field point in an illuminator field, providing an array of sensors, the array of sensors configured to provide a plurality of polarization retardation conditions to received radiation; scanning the array of sensors through the first field point to produce a plurality of radiation beams corresponding to the plurality of polarization retardation conditions; directing the plurality of radiation beams toward a polarizing element configured to forward radiation having a predetermined polarization; measuring a radiation intensity of each of the plurality of radiation beams forwarded from the polarizing element; determining a polarization condition of radiation located at the first field point in the illuminator field; and adjusting an illuminator based on the determined polarization condition.
• a polarization analyzer for analyzing the polarization of a field in a beam of radiation comprising a base member having a field stop arranged to be transmissive in a first region, and the base member having a polarizing element arranged to polarize the beam of radiation transmitted through the first region of the field stop; characterized in that the base member is arranged to be moved by a first stage of a lithographic apparatus to a position in which the first region of the field stop matches the field to be analyzed.
• the polarization analyzer comprises a base member arranged to be positioned by a reticle stage (or substrate stage) of a lithographic apparatus.
• the base member itself has a field stop and a polarizing element.
• the field stop transmits radiation in a first. Because of the field stop, the analysis of the polarization state will mainly concern information about radiation transmitted by that first region.
• the polarizing element polarizes the radiation that is transmitted by the field stop so that polarized radiation is available for analyses.
• a reticle stage in a lithographic apparatus positions reticles at a desired position relative to a projection lens and illumination unit of the lithographic apparatus so that a pattern on the reticle can be imaged by the projection lens onto a substrate.
• the reticle stage brings the field stop to the desired position, being a position in the beam of radiation for which the polarisation radiation needs to be analysed.
• the substrate stage brings substrates to the required positions during production.
• the polarization analyser can be brought into the reticle stage compartment without collision risks between the polarization analyzer and the reticle stage or substrate stage.
• the polarization analyser by moving the polarization analyser with the first stage, no additional motor nor a combination of several polarizing elements and several shutters needs to be placed in an area also needed by the first stage.
• a polarization sensor for a lithographic apparatus comprising the polarization analyzer, the polarization sensor being characterized by a detector arranged to measure intensity of radiation in a measurement plane after passing the field stop and arranged to be positioned by a second stage of a lithographic apparatus in a predetermined position in the beam of radiation. [0040] By moving the detector with the second stage, no additional motors nor a combination of several polarizing elements and several shutters needs to be placed in an area also needed by the second stage.
• Figure 1 illustrates polarized light from the illuminator entering a polarization sensor module under angles corresponding to the numerical aperture (NA);
• Figure 2 illustrates a camera positioned at wafer level in a polarization sensor system, according to a configuration of the invention
• Figure 3 is a chart that discloses the relation between features associated with a polarization sensor according to several embodiments of the present invention
• FIG. 4 is a drawing of an active reticle tool, according to an embodiment of the invention.
• Figure 5(a) depicts a portion of a polarization sensor according to one configuration of the invention
• Figure 5(b) illustrates a spring loaded retarder arranged according to a further configuration of the present invention
• Figure 6 depicts a portion of another polarization sensor according to another configuration of the invention
• Figure 7 depicts a portion of another polarization sensor according to another configuration of the invention
• Figure 8(a) depicts a portion of another polarization sensor according to another configuration of the invention.
• Figure 8(b) illustrates a passive reticle system arranged according to one configuration of the present invention
• Figure 8(c) illustrates details of a polarization sensor module
• Figures 9a-c depict schematic diagrams of three different polarization sensors according to three respective embodiments of the invention.
• Figure 9(d) illustrates details of a multipass system having a beam splitting polarizer provided below a pinhole at a reticle;
• Figure 10 depicts interaction of an unpolarized light wave with a surface
• Figure 11 depicts a lithographic apparatus according to an embodiment of the invention.
• Figure 12 shows schematically the lithographic apparatus according to another embodiment of the invention.
• Figure 13 shows schematically the lithographic apparatus according to a modification of the embodiment illustrated in Figure 12;
• Figure 14 shows schematically the lithographic apparatus according to a further embodiment of the invention.
• Figure 15 schematically illustrates an arrangement for collimating the radiation in the region of the polarization-active components.
• the polarization state be well defined and known during wafer exposure, so that the image quality at wafer level can be improved, resulting in small line widths, especially with projection lenses with high NA values.
• polarization measurements have to be performed in the wafer scanner.
• the sensor can be positioned at reticle level. If, in addition, the polarization behavior of the projection lens needs to be monitored or quantified, additional optics could be implemented at wafer level.
• the polarization sensor can be viewed as having two parts.
• the first part comprises an optical element that treats the polarization of the illuminator light (for instance a retarder or a polarizing beam splitter) and is here called the polarization sensor module.
• the second part comprises a detector.
• the detector is used to measure the intensity of the treated light.
• the polarization sensor module can comprise a group of parts that are physically housed together.
• the detector can be located at a relatively large distance from the polarization sensor module. However, in some configurations of the invention, the detector can be housed or located in close proximity to components comprising the polarization sensor module.
• a number of field points are defined over the pupil.
• a minimum of three different configuration of the polarization sensor module are used to measure the polarization.
• Three different measurements can define the polarization state if one is not concerned with an unpolarized state. Taking into account an unpolarized state, measurements taken at four different configurations of the polarization sensor module are needed.
• each configuration has a different retardation property and belongs to a specific input polarization state.
• the 12 detector measures different intensities for all configurations used to measure each field point.
• the original polarization state of the light at that particular field point can be found, using calculations based on the Stokes vectors. This can be performed for all field points, resulting in a polarization map of the pupil.
• the reason for using Stokes instead of Jones is that the Stokes vectors include unpolarized light, and the Jones vectors do not.
• the Stokes parameters can be derived from the measured intensities of the polarization spots, at a certain combination between the input illumination polarization mode and the optical configuration of the polarization sensor module.
• the Stokes vector consists of four parameters So to S 3 , see equation 1.
• SOP means State Of Polarization.
• the Stokes parameters may be calculated by measuring intensities transmitted at combinations of for example horizontal, vertical, 45° and left- and right-circular polarizers. To resolve all 4 components of the Stokes vector, four measurements can be used per field point.
• polarization states are often specified in terms of the polarization ellipse, specifically its orientation and elongation.
• a common parameterization uses the azimuth (or "rotation") angle a which is the angle between the major semi-axis of the ellipse and the x-axis, and the ellipticity angle ⁇ where tan( ⁇ ) is the ratio of the two semi-axes.
• An ellipticity of tan( ⁇ ) +/- 1 corresponds to fully circular polarization.
• the relation between this representation and the Stokes parameters is equation 3.
• Equation 5 For example, for a system consisting of a rotating retarder and a polarizer, after multiplication of the individual Mueller matrices the output Stokes vector can be computed using equation 5.
• M po i and M ret are the Mueller matrices of respectively the polarizer and retarder.
• R(a) is a rotation matrix which is a function of rotation angle ⁇ , and represents the rotation of the retarder.
• At least three measurements are used to solve the 4 parameters of the unknown S 1n vector.
• four Stokes parameters there is some redundancy between them, so that three measurements can suffice to determine them at least normalized with respect to the overall intensity of the radiation.
• four measurements are used to solve the four parameters of the unknown Sm vector.
• the measurements can still be used to characterize the polarization state of the illuminator or the projection lens. For instance, if one measurement is done, i.e. a measurement for a fixed polarization state, and that measurement is repeated over time, for instance between two batches of wafers in a
• changes to the polarization state of the wafer scanner can be detected.
• this change passes a certain threshold, this can trigger a calibration or maintenance of the wafer scanner.
• Polarized light from the illuminator enters the polarization sensor module under angles corresponding to the numerical aperture (NA).
• NA numerical aperture
• the polarized light passes respectively through a first collimating lens, a mirror and a positive lens, together forming beam shaping and collimating optics.
• the collimating lens is arranged to give parallel beams onto the mirror.
• the mirror is arranged to reflect the light in a desired direction.
• the desired direction is perpendicular to the optical axis of the projection system. With a perpendicular direction and parallel beams the polarization sensor module has a relatively low height (values along the optical axis of the projection system along with the sensor extends mechanically).
• the light passes through a positive lens, a field stop and a lens to collimate the light again.
• the field stop is used to select a particular field point.
• the light After passing the beam shaping and collimating optics, the light enters a polarization state analyzer. To change the polarization state of the incoming light in a defined way, a set of optics is used that will influence the retardation of the light, i.e. Tm and Te waves are shifted with respect to each other resulting in a netto phase difference. Then a polarizer selects one polarization. In the second part of the polarization sensor the intensity of the desired polarization mode is detected with a camera. [0073] Other positions of the field stop are possible as well as will be obvious to the skilled person.
• Figure 3 is a chart that discloses the relation between features associated with polarization sensors arranged according to several embodiments of the present invention.
• polarization sensor modules configured on the one hand to quantify the polarization of light emerging from the illuminator (A. illuminator polarization sensor) and polarization sensors configured on the other hand to monitor/quantify the polarization of light traveling through the projection lens (B. projection lens polarization sensor).
• a reticle tool comprises a carrier and the polarization sensor module.
• the polarization sensor may comprise additional parts at wafer level (see figure 2).
• “At wafer level” means the level where, during normal operation, a wafer
• At "reticle level” a reticle is present during normal operation of the wafer scanner when illuminating the wafer.
• the wafer scanner comprises a reticle stage RS to support and position a reticle R.
• the reticle tool is configured to replace a reticle on the reticle stage; in other words the mechanical interface between the reticle stage and a reticle is the same as the mechanical interface between the reticle stage and the reticle tool. This make the reticle tool loadable in the manner of a production reticle.
• the reticle tool is compatible with already existing wafer scanners; it is wafer scanner independent. Also, a qualification and calibration procedure of the reticle tool can be performed outside the wafer scanner.
• the reticle tool can comprise one or more polarization sensor modules.
• the carrier of the reticle tool comprises a layer of known reticle material as used for production reticles that comprise circuit patterns during operation of a wafer scanner.
• Known reticle material is highly stable under temperature differences, so that the position of the modules will be stable.
• the reticle tool can comprise marks configured to measure the position of the sensor modules and any deformations of the reticle tool. Such a measurement can be performed with a sensor as known from EP 1267212, which is hereby incorporated for reference.
• Aspects of the invention that employ the illuminator polarization sensor module (A) are divided into active reticle configurations (1) and passive reticle configurations (2).
• both an active reticle tool and a passive reticle tool can comprise a retarder or wedged prisms (indicated in Figure 3 by "same combinations as for active reticle”).
• a passive reticle tool may comprise birefringent prisms.
• the reticle tool does not need any interfaces for power, control signals (such as a trigger to
• a camera may be placed at reticle level for an active reticle tool.
• Figure 3 lists different types of projection lens polarization sensors (B), in accordance with further embodiments of the invention.
• the three general configurations listed are based on whether a light beam passes through the projection lens (PL) once, twice or three times.
• For the projection lens polarization modules besides components positioned at the reticle level, some additional optics are located at wafer level.
• A. Illuminator polarization sensor [0082] In embodiments described below, active and passive reticle tools are disclosed, wherein a reticle tool comprises a collimation lens and a folding mirror.
• the reticle tools By collimating the light received from an illuminator and reflecting it in a direction perpendicular to the optical axis of the illuminator, the reticle tools have a relatively low overall height, so that the tools have the same mechanical interface with the reticle stage. This permits an active or passive reticle tool to be simply substituted for a production reticle on a reticle stage without having to reconfigure the reticle stage.
• an active reticle tool 40 contains one optical channel with an active rotating retarder.
• Light emerging from the illuminator is incident at collimating lens CL and is reflected at a 90 degree angle by prism PRl, emerges through positive lens PLl and passes through field stop (pinhole) FS.
• Brewster plate (or "Brewster element") BP is used as a polarizer, wherein the angle of BP is arranged at a Brewster angle to reflect light of one polarization state while passing light of another polarization state.
• the Brewster plate BP can be configured to reflect from the surface of the plate, or can be configured as a prism that reflects polarized light at an internal surface of the prism.
• Light reflected from the surface of BP is reflected off a mirror M and passes through lenses Ll and L2 before entering prism PR2, in which the light is directed downwards to detector D.
• detector D is a CCD chip.
• Reticle tool 40 is also provided with drive motor MR which can rotate the optical system. In other configurations, other types of motors are possible.
• the active reticle tool is configured to couple to a reticle stage of a lithographic apparatus wherein the active reticle tool can be exchanged for a reticle used to pattern substrates.
• the complete optical system of the reticle tool is preferably configured to rotate around the z-axis relative to the carrier of the reticle tool. By rotating the optical system of the reticle tool, the first collimation lens will change both x and y position. This is used to be able to measure several field points and to assemble a polarization pupil map.
• the reticle tool is positioned on a reticle stage that is arranged to be movable in y direction.
• the movement in y direction of the reticle stage supporting the reticle tool facilitates measurements at even more positions. This implies an active rotation of the field point on the reticle to cover the field in x (for example by two DC motors), and the present reticle-y-movement to position the channel in y direction.
• dedicated data acquisition electronics, power and communication are provided to enable the two active rotations.
• the camera for instance, a CCD chip
• the camera can be positioned on the reticle-shaped tool, or a camera at wafer level can be used.
• the reticle tool 40 comprises a first collimation lens CL and a folding mirror M.
• the reticle tool has a relatively low overall height, so that it has the same mechanical interface with the reticle stage, i.e. the reticle tool can be positioned on the reticle stage arranged to support production reticles without changes.
• the data acquisition of this embodiment will be relatively simple. Also, the image intensity does not need to be continuous, so that for instance parcellation will not influence the polarization state determination. [0088] It will be clear to one of ordinary skill that using one optical channel for measurements of several polarization states reduces calibration requirements. Additionally, the calibration of the reticle tool can be performed outside the machine, using a defined light source.
• Figure 5 (a) depicts a portion of a polarization sensor, including a rotating retarder R, in accordance with one configuration of the invention.
• a rotating retarder for example, a quarter- wave plate
• the rotation movement could be performed, for example, by a miniature worm-wheel construction.
• the detector is a camera C, but could be a photo cell or a photo multiplier. It will be appreciated that any detector arranged to detect intensity is usable.
• a CCD-camera can be used to measure the rotation of the retarder.
• the rotation angle of the retarder need not be exactly manipulated, because the rotation angle can be checked, for example, by placing a small radial marker onto the retarder, and imaging the marker onto the camera. From this image marker position, the exact rotation of the retarder can be derived and corrected for afterwards.
• the resolution of the CCD-camera can be relatively low, and still permit an accurate determination of the rotational position of the retarder.
• the detector is placed at wafer level. This means that after passing through the reticle tool, the light passes through the projection lens system before reaching the detector. The light passes the projection lens system at the same position (i.e. the same part of the cross section of the projection lens) the influence of the projection lens system will be equal. This is because the polarizer of the reticle tool has the same rotation relative to the projection lens system, so that the light when passing the projection lens system is constant.
• Figure 5(b) illustrates a spring loaded retarder 50 arranged according to a further configuration of the present invention.
• two separate cylinders 52 each are provided with two optical retarders 54.
• cylinders 52 can be relatively displaced with respect to each other to produce four possible combinations of retarders for light passing, for example, from left to right. This results in four possible degrees of rotation of light.
• Wedged Prisms
• each wedge prism consists of a pair of wedges of material whose optical axis is mutually rotated between wedges, for example, a 90 degree rotation.
• the physical thickness of the wedge varies as a function of position along a given direction, for example, along the y direction in the first wedge prism. Accordingly, the degree of optical retardation also varies along the y direction, wherein the polarization direction of light emitted from the wedge, varies as a function of y position. This results in a variation of the component of polarized light parallel to the polarizer direction as a function of y position, resulting in a variation of the intensity of light passed by the polarizer (only light parallel to the polarizer direction gets passed) as a function of y position.
• the optical direction of the crystal forming the second wedge is rotated at 90 degrees with respect to the first wedge, so that, although the physical thickness is constant along the Y- direction, the effective optical rotation still can vary.
• the Fourier analysis of the obtained fringes provides information for determining the two-dimensional distribution of the state of polarization. No mechanical or active elements for analyzing polarization are used, and all the parameters related to the spatially-dependent monochromatic Stokes parameters corresponding to azimuth and ellipticity angles can be determined from a single frame.
• resulting intensity pattern detected at a detector typically assumes a mesh shape of varying intensity in both x and y directions.
• the Fourier analysis of the intensity mesh allows a reconstruction of the 2-dimensional distribution of input polarization states of light received through a pinhole at a given field position.
• wedge angle which determines how rapidly the polarization retardation of emitted light changes with x or y position, as well as camera resolution, the measurement resolution of the two-dimensional polarization state distribution can be optimized.
• the detector is placed at wafer level. This means that after passing through the reticle tool, the light will pass through the projection lens system before reaching the detector. The light passes through the projection lens system at the same position (i.e. the same part of the cross section of the projection lens) the influence of the projection lens system will be equal. This is because the polarized of the reticle tool has the same rotation relative to the projection lens system, so that the light when passing the projection lens system is constant. [0099] It will be appreciated that repeated measurements of a given rotation angle of the retarder and of the optical system of the reticle tool can be performed in order to average out angular positioning errors that might occur for a single measurement.
• a passive reticle-shaped tool contains multiple optical channels.
• at least four different channels each having a different rotation angle of the retarder be used for each field point.
• these optical channels are copied and positioned in the x direction on the reticle.
• the present reticle-y-movement can be used to position the different channels in the y direction.
• a Brewster plate is a plate operated at Brewster's angle (also known as
• n ⁇ and nj are the refractive indices of the two media.
• any light reflected from the interface at this angle must be s-polarized.
• a glass plate placed at Brewster's angle in a light beam can thus be used as a polarizer.
• Figure 10 depicts interaction of an unpolarized light wave with a surface.
• a randomly polarized ray incident at Brewster's angle the reflected and refracted rays are at 90° with respect to one another.
• Brewster's angle for visible light is approximately 56° to the normal.
• the refractive index for a given medium changes depending on the wavelength of light, but typically does not vary much.
• the difference in the refractive index between ultra violet ( ⁇ 100nm) and infra red (-lOOOnm) in glass, for example, is -0.01.
• the Wollaston prism is a useful optical device that manipulates polarized light.
• the Wollaston prism consists of two orthogonal birefringent prisms, such as calcite prisms, cemented together on their base to form two right triangle prisms with perpendicular optic axes. Outgoing light beams diverge from the prism, giving two polarized rays, with the angle of divergence determined by the prisms' wedge angle and the wavelength of the light. Commercial prisms are available with divergence angles from 15° to about 45°.
• Figure 8(b) illustrates a passive reticle system 80 arranged according to one configuration of the present invention.
• System 80 includes a 3X4 array of polarization sensor modules 82.
• Sensor modules 82 include field stops 84 that are configured to admit light into the sensor module.
• Figure 8(c) illustrates details of a polarization sensor module 82.
• Light passing through field stop 84 is reflected off mirror 86, passes through fixed retarder 87, and is reflected off of Brewster plate polarizer (prism polarizer) to emerge through collimator lens 89.
• Reticle system 80 is preferably configured to be interchangeable with a reticle used in a lithography tool. When tool 80 is placed in a reticle stage, field stops 82 sample different field points.
• each of the four sensor modules within a "column" is configured with a different effective retarder.
• a detector measuring light emerging from all four sensor modules 82 within a column receives light that is subject to four different amounts of retardation.
• the reticle system is preferably configured to translate within a field of illuminator radiation, for example, by applying an x- or y- movement to a reticle stage.
• each sensor module can intercept a common field point, and a series of four measurements corresponding can therefore be recorded corresponding to one measurement each for each sensor module of the column. Accordingly, four different retardation conditions can be recorded for a given field point.
• each polarization sensor module is provided with a movable shutter that can block radiation from the illuminator, such that a single sensor module can be designated to receive radiation from the illuminator at a given time, while radiation is simultaneously blocked from entering other sensor modules.
• each column represents a fixed Y position with respect to an illuminator.
• reticle system 80 can be used to measure at least three different Y field positions.
• a detector could be arranged near the collimating lens.
• the detector is arranged at a wafer level to receive radiation after it is reflected from a Brewster plate. In the latter case, the reflected light passes through a projection lens before being detected.
• other configurations of the invention provide for independent measurement of the effect on polarization of the projection lens.
• Projection lens polarization sensor [00116]
• the projection lens can influence the polarization state of the light that passes through the projection lens. The final polarization of the light after passing through the projection lens also depends on the illuminator polarization settings and on which position of the lens is exposed.
• the contribution of the projection lens to the polarization state can be measured using the illuminator polarization sensor at reticle level (on active or passive reticle) and additional optics that treat the polarization at the reticle and/or wafer level.
• Three configurations, including a one-pass system, two-pass system and three-pass system are shown in Figs. 9a-c. For convenience, only one light path is shown through the center of the lens.
• the standard illuminator polarization states is defined and fine-tuned by an illuminator polarization sensor, so the input polarization states (polarization states of light entering the projection system) are exactly known. In one aspect of the invention, at least four well- defined input polarization states (in terms of Stokes vectors) are used. [00117] One-Pass System
• the illuminator IL light which has a well known polarization state passes a pinhole P at reticle level, followed by the projection lens PL, optional rotating retarder (not shown) and then a polarizer P at wafer level positioned at a close distance above a camera C located at wafer level WS.
• the light passes through a collimator and rotating retarder (not shown) before entering the polarizer.
• Fig. 9(b) illustrates one configuration of the invention that employs a two-pass system. The light passes through the projection a second time after being reflected by a mirror
• This wafer level mirror M displaces the incoming beam in an (x,y) (horizontal) direction so a reflected beam can be received by a mirror at reticle level, after which it is detected by the camera. For example, this could be performed by arranging the wafer level mirror as a cube edge mirror.
• the x-y displacement is kept minimal to ensure approximately the same optical path through the lens for light passing the projection lens the first time and the second time.
• a first beam of light impinging on the wafer level mirror M is reflected back towards the reticle level as a second beam of light without undergoing any substantial x-y translation at the wafer level, thus substantially overlapping the second beam of light.
• the second beam of light attains an optical attribute different than the first beam of light, such that the second beam of light can be directed to a polarizer and camera, as illustrated in Figure 9(b).
• a beam splitting polarizer PBS is provided below a pinhole FS supplied at a reticle.
• PBS is Y-polarized 2 after leaving the polarizing beam splitter.
• the light After exiting the beam splitter the light passes through a retarder R (such as a quarter wave plate) and assumes a circular polarization, shown as a right handed circular polarization 3 in Figure 9(d).
• R such as a quarter wave plate
• the light assumes a left handed circular polarization 4, travels though the quarter wave plate, and becomes x-polarized 5, such that the light reflects from the beam splitter PBS to the detector D provided at reticle level. Accordingly, the reflected light
• the projection lens can in general affect circularly polarized light, such that the light becomes elliptically polarized, such that light 4 entering the quarter wave plate may be elliptically polarized rather than circularly polarized.
• effects can be accounted for and in fact provide information about the affect on polarization of the projection lens.
• a collimating lens (not shown) can be used in front of the polarizer. This reduces the requirements for the polarizing element to have small retardation errors for incident light under high NA values.
• the one-pass system has the advantage of using an existing camera at the wafer level.
• the two-pass system employs a separate camera at reticle level.
• One advantage of the two pass configuration as illustrated in Figure 9(b) is that most of the optical components, including the reticle with pinhole, polarizer, camera, reticle level mirror (but not including the wafer stage reflector (mirror)) can be configured to be part of a loadable reticle-
• the reflector can be positioned anywhere on the wafer stage, since the camera at wafer level is not in use.
• the measured polarization effect exerted by the projection lens is essentially the same as the two-pass configuration.
• the polarizer in both 9(b) and 9(c ⁇ is positioned to intercept light after passing through the projection lens twice.
• the intensity of the polarized light which is what is measured by the detector, should not be sensitive to whether the light passes through the projection lens.
• the invention also applies to wafer steppers, which are just like wafer scanners lithographic apparatus, or lithographic apparatus for flat panel displays, PCB's etc. Also the invention applies to reflective optics as well.
• FIG. 11 schematically depicts a lithographic apparatus according to the embodiments of the invention.
• the apparatus of Figure 11 comprises: an illumination system (illuminator) IL configured to condition a radiation beam PB (e.g. UV radiation or EUV 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 radiation beam PB (e.g. UV radiation or EUV 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)
• PB e.g. UV radiation or EUV radiation
• a support structure e.g. a mask table
• MT constructed to
• 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.
• a projection system e.g. a refractive projection lens system
• 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 supports, i.e. bears the weight of, the patterning device. It 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.”
• 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.
• 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”.
• the apparatus is of a transmissive type (e.g. employing a transmissive mask).
• 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 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.
• 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. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems.
• the illuminator IL receives a radiation beam from a radiation source SO.
• the source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD comprising, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp.
• the source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.
• the illuminator IL may comprise an adjuster AD for adjusting the angular intensity distribution of the radiation beam.
• an adjuster AD for adjusting the angular intensity distribution of the radiation beam.
• 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 illuminator may also control the polarization of the radiation, which need not be uniform over the cross-section of the beam.
• 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 mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W.
• 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.
• the first positioner PM and another position sensor can be used to accurately position the mask MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan.
• movement of the mask table MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM.
• movement of the substrate table WT may be realized using a long- stroke module and a short-stroke module, which form part of the second positioner PW.
• the mask table MT may be connected to a short- stroke actuator only, or may be fixed.
• Mask MA and substrate W may be aligned using mask alignment marks Ml, M2 and substrate alignment marks Pl, P2.
• the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks).
• the mask alignment marks may be located between the dies.
• the depicted apparatus could be used in at least one of the following modes:
• step mode the mask table 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.
• step mode the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure.
• the mask table 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 mask table MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS.
• 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.
• the mask table 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.
• 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 analyzer 12 is a linear polarizer, such as a beam-splitter cube, in a first fixed
• the polarization changing element 10 is a retarder, or retardation plate, and is, in an embodiment, a quarter-wave plate for the particular wavelength of illumination radiation.
• a quarter-wave plate introduces a relative phase shift of B/2 between orthogonally linearly polarized components of incident radiation. This can convert suitably oriented linearly polarized radiation to circularly polarized radiation and vice versa. In general, it changes a general elliptically polarized beam into a different elliptically polarized beam.
• the polarization changing element 10 is adjustable such that the polarization change induced can be varied.
• the polarization changing element 10 is rotatable such that the orientation of its principal axis can be adjusted.
• the polarization changing element 10 is replaceable by a number of differently oriented polarization changing elements which can each be inserted in the beam path.
• the polarization changing element 10 can be completely removable and replaceable by a differently oriented polarization changing element 10, or a plurality of differently oriented polarization changing elements may be provided integrally on a carrier, similar to a reticle, for example in the form of an array. By translating the carrier then the polarization changing element corresponding to any particular field point can be adjusted.
• a detector 14 for detecting the intensity of the radiation is provided in this embodiment of the invention after the radiation has passed through the projection system PS.
• the detector 14 can be a pre-existing detector provided at the substrate table.
• One form is a spot sensor which measures the radiation intensity at a particular field point.
• Another form is a CCD camera that is provided for wavefront measurements.
• the CCD camera can be provided with a small aperture or pinhole at the focal plane of the projection system to select a desired field point.
• the CCD sensor itself is then defocused such that each pixel of the CCD detects radiation that has traversed a specific path through the projection system to reach that field point; in other words each pixel corresponds to a point in the pupil plane of the projection system (or pupil plane of the illuminator).
• a controller 16 receives measurements from the detector 14, which in conjunction with the control and/or detection of the adjustment of the polarization changing element 10, such as its rotational orientation, can calculate the state of polarization e.g. Stokes parameters, for each pupil pixel.
• the detector can be moved and the measurements repeated for different field points.
• the analyzer 12 closely follows the polarization changing element 10; and it does not matter that there are further components between the analyzer 12 and the detector 14 because the detector 14 is insensitive to polarization variation.
• the situation can be considered in the following way. If the radiation exiting the polarization changing element 10 has a state of polarization represented by the Stokes vector S 1n then the state of polarization following the analyzer 12, called S out , can be found by multiplying .S 1n by the M ⁇ ller matrix M po ⁇ representing the operation of the analyzer 12 (linear polarizer).
• the coordinate system can be arbitrarily chosen such that the analyzer 12 is a polarizer in the X- direction.
• the state of polarization (Stokes vector) of the radiation at the ideal detector position is as follows:
• polarization properties such as polarization degree and polarization purity at the level of the reticle can be completely determined.
• the influence of the projection system is almost completely eliminated by having the polarizer 12 at reticle level; only the intensity is altered.
• polarization changing element 10, analyzer 12, and detector 14 together comprise an illumination polarization sensor having a detector located at the wafer level rather than reticle level.
• Figure 13 shows a further embodiment of the invention.
• the polarization changing element 10 and the analyzer 12 are integrated into a carrier 18 that can be inserted into the lithographic apparatus in place of a reticle. Radiation 20 from the illuminator is incident on a pinhole 22 comprising an aperture in an opaque layer, such as chromium, formed on the upper surface of the carrier 18.
• the polarization changing element 10 is, in an embodiment, a quarter- wave plate such as a low order quarter- wave plate to minimize its thickness, and can be made of a suitable material such as quartz.
• the analyzer 12 in this embodiment does not simply block or absorb one linear polarization component, but instead is a prism made of a birefringent material arranged such that the two orthogonal linearly polarized components are spatially separated, in other words it is a polarizing beam splitter.
• the prism comprises two wedges of crystals of the birefringent material in contact with each other, but the orientation of the principal optical axis of the crystal in one wedge is in the X direction, and in the other wedge is in the Y
• a suitable birefringent material from which to make the prism, and which can be used with short-wavelength illumination radiation, is KDP (potassium dihydrogen phosphate).
• the effect of the polarizing beam splitter as the analyzer 12 is that when looking from underneath into the illumination radiation, one sees two pinholes next to each other, the radiation from one pinhole being polarized along the X axis, and the radiation from the other pinhole being polarized along the Y axis.
• a second pinhole 24, which may be an integral part of the detector, can be positioned at the focal plane of the projection system to selectively transmit one polarized image of the first pinhole 22 and block radiation from the other.
• a defocused detector 14, such as a CCD measures the intensity for a plurality of pixels corresponding to locations in the pupil plane of the projection system and illuminator.
• the apparatus can be used in exactly the same way as described for Figure 12 to determine the state of polarization of the illumination radiation at reticle level.
• the carrier 18 can be provided with a plurality of pinholes 22, polarization changing elements 10, and analyzers 12, with the polarization changing element 10 being at different rotational orientations, such as with its fast axis along the X direction, along the Y direction and at 45° to the X and Y directions.
• the polarization changing element corresponding to a particular field location can be adjusted, and ellipsometry measurements can be made as before.
• the diffractive element located in the beam between the illumination system and the projection system.
• the diffractive element such as a grating, also known as the object grating, diffracts the radiation and spreads it out such that it passes through the projection system along a plurality of different paths.
• the diffractive element is typically located at the level at which the patterning device, e.g. mask MA is located.
• the diffractive element can be a grating or can be an array of features of suitable size, and may be provided within a bright area in a dark field reticle, said area being small with respect to an object field size of the projection system (i.e., sufficiently small so that image aberrations are substantially independent of the position of an object point in that area).
• Such an area may be embodied as a pinhole.
• the pinhole may have some structuring within, such as for example said object grating, or diffractive features such as grating patterns, or checkerboard patterns.
• this is in principle optional (for example, in the first embodiment of the present invention, pinholes can be used to select small portions of the field, and, in an embodiment, there is no structuring within the pinholes).
• a function of the pinhole and its optional internal structure is to define a preselected mutual coherence having local maxima of mutual coherence in the pupil of the projection system, whereby the preselected mutual coherence is related to the pinhole and its optional internal structure through a spatial Fourier transformation of the pinhole and its structure. Further information on patterns within the pinhole can be gleaned from U.S. patent application publication no. US 2002-0001088.
• One or more lenses may also be associated with the diffractive element.
• This assembly as a whole, located in the projection beam between the illuminator and the projection system will be referred to hereafter as the source module. [00162] Referring to Figure 14, a source module SM for use with an embodiment of the present invention is illustrated.
• a pinhole plate PP which is a quartz glass plate with an opaque chromium layer on one side, same as a reticle, and with a pinhole PH provided in the chromium layer. It also comprises a lens SL for focusing the radiation on to the pinhole.
• a pinhole plate PP which is a quartz glass plate with an opaque chromium layer on one side, same as a reticle, and with a pinhole PH provided in the chromium layer. It also comprises a lens SL for focusing the radiation on to the pinhole.
• a lens SL for focusing the radiation on to the pinhole.
• the source module should ideally generate radiation within a wide range of angles such
• the pupil of the projection system is filled, or indeed overfilled, for numerical aperture measurements, and, in an embodiment, the pupil filling should be uniform.
• the use of the lens SL can achieve the over-filling and also increases the radiation intensity.
• the pinhole PH limits the radiation to a specific location within the field.
• Alternative ways to obtain uniform pupil filling are to use a diffuser plate (such as an etched ground glass plate) on top of the pinhole plate, or an array of microlenses (similar to a diffractive optical element DOE), or a holographic diffusor (similar to a phase-shift mask PSM).
• the further diffractive element GR is mounted on a carrier plate CP, for example made of quartz.
• This further diffractive element acts as the "shearing mechanism" that generates different diffractive orders which can be made to interfere (by matching diffracted orders to said local maxima of mutual coherence) with each other. For example, the zero order may be made to interfere with the first order. This interference results in a pattern, which can be detected by a detector to reveal information on the wavefront aberration at a particular location in the image field.
• the detector DT can be, for example, a CCD or CMOS camera which captures the image of the pattern electronically without using a resist.
• the further diffractive element GR and the detector DT will be referred to as the interferometric sensor IS.
• the further diffractive element GR is located at the level of the substrate at the plane of best focus, such that it is at a conjugate plane with respect to the first-mentioned diffractive element in the source module SM.
• the detector DT is below the further diffractive element GR and spaced apart from it.
• ILIAS trademark
• ILIAS Integrated Lens Interferometer At Scanner.
• the interferometric sensor essentially measures the derivative phase of the wavefront.
• the detector itself can only measure radiation intensity, but by using interference
• the phase can be converted to intensity.
• Most interferometers require a secondary reference beam to create an interference pattern, but this would be hard to implement in a lithographic projection apparatus.
• a class of interferometer which does not have this requirement is the shearing interferometer.
• interference occurs between the wavefront and a laterally displaced (sheared) copy of the original wavefront.
• the further diffractive element GR splits the wavefront into multiple wavefronts which are slightly displaced (sheared) with respect to each other. Interference is observed between them. In the present case only the zero and +/- first diffraction orders are considered.
• the intensity of the interference pattern relates to the phase difference between the zero and first diffraction orders.
• E 0 and Ei are the diffraction efficiencies for the zero and first diffracted orders
• k is the phase stepping distance
• p is the grating periodicity (in units of waves)
• W is the wavefront aberration (in units of waves)
• p is the location in the pupil.
• the wavefront phase difference approximates the wavefront derivative.
• amplitude measurements can also be made. These are done by using a source at reticle level with a calibrated angular intensity distribution.
• a source at reticle level with a calibrated angular intensity distribution.
• One example is to use an array of effective
• each point source has an intensity distribution which is effectively uniform over the range of solid angles present within the projection system pupil.
• Variations in detected intensity can then be related to attenuation along particular transmission paths through the projection system.
• amplitude measurements and obtaining the angular transmission properties of the projection system are given in U.S. patent application no. US 10/935,741, hereby incorporated by reference in its entirety.
• the above wavefront measurements are performed using a polarized radiation source.
• One embodiment, as shown in Figure 14, is to incorporate a polarizer 30, such as a beam splitter cube, into the source module SM; an alternative embodiment would be to use separate discrete insertable polarizers, for example insertable at the illuminator or reticle level. No modification of the interferometric sensor IS is required.
• a polarizer 30, such as a beam splitter cube such as a beam splitter cube
• No modification of the interferometric sensor IS is required.
• a wavefront Wxx is first measured using the source radiation linearly polarized in one direction, such as the X direction.
• the polarizer or source module is then rotated or exchanged/displaced, such that the radiation is linearly polarized in the Y-direction, and the new wavefront Wxy is then measured.
• a single source module carrier can be provided with an unpolarized, a X-polarized and a Y-polarized source structure, and loaded as a normal reticle.
• the reticle stage is able to move freely in the scanning direction, so for each field point (normal to the scanning direction) the unpolarized, a X-polarized and a Y- polarized source structure can be provided.
• the effect on polarized radiation of an optical element or combination of optical elements, such as the projection system can be represented by a Jones matrix.
• the X and Y components of the electric field vector of incident and outgoing electromagnetic radiation are related by the Jones matrix as follows:
• a Jones matrix can be calculated for each pupil point in the projection system (each Jones matrix corresponding to the effect on polarization of a ray of radiation taking a particular path through the projection system).
• the source module and interferometric sensor can be moved to a different field point and a set of Jones matrices obtained.
• each combination of field point and pupil point has its own specific Jones matrix.
• One concern might be that the device in the source module for ensuring that the projection system pupil is over-filled, such as a diffusor, might result in mixing of polarization states. However, this is not expected to be a significant effect because the characteristic length scales of small-angle diffusors are typically about 0.05 mm.
• the mixing factor a can be found either theoretically or by a calibration (done off-line) and then the equations can be resolved to find the desired X and Y polarized wavefronts Wx and Wy. The same procedure can also be applied if the polarizer used does not yield satisfactory polarization purity.
• An indication of a state of polarization of the radiation beam at substrate level may be based on the specification of a target polarization state that is desired.
• a convenient metric is defined as the polarization purity (PP) or the percentage of polarized radiation that is in the targeted or preferred polarization state.
• PP polarization purity
• Ejarget and E Ac tuai are electric field vectors of unit length.
• PP is a valuable metric it does not completely define the illuminating radiation.
• a fraction of the radiation can be undefined or de-polarized, where the electric vectors rotate within a timeframe beyond an observation period. This can be classified as unpolarized radiation. If radiation is considered to be the sum of polarized radiation with an intensity I po iar ⁇ :ed and unpolarized radiation with an intensity l un poianzed, whereby the summed intensity is hotai, it is possible to define a degree of polarization (DOP) by the following equation: DQP — pol""zed _ ⁇ * polarized
• DOP may be used to account for unpolarized portions. Since unpolarized (and polarized) radiation can be decomposed into 2 orthogonal states, an equation for the total intensity in the preferred state (IPS) of polarization as a function of DOP and PP can be derived, i.e.,
• the measurement method of the embodiment described above with respect to figure 14 is arranged to examine and compute a spatial distribution of IPS.
• the wavefront Wxx is
• the polarizer 30 is then rotated or exchanged/displaced, such that the radiation is linearly polarized in the Y- direction, further the object grating is, as before, arranged to provide in the projection system pupil a wavefront shearing in the X direction, and the corresponding linearly polarized wavefront Wxy is then measured.
• a first pinhole PHl with X polarization is used for the spatially resolved aberration measurement of the wavefront Wxx.
• This process is repeated with another pinhole PH2, with Y polarization, and with the same grating orientation as was provided with the pinhole PHl.
• the measurement results can be used to compute, spatially resolved in the pupil, a Jones matrix and the intensity in the preferred state (IPS).
• IPS intensity in the preferred state
• phase ⁇ (x,y) of the wavefront is measured using an object grating in the pinhole PH to provide a preselected spatial coherence in the pupil of the projection system, and a shearing grating.
• the shearing grating is the image grating GR mentioned above.
• the grating GR brings different diffraction orders together on a detector DT.
• the detector DT will detect an intensity which oscillates with displacement of the grating GR relative to the pupil.
• the amplitude of oscillation will also be referred to as a contrast, and the average intensity (at amplitude zero) will also be referred to as a DC signal.
• the shearing interferometric aberration measurement method includes a mixing (i.e., a coherent addition) of electric fields diffracted at the grating GR, including a zeroth order diffracted electric field and a first order diffracted electric field.
• the zeroth and first order diffracted fields are images of the electric field at the pupil of the projection system, and are respectively denoted by an electric field E Q (x, y) at a pupil-position (;t,.y) in the pupil of the projection system and an electric field E ] (x + dx,y) at a "neighbor" pupil- position (x + dx,y) .
• the electric fields are scalar fields (with a same state of polarization, independent of the X, Y coordinates in the pupil) and the subscripts refer to the order of
• the detector DT measures an intensity I(x,y) given by:
• the intensity I(xy) varies as a cosine with respect to the phase difference between the two fields EQ and E ⁇ .
• the wavefront-measurements include measuring the cosine-behavior by introducing an extra, varying "stepping" phase ⁇ slep . At each step a new value of the intensity at one pixel of the detector DT is measured.
• I 2 (x,y) A 0 2 +A x 2 +2A 0 A x cos[d ⁇ (x,y) + 2 ⁇ (2 ⁇ /8)],
• phase d ⁇ x,y) ⁇ (x + dx,y) - ⁇ (x,y) can be extracted. Alternatively either more or less than eight data points can be used, depending on signal/noise constraints.
• a fit for every eligible pixel of the detector DT corresponding to a pupil position (x,y) results in a full map d ⁇ (x,y) of the wavefront phase-shifts. 5 [00186]
• the vector nature of the electric field is to be included. It is assumed that the shearing grating GR is non-polarizing, so that only vector properties of the radiation upstream of the grating GR are examined.
• phase retardation between X- components is absorbed by the previously introduced phase difference ⁇ x,y) .
• the intensity measured with a detector pixel of the detector DT is given by:
• a BF 2 V4), 2 ⁇ l, 2 + Ay 2 Ay 2 + 2 AxAxAyAy ⁇ S [ d( Pre l ] > ( ⁇ )
• the polarization state of the electric field E 0 (x,y) is obtained from interferometric measurements of the intensity I(xj>).
• This polarization state is fully defined by the Stokes vector of E 0 , which is given by:
• the I(x,y) measurements include the step of selecting two different, preselected polarization states for the radiation impinging on the object grating in the pinhole PH, for two corresponding I(x,y) measurements.
• preferred states of polarization are defined as fully X- polarized polarization and fully Y-polarized polarization; these polarization states correspond to preferred illumination-modes for enhancing resolution of the lithographic printing process.
• the corresponding values for the IPS are:
• index ",x" indicates the incident, linear X polarization.
• a Xy x is the amplitude of the Y-component of the first order diffracted electric field, when incident X-polarized radiation is used at reticle level.
• the interferometric shearing measurement is repeated with an arrangement of the polarization of E 0 (x, y) taken to be linearly polarized in the Y-direction at reticle level, again by using a corresponding polarizer 30 in the source module aligned with the direction of polarization along the Y direction.
• a 0x 0.
• ",y" sub-indexing is used to indicate the linear Y polarization of the incident radiation at reticle level, e.g. A 1x y is the amplitude of the X-component of the first order diffracted electric field, when incident Y-polarized radiation is used.
• a 1x y is the amplitude of the X-component of the first order diffracted electric field, when incident Y-polarized radiation is used.
• the contrast of the interference pattern is related to the amplitude of the intensity oscillation as described by equations 24-2 and 25-2. Therefore, the measurement of the entities A BF 2 is referred to as a "contrast" measurement. Further, a “DC” component of the interference fringe pattern is described by the equations 24-3 and 25-3. Accordingly, a measurement of DC x and DC y is referred to as a "DC" measurement. Said contrast and DC measurements lead to 4 equations with four unknowns A 1x x , A Xx y , A Xy x ,A x y y .
• the position (x p + dx, y p ) may be referred to as a first position (x ⁇ ,y ⁇ ) in the pupil.
• the above described measurement process can be repeated in going from the first
• the corresponding spatial distribution of IPS can be obtained; for example, the distribution of IPS x (xy) can be found by substituting the measured values of A 1x x , A ⁇ y x for A 0x , A 0 y in equation 22.
• the two different settings of the polarizer 30 include a linear polarization along the direction of shear and a linear polarization perpendicular to the direction of shear.
• additional settings of the polarizer 30 may be used.
• DC and contrast measurements as described above may further be executed with a polarization at reticle level different from either linear X polarization or linear Y polarization, by providing a source module SM with a polarizer 30 arranged for linear polarization at an angle different from zero or 90 degrees with respect to the direction of shear.
• Such additional measurements may be used to enhance the accuracy of the process of solving equations for the electric field amplitudes, as described above, or to obtain information on the presence of unpolarized radiation in the case that DOP ⁇ 1.
• 49 amplitudes are determined by measuring interferometric mixing data such as said DC components and contrasts, as well as by measuring d ⁇ .
• the Jones matrices in all other pupil points can be obtained by iteration analogous to the iteration described in the previous embodiment. Since each of the four matrix-elements of a Jones matrix has a real part and an imaginary part, there are 8 unknowns and hence, 8 equations are needed to solve for the unknowns.
• Six equations are provided by the fit of the interferometric intensity data to the equations 24-1, 24-2 and 24-3 and equations 25-1, 25-2 and 25-3.
• Two additional equations are provided by supplementary measurements of output intensities for the two polarization states of the radiation incident on the pinhole PH, for the first order diffracted beam, in the absence of interference with other diffracted beams.
• One option is to locate the elements such as the polarization changing element 10 and the analyzer 12 at a suitable location in the illuminator where the radiation is already substantially collimated.
• a second alternative is to provide optical elements 40 and 42, as shown in Figure 15, which firstly collimate the
• the results of the measurements according to any of the above embodiments of the invention can be used to provide feedback.
• one or more actuators may be provided to adjust components of the lithographic apparatus by way of feedback based on the obtained measurements.
• Figure 12 illustrates, by way of example, that the illuminator IL may be adjusted under the control of the controller 16 to correct or compensate for any measured deviations in the desired polarization pattern.
• 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. [00208] 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.
• UV radiation e.g. having a wavelength of or about 365, 248, 193, 157 or 126 nm
• EUV radiation e.g. having a wavelength in the range of 5-20 nm
• lens may refer to any one or combination of various types of optical components, including refractive, and reflective optical components.

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