Lithographic apparatus and ultraviolet radiation control system

Abstract

The present disclosure provides an ultraviolet radiation control system and associated methods for controlling ultraviolet radiation in a lithographic apparatus, the ultraviolet radiation control system comprising: a housing; a conversion crystal (540) disposed on or within the housing and configured to convert ultraviolet radiation into fluorescent radiation; a plurality of photodetectors (550) configured to detect the intensity of a scattered portion of the fluorescent radiation; and at least one diffusing surface (545) disposed on or within the conversion crystal and configured to increase the intensity of the scattered portion of the fluorescent radiation.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 62 / 886,532, filed August 14, 2019, which is incorporated by reference in its entirety.

[0002] The present disclosure relates to a lithographic apparatus and an ultraviolet radiation control system, for example a system for controlling ultraviolet radiation in a lithographic apparatus. [Background technology]

[0003] A lithographic apparatus is a machine that applies a desired pattern to a substrate, usually to a target portion of the substrate. Lithographic apparatus are used, for example, in the manufacture of integrated circuits (ICs). A patterning device, also referred to as a mask or reticle, may be used to generate a circuit pattern for an individual layer of the IC. This pattern may be transferred onto a target portion (e.g. comprising part of a die, one die or several dies) on the substrate (e.g. a silicon wafer). Transfer of the pattern is typically by imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a substrate will contain a network of adjacent target portions, which are successively exposed to light. Known lithographic apparatus include the so-called steppers and scanners. In a stepper, each target portion is irradiated in such a way that the entire pattern is exposed onto the target portion at once. In a scanner, each target portion is irradiated while the radiation beam scans the pattern in a given direction (the "scan" direction) and the substrate is synchronously scanned parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.

[0004] Deep ultraviolet (DUV) radiometers are used in DUV dose control systems of lithography equipment to measure the power of a beam of DUV radiation. Such a DUV beam is typically generated by a laser and the power of the DUV laser beam is measured to ensure the laser is calibrated and adjusted if necessary. If the power of the laser is not measured accurately, the laser may not perform as desired in sensitive or precise applications. In a DUV radiometer, a small part of the main beam of DUV radiation is tapped off and converted into fluorescent radiation. Measuring this fluorescent radiation provides an indirect measurement of the power of the incident beam of DUV radiation.

[0005] However, conventional collection of fluorescent radiation is not efficient or well controlled. Therefore, it is desirable to introduce a more robust and reproducible system for collecting fluorescent light in a DUV dose control system of a lithography apparatus, and to improve the collection efficiency of the fluorescent light to enhance precise control of the DUV radiation, while at the same time reducing the manufacturing cost of the DUV dose control system of the lithography apparatus. Summary of the Invention

[0006] One aspect of the present disclosure provides an ultraviolet radiation control system comprising a housing, a conversion crystal disposed on or within the housing and configured to convert ultraviolet radiation into fluorescent radiation, a plurality of photodetectors configured to detect an intensity of a scattered portion of the fluorescent radiation, and at least one diffusing surface disposed on or within the conversion crystal and configured to increase an intensity of the scattered portion of the fluorescent radiation.

[0007] In an embodiment, the at least one diffusive surface is disposed in spatial proximity to the multiple photodetectors.

[0008] In an embodiment, the ultraviolet radiation control system comprises only a single conversion crystal.

[0009] In an embodiment, the conversion crystal has a disk shape and the multiple photodetectors are equally spaced around an annular periphery of the conversion crystal.

[0010] In an embodiment, at least one diffusing surface has a ring shape.

[0011] In an embodiment, the at least one diffusive surface comprises a plurality of segments arranged in a discontinuous ring shape, each of the plurality of segments being positioned adjacent a predetermined one of the plurality of photodetectors.

[0012] In an embodiment, the plurality of photodetectors are disposed on a first side of the conversion crystal and the at least one diffusive surface is disposed on a second side of the conversion crystal opposite the first side.

[0013] In an embodiment, the plurality of photodetectors are disposed on a first side of the conversion crystal and the at least one diffusive surface is disposed on the first side of the conversion crystal.

[0014] In an embodiment, the multiple photodetectors are disposed on a first side of the conversion crystal, and the at least one diffusing surface comprises a first diffusing surface disposed on the first side of the conversion crystal and a second diffusing surface disposed on a second side of the conversion crystal opposite the first side.

[0015] In an embodiment, the plurality of photodetectors are disposed around an annular periphery of the conversion crystal, and the at least one diffusive surface is disposed on the annular periphery of the conversion crystal.

[0016] In an embodiment, the ultraviolet radiation is deep ultraviolet radiation.

[0017] In an embodiment, the ultraviolet radiation is a beam split from a 193 nm excimer pulsed laser.

[0018] In an embodiment, the multiple photodetectors are disposed on a ring-shaped spacer that is disposed on an insulator.

[0019] In an embodiment, the ultraviolet radiation control system further comprises a light dump or mirror disposed at the center of the ring-shaped spacer and configured to reflect a portion of the ultraviolet radiation transmitted through the conversion crystal back to the conversion crystal to increase the amount of fluorescent radiation converted from the ultraviolet radiation.

[0020] In an embodiment, the housing is configured to protect the conversion crystal and the plurality of photodetectors. The ultraviolet radiation control system further comprises a purge cap secured to the housing and a purge channel disposed within the purge cap or between the housing and the purge cap.

[0021] In an embodiment, the ultraviolet radiation control system further comprises a first seal disposed between the purge cap and the insulator, a plurality of springs, and a crystal spring holder.

[0022] In an embodiment, the ultraviolet radiation control system further comprises a second seal and centering O-ring disposed between the conversion crystal and the crystal housing.

[0023] In an embodiment, the at least one diffusive surface comprises an impurity embedded in a layer of conversion crystal configured to scatter the fluorescent radiation.

[0024] Another aspect of the present disclosure provides a lithographic apparatus comprising the disclosed ultraviolet radiation control system.

[0025] Another aspect of the present disclosure provides a method of measuring ultraviolet radiation, the method comprising using a conversion crystal to convert a branched portion of the ultraviolet radiation into fluorescent radiation, using at least one diffusive surface disposed on or within the conversion crystal to scatter the fluorescent radiation, and using a plurality of photodetectors to measure an intensity of the scattered fluorescent radiation.

[0026] Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. It should be noted that the present invention is not limited to the specific embodiments described herein. Such embodiments are presented for illustrative purposes only. Additional embodiments will be apparent to one skilled in the relevant art based on the teachings contained herein. [Brief description of the drawings]

[0027] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate the present invention and, together with the detailed description, serve to explain the principles of the invention and to enable those skilled in the art to make and use the invention.

[0028] [Figure 1] 1 depicts a schematic diagram of a lithographic apparatus according to an embodiment;

[0029] [Diagram 2] 1 is a schematic diagram of a transmission lithographic apparatus according to an embodiment;

[0030] [Diagram 3] 1 is a schematic diagram of an energy sensor ES according to an embodiment.

[0031] [Figure 4] FIG. 1 is a schematic cross-sectional view of an existing energy sensor.

[0032] [Diagram 5] 1 is a schematic cross-sectional view of an exemplary detector module of an energy sensor according to an embodiment;

[0033] [Figure 6] 6 is a schematic cross-sectional view of a conversion crystal and a plurality of photodetectors of the exemplary detector module of FIG. 5 according to an embodiment.

[0034] [Figure 7]6 shows a schematic exploded perspective view of the exemplary detector module of FIG. 5 according to an embodiment.

[0035] [Figure 8] 6 is a schematic top view of a conversion crystal and multiple photodetectors of the exemplary detector module of FIG. 5 according to an embodiment.

[0036] [Figure 9] 1 is a schematic cross-sectional view of a conversion crystal and multiple photodetectors of an exemplary detector module according to another embodiment.

[0037] [Figure 10] 13 is a schematic cross-sectional view of a conversion crystal and multiple photodetectors of another exemplary detector module according to another embodiment.

[0038] The features and advantages of the present invention will become more apparent from the following detailed description of the invention when taken in conjunction with the drawings, in which like reference characters identify corresponding elements. Like reference numbers in the drawings generally indicate identical, functionally similar, and / or structurally similar elements. Additionally, the leftmost digit(s) of a reference number generally identifies the drawing in which that reference number first appears. Unless otherwise indicated, the drawings provided throughout this disclosure should not be construed as drawn to scale. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] This specification discloses one or more embodiments incorporating the features of this invention. The disclosed embodiments are merely exemplary of the invention. The scope of the invention is not limited to the disclosed embodiments. The invention is defined by the appended claims.

[0040] References to the described embodiments, and to "one embodiment," "an embodiment," "an example embodiment," and the like herein, indicate that the described embodiment may include a particular feature, structure, or characteristic, but not every embodiment necessarily includes that particular feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that such feature, structure, or characteristic is within the knowledge of one of ordinary skill in the art to operate in conjunction with other embodiments, whether or not expressly stated.

[0041] For ease of description, spatially relative terms such as "lower," "bottom," "upper," "top," and the like may be used herein to describe the relationship of one element or feature to another element or feature depicted in the figures. Such spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptions used herein may be interpreted accordingly.

[0042] The term "about" as used herein indicates a given quantity value that may vary based on a particular technique. Based on a particular technique, the term "about" can indicate, for example, a given quantity value that varies within a range of 10-30% of the value (e.g., ±10%, ±20%, or ±30% of the value).

[0043] The embodiments of the present disclosure may be implemented in hardware, firmware, software, or any combination thereof. The embodiments of the present disclosure may also be implemented as instructions stored on a machine-readable medium that may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may be a read-only memory (ROM), a random access memory (RAM), a magnetic disk storage medium, an optical storage medium, a flash memory device, an electrical, optical, acoustic or other form of propagated signal (e.g., carrier wave, infrared signal, digital signal), and the like. Furthermore, firmware, software, routines, and / or instructions may be described herein as performing certain operations. However, it should be understood that such description is merely for convenience and that such operations actually result from a computing device, processor, controller, or other device executing the firmware, software, routines, instructions, and the like.

[0044] Before describing such embodiments in greater detail, however, it is helpful to present an example environment in which embodiments of the present disclosure may be implemented.

[0045] Exemplary Lithography System

[0046] 1 and 2 respectively show schematics of a lithographic apparatus 100 and a lithographic apparatus 100' in which embodiments of the present disclosure may be implemented. Each of the lithographic apparatuses 100 and 100' includes an illumination system (illuminator) IL configured to condition a radiation beam B, such as deep ultraviolet (DUV) radiation, a support structure (e.g. a mask table) MT configured to support a patterning device (e.g. a mask, reticle, or dynamic patterning device) MA and connected to a first positioner PM configured to accurately position the patterning device MA, and a substrate table (e.g. a wafer table) WT configured to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate W. The lithographic apparatuses 100, 100' also include a projection system PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W. In lithographic apparatus 100, the patterning device MA and the projection system PS may be either reflective or transmissive. In lithographic apparatus 100', the patterning device MA and the projection system PS are transmissive.

[0047] The illumination system IL may include various optical components, such as refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic or other types of optical components, or combinations thereof, for directing, shaping or otherwise controlling the radiation beam B. The illumination system IL may also include an energy sensor ES providing one or more measurements of, for example, energy per pulse, photon energy, intensity, average power, etc. The illumination system IL may include a measurement sensor MS for measuring the movement of the radiation beam B, and a uniformity compensator UC allowing the uniformity of the illumination slit to be controlled.

[0048] The support structure MT holds the patterning device MA in a manner that depends on the position of the patterning device MA relative to a reference frame, the design of the lithographic apparatus 100, 100', and other conditions, such as whether or not the patterning device MA is held in a vacuum environment. The support structure MA may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device MA. The support structure MT may be for example a frame or a table, which may be fixed or movable as required. By using sensors the support structure MT can ensure that the patterning device MA is at a desired position, for example with respect to the projection system PS.

[0049] The term "patterning device" MA should be interpreted broadly to refer to any device that can be used to impart a radiation beam B with a pattern in its cross-section to create a pattern in a target portion C of the substrate W. The pattern imparted to the radiation beam B may correspond to a particular functional layer in a device being created in the target portion C to form an integrated circuit.

[0050] In an embodiment, the patterning device MA compatible with the DUV source may be transmissive, such as the lithographic apparatus 100' of FIG. 2. Patterning devices MA include, for example, reticles, masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography and include binary, alternating phase shift, attenuated phase shift, as well as various hybrid masks. The term "projection system" PS may encompass any projection system including refractive, reflective, catadioptric, magnetic, electromagnetic, electrostatic, or a combination thereof, as appropriate depending on the exposure radiation used and other factors such as the use of an immersion liquid or a vacuum on the substrate W. A vacuum environment may be used for DUV radiation or electron beam radiation, since gases may excessively absorb radiation or electrons. Thus, a vacuum environment may be provided throughout the beam path by use of a vacuum wall and vacuum pumps.

[0051] Lithographic apparatus 100 and / or lithographic apparatus 100' may be of a type having two (dual stage) or more substrate tables WT (and / or two or more mask tables). In such a multi-stage apparatus, the additional substrate tables WT may be used in parallel, or preparation steps may be carried out on one or more tables while one or more substrate tables WT are being used for exposure. It is also possible that the additional tables are not substrate tables WT.

[0052] The lithographic apparatus may also be of a type in which at least a part of the substrate may be covered with a liquid having a relatively high refractive index, e.g. water, to fill a space between the projection system and the substrate. Immersion liquids may also be applied to other spaces in the lithographic apparatus, for example between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term "immersion" as used herein does not imply that a structure such as the substrate has to be immersed in liquid, but simply that a liquid is located between the projection system and the substrate during exposure.

[0053] With reference to Figures 1 and 2, the illuminator IL receives a radiation beam from a radiation source SO. The source SO and the lithographic apparatus 100, 100' may be physically separate entities, for example when the source SO is an excimer laser. In this case, the source SO is not considered to form part of the lithographic apparatus 100, 100' and the radiation beam B passes from the source SO to the illuminator IL via a beam delivery system BD (in Figure 2), which may for example comprise suitable redirecting mirrors and / or beam expanders. In other cases the source SO may be an integral part of the lithographic apparatus 100, 100' (for example when the source SO 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.

[0054] The illuminator IL may comprise an adjuster AD (in FIG. 2 ) for adjusting the angular intensity distribution of the radiation beam. Typically, at least the outer and / or inner magnitude (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator is adjusted. In addition, the illuminator IL may comprise various other elements (in FIG. 2 ), such as an integrator IN and a condenser CO. The illuminator IL may be used to adjust the radiation beam B to obtain a desired uniformity and intensity distribution in its cross-section. The desired uniformity of the radiation beam B may be maintained by means of a uniformity compensator UC. The uniformity compensator UC comprises a number of adjustable protrusions (e.g. fingers) in the path of the radiation beam B to control the uniformity of the radiation beam B. A sensor ES may be used to monitor the uniformity of the radiation beam B.

[0055] Referring to Figure 1, a radiation beam B is incident on a patterning device (e.g. mask) MA, which is held on a support structure (e.g. mask table) MT, and is patterned by the patterning device MA. In the lithographic apparatus 100, the radiation beam B is reflected from the patterning device (e.g. mask) MA. After reflection from the patterning device (e.g. mask) MA, the radiation beam B passes through a projection system PS. The projection system PS focuses the radiation beam B onto a target portion C of a substrate W. The substrate table WT can be moved precisely (e.g. to position different target portions C in the path of the radiation beam B) by a second positioner PW and a position sensor IF2 (e.g. an interferometer device, a linear encoder or a capacitive sensor). Similarly, a first positioner PM and another position sensor IF1 may be used to accurately position the patterning device (e.g. mask) MA with respect to the path of the radiation beam B. The patterning device (e.g. mask) MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2.

[0056] Referring to FIG. 2 , a radiation beam B is incident on a patterning device (e.g. mask MA), which is held on a support structure (e.g. mask table MT), and is patterned by the patterning device. After passing through the mask MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. The projection system has a pupil PPU, which is conjugate with the illumination system pupil IPU. Portions of radiation originate from the intensity distribution at the illumination system pupil IPU, pass through the mask pattern without being affected by diffraction at the mask pattern, and generate an image of the intensity distribution at the illumination system pupil IPU. A desired uniformity of the radiation beam B can be maintained by controlling the uniformity of the radiation beam B using a uniformity compensator UC. A sensor ES may be used to monitor the uniformity of the radiation beam B.

[0057] The projection system PS projects an image MP' of the mask pattern MP, where the image MP' is formed on a photoresist layer coated on the substrate W by diffracted beams generated from the mask pattern MP by radiation from an intensity distribution. For example, the mask pattern MP may include an array of lines and spaces. Diffraction of radiation other than the zeroth diffraction order at this array generates redirected diffracted beams with a change of direction in a direction perpendicular to the lines. The non-diffracted beams (so-called zeroth diffraction order beams) cross the pattern without a change of propagation direction. The zeroth diffraction order beams reach the conjugate pupil PPU through an upper lens or an upper lens group of the projection system PS, which is upstream of the conjugate pupil PPU of the projection system PS. The part of the intensity distribution in the plane of the conjugate pupil PPU that is related to the zeroth diffraction order beams is an image of the intensity distribution in the illumination system pupil IPU of the illumination system IL. The aperture device PD is for example arranged in a plane containing the conjugate pupil PPU of the projection system PS or substantially in this plane.

[0058] The projection system PS is configured to capture not only the zeroth order diffracted beam, but also the first order diffracted beam, or the first and higher order diffracted beams (not shown) by means of a lens or lens group L. In an embodiment, the resolution enhancement effect of dipole illumination can be exploited by using dipole illumination to form an image of a line pattern extending in a direction perpendicular to the line. For example, a first order diffracted beam interferes with a corresponding zeroth order diffracted beam at the level of the wafer W to generate an image of the line pattern MP with the best possible resolution and process window (i.e., a combination of a usable depth of focus and an acceptable exposure dose deviation). In an embodiment, astigmatism can be reduced by providing a pole of radiation (not shown) in the opposite quadrant at the illumination system pupil IPU. Furthermore, in an embodiment, astigmatism can be reduced by blocking the zeroth order beam in the conjugate pupil PPU of the projection system associated with the pole of radiation in the opposite quadrant. This is described in detail in U.S. Pat. No. 7,511,799, issued Mar. 31, 2009, which is incorporated herein by reference in its entirety.

[0059] The substrate table WT can be moved accurately (e.g. to position different target portions C in the path of the radiation beam B) by means of the second positioner PW and a position sensor IF (e.g. an interferometer device, a linear encoder or a capacitive sensor). Similarly, the first positioner PM and a further position sensor (not shown in Fig. 2) may be used to accurately position the mask MA with respect to the path of the radiation beam B (e.g. during a scan or after mechanical retrieval from a mask library).

[0060] In general, movement of the mask table MT is realized by a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT is realized by a long-stroke module and a short-stroke module, which form part of the second positioner PW. In a stepper (as opposed to a scanner), the mask table MT may be connected to a short-stroke actuator only, or may be fixed. The mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks occupy dedicated target portions (as shown), the alignment marks may be located in spaces between the target portions (these are known as scribe-line alignment marks). Similarly, in a case where the mask MA is provided with more than one die, the mask alignment marks may be located between the dies.

[0061] The mask table MT and patterning device MA may be inside the vacuum vessel V. Here, an in-vacuum robot IVR may be used to move the patterning device, such as a mask, in and out of the vacuum vessel V. Alternatively, if the mask table MT and patterning device MA are outside the vacuum vessel, an ex-vacuum robot may be used for various transfer operations, similar to the in-vacuum robot IVR. Both in-vacuum and ex-vacuum robots need to be calibrated relative to fixed kinematic mounts of the transfer station for smooth transfer of any payload (e.g. a mask).

[0062] The lithographic apparatus 100, 100' can be used in at least one of the following modes.

[0063] 1. In step mode, the support structure (e.g. mask table) MT and substrate table WT are kept substantially stationary while the entire pattern imparted to the radiation beam B is projected onto the target portion C in one go (i.e. a single static exposure), and the substrate table WT is then moved in the X and / or Y direction so that a different target portion C can be exposed.

[0064] 2. In scan mode, the support structure (e.g. mask table) MT and the substrate table WT are scanned synchronously (i.e. a single dynamic exposure) while a pattern imparted to the radiation beam B is projected onto a target portion C. The velocity and direction of the substrate table WT relative to the support structure (e.g. mask table) MT is determined by the (de-)magnification and image reversal characteristics of the projection system PS.

[0065] 3. In another mode, the support structure (e.g. mask table) MT holds a programmable patterning device and is held substantially stationary, while the substrate table WT is moved or scanned, while a pattern imparted to the radiation beam B is projected onto a target portion C. A pulsed radiation source SO is used, and the programmable patterning device is updated as required each time the substrate table WT is moved, or between successive pulses during a scan. This mode of operation is readily applicable to maskless lithography using a programmable patterning device such as a programmable mirror array.

[0066] The above-mentioned usage modes may be combined, or a usage mode may be modified, or even a completely different usage mode may be used.

[0067] Exemplary Energy Sensor

[0068] FIG. 3 is a schematic diagram of an energy sensor ES according to an embodiment. In an embodiment, the energy sensor ES is a key component of the dose control subsystem of the illumination system IL and is configured to provide a measurement of a radiation beam B, such as a DUV radiation beam. The energy sensor ES may be located at a midpoint of the illumination optical train. A small portion (e.g., about 1%) of the radiation beam B, i.e., the DUV radiation beam 310 as shown in FIG. 3, may be split off and sent into a housing 320 of the energy sensor ES. In one example, the DUV radiation beam 310 may be a 193 nm excimer laser radiation beam. The DUV radiation beam 310 may then be focused onto a detector module 330 by a mirror 322 and a lens 324.

[0069] As shown in FIG. 4, in the existing energy sensor ES, the detector module 330 includes two sandwiched thin disk-shaped crystals 410 configured to absorb and convert a portion of the DUV radiation beam 310 into longer wavelength radiation. In an embodiment, the crystals 410 can be sapphire crystals that can convert the DUV radiation into fluorescent radiation 420, such as visible light or infrared radiation IR. The fluorescent radiation 420 born in the central region of the crystals 410 exposed to the DUV radiation beam 310 propagates inside each crystal 410 to its edge by total internal reflection. The fluorescent radiation 420 can be detected by a number of photodetectors 430, such as Si diodes.

[0070] Multiple photodetectors 430 can be placed along the periphery of the crystal to homogenize the fluorescence radiation and increase the useful signal. However, collection of the fluorescence radiation 420 by multiple photodetectors 430 is ineffective. As shown in FIG. 4, the fluorescence radiation 420 propagates from the center to the edge of the disk-shaped crystal 410, bouncing multiple times off both surfaces. Assuming that the surface of the crystal 410 is ideally polished and flat, the rays of fluorescence light that make an angle with the surface that exceeds the angle of total internal reflection will reach the edge of the crystal 410 intact. At the edge, the fluorescence radiation 420 will escape by scattering, and only a small portion will be picked up by the photodetector 430. The collection efficiency of the fluorescence light in such a configuration is relatively low, and the amount of fluorescence collected depends on the quality of the edge of the crystal 410. Therefore, the present disclosure provides a new design of a detector module that can increase the collection efficiency of the fluorescence light.

[0071] Referring to Figures 5 to 8, Figure 5 shows a schematic cross-sectional view of an exemplary detector module 500 of an energy sensor according to an embodiment, Figure 6 shows a schematic exploded oblique view of the exemplary detector module 500 of Figure 5 according to an embodiment, Figure 7 shows a schematic cross-sectional view of a conversion crystal and multiple photodetectors of the detector module 500 of Figure 5, and Figure 8 shows a schematic top view of the conversion crystal and multiple photodetectors of the exemplary detector module 500 of Figure 5.

[0072] 5, the detector module 500 can include a purge cap 510 and a crystal housing 520. A purge channel 515 can be formed in the purge cap 510 or between the purge cap 510 and the crystal housing 520. A conversion crystal 540 can be disposed in the crystal housing 520.

[0073] In an embodiment, the conversion crystal 540 may be a disk-shaped crystal having a distribution of fluorescent impurities. The conversion crystal 540 may be any crystal having any fluorescent impurities, which may be selectively doped as required to enhance the response to various wavelengths of the incident beam of ultraviolet radiation. For example, the crystal may be a sapphire crystal. The fluorescent impurities may include undoped oxide crystals and / or rare earth doped crystals. In one example, Ce 3+ :Y3AL5O 12 Rare earth doped garnets such as YAG may be used as fluorescent dopants. Rare earth doped garnets may also include other rare earth elements such as neodymium (Nd), lanthanum (La), and europium (Eu). In an embodiment, conversion crystal 540 may be a titanium doped sapphire crystal.

[0074] The conversion crystal 540 can be positioned such that a center of the conversion crystal 540 can be exposed to the DUV radiation beam 310, as shown in Figure 6. The conversion crystal 540 can convert the DUV radiation beam 310 into fluorescent radiation 420 depending on and in proportion to the power of the DUV radiation beam 310. In an embodiment, a slow crystal may not be suitable for the conversion crystal 540, since the fluorescence lifetime is short, e.g., less than 5 microseconds, and the E-sensor must detect each pulse of the laser and the frequency at which the E-sensor detects is at a frequency of 6 kHz.

[0075] The multiple photodetectors 550 may be mounted on a ring-shaped spacer 533 mounted on the insulator 531 and are configured to measure the intensity of the scattered portion of the fluorescent radiation 420. In an embodiment, the multiple photodetectors 550 may be equally spaced around the ring-shaped spacer 533 and thus around the annular periphery of the conversion crystal 540. Based on the measurements of the multiple photodetectors 550, the power of the DUV radiation beam 310 may be determined and also the power of the radiation beam B as shown in Figures 1 and 2. In this way, the calibration of the pulsed radiation source SO may be ensured and, if desired, adjusted.

[0076] Further, in an embodiment, the light dump 560, or alternatively the light dump 560, may comprise a mirror located at the center of the ring-shaped spacer 533 and may be configured to send the transmitted UV radiation 565 back to the conversion crystal 540 to increase the amount of fluorescent radiation 420 converted from the UV radiation.

[0077] In an embodiment, as shown in FIG. 7, the purge cap 510 can be fixed on the crystal housing 520 by fasteners 610, such as clips or screws. A first sealing O-ring 622, a number of springs 624, and a crystal spring holder 626 can be disposed between the purge cap 510 and the insulator 531. The photodetector 550 can be attached to the bottom of the ring-shaped spacer 533. A second sealing O-ring 631 and a centering O-ring 633 can be disposed between the conversion crystal 540 and the crystal housing 520. A number of springs 624 can secure the multiple parts between the purge cap 510 and the crystal housing 520.

[0078] As shown in FIG. 6, a portion of the surface of the conversion crystal 540 near the annular periphery of the conversion crystal 540 on which the multiple photodetectors 550 are disposed can be treated to form a diffusive surface 545. The diffusive surface 545 can be formed, for example, by matte polishing, metallization, or other suitable treatment. The diffusive surface 545 can scatter the fluorescent radiation 420 and thus function as a total internal reflection breaker. The fluorescent radiation 420 scattered by the diffusive surface 545 can reach the multiple photodetectors 550 and significantly increase the intensity of the signal detected by the multiple photodetectors 550. Thus, a single conversion crystal 540 can provide a sufficient amount of fluorescent radiation 420 to be collected by the multiple photodetectors 550.

[0079] In an embodiment, the diffusing surface 545 may have a ring shape, as shown in FIG. 8. In an alternative embodiment, the diffusing surface 545 may have a discontinuous ring shape (not shown). That is, the diffusing surface 545 includes multiple segments, each of which is arranged corresponding to a photodetector 550. The polished surfaces of the conversion crystal 540 between the multiple segments of the diffusing surface 545 may participate in further light mixing by total internal reflection. Thus, such an arrangement may further reduce the depletion of the scattered fluorescent radiation 420, thereby further increasing the fluorescent light collection efficiency of the multiple photodetectors 550.

[0080] In an embodiment, the diffusing surface 545 may be located on a distal side of the conversion crystal 540, opposite the multiple photodetectors 550, as shown in Figure 6. In other embodiments, the diffusing surface 545 may be located on a proximal side of the conversion crystal 540, closer to the multiple photodetectors 550.

[0081] 9 and 10, schematic cross-sectional views of a conversion crystal and multiple photodetectors of an exemplary detector module are shown according to another embodiment.

[0082] 9, in other embodiments, two diffusing surfaces 545 can be formed on either side of the conversion crystal 540. A first diffusing surface can be located on a distal side of the conversion crystal 540 opposite the multiple photodetectors 550, and a second diffusing surface can be located on a proximal side of the conversion crystal 540 closer to the multiple photodetectors 550.

[0083] In an alternative embodiment, the diffusing surface 545 may include impurities (also referred to as scattering particles) embedded in a portion of the conversion crystal 540 corresponding to the multiple photodetectors 550. In an embodiment, the conversion crystal 540 may be layered and the impurities may be isolated to a layer of the conversion crystal. The layer may be sandwiched between layers of crystal that do not include impurities, may be located at the top or bottom layer, or may be in other configurations (e.g., multiple isolated layers with scattering particles), as long as sufficient reflection is achieved for efficient detection of the fluorescent emission 420 by the multiple photodetectors 550.

[0084] 10, in other embodiments, multiple photodetectors 550 can be positioned around the annular periphery of the conversion crystal 540. A diffusing surface 545 can cover the annular periphery of the conversion crystal 540 and corners to either side of the conversion crystal 540.

[0085] In an embodiment, any other suitable configuration can be used to further increase the fluorescent light collection efficiency of the multiple photodetectors 550. For example, a reflective coating can be formed on the diffusing surface 545 to increase the light scattering effect. As another example, the multiple photodetectors 550 can be positioned at an angle to the surface of the conversion crystal 540 to optimize the collection efficiency of the fluorescent light.

[0086] In this way, by increasing the collection efficiency of the fluorescent light, the disclosed energy sensor ES switches from the existing two crystal design to a single crystal design that produces a stronger signal (e.g., 30% stronger or more).The disclosed energy sensor ES therefore provides a more robust and reproducible system for collecting fluorescent light in an ultraviolet radiation control system of a lithography apparatus, thereby ensuring precise control of the ultraviolet radiation and at the same time reducing the manufacturing costs of the ultraviolet radiation control system of the lithography apparatus.

[0087] In an embodiment, the disclosed ultraviolet radiation control system comprises a housing, a conversion crystal disposed on or within the housing and configured to convert ultraviolet radiation into fluorescent radiation, a plurality of photodetectors configured to detect an intensity of a scattered portion of the fluorescent radiation, and at least one diffusing surface disposed on or within the conversion crystal and configured to increase the intensity of the scattered portion of the fluorescent radiation.

[0088] In an embodiment, the at least one diffusive surface is disposed in spatial proximity to the multiple photodetectors.

[0089] In an embodiment, the ultraviolet radiation control system comprises only a single conversion crystal.

[0090] In an embodiment, the conversion crystal has a disk shape and the multiple photodetectors are equally spaced around an annular periphery of the conversion crystal.

[0091] In an embodiment, at least one diffusing surface has a ring shape.

[0092] In an embodiment, the at least one diffusive surface comprises a plurality of segments arranged in a discontinuous ring shape, each of the plurality of segments being positioned adjacent a predetermined one of the plurality of photodetectors.

[0093] In an embodiment, the plurality of photodetectors are disposed on a first side of the conversion crystal and the at least one diffusive surface is disposed on a second side of the conversion crystal opposite the first side.

[0094] In an embodiment, the plurality of photodetectors are disposed on a first side of the conversion crystal and the at least one diffusive surface is disposed on the first side of the conversion crystal.

[0095] In an embodiment, the multiple photodetectors are disposed on a first side of the conversion crystal, and the at least one diffusing surface comprises a first diffusing surface disposed on the first side of the conversion crystal and a second diffusing surface disposed on a second side of the conversion crystal opposite the first side.

[0096] In an embodiment, the plurality of photodetectors are disposed around an annular periphery of the conversion crystal, and the at least one diffusive surface is disposed on the annular periphery of the conversion crystal.

[0097] In an embodiment, the ultraviolet radiation is deep ultraviolet radiation.

[0098] In an embodiment, the ultraviolet radiation is a beam split from a 193 nm excimer pulsed laser.

[0099] In an embodiment, the multiple photodetectors are disposed on a ring-shaped spacer that is disposed on an insulator.

[0100] In an embodiment, the ultraviolet radiation control system further comprises a light dump or mirror disposed at the center of the ring-shaped spacer and configured to reflect a portion of the ultraviolet radiation transmitted through the conversion crystal back to the conversion crystal to increase the amount of fluorescent radiation converted from the ultraviolet radiation.

[0101] In an embodiment, the housing is configured to protect the conversion crystal and the plurality of photodetectors. The ultraviolet radiation control system further comprises a purge cap secured to the housing and a purge channel disposed within the purge cap or between the housing and the purge cap.

[0102] In an embodiment, the ultraviolet radiation control system further comprises a first seal disposed between the purge cap and the insulator, a plurality of springs, and a crystal spring holder.

[0103] In an embodiment, the ultraviolet radiation control system further comprises a second seal and centering O-ring disposed between the conversion crystal and the crystal housing.

[0104] In an embodiment, the at least one diffusive surface comprises an impurity embedded in a layer of conversion crystal configured to scatter the fluorescent radiation.

[0105] Another aspect of the present disclosure provides a lithographic apparatus comprising the disclosed ultraviolet radiation control system.

[0106] Another aspect of the present disclosure provides a method of measuring ultraviolet radiation, the method comprising using a conversion crystal to convert a branched portion of the ultraviolet radiation into fluorescent radiation, using at least one diffusive surface disposed on or within the conversion crystal to scatter the fluorescent radiation, and using a plurality of photodetectors to measure an intensity of the scattered fluorescent radiation.

[0107] Other aspects of the invention are described in the following numbered paragraphs: 1. Housing and a conversion crystal disposed on or within the housing and configured to convert ultraviolet radiation into fluorescent radiation; a plurality of photodetectors configured to detect intensities of scattered portions of the fluorescent radiation; and at least one diffusing surface disposed on or within the conversion crystal and configured to increase an intensity of a scattered portion of the fluorescent radiation. 2. The ultraviolet radiation control system described in item 1, wherein the at least one diffusive surface is positioned in spatial proximity to the multiple photodetectors. 3. The ultraviolet radiation control system of item 1, comprising only a single conversion crystal. 4. The conversion crystal has a disk shape; Item 3. The ultraviolet radiation control system of item 2, wherein the plurality of photodetectors are equally spaced around an annular periphery of the conversion crystal. 5. The ultraviolet radiation control system of claim 4, wherein the at least one diffusing surface has a ring shape. 6. The ultraviolet radiation control system described in paragraph 4, wherein the at least one diffusive surface comprises a plurality of segments arranged in a discontinuous ring shape, each of the plurality of segments being positioned adjacent to a predetermined one of the plurality of photodetectors. 7. The plurality of photodetectors are disposed on a first side of the conversion crystal; Item 5. The ultraviolet radiation control system of item 4, wherein the at least one diffusive surface is disposed on a second side of the conversion crystal opposite the first side. 8. The plurality of photodetectors are disposed on a first side of the conversion crystal; Item 5. The ultraviolet radiation control system of item 4, wherein the at least one diffusive surface is disposed on the first side of the conversion crystal. 9. The plurality of photodetectors are disposed on a first side of the conversion crystal; 5. The ultraviolet radiation control system of claim 4, wherein the at least one diffusing surface comprises a first diffusing surface disposed on the first side of the conversion crystal, and a second diffusing surface disposed on a second side of the conversion crystal opposite the first side. 10. The plurality of photodetectors are arranged to surround the annular outer periphery of the conversion crystal; Item 5. The ultraviolet radiation control system of item 4, wherein the at least one diffusive surface is disposed on the annular outer periphery of the conversion crystal. 11. The ultraviolet radiation control system described in item 1, wherein the ultraviolet radiation is deep ultraviolet radiation. 12. The ultraviolet radiation control system described in item 11, wherein the ultraviolet radiation is a beam branched from a 193 nm excimer pulse laser. 13. The ultraviolet radiation control system described in item 1, wherein the multiple photodetectors are arranged on a ring-shaped spacer arranged on an insulator. 14. The ultraviolet radiation control system described in item 13, further comprising an optical dump or mirror disposed at the center of the ring-shaped spacer and configured to reflect a portion of the ultraviolet radiation transmitted through the conversion crystal back to the conversion crystal to increase the amount of fluorescent radiation converted from the ultraviolet radiation. 15. The housing is configured to protect the conversion crystal and the plurality of photodetectors; The system comprises: a purge cap secured to the housing; Item 14. The ultraviolet radiation control system of item 13, further comprising a purge channel disposed within the purge cap or between the housing and the purge cap. 16. The ultraviolet radiation control system of claim 15, further comprising a first seal, a plurality of springs, and a crystal spring holder disposed between the purge cap and the insulator. 17. The ultraviolet radiation control system of claim 16, further comprising a second seal and centering O-ring disposed between the conversion crystal and the crystal housing. 18. The ultraviolet radiation control system of claim 1, wherein the at least one diffusive surface includes an impurity embedded in a layer of the conversion crystal configured to scatter the fluorescent radiation. 19. A lithographic apparatus comprising an ultraviolet radiation control system according to clause 1. 20. A method for measuring ultraviolet radiation comprising the steps of: using a conversion crystal to convert the branched portion of the ultraviolet radiation into fluorescent radiation; using at least one diffusive surface disposed on or within the conversion crystal to scatter the fluorescent radiation; using a plurality of photodetectors to measure the intensity of the scattered fluorescent radiation.

[0108] Although specific reference may be made herein to the use of lithography apparatus in the manufacture of ICs, it is to be understood that the lithography apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, LCDs, thin film magnetic heads, and the like. In these other applications, one skilled in the art will appreciate that the terms "wafer" or "die" herein are to be considered synonymous with the more general terms "substrate" or "target portion", respectively. Substrates referred to herein may be processed, before or after exposure, for example, in a track unit (a device that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology unit, and / or an inspection unit. Where applicable, the disclosure herein may also be applied to these or other substrate processing apparatus. A substrate may also be processed multiple times, for example to manufacture a multi-layer IC, in which case the term substrate herein may refer to a substrate that already includes multiple layers that have been processed.

[0109] Although specific reference may be made above to the use of embodiments of the invention in optical lithography, it will be appreciated that, where the context permits, the invention is not limited to optical lithography but may be used in other applications such as, for example, imprint lithography. In imprint lithography, the topography of a patterning device defines the pattern created on a substrate. The topography of the patterning device is pressed into a layer of resist supplied to the substrate and the resist is subsequently cured by means of electromagnetic radiation, heat, pressure or a combination thereof. When the patterning device is moved away from the resist, a pattern is left in the hardened resist.

[0110] The language or terminology of the present disclosure is for the purpose of description rather than limitation and should be interpreted by one of ordinary skill in the relevant art in light of the teachings herein.

[0111] The terms "illumination conditioner," "radiation correction system," and the like may be used herein to describe an apparatus that adjusts one or more characteristics of a beam of radiation. For example, a uniformity correction system may be referred to as an illumination conditioner.

[0112] Additionally, the terms "radiation," "beam," "light," "illumination," and the like, as used herein, may encompass any electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength λ of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm), extreme ultraviolet (EUV or soft x-ray) radiation (e.g., having a wavelength in the range of 5 to 20 nm, e.g., 13.5 nm), or hard x-ray operating below 5 nm, as well as particle beams such as ion beams or electron beams. Generally, radiation having a wavelength between about 400 and about 700 nm is considered visible radiation, and radiation having a wavelength between about 780 and 3000 nm (or greater) is considered infrared radiation. UV refers to radiation having a wavelength between approximately 100 and 400 nm. In lithography, the term "UV" is also used to refer to wavelengths that can be produced by mercury discharge lamps, namely G-line at 436 nm, H-line at 405 nm, and I-line at 365 nm. Vacuum UV or VUV (i.e. UV absorbed by gases) refers to radiation having a wavelength of approximately 100-200 nm. Deep UV (DUV) generally refers to radiation having a wavelength of about 126 nm to about 428 nm. In an embodiment, an excimer laser can generate DUV radiation for use in a lithography tool. It should be understood that radiation having a wavelength within the range of, for example, 5-20 nm, refers to radiation having a wavelength range that is at least a portion of the 5-20 nm range.

[0113] As used herein, the term "substrate" describes a material to which layers of material have been added. In embodiments, the substrate itself may be patterned and the materials added thereon may also be patterned, or may remain unpatterned.

[0114] Although specific reference may be made herein to the use of the apparatus and / or system according to the present invention in the manufacture of ICs, it should be understood that such apparatus and / or systems may have many other applications, such as, for example, the manufacture of integrated optical systems, guide and detection patterns for magnetic domain memories, LCD panels, thin film magnetic heads, etc. Those skilled in the art will appreciate that in the context of these alternative applications, the terms "reticle," "wafer," or "die" herein may be considered to be replaced by the more general terms "mask," "substrate," and "target portion," respectively.

[0115] While specific embodiments of the invention have been described above, the invention may be practiced otherwise than as described, and this description is not intended to limit the invention.

[0116] It should be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections describe one or more embodiments contemplated by the inventor, but do not describe every exemplary embodiment, and thus are not intended to limit the scope of the invention and the appended claims in any manner.

[0117] In the above, the present invention is described using functional blocks showing implementation of specific functions and their relationships. The boundaries of these functional blocks are arbitrarily defined in this document for the convenience of description. Alternative boundaries may be defined as long as the specific functions and their relationships are appropriately performed.

[0118] The above description of the specific embodiments fully discloses the general nature of the present invention, and thus, by applying the knowledge of those skilled in the art, these specific embodiments can be readily modified and / or adapted to various applications without undue experimentation and without departing from the general concept of the present invention. Accordingly, such modifications and adaptations are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein.

[0119] The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. Housing and a single conversion crystal disposed on or within the housing and configured to convert ultraviolet radiation into fluorescent radiation; a plurality of photodetectors configured to detect intensities of scattered portions of the fluorescent radiation; at least one diffusing surface disposed on or within the conversion crystal and configured to increase an intensity of a scattered portion of the fluorescent radiation; the at least one diffusive surface is disposed in spatial proximity to the plurality of photodetectors; the conversion crystal has a disk shape, the center of which is exposed to the ultraviolet radiation; The plurality of photodetectors are spaced apart about an annular periphery of the conversion crystal.

2. The ultraviolet radiation control system of claim 1 , wherein the at least one diffusing surface has a ring shape.

3. 2. The ultraviolet radiation control system of claim 1, wherein the at least one diffusing surface comprises a plurality of segments arranged in a discontinuous ring shape, each of the plurality of segments being positioned adjacent a predetermined one of the plurality of photodetectors.

4. the plurality of photodetectors are disposed on a first side of the conversion crystal; 2. The ultraviolet radiation control system of claim 1, wherein the at least one diffusive surface is disposed on a second side of the conversion crystal opposite the first side.

5. the plurality of photodetectors are disposed on a first side of the conversion crystal; The ultraviolet radiation control system of claim 1 , wherein the at least one diffusive surface is disposed on the first side of the conversion crystal.

6. the plurality of photodetectors are disposed on a first side of the conversion crystal; 2. The ultraviolet radiation control system of claim 1, wherein the at least one diffusing surface comprises a first diffusing surface disposed on the first side of the conversion crystal and a second diffusing surface disposed on a second side of the conversion crystal opposite the first side.

7. the plurality of photodetectors are arranged to surround the annular periphery of the conversion crystal; The ultraviolet radiation control system of claim 1 , wherein the at least one diffusive surface is disposed on the annular periphery of the conversion crystal.

8. 8. The ultraviolet radiation control system of claim 1, wherein the ultraviolet radiation is deep ultraviolet radiation.

9. 9. The ultraviolet radiation control system of claim 8, wherein the ultraviolet radiation is a beam branched from a 193 nm excimer pulsed laser.

10. 10. The ultraviolet radiation control system of claim 1, wherein the plurality of photodetectors are arranged on a ring-shaped spacer disposed on an insulator.

11. 11. The ultraviolet radiation control system of claim 10, further comprising a light dump or mirror disposed at the center of the ring-shaped spacer and configured to reflect a portion of the ultraviolet radiation transmitted through the conversion crystal back to the conversion crystal to increase the amount of fluorescent radiation converted from the ultraviolet radiation.

12. the housing is configured to protect the conversion crystal and the plurality of photodetectors; The system comprises: a purge cap secured to the housing; 12. The ultraviolet radiation control system of claim 10 or 11, further comprising a purge channel disposed within the purge cap or between the housing and the purge cap.

13. 13. The ultraviolet radiation control system of claim 12, further comprising a first seal, a plurality of springs, and a crystal spring holder disposed between the purge cap and the insulator.

14. 14. The ultraviolet radiation control system of claim 13, further comprising a second seal and centering O-ring disposed between the conversion crystal and a crystal housing.

15. 15. The ultraviolet radiation control system of claim 1, wherein the at least one diffusive surface comprises an impurity embedded in a layer of the conversion crystal configured to scatter the fluorescent radiation.

16. A lithographic apparatus comprising an ultraviolet radiation control system according to any one of the preceding claims.

17. 1. A method for measuring ultraviolet radiation, comprising: using a single conversion crystal to convert a branched portion of said ultraviolet radiation into fluorescent radiation; using a plurality of photodetectors to detect intensities of scattered portions of said fluorescent radiation; using at least one diffusing surface disposed on or within the conversion crystal to increase the intensity of the scattered portion of the fluorescent radiation; the at least one diffusive surface is disposed in spatial proximity to the plurality of photodetectors; the conversion crystal has a disk shape, the center of which is exposed to the ultraviolet radiation; The method wherein the plurality of photodetectors are spaced apart about an annular periphery of the conversion crystal.

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