Cleaning procedures for photomasks and the apparatus therefor

Abstract

Method for cleaning a photomask (12), comprising: placing the photomask (12) on a support such that a structured surface of the photomask (12) is facing downwards; and applying an adhesive sheet (22) to edges of a rear surface of the photomask (12), wherein the adhesive sheet (22) is attached to a flat main face of a cuboid body (24, 24A-B).

Description

BACKGROUND A lithographic apparatus projects a structure from a structuring device (e.g., a photomask) onto a layer of radiation-sensitive material (resist) provided on the semiconductor substrate. When a photomask is not in use (stored) or being transferred from storage to a lithographic apparatus such as a stepper or scanner, it is appropriately protected from contaminants such as dust or particles by being housed in a mask casing (pod, capsule). US 2015 / 0241797 A1 discloses methods and systems for removing contaminants from the surface of an object in a lithographic apparatus. US 2009 / 0277810 A1 discloses a semiconductor reticle transport container. The invention is defined in the claims. BRIEF DESCRIPTION OF THE DRAWINGS Aspects of the present disclosure are best understood with reference to the following detailed description in conjunction with the accompanying drawings. It should be noted that, in accordance with industry practice, various features are not shown to scale. In fact, the dimensions of the various features may have been arbitrarily enlarged or reduced for the sake of clarity. Fig. 1 is a schematic view of an extreme ultraviolet lithography system with an LPP-EUV radiation source, constructed according to some embodiments of the present disclosure. Fig. 2 is a schematic view of an exposure tool for an EUV lithography system according to embodiments of the disclosure. Fig. 3 is a schematic cross-sectional view of a mask capsule device. Fig. 4 shows a configuration of the mask capsule device's support supports.Figure 5 shows a configuration in which a photomask is in contact with the support supports. Figure 6 shows a configuration of a cleaning device and a cleaning process according to an embodiment of the disclosure. Figure 7 shows a configuration of a cleaning device and a cleaning process according to an embodiment of the disclosure. Figure 8 shows a configuration of a cleaning device and a cleaning process according to an embodiment of the disclosure. Figure 9 shows a configuration of a cleaning device according to an embodiment of the disclosure. Figure 10 shows a configuration of a cleaning device and a cleaning process according to an embodiment of the disclosure. Figure 11 shows a configuration of a cleaning device and a cleaning process according to an embodiment of the disclosure. Figure 12 shows a manual cleaning process according to an embodiment of the disclosure. Figures 13A and 13B show...Figure 13B shows process flows for cleaning an EUV photomask according to embodiments of the present disclosure. DETAILED DESCRIPTION It is understood that the following disclosure provides many different embodiments and examples for the implementation of various features of the invention. To simplify the present disclosure, certain embodiments or examples of components and arrangements are described below. For example, the dimensions of the elements are not limited to the disclosed range or values, but may depend on the process conditions and / or the desired properties of the device. Furthermore, the formation of a first feature above or on top of a second feature in the following description may include embodiments in which the first and second features are in direct contact, but may also include embodiments in which additional features may be formed between the first and second features, so that the first and second features are not in direct contact.For the sake of simplicity and clarity, various features may be drawn arbitrarily at different scales. Some layers / features may be omitted from the accompanying drawings for simplification. Furthermore, to simplify the description, spatially relative terms such as "below," "down," "over," "above," "up," and the like may be used to describe the relationship of one element or feature to another, as shown in the drawings. These spatially relative terms are intended to encompass various orientations of the device during use or operation, in addition to the orientation shown in the drawings. The device may be oriented differently (rotated by 90 degrees or in other orientations), and the spatially relative terms used here may be interpreted accordingly. Furthermore, the term "formed of" may mean either "comprising" or "consisting of." Additionally, the following manufacturing process may include one or more additional operations between the operations described, and the sequence of operations may be modified.In the present disclosure, the phrase "at least one of A, B and C" means either one of A, B, C, A+B, A+C, B+C or A+B+C and does not mean one of A, one of B and one of C, unless otherwise specified. Materials, configurations, dimensions and / or processes described with reference to one embodiment may be applied to other embodiments and a detailed explanation thereof may be omitted. The present disclosure relates generally to an EUV lithography system and EUV lithography method. The embodiments disclosed herein relate to an improved method and an improved apparatus for cleaning an EUV photomask. The need for protection against particles (i.e., dust, dirt, etc.) that contaminate objects is required in many applications, including semiconductor manufacturing applications such as extreme ultraviolet lithography. A lithographic apparatus projects a structure from a patterning device (e.g., a photomask or reticulum) onto a layer of radiation-sensitive material (resist) provided on the semiconductor substrate. The wavelength of the radiation used by a lithographic apparatus to project a structure onto a substrate determines the minimum size of features that can be formed on that substrate. A lithographic apparatus that uses extreme ultraviolet radiation, i.e.,Electromagnetic radiation with a wavelength in the range of 4 to 20 nm can be used to form smaller features on a substrate than a related lithographic apparatus (which can use electromagnetic radiation with a wavelength of 193 nm, for example). The structuring device (photomask or reticulum) is protected from particle contamination by a pellicle. The pellicle is positioned at a distance from the structuring device and lies outside the focal plane of the lithographic apparatus. Because the pellicle is located outside the focal plane of the lithographic apparatus, any contaminant particles landing on the pellicle are out of focus. Consequently, the images of the contaminant particles are not projected onto the substrate. Without the pellicle, a contaminant particle landing on the structuring device would be projected onto the substrate and introduce a defect into the projected structure. The photomask, with or without a pellicle, is stored in a mask capsule device, and the mask capsule device is stored in a photomask library (storage or memory) when not in use and transferred from the photomask library to an EUV lithography apparatus (e.g., an EUV scanner). In the present disclosure, the terms mask, photomask, and reticule are used interchangeably. Furthermore, the terms resist and photoresist are used interchangeably. In some embodiments, the mask is a reflective mask. Fig. 1 shows a schematic view of an EUV lithography system with an LPP-EUV radiation source (laser-generated plasma EUV radiation source) according to some embodiments of the present disclosure. The EUV lithography system comprises an EUV radiation source 100 (an EUV light source) for generating EUV radiation, an exposure device 200, such as a scanner, and an excitation laser source 300. As shown in Fig. 1, in some embodiments the EUV radiation source 100 and the exposure device 200 are installed on a main floor MF of a cleanroom, with the excitation laser source 300 being installed in a base floor BF located beneath the main floor. The EUV radiation source 100 and the exposure device 200 are mounted via dampers DMP1 and DMP2 on base plates PP1 and PP2.The EUV radiation source 100 and the exposure device 200 are coupled to each other via a coupling mechanism, which may include a focusing unit. In some embodiments, a lithography system comprises the EUV radiation source 100 and the exposure device 200. In a particular example, the EUV radiation source 100 generates EUV light with a wavelength centered at approximately 13.5 nm. In the present embodiment, the EUV radiation source 100 utilizes a laser-generated plasma (LPP) mechanism to generate the EUV radiation. The exposure device 200 comprises various reflective optical components, such as convex / concave / plane mirrors, a mask holding mechanism comprising a mask stage, and a wafer holding mechanism, such as a substrate holding mechanism. The EUV radiation generated by the EUV radiation source 100 is directed by the reflective optical components onto a mask mounted on the mask stage. In some embodiments, the mask stage includes an electrostatic chuck (E-chuck) for securing the mask. Since gas molecules absorb EUV light, the lithography system for EUV lithography structuring is maintained in a vacuum or low-pressure environment to avoid EUV intensity loss. The exposure device 200 is described in detail with reference to Fig. 2. In some embodiments, a reticule is transported into the exposure device 200.As mentioned above, the exposure device 200 is held in a vacuum environment, and the reticle is mounted over a substrate, the substrate being a photoresist layer. The reticle includes a pellicle mounted over it. After the reticle and pellicle are transported into the exposure device 200, the air pressure in the enclosure between the reticle and the pellicle is equalized to the vacuum environment of the exposure device 200 through the holes in the mounting bracket (the frame). The EUV radiation generated by the EUV radiation source 100 is directed through the optical components to project the mask onto the photoresist layer of the substrate. In some embodiments, after exposure of the mask onto the photoresist layer of the substrate, the reticle and pellicle are transported out of the exposure device 200.After the reticulum with the pellicle has been transported out of the exposure device 200, the air pressure in the enclosure between the reticulum and the pellicle is equalized to the atmospheric pressure outside the exposure device 200 through the holes in the mounting bracket. The exposure device 200 comprises a projection optics module for imaging the structure of the mask onto a semiconductor substrate with a resist coated thereon, which is mounted on a substrate stage of the exposure device 200. The projection optics module generally comprises reflective optics. The EUV radiation (EUV light) emitted from the mask, carrying the image of the structure defined on the mask, is captured by the projection optics module, thereby forming an image on the resist. As shown in Fig. 1, the EUV radiation source 100 comprises a droplet generator 115 and an LPP collector mirror 110 enclosed in a chamber 105. The droplet generator 115 produces several target droplets DP, which are fed into the chamber 105 through a nozzle 117. In some embodiments, the target droplets DP are tin (Sn), lithium (Li), or an alloy of Sn and Li. In some embodiments, the target droplets DP each have a diameter in the range of about 10 micrometers (µm) to about 100 µm. In one embodiment, for example, the target droplets DP are tin droplets, each with a diameter of about 10 µm, about 25 µm, about 50 µm, or any diameter between these values. In some embodiments, the target droplets DP are ejected through the nozzle 117 at a rate ranging from about 50 droplets per second (i.e., an ejection frequency of about 50 Hz) to about 50,000 droplets per second (i.e.,at an ejection frequency of approximately 50 kHz). In one embodiment, the target droplets DP are supplied, for example, at an ejection frequency of approximately 50 Hz, approximately 100 Hz, approximately 500 Hz, approximately 1 kHz, approximately 10 kHz, approximately 25 kHz, approximately 50 kHz, or any ejection frequency between these frequencies. In various embodiments, the target droplets DP are ejected through the nozzle 117 and into an excitation zone ZE (e.g., a target droplet position) at a speed of approximately 10 meters per second (m / s) to approximately 100 m / s. For example, in one embodiment, the target droplets DP have a speed of approximately 10 m / s, approximately 25 m / s, approximately 50 m / s, approximately 75 m / s, approximately 100 m / s, or any speed between these speeds. The excitation laser beam LR2, generated by the excitation laser source 300, is a pulsed beam. The laser pulses of the laser beam LR2 are generated by the excitation laser source 300. The excitation laser source 300 can comprise a laser generator 310, laser guidance optics 320, and a focusing apparatus 330. In some embodiments, the laser generator 310 comprises a carbon dioxide (CO2) or neodymium-doped yttrium aluminum garnet (Nd:YAG) laser source with a wavelength in the infrared region of the electromagnetic spectrum. For example, in one embodiment, the laser source 310 has a wavelength of 9.4 µm or 10.6 µm. The laser light beam LR0, which is generated by the excitation laser source 300, is guided through the laser guidance optics 320 and focused by the focusing apparatus 330 into the excitation laser beam LR2, which is introduced into the EUV radiation source 100.In some embodiments, the laser beam LR2 is generated, in addition to CO2 and Nd:YAG lasers, by a gas laser including an excimer gas discharge laser, helium-neon laser, nitrogen laser, transversely excited atmospheric (TEA) laser, argon-ion laser, copper vapor laser, KrF laser or ArF laser, or a solid-state laser including an Nd:glass laser, ytterbium-doped glass or ceramic laser or ruby ​​laser. In some embodiments, a non-ionizing laser beam LR1 is also generated by the excitation laser source 300 and the laser beam LR1 is also focused by the focusing apparatus 330. In some embodiments, the excitation laser beam LR2 comprises a preheating laser pulse and a main laser pulse. In such embodiments, the preheating laser pulse (hereafter referred to interchangeably as the "prepulse") is used to heat (or preheat) a specific target droplet to create a low-density target plume with multiple smaller droplets, which is subsequently heated (or reheated) by a pulse of the main laser (main pulse), thereby producing an increased emission of EUV light compared to when no preheating laser pulse is used. In various embodiments, the preheating laser pulses have a spot size of approximately 100 µm or less, and the main laser pulses have a spot size of approximately 150 µm to approximately 300 µm. In some embodiments, the preheating laser and the main laser pulses have a pulse duration of approximately 10 ns to approximately 50 ns and a pulse frequency of approximately 1 kHz to approximately 100 kHz. In various embodiments, the preheating laser and the main laser have an average power of approximately 1 kilowatt (kW) to approximately 50 kW. In one embodiment, the pulse frequency of the excitation laser beam LR2 is matched to the ejection frequency of the target droplets DP. The laser beam LR2 is guided through windows (or lenses) into the excitation zone ZE. The windows employ a suitable material that is essentially transparent to the laser beams. The generation of the laser pulses is synchronized with the ejection of the target droplets DP through the nozzle 117. As the target droplets move through the excitation zone, the pre-pulses heat the target droplets and transform them into low-density target plumes. A delay between the pre-pulse and the main pulse is controlled to allow the target plume to form and expand to an optimal size and geometry. In various embodiments, the pre-pulse and the main pulse have the same pulse duration and maximum power consumption. When the main pulse heats the target plume, a high-temperature plasma is generated. The plasma emits EUV radiation, which is captured by the collector mirror 110.The collector mirror 110, which is an EUV collector mirror, reflects and further focuses the EUV radiation for the lithography exposure processes carried out by the exposure device 200. A droplet DP that does not interact with the laser pulses is captured by the droplet catcher 85. Fig. 2 shows a schematic view of an EUV lithography exposure tool (EUVL exposure tool) according to some embodiments of the present disclosure. The EUVL exposure tool of Fig. 2 comprises the exposure device 200, which shows the exposure of a photoresist-coated substrate, a target semiconductor substrate 210, with a structured beam of EUV light. The exposure device 200 is an integrated circuit lithography tool, such as a stepper, scanner, step-and-scan system, direct-write system, a device using a contact and / or proximity mask, etc., which is equipped with one or more optics 205a, 205b to, for example, provide a structuring optic, such as a reticulum.A reflection mask 205c is illuminated with a beam of EUV light to generate a structured beam, and one or more reduction projection optics 205d, 205e are used to project the structured beam onto the target semiconductor substrate 210. A mechanical assembly (not shown) can be provided to generate controlled relative motion between the target semiconductor substrate 210 and the structuring optics, e.g., a reflection mask 205c. As further shown, the EUVL exposure tool of Fig. 2 also includes the EUV radiation source 100, which has a plasma plume 23 in the excitation zone ZE and emits EUV light in the chamber 105. This light is captured by a collector mirror 110 and reflected into the exposure device 200 to irradiate the target semiconductor substrate 210. In some embodiments, the mask capsule device 10 conforms to SMIF standards (Standard Mechanical Interface Standards), e.g.RSP200 pod, designed and manufactured. Fig. 3 shows a configuration of a mask capsule device 10 in which an EUV photomask 12 is stored. The EUV photomask 12 comprises a substrate 12-1, a multilayer Mo / Si stack 12-2 consisting of several alternating layers of silicon and molybdenum, a cover layer 12-3, an absorber layer 12-4, and a backside conductive layer 12-5 formed on the back of the substrate 12-1. In some embodiments, the substrate 12-1 is formed from a low-thermal-expansion material. In some embodiments, the substrate is a low-thermal-expansion glass or quartz, such as molten silica or molten quartz. In some embodiments, the low-thermal-expansion glass substrate is transparent to light with wavelengths in the visible range, with wavelengths partially in the infrared near-visible range (near-infrared), and with wavelengths partially in the ultraviolet range. In some embodiments, the low-thermal-expansion glass substrate absorbs extreme ultraviolet wavelengths and low ultraviolet wavelengths near the extreme ultraviolet. In some embodiments, the size of the substrate 12-1 is 152 mm × 152 mm (or 150 mm × 150 mm) with a thickness of about 20 mm. The shape of the substrate 12-1 is square or rectangular. In some embodiments, the Mo / Si multilayer stack 12-1 comprises approximately 30 to approximately 60 alternating layers of silicon and molybdenum. In certain embodiments, approximately 40 to approximately 50 alternating layers of silicon and molybdenum are formed. In some embodiments, the reflectance is higher than approximately 70% for relevant wavelengths, e.g., 13.5 nm. Each silicon and molybdenum layer is approximately 2 nm to approximately 10 nm thick. In some embodiments, the silicon and molybdenum layers are approximately the same thickness. In other embodiments, the silicon and molybdenum layers have different thicknesses. In some embodiments, the thickness of each silicon layer is approximately 4 nm and the thickness of each molybdenum layer is approximately 3 nm. In some embodiments, the top layer 12-3 is arranged over the Mo / Si multilayer 12-2 to prevent oxidation of the multilayer stack 12-2. In some embodiments, the top layer 12-3 is formed of ruthenium, a ruthenium alloy (e.g., RuNb, RuZr, RuZrN, RuRh, RuNbN, RuRhN, RuV, or RuVN), or a ruthenium-based oxide (e.g., RuO2, RuNbO, RiVO, or RuON), with a thickness of about 2 nm to about 10 nm. The absorber layer 12-4 is arranged above the cover layer 12-3, and circuit structures are formed within it. In some embodiments, the absorber layer 12-4 is a Ta-based material. In some embodiments, the absorber layer 12-4 consists of TaN, TaO, TaB, TaBO, or TaBN with a thickness of approximately 25 nm to approximately 100 nm. In certain embodiments, the thickness of the absorber layer 12-4 ranges from approximately 50 nm to approximately 75 nm. In other embodiments, the absorber layer 12-4 contains a Cr-based material, such as CrN, CrO, and / or CrON. In some embodiments, the absorber layer 12-4 has a multilayer structure of Cr, CrO, or CrON. In some embodiments, an antireflection layer (not shown) is optionally arranged above the absorber layer 12-4. In some embodiments, the antireflection layer is formed from a silicon oxide and has a thickness of about 2 nm to about 10 nm.In other embodiments, a TaBO layer with a thickness in the range of approximately 12 nm to approximately 18 nm is used as the antireflective layer. In some embodiments, the thickness of the antireflective layer is from approximately 3 nm to approximately 6 nm. In some embodiments, the backside conductive layer 12-5 is formed from TaB (tantalum boride) or another Ta-based conductive material. In other embodiments, the backside conductive layer 45 is formed from a Cr-based conductive material (CrN or CrON). The thickness of the backside conductive layer 45 is approximately 50 nm to approximately 400 nm in some embodiments. In other embodiments, the backside conductive layer 45 has a thickness of approximately 50 nm to approximately 100 nm. In certain embodiments, the thickness is approximately 65 nm to approximately 75 nm. The mask capsule device 10 comprises an outer capsule 15 and an inner capsule 16 enclosed by the outer capsule 15. The outer capsule 15 comprises an upper housing 15-1 and a lower housing 15-2, and the inner capsule comprises an upper cover 16-1 and a lower cover 16-2. As shown in Fig. 3, the EUV photomask 12 is placed inside the inner capsule with its upper side facing down (the absorber layer facing down toward the lower cover 16-2). For clarity, the pellicle is not shown installed over the structured surface (absorber layer). However, it should be noted that a pellicle is installed over the photomask 12. The lower cover 16-2 of the inner capsule 16 comprises one or more supports 16-3 to support the front surface of the photomask 12, and the upper cover 16-1 of the inner capsule 16 comprises one or more retaining supports 16-4 to support the rear surface of the photomask 12. As shown in Fig. 4, which is a view from the rear of the photomask, in some embodiments four retaining supports 16-4 support the four corners of the photomask 12. Fig. 5 shows a cross-sectional view when the upper cover 16-2 is closed and the retaining supports 16-4 are in contact with the photomask 12. Note that Fig. 5 is upside down, unlike Fig. 3. An EUV photomask 12 and the mask capsule assembly have a specific shape and dimensions. For example, the four corners are rounded with a radius of approximately 2 mm to approximately 3 mm, and the edge between the main surface and the side surface is chamfered by approximately 0.2 mm to approximately 0.6 mm, as shown in Fig. 5. The chamfer angle is approximately 45 degrees, as shown in Fig. 5. In contrast, the support supports 16-4 have an inclined surface against which the chamfered edge of the photomask rests, but at an angle of 34.4 degrees, as shown in Fig. 5. Due to the different angle, the chamfered corner of the photomask can damage or dig into the support assembly 16-4, producing a particle 18. Such a particle can compromise the flatness of the photomask 12 when it is mounted on a mask table in an EUV lithography machine.To clean the photomask, an air blower or a cleaning wiper has been used so far, but these can only remove the particles from the flat surface of the photomask. Therefore, it is necessary to effectively remove the particles from the edge or the back of the photomask 12. According to embodiments of the present disclosure, a cleaning device 20A as shown in Fig. 6 is used to remove particles from the edge or back of the photomask 12. In some embodiments, the cleaning device 20A comprises an adhesive or sticky sheet or strip 22 attached to a body 24A or 24B, as shown in Fig. 6. In some embodiments, the adhesive sheet 22 comprises an elastomer or a gelatinous material. In some embodiments, the adhesive sheet 22 is formed of silicone, a styrene-ethylene-butylene-styrene copolymer, a styrene-ethylene-propylene-styrene copolymer, or another suitable adhesive material. In some embodiments, the adhesive sheet 22 is arranged on at least one major surface of the body 24A or 24B. In some embodiments, the body 24A has a cuboid shape, and the adhesive sheet 22 is attached to a flat major surface of the body 24A. In other embodiments, the body 24B has at least one curved surface (convex or concave) to which the adhesive sheet 22 is attached. Furthermore, in some embodiments, a handle 28 (see Fig. 9) is attached to the body 24A via a rod 26. As shown in Fig. 6, the adhesive sheet 22 of the cleaning device 20A is applied from the back of the photomask 12 to the beveled edge of the back of the photomask 12. In some embodiments, the photomask 12 is positioned on the supports 16-3 of the lower cover 16-2 by opening or removing the upper cover 16-1; in other embodiments, the photomask 12 is positioned on a different support table or pedestal. Particles at the edge of the photomask 12 are removed by sliding the cleaning device 20 along the edges of the photomask 12 and / or over it, as shown in Fig. 6. In some embodiments, the main surface of the adhesive sheet 22 is inclined at an angle θ of about 0 degrees to about 90 degrees relative to the back of the photomask 12. In other embodiments, the angle θ is about 30 degrees to about 75 degrees, and in certain embodiments, the angle θ is about 40 degrees to about 50 degrees. The cleaning device 20A is operated manually in some embodiments and mechanically in others.By adjusting the angle, the beveled edge on the front and side surfaces can be cleaned. In some embodiments, the beveled edge on the back is not treated by the cleaning device 20A. In some embodiments, the thickness of the adhesive sheet 22 is approximately 1 mm to approximately 5 mm. In some embodiments, the adhesive sheet 22 is replaceable by a new adhesive sheet. In some embodiments, the body 24A, 24B is made of an elastic material such as rubber or sponge. The elastic material of the body 24A, 24B can exert sufficient pressure on the adhesive sheet 22 when applied to the photomask 12, thus improving the effectiveness of particle removal. If the adhesive sheet 21 has sufficient elasticity, the body 24A, 24B can be made of a non-elastic material such as glass, plastic, ceramic, or metal. Fig. 7 shows a configuration of a cleaning device and a cleaning process according to one embodiment of the present disclosure. The materials, configuration, dimensions and / or processes described in the above embodiments can be applied to the following embodiments, and a detailed explanation thereof is unnecessary. In some embodiments, a cleaning device 20B comprises an adhesive sheet or tape 22 attached to a body 24C, as shown in Fig. 7. In some embodiments, the adhesive sheet 22 contains an elastomer or a gelatinous material. In some embodiments, the adhesive sheet 22 is formed of silicone, a styrene-ethylene-butylene-styrene copolymer, a styrene-ethylene-propylene-styrene copolymer, or another suitable adhesive material. In some embodiments, the body 24C has a cylindrical shape that is wrapped by the adhesive sheet 22. Furthermore, in some embodiments, a handle 28 (see Fig. 9) is attached to the body 24C via a rod 26. As shown in Fig. 7, the adhesive sheet 22 of the cleaning device 20B is applied from the back of the photomask 12 to the beveled edge of the back of the photomask 12. In some embodiments, the body 24C is moved manually or mechanically linearly along the axis of the rod 26. Fig. 8 shows a configuration of a cleaning device and a cleaning process according to one embodiment of the present disclosure. Materials, configurations, dimensions and / or processes described in the above embodiments can be applied to the following embodiments, and a detailed explanation thereof is unnecessary. In some embodiments, as shown in Fig. 8, the cleaning device 20C is a rotary type in which the body 24C, together with the adhesive sheet 22, rotates about the axis of the rod 26. In some embodiments, as shown in Fig. 9, the rod is rotated by a drive mechanism 27, such as a motor, which is arranged in the handle 28. In some embodiments, the drive mechanism 27 also moves the rod 26 linearly back and forth, as shown in Fig. 7. In some embodiments, the speed and direction of movement of the rod 26 are adjustable. In some embodiments, the rod 26 is flexible and can be bent to conform to the beveled edges of the photomask 12. In some embodiments, the drive mechanism 27 also exerts vibrations on the body via the rod 26.In some embodiments, the vibration is in the ultrasonic range, and in other embodiments, the vibration is approximately 1 Hz to 10 kHz. Fig. 10 shows a configuration of a cleaning device and a cleaning process according to one embodiment of the present disclosure. The materials, configuration, dimensions and / or processes described in the above embodiments can be applied to the following embodiments, and a detailed explanation thereof is unnecessary. Fig. 10 shows a cleaning device according to another embodiment of the present disclosure. In the cleaning device 20D shown in Fig. 10, an adhesive tape or adhesive tape 22A is wrapped around a first rod or body 26-1 in some embodiments, and one end of the adhesive tape or adhesive tape 22A is attached to a second rod or body 26-2, so that by rotating the second rod or body 26-2, the adhesive tape or adhesive tape 22A is released from the first rod or body 26-1 and wrapped around the second rod or body 26-2. The adhesive tape or adhesive tape 22A is applied to the edge of the photomask 12 to remove particles.The used part of the adhesive sheet or tape 22A is transferred to the second rod or body 26-2, so that a new and fresh part of the adhesive sheet or tape 22A can be applied to the next part of the photomask 12 to be cleaned. In some embodiments, the rotation of the second rod or body 26-2 or the movement of the adhesive sheet or tape 22A is continuous. In other embodiments, the rotation of the second rod or body 26-2 or the movement of the adhesive sheet or tape 22A is incremental. For example, after one edge of the four sides of the photomask 12 is cleaned, the adhesive sheet or tape 22A is renewed by the rotation of the second rod or body 26-2. In other embodiments, the adhesive sheet or tape 22A is renewed after a time interval. In some embodiments, similar to that in Fig. 9, at least the second rod or body 26-2 is coupled to a drive mechanism 27, such as a motor, to control the rotation of the second rod or body 26-2. In other embodiments, the first rod or body 26-1 is also coupled to another motor or the same motor via one or more gears. In some embodiments, the rotation speed is adjustable. In some embodiments, the drive mechanism 27 also applies vibrations to the body via the rod 26. In some embodiments, the vibration is in the ultrasonic range; in other embodiments, the vibration is approximately 1 Hz to 10 kHz. In some embodiments, the main surface of the adhesive sheet or tape 22A is inclined at an angle θ' of approximately 0 degrees to approximately 90 degrees relative to the back of the photomask 12. In other embodiments, the angle θ' is approximately 30 degrees to approximately 75 degrees, and in certain embodiments, the angle θ' is approximately 40 degrees to approximately 50 degrees. By adjusting the angle, the beveled edge on the front and side surfaces can be cleaned. In some embodiments, the beveled edge on the back is not treated by the cleaning device 20D. In some embodiments, the angle θ' as shown in Fig. 10 and the angle θ as shown in Figs. 6-8 can be set or changed by a mounting device 30 as shown in Fig. 11. In some embodiments, the mounting device 30 comprises a base plate with an arc-shaped section, which may be an outer circumference of the base plate or an arc-shaped slot in the base plate, and a movable plate 32 that moves along the arc-shaped section. The movable section 32 is coupled to the cleaning device 20 or 20A, and the angle θ' or θ can be changed by moving the movable plate 32 along the arc-shaped section. In some embodiments, the mounting device 30 comprises one or more motors, gears, or other mechanisms for changing the angle θ' or θ. Furthermore, the mounting device 30 is configured to change the position of the entire cleaning device (the adhesive sheet) relative to the photomask 12. In some embodiments, the mounting device 30 is attached to, or can be attached to, a capsule mounting device 40. As shown in Fig. 3, an EUV photomask is mounted on the inner capsule 16, and the inner capsule 16 is mounted on the outer capsule 15; and the inner capsule is removed from the outer capsule, and the photomask is removed from the inner capsule. In some embodiments, these mounting and removal operations are performed by a capsule mounting device 40. In some embodiments, the mounting and removal operations of the photomask onto and from the inner capsule 16 are performed by a different capsule mounting device than the capsule mounting device used for the mounting and removal operations of the inner capsule 16 onto and from the outer capsule 15. In some embodiments, after the upper cover 16-4 is removed from the inner capsule to expose the back of the photomask 12, the cleaning device is applied to the beveled edge of the back of the photomask 12. When the mounting device 30 is attached to the capsule mounting device 40, the beveled edge of the photomask 12 can be effectively cleaned. In some embodiments, the cleaning is performed mechanically and automatically by using one or more control circuits programmed to control the mounting device 30 and the cleaning devices 20 and 20A. In other embodiments, the mounting device 30 is attached or can be attached to another independent table which is used for cleaning purposes. In some embodiments, as shown in Fig. 12, an adhesive sheet 22B is manually applied to the beveled edge of the underside of the photomask 12. In some embodiments, the cleaning device comprises a body 24, 24A, 24B and a flexible support having a frame shape and an inclined surface. An adhesive sheet or tape is attached to the inclined surface (application surface). The inclined surface has an angle of inclination θ, which in some embodiments is approximately 40 degrees to 50 degrees, and in one particular embodiment, the angle θ is 45 degrees. In some embodiments, the flexible support has a greater or lesser flexibility than the adhesive sheet. In some embodiments, the flexible support comprises rubber, sponge, polymer, or another suitable material. In some embodiments, the thickness of the adhesive sheet is approximately 0.5 mm to approximately 5 mm, and in others, it is approximately 1 mm to approximately 3 mm.During operation, the cleaning device is applied to the back of the photomask 12 from above, so that the adhesive sheet contacts the beveled edges of the photomask 12. The cleaning device is pressed against the photomask 12, deforming the flexible support. By repeatedly pressing and releasing the cleaning device, the edge of the photomask 12 is cleaned. In some embodiments, the cleaning device 12 is rotated 90 or 180 degrees after being released from the photomask 12. Vibrations can be applied as described above while pressing the cleaning device against the photomask. In some embodiments, the flexible body is formed from the adhesive tape materials and is made of silicone, a styrene-ethylene-butylene-styrene copolymer, a styrene-ethylene-propylene-styrene copolymer, or another suitable adhesive material. In such a case, an adhesive is not required.In some embodiments, the cleaning device is attached to the photomask 12 by means of an automated mechanical structure. Fig. 13A and Fig. 13B show a process flow for cleaning an EUV photomask according to embodiments of the present disclosure. In Fig. 13A, the EUV photomask is unloaded from the EUV lithography apparatus after use. In some embodiments, the EUV photomask is loaded into an inner capsule in a vacuum environment. The inner capsule is then unloaded from the vacuum apparatus and loaded into an outer capsule of the mask capsule assembly. The mask capsule assembly is then loaded onto a capsule removal device, and the outer and inner capsules are removed. In some embodiments, the pellicle is removed before the photomask is loaded into the inner capsule. In some embodiments, the photomask is then subjected to a cleaning process. In some embodiments, the cleaning process includes cleaning the entire photomask by wet and / or dry cleaning. In some embodiments, the cleaning process includes cleaning the beveled edges of the back of the photomask as described above.After the cleaning process, the photomask is loaded into a mask library or mask storage. In Fig. 13B, when an EUV photomask is used, the photomask is taken from the mask library or stock and then subjected to the cleaning process. In some embodiments, the cleaning process includes cleaning the entire photomask by wet and / or dry cleaning. In some embodiments, the cleaning process includes cleaning the beveled edges on the back of the photomask as described above. After the cleaning process, if no pellicle has been mounted over the photomask, a pellicle is mounted over the photomask. Then the photomask is loaded into an inner capsule, and the inner capsule into an outer capsule; and the mask capsule assembly is transported to an EUV lithography apparatus. The inner capsule is removed from the outer capsule in a vacuum environment, and the inner capsule is transported into the lithography apparatus.In the EUV lithography machine, the photomask is unloaded from the inner capsule under vacuum and placed on a mask table of the EUV lithography machine. According to embodiments of the present disclosure, an adhesive sheet or tape can effectively remove particles from the beveled edges of the back of an EUV photomask. Since the adhesive sheet or tape is relatively inexpensive, the cleaning costs can be reduced. Although cleaning methods for an EUV photomask are described herein, the cleaning method of the present disclosure can be applied to the cleaning of any type of photomask, e.g., photomasks for deep UV lithography or UV lithography, or a photomask without beveled edges. It should be understood that not all advantages are necessarily discussed herein, no particular advantage is required for all embodiments or examples, and other embodiments or examples may offer other advantages. According to some embodiments of the present disclosure, in a method for cleaning a photomask, the photomask is placed on a support such that a structured surface faces downwards, and an adhesive sheet is applied to the edges of a rear surface of the photomask. In one or more of the preceding or subsequent embodiments, the edges of the rear surface of the photomask are chamfered. In one or more of the preceding or subsequent embodiments, the adhesive sheet is made of silicone. In one or more of the preceding or subsequent embodiments, the adhesive sheet is made of a styrene-ethylene-butylene-styrene copolymer or a styrene-ethylene-propylene-styrene copolymer. In one or more of the preceding or subsequent embodiments, the adhesive sheet is attached to a body.In one or more of the preceding or following embodiments, the body is formed from an elastic material. In one or more of the preceding or following embodiments, applying the adhesive sheet involves moving the body while the adhesive sheet is in contact with the edges. In one or more of the preceding or following embodiments, the movement involves a linear motion. According to another aspect of the present disclosure, in a method for cleaning a photomask, the photomask is loaded into an inner capsule, the inner capsule is loaded into an outer capsule, the outer capsule is opened, the inner capsule is opened such that the photomask is placed over a lower cover of the inner capsule, with a textured surface facing downwards, and an adhesive sheet is applied to the edges of a rear surface of the photomask while the photomask is placed over the lower cover of the inner capsule. In one or more of the preceding or subsequent embodiments, an adhesive sheet is attached to a surface of a body, and the body is coupled to a handle via a rod, and the handle is actuated when the adhesive sheet is applied to clean the edges of the rear surface of the photomask.In one or more of the preceding or subsequent embodiments, the body has a cylindrical shape and the adhesive sheet wraps around the body. In one or more of the preceding or subsequent embodiments, applying the adhesive sheet involves rotating the body. In one or more of the preceding or subsequent embodiments, the body has a curved surface and the adhesive sheet is attached to the curved surface. In one or more of the preceding or subsequent embodiments, applying the adhesive sheet involves applying vibration to the body. In one or more of the preceding or subsequent embodiments, the vibration is in the ultrasonic range. In one or more of the preceding or subsequent embodiments, the edges of a textured surface are not cleaned by the adhesive sheet. According to a further aspect of the present disclosure, a cleaning device for removing a particle from an edge of the back surface of an EUV photomask comprises: a first body wrapped with adhesive tape, a second body to which one end of the adhesive tape is attached, and a drive mechanism for rotating the second body. The adhesive tape is formed of silicone, a styrene-ethylene-butylene-styrene copolymer, or a styrene-ethylene-propylene-styrene copolymer. In one or more of the preceding or subsequent embodiments, the cleaning device further comprises an assembly device configured to change an angle between a surface of the adhesive tape and the back surface of the photomask. In one or more of the preceding or subsequent embodiments, the assembly device is attached to a mask capsule assembly / removal device.In one or more of the preceding or following embodiments, the drive mechanism is arranged to set a rotational speed of the second body.

Claims

Method for cleaning a photomask (12), comprising: placing the photomask (12) on a support such that a structured surface of the photomask (12) is facing downwards; and applying an adhesive sheet (22) to edges of a rear surface of the photomask (12), wherein the adhesive sheet (22) is attached to a flat main face of a cuboid body (24, 24A-B). Method according to claim 1, wherein the edges of the rear surface of the photomask (12) are chamfered edges. Method according to claim 1 or 2, wherein the adhesive sheet (22) is formed of silicone or wherein the adhesive sheet (22) is formed of a styrene-ethylene-butylene-styrene copolymer or a styrene-ethylene-propylene-styrene copolymer. Method according to one of the preceding claims, wherein the body (24, 24A-B) is formed from an elastic material. Method according to any of the preceding claims, wherein the application of the adhesive sheet (22) comprises: moving the body (24, 24A-C) while the adhesive sheet (22) is in contact with the edges. Method according to claim 5, wherein the movement comprises a linear movement. Method for cleaning a photomask (12), comprising: loading the photomask (12) into an inner capsule (16); loading the inner capsule (16) into an outer capsule (15); opening the outer capsule (15); opening the inner capsule (16) so that the photomask (12) is placed above a lower cover of the inner capsule (16) with a textured surface of the photomask (12) facing downwards; and applying an adhesive sheet (22) to the edges of a rear surface of the photomask (12) while the photomask (12) is positioned over the lower cover of the inner capsule (16) wherein: an adhesive sheet (22) is attached to a flat main surface of a cuboid body (24, 24A-B) and the body (24, 24A-C) is coupled to a handle via a rod (26), and the application of the adhesive sheet (22) comprises: - actuating the handle to clean the edges of the rear surface of the photomask (12). Method according to claim 7, wherein the edges of the rear surface of the photomask (12) are chamfered edges. Method according to claim 7 or 8, wherein the body is formed from an elastic material. Method according to any one of claims 7 to 9, wherein the application of the adhesive sheet (22) comprises: exerting vibration on the body (24, 24A-B). Method according to claim 10, wherein the vibration is in an ultrasonic range. Method according to one of claims 7 to 11, wherein the edges of the structured surface of the photomask (12) are not cleaned by the adhesive sheet (22). Cleaning device (20, 20A-D) for removing a particle from an edge of a back side of an EUV photomask (12), wherein the cleaning device (20, 20A-D) comprises: a cuboid body (24, 24A-B) to the flat main surface of which an adhesive sheet (22) is attached; a handle (28) which is attached to the body (24, 24A-B) via a rod (26); wherein the adhesive sheet (22) is formed of a silicone, a styrene-ethylene-butylene-styrene copolymer or a styrene-ethylene-propylene-styrene copolymer.

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