Clogging-preventing droplet generator for EUV light sources

Abstract

A droplet generator for an EUV light source includes: a fluid cavity within a structure having a first fluid cavity end that is open or capable of receiving fluid, and a second fluid cavity end; a particle filter within the fluid cavity that divides the fluid cavity into an upstream volume between the upstream surface of the particle filter and the first fluid cavity end, a filter volume occupied by the filter, and a downstream volume located downstream of the downstream surface of the filter; and a tube having a first opening located outside the fluid cavity, extending from the first opening through the second fluid cavity end to a second opening in the downstream volume, and extending into the downstream volume by more than 10% of the distance from the first opening to the second opening.

Description

Technical Field

[0001] Cross-Reference to Related Applications

[0001] This application claims the priority benefit of U.S. Application Serial No. 63 / 580,549, filed September 5, 2023, entitled "Clog-Resistant Droplet Generator for EUV Light Sources", the entire content of which is incorporated herein by reference.

[0002]

[0002] The present disclosure relates to a clog-resistant droplet generator for generating droplets in an extreme ultraviolet (EUV) light source without causing clogging or with reduced clogging.

Background Art

[0003]

[0003] EUV light used in semiconductor photolithography is provided by a system called an EUV light source. In an EUV light source, a droplet generator generates droplets, which are irradiated with light from a light source often referred to as a source laser. The droplets are formed from or comprise a material capable of emitting EUV radiation when in a plasma state. Energy resulting from irradiation of the droplet with light from the source laser generates EUV-emitting plasma from at least a portion of the material of the irradiated droplet. EUV light originating from the plasma is collected and sent to a lithography apparatus, where it is used to form a pattern in or on a semiconductor substrate. The uptime of EUV light sources is of great importance to users of EUV light sources due to the high cost and high value generated by semiconductor manufacturing processes.

Summary of Invention

[0004]

[0004] In some common embodiments, a droplet generator for an EUV light source includes: a fluid cavity within a structure having a first fluid cavity end that is open or capable of receiving fluid, and a second fluid cavity end; a particle filter within the fluid cavity that divides the fluid cavity into an upstream volume between the upstream surface of the particle filter and the first fluid cavity end, a filter volume occupied by the filter, and a downstream volume downstream of the downstream surface of the filter; and a tube having a first opening located outside the fluid cavity, extending from the first opening through the second fluid cavity end to a second opening in the downstream volume, and extending into the downstream volume by more than 10% of the distance from the first opening to the second opening.

[0005]

[0005] The implementation may include one or more of the following features:

[0006]

[0006] The tube may extend into the downstream volume by more than 20% of the distance from the first opening to the second opening, or by more than 30% of the distance from the first opening to the second opening. The distance from the second opening to any surface other than the surface of the tube may be at least 1 millimeter (1 mm) or at least 3 millimeters. The downstream volume may include at least one dead volume. The downstream volume may include at least two dead volumes. The downstream volume may include a dead volume gravitationally positioned below the fluid flow path when the droplet generator is operating. The downstream volume may include a dead volume gravitationally positioned above the fluid flow when the droplet generator is operating. The downstream volume may include a dead volume gravitationally positioned above the fluid flow when the droplet generator is operating.

[0007]

[0007] The tube may be positioned so as to be substantially perpendicular to gravity when the droplet generator is operating. The tube may have at least one bend located within the downstream volume.

[0008]

[0008] The downstream volume may include one or more dead volumes, one or more initial filling channels may extend from the filter to one or more dead volumes, and one or more initial filling channels may avoid the second opening of the tube so as not to surround the second opening of the tube.

[0009]

[0009] The filter may be positioned in a straight line between the first fluid cavity end and the second fluid cavity end. The filter may be a cylindrical filter having a central opening that extends axially through the filter at least partially. The second opening of the tube may be located within the central opening of the filter. The filter may be a cylindrical filter having a central opening that extends axially through the filter. The tube may extend entirely through the central opening of the filter, and the second opening may be located outside the central opening of the filter.

[0010]

[0010] During use of the droplet generator, the droplet material flowing in the fluid cavity may change direction by about 90 degrees or more and enter the second opening of the tube. During use of the droplet generator, the droplet material flowing in the fluid cavity may change direction by about 180 degrees and enter the second opening of the tube.

[0011]

[0011] In an additional general embodiment, a droplet generator for an EUV light source includes a filter having an internal volume, configured to prevent particles in a fluid from passing through the filter and reaching the internal volume, and a tube for supplying droplets of fluid by the droplet generator, the tube having an upstream tube opening extending into the internal volume of the filter, thereby allowing the fluid to flow through the filter into the upstream tube opening and preventing particles from entering the upstream tube opening.

[0012]

[0012] The implementation may include one or more of the following features:

[0013]

[0013] The tube may extend close to the upstream end of the filter. The tube may further include an upstream end having an outer diameter smaller than the inner diameter of the internal volume, the outer diameter which may at least partially form a capture volume for particles downstream of the filter. The filter may surround the internal volume in the circumferential direction, and the fluid may enter the filter in the circumferential direction.

[0014]

[0014] One or more embodiments will be described in detail in the attached drawings and the following description. Other features will be apparent from the following description and drawings, as well as from the claims. [Brief explanation of the drawing]

[0015] [Figure 1]

[0015] This is a block diagram of an extreme ultraviolet (EUV) light source. [Figure 2]

[0016] This is a functional diagram of a clog-prevention type droplet generator. [Figure 3A]

[0017] This is a cross-sectional view of one embodiment of a clog-preventing droplet generator. [Figure 3B]

[0017] This is a cross-sectional view of one embodiment of a clogging prevention type droplet generator. [Figure 3C]

[0017] This is a cross-sectional view of one embodiment of a clogging prevention type droplet generator. [Figure 3D]

[0017] This is a cross-sectional view of one embodiment of a clogging prevention type droplet generator. [Figure 3E]

[0017] This is a cross-sectional view of one embodiment of a clogging prevention type droplet generator. [Figure 3F]

[0017] This is a cross-sectional view of one embodiment of a clogging prevention type droplet generator. [Figure 3G]

[0017] This is a cross-sectional view of one embodiment of a clogging prevention type droplet generator. [Figure 4]

[0018] This is a diagram of an EUV light source used with a photolithography system. [Modes for carrying out the invention]

[0016]

[0019] Referring to Figure 1, a block diagram of the EUV light source 100 including a droplet generator 110 is shown. The droplet generator 110 emits a stream of droplets 121p so that the droplets 121p are transported to a plasma formation position 123 in a vacuum chamber 109. The droplets 121p contain one or more materials that emit EUV light when in a plasma state or in one or more of several possible plasma states. Examples of materials include water, tin, lithium, and / or xenon, but tin is commonly used. The plasma formation position 123 receives a light beam 106. The light beam 106 is generated by the light source 105 and transported to the vacuum chamber 109 via an optical path 107. The interaction between the light beam 106 and the droplet material in the droplets 121p generates a plasma 196 that emits EUV light, which is collected and sent from the light source 100 as transmitted EUV light 155.

[0017]

[0020] The droplet generator 110 may include a tube 114, such as a capillary tube, fluidly connected to a reservoir 112. The tube 114 may be held by a nozzle device 140. The tube 114 defines an orifice 119 through which droplet material flows to form a droplet stream 121. The tube 114 is mechanically coupled to an actuator 193, which is coupled to a control system 190 via a control link 192. The control system 190 may include a function generator, an electronic processor (not shown), and an electronic storage device (not shown) to implement the functions of the control system 190. The control link 192 is any type of connection capable of transmitting electronic signals and / or actuation signals from the control system 190 to the actuator 193. For example, the control link 192 may be a wired connection and / or a wireless connection configured to transmit electronic signals and / or actuation signals and commands from the control system 190 to the actuator 193.

[0018]

[0021] The control system 190 generates a signal that moves the actuator 193 when applied to the actuator 193 or a component associated with the actuator 193. For example, the actuator 193 may be a piezoelectric ceramic material that changes shape in response to an applied voltage. The magnitude and / or polarity of the voltage applied to the actuator 193 is based on a signal from the control system 190. Due to the mechanical coupling between the tube 114 and the actuator 193, when the actuator 193 moves or vibrates, the tube 114 also experiences corresponding movement and vibration. More specifically, radial contraction of the actuator 193 causes local contraction of the tube 114, and expansion of the actuator 193 causes local expansion of the tube 114. This expansion and contraction generates acoustic waves at the frequency of the applied electrical signal in the droplet material inside the tube.

[0019]

[0022] Reservoir 112 contains droplet material under pressure P. The droplet material is in a fluid liquid state (such as molten tin), and the pressure inside the vacuum chamber 109 is lower than pressure P. Therefore, the droplet material flows through tube 114 and is released into chamber 109 through orifice 119. The droplet material exits orifice 119 as a jet 124 or a continuous stream of droplet material. The jet 124 of droplet material splits into individual droplets. The splitting of jet 124 can be controlled to vibrate tube 114 and generate sound waves inside tube 114, causing the individual droplets to merge into larger droplets that reach the plasma formation position 123 at a desired speed.

[0020]

[0023] For example, the control system 190 provides a signal having at least a first frequency and a second frequency via the control link 192, thereby causing the actuator 193 to vibrate at the first and second frequencies. The first frequency can be in the megahertz (MHz) range. When the tube 114 is vibrated at the first frequency, the jet 124 splits into relatively small droplets of a desired size. The second frequency is lower than the first frequency. For example, the second frequency may be in the kilohertz (kHz) range. The second frequency is used to adjust the velocity of the droplets in the flow and to promote droplet coalescence. When the tube 114 is driven at the second frequency, a group of droplets is formed, and the droplets within this group move at different velocities. Faster-moving droplets coalesce with slower-moving droplets to form larger coalesced droplets, which constitute the droplet flow 121 for the EUV light source. After coalescence, the resulting larger droplets are separated from each other at greater distances than the smaller droplets before coalescence. By increasing the distance between droplets, the influence of plasma formed from one droplet on subsequent droplets in the droplet flow can be reduced. The droplets in the droplet flow 121 may be, for example, nearly spherical with a diameter of about 20 or 35 μm.

[0021]

[0024] By vibrating the tube 114 in this manner, final droplets are ultimately generated at a frequency of, for example, 40 to 300 kHz or higher, and can travel toward the plasma formation position 123 at a velocity of, for example, 40 to 120 meters per second (m / s), or up to 500 m / s or higher. The spatial distance between two adjacent droplets in the droplet stream 121 may be, for example, 1 to 3 millimeters (mm). 50 to 300 initial droplets (also referred to as Rayleigh droplets) may coalesce to form a single larger droplet.

[0022]

[0025] Figure 2 is a functional diagram of a clogging-resistant droplet generator 210, which may for example be the droplet generator 110 of Figure 1. Similar to the droplet generator 110 of Figure 1, a pressurized reservoir 212 contains droplet material under pressure in liquid form. The droplet material is conveyed from the reservoir 212 to a first fluid cavity end 241-fe of a fluid cavity 241. The fluid cavity 241 may be defined within a structure 242, a portion of which is shown in partial cross-section in Figure 2, and the structure 242 may be a nozzle assembly 240 such as the nozzle assembly 140 of Figure 1, or may form a part of the nozzle assembly 240. A filter 244 is provided in or along the fluid cavity 241 to selectively pass particles that can or may become entrained in the droplet material. At a second fluid cavity end 241-se, a tube such as a capillary tube 214 is connected to the fluid cavity 241, and the tube 214 extends from a first opening 214-О1 or orifice 219 of the tube 214 to a second opening 214-О2 via a seal 245 at the second fluid cavity end 241-se. The tube may be a glass tube such as a borosilicate glass tube or an aluminosilicate glass tube, a quartz tube, a ceramic tube such as silicon carbide, or other ceramic material resistant to corrosion by liquid tin, which is a typical main component of droplet materials.

[0023]

[0026] A dead volume 236 is provided inside or along the fluid cavity 241, after the filter 244 and before the tube 214. A dead volume such as the dead volume 236 can be defined as a volume that, during use, is occupied by the fluid droplet material before it enters the tube 214, and substantially alters the direction of the flow before it enters the tube 214, during the initial filling of the fluid cavity 241. Thus, once the dead volume is filled, it does not exist in the flow pattern or flow path (e.g., a flow path from the first fluid cavity end 241-fe to the second fluid cavity end 241-se), and after the initial filling, little to no pressure-driven flow occurs within the dead volume.

[0024]

[0027] Similar to Figure 1, the tube 214 is mechanically coupled to the actuator 293, which is coupled to the control system 290 via a control link 292. Similar to the operation described above with respect to Figure 1, a flow of droplet material (e.g., a flow of liquid tin) is pressurized and ejected from the first opening 214-O1 of the tube 214, and the droplet material coalesces due to modulation of the actuator 293 to form droplets 221 that move along direction A. Note that direction A of droplet movement may be directed in any direction relative to gravity; that is, gravity may be downward in the plane of Figure 2, but does not necessarily have to be downward.

[0025]

[0028] Tube 214 extends into the fluid cavity 241 (beyond the seal 245) for a length L. Length L may be greater than 10% of the total length of tube 214 (the distance from the first opening 214-O1 to the second opening 214-O2), or greater than 15%, 20%, 30%, or 40% of the length of tube 214. Alternatively, length L may be 1 millimeter (mm), 2 mm, 3 mm, 4 mm, 5 mm, 7 mm, 10 mm, 15 mm, or 20 mm or more. The distance D between the second opening 214-O2 and the nearest solid surface inside the fluid cavity 241 (excluding the surface of tube 214) may be 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, or 10 mm or more. Considering the length L and distance D together, the second opening 241-02 is effectively positioned away from any solid surfaces or walls within the fluid cavity 241 (except for the tube 214 itself). Because the material of the tube 214 is relatively inert, contaminants in the form of tin reaction products do not generally form on or near the tube 214, even in the presence of liquid tin, for example. By positioning the second opening 214-02 away from other surfaces, the likelihood of reaction products that may be generated on such other surfaces flowing into the second opening 214-02 during the operation of the clog-preventing droplet generator 210 is reduced, thereby decreasing the possibility of clogging of the tube 214 by reaction products of the droplet material.

[0026]

[0029] By placing a dead volume 236 between the filter 244 and the second fluid cavity end 241-se, or between the filter 244 and the second opening 214-O2 of the tube 214, any particles that may initially be present in the filter 244, on the downstream surface of the filter 244, or near this downstream surface are allowed to enter and remain in the dead volume 236 during its initial filling, thereby preventing or reducing the chance of clogging of the tube 214.

[0027]

[0030] Figures 3A to 3G are cross-sectional views of various embodiments of a clogging-prevention droplet generator. For ease of illustration, reservoirs such as reservoirs 112 and 212 in Figures 1 and 2, and actuators such as actuators 193 and 293 in Figures 1 and 2 have been omitted.

[0028]

[0031] Referring to Figures 3A to 3G, the clog-proof droplet generator 310 includes a fluid cavity 341 within a structure 342. The fluid cavity 341 has a second cavity end 341-se and a first cavity end 341-fe that is open or capable of receiving a fluid such as a droplet material such as liquid tin. The structure 342 may contain, or be formed from, tungsten, molybdenum, tantalum, titanium, rhenium, or alloys thereof, ceramics such as alumina or silicon carbide, or other materials resistant to corrosion or other undesirable interactions with liquid tin.

[0029]

[0032] A tube 314, such as a capillary tube, extends from a first opening 314-O1A on the outside of the structure 342 through a seal 345 to a second opening 314-O2 on the inside of the fluid cavity 341. The seal 345 may be, for example, a compression seal using a high-temperature compressible material such as a high-temperature polymer, or a glass-metal fusion seal fused to the tube 314, or a combination thereof, such as glass-metal fusion to a metal ring or metal collar and a compression seal of the metal ring or metal collar to the structure 342.

[0030]

[0033] The particle filter 344 in the fluid cavity 341 divides the fluid cavity 341 into (1) an upstream volume VU between the upstream surface US of the particle filter 344 and the first fluid cavity end 341-fe, a filter volume VF occupied by the filter, and a downstream volume VD on the downstream side of the downstream surface DS of the filter 344.

[0031]

[0034] The first opening 341-01 of tube 314 is located in the downstream volume VD, and tube 314 extends in the downstream volume VD by a length L that is greater than 10% of the distance from the first opening 314-O1 to the second opening 314-O2, or greater than 15%, 20%, 30%, or 40% of the distance from the first opening 314-O1 to the second opening 314-O2. Alternatively, the length L may be 1 millimeter (mm), 2 mm, 3 mm, 4 mm, 5 mm, 7 mm, 10 mm, 15 mm, or 20 mm or more. The distance D between the second opening 314-O2 and the nearest solid surface inside the fluid cavity 341 may be 0.5 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 8 mm, or 10 mm or more.

[0032]

[0035] The downstream volume VD includes at least one dead volume 336 (Figures 3A, 3D, 3F) or dead volume 336a (Figures 3B, 3C, 3E, 3G), where the term “dead volume” is understood as described above with respect to Figure 2. As described above, the length L and distance D position the second opening 314-O2 away from any solid surface or wall within the fluid cavity 341, thereby reducing the likelihood that reaction products that may be generated on such surfaces will flow into the second opening 314-O2 during the operation of the clog-proof droplet generator 310, thereby reducing the likelihood of clogging of the tube 314 by reaction products of the droplet material. Furthermore, as described above, the dead volume 346 between the filter 344 and the second fluid cavity end 341-se, or between the filter 344 and the second opening 314-O2 of the tube 314, allows particles that may initially be present in the filter 344, on the downstream surface of the filter 344, or near this downstream surface, to enter and remain in the dead volume 346 during its initial filling, thereby further reducing clogging of the tube 314.

[0033]

[0036] Referring particularly to Figure 3A, the dead volume 336 may take the form of a gravity-downward dead volume 337, that is, a dead volume located gravity-downward in the fluid flow path P from the filter 344 to the second opening 314-O2 of the tube 314 (when gravity is directed as indicated by arrow G in Figure 3A). (Note that the illustrated orientation is arbitrary, and the anti-clogging droplet generator 310 in Figure 3A can also operate in orientations other than those shown.) In the gravity-downward dead volume 337, when the anti-clogging droplet generator 301 is operating, contaminants heavier than the droplet fluid in the fluid cavity 341 located between the downstream surface DS and the dead volume 337 tend to fall into and remain in the dead volume 337, even after the dead volumes 336 and 337 have been initially filled. Thus, relatively heavy particles, such as (temporarily) solidified tin and / or other material particles, can be prevented from clogging the tube 314, at least partially.

[0034]

[0037] Referring particularly to Figure 3B, a clog-preventing droplet generator 310 is shown, which shares many similarities with the clog-preventing droplet generator 310 in Figure 3A, while several differences are highlighted below.

[0035]

[0038] In the implementation shown in Figure 3B, the downstream volume VD of the fluid cavity 341 includes three dead volumes: two relatively large dead volumes 336a and 336b, and one smaller dead volume 336c. The downstream volume VD includes two gravity-downward dead volumes 337a1 and 337a2, which are gravity-depressed and located below the flow path P from the filter VF to the second opening 314-O2 of the tube 314 when the clog-preventing droplet generator 310 is operating with gravity in the illustrated (optional) orientation. The downstream volume VD also includes a gravity-upward dead volume 337b, which is gravity-upward and located above the flow path P from the filter VF to the second opening 314-O2 of the tube 314. Similar to the implementation in Figure 3A, when the anti-clogging droplet generator 310 is operating, contaminants heavier than the droplet fluid in the downstream volume VD of the fluid cavity 341 tend to fall into and remain inside one of the two dead volumes 337a1 and 337a2, even after these two dead volumes have been initially filled, thereby preventing or reducing heavy particles from clogging the tube 314. Furthermore, if relatively light particulate contaminants are present in the droplet material in the downstream volume VD of the fluid cavity 341, such relatively light particulate contaminants tend to accumulate in the gravity-upward dead volume 337b, thereby preventing or reducing light particles from clogging the tube 314.

[0036]

[0039] The relative arrangement of the filter 344, dead volumes 336a and 366b, and the second opening 314-O2 of the tube 314 means that each dead volume 336a and 336b has corresponding initial filling channels IFP-1 and IFP-2, respectively, which extend from the filter 344 to the dead volumes 336a and 336, respectively, and these initial filling channels IFP-1 and IFP-2 do not surround, directly pass over, or directly adjacent to the second opening 314-O2 of the tube 341. Therefore, when the fluid cavity 341 is initially filled, initial particles generated in or from the filter 344 or its downstream surface DS can enter the dead volumes 336a and 336b without necessarily approaching the second opening 314-O2.

[0037]

[0040] Referring particularly to the implementation shown in Figure 3C, a clog-resistant droplet generator 310 is shown that shares many similarities with the clog-resistant droplet generators 310 in Figures 3A and 3B, with some differences highlighted below.

[0038]

[0041] In the implementation shown in Figure 3C, the clog-preventing droplet generator 310 may be oriented (optionally) in accordance with gravity as indicated by arrow G, and the upper volume VU and tube 314 of the fluid cavity 341 are oriented parallel to each other and at a given angle to gravity. The fluid cavity 341 includes three dead volumes 336a, 336b, and 336c, which take the form of a gravity-upward dead volume 337a and a gravity-downward dead volume 337b (above and below the path P) and a dead volume 337c near the tube 314 at a given angle to gravity. Similar to the implementation in Figure 3B, the relative arrangement of the filter 344, dead volumes 336a and 366b, and the second opening 314-O2 of the tube 314 results in each dead volume 336a and 336b having corresponding initial filling channels IFP-1 and IFP-2, respectively, which extend from the filter 344 to the dead volumes 336a and 336b, and these initial filling channels IFP-1 and IFP-2 do not surround, directly pass over, or directly adjacent to the second opening 314-O2 of the tube 341.

[0039]

[0042] In the implementation shown in Figure 3C, tube 314 has a bend 314b near the second opening 314-O2. The bend 314b makes the second opening 314-O2 perpendicular to gravity (in other words, the cross-section of the second opening 314-O2 is parallel to gravity), so that particles moving upward or downward relative to gravity tend to pass through the second opening 312-O2. In implementations without a bend in the tube, the same effect can be achieved by making the entire tube perpendicular to gravity. Other bends and curves, including snorkel-shaped bends, can also be used in this and other implementations.

[0040]

[0043] As shown in Figure 3C, if the tube 314 has a bend 314b, the distance D is measured from the edge of the cross-section of the second opening 314-O2 to the nearest point to any solid surface (other than the surface of the tube 314 itself), and the length L is measured parallel to the unbent portion of the tube 314 from the seal 345 or any other structure defining the fluid cavity 341 at its second end 341-se to the nearest edge of the cross-section of the second opening 314-O2.

[0041]

[0044] Referring particularly to Figure 3D, a cross-section of another embodiment of the clog-proof droplet generator 310 is shown, in which the filter 344 is positioned in a straight line between the first fluid cavity end 341-fe and the second fluid cavity end 341-se. The clog-proof droplet generator 310 may be oriented during operation such that gravity is perpendicular to the tube 314, as indicated by arrow G, although other orientations may also be used. In this embodiment, there is a dead volume 336 surrounding the tube 314 inside the downstream volume VD of the fluid cavity 341.

[0042]

[0045] Referring in particular to Figure 3E, a cross-section of yet another embodiment of the clog-proof droplet generator 310 is shown. Similar to the embodiment in Figure 3D, the filter 344 is positioned linearly as a whole between the first fluid cavity end 341-fe and the second fluid cavity end 341-se, but in this embodiment, the filter 344 has the shape of a cylindrical filter 344a with a central opening that passes at least partially through in the axial direction, resulting in an internal open volume 344iv of the filter 344a. Thus, the upstream surface US of the filter 344 is oriented perpendicularly in the figure, and the downstream surface DS of the filter 344 is also oriented perpendicularly in the figure. Similar to the embodiment in Figure 3F, the clog-proof droplet generator 310 of Figure 3E may be oriented during operation such that gravity is perpendicular to the tube 314, as indicated by arrow G, resulting in the second opening 314-O2 being perpendicular to the direction of gravity. Other orientations are also possible.

[0043]

[0046] In the embodiment of Figure 3E, tube 314 extends into the central opening or internal open volume 344iv of filter 344a, and a second opening of tube 314-O2 is located within the central opening or internal open volume 344iv of filter 344a. Tube 324 may extend near the upstream end of filter 344a, and thus the second opening 314-O2 is located near the upstream end of filter 344a. The upstream end of tube 314 within the open internal volume 344iv of filter 344a has an outer diameter smaller than the diameter of the open internal volume 344iv (and, in this embodiment, also smaller than the inner diameter of the fluid cavity 341 in the downstream volume VD), so the first outer diameter of tube 314 helps to at least partially form a dead volume 336 or “capture volume” for particles downstream of filter 344a. As shown in Figure 3E, the filter 344a surrounds the internal open volume 344iv in the circumferential direction, allowing droplet material in fluid form to enter the filter 344a circumferentially during use. The clog-resistant droplet generator 310 in Figure 3D can operate in a direction where gravity acts in the direction indicated by arrow G, resulting in the second opening 314-O2 being perpendicular to the direction of gravity. Other orientations can be used as needed. For example, if gravity is downward in the plane of the figure during the operation of the clog-resistant droplet generator 310, the dead volume 336 also functions as a gravity-down dead volume. This also occurs in the implementations shown in Figure 3D and Figure 3F below.

[0044]

[0047] Referring to Figure 3F, a cross-section of yet another embodiment of the clog-preventing droplet generator 310 is shown, where the filter 344 again takes the form of a cylindrical filter 344a and is positioned linearly between a first fluid cavity end 341-fe and a second fluid cavity end 341-se. The cylindrical filter 344b has a central opening or inner open volume 344iv that extends axially throughout the filter 344b, and the tube 314 extends axially throughout the central opening or inner open volume 344iv, with a second opening 314-O2 located outside the central opening or inner open volume 344iv, substantially between the filter 344b and the first end 341-fe of the fluid cavity 341. Alternatively, the second opening 314-O2 may be located inside the filter 344b.

[0045]

[0048] Tube 314 extends throughout the central opening of filter 344b, and the second opening 314-O2 is located outside the central opening of filter 344b. Therefore, there is an initial flow path IFP that extends from filter 344b or its downstream surface DS to the dead volume 336 without surrounding, crossing, or passing near the second opening 314-O2 (the initial part of the path is indicated by the arrow in the figure).

[0046]

[0049] The clog-preventing droplet generator 310 in Figure 3F can operate in a direction where gravity acts in the direction indicated by arrow G, and as a result, the second opening 314-O2 is perpendicular to the direction of gravity. Other orientations can also be used if necessary.

[0047]

[0050] In the implementation shown in Figure 3F, the droplet material flowing from the filter 344 to the second opening 314-O2 of the tube 314 is forced to make a relatively sharp change of direction of approximately 180 degrees before flowing into the second opening 314-O2. In other words, when the clog-preventing droplet generator 310 is used, the droplet material flowing through the fluid cavity makes a change of direction of approximately 180 degrees before flowing into the second opening 314-O2 of the tube 314. By positioning the second opening 314-O2 at a location where the droplet material needs to make a relatively sharp change of direction, additional protection against clogging can be provided by effectively preventing particles with sufficient momentum from "escaping the change of direction" and entering the second opening 314-O2. In other implementations, relatively sharp changes of direction of less than about 180 degrees, such as changes of about 90 degrees or more, 120 degrees or more, 135 degrees or more, or 150 degrees or more, imposed on the droplet material entering the second opening 314-O2 can produce at least some of the same effect.

[0048]

[0051] Figure 3G is a cross-sectional view of another embodiment of the clog-preventing droplet generator 310, where again the filter 344 takes the shape of a cylindrical filter 344a, with the central opening passing through the filter 344a axially (overall). The filter 344a is aligned in line with the first fluid cavity end 341-fe, but the second fluid cavity end 341-se is not aligned in line with the filter 341a and the first fluid cavity end 341-fe, but is located behind the bend in the fluid cavity 341 in the lower right of Figure 3G, thereby enabling the first dead volume 336a in the form of a gravity-downward dead volume 337a extending below the bend in the fluid cavity 341 at the bottom of the figure (when the clog-preventing droplet generator 310 is operating in the orientation relative to gravity as shown). Above filter 344a (i.e., between filter 344a and the first fluid cavity end 314-fe), a second dead volume 336b is provided in the form of a gravity-upward dead volume 337b. A first initial flow path IFP-1 exists from filter 344a to the first dead volume 336a (gravity-downward dead volume 337a) without surrounding, crossing, or passing near the second opening 314-O2. Similarly, a second initial flow path IFP-2 exists from filter 344a to the second dead volume 336b (gravity-upward dead volume 337b) without surrounding, crossing, or passing near the second opening 314-O2. A third dead volume 336c surrounds a portion of tube 314 extending into the downstream volume VD.

[0049]

[0052] Figure 4 shows an EUV light source 400 used with a photolithography apparatus 471. The EUV light source 400 can be an EUV light source such as the EUV light source 100 in Figure 1, or another EUV light source utilizing a clog-prevention droplet generator (not shown), such as one of the implementations of the clog-prevention droplet generator 310 in Figures 3A to 3G. The lithography exposure apparatus 471 receives EUV light 455 generated by the EUV light source 400 and reflects it with one or more illumination mirrors 472 to illuminate a reflection pattern or reticle 473. The EUV light reflected from the pattern or reticle 473 is further reflected and reduced by one or more reduction mirrors 474 and irradiated onto a substrate or wafer 475 (or one or more photosensitive layers on the substrate or wafer 475, not shown) to form a patterned structure in or on the substrate or wafer 475. By using a clogging-prevention droplet generator in the EUV light source 400, the operating time of the EUV light source 400 and the associated photolithography apparatus 471 can be increased.

[0050]

[0053] Implementation can be further explained using the following numbered clauses. 1. A droplet generator for an EUV light source, comprising: a fluid cavity within a structure having a first fluid cavity end that is open or capable of receiving fluid, and a second fluid cavity end; a particle filter within the fluid cavity that divides the fluid cavity into an upstream volume between the upstream surface of the particle filter and the first fluid cavity end, a filter volume occupied by the filter, and a downstream volume located downstream of the downstream surface of the filter; and a tube having a first opening located outside the fluid cavity, extending from the first opening through the second fluid cavity end to a second opening in the downstream volume, and extending into the downstream volume by more than 10% of the distance from the first opening to the second opening. 2. The droplet generator as described in Clause 1, wherein the tube extends into the downstream volume by more than 20% of the distance from the first opening to the second opening. 3. The droplet generator as described in Clause 1, wherein the tube extends into the downstream volume by more than 30% of the distance from the first opening to the second opening. 4. The droplet generator according to Clause 1, wherein the distance from the second opening to any surface other than the surface of the tube is at least 1 millimeter (1 mm). 5. The droplet generator according to Clause 1, wherein the distance from the second opening to any surface other than the surface of the tube is at least 3 mm. 6. The downstream volume is a droplet generator as described in Clause 1, including at least one dead volume. 7. The downstream volume is a droplet generator as described in Clause 6, including at least two dead volumes. 8. The downstream volume includes a dead volume located gravitationally below the fluid flow path when the droplet generator is operating, as described in Clause 1 of the droplet generator. 9. The downstream volume includes a dead volume that is gravitationally above the fluid flow when the droplet generator is operating, as described in Clause 8 of the droplet generator. 10. The downstream volume includes a dead volume that is gravitationally above the fluid flow when the droplet generator is operating, as described in Clause 1 of the droplet generator. 11. The droplet generator as described in Clause 1, wherein the second opening of the tube is positioned substantially perpendicular to gravity when the droplet generator is in operation. 12. The droplet generator according to Clause 11, wherein the tube has at least one bend located within the downstream volume. 13. The droplet generator according to Clause 1, wherein the tube has at least one bend located within the downstream volume. 14. The droplet generator as described in Clause 1, wherein the downstream volume includes one or more dead volumes, one or more initial filling channels extend from the filter to one or more dead volumes, and one or more initial filling channels do not surround the second opening of the tube. 15. The droplet generator according to Clause 1, wherein the filter is positioned in a straight line between the first fluid cavity end and the second fluid cavity end. 16. The droplet generator according to Clause 1, wherein the filter is a cylindrical filter having a central opening that extends axially through the filter at least partially. 17. The second opening of the tube is located within the central opening of the filter, as described in Clause 16, for the droplet generator. 18. The droplet generator according to Clause 1, wherein the filter is a cylindrical filter having a central opening that extends axially through the filter. 19. The droplet generator as described in Clause 18, wherein the second opening of the tube is located within the central opening of the filter. 20. The droplet generator as described in Clause 18, wherein the tube extends throughout the central opening of the filter, and the second opening is located outside the central opening of the filter. 21. A droplet generator according to Clause 18, wherein during use, the droplet material flowing within the fluid cavity changes direction by approximately 90 degrees or more before entering the second opening of the tube. 22. The droplet generator according to Clause 18, wherein during use, the droplet material flowing within the fluid cavity changes direction by approximately 180 degrees and enters the second opening of the tube. 23. A droplet generator for an EUV light source, A filter having an internal volume, configured to prevent particles in a fluid from passing through the filter and reaching the internal volume, and a tube for transporting fluid droplets by the droplet generator, the tube having an upstream tube opening extending into the internal volume of the filter, thereby allowing the fluid to flow through the filter into the upstream tube opening and preventing particles from entering the upstream tube opening. 24. The droplet generator as described in Clause 23, the tube extending in close proximity to the upstream end of the filter. 25. The droplet generator according to Clause 23, wherein the tube further includes an upstream end having an outer diameter smaller than the inner diameter of the internal volume, the outer diameter at least partially forming a capture volume for particles downstream of the filter. 26. A droplet generator as described in Clause 23, wherein the filter surrounds the internal volume in the circumferential direction, and the fluid enters the filter in the circumferential direction.

[0051]

[0054] The above implementations and other implementations fall within the scope of the following claims.

Claims

1. A droplet generator for an EUV light source, A fluid cavity within a structure, having a first fluid cavity end that is open or capable of receiving fluid, and a second fluid cavity end, A particle filter in the fluid cavity, wherein the particle filter divides the fluid cavity into an upstream volume between the upstream surface of the particle filter and the first fluid cavity end, a filter volume occupied by the filter, and a downstream volume located downstream of the downstream surface of the filter. A tube having a first opening located outside the fluid cavity, extending from the first opening through the end of the second fluid cavity to a second opening in the downstream volume, and extending into the downstream volume by more than 10% of the distance from the first opening to the second opening, A droplet generator, including...

2. The droplet generator according to claim 1, wherein the tube extends into the downstream volume by an amount exceeding 20% ​​of the distance from the first opening to the second opening.

3. The droplet generator according to claim 1, wherein the tube extends into the downstream volume by an amount exceeding 30% of the distance from the first opening to the second opening.

4. The droplet generator according to claim 1, wherein the distance from the second opening to any surface other than the surface of the tube is at least 1 millimeter (1 mm).

5. The droplet generator according to claim 1, wherein the distance from the second opening to any surface other than the surface of the tube is at least 3 mm.

6. The droplet generator according to claim 1, wherein the downstream volume includes at least one dead volume.

7. The droplet generator according to claim 6, wherein the downstream volume includes at least two dead volumes.

8. The droplet generator according to claim 1, wherein the downstream volume includes a dead volume gravitationally positioned below the fluid flow path when the droplet generator is operating.

9. The droplet generator according to claim 8, wherein the downstream volume includes a dead volume gravitationally positioned above the fluid flow when the droplet generator is operating.

10. The droplet generator according to claim 1, wherein the downstream volume includes a dead volume gravitationally positioned above the fluid flow when the droplet generator is operating.

11. The droplet generator according to claim 1, wherein the second opening of the tube is positioned substantially perpendicular to gravity when the droplet generator is operating.

12. The droplet generator according to claim 11, wherein the tube has at least one bent portion disposed within the downstream volume.

13. The droplet generator according to claim 1, wherein the tube has at least one bent portion disposed within the downstream volume.

14. The droplet generator according to claim 1, wherein the downstream volume includes one or more dead volumes, one or more initial filling channels extend from the filter to the one or more dead volumes, and the one or more initial filling channels do not surround the second opening of the tube.

15. The droplet generator according to claim 1, wherein the filter is arranged in a straight line between the first fluid cavity end and the second fluid cavity end.

16. The droplet generator according to claim 1, wherein the filter is a cylindrical filter having a central opening that extends axially at least partially through the filter.

17. The droplet generator according to claim 16, wherein the second opening of the tube is located within the central opening of the filter.

18. The droplet generator according to claim 1, wherein the filter is a cylindrical filter having a central opening that extends axially through the filter.

19. The droplet generator according to claim 18, wherein the second opening of the tube is located within the central opening of the filter.

20. The droplet generator according to claim 18, wherein the tube extends throughout the central opening of the filter, and the second opening is located outside the central opening of the filter.

21. The droplet generator according to claim 18, wherein during use, the droplet material flowing in the fluid cavity changes direction by about 90 degrees or more and enters the second opening of the tube.

22. The droplet generator according to claim 18, wherein during use, the droplet material flowing in the fluid cavity changes direction by approximately 180 degrees and enters the second opening of the tube.

23. A droplet generator for an EUV light source, A filter having an internal volume, configured to prevent particles in a fluid from passing through the filter and reaching the internal volume, A tube for supplying droplets of the fluid by the droplet generator, The tube includes an upstream tube opening that extends into the internal volume of the filter, This allows the fluid to flow through the filter into the upstream tube opening, preventing the particles from entering the upstream tube opening, thus creating a droplet generator.

24. The droplet generator according to claim 23, wherein the tube extends in close proximity to the upstream end of the filter.

25. The droplet generator according to claim 23, wherein the tube further includes an upstream end having an outer diameter smaller than the inner diameter of the internal volume, the outer diameter at least partially forming a capture volume for particles downstream of the filter.

26. The droplet generator according to claim 23, wherein the filter surrounds the internal volume in the circumferential direction, and the fluid enters the filter in the circumferential direction.

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