Photolithography is a process by which a reticle having a pattern is irradiated with light to transfer the pattern onto a photosensitive material overlying a semiconductor substrate. Over the history of the semiconductor industry, smaller integrated chip minimum features sizes have been achieved by reducing the exposure wavelength of optical lithography radiation sources to improve photolithography resolution. Extreme ultraviolet (EUV) lithography, which uses extreme ultraviolet (EUV) light is a promising next-generation lithography solution for emerging technology nodes.
Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.
The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.
An extreme ultraviolet (EUV) photolithography system uses extreme ultraviolet radiation having a wavelength between about 10 nm and about 130 nm. One method of producing the extreme ultraviolet radiation is to fire a carbon dioxide (CO2) laser at droplets of tin (Sn). The tin droplets are dropped into an EUV source vessel. As the droplets fall into the EUV source vessel, the CO2 laser hits the tin droplets and heats the tin droplets to a critical temperature that causes atoms of tin to shed their electrons and become a plasma of ionized tin droplets. The ionized tin droplets emit photons having a wavelength between about 1 nm and about 100 nm, which is provided as EUV radiation to an optical lithography system.
The lithography system 100 also employs an illuminator 110. In some embodiments, the illuminator 110 includes various reflective optics such as a single mirror or a mirror system having multiple mirrors in order to direct the light EL from the radiation source 200 onto a mask stage 120, particularly to a mask 130 secured on the mask stage 120.
The lithography system 100 also includes the mask stage 120 configured to secure the mask 130. In some embodiments, the mask stage 120 includes an electrostatic chuck (e-chuck) used to secure the mask 130. In this context, the terms mask, photomask, and reticle are used interchangeably. In the present embodiment, the lithography system 100 is an EUV lithography system, and the mask 130 is a reflective mask. One exemplary structure of the mask 130 includes a substrate with a low thermal expansion material (LTEM). For example, the LTEM may include TiO2 doped SiO2, or other suitable materials with low thermal expansion. The mask 130 includes a reflective multi-layer (ML) deposited on the substrate. The ML includes a plurality of film pairs, such as molybdenum-silicon (Mo/Si) film pairs (e.g., a layer of molybdenum above or below a layer of silicon in each film pair). Alternatively, the ML may include molybdenum-beryllium (Mo/Be) film pairs, or other suitable materials that are configurable to highly reflect the EUV light EL. The mask 130 may further include a capping layer, such as ruthenium (Ru), disposed on the ML for protection. The mask 18 further includes an absorption layer, such as a tantalum boron nitride (TaBN) layer, deposited over the ML. The absorption layer is patterned to define a layer of an integrated circuit (IC). The mask 130 may have other structures or configurations in various embodiments.
The lithography system 100 also includes a projection optics module (or projection optics box (POB)) 140 for imaging the pattern of the mask 130 onto a semiconductor substrate W secured on a substrate stage (or wafer stage) 150 of the lithography system 100. The POB 140 includes reflective optics in the present embodiment. The light EL that is directed from the mask 130 and carries the image of the pattern defined on the mask 130 is collected by the POB 140. The illuminator 110 and the POB 140 may be collectively referred to as an optical module of the lithography system 100. In the present embodiment, the semiconductor substrate W is a semiconductor wafer, such as a silicon wafer or other type of wafer to be patterned. The semiconductor substrate W is coated with a resist layer sensitive to the EUV light EL in the present embodiment. Various components including those described above are integrated together and are operable to perform lithography exposing processes.
The target droplet generator 230 generates plural target droplets TD, which are introduced into a space in the vessel 210 of the radiation source 200. In some embodiments, the target droplets TD are tin (Sn) droplets. Other materials may also be used for the target droplets TD, for example, a tin-containing liquid material such as eutectic alloy containing tin, lithium (Li), and xenon (Xe). In the present embodiments, a temperature control system 300 may be arranged adjacent to or connected to the droplet generator 230, in which the temperature control system 300 is at least configured for cooling the droplet generator 230. In some embodiments, the temperature control system 300 may be configured for cooling and heating the droplet generator 230.
The laser source 220 may include a carbon dioxide (CO2) laser source, a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser source, or another suitable laser source to generate a laser beam LB. The laser beam LB is directed through an output window OW integrated with the collector 240. The output window OW adopts a suitable material substantially transparent to the laser beam LB. The laser beam LB is directed to heat the target droplets TD, such as tin droplets, thereby generating high-temperature plasma which further produces the EUV light EL. The pulses of the laser source 220 and the droplet generating rate of the droplet generator 230 are controlled to be synchronized such that the target droplets TD receive peak powers consistently from the laser pulses of the laser source 220.
The EUV light EL is collected by the collector 240, which further reflects and focuses the EUV light EL for the lithography exposure processes. The collector 240 is designed with suitable coating material and shape, functioning as a mirror for EUV collection, reflection, and focus. In some examples, the collector 240 is designed to have an ellipsoidal geometry. In some examples, the coating material of the collector 240 is similar to the reflective multilayer of the EUV mask 130 (referring to
In some embodiments, the laser beam LB may or may not hit every target droplet TD. For example, some target droplets TD may be purposely missed by the laser beam LB. In the present embodiments, the droplet catcher 250 is installed opposite the target droplet generator 230 and in the direction of the movement of the target droplets TD. The droplet catcher 250 is configured to catch any target droplets that are missed by the laser beam LB.
In some embodiments, the high-temperature plasma may cool down and become vapors or small particles (collectively, debris) PD. The debris PD may deposit onto the surface of the collector 240, thereby causing contamination thereon. Over time, the reflectivity of the collector 240 degrades due to debris accumulation and other factors such as ion damages, oxidation, and blistering. Once the reflectivity is degraded to a certain degree, the collector 240 reaches the end of its usable lifetime and may need to be swapped out.
The vessel 210 has a cover 212 surrounded itself for ventilation and for collecting debris PD. In some embodiments, the cover 212 is made of a suitable solid material, such as stainless steel. The cover 212 is designed and configured around the collector 240. The cover 212 may include a plurality of vanes, which are evenly spaced around the cone-shaped cover 212. In some embodiments, the radiation source 200 further includes a heating unit HU configured around part of the cover 212. The heating unit HU functions to maintain the temperature inside the cover 212 above a melting point of the debris PD so that the debris PD does not solidify on the inner surface of the cover 212. When the debris PD vapor comes in contact with the vanes, it may condense into a liquid form and flow into a lower section of the cover 212. The lower section of the cover 212 may provide holes (not shown) for draining the debris liquid out of the cover 212.
In some embodiments, the radiation source 200 further includes a gas flow mechanism, including a gas supply module 270, an exhaust system 280, and various pipelines for integrating the gas flow mechanism with the collector 240. The gas supply module 270 is configured to provide a gas GA into the vessel 210 and particularly into a space proximate the reflective surface of the collector 240. In some embodiments, the gas GA is hydrogen gas, which has less absorption to the EUV radiation. The gas GA is provided for various protection functions, which include effectively protecting the collector 240 from the contaminations by tin particles. Other suitable gas may be alternatively or additionally used. The gas GA may be introduced into the collector 240 through openings (or gaps) near the output window OW through one or more gas pipelines. The exhaust system 280 includes one or more exhaust lines 282 and one or more pumps 284. The exhaust line 282 is connected to the wall of the vessel 210 for receiving the exhaust. In some embodiments, the cover 212 is designed to have a cone shape with its wide base integrated with the collector 240 and its narrow top section facing the illuminator 110 (
The radiation source 200 is configured in an enclosed space in the vessel 210. The space in the vessel 210 is maintained in a vacuum environment since the air absorbs the EUV radiation. The radiation source 200 may include other components. For example, it may include a central obscuration (not shown) designed and configured to obscure the laser beam LB; and it may include an intermediate focus (IF)-cap module (not shown) configured to provide intermediate focus to the EUV radiation EL.
The reservoir 231 is configured for holding the target material TM. The reservoir 231 may include a sidewall 231a and a bottom wall 231b. The sidewall 231a may be made of steel (e.g., stainless steel) or other suitable thermal conductive material. The sidewall 231a surrounds the outer edge of the bottom wall 231b and extends away from the bottom wall 231b. The heating elements 236b may surround the reservoir 231 for heating the target material TM and keeping the target material TM at a temperature above a melting point of the target material TM for generating liquid droplets. For example, during operation of the EUV radiation source 200 (referring to
In some embodiments, one gas inlet 2321 and one gas outlet (not shown) are formed on the cover 232. The gas inlet 2321 is connected to a gas line PCL for introducing pumping gas, such as argon, into the reservoir 231. For example, a pressurizing device PC is configured to supply gas into the reservoir 231 through the gas line PC. The gas outlet is connected to a gas line and a pump (not shown) for pumping out the gas in the reservoir. By controlling the gas flow in the gas lines connected to the gas inlet 2321 and the gas outlet, the pressure in the reservoir 231 can be manipulated. For example, when gas is continuously supplied into the reservoir 231 via the gas inlet 2321 and when the gas outlet is blocked and not exhausting gas, the pressure in the reservoir 231 increases. As a result, the target material TM in the reservoir 231 can be forced out of the reservoir 231.
The capillary tube 234 includes a first end 234a, a second end 234b, and a sidewall 234c. The sidewall 234c is between the first end 234a and the second end 234b. The first end 234a is coupled, directly or indirectly, to the reservoir 231 that holds the target material TM. The second end 234b includes a nozzle 235 that defines an orifice 2350 through which the target material TM escapes to form the target droplets TD of the target material TM (referring to
In some embodiments, the droplet generator 230 includes a holder 233 connected to the outer shell 237, and the outer shell 237 has portions 237a and 237b on opposite sides of the holder 233. The temperature control system 300 is at least partially over the portion 237b of the outer shell 237. When the droplet generator 230 is inserted into the vessel 210 of the radiation source 200 (referring to
In some cases, when the target material TM in the reservoir 231 is exhausted, a refill process is performed. The refill process includes cooling down the reservoir 231, filling the target material into the reservoir 231, and reheating the reservoir 231, in which the cooling down and reheating steps takes a long time. To be specific, it takes several hours to reduce the temperature of the target material TM/the droplet generator 230 from the operable temperature (e.g., from about 231° C. to about 300° for tin) to a refill temperature lower than the operable temperature, in which the refill temperature may be lower than the melting point of the target material TM. For example, for tin target material TM, the refill temperature may be in a range from about 0° C. to about 210° C., such that operators may then refill target material TM manually and the tin does not vaporize.
In some cases, contaminations in the target material TM may result in clogging (i.e., at least partial blocking) of the nozzle 235, which may impose a lifetime limit on the nozzle 235 and thus the droplet generator 230, such that a maintenance, replacement, or cleaning process (which are in combination briefly referred to as a maintenance process hereinafter) for the droplet generator 230 is performed on a weekly basis. The prevention maintenance process includes depressurizing, cooling down, disassembly, reassembly, and reheat, in which the cooling down and reheating steps also takes a long time. To be specific, it takes several hours to reduce the temperature of the target material TM/the droplet generator 230 from the operable temperature (e.g., from about 231° C. to about 300° for tin) to a maintenance temperature lower than the operable range, such that the operator can detach the droplet generator 230 from the vessel 210 and mount a new droplet generator 230 onto the vessel 210. For example, for tin target material TM, the prevention maintenance temperature may be in a range from about 0° C. to about 130° C., such that operators may perform the maintenance process manually and the tin does not vaporize. As such, the refill process and the prevention maintenance process take a long process time.
In some embodiments of the present disclosure, the temperature control system 300 is disposed adjacent to the reservoir 231 for accelerating the cool down process. The temperature control system 300 may include a passive heat dissipation device (e.g., a heat sink 310) and an active heat dissipation device (e.g., the fan 320). The heat sink 310 is capable of absorbing heats of the reservoir 231 and dissipates the heat by its fins. For example, the heat sink 310 may be mounted on the portion 237b of the outer shell 237. In some embodiments, the heat sink 310 is in contact with the portion 237b of the outer shell 237. The fan 320 may be fixed with respect to the droplet generator 230. For example, herein, the temperature control system 300 may include a bracket 390 supports the fan 320 and connects the fan 320 to the outer shell 237. The fan 320 is disposed on a side of the fins of the heat sink 310 for generating gas flow to accelerate the heat dissipation. In some embodiments, the gas flow may be in a direction normal to the portion 237b of the outer shell 237. In some embodiments, the gas flow may be in a direction inclined with respect to the portion 237b of the outer shell 237. Exemplary fan 320 may be a single fan, a multi fan (e.g., a double fan, a triple fan, or a quadruple fan), an industry-fan, a high-power Fan, or a Turbo Fan. In some embodiments, the droplet generator 230 may optionally include a temperature control circuit or controller 400 electrically connected to the heating elements 236a and 236b and the fan 320 for modulating the temperature of the droplet generator 230. In some other embodiments, the passive heat dissipation device (e.g., a heat sink 310) can be omitted. In some other embodiments, the active heat dissipation device (e.g., the fan 320) can be omitted.
Through the configuration of the temperature control system 300, the target material TM in the reservoir 231 may be fast cooled, and the refill process and the prevention maintenance process take less process time, such that the yield rate is increased. Due to the short refill time and/or the short maintenance time, the contamination or particle in the vessel 210 or on the collector 240 can be effectively reduced. Furthermore, due to the short refill time and/or the short maintenance time, it is less likely that the target droplets TD in the vessel 210 are oxidized by oxygen-containing gas, e.g., O2, H2O, the like. Also, it is less likely that the target material TM in the droplet generator 230 is oxidized. The short refill time and/or the short maintenance time may also increase the spatial stability of the target droplets TD, which is advantageous for a high repetition operation.
In some embodiments, the droplet generator 230 may further include sensors 510 located adjacent to the reservoir 231. For example, the sensors 510 are between the portion 237b of the outer shell 237 and the sidewall 231a of the reservoir 231. In some embodiments, the droplet generator 230 may further include sensors 520 near the tube 234. The sensors 510 and 520 may detect a condition of the droplet generator, such as a pressure condition, a temperature condition, or the like. The controller 400 is connected with the sensor 500, the heating elements 236a and 236b, and the temperature control system 300. In some embodiments, the controller 400 may further be connected with the pressurizing device PC.
In some embodiments, the droplet generator 230 may optionally include a charging circuit configured for charging ions into the droplet generator 230. The charging circuit may include an electrode positioned at the bottom wall 231b of the reservoir 231. The electrode is connected to ground or connected to a power supply. However, it should be appreciated that many variations and modifications can be made to embodiments of the disclosure. In some other embodiments, the electrode is omitted, and the bottom wall 231b and/or the sidewall 231a of the reservoir 231 is made of electrically conductive material and is electrically connected to ground or connected to the power supply.
When the refill process or the prevention maintenance process is performed, a liquid stored in the liquid tank 332L is introduced to adjacent the reservoir 231 though the liquid input pipe LIP, and absorbs the heat of the reservoir 231. Then, the liquid is directed to the heating/cooling element 334L. The heating/cooling element 334L remove the heat of the liquid, and send the liquid to the liquid tank 332L. The liquid may be water, polar liquids, fluorinates, low viscosity oils, other organic liquids, molten salts, molten metals, or other suitable thermally conductive liquid. For example, suitable thermally conductive liquid includes a carrier liquid (e.g., water) dispersed with suitable thermally conductive nanoparticles, such as copper oxide, alumina, titanium dioxide, carbon nanotubes, silica, copper, silver rods, or other metals.
In some embodiments, the heating/cooling element 334L is a cooling system, such as a liquid nitride system, a liquid hafnium system, a cryogenics system, or a water cooling system. In some other embodiments, the heating/cooling element 334L is a heating and cooling system, in which the heating/cooling element 334L may heat or cool the liquid. For example, after the refill process or the prevention maintenance process is performed, the temperature control system 300 may heat the droplet generator 230 by the heating/cooling element 334L. In some other embodiments, the active temperature control device 330 may include a cooling liquid gun ejecting a cooling liquid to the heat sink 310 directly, in which the cooling liquid may absorb the heat of the heat sink 310 and evaporate. For example, the cooling liquid may be water. The cooling liquid gun may be physically separated from the heat sink 310 and the droplet generator 230. In some other embodiments, a pipe (e.g., the pipe LIP) may connect the cooling liquid gun to the heat sink 310, such that the cooling liquid is ejected from the cooling liquid gun to reach the heat sink 310 through the pipe LIP. Other details of the present embodiments are similar to those aforementioned, and not repeated herein.
The heating/cooling element 334G may be a gas thermal exchanger with a compressor, a refrigerant based system (e.g., refrigerator) with a compressor, or the like. For example, by compressing the coolant from a gas state into a liquid state, heat is released from the coolant; by letting the coolant expands from the liquid state into the gas state, the coolant can soak up heat. In some embodiments, the heating/cooling element 334G may be a heating and cooling system, which may conduct a rapid thermal process to heat the droplet generator 230 after the refill process or the prevention maintenance process. For example, the heating/cooling element 334G may heat the gas coming from the gas output pipe GOP, and the heated gas is sent to the heat sink 310 through the gas input pipe GIP. In some embodiments where a rapid thermal process is conducted, the gas may be water vapor. Other details of the present embodiments are similar to those aforementioned, and not repeated herein. In some other embodiments, the active temperature control device 330 may include a cooling gas gun ejecting cooling gas to the heat sink 310 directly. For example, the cooling gas may be nitrogen. The cooling gas gun may be physically separated from the heat sink 310 and the droplet generator 230. In some other embodiments, a pipe (e.g., the pipe GIP) may connect the cooling gas gun to the heat sink 310, such that the cooling gas is ejected from the cooling gas gun to reach the heat sink 310 through the pipe GIP.
In some embodiments, the wires OM and IM are made of solid conductive material (e.g., aforementioned Cu, Al, Cu—Al Alloy), and when the refill process or the prevention maintenance process is performed, the thermal conductive wires OM and IM may absorbs the heat of the reservoir 231 and transmits the heat to the solid heating/cooling element 334S. The solid heating/cooling element 334S absorbs and removes the heat of the thermal conductive wire OM, such that the thermal conductive wire OM is capable of continuing absorbing the heat of the reservoir 231. In some embodiments, the passive dissipation device (e.g., the heat sink 310) is thermally coupled to the thermal conductive wire IM and thermal conductive wire OM for drawing heat from the thermal conductive wire IM and thermal conductive wire OM to the ambient, thereby cooling the liquid. In some other embodiments, the wires OM and IM are composited. For example, the wires OM and IM has a hollow tube surrounding by solid conductive walls, and the hollow tube may accommodate liquid or gas for heat transmission. The composited wires OM and IM may be connected to the solid heating/cooling element 334S and the solid tank 332S, respectively. In some embodiments, the fan device (referring to
In some embodiments, the temperature control system 300 may conduct a rapid thermal process to heat or cool the droplet generator 230. For example, the thermal conductive wire IM/OM can be connected to a heating wire, heating rod, heating piece, or the like. In some embodiments, the solid heating/cooling element 334S may act as a heating and cooling element. The droplet generator 230 can be fast controlled between room temperature and the target temperature such as about 300° C. or up to about 2602° C. Other details of the present embodiments are similar to those aforementioned, and not repeated herein.
The storage tank ST is configured to contain the target material TM. The target material TM in the storage tank ST is supplied to the droplet generator 230 via a refill system 260. The refill system 260 may include a low-pressure vessel 262, a refill line 264, a high-pressure vessel 266, and a transfer line 268. The low-pressure vessel 262 is coupled to the storage tank ST through a supply line SL. The refill line 264 connects the low-pressure vessel 262 to the high-pressure vessel 266. The transfer line 268 connects the high-pressure vessel 266 to the droplet generator 230. The refill system 260 may further include pumps or valves (not shown in
During the EUV lithography process, the pressurizing device PC may be configured to pressurize the target material TM into the tube 234 for generate droplet of the target material TM. The pressurizing device PC may be a gas supply connected with the reservoir 231 through the gas inlet 2321.
As aforementioned embodiments, the temperature control system 300 may include a heat sink 310 and a fan 320. The controller 400 is connected to the fan 320 for controlling the operation of the fan 320. The temperature control system 300 (e.g., including the heat sink 310 and/or the fan 320) may be over the portion 237b of the outer shell 237, the transfer line 268, a portion of a sidewall of the high-pressure vessel 266, and/or a portion of a sidewall of the low-pressure vessel 262. That is, the temperature control system 300 may be used to control a temperature of the refill system 260. Other details of the present embodiments are similar to those aforementioned, and not repeated herein.
As shown in step S21, under the control of the controller 400, the heating elements 236a and 236b are turned off. At step S22, the temperature control system 300 cools the reservoir 231 of the droplet generator 230 and/or the refill system 260 down to a maintenance temperature (e.g., the temperature point TM), such that operators may approach and touch the droplet generator 230. At step S23, the droplet generator 230 having the clogged nozzle is dissembled from the vessel 210 by operators. At step S24, another generator 230 having a clean nozzle is assembled onto the vessel 210 by operators. At step S25, the reservoir 231 of the another droplet generator 230 is purged for removing oxide-containing gas, thereby preventing the target material TM from oxidation. At step S26, under the control of the controller 400, the heating elements 236a and 236b are turned on to heat the nozzle 235 and the reservoir 231 of the droplet generator 230. In some embodiments, at step S26, the temperature control system 300 may also be controlled to heat the reservoir 231.
In
Based on the above discussions, it can be seen that the present disclosure offers advantages. It is understood, however, that other embodiments may offer additional advantages, and not all advantages are necessarily disclosed herein, and that no particular advantage is required for all embodiments. One advantage is that refill process and the prevention maintenance process take less process time, such that the yield rate is increased. Another advantage is that the contamination or particles in the EUV vessel or on the collector can be effectively reduced due to the short refill time and/or the short maintenance time. Still another advantage is that, due to the short refill time and/or the short maintenance time, it is less likely that the target droplets in the EUV vessel are oxidized. Also, it is less likely that the target material in the droplet generator is oxidized. Still another advantage is that the short refill time and/or the short maintenance time may also increase the spatial stability of the target droplets, which is advantageous for a high repetition operation.
According to some embodiments of the present disclosure, a droplet generator assembly includes a storage tank, a refill system, a droplet generator, and a temperature control system. The storage tank is configured to store a target material. The refill system is connected to the storage tank. The droplet generator includes a reservoir and a nozzle connected to the reservoir, in which the droplet generator is connected to the refill system, and the refill system is configured to deliver the target material to the reservoir. The temperature control system is adjacent to the refill system or the reservoir.
According to some embodiments of the present disclosure, a radiation source apparatus includes a vessel, a droplet generator, and a temperature control system. The droplet generator is detachably mounted on the vessel. The droplet generator includes a reservoir, a nozzle connected to the reservoir, and an outer shell accommodating the reservoir, and the outer shell has a first portion inserted into the vessel and a second portion extending out of the vessel when the droplet generator is mounted on the vessel. The temperature control system is on the second portion of the outer shell and configured to cool the reservoir.
According to some embodiments of the present disclosure, a method includes heating a target material in a reservoir; generating a target droplet from the heated target material; impinging a laser onto the target droplet for producing extreme violet light; and cooling down the reservoir.
The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.
This application claims priority to U.S. Provisional Application Ser. No. 62/738,739, filed Sep. 28, 2018, which is herein incorporated by reference.
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8154000 | Hergenhan | Apr 2012 | B2 |
9018604 | Niimi | Apr 2015 | B2 |
10495974 | Tsai | Dec 2019 | B2 |
20060192155 | Algots | Aug 2006 | A1 |
Number | Date | Country | |
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20200107427 A1 | Apr 2020 | US |
Number | Date | Country | |
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62738739 | Sep 2018 | US |