Patent Application
20110140008
The disclosed subject matter relates to a beam transport system for amplified light of a high power laser system.
Extreme ultraviolet (“EUV”) light, for example, electromagnetic radiation having wavelengths of around 50 nm or less (also sometimes referred to as soft x-rays), and including light at a wavelength of about 13 nm, can be used in photolithography processes to produce extremely small features in substrates, for example, silicon wafers.
Methods to produce EUV light include, but are not necessarily limited to, converting a material into a plasma state that has an element, for example, xenon, lithium, or tin, with an emission line in the EUV range. In one such method, often termed laser produced plasma (“LPP”), the required plasma can be produced by irradiating a target material, for example, in the form of a droplet, stream, or cluster of material, with an amplified light beam that can be referred to as a drive laser. For this process, the plasma is typically produced in a sealed vessel, for example, a vacuum chamber, and monitored using various types of metrology equipment.
CO2 amplifiers and lasers, which output an amplified light beam at a wavelength of about 10600 nm, can present certain advantages as a drive laser irradiating the target material in an LPP process. This may be especially true for certain target materials, for example, for materials containing tin. For example, one advantage is the ability to produce a relatively high conversion efficiency between the drive laser input power and the output EUV power. Another advantage of CO2 drive amplifiers and lasers is the ability of the relatively long wavelength light (for example, as compared to deep UV at 198 nm) to reflect from relatively rough surfaces such as a reflective optic that has been coated with tin debris. This property of 10600 nm radiation can allow reflective mirrors to be employed near the plasma for, for example, steering, focusing and/or adjusting the focal power of the amplified light beam.
In some general aspects, an extreme ultraviolet (EUV) light system includes a drive laser system that produces an amplified light beam; a target material delivery system configured to produce a target material at a target location; and a beam delivery system that is configured to receive the amplified light beam emitted from the drive laser system and to direct the amplified light beam toward the target location. The beam delivery system includes a beam expansion system that includes a curved mirror having a reflective surface that is an off-axis segment of an elliptic paraboloid.
Implementations can include one or more of the following features. For example, the EUV light system can include an extreme ultraviolet light vacuum chamber within which the target location is positioned, the chamber housing an extreme ultraviolet light collector configured to collect extreme ultraviolet light emitted from the target material when the amplified light beam crosses the target location and strikes the target material.
The target material delivery system can include a target material outlet capable of outputting the target material along a target material path that crosses the target location.
The curved mirror can be a diverging curved mirror. In this case, the EUV light system can also include a converging lens. The curved mirror can receive the amplified light beam from the drive laser system, and the converging lens can receive the diverging light beam reflected off the curved mirror and substantially collimate the light beam into a collimated amplified light beam having a cross section that is larger than the cross section of the amplified light beam impinging upon the curved mirror. The converging lens can be made of diamond.
The curved mirror can be a converging curved mirror. In this case, the EUV light system can also include a diverging lens. The diverging lens can receive the amplified light beam from the drive laser system. The converging mirror can receive the diverging light beam transmitted through the diverging lens and reflect a substantially collimated amplified light beam having a cross section that is larger than the cross section of the amplified light beam impinging upon the diverging lens. The diverging lens can be made of diamond.
The EUV light system can include another curved mirror having a reflective surface that is an off-axis segment of an elliptic paraboloid. The curved mirror can be a diverging curved mirror that receives the amplified light beam from the drive laser system, and the other curved mirror can be a converging curved mirror that is placed to receive the diverging light beam reflected off the curved mirror and to substantially collimate the light beam into a collimated amplified light beam having a cross section that is larger than the cross section of the amplified light beam impinging upon the curved mirror.
The curved mirror can include a copper substrate and the reflective surface can include a highly reflective coating applied to the copper substrate. The coating can reflect light at the wavelength of the amplified light beam.
In another general aspect, an extreme ultraviolet light system includes a drive laser system that produces an amplified light beam; a target material delivery system configured to produce a target material at a target location; and a beam delivery system that is configured to receive the amplified light beam emitted from the drive laser system and to direct the amplified light beam toward the target location. The beam delivery system includes a beam expansion system that includes at least one curved mirror that expands a size of the amplified light beam, and a focusing element that includes a converging lens configured and arranged to focus the amplified light beam at the target location.
Implementations can include one or more of the following features. For example, the converging lens can include one or more aspheric surfaces. The converging lens can be a meniscal lens. The converging lens can be made of zinc selenide. The converging lens can include an anti-reflective coating and transmit at least 95% of the light at the wavelength of the amplified light beam.
The EUV light system can include an extreme ultraviolet light vacuum chamber within which the target location is positioned, the chamber housing an extreme ultraviolet light collector configured to collect extreme ultraviolet light emitted from the target material when the amplified light beam crosses the target location and strikes the target material. The converging lens can be inside the light chamber. The converging lens can be a window of the light chamber that provides a leak tight barrier between the vacuum within the light chamber and an external environment. The converging lens can have a numerical aperture of at least 0.1.
The beam delivery system can include an actuation system mechanically coupled to the converging lens and configured to move the converging lens to focus the amplified light beam to the target location.
The beam delivery system can include a metrology system that detects the amplified light beam reflected at the converging lens. The EUV light system can include a controller connected to the metrology system and to the actuation system coupled to the converging lens. The controller can be configured to move the converging lens based on the output from the metrology system. The beam delivery system can include a pre-lens mirror that redirects the amplified light beam from the expansion system toward the converging lens. The pre-lens mirror can be coupled to a mirror actuation system that is connected to the controller to permit movement of the mirror based on the output from the metrology system.
The target material delivery system can include a target material outlet capable of outputting the target material along a target material path that crosses the target location.
In another general aspect, extreme ultraviolet light is produced by producing a target material at a target location; supplying pump energy to a gain medium of at least one optical amplifier in a drive laser system to produce an amplified light beam; expanding a transverse cross sectional area of the amplified light beam; and focusing the expanded amplified light beam onto the target location by directing the expanded amplified light beam through a converging lens.
Implementations can include one or more of the following features. For example, extreme ultraviolet light emitted from the target material when the amplified light beam crosses the target location and strikes the target material can be collected.
The converging lens can be moved to focus the amplified light beam to the target location based on an analysis of light reflected off the converging lens.
The expanded amplified light beam can be reflected off a pre-lens mirror that redirects the expanded amplified light beam toward the converging lens. The pre-lens mirror can be moved based on an analysis of light reflected off the converging lens.
In another general aspect, an extreme ultraviolet light system includes a drive laser system that produces an amplified light beam; a target material delivery system configured to produce a target material at a target location; an extreme ultraviolet light vacuum chamber defining an interior space that is configured to be evacuated to sub-atmospheric pressure, a beam delivery system that is configured to receive the amplified light beam emitted from the drive laser system and to direct the amplified light beam toward the target location. The vacuum chamber houses within the interior space an extreme ultraviolet light collector configured to collect extreme ultraviolet light emitted from the target material when the amplified light beam crosses the target location and strikes the target material. The target location is in the interior space of the vacuum chamber. The beam delivery system includes a beam expansion system that expands a size of the amplified light beam, and a focusing element that includes a converging lens configured and arranged to focus the amplified light beam at the target location. The focusing element forms a pressure-resistant window of the vacuum chamber to separate the interior space from an exterior space.
In another general aspect, an extreme ultraviolet light system includes a drive laser system that produces an amplified light beam; a target material delivery system configured to produce a target material at a target location; a mirror that receives the amplified light beam and redirects the amplified light beam, and a focusing element that includes a converging lens configured and arranged to focus the redirected amplified light beam at the target location. The mirror includes a feature that separates a diagnostic portion of light reflected from a surface of the converging lens from the amplified light beam and directs the separated diagnostic light portion to a metrology system that is configured to analyze properties of the amplified light beam based on the collected separated diagnostic light portion.
Implementations can include one or more of the following features. For example, the mirror and the focusing element can be a part of a beam delivery system that is configured to receive the amplified light beam emitted from the drive laser system and to direct the amplified light beam toward the target location. The beam delivery system can include a set of optical components that change one or more of a direction and a wavefront of the amplified light beam before directing the amplified light beam toward the mirror.
The mirror feature can be an opening defined within a central region of the mirror. The mirror feature can be a facet defined at a central region of the mirror.
In another general aspect, extreme ultraviolet light is produced by receiving a measured light parameter associated with extreme ultraviolet light emitted from a target material at a target location when an amplified light beam from a laser system strikes the target material; receiving an image of a diagnostic extreme ultraviolet light portion reflected off the target material at the target location; receiving an image of a diagnostic amplified light portion that is reflected off a converging lens that focuses the amplified light beam to the target location to strike the target material; analyzing the received measured light parameter, the received diagnostic extreme ultraviolet light portion image, and the received diagnostic amplified light portion image; and controlling one or more of components within a beam transport system placed between the laser system and the target location to adjust a relative position between the amplified light beam and the target location to thereby increase an amount of extreme ultraviolet light produced when the amplified light beam strikes the target material based on the analysis.
Implementations can include one or more of the following features. For example, the one or more of components within the beam transport system can be controlled by adjusting one or more of a position of the converging lens and a position of one or more mirrors within the beam transport system. The position of one or more mirrors within the beam transport system can be adjusted by adjusting a mirror that includes a feature that separates the diagnostic amplified light portion from the amplified light beam. An image of a diagnostic portion of a guide laser beam that is directed to the target location can be received, and the received diagnostic amplified light portion image can be analyzed by analyzing the diagnostic guide laser beam portion image.
In another general aspect, extreme ultraviolet light is produced by producing a target material at a target location; supplying pump energy to a gain medium of at least one optical amplifier in a drive laser system to produce an amplified light beam; expanding a transverse cross sectional area of the amplified light beam by directing the amplified light beam through a beam expansion system that includes impinging the amplified light beam upon a curved mirror having a reflective surface that is an off-axis segment of an elliptic paraboloid; and delivering the expanded amplified light beam to the target location.
Implementations can include one or more of the following features. For example, extreme ultraviolet light emitted from the target material at the target location can be collected when the amplified light beam crosses the target location and strikes the target material. The target material can be outputted along a target material path that crosses the target location.
The curved mirror can be a diverging curved mirror, and the amplified light beam can be directed through the beam expansion system by causing the amplified light beam to diverge by reflection off the diverging curved mirror and by collimating the diverging amplified light beam with another curved mirror having a reflective surface that is an off-axis segment of an elliptic paraboloid.
Referring to
The light source 100 also includes a beam delivery system between the laser system 115 and the target location 105, the beam delivery system including a beam transport system 120 and a focus assembly 122. The beam transport system 120 receives the amplified light beam 110 from the laser system 115, and steers and modifies the amplified light beam 110 as needed and outputs the amplified light beam 110 to the focus assembly 122. The focus assembly 122 receives the amplified light beam 110 and focuses the beam 110 to the target location 105.
As discussed below, the beam transport system 120 includes, among other components, at least one mirror that has a reflective surface shape that is an off-axis segment of paraboloid of revolution. Such a design enables the beam 110 to be expanded between the laser system 115 and the focus assembly 122. As also discussed below, the focus assembly 122 includes, among other components, a lens or mirror that focuses the beam 110 onto the target location 105. Before providing details about the beam transport system 120 and the focus assembly 122, a general description of the light source 100 is provided with reference to
The light source 100 includes a target material delivery system 125, for example, delivering the target material 114 in the form of liquid droplets, a liquid stream, solid particles or clusters, solid particles contained within liquid droplets or solid particles contained within a liquid stream. The target material 114 can include, for example, water, tin, lithium, xenon, or any material that, when converted to a plasma state, has an emission line in the EUV range. For example, the element tin can be used as pure tin (Sn), as a tin compound, for example, SnBr4, SnBr2, SnH4, as a tin alloy, for example, tin-gallium alloys, tin-indium alloys, tin-indium-gallium alloys, or any combination of these alloys. The target material 114 can include a wire coated with one of the above elements, such as tin. If the target material is in a solid state, it can have any suitable shape, such as a ring, a sphere, or a cube. The target material 114 can be delivered by the target material delivery system 125 into the interior of a chamber 130 and to the target location 105. The target location 105 is also referred to as an irradiation site, the place where the target material 114 is irradiated by the amplified light beam 110 to produce plasma.
In some implementations, the laser system 115 can include one or more optical amplifiers, lasers, and/or lamps for providing one or more main pulses and, in some cases, one or more pre-pulses. Each optical amplifier includes a gain medium capable of optically amplifying the desired wavelength at a high gain, an excitation source, and internal optics. The optical amplifier may or may not have laser mirrors or other feedback devices that form a laser cavity. Thus, the laser system 115 produces an amplified light beam 110 due to the population inversion in the gain media of the laser amplifiers even if there is no laser cavity. Moreover, the laser system 115 can produce an amplified light beam 110 that is a coherent laser beam if there is a laser cavity to provide enough feedback to the laser system 115. The term “amplified light beam” encompasses one or more of: light from the laser system 115 that is merely amplified but not necessarily a coherent laser oscillation and light from the laser system 115 that is amplified and is also a coherent laser oscillation.
The optical amplifiers in the laser system 115 can include as a gain medium a filling gas that includes CO2 and can amplify light at a wavelength of between about 9100 and about 11000 nm, and in particular, at about 10600 nm, at a gain greater than or equal to 1000. Suitable amplifiers and lasers for use in the laser system 115 can include a pulsed laser device, for example, a pulsed, gas-discharge CO2 laser device producing radiation at about 9300 nm or about 10600 nm, for example, with DC or RF excitation, operating at relatively high power, for example, 10 kW or higher and high pulse repetition rate, for example, 50 kHz or more. The optical amplifiers in the laser system 115 can also include a cooling system such as water that can be used when operating the laser system 115 at higher powers.
Referring to
Although three optical amplifiers 202, 204, 206 are shown, it is possible that as few as one amplifier and more than three amplifiers could be used in this implementation. In some implementations, each of the CO2 amplifiers 202, 204, 206 can be an RF pumped axial flow CO2 laser cube having a 10 meter amplifier length that is folded by internal mirrors.
Alternatively, and with reference to
In this implementation, a laser cavity can be formed by adding a rear partially reflecting optic 264 to the laser system 115 and placing the target material 114 at the target location 105. The optic 264 can be, for example, a flat mirror, a curved mirror, a phase-conjugate mirror, or a corner reflector having a reflectivity of about 95% for wavelengths of about 10600 nm (the wavelength of the amplified light beam 110 if CO2 amplifier chambers are used).
The target material 114 and the rear partially reflecting optic 264 act to reflect some of the amplified light beam 110 back into the laser system 115 to form the laser cavity. Thus, the presence of the target material 114 at the target location 105 provides enough feedback to cause the laser system 115 to produce coherent laser oscillation and in this case, the amplified light beam 110 can be considered a laser beam. When the target material 114 isn't present at the target location 105, the laser system 115 may still be pumped to produce the amplified light beam 110 but it would not produce a coherent laser oscillation unless some other component within the source 100 provides enough feedback. In particular, during the intersection of the amplified light beam 110 with the target material 114, the target material 114 may reflect light along the beam path 262, cooperating with the optic 264 to establish an optical cavity passing through the amplifier chambers 250, 252, 254. The arrangement is configured so the reflectivity of the target material 114 is sufficient to cause optical gains to exceed optical losses in the cavity (formed from the optic 264 and the droplet) when the gain medium within each of the chambers 250, 252, 254 is excited generating a laser beam for irradiating the target material 114, creating a plasma, and producing an EUV light emission within the chamber 130. With this arrangement, the optic 264, amplifiers 250, 252, 254, and the target material 114 combine to form a so-called “self-targeting” laser system in which the target material 114 serves as one mirror (a so-called plasma mirror or mechanical q-switch) of the optical cavity. Self-targeting laser systems are disclosed in U.S. application Ser. No. 11/580,414 filed on Oct. 13, 2006 entitled, Drive Laser Delivery Systems for EUV Light Source, Attorney Docket Number 2006-0025-01, the entire contents of which are hereby incorporated by reference herein.
Depending on the application, other types of amplifiers or lasers can also be suitable, for example, an excimer or molecular fluorine laser operating at high power and high pulse repetition rate. Examples include a solid state laser, for example, having a fiber or disk shaped gain medium, a MOPA configured excimer laser system, as shown, for example, in U.S. Pat. Nos. 6,625,191; 6,549,551; and 6,567,450; an excimer laser having one or more chambers, for example, an oscillator chamber and one or more amplifying chambers (with the amplifying chambers in parallel or in series); a master oscillator/power oscillator (MOPO) arrangement, a power oscillator/power amplifier (POPA) arrangement; or a solid state laser that seeds one or more excimer or molecular fluorine amplifier or oscillator chambers, may be suitable. Other designs are possible.
At the irradiation site, the amplified light beam 110, suitably focused by the focus assembly 122, is used to create plasma having certain characteristics that depend on the composition of the target material 114. These characteristics can include the wavelength of the EUV light produced by the plasma and the type and amount of debris released from the plasma.
The light source 100 includes a collector mirror 135 having an aperture 140 to allow the amplified light beam 110 to pass through and reach the target location 105. The collector mirror 135 can be, for example, an ellipsoidal mirror that has a first focus at the target location 105 and a second focus at an intermediate location 145 (also called an intermediate focus) where the EUV light can be output from the light source 100 and can be input to, for example, an integrated circuit lithography tool (not shown). The light source 100 can also include an open-ended, hollow conical shroud 150 (for example, a gas cone) that tapers toward the target location 105 from the collector mirror 135 to reduce the amount of plasma-generated debris that enters the focus assembly 122 and/or the beam transport system 120 while allowing the amplified light beam 110 to reach the target location 105. For this purpose, a gas flow can be provided in the shroud that is directed toward the target location 105.
The light source 100 can also include a master controller 155 that is connected to a droplet position detection feedback system 156, a laser control system 157, and a beam control system 158. The light source 100 can include one or more target or droplet imagers 160 that provide an output indicative of the position of a droplet, for example, relative to the target location 105 and provide this output to the droplet position detection feedback system 156, which can, for example, compute a droplet position and trajectory from which a droplet position error can be computed either on a droplet by droplet basis or on average. The droplet position detection feedback system 156 thus provides the droplet position error as an input to the master controller 155. The master controller 155 can therefore provide a laser position, direction, and timing correction signal, for example, to the laser control system 157 that can be used, for example, to control the laser timing circuit and/or to the beam control system 158 to control an amplified light beam position and shaping of the beam transport system 120 to change the location and/or focal power of the beam focal spot within the chamber 130.
The target material delivery system 125 includes a target material delivery control system 126 that is operable in response to a signal from the master controller 155, for example, to modify the release point of the droplets as released by a delivery mechanism 127 to correct for errors in the droplets arriving at the desired target location 105.
Additionally, the light source 100 can include a light source detector 165 that measures one or more EUV light parameters, including but not limited to, pulse energy, energy distribution as a function of wavelength, energy within a particular band of wavelengths, energy outside of a particular band of wavelengths, and angular distribution of EUV intensity and/or average power. The light source detector 165 generates a feedback signal for use by the master controller 155. The feedback signal can be, for example, indicative of the errors in parameters such as the timing and focus of the laser pulses to properly intercept the droplets in the right place and time for effective and efficient EUV light production.
The light source 100 also includes a guide laser 175 that can be used to align various sections of the light source 100 or to assist in steering the amplified light beam 110 to the target location 105. In connection with the guide laser 175, the light source 100 includes a metrology system 124 that is placed within the focus assembly 122 to sample a portion of light from the guide laser 175 and the amplified light beam 110. In other implementations, the metrology system 124 is placed within the beam transport system 120.
The metrology system 124 can include an optical element that samples or re-directs a subset of the light, such optical element being made out of any material that can withstand the powers of the guide laser beam and the amplified light beam 110. For example, the sample optical element within the metrology system 124 can include a substrate made of zinc selenide (ZnSe) that is coated with an anti-reflection coating. The sample optical element within the metrology system 124 can be a diffraction grating positioned at an angle relative to the longitudinal direction of the amplified light beam 110 to decouple some light from the amplified light beam 110 and from the guide laser 175 for diagnostic purposes. Because the wavelengths of the amplified light beam 110 and beam of the guide laser 175 are distinct from each other, they can be directed away from the diffraction grating at separate angles to enable separation of the beams. A beam analysis system is formed from the metrology system 124 and the master controller 155 since the master controller 155 analyzes the sampled light from the guide laser 175 and uses this information to adjust components within the focus assembly 122 through the beam control system 158. In other implementations, the metrology system 124 includes one or more dichroic mirrors placed within the focus assembly 122 to separate the amplified light beam 110 from the guide laser 175 and to provide for separate analyses. Such a metrology system is described in “Metrology System for Extreme Ultra-Violet Light Source”, filed concurrently with this application, and assigned docket number 002-017001/2009-0027-01, which is incorporated herein by reference in its entirety.
Thus, in summary, the light source 100 produces an amplified light beam 110 that is directed at the target material at the target location 105 to convert the target material into plasma that emits light in the EUV range. The amplified light beam 110 operates at a particular wavelength that is determined based on the design and properties of the laser system 115, as will be discussed in more detail below. Additionally, the amplified light beam 110 can be a laser beam when the target material provides enough feedback back into the laser system 115 to produce coherent laser light or if the drive laser system 115 includes suitable optical feedback to form a laser cavity.
As discussed above, the drive laser system 115 includes one or more optical amplifiers and several optical components (for example, about 20 to 50 mirrors), the beam transport system 120 and the focus assembly 122 include several optical components such as, for example, mirrors, lenses, and prisms. All of these optical components have a wavelength range that encompasses the wavelength of the amplified light beam 110 to permit efficient formation of the amplified light beam 110 and output of the amplified light beam 110 to the target location 105. Additionally, one or more of the optical components can be formed with a multilayer dielectric anti-reflective interference coating on a substrate.
Referring to
The beam transport system 315 includes a set of mirrors 330, 332, 334, 336, and 338 (which are sometimes referred to as fold mirrors) that change the direction of the amplified light beam 325. The fold mirrors 330, 332, 334, 336, 338 can be made of any substrates and coatings that are suitable for reflecting the amplified light beam 325. Thus, they can be made of substrates and coatings that are selected to reflect most light at the wavelength of the amplified light beam 325. In some implementations, one or more of the fold mirrors 330, 332, 334, 336, 338 are made of a highly reflective coating such as maximum metal reflector (MMR) coating produced by II-VI Infrared of Saxonburg, Pa. over an oxygen-free high conductivity (OFHC) copper substrate. Other coatings that can be used for the fold mirrors 330, 332, 334, 336, 338 include gold and silver, and other substrates to which the coating can be applied include silicon, molybdenum, and aluminum. One or more of the fold mirrors 330, 332, 334, 336, 338 can be water cooled, for example, by flowing water or some other appropriate coolant through their substrates.
The beam transport system 315 also includes a beam expansion system 340 that expands the amplified light beam 325 such that the transverse size of the amplified light beam 325 that exits the beam expansion system 340 is larger than the transverse size of the amplified light beam 325 that enters the beam expansion system 340. The beam expansion system 340 includes at least a curved mirror that has a reflective surface that is an off-axis segment of an elliptic paraboloid (such a mirror is also referred to as an off-axis paraboloid mirror). The beam expansion system 340 can include other optical components that are selected to redirect and expand or collimate the amplified light beam 325. Various designs for the beam expansion system 340 are described below with respect to
As shown in
As also shown in
The focus assembly 320 can also include a metrology system 360 that captures light 365 reflected from the lens 355. This captured light can be used to analyze properties of the amplified light beam 325 and light from the guide laser 175, for example, to determine a position of the amplified light beam 325 and monitor changes in a focal length of the amplified light beam 325. Specifically, the captured light can be used to provide information regarding the position of the amplified light beam 325 on the lens 355, and to monitor focal length changes of the lens 355 due to changes in temperature (for example heating) of the lens 355.
The lens 355 can be a meniscus lens to enable or facilitate focusing of the amplified light beam 325 reflected from the mirror 350 to the desired position of the target location 310. Additionally, the lens 355 can include an aspheric correction on each of its surfaces to simultaneously provide a tightly focused transmitted amplified light beam 325 and a tightly focused light 365 that is reflected from the lens 355. The lens 355 can be designed with at least one surface that is an on-axis segment of a paraboloid.
Each of the fold mirrors 330, 332, 334, 336, 338 can redirect the amplified light beam 325 by any suitable angle, for example, by about 90 degrees. Additionally, at least two of the fold mirrors 330, 332, 334, 336, 338 can be movable with the use of a movable mount that is actuated by a motor that can be controlled by the master controller 155 to provide active pointing control of the amplified light beam 325 to the target location 310. The movable fold mirrors can be adjusted to maintain the position of the amplified light beam 325 on the lens 355 and the focus of the amplified light beam 325 at the target material.
The beam delivery system 300 can also include an alignment laser 370 that is used during set up to align the location and angle or position of one or more of the components (such as the fold mirrors 330, 332, 332, 334, 336, 338, the curved mirrors 342, 346, and the final fold mirror 350) of the beam delivery system 300. The alignment laser 370 can be a diode laser that operates in the visible spectrum to aid in a visual alignment of the components. The alignment laser 370 reflects off a dichroic beam combiner 371 that reflects visible light and transmits infrared light. This permits the alignment beam to propagate simultaneously with the amplified light beam.
The beam delivery system 300 can also include a detection device 375 such as a camera that monitors light reflected off the target material 114 at the target location 310, such light reflects off a front surface of the drive laser system 305 to form a diagnostic beam 380 that can be detected at the detection device 375. The detection device 375 can be connected to the master controller 155 to provide feedback on a position of the plasma along an x-axis (which is the direction of flow of the target material (for example, the droplet)). The master controller 155 can thereby adjust a position of one or more components (for example, the mirror 350 and/or the lens 355) within the beam delivery system 300 to adjust the location of the amplified light beam 325 to better coincide or overlap the target material 114.
Referring also to
The first curved mirror 342 can be made of any substrate and coating that is suitable for reflecting the amplified light beam 325. Thus, it can be made of a substrate and a coating that are selected to reflect light at the wavelength of the amplified light beam 325. The first curved mirror 342 can be cooled with a fluid coolant such as water that can flow through the substrate of the mirror 342. The reflective surface 343 of the first curved mirror 342 can be formed from a coating of maximum metal reflector (MMR) produced by II-VI Infrared of Saxonburg, Pa. over an oxygen-free high conductivity (OFHC) copper substrate.
Referring also to
The second curved mirror 346 can be made of any substrate and coating that is suitable for reflecting the amplified light beam 325. Thus, it can be made of a substrate and a coating that are selected to reflect light at the wavelength of the amplified light beam 325. The reflective surface 347 of the second curved mirror 346 can be a maximum metal reflector (MMR) produced by II-VI Infrared of Saxonburg, Pa. over an oxygen-free high conductivity (OFHC) copper substrate. The second curved mirror 346 can be cooled with a fluid coolant such as water that can flow through the substrate of the mirror 346.
The combination of the first curved mirror 342 and the second curved mirror 346 provides a magnification of the amplified light beam 325, for example, of about 3.6×, and such magnification reduces the divergence of the beam, for example, by 3.6×. The design of the beam expansion system 340 that has at least one off-axis paraboloid mirror also enables a more compact arrangement within the beam transport system 315 when compared with prior arrangements that used spherical mirrors for beam expansion. The amplified light beam 325 can be transported over distances longer and with less divergence than would have been possible in prior beam expanders that used spherical mirrors because the beam expansion system 340 includes at least one off-axis paraboloid mirror (for example, the first curved mirror 342, the second curved mirror 346, the combination of the two mirrors 342, 346, or the combination of one of the curved mirrors 342, 346 and a lens). Moreover, the off-axis paraboloid mirror provides an improved quality wavefront (for example, reduced aberration so that the wavefront is nearer to a planar wavefront) of the amplified light beam 325 when compared with spherical mirrors that have been used in prior beam expanders.
Referring to
The beam transport system 615 includes a beam expansion system 640 that expands the amplified light beam 625 and a set of additional redirecting optical components 645 such as the fold mirrors described above. The beam expansion system 640 includes a curved mirror 642 that has a reflective surface that is an off-axis segment of an elliptic paraboloid and a diverging lens 646 at the output of the drive laser system 605. The diverging lens 646 can be made of any material that transmits light at the wavelength of the amplified light beam 110 and is able to withstand heat that can accumulate due to the intensity of the amplified light beam 110. In some implementations, the diverging lens 646 is made of diamond and is polished to form the two concave surfaces. The diverging lens 646 can be configured as an output window of the drive laser system 605.
Referring to
The focus assembly 720 can also include a metrology system 760 that captures light 765 reflected from the lens 755 and transmitted through an opening within the central region of the mirror 750.
The extreme ultraviolet light vacuum chamber 730 houses the extreme ultraviolet light collector 735 that is configured to collect extreme ultraviolet light emitted from the target material at the target location 710 when the amplified light beam 325 crosses the target location 710 and strikes the target material.
Referring to
The extreme ultraviolet light vacuum chamber 830 houses the extreme ultraviolet light collector 835 that is configured to collect extreme ultraviolet light emitted from the target material at the target location 810 when the amplified light beam 325 crosses the target location 810 and strikes the target material.
Referring to
The extreme ultraviolet light vacuum chamber 930 houses the extreme ultraviolet light collector 935 that is configured to collect extreme ultraviolet light emitted from the target material at the target location 910 when the amplified light beam 325 crosses the target location 910 and strikes the target material.
In the implementations of
In general, the converging lens 355, 755, 855, 955 can be an aspheric lens to reduce spherical aberrations and other optical aberrations that can occur with spherical lens.
In the implementations shown above, the converging lens 755, 855, 955 is mounted as a window on a wall 790, 890, 990 of the chamber 730, 830, 930 by mounting the lens in a housing that is located outside the chamber but is mounted to the chamber wall. In the implementation shown in
The lens 355 can be configured to be movable; in this case, the lens 355 can be mounted to one or more actuators to provide a mechanism for active focus control during operation of the system. In this way, the lens 355, 755, 855, 955 can be moved to more efficiently collect the amplified light beam 325 and direct the light beam 325 to the target location to increase or maximize the amount of EUV production. The amount and direction of displacement of the lens 355, 755, 855, 955 is determined based on the feedback provided by the metrology system 760, 860, 960, as described in the application noted above.
The converging lens 355, 755, 855, 955 has a diameter that is large enough to capture most of the amplified light beam 325 yet provide enough curvature to focus the amplified light beam 325 to the target location. In some implementations, the converging lens 355, 755, 855, 955 can have a numerical aperture of at least about 0.1, and, in particular, at least about 0.2.
In some implementations, the converging lens 355, 755, 855, 955 is made of ZnSe, which is a material that can be used for infrared applications. ZnSe has a transmission range covering 0.6 to 20 μm and can be used for high power light beams that are produced from high power amplifiers. ZnSe has a low thermal absorption in the red (specifically, the infrared) end of the electromagnetic spectrum. Other materials that can be used for the converging lens include, but aren't limited to: gallium arsenide (GaAs), germanium, silicon, amorphous material transmitting infrared radiation (AMTIR), and diamond.
Moreover, the converging lens 355, 755, 855, 955 can include an anti-reflective coating and can transmit at least 95% of the amplified light beam 325 at the wavelength of the amplified light beam 325.
Referring also to
Referring also to
As shown in
Other implementations are within the scope of the following claims.
Although the detector 165 is shown in
In general, irradiation of the target material 114 can also generate debris at the target location 105, and such debris can contaminate the surfaces of optical elements including but not limited to the collection mirror 135. Therefore, a source of gaseous etchant capable of reaction with constituents of the target material 114 can be introduced into the chamber 130 to clean contaminants that have deposited on surfaces of optical elements, as described in U.S. Pat. No. 7,491,954, which is incorporated herein by reference in its entirety. For example, in one application, the target material can include Sn and the etchant can be HBr, Br2, Cl2, HCl, H2, HCF3, or some combination of these compounds.
The light source 100 can also include one or more heaters 170 that initiate and/or increase a rate of a chemical reaction between the deposited target material and the etchant on a surface of an optical element. For a plasma target material that includes Li, the heater 170 can be designed to heat the surface of one or more optical elements to a temperature in the range of about 400 to 550° C. to vaporize Li from the surface, that is, without necessarily using an etchant. Types of heaters that can be suitable include radiative heaters, microwave heaters, RF heaters, ohmic heaters, or combinations of these heaters. The heater can be directed to a specific optical element surface, and thus be directional, or it can be non-directional and heat the entire chamber 130 or substantial portions of the chamber 130.
