TW202527603A - Euv source vessel heated gas delivery apparatus and method - Google Patents

Abstract

A system for generating extreme ultraviolet (EUV) radiation includes a source vessel having an interior volume, a source laser configured to generate light to enter the interior volume in an entering light direction along a light axis to provide energy to a target to cause the generation of EUV within the interior volume, and a heated gas delivery apparatus within the interior volume configured to deliver heated gas into the interior volume and positioned on and extending along the light axis, the heated gas delivery apparatus having outlets to dispense the heated gas into the interior volume and one or more inlet openings to receive light from the source laser to heat the heated gas delivery apparatus. A process for providing EUV radiation is also disclosed.

Description

EUV source container heating gas delivery device and method

The present disclosure relates to an extreme ultraviolet ("EUV") source container having an apparatus for delivering a heated gas into the source container, and to a method of delivering a heated gas into the source container.

Extreme ultraviolet (EUV) light (i.e., electromagnetic radiation (sometimes also called soft x-rays) with a wavelength of approximately 50 nm or less, including radiation with a wavelength of approximately 13.5 nm) can be used in lithography processes to create extremely small features in or on substrates such as silicon wafers. Methods for generating EUV light include converting a target material into a plasma state. The target material includes at least one element, such as xenon, lithium, or tin, having one or more emission lines in the EUV portion of the electromagnetic spectrum. The target material can be a solid, liquid, or gas. In one such method, often referred to as laser-produced plasma (LPP), the plasma required to irradiate a target containing one or more EUV light-emitting elements with one or more pulsed pulses is generated using a "source" laser, typically a _CO2 laser emitting infrared light at a wavelength of about 10,600 nanometers (nm). The plasma is typically generated in a sealed "source vessel," typically a vacuum chamber.

The generation of a plasma from a target material within a source container can generate vapors, ions, particles, and other debris that can deposit on and contaminate surfaces within the source container, including optical surfaces. Consequently, it is desirable to remove the one or more residual target materials from the source container to reduce or eliminate surface contamination within the source container. This need is typically at least partially met through the use of a gas stream that is introduced into the source container and subsequently removed from the source container along with the one or more residual target materials.

In some general aspects, a system for generating extreme ultraviolet (EUV) radiation is provided, the system comprising: a source container having an inner volume; a source laser configured to generate light into the inner volume in an incoming light direction along an optical axis to provide energy to a target to induce EUV generation within the inner volume; and a heated gas delivery system. A device is disposed within the inner volume and configured to deliver heated gas into the inner volume, the heated gas delivery device being positioned on and extending along the optical axis, the heated gas delivery device having an outlet for distributing the heated gas into the inner volume and one or more inlet openings for receiving light from the source laser to heat the heated gas delivery device.

Implementations may include one or more of the following features. The heated gas delivery device may further include an inner surface having a reflectivity for the light from the source laser equal to or less than 0.9 to absorb at least some of the light received from the source laser through the one or more inlet openings. The heated gas delivery device may further include a tapered inner surface to receive, partially reflect one or more times, and at least partially absorb the light received from the source laser through the one or more inlet openings. The tapered inner surface may be or may include a circular conical inner surface.

The system may further include a heated gas source connected to the heated gas delivery device to deliver heated gas to the heated gas delivery device. The heated gas source may be located outside the inner volume.

The heated gas delivery device may further include a gas pipe connected to the outlets. The heated gas delivery device may further include a heating element configured to heat the heated gas delivery device and/or the gas delivered by the heated gas delivery device.

The system may further include a collector configured to reflect EUV light generated at or near a principal focus of the collector to an intermediate focus of the collector, wherein the collector has an optical axis substantially coincident with the optical axis and a through-hole along the optical axis, the through-hole configured to allow the light to enter the interior volume such that most or all of the EUV light reflected from the collector (1) is within a volume that is a first approximate cone having the periphery of the collector as a base and the intermediate focus as an apex, and (2) travels from the collector to the intermediate focus outside a volume that is a second approximate cone having the through-hole as a base and the intermediate focus as an apex, and wherein the heated gas delivery device is disposed within the second approximate cone along the optical axis. The heated gas delivery device may have a conical outer surface that is spaced apart from the surface of the second approximately cone when the heated gas delivery device is at an operating temperature so that the outer surface does not impact the second approximately cone during operation.

The heated gas delivery device may extend a distance along the optical axis in a range of 90 to 110 centimeters. The heated gas delivery device may extend a distance along the optical axis in a range of 50% to 70% of a distance along the optical axis from the primary focal point to the intermediate focal point. At least some of the outlets of the heated gas delivery device may be positioned in a conical outer surface of the heated gas delivery device, wherein the conical outer surface narrows in a direction along the optical axis and extends away from the incoming light direction.

In some additional general aspects, a process for providing extreme ultraviolet (EUV) radiation is provided, the process comprising: irradiating a target within an interior volume of a source container with light from a source laser to generate an EUV-generating plasma; generating reflected EUV light within the interior volume by reflecting EUV light from the plasma along a reflected EUV path; receiving the light from the source laser into a heated gas delivery device to heat the heated gas delivery device; and delivering heated gas from the heated gas delivery device along the reflected EUV path into the interior volume of the source container.

Implementations may include one or more of the following features. A side of the heated gas delivery device may include an outlet. The heated gas delivery device may include or have a conical shape that narrows in a direction toward a central focus of the collector. The heated gas delivery device may extend a distance in a range of 90 cm to 110 cm in a direction parallel to an optical axis of the source laser. The heated gas delivery device extends 50% to 70% of a distance from a primary focus to a central focus of the collector in a direction parallel to an optical axis of the source laser.

The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

FIG1A is a simplified schematic cross-sectional view of some components of an implementation of an EUV light source 110. As shown by the reference axes, the cross-section of the EUV light source 110 in FIG1A is taken in the x-z plane, where x is positive in an upward direction relative to the plane of the page and z is positive to the right of the plane of the page, and the z-axis is aligned with the optical axis A of the source laser 112, which will be described below.

As shown in FIG1A , EUV light source 110 includes a source laser 112 for generating a pulsed (e.g., laser pulse) beam 113 and delivering beam 113 from source laser 112 into an interior volume 114 of a source container 111 to individually irradiate a target 115 located at or near an irradiation site 116. Target 115 travels downward (in the negative x-direction) in the plane of the page from a target delivery system 117a to irradiation site 116. Source container 111 has an interior surface 156 surrounding interior volume 114.

As also shown in FIG1A , the EUV light source 110 includes a target delivery system 117 a that delivers a target 115 into the interior 114 of the source container 111 to an irradiation site 116. At the irradiation site 116, the target 115 interacts individually with one or more pulses (of the beam 113) to generate a plasma 118, which generates EUV light 119 (represented in the figure by the boundary rays indicated by reference character 119). The radiation from the plasma 118, the position of the target 115, and other data can be monitored by one or more metrology devices 150, and the information collected by the one or more metrology devices 150 can be used to control and operate the EUV light source 110.

The targets 115 may be conveyed along at least a portion of the target shield 115s through which they travel. The shield 115s may be in the form of a tube (which may have an aperture for metrology) or other shielding structure that shields or partially shields the targets 115 from gases and other materials within the interior volume 114 of the source container 111, such that the trajectory of the targets 115 is not excessively disturbed by such gases or other materials. Unused portions of the targets 115 (e.g., those not converted into plasma 118) may be captured in a target trap 117b.

Target 115 is or includes an EUV emission target material, such as, but not necessarily limited to, tin, lithium, xenon, or a combination thereof. Target 115 may be in the form of liquid droplets, or alternatively, may be solid particles or liquid droplets containing solid particles. For example, elemental tin may be present as a target in the following forms: pure tin; a tin compound (such as _SnBr4 , _SnBr2 , _SnH4 ); a tin alloy (e.g., tin-gallium alloy, tin-indium alloy, or tin-indium-gallium alloy); or a combination thereof.

The EUV light source 110 may also include a collector 120 that redirects the EUV light 119 into redirected EUV light 124. The collector 120 may be a near-normal-incidence collector mirror having an optical axis coinciding with the optical axis A and a reflective surface 121. The reflective surface 121 may be in the form of a prolate spheroid (i.e., an ellipse rotated about its long axis) such that the collector 120 has a first or principal focus 122 within or near the irradiation location 116 and a second focus at a so-called intermediate focus 123, with the optical axis of the collector being defined as a line extending along the optical axis A between the foci. The source container 111 of the EUV light source 110 thus at least partially encloses a volume 114, wherein, when the EUV light source 110 and the source container 111 are in use, EUV light 119 is redirected (reflected) by the collector 120 along axis A from the main focus 122 to the intermediate focus 123 as EUV light 124. The reflected EUV light 124 from the collector 120 can be output from the EUV light source 110 at the intermediate focus 123 and input into a device that utilizes the EUV light 124, such as a lithography exposure apparatus (as shown in FIG. 2 ). The collector 120 is formed with an aperture in the form of a through-hole 125 passing through the collector 120 to allow the light beam 113 of the light pulse generated by the source laser 112 to pass through the through-hole 125 and reach the irradiation site 116. The perforations 125 create a shadow or large gap 154 along the optical axis A in the reflected EUV light 124 from the collector 120 .

To reflect EUV light 119, collector 120 may be in the form of a multi-layer mirror (MLM), wherein reflective surface 121 has a graded multi-layer coating with alternating layers of molybdenum and silicon, and in some cases, one or more high-temperature diffusion barrier layers, smoothing layers, capping layers, and/or etch stop layers. Surface shapes other than prolate spheroids may also be used for reflective surface 121. For example, reflective surface 121 may alternatively be in the form of a parabola rotated about its long axis. In implementations, reflective surface 121 may be configured to deliver a beam of EUV light 124 having a toroidal or other cross-section at a central focus 123. In other implementations, the reflective surface 121 may utilize coatings and layers other than those described above.

The collector 120 can be expensive to manufacture. The efficiency and power of the light produced by the EUV light source 110 depends on the quality of the reflective surface 121 of the collector 120. For these and other reasons, it is desirable to protect the collector 120 from damage to its reflective surface 121.

However, the collector 120 must be placed within the volume 114 within the source container 111 and in close proximity to the plasma 118 in order to collect and redirect the EUV light 119. The structures within the source container 111, including the collector 120, can be exposed to or contain energetic ions and/or particles and vapors of the target material. Particles and energetic ions and vapors of the target material (which are essentially debris or byproducts from light-based vaporization or ablation processes) can contaminate the exposed reflective surface 121 of the collector. Particles and energetic ions and vapors of the target material can also cause physical damage and localized heating of the reflective surface 121 of the collector 120.

As also shown in FIG. 1A , the EUV light source 110 may include a focusing unit 126 including one or more optical elements (not shown) for focusing the light beam 113 to a focal point or beam waist at or near the irradiation location 116 .

FIG2 is a diagram illustrating an embodiment of an EUV light source 210 (such as the EUV light source 110 of FIG1A or another EUV source) and a lithography exposure apparatus 271. The lithography exposure apparatus 271 receives EUV light 224 generated by the EUV light source 210 and reflects the EUV light at one or more illumination mirrors 272 to illuminate a reflective pattern or a zoom mask 273. The EUV light reflected from the pattern or zoom mask 273 is further reflected and reduced by one or more de-emitter mirrors 274 and irradiated onto a substrate or wafer 275 (or onto one or more photosensitive layers (not shown) on the substrate or wafer 275) to allow patterned structures to be formed in or on the substrate or wafer 275.

1A and 2 , the optical components and sensors within the lithography exposure apparatus 271 and the photosensitive layer on the substrate or wafer 275 are generally sensitive to many types of radiation, or even any type of radiation. Therefore, particularly in view of the high power levels generated by the source laser 112 of FIG. 1A , it is important to prevent any portion of the beam 113 of the light pulse from the source laser 112 (including the beam 113 e shown in FIG. 1A , which corresponds to the portion of the beam 113 extending beyond the irradiation site 116 ) from reaching the intermediate focus 123 and potentially entering the lithography exposure apparatus (e.g., lithography exposure apparatus 271 ).

To this end, as shown in FIG1A , a beam stop element, such as the shield bar 127 of the present disclosure, can be used. The shield bar 127 can include a base 128, a shaft 129 extending from the base 128, and a head 130 supported on the shaft 129. When the shield bar 127 is used, the head 130 is positioned on axis A, as shown, so that the optical axis (and optical axis) A intersects the head 130. Furthermore, the head 130 can be positioned and sized to fit within a shadow or large gap 154 in the reflected EUV light 124 from the collector 120. For example, the head 130 can have a cross-section taken perpendicular to the optical axis A that is circular and centered on the optical axis A and matches the shadow or large gap 154. This geometry prevents the head 130 from blocking any or any significant portion of the EUV light 124 reflected from the collector 120 and directed toward the lithographic exposure apparatus 121, while also effectively protecting the intermediate focus 123 from direct illumination by the pulsed beam 113 of the source laser 112. In other words (with respect to positioning in the shadow or gap 154), the head 130 is positioned such that little or no direct EUV light 119 from the main focus 122 is reflected from the collector 120 toward the head 130 as EUV light 124.

In a source container using a target shield 115s, as shown, the shaft 129 of the masking strip 127 can be aligned with the shield 115s, that is, the shaft can be positioned as closely as possible within the shadow created by the shield 115s in the reflected EUV light 124. In other words, the image of the shaft 129 can be aligned with the image of the shield 115s when viewed from the primary focus 122 of the collector 120 in reflection from the collector surface 121. In some implementations, the shaft 129 can be completely hidden in the shadow of the shield 115s, as when the image of the shaft 129 is hidden by the image of the shield 115s when viewed from the primary focus 122 of the collector 120 in reflection from the collector surface 121. This configuration reduces or eliminates the situation where the reflected EUV light 124 is blocked from leaving the EUV light source 110 by the shaft 129.

A heated gas delivery device 136 can be attached to the head 130 of the shield bar 127 (or, as shown and discussed below, formed as a single piece with the head 130 of the shield bar 127). As will be shown below, the head 130 of the shield bar 127 can be attached to the shaft 129 or formed as a single piece with the shaft 129. A gas supply channel 131 is connected to the base 128 and shaft 129 of the shield bar 127 and to a source 131a of a gas, such as hydrogen ( _H2 ) gas 132, thereby allowing the shield bar 127 to supply heated gas, represented by arrows HG, to the interior volume 114 of the source container via the heated gas supply device 136. The heated gas, represented by arrows HG, is heated by light received into the heated gas delivery device 136, as will be shown below. Source laser light and EUV light received on the exterior surfaces of the heated gas delivery device 136 will generate some additional heating. Optionally, additional heating can be provided, for example, by heaters 131h at or near the gas source 131a and/or gas supply channel 131, as shown, or by resistive heating in the shield bar 127 and/or in the shield bar header 130 or heated gas delivery device 136, as described further below.

FIG1B is a simplified schematic cross-sectional view of the EUV light source 110 of FIG1 rotated 90 degrees about the z-axis to show a cross-section in the y-z plane (as indicated by the reference axes) and rotated so that gravity is downward in the plane of the page. When in use, the EUV source 110 can be tilted relative to gravity as shown, but other orientations can also be used. In this view, the shaft 129 and base 128 of the shielding bar 127 are located behind the head 130, into the page. Also, in this view, the exhaust port 133 and associated exhaust opening 155 are visible. As shown, the exhaust port 133 is a structure extending from the source container 111 and defining the exhaust opening 155, which is in fluid communication with the interior 114 of the source container 111 and extends out from the interior. Gas and entrained ions, vapors, and debris may be evacuated from the source container 111 by one or more vacuum pumps (not shown) through an exhaust opening 155 of the exhaust port 133. The exhaust opening 155 is positioned between the collector 120 and the head 130, measured along the optical axis A.

As also shown in the embodiment of FIG1B , the heated gas delivery device 136 is formed as a unit with the head 130 of the shielding strip 127. The heated gas delivery device 136 in this embodiment thus includes a surface or "exposed surface" 134 exposed to the primary focal point 122. The exposed surface 134 may be or may include a slanted surface 134s (meaning a surface that is not perpendicular to the axis A) and may generally face in the direction of the exhaust opening 155 of the exhaust port 133 and/or in the direction of the portion 135 of the interior surface 156 of the source container 111 on the central focal point side of the exhaust opening 155.

Various gas flows that can be used with the EUV light source 110 are indicated by outlined arrows in the figure. A gas flow at a pressure in the range of about 50 to about 300 Pascals (Pa), such as a hydrogen (H ₂ ) gas flow, can be used within the source container 111 as a buffer gas for debris and/or vapor control. Without the use of such a gas flow, it would be difficult to adequately protect the collector 120 from target material debris and vapor originating from the irradiation site 116, given that a vacuum is required within the interior 114 of the source container 111 to prevent excessive absorption of EUV light 119, 124 by gas molecules. Hydrogen (H ₂ ) is relatively transparent to EUV light at a wavelength of approximately 13.5 nm and is therefore often preferred over other candidate gases such as helium, argon, and other gases that exhibit high absorption at approximately 13.5 nm.

_H gas can be introduced into source vessel 111 to slow down and direct the high-energy fragments (ions, atoms, and clusters) of the target material generated by irradiating target 115 and irradiation site 116 and the resulting plasma 118. The fragments are slowed down by collisions with gas molecules. A _flow CF of H at central aperture 125 of collector 120 can be used for this purpose. Sometimes referred to as a "conical flow" CF, the flow CF can be directed by a tube or nozzle 137 or the like from aperture 125 at the center of collector 120 toward irradiation site 116, where plasma 118 is repeatedly generated. This direction is opposite to the trajectory of the debris from the irradiation site 116 toward the collector 120, and the conical flow CF therefore serves to reduce damage to the collector 120 caused by vapor deposition, implantation, and deposition of the sputtering target material.

A gas flow, often referred to as an umbrella flow 139, can be directed (from an outlet (not shown)) along the surface of the collector 120. So-called showerhead flows (in which gas flows through a plurality of parallel apertures oriented generally perpendicular to the surface to be protected) (such as showerhead flow S1 and showerhead flow S2) can be provided in the region of the source container 111 closest to the collector 120. In additional regions, such as the region near the central focal point 123, a shielding gas flow parallel to the surface to be protected or having a flow component directed parallel to the surface to be protected can be introduced by aiming the apertures in a direction having a component along or parallel to the surface to be protected. For example, gas flows (such as gas flows F1, F2, F3, and F4) may be introduced to protect the interior surface 156 of the source container 111 in a region near the intermediate focus 123.

A dynamic gas lock ("DGL") is a gas flow or flows that are used to prevent any material from leaving the EUV source 110 in the region of the intermediate focus 123. The DGL can generate a gas flow (such as DGL flow 138) from the region of the intermediate focus 123 toward the irradiation site 116. This flow 138 can also be referred to as a "mid-focus protection" gas flow 138.

A stable, guided debris-laden stream 140 exiting the collector 120 can be formed and maintained by the cone flow CF, umbrella flow 139, and showerhead flows S1 and S2 (and other flows not shown, as appropriate). The solid curve in FIG1C illustrates an example boundary of the debris-laden guided stream 140. This guided stream 140 helps contain and carry away collector 120 materials generated by the target 115 during the generation of the plasma 118, including vapor, ions, and micro- and nanoparticles.

Counterflow 141, moving from central focal point 123 toward collector 120, may be primarily formed by DGL flow 138, along with heated gas (arrow HG) and streams ("curtain" streams) F1, F2, F3, and F4) from heated gas delivery device 136 (and optionally other streams not shown). Curved boundary line 141b, along with interior surface 156 of vessel 111 in the upper portion of the figure, represents an example boundary of counterflow 141. Heated gas (arrow 143) may also flow from exposed surface 134 or exposed inclined surface 134s.

Considering the low pressure used within the source container 111, the pressure differential at the exhaust opening 155 of the exhaust port 133 is not significant. However, the relatively small pressure differential at the exhaust opening 155, created by evacuating the exhaust port 133, combined with the flow momentum balance between the guide stream 140 and the counterstream 141 at the merging region 142 of the two streams 140, 141, where the merging region 142 is close to the exhaust opening 155, can produce a stable guide flow of the target material byproduct entrained and contained in the guide stream 140 into the exhaust opening 155, without the target material byproduct coming into contact with substantially any internal surface of the source container 111.

When tin or tin-containing targets 115 are used, the use of hydrogen (such as in the cone flow CF) with such targets 115 results in another potential source of contamination in the source container 111. When hydrogen bubbles form and grow in or under the conditions of the molten tin and then collapse, this is the ejection or "spewing" of molten tin from the container onto the surface coated with or undergoing coating with the molten tin.

One way to prevent tin splattering is to prevent the molten target material from accumulating on surfaces in the source container 110, namely by maintaining the surface below or substantially below the melting point of the target material, which for tin is approximately 232° C. For example, portions of the interior surface 156 of the source container 111 can be maintained at a temperature below 232° C., such as a temperature in the range of 50° C. to 110° C. or 50° C. to 100° C. Any tin deposited on such surfaces remains in solid form and prevents or resists splattering.

While reducing sparging, using a "cool" surface also reduces the temperature and increases the density of the gas in the inner volume 114 of the container 111. The higher gas density within the inner volume 114 increases the absorption of EUV light, especially for reflected EUV light 124 ( FIG. 1A ) that is reflected from the collector 120 and passes through the generally cooler "upper" region of the inner volume 114 (towards the top of the page in FIG. 1B ).

Delivering heated gas, represented by arrows HG, from one or more sides of heated gas delivery device 136 and, optionally, through exposed surfaces 134, 134s into the interior volume 114 of container 111 helps provide a region 144 of lower-density gas (depicted by a dashed-line boundary) through which the majority of EUV light 124 traveling from collector 120 to intermediate focus 123 can pass. In practice, there is typically no sharp boundary between heated and unheated gas in interior volume 114; rather, a temperature gradient may exist, with higher temperatures closer to the heated gas delivery device and the stream represented by arrows HG. Thus, the dashed-line boundary in FIG. 1B represents an example region of relatively higher temperature and lower-density gas. The lower density of the gas in region 144 thereby reduces absorption of EUV light 124, which allows for increased brightness of the EUV light generated by EUV source 110 (ie, EUV light 124 output by EUV source 110), thereby improving the performance and operating economy of EUV source 110 and downstream components, such as lithography apparatus 217 ( FIG. 2 ). Optionally, heated gas delivery device 136 can also be used within a container having a "hot" interior surface to achieve similar benefits from the higher density gas in the region surrounding heated gas delivery device 136. Heated gas delivery device 136 can include or be formed from high-temperature metals (such as molybdenum, tungsten, and arsenic) and their alloys. Ceramic materials with relatively good electrical conductivity and formability, such as aluminum nitride, can also be used.

FIG3A is a perspective view of an implementation of a heated gas delivery device 336 that can be positioned within the EUV light source 110 of FIG1A or FIG1B and used as heated gas delivery device 136. Heated gas delivery device 336 (or shield bar head 330) is shown in a view corresponding to heated gas delivery device 136 (or shield bar head 130) of FIG1B , but with its z-axis oriented to the right in the plane of the page of FIG3A . FIG3B is a perspective view of heated gas delivery device 336 and shield bar head 330 rotated 90 degrees about the z-axis relative to FIG3A , so that shield bar 327 is visible as a whole, including shaft 329 and base 328 in addition to head 330. Shaft 329 includes facets 352a and 352c (and corresponding facets on the side not visible) that gradually taper or narrow shaft 329 toward the positive z-axis and toward the negative z-axis. FIG3C is a cross-sectional view of heated gas delivery device 336 and shielding strip 327 of FIG3A and FIG3B taken along line 3C-3C shown in FIG3A.

As seen in Figures 3A, 3B, and 3C, heated gas delivery device 336 (which also serves as head 330 of shielding strip 327) has a tapered shape that tapers to a tip 336t in the positive z-direction, or (in Figures 1A and 1B) along optical axis A toward intermediate focus 123. An outlet 336o in side surface 336s (the tapered surface) can be used to deliver heated gas to the interior volume of a light source container, such as interior volume 114 of container 111 of light source 110 in Figures 1A and 1B. Outlet 336o can be in the form of a circular or nearly circular hole, as shown, but other forms, such as a slit and other shapes, are possible. Tip 336t can be closed, that is, it may not have an outlet. Surface or "exposed surface" 334 is located at the negative z-axis end of heated gas delivery device 336 (or on the side exposed to primary focus 122 in Figures 1A and 1B). Exposed surface 334 may be or include a slanted surface 334s, meaning a surface that is not perpendicular to axis A (of Figures 1A and 1B).

As further shown in Figures 3B and 3C, the exposed surface 334 may include one or more inlet openings 336io. When in use, the openings 336io can be irradiated by the light beam 113e (Figures 1A and 3C) from the source laser 112 (Figures 1A and 1B) and can allow a portion of the light beam 113e to enter the interior 336i of the heated gas delivery device 336 in the form of internal radiation RADi (Figure 3C). The internal radiation RADi irradiates the interior surface 336is of the heated gas delivery device 336 to heat the heated gas delivery device 336 and thereby heat the gas (e.g., hydrogen _H2 ) delivered through or by the heated gas delivery device 336 to produce heated gas HG. Internal surface 336is is a tapered internal surface that receives, absorbs, and partially reflects one or more radiation RADi within interior 336i. In this embodiment, inlet opening 336io in exposed surface 334 also serves as a gas outlet (outlet not shown in Figures 3A-3C), and in this embodiment, may take the form of concentric annular outlets 348c and holes 348h (Figure 3B). In this embodiment, internal surface 336is illuminated by internal radiation RADi is also the shielded header portion of the internal surface of gas conduit 347, which extends along and within shaft 329 and along and within heated gas delivery device 336 or head 330 (Figure 3C).

As seen in FIG3C , the shaft 329 of the shielding strip 330 may optionally include a resistive heating element (RHE) positioned along the gas conduit 347 to add heat to the passing gas. The resistive heating element may also or alternatively be included in the heated gas delivery device 336 or head 330. A coating or other surface modification 336isc may be included on the interior surface 336is or a portion thereof to reduce the reflectivity of the interior surface so that the internal radiation RADi is reflected less than by the unmodified portion of the interior surface 336is. In cases where the reflectivity of the unmodified or uncoated interior surface is greater than 0.9, the coating or other surface modification 336isc may be applied to reduce the reflectivity to, for example, or less than, 0.9. Both the internal reflectivity of the interior 336i of the heated gas delivery device 336 being equal to or less than 0.9 and the tapered shape of the interior 336i in the positive z-axis direction of the heated gas delivery device 336 (a shape that helps generate multiple reflections within the interior 336i) can help capture energy from the internal radiation RADi to heat the heated gas delivery device 336.

FIG4 is a cross-sectional view similar to FIG3C showing another embodiment including a heated gas delivery device 436 as part of a masking strip 427 having a shaft 429, a base 428, and a head 430 also serving as the heated gas delivery device 436. Similar to FIG3C and as seen in FIG4 , the heated gas delivery device 436 has a tapered shape that tapers to a tip 436t ( FIG4 ) in the positive z-direction, or (in FIG1A and FIG1B ) in a direction along the optical axis A toward the intermediate focus 123. Outlets 436o in side surface 436s (tapered surface) can be used to deliver heated gas to the interior volume of a light source container, such as interior volume 114 of container 111 of light source 110 in Figures 1A and 1B. Tip 436t can be closed, that is, it can have no outlets. Surface or "exposed surface" 434 is located at the negative z-axis end of heated gas delivery device 436 (or on the side exposed to primary focus 122 in Figures 1A and 1B). Exposed surface 434 can be or include an inclined surface 434s, meaning a surface that is not perpendicular to axis A (of Figures 1A and 1B).

As further shown in FIG4 , the exposed surface 434 may include one or more inlet openings 436 io, one of which is shown in cross-section in FIG4 . When in use, the openings 436 io can be irradiated by the light beam 113 e ( FIG1A and FIG4 ) from the source laser 112 ( FIG1A , FIG1B ) and can allow a portion of the light beam 113 e to enter the interior 436 i of the heated gas delivery device 436 in the form of internal radiation RADi ( FIG4 ). The internal radiation RADi irradiates the interior surface 436 i of the heated gas delivery device 436 to heat the heated gas delivery device 436 and thereby heat the gas delivered by or through the heated gas delivery device 436 to produce heated gas HG. In this embodiment, one or more inlet openings 43610 in the exposed surface 434 do not also serve as gas outlets. This embodiment may be useful if gas flow from the exposed surface 434 is not desired (the alternative represented by the closed end CE of the gas sub-duct 447o at the lower end of the exposed surface 434 in FIG4 ), or if gas flow from the exposed surface 434 is desired but a baffle BF is used to significantly limit or prevent radiation from the beam 113e from reaching the gas duct or sub-duct 447p (the alternative represented at the upper end of the exposed surface 434 in FIG4 ).

In this embodiment, the light beam 113e can enter one or more internal regions (such as internal region 436i) through one or more associated inlet openings 436i. These inlet openings 436i allow some light from the light beam 113e to enter the one or more internal regions 436i, generating internal radiation RADi. As noted, the one or more internal regions 436i are not part of the heated gas delivery device 436 or the gas conduit within the head 430. Instead, one or more gas sub-conduits 447o, 447p are fed by a gas conduit 447 positioned within and along the shaft 427. The gas sub-ducts 447o, 447p can be opposite sides of a single annular duct extending along the interior of the outer surface 436s, or can be connected by one or more annular or semi-annular feed channel fluids, such as a single annular or semi-annular feed channel fluid connection positioned at or near the duct 447 or the heated gas delivery device 436 or the head 430 (not shown).

Internal radiation RADi illuminates the interior surface of heated gas delivery device 436 in the form of interior surface 436is of interior region 436i, heating heated gas delivery device 436, thereby heating the gas delivered by or through heated gas delivery device 436 to produce heated gas HG. A coating or other surface modification 436isc may be included on interior surface 436is or a portion thereof to reduce the reflectivity of the interior surface so that internal radiation RADi will be less reflected than the unmodified portion of interior surface 436is. In cases where the reflectivity of the unmodified or uncoated interior surface is greater than 0.9, coating or other surface modification 436isc may be used, for example, to reduce the reflectivity to or below 0.9. The internal reflectivity of the inner region 436i of the heated gas delivery device 436 being equal to or less than 0.9 and the tapered shape of the inner region 436i in the positive z-axis direction of the heated gas delivery device 436 (a shape that helps to generate multiple reflections within the inner region 436i) can both help to capture energy from the internal radiation RADi to heat the heated gas delivery device 436.

FIG5 is a cross-sectional view of a gas collector 520 (e.g., collector 120 of FIG1A and FIG1B ) and a heated gas delivery device 536 (e.g., heated gas delivery device 136 of FIG1A and FIG1B , 336 of FIG3A through FIG3C , and 436 of FIG4 ). Advantageous aspects of the gas heated gas delivery device and process disclosed herein may be explained in part with reference to FIG5 .

The outer and inner peripheries of the collector 520 or collector surface 521 define the outer edges or edge rays of reflected EUV light 524 reflected from the plasma 518 at or near the principal focus 522 of the collector 520 into the collector surface 521. The EUV light 524 reflected from the collector 520 is substantially confined within a first cone defined by the outer edge of the collector 520 or the collector reflective surface 521 as its base and the central focus 523 as its apex. This first cone can be referred to as a first approximate cone or a first slightly truncated cone because the central focus effectively covers some area and is therefore not a single point. In FIG5 , the first approximate cone is represented in cross-section by a triangle with vertices A1, B, and C. Similarly, EUV light 524 reflected from collector 520 is substantially confined to the exterior of a second cone, or a second approximate cone, or a second truncated cone. The second approximate cone is defined by the perimeter of the inner edge of through-hole 525 or collector reflective surface 521 as its base and the central focus 523 as its apex. In FIG5 , the second approximate cone is represented in cross-section by a triangle with vertices A1, D, and E. The second approximate cone corresponds to the "shadow or large gap 154" along optical axis A of FIG1A .

Although the reflected EUV light 524 from the collector 520 is substantially confined there, the intensity of the reflected EUV light is not uniformly distributed within the volume between the first and second cones. To illustrate this, as shown in FIG5 , the angles given by the BFG and DFG are equal and therefore substantially equally split the EUV light 524 that leaves the primary focus 522 toward the left side of the collector 520 in the plane of FIG5 . However, as shown, radiation traveling within the angle BFG is more diffuse across the surface 521 of the collector 520 than radiation traveling within the angle DFG. Thus, after reflection in the collector 520, nominally about one-half of the radiation (EUV light 524) from the collector 520 travels within the gray highlighted area in Figure 5, and one-half of the radiation travels outside the gray highlighted area. Thus, the gray highlighted area is the concentration region CR, where the EUV light 524 is more concentrated than the EUV light 524 outward from the concentration region CR.

This concentrating effect is often enhanced by the properties of the surface 521 of the collector 520. EUV light 524 reflected at lower angles of incidence (closer to normal to the surface 521, such as within the concentrating region CR) tends to be reflected more completely (with a higher reflectivity) than EUV light 524 reflected at higher angles of incidence (such as outside the concentrating region CR). Consequently, more than half of the light traveling from the collector 520 to the intermediate focus 523 typically travels within the relatively radially narrow concentrating region CR. By introducing the heated gas HG directly into the concentrating region CR (and from there into the surrounding area) and thereby reducing gas absorption losses, which are particularly severe in the concentrating region CR, the brightness of a given EUV light source 110 can be increased by, for example, 1%, 2%, 3%, or 4% or more. To deliver the heated gas directly to the concentrated region CR without impinging on the region CR and thereby interfering with the transmission of the EUV light 524, the outer surface of the heated gas delivery device 536 can be conical and can be spaced apart from the second approximate cone when the heated gas delivery device 536 is at an operating temperature so that the outer surface of the heated gas delivery device 536 does not encroach on the second approximate cone during operation. The operating temperature of the heated gas delivery device 536 (and heated gas delivery devices 336 and 436) can be, for example, in the range of 400° C. to 2000° C., or 400° C. to 1200° C., or 400° C. to 800° C. The heated gas delivery device can extend a distance along axis A within a range of 90 centimeters (cm) to 110 cm, or 95 cm to 105 cm. Alternatively or additionally, the heated gas delivery device can extend within a range of 50% to 70%, or 55% to 65%, of the distance from the main focal point 522 to the intermediate focal point 523 along axis A. The tip of the heated gas delivery device 536 can extend within 10 cm to 25 cm, or 10 cm to 20 cm, or 10 cm to 15 cm from the intermediate focal point 523.

FIG6 is a flow chart of process P600 for operating an EUV light source (e.g., EUV light source 110) according to the present disclosure. As shown in FIG6, process P600 includes irradiating a target (e.g., target 115 in FIG1A) with light (e.g., beam 113 in FIG1A) from a source laser (e.g., 112 in FIG1A) within an interior volume 114 (FIGS. 1A, 1B) of the EUV light source 110 (FIGS. 1A, 1B) to generate an EUV-emitting plasma (e.g., 118 in FIG1A, 1B; 518 in FIG5). (S10); EUV light (124 in FIG. 1A and FIG. 1B; 524 in FIG. 5) is reflected from the collector (120 in FIG. 1A and FIG. 1B; 520 in FIG. 5) along the path of the reflected EUV light within the inner volume (114 in FIG. 1A and FIG. 1B) (S20); receiving light (such as light beam 113 in FIG. 1A ) from the source laser ( 112 in FIG. 1A ) into the heated gas delivery device ( 136 in FIG. 1A and FIG. 1B ; 336 in FIG. 3A to FIG. 3C ; 436 in FIG. 4 ; 536 in FIG. 5 ), thereby heating the heated gas delivery device ( 136 in FIG. 1A and FIG. 1B ; 336 in FIG. 3A to FIG. 3C ; 436 in FIG. 4 ; 536 in FIG. 5 ). (S30); and delivering the heated gas (HG in Figures 1A, 1B, 3C, 4, and 5) from the heated gas delivery device (136 in Figures 1A and 1B; 336 in Figures 3A to 3C; 436 in Figure 4; 536 in Figure 5) to the inner volume (114 in Figures 1A and 1B) along the path of the reflected EUV light (124 in Figures 1A and 1B; 524 in Figure 5).

The implementation may be further described in the following numbered clauses: 1. A system for generating extreme ultraviolet (EUV) radiation includes: a source container having an inner volume; a source laser configured to generate light that enters the inner volume in an incoming light direction along an optical axis to provide energy to a target to induce EUV generation within the inner volume; and a heated gas delivery device disposed within the inner volume and configured to deliver heated gas into the inner volume, the heated gas delivery device being positioned on and extending along the optical axis, the heated gas delivery device having an outlet for distributing the heated gas into the inner volume and one or more inlet openings for receiving light from the source laser to heat the heated gas delivery device. 2. The system of clause 1, wherein the heated gas delivery device further comprises an inner surface having a reflectivity with respect to the light equal to or less than 0.9 to absorb at least some of the light received from the source laser through the one or more inlet openings. 3. The system of clause 1, wherein the heated gas delivery device further comprises a tapered inner surface to receive, partially reflect one or more times, and at least partially absorb the light received from the source laser through the one or more inlet openings. 4. The system of clause 3, wherein the tapered inner surface comprises a circular tapered inner surface. 5. The system of clause 1, further comprising a heated gas source connected to the heated gas delivery device to deliver heated gas to the heated gas delivery device. 6. The system of clause 5, wherein the heated gas source is located outside the internal volume. 7. The system of clause 1, wherein the heated gas delivery device further comprises a gas conduit connected to the outlets. 8. The system of clause 1, wherein the heated gas delivery device further comprises a heating element configured to heat the heated gas delivery device and/or the gas delivered by the heated gas delivery device. 9. The system of clause 1, further comprising a collector configured to reflect EUV light generated at or near a principal focus of the collector to a central focus of the collector, the collector having an optical axis substantially coincident with the optical axis and a perforation along the optical axis, the perforation configured to allow the light to enter the interior volume such that most or all EUV light reflected from the collector travels from the collector to the central focus inside a first approximately pyramidal volume having the periphery of the collector as a base and the central focus as an apex, and outside a second approximately pyramidal volume having the perforation as a base and the central focus as an apex, and wherein the heated gas delivery device is disposed within the second approximately pyramidal volume along the optical axis. 10. The system of clause 9, wherein the heated gas delivery device has a conical outer surface that is spaced apart from the surface of the second approximately conical body when the heated gas delivery device is at operating temperature such that the outer surface does not impinge on the second approximately conical body during operation. 11. The system of clause 9, wherein the heated gas delivery device extends a distance along the optical axis in the range of 90 to 110 centimeters. 12. The system of clause 9, wherein the heated gas delivery device extends a distance along the optical axis in the range of 50% to 70% of the distance from the main focal point to the intermediate focal point along the optical axis. 13. The system of clause 1, wherein at least some of the outlets of the heated gas delivery device are positioned in a conical outer surface of the heated gas delivery device, the conical outer surface narrowing in a direction along the optical axis and extending away from the direction of the incoming light. 14. The system of clause 13, wherein the heated gas delivery device extends a distance along the optical axis in the range of 90 to 110 centimeters. 15. The system of clause 13, wherein the heated gas delivery device extends a distance along the optical axis in the range of 50% to 70% of the distance along the optical axis from the main focal point to the intermediate focal point. 16. The system of clause 13, wherein the tip of the heated gas delivery device extends to within 10 cm to 15 cm of the central focus of the collector. 17. A process for providing extreme ultraviolet (EUV) radiation, the process comprising: irradiating a target with light from a source laser within an interior volume of a source container to generate an EUV-generating plasma; generating reflected EUV light within the interior volume by reflecting the EUV light from the plasma along a reflected EUV path; receiving the light from the source laser into the heated gas delivery device to heat the heated gas delivery device; and delivering heated gas from the heated gas delivery device along the reflected EUV path into the interior volume of the source container. 18. The process of clause 17, wherein one side of the heated gas delivery device includes an outlet. 19. The process of clause 18, wherein the heated gas delivery device comprises a conical shape that narrows in a direction toward the central focus of the collector. 20. The process of clause 19, wherein the heated gas delivery device extends a distance in the range of 90 cm to 110 cm in a direction parallel to the optical axis of the source laser. 21. The process of clause 19, wherein the heated gas delivery device extends 50% to 70% of the distance from the primary focus to the central focus of the collector in a direction parallel to the optical axis of the source laser.

The implementations described above and other implementations are within the scope of the following patent applications.

3C-3C: Line 110: EUV light source 111: Source container 112: Source laser 113: Beam 113e: Beam 114: Internal volume 115: Target 115s: Target shield 116: Irradiation site 117a: Target delivery system 117b: Target interceptor 118: Plasma 119: EUV light 120: Collector 121: Reflective surface 122: Prime focus 123: Intermediate focus 124: Redirected EUV light 125: Perforation 126: Focusing unit 127: Shielding strip 128: Base 129: Shaft 130: Head 131: Gas supply channel 131a: Gas source 131h: Heater 132: Hydrogen gas 133: Exhaust port 134: Surface 134s: Inclined surface 135: Section 136: Heated gas delivery device 137: Nozzle 138: DGL flow 139: Umbrella flow 140: Debris-carrying guide flow 141: Counterflow 141b: Boundary line 142: Merging area 143: Arrow 144: Area 150: Metrology device 154: Large gap 155: Exhaust opening 156: Internal surface 210: EUV light source 224: EUV light 271: Lithography exposure device 272: Illumination mirror 273: Reduction mask 274: Density filter 275: Wafer 323: Intermediate focus 327: Masking strip 328: Base 329: Shaft 330: Head 334: Exposed surface 334s: Inclined surface 336: Heated gas delivery device 336i: Interior 336io: Inlet opening 336is: Interior surface 336isc: Surface modification 336o: Outlet 336s: Side surface 336t: Tip 347: Gas duct 348c: Concentric ring outlet 348h: Hole 352a: Facet 352c: Facet 427: Masking strip 428: Base 429: Shaft 430: Head 434: Exposed surface 434s: Inclined surface 436: Heated gas delivery device 436i: Interior 436io: Inlet opening 436is: Interior surface 436isc: Surface modification 436o: Outlet 436s: Side surface 436t: Tip 447: Gas duct 447o: Gas sub-duct 447p: Gas sub-duct 518: Plasma 520: Collector 521: Collector surface 522: Primary focus 523: Intermediate focus 524: Reflected EUV light 525: Perforation 536: Heating Gas Delivery Device A: Optical Axis A1: Apex B: Apex BF: Baffle C: Apex CE: Closed End CF: Conical Flow CR: Concentrated Area D: Apex E: Apex F1: Airflow F2: Airflow F3: Airflow F4: Airflow HG: Heating Gas/Arrow P600: Program RADi: Internal Radiation RHE: Resistive Heating Element S1: Shower Head Flow S2: Shower Head Flow S10: Step S20: Step S30: Step S40: Step x: Axis y: Axis z: Axis

FIG1A is a schematic cross-sectional view of an extreme ultraviolet (EUV) light source.

1B is a schematic cross-sectional view of the EUV light source of FIG. 1A , rotated 90 degrees about the z-axis and rotated so that gravity is directed downward in the plane of the page.

FIG2 is a block diagram of an EUV source used with a lithography exposure apparatus.

3A is a perspective view of an implementation of a heated gas delivery device that may be positioned in the EUV light source of FIG. 1A or FIG. 1B .

FIG3B is a perspective view of the heated gas delivery device of FIG3A rotated 90 degrees about the z-axis relative to the view of FIG3A.

FIG3C is a cross-sectional view of the heated gas delivery device of FIG3B taken along line 3C-3C of FIG3A.

FIG4 is a cross-sectional view similar to FIG3C of another embodiment of a heated gas delivery device.

Figure 5 is a schematic cross-sectional view of the collector and heated gas delivery device.

6 is a flow chart of a process for operating a light source including the heated gas delivery device of FIG. 1A , FIG. 1B , FIG. 3A , FIG. 3B , FIG. 4 , FIG. 5 , or FIG. 6 .

3C-3C: Line

330: Head

334: Exposed surface

334s: Inclined surface

336: Heating gas delivery device

336o: Exit

336s: Side surface

336t: Cutting-edge

y: axis

z:axis

Claims (20)

A system for generating radiation includes: a source container having an inner volume; a source laser configured to generate light that enters the inner volume in an incoming light direction along an optical axis to provide energy to a target to induce EUV generation within the inner volume; and a heated gas delivery device disposed within the inner volume and configured to deliver heated gas into the inner volume, the heated gas delivery device being positioned on and extending along the optical axis, the heated gas delivery device having an outlet for distributing the heated gas into the inner volume and one or more inlet openings for receiving light from the source laser to heat the heated gas delivery device. The system of claim 1, wherein the heated gas delivery device further comprises an interior surface having a reflectivity with respect to the light equal to or less than 0.9 to absorb at least some of the light received from the source laser through the one or more entrance openings. The system of claim 1, wherein the heated gas delivery device further comprises a tapered inner surface configured to receive, partially reflect one or more times, and at least partially absorb the light received from the source laser through the one or more entrance openings. The system of claim 3, wherein the tapered interior surface comprises a circular tapered interior surface. The system of claim 1, further comprising a heated gas source connected to the heated gas delivery device to deliver heated gas to the heated gas delivery device. The system of claim 5, wherein the heated gas source is positioned outside the inner volume. The system of claim 1, wherein the heated gas delivery device further comprises a gas pipe connected to the outlets. The system of claim 1, wherein the heated gas delivery device further comprises a heating element configured to heat the heated gas delivery device and/or the gas delivered by the heated gas delivery device. The system of claim 1, further comprising a collector configured to reflect EUV light generated at or near a principal focus of the collector to an intermediate focus of the collector, the collector having an optical axis substantially coincident with the optical axis and a through-hole along the optical axis, the through-hole configured to allow the light to enter the interior volume such that most or all of the EUV light reflected from the collector is inside a volume having a first approximate cone as a base and having the intermediate focus as an apex, and travels from the collector to the intermediate focus outside a volume having a second approximate cone as a base and having the through-hole as a apex, and wherein the heated gas delivery device is disposed within the second approximate cone along the optical axis. A system as claimed in claim 9, wherein the heated gas delivery device has a conical outer surface, and when the heated gas delivery device is at an operating temperature, the conical outer surface is separated from the surface of the second approximately cone so that the outer surface does not impact the second approximately cone during operation. The system of claim 9, wherein the heated gas delivery device extends a distance along the optical axis in a range of 90 to 110 centimeters. The system of claim 9, wherein the heated gas delivery device extends along the optical axis a distance within a range of 50% to 70% of a distance along the optical axis from the primary focus to the intermediate focus. The system of claim 1 , wherein at least some of the outlets of the heated gas delivery device are positioned in a conical outer surface of the heated gas delivery device, the conical outer surface narrowing in a direction along the optical axis and extending away from the incoming light direction. The system of claim 13, wherein the heated gas delivery device extends a distance along the optical axis in a range of 90 to 110 centimeters. The system of claim 13, wherein the heated gas delivery device extends along the optical axis a distance within a range of 50% to 70% of a distance along the optical axis from the primary focus to the intermediate focus. The system of claim 13, wherein a tip of the heated gas delivery device extends to within 10 cm to 15 cm of a central focus of a collector. A process for providing extreme ultraviolet (EUV) radiation, the process comprising: irradiating a target within an interior volume of a source container with light from a source laser to generate an EUV-generating plasma; generating reflected EUV light within the interior volume by reflecting the EUV light from the plasma along a reflected EUV path; receiving the light from the source laser into a heated gas delivery device to heat the heated gas delivery device; and delivering heated gas from the heated gas delivery device along the reflected EUV path into the interior volume of the source container. The process of claim 17, wherein a side of the heated gas delivery device includes an outlet, and the heated gas delivery device includes a conical shape that narrows in a direction toward a central focus of the collector. The process of claim 18, wherein the heated gas delivery device extends a distance in the range of 90 cm to 110 cm in a direction parallel to an optical axis of the source laser. The process of claim 18, wherein the heated gas delivery device extends 50% to 70% of a distance from a primary focus to an intermediate focus of the collector in a direction parallel to an optical axis of the source laser.