RADIATION COLLECTOR

Methods and apparatuses for a lithography exposure process are described. The method includes irradiating a target droplet with a laser beam to create an extreme ultraviolet (EUV) light. The methods utilized and the apparatuses include two or more collectors for collecting the generated EUV light and reflecting the collected EUV light to a focal point of one of the collectors. In some embodiments, one of the two collectors includes a ring-shaped collector.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometric size (i.e., the smallest component (or line) that may be created using a fabrication process) has decreased. This scaling-down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling-down has also increased the complexity of processing and manufacturing ICs.

For example, there is a growing need to perform higher-resolution lithography processes. One lithography technique is extreme ultraviolet lithography (EUVL). The EUVL employs scanners using light in the extreme ultraviolet (EUV) region, having a wavelength of about 1 nm to about 100 nm. Some EUV scanners provide a projection printing, similar to some optical scanners, except that the EUV scanners use reflective rather than refractive optics, i.e., mirrors instead of lenses.

One type of EUV light source is laser-produced plasma (LPP). LPP technology produces EUV light by focusing a high-power laser beam onto small fuel droplet targets to form highly ionized plasma that emits EUV light with a peak of maximum emission at 13.5 nm. The EUV light is then collected by a collector and reflected by optics towards a lithography exposure object, e.g., a wafer.

Although existing methods and devices for generating EUV light have been adequate for their intended purposes, they have not been entirely satisfactory in all respects. Consequently, it would be desirable to provide a solution for increasing power conversion efficiency from the input energy for ionization.

DETAILED DESCRIPTION

“Vertical direction” and “horizontal direction” are to be understood as indicating relative directions. Thus, the horizontal direction is to be understood as substantially perpendicular to the vertical direction and vice versa. Nevertheless, it is within the scope of the present disclosure that the described embodiments and aspects may be rotated in its entirety such that the dimension referred to as the vertical direction is oriented horizontally and, at the same time, the dimension referred to as the horizontal direction is oriented vertically.

Embodiments described herein relate to methods and apparatuses for generating electromagnetic radiation useful in lithography processes, such as the lithography process utilized to manufacture semiconductor devices. Embodiments described below refer to the generation of EUV radiation; however embodiments in accordance with the present disclosure are not limited to generation of EUV radiation. The methods and apparatuses described herein increase the conversion efficiency of laser energy to EUV radiation. The throughput of EUV lithography processes is limited by the conversion efficiency of the laser power to EUV radiation generated utilizing the laser energy and also by the amount of the generated EUV radiation that is collected and directed to the lithography system optics. Methods and apparatuses described herein utilize a reflective collector ring to supplement the amount of EUV radiation that is reflected to the intermediate focus of the EUV source collector.

Embodiments in accordance with the present disclosure are generally related to extreme ultraviolet (EUV) lithography systems and methods, but are not limited to EUV lithography systems and methods. More particularly, they are related to apparatuses and methods that increase the power of radiation that is available (in the patterning materials) and is generated from a laser of a given power, e.g., they increase the conversion efficiency of laser used to produce the plasma. In other words, use of apparatuses and/or methods in accordance with embodiments of the present disclosure increase the ratio of the radiation power generated versus the power of the laser used to generate such radiation. In accordance with embodiments of the present disclosure, multiple collectors are used to increase the ratio of the radiation power collected and available for material patterning versus the power of the laser used to generate such radiation. Since throughput of lithographic processes is directly related to the power of the radiation available for the lithographic patterning, implementation of embodiments of methods and apparatuses described herein can increase the throughput of lithographic processes without significantly increasing the power requirements of the process. The collectors, which in some embodiments collect laser produced plasma (LPP) are configured to collect and reflect EUV light and contribute to EUV conversion efficiency and lithography throughput. However, LPP collectors are subjected to damages and degradations due to the impact of particles, ions, radiation, and debris deposition. Other embodiments in accordance with the present disclosure are directed to reducing debris deposition onto LPP collectors formed in accordance with the present disclosure, thereby increasing their usable lifetime.

The advanced lithography processes, methods, and apparatuses described in the current disclosure may be used in many applications, including in the manufacture of fin-type field effect transistors (FinFETs) and field effect transistors including nanostructure or nanosheet structures. For example, the fins of such transistors may be patterned to produce a relatively close spacing between features, for which the methods and apparatuses described herein are well suited to produce.

FIG.1is a schematic view of a lithography system10, constructed in accordance with some embodiments. The lithography system10may also be generically referred to as a scanner that is operable to perform lithography exposure processes. In accordance with embodiments of the present disclosure, the lithography system10is an extreme ultraviolet (EUV) lithography system designed to expose a resist layer by EUV light (or EUV light). The resist layer is a material sensitive to the EUV light. It is understood that embodiments in accordance with the present disclosure are not limited to lithography systems for carrying out EUV lithography.

In some embodiments, the EUV lithography system10employs a radiation source12to generate EUV light90, such as EUV light having a wavelength ranging between about 1 nm and about 100 nm. In one particular example, the EUV light90has a wavelength centered at about 13.5 nm. Accordingly, the radiation source12is also referred to as an EUV light source. The EUV light source may utilize a mechanism of laser-produced plasma (LPP) to generate the EUV light, which will be further described later.

The lithography system10also employs an illuminator14. In some embodiments, the illuminator14includes various reflective optics such as a mirror system having multiple mirrors in order to direct the EUV light90from the radiation source12onto a mask stage16, particularly to a mask18secured on the mask stage16.

The lithography system10also includes the mask stage16configured to secure the mask18. In some embodiments, the mask stage16includes an electrostatic chuck (e-chuck) to secure the mask18. In the present disclosure, the terms mask, photomask, and reticle are used interchangeably. In the embodiment described below, the lithography system10is a EUV lithography system, and the mask18is a reflective mask.

One exemplary structure of the mask18includes a substrate with a low thermal expansion material (LTEM). For example, the LTEM may include TiO2doped SiO2, or other suitable materials with low thermal expansion. The mask18includes a reflective multi-layer (ML) deposited on the substrate. The ML includes a number of film pairs, such as molybdenum-silicon (Mo/Si) film pairs (e.g., a layer of molybdenum above or below a layer of silicon in each film pair).

Alternatively, the ML may include molybdenum-beryllium (Mo/Be) film pairs, or other suitable materials that are configurable to highly reflect the EUV light90. The mask18may further include a capping layer, such as ruthenium (Ru), disposed on the ML for protection. The mask18further includes an absorption layer, such as a tantalum boron nitride (TaBN) layer, deposited over the ML. The absorption layer is patterned to define a layer of an integrated circuit (IC). The mask18may have other structures or configurations in various embodiments.

The lithography system10also includes a projection optics module (or projection optics box (POB))20for imaging the pattern of the mask18on to a semiconductor substrate22secured on a substrate stage (or wafer stage)24of the lithography system10. The POB20includes reflective optics in the present embodiment. The EUV light90directed from the mask18, carrying the image of the pattern defined on the mask18, is collected by the POB20. The illuminator14and the POB20may be collectively referred to as an optical module of the lithography system10.

In the present embodiment, the semiconductor substrate22is a semiconductor wafer, such as a silicon wafer or other type of wafer to be patterned. The semiconductor substrate22is coated with a resist layer sensitive to the EUV light90in the present embodiment. Various components including those described above are integrated together and are operable to perform lithography exposing processes.

The lithography system10may further include other modules or be integrated with (or be coupled with) other modules. In the present embodiment, the lithography system10includes a gas-supply module40. The gas-supply module40is designed to provide a cleaning gas (e.g., hydrogen gas) to the radiation source12. The cleaning gas helps reduce contamination in the radiation source12. In addition, the lithography system10includes an exhaust module60. The exhaust module60is designed to extract debris, such as ions, gases and atoms of the target droplet (which will be described in detail below), out of the radiation source12.

In the present embodiment, the lithography system10further includes a radio frequency device50. The radio frequency device50is designed to generate an electric field in the radiation source12to convert a cleaning gas into free radicals. In one certain embodiment, the lithography system10also includes a controller70. The controller70controls the operation of the radiation source12, the gas-supply module40, the radio frequency device50, and the exhaust module60.

Referring toFIG.2, in some embodiments, the radiation source12employs a laser produced plasma (LPP) mechanism to generate plasma and further generate EUV light from the plasma and includes a target droplet generator26, a laser source configuration28, a collector31, and a gas distributor32, a droplet catcher34, and a debris collection mechanism (DCM)36. The radiation source12may be configured in a source vessel25which is maintained in a vacuum environment. In accordance with embodiments of the present disclosure, the radiation source12further includes an additional collector (not shown inFIG.2, but illustrated inFIGS.4A-4C and5). In some embodiments, this additional collector is positioned concentrically relative to the axial centerline33of collector31such that the axial centerline of the additional collector and collector31coincide.

The target droplet generator26is configured to generate a number of target droplets27. In one certain embodiment, the target droplets27are tin (Sn) droplets. In some examples, the target droplets27each may have a diameter about 30 microns and are generated at a rate about 50 kilohertz (kHz). The target droplets27are introduced into a zone of excitation in the radiation source12at a speed about 70 meters per second (m/s) in one example. Other material may also be used for the target droplets27, for example, a tin-containing liquid material such as eutectic alloy containing tin, lithium (Li), and xenon (Xe).

The laser source configuration28may include a carbon dioxide (CO2) laser source, a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser source, or other suitable laser source capable of generating two laser beams29and30. Normally, the two laser beams are implemented as a pre-pulse (PP) laser29and main-pulse (MP) laser30configuration. Those pulse lasers are directed through an aperture313formed through the collector31, e.g., along the axial centerline33. In some embodiments, the initial PP laser29has sufficient power and pulse duration to heat the target droplet27of less than 20 micron dimension and transform the target droplet into a submicron mist which expands to form a pancake-like or dome-like cloud35of the droplet material in mist form, sometimes referred to as a precursor target. In some embodiments, the cloud35of the mist has a dimension of less than 300 microns and is comprised of atoms of the droplet material. Subsequent to the formation of the cloud35of mist, the MP laser30with relatively higher power and appropriate duration is fired at a certain angle to impact the cloud35of mist, thereby generating high-temperature plasma in which the atoms of the mist are ionized into high charge states. As the ionized atoms of the mist recombine, EUV light90is emitted from the plasma. Those laser properties may be applied in the range of power of such 1 to 30 kilowatt and pulse duration of such femtosecond order to nanosecond order, which are related to desired EUV power within the range of several watts to hundreds of watts. In some embodiments, the pulses of the laser source configuration28and the droplet generating rate of the target droplet generator26are controlled to be synchronized such that the target droplets27consistently receive peak powers from the PP laser29and the MP laser30of the laser source configuration28.

The droplet catcher34is configured to catch any target droplets that are missed by the laser beams29and30. The droplet catcher34is installed opposite the target droplet generator26and in the direction of the movement of the target droplets27. In some embodiments, the target droplet generator26and the droplet catcher34are positioned at two sides of the collector31.

Referring toFIG.3, in some embodiments, the EUV emitted from the mist of target material atoms is emitted in multiple directions as indicated by the arrows300a,300band300c. For example, inFIG.3, EUV radiation is emitted in a downward direction represented by arrows300awhich is in the direction of collector31. As explained below in more detail below, EUV radiation represented by arrows300apropagates in a direction that results in the EUV radiation represented by arrows300aimpinging upon a surface of collector31. In other words, EUV radiation represented by arrows300apropagates in a direction that intersects with a surface of collector31and the EUV radiation represented by arrows300ais intercepted at a surface of collector31. EUV radiation represented by arrows300bis emitted in a more generally horizontal direction, which is a direction that is approximately parallel with the surface of collector31upon which EUV represented by arrows300aimpinges. In the embodiment ofFIG.3, EUV radiation which is represented by arrows300bdoes not impinge upon collector31. In other words, EUV radiation represented by arrows300bpropagates in a direction that does not intersect a surface of collector31. The EUV radiation represented by arrows300bis not intercepted by a surface of collector31. EUV radiation represented by arrows300cis emitted in a generally upward direction, which is a direction that is away from the surface of collector31upon which EUV represented by arrows300aimpinges. In the embodiment ofFIG.3, EUV radiation which is represented by arrows300cdoes not impinge upon collector31. In other words, EUV radiation represented by arrows300cpropagates in a direction that does not intersect a surface of collector31. The EUV radiation represented by arrows300cis not intercepted by a surface of collector31. In some embodiments the EUV radiation emitted from the mist of target material ions is isotropic while in other embodiments the EUV radiation from the mist of target material ions is not isotropic. It is understood that arrows300a,300band300cdo not represent the entirety of the EUV radiation generated from the mist of target material and that EUV radiation is generated from the mist of target material35that travels in directions other than the directions represented by arrows300a,300band300c, but can be generally categorized as including EUV radiation that travels in a direction that has an upward vector, a downward vector or neither an upward or a downward vector. As illustrated inFIG.3, the portion of the EUV radiation generated from the mist of target material35that is not intercepted by collector31and does not impinge upon collector31cannot be reflected by collector31. This negatively affects the efficiency of the conversion of the laser energy to EUV energy, i.e., conversion efficiency.

In accordance with embodiments of the present disclosure illustrated inFIGS.4A-4C, a secondary collector400illustrated inFIGS.4A-4Cis provided. In the embodiment ofFIGS.4A-4C, secondary collector400is a ring-shaped mirror having a concave elliptical inner surface401and positioned so that EUV radiation, such as the EUV radiation represented by arrows300band300cis intercepted by and impinges upon an inner surface401of secondary collector400. The EUV radiation represented by arrows300band300cis reflected towards the intermediate focus or focal point A1(inFIG.2) of the primary collector31. In the embodiment ofFIGS.4A-4Csecondary collector400is a mirror having an outer surface402and an inner reflective surface401, at least the inner reflective surface401being elliptical, having an elliptical profile. In other embodiments, portions of the outermost peripheral portions of secondary collector400are not elliptical. For example, such outer portions can have a more spherical shape. In some instances, a secondary collector400that includes an elliptical portion and a spherical portion may be less challenging to manufacture compared to a secondary collector that includes only an elliptical portion. Referring more specifically toFIG.4B, as described above with reference toFIG.4A, EUV radiation emitted by cloud35of target material mist includes EUV radiation traveling in the direction of arrows300a,300band300c. EUV radiation traveling in the direction of arrows300aimpinges upon collector31and is reflected directly by collector31towards the intermediate focus point A1of collector31. This reflected EUV radiation is represented by arrow90a. In accordance with embodiments of the present disclosure, EUV radiation traveling in the direction of arrow300bimpinges upon an inner surface401of secondary collector400where it is reflected by secondary collector400to the intermediate focus point A1of primary collector31. This reflected EUV radiation is represented by arrow90b. EUV radiation traveling in the direction of arrow300cimpinges upon an inner surface of secondary collector400where it is reflected by secondary collector400to the intermediate focus point A1of primary collector31. This reflected EUV radiation is represented by arrow90c. Thus, in accordance with embodiments of the present disclosure, secondary collector400captures and reflects EUV radiation from cloud35that would not impinge upon, not be intercepted by primary collector31and not be reflected to intermediate focus point A1by the primary collector31. Utilization of secondary collector400in accordance with embodiments of the present disclosure causes EUV radiation that impinges on an inner surface of collector400to be reflected to the intermediate focus point A1along a path that is the same as the path that such EUV radiation would travel if it was reflected by the primary collector31. Utilization of secondary collector400in accordance with embodiments of the present disclosure increases the conversion efficiency of the laser power to EUV radiation directed to focal point A1. In accordance with some embodiments, utilizing methods and apparatuses in accordance with embodiments described herein may increase the conversion efficiency by 50 to 200 percent.

FIG.4Bis a schematic cross-sectional view of secondary collector400and primary collector31illustrated inFIG.4A. InFIG.4B, secondary collector400is illustrated in solid lines.FIG.4Cis the same schematic cross-sectional view of secondary collector400as inFIG.4B, with the solid line representation of secondary collector400inFIG.4Boverlaid with a broken line ellipse404representing shape of the ellipse which defines the curvature of the inner surface401of secondary collector400. Ellipse404includes a center406, a major axis a and a minor axis b. In the illustrated embodiment, one focus of ellipse404is coincident with the intermediate focus A1of primary collector31and the other focus of ellipse404is coincident with the location where the cloud35of target material is generated, i.e., the location where the laser intercepts the droplets of target material. Ellipse404can be represented by the mathematical formula:

x2a2+y2b2=1wherein a is the major axis a and b is the minor axis b. In accordance with disclosed embodiments, the foci of ellipse404(and the intermediate focus A1and cloud35) are separated by a distance in the range of 100 to 160 cm. In some embodiments the foci of ellipse404are separated by a distance in the range of 110 cm to 150 cm. Though not illustrated, as noted above, the upper and lower edges of secondary collector400inFIG.4Cmay include portions that do not fall on ellipse404. For example, portions of secondary collector400at its upper and lower edges can include a spherical, as opposed to an elliptical, shape. In the embodiment illustrated inFIG.4C, the center point of the secondary collector400on each side of the location of cloud35and the location of cloud35lie in a common plane408. The top edge410of collector400lies in a plane412spaced above plane408. The bottom edge414of collector400lies in a plane416space below plane408. In the embodiment illustrated inFIG.4C, plane408and412are spaced apart by a distance418and plane416and408are spaced apart a distance420. In embodiments of the present disclosure, the ratio of distances represented by418and420is between 0.5 to 2.0. In other embodiments, the ratio of distances represented by418and420is about 1.0. When collector400has a ratio of distances represented by418and420that falls within the foregoing range, meaningful amounts of EUV radiation is incident upon secondary collector400and is reflected to intermediate focus A1from secondary collector400. Embodiments in accordance with the present disclosure are not limited to the ratio of distances represented by418and420falling within the foregoing range of ratios. In accordance with some embodiments, the sum of distances418and420falls within the range of 5 to 20 cm.

In the embodiment illustrated inFIG.4C, primary collector31includes upper edges422which lie within a plane424. Plane424is separated from plane416by a distance426. In accordance with embodiments of the present disclosure, a ratio of distance426(distance between bottom edge of secondary collector400and upper edge of primary collector31) to the sum of distances418and420(height of secondary collector400) is in the range of 1 to 2. In accordance with embodiments of the present disclosure, distance426is between 5 and 15 centimeters. When the ratio of distance426to the sum of distances418and420or the distance426falls within the above ranges, the amounts of EUV radiation captured by primary collector31and secondary collector400and reflected to intermediate focus A1results in an increased conversion efficiency compared to when only the primary collector31is utilized.

InFIG.4C, a distance428exists between the opposing walls of collector400. InFIG.4Cprimary collector has a diameter430at its upper edge422. In accordance with embodiments of the present disclosure, a ratio of diameter430to distance428is between 4:1 to 1:1. In other embodiments, this ratio is between 3:1 to 2:1. Embodiments in accordance with the present invention include a distance428that is between 15 and 35 centimeters. In some embodiments, the distance428is between 20 and 30 centimeters. Embodiments in accordance with the present invention include a diameter430between 40 and 80 centimeters and, in some embodiments, between 50 and 70 centimeters. When the ratio of diameter430to distance428, includes distance428or diameter430falling within these ranges, the amounts of EUV radiation captured by primary collector31and secondary collector400, and reflected to intermediate focus A1, results in an increased conversion efficiency compared to when only the primary collector31is utilized.

Embodiments in accordance with the present disclosure provide an effective reflective surface area of the secondary collector400that is at least equal to 50% of the effective reflective surface area of primary collector31. For example, a ratio of the effective surface area of the secondary collector400to the effective reflective surface area of the primary collector31is at least 0.5:1. In some embodiments, a ratio of the effective surface area of the secondary collector400to the effective reflective surface area of the primary collector31is at least 1:1 and in some embodiments, the ratio is at least 2:1. When the ratio of the effective surface area of the secondary collector400to the effective reflective surface area of the primary collector31falls within these ranges, the total effective reflective surface area available to reflect EUV radiation to the intermediate focus A1is increased compared to if only the primary collector is deployed.

In accordance with embodiments of the present disclosure, dimensions a, b,418,420,426and428are selected so that EUV radiation generated by cloud35is able to impinge upon collector31and be reflected to intermediate focus A1, while at the same time maximizing the amount of EUV radiation that is reflected by secondary collector400to intermediate focus A1. For instance, selection of the foregoing dimensions should take into account minimizing the amount of EUV radiation that is propagating with a downward direction vector which does not impinge upon either the primary collector31or the secondary collector400. In addition, selection of the foregoing dimensions should take into account minimizing the amount of EUV radiation reflected by primary collector31toward intermediate focus A1that would intercept secondary collector400and therefore be prevented from reaching intermediate focus A1.

In another embodiment illustrated inFIG.5, the description of features with reference toFIG.4Bapplies equally to the features inFIG.5, wherein they are the same reference numerals as utilized inFIG.4B. In the embodiment ofFIG.5, the inner reflective surface of secondary collector500is capable of reflecting EUV radiation500cthat is incident on the inner reflective surface to collector31where it is reflected toward intermediate focus point600as indicated by arrows590c. In the embodiment ofFIG.5, secondary collector500is capable of reflecting EUV radiation500bdirectly toward intermediate focus point600as indicated by arrows590b. In such embodiment, secondary collector500ofFIG.5will have a different curvature profile than secondary collector400ofFIGS.4A-4C. For example, secondary collector500may have sections that have different curvature profiles, e.g., non-elliptical curvature, a section with an elliptical curvature and a section with a non-elliptical curvature, e.g., a hyperbolic curvature or other curvatures.

Referring back toFIG.2, the primary collector31is configured to collect, reflect and focus the (1) EUV radiation300athat is emitted by the plasma and impinges directly thereon, without reflection by an intermediary collector/reflector, and (2) referring toFIG.4B, the EUV radiation300band300cemitted by the plasma, impinges on the collector ring400and is reflected by the collector ring400to the intermediate focus point A1as represented by arrows and90c, or (3) referring toFIG.5, the EUV radiation500cimpinges on the collector ring500and is reflected to the primary collector31as represented by arrow590cand the EUV radiation500bimpinges on the collector ring500and is reflected to the intermediate focus point600as represented by arrow590b.

In some embodiments, the collector31is designed to have an ellipsoidal geometry with an aperture313formed thereon. The aperture313may be formed on a center of the collector31. Alternatively, the aperture313may be located offset from the center of the collector31. In one certain embodiment, the laser source configuration28is positioned relative to the aperture313, and the laser beams29and30emitted by the laser source configuration28pass through the aperture313before its irradiation upon the target droplet27as described above.

In some embodiments, the collector31and secondary collectors400and500are designed with proper coating material functioning as a mirror for EUV light collection, reflection, and focus. In some examples, the coating material of the collector31and secondary collectors400and500is similar to the reflective multilayer of the mask18(FIG.1). In some examples, the coating material includes a number of Mo/Si film pairs and may further include a capping layer (such as Ru) coated on the film pairs to substantially reflect the EUV light. In some examples, the collectors may further include a grating structure designed to effectively scatter the laser beam directed onto the collectors. For example, a silicon nitride layer may be coated on the collectors and patterned to have a grating structure.

The gas distributor32is configured to discharge a cleaning gas from the gas-supply module40to the collector31. In some embodiments, the gas distributor32includes a number of flow guiding members, such as flow guiding members321,322and323. The flow guiding member323is positioned relative to the aperture313. The flow guiding member323may include a tube structure and extends along a straight line. One end326of the flow guiding member323is directly connected to the aperture313and the other end is connected to the laser source configuration28.

The flow guiding members321and322are positioned at two sides of the collector31. Each of the flow guiding members321and322is formed with a tube structure and includes one or more gas holes located next to the circumference311of the collector31. For example, the flow guiding member321includes a number of gas holes positioned relative to the circumference311of the collector31. The gas holes may be configured with the same size, and spaced apart from each other by a predetermined pitch. In addition, the flow guiding member322includes a number of gas holes positioned relative to the circumference311of the collector31. These gas holes of flow guiding member322may be configured with the same size, and spaced apart from one another by a predetermined pitch.

Continuing to refer toFIG.2, in some embodiments, each of the flow guiding members321and322has a cane-like shape cross-section in a plane that is parallel to the optical axis A1. Specifically, the flow guiding member321has an end portion327connected to a gas hole in flow guiding member321, and the flowing guiding member322has an end portion328connected to a gas hole in flow guiding member322. Extension directions of two side walls of the end portions327and328intersect with the optical axis A1by different angles. In one certain embodiment, upper side walls U1and U2of the end portions327and328intersect with the optical axis A1at an angle about 90 degree, and inner side walls I1and I2of the end portions327and328intersect with the optical axis A1at an angle less than 90 degrees. As a result, the cleaning gas discharged by the flow guiding members321and322is redirected to form gas shield toward the surface of collector31that is used to reflect and focus the EUV light90.

The gas-supply module40is fluidly connected to the gas distributor32and is configured to supply the cleaning gas to the collector31via the gas distributor32. In some embodiments, the gas-supply module40includes a gas source44and a number of pipelines, such as pipelines41,42and43. The pipeline41fluidly connects the gas source44to the flow guiding member321. The pipeline42fluidly connects the gas source44to the flow guiding member322. The pipeline43fluidly connects the gas source44to the flow guiding member323. As noted above, this same gas-supply module40can supply cleaning gas to gas distributors632ofFIG.6.

In some embodiments, since the pipelines41,42and43and the flow guiding members321,322and323collectively guide cleaning gas supplied from the gas source44to the collector31, the pipelines41,42and43and the flow guiding members321,322and323are referred to as a gas flowing path.

The gas-supply module40further includes a regulating unit45configured to regulate the flow of the cleaning gas in the gas-supply module40according to a control signal from the controller70. In some embodiments, the regulating unit45includes one or more valves configured to control flowing rate of the cleaning gas in the pipelines41,42and43. For example, the regulating unit45includes three flow rate regulators V1, V2and V3, such as valves. The three flow rate regulators V1, V2and V3are respectively connected to the pipelines41,42and43. The three flow rate regulators V1, V2and V3may be independently controlled by the controller70to allow the cleaning gas in the pipelines41,42and43have different flowing rates.

In some embodiments, the regulating unit45further includes one or more energy converters configured to control temperature of the cleaning gas in the pipelines41,42and43. For example, the regulating unit45includes three energy converters H1, H2and H3. The three energy converters H1, H2and H3are respectively connected to the pipelines41,42and43. The three energy converters H1, H2and H3include heating members that convert electric energy into thermal energy. The energy converters H1, H2and H3apply the thermal energy into the cleaning gas in the pipelines41,42and43to heat up the cleaning gas to a predetermined temperature. In the following descriptions, the energy converters H1, H2and H3are referred to as “first energy converters.” These first energy converters may be used to heat the cleaning gas supplied to gas distributors632.

The predetermined temperature may be a temperature at which at least a portion of cleaning gas is converted to free radicals. That is, at the predetermined temperature, a specific bond between two atoms of the cleaning gas is broken so as to form the free radicals of the cleaning gas. Alternatively, the predetermined temperature may be a temperature that improves the conversion efficiency of the cleaning gas into free radicals as an electromagnetic radiant energy from the radio frequency device50is applied to the pre-heated cleaning gas. The first energy converters H1, H2and H3may be independently controlled by the controller70to allow the cleaning gas in the pipelines41,42and43to have different temperatures.

However, it should be appreciated that many variations and modifications may be made to embodiments of the disclosure. In some embodiments, a conduit46connects the gas source44and the pipelines41,42and43. The regulating unit45includes one valve and one first energy converter connected to the pipelines41,42and43. In some other embodiments, the pipelines41,42and43are omitted, and the gas source44is directly connected to the gas distributor32via the conduit46.

Still referring toFIG.2, the radio frequency device50is configured to convert the cleaning gas in the gas distributor32into free radicals by electromagnetic radiant energy before the cleaning gas is discharged over the collector31. In some embodiments, the radio frequency device50includes a number of energy converters, such as energy converters51,52and53. The energy converters51,52and53are respectively connected to the flow guiding members321,322and323. In one certain embodiment, each of the energy converters51,52and53includes a pair of electrodes. The energy converters51,52and53convert electric energy to electromagnetic radiant energy. In the following descriptions, the energy converters51,52and53are referred to as “second energy converters”. These second energy converters can be utilized to generate free radicals which will be discharged from gas distributors632.

The radio frequency device50further includes a power source54electrically connected to the second energy converters51,52and53to supply electromagnetic energy to the second energy converters51,52and53. The power source54may be connected to the second energy converters51,52and53via a control circuit55. The control circuit55controls the voltage applied to the second energy converters51,52and53according to the control signal from the controller70.

The DCM36is configured to trap the debris of the target droplet27. The DCM36is disposed along the optical axis A1connecting the aperture313of the collector31and an output port250of the source vessel25. The DCM36includes a number of vanes361that are arranged surrounding the optical axis A1. The vanes361are thin and elongate plates and are aligned so that their longitudinal axes are parallel to the optical axis A1. The vanes361project towards the optical axis A1, but do not extend as far as the optical axis. The DCM36is configured to guide any droplet debris attached on the vanes structure. As a result, the vanes361serve to prevent such droplet debris directly falling on a surface of the collector31.

The vanes361are configured to guide droplet material debris and cause the droplet material debris to attach to the vanes through thermal control of the vane temperature. For example such temperature control may be performed with warm and hot cycles. The hot cycle is intended to melt the droplet material debris that comes in contact with the vane and avoid formation of contamination due to bubble defect burst at a spitting temperature, and hence the hot cycle is operated at a temperature in the range from about 232 degree C. to about 350 degree C. The spitting temperature range may depend on internal gas components and chamber pressure, for examples the above temperature range applies to conditions of a hydrogen atmosphere and a medium vacuum of several mbar. The warm cycle is intended be performed under conditions that allow the droplet material debris to slide and roll along vane surfaces appropriately. Warm cycle temperatures are in the range from about 100 degree C. to about 232 degree C. Consequently, the temperature of the vane should be adjustable within a range of from about 100 degree C. to about 350 degree C. Furthermore, the droplet material debris trapped by the vanes may flow smoothly into a bottom vane gutter362. Finally, melting droplet material debris may flow through the drip pipe363and fall into a bucket37for droplet material waste storage. In one certain embodiment, the EUV light90is projected upwardly along the optical axis A1, and thus the melting droplet material is moved via gravity force.

The vanes361are made of a suitable material such as stainless steel, Cu, A1or ceramics. In certain embodiments, the vanes361are made of stainless steel. In the present embodiments, the surfaces of vanes361, are coated with a catalytic layer including ruthenium (Ru), tin (Sn), tin oxide, titanium oxide, or any combination thereof. In some embodiments, Ru is used. For embodiments where the droplet material is tin, the Ru coated surfaces of the vanes361reduce SnH4to Sn, and traps Sn thereon. By applying a catalytic layer made of, for example, Ru, on the surface of vanes in the DCM36, it is possible to reduce the conversion of SnH4vapor to metal Sn and to collect debris directly, and thus it is possible to prevent contamination of the collector31by Sn debris. It is appreciated that when the target droplet material used to generate EUV radiation is made of a different material than Sn, the same or a different catalytic material may be used as the catalytic material layer.

The exhaust module60includes an exhaust line61, an exhaust pump62, a heated scrubber63and a scrubber gutter64. One end of the exhaust line61is connected to and around the source vessel25to receive the exhaust. The heated scrubber63is connected to the exhaust line61and is configured to guide and trap the debris gas flow (or debris vapor). For example, the heated scrubber63has functions of a thermal control for heating or warming, an exhaust filtering and a debris trapping, which may include certain structure(s), such as labyrinth structures, nano rods, and porous macrostructures. When the debris hits the structure, it is heated and condensed into liquid, thereby being “trapped” inside the heated scrubber63. The debris may be guided and gathered together and collected in a scrubber gutter64. As a result, the droplet material debris is collected and drained into the vane structure of the DCM36.

Another end of the exhaust line61is connected to the pump62which is a vacuum pump. The pump62creates gas flow from the source vessel25into the heated scrubber63and the exhaust line61, to pump out the exhaust in the source vessel25. The exhaust of vessel25may be further directed into the factory exhaust system.

It should be appreciated that while there are three flow guiding members321,322and323illustrated inFIG.2, this is merely intended for clarity and is not intended to be limiting. Rather, any number of the flow guiding members may additionally be included within the radiation source12.

FIG.6illustrates other aspects of the embodiments in accordance with the present disclosure. InFIG.6, similar toFIG.2, gas distributors632are provided to discharge a cleaning gas from the gas-supply module to the inner reflective surface of secondary collector400/500. In some embodiments, the gas distributor632includes a number of flow guiding members or orifices from which the cleaning gas is dispensed. These orifices may be configured with the same size, and spaced apart from each other by a predetermined pitch. In other embodiments, the orifices may not be the same size and may be spaced apart with varying pitches. Orifices are disposed such that cleaning gas discharge from the orifices flows across the inner surface of the secondary collector400to displace unwanted material, e.g., particles of target materials droplets. The description above regardingFIG.2and the cleaning system utilized to clean primary collector31is equally applicable to the implementation of a cleaning system for cleaning secondary collector400/500. In addition, in the embodiment illustrated inFIG.6, in order to synchronize the timing of the laser pulses to optimize its contact with droplets of the target material mist35, various sensors634are provided. Data collected from sensors634can be analyzed to optimize exposure of the target material droplets with the laser pulses.

Referring toFIG.7, an embodiment of the present disclosure includes a method700for collecting electromagnetic radiation, e.g., electromagnetic radiation for use in a lithography process for exposing a material. The method700utilizes a secondary collector for collecting electromagnetic radiation, which would otherwise not be collected. Method700includes a first operation702of generating droplets of a target material, e.g., tin. Target droplet generator26inFIG.2is an example of a semiconductor tool useful in operation702. Method700includes operation704of generating electromagnetic radiation from the droplets of target material. Electromagnetic radiation can be generated from the droplets of material by exposing the target droplets with a laser from laser source configuration28inFIG.2. Method700includes operation706of reflecting, at a primary collector, a portion of the generated electromagnetic radiation to an intermediate focus point of the primary collector. Primary collector31inFIG.2is an example of a primary collector useful in operation706. Method700includes operation708of reflecting, at a secondary collector, another portion of the generated electromagnetic radiation. Secondary collector400inFIGS.4A-4Cand secondary collector500inFIG.5are examples of secondary collectors useful in operation708. In accordance with embodiments of the present disclosure, use of the secondary collector to collect generated electromagnetic radiation, in addition to the electromagnetic radiation collected by the primary collector, increases the conversion efficiency of the laser to electromagnetic radiation for use in a lithography process.

In another embodiment of the present disclosure, a method800ofFIG.8is provided. Method800is a method of photolithographically patterning a material, e.g., a material used in processes for manufacturing semiconductor devices. The method800utilizes a secondary collector for collecting and reflecting electromagnetic radiation, which would otherwise not be collected and reflected, to an intermediate focus point of a primary collector. Method800is initiated at operation802by generating droplets of a target material, e.g., tin. Target droplet generator26inFIG.2is an example of a semiconductor tool useful in operation802. Method800includes operation804of irradiating the droplets of target material with a laser. Laser source configuration28ofFIG.2is an example of a processing tool useful for generating laser that irradiates the droplets in operation804. Method800includes operation806of generating electromagnetic radiation from the exposed droplets of the target material. Irradiating droplets of the target material with a laser from laser source configuration28of FIG.2is an example of how electromagnetic radiation is generated in operation806. Method800includes operation808of intercepting at a primary collector, e.g., primary collector31inFIGS.4A-4C, a portion of the electromagnetic radiation generated in operation806. Method800proceeds with operation810of reflecting, at the primary collector, the intercepted portion of generated electromagnetic radiation to an intermediate focus point of the primary collector. At operation812of method800, another portion of the generated electromagnetic radiation is intercepted at a secondary collector, e.g., collector ring400inFIGS.4A-4C. At operation814of method800, the another portion of generated electromagnetic radiation intercepted at the secondary collector is reflected to an intermediate focus point of the primary collector. Method800proceeds with operation816of exposing material to the reflected portion of the electromagnetic radiation and the reflected another portion of the electromagnetic radiation. Illuminator14, mask stage16and projection optics20are examples of semiconductor process tools useful in carrying out operation816. In accordance with embodiments of the present disclosure, use of the secondary collector to collect generated electromagnetic radiation, in addition to the electromagnetic radiation collected by the primary collector, increases the conversion efficiency of the laser to electromagnetic radiation for use in a lithography process.

One aspect of this description relates to a method of collecting electromagnetic radiation, e.g., EUV radiation, which will be used in a EUV lithography process to manufacture a semiconductor device. The method generates droplets of a target material, such as tin, and irradiates them with a laser. EUV radiation is emitted by the irradiated droplets of target material. A portion of the emitted EUV radiation is reflected at a primary collector to a focal point of the primary collector. This focal point of the primary collector is also referred to as an intermediate focus point. The method also reflects, at a secondary collector, another portion of the generated electromagnetic radiation to the focal point of the primary collector. The secondary collector collects and reflects radiation that would otherwise not be directed to the focal point of the primary collector because such radiation would not be collected and reflected by the primary collector.

Another aspect of this description relates to a method of photolithographically patterning a material, such as a material used in a process to manufacture a semiconductor device. The method includes the step of generating droplets of a target material, e.g., tin. These droplets are irradiated with a laser to initiate generation of electromagnetic radiation by droplets of target material. A portion of the generated electromagnetic radiation is intercepted, at a primary collector. The intercepted portion of the generated electromagnetic radiation is reflected by the primary collector to a focal point of the primary collector. Another portion of the generated electromagnetic radiation is intercepted at a secondary collector. The intercepted another portion of the generated electromagnetic radiation is reflected by the secondary collector to a focal point of the primary collector. The portion of the generated electromagnetic radiation reflected by the primary collector and the another portion of the generated electromagnetic radiation reflected by the secondary collector is utilized to expose a material. The secondary collector collects and reflects radiation that would otherwise not be directed to the focal point of the primary collector because such radiation would not be collected and reflected by the primary collector.

Still another aspect of this description relates to a radiation source for generating electromagnetic radiation for use in a lithography exposure process. The radiation source includes a source of target material droplets, a source of a laser, a primary collector of radiation generated from the target material droplets and a secondary collector of radiation generated by the target material droplets. The primary collector collects a portion of the radiation generated from the target material droplets and directs it to an intermediate focus point of the radiation source. The secondary collector collects another portion of the radiation generated from the target material droplets and directs it to the same intermediate focus point of the radiation source. The combined electromagnetic radiation that arrives at the intermediate focus point of the radiation source is utilized to expose a material in a semiconductor process.