TW202333539A - Optical system and method for a radiation source - Google Patents

Abstract

An optical system for directing first and second laser pulses along an optical axis to a target to generate extreme ultraviolet radiation from said target. The optical system comprises a first optical component configured to redistribute a first laser pulse to form a shaped laser pulse having a hollow region. The optical system comprise a second optical component configured to focus the shaped laser pulse toward the target. The optical system comprises a third optical component configured to focus a second laser pulse toward the target within the hollow region of the shaped laser pulse. The first, second and third optical components are coaxially arranged on the optical axis.

Description

Optical systems and methods for radiation sources

The present invention relates to an optical system and a method for a radiation source, and in particular to a method for directing the first laser pulse and the second laser pulse along an optical axis to a target from the Optical systems that target the production of extreme ultraviolet radiation. The optical system is suitable for use as an EUV radiation source and/or as part of a lithography system.

Lithography equipment is a machine constructed to apply a desired pattern to a substrate. Lithography equipment may be used, for example, in the manufacture of integrated circuits (ICs). A lithography apparatus may, for example, project a pattern at a patterning device (eg, a photomask) onto a layer of radiation-sensitive material (resist) provided on a substrate.

To project patterns onto substrates, lithography equipment may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features that can be formed on the substrate. Compared to lithography equipment that uses radiation with a wavelength of, for example, 193 nm, lithography that uses extreme ultraviolet (EUV) radiation with a wavelength in the range of 4 to 20 nm, such as 6.7 nm or 13.5 nm. Equipment can be used to form smaller features on substrates.

One system that can be used to generate EUV radiation is a laser-produced plasma (LPP) system that involves the use of lasers to deposit energy into the fuel material via a laser beam. The deposition of laser energy into the fuel material creates a plasma. During the deexcitation of electrons by and recombination with ions of the plasma, emission from the plasma includes EUV radiation.

WO2012069898 discloses an LPP system that uses two laser beams, namely a main pulse laser beam and a pre-pulse laser beam, to generate EUV radiation from fuel materials. The beam shaping unit is disposed on the beam path of the main pulse laser beam, thereby transforming the main pulse laser beam into the hollow laser beam. The first focusing optical element is disposed downstream of the beam shaping device to focus the hollow laser beam. A second focusing optical element is provided which focuses the pre-pulse laser beam such that the pre-pulse laser beam and the hollow main pulse laser beam travel in the same direction towards the fuel material. Beam shaping of the main pulse laser beam and focusing of the pre-pulse laser beam occur on different vertical optical axes.

It is an object of the present invention to provide an improved optical system for generating EUV radiation from an LPP system.

According to a first aspect of the invention, an optical system is provided for directing a first laser pulse and a second laser pulse to a target along an optical axis to generate extreme ultraviolet radiation from the target. The optical system includes: a first optical component configured to redistribute the first laser pulse to form a shaped laser pulse having a hollow region; and a second optical component configured to focus the shaping laser pulse toward the target. The optical system includes a third optical component configured to focus the second laser pulse toward the target within the hollow region of the shaped laser pulse, wherein the first optical component, the second optical component The component and the third optical component are coaxially arranged on the optical axis.

The optical system of the present invention advantageously benefits from increased conversion efficiency compared to an optical system that reshapes the first laser pulse and focuses the second laser pulse along a different axis. The increase in conversion efficiency is due, at least in part, to the negligible (or zero) angle between the shaped first laser pulse and the focused second laser pulse, the relationship between the shaped first laser pulse and the focused second laser pulse. A negligible (or zero) angle between the optical axes of the optical system, and a negligible (or zero) angle between the focused second laser pulse and the optical axis of the optical system. Furthermore, the conversion efficiency is further improved due to the increased numerical aperture of the first laser pulse and the second laser pulse compared to known optical systems. In addition, the conversion efficiency is further improved because the first pulse and the second pulse share the same plane.

Compared to known optical systems in which the first laser pulse and the second laser pulse occupy the same area along the optical axis, the optical system according to the invention advantageously benefits from reduced heat on the optical components included therein. load (and associated risk of damage to optical components). This is because the first laser pulse and the second laser pulse may interact with different optical elements and/or different parts of optical elements rather than with the same part of the same optical element. Furthermore, compared to known optical systems that allow the first laser pulse and the second laser pulse to occupy the same area along the optical axis, the optical efficiency of the optical system disclosed herein is increased due to different optical components, such as , different optical elements and/or different portions of the same optical element) can be customized to interact with the first laser pulse and the second laser pulse (which can include different characteristics, such as wavelength, power, etc.).

Compared to known optical systems used in known EUV radiation sources, the optical system according to the invention advantageously benefits from an increased stability of the spatial profile of the first and second laser pulses at the target and Reproducibility. This is because the coaxial configuration enables a more uniform distribution of the spatial profile of the first and second laser pulses at the target compared to known optical systems used in known EUV radiation sources. Furthermore, redistributing the spatial profile of the first laser pulse ensures that the energy of the first laser pulse is maintained rather than at least partially lost. Additionally, the coaxial configuration of the optical components provides a compact design that includes easy repair and/or replacement of the optical components.

The words "first" and "second" and the like are used only to identify different features and do not indicate a temporal or spatial order. After the second laser pulse is incident on the target, the first laser pulse can be incident on the target.

The plurality of optical components may include reflective optical components. The plurality of optical components may include transmissive optical components.

The first laser pulse and the second laser pulse may include different wavelengths.

The target may be a fuel droplet (eg, tin).

The second laser pulse can be configured to change the shape of the target. For example, the second laser pulse can be configured to change the target from a droplet shape to a cookie shape.

The second laser pulse may contain a wavelength of approximately 1030 nm.

The first laser pulse may be configured so that the target emits extreme ultraviolet radiation. For example, a first laser pulse can convert the target into a plasma that emits extreme ultraviolet radiation.

The first laser pulse may contain a wavelength of approximately 10.6 µm.

The first optical component and the third optical component can be positioned on different surfaces of a single optical element.

This configuration advantageously reduces the number of optical elements compared to known optical systems, thereby reducing cost and complexity, while simplifying repair and replacement compared to known optical systems.

The first optical component may be formed on the front side of the single optical element. The third optical component can be formed on the backside of the single optical element.

The optical system may include a radiation collector configured to receive extreme ultraviolet radiation emitted by the target. The radiation collector may include apertures coaxially disposed on the optical axis. The second optical component and the third optical component may be configured to shape and focus the second laser pulse through the aperture.

Compared to known optical systems with a shaped and second laser pulse and/or off-axis positioned collector aperture along different axes, having a collector aperture coaxial with the shaped and second laser pulse and the target Advantageously, the conversion efficiency of the optical system (when generating EUV radiation) is increased.

The second optical component can be configured to interact only with the shaping laser pulses. The third optical component can be configured to interact only with the second laser pulse.

This configuration advantageously enables the optical components to be tailored to the different characteristics (eg, wavelength) of the first and second pulses.

The second optical component may include openings coaxially disposed on the optical axis.

This configuration advantageously provides a more compact system compared to known optical systems.

A third optical component may be configured to focus a third laser pulse along an optical axis to the target within the hollow region of the shaped laser pulse. The third laser pulse may include a different wavelength than the first laser pulse and the second laser pulse.

After the first laser pulse and before the second laser pulse, a third laser pulse may be incident on the target.

The third laser pulse may be configured to prepare the target for receiving the second laser pulse. For example, the third laser pulse may be configured to atomize the target in preparation (i.e., convert the cookie droplets into many small particles, similar to a gaseous state) to receive the first laser pulse for EUV radiation is generated. The third laser pulse may be used to increase absorption of the first laser pulse by the target.

The third laser pulse may have a wavelength of approximately 1064 nm.

According to a second aspect of the present invention, an extreme ultraviolet radiation source comprising an optical system of the first aspect is provided.

According to a third aspect of the present invention, an etching system including an extreme ultraviolet radiation source of the second aspect is provided.

According to a fourth aspect of the invention, a method of directing a first laser pulse and a second laser pulse to a target along an optical axis to generate extreme ultraviolet radiation from the target is provided. The method includes: using a first optical component to redistribute the first laser pulse to form a shaped laser pulse having a hollow region; and using a second optical component to direct the shaped laser pulse towards the target focus. The method further includes using a third optical component to focus the second laser pulse toward the target within the hollow region of the shaped laser pulse. The method also includes arranging the first optical component, the second optical component and the third optical component coaxially on the optical axis.

The first laser pulse and the second laser pulse may include radiation of different wavelengths.

The method may include positioning the first optical component and the third optical component on different surfaces of a single optical element.

The method may include positioning the first optical component on a front side of the single optical element and positioning the third optical component on a back side of the single optical element.

The method may include using a radiation collector to receive extreme ultraviolet radiation emitted by the target. The method may include arranging an aperture of the radiation collector coaxially on the optical axis. The method may include using a second optical component and a third optical component to shape and focus the second laser pulse through an aperture.

The method may include using a second optical component to interact only with the shaping laser pulse. The method may include using the third optical component to interact only with the second laser pulse. The method may include providing an opening in the second optical component and arranging the opening coaxially on the optical axis. The method may include using a third optical component to focus a third laser pulse along an optical axis to the target within the hollow region of the shaped pulse. The third laser pulse may include a different wavelength than the first laser pulse and the second laser pulse.

According to a fifth aspect of the present invention, a method of projecting a patterned radiation beam onto a substrate is provided, which includes using the method of the fourth aspect to generate extreme ultraviolet radiation.

Figure 1 illustrates a lithography system including a radiation source SO and a lithography apparatus LA. Radiation source SO is configured to generate EUV radiation beam B and supply EUV radiation beam B to lithography apparatus LA. Lithography apparatus LA includes an illumination system IL, a support structure MT configured to support a patterning device MA (eg, a photomask), a projection system PS, and a substrate table WT configured to support a substrate W.

The illumination system IL is configured to condition the EUV radiation beam B before the EUV radiation beam B is incident on the patterning device MA. In addition, the illumination system IL may include a faceted field mirror device 10 and a faceted pupil mirror device 11 . The faceted field mirror device 10 and the faceted pupil mirror device 11 together provide an EUV radiation beam B having a desired cross-sectional shape and a desired intensity distribution. As a supplement or alternative to the faceted field mirror device 10 and the faceted pupil mirror device 11 , the illumination system IL may also include other mirrors or devices.

After such conditioning, the EUV radiation beam B interacts with the patterning device MA. Due to this interaction, a patterned EUV radiation beam B' is generated. Projection system PS is configured to project patterned EUV radiation beam B' onto substrate W. For this purpose, the projection system PS may comprise a plurality of mirrors 13, 14 configured to project the patterned EUV radiation beam B' onto the substrate W held by the substrate table WT. Projection system PS can apply a reduction factor to patterned EUV radiation beam B', thereby forming an image with features that are smaller than corresponding features on patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Although projection system PS is illustrated in Figure 1 as having only two mirrors 13, 14, projection system PS may include a different number of mirrors (eg, six or eight mirrors).

The substrate W may include previously formed patterns. In this case, lithography apparatus LA aligns the image formed by the patterned EUV radiation beam B' with the pattern previously formed on the substrate W.

A relative vacuum, ie, a small amount of gas (eg, hydrogen) at a pressure well below atmospheric pressure, may be provided in the radiation source SO, in the illumination system IL, and/or in the projection system PS.

The radiation source SO shown in Figure 1 is of a type that may be called a laser produced plasma (LPP) source, for example. A laser system 1 , which may include, for example, a _CO2 laser, is configured to deposit energy via two or more laser pulses 2 of different wavelengths into a fuel, such as tin (Sn), emitted from, for example Provided by Device 3. Although tin is mentioned in the following description, any suitable fuel may be used. The fuel may, for example, be in liquid form, and may be, for example, a metal or alloy. The fuel injector 3 may comprise a nozzle configured to direct tin, for example in the form of small droplets, along a trajectory towards the plasma formation zone 4 . The laser pulse 2 is incident on the tin at the plasma formation zone 4. Deposition of laser energy into tin generates tin plasma 7 at the plasma formation area 4 . During the deexcitation of electrons by the ions of the plasma and their recombination with the ions, radiation including EUV radiation is emitted from the plasma 7 .

The lithography apparatus LA contains an optical system 100 for directing the laser pulse 2 along the optical axis to the tin at the plasma formation region 4 to generate EUV radiation. An example of optical system 100 is shown in greater detail in FIG. 2 . An example of an alternative optical system 400 that may be used as part of a lithography apparatus LA is shown in detail in FIG. 4 . Optical system 100 or alternative optical system 400 may be considered as part of a radiation source SO for generating EUV radiation.

EUV radiation from the plasma is collected and focused by collector 5 . The collector 5 includes, for example, a near normal incidence radiation collector 5 (sometimes more commonly referred to as a normal incidence radiation collector). Collector 5 may have a multilayer mirror structure configured to reflect EUV radiation (eg, EVU radiation having a desired wavelength, such as 13.5 nm). The collector 5 may have an ellipsoidal configuration with two foci. As discussed below, a first of the foci may be at plasma formation zone 4 and a second of the foci may be at intermediate foci 6 . The collector 5 may comprise an aperture 20 through which the laser pulse 2 travels to reach the plasma formation zone 4 .

The laser system 1 may be spatially separated from the radiation source SO. In this case, the laser pulse 2 can be delivered from the laser system 1 to the radiation source SO by means of a beam delivery system (not shown), which beam delivery system includes, for example, suitable guide mirrors and/or beam expanders and /or other optical parts. The laser system 1, the radiation source SO and the beam delivery system may collectively be considered to be radiation systems.

The radiation reflected by collector 5 forms EUV radiation beam B. The EUV radiation beam B is focused at the intermediate focus 6 to form an image at the intermediate focus 6 of the plasma present in the plasma formation region 4 . The image at intermediate focus 6 serves as a virtual radiation source for illuminating system IL. The radiation source SO is configured such that the intermediate focus 6 is located at or near the opening 8 in the enclosure 9 of the radiation source SO.

2 schematically depicts a cross-sectional side view of an optical system 100 for directing a first laser pulse 110 and a second laser pulse 120 along an optical axis 130 to a target (not shown) for self-direction. The target generates EUV radiation. The target may be a droplet of fuel (eg, tin) present at a plasma formation orientation 4, such as the one depicted in FIG. 1 . Optical system 100 includes a first optical component 140 configured to redistribute first laser pulse 110 to form a shaped laser pulse 150 having a hollow region 155 . In the example of FIG. 1 , the first optical component 140 includes an axicon mirror with a convex reflective surface on which the first laser pulse 110 is incident. Convex surfaces can contain off-axis parabolas. In the example of FIG. 1, the first optical component 140 is generally a cone. The first optical component 140 may take other shapes. The apex of the convex conical reflective surface is coaxially disposed on the optical axis 130 . The first optical component 140 spatially redistributes the energy of the first laser pulse 110 . The axicon mirror of the first optical component 140 spatially redistributes the energy of the first laser pulse 110 by reflecting different parts of the first laser pulse 110 in different directions to form a shaped laser pulse 150 . In the example of Figure 2, the shaping laser pulse 150 takes the form of a hollow cone with an annular cross-section (an example of which is shown in Figure 3 as seen along the optical axis 130). It will be appreciated that the shaped laser pulse 150 may take the form of other shapes including hollow areas.

In the example of Figure 2, optical system 100 may include the features described in the preceding paragraphs. In addition, shaping laser pulse can also be understood as shaping beam pulse or shaping beam. In additional embodiments, the first optical component 140 may be a cone, a sphere, an aspheric or have a free form.

Optical system 100 includes a second optical component 160 configured to focus shaping laser pulse 150 toward a target. In the example of FIG. 2 , the second optical component 160 includes a focusing mirror having a concave reflective surface upon which the shaping laser pulse 150 is incident. The first optical component 140 forms the shaping laser pulse 150 and directs the shaping laser pulse 150 towards the concave reflective surface of the second optical component 160 via reflection of the first laser pulse 110 . The concave reflective surface of the second optical component 160 reflects the shaping laser pulse 150 and focuses the shaping laser pulse 150 toward the target (e.g., at the plasma formation orientation 4, such as that illustrated in FIG. 1 small droplets of fuel). The second optical component 160 includes an opening 190 coaxially arranged on the optical axis 130 . That is, the center of the opening 190 of the second optical component 160 is coaxially disposed on the optical axis 130 . Therefore, the concave reflective surface of the second optical element 160 takes the form of a concave torus surrounding the optical axis 130 . Opening 190 is shown in Figure 2 by dashed lines. The first laser pulse 110 propagates through the aperture 190 along the optical axis 130 to reach the first optical component 140 .

Optical system 100 includes a third optical component 170 configured to focus second laser pulse 120 toward the target within hollow region 155 of shaped laser pulse 150 . That is, the third optical component 170 guides and focuses the second laser pulse 120 to the target along the optical axis 130 so that the second laser pulse 120 propagates within the hollow region 155 of the shaped laser pulse 150 . The annular cross-section of the second laser pulse 120 is nested within the inner circle of the annular cross-section of the shaping laser pulse 150 (an example of which can be seen along the optical axis 130 as shown in FIG. 3 ). In the example of FIG. 2 , the third optical component 170 includes a focusing mirror having a concave reflective surface upon which the second laser pulse 120 is incident. The first optical component 140 , the second optical component 160 and the third optical component 170 are coaxially disposed on the optical axis 130 and therefore are coaxially disposed with respect to each other and the target (eg, plasma formation orientation 4 of FIG. 1 ).

Advantageously, the coaxial configuration of the first optical component 140 , the second optical component 160 and the third optical component 170 allows the laser pulses 110 , 120 (or laser beams) to be directed coaxially to the plasma formation zone orientation 4 and to the target. Interaction, even when the target is slightly off-axis.

In another embodiment, the third optical component 170 includes a focusing mirror having a concave reflective surface or a flat surface, and the second laser pulse 120 is incident on the focusing mirror. In embodiments in which the third optical component 170 includes a mirror with a flat surface, the optical system 100 further includes an additional focusing system (not shown) located upstream and configured such that the second radar The emission pulse 120 is focused.

In the example of FIG. 2 , the first optical component 140 and the third optical component 170 are located on different surfaces of a single optical element 180 . The first optical component 140 is formed on the front side of the single optical element 180 facing the first laser pulse, and the third optical component 170 is formed on the back side of the single optical element 180 facing the target. That is, the convex conical surface of the axicon mirror of the first optical component 140 is positioned on the front side of the single optical element 180 , and the concave reflective surface of the focusing mirror of the third optical component 170 is positioned on the back side of the single optical element 180 superior. This configuration advantageously contributes to the compactness of optical system 100.

The first optical component 140 is configured to interact only with the first laser pulse 110 . The second optical component 160 is configured to interact only with the shaping laser pulse 150 . The third optical component 170 is configured to interact only with the second laser pulse 120 . This advantageously allows each optical component 140, 160, 170 to be customized to interact with its respective laser pulse 110, 120. For example, the first laser pulse 110 and thus the shaping laser pulse 150 may have a wavelength of approximately 10.6 μm. The first laser pulse 110 may be a CO2 laser pulse (ie, generated by a carbon dioxide laser). The first optical component 140 and the second optical component 160 may therefore be designed in particular to be as reflective as possible for a wavelength of approximately 10.6 μm. For example, the first optical component 140 and/or the second optical component 160 may include a reflective coating material such as copper, silicon carbide, silicon, coated steel, or the like. As another example, second laser pulse 120 may have a wavelength of approximately 1030 nm or 1064 nm. The second laser pulse 120 may be a pulse generated by a solid-state laser, such as a YAG laser. The third optical component 170 can thus be designed in particular to be as reflective as possible for wavelengths of approximately 1030 nm or 1064 nm. For example, the third optical component 170 may include a reflective coating material such as silver, gold, or the like. Dedicating different optical components 140, 160, 170 to different laser pulses 110, 120 also advantageously reduces the risk of overheating of the optical components compared to known optical systems that use a single optical element to interact with two laser pulses. , and thereby be deformed or damaged.

Additionally, the optical system of the present invention advantageously facilitates the coating selection process, allowing well-known coatings to be used for each laser pulse or laser beam.

Although FIG. 2 only shows the first laser pulse 110 and the second laser pulse 120, the optical system 100 can guide another laser pulse to the target. For example, third optical component 170 may be configured to focus a third laser pulse (not shown) along optical axis 130 to a target within hollow region 155 of shaped laser pulse 150 . An example of the relative positioning of the first, second, and third laser pulses along the optical axis 130 is illustrated in FIG. 3 from a perspective view.

Figure 3 schematically depicts a front view of the aperture 20 of the radiation collector of Figure 1 . The aperture 20 of the radiation collector is coaxially arranged on the optical axis 130 . Thus, the aperture 20 of the radiation collector is coaxially aligned with respect to the first optical component 140 , the second optical component 160 , and the third optical component 170 and the target (eg, plasma formation orientation 4 of FIG. 1 ). The view depicted in FIG. 3 can be viewed as a numerical aperture view along the optical axis 130 . That is, the space occupied by different laser pulses 120, 150, 200 may correspond to different angles of incidence occupied by the laser pulses. The second pulse 120 has a circular cross-sectional shape centered on the optical axis 130 . The third laser pulse 200 also has a circular cross-sectional shape centered on the optical axis 130 . The diameter of the third laser pulse 200 is larger than the diameter of the second laser pulse 120 . Shaping laser pulse 150 has an annular cross-sectional shape centered on optical axis 130 . The hollow region 155 of the shaping laser pulse 150 has an annular cross-sectional shape centered on the optical axis 130 . The second laser pulse 120 and the third laser pulse 200 are positioned within the hollow region 155 of the shaped laser beam 150 .

A second optical component (not shown in Figure 3) is configured to focus the shaping laser pulse 150 through the aperture 20 and toward the target. A third optical component (not shown in Figure 3) is configured to focus the second laser pulse 120 through the aperture 20 and toward the target. When propagating toward the target along the optical axis 130, the shaping laser pulse 150 does not occupy the same space as the second laser pulse 120 and the third laser pulse 200, but part of the third laser pulse 200 occupies the same space as the second laser pulse 120 and the third laser pulse 200. Two laser pulses 120 in the same space. However, each laser pulse 120, 150, 200 is focused towards the target and therefore may be incident on the same part of the target.

In another embodiment, laser pulses 120 and 200 may be positioned immediately adjacent to each other on third optical component 170 . Therefore, the third optical component 170 is configured to focus the pulses even if they are placed in different areas of the third optical component 170 . This situation means that the second laser pulse 120 and the third laser pulse 200 are close to the axis. Therefore, the angle with respect to the optical axis 130 is reduced compared to other configurations of the state of the art, which in turn advantageously increases the conversion efficiency of the extreme ultraviolet radiation source SO.

It will be appreciated that each laser pulse 120, 150, 200 travels along the optical axis 130 and reaches the target at a different time. The view of Figure 3 depicts all three laser pulses simultaneously to demonstrate the relative positions of laser pulses 120, 150, 200 for ease of understanding.

Each laser pulse contains one or more different characteristics (eg, wavelength, power, shape, etc.) for interacting with the target in a different manner. The second laser pulse 120 may reach the target first. The second laser pulse 120 can be configured to change the shape of the target. For example, the second laser pulse 120 may be configured to cause the target to change from a small droplet shape to a flat circular, or "cookie" shape. The second laser pulse 120 may include a wavelength of approximately 1030 nm or approximately 1064 nm. The second laser pulse 120 may be generated by any suitable laser, such as one or more of a solid-state laser, a semiconductor laser, and the like.

The third laser pulse 200 may reach the target second. That is, after the second laser pulse 120 and before the first laser pulse 110, the third laser pulse 200 may be incident on the target. The third laser pulse 200 may be configured to prepare the target for receiving the first laser pulse 110 . For example, the third laser pulse 200 may be configured to atomize the target in preparation (ie, convert cookie droplets into many small particles similar to a gaseous state) to receive the first laser pulse 110 Used to generate EUV radiation. The third laser pulse 200 may be used to increase absorption of the first laser pulse 110 by the target. The third laser pulse 200 may have a wavelength of approximately 1064 nm. The third laser pulse 200 may be generated by any suitable laser, such as one or more of a solid-state laser, a semiconductor laser, and the like. A single laser can be used to generate the second laser pulse 120 and the third laser pulse 200 .

It should be understood that another definition of atomizing a target could be thinning the target.

The first laser pulse 110 may reach the target last. That is, after the second laser pulse 120 and after the third laser pulse 200, the first laser pulse 110 may be incident on the target. The first laser pulse 110 may be configured to cause the target to emit EUV radiation. For example, the first laser pulse 110 may convert the target into a plasma that emits EUV radiation. The first laser pulse 110 may include a wavelength of approximately 10.6 µm. The first laser pulse 110 may be generated by any suitable one or more lasers, such as a _CO2 laser.

As previously described with reference to Figure 1, the radiation reflected by collector 5 forms beam B of EUV radiation. The EUV radiation beam B is focused at the intermediate focus 6 to form an image at the intermediate focus 6 of the plasma present in the plasma formation region 4 . The image at intermediate focus 6 serves as a virtual radiation source for illuminating system IL. In contrast to known optical systems, the coaxial configuration of the laser pulses 120, 150, 200 (eg, as shown in Figure 3) is due to the angle between the laser pulses 120, 150, 200 and the optical axis 130 The reduction in offset provides several advantages.

The examples of the previous paragraphs are applicable to lithography systems with high numerical aperture NA optics. For EUV lithography systems, by high NA is understood to be systems with an NA higher than 0.33, for example 0.55. High NA optics yield a shorter effective focal length for these optics. A coaxial configuration of laser pulses 120, 150, 200 (eg, as shown in Figure 3) provides an additional advantage for high NA systems: lower sensitivity of the beam focus position to input beam tilt. It is known that this tilt can be attributed to laser jitter. Therefore, the optical system of the present invention advantageously produces more stable EUV radiation doses for high NA EUV lithography systems.

Compared to known optical systems, the coaxial arrangement of laser pulses 120, 150, 200 reduces the angle between the angle of incidence of the first laser pulse 110 on the target and the angle of incidence of the second laser pulse 120 on the target. This situation advantageously improves the efficiency of the radiation source SO and/or the lithography apparatus LA including the optical system 100 since less EUV radiation is present at the target and/or in the far field (ie, in the illumination system of the lithography apparatus LA IS and/or projection system PS) is lost. The angle between the angle of incidence of the first laser pulse 110 on the target and the angle of incidence of the second laser pulse 120 on the target may be substantially zero.

Compared to known optical systems, the coaxial configuration of laser pulses 120, 150, 200 reduces the angle between the angle of incidence of the first laser pulse 110 at the target and the optical axis 130, centering the aperture 20 of the radiation collector on the optical axis 130. This situation advantageously improves the efficiency of the radiation source SO and/or the lithography apparatus LA containing the optical system 100 since less EUV radiation is lost via the inclination of the EUV radiation in the far field (i.e. in the lithography apparatus LA lighting system IS and/or projection system PS). Furthermore, the loss of EUV radiation at the intermediate focus 6 is reduced due to the fact that the image of the plasma at the intermediate focus (ie, the virtual radiation source of the illumination system IS) is not tilted. The angle between the angle of incidence of the first laser pulse 110 at the target and the optical axis 130 on which the aperture 20 of the radiation collector is centered can be substantially zero.

The coaxial configuration of laser pulses 120, 150, 200 increases the numerical aperture available for laser pulses 110, 120, 200 compared to known optical systems. Increasing the numerical aperture available for the laser pulses 110, 120, 200 advantageously reduces the presence of optical aberrations, which in turn reduces the loss of EUV radiation and/or reduces the interference in the optical system 100 and/or the lithography apparatus LA. The intensity of undesired back reflections that occur in Increasing the numerical aperture available for laser pulses 110, 120, 200 also advantageously reduces the limit of the third laser pulse 200 at the target, which in turn improves the efficiency of EUV radiation generation.

The coaxial configuration of the laser pulses 120, 150, 200 advantageously increases the conversion efficiency of the extreme ultraviolet radiation source SO.

The coaxial configuration of the laser pulses 120, 150, 200 advantageously increases the stability and reproducibility of the beam profile of the first laser pulse 110 incident on the target, which improves EUV when incorporated into the optical system 100 The efficiency and stability of production and lithography printing.

The optical system of Figure 2 is an example of an optical system including a reflective component. Compact coaxial optical systems containing other optical components, such as transmission optics, may also be used.

Figure 4 schematically depicts a cross-sectional side view of an alternative optical system 400 including a transmissive optical component in accordance with one embodiment of the present invention. As with optical system 100 of Figure 2, alternative optical system 400 is adapted to direct first laser pulse 110 and second laser pulse 120 along optical axis 130 to a target (eg, as shown in Figure 1 The plasma forms fuel droplets in zone 4) to generate EUV radiation from the target. The alternative optical system 400 includes a first optical component 440 configured to redistribute the first laser pulse 110 to form a shaped laser pulse 150 having a hollow region 155 . In the example of FIG. 4 , the first optical component 440 includes a first optical element 441 and a second optical element 442 . The first optical element 441 includes a beam expander configured to convert the first laser pulse 110 into a divergent beam. The second optical element 442 includes an axicon lens configured to receive the first laser pulse 110 from the first optical element 441 and spatially redistribute the energy of the first laser pulse 110 . The axicon lens of the second optical element 442 spatially redistributes the energy of the first laser pulse 110 by transmitting different portions of the first laser pulse 110 in different directions to form a shaped laser with a hollow region 155 Pulse 450.

The alternative optical system 400 includes a second optical component 460 configured to focus the shaping laser pulse 150 toward a target. In the example of FIG. 4 , the second optical component 460 includes a third optical element 461 and a fourth optical element 462 . The third optical element 461 includes a collimator configured to collimate the shaping laser pulse 150 . The fourth optical element 462 includes a lens configured to receive the shaping laser pulse 150 from the third optical element 461 and focus the shaping laser pulse 150 along the optical axis 130 toward a target (not shown).

The alternative optical system 400 includes a third optical component 470 configured to focus the second laser pulse 120 toward the target within the hollow region 455 of the shaped laser pulse 450 . In the example of FIG. 4 , the third optical component 470 includes a lens configured to focus the second laser pulse 120 toward the target along the optical axis 130 within the hollow region 455 of the shaped laser pulse 450 . The first optical component 440 , the second optical component 460 and the third optical component 470 are coaxially arranged on the optical axis 130 .

In another embodiment, the third optical element may be an opening or aperture. In this embodiment, additional optical elements may be located upstream configured to focus the second laser pulse 120 .

Regardless of including transmissive components rather than reflective components, the alternative optical system 400 modulates the laser pulses 110 , 120 to achieve the same results as the optical system 100 of FIG. 2 (i.e., the laser pulses 110 , 150 depicted in FIG. 3 , 200 coaxial configuration). Alternative optical system 400 may include a radiation collector (not shown) configured to receive EUV radiation emitted by the target, and the radiation collector may include an aperture disposed coaxially on optical axis 130 . The second optical component 460 and the third optical component 470 may be configured to focus the shaped laser pulse 150 and the second laser pulse 120 through the aperture of the radiation collector. The second optical component 460 includes an opening 490 coaxially arranged on the optical axis 130 . The third optical component 470 may be configured to focus a third laser pulse (not shown) along the optical axis 130 to the target within the hollow region 455 of the shaped laser pulse 450 . The third laser pulse may include a different wavelength than the first laser pulse 110 and the second laser pulse 120 (eg, the third laser pulse may be the third laser pulse 200 illustrated in FIG. 3 ).

The first optical component 440 is configured to interact only with the first laser pulse 110 . The second optical component 460 is configured to interact only with the shaping laser pulse 150 . The third optical component 470 is configured to interact only with the second laser pulse 120 . This advantageously allows each optical component 440, 460, 470 to be customized to interact with its respective laser pulse 110, 120. For example, the first laser pulse 110 and thus the shaping laser pulse 150 may have a wavelength of approximately 10.6 μm. The first optical component 440 and the second optical component 460 may therefore be specifically designed to be as transmissive as possible for a wavelength of approximately 10.6 μm. For example, the first optical component 140 and/or the second optical component 160 may include a material such as ZnSe. As another example, second laser pulse 120 may have a wavelength of about 1030 nm or about 1064 nm. The third optical component 470 may therefore be designed in particular to be as reflective as possible for wavelengths of about 1030 nm or about 1064 nm. For example, the third optical component 170 may include materials such as quartz, fused silica, BK7, etc. Dedicating different optical components 440, 460, 470 to different laser pulses 110, 120 also advantageously reduces the risk of overheating of the optical components compared to known optical systems that use a single optical element to interact with two laser pulses. , and thereby prevent deformation or damage.

5 illustrates a flowchart of a method of directing a first laser pulse and a second laser pulse along an optical axis to a target to generate extreme ultraviolet radiation from the target, according to one embodiment of the present invention. It will be understood that use of the terms "first step," "second step," etc. does not indicate a temporal order of steps, but rather is used only to distinguish steps of a method. For example, the second step 602 may be performed before the first step 601. As explained above, it should be understood that the various pulses are not incident on the target simultaneously. The first step 601 of the method includes using a first optical component to redistribute a first laser pulse to form a shaped laser pulse with a hollow region. The second step 602 of the method includes using a second optical component to focus the shaped laser pulse toward the target. The third step 603 of the method includes using a third optical component to focus the second laser pulse toward the target within the hollow region of the shaped laser pulse. The fourth step 604 of the method includes arranging the first optical component, the second optical component and the third optical component coaxially on the optical axis. It will be appreciated that the optical system 100 of FIG. 2 or the alternative optical system 400 of FIG. 4 may be used to perform the method of FIG. 5 .

The method may include the optional step of positioning the first optical component and the third optical component on different surfaces of a single optical element (eg, single optical element 180 illustrated in Figure 2). The method may include the optional step of positioning the first optical component on the front side of the single optical element. The method may include the optional step of positioning a third optical component on the backside of the single optical element.

The method may include the optional step of using a radiation collector to receive extreme ultraviolet radiation emitted by the target (eg, radiation collector 5 illustrated in Figure 1). The method may include the optional step of arranging the aperture of the radiation collector (eg, aperture 20 illustrated in Figure 3) coaxially on the optical axis.

The method may include using the second optical component and the third optical component to focus the shaping of the laser pulse and the second laser pulse through the aperture (e.g., as shown in FIG. 3 as performed by the optical system of FIG. 2 or FIG. 4 Optional step for coaxial configuration).

The method may include the optional step of using the first optical component to interact only with the first laser pulse. The method may include the optional step of using a second optical component to interact only with the shaping laser pulse. The method may include the optional step of using a third optical component to interact only with the second laser pulse. Each of these optional steps is illustrated by optical systems such as Figures 2 and 4.

The method may include the optional step of providing an opening in the second optical component. The method may include the optional step of arranging the openings coaxially on the optical axis. Each of these optional steps is illustrated by optical systems such as Figures 2 and 4.

The method may include the optional step of using a third optical component to focus a third laser pulse along the optical axis to the target within the hollow region of the shaped pulse. The third laser pulse may include a different wavelength than the first laser pulse and the second laser pulse. Each of these optional steps is illustrated by, for example, the coaxial configuration of Figure 3 as performed by the optical system of Figure 2 (or Figure 4).

A method of projecting a patterned radiation beam onto a substrate may include using the method of Figure 5, along with any optional steps to generate extreme ultraviolet radiation (e.g., as provided by the optics forming part of the lithography apparatus LA of Figure 1 System 100 is shown).

Although specific reference may be made herein to the use of lithography equipment in IC fabrication, it will be understood that the lithography equipment described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

Although specific reference may be made herein to embodiments of the invention in the context of lithography equipment, embodiments of the invention may be used in other equipment. Embodiments of the present invention may form part of a reticle inspection equipment, a metrology equipment, or any equipment that measures or processes items such as wafers (or other substrates) or reticles (or other patterned devices). Such equipment may generally be referred to as lithography tools. This lithography tool can be used under vacuum conditions or ambient (non-vacuum) conditions.

Where the context permits, embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. For example, embodiments of the invention may be implemented using a computer program comprising computer readable instructions configured to cause a computer to perform methods according to the invention. Embodiments of the invention may include computer-readable media carrying the computer program. As another example, embodiments of the invention may be implemented using a computer device that includes a memory storing processor-readable instructions and a processor configured to read and execute the instructions stored in the memory. The processor-readable instructions include instructions configured to control the computer to perform methods according to embodiments of the invention. Embodiments of the invention may also be implemented as instructions stored on a machine-readable medium, which instructions may be read and executed by one or more processors. Machine-readable media may include any mechanism for storing or transmitting information in a form readable by a machine (eg, a computing device). For example, machine-readable media may include: read-only memory (ROM); random access memory (RAM); magnetic storage media; optical storage media; flash memory devices; electrical, optical, Acoustic or other forms of propagated signals (such as carrier waves, infrared signals, digital signals, etc.) and others. In addition, firmware, software, routines, and instructions may be described herein as performing certain actions. However, it should be understood that such descriptions are for convenience only and that such actions are in fact produced by a computing device, processor, controller or other device executing firmware, software, routines, instructions, etc.; and so Performing can cause an actuator or other device to interact with the physical world.

While specific embodiments of the invention have been described above, it will be understood that the invention may be practiced otherwise than as described. The above description is intended to be illustrative and not restrictive. Accordingly, it will be apparent to those skilled in the art that modifications can be made in the invention described without departing from the scope of the terms set forth below. 1. An optical system for directing a first laser pulse and a second laser pulse to a target along an optical axis to generate extreme ultraviolet radiation from the target, comprising: a first optical component configured to redistribute the first laser pulse to form a shaped laser pulse having a hollow region; a second optical component configured to focus the shaping laser pulse toward the target; and, a third optical component configured to focus the second laser pulse toward the target within the hollow region of the shaped laser pulse, wherein the first optical component, the second optical component and the third optical component The three optical components are coaxially arranged on the optical axis. 2. The optical system of item 1, wherein the first laser pulse and the second laser pulse contain different wavelengths. 3. The optical system of Item 1 or Item 2, wherein the first optical component and the third optical component are located on different surfaces of a single optical element. 4. The optical system of clause 3, wherein the first optical component is formed on a front side of the single optical element, and the third optical component is formed on a back side of the single optical element. 5. The optical system of any of the preceding clauses, which includes a radiation collector configured to receive extreme ultraviolet radiation emitted by the target, wherein the radiation collector includes an aperture coaxially disposed on the optical axis , and wherein the second optical component and the third optical component are configured to shape and focus the second laser pulse through the aperture. 6. The optical system of any of the preceding clauses, wherein the second optical component is configured to interact only with the shaping laser pulse, and the third optical component is configured to interact only with the second laser pulse interaction. 7. The optical system of any of the preceding items, wherein the second optical component includes an opening coaxially arranged on the optical axis. 8. If the optical system of any of the preceding clauses, wherein the third optical component is configured to focus a third laser pulse along the optical axis to the target within the hollow region of the shaping laser pulse, The third laser pulse includes a wavelength different from the first laser pulse and the second laser pulse. 9. An extreme ultraviolet radiation source comprising an optical system as in any one of items 1 to 8. 10. A lithography system including the extreme ultraviolet radiation source of clause 9. 11. A method of directing a first laser pulse and a second laser pulse to a target along an optical axis to generate extreme ultraviolet radiation from the target, comprising: using a first optical component to redistribute the first laser pulse to form a shaped laser pulse having a hollow region; using a second optical component to focus the shaping laser pulse toward the target; using a third optical component to focus the second laser pulse toward the target within the hollow region of the shaped laser pulse; and, The first optical component, the second optical component and the third optical component are coaxially arranged on the optical axis. 12. The method of item 11, wherein the first laser pulse and the second laser pulse contain radiation of different wavelengths. 13. The method of Item 11 or Item 12, which includes positioning the first optical component and the third optical component on different surfaces of a single optical element. 14. The method of item 13 includes: Positioning the first optical component on a front side of the single optical element; and, Position the third optical component on one of the backsides of the single optical element. 15. The method of any one of items 11 to 14 includes: using a radiation collector to receive extreme ultraviolet radiation emitted by the target; An aperture of the radiation collector is disposed coaxially on the optical axis; and, The second optical component and the third optical component are used to focus the shaping laser pulse and the second laser pulse through the aperture. 16. The method of any one of items 11 to 15 includes: Use the second optical component to interact only with the shaping laser pulse; and, The third optical component is used to interact only with the second laser pulse. 17. The method of any one of items 11 to 16 includes: providing an opening in the second optical component; and, The opening is arranged coaxially on the optical axis. 18. The method of any one of clauses 11 to 17, comprising using the third optical component to focus a third laser pulse along the optical axis to the target within the hollow region of the shaping pulse , wherein the third laser pulse includes a wavelength different from the first laser pulse and the second laser pulse. 19. A method of projecting a patterned radiation beam onto a substrate, comprising using the method of any one of clauses 11 to 18 to generate extreme ultraviolet radiation. 20. A computer program containing computer-readable instructions configured to cause a computer to perform any of the methods of clauses 11 to 19. 21. A computer-readable medium carrying a computer program as specified in clause 20. 22. A computer device containing: a memory storing instructions readable by the processor; and a processor configured to read and execute instructions stored in the memory; The processor-readable instructions include instructions configured to control the computer to perform any of the methods of clauses 11 to 19.

1:Laser system 2:Laser pulse 3:Fuel Launcher 4: Plasma formation area/plasma formation direction 5: Collector 6: Middle focus 7: Tin plasma 8: Open your mouth 9: Enclosed structure 10: Faceted field mirror device 11: Faceted pupil mirror device 13:Mirror 14:Mirror 20:Aperture 100:Optical system 110: First laser pulse 120: Second laser pulse 130:Optical axis 140: First optical component 150: Shaping Laser Pulse 155: Hollow area 160: Second optical component 170:Third optical component 180:Single optical element 190:Open your mouth 200: The third laser pulse 400:Alternative optical systems 440: First optical component 441:First optical element 442: Second optical element 450:Shaping Laser Pulse 455: Hollow area 460: Second optical component 461:Third optical element 462: The fourth optical element 470:Third optical component 490:Open your mouth 601:First step 602:Second step 603:The third step B: EUV radiation beam B': Patterned EUV radiation beam IL: lighting system IS: lighting system LA: Lithography equipment MA: Patterned installation MT: support structure PS:Projection system SO: Radiation source W: substrate WT: substrate table

Embodiments of the invention will now be described by way of example only with reference to the accompanying schematic drawings, in which: - Figure 1 depicts a lithography system according to one embodiment of the present invention. The lithography system includes a lithography equipment, a radiation source and an optical system. - Figure 2 schematically depicts a cross-sectional side view of an optical system for directing a first laser pulse and a second laser pulse along an optical axis to a target for removal from the target, according to an embodiment of the invention EUV radiation is generated. - Figure 3 schematically depicts a front view of the aperture of a radiation collector forming part of the lithography system of Figure 1. - Figure 4 schematically depicts a cross-sectional side view of an alternative optical system including a transmissive optical component according to an embodiment of the invention. - Figure 5 illustrates a flow chart of a method of directing a first laser pulse and a second laser pulse along an optical axis to a target to generate extreme ultraviolet radiation from the target, according to one embodiment of the present invention.

100:Optical system

110: First laser pulse

120: Second laser pulse

130:Optical axis

140: First optical component

150: Shaping Laser Pulse

155: Hollow area

160: Second optical component

170:Third optical component

180:Single optical element

190:Open your mouth

Claims (15)

An optical system for directing first and second laser pulses to a target along an optical axis to generate extreme ultraviolet radiation from the target, comprising: a first optical component configured to redistribute the first laser pulse to form a shaped laser pulse having a hollow region; a second optical component configured to focus the shaping laser pulse toward the target; and, a third optical component configured to focus toward the target within the hollow region of the shaped laser pulse, wherein the first optical component, the second optical component and the third optical component are coaxially disposed on the optical axis. The optical system of claim 1, wherein the first laser pulse and the second laser pulse include different wavelengths. The optical system of claim 1 or claim 2, wherein the first optical component and the third optical component are located on different surfaces of a single optical element. The optical system of claim 3, wherein the first optical component is formed on a front side of the single optical element, and the third optical component is formed on a back side of the single optical element. The optical system of any one of claims 1 to 2, which includes a radiation collector configured to receive extreme ultraviolet radiation emitted by the target, wherein the radiation collector includes a coaxial arrangement on the An aperture on the optical axis, and wherein the second optical component and the third optical component are configured to focus the shaping laser pulse and the second laser pulse through the aperture. The optical system of any one of claims 1 to 2, wherein the second optical component is configured to interact only with the shaping laser pulse, and the third optical component is configured to interact only with the second Laser pulse interaction. The optical system of any one of claims 1 to 2, wherein the second optical component includes an opening coaxially arranged on the optical axis. The optical system of any one of claims 1 to 2, wherein the third optical component is configured to focus a third laser pulse along the optical axis within the hollow region of the shaped laser pulse. The target, wherein the third laser pulse includes a wavelength different from the first laser pulse and the second laser pulse. An extreme ultraviolet radiation source comprising an optical system according to any one of claims 1 to 8. A lithography system including the extreme ultraviolet radiation source of claim 9. A method of directing a first laser pulse and a second laser pulse to a target along an optical axis to generate extreme ultraviolet radiation from the target, comprising: using a first optical component to redistribute the first laser pulse to form a shaped laser pulse having a hollow region; using a second optical component to focus the shaping laser pulse toward the target; using a third optical component to focus the second laser pulse toward the target within the hollow region of the shaped laser pulse; and, The first optical component, the second optical component and the third optical component are coaxially arranged on the optical axis. The method of claim 11, wherein the first laser pulse and the second laser pulse comprise radiation of different wavelengths, and/or the method includes positioning the first optical component and the third optical component on different surfaces of a single optical component, And optionally position the first optical component on a front side of the single optical element and position the third optical component on a back side of the single optical element. If the method of any one of items 11 to 12 is requested, it includes: using a radiation collector to receive extreme ultraviolet radiation emitted by the target; An aperture of the radiation collector is disposed coaxially on the optical axis; and, The second optical component and the third optical component are used to focus the shaping laser pulse and the second laser pulse through the aperture. If the method of any one of items 11 to 12 is requested, it includes: Use the second optical component to interact only with the shaping laser pulse; and, using the third optical component to interact only with the second laser pulse, and/or an opening is provided in the second optical component and the opening is arranged coaxially on the optical axis, and/or using the third optical component to focus a third laser pulse along the optical axis to the target within the hollow region of the shaping pulse, wherein the third laser pulse contains a component different from that of the first A wavelength of the laser pulse and the second laser pulse. A method of projecting a patterned radiation beam onto a substrate, comprising using the method of any one of claims 11 to 14 to generate extreme ultraviolet radiation.