Lithographic apparatus, a radiation system, a device manufacturing method and a radiation generating method

A lithographic apparatus includes a radiation system for providing a beam of radiation from radiation emitted by a radiation source. The radiation system includes a contaminant trap for trapping material emanating from the radiation source. The rotation contaminant trap includes a multiple number of elements extending in a radial direction from a common rotation trap axis and being arranged for allowing contaminant material emanating from the radiation source to deposit during propagation of the radiation beam in the radiation system. The radiation system further includes a contaminant catch for receiving contaminant material particles from the rotation trap elements, the contaminant catch having a constitution, during operation of the radiation, for retaining said contaminant material particles.

BACKGROUND

1. Field of the Invention

The present invention relates to a lithographic apparatus, a radiation system, a device manufacturing method and a radiation generating method.

2. Related Art

To image smaller features, it has been proposed to use extreme ultraviolet radiation (EUV) with a wavelength in the range of 5-20 nanometers, in particular, 13.5 nanometers, or a charged particle beam, e.g., an ion beam and an electron beam, as the exposure radiation in a lithographic apparatus. These types of radiation need the beam path in the apparatus to be evacuated to avoid absorption. Since there are no known materials for making a refractive optical element for EUV radiation, EUV lithographic apparatus use mirrors in the radiation, illumination and projection systems. Such mirrors are highly susceptible to contamination, thereby reducing their reflectivity and hence the throughput of the apparatus. Further, sources for EUV may produce debris whose entry into the illumination system should be avoided.

In order to reduce the chance of debris entering the illumination system, the use of contaminant traps is known. Such traps are disposed in the radiation system downstream the source. The traps comprise elements that provide a surface on which debris can deposit. Conventional radiation systems may also comprise a collector that collects the radiation beam. It has been found that debris may also deposit on elements in the collector. The deposit of debris on the collector significantly reduces its operational lifetime before it must be cleaned.

A rotation element trap is a specific contaminant trap type comprising a multiple number of elements extending in a radial direction from a common rotation trap axis. During operation of the lithographic apparatus, the rotation element trap rotates in the path of the radiation beam around the rotation trap axis thereby enabling the elements to catch contamination material, typically tin particles. It is also known to provide a ring shaped contaminant catch for receiving contaminant material particles that are ejected from the rotation element trap elements due to centrifugal forces. The received tin particles flow from the catch towards a tin collection vessel.

Another specific contamination trap type is a static element trap that may also be arranged in the path of the radiation beam, e.g., downstream to the rotation element trap.

It is further known to apply an Argon gas barrier in the rotation element trap to counteract an exponential decrease of the collector lifetime. In order to maintain the Argon gas barrier, a relatively small distance is present between the rotation element trap elements and the ring-shaped catch. However, Tin particles being in the liquid phase when traveling towards the catch tend to become solid particles when hitting the catch, thereby accumulating in the small space between the elements and the catch. In order to prevent the tin particles to solidify it is known to heat the catch so that the tin droplets may flow to the tin collection vessel. In practice, it appears that thermal shorts are created between the heated catch and a cooled static element trap arranged downstream to the rotating element trap. The thermal shorts may cause a drop in the catch temperature leading to a source interlock. Further it appears that the static element trap may crash due to the presence of tin droplets. Therefore, in order to counteract the above-mentioned effects, the tin particles must be frequently removed from the catch and from the static element trap thus causing an undesired increase in downtime of the radiation system.

SUMMARY

Therefore, what is needed is an effective system and method to reduce the occurrence of solidified tin particles in a radiation system without performing tin cleaning activities on a frequent or regular basis.

In an embodiment of the present invention, there is provided a lithographic apparatus comprising a radiation system for providing a beam of radiation from radiation emitted by a radiation source where the radiation system comprises a rotation contaminant trap arranged in the path of the radiation beam for trapping material emanating from the radiation source. The rotation contaminant trap comprises multiple elements extending in a radial direction from a common rotation trap axis and are arranged to allow contaminant material emanating from the radiation source to deposit during propagation of the radiation beam in the radiation system. The radiation system further comprises a contaminant catch for receiving contaminant material particles from the contaminant trap elements where the contaminant catch comprises a constitution, which during operation of the radiation system retains the contaminant material particles and an illumination system configured to condition the radiation beam with a support constructed to support a patterning device with the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam. Further, the apparatus comprises a substrate table constructed to hold a substrate and a projection system configured to project the patterned radiation beam onto a target portion of the substrate.

In another embodiment of the present invention, there is provided a radiation system for providing a beam of radiation from radiation emitted by a radiation source where the radiation system comprises a rotation contaminant trap arranged in the path of the radiation beam for trapping material emanating from the radiation source. The rotation contaminant trap comprises multiple elements extending in a radial direction from a common rotation trap axis and are arranged to allow contaminant material emanating from the radiation source to deposit during propagation of the radiation beam in the radiation system. The radiation system further comprises a contaminant catch for receiving contaminant material particles from the contaminant trap elements where the contaminant catch comprises a constitution, which during operation of the radiation system retains the contaminant material particles.

In a further embodiment of the present invention, there is provided a device manufacturing method comprising providing a beam of radiation by a radiation system, from radiation emitted by a radiation source which provides the radiation system a rotation contaminant trap for trapping material emanating from the radiation source, in which the rotation contaminant trap comprises multiple elements extending in a radial direction from a common rotation trap axis and are arranged to allow contaminant material emanating from the radiation source to deposit during propagation of the radiation beam in the radiation system. The method continues by receiving contaminant material particles from the contaminant trap elements, where the contaminant catch comprises a constitution, which during operation of the radiation system retains the contaminant material particles. Furthermore, the method conditions the radiation beam while supporting a patterning device and imparting the radiation beam with a pattern in its cross-section using the patterning device to form a patterned radiation beam while holding a substrate on a substrate table and projecting the patterned radiation beam onto a target portion of the substrate.

In yet another embodiment of the present invention, there is provided a radiation generating method comprising providing a beam of radiation by a radiation system, from radiation emitted by a radiation source, and providing in the radiation system a contaminant trap for trapping material emanating from the radiation source, the rotation contaminant trap comprising a multiple number of elements extending in a radial direction from a common rotation trap axis and being arranged for allowing contaminant material emanating from the radiation source to deposit during propagation of the radiation beam in the radiation system. Further, the method provides a contaminant catch for receiving contaminant material particles from the contaminant trap elements, the contaminant catch having a constitution, which during operation of the radiation system, retains the contaminant material particles.

DETAILED DESCRIPTION

As here depicted, the apparatus is of a reflective type (e.g., employing a reflective mask). Alternatively, the apparatus may be of a transmissive type (e.g., employing a transmissive mask).

FIG. 2depicts a schematic cross sectional view of a rotation contaminant trap section8of a radiation system. The radiation system is arranged for providing a beam of radiation from a radiation emitted by a radiation source SO. The radiation source SO can be formed by a discharge plasma. The radiation source SO can be of the EUV type and may a tin (Sn) based plasma source. Alternatively, the EUV type radiation source SO might use a gas or vapor, such as Xe gas or Li vapor. The radiation system10comprises a rotation contaminant trap8, also called rotating element trap (RFT), arranged in the path of the radiation beam for trapping material emanating from the radiation source SO. Thereto, the contaminant trap8comprises a multiple number of elements11extending in a radial direction Ra from a common rotation trap axis A and being arranged in the path of the radiation beam on which the material emanating from the radiation source can deposit during propagation of the radiation beam in the radiation system. InFIG. 2, a cross section is shown viewing a plane wherein the common rotation trap axis A extends.FIG. 3depicts another schematic cross sectional view of the known rotation contaminant trap section8. Here, a cross section is shown viewing a plane transversely to the common rotation trap axis A.

The multiple elements11arranged in the path of the radiation beam may comprise metal platelets, also called foils or blades, to prevent debris, i.e., contaminant material, including particles, thrust by the source to reach optical components of the radiation system, e.g., a collector and the illuminator IL. The foils are arranged radially around the common rotation trap axis A.

The radiation system further comprises a contaminant catch12for receiving contaminant material particles from the RFT foils. The catch12, also called gutter, comprises a profile surrounding radial end portions of the foils11, the profile comprising side portions13,14extending substantially mutually parallel and in the radial direction Ra with respect to the common rotation trap axis A. The profile further comprises a radial end portion15interconnecting the side portions13,14. The profile forms a ring-shaped open channel-like structure with the open side oriented radially inwardly, towards radial end portions of the RFT foils, see alsoFIG. 3. It is noted that one of the side portions14can be removed by maintaining a side portion facing the source.

During operation of the radiation system, contaminant particles emanating from the source may hit at least one of the multiple number of RFT elements. Further, an Argon gas pressure is applied in the RFT to catch contaminant particles. Due to the rotation of the RFT elements in the rotation direction R, the particles are driven radially outwardly towards the catch12. The catch12is heated by a heating element (not shown) so that in case of tin particles, solidification and accumulating is avoided at the profile of the catch12. Further, the catch12comprises a drain27and a tin collection vessel28to collect the contamination particles. The vessel28can periodically be replaced. The radial end portion15of the catch profile is located at a distance d1from the radial end surface of the RFT element, thereby providing a volume16for contaminant particles to flow between said catch end portion15and said RFT end surface towards the drain27. Since the RFT is located in a vacuum, a major vacuum resistance is required to keep an Argon bas barrier in the RFT. Therefore, the distance d1is relatively small.

According to an embodiment of the invention, it has been observed that tin particles hitting the catch12may generate secondary droplets that are not collected by the catch. When being ejected from a RFT foil, the tin particles have a large tangential speed component, so that the tin liquid surface on the catch12is hit under a grazing angle. It appears that secondary droplets are generated having a different trajectory than the primary droplets. As an example, the secondary droplets may enter a static foil trap that may also be located in the radiation beam path. Upon entrance of the static foil trap, the tin particles may cause problems including the forming of thermal shorts between the heated catch12and a cooled static foil trap, and the crash of a foil trap.

FIG. 4depicts a schematic cross sectional view of a rotation contaminant trap10of a radiation system according to a first embodiment of the invention. The RFT10comprises again a ring-shaped open channel-like catch structure12wherein its side portions13,14have been extended in the radial direction Ra thereby enlarging the volume16that is available to catch the contaminant particles. Further, the catch12is not heated. Experiments have shown that hardly any secondary particles are generated when hitting and solidifying on a relatively cold catch surface. The primary particles are retained by the catch without entering the static foil trap. Since the (accumulation) volume16has increased in view of the prior art volume, solidified particles may accumulate to some extend without hitting the foils11. After a predetermined number of source shots, e.g., circa 10 Gshots, the catch12may be replaced or cleaned to remove the accumulated contaminant particles. A cleaning operation can e.g., be performed by temporarily heating the catch12. Preferably, the RFT foils are also extended in the radial direction Ra so that a lost vacuum resistance over the axial dimension of the foils is mainly compensated by additional resistance between the sides of the foils and the extended catch side portions13,14. More specifically, an additional vacuum resistance may than be generated over a distance d2along the catch side portions13,14, seeFIG. 4. The accumulation space16provides that the contaminant catch12has a constitution, during operation of the radiation system, for retaining said contaminant material particles, thereby counteracting that the particles re-enter the radiation beam path and/or a contaminant trap.

FIG. 5depicts a schematic cross sectional view of a rotation contaminant trap10of a radiation system according to a second embodiment of the invention. Here, the radial end portion15is movable in the radial direction Ra. More specifically, the radial end portion15can be moved from a smaller radial inner position15aalong a moving path D towards a larger radial inner position15bthereby increasing the distance d1and the accumulation space16between the foil ends and the catch radial end portion15. The movable radial end portion15can e.g., be realized by using a flexible metal material and a pressure cylinder with spring to slowly move the portion15. Preferably, the radial end portion is cooled during operation of the radiation system while the side portions13,14are heated to avoid mechanical connections between the end portion15and the side portions13,14to occur.

FIG. 6depicts a schematic cross sectional view of a rotation contaminant trap10of a radiation system according to a third embodiment of the invention wherein the radiation system comprises a heating device (not shown) for heating the contaminant catch12and wherein the radial end portion15of the catch profile comprises segments18that are oriented nearly parallel to the radial direction Ra, thus forming steep slopes like optical beam dumps. Preferably, the angle α between said segments and the radial direction does not exceed circa 45°, more preferably said angle α does not exceed a smaller angle, e.g., approximately 20° or less. By providing the radial end portion15of the catch12with nearly radially oriented segments18, the secondary droplets that may be generated by the primary droplets will generally flow radially outwardly, so that also the secondary droplets can be caught, optionally after multiple reflections against the catch surface, and retained by the catch12. Then, the droplets may flow via a drain to a collection vessel. It is noted that, in principle, instead of a zigzag counter also another can be applied, such as a harmonic profile.

FIG. 7depicts a schematic cross sectional view of a rotation contaminant trap10of a radiation system according to a fourth embodiment of the invention. The view is similar to the view of Fig. In the fourth embodiment, the radial end portion of the catch profile comprises a cone like contour20, thereby minimizing a chance that a primary droplet21generates a secondary droplet that might escape from the catch12. Thereto, the cone orientation nearly coincides with the tangential direction of the foils11. The catch12thus has a constitution, during operation of the radiation system, for retaining the contaminant material particles. Again, it is noted that also other contours can be applied, such as a tooth like contour or a needle contour.

FIG. 8depicts a schematic cross sectional view of a rotation contaminant trap10of a radiation system according to a fifth embodiment of the invention, whileFIG. 9depicts a schematic perspective view of the rotation contaminant trap10. Here, the radiation system further comprises a static contaminant trap17that remains static during operation of the radiation system. The static contaminant trap17is also arranged in the path of the radiation beam for trapping material emanating from the radiation source. The side portion14of the profile facing the static contamination trap forms a rim19having a shorter radial length than the other profile side portion13, thereby counteracting that secondary droplets enter the static contaminant trap17.FIG. 9depicts an amount of solidified contaminant particles23. Since the rim19is preferably heated, entrance of accumulated particles in the static foil trap is counteracted.

It is noted that not only the embodiment shown inFIGS. 8 and 9can be provided with a static contaminant trap. Also other embodiments can be provided with a static contaminant trap.

CONCLUSION

The present invention has been described above with the aid of functional storing blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional storing blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed.