TWI412056B - Optical device and method of in situ treating an euv optical component to enhance a reduced reflectivity - Google Patents

Abstract

The present invention relates to an optical device and a method of in situ treating an optical component (2, 6, 13) reflecting EUV and/or soft X-ray radiation in said optical device, said optical component (2, 6, 13) being arranged in a vacuum chamber (14) of said optical device and comprising one or several reflecting surfaces (3) having a top layer of one or several surface materials. In the method, a source (1, 5) of said one or several surface materials is provided in said chamber (14) of said optical device and surface material from said source (1, 5) is deposited on said one or several reflecting surfaces (3) during operation and/or during operation-pauses of said optical device in order to cover or substitute deposited contaminant material and/or to compensate for ablated surface material.

Description

Method and optical device for processing a pole ultraviolet optical element on site to enhance reduced reflectivity

The present invention relates to an optical device for extreme ultraviolet and/or weak X-ray radiation comprising at least one optical element in a vacuum chamber having one or several top layers of one or several surface materials Reflective surface. The invention also relates to a method of in situ processing of such an optical element that reflects extreme ultraviolet and/or weak X-ray radiation in an optical device to enhance the reduced reflectivity of the optical element.

The invention relates to the field of optical devices for the spectral range of extreme ultraviolet (EUV) and/or weak X-ray radiation, comprising optical elements having reflective surfaces for reflecting extreme ultraviolet and/or weak X-ray radiation . For example, extreme ultraviolet lithography requires such an optical device in which a grazing incidence mirror and/or a multi-layer mirror is disposed in a vacuum chamber between the radiation source and the wafer substrate to be illuminated. Typical materials for the reflective surface of the grazing incidence mirror are, for example, ruthenium (Ru), palladium (Pd) or molybdenum (Mo). Multilayer mirrors for the above spectral range suitable for vertical or near normal incidence typically comprise a combination of molybdenum and bismuth (Si) layers. A top layer of ruthenium is often also applied to protect the lower layer.

A major problem that arises during operation of optical devices having such reflective optical elements is that the reflectance decreases over time. This decrease in reflectivity may be caused by contaminants from the reflective surface that are due to fouling from the source or react with gases remaining in the vacuum chamber during operation. The radiation sources currently used for extreme ultraviolet lithography are gas discharge plasma or laser plasma. However, the material used for plasma generation moves from the source to the optical element and condenses on the optical surface, reducing its reflectivity. The material that is released from the radiation source and moves toward the optical element is called dirt. Other contaminants of the optical component may result from the manufacturing process, shipping, or installation of the optical component. In addition, the increased surface roughness, reduced density, or reduced thickness of the reflective layer can reduce the reflectivity of the reflective surface due to the operation of the radiation source.

WO 2004/092693 A2 discloses a method and apparatus for removing dirt from a reflective surface of a very ultraviolet collector in an extreme ultraviolet lamp. In this method, a source of controlled sputter ion is provided which comprises a gas having an atom that sputters the ionic material and a stimulating mechanism that causes the atoms of the sputtered ionic material to exit in an ionized state. With this source of sputtered ions, the fouling material deposited on the reflective surface of the extreme ultraviolet collector can be removed by sputtering. In order to avoid removal of the top layer of the reflective surface, the ionization state of the sputtered ionic material is selected to have a distribution near the peak of the selected energy, which has a higher probability of sputtering the material and a very low sputter reflection. The probability of the material of the top layer of the surface.

It is an object of the present invention to provide a method of processing an optical element that reflects extreme ultraviolet and/or weak X-ray radiation in an optical device and a corresponding optical device that allows for enhanced reduced reflectivity of the optical element. At the same time, the life of the optical component is enhanced.

This object is achieved by a method and an optical device as claimed in claims 1 and 10. Advantageous embodiments of the method and the optical device are the subject matter of the claims of the patent application or are described in the subsequent sections and examples of the description.

In the proposed method of processing an optical component in an optical device in situ, the optical component is disposed in a vacuum chamber of the optical device and includes one or more reflective surfaces having a top layer of one or more surface materials Providing a source of the one or more surface materials in the vacuum chamber of the optical device and depositing surface material from the source onto the one or more reflective surfaces during operation of the optical device and/or during operation pauses Covering or replacing the deposited contaminant material and/or compensating the ablated surface material.

Thus, in the proposed method, the one or more materials of the top layer of the one or more reflective surfaces are deposited on the surface (i.e., without disassembling the optical device). Due to the deposition of this surface material, the surface material will cover the contaminants on the reflective surface, resulting in improved reflectivity of this surface. In addition, the material deposited by the proposed method also compensates for the ablated material due to the possible erosion of the surface material of the reflective surface in the extreme ultraviolet lamp during operation. This means that the reflective layer of the optical device does not lose its reflectivity due to corrosion of the equal layer, and thus the lifetime of such optical components will be higher than the lifetime of optical components that are not treated by the proposed method.

The deposition of materials can be accomplished by a variety of well known methods, for example, by evaporating materials from a material source or by chemical (eg, metal organic) chemical vapor deposition (CVD/MOCVD) or by a sputtering technique ( Wherein a sputtering target comprising a surface material is provided in the vacuum chamber). Using sputtering techniques, surface material ions with high kinetic energy can also be generated so that some of the ions in the plasma then replace atoms or molecules of the contaminant material on the reflective surface.

The method can be applied continuously during operation of the optical device, after installation, and prior to the first use of the optical components of the optical device, repeatedly applying the method during operation of the device or during operation pauses, and reducing the apparent reflectance during operation Apply this method. In the final case, it is preferred to continuously or repeatedly measure the reflectivity of at least one of the reflective surfaces of the one or more reflective surfaces. Therefore, the surface material is deposited only when the reflectance is reduced below a threshold (which can be set by the operator). When measuring reflectance, the reflectance in the extreme ultraviolet or weak X-ray spectrum can be measured. The reflectance in other wavelength ranges can also be measured, assuming that the reflectance in these wavelength ranges also indicates the reflectance in the range of extreme ultraviolet and/or weak X-ray radiation. However, other types of measurements can be performed to derive a reduction in reflectivity. Such measurements may include measurement of the composition of the gas in the optical device, for example, the ratio of mirror material in the gas, the use of crystal balance, the use of a diffractometer, the use of energy dispersive X-ray analysis, or the use of spectral ellipsometry.

In a preferred embodiment, the source of one or more surface materials is provided as a sputtering target in a vacuum chamber of the optical device. The deposition of the surface material is then performed by sputtering deposition using a suitable sputtering gas, particularly an inert gas such as argon (Ar), which is typically used as a buffer gas during operation of the optical device. The gas can be ionized by well known methods, for example by light (eg, ultraviolet, vacuum, or extreme ultraviolet), by generating microwaves around the optical element, by the target and the optical element, or between the optical elements. An RF field is applied between another electrode disposed in the vacuum chamber. In addition, an ion gun can be used to provide the necessary sputter ions. The sputtering can be performed with or without a magnetron unit or an additional reactive gas continuously or pulsed. In addition, application of rf substrate bias to control ion impact and substrate cooling or heating to affect surface mobility and diffusion is feasible.

The sputtering target can be provided as a separate component disposed in the optical device. In this case, the separate component is preferably movable between a location adjacent to the reflective surface for sputter deposition and a location remote from the surface for normal operation of the optical device. In a preferred embodiment, at least one of the plurality of sputtering targets is provided as a substrate material layer on the surface of the optical component of the optical device, the surfaces are not used to reflect extreme ultraviolet rays and/or weak X-ray radiation.

The proposed optical device has at least one optical element in a vacuum chamber having one or several reflective surfaces with a top layer of a surface material (e.g., Ru or Mo/Si multilayer). Preferably, the optical device, for example, for an extreme ultraviolet lithography extreme ultraviolet lamp, comprises at least one source of one or more surface materials that are usable or operable to operate during operation of the optical device and / or surface material is deposited on the one or several reflective surfaces during operation pauses to cover or replace the deposited contaminant material and/or to compensate for the ablated surface material.

Preferably, the optical device also includes means for depositing surface material from the source onto the one or more reflective surfaces. Preferably, such members are used to evaporate the material from the source or to ionize a sputtering gas and sputter the electrical material of the surface material from a sputtering target. For this purpose, the optical element or part of the optical element is connected to the electrical component to apply an RF voltage between the reflective surface and the sputter target. Additionally, a DC voltage can be applied to create a DC bias at the reflective surface.

Preferably, the source of the surface material is configured to be movable between at least two locations within the vacuum chamber of the optical device. A location is a location near the reflective surface to achieve optimal material deposition on the surface. The other location is a location remote from the surface to enable operation of the optical device that is not interfered with by the source.

The optical device can include a control unit that controls deposition of the surface material on the reflective surface. Preferably, means for measuring the reflectivity of at least one of the reflective surfaces is provided in the optical device, wherein the control unit only when the reflectance decreases below a predetermined threshold The means for depositing the surface material deposits the surface material to control the deposition member. The control unit can also control the movement of the source of material between the two locations.

In a preferred embodiment, the optical device includes an extreme ultraviolet collector having a plurality of shells for collecting extreme ultraviolet and/or weak X-ray radiation from a corresponding source of radiation. In this particular embodiment, the front side of the collector shell represents the reflective surface and the rear sides of the shells do not contribute to reflection. The back side is covered with a layer of thick surface material and serves as a sputtering target for sputter deposition. An additional dummy shell is placed adjacent to the reflective surface of the inner layer of the collector and is also covered with surface material on its rear side. One or several surface materials from the back side are then sputtered according to the proposed method and deposited on the front side of the corresponding opposing collector shell (ie, on the reflective surface).

In the present specification and claims, the word "comprising" does not exclude other elements or steps. The indefinite article "a" or "an" does not exclude the plural. In addition, any reference signs in the claims should not be construed as limiting the scope of the claims.

The method and corresponding apparatus are illustrated below by way of an example of an extreme ultraviolet lamp for extreme ultraviolet lithography. In this lamp, a thermo-plasma is generated to emit the desired extreme ultraviolet radiation, which is focused by a collector and can be reflected by one or more other optical elements. The collector in this example contains a plurality of ash-preserving mirrors having a reflective surface made of a metal tantalum layer. The other optical elements have a multilayer reflective surface covered with a protective top layer. Although the proposed method is illustrated by the use of 钌 as an example of a surface material, it should be understood that the method can also be applied to other surface materials used as reflective or protective layers in the extreme ultraviolet or weak X-ray spectrum.

During operation of the extreme ultraviolet lamp, dirt (e.g., tin) from the plasma source escapes toward the optical element and can deposit on the reflective surface. The reflectivity of the collector and other optical components is thus reduced by the deposition of contaminant material. After the reflectance is reduced to a predetermined threshold, the reflective surfaces are processed in situ using the proposed method.

For this purpose, a source 1 is arranged in the optical device away from the optical path of the extreme ultraviolet lamp. The 反射 source 1 is then moved near the reflective surface 3 of the optical element 2, as schematically indicated in FIG. Source 1 can be, for example, a sputtering target or an evaporator. It is then sputtered from source 1 or evaporated to deposit on reflective surface 3. The contaminant material (e.g., tin) on this surface is covered with a deposit of germanium. In the same manner, the erosion of the tantalum material in the reflective surface due to corrosion during operation of the extreme ultraviolet lamp can also be compensated for by depositing additional flaws on the reflective surface.

Fig. 2 shows an example in which the source of germanium is a sputtering target formed by a carrier substrate 4 which is covered with a thick target layer 5 of a crucible. The carrier substrate 4 and the optical component 2 are connected to a power supply for generating DC and AC (RF) voltages. The carrier substrate 4 serves as a cathode and the optical element 2 serves as an anode, as is generally known in the art of physical vapor deposition. There is a working gas, such as argon, between the anode and the cathode. The argon atoms are ionized by the applied RF voltage, and at, for example, about 300 eV, argon ions are accelerated toward the target layer 5 to release free eatomic atoms of several eV. In the present example, display optical element 2 has a planar reflective surface 3. For optical elements having such a geometrical shape that is easily accessible, which is typically the case, for example, of a multi-layered mirror, the sputter target can have the same design and can move in front of the reflective surface 3 to be treated and be oriented parallel to the reflective surface 3 ,as shown in picture 2.

If the applied RF and/or DC voltage is selected such that helium ions are generated, sputtering of the reflective surface can be achieved, with the result that the contaminant material is removed from the surface and replaced with helium ions. At an ion energy of about 1 keV, the sputtering efficiency of tantalum is about one. This means that for each cesium ion, one of the atoms of the contaminant material or one of the top layers of the reflective surface can be removed. Therefore, after a proper processing time, a relatively pure layer of germanium is obtained.

At least one of the plurality of target layers of the source of germanium may also be produced on a non-reflective surface of the optical component (ie, a surface that is not used during operation of the extreme ultraviolet lamp). Figure 3 shows an example of an optical device in which the rear side of the collector 6 serves as a sputtering target. The extreme ultraviolet radiation emitted from the radiation source 11 (plasma source) is focused by the collector 6. The collector 6 contains four collector shells 7. The front side 8 of each shell 7 has a reflective surface; the back side 9 is not used to reflect radiation. The rear side 9 of the shell 7 of the collector 6 is covered with a thick target layer, and the reflective surface on the front side is also made of a layer of tantalum. The target layers can be applied by electroplating. In addition to the four collector shells 7, a dummy shell 10 is also provided in front of the inner casing. The dummy shell 10 has the same target layer as the other shells on the rear side; however, the front side of this dummy layer does not have any function.

The casing 7 of the collector 6 is electrically insulated and connected to a power supply 12. This power supply 12 produces a constant current (bias) and an RF alternating current for generating plasma between the shells. There is a working gas, such as argon, between the shells. This working gas system is used as a buffer gas during the operation of the extreme ultraviolet lamp. The DC potentials U1, U2, U3 and U4 of the different shells are selected such that the front side 8 of each shell 7 is positively charged relative to the rear side of the shell. This means U0>U1>U2>U3>U4. During operation of the power supply 12, argon gas between the shells is ionized, whereby helium atoms are sputtered from the back side of each shell, which are then deposited on the front side of each shell, i.e., the reflective surface.

This procedure can be performed during normal operation of the extreme UV lamp. However, it is preferred to perform this sputter deposition only during the operation pause of the extreme ultraviolet lamp. In addition, it is not necessary in any case to produce a sputtering plasma between the shells at the same time. Individual shells can also be processed one by one. In this case, the DC and RF voltages are applied simultaneously between a pair of opposing shells and then switched to another pair of opposing shells, and so on.

Figure 4 is a schematic illustration of a typical layout of an extreme ultraviolet lithography system having a corresponding extreme ultraviolet lamp. The extreme ultraviolet lamp consists essentially of a radiation source 11, a collector 6 and a multilayer mirror 13 in a vacuum vessel 14. The radiation emitted from the radiation source 11 is collected by the reflective collector 6 and focused on an intermediate focus 15. At the location of the intermediate focus 15, an aperture connects the first volume 16 of the extreme ultraviolet lamp to a second volume 17. In this second volume 17, a multilayer mirror 13 is disposed to direct radiation from the intermediate focus 15 to a lithographic mask (not shown) and wafer substrate 18. In most extreme ultraviolet lithography systems, the dirt mitigation member 19 is disposed between the radiation source 11 and the collector 6. In this extreme UV lamp, the collector 6 is designed as described in connection with Figure 3 to continuously or repeatedly enhance the reduced reflectivity of the reflective surface.

1. . . Source

2. . . Optical element

3. . . Reflective surface

4. . . Carrier substrate

5. . . Target layer

6. . . collector

7. . . shell

8. . . Front side

9. . . Back side

10. . . Fake shell

11. . . Radiation source

12. . . Power Supplier

13. . . Multi-layer mirror

14. . . Vacuum container

15. . . Intermediate focus

16. . . First volume

17. . . Second volume

18. . . Substrate

19. . . Debris relief member

The above specific embodiments show examples of the present method and a corresponding optical device with reference to the accompanying drawings, which do not limit the scope of the present invention. The drawings show: Figure 1 is a schematic diagram of the principle of the method; Figure 2 is a schematic diagram of the principle of sputter deposition as an example of the method; Figure 3 is a partial view of an example of the proposed optical device; and Figure 4 A schematic configuration of a polar ultraviolet irradiation unit.

6. . . collector

7. . . shell

8. . . Front side

9. . . Back side

10. . . Fake shell

11. . . Radiation source

12. . . Power Supplier

Claims (10)

A method of in situ processing an optical component (2, 6, 13) that reflects extreme ultraviolet and/or soft X-ray radiation in an optical device, the optical component (2, 6, 13) Disposed in a vacuum chamber (14) of the optical device and comprising one or more reflective surfaces (3) having a top layer of one or more surface materials, the method comprising the steps of: - in the optical device Providing at least one source (1, 5) of the one or more surface materials in the chamber (14), and - from the source (1, 5) during operation of the optical device and/or during operation suspension a surface material deposited on the one or more reflective surfaces (3) to cover or replace the deposited contaminant material and/or to compensate for the ablated surface material, wherein the surface material is deposited by sputtering deposition, The source (1, 5) of the surface material is moved closer to the one or more reflective surfaces during operation of the optical device, and/or the source (1, 5) of the surface materials is used as a target layer (5) one of the optical elements (2, 6, 13) or other optical elements (6, 13) provided for the optical device A plurality of non-reflective surface. A method of claim 1, wherein a buffer gas system for operation of the optical device is used as a working gas for sputter deposition. The method of claim 1, wherein the reflectivity of one of the at least one reflective surface of the one or more reflective surfaces (3) is continuously or repeatedly measured and the surface material is deposited only when the reflectance decreases below a critical value. . The method of claim 1, wherein the optical device is ultraviolet light and/or Weak X-ray lamp. The method of claim 1, wherein the optical element (2, 6, 13) is a collector. An optical device for extreme ultraviolet and/or weak X-ray radiation, in particular an extreme ultraviolet and/or weak X-ray lamp comprising at least one optical component (2, 6) located in a vacuum chamber (14) 13) The optical element (2, 6, 13) has one or more reflective surfaces (3) having a top layer of one or more surface materials, wherein the optical device comprises at least one of the one or more surface materials Source (1, 5), which may be used to deposit surface material on the one or more reflective surfaces (3) during operation of the optical device and/or during operation pauses so that Covering or replacing the deposited contaminant material and/or compensating for a plurality of ablated surface materials, wherein the source of the plurality of surface materials (1, 5) is a sputter target and the optical device comprises a deposition member for sputtering Plating deposition deposits surface material from the source (1, 5) onto the one or more reflective surfaces (3), the source (1, 5) being configured to be adjacent to the optical device during operation pauses Or a plurality of reflective surfaces (3) are moved, and/or the sputtering target comprises a optical device The optical layer (2, 6, 13) or one of the other optical elements (6, 13) or the target layer (5) on a plurality of non-reflective surfaces. The optical device of claim 6, wherein the member for depositing a plurality of surface materials comprises a DC and RF power supply (12) coupled to the source (1, 5) of the plurality of surface materials and coupled to the optical Components (2, 6, 13). The optical device of claim 6 or 7, wherein the optical element (2, 6, 13) is a collector (6) having a plurality of collector shells (7) and the target layer (5) is provided On the rear side of the collector shell (7). The optical device of claim 6, wherein the optical element (2, 6, 13) is a collector (6) formed by one or more layers of mirrors. The optical device of claim 6, wherein the optical device comprises means for continuously or repeatedly measuring the reflectivity of one of the at least one reflective surface of the one or more reflective surfaces (3), and for using only the reflectivity The means for depositing the surface material by the member for depositing the surface material is reduced to a threshold value to control one of the control members of the deposition member.