Method of cleaning collector of EUV light source system

A method of cleaning a collector of an extreme ultraviolet light source system includes introducing the collector separated from the extreme ultraviolet light source system into a chamber; capturing an optical image of a reflective surface of the collector; measuring a contamination level of the reflective surface by comparing the optical image with a prestored standard image; performing a first cleaning operation if the contamination level exceeds a preset first reference value, the first cleaning operation including cleaning the reflective surface by spraying dry ice particles onto the reflective surface; and performing a second cleaning operation if the contamination level is less than or equal to the preset first reference value. The second cleaning operation includes cleaning the reflective surface by radiating atmospheric plasma onto the reflective surface and measuring a microcontamination level and a damage level of the reflective surface.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit under 35 USC 119(a) of Korean Patent Application No. 10-2021-0037580, filed on Mar. 23, 2021 in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes.

BACKGROUND

The present disclosure relates to a method of cleaning a collector of an extreme ultraviolet light source system.

Collectors of an extreme ultraviolet (EUV) source system reflect and concentrate extreme ultraviolet light emitted from source materials and transmit the concentrated light to exposure systems, for example, scanner systems. When a collector is contaminated, the output of an extreme ultraviolet light source system may deteriorate, which may be a factor in lowering operating performance of extreme ultraviolet exposure equipment. Therefore, contaminants adhering to the surface of a collector may need to be cleaned after a desired and/or alternatively predetermined operating time has elapsed.

SUMMARY

Example embodiments provide a method of cleaning a collector of an extreme ultraviolet light source system, in which contaminants attached to a surface of the collector may be effectively cleaned.

According to example embodiments, a method of cleaning a collector of an extreme ultraviolet light source system includes introducing the collector, separated from the extreme ultraviolet light source system, into a chamber; capturing an optical image of a reflective surface of the collector; measuring a contamination level of the reflective surface by comparing the optical image with a prestored standard image; performing a first cleaning process if the contamination level exceeds a preset first reference value, the first cleaning process including cleaning the reflective surface by spraying dry ice particles onto the reflective surface, and performing a second cleaning process if the contamination level is less than or equal to the preset first reference value. The second cleaning process includes cleaning the reflective surface by radiating atmospheric plasma onto the reflective surface. The second cleaning process includes measuring a microcontamination level and a damage level of the reflective surface, generating a microcontamination level map of the reflective surface and a damage level map of the reflective surface, based on the microcontamination level and the damage level, and cleaning by radiating the atmospheric plasma onto an area of the reflective surface in which the microcontamination level and the damage level exceed a preset second reference value and a present third reference value, respectively, based on the microcontamination level map and the damage level map.

According to example embodiments, a method of cleaning a collector of an extreme ultraviolet light source system includes inputting the collector separated from the extreme ultraviolet light source system into a chamber; capturing an optical image of a reflective surface of the collector; measuring a contamination level of the reflective surface by comparing the optical image with a pre-stored standard image; performing a first cleaning operation if the contamination level exceeds a preset first reference value, the first cleaning operation including cleaning the reflective surface by spraying dry ice particles onto the reflective surface; performing a second cleaning operation if the contamination level is less than or equal to the preset reference value. The second cleaning operation includes cleaning the reflective surface by radiating atmospheric plasma onto the reflective surface and measuring a microcontamination level and a damage level of the reflective surface.

According to example embodiments, a method of cleaning a collector of an extreme ultraviolet light source system includes introducing the collector, separated from the extreme ultraviolet light source system, into a chamber; capturing an optical image of a reflective surface of the collector using a first measuring device; measuring a contamination level of the reflective surface by comparing the optical image with a pre-stored standard image; performing a first cleaning operation if the contamination level exceeds a preset first reference value, the first cleaning operation including physically cleaning the reflective surface by spraying dry ice particles onto the reflective surface using a first cleaning apparatus; and performing a second cleaning operation if the contamination level is less than or equal to the preset first reference value, the second cleaning operation including chemically cleaning the reflective surface by radiating atmospheric plasma onto the reflective surface using a second cleaning apparatus and measuring a microcontamination level of the reflective surface and a damage level of the reflective surface using a second measuring device.

DETAILED DESCRIPTION

Hereinafter, various embodiments will be described in detail with reference to the accompanying drawings.

Referring toFIGS.1and2, an extreme ultraviolet light source system and an extreme ultraviolet exposure facility in which a collector to be cleaned by a collector cleaning apparatus according to an embodiment is employed will be described.FIG.1is a diagram schematically illustrating an extreme ultraviolet exposure facility employing an extreme ultraviolet light source system, andFIG.2is a diagram schematically illustrating the extreme ultraviolet light source system ofFIG.1.

Referring toFIG.1, an extreme ultraviolet exposure facility1may include an exposure chamber90, an extreme ultraviolet light source system SO, a lithographic apparatus LA, a projection system PS, an upper electrostatic chuck (ESC)72, and a lower electrostatic chuck80.

The exposure chamber90has an internal space91, in which the extreme ultraviolet light source system SO, the lithographic apparatus LA, the projection system PS, the upper electrostatic chuck72and the lower electrostatic chuck80may be located. A mask71may be loaded/unloaded on/from the upper electrostatic chuck72by electrostatic force generated by power applied from a power supply73, and a substrate W such as a semiconductor wafer may be loaded/unloaded on/from the lower electrostatic chuck80.

Referring toFIG.2, the extreme ultraviolet light source system SO may generate extreme ultraviolet light B having a wavelength of less than about 100 nm. The extreme ultraviolet light source system SO may be a laser-produced plasma (LPP) light source generating plasma by irradiating laser light DL oscillated from a light source unit30to a droplet formed of any one of tin (Sn), lithium (Li), and xenon (Xe). In addition, the extreme ultraviolet light source system SO may use a so-called Master Oscillator Power Amplifier (MOPA) method. For example, by using a seed laser irradiated from the light source unit30, a pre-pulse and a main pulse are generated, and the pre-pulse is irradiated to expand the droplets, and then the main pulse is re-irradiated to the droplets (DP), thereby generating plasma P and emitting extreme ultraviolet light (B) using the plasma (P). Residues of the droplets DP remaining after being irradiated with the main pulse may be accommodated in a catcher40(e.g., container with housing).

Inside a light source chamber10of the extreme ultraviolet light source system SO, the laser light DL supplied by the light source unit30and the droplets supplied by a droplet supply unit20collide 50000 or more times per second, and thus, the plasma (P) may be generated. The collector11of the light source chamber10may collect the extreme ultraviolet light B emitted in all directions from the plasma P, focus the collected light forward, and provide the light to the lithographic apparatus LA. The light source chamber10may include a collector11for condensing the generated extreme ultraviolet light B, and an upper body12coupled to the collector11and having a conical outer shape. The inside of the light source chamber10may be maintained in an ultra-low pressure state to limit and/or prevent the generated extreme ultraviolet light B from being absorbed by the gas inside the light source chamber10. A reflective layer11C for improving reflectivity of the extreme ultraviolet light B may be formed on a reflective surface11A of the collector11. The reflective layer11C may be formed of a multi-thin layer in which molybdenum and silicon (Mo—Si) are alternately stacked or of a material such as zirconium.

The lithographic apparatus LA may include a plurality of mirrors to irradiate the extreme ultraviolet light B emitted from the extreme ultraviolet light source system SO toward the upper electrostatic chuck72. Since a plurality of mirrors included in the lithographic apparatus LA may have a known structure, only two mirrors61and62are illustrated for simplification of the drawing and convenience of description.

The projection system PS includes a plurality of mirrors to project the pattern of extreme ultraviolet light B reflected from the mask71attached to the upper electrostatic chuck72to the substrate W disposed on the lower electrostatic chuck80, to expose the pattern on the surface of the substrate W. Since a number of mirrors included in the projection system PS may have a known structure, only two mirrors63and64are illustrated for simplicity of drawing and convenience of explanation.

A cleaning apparatus according to an example embodiment of inventive concepts may be used in the process of cleaning the collector11of the extreme ultraviolet light source system SO. Hereinafter, a cleaning apparatus100according to an example embodiment will be described with reference toFIG.3.

Referring toFIG.3, the cleaning apparatus100according to an example embodiment may include a cleaning chamber110, a support130disposed inside of the cleaning chamber110to support a collector11described above, first and second measuring devices140and160disposed above the support130, first and second cleaning apparatuses150and170, and an inlet112into which process gas provided from a gas supply source120may be introduced. Respective components constituting the cleaning apparatus100may be controlled by a controller190.

The controller190controls the overall operation of the cleaning apparatus100, and for example, may be implemented as a processor, such as a central processing unit (CPU), a graphics processing unit (GPU), a microprocessor, an application specific integrated circuit (ASIC), Field Programmable Gate Arrays (FPGA), or the like, and may include a memory for storing various data required for the operation of the cleaning apparatus100.

The first and second measuring devices140and160and the first and second cleaning apparatuses150and170are disposed on one end of an arm180, and may move along the reflective surface11A of the collector11according to the rotation of the arm180. In addition, the first and second measuring devices140and160and the first and second cleaning apparatuses150and170are raised and lowered by the arm180to be spaced apart from or to be adjacent to the reflective surface11A of the collector11.

The cleaning chamber110has an internal space111in which a cleaning process for cleaning the collector11is performed, and may be formed of a material having excellent wear resistance and corrosion resistance. The internal space111is filled with process gas to maintain atmospheric pressure, which may be used for generating atmospheric plasma in the internal space111. In an example embodiment, the first and second measuring devices140and160and the first and second cleaning apparatuses150and170are all disposed in one cleaning chamber110as an example, but a plurality of chambers may also be employed. For example, the first measuring device140and the first cleaning apparatus150may be disposed in a first cleaning chamber, and the second measuring device160and the second cleaning apparatus170may be disposed in a second cleaning chamber.

The first measuring device140may generate an optical image by capturing an image of the reflective surface11A. The first measuring device140may be a camera employing an image sensor such as a CCD sensor or a CMOS sensor. The optical image is for roughly measuring the level of contamination of the reflective surface11A, and may be generated by the first measuring device140and transmitted to the controller190. The controller190may calculate a contamination level of the reflective surface11A by comparing the transmitted optical image with a preset standard image. For example, the standard image may be an optical image obtained by imaging that the reflective surface11A is totally contaminated. The controller190may calculate the contamination level of the captured optical image by considering the contamination level of the standard image as 100%. Also, when (or if, or in response to) the calculated contamination level exceeds a preset reference value (and/or present threshold value), the controller190may perform a first cleaning process of physically cleaning the reflective surface11A. Also, when (or if, or in response to) the calculated contamination level is less than or equal to a preset reference value (and/or preset threshold value), the controller190may perform a second cleaning process of chemically cleaning the reflective surface11A.

The first cleaning process may be performed by the first cleaning apparatus150, and the second cleaning process may be performed by the second cleaning apparatus170.

The first cleaning apparatus150is for removing contaminants P1having relatively large particles among contaminants P1and P2attached to the reflective surface11A. The first cleaning apparatus150may perform so-called CO2snow cleaning, in which high-speed dry ice particles S are sprayed on the reflective surface11A for several hours to several tens of hours. The dry ice particles S sprayed on the reflective surface11A may instantaneously expand the contaminants attached to the reflective surface11A to separate the contaminants P1from the reflective surface11A. The first cleaning apparatus150may include a nozzle for spraying the dry ice particles.

The second measuring device160is for precisely measuring the level of contamination of the reflective surface11A. The second measuring device160may measure a microcontamination level, which is a contamination level lower than the contamination level previously measured by the first measuring device140. For example, the second measuring device160may be a measuring device for detecting chemical species emitted from the reflective surface11A by atmospheric plasma radiated to the reflective surface11A. As the second measuring device160, an optical emission spectrometer, an optical absorption spectrometer, or a laser induced fluorescence detector may be employed. In addition, a gas detector may be additionally employed on the second measuring device160as an auxiliary. The second measuring device160moves to be adjacent to the reflective surface11A and then moves along the reflective surface11A to detect a chemical species from the reflective surface11A. Therefore, the surface state of the reflective surface11A may be measured. For example, a region in which a chemical species of a material included in a droplet is detected by the second measuring device160may be regarded as a region to which contaminants are attached. Also, a region in which a chemical species of a material constituting the reflective layer11C is detected by the second measuring device160may be regarded as being an uncontaminated region. In addition, when the second measuring device160(e.g., image sensor circuit) detects a material not included in a droplet and the reflective layer11C, for example, a chemical species of a material constituting the collector body disposed below the reflective layer11C, it may be regarded that the reflective layer11C is damaged.

The second cleaning apparatus170may be an atmospheric plasma cleaning apparatus in which atmospheric plasma cleaning is performed. Accordingly, in a state in which the internal space111of the cleaning chamber110is maintained at atmospheric pressure, atmospheric plasma is radiated to the reflective surface11A to clean the reflective surface11A. The second cleaning apparatus170may include a plasma jet.

Next, referring toFIGS.4to9, a method of cleaning a collector of an extreme ultraviolet light source system according to an example embodiment will be described.FIG.4is a flowchart illustrating a method of cleaning a collector of an extreme ultraviolet light source system according to an example embodiment,FIG.5is a detailed flowchart of a second cleaning process ofFIG.4.FIGS.6to9are views illustrating a method of cleaning a collector of an extreme ultraviolet light source system according to an example embodiment. Among the reference numbers ofFIGS.6to9, the same reference numerals as those ofFIG.3described above may be understood to have the same configuration.

Referring toFIGS.4and6, the collector11may be separated from the extreme ultraviolet light source system and disposed on the support130in the cleaning chamber110, and an operation of measuring a contamination level of the reflective surface11A of the collector11may be performed (S100). The contamination level of the reflective surface11A may be measured through the first measuring device140.

The first measuring device140may capture an optical image of the reflective surface11A of the collector11and transmit the captured image to the controller190. The controller190may calculate the overall contamination level of the reflective surface11A by comparing the transmitted image with a standard image stored in advance. For example, the standard image is an optical image obtained by imaging that the reflective surface11A is totally contaminated, and may be pre-stored in the controller190. The first measuring device140may generate one image by capturing an image of the entire reflective surface11A of the collector11once. In addition, the first measuring device140may also divide the reflective surface11A of the collector11into a plurality of regions, generates images of the respective regions, and then merges the images into one image, and transmit the merged image to the controller190.

Next, the measured contamination level is compared with a preset reference value, and one of first and second cleaning processes may be performed according to the comparison result (S200). The controller190may calculate the contamination level of the captured optical image by considering the contamination level of the standard image as 100%. The controller190may perform the first cleaning process when the calculated contamination level exceeds the reference value, and may perform the second cleaning process when the calculated contamination level is less than or equal to the reference value. In an example embodiment, when the captured optical image exceeds 10% of the contamination level of the standard image, the controller190determines that the reflective surface11A is relatively heavily contaminated and performs the first cleaning process. In addition, when the captured optical image is 10% or less of the contamination level of the standard image, the controller190may determine that the reflective surface11A is relatively less contaminated and perform a second cleaning process. Such a reference value may be determined in consideration of the overall size and weight of contaminants P1and P2attached to the reflective surface11A.

Referring toFIGS.4and7, a first cleaning process (S300) may be performed when the reflective surface11A is relatively heavily contaminated. The first cleaning process S300is a process for first removing the large contaminants P1attached to the reflective surface11A, and physical cleaning may be performed in the first process S300. As the physical cleaning, for example, the first cleaning process may be performed by spraying high-speed dry ice particles S onto the reflective surface11A for several hours to several tens of hours, so-called CO2snow cleaning. The dry ice particles sprayed on the reflective surface11A may instantaneously expand the contaminants attached to the reflective surface11A to separate the contaminants from the reflective surface11A. In the first cleaning process S300, the first cleaning apparatus150is moved along the surface of the reflective surface11A, and sprays dry ice particles S on the reflective surface11A in a uniform amount per unit time. For example, the first cleaning process S300may be performed entirely on the reflective surface11A without taking into account the level of partial contamination of the reflective surface11A. Through this process, relatively large contaminants P1among the contaminants P1and P2attached to the reflective surface11A may be removed. After the first cleaning process (S300) is performed, the operation (S100) of measuring the contamination level of the reflective surface11A with the first measuring device140may be performed again. This process may be repeated until the contamination level of the reflective surface11A is measured to be less than or equal to the reference value.

Referring toFIGS.4and8, a second cleaning process (S400) is a process of removing the microcontaminants P2attached to the reflective surface11A. In the second cleaning process S400, chemical cleaning may be performed to remove microcontaminants P2having a size smaller than the contaminants P1removed in the first cleaning process. The microcontaminants P2may be firmly adhered to the reflective surface11A and remain on the reflective surface11A even after the first cleaning process is performed. Referring toFIG.5, in the second cleaning process, measuring the level of microcontamination of the reflective surface11A with the second measuring device160(S410), measuring the level of damage to the reflective surface11A (S420), and cleaning the reflective surface11A with atmospheric plasma (S430) may be performed. Operations S410to S430may be performed sequentially, but inventive concepts are not limited thereto, and may be performed simultaneously according to an example embodiment. In an example embodiment, a case in which operations S410to S430are sequentially performed will be described as an example.

Referring toFIGS.5and8, the operation (S410) of measuring the microcontamination level of the reflective surface11A by the second measuring device160is an operation of measuring a microcontamination level of a contamination area to which the microcontaminants P2are attached to the reflective surface11A by using the second measuring device160. The controller190may generate a microcontamination level map by matching the measured distribution of the contamination area to a location value. The operation (S420) of measuring the level of damage of the reflective surface11A by the second measuring device160is an operation of measuring the area in which the reflective layer11C constituting the reflective surface11A is damaged. The controller190may measure the level of damage of the reflective surface11A with the second measuring device160, and may generate a damage level map by matching the measured damage value to the location value.

Referring toFIG.8, in the operation of measuring the microcontamination level of the reflective surface11A with the second measuring device160(S410), the second measuring device160is brought close to the reflective surface11A, the atmospheric plasma (PL1) is radiated to the reflective surface11A, and a chemical species detected on the reflective surface11A is detected, thereby measuring the level of microcontamination of the reflective surface11A. To this end, a first process gas GAS1may be injected into the cleaning chamber110. As the first process gas GAS1, a hydrogen-based gas or an argon-based gas may be used. When a hydrogen-based gas including a hydrogen radical is used as the first process gas GAS1, operations S410to S430may be simultaneously performed. For example, measurement by the second measuring device160and cleaning by the second cleaning apparatus170may be performed simultaneously, and there is no need to inject a separate second process gas in a subsequent process, which will be described later.

On the other hand, when an argon-based gas is used as the first process gas GAS1, only the microcontamination level of the reflective surface11A by the second measuring device160may be measured, and in the subsequent process, it is necessary to inject a separate process gas necessary for cleaning, into the second cleaning apparatus170. According to an example embodiment, an example in which an argon-based gas is used as the first process gas GAS1will be described.

The microcontamination level of the reflective surface11A may be measured by checking the type of chemical species detected through the second measuring device160. For example, a region in which a substance, e.g., tin (Sn), included in the droplet is detected as a chemical species may be regarded as a region to which the microcontaminants P2are attached. Also, a region in which a material included in the reflective layer11C constituting the reflective surface11A is detected as a chemical species may be regarded as an uncontaminated region. In addition, a region in which a material included in the body11B below the reflective layer11C is detected as a chemical species may be regarded as the reflective layer11C of the reflective surface11A is damaged

Next, referring toFIGS.5and9, atmospheric plasma cleaning (S430) may be performed on an area in which the microcontamination level exceeds a reference value, based on the generated microcontamination level map and the damage level map. To this end, second process gas GAS2may be injected into the cleaning chamber110. In an example embodiment, a hydrogen-based gas including a hydrogen radical may be used as the second process gas GAS2. The microcontaminants P2not removed in the first cleaning process (S300) are strongly attached to the reflective surface11A and are not easily removed by physical cleaning. Therefore, in the second cleaning process (S400), atmospheric plasma cleaning, which is chemical cleaning stronger than physical cleaning, may be performed using the second cleaning apparatus170to remove the microcontaminants P2.

Since atmospheric plasma cleaning is performed by radiating plasma (PL2) in a relatively significantly narrow range, a lot of time may be consumed for cleaning. In an example embodiment, the controller190may restrict how the atmospheric plasma cleaning is performed. For example, the controller190may restrict the atmospheric plasma cleaning so the atmospheric plasma cleaning is performed only in a region in which the contamination level exceeds a reference value by referring to the microcontamination level map.

In addition, since atmospheric plasma cleaning is performed by irradiating plasma (PL2) in a significantly narrow range, if the cleaning is performed in a case in which the reflective layer11C constituting the reflective surface11A of the collector11is damaged, permanent damage to the collector11may occur. Accordingly, the controller190may restrict how the atmospheric plasma cleaning is performed. For example the controller190may restrict the atmospheric plasma cleaning so the atmospheric plasma cleaning is performed only on the region excluding a region D in which the reflective layer11C is damaged by referring to the previously generated damage level map.

Next, a case in which operations S410to S430of the second cleaning process S400are simultaneously performed will be described.

When a hydrogen-based gas including a hydrogen radical is used as the first process gas GAS1, operations S410to S430may be simultaneously performed. For example, the operation of measuring the level of contamination and damage of the reflective surface11A with the second measuring device160and the operation of cleaning the reflective surface11A with the second cleaning apparatus170may be performed simultaneously.

The controller190may perform atmospheric plasma cleaning of the entire reflective surface11A using the second cleaning apparatus170in a state in which the hydrogen-based first process gas GAS1is injected into the cleaning chamber110. The atmospheric plasma cleaning may be performed as the second cleaning apparatus170moves along the reflective surface11A after the second cleaning apparatus170approaches the reflective surface11A. The controller190may detect a chemical species emitted from the reflective surface11A in the atmospheric plasma cleaning process, using the second measuring device160, and measure the level of microcontamination and damage of the region in which plasma cleaning is performed. The controller190may increase the time during which atmospheric plasma cleaning is performed in an area having a relatively high level of microcontamination, thereby intensively cleaning an area having a high level of microcontamination. Also, when the damaged area D is detected in the reflective surface11A, the controller190may stop the second cleaning process (S400) from being performed to limit and/or prevent damage to the collector11.

As set forth above, according to an example embodiment, a method of cleaning a collector of an extreme ultraviolet light-source system, in which contaminants on a surface of the collector may be cleaned effectively by changing a cleaning process depending on the level of contamination on the surface of the collector.

While example embodiments have been illustrated and described above, it will be apparent to those skilled in the art that modifications and variations could be made without departing from the scope of inventive concepts as defined by the appended claims.