Optical device and method for preventing contamination of optical device

Abstract

To provide an optical device that can prevent contamination more efficiently, and a method for preventing contamination of the device.SOLUTION: An optical device comprises: a light source 210 which creates irradiation light L11 including EUV light; an optical system chamber 100 in which a subject to be irradiated with the irradiation light L11 is arranged; a grazing incidence mirror 13 which is provided in the optical system chamber 100 in order to introduce the irradiation light L11; an introduction part 500 which introduces argon into the optical system chamber 100; a power source 52 which gives a negative voltage to the grazing incidence mirror 13 in the optical system chamber 100; an ammeter 51 which measures an ion current flowing in the grazing incidence mirror 13; and a control part 53 which controls an introduction amount of argon corresponding to a measurement result of the ammeter 51.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to optical devices and methods for preventing contamination of optical devices. [Background technology]

[0002] In Patent Document 1, it is proposed to clean reflective optical elements with a cleaning gas in order to reduce contamination in an EUV (Extreme UltraViolet) lithography apparatus. In Patent Document 1, a cleaning gas such as atomic hydrogen, hydrogen molecules, or helium is added to the EUV lithography apparatus.

[0003] US Patent No. 5,399,636 discloses a method for removing a contaminant layer from an optical surface. In this patent, a cleaning gas containing atomic hydrogen is contacted with the contaminant layer. One of the cleaning heads uses helium as the sputtering gas. The voltage generator in this patent generates a potential difference between the EUV reflective optical element and the cleaning head, and the generated potential difference accelerates helium ions in the cleaning gas jet.

[0004] Patent Document 3 discloses a method of removing an oxide film from a substrate using argon plasma (Ar plasma). In Patent Document 3, a substrate from which the photoresist has been removed is bombarded with Ar plasma in an oxygen-free atmosphere to remove the native oxide film.

[0005] Patent Document 4 discloses cleaning of optical elements with hydrogen plasma or helium plasma (He plasma). In Patent Document 4, hydrogen plasma or He plasma is generated by a remote plasma generator and introduced into a chamber. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special table 2013-506308 publication [Patent Document 2] JP 2012-256944 A [Patent Document 3] JP 2010-192503 A [Patent Document 4] Patent No. 6844798 Summary of the Invention [Problem to be solved by the invention]

[0007] EUV light is absorbed by air and nitrogen. For this reason, optical systems that use EUV light are operated inside a vacuum chamber. During this process, residual organic gases generated from lubricants used in mechanical parts and electrical wiring materials are adsorbed onto the surfaces of optical components. When the adsorbed residual organic gases are irradiated with EUV light, the organic molecules decompose and carbon adheres to the surface of the components. This causes a problem of a decrease in the reflectance of the mirror.

[0008] Although there is a technique for cleaning contaminants such as carbon adhering to optical elements such as mirrors using hydrogen plasma or He plasma, a cleaning method with a higher etching rate is desired.

[0009] The present disclosure has been made in consideration of such problems, and provides an optical device capable of more effectively preventing contamination of optical elements, and a method for preventing contamination thereof. [Means for solving the problem]

[0010] An optical device according to one aspect of this embodiment includes a light source that generates light including EUV light, a chamber in which an object to be irradiated with the light is placed, an optical element provided in the chamber for guiding the light, an introduction unit that introduces argon into the chamber, a power supply that applies a negative voltage to the optical element in the chamber, an ammeter that measures an ion current flowing through the optical element, and a control unit that controls the amount of argon introduced in accordance with the measurement result of the ammeter.

[0011] In the above optical device, the argon introduced into the chamber may include argon gas, the inlet unit may include an inlet pipe connected to the chamber, the control unit may control the flow rate of the argon gas supplied into the chamber via the inlet pipe, and the EUV light introduced into the chamber may convert the argon gas into argon plasma.

[0012] In the above optical device, the introduction section may include a remote plasma generator that generates argon plasma, an introduction pipe provided between the remote plasma generator and the chamber, and a variable conductance valve provided in the introduction pipe, and the control section may control the flow rate of the argon plasma supplied into the chamber via the introduction pipe by controlling the conductance of the variable conductance valve.

[0013] The optical device may be provided with a cooling mechanism for cooling the inlet pipe.

[0014] In the optical apparatus described above, the object may be an EUV mask having a pellicle.

[0015] In the above optical device, the light source may further generate the light including VUV light, a grazing incidence mirror that reflects the VUV light may be provided within the chamber, the VUV light reflected by the grazing incidence mirror may be incident on the optical element, and the VUV light guided into the chamber may convert the argon gas into argon plasma.

[0016] A method for preventing contamination of an optical device according to one aspect of this embodiment is a method for preventing contamination of an optical device including a light source that generates light including EUV light, a chamber in which an object to be irradiated with the light is placed, and an optical element provided in the chamber for guiding the light, and includes the steps of introducing argon into the chamber, applying a negative voltage to the optical element in the chamber, measuring an ion current flowing through the optical element, and controlling the amount of argon introduced depending on the measurement result of the ion current.

[0017] In the above contamination prevention method, an inlet pipe is connected to the chamber, and in the step of introducing argon into the chamber, the argon introduced into the chamber includes argon gas, and in the step of controlling the amount of argon introduced according to a measurement result of the ion current, a flow rate of the argon gas supplied into the chamber via the inlet pipe is controlled according to the measurement result, and the EUV light introduced into the chamber may convert the argon gas into argon plasma.

[0018] In the above contamination prevention method, the optical device includes a remote plasma generator that generates argon plasma, an inlet pipe provided between the remote plasma generator and the chamber, and a variable conductance valve provided in the inlet pipe, and in the step of introducing argon into the chamber, the argon introduced into the chamber includes the argon plasma, and in the step of controlling the amount of argon introduced according to a measurement result of the ion current, the flow rate of the argon plasma supplied into the chamber via the inlet pipe may be controlled by controlling the conductance of the variable conductance valve according to the measurement result.

[0019] In the above contamination prevention method, a cooling mechanism for cooling the inlet pipe may be provided.

[0020] In the above contamination prevention method, the object may be an EUV mask having a pellicle.

[0021] In the above contamination prevention method, the light source may further generate the light including VUV light, a grazing incidence mirror that reflects the VUV light is provided within the chamber, the VUV light reflected by the grazing incidence mirror is incident on the optical element, and the VUV light guided into the chamber may convert the argon gas into argon plasma. Effect of the Invention

[0022] According to the present disclosure, it is possible to provide an optical device capable of more effectively preventing contamination of optical elements, and a method for preventing contamination thereof. [Brief description of the drawings]

[0023] [Figure 1] 1 is a schematic diagram illustrating an optical device according to a first embodiment. [Diagram 2] FIG. 4 is a flow chart illustrating a method for preventing contamination of the optical device according to the first embodiment. [Diagram 3] 6 is a schematic diagram illustrating an optical device according to a second embodiment. FIG. [Figure 4] 11 is a schematic diagram illustrating an optical device according to a third embodiment. FIG. [Diagram 5] 11 is a schematic diagram illustrating an optical device according to a fourth embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. The following description shows a preferred embodiment of the present disclosure, and the scope of the present disclosure is not limited to the following embodiment. In the following description, parts with the same reference numerals indicate substantially the same contents.

[0025] (Overview of the embodiment) The optical device according to the embodiment has a function of preventing contamination of optical elements arranged in the device. Specifically, the optical device uses Ar plasma to prevent contamination of the optical elements. There are two methods for generating Ar plasma:

[0026] 1. Argon gas (Ar gas) is introduced into the EUV light path. 2. Use a remote plasma generator.

[0027] First, in the following embodiment 1, an optical device that introduces Ar gas into the EUV light path and a method for preventing contamination are described. In embodiment 2, an optical device that uses a remote plasma generator and a method for preventing contamination are described. In embodiment 3, an optical device that introduces Ar gas into the VUV light path and a method for preventing contamination are described. In embodiment 4, a mechanism for cooling the introduction pipe for Ar plasma is described.

[0028] (Embodiment 1) An optical device according to the first embodiment will be described. FIG. 1 is a schematic diagram illustrating the optical device according to the first embodiment. As shown in FIG. 1, in this embodiment, the optical device is, for example, an inspection device 1 that inspects an EUV mask using EUV light. In this case, the sample 40 is an EUV mask. The EUV mask serving as the sample 40 may be a mask with a pattern or a mask blank without a pattern. Note that the optical device is not limited to the inspection device 1, but may be another optical device such as an exposure device, as long as the atmosphere inside the device can be controlled. Also, the sample 40 is not limited to an EUV mask, as long as it is an object to be irradiated with light.

[0029] <Device configuration> The inspection apparatus 1 according to this embodiment includes an optical system chamber 100, a light source chamber 200, an introduction section 500, an ammeter 51, a power source 52, and a control section 53.

[0030] The light source chamber 200 is a vacuum chamber and is connected to a vacuum pump (not shown). A light source 201 is disposed in the light source chamber 200.

[0031] The light source 201 generates light including EUV light. Here, the light source 201 generates EUV light of 13.5 nm, which is the same as the exposure wavelength of the sample 40 to be irradiated. The light generated by the light source 201 is set as irradiation light L11. The light source 201 is, for example, a DPP (Discharge Produced Plasma) light source that uses discharge. In addition to the EUV light, the light source 201 may further generate VUV (Vacuum UltraViolet) light, which is out-of-band light. The light source 201 may generate light including at least one of VUV light and EUV light. The VUV light may be light having a wavelength of 100 nm or more and 200 nm or less.

[0032] The optical system chamber 100 is a vacuum chamber and is connected to a vacuum pump (not shown). The optical system chamber 100 is connected to a light source chamber 200. Since the internal spaces of the light source chamber 200 and the optical system chamber 100 are in a vacuum state, the EUV light propagates through the vacuum. Note that the light source chamber 200 and the optical system chamber 100 may be evacuated by a common vacuum pump or by separate vacuum pumps.

[0033] In the optical system chamber 100, an optical system 10, a photodetector 20, a stage 30, and a sample 40 are arranged. The optical system 10 includes optical elements and propagates the irradiation light L11, which is EUV light. The optical system 10 includes a concave mirror 11, a concave mirror 12, a drop mirror 13, and a Schwarzschild optical system 16 as optical elements. Each optical element may be provided in the optical system chamber 100 to guide the irradiation light L11. The optical system 10 is a dark-field optical system for imaging the sample 40. The optical system 10 may be a bright-field optical system for imaging the sample 40. In the optical system chamber 100, a sample 40 is arranged. The sample 40 is an object to be irradiated with the irradiation light L11.

[0034] The optical system 10 for guiding the EUV light will be described below. The irradiation light L11 generated by the light source 201 advances while diverging. The irradiation light L11 generated by the light source 201 is reflected by the concave mirror 11. The concave mirror 11 is, for example, an ellipsoidal mirror. The concave mirror 11 is a multilayer mirror in which Mo films and Si films are alternately stacked, and reflects the EUV light. The irradiation light L11 reflected by the concave mirror 11 advances while being narrowed. After the irradiation light L11 is focused, it advances while diverging. Then, the irradiation light L11 is reflected by the concave mirror 12.

[0035] The concave mirror 12 is, for example, an ellipsoidal mirror. The concave mirror 12 is a multilayer mirror in which Mo films and Si films are alternately stacked, and reflects EUV light. The irradiation light L11 reflected by the concave mirror 12 travels while being narrowed down, and is incident on the drop-in mirror 13. The drop-in mirror 13 is a plane mirror, and is disposed directly above the sample 40. The irradiation light L11 reflected by the drop-in mirror 13 is incident on the sample 40. The drop-in mirror 13 focuses the irradiation light L11 on the sample 40. In this way, the inspection area of ​​the sample 40 is illuminated with the irradiation light L11, which is EUV light. Therefore, the irradiation light L11 becomes the illumination light that illuminates the sample 40.

[0036] The optical system chamber 100 is provided with a stage 30. A sample 40 is placed on the stage 30. The stage 30 is a movable stage such as an XYZ stage. The stage 30 moves in an XY plane perpendicular to the optical axis and in a Z-axis direction parallel to the optical axis, thereby moving the sample 40. This changes the illumination position of the sample 40, making it possible to observe any position of the sample 40. In addition, the inspection area where the sample 40 is illuminated can be changed.

[0037] Next, the detection optical system that detects light from the sample 40 will be described. As described above, the illumination light L11 illuminates the inspection area of ​​the sample 40. The EUV light reflected by the sample 40 is used as detection light L12. The detection light L12 reflected by the sample 40 is incident on the Schwarzschild optical system 16. The Schwarzschild optical system 16 includes a holed concave mirror 14 and a convex mirror 15 that are arranged above the sample 40.

[0038] The detection light L12 reflected by the sample 40 is incident on the concave mirror 14 with a hole. The concave mirror 14 with a hole has a hole 14a at its center. The detection light L12 reflected by the concave mirror 14 with a hole is incident on the convex mirror 15. The convex mirror 15 reflects the detection light L12 from the concave mirror 14 with a hole toward the hole 14a in the concave mirror 14 with a hole. The detection light L12 that passes through the hole 14a in the concave mirror 14 with a hole is incident on the photodetector 20. The Schwarzschild optical system 16 enlarges and projects the inspection area of ​​the sample 40 onto the photodetector 20.

[0039] The detection light L12 reflected by the convex mirror 15 is detected by the photodetector 20. The photodetector 20 is an imaging device such as a CCD (Charge Coupled Device) sensor, a CMOS (Complementary Metal Oxide Semiconductor) sensor, or a TDI (Time Delay Integration) sensor, and captures an image of the sample 40. In other words, the photodetector 20 captures an enlarged image of the inspection area of ​​the sample 40.

[0040] The image of the sample 40 captured by the photodetector 20 is output to the processing device 21. The processing device 21 is an arithmetic processing device having a processor, memory, etc., and performs inspection based on the image of the sample 40. For example, the processing device 21 performs defect inspection by comparing the brightness of the image of the sample 40 with a threshold value. The processing device 21 also controls the coordinates of the stage 30. This makes it possible to identify defect coordinates in the sample 40. The processing device 21 then stores the defect coordinates and the image of the defect in a memory or the like. The processing device 21 displays the image of the defect, etc., on a monitor. This allows the user to check the defect.

[0041] The ammeter 51, the power supply 52, and the control unit 53 are disposed outside the optical system chamber 100. The power supply 52 is connected to the optical element. When the optical element is the drop-in mirror 13, the power supply 52 is connected to the drop-in mirror 13. The power supply 52 is a DC (Direct Current) power supply and generates a DC voltage. The power supply 52 supplies a negative direct current voltage to the drop-in mirror 13. For example, the optical system chamber 100 is at ground potential, and the drop-in mirror 13 is at negative potential. The ammeter 51 is connected between the power supply 52 and the drop-in mirror 13. The ammeter 51 measures the ion current flowing through the optical element. When the optical element is the drop-in mirror 13, the ammeter 51 measures the current flowing from the power supply 52 to the drop-in mirror 13. The control unit 53 controls the amount of argon introduced into the optical system chamber 100 according to the measurement result of the ammeter 51.

[0042] <Prevention of contamination> Next, a method for preventing contamination of an optical device will be described. Mechanical parts and electrical wiring materials are provided inside the optical system chamber 100 and the light source chamber 200. Organic residual gases are generated from the lubricating oil and electrical wiring materials used in the mechanical parts, and are adsorbed onto the surfaces of the optical elements. When the optical elements are irradiated with EUV light, contaminants such as carbon are deposited on the surfaces of the optical elements.

[0043] In the contamination prevention method of the present embodiment, Ar plasma is generated and the contaminants deposited on the optical element are etched by the generated Ar plasma, thereby removing the contaminants from the optical element.

[0044] The etching rate of an optical element can be controlled mainly by the following two parameters.

[0045] A. Ar plasma density B. Bias voltage applied to the optical element

[0046] First, a method for controlling the density of the Ar plasma will be described, followed by a method for controlling the bias voltage applied to the optical element.

[0047] <Density of Ar Plasma> In this embodiment, the density of the Ar plasma is controlled by the flow rate of argon introduced into the optical system chamber 100. In this embodiment, the argon introduced into the optical system chamber 100 contains Ar gas. Hereinafter, as an example of removing the contamination of the optical element, the prevention of the contamination of the drop mirror 13 will be described.

[0048] As shown in FIG. 1, the irradiated light L11 reflected by the concave mirror 12 travels while being focused. For this reason, in the drop mirror 13, the spot of the irradiated light L11 becomes small. The light density of the irradiated light L11 becomes high in the drop mirror 13, and the contamination of the drop mirror 13 is promoted. Therefore, in this embodiment, the drop mirror 13 is an optical element to be protected from contamination.

[0049] In this embodiment, an introduction unit 500 is provided to remove the contamination of the optical element. The introduction unit 500 introduces Ar gas into the optical system chamber 100. The introduction unit 500 includes a gas supply unit 501, an MFC (Mass Flow Controller) 502, and an introduction pipe 503.

[0050] The gas supply unit 501 has a gas cylinder or the like and supplies Ar gas. The gas supply unit 501 is connected to the introduction pipe 503. The gas supply unit 501 supplies Ar gas to the introduction pipe 503.

[0051] The introduction pipe 503 is connected to the optical system chamber 100. Therefore, the Ar gas from the gas supply unit 501 is supplied to the optical system chamber 100 through the introduction pipe 503. Further, an MFC 502 is provided in the introduction pipe 503. The MFC 502 controls the gas flow rate. The control unit 53 outputs a control signal to the MFC 402 according to the measurement result of the ammeter 51. MFC502 controls the gas flow rate based on the control signal.

[0052] In this manner, the control unit 53 controls the flow rate of Ar gas supplied into the optical system chamber 100 via the inlet pipe 503. The EUV light introduced into the optical system chamber 100 converts the Ar gas into Ar plasma. For example, the irradiation light L11 incident on the drop-in mirror 13 irradiates the Ar gas introduced into the optical path, converting the Ar gas into Ar plasma. Note that the Ar gas absorbs the EUV light. Therefore, the flow rate of the Ar gas may be determined taking into consideration the absorption by the EUV light.

[0053] <Bias voltage applied to optical element> Next, the bias voltage applied to the optical element will be described. As described above, the EUV light converts the Ar gas into Ar plasma. The generated Ar plasma is composed of Ar ions (Ar + ) and is directed toward an optical element to which a negative voltage is applied. Therefore, by changing the bias voltage applied to the optical element, it is possible to change the energy with which the Ar plasma collides with the optical element. This makes it possible to change the etching rate by the Ar plasma. Therefore, by changing the bias voltage according to the contamination state of the optical element, it is possible to achieve an appropriate cleaning effect. Details are given below.

[0054] A drop-in mirror 13 is disposed inside the optical system chamber 100. A DC voltage is applied between the optical system chamber 100 and the drop-in mirror 13. This generates an electric field around the drop-in mirror 13, accelerating the generated Ar plasma. The Ar plasma then collides with the drop-in mirror 13. This allows the Ar plasma to etch away contamination on the drop-in mirror 13. That is, Ar ions are accelerated by the electric field and collide with the surface of the optical element, thereby removing carbon. This makes it possible to suppress a decrease in the reflectance of the drop-in mirror 13.

[0055] It is preferable that the negative DC voltage applied to drop mirror 13 is at a level that does not cause damage to drop mirror 13 due to ion collisions. For example, a voltage of -50 V to -100 V is applied to drop mirror 13. This makes it possible to effectively remove carbon adhering to the surface of drop mirror 13.

[0056] Ammeter 51 monitors the current flowing from power supply 52 to drop mirror 13. Specifically, since Ar ions collide with drop mirror 13, a current flows from drop mirror 13 to power supply 52. ​​In other words, ammeter 51 measures the current of ions colliding with drop mirror 13.

[0057] The control unit 53 controls the amount of Ar gas introduced according to the measurement result of the ammeter 51. For example, the control unit 53 controls the opening degree of the MFC 502 according to the measurement result of the ammeter 51. The control unit 53 may set a target value so that the ion current corresponds to the surface area of ​​the optical element. The control unit 53 feedback controls the MFC 502 so that the ion current measured by the ammeter 51 becomes the target value. Note that when the drop-in mirror 13 is irradiated with EUV light, a photoemission current is superimposed on the measured current. Therefore, it is preferable to set the target value in a state where the drop-in mirror 13 is not irradiated with EUV light.

[0058] Furthermore, the introduction unit 500 can introduce Ar gas during the inspection of the sample 40. That is, the contamination prevention method can be carried out in parallel with the inspection of the sample 40. This can improve productivity.

[0059] Argon has a higher mass than helium and hydrogen. Therefore, the energy of the Ar plasma when it collides with an optical element is large. Therefore, the etching rate of the Ar plasma is higher than that of the He plasma and hydrogen plasma. This makes it possible to improve the contamination prevention effect compared to the method using the He plasma and hydrogen plasma.

[0060] In addition, since argon has a high absorption coefficient for EUV light, there is a risk of reducing the EUV light illuminating the sample 40. However, since the etching rate by Ar plasma is high as described above, the pressure of the Ar gas can be reduced. In addition, if the bias voltage is increased, the pressure of the Ar gas can be further reduced. This makes it possible to improve the contamination prevention effect while suppressing the reduction in the EUV light illuminating the sample 40.

[0061] In addition, since Ar gas has a larger mass than hydrogen and helium, it is possible to suppress the scattering of debris generated from the light source 201.

[0062] Furthermore, in the case where the sample 40 is an EUV mask with a pellicle, damage to the pellicle can be prevented, for the reasons described below.

[0063] The pellicles attached to EUV masks are very thin and therefore easily torn, one of the reasons for this is the charging of the pellicle. As the pellicle is insulated, photoelectrons are emitted when irradiated with EUV light. When photoelectrons are emitted from the pellicle, the pellicle becomes positively charged. If the pellicle becomes highly charged and electrostatically breaks down and discharges, the pellicle may be damaged at the point of discharge. As the pellicle is under tensile stress, damage may spread from the point of discharge. The pellicle may also be torn when excessive force is applied to it by Coulomb force.

[0064] In this embodiment, Ar plasma is generated in the optical system chamber 100 by EUV light. When the pellicle is charged to a positive potential by emitting photoelectrons, the electrons in the plasma can be absorbed by the pellicle and neutralized. In this case, the potential of the pellicle is suppressed to a floating potential in the plasma, so that discharge can be prevented.

[0065] Moreover, the Ar gas introduced by the introduction part 500 has the effect of expelling residual gas from the optical system chamber 100 .

[0066] Next, a method for preventing contamination of an optical device according to this embodiment will be described. Fig. 2 is a flow chart illustrating a method for preventing contamination of an optical device according to the first embodiment. As shown in Fig. 2, the method for preventing contamination of an optical device includes step S11 of introducing argon into optical system chamber 100, step S12 of applying a negative voltage to optical elements such as drop mirror 13 in optical system chamber 100, step S13 of measuring an ion current flowing through the optical elements, and step S14 of adjusting the amount of argon introduced according to the measurement result of the ion current. control and step S14.

[0067] In this embodiment, in the step of introducing argon into the chamber in step S11, the argon introduced into the optical system chamber 100 includes Ar gas. Also, in the step of controlling the amount of argon introduced in accordance with the measurement result of the ion current in step S14, the flow rate of Ar gas supplied into the optical system chamber 100 via the introduction pipe 503 is controlled in accordance with the measurement result. The EUV light introduced into the optical system chamber 100 converts the Ar gas into Ar plasma.

[0068] In this embodiment, the optical element to be prevented from being contaminated is the recessed mirror 13, but other optical elements and optical components may also be prevented from being contaminated. For example, the concave mirror 11, the concave mirror 12, the perforated concave mirror 14, and the convex mirror 15 may also be prevented from being contaminated. In this case, a negative DC voltage may be applied to the optical element from which contamination is to be prevented. A negative voltage may also be applied to two or more optical elements at the same time. This makes it possible to prevent contamination of two or more optical elements.

[0069] In this manner, in this embodiment, the introduction unit 500 introduces argon into the optical system chamber 100. In this manner, contamination of the optical element can be more effectively prevented. In contrast, when carbon is oxidized and removed with oxygen radicals, it is necessary to irradiate high-energy EUV light. In other words, it was necessary to activate the optical element surface or oxygen and dissociate oxygen molecules into radicals. However, it was difficult to irradiate the amount of light according to the film thickness of the carbon on the optical element surface, and the removal result was prone to non-uniformity. Since the surface of silicon or the like is easily oxidized by oxygen radicals, silicon is exposed after the deposited carbon is removed, and the silicon is oxidized, which may result in a decrease in reflectance. In contrast, in this embodiment, argon is used, so contamination can be easily prevented.

[0070] (Embodiment 2) Next, an optical device according to a second embodiment will be described. FIG. 3 is a schematic diagram illustrating an inspection device according to the second embodiment. As shown in FIG. 3, the inspection device 2 of this embodiment is provided with an introduction part 300 instead of the introduction part 500. In this embodiment, the argon introduced into the optical system chamber 100 contains Ar plasma. The introduction part 300 includes a gas supply source 301, an MFC 302, a gas pipe 303, an introduction pipe 304, a variable conductance valve 305, and a remote plasma generator 310. The remote plasma generator 310 generates a remote plasma of argon.

[0071] The gas supply source 301 has a gas cylinder for storing Ar gas, etc. The gas supply source 301 is connected to a remote plasma generator 310 via a gas pipe 303. The gas supply source 301 supplies Ar gas to the remote plasma generator 310. The Ar gas from the gas supply source 301 is introduced into the remote plasma generator 310 via the gas pipe 303. The introduced Ar gas fills a plasma chamber 313 of the remote plasma generator 310. The gas pipe 303 is provided with an MFC 302. The MFC 302 controls the flow rate of the Ar gas.

[0072] The remote plasma generator 310 includes a coil 311, an RF (Radio Frequency) power supply 312, and a plasma chamber 313. The plasma chamber 313 is a vacuum chamber, and is connected to a vacuum pump (not shown). The plasma chamber 313 is filled with Ar gas from a gas supply source 301. The RF power supply 312 supplies an RF voltage to the coil 311. This causes a current to flow through the coil 311, generating a magnetic field within the plasma chamber 313. Ar molecules are converted into Ar ions (Ar + ) and electrons to generate plasma 315. The plasma 315 may be generated by capacitive coupling instead of inductive coupling. The plasma 315 may be generated by RF glow discharge. Alternatively, ECR (Electron Cyclotron Resonance) plasma may be used.

[0073] An inlet pipe 304 is connected to the plasma chamber 313. The inlet pipe 304 is further connected to the optical system chamber 100. That is, the inlet pipe 304 is provided between the remote plasma generator 310 and the optical system chamber 100. The plasma chamber 313 is connected to the optical system chamber 100 via the inlet pipe 304. Plasma 315 generated in the plasma chamber 313 is introduced into the optical system chamber 100 through the inlet pipe 304. A variable conductance valve 305 is provided in the inlet pipe 304. The conductance (opening) of the variable conductance valve 305 is variable.

[0074] The control unit 53 changes the opening of the variable conductance valve 305. The control unit 53 controls the flow rate of Ar plasma supplied into the optical system chamber 100 via the introduction pipe 304 by controlling the conductance of the variable conductance valve 305. For example, the amount of plasma introduced is increased by increasing the conductance of the variable conductance valve 305. Conversely, the amount of plasma 315 introduced is decreased by decreasing the conductance of the variable conductance valve 305. The control unit 53 may also control the RF power supply 312. This makes it possible to control the density of the plasma 315, and therefore to adjust the amount of plasma 315 introduced.

[0075] In this manner, the introducing unit 300 introduces the plasma 315 into the optical system chamber 100. That is, the remote plasma generating device 310 generates the plasma 315. The plasma 315 containing electrons, Ar ions, Ar gas, radicals, etc. is introduced into the optical system chamber 100.

[0076] This embodiment has a remote plasma generator 310. Ar plasma can be generated in a plasma chamber 313 separate from the optical system chamber 100. The plasma chamber 313 and the optical system chamber 100 are connected by an inlet pipe 304, so that the thermal coupling can be loose. Heat from the remote plasma generator 310 is not easily transferred to the optical system chamber 100, so the precision of the optical system 10 can be maintained high.

[0077] In this embodiment, plasma 315 is introduced into the optical system chamber 100. When the pellicle is charged to a positive potential by emitting photoelectrons, the electrons in the plasma can be absorbed by the pellicle and neutralized. In this case, the potential of the pellicle is suppressed to a floating potential in the plasma, so that discharge can be prevented.

[0078] Moreover, the Ar introduced by the introduction part 300 may be not only Ar plasma but also neutral Ar molecules (Ar gas). In this case as well, there is an effect of expelling residual gas from the chamber.

[0079] In the above description, Ar plasma generated by the remote plasma generator 310 is used, but He plasma and hydrogen plasma generated by the remote plasma generator 310 may also be used. For example, hydrogen plasma can be used when the surface of the optical element is coated with a substance with high hydrogen radical resistance, such as ruthenium. When hydrogen plasma is used, hydrogen has a smaller mass than He and Ar. Therefore, the ion bombardment effect is reduced, and the voltage of the power supply 52 is increased. This increases the velocity energy of the ions, making it possible to effectively prevent contamination.

[0080] Furthermore, the hydrogen introduced into the optical system chamber 100 is not limited to hydrogen plasma, but may be hydrogen gas, hydrogen radicals, etc. Of course, the introduction unit 300 may introduce a mixture of gas, plasma, radicals, etc. In other words, the introduction unit 300 may introduce argon, hydrogen, or helium into the chamber.

[0081] In the method for preventing contamination of an optical device according to this embodiment, in the step of introducing argon into the optical system chamber 100 in the above-mentioned step S11, the argon introduced into the optical system chamber 100 contains Ar plasma. Also, in the step of controlling the amount of argon introduced according to the measurement result of the ion current in step S14, the control unit 53 controls the flow rate of Ar plasma supplied into the optical system chamber 100 via the introduction pipe 304 by controlling the conductance of the variable conductance valve 305 according to the measurement result. This makes it possible to effectively prevent contamination of optical elements. Other configurations and effects are included in the description of the first embodiment.

[0082] (Embodiment 3) Next, an optical device according to the third embodiment will be described. FIG. 4 is a schematic diagram illustrating an optical device according to the third embodiment. As shown in FIG. 4, the inspection device 3 of this embodiment is provided with a concave mirror 18 and a concave mirror 19 instead of the concave mirror 11 and the concave mirror 12 of FIG. 1. The concave mirror 18 and the concave mirror 19 are oblique incidence mirrors. The light source 201 generates light including VUV light in addition to EUV light. The configuration other than the concave mirror 18 and the concave mirror 19 is the same as that of FIG. 1, and therefore the description will be omitted as appropriate. For example, the Schwarzschild optical system 16 has the same configuration as that of the first embodiment.

[0083] Concave mirror 18 and concave mirror 19 are oblique incidence mirrors, so the optical axis of irradiation light L11 is not perpendicular to the optical axis before and after reflection by concave mirror 18. On the other hand, concave mirror 11 in embodiment 1 is tilted 45 degrees with respect to the optical axis of irradiation light L11, so that the optical axis of irradiation light L11 is perpendicular to the optical axis before and after reflection by concave mirror 11.

[0084] Similarly, the optical axis of the irradiation light L11 is not perpendicular to the optical axis before and after reflection by the concave mirror 19. On the other hand, in the concave mirror 12 of the first embodiment, the concave mirror 12 is tilted at 45 degrees with respect to the optical axis of the irradiation light L11, so that the optical axis of the irradiation light L11 is perpendicular to the optical axis before and after reflection by the concave mirror 12.

[0085] The illumination light L11 reflected by the concave mirror 18 and the concave mirror 19 is incident on the drop-in mirror 13, similar to the first embodiment. The drop-in mirror 13 reflects the illumination light L11, thereby illuminating the sample 40. Therefore, the photodetector 20 can image the sample 40, similar to the first embodiment.

[0086] Concave mirrors 18 and 19, which are grazing incidence mirrors, are metal mirrors. For example, concave mirrors 18 and 19 are metal mirrors on which a Ru (ruthenium) film is formed. Because concave mirrors 18 and 19 are metal mirrors, they reflect VUV light and EUV light from light source 201. That is, not only EUV light but also VUV light is guided to drop-in mirror 13. In contrast, in embodiment 1, concave mirrors 11 and 12 are multilayer film mirrors, and therefore most of the VUV light is not guided to drop-in mirror 13.

[0087] By using grazing incidence mirrors as the concave mirrors 18 and 19, the VUV light can be guided to the drop-in mirror 13. The irradiation light L11 reflected by the concave mirror 19 includes EUV light and VUV light. The concave mirror 19 focuses the irradiation light L11 on the sample 40. Since the irradiation light L11 reflected by the concave mirror 19 is narrowed as it travels, the light density of the irradiation light L11 becomes high in the vicinity of the drop-in mirror 13. Furthermore, Ar gas is supplied to the optical system chamber 100.

[0088] The EUV light and VUV light contained in the irradiation light L11 are absorbed by the Ar gas. Then, in the vicinity of the drop-in mirror 13 where the light density is high, the Ar gas is ionized, and Ar plasma is generated. A negative DC voltage is applied to the drop-in mirror 13 as in the first embodiment. Therefore, the Ar plasma collides with the drop-in mirror 13. That is, the VUV light guided into the optical system chamber 100 converts the Ar gas into Ar plasma. This makes it possible to prevent contamination as in the first embodiment.

[0089] In this embodiment, the control unit 53 controls the MFC 502 according to the measurement result of the ammeter 51. That is, the MFC 502 controls the gas flow rate so that the measurement value of the ammeter 51 becomes a target value. This makes it possible to appropriately adjust the amount of argon introduced into the optical system chamber 100. Therefore, contamination can be effectively prevented.

[0090] In this embodiment, plasma is generated using VUV light, which is out-of-band light generated by the light source 201. That is, Ar plasma can be generated by the inspection light source 201. This eliminates the need for the remote plasma generator 310, simplifying the device configuration. It is only necessary to add an introduction unit 500 for introducing Ar gas, which can suppress an increase in device costs.

[0091] In the method for preventing contamination of an optical device according to this embodiment, in the step of introducing argon into the optical system chamber 100 in step S11 described above, the argon introduced into the optical system chamber 100 contains Ar plasma. Also, in the step of controlling the amount of argon introduced according to the measurement result of the ion current in step S14, the control unit 53 controls the flow rate of Ar gas supplied into the optical system chamber 100 via the introduction pipe 503 according to the measurement result. The VUV light introduced into the optical system chamber 100 converts the Ar gas into Ar plasma. This makes it possible to effectively prevent contamination of optical elements.

[0092] (Embodiment 4) Next, an optical device according to embodiment 4 will be described. Fig. 5 is a schematic diagram illustrating an optical device according to embodiment 4. As shown in Fig. 5, in the inspection device 4 of this embodiment, in addition to the configuration in Fig. 3, a cooling mechanism 330 is added to the introduction section 300. The configuration other than the cooling mechanism 330 is similar to that of embodiment 2, so description thereof will be omitted.

[0093] The cooling mechanism 330 has, for example, a water-cooled jacket through which cooling water flows. The cooling mechanism 330 is attached to the inlet pipe 304. The attachment position of the cooling mechanism 330 is not limited to the inlet pipe 304, and may be the plasma chamber 313 or the like.

[0094] The cooling mechanism 330 cools the introduction pipe 304. This makes it possible to prevent the heat generated by the remote plasma generator 310 from being conducted to the optical system chamber 100. This makes it possible to stabilize the temperature of the optical system chamber 100. This makes it possible to suppress deviation of the optical system 10 due to thermal expansion, etc., making it possible to perform highly accurate inspection.

[0095] The configurations of the first to fourth embodiments may be appropriately combined. For example, the concave mirrors 18 and 19, which are grazing incidence mirrors, may be used in the first, second, and fourth embodiments. Furthermore, both gas and plasma may be introduced. In other words, the introduction part 300 and the introduction part 500 may be connected to the optical system chamber 100.

[0096] Although the embodiments of the present disclosure have been described above, the present disclosure includes appropriate modifications that do not impair the objects and advantages thereof, and is not limited to the above-described embodiments. [Explanation of symbols]

[0097] 1, 2, 3, 4 Inspection equipment 10 Optical system 11 concave mirror 12 concave mirror 13. Recessed mirror 14 Holed concave mirror 14a hole 15 Convex mirror 16 Schwarzschild Optical System 18 concave mirror 19 concave mirror 20 Photodetector 21 Processing equipment 30 Stages 40 Samples 51 Ammeter 52 Power supply 53 Control section 100 Optical chamber 200 Light source chamber 201 Light source 300 Introduction 301 Gas supply source 302 MFC 303 Gas piping 304 Inlet piping 305 Variable Conductance Valve 310 Remote Plasma Generator 311 Coil 312 RF power supply 313 Plasma Chamber 315 Plasma 330 Cooling mechanism 500 Introduction 501 Gas Supply Section 502 MFC 503 Inlet piping L11 irradiation light L12 Detection light

Claims

1. a light source that generates light including EUV light; a chamber in which an object to be irradiated with the light is placed; an optical element disposed within the chamber for directing the light; an introduction part for introducing argon into the chamber; a power supply that applies a negative voltage to the optical element within the chamber; an ammeter that measures an ion current flowing through the optical element; A control unit that controls the amount of argon introduced according to the measurement result of the ammeter; Equipped with The argon introduced into the chamber comprises argon gas; the light source further generates the light including VUV light; a mirror that reflects the VUV light is provided within the chamber; The VUV light reflected by the mirror is incident on the optical element, The VUV light introduced into the chamber converts the argon gas into an argon plasma. optical equipment.

2. The argon introduced into the chamber comprises argon gas; the introduction section includes an introduction pipe connected to the chamber, the control unit controls a flow rate of the argon gas supplied into the chamber through the introduction pipe; The EUV light introduced into the chamber converts the argon gas into argon plasma.

2. The optical device of claim 1.

3. The introduction section is A remote plasma generator that generates argon plasma; an introduction pipe provided between the remote plasma generator and the chamber; A variable conductance valve provided in the inlet pipe; Equipped with the control unit controls the flow rate of the argon plasma supplied into the chamber through the introduction pipe by controlling the conductance of the variable conductance valve.

2. The optical device of claim 1.

4. A cooling mechanism for cooling the inlet pipe is provided.

4. The optical device according to claim 3.

5. The object is an EUV mask having a pellicle.

2. The optical device of claim 1.

6. a light source that generates light including EUV light; a chamber in which an object to be irradiated with the light is placed; an optical element disposed within the chamber for directing the light; A method for preventing contamination of an optical device comprising: introducing argon into the chamber; applying a negative voltage to the optical element within the chamber; measuring an ion current flowing through the optical element; controlling the amount of argon introduced in response to the measurement result of the ion current; Equipped with the light source further generates the light including VUV light; An introduction pipe is connected to the chamber, a mirror that reflects the VUV light is provided within the chamber; The VUV light reflected by the mirror is incident on the optical element, In the step of introducing argon into the chamber, The argon introduced into the chamber comprises argon gas; In the step of controlling the amount of argon introduced in response to the measurement result of the ion current, controlling a flow rate of the argon gas supplied into the chamber through the introduction pipe in response to the measurement result; The VUV light introduced into the chamber converts the argon gas into an argon plasma. A method for preventing contamination of optical devices.

7. An introduction pipe is connected to the chamber, In the step of introducing argon into the chamber, The argon introduced into the chamber comprises argon gas; In the step of controlling the amount of argon introduced in response to the measurement result of the ion current, controlling a flow rate of the argon gas supplied into the chamber through the introduction pipe in response to the measurement result; The EUV light introduced into the chamber converts the argon gas into argon plasma. The method for preventing contamination of an optical device according to claim 6.

8. The optical device comprises: A remote plasma generator that generates argon plasma; an introduction pipe provided between the remote plasma generator and the chamber; A variable conductance valve provided in the inlet pipe; Equipped with In the step of introducing argon into the chamber, the argon introduced into the chamber comprises the argon plasma; In the step of controlling the amount of argon introduced in response to the measurement result of the ion current, a flow rate of the argon plasma supplied into the chamber through the introduction pipe is controlled by controlling the conductance of the variable conductance valve in accordance with the measurement result. The method for preventing contamination of an optical device according to claim 6.

9. A cooling mechanism for cooling the inlet pipe is provided. The method for preventing contamination of an optical device according to claim 8.

10. The object is an EUV mask having a pellicle. The method for preventing contamination of an optical device according to claim 6.

11. a light source that generates light including EUV light; a chamber in which an object to be irradiated with the light is placed; a plurality of optical elements disposed within the chamber for directing the light; a first introduction part for introducing argon into the chamber; a first power supply for applying a negative voltage to a first optical element within the chamber; a first ammeter for measuring an ion current flowing through the first optical element; A first control unit that controls the amount of argon introduced according to a measurement result of the first ammeter; a second introduction section for introducing hydrogen or helium into the chamber; a second power supply that applies a negative voltage to a second optical element within the chamber; a second ammeter that measures an ion current flowing through the second optical element; and a second control unit that controls the amount of hydrogen or helium introduced according to a measurement result of the second ammeter; Equipped with The argon introduced into the chamber comprises argon gas; the first introduction section includes a first introduction pipe connected to the chamber, the first control unit controls a flow rate of the argon gas supplied into the chamber via the first introduction pipe; the light source further generates the light including VUV light; a mirror that reflects the VUV light is provided within the chamber; The VUV light reflected by the mirror is incident on the first optical element, The VUV light introduced into the chamber converts the argon gas into an argon plasma; The second introduction part is A remote plasma generator that generates hydrogen plasma or helium plasma; a second introduction pipe provided between the remote plasma generator and the chamber; a variable conductance valve provided in the second inlet pipe; Equipped with the second control unit controls a flow rate of the hydrogen plasma or the helium plasma supplied into the chamber via the second introduction pipe by controlling a conductance of the variable conductance valve; the first optical element is an optical element that reflects the light traveling while being narrowed; a negative voltage applied to the second optical element is greater than a negative voltage applied to the first optical element; optical equipment.

12. a light source that generates light including EUV light; a chamber in which an object to be irradiated with the light is placed; a plurality of optical elements disposed within the chamber for directing the light; a first introduction part for introducing argon into the chamber; a first power supply for applying a negative voltage to a first optical element within the chamber; a first ammeter for measuring an ion current flowing through the first optical element; A first control unit that controls the amount of argon introduced according to a measurement result of the first ammeter; a second introduction section for introducing hydrogen or helium into the chamber; a second power supply that applies a negative voltage to a second optical element within the chamber; a second ammeter that measures an ion current flowing through the second optical element; and a second control unit that controls the amount of hydrogen or helium introduced according to a measurement result of the second ammeter; A method for preventing contamination of an optical device comprising: introducing argon into the chamber; applying a negative voltage to the first optical element within the chamber; measuring an ion current flowing through the first optical element; controlling the amount of argon introduced according to a measurement result of the first ammeter; introducing hydrogen or helium into the chamber; applying a negative voltage to the second optical element within the chamber; measuring an ion current flowing through the second optical element; controlling the amount of hydrogen or helium introduced in response to a measurement result of the second ammeter; Equipped with A first introduction pipe is connected to the chamber, In the step of introducing argon into the chamber, The argon introduced into the chamber comprises argon gas; In the step of controlling the amount of argon introduced in response to a measurement result of the first ammeter, controlling a flow rate of the argon gas supplied into the chamber via the first introduction pipe in response to the measurement result; the light source further generates the light including VUV light; a mirror that reflects the VUV light is provided within the chamber; The VUV light reflected by the mirror is incident on the first optical element, The VUV light introduced into the chamber converts the argon gas into an argon plasma; The second introduction part is A remote plasma generator that generates hydrogen plasma or helium plasma; a second introduction pipe provided between the remote plasma generator and the chamber; a variable conductance valve provided in the second inlet pipe; Equipped with In the step of controlling the amount of hydrogen or helium introduced in response to the measurement result of the second ammeter, a flow rate of the hydrogen plasma or the helium plasma supplied into the chamber through the second introduction pipe is controlled by controlling the conductance of the variable conductance valve; the first optical element is an optical element that reflects the light traveling while being narrowed; the negative voltage applied to the second optical element is greater than the negative voltage applied to the first optical element; A method for preventing contamination of optical devices.

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