Extreme ultraviolet (EUV) light source device for extreme ultraviolet (EUV) mask inspection

Abstract

To provide an extreme ultraviolet (EUV) light source device for extreme ultraviolet (EUV) mask inspection. [Solution] An EUV light source device for EUV mask inspection comprising: an IR laser source that emits an infrared (IR) laser beam; a focusing lens that focuses the IR laser emitted from the IR laser source; a collector mirror with a hole formed in the center that allows the IR laser focused by the focusing lens to pass through, and which collects the EUV light reflected from the target when the IR laser reacts with the target to generate EUV light; a target supply unit that continuously supplies the liquid target so that the IR laser that has passed through the hole formed in the collector mirror reacts with the liquid target; and a heater unit configured in the collector mirror to heat and evaporate liquid target contaminants deposited on the surface of the collector mirror.

Description

Technical Field

[0001] The present invention relates to an EUV light source device for EUV mask inspection, and more particularly to an EUV light source device for EUV mask inspection applicable to equipment for inspecting an EUV exposure process and a disk EUV mask used in the EUV exposure process.

Background Art

[0002] Recently, EUV exposure machines for manufacturing semiconductor devices using EUV light with a wavelength of 13.5 nm have been fully introduced into the semiconductor manufacturing process. Since an EUV exposure machine uses a shorter wavelength compared to an existing ArF exposure machine with a wavelength of 193 nm, it is said to be advantageous for device miniaturization.

[0003] In the future, it is expected that an EUV exposure machine having a numerical aperture (NA) of 0.55, which is larger than the current 0.33 NA, will be introduced to form a finer pattern with a smaller size.

[0004] And there is also a possibility that an EUV exposure machine using EUV light near 6 nm, which is shorter than the 13.5 nm wavelength in the EUV wavelength region (5 nm to 15 nm), will be introduced into the industry.

[0005] EUV exposure machines currently applied in the industry use an EUV mask as a disk mask for forming a fine pattern. The EUV mask has a structure different from that of an existing ArF (argon fluoride) exposure machine.

[0006] Among them, the biggest difference is that it has been changed from a transmission structure to a reflection structure. Moreover, since the EUV mask has a reflectance optimized for a wavelength of 13.5 nm, applying EUV light as a light source of an inspection machine is advantageous for improving the performance of the inspection device.

[0007] In the manufacturing process of EUV masks, the defect inspection and defect correction processes of the mask disk pattern are the main processes that directly affect wafer yield. This is because any defects in the disk mask are repeatedly transferred to the wafer.

[0008] However, despite the necessity of introducing equipment to inspect EUV masks, the high development costs of the EUV optical system, a core component of the inspection equipment, result in high overall equipment prices and considerably long delivery times. Therefore, there is a need for EUV mask inspection equipment technology and EUV light sources that can reduce the number of EUV optical components and shorten the manufacturing period. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] U.S. Patent No. 9476841 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] To solve the above-mentioned problems, the object of the present invention is to provide an EUV light source device necessary for an EUV exposure machine and an EUV mask inspection machine.

[0011] Another technical problem that the present invention aims to solve is to provide a lithium LPP type EUV light source necessary for EUV exposure machines and EUV mask inspection machines that apply diffractive optical elements.

[0012] Furthermore, another technical problem that the present invention aims to solve is to improve the collection efficiency of EUV light emitted from an EUV light source and to provide a high-performance EUV light source device that is highly mass-producible by maintaining the performance of the collecting mirror for collecting EUV light at the highest level. [Means for solving the problem]

[0013] To achieve the above-mentioned objectives, the present invention comprises an IR laser source that emits an infrared (IR) laser beam; a focusing lens that focuses the IR laser emitted from the IR laser source; a collector mirror with a hole formed in the center to allow the IR laser focused by the focusing lens to pass through, and which collects the EUV light reflected from the target when the IR laser reacts with the target to generate EUV light; a target supply unit that continuously supplies the liquid target so that the IR laser that has passed through the hole formed in the collector mirror reacts with the liquid target; and a heater unit configured in the collector mirror to heat and evaporate liquid target contaminants deposited on the surface of the collector mirror.

[0014] Furthermore, the EUV light source device generates laser plasma by the reaction of the collector mirror equipped with the heater, the IR laser source, and the liquid target within a single chamber.

[0015] Furthermore, the chamber is further equipped with a debris shield to prevent leakage of splashing liquid target contaminants that supply EUV light generated in the collector mirror to the outside.

[0016] Furthermore, the target supply unit comprises a storage container for containing liquid targets, a pump for pumping and supplying the liquid targets contained in the storage container, a transport pipe for transporting the liquid targets pumped via the pump, a heater body for heating the liquid targets transported via the transport pipe to a predetermined temperature, a nozzle for ejecting the liquid targets supplied via the transport pipe, and a capture pipe for capturing the liquid targets ejected from the nozzle and supplying them to the storage container.

[0017] Furthermore, the target supply unit is further provided with a support that supports the liquid target so that the liquid target ejected from the nozzle unit is ejected with a certain thickness and position.

[0018] Furthermore, the liquid target is used as liquid lithium (Li) or a liquid lithium alloy (Li alloy).

[0019] Furthermore, the heater unit is configured to evaporate the liquid target contaminants deposited by heating the collector mirror to 350°C to 600°C.

[0020] Furthermore, the EUV light emitted from the plasma spreads in the range of a 2π steradian solid angle in a direction opposite to the irradiation direction of the laser beam, and an axially symmetric collector mirror having a hole through which the laser irradiation beam can pass at the center is applied to collect as much of the EUV light spreading at the 2π steradian as possible.

[0021] Furthermore, the collector mirror is configured to be coated with a multilayer film capable of reflecting the EUV light.

[0022] Furthermore, the debris shield is configured in a thin film shape with carbon nanotubes (CNTs) or a graphene layer, which are substances containing carbon.

[0023] In addition to these, the nozzle unit continuously supplies the liquid target from the upper part to the lower part in the form of droplets.

Advantages of the Invention

[0024] The present invention configured and operated as described above has the advantage of being able to realize an excellent EUV light source device of the lithium LPP method required for EUV exposure machines and EUV mask inspection machines.

[0025] In particular, there is an effect that the collection efficiency of the EUV light emitted from the EUV light source according to the present invention is increased, and the performance of the collector mirror for collecting the EUV light is maintained at an optimal level to obtain high mass productivity.

Brief Description of the Drawings

[0026] [Figure 1] Schematic configuration diagram of an EUV light source device for EUV mask inspection according to the present invention. [Figure 2] Detailed configuration diagram of an EUV light source device for EUV mask inspection according to the present invention. [Figure 3] Configuration diagram showing a collector mirror in an EUV light source device for EUV mask inspection according to the present invention. [Figure 4] Diagrams of various embodiments of a target supply unit for supplying a liquid target in an EUV light source device for EUV mask inspection according to the present invention. [Figure 5] Configuration diagram of a collector mirror in which a heater unit is integrally formed in an EUV light source device for EUV mask inspection according to the present invention.

Embodiments for Carrying Out the Invention

[0027] Hereinafter, based on the accompanying drawings, an EUV light source device for EUV mask inspection according to the present invention will be described in detail as follows.

[0028] An EUV light source device for EUV mask inspection according to the present invention includes an IR laser source that emits an IR laser beam, a converging lens that converges the IR laser emitted from the IR laser source, a collector mirror that has a hole formed in the center so that the IR laser converged by the converging lens can pass through, and that collects the EUV light reflected from the target when the IR laser reacts with the target to generate EUV light, a target supply unit that continuously supplies the liquid target so that the IR laser passing through the hole formed in the collector mirror reacts with the liquid target, and a heater unit configured on the collector mirror to heat and evaporate the liquid target contaminants deposited on the surface of the collector mirror.

[0029] The EUV light source device for EUV mask inspection according to the present invention is composed of four main parts, each comprising an IR laser irradiation unit, a lithium jet that serves as a target for the IR laser, a light collection device unit that collects the EUV light source generated by the interaction of the IR laser and the Li jet, and a heating device for removing contamination from the light collection device.

[0030] Figure 1 is a schematic diagram of the EUV light source device for EUV mask inspection according to the present invention.

[0031] Specifically, the EUV light source device according to the present invention comprises an IR laser source 1, a focusing lens 2 for focusing the laser beam emitted from the laser source, a liquid target 3 supplied by a jet to generate a laser plasma from the light emitted from the IR laser source 1, and a collector mirror 5 for focusing the EUV light generated via the laser plasma.

[0032] Herein, the main technical component of the present invention is that, in order to prevent target contaminants generated during the laser plasma generation process from the liquid target 3 from being deposited and contaminating the surface of the collector mirror that focuses the EUV light, the collector mirror is configured with at least one heater section 6, and the collector mirror can be heated overall via the heater section to heat and evaporate the deposited target material, thereby ensuring the focusing efficiency of the collector mirror and enabling the continuous generation of the highest level of EUV light (wavelength 10-14 nm).

[0033] The IR laser source 1 according to the present invention is preferably used as an IR laser source, and in the present invention, when EUV light 4 generated by a plasma reaction through a liquid target is focused and reflected by the on-axial structure when it is supplied to the application.

[0034] To achieve this, in the present invention, when a laser is irradiated onto a lithium target (liquid target) to collect EUV light from the generated plasma, a collector mirror 5, which corresponds to a light collecting mirror, is applied. In the present invention, a hole is drilled in the center of the collector mirror to allow the laser irradiating the target to pass through, and the other regions are configured to collect EUV light emitted from the target over the widest possible solid angle range.

[0035] This method expands the range of solid angles that can be collected compared to existing off-axis collecting microscopes, and allows for the transmission of even more light to the optical systems of inspection and exposure machines.

[0036] Therefore, the EUV light collected by the collector mirror 5 ultimately irradiates the application with focused EUV light 7.

[0037] EUV light is emitted from a Li plasma generated by focusing an IR laser onto a Li material. These conditions must be achieved continuously and stably.

[0038] In this invention, a liquid target is provided in the form of a jet to stably form a consistent Li target. To create stable lithium target conditions, lithium is heated to liquefy it, and a pump using the electromagnetic principle is used to form the conductive metallic lithium liquid into a target in the form of a jet. This pump is used to create pressure in the liquid lithium pipe, causing the jet to be ejected through a nozzle as it is formed. Through this process, lithium targets of a constant thickness are continuously formed at a constant position.

[0039] Furthermore, it is necessary to be able to effectively process the debris generated when the IR laser and the lithium liquid target interact to produce EUV light. If the debris accumulates on the collector mirror 5, the reflectivity of the collecting mirror will decrease, and the collecting mirror must be replaced or the debris on the surface removed immediately.

[0040] In this invention, a special EUV reflective layer that can withstand high temperatures is coated on the collector mirror 5, and the collector mirror is raised to a temperature at which lithium vaporizes so that the surface is always kept clean.

[0041] Therefore, in this invention, a heater unit 6 is configured in the collector mirror 5, and by heating the liquid target within a temperature range in which the liquid target can vaporize to remove liquid target contaminants deposited on its surface, stable generation of EUV light can be achieved. In other words, a configuration is adopted in which heat is transmitted to the collector mirror 5 itself to vaporize and remove contaminants contaminating the surface of the mirror.

[0042] Figure 2 is a detailed configuration diagram of the EUV light source device for EUV mask inspection according to the present invention, and Figure 3 is a configuration diagram showing the collector mirror in the EUV light source device for EUV mask inspection according to the present invention.

[0043] In this invention, a liquid target supply unit is configured to continuously supply the liquid target by a jet system, as a method for inducing a laser plasma reaction with a constant thickness and width.

[0044] As mentioned above, an electromagnetic pump is used to form a target from conductive metallic lithium liquid in the form of a jet. This pump creates pressure in the liquid lithium pipe, causing the jet to be ejected through a nozzle and formed. Through this process, lithium targets of a certain thickness are continuously formed at a fixed position.

[0045] Furthermore, to prevent debris from moving when the light source is transmitted from the light source device to the inspection machine or exposure machine optical system, a debris shield 15 is applied between them. The debris shield is mainly composed of a thin carbon-based film made of CNTs or graphene, and is also heated by methods such as passing an electric current through it to remove contamination by evaporation.

[0046] In the present invention, a target supply unit is configured for supplying a liquid target. The target supply unit is a supply system for continuously supplying liquid lithium by jet, and comprises a storage container 12, a pump 14, a transport pipe 17, and a nozzle 10.

[0047] Furthermore, a capture tube 11 for capturing the liquid lithium ejected from the nozzle 10 again at the lower side, and a heater body 13 are partially provided in the transport tube 17 so that the liquid lithium can be supplied while being kept in a liquid state.

[0048] Therefore, the liquid lithium contained in the storage container 12 is transmitted to the transport pipe 17 via the pump 14 and ejected through the nozzle 10, at which point it triggers a plasma reaction with the focused laser beam to generate EUV light.

[0049] In the present invention, preferably, the liquid target 3 is liquid lithium or liquid lithium alloy. In order for the liquid target to be kept in a liquid state, the nozzle 10 and the capture tube 11 must be kept at 180°C to 350°C by their respective heaters. The melting point of lithium is 180.5°C.

[0050] The liquid target ejected from the nozzle 10 is exposed to a vacuum chamber, then captured again by the target capture tube 11, and finally collected again in a storage container.

[0051] In this case, the liquid target ejected from the nozzle 10 may be configured to flow through the support 18, which is the rear wall, and into the capture tube. The support 18 is configured to stabilize the thickness and position of the target as the liquid target flows through it.

[0052] This method has the advantage of being able to form a stable target for a high-brightness EUV light source by applying a jet-type liquid target and inducing a laser-plasma reaction.

[0053] On the other hand, the EUV light source device according to the present invention generates EUV light by configuring its components in a single chamber 8, and the generated light is transmitted to an external chamber 16 via a debris shield 15 to be used as EUV light.

[0054] In other words, the focused EUV light 7 collected by the collector mirror is transmitted to the destination of the light via the debris shield 15. The debris shield 15 is made up of carbon nanotubes (CNTs), which are carbon-containing materials, or a thin film with a graphene layer, and is heated by passing an electric current through it to maintain a temperature of 350°C or higher, thereby evaporating lithium contaminants.

[0055] The collector's collection efficiency can be maintained at a high level by evaporating the target material (debris) that can form on the surface of the collector mirror 5 heated by the heater unit 6.

[0056] Figure 4 shows various embodiments of the target supply unit that supplies a liquid target in an EUV light source device for EUV mask inspection according to the present invention.

[0057] As described above, when the liquid target is ejected from the nozzle, a separate support 18 can be provided to maintain a constant thickness and position of the liquid target. However, in case (A), the structure is such that the liquid target, which is the capture tube 11 ejected from the nozzle, flows directly into the support without the support. (B) and (C) show the support 18 in a configuration, with a side view and a front view. The support 18 plays a role in supporting the liquid target so that it can be ejected with a stable position and thickness.

[0058] Alternatively, as shown in (D), the support 18 may be formed to have a bending structure with a predetermined radius. The liquid target is configured to flow down stably through the bending structure of the support 18.

[0059] Furthermore, the present invention enables the provision of a liquid target using a droplet method. In the above description, the shape of a jet continuously supplying liquid from the top to the bottom of the liquid target has been given as one example, but in the present invention, the liquid target can be supplied in the shape of a droplet, which is a small water droplet that is continuously supplied from the top to the bottom.

[0060] Such a droplet system can be implemented by continuously dropping small, droplet-shaped liquid targets from top to bottom through a nozzle to supply the liquid target. In this method, the droplet size and supply rate can be determined by appropriately adjusting the discharge rate from the nozzle.

[0061] Figure 5 is a diagram showing the configuration of a collector mirror in an EUV light source device for EUV mask inspection according to the present invention, in which the heater section is formed as an integrated unit.

[0062] Figure 5 shows an example of a mount for applying a heater unit 6 to a collector mirror 5 according to the present invention. A mount 5-1 with a structure that encloses a circular collector mirror 5 is assembled, and a number of heater units 6 are attached to the surface of the mount, thereby transferring heat to the collector mirror.

[0063] In this invention, when heat is applied via the heater unit 6, the distribution of heat transmitted to the collector mirror is measured to complete the stability evaluation. The collector mirror is heated to 350°C to 600°C via the heater unit 6 to evaporate the deposited liquid target contaminant.

[0064] The present invention, configured in this manner, has the advantage of realizing an excellent lithium-LPP type EUV light source device necessary for EUV exposure machines and EUV mask inspection machines.

[0065] In particular, the present invention has the effect of increasing the collection efficiency of EUV light emitted from the EUV light source, maintaining the performance of the EUV light collecting mirror at an optimal level, and achieving high mass productivity.

[0066] Although the principles of the present invention have been described and illustrated in conjunction with preferred embodiments to illustrate them, the present invention is not limited in any way to the configuration and operation as so illustrated and described. Rather, it should be readily apparent to those skilled in the art that numerous changes and modifications to the present invention are possible without departing from the spirit and scope of the appended claims. Accordingly, all such appropriate changes and modifications and their equivalents should also be considered to fall within the scope of the present invention. [Explanation of Symbols]

[0067] 1: IR laser source 2: Focusing lens 3:Liquid target 4: EUV light 5: Collector's Mirror 6: Heater section 7: Focused EUV light 8: Chamber 9: Window 10: Nozzle 11: Capture tube 12: Storage containers 13: Heater body 14: Pump 15: Debris Shield 16: External Chamber 17: Conveyor pipe 18:Support

Claims

1. An infrared (IR) laser source that emits an infrared (IR) laser beam, A focusing lens that focuses the infrared (IR) laser emitted from the aforementioned infrared (IR) laser source, A hole is formed in the center of the focusing lens so that the focused infrared (IR) laser can pass through, and when the infrared (IR) laser reacts at the target and generates extreme ultraviolet (EUV) light, a collector mirror is provided to collect the extreme ultraviolet (EUV) light reflected from the target, A target supply unit that continuously supplies the liquid target so as to react the infrared (IR) laser that has passed through the holes formed in the collector mirror with the liquid target, A heater unit is provided in the collector mirror to heat and evaporate the liquid target contaminant deposited on the surface of the collector mirror, An extreme ultraviolet (EUV) light source device for extreme ultraviolet (EUV) mask inspection, comprising the following:

2. The aforementioned extreme ultraviolet (EUV) light source device is An extreme ultraviolet (EUV) light source device for extreme ultraviolet (EUV) mask inspection according to claim 1, wherein the collector mirror equipped with the heater, the infrared (IR) laser source, and a liquid target react within a single chamber to generate a laser plasma.

3. The aforementioned chamber An extreme ultraviolet (EUV) light source device for extreme ultraviolet (EUV) mask inspection according to claim 2, further comprising a debris shield to prevent leakage of splashing liquid target contaminants that supply extreme ultraviolet (EUV) light generated in the collector mirror to the outside.

4. The aforementioned target supply unit is A storage container for containing a liquid target, A pump for pumping and supplying the liquid target contained in the storage container, A transport pipe for transporting a liquid target pumped via the aforementioned pump, A heater body that heats a liquid target being transported via the transport pipe to a predetermined temperature, A nozzle unit that ejects a liquid target supplied via the aforementioned transport pipe, A capture tube that captures the liquid target ejected from the nozzle and supplies it to the storage container, An extreme ultraviolet (EUV) light source device for extreme ultraviolet (EUV) mask inspection according to claim 1, comprising the above.

5. The aforementioned target supply unit is The extreme ultraviolet (EUV) light source device for extreme ultraviolet (EUV) mask inspection according to claim 4, further comprising a support for supporting a liquid target so that the liquid target ejected from the nozzle portion is ejected with a constant thickness and position.

6. The aforementioned liquid target is An extreme ultraviolet (EUV) light source device for extreme ultraviolet (EUV) mask inspection according to claim 1, used as liquid lithium (Li) or liquid lithium alloy (Li alloy).

7. The aforementioned heater section is An extreme ultraviolet (EUV) light source device for extreme ultraviolet (EUV) mask inspection according to claim 1, configured to heat the collector mirror to 350°C to 600°C to evaporate the deposited liquid target contaminant.

8. The extreme ultraviolet (EUV) light emitted from the plasma spreads in the direction opposite to the irradiation direction of the laser beam within a range of 2pi SR (steradian) solid angle. An extreme ultraviolet (EUV) light source device for extreme ultraviolet (EUV) mask inspection according to claim 1, wherein an axially symmetric collector mirror with an axial structure having a hole in the center through which a laser irradiation beam can pass is applied in order to capture as much extreme ultraviolet (EUV) light as possible that spreads in the 2pi SR.

9. The extreme ultraviolet (EUV) light source device for extreme ultraviolet (EUV) mask inspection according to claim 1, wherein the collector mirror is configured to be coated with a multilayer capable of reflecting the extreme ultraviolet (EUV) light.

10. The aforementioned debris shield is An extreme ultraviolet (EUV) light source device for extreme ultraviolet (EUV) mask inspection according to claim 3, comprising carbon nanotubes (CNTs), which are carbon-containing materials, or a thin film with a graphene layer.

11. The nozzle portion is An extreme ultraviolet (EUV) light source device for extreme ultraviolet (EUV) mask inspection according to claim 4, wherein the liquid target is continuously supplied in a droplet-like manner from the top to the bottom.

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