Flushing system and method for a lithographic apparatus

Abstract

A flushing system for a lithographic apparatus is provided, the flushing system including a gas outlet configured to choke a flow of gas through the gas outlet at a predetermined rate. A method of flushing a lithographic apparatus is also provided, the method comprising providing a flow of gas through the lithographic apparatus and operating the gas outlet such that the flow of gas from the lithographic apparatus through the gas outlet is choked.

Description

[Technical Field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims priority to European Application No. 22213693.9, filed December 15, 2022, which is incorporated herein by reference in its entirety.

[0002] [Technical field] The present disclosure relates to a flushing system for a lithographic apparatus, in particular for an EUV lithographic apparatus. The present disclosure also relates to a method for flushing a lithographic apparatus, a lithographic apparatus including such a flushing system, and the use of such a flushing system, lithographic apparatus, or flushing method in a lithographic process or lithographic apparatus. [Background technology]

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). For example, a lithographic apparatus may project a pattern from a patterning device (e.g. a mask) onto a layer of radiation-sensitive material (resist) provided on the substrate.

[0004] The wavelength of the radiation used by a lithographic apparatus to project a pattern onto a substrate determines the minimum size of features that can be formed on the substrate. Lithographic apparatus that use EUV radiation, which is electromagnetic radiation having a wavelength in the range of 4-20 nm, can be used to form smaller features on a substrate than conventional lithographic apparatus (which may, for example, use electromagnetic radiation having a wavelength of 193 nm).

[0005] A lithographic apparatus includes a patterning device (e.g. a mask or reticle). Radiation is transmitted through or reflected from the patterning device to form an image on a substrate. A membrane assembly, also called a pellicle, may be provided to protect the patterning device from airborne particles and other forms of contamination. Contamination on the surface of the patterning device can cause manufacturing defects in the substrate.

[0006] Because lithography equipment requires extremely high precision to efficiently form images on a substrate, it is important to keep the interior of the lithography equipment clean. Over time, contaminants can build up inside the equipment, so the interior of the lithography equipment needs to be cleaned periodically. One way to do this is to provide a flow of gas through the equipment. The gas flow allows contaminants to be removed from the interior of the lithography equipment and prevents them from adversely affecting the operation of the lithography equipment.

[0007] Although flushing is a critical requirement, the flushing process takes time to complete, during which the lithography apparatus cannot operate and cannot image wafers, thereby reducing the uptime of the lithography apparatus. It is therefore desirable to reduce the downtime required for flushing of the lithography apparatus. Furthermore, it is important that the flushing process is consistent and predictable so that the effectiveness of the flushing can be guaranteed.

[0008] The present invention has been devised to solve at least some of the problems identified above. Summary of the Invention [Problem to be solved by the invention]

[0009] According to a first aspect of the present disclosure, there is provided a flushing system for a lithographic apparatus, the flushing system including a gas outlet configured to choke (throttle) a flow of gas through the gas outlet at a predetermined rate.

[0010] When flushing a lithography apparatus, a gas outlet is connected to a pump, such as a turbomolecular pump, via a so-called customer interface. The gas flows through the lithography apparatus to remove contaminants. The gas exits the gas outlet and is removed by a pump in fluid communication with the customer interface. The pump is separate from the lithography apparatus, and the quality of the vacuum provided by such a pump varies from location to location. Proper gas flow within the lithography apparatus must be ensured to prevent contaminant deposition on critical optical elements, such as mirrors, reticles, and wafer stages. Therefore, tight control of the flow within the lithography apparatus is useful. The present disclosure enables the gas flow within the lithography apparatus to be independent of the quality of the customer's pump. This is achieved by configuring the apparatus so that the gas flow is choked. When the gas flow is choked, the gas flow rate depends on the gas properties and the outlet through which the gas flows. Therefore, the gas flow rate can be independent of the quality of the customer's pump. For example, without choked flow, a weak pump will have a low flow rate of gas exhausted from the lithography apparatus, while a more powerful pump will have a high flow rate. Thus, without choked flow, the flushing process must be conservatively selected to accommodate all pump specifications and ensure that even pumps that meet minimal requirements can effectively flush the lithography apparatus. As a result, the flushing process is not optimized. In the present disclosure, the flow rate is decoupled from the quality of the customer's pump, allowing the flushing process to be optimized and improving flushing consistency across all lithography apparatuses. Furthermore, the flushing speed requirement is strict due to the need to accommodate a wide range of customer pumps. Furthermore, a large portion of the time required for the flushing process is dependent on the ramp-up and ramp-down of the slow-acting mass flow controllers. Increasing the time required for the mass flow controllers to ramp up and down increases the time required for the flushing process and the downtime of the lithography apparatus.

[0011] The system may include a controller configured to control the gas outlet. The gas outlet may be variable to control a desired choked condition. For example, in some cases, it may be necessary to prevent the flow from becoming choked, and in such cases, the outlet may be controlled to allow the gas flow to exit the outlet without becoming choked. Similarly, if the gas flow is not constant, the controller may control the outlet to accommodate different gas flow rates while still providing a choked flow at the outlet. For example, the controller may control the opening of the outlet to control the choked condition.

[0012] The flushing system may include one or more pilot valves configured to selectively open and close. Selectively opening and closing the one or more pilot valves may generate pressure fluctuations in the gas flow. The pilot valves may be configured to open at a predetermined pressure. The pilot valves may be configured to open and close via a solenoid. The opening and closing of the valves may be controlled by a controller. The frequency and / or duty cycle of the pilot valves may be predetermined depending on the desired flushing parameters. The pressure fluctuations may more effectively remove contaminants, thus speeding up the flushing process and / or making the flushing process more thorough. Any suitable pilot valve may be used. Because the gas flow is choked at the gas outlet, the pilot valves may operate more quickly than currently used mass flow controllers. Furthermore, the flushing process may be more easily controlled.

[0013] The flushing system may be configured to provide a gas flow rate of about 20 normal liters per minute (nlm) to about 700 nlm, optionally about 100 nlm, about 200 nlm, about 300 nlm, about 400 nlm, about 500 nlm, or about 600 nlm.

[0014] The flushing system may be configured to provide a pressure within the lithographic apparatus of up to 2000 Pa, up to 1500 Pa, up to 1000 Pa, up to 500 Pa, up to 250 Pa, or up to 100 Pa. The pressure within the lithographic apparatus needs to be controlled to prevent damage to components within the apparatus, such as the pellicle or dynamic gas lock membrane. By having a choked flow at the outlet, the flow rate of gas exiting the apparatus is choked to a predetermined level, making it easier to control the pressure within the apparatus during flushing.

[0015] The flushing system may be configured to operate at a constant gas flow rate. By providing a constant gas flow rate, time-consuming filling and evacuating of piping is avoided.

[0016] According to a second aspect of the present disclosure, there is provided a method of flushing a lithographic apparatus, the method comprising providing a flow of gas through the lithographic apparatus, and operating a gas outlet such that the flow of gas through the gas outlet from the lithographic apparatus is choked.

[0017] As described in relation to the first aspect of the present disclosure, the gas flow choked outlet allows the flow within the lithographic apparatus to be decoupled from the quality of the pump being used to extract gas from the lithographic apparatus.

[0018] The method may comprise providing a gas flow through the lithographic apparatus of about 20 nlm to about 700 nlm, optionally about 100 nlm, about 200 nlm, about 300 nlm, about 400 nlm, about 500 nlm, or about 600 nlm.

[0019] The method may include providing the flow of gas at a constant rate. Providing the gas at a constant rate reduces the need for a controller and makes the flushing process more consistent.

[0020] The method may include generating pressure pulses in the gas flow. The method may include generating pressure pulses in the gas flow by opening and closing one or more pilot valves. These valves can operate faster than previous systems using mass flow controllers because they do not need to precisely control the flow rate of gas, but rather only vary the amount allowed to flow out of the lithographic apparatus to change the pressure within the apparatus. Furthermore, greater control allows for lower flow rates to be used within the system, reducing the requirements for accessories needed to control flow rates, thereby saving space and cost.

[0021] According to a third aspect of the present disclosure, there is provided a lithographic apparatus including a flushing system according to the first aspect of the present disclosure.

[0022] According to a fourth aspect of the present disclosure, there is provided use of a flushing system according to the first aspect of the present disclosure, a lithographic apparatus according to the third aspect of the present disclosure, or a method according to the second aspect of the present disclosure in a lithographic method or lithographic apparatus.

[0023] It will be understood that features described with respect to one embodiment may be combined with any features described with respect to another embodiment, and all such combinations are expressly contemplated and disclosed herein. [Brief explanation of the drawings]

[0024] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0025] [Figure 1] 1 depicts a lithographic apparatus according to an embodiment of the present disclosure;

[0026] [Figure 2] 1 shows a schematic diagram of a system according to certain aspects of the present disclosure.

[0027] [Figure 3] 1 illustrates an exemplary flushing cycle.

[0028] The features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the drawings, in which like reference numbers indicate corresponding elements and in which like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. DETAILED DESCRIPTION OF THE INVENTION

[0029] Figure 1 shows a lithography system according to the present invention. The lithography system comprises a radiation source SO and a lithography apparatus LA. The radiation source SO is configured to generate a beam of extreme ultraviolet (EUV) radiation B. The lithography apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g., a mask), a projection system PS, and a substrate table WT configured to support a substrate W. The illumination system IL is configured to condition the radiation beam B before it is incident on the patterning device MA. The projection system is configured to project the radiation beam B (patterned by the mask MA) onto the substrate W. The substrate W may contain a pre-formed pattern. In this case, the lithography apparatus aligns the patterned radiation beam B with the pattern pre-formed on the substrate W. In this embodiment, a pellicle 15 is depicted in the path of the radiation to protect the patterning device MA. It will be appreciated that the pellicle 15 may be positioned at any required position and may also be used to protect any mirrors in the lithography apparatus.

[0030] The source SO, illumination system IL and projection system PS may all be constructed and arranged so as to be isolated from the external environment. The source SO may be provided with a gas (e.g. hydrogen) at a pressure below atmospheric pressure. The illumination system IL and / or projection system PS may be provided with a vacuum. The illumination system IL and / or projection system PS may be provided with a small amount of gas (e.g. hydrogen) at a pressure much lower than atmospheric pressure.

[0031] The radiation source SO shown in FIG. 1 is of a type called a laser-produced plasma (LPP) source. A laser, which may be, for example, a CO laser, is configured to impart energy via a laser beam to a fuel, such as tin (Sn), provided from a fuel emitter. While the following description refers to tin, any suitable fuel may be used. The fuel may be, for example, a liquid, or may be, for example, a metal or alloy. The fuel emitter may include a nozzle configured to direct tin, for example, in the form of droplets, along a trajectory toward the plasma formation region. The laser beam is incident on the tin in the plasma formation region. The application of laser energy to the tin generates a plasma in the plasma formation region. Radiation, including EUV radiation, is emitted from the plasma during de-excitation and recombination of the ions of the plasma.

[0032] The EUV radiation is collected and focused by a near-normal incidence radiation collector (sometimes more commonly referred to as a normal incidence radiation collector). The collector may have a multi-layer structure arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength, such as 13.5 nm). The collector may have an elliptical configuration with two elliptical foci. The first focus may be located in the plasma formation region, and the second focus may be located at an intermediate focus, as described below.

[0033] The laser may be separate from the radiation source SO. In this case, the laser beam may be transmitted from the laser to the radiation source SO with the aid of a beam delivery system (not shown), e.g., comprising appropriate directing mirrors, and / or beam expanders, and / or other optics. The laser and radiation source SO may together be considered a radiation system.

[0034] The radiation reflected by the collector forms a radiation beam B. The radiation beam B is focused to a point that forms an image of the plasma formation region and acts as a virtual radiation source for the illumination system IL. The point at which the radiation beam B is focused may be referred to as the intermediate focus. The radiation source SO is positioned such that the intermediate focus is located at or near an opening in an enclosing structure of the radiation source.

[0035] The radiation beam B passes from the radiation source SO to an illumination system IL configured to condition the radiation beam. The illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. Together, the facetted field mirror device 10 and the facetted pupil mirror device 11 provide the radiation beam B with a desired cross-sectional shape and a desired angular distribution. Having passed through the illumination system IL, the radiation beam B is incident on a patterning device MA, which is held by a support structure MT. The patterning device MA reflects and patterns the radiation beam B. The illumination system IL may include other mirrors or devices in addition to, or instead of, the facetted field mirror device 10 and the facetted pupil mirror device 11.

[0036] After being reflected from the patterning device MA, the patterned radiation beam B is incident on a projection system PS. The projection system comprises a number of mirrors 13, 14 arranged to project the radiation beam B onto a substrate W held by a substrate table WT. The projection system PS may apply a demagnification factor to the radiation beam to form an image having smaller features than corresponding features on the patterning device MA. For example, a demagnification factor of 4 may be applied. Although in Figure 1 the projection system PS comprises two mirrors 13, 14, the projection system may include any number of mirrors (for example six mirrors).

[0037] The radiation source SO shown in Figure 1 may include components not shown. For example, the radiation source may be provided with a spectral filter that substantially transmits EUV radiation but substantially blocks radiation of other wavelengths, such as infrared radiation.

[0038] In one embodiment, the membrane assembly 15 is a pellicle for a patterning device MA for EUV lithography. The membrane assembly 15 can be used as a dynamic gas lock, a pellicle, or in other applications. In one embodiment, the membrane assembly 15 includes a membrane formed from at least one thin film layer having an emissivity of 0.3 or greater. To maximize EUV transmittance and minimize impact on imaging performance, the membrane is preferably supported only at the edges.

[0039] If the patterning device MA is left unprotected, contamination can result in the need to clean or discard the patterning device MA. Cleaning the patterning device MA interrupts valuable production time, and discarding the patterning device MA is costly. Replacing the patterning device MA also interrupts valuable production time. The disclosed system enables fast, consistent, and effective cleaning of the interior of a lithographic apparatus.

[0040] FIG. 2 is a schematic diagram of a lithographic apparatus including a flushing system according to the present disclosure. An inlet flow 16 for gas entering the lithographic apparatus LA is provided. An outlet 17 is also provided through which gas can be exhausted from the lithographic apparatus. A pump 18, which does not form part of the lithographic apparatus but is provided at a customer site for attachment to the lithographic apparatus, is fluidly connected to the outlet 17 and functions to remove gas from the lithographic apparatus. The outlet 17 is configured to choke the flow of gas at the operating parameters of the lithographic apparatus during flushing. As mentioned above, the choke flow decouples the flow of gas within the lithographic apparatus from a particular pump that is attached to the lithographic apparatus during use. The lithographic apparatus LA may also include one or more pilot valves (not shown) configured to open and close to generate pressure variations within the lithographic apparatus to assist in the removal of contaminants.

[0041] FIG. 3 illustrates an exemplary flushing cycle. As can be seen, the pressure within the lithography apparatus is varied periodically to remove contaminants and clear them from the lithography apparatus. During each cycle, the gas flow may be constant or may vary. Alternatively, or additionally, pressure pulses may be introduced by opening or closing one or more pilot valves. Because the outlet flow is choked and the pressure is decoupled from the customer interface pressure, greater flexibility in pressure selection may be achieved to optimize the flushing procedure, resulting in more effective flushing and a cleaner apparatus. In this way, not only are each cycle faster, but each cycle is also more effective at cleaning, allowing for fewer cycles and further saving additional time.

[0042] Table 1 shows some exemplary operating parameters for a system according to the present disclosure. [Table 1]

[0043] An exemplary system includes two valves that can be controlled by a controller. In a first option, the flow rate is 300 nlm, which can be split into two separate streams: a first stream of approximately 200 nlm for flushing and a second stream of approximately 100 nlm for flow stabilization. The first valve is opened sufficiently to provide a choking flow, and the second valve (which is more restrictive when open) is closed. In a second option, a smaller gas flow rate of 200 nlm can be used. In this option, the first valve can be closed and a second, smaller valve can be opened sufficiently to provide a choking flow. The smaller valve can be used to allow for a smaller flow rate. In a third option, a pilot valve is used to provide a pressure pulse, and the choking flow can be provided according to either the first or second option. In the third option, one or more mass flow controllers can maintain a fixed flow rate, eliminating the time required to repeatedly charge and discharge gas within the piping.

[0044] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

[0045] The above description is given by way of example and not by way of limitation, and it will be apparent to one skilled in the art that various modifications may be made to the present invention without departing from the scope of the appended claims.

Claims

1. 1. A flushing system for a lithographic apparatus, comprising: the flushing system includes a gas outlet configured to choke the flow of gas through the gas outlet at a predetermined rate; Flushing system.

2. the flushing system including a controller configured to control the gas outlet; The flushing system of claim 1 .

3. the flushing system includes one or more pilot valves configured to selectively open and close; The flushing system according to claim 1 or 2.

4. the flushing system is configured to provide a gas flow rate of about 20 nlm to about 700 nlm, optionally about 100 nlm, about 200 nlm, about 300 nlm, about 400 nlm, about 500 nlm, or about 600 nlm; A flushing system according to any one of claims 1 to 3.

5. the flushing system is configured to provide a pressure in the lithographic apparatus of up to 2000 Pa, up to 1500 Pa, up to 1000 Pa, up to 500 Pa, up to 250 Pa, or up to 100 Pa; A flushing system according to any one of claims 1 to 4.

6. the flushing system is configured to operate at a constant gas flow rate; A flushing system according to any one of claims 1 to 5.

7. 1. A method of flushing a lithographic apparatus, comprising the steps of: The method comprises providing a flow of gas through a lithographic apparatus; and operating a gas outlet from the lithographic apparatus such that the flow of gas through the gas outlet is choked. method.

8. The method comprises providing a gas flow through the lithographic apparatus of about 20 nlm to about 700 nlm, optionally about 100 nlm, about 200 nlm, about 300 nlm, about 400 nlm, about 500 nlm, or about 600 nlm; The method of claim 7.

9. The method includes providing a flow of gas at a constant flow rate; 9. The method according to claim 7 or 8.

10. The method includes generating a pressure pulse in the gas flow.

10. The method according to any one of claims 7 to 9.

11. the pressure pulses are generated by opening and closing one or more pilot valves; The method of claim 10.

12. 7. A flushing system comprising: a flushing system according to any one of claims 1 to 6; Lithography equipment.

13. Use of a flushing system according to any one of claims 1 to 6, a lithographic apparatus according to claim 12 or a method according to any one of claims 7 to 11 in a lithographic method or lithographic apparatus.

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