Rinse system and method for lithographic apparatus

Abstract

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

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to EP application 22213693.9 filed on December 15, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to a flushing system for a lithographic apparatus, in particular an EUV lithographic apparatus, a method for flushing a lithographic apparatus, a lithographic apparatus comprising the flushing system, and the use of the flushing system, lithographic apparatus or flushing method in a lithographic process or apparatus. Background Art

[0004] A lithographic apparatus is a machine configured to apply a desired pattern to a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can, for example, project a pattern from a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) disposed on a substrate.

[0005] The wavelength of radiation used by a lithographic apparatus to project a pattern onto a substrate determines the minimum size of features that can be formed on that substrate. A lithographic apparatus using 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 a conventional lithographic apparatus (which may, for example, use electromagnetic radiation having a wavelength of 193 nm).

[0006] A lithographic apparatus includes a patterning device (e.g., a mask or reticle). Radiation is provided to or reflected from the patterning device to form an image on a substrate. A film assembly (also referred to as 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 lead to manufacturing defects on the substrate.

[0007] Due to the extremely high precision required for lithographic equipment to effectively form an image on a substrate, it is important to keep the interior of the lithographic equipment clean. Over time, contaminants may accumulate within the equipment during use, necessitating regular cleaning of the interior of the lithographic equipment. One way to achieve this is to provide an airflow through the equipment. This airflow removes contaminants from the interior of the lithographic equipment, thereby preventing these contaminants from adversely affecting the operation of the lithographic equipment.

[0008] While rinsing is a crucial requirement, the rinsing process takes time to complete, and during this time, the lithography equipment cannot operate and image wafers. This reduces the uptime of the lithography equipment. Therefore, it is desirable to reduce the downtime required to rinse the lithography equipment. Furthermore, it is important that the rinsing process is consistent and predictable to ensure the effectiveness of the rinse.

[0009] The present invention is designed to address at least some of the above-mentioned problems. Summary of the Invention

[0010] According to a first aspect of the present disclosure, there is provided a flushing system for a lithographic apparatus, the flushing system comprising a gas outlet configured to block a flow of gas through the gas outlet at a predetermined rate.

[0011] When flushing a lithographic apparatus, a gas outlet is connected to a pump, such as a turbomolecular pump, via a so-called user interface. Gas flows through the lithographic apparatus to remove contaminants. Gas flows out of the gas outlet and is carried away by a pump in fluidic communication with the user interface. The pump is separate from the lithographic apparatus, and the quality of the vacuum provided by such a pump varies with location. It is necessary to ensure that the gas flow within the lithographic apparatus is adequate to prevent contaminants from depositing on critical optical components such as mirrors, reticles, or wafer stages. Therefore, careful control of the flow within the lithographic apparatus is essential. The present disclosure allows the gas flow within the lithographic apparatus to be independent of the quality of the user's pump. This is achieved by configuring the apparatus so that the gas flow can be blocked. When the gas flow is blocked, the gas flow rate depends on the properties of the gas and the outlet through which the gas flows. Thus, the gas flow can be made independent of the quality of the user's pump. For example, without blocked flow, a weaker pump will result in a lower gas flow rate leaving the lithographic apparatus, while a more powerful pump will result in a higher gas flow rate. Thus, without blocked flow, the flushing process needs to be selected to accommodate all pump specifications and be conservative, so that even a pump that meets only the minimum requirements can effectively flush the lithographic apparatus. Therefore, the flushing process is not optimal. Because the present disclosure decouples the flow rate from the quality of the user's pump, the flushing process can be optimized and made more consistent across all lithographic equipment. Moreover, due to the need to accommodate a wide range of user pumps, flushing rate requirements are stringent. Furthermore, the majority of the time spent in the flushing process involves spooling up and down the mass flow controller, as these operations are slow. The additional time spent spooling up and down the mass flow controller causes the flushing process to take longer, thereby increasing downtime of the lithographic equipment.

[0012] The system may include a controller configured to control the gas outlet. The gas outlet may be variable, thereby controlling the desired obstruction. For example, in some cases, the airflow may not need to be obstructed, and in such cases, the outlet may be controlled to allow the airflow to exit the outlet without obstruction. Similarly, in cases where the airflow is not constant, the controller may control the outlet to accommodate different airflow rates while still providing an obstructed flow at the outlet. For example, the controller may control the degree to which the outlet is opened to control obstruction.

[0013] The flushing system may include one or more pilot valves configured to selectively open and close. By selectively opening and closing one or more pilot valves, pressure fluctuations in the gas flow can be induced. The pilot valves may be configured to open at a predetermined pressure. The pilot valves may be configured to be opened and closed by 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 based on the desired flushing parameters. Pressure fluctuations allow for more efficient removal of contaminants and may therefore accelerate and / or make the flushing process more thorough. Any suitable pilot valve may be used. Because the gas flow is blocked at the gas outlet, the pilot valves can operate more quickly than currently used mass flow controllers. This further allows for easier control of the flushing process.

[0014] The flushing system can be configured to provide a gas flow rate from about 20 standard 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.

[0015] The flushing system can 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. It is desirable to control the pressure within the lithographic apparatus to avoid damage to components therein, such as membranes or dynamic gas lock membranes. By having a blocked flow at the outlet, it is easier to control the pressure within the apparatus during flushing because the gas flow rate leaving the apparatus is blocked at a predetermined level.

[0016] The flushing system can be configured to operate at a constant gas flow rate. By providing a constant gas flow rate, there is no need to wait for the lines to be filled and drained of gas, which is time consuming.

[0017] According to a second aspect of the present invention, 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 from the lithographic apparatus such that the flow of gas through the gas outlet is blocked.

[0018] As described in relation to the first aspect of the invention, a blocked outlet for gas flow allows the gas flow within the lithographic apparatus to be decoupled from the mass of the pump used to extract gas from the lithographic apparatus.

[0019] The method may include providing a gas flow 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 through the lithographic apparatus.

[0020] The method may include providing the gas flow at a constant rate. Providing the gas at a constant rate reduces the need for a controller and makes the flushing process more consistent.

[0021] The method may include generating pressure pulses in the gas flow. The method may include causing the pressure pulses in the gas flow by opening and closing one or more pilot valves. Because the valves do not need to precisely control the flow rate of the gas, but rather only need to change the amount allowed to flow out of the lithographic apparatus to change the pressure therein, they can operate more quickly than existing systems using mass flow controllers. In addition, better control allows the use of less flow in the system, which reduces the need for accessories needed to control the flow, thereby saving space and cost.

[0022] According to a third aspect of the present disclosure, there is provided a lithographic apparatus comprising the washing system according to the first aspect of the present disclosure.

[0023] According to a fourth aspect of the present disclosure, there is provided use of the flushing system according to the first aspect of the present disclosure, the lithographic apparatus according to the third aspect of the present disclosure, or the method according to the second aspect of the present disclosure in a lithographic method or apparatus.

[0024] It will be appreciated that features described with respect to one embodiment may be combined with any features described with respect to another embodiment, and that all such combinations are expressly contemplated and disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which corresponding reference numerals indicate corresponding parts, and in which:

[0026] Figure 1 depicts a lithographic apparatus according to one embodiment of the present disclosure;

[0027] Figure 2 A schematic diagram depicting a system according to one aspect of the present disclosure; and

[0028] Figure 3 An exemplary flush cycle is described.

[0029] The features and advantages of the present invention will become more apparent from the detailed description set forth below in conjunction with the accompanying drawings, in which like reference numerals identify corresponding elements throughout. In the drawings, like reference numerals generally indicate identical, functionally similar, and / or structurally similar elements. DETAILED DESCRIPTION

[0030] Figure 1A lithography system according to the present invention is shown. The lithography system comprises a radiation source SO and a lithography apparatus LA. The radiation source SO is configured to generate an extreme ultraviolet (EUV) radiation beam 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 (now patterned by the mask MA) onto the substrate W. The substrate W may comprise a previously formed pattern. In this case, the lithography apparatus aligns the patterned radiation beam B with the pattern previously formed on the substrate W. In this embodiment, a pellicle 15 is depicted in the radiation path and protects the patterning device MA. It will be appreciated that the pellicle 15 may be located in any desired position and may be used to protect any mirror in the lithography apparatus.

[0031] The radiation source SO, illumination system IL, and projection system PS may all be constructed and arranged so as to be isolated from the external environment. A gas (e.g., hydrogen) at a pressure below atmospheric pressure may be provided in the radiation source SO. A vacuum may be provided in the illumination system IL and / or the projection system PS. A small amount of gas (e.g., hydrogen) at a pressure well below atmospheric pressure may be provided in the illumination system IL and / or the projection system PS.

[0032] Figure 1 The radiation source SO shown is of a type that may be referred to as a laser produced plasma (LPP) source. A laser, which may be a CO2 laser, is arranged to deposit energy via a laser beam into a fuel, such as tin (Sn), provided from a fuel emitter. Although tin is mentioned in the following description, any suitable fuel may be used. The fuel may, for example, be in liquid form and may, for example, be 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 a plasma formation region. The laser beam is incident on the tin in the plasma formation region. The deposition of laser energy into the tin generates a plasma in the plasma formation region. During de-excitation and recombination of ions of the plasma, radiation including EUV radiation is emitted from the plasma.

[0033] EUV radiation is collected and focused by a near normal incidence radiation collector (sometimes more generally referred to as a normal incidence radiation collector). The collector can have a multilayer structure arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm). The collector can have an elliptical configuration with two elliptical foci. The first focus can be in the plasma formation region, and the second focus can be at an intermediate focus, as described below.

[0034] The laser may be separate from the radiation source SO. In this case, the laser beam may be transferred from the laser to the radiation source SO by means of a beam delivery system (not shown) comprising, for example, suitable directing mirrors and / or a beam expander and / or other optical devices. The laser and the radiation source SO may together be considered a radiation system.

[0035] The radiation reflected by the collector forms a radiation beam B. The radiation beam B is focused at a point to form an image of the plasma formation region, which serves as a virtual radiation source for the illumination system IL. The point at which the radiation beam B is focused can be referred to as an intermediate focus. The radiation source SO is arranged so that the intermediate focus is located at or near an opening in the enclosure of the radiation source.

[0036] A radiation beam B enters an illumination system IL from a radiation source SO, which is configured to condition the radiation beam. The illumination system IL may include a faceted field mirror arrangement 10 and a faceted pupil mirror arrangement 11. The faceted field mirror arrangement 10 and the faceted pupil mirror arrangement 11 together provide a radiation beam B having a desired cross-sectional shape and a desired angular distribution. The radiation beam B passes from the illumination system IL and is incident on a patterning device MA held by a support structure MT. The patterning device MA reflects the radiation beam B and patterns the radiation beam B. The illumination system IL may include other mirrors or arrangements in addition to or instead of the faceted field mirror arrangement 10 and the faceted pupil mirror arrangement 11.

[0037] After reflection from the patterning device MA, the patterned radiation beam B enters the projection system PS. The projection system comprises a plurality of mirrors 13, 14 configured to project the radiation beam B onto a substrate W held by a substrate table WT. The projection system PS may apply a reduction factor to the radiation beam, forming an image having features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 may be applied. Although Figure 1 The projection system PS has two mirrors 13, 14, but the projection system may comprise any number of mirrors (eg six mirrors).

[0038] Figure 1 The radiation source SO shown may include components not shown. For example, a spectral filter may be provided in the radiation source. The spectral filter may be substantially transmissive for EUV radiation, but substantially blocking radiation of other wavelengths, such as infrared radiation.

[0039] In one embodiment, membrane assembly 15 is a pellicle for a patterning device MA used for EUV lithography. Membrane assembly 15 can be used for a dynamic airlock, a pellicle, or other purposes. In one embodiment, membrane assembly 15 includes a membrane formed from at least one film layer having an emissivity of 0.3 or greater. To ensure maximum EUV transmission and minimize the impact on imaging performance, it is preferred that the membrane be supported only at its edges.

[0040] If the patterning device MA is not protected, contamination may require cleaning or discarding the patterning device MA. Cleaning the patterning device MA interrupts valuable manufacturing time, and discarding the patterning device MA is expensive. Replacing the patterning device MA also interrupts valuable manufacturing time. The system of the present disclosure allows for fast, consistent, and efficient cleaning of the interior of a lithographic apparatus.

[0041] Figure 2 is a schematic diagram of a lithographic apparatus including a flushing system according to the present disclosure. An inlet gas flow 16 is provided into the lithographic apparatus LA. An outlet 17 is also provided through which gas can leave the lithographic apparatus. A pump 18 is in fluid communication with the outlet 17 and is used to remove gas from the lithographic apparatus, the pump 18 not forming part of the lithographic apparatus and being provided at the customer's location for attachment to the lithographic apparatus. The outlet 17 is configured such that during flushing, within the operating parameters of the lithographic apparatus, the gas flow is blocked. As described above, the blocked flow decouples the gas flow within the lithographic apparatus from the particular pump to which the lithographic apparatus is attached during use. The lithographic apparatus LA may include one or more pilot valves (not shown) configured to open and close to create a pressure change within the lithographic apparatus to assist in removing contaminants.

[0042] Figure 3 An exemplary flushing cycle is depicted. As can be seen, the pressure within the lithographic apparatus is cycled to remove contaminants and remove them from the apparatus. During each cycle, the gas flow rate can be constant or varied. Alternatively, or additionally, pressure pulses can be introduced by opening and closing one or more pilot valves. Because the outlet flow is blocked and the pressure is decoupled from the pressure at the user interface, the pressure can be selected more freely, allowing for optimization of the flushing process, making flushing more efficient and resulting in a cleaner apparatus. This allows for faster cycles, as fewer cycles can be used because each cycle is more efficient at cleaning, further saving additional time.

[0043] Table 1 shows some exemplary operating parameters of a system according to the present disclosure.

[0044]

[0045] The exemplary system includes two valves that can be controlled by a controller. In the first option, the flow rate is 300 nlm, which can be divided into two separate streams, the first stream for cleaning of approximately 200 nlm and the second stream for flow stabilization of approximately 100 nlm. The first valve can be fully opened to provide a choked flow, while the second valve can be closed, and when open, the second valve has a greater restriction on the airflow. In the second option, a lower gas flow rate of 200 nlm can be used. In this option, the first valve can be closed, and the second, smaller valve can be fully opened to provide a choked flow. Taking into account the lower flow rate, a smaller valve can be used. In the third option, a pilot valve can be used to provide a pressure pulse, and a choked flow can be provided according to either the first or second option. In the third option, one or more mass flow controllers can be maintained at a fixed flow rate so that no time is spent on repeatedly filling and releasing the gas in the pipeline.

[0046] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

[0047] The above description is intended to be illustrative and not restrictive. It will therefore be apparent to those skilled in the art that modifications may be made to the invention as described without departing from the scope of the following claims.

Claims

1. A flushing system for a lithographic apparatus, the flushing system comprising a gas outlet, the gas outlet being configured to block a flow of gas through the gas outlet at a predetermined rate. 2 . The flushing system of claim 1 , wherein the system comprises a controller configured to control the gas outlet.

3. The flushing system according to any one of the preceding claims, wherein the flushing system comprises one or more pilot valves configured to be selectively opened and closed.

4. The irrigation system of any one of the preceding claims, wherein the irrigation system is configured to provide a gas flow rate of from about 20 nm to about 700 nm, optionally about 100 nm, about 200 nm, about 300 nm, about 400 nm, about 500 nm or about 600 nm.

5. The rinsing system of any preceding claim, wherein the rinsing system is configured to provide a pressure 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 within the lithographic apparatus.

6. The flushing system according to any one of the preceding claims, wherein the flushing system is configured to operate at a constant gas flow rate.

7. A method for flushing a lithographic apparatus, the method comprising: providing a flow of gas through the lithographic apparatus; and operating a gas outlet from the lithographic apparatus such that the flow of gas is blocked through the gas outlet.

8. A method of flushing a lithographic apparatus according to claim 7, wherein the method comprises providing a gas flow of about 20 nm to about 700 nm, optionally about 100 nm, about 200 nm, about 300 nm, about 400 nm, about 500 nm or about 600 nm through the lithographic apparatus.

9. A method of flushing a lithographic apparatus according to claim 7 or 8, wherein the method comprises providing a gas flow at a constant rate.

10. A method of flushing a lithographic apparatus according to any one of claims 7 to 9, wherein the method comprises generating pressure pulses in the gas flow.

11. A method of flushing a lithographic apparatus according to claim 10, wherein the pressure pulses are caused by opening and closing of one or more pilot valves.

12. A lithographic apparatus comprising a washing system according to any one of claims 1 to 6.

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

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