Inductively coupled plasma light source with direct gas injection

Abstract

An ultraviolet light source with direct feed gas injection includes a cavity containing a plasma confinement region and defining an aperture proximate the plasma confinement region for transmission of plasma generated light. A magnetic core is disposed around the plasma confinement region and is configured to create a plurality of plasma current loops during operation, the loops converging within the plasma confinement region. A feed gas injector is connected with a gas port in the cavity, and an output end of the feed gas injector is close to the boundary of the plasma confinement area, so that the feed gas injector provides feed gas to the plasma confinement area, and a pressure difference is generated in the plasma confinement area. And the high-voltage region is connected with the plasma confinement region. The exhaust port is configured to be connected to a pump to control pressure within the cavity.

Description

[0001] The section headings used herein are for organizational purposes only and are not to be construed in any way as limiting the subject matter described in this application. Background Art

[0002] Many commercial and academic applications require high brightness light in the extreme ultraviolet (EUV) region of the spectrum. For example, EUV light is in great demand in many industrial applications, including lithography, metrology, accelerated life testing, photoresist development and testing, defect detection, and microscopic analysis. Other applications of EUV light include spectral analysis, aerial imaging, and blank mask inspection. These and other applications require EUV light sources with high reliability, miniaturization, low fixed cost, low operating cost, flexible operating space to optimize for specific application needs, and low complexity. However, due to various engineering and technical challenges, the performance and practicality of known ultraviolet light sources in the extreme ultraviolet (EUV) spectral region are limited. Summary of the invention

[0003] A UV light source with direct feed gas injection includes a chamber containing a plasma confinement region and defining an aperture near the plasma confinement region to transmit light generated by the plasma. A magnetic core is arranged around the plasma confinement region and is configured to generate a plurality of plasma current loops during operation that converge within the plasma confinement region. A high voltage region is connected to the plasma confinement region. An exhaust port is configured to be connected to a pump that controls the pressure within the chamber. In different configurations, a butterfly valve or other gas conductance control device can be used, as can a gas controller and a variable speed vacuum pump.

[0004] The feed gas injector is connected to a gas port in the chamber, and its output end is arranged close to the boundary of the plasma confinement region, ensuring that the feed gas injector provides feed gas to the plasma confinement region, thereby generating a pressure difference in the plasma confinement region. The feed gas injector may include a plurality of holes for providing feed gas to the plasma confinement region. In different configurations, the output end of the feed gas injector may be located within 1 cm or 1 / 2 cm from the boundary of the plasma confinement region. In some configurations, the output end of the feed gas injector may be located between a low voltage region and a high voltage region of the chamber.

[0005] The feed gas injector can be positioned and configured to maintain a desired ratio between the pressure within the plasma confinement region and the pressure within the chamber near the exhaust port during operation. In addition, the feed gas injector can be positioned and configured so that, during operation, substantially all of the feed gas passes through the plasma confinement region before entering the exhaust port. In addition, the feed gas injector can be positioned and configured so that, during operation, the feed gas injector injects gas into the plasma confinement region at a time when the plasma confinement region is refilled after the pinch expands.

[0006] In some configurations, a second gas injector is included, the output of which is located near a second boundary of the plasma confinement region. The second gas injector is connected to a second port in the chamber and can be configured to deliver a feed gas or other type of gas. In some configurations, the second gas injector can be configured to inject gas into the chamber after the plasma confinement region forms a pinch expansion, where a desired amount of return flow to the plasma confinement region is provided. In addition, the second gas injector can be arranged in the chamber to inject gas, thereby reducing self-absorption of the feed gas outside the plasma confinement region. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The present teachings, according to preferred and exemplary embodiments, and in combination with further advantages thereof, are described in more detail in the following detailed description and illustrated in conjunction with the accompanying drawings. It should be understood by those skilled in the art that the drawings described below are for illustrative purposes only. The drawings are not necessarily drawn to scale, but rather focus on illustrating the principles of the present teachings. These drawings should not limit the scope of the applicant's technical solution in any way.

[0008] Figure 1 A known plasma chamber for generating Z-pinch UV light is shown.

[0009] Figure 2 A plasma chamber for generating Z-pinch ultraviolet light in accordance with the present teachings is shown.

[0010] Figure 3 A graph of experimental data is shown, comparing the total optical output power of light generated by a known EUV light source at different pressures in a plasma confinement region and the total optical output power of light generated by an EUV light source that directly injects gas into the plasma generation region according to the present teachings at different pressures in the plasma confinement region.

[0011] Figure 4 A graph of experimental data is shown, comparing the brightness of light generated by a known EUV light source at different pressures in a plasma confinement region and the brightness of light generated by an EUV light source that directly injects gas into a plasma generation region according to the present teachings at different pressures in a plasma confinement region.

[0012] Figure 5 A graph of experimental data is shown, comparing the beamline pressures of a known EUV light source at different pressures in the plasma confinement region and the beamline pressures of an EUV light source that directly injects gas into the plasma generation region according to the present teachings at different pressures in the plasma confinement region.

[0013] Figure 6 A graph of experimental data is shown, comparing the optical power detected by a known EUV light source at different pressures in a plasma confinement region and the optical power detected by an EUV light source that directly injects gas into a plasma generation region according to the present teachings at different pressures in a plasma confinement region. DETAILED DESCRIPTION

[0014] This teaching will now be described in more detail in conjunction with the exemplary embodiments in the accompanying drawings. Although this teaching is described in conjunction with various embodiments and examples, it is not intended to limit this teaching to these embodiments. On the contrary, this teaching includes various alternatives, modifications and equivalents understood by those skilled in the art. Those of ordinary skill in the art will be able to identify other implementations, modifications and embodiments, as well as other applicable fields after reading this teaching, which are all within the scope of this disclosure.

[0015] References to "one embodiment" or "an embodiment" in this specification mean that a particular feature, structure, or characteristic associated with the embodiment is included in at least one embodiment of the present teachings. The phrase "in one embodiment" appearing in multiple places in the specification does not necessarily refer to the same embodiment.

[0016] It should be understood that the individual steps of the method of this teaching can be performed in any order and / or performed simultaneously, as long as this teaching is still operable. In addition, it should be understood that the apparatus and method of this teaching can include any number or all of the described embodiments, as long as this teaching is still operable.

[0017] Extreme ultraviolet (EUV) light sources play an important role in numerous optical metrology and exposure applications. It is desirable for these light sources to be adaptable to a variety of usage scenarios. One challenge is to produce high-power and high-brightness EUV light in a configuration that allows integration into a variety of applications, while also having high stability and reliability.

[0018] In the art, extreme ultraviolet radiation is referred to by many different names. Some people in the industry sometimes refer to extreme ultraviolet radiation as high-energy ultraviolet radiation, or EUV for short. Extreme ultraviolet radiation generally refers to electromagnetic radiation in the electromagnetic spectrum with a nominal wavelength of approximately between 124nm and 10nm. There is some overlap between extreme ultraviolet radiation and the portion of the optical spectrum that is considered to be. One EUV wavelength of particular interest is 13.5nm because this wavelength is commonly used in lithography. According to the present teachings, extreme ultraviolet radiation sources are not limited to generating EUV radiation. It is well known that plasmas can be used to generate photons over a wide spectral range. For example, plasmas generated according to the present teachings can also be used to generate soft X-ray (SXR) photons, which include photons with wavelengths less than 10nm.

[0019] So-called Z-pinch plasmas, where the current flows axially, have proven to be very effective in producing EUV and SXR light. However, most known light sources use electrodes to introduce high discharge currents into the plasma. These electrodes, which are usually in contact with the high-temperature plasma, can melt and generate a lot of debris, which is highly undesirable because it can significantly shorten the life of the light source.

[0020] Electrodeless EUV generation methods are ideal and meet a huge need in the market. Such light sources are provided, for example, by Energetiq, a Hamamatsu Corporation company located in Wilmington, Massachusetts, USA. Such light sources are based on Z-pinch plasmas, but avoid the use of electrodes entirely by inductively coupling current flow to the plasma. The plasma in these EUV light sources is confined by a magnetic field away from the walls of the source, thereby minimizing heat load and reducing debris, while providing excellent open-loop spatial stability and stable, repeatable power output. However, one challenge with known Z-pinch light sources is that their performance, especially brightness, is limited by their power supply because they use magnetic switches, which is highly non-ideal.

[0021] One feature of the EUV light sources of the present teachings is their versatility, which enables them to support a variety of high brightness applications. In particular, the EUV light sources of the present teachings improve upon known Z-pinch designs because they can be optimized to meet the desired power and / or brightness requirements based on the needs of a user's specific application. In addition, the EUV light sources of the present teachings have a more compact physical footprint and more flexible component layout.

[0022] Figure 1 A known plasma chamber 100 for generating Z-pinch ultraviolet light is shown. See, for example, U.S. Patent Application No. 17 / 676,712, entitled "Inductively Coupled Plasma Light Source," which is assigned to the same assignee as the present application. The entire contents of U.S. Patent Application No. 17 / 676,712 are incorporated herein by reference.

[0023] The chamber 100 includes an interface 102 for delivering a feed gas 104 into the chamber 100. A pump 106 is used to pump a chamber region 108 to a desired operating pressure. The desired operating pressure of the chamber region 108 can be achieved by controlling the amount of gas entering the chamber, controlling the conductivity of the gas entering the pump, and / or controlling the pumping rate of the pump itself. For example, a butterfly valve 107 or other gas conductance control means can be used, as can a gas controller and a variable speed vacuum pump. The chamber 100 is equipped with a port 110 to transmit EUV radiation 112 generated by the EUV plasma.

[0024] In various systems, the port 110 is configured to allow the user to connect to an application system (not shown) so that EUV radiation can be directly passed through the port 110. The plasma generation region 114 defines a plasma confinement region 116. The plasma confinement region 116 is formed by magnetic induction, and when a pulse shaping and power delivery system 118 provides current, the current will actively and passively interact with the magnetic cores 120 and 121. The high voltage region 122 is connected to the plasma generation region 114. The ground region 124 has an outer surface connected to the ground terminal 126. The pulse power supply 119 is electrically connected to the power delivery system 118. The chamber 100 also includes regions 128 and 130 for arranging the magnetic cores 120 and 121 to provide induced current when the chamber 100 is in operation.

[0025] During operation of the Z-pinch plasma of the known chamber 100, feed gas in the plasma generation region 114 is compressed by the electrical pulses generated by the pulse power supply 119, and the gas subsequently expands after the pulse. During the compression and expansion process, a portion of the feed gas escapes from the plasma generation region 114 and must be replaced. In known EUV Z-pinch plasma sources, this is achieved by allowing gas to migrate from the area surrounding the plasma generation region into the plasma generation region.

[0026] One aspect of the present teachings is the recognition that in known EUV Z-pinch plasma sources, the performance of EUV Z-pinch plasma sources is severely limited by the slow replenishment of gas from the region surrounding the plasma generation region to the plasma generation region. Another aspect of the present teachings is the recognition that the performance of known Z-pinch plasma EUV sources can be significantly improved by injecting feed gas directly into the plasma generation region using a direct gas supply system and method, so that there is no significant time delay in replenishing gas to the plasma generation region to achieve the desired light source performance, or at least to create operating conditions without feed gas limitation.

[0027] This method of directly supplying gas to the plasma generation region can be achieved by providing an independent gas conduit structure or an integrated channel structure, which can directly transport gas from the gas source through the cavity to an area in contact with or close to the boundary of the plasma generation region without gas leakage. In various embodiments, the gas conduit structure includes one or more holes for providing feed gas to the plasma generation region. In addition, in various embodiments, the plasma generation region and its surrounding structures can be separated into independent parts spaced apart from each other so that the target gas can enter the plasma generation region through the gaps between these parts. As a result, the target gas used in the process is forced to enter the cavity directly through the plasma generation region. This feature of the present teaching allows operation at higher pulse rates, which would otherwise be impractical if the gas slowly migrates back to the plasma generation region after Z-pinch.

[0028] Figure 2 A plasma chamber 200 is shown for generating Z-pinch ultraviolet light according to the present teachings. The chamber 200 and Figure 1 The chamber 100 described is similar, but the chamber 200 uses the direct gas supply device of the present teaching. The chamber 200 includes an interface 202, which delivers a feed gas 204 to the chamber 200. The interface 202 can be a gas pipeline structure independent of the chamber 200, or it can be an integrated channel structure formed directly in the chamber 200. The interface 202 directly delivers gas from the gas source through the chamber 200 to an area in contact with or close to the boundary of the plasma generation area without gas leakage.

[0029] In some embodiments, a second interface 202' is included for delivering a feed gas 204' and / or a second gas at a second location of the cavity. A pump 206 is used to pump the cavity region 208 to a desired operating pressure. The desired operating pressure of the cavity region 208 can be achieved by controlling the amount of gas supplied to the cavity, controlling the flow conductivity of the gas entering the pump, and / or controlling the pump speed of the pump itself. For example, a butterfly valve 207 or other gas conduction control means can be used, or a gas controller and a variable speed vacuum pump can be used.

[0030] A port 210 is provided to transmit EUV radiation 211 generated by the EUV plasma. The port 210 may include an EUV output port that transmits desired EUV radiation and substantially blocks radiation of other wavelengths. The port 210 may be configured to include a filtering structure to block unwanted radiation. In certain embodiments, the port 210 is configured to be opaque to visible light. For example, in various embodiments, the EUV transparent port 210 is a hole that may include a spectral purification foil. Typically, the port 210 is a beamline hole port that transmits radiation propagating along the beamline. The port 210 may also be configured to have a desired diameter to physically block light propagating in certain directions. In addition, the diameter of the hole defining the port 210 may be selected to provide a desired pressure difference between the interior and exterior of the chamber 200.

[0031] In various systems, the port 210 is configured to allow the user to connect to an application system (not shown) so that EUV radiation can be directly passed through the port 210. The plasma generation region 214 defines a plasma confinement region 216. When the pulse shaping and power delivery section 218 provides current, the current actively and passively interacts with the magnetic cores 220, 222 located in the regions 224, 226 to form the plasma confinement region 216, whereby an induced current flows within the chamber 200 during operation. The magnetic confinement of the plasma in the plasma confinement region 216 is beneficial because the plasma is kept away from the components of the chamber 200, thereby reducing erosion and related contamination and improving the reliability and stability of the light source.

[0032] The high voltage region 228 is connected to the plasma generation region 214. The ground region 230 has an outer surface connected to the ground terminal 232. The pulse power supply 234 is electrically connected to the power transmission portion 218, and the power transmission portion 218 is connected to the high voltage region 228 and the ground region 230. The pulse power supply 234 includes a capacitor 238 connected in parallel. In many embodiments, the capacitor 238 is a capacitor bank, and the capacitor bank includes a plurality of capacitors. The pulse generator 234 applies a negative high voltage pulse across the capacitor 238 and drives a current through the power transmission portion 218 to the ground terminal 226.

[0033] Thus, the power delivery portion 218 of the chamber 200 has a high voltage side 228 and a ground side 230. At least three inductively coupled plasma rings (not shown) are formed from the current pulses flowing through the power delivery portion 218 and actively and passively interact with the magnetic cores 220, 221. These plasma rings converge in the plasma generation region 214 forming a magnetically confined Z-pinch. These plasma rings flow through the region between the inner magnetic core 220 and the outer magnetic core 222 and through the plasma generation region 214.

[0034] Those skilled in the art will recognize that there are a variety of methods for generating ultraviolet light according to the present teachings. These methods generally provide a feed gas to the boundary of the plasma confinement region of the plasma chamber. The feed gas is provided to the interface 202 to be directly injected into the cavity 200 at the boundary of the plasma generation region 214. In some operating methods, the feed gas can be xenon. In some operating methods, the feed gas can be argon, nitrogen, neon, helium, or a combination of gases having a desired wavelength of light emission. In addition, in some operating methods, the selection of a mixture of feed gases is intended to provide the desired light emission characteristics or increase the stability of the optical power. For example, the introduction of helium into the cavity can improve the stability of the pinch without diluting the target gas in the plasma generation region. The introduction of a second gas or additional gas into the cavity may further reduce the self-absorption effect in the cavity.

[0035] It should be understood that in some approaches, feed gas and / or other gases are also supplied to the second port 202 ′, which is disposed at one or more different locations of the chamber 200 , such as near the plasma generation region but not at the boundary of the plasma generation region.

[0036] The pulse power supply 234 generates voltage pulses. A series of voltage pulses are applied to at least one capacitor 238, which is electrically connected across the outer core 222, which surrounds the inner core 220, which is located around the plasma confinement region 214. The outer core 222 will eventually saturate, causing the impedance to drop to zero. That is, the voltage pulse charges the at least one capacitor 238, causing the outer core 222 to saturate, which in turn causes the capacitor to discharge, causing the inner core 220 to couple the current pulse into the plasma ring, thereby generating a large pulse in the plasma current to drive the Z-pinch. During the charging period, a small leakage current from the cores 220 and 222 maintains the plasma ring. The Z-pinch operation requires a continuous ring because its normal operation requires the continuous presence of ionized gas.

[0037] During operation of the Z-pinch plasma in the chamber 200, the feed gas in the plasma generation region 214 is compressed by the electrical pulse generated by the pulse power supply 234, and the gas is subsequently expanded after the pulse. Unlike known chambers for generating EUV light, during the pulse compression and expansion, the feed gas is delivered directly to the plasma generation region 214 at a specific flow rate and volume, thereby providing sufficient feed gas to replenish the feed gas lost due to the pulse compression to form the Z-pinch plasma. Importantly, during Figure 2 In the configuration shown, no gas flows directly from the feed gas inlet 204 to the vacuum pump 206 without passing through the plasma generation region.

[0038] As a result, the plasma generation region 214 generates and emits nearly 100% of the EUV radiation generated by the plasma. The plasma ring itself does not generate EUV light. As a result, the light source 200 generates a high-quality, relatively compact EUV light source from a well-defined and stable Z-pinch plasma confinement region 216 within the plasma generation region 214. One feature of the present teachings is that by using a pulse shaping and power delivery section 218 to drive and contain the plasma in the Z-pinch plasma confinement region 216, the light source 200 can operate without the use of electrodes, which are commonly used by known systems to conduct discharge current to the plasma.

[0039] According to the present teachings, methods and apparatus for using direct feed gas injection in the plasma confinement region of a light source have numerous advantages. First, direct feed gas injection at an appropriate flow rate eliminates light source performance limitations caused by insufficient feed gas molecules in the plasma generation region of the chamber. In addition, direct feed gas injection utilizes feed gas more efficiently because unused gas does not flow directly from the feed gas inlet 204 to the vacuum pump 206 without passing through the plasma generation region. Direct feed gas injection significantly reduces the operating cost of the light source because the total amount of feed gas required to achieve the same operating conditions is significantly reduced compared to known EUV light sources. This is particularly beneficial for expensive target gases such as xenon (Xe).

[0040] In addition, another feature of the present teachings is that direct injection of feed gas can reduce self-absorption of EUV light generated in the plasma confinement region 214, which is caused by the pressure difference between the plasma generation region and other areas of the chamber. The following example helps to illustrate this feature. Assuming that the desired operating pressure of the plasma generation region 214 is 100mTorr, in known EUV light sources, the pressure in the plasma generation region must be at least 100mTorr. Therefore, if there is no direct feed gas injection, to achieve a pressure of 100mTorr in the plasma generation region 214, the pressure near this region may need to be higher than 100mTorr because of the flow restriction to the plasma generation region and because there is a higher flow conductivity near the plasma generation region 214. The resulting pressure difference between the plasma generation region 214 and its surrounding areas will reduce the amount of light generated by the light source through self-absorption.

[0041] In contrast, injecting gas directly into the plasma generation region at a pressure of 100 mTorr eliminates the need to keep the rest of the system at the same pressure. For example, a lower pressure of 50 mTorr may suffice. In this example, the pressure in the adjacent cavity may be less than 5 mTorr. Therefore, at such pressures, light losses due to self-absorption will be significantly reduced.

[0042] In addition, another feature of the present teachings is that contamination of the plasma generation region will be reduced because the main material flow is from the plasma generation region to the area surrounding the plasma generation region. This is in contrast to known EUV light sources, in which gas flows from the surrounding area into the plasma generation region. In a typical system that does not use the direct gas supply configuration of the present teachings, the material entering the plasma generation region may be a mixture of target gas and contaminants. This prior art may bring contaminants from the surrounding area into the plasma generation region.

[0043] Figure 3 A graph 300 of experimental data is shown comparing the total optical output power generated by a known EUV light source at different pressures in a plasma confinement region and the total optical output power generated by an EUV light source with direct gas injection in the plasma generation region according to the present teachings at different pressures in the plasma confinement region. The optical output power is measured at the output section of the light source and the pressure is measured in the region surrounding the plasma generation region. The data is obtained with the same cavity configuration, geometry, and with the same operating parameters of the light source.

[0044] More specifically, graph 302 shows the total optical output power of a known EUV light source at different pressures in a plasma confinement region that generates a Z-pinch. Graph 304 shows the total optical output power of an EUV light source that directly injects gas into the plasma generation region at different pressures in a plasma confinement region that generates a Z-pinch. From the data in graphs 302 and 304, it can be seen that the optical power generated by the EUV light source according to the present teachings is approximately 28% higher than the optical power generated by the known system under the same cavity configuration, geometry, and the same operating parameters of the light source. In addition, the data in graphs 302 and 304 show that the EUV light source of the present teachings that includes direct feed gas injection in the plasma generation region has the highest power output at a lower pressure around the plasma generation region. This is advantageous because lower pressure can reduce light losses due to self-absorption.

[0045] Figure 4 A graph 400 of experimental data is shown, comparing the brightness of light generated by a known EUV light source at different pressures in a plasma confinement region, and the brightness of light generated by an EUV light source with direct gas injection in the plasma generation region according to the present teachings at different pressures in the plasma confinement region. The output brightness is measured at the output end of the light source, and the pressure is measured in the region surrounding the plasma generation region. The data is obtained with the same cavity configuration, geometry, and the same operating parameters of the light source.

[0046] More specifically, graph 402 shows the brightness of a known EUV light source at different pressures in a plasma confinement region that generates a Z-pinch. Graph 404 shows the brightness of an EUV light source that directly injects gas into the plasma generation region at different pressures in a plasma confinement region that generates a Z-pinch. From the data in graphs 402 and 404, it can be seen that the brightness of the light generated by the EUV light source according to the present teaching is approximately 11% higher than the brightness generated by the known system under the same cavity configuration, geometric structure, and the same operating parameters of the light source. In addition, the data in graphs 402 and 404 show that the EUV light source of the present teaching including direct gas injection has a higher and maximum brightness at a lower pressure. This is also advantageous because a lower pressure can reduce light loss due to self-absorption.

[0047] Figure 5 An experimental data graph 500 is shown comparing beam line pressures of a known EUV light source at different pressures in the plasma confinement region and beam line pressures of an EUV light source with direct gas injection in the plasma generation region according to the present teachings at different pressures in the plasma confinement region. Beam line pressure refers to the pressure of the attached system that couples the light generated by the EUV light source to a particular application.

[0048] More specifically, graph 502 shows experimental data of beamline pressures of known EUV light sources at different pressures in the plasma confinement region. Graph 504 shows experimental data of beamline pressures of EUV light sources that directly inject gas into the plasma generation region according to the present teachings at different pressures in the plasma confinement region. The data of graphs 502 and 504 show that for an EUV light source that includes direct feed gas injection into the plasma generation region according to the present teachings, the beamline pressures at different pressures in the plasma confinement region are low under all operating conditions used to observe the EUV light source, and the observed EUV light source includes an EUV light source that directly feeds gas injection into the plasma generation region according to the present teachings. This is advantageous because the attached application system needs to maintain a lower pressure because the gas in the application system absorbs a portion of the light generated by the light source.

[0049] Figure 6 An experimental data graph 600 is shown comparing the optical power detected by a known EUV light source at different pressures in the plasma confinement region and the optical power detected by an EUV light source with direct gas injection in the plasma generation region according to the present teachings at different pressures in the plasma confinement region. The output optical power is measured at the detector location and the pressure is measured in the region surrounding the plasma generation region. The data was acquired with the same chamber configuration, geometry, and the same operating parameters of the light source.

[0050] More specifically, graph 602 shows experimental data of optical power detected by a known EUV light source at different pressures in a plasma confinement region. Graph 604 shows experimental data of optical power detected by an EUV light source that directly injects gas into a plasma generation region according to the present teachings at different pressures in a plasma confinement region. The data in graph 604 corresponds to an EUV light source that includes direct gas injection into a plasma generation region according to the present teachings, and the data in graph 604 show the effect of reducing self-absorption in an attached application system based on the optical power measured at the detector position.

[0051] In particular, the data in graph 604 show that by directly supplying the feed gas to the plasma generation region, the detected light output is about 35% higher than that of the known system (having the same cavity configuration, geometry, and under the same operating parameters of the light source). According to the EUV light source of the present teachings, the target gas can be more efficiently delivered to the plasma generation region at a higher pressure, so the light source can be operated at a higher repetition rate, thereby improving the EUV output.

[0052] Thus, according to the present teachings, an important feature of EUV light sources using direct feed gas injection is that such light sources shift the optimal operating performance point toward the low pressure range of the plasma confinement region. This shift toward the low pressure of the plasma confinement region not only reduces the pressure in the application system, but also reduces the self-absorption of light.

[0053] The following examples help illustrate the performance that can be achieved with an EUV light source using direct feed gas injection according to the present teachings. Figure 2 , experiments show that the light source 200 can be configured and operated under operating conditions to generate about 20 watts of EUV radiation with a wavelength of 13.5 nm, a radiation angle of 2π steradian, and a brightness of 8 W / mm 2 -sr. In these experiments, the pulse frequency was adjustable. For example, in some of the experiments in which these data were recorded, the pulse frequency was set to 2.5 kHz. Under these conditions, the diameter of the plasma confinement region 214 was less than 1 mm, and by changing certain operating conditions, the diameter could be reduced to less than 0.5 mm. In certain operating methods, the actual position of the plasma confinement region 214 changed by less than a few microns between each pulse.

[0054] These experimental results data show that the EUV light source using direct gas supply according to the present teaching can be widely used in various test and measurement systems. According to the present teaching, the EUV light source using direct feed gas injection can operate at a lower pressure, thereby providing more flexible access to EUV radiation generated by the plasma compared to known EUV systems, making it suitable for more application configurations. In addition, according to the present teaching, the EUV light source using direct feed gas injection can provide more flexible access to EUV radiation generated by the plasma compared to known EUV systems due to reduced self-absorption, making it suitable for more application configurations. In addition, according to the present teaching, the EUV light source using direct feed gas injection can provide more flexible access to EUV radiation generated by the plasma compared to known EUV systems due to its wider range of operating conditions, making it suitable for more application configurations. In addition, according to the present teaching, the EUV light source using direct feed gas injection can provide more flexible access to EUV radiation generated by the plasma compared to known EUV systems due to its wider range of operating conditions, making it suitable for more application configurations. In addition, according to the present teaching, the EUV light source using direct feed gas injection can provide more flexible access to EUV radiation generated by the plasma compared to known EUV systems, making it suitable for more application configurations.

[0055] Therefore, the EUV light source according to the present teachings provides numerous performance advantages by delivering the supply gas directly to the plasma generation region without the gas migrating from the vacuum chamber to the plasma generation region. This feature is particularly useful when it is necessary to increase the total output of the transmitted EUV at a pulse rate of the order of 2500 Hz. Under such and similar conditions, the performance of the known EUV light source is reduced due to the slow re-supply of the plasma generation region. With direct feed gas injection, the feed gas is delivered directly to the plasma generation region without the feed gas migrating slowly to the region, thereby achieving faster and more efficient refilling of the plasma generation region. This feature allows the plasma light source to operate at a higher repetition rate, beyond the level that can be achieved by a light source that does not use direct feed gas injection. In addition, there are the advantages of reducing self-absorption, improving gas utilization, and introducing different gas species at multiple different locations.

[0056] Equivalent solutions

[0057] Although the applicant's teachings are described in conjunction with various embodiments, it is not intended to limit the applicant's teachings to these embodiments. On the contrary, the teachings include various alternatives, modifications, and equivalents, and those skilled in the art can adjust and improve them without departing from the spirit and scope of the teachings.

Claims

1. A UV light source with direct feed gas injection, wherein: include: a) a cavity containing a plasma confinement region and defining an aperture proximate the plasma confinement region, the aperture transmitting light generated by the plasma; b) a magnetic core located around the plasma confinement region and configured to generate a plurality of plasma current loops during operation, the plurality of plasma current loops converging in the plasma confinement region; c) a feed gas injector connected to a gas port in the chamber and having an output end, the output end being located near a boundary of the plasma confinement region, the feed gas injector providing a feed gas to the plasma confinement region to generate a pressure difference in the plasma confinement region; d) a high voltage region coupled to the plasma confinement region; and e) an exhaust port configured to be connected to a pump to control the pressure within the chamber.

2. The light source according to claim 1, wherein The output end of the feed gas injector is located within 1 centimeter of the boundary of the plasma confinement region.

3. The light source according to claim 1, wherein The output end of the feed gas injector is located within 1 / 2 centimeter of the boundary of the plasma confinement region.

4. The light source according to claim 1, wherein The output end of the feed gas injector is located between the low voltage region and the high voltage region of the chamber.

5. The light source according to claim 1, wherein The feed gas injector includes a gas conduit having an output end located near the boundary of the plasma confinement region.

6. The light source of claim 1, wherein: The feed gas injector is formed within the cavity.

7. The light source of claim 1, wherein: The feed gas injector includes a plurality of holes to provide the feed gas to the plasma confinement region.

8. The light source of claim 1, wherein: The feed gas injector is positioned such that substantially all of the feed gas flows through the plasma confinement region before entering the exhaust port.

9. The light source of claim 1, wherein: The feed gas injector is positioned and configured to maintain a desired ratio of pressure within the plasma confinement region to pressure within the chamber proximate the exhaust port during operation.

10. The light source of claim 1, wherein: Further comprising a second gas injection port.

11. The light source of claim 10, wherein: The second gas injection port is located near the high voltage region.

12. The light source of claim 10, wherein: The second gas injection port is located near a low voltage portion of the chamber.

13. The light source of claim 10, wherein: The second gas injection port is configured to introduce a second type of feed gas.

14. The light source of claim 10, wherein: The second gas injection port includes an output end located near a second boundary of the plasma confinement region.

15. The light source of claim 10, wherein: Further included is a second feed gas injector connected to the second gas injection port, the second feed gas injector including an output end located at a second boundary of the plasma confinement region.

16. The light source according to claim 10, wherein The second gas injection port is configured to inject gas into the chamber at a location that provides a desired amount of gas backflow into the plasma confinement region after forming a pinch expansion within the plasma confinement region.

17. The light source according to claim 10, wherein: The second gas injection port is positioned to inject gas into the chamber to reduce self-absorption of the feed gas outside the plasma confinement region.

18. The light source of claim 1, wherein: The feed gas injector comprises a pulsed gas injector configured to inject gas into the plasma confinement region at a time when the plasma confinement region is refilled after pinch expansion.

19. A method of generating ultraviolet light, wherein: include: a) providing a chamber, the chamber defining a plasma confinement region therein, the chamber defining: a port for transmitting plasma-generated light to the outside of the chamber, a high voltage region coupled to the plasma confinement region, and an exhaust port configured to be connected to a vacuum pump to control the pressure within the chamber; b) injecting a feed gas directly into the boundary of the plasma confinement region; c) supplying a voltage to the high voltage region to generate plasma; as well as d) controlling the pressure of the plasma confinement region relative to the chamber to provide a desired pressure differential.

20. The method according to claim 19, wherein: Controlling the pressure of the plasma confinement region relative to the chamber includes controlling the flow of the feed gas using a mass flow controller.

21. The method according to claim 19, wherein: Also included is injecting a feed gas into the chamber.

22. The method according to claim 21, wherein: The feed gas injected into the chamber is injected near the high voltage region.

23. The method according to claim 21, wherein: The feed gas injected into the chamber is injected near the low voltage region.

24. The method according to claim 19, wherein: The method also includes adjusting the flow rate of the feed gas injected into the chamber to provide a desired amount of gas reflux into the plasma confinement region after forming a pinch expansion in the plasma confinement region.

25. The method of claim 19, wherein: Also included is injecting a second feed gas directly into a second boundary of the plasma confinement region.

26. The method of claim 19, wherein: Injecting the feed gas directly into the boundary of the plasma confinement region includes injecting the feed gas through a conduit having an output end located within the boundary of the plasma confinement region.

27. The method of claim 19, wherein: Injecting a feed gas directly into a boundary of the plasma confinement region includes injecting the feed gas at a plurality of locations within the boundary of the plasma confinement region.

28. The method of claim 19, wherein: Also included is configuring the chamber so that substantially all of the feed gas flows through the plasma confinement region before entering the exhaust port.

29. The method according to claim 19, wherein: Also included is evacuating the chamber through an exhaust port to provide a desired ratio of pressure in the plasma confinement region to pressure within the chamber proximate the exhaust port.

30. The method of claim 19, wherein: Also included is adjusting the flow rate of a feed gas injected directly into a boundary of the plasma confinement region to provide a desired ratio of pressure in the plasma confinement region to pressure within the chamber proximate the exhaust port.

31. The method of claim 19, wherein: Injecting feed gas directly into a boundary of the plasma confinement region includes injecting gas into the plasma confinement region at a time when the plasma confinement region is refilled after pinch expansion.

32. The method of claim 19, wherein: Injecting the feed gas directly into the boundary of the plasma confinement region includes injecting the feed gas at a flow rate that reduces self-absorption of the feed gas outside the plasma confinement region.

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