JP2008135586A - Aligner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To decrease an outgas partial pressure in a projection optical system space in an aligner using an extreme ultraviolet light and to prevent a reduction of reflection factor of a projection optical system mirror. <P>SOLUTION: The aligner has: a chamber surrounding a space 18 enclosing at least part of projection optical systems 2 to 7 for projecting light from an original form 11 into a substrate 22; an exhaust means 31 to 34 for exhausting the space; and a supply means 41 for supplying a gas into the space, and exposes the substrate through the original form and the projection optical systems. A control means 42 is provided for controlling a flow rate of the gas which is supplied into the space by the supply means to be in a range of 0.05 to 50 Pa m<SP>3</SP>/s. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exposure apparatus that exposes a substrate through an optical element in a vacuum atmosphere.

  In recent years, in the photolithography technology for manufacturing semiconductors, exposure light has been shortened in wavelength, and has evolved from i-line and g-line to KrF excimer laser and ArF excimer laser. If the wavelength of the exposure light is shortened, a finer mask pattern can be transferred to the wafer. However, in order to expose a pattern with a narrow line width, there is a theoretical limit in lithography using ultraviolet light. Therefore, EUV lithography using extreme ultraviolet light (EUV light, 13 to 20 nm) having a shorter wavelength than ultraviolet light has attracted attention.

  Since a typical wavelength used in EUV light is 13.5 nm, it is possible to realize a resolution far exceeding that of conventional optical lithography. However, on the other hand, EUV light has the property of being easily absorbed by a substance. For this reason, when performing reduced exposure using a refractive optical system, as in conventional lithography using ultraviolet light as a light source, EUV light is absorbed by the glass material, and the amount of light that reaches an object to be exposed such as a wafer Will become extremely small. Therefore, when performing exposure using EUV light, it is necessary to configure reduced exposure using a reflective optical system.

  FIG. 6 shows a schematic view of a conventional reduction projection exposure apparatus using EUV light (see Patent Document 1). The EUV exposure apparatus 200 includes an original stage 250 on which an EUV light source 210, an illumination optical system 220, and an original (mask) 230 are mounted. Further, a wafer stage 260 on which a wafer 270 is mounted, an alignment optical system 240, and a reflective reduction projection optical system 100 are provided. Further, a vacuum vessel 280 that houses the optical systems 220, 100, 240, the original stage 250, the wafer stage 260, and the like, an exhaust system (not shown) that exhausts the gas in the vacuum vessel 280, and the like are also provided. The reflective reduction projection optical system 100 includes a first mirror 110, a second mirror 120, a third mirror 130, a fourth mirror 140, a fifth mirror 150, and a sixth mirror 160.

  There are several types of EUV light sources, and one of them, a laser-produced plasma light source, can emit light only in a necessary wavelength band by selecting a target material. For example, when Xe is ejected from a pulse nozzle as a target material and plasma is generated by irradiating it with a pulse laser, EUV light having a wavelength of 13 to 14 nm is emitted.

  The illumination optical system includes a plurality of multilayer mirrors, an optical integrator, and the like. The role of the illumination optical system includes condensing light emitted from the light source efficiently and making the illuminance of the exposure area uniform. The optical integrator has a role of uniformly illuminating the mask with a predetermined numerical aperture.

  The projection optical system is composed of a reflection optical system using a multilayer mirror in which Mo and Si are alternately coated. This Mo / Si multilayer film can obtain a direct incidence reflectance of about 67% at a wavelength of around 13 nm. It is difficult in principle to make the reflectivity 100%, and most of the absorbed energy is converted to heat. Therefore, low thermal expansion glass or the like is used as the mirror base material. In the reflection optical system, a plurality of such Mo / Si multilayer mirrors are used for aberration correction, but in order to maintain the transmittance of EUV light, it is necessary to reduce the number of multilayer mirrors as much as possible.

The original stage and the wafer stage of the EUV exposure apparatus have a mechanism that is driven in a vacuum environment, and the original stage and the wafer stage are scanned synchronously at a speed ratio proportional to the reduction magnification. The positions and orientations of the original stage and wafer stage are observed and controlled by a laser interferometer (not shown).
The original held on the original chuck and the wafer held on the wafer chuck are positioned with high accuracy by a fine movement mechanism mounted on the original stage and the wafer stage.

  The alignment optical system is a device that detects the positional relationship between the position of the original and the optical axis of the projection optical system, and the positional relationship between the wafer and the optical axis of the projection optical system. Thereby, the positions and angles of the original stage and the wafer stage are set so that the projected image is irradiated to a predetermined position on the wafer. Further, the focus detection mechanism detects the focus position in the direction perpendicular to the wafer surface, and controls the position and angle of the wafer stage, so that the imaging position on the wafer surface is always maintained.

In order to avoid absorption of EUV light by a substance, the EUV exposure apparatus needs to keep a space where the EUV light is irradiated in a vacuum. Therefore, a plurality of exhaust systems such as vacuum pumps are attached to the exposure apparatus.
JP 2003-45782 A

EUV light used in an EUV exposure apparatus is easily absorbed by the atmosphere in the apparatus. In particular, oxygen and moisture strongly absorb EUV light. Therefore, in order to keep the transmittance of EUV light high, it is necessary to make the inside of the chamber in a vacuum state using a vacuum pump or the like. It is desirable that the pressure in the chamber through which EUV light passes is 10 ⁻³ Pa or less and the partial pressures of oxygen and moisture are extremely low. However, moisture and the like that have adhered to the wafer diffuse in the chamber as the wafer is transported. Furthermore, moisture tends to adhere to the inner wall of the chamber and is difficult to exhaust. When moisture adheres to the optical element, the optical element is oxidized, which causes a decrease in the reflectance of the optical element.

  Further, when the inside of the chamber is in a vacuum state, hydrocarbons are generated from a mechanism such as a stage. Further, during the exposure, the reaction of the exposure light with the resist also generates hydrocarbons, and when these hydrocarbons are exposed to the exposure light on the optical element surface, they adhere to the optical element surface as carbon. Carbon adhering to the optical element absorbs EUV light and reduces the reflectivity of the optical element. Decreasing the reflectance of the optical element leads to a decrease in throughput. Hereinafter, it is expressed as outgas including hydrocarbon and moisture.

From the above, it is necessary to keep the outgas partial pressure low particularly in the space where the optical element in the EUV exposure apparatus is installed.
In order to lower the outgas partial pressure in the exposure apparatus, measures for increasing the capacity of the exhaust system such as a vacuum pump are also effective. However, it is difficult to improve the throughput because moisture adhering to the transferred wafer and hydrocarbons generated from the resist and stage mechanism are not allowed to drift into the space where the optical element is installed due to diffusion.
The present invention has been made in view of the above-described background, and an object of the present invention is to reduce contamination of the exposure atmosphere.

An exposure method for solving the above problem is an exposure method in which a space surrounding at least a part of the projection optical system is decompressed and ventilated, and the substrate is exposed through the original and the projection optical system. And in this invention, the flow volume of the gas supplied to this space is made into the range of 0.05-50 Pa * m < ³ > / s, It is characterized by the above-mentioned.

An exposure apparatus for solving the above-described problems includes a projection optical system that projects light from an original onto a substrate, and a chamber that surrounds a space surrounding at least a part of the projection optical system. The exposure apparatus further includes an exhaust unit that exhausts the space and a supply unit that supplies a gas to the space, and exposes the substrate through the original and the projection optical system. And in this invention, it has a control means which controls the flow volume of the gas supplied to this space by the said supply means in the range of 0.05-50 Pa * m < ³ > / s.

  According to the present invention, for example, contamination of the exposure atmosphere can be reduced.

  In a preferred embodiment of the present invention, a partition for separating the space into a plurality of spaces is provided, and the supply means supplies the gas to a space adjacent to the space including the substrate among the plurality of spaces. The control means controls the supply means or the exhaust means. Alternatively, there may be provided means for changing conductance in a space surrounding at least a part of the projection optical system.

In an exposure apparatus having detection means for detecting a predetermined amount of gas in a space surrounding at least a part of the projection optical system, the control means is configured to control the flow rate of the gas based on a signal from the detection means. It is preferable to be configured to control.
The control means controls the flow rate of the gas within a range in which the pressure in the space surrounding at least a part of the projection optical system becomes positive with respect to the pressure in the space including the substrate.
The gas is, for example, either a rare gas such as helium or argon and hydrogen.
The present invention is particularly effective when the light for exposing the substrate is extreme ultraviolet light.

The features of the preferred embodiments of the present invention and the corresponding objects and advantages will be apparent from the following description made with reference to the accompanying drawings. Note that in the drawings, the same or similar reference numerals represent the same or similar components throughout the drawings.
Embodiments according to the present invention will be described below in detail with reference to the embodiments shown in the accompanying drawings.

FIG. 1 shows an embodiment 1 of an exposure apparatus using EUV light of the present invention (here, light having a wavelength of 0.1 to 30 nm, more preferably 10 to 15 nm).
In FIG. 1, reference numeral 8 denotes EUV light emitted from an unillustrated EUV light source and guided by an unillustrated illumination optical system, and this EUV light 8 is applied to the original 11 through the original illumination mirror 1. 2 is a projection system first mirror, 3 is a projection system second mirror, 4 is a projection system third mirror, 5 is a projection system fourth mirror, 6 is a projection system fifth mirror, and 7 is a projection system sixth mirror. Reference numeral 12 denotes an original holding apparatus, 15 denotes an original stage, 16 denotes an original alignment optical system, and 17 denotes an original stage space surrounding the original stage 15. Further, 22 is a wafer (substrate), 24 is a wafer holding device, 21 is a wafer stage, 25 is a wafer alignment optical system, 26 is a focus position detection mechanism, and 27 is a wafer stage space surrounding the wafer stage 21. The wafer stage space 27 is a space including a wafer (substrate). Reference numerals 31 to 34 denote turbo molecular pumps as exhaust means, 41 denotes a gas supply unit, 42 denotes a gas flow rate control unit, 61 to 66 denote pressure sensors, 72 denotes openings, and 74 and 75 denote gas component detection units.

  There are several types of EUV light sources (not shown), and one of them, a laser-produced plasma light source, can emit light only in a necessary wavelength band by selecting a target material. For example, when Xe is ejected from a pulse nozzle as a target material and plasma is generated by irradiating it with a pulse laser, EUV light having a wavelength of 13 to 14 nm is emitted.

  An illumination optical system (not shown) includes a plurality of multilayer mirrors and an optical integrator. The role of the illumination optical system includes condensing light emitted from the light source efficiently and making the illuminance of the exposure area uniform. The optical integrator has a role of uniformly illuminating the mask with a predetermined numerical aperture.

  The projection optical system is composed of a plurality of multilayer mirrors coated with Mo and Si alternately. Since this multilayer film has a direct incidence reflectance of EUV light of about 67%, most of the energy absorbed by the multilayer mirror is changed to heat. Therefore, low thermal expansion glass or the like is used as the mirror base material.

The original stage 15 and the wafer stage 21 have a mechanism that is driven in a vacuum environment, and perform scanning in synchronization with a speed ratio proportional to the reduction magnification. The positions and orientations of the original stage 15 and the wafer stage 21 are observed and controlled by a laser interferometer (not shown).
The original 11 is held by the original holding device 12 on the original stage 15. The wafer 22 is held by a wafer holding device 24 on the wafer stage 21. Each of the original stage 15 and the wafer stage 21 has a fine movement mechanism, and the original 11 or the wafer 22 can be positioned.

The alignment detection mechanisms 16 and 25 measure the positional relationship between the position of the original 11 and the optical axis of the projection optical system, and the positional relationship between the wafer 22 and the optical axis of the projection optical system, respectively. Based on the result, the positions and angles of the original stage 15 and the wafer stage 21 are adjusted so that the projected image of the original 11 coincides with a predetermined position on the wafer 22.
The focus position detection mechanism 26 detects a vertical focus position on the wafer 22 surface in order to keep the imaging position of the projection optical system on the wafer 22 surface.
When one exposure is completed, the wafer stage 21 moves stepwise in the X and Y directions, moves to the next scanning exposure start position, and performs exposure again.

As described above, in order to maintain a stable throughput, it is necessary to prevent as much as possible the decrease in reflectance of the projection system mirrors 2 to 7 due to outgas.
The exposure apparatus of the present embodiment solves the above-described problems and prevents the exposure performance and throughput from decreasing.

The exposure apparatus of the present embodiment includes a gas supply unit 41 that supplies gas into the projection optical system space 18 and turbo molecular pumps 32 and 33 that exhaust the gas in the projection optical system space 18 to the outside.
The projection optical system space 18 and the wafer stage space 27 have a communicating opening 72 that does not block the EUV light 8. The opening 72 is a path through which outgas generated by the reaction between the EUV light 8 and the resist or outgas generated in the wafer stage space 27 enters the projection optical system space 18. By suppressing the outgas entering from this path as much as possible and reducing the outgas partial pressure in the projection optical system space 18, it is possible to prevent the reflectance of the projection optical system mirrors 2 to 7 from decreasing.

  As means for suppressing outgas entering the projection optical system space 18 through the opening 72, gas is supplied into the projection optical system space 18, and the projection optical system space 18 is kept at a positive pressure from the wafer stage space 27 to perform projection. A method using a pressure difference between the optical system space 18 and the wafer stage space 27 can be considered. Due to the pressure difference between the projection optical system space 18 and the wafer stage space 27, the gas supplied into the projection optical system space 18 flows into the wafer stage space 27. The gas flowing through the opening 72 can prevent outgas from entering the projection optical system space 18.

  If the gas flow in the opening 72 is considered a little more microscopic, gas molecules flowing through the opening 72 toward the wafer stage space 27 successively collide with outgas molecules. The collision between the molecules prevents outgas molecules from entering the projection optical system space 18. Therefore, it is a condition that the mean free path of gas molecules flowing through the opening 72 is shorter than the opening width of the opening 72, and an intermediate flow region or a viscous flow region is preferable as the gas flow field.

  FIG. 2 shows the state of the gas flow field depending on the opening width and the pressure in the space when helium is supplied into the projection optical system space 18. From FIG. 2, the pressure in the projection optical system space 18 takes into account the transmittance of the EUV light 8 shown in FIG. 3 and the flow field of the opening 72 satisfies the intermediate flow region or the viscous flow region according to the opening width. Select a value. For example, when the opening width of the opening 72 is about 10 mm, as shown in FIG. 2, the pressure in the projection optical system space 18 is about 1 Pa or more for the flow field of the opening 72 to satisfy the intermediate flow region or the viscous flow region. You can see that Further, FIG. 3 shows that in order to ensure the transmittance of the EUV light 8 to about 90%, it is sufficient to set it to about 10 Pa or less (when the optical path length is 1 m). The gas supplied into the projection optical system space 18 is preferably a rare gas such as helium or argon or hydrogen. Among these, helium is more preferable because it has a high transmittance for EUV light 8.

  In order to make it easier to ensure the transmittance of the EUV light 8, it is preferable that the projection optical system space 18 is separated by the partition wall 13 and the space to which the gas is supplied is made as narrow as possible. Furthermore, when the projection optical system space 18 is divided into two or more spaces, it is preferable to supply gas to a space adjacent to the wafer stage space 27 among the two or more spaces. A space adjacent to the wafer stage space 27 communicates with the wafer stage space 27 through an opening 72.

  Outgas generated in the projection optical system space 18 is exhausted by turbo molecular pumps 32 and 33 installed in the projection optical system space 18. The exhaust means in this embodiment is a turbo molecular pump, but other cold traps or ion pumps may be used.

  However, in order to protect the projection optical system mirrors 2 to 7 in the projection optical system space 18 from outgassing, it is not sufficient to make the projection optical system space 18 described above positive. In addition to the exposure area (not shown) on the wafer 22 and the driving unit for the wafer stage 21, the outgas is generated from a fine movement mechanism (not shown), a sensor, etc. Also occurs. FIG. 4 shows a value obtained by estimating the outgas partial pressure in the projection optical system space 18 according to the gas supply amount under the condition that the pressure in the projection optical system space 18 is maintained at a constant value of 1 Pa or 10 Pa. An empirical estimated value was used as the amount of outgas generated in the projection optical system space 18. Here, it goes without saying that if the gas supply amount is increased while the pressure in the projection optical system space 18 is kept constant, the exhaust speed in the projection optical system space 18 also increases at the same time. In FIG. 4, if the amount of gas supplied into the projection optical system space 18 increases, the exhaust velocity also increases, so the outgas partial pressure in the projection optical system space 18 tends to decrease.

As described above, in order to suppress outgas entering the projection optical system space 18 from the opening 72, the pressure in the projection optical system space 18 is such that the flow field of the opening 72 satisfies the intermediate flow region or the viscous flow region. In addition, a value considering the transmittance of the EUV light 8 shown in FIG. 3 may be selected. However, even if the pressure in the projection optical system space 18 is maintained at 1 Pa or 10 Pa shown in FIG. 4, the outgas partial pressure in the projection optical system space 18 is the supply amount of gas supplied into the projection optical system space 18. It depends on. On the other hand, to maintain the reflectance of the projection optical system mirror 2-7, in order to continue the stable throughput is preferably outgas partial pressure in the projection optical system space 18 is less than 10 -4 ^Pa, 10 ^- More preferably, it is ⁵ Pa or less. Considering the above, the supply amount of the gas supplied into the projection optical system space 18 is preferably in the range of 0.05 to 50 Pa · m ³ / s. In this range, the outgas partial pressure in the projection optical system space 18 is 10 ⁻⁴ Pa or less, the flow field at the opening 72 described above is an intermediate flow region or a viscous flow region, and the transmittance of the EUV light 8 is 90. It is a preferable range as the supply amount of the gas for securing about%.

  In this embodiment, the gas supply amount supplied into the projection optical system space 18 is controlled to an arbitrary flow rate by the gas flow rate control unit 42. Furthermore, when the exhaust means installed in the EUV exposure apparatus 90 is stopped for some reason, the gas flow rate control unit 42 stops the supply of gas.

A second embodiment of the present invention will be described.
In the present embodiment, a configuration for reducing the running cost of the EUV exposure apparatus 90 in the first embodiment will be described. FIG. 5 shows the arrangement of an exposure apparatus according to Embodiment 2 of the present invention. A channel cross-sectional area control unit 48 and a channel area variable unit 49 are added to the configuration shown in FIG.
As shown in FIGS. 1 and 5, gas component detectors 74 and 75 are installed in the projection optical system space 18 in order to manage the gas components in the projection optical system space 18 periodically or continuously. . The gas component detectors 74 and 75 can accurately measure the partial pressure (amount) of a specific outgas (a predetermined gas such as water or hydrocarbon) in the projection optical system space 18.

  At least during exposure, the inside of the EUV exposure apparatus 90 is evacuated by the evacuation means, so that it is considered that the amount of outgas generated from the projection optical system space 18 gradually decreases when the exposure apparatus is used for a long time. If the outgas partial pressure in the projection optical system space 18 is significantly below the allowable value, the outgas partial pressure is maintained at a constant value while the pressure in the projection optical system space 18 is maintained constant. The flow rate of the gas supplied into the projection optical system space 18 and the exhaust speed of the exhaust means for exhausting the gas in the projection optical system space 18 can be reduced. For example, helium, which has a high EUV transmittance, is more expensive than nitrogen, argon, and the like. Therefore, it is possible to reduce the running cost of the apparatus by reducing the consumption of helium.

  In the exposure apparatus of FIG. 5, the flow rate of the gas supplied into the projection optical system space 18 is controlled by the gas flow rate control unit 42. Further, the exhaust speed in the projection optical system space 18 is adjusted by changing the conductance immediately before the exhaust means 33 by the flow path area variable section 49 installed immediately before the exhaust means, and is controlled by the flow path area control section 48. The The flow path area varying unit 49 is preferably configured to absorb radiant heat such as temperature control so that the radiant heat from the exhaust means does not affect the projection optical system mirrors 6 and 7.

  By controlling the gas flow rate control unit 42 and the flow path area control unit 48 in accordance with signals from the gas component detection units 74 and 75, the pressure in the projection optical system space 18 is kept constant, and the outgas partial pressure is managed. Is possible. If the gas supply amount and the exhaust amount are controlled in accordance with the outgas partial pressure, supply and exhaust of gas more than necessary to the projection optical system space 18 can be suppressed, and the running cost of the EUV exposure apparatus 90 can be reduced. The flow rate control method for the gas supplied into the projection optical system space 18 and the exhaust velocity control method for exhausting the gas in the projection optical system space are not limited to the above-described examples, and various methods can be applied. In this embodiment, both the gas supply amount and the exhaust speed (flow channel area) are controlled. However, the gas supply amount is such that only the exhaust speed is controlled with the opening of the supply valve kept constant. Anyway.

Next, a manufacturing process of a micro device (a semiconductor chip such as an IC or LSI, a liquid crystal panel, a CCD, a thin film magnetic head, a micromachine, etc.) using the exposure apparatus will be described.
FIG. 7 shows a flow of manufacturing a semiconductor device.
In step 1 (circuit design), a semiconductor device circuit is designed. In step 2 (mask production), a mask on which the designed pattern is formed is produced.
On the other hand, in step 3 (wafer manufacture), a wafer is manufactured using a material such as silicon. Step 4 (wafer process) is called a pre-process, and an actual circuit is formed on the wafer by lithography using the wafer and the exposure apparatus provided with the prepared mask.
The next step 5 (assembly) is called a post-process, and is a process for forming a semiconductor chip using the wafer manufactured in step 4. The post-process includes assembly processes such as an assembly process (dicing and bonding) and a packaging process (chip encapsulation). In step 6 (inspection), the semiconductor device manufactured in step 5 undergoes inspections such as an operation confirmation test and a durability test. A semiconductor device is completed through these processes, and is shipped in Step 7.

  The wafer process in step 4 includes an oxidation step for oxidizing the surface of the wafer, a CVD step for forming an insulating film on the wafer surface, and an electrode formation step for forming electrodes on the wafer by vapor deposition. Also, an ion implantation step for implanting ions into the wafer, a resist processing step for applying a photosensitive agent to the wafer, and an exposure step for printing and exposing the circuit pattern on the wafer after the resist processing step by the exposure apparatus described above. Further, there are a development step for developing the wafer exposed in the exposure step, an etching step for removing portions other than the resist image developed in the development step, and a resist stripping step for removing the resist that has become unnecessary after the etching. By repeating these steps, multiple circuit patterns are formed on the wafer.

It is a figure which shows schematically the structure of the EUV exposure apparatus which concerns on Example 1 of this invention. It is a figure which shows the state of the flow field in space. It is the figure which showed the transmittance | permeability of EUV light. It is a figure which shows the relationship between a gas supply amount and an outgas partial pressure. It is a figure which shows schematically the structure of the EUV exposure apparatus which concerns on Example 2 of this invention. It is the schematic of the conventional EUV exposure apparatus. It is a figure explaining the flow of the manufacturing process of a device.

Explanation of symbols

  1: original illumination mirror, 2-7: projection system first to sixth mirrors, 8: EUV light, 9: main body chamber, 11: original plate, 12: original plate holding device, 15: original plate stage, 16: original plate alignment optical system, 17: original stage space, 18: projection optical system space, 20: original load lock space, 21: wafer stage, 22: wafer, 24 wafer holding device, 25: wafer alignment optical system, 26: focus position detection mechanism, 27: Wafer stage space, 28: Wafer load lock space, 31-36: Turbo molecular pump, 41: Gas supply unit, 42: Gas flow rate control unit, 48: Channel cross-sectional area control unit, 49: Channel cross-sectional area variable unit, 61-66: Pressure sensor, 72: Opening part, 74, 75: Gas component detection part, 90: Exposure apparatus.

Claims (11)

An exposure method in which a space surrounding at least a part of the projection optical system is decompressed and ventilated, and the substrate and the substrate are exposed through the projection optical system,
An exposure method characterized in that the flow rate of the gas supplied to the space is in the range of 0.05 to 50 Pa · m ³ / s. A projection optical system for projecting light from the original onto a substrate; a chamber surrounding a space surrounding at least a part of the projection optical system; an exhaust means for exhausting the space; and a supply means for supplying gas to the space An exposure apparatus that exposes the substrate through the master and the projection optical system,
An exposure apparatus comprising control means for controlling the flow rate of the gas supplied to the space by the supply means within a range of 0.05 to 50 Pa · m ³ / s.   3. The partition according to claim 2, further comprising a partition wall that separates the space into a plurality of spaces, wherein the supply unit supplies the gas to a space adjacent to the space including the substrate among the plurality of spaces. Exposure equipment.   The exposure apparatus according to claim 2, wherein the control unit controls the supply unit.   The exposure apparatus according to claim 2, wherein the control unit controls the exhaust unit.   4. The exposure apparatus according to claim 2, wherein the control means includes means for changing conductance in a space surrounding at least a part of the projection optical system.   It has a detection means for detecting a predetermined amount of gas in a space surrounding at least a part of the projection optical system, and the control means controls the flow rate of the gas based on a signal from the detection means. An exposure apparatus according to claim 2, wherein   The control means controls the flow rate of the gas within a range in which a pressure in a space surrounding at least a part of the projection optical system becomes a positive pressure with respect to a pressure in a space including the substrate. Item 8. The exposure apparatus according to any one of Items 2 to 7.   9. The exposure apparatus according to claim 2, wherein the gas is one of a rare gas and hydrogen.   The exposure apparatus according to claim 2, wherein the light for exposing the substrate is extreme ultraviolet light.   11. A device manufacturing method comprising: exposing a substrate using the exposure apparatus according to claim 2; and developing the exposed substrate.

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