JP4973425B2 - Cleaning method of condensing optical means in extreme ultraviolet light source device and extreme ultraviolet light source device - Google Patents

Description

  The present invention relates to a method for cleaning condensing optical means in an extreme ultraviolet light source device that emits extreme ultraviolet light, and an extreme ultraviolet light source device. More specifically, for effectively removing debris that is emitted from the extreme ultraviolet light generating portion toward the condensing optical means and eventually adheres to and accumulates on the condensing optical means, thereby reducing its condensing performance, that is, reflectance. The present invention relates to a cleaning method and an extreme ultraviolet light source device.

  With the miniaturization and high integration of semiconductor integrated circuits, improvement in resolving power is demanded in the projection exposure apparatus for production. In order to meet this demand, the exposure light source has been shortened. As a next-generation semiconductor exposure light source following the excimer laser apparatus, extreme ultraviolet light having a wavelength of 13 to 14 nm, particularly a wavelength of 13.5 nm (hereinafter referred to as “ultraviolet light”). An extreme ultraviolet light source device (hereinafter also referred to as an EUV light source device) that emits EUV (also referred to as Extreme Ultra Violet) has been developed.

Several methods are known for generating EUV light in an EUV light source device. One of them is heated to excite EUV radiation that emits EUV light, thereby generating a high-temperature plasma. There is a method for extracting the emitted EUV light.
This EUV light source device is roughly classified into an LPP (Laser Produced Plasma) method and a DPP (Discharge Produced Plasma, discharge generated plasma) method according to a high temperature plasma generation method.

In the LPP type EUV light source device, a laser beam is irradiated onto a target made of a raw material containing EUV radiation species. At that time, high-temperature plasma is generated by laser ablation, and EUV light emitted from the plasma is used.
On the other hand, in the DPP type EUV light source device, high temperature plasma is generated by current driving from a raw material containing EUV radiation species, and EUV light emitted from the high temperature plasma is used. As a discharge method in the DPP type EUV light source device, there are a Z pinch method, a capillary discharge method, a plasma focus method, a hollow cathode trigger Z pinch method, and the like. The DPP type EUV light source device has advantages such as downsizing of the light source device and low power consumption of the light source system as compared with the LPP type EUV light source device, and is expected to be put to practical use.

In both types of EUV light source devices described above, as a radioactive species that emits EUV light having a wavelength of 13.5 nm, that is, as a raw material for high-temperature plasma, xenon (Xe) ions and tin (Sn) ions of about 10 valence are currently used. Are known. Among these, tin has a ratio of an electric input necessary for generating high-temperature plasma to an EUV light output having a wavelength of 13.5 nm, that is, EUV conversion efficiency (= light output / electric input) several times larger than xenon.
Therefore, it is regarded as promising as a radiation type of mass-produced EUV light sources for which high output is required. For example, as disclosed in Patent Document 1, a gaseous tin compound (for example, stannane gas: SnH ₄ gas) In addition, development of an EUV light source using solid or liquid tin as an EUV radiation species is underway.

Hereinafter, a configuration example of the EUV light source apparatus will be described taking the DPP method as an example.
FIG. 6 shows a schematic configuration example of a DPP EUV light source device. As shown in the figure, the DPP EUV light source device has a vacuum container (light source chamber 10), and the chamber 10 is divided into a first chamber 10a and a second chamber 10b. In the first chamber 10a, for example, a ring-shaped first electrode (cathode) 11 and a second electrode (anode) 12 sandwich a ring-shaped insulator 13, and the respective through holes are positioned substantially coaxially. Are arranged as follows. Hereinafter, the first electrode 11, the second electrode 12, and the insulating material 13 may be collectively referred to as the discharge part 1.

A raw material containing EUV radiation species is supplied into the chamber 10 from the raw material supply means 14 connected to the raw material inlet 14a provided in the first chamber 10a. The raw material is, for example, SnH ₄ gas.
Further, on the second chamber 10b side, a gas exhaust unit 9 for adjusting the pressure in the chamber and exhausting the chamber based on the measured value of the pressure monitor that monitors the pressure in the chamber (not shown) is provided in the second chamber 10b. It is connected to the gas outlet provided in the.

  A condensing mirror 2 is provided in the second chamber 10b. For example, the condensing mirror 2 includes a plurality of concave mirrors whose reflecting surface shape is a spheroid, a rotating paraboloid shape, a Walter shape, or the like. These concave mirrors have rotating body shapes with different diameters. The condensing mirror 2 is configured as a grazing incidence type reflecting mirror in which the plurality of concave mirrors are arranged on the same axis so that the rotation center axes are overlapped so that the focal positions substantially coincide with each other.

  In such a DPP-type light source device, when pulse power is supplied from the pulse power generator 15 between the first electrode 11 and the second electrode 12, creeping discharge is generated on the surface of the insulator 13 and the first discharge is generated. The first electrode 11 and the second electrode 12 are substantially short-circuited, and a large pulse current flows. At this time, plasma is formed in or near the communication hole formed by the ring-shaped first electrode 11, second electrode 12, and insulator 13 arranged substantially coaxially. Thereafter, a high temperature plasma region is formed at the substantially central portion of the plasma by the pinch effect and Joule heating, and EUV light having a wavelength of 13.5 nm is emitted from the high temperature plasma region.

  EUV light having a wavelength of 13.5 nm emitted from the high temperature plasma region is collected by the condenser mirror 2 and taken out from the EUV light take-out unit 7 provided in the second chamber 10b. The EUV light extraction unit 7 is connected to an EUV light incident unit provided in an exposure machine casing of an exposure machine (not shown). That is, the EUV light condensed by the EUV collector mirror 2 enters the exposure device via the EUV light extraction unit.

Debris is also emitted from the high temperature plasma together with EUV light. Some debris is caused by a metal powder (for example, the first electrode 11 and the second electrode 12) sputtered by plasma and a radioactive seed material such as tin.
When the debris reaches the collecting mirror 2 and collides with or adheres to the reflecting surface of the collecting mirror 2, the reflecting performance of the collecting mirror 2 is impaired.
Therefore, the high-temperature plasma region (in the configuration example shown in FIG. 6, the communication hole formed in the ring-shaped first electrode 11, the second electrode 12, and the insulator 13 arranged substantially coaxially or in the vicinity of the communication hole) and condensing. A foil trap 3 is installed between the mirror 2.
The foil trap 3 suppresses the passage of debris while allowing the EUV light to pass. For example, as described in Patent Document 2, the foil trap 3 includes a plurality of plates installed in the radial direction of the high-temperature plasma generation region. . The pressure in the space in which the foil trap 3 is arranged rises, and the debris that passes through the space is less likely to reach the condenser mirror 2 because the kinetic energy is reduced.

In order to further reduce the amount of debris reaching the condenser mirror 2, a gas curtain may be formed in a region between the discharge unit 1 and the condenser mirror 2. Specifically, a gas curtain nozzle 4 connected to a gas supply unit 16 that supplies a gas that does not attenuate EUV light is disposed. The gas supplied from the gas supply unit 16 is supplied by the gas curtain nozzle 4 so that the gas flow intersects with debris. The gas curtain formed in this way creates a portion where the gas pressure is locally increased with respect to the debris emitted from the discharge unit 1 and scattered toward the condenser mirror 2 to decelerate the debris. Reaching the optical mirror 2 is prevented.
The DPP EUV light source device shown in FIG. 6 has a control unit (not shown). This control unit controls the pulse power generator 15, the raw material supply unit 14, the gas exhaust unit 9, and the gas supply unit 16 based on an EUV emission command from the exposure unit control unit.

JP 2004-279246 A JP-T-2002-504746 JP 2006-529057 A International Publication No. 2006/049886 Pamphlet JP 2007-165874 A

As described above, development of an EUV light source that uses tin as an EUV radiation species is underway.
However, when tin and / or tin compounds are heated and excited to generate high-temperature plasma, a large amount of debris due to tin is generated.
Some of the generated debris passes through the foil trap 3 and the gas curtain and reaches the condenser mirror 2.
Tin has a low vapor pressure and is solid at room temperature. Therefore, when the debris caused by tin reaches the condenser mirror 2, the solid tin adheres to and accumulates on the reflecting surface, thereby reducing the reflectance of the EUV light. As a result, the EUV light output emitted to the outside decreases.

In order to solve this problem, a cleaning method has been proposed in which a cleaning gas is flowed to remove tin deposited and deposited on the reflecting surface of the condenser mirror. For example, Patent Documents 3 and 4 show that a halogen element is introduced into a chamber and reacted with tin attached to a condenser mirror to be removed.
In the configuration example shown in FIG. 6, chlorine gas or the like, which is a cleaning gas, is supplied from the cleaning gas supply unit 5 and introduced into the condenser mirror 2 from the cleaning gas supply nozzle 6. At this time, at least a part of the cleaning gas may be converted into plasma and / or radical. The plasmaized and / or radicalized cleaning gas reacts better with tin than the molecular state gas, so that the tin removal rate is improved and cleaning can be completed in a short time. The cleaning gas supply nozzle 6 is arbitrarily configured so as not to shield as much as possible a part of the EUV light collected by the condenser mirror 2.
Since the cleaning gas that has reached the condenser mirror 2 is vaporized as a high vapor pressure tin compound by a chemical reaction with tin, it can be removed from the condenser optical means.

Patent Document 5 discloses that the partial pressure of the cleaning gas is in the range of 1 to 10 Pa.
However, we used halogen gas (chlorine gas) as the cleaning gas to clean the condensing optical means (condenser mirror) on which tin was deposited, and the partial pressure was in the range of 1-10 Pa. It was found that tin attached to the condenser mirror could not be removed in a short time such as 1 minute.
There is a demand for cleaning the condenser mirror as soon as possible when the reflectance decreases. Therefore, the cleaning is performed during the time until the exposure apparatus carries out the exposed wafer from the apparatus, carries in the next wafer, aligns it, and starts the next exposure process, that is, the wafer exchange time. Can be considered.
At present, the mirror is required to be cleaned when the reflectance drops to 90% of the initial value before tin deposition. When the reflectivity drops to 90% of the initial value before tin deposition, the amount of tin deposited (thickness) is 0.5 nm to 1 nm when the density of solid tin is 7.31 g / cm ^3. (See http://www.cxro.lbl.gov/) X-ray tools calculation.
Considering that cleaning of the condenser mirror is performed at the time of wafer replacement, the wafer replacement time is currently 30 seconds to 1 minute, and within that time, tin having a thickness of 0.5 nm to 1 nm is cleaned. Is desirable.

Here, the higher the partial pressure of the cleaning gas, the higher the cleaning rate of tin. If the cost is neglected, the chlorine gas partial pressure can be physically increased without limit by using a special cleaning gas supply and exhaust device.
For example, the cleaning gas supply unit 5 includes a reservoir tank having a volume comparable to that of the second chamber 10b, and a plurality of gas exhaust units 9 are connected to increase the displacement of a large amount of cleaning gas in a short time. To a partial pressure far exceeding 50 Pa in the chamber.
However, in a practical EUV light source device, it is desirable to keep the gas supply equipment and the exhaust unit required for the cleaning gas supply, the exhaust unit maintenance cost, and the installation location to the minimum necessary.
Further, since the cleaning gas is a highly reactive gas such as a halogen gas, if the partial pressure of the cleaning gas is increased too much, the apparatus may be adversely affected.

As described above, when the partial pressure of the cleaning gas is too small, cleaning cannot be performed within a desired time. On the other hand, in order to perform cleaning in a short time by increasing the partial pressure of the cleaning gas, it is not possible to perform cleaning. Costs increase due to the need to prepare equipment.
For this reason, it is necessary to introduce a cleaning gas with an appropriate partial pressure to clean the condensing optical means of the extreme ultraviolet light source device. In the past, it is desirable to introduce a cleaning gas with an appropriate partial pressure. It was not clear whether the cleaning could be effectively performed within the time.
SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the problem to be solved by the present invention is to use condensing optical means (condensing mirror) in which halogen gas is used as a cleaning gas and debris adheres and accumulates. ), An extreme ultraviolet light source that can be effectively cleaned within a desired time without providing special equipment for supplying and collecting cleaning gas and without adversely affecting the apparatus. It is an object of the present invention to provide a method for cleaning condensing optical means in an apparatus and an extreme ultraviolet light source apparatus having such a function.

As a result of intensive studies by the inventor, when the cleaning time is tc, the partial pressure X (Pa) of the cleaning gas is obtained by the following equation (1), and the above equation is obtained from the above equation for the cleaning time tc in the container. It has also been found that cleaning can be effectively performed by introducing a cleaning gas having a partial pressure X (Pa) which is also obtained.
Y = 1.6 × Ln (X) −5.6 (1)
Here, Y is the cleaning rate Y (Y = [film thickness d of attached debris] / [required cleaning time tc])

The present inventor confirmed the above relationship through the following experiment.
FIG. 1 shows the experimental results of the removal rate (cleaning rate) of tin adhering to the condenser mirror with respect to the cleaning gas partial pressure.
In this experiment, chlorine gas is used as the cleaning gas, a substrate (sample) on which tin adheres is placed in a container, sealed with chlorine gas in the container for 5 minutes, and the film thickness of tin on the substrate is measured. The film thickness decreased in 5 minutes was obtained, and this operation was repeated at each partial pressure of the cleaning gas while exchanging the sample. Each experimental result (thickness reduction amount) was divided by the time per unit time. The cleaning rate was obtained, plotted on a graph, and approximated by the method of least squares.
In the figure, the horizontal axis represents the chlorine gas partial pressure (unit Pa), and the vertical axis represents the tin cleaning rate (unit: nm / min). The straight line in the graph approximates the cleaning rate of tin at a partial pressure of chlorine gas of 48 Pa, 80 Pa, 133.3 Pa, 400 Pa, and 893 Pa by the least square method, and is the above-described equation (1).

For example, if the cleaning time is 1 minute (wafer replacement time) and 1 nm of tin is to be removed, 1 nm of tin is removed in 1 minute, so Y = 1 (nm / min). Is substituted into the above equation (1), the partial pressure X (Pa) of the cleaning gas can be obtained. Substituting the above Y into the equation (1) and converting with respect to X, the following equation is obtained.
X = e ^z (1 ′)
Here, z = (Y + 5.6) /1.6
Substituting Y = 1 into the above equation results in X = 61.9 Pa, and if halogen gas is introduced at a partial pressure of 61.9 Pa, 1 nm of tin can be cleaned in 1 minute of cleaning time. .
Also, when the cleaning time can be a relatively long time of 10 minutes, for example, during regular maintenance, it is sufficient to remove 0.1 nm in 1 minute, so that Y = 0. 1 (nm / min) is substituted. As a result, X = 35.3 (Pa), and a halogen gas may be introduced at a partial pressure of 35.3 Pa or more.
Similarly, if it is only necessary to remove 0.5 nm of tin with a cleaning time of 1 minute, Y = 0.5 (nm / min), and as a result, X = 45.3 (Pa). A gas may be introduced at a partial pressure of 45.3 Pa or more.
That is, the partial pressure of the introduced halogen gas can be obtained by substituting the cleaning time and the thickness of the tin film that needs to be removed into the above equation (1).

Here, as shown in the figure, when the partial pressure of the halogen gas is about 50 Pa, the cleaning rate of tin is about 0.8 nm / min. As the partial pressure of chlorine gas increases, the cleaning rate increases. When the pressure is about 900 Pa, the cleaning rate is about 5.5 nm / min.
When the cleaning rate shown in the figure is extrapolated in the direction in which the partial pressure is low, the cleaning rate becomes substantially zero when the chlorine gas partial pressure is about 30 Pa. Therefore, if the partial pressure of chlorine gas is not 30 Pa or more, it is considered that the tin actually attached to the condenser mirror cannot be cleaned.
On the other hand, as will be described later, the condenser mirror for cleaning has a structure in which a large number of cylindrical mirrors are stacked, and the gap between the mirrors is as narrow as about 5 mm.
Therefore, in order to smoothly flow the cleaning gas between the mirrors, the chlorine gas is desirably laminar. Here, since it is considered that the chlorine gas forms a laminar flow at 1000 Pa or less, the partial pressure of the chlorine gas is preferably 1000 Pa or less.

When the partial pressure of chlorine gas is 30 Pa or more, the EUV light is almost absorbed and does not pass to the EUV light extraction part. Therefore, the condenser mirror cannot be cleaned while emitting EUV light and performing the exposure process.
Therefore, it is desirable that the cleaning be performed during the wafer exchange time as described above, and considering that the condenser mirror is cleaned during the wafer exchange, 0.5 nm to 1 nm within 30 minutes to 1 minute. In this case, it is desirable that the partial pressure of chlorine gas is 50 Pa or more.
Further, if the cleaning is frequently performed before the reflectance of the reflecting mirror is reduced to 90%, that is, before the thickness of tin becomes 0.5 nm to 1 nm, the partial pressure of chlorine gas is 30 Pa to 50 Pa. Even within this range, it can be sufficiently cleaned.
From the above, the range of the partial pressure of chlorine gas for cleaning is considered to be at least 30 Pa or more, preferably 50 Pa to 1000 Pa.

The extreme ultraviolet light source device which is the subject of the present invention has the following basic configuration.
(i) Raw material supply means for supplying a raw material containing tin and / or a tin compound into the vacuum vessel.
(ii) Heating excitation means that is a discharge part that generates high-temperature plasma by heating and exciting the raw material.
(iii) Condensing optical means for condensing extreme ultraviolet light emitted from the high-temperature plasma at a predetermined position.
(iv) A light extraction portion for extracting the condensed light formed in the container.
(v) Cleaning gas introduction / exhaust means for introducing / exhausting a cleaning gas for removing contamination adhering to the condensing optical means.
(vi) Provided between the heating excitation means and the condensing optical means, and the vacuum container is placed in a first space in which the heating excitation means is disposed and a second space in which the condensing optical means is disposed. First shutter to divide (separate).
(vii) A second shutter provided in the light extraction portion of the container.

In the extreme ultraviolet light source apparatus having the above-described configuration, in the present invention, cleaning of debris deposited on the condensing optical means is performed by the following procedure.
(1) Stop generation of high-temperature plasma by the heating excitation means.
(2) The first and second shutters are closed and the second space in which the condensing optical means is arranged is replaced with the first space in which the heating excitation means is arranged and the light extraction unit to which the exposure machine is connected. Separate from the outside space.
(3) From the film thickness d of the attached debris and the required cleaning time tc, the cleaning rate Y is determined as Y = [film thickness d of the attached debris] / [necessary cleaning time tc]. The partial pressure X of the cleaning gas is obtained from the equation (1), Y = 1.6 × Ln (X) −5.6, and the cleaning gas is introduced into the second space from the cleaning gas introduction / exhaust means, and the partial pressure is X is introduced.

In the extreme ultraviolet light source device having the above-described configuration, the film thickness measuring unit, the pressure measuring unit for measuring the pressure of the cleaning gas in the container, and the opening and closing of the first and second shutters are controlled. Control means for controlling the cleaning gas introduction / exhaust means based on the output of the film thickness measuring means is provided, and when performing cleaning, the control means calculates the partial pressure of the cleaning gas to be introduced, and calculates the partial pressure of the cleaning gas. It can also be configured to perform cleaning by controlling the calculated value.
That is, when the cleaning means performs the cleaning, the cleaning rate Y (Y = [attached debris film thickness d]) from the debris film thickness d measured by the film thickness measurement means and the given cleaning time tc. / [Required cleaning time tc]) is calculated, and the cleaning rate Y is substituted into the following equation (2) to determine the partial pressure X (pa) of the cleaning gas in the container, and the cleaning gas introduction / By controlling the exhaust means, the cleaning gas having the partial pressure X obtained from the above formula is introduced into the container during the cleaning time tc.
Y = a × Ln (X) −b (2)
Here, the values of a and b in the above formula (2) are appropriately updated based on the cleaning processing time, the partial pressure of the cleaning gas, and the film thickness before and after cleaning obtained by the film thickness measuring means, It may be automatically updated to an appropriate value according to the above.

In the present invention, the following effects can be obtained.
(1) Since the partial pressure of the cleaning gas is obtained by the above equation (1) and the cleaning gas having this partial pressure is introduced for cleaning, the cleaning can be effectively performed within a desired time. it can.
Further, it is not necessary to provide special equipment for supplying and collecting the cleaning gas, and the cost can be reduced.
(2) During cleaning, the first and second shutters are closed so that the space where the condensing optical means for cleaning is arranged is separated from other spaces, so that the halogen gas as the cleaning gas can be changed. (The first space or the space on the exposure machine side).
Therefore, parts arranged in other spaces are not eroded by the halogen gas, and consumption of performance and life of the apparatus can be suppressed.
(3) The extreme ultraviolet light source device further controls film thickness measuring means, pressure measuring means for measuring the pressure of the cleaning gas in the container, and opening and closing of the first and second shutters, and the film thickness. Control means for controlling the cleaning gas introduction / exhaust means based on the output of the measuring means is provided, and when performing cleaning, the control means calculates the partial pressure of the introduced cleaning gas and controls the partial pressure of the cleaning gas. Thus, cleaning can be performed by automatically introducing a cleaning gas having an optimum partial pressure.

FIG. 2 is a diagram illustrating a schematic configuration example of the DPP type EUV light source apparatus according to the first embodiment of the present invention.
In FIG. 2, a first shutter (gate valve) 8 a that separates the first chamber 10 a and the second chamber 10 b is provided between the discharge unit 1 and the condenser mirror 2.
The EUV light extraction unit 7 of the second chamber 10b is also provided with a second shutter (gate valve) 8b that closes the opening.
The first shutter 8a is moved by the first shutter (gate valve) moving mechanism 8c, and is between the first chamber 10a in which the discharge unit 1 is arranged and the second chamber 10b in which the condenser mirror 2 is arranged. Block the communication hole. The second shutter 8b is moved by a second shutter (gate valve) moving mechanism 8d to block the EUV light extraction unit 7.
Thereby, the space of the second chamber 10b is isolated from the first chamber 10a and the exposure machine.

Further, a film thickness sensor 17 is provided in the vicinity of the foil trap 3 and the condenser mirror 2, and the film thickness d of debris attached to the foil trap 3 and the condenser mirror 2 is measured. The film thickness measured by the film thickness sensor 17 is sent to the control unit 19.
The pressure in the second chamber 10 b is measured by the pressure sensor 18, and the measured pressure is sent to the control unit 19.
As described above, the cleaning gas supply unit 5 supplies the halogen gas, which is a cleaning gas, and introduces it into the condenser mirror 2 from the cleaning gas supply nozzle 6. The cleaning gas that has reached the condenser mirror 2 is vaporized as a high vapor pressure tin compound by a chemical reaction with tin, and removes debris from the condenser mirror 2.
For example, as shown in the front view of FIG. 2 (b), the cleaning gas supply nozzle 6 is provided with a mirror for the condensing mirror 2 so as to shield as little as possible a part of the EUV light collected by the condensing mirror 2. The gas is disposed along the fixing member and the like, and the cleaning gas is discharged as indicated by the arrows in the figure. Here, as described above, at least a part of the cleaning gas may be converted into plasma and / or radical.
The other structures, for example, the configuration of the discharge unit for generating EUV, the vacuum vessel, and the like are the same as those in FIG.

The cleaning operation of debris such as tin deposited on the condenser mirror 2 will be described.
A film thickness sensor 17 attached in the vicinity of the condenser mirror 2 detects the amount of debris (tin) deposited on the condenser mirror 2, and performs a cleaning operation when the film thickness exceeds a predetermined thickness.
Note that the intensity of the EUV light reflected by the condenser mirror 2 may be monitored by a photodiode (not shown) or the like, and cleaning may be performed when the light amount falls below a predetermined value. When cleaning is performed, first, the introduction of the raw material gas from the raw material supply means 14 and the supply of power from the pulse power generator 15 to the discharge unit 1 are stopped, and the discharge in the discharge unit 1 is stopped.
Next, the first shutter 8a and the second shutter 8b are closed, and the second chamber 10b in which the condenser mirror 2 is disposed is isolated from the first chamber 10a and the exposure machine (not shown).
Then, the cleaning gas containing the halogen element is supplied from the cleaning gas supply unit 5 provided on the light emission side of the condenser mirror 2 to the inside of the condenser mirror 2 through the cleaning gas supply nozzle 6 so that the partial pressure is 30 Pa or more. The pressure sensor 18 is preferably introduced so that the pressure is within a range of 50 Pa to 1000 Pa.

At that time, the control unit 19 calculates a necessary partial pressure from an approximate expression of the relationship between the tin removal rate Y (= film thickness d / tin removal time t) and the cleaning gas partial pressure (X), which has been obtained in advance through experiments or the like. The cleaning gas supply unit 5 is operated until the partial pressure is determined, and gas is supplied. For example, when the approximate expression is Y = 1.6 × Ln (X) −5.6, if 1 nm of tin is removed per minute, that is, if Y = 1 nm / min is substituted, X = 61.9 Pa Become.
Here, the constant of the approximate expression does not always have to be the same value every time cleaning is performed. That is, in the second and subsequent cleanings, the optimal constant can be corrected by the control unit 19 by learning the history before and after the past cleaning. That is, the approximate expression is rewritten by adding the detected values and command values of the film thickness sensor 17, the pressure sensor 18, and the cleaning gas supply unit 5 before and after cleaning to the data.

The condensing mirror 2 has, for example, a structure in which a large number of cylindrical mirrors are stacked. Therefore, in order to distribute the cleaning gas through the gaps between the mirrors, the cleaning gas spreads over the entire light exit port of the condensing mirror 2. Then, it is blown out like a shower from a large number of holes formed in the cleaning gas supply nozzle 6. And it exhausts from the gas exhaust unit 9 provided in the light-incidence side of the condensing mirror 2. FIG.
If the value of the film thickness sensor 17 returns to the same level as before cleaning, the control unit 19 determines that the cleaning is finished.
Thereafter, after the cleaning gas is sufficiently exhausted by the gas exhaust unit 9, the first shutter 8a and the second shutter 8b are opened, the raw material gas is introduced, and power is supplied from the pulse power generator to the discharge unit 1. Is resumed and EUV irradiation is performed.

Since the first shutter 8a and the second shutter 8b are closed during the cleaning operation as described above, the space in which the cleaning gas spreads is limited in the second chamber 10b, and the first chamber 10a and the exposure machine Does not penetrate. Therefore, problems such as corrosion of the discharge electrode by halogen elements and corrosion of parts of the exposure apparatus do not occur.
When the discharge unit 1 is operated to generate EUV light, the cleaning supply nozzle 6 is provided with a moving mechanism so that the cleaning supply nozzle 6 does not block the EUV light. You may make it evacuate from.
Furthermore, if the exhaust gas unit 9 is provided on the light incident side of the foil trap 3, the cleaning gas flows not only in the condenser mirror 2 but also in the foil trap 3, so that debris adhering to the foil trap 3 is also cleaned. Can do. Since the debris adhering to the foil trap 3 may block the EUV light passing therethrough, it is desirable to remove it.
Further, the operation of the exhaust gas unit 9 may be stopped during cleaning to collect the cleaning gas in the second chamber.

FIG. 3 is a diagram illustrating a configuration example of the control unit 19 of the present embodiment.
As shown in the figure, the control unit 19 of the present embodiment includes a cleaning process in addition to the EUV light emission control unit 19a that controls the pulse power generator 15, the gas supply unit, the raw material supply means 14, etc. to emit EUV light. A cleaning processing unit 19b for controlling the operation is provided.
The cleaning control unit 19b includes a cleaning process start / end determination unit 191, a cleaning gas partial pressure calculation unit 192, a cleaning gas supply unit control unit 193, and a gas exhaust unit control unit 194. Cleaning is performed as follows. Control processing.
The cleaning process start / end determination unit 191 monitors the thickness of the debris measured by the film thickness sensor 17, and sends a cleaning start notification to the EUV light emission control unit 19a when the film thickness exceeds the preset value ds1. To do. The EUV light emission control unit 19a stops the introduction of the raw material gas from the raw material supply means 14 and the supply of electric power from the pulse power generator 15 to the discharge unit 1 as described above when the timing at which the cleaning process is possible comes. Then, a cleaning processing permission signal is sent to the cleaning processing unit 19b.
Upon receipt of the cleaning process permission signal, the cleaning process start / end determination unit 191 closes the first and second shutters 8a and 8b, and the cleaning gas partial pressure calculation unit 192 and the cleaning gas supply unit control unit. A cleaning start command is sent to 193.

When the cleaning start command is received, the cleaning gas partial pressure calculation unit 192 calculates the cleaning rate Y as described above from the film thickness d of the debris output from the film thickness sensor 17 and the preset cleaning time ts. The partial pressure X of the cleaning gas is obtained from equation (2).
Here, as described above, constant values may be used as the values of the coefficients a and b in the equation (2), but they may be automatically updated according to the result of cleaning.
For example, the initial values are set as a = 1.6 and b = 5.6, and the coefficient a is calculated based on the value of the film thickness sensor 17 before and after cleaning, the partial pressure value of the cleaning gas, and the cleaning time each time cleaning is performed. , B is recalculated. Based on this result, the values a and b are updated so as to be appropriate values according to the use environment.
When receiving the cleaning start command, the cleaning gas supply unit control unit 193 controls the cleaning gas supply unit 5 to start supplying the cleaning gas into the chamber 10b. Then, based on the output of the pressure sensor 18, control is performed so that the partial pressure of the cleaning gas becomes the partial pressure value obtained by the cleaning gas partial pressure calculation unit 192.

The cleaning process start / end determination unit 191 monitors the output of the film thickness sensor 17, and outputs a cleaning end command when the thickness of the debris becomes thinner than the preset film thickness ds2. Note that a cleaning end command may be output when the preset cleaning time ts has elapsed since the start of the cleaning process.
In response to this, the cleaning gas supply unit controller 193 stops the supply of the cleaning gas. Further, the gas exhaust unit controller 194 controls the gas exhaust unit 9 to exhaust the cleaning gas from the chamber 10b.
When the cleaning gas is sufficiently exhausted, the gas exhaust unit control unit 194 notifies the cleaning process start / end determination unit 191 that the exhaust of the cleaning gas has ended. In response to this, the cleaning process start / end determination unit 191 opens the first shutter 8a and the second shutter 8b, and notifies the EUV light emission control unit that the cleaning process has ended.

4 and 5 are diagrams showing a schematic configuration example of a second embodiment of the present invention in which the present invention is applied to a rotating electrode DPP type EUV light source device for rotating an electrode. FIG. 4 is a side view, FIG. 5 shows a top view.
The configuration of the discharge unit is different from the DPP type EUV light source device shown in FIG. 2, but the other configurations are basically the same.
In FIG. 4, the discharge part is arranged in the first chamber 10a, and the condenser mirror 2 is arranged in the second chamber 10b. A partition wall having a connection hole through which EUV light passes is provided between the first chamber 10a and the second chamber 10b. Gas exhaust units 9a and 9b are attached to both chambers, and the pressures in both chambers are maintained at preset values.
Then, the first shutter 8a closes the communication hole provided in the partition wall. Further, the second shutter 8b blocks an EUV light extraction portion formed in the second chamber 10b. In the figure, the shutter (gate valve) moving mechanism is omitted.

The structure of the discharge part of the rotating electrode DPP type EUV light source device of FIGS. 4 and 5 will be briefly described.
The discharge part is a first disc electrode 11 (first rotating electrode) which is a metal disc-like member, and is also a disc-like member made of metal, and is disposed on the back side of the first discharge electrode in FIG. The second discharge electrode 12 (second rotating electrode) (see FIG. 5).
Both the discharge electrodes 11 and 12 are made of, for example, a high melting point metal such as tungsten, molybdenum, or tantalum, and are disposed so as to face each other with a predetermined distance therebetween. Here, one of the two electrodes is a ground side electrode, and the other is a high voltage side electrode.
The surfaces of both electrodes 11 and 12 may be arranged on the same plane. However, as shown in FIGS. 4 and 5, the edge portions of the peripheral portion where the electric field concentrates when power is applied are separated from each other by a predetermined distance. It is preferable to arrange each electrode so as to face each other, that is, so that a virtual plane including each electrode surface intersects. Since discharge is likely to occur in the portion where the distance between the edge portions of the peripheral portions of the electrodes 11 and 12 is the shortest, the discharge position is stabilized by arranging in this way.

A rotation shaft 22f of the first motor 22a is attached to the substantially central portion of the disc-shaped first rotation electrode 11, and the first motor 22a rotates the rotation shaft 22f, whereby the first rotation electrode 11 is rotated. Rotates. Similarly, in FIG. 5, the second rotating electrode 12 is also attached with the rotating shaft 22e of the second motor 22b and is rotated by the second motor 22b. The direction of rotation is not particularly restricted.
Here, the rotating shafts of both electrodes are introduced into the first chamber 10a via, for example, mechanical seals 22c and 22d. The mechanical seals 22c and 22d allow the rotation shaft to rotate while maintaining a reduced-pressure atmosphere in the chamber 10a.

As shown in FIGS. 4 and 5, the first rotating electrode 11 is arranged so that a part of the first rotating electrode 11 is immersed in the conductive first container 11 b that houses the conductive molten metal 11 a for power feeding. Is done. Similarly, the second rotating electrode 12 is also arranged so that a part of the second rotating electrode 12 is immersed in the conductive second container 12b containing the conductive molten metal for power supply 12a.
Both containers 11b and 12b are connected to a pulse power generator 15 via insulating power introduction portions 11c and 12c capable of maintaining a reduced pressure atmosphere in the chamber 10a.
As described above, the molten metal for power supply 11a, 12a and the containers 11b, 12b for accommodating the same are conductive, and the first and second rotating electrodes 11, 12 are part of the molten metal for power supply 11a, Since it is immersed in 12a, by applying pulse power from the pulse power generator 15 between the first and second containers 11b, 12b, the first rotary electrode 11 and the second rotary electrode 12 are not connected. Pulse power is applied.

As the molten metal for power supply, a metal that does not affect EUV radiation during discharge is employed. The molten metal for power supply also functions as a cooling means for the discharge part of each of the rotating electrodes 11 and 12. Although not shown, the first and second containers 11b and 12b are provided with temperature adjusting means for maintaining the molten metal in a molten state.
The pulse power generator 15 has a first container 11b and a second container 12b as loads, that is, a first rotating electrode 11 and a second container, via a magnetic pulse compression circuit unit including a capacitor and a magnetic switch. A pulse power having a short pulse width is applied between the rotating electrode 12 and the rotating electrode 12.
By rotating the electrodes 11 and 12, consumption of the discharge electrode can be suppressed and the life of the discharge electrode can be extended.

Supply of EUV radiation species (hereinafter also referred to as high-temperature plasma raw material 21), for example, tin, for emitting extreme ultraviolet light to the discharge part is performed by the following method.
In the liquid or solid state from the raw material supply means 20 provided in the chamber 10a, the discharge region (the space between the edge portion of the peripheral portion of the first rotating electrode 11 and the edge portion of the peripheral portion of the second rotating electrode 12). And is supplied in the vicinity of a space where discharge occurs.
The raw material supply means 20 is provided, for example, on the upper wall of the chamber 10a, and tin, which is a high-temperature plasma raw material, is heated and supplied (dropped) in the form of droplets in the space near the discharge region.
The dropped droplet-shaped high-temperature plasma raw material (tin) is vaporized by being irradiated with a laser beam emitted from the laser device 23 when reaching the space near the discharge region.
The high temperature plasma raw material 21 (tin) vaporized by the laser beam irradiation spreads around the normal direction of the surface of the high temperature plasma raw material on which the laser beam is incident.

When the high-temperature plasma raw material 21 (tin) thus vaporized and spreads reaches the discharge region sandwiched between the first rotating electrode 11 and the second rotating electrode 12, the pulse power generator 15 is applied to both electrodes. Pulse power is applied. The discharge generated between the electrodes 11 and 12 forms high-temperature plasma from the raw material and emits EUV light.
Note that a raw material recovery means 25 for recovering the high temperature plasma raw material (tin) that has not been vaporized may be provided below the space to which the high temperature plasma raw material is supplied, as shown in FIG.

Also in the present embodiment, when the amount of tin deposited on the collector mirror 2 is detected by the film thickness sensor 17 attached in the vicinity of the collector mirror 2, and when the thickness exceeds a predetermined thickness, the control unit 19 Perform the cleaning operation.
Note that, as described above, the intensity of the EUV light reflected by the condenser mirror 2 may be monitored by a photodiode (not shown) or the like, and cleaning may be performed when the light amount falls below a predetermined value.
When performing the cleaning, first, the EUV irradiation is performed by stopping the supply of the plasma raw material 21 from the raw material supply means 20, the supply of power from the pulse power generator 15 to the discharge unit, and the laser irradiation from the laser device 23. Stop.
Next, the first shutter 8a and the second shutter 8b are closed.

Then, the cleaning gas containing the halogen element is supplied from the cleaning gas supply unit 5 provided on the light emission side of the condenser mirror 2 to the inside of the condenser mirror 2 through the cleaning gas supply nozzle 6 so that the partial pressure is 30 Pa or more. The pressure sensor 18 is preferably introduced so that the pressure is within a range of 50 Pa to 1000 Pa.
At that time, as described in the above embodiment, the control unit 19 determines the relationship between the tin removal rate Y (= film thickness d / tin removal time t) and the cleaning gas partial pressure (X) obtained in advance through experiments or the like. The necessary partial pressure is determined from the approximate expression, and the cleaning gas supply unit 5 is operated to supply gas until the desired partial pressure is reached.
The control method of the cleaning gas supply unit 5 is the same as that in the embodiment of FIG.
If the value of the film thickness sensor 17 returns to the same level as before cleaning, the control unit 19 determines that the cleaning is finished. Thereafter, after sufficiently exhausting the cleaning gas, the first shutter 8a and the second shutter 8b are opened, the plasma raw material is supplied, the power is supplied from the pulse power generator 15 to the discharge unit 1, and the laser device Laser irradiation is resumed and EUV irradiation is performed.

  When exhausting the cleaning gas, if a gas other than the cleaning gas (flushing gas) is introduced into the chamber, the cleaning gas can be exhausted quickly. This is because the cleaning gas in the chamber is diluted with a large amount of flushing gas, and the cleaning gas can be flushed with the flushing gas and exhausted. Also, the amount of cleaning gas remaining in the chamber can be reduced. Examples of gases other than the cleaning gas introduced at this time include inert gases such as helium, argon, neon, and nitrogen. Among them, helium is desirable because it absorbs less EUV light even if it remains in the chamber.

It is a figure which shows the relationship of the removal rate (cleaning rate) of the tin adhering to the condensing mirror with respect to the partial pressure of cleaning gas. 1 is a diagram illustrating a schematic configuration example of a DPP-type EUV light source apparatus according to a first embodiment of the present invention. It is a figure which shows the structural example of the control part of the EUV light source device of 1st Example of this invention. It is a figure (side view) which shows the example of schematic structure of the 2nd Example of this invention which applied this invention to the EUV light source device of a rotating electrode DPP system. It is a figure (top view) which shows the example of schematic structure of the 2nd Example of this invention which applied this invention to the EUV light source device of a rotating electrode DPP system. It is a figure which shows the example of schematic structure of the conventional EUV light source device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Discharge part 2 Condensing mirror 3 Foil trap 4 Gas curtain nozzle 5 Cleaning gas supply unit 6 Cleaning gas supply nozzle 7 EUV light extraction part 8a Shutter (gate valve)
8b Shutter (Gate valve)
9 Gas exhaust unit 10 Light source chamber (container)
DESCRIPTION OF SYMBOLS 10a 1st chamber 10b 2nd chamber 11 1st electrode 12 2nd electrode 13 Insulator 14 Raw material supply means 15 Pulse power generator 16 Gas supply unit 17 Film thickness sensor 18 Pressure sensor 19 Control unit 20 Raw material supply means 21 Plasma raw material 22a 22b Motor 23 Laser device P Plasma

Claims (3)

A container,
Raw material supply means for supplying a raw material containing tin and / or a tin compound into the container;
Heating excitation means for generating high-temperature plasma by heating and exciting the supplied raw material in the container;
A condensing optical means for condensing the extreme ultraviolet light emitted from the high-temperature plasma at a predetermined position; a light extraction portion formed on the container for extracting the condensed light;
A cleaning method for the condensing optical means in an extreme ultraviolet light source device comprising a cleaning gas supply means for introducing a cleaning gas containing a halogen element for removing debris attached to the condensing optical means,
The cleaning rate Y (Y = [attached debris film thickness d] / [required cleaning time tc]) is calculated from the film thickness of the attached debris and the required cleaning time, and the cleaning rate Y is calculated. Substituting into the following formula (1) to obtain the partial pressure X (Pa) of the cleaning gas in the container,
Y = 1.6 × Ln (X) −5.6 (1)
A cleaning method for condensing optical means in an extreme ultraviolet light source device, wherein cleaning is performed by introducing a cleaning gas having a partial pressure X obtained from the above formula into the container for the cleaning time tc. Between the heating excitation means and the condensing optical means, the container is divided into a first space in which the heating excitation means is arranged and a second space in which the condensing optical means is arranged. 1 and a second shutter is provided at the light extraction portion of the container, and the generation of high temperature plasma by the heating excitation means is stopped, and the first shutter and the second shutter are stopped. Close the shutter, separate the second space from the other space,
Cleaning in the extreme ultraviolet light source device according to claim 1, wherein cleaning is performed by introducing a cleaning gas having a partial pressure X obtained from the equation (1) into the container for the cleaning time tc. Cleaning method for optical optical means. A container,
Raw material supply means for supplying a raw material containing tin and / or a tin compound into the container;
Heating excitation means for generating high-temperature plasma by heating and exciting the supplied raw material in the container;
A condensing optical means for condensing the extreme ultraviolet light emitted from the high-temperature plasma at a predetermined position; a light extraction portion formed on the container for extracting the condensed light;
A cleaning gas supply means for introducing a cleaning gas containing a halogen element for removing debris (contamination) adhering to the condensing optical means;
The container is provided between the heating excitation unit and the condensing optical unit, and the container is divided into a first space in which the heating excitation unit is disposed and a second space in which the condensing optical unit is disposed. A first shutter;
A second shutter provided in the light extraction portion of the container;
A film thickness measuring means for measuring the thickness of the attached debris, a cleaning gas introduction / exhaust means for introducing a cleaning gas into the container and exhausting the cleaning gas in the container;
Pressure measuring means for measuring the pressure of the cleaning gas in the container;
Control means for controlling opening and closing of the first and second shutters, and control means for controlling the cleaning gas introduction / exhaust means based on the output of the film thickness measuring means,
When performing the cleaning, the control means determines the cleaning rate Y (Y = [attached debris film thickness d] / [) from the debris film thickness d measured by the film thickness measurement means and the given cleaning time tc. Means for calculating the required cleaning time tc]), and substituting the cleaning rate Y into the following equation (2) to obtain the partial pressure X (pa) of the cleaning gas in the container,
Y = a × Ln (X) −b (2)
The extreme ultraviolet light source characterized in that the control means controls the cleaning gas introduction / exhaust means to introduce a cleaning gas having a partial pressure X obtained from the above equation into the container during the cleaning time tc. apparatus.

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