JP2012019226A - Extreme ultraviolet light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately determine a timing to replace an extreme ultraviolet (EUV) collector mirror by accurately considering influence of a sputtering amount of the mirror in a laser-produced plasma (LPP) EUV light source device.SOLUTION: An EUV light source device comprises: a sputtering amount detector which is arranged in a vacuum chamber and has a sensor with a film formed on its surface, and monitors a change in film thickness caused when ion-containing particles generated from plasma sputter the film formed on the sensor surface, thereby outputting a detection signal indicating the change in film thickness; a calculation unit which calculates an amount of change in film thickness based on the detection signal output from the sputtering amount detector; and a determination unit which outputs a determination signal indicating a timing to replace or repair a collector mirror when the amount of change in film thickness calculated by the calculation unit reaches a predetermined reference value.

Description

  The present invention relates to an extreme ultra violet (EUV) light source device used as a light source of an exposure machine.

  With the miniaturization of semiconductor processes, the miniaturization of optical lithography is rapidly progressing, and in the next generation, fine processing of 100 to 70 nm and further fine processing of 50 nm or less are required. Therefore, for example, in order to meet the demand for fine processing of 50 nm or less, it is expected to develop an exposure machine that combines an EUV light source having a wavelength of about 13 nm and a reduced projection reflection optical system (catadioptric system).

  As an EUV light source, an LPP (laser produced plasma) light source (hereinafter also referred to as an “LPP type EUV light source”) using plasma generated by irradiating a target with a laser beam, and generated by discharge There are three types: a DPP (discharge produced plasma) light source using plasma and an SR (synchrotron radiation) light source using orbital radiation. Among these, since the LPP light source can considerably increase the plasma density, extremely high luminance close to that of black body radiation can be obtained, and light emission only in a necessary wavelength band is possible by selecting a target material. Because it is a point light source with a typical angular distribution, there is no structure such as electrodes around the light source, and it is possible to secure a very large collection solid angle of 2πsteradian. It is considered to be a powerful light source for required EUV lithography.

  FIG. 10 is a schematic diagram showing a general configuration of an LPP type EUV light source. The EUV light source includes a vacuum chamber 100, a target generation device 101, an injection nozzle 102, a laser oscillator 103, a condensing optical system 104, an EUV collector mirror 105, and a target recovery device 106. The vacuum chamber 100 is provided with a window 107 for introducing the excitation laser beam 109 into the vacuum chamber 100 and a port 108 for leading the generated EUV light 110 to the exposure machine. Note that the exposure machine that is the output destination of the EUV light 110 is also installed under vacuum (or reduced pressure). In addition, on the reflective surface of the EUV collector mirror 105, in order to selectively reflect EUV light having a wavelength of around 13.5 nm, for example, a film (Mo / Si multilayer film) in which molybdenum and silicon are alternately laminated is formed. Has been.

  By injecting the target material generated by the target generation device 101 into the vacuum chamber 100 from the injection nozzle 102, a droplet (droplet) or a jet-shaped target 111 is formed. The laser beam 109 emitted from the laser oscillator 103 is condensed and irradiated to the target 111 via the condensing optical system 104, and thereby the plasma 112 is generated. Of the light generated from the plasma, EUV light 110 having a wavelength of 13.5 nm is condensed and reflected by the EUV collector mirror 105 and guided to the exposure machine through the outlet port 108.

  By the way, in such an LPP type EUV light source, there is a problem of debris generated when plasma is generated. Debris in an EUV light source is mainly scattered particles such as high-speed ions and neutral particles having high energy. If debris adheres to the reflective surface of the EUV collector mirror 105 or the multilayer film formed on the reflective surface is sputtered away, the reflectance and uniformity of the reflectance are reduced. As the EUV collector mirror deteriorates in this way, it becomes difficult to obtain light energy and optical quality at a level necessary for semiconductor exposure processing or the like in an exposure machine that uses the EUV light.

  For this reason, various proposals have been made to suppress the generation of debris itself and to prevent the debris from adhering to the EUV collector mirror or from sputtering the multilayer film. However, although it is possible to delay the deterioration rate of the EUV collector mirror by such a device, the deterioration cannot be completely eliminated. Therefore, it is necessary to replace the EUV mirror with a new one in consideration of the deterioration of the EUV collector mirror, and it is necessary to determine an appropriate time to replace it.

  As a related technique, Patent Document 1 discloses a consumable management method for an EUV light source that generates EUV light by generating plasma, and monitors the remaining amount or life of the consumables to determine the amount of light that can be emitted. A consumable management method characterized by estimation is disclosed (page 2). In this consumable management method, the amount of light that can be emitted is estimated as a monitoring means by counting the number of light emission since the replacement of the consumable. Specifically, the intensity detection value of the EUV light is a predetermined value (for example, 10%) when the emission count reaches a predetermined number after the EUV collector mirror is replaced or immediately after the EUV collector mirror is replaced. The time when the EUV collector mirror is lowered is regarded as the replacement time of the EUV collector mirror.

JP 2004-111454 A (pages 2 and 6)

Grunrow et al., “Rate and mechanism of optic contamination in the EUV engineering test stand”, Proceeding of SPIE, Volume 5037, 418 ~ 428 pages, 2003

However, as disclosed in Patent Document 1, it is considered difficult to estimate the replacement period of the EUV collector mirror based only on the EUV light emission count and the EUV light intensity detection value. The reason is as follows.
FIG. 11 is a graph quoted from Non-Patent Document 1 and shows the relationship between the number of Mo / Si multilayers formed on the reflective surface of the EUV collector mirror and the reflectance of the EUV collector mirror. As shown in FIG. 11, when the number of layers of the multilayer film (horizontal axis) is 20 or less, the reflectance (vertical axis) is greatly reduced. From this, it can be said that the disappearance of the multilayer film due to the sputtering of debris has a great influence on the lifetime of the EUV collector mirror.

  FIG. 12 shows the erosion rate (erosion rate or spatter amount per 1M pulse) of gold (Au) by neutral ions and fast ions generated from plasma, and ions per 1M pulse generated from plasma. The relationship between the amount and the pulse energy of EUV light (EUV pulse energy) in a bandwidth of 2% centered at 13.5 nm is shown. These relationships are obtained by actual measurement by the inventor of the present application. In this measurement, QCM (quartz crystal microbalance) was used for the evaluation of the sputtering amount. QCM is a detector that can measure the film thickness of the sample film (gold) formed on the sensor surface in real time with an accuracy of angstrom (Å) or less based on the change in the resonance frequency of the crystal resonator. . By using this QCM, the amount of sputtering in the gold film due to ions scattered from the plasma was calculated in real time. Further, a Faraday cup was used for the detection of the amount of ions. The Faraday cup is a device that detects the amount of ions by causing charged particles such as ions to enter a metal cup and measuring a current value.

As shown in FIG. 12, the erosion rate increases almost linearly as the EUV pulse energy increases. Moreover, the same tendency is seen also about the amount of ions. From this, it is considered that the amount of sputtering increases with the same tendency because the amount of ions increases as the EUV pulse energy per shot increases.
Therefore, when the mirror replacement timing is determined by simply counting only the number of emitted light, it is not possible to cope with such a change in the sputtering amount accompanying a change in EUV pulse energy or ion amount per shot.

  Further, the EUV pulse energy collected by the EUV collector mirror is reduced not only by the deterioration of the EUV collector mirror but also by various other factors. Specific factors include, for example, target defects (position, size, speed change, etc.), laser defects (output reduction, beam quality deterioration, etc.), laser light propagation optical system defects (optical element deterioration, position, etc.) A malfunction of the control mechanism), a malfunction of the laser beam condensing optical system (deterioration of the optical element, a malfunction of the position control mechanism, etc.), and a malfunction of the EUV pulse energy measurement system. Therefore, as disclosed on page 6 of Patent Document 1, the energy intensity of the collected EUV pulse (condensed EUV pulse) is detected, and the detected value is compared with that immediately after replacement of the EUV collector mirror. Even if it decreases by 10%, it is difficult to determine whether the cause is due to deterioration of the EUV collector mirror. That is, it is not possible to estimate or determine the mirror replacement time due to the deterioration of the EUV collector mirror only by detecting the collected EUV pulse energy. Furthermore, since it is difficult to measure the collected EUV pulse without loss, it is inappropriate to always measure the collected EUV pulse used as exposure light in the exposure machine.

  In general, since the EUV collector mirror is formed of a multilayer film composed of several tens to several hundred layers (for example, 300 layers), the multilayer film gradually disappears by sputtering, and a sufficient reflectivity is obtained. When the number falls below, the reflectance may suddenly drop significantly (for example, 20 layers or less in FIG. 11). Therefore, it is not practical to estimate or judge the replacement timing of the EUV collector mirror based only on the emission count number and the intensity reduction of the collected EUV pulse energy without considering the relationship between the EUV pulse energy and the sputtering amount.

  Therefore, in view of the above-described problems, the present invention has an object of enabling an appropriate determination of the timing of mirror replacement by accurately reflecting the amount of spatter of an EUV collector mirror in an LPP type EUV light source device. To do.

  In order to solve the above problems, an extreme ultraviolet light source device according to one aspect of the present invention generates plasma by exciting a target material by irradiating the target material supplied into the vacuum chamber with a laser beam, A laser-excited plasma type extreme ultraviolet light source device that condenses and outputs extreme ultraviolet light radiated from the plasma by a condensing mirror, the sensor being disposed in a vacuum chamber and having a film formed on the surface A spatter amount detector that monitors changes in film thickness caused by sputtering a film formed on the sensor surface by particles containing ions generated from plasma and outputs a detection signal indicating the change in film thickness And a calculation unit for calculating a change amount of the film thickness based on the detection signal output from the sputtering amount detector, and a change amount of the film thickness calculated by the calculation unit. When that led to the reference value, and a determination section for outputting a determination signal representing the replacement time or repaired times of the collector mirror.

  According to the present invention, since the mirror replacement time is calculated based on the amount of change in the film thickness of the sensor surface that correlates with the amount of sputtering of the EUV collector mirror, the EUV energy per pulse changes under various conditions. In addition, it is possible to accurately estimate or judge the mirror replacement or repair timing.

It is a schematic diagram which shows the structure of the EUV light source device which concerns on one Embodiment of this invention. It is a schematic diagram which shows the structure of the apparatus for performing experiment which measures EUV pulse energy, the amount of ions, and the amount of sputtering. It is a figure which shows the relationship between the film thickness of a sensor surface, and the total amount of EUV pulse energy. It is a figure which shows the relationship between the film thickness of a sensor surface, and ion total amount. It is a figure which shows the relationship between the ion amount per pulse, and EUV pulse energy. It is a schematic diagram which shows the structure of the apparatus for measuring the correlation of EUV pulse energy, ion amount, and sputtering amount. It is a schematic diagram which shows another structure of the apparatus for measuring the correlation of EUV pulse energy, the amount of ions, and the amount of sputtering. It is a diagram showing the correlation between the total and the sputtering amount of EUV pulse energy in the case of using a YAG laser and CO ₂ laser as an excitation laser. It is a figure for demonstrating the data processing in the control apparatus shown in FIG. It is a schematic diagram which shows the general structure of a LPP type EUV light source. It is a figure which shows the relationship between the number of layers of the Mo / Si multilayer film formed in the reflective surface of an EUV collector mirror, and the reflectance of an EUV collector mirror. It is a figure which shows the relationship between an erosion rate and the amount of ions, and EUV pulse energy.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. The same constituent elements are denoted by the same reference numerals, and the description thereof is omitted.
FIG. 1 is a schematic diagram showing an extreme ultraviolet (EUV) light source device according to an embodiment of the present invention. This EUV light source apparatus employs an LPP (laser excitation plasma) method and is used as a light source for an exposure machine.

  As shown in FIG. 1, the EUV light source apparatus according to the present embodiment includes a vacuum chamber (EUV light generation chamber) 10 in which EUV light is generated, a target generation apparatus 11, an injection nozzle 12, and a laser oscillator 13. , A condensing optical system 14, an EUV collector mirror (condensing mirror) 15, a target recovery device 16, an EUV light detection unit 20, an ion detector 21, a sputter amount detector 22, and a control device 30. Contains. In the vacuum chamber 10, a window 17 for introducing a laser beam (excitation laser beam) 3 for exciting a target 1 and generating a plasma 2, and derivation of the generated EUV light 4 to an exposure machine. Port 18 is provided. Note that the exposure machine that is the output destination of the EUV light 4 is also installed under the same vacuum (or reduced pressure) as in the vacuum chamber 10.

  The target generation device 11 supplies the target material to the injection nozzle 12 in a desired state. For example, when liquid xenon (Xe) is used as a target, xenon liquefied by cooling xenon gas is supplied to the injection nozzle 12. When tin is used as a target material, tin liquefied by heating solid tin, an aqueous solution containing tin fine particles, or the like is supplied to the injection nozzle 12.

The injection nozzle 12 injects the supplied target material into the vacuum chamber 10. The target 1 may be in a jet (jet) state, or may be in a droplet (droplet) state, as shown in FIG. In the latter case, a vibration mechanism (for example, a PZT vibrator) for vibrating the injection nozzle 12 at a predetermined frequency is provided. Further, a position adjusting mechanism for adjusting the position of the injection nozzle 12 may be provided so that the injected target 1 passes through the irradiation position of the excitation laser light 3.
The laser oscillator 13 emits laser light 3 for excitation for irradiating the target 1 by performing laser oscillation. The condensing optical system 14 condenses the laser light 3 emitted from the laser oscillator 13 and irradiates the target 1 through the window 17.

  The EUV collector mirror 15 has a concave reflecting surface, reflects a predetermined wavelength component (for example, EUV light of 13.5 nm ± 0.135 nm) of light generated from plasma, Concentrate in the direction. Therefore, a multilayer film (for example, Mo / Si multilayer film) for selectively reflecting such wavelength components is formed on the reflection surface of the EUV collector mirror 15. The number of layers of the multilayer film is generally about several tens to several hundreds. The EUV collector mirror 15 has a hole for allowing the laser beam 3 to pass therethrough.

  The target recovery device 16 recovers a target that has not been irradiated with the laser light 3 and has not contributed to plasma generation, although it has been ejected from the ejection nozzle 12. This prevents a decrease in the degree of vacuum (pressure increase) in the vacuum chamber 10 and contamination of the EUV collector mirror 15 and the window 17 and the like.

  In such an EUV light source device, the target 1 is formed, and laser oscillation is performed to irradiate the target 1 with the laser beam 3 to generate plasma 2. The light emitted from the plasma 2 contains various wavelength components at various energy levels. Among them, a predetermined wavelength component (EUV light) is condensed and reflected by the EUV collector mirror 15 toward the outlet port 18 to the exposure machine. The EUV light generated in this way is used as exposure light in an exposure machine.

  The EUV light detection unit 20 is a monitor for detecting the light emission amount of the EUV light by directly receiving the light emission of the plasma 2 without passing through an optical element such as the EUV collector mirror 15. The EUV light detection unit 20 includes a multilayer mirror 20a, a zirconium (Zr) filter 20b, and a photodiode 20c. On the multilayer mirror 20a, for example, a Mo / Si multilayer film having a high reflectance with respect to a wavelength in the vicinity of 13.5 nm is formed. The zirconium filter 20b is a filter that has almost no transmittance with respect to light having a wavelength of 20 nm or more. Furthermore, the photodiode 20c outputs a detection signal corresponding to the amount of incident light. As the photodiode 20c, for example, an AXUV series manufactured by IRD of the United States is used. This series is a photodiode with a guaranteed quantum efficiency for wavelengths in the EUV region.

  Such an EUV light detection unit 20 is arranged in a region excluding an incident optical path and a reflected optical path to the EUV collector mirror 15. As a result, no energy loss is given to the EUV light output to the exposure device, and the EUV light emitted from the light emission point of the plasma 2 is directly received, and therefore, it is affected by the characteristic change of the EUV collector mirror 15. In addition, the amount of EUV light at the plasma emission point can be detected. In the present application, the light emission amount or light energy at the plasma emission point refers to the light emission amount or energy of light directly received from the plasma without passing through the EUV collector mirror 15.

  While the EUV light is being generated, a part of the light emitted from the plasma 2 enters the EUV light detection unit 20. This light is reflected by the Mo / Si multilayer mirror 20a and passes through the zirconium filter 20b. As a result, a desired wavelength component (EUV light having a wavelength of 13.5 nm ± 0.135 nm) enters the photodiode 20c. The photodiode 20c outputs a detection signal corresponding to the amount of incident EUV light.

The ion detector 21 is provided to detect the amount of ions generated from the plasma 2 and includes, for example, a Faraday cup.
The spatter amount detector 22 is provided for detecting a spatter amount due to ions generated from plasma, and includes, for example, a QCM (quartz crystal microbalance). The QCM is a device that measures the thickness of a sample film such as gold (Au) formed on the sensor surface in real time with an accuracy of angstrom (Å) or less based on a change in the resonance frequency of the crystal resonator.

By using such a sputtering amount detector 22, it is possible to indirectly detect a change in the film thickness of the multilayer film formed on the EUV collector mirror 15. Hereinafter, the detection principle will be described.
There are two major differences between the film on the sensor surface of the spatter amount detector 22 and the multilayer film of the EUV collector mirror 15: the material of the film and the installation position. For example, even if ions having the same energy collide, the amount of sputtering varies depending on the type of material to be sputtered. Therefore, when the amount of sputtering of the multilayer film is obtained using QCM, the substance (for example, gold, Mo, Si, etc.) formed on the sensor surface and the multilayer film formed on the reflective surface of the EUV collector mirror 15 ( For example, the sputtering ratio with the Mo / Si multilayer film) is obtained in advance. For example, Anderson et al., “Investigation of plasma-induced erosion of multilayer condenser optics” (Proceeding of SPIE, Vol. 5751, pages 128-139). Table 1 shows the ratio (Au: Mo: Si = 1: 0.26: 0.19) of the sputtering amount (erosion rate) of gold, molybdenum, and silicon (page 133).

  On the other hand, regarding the installation position, the main cause of sputtering is high-speed ions generated from plasma, but the ion distribution is not spatially uniform. Therefore, the amount of spatter varies depending on the installation position of the film. Therefore, the sputtering ratio between the film on the sensor surface of the sputtering amount detector 22 installed at a different position and the multilayer film of the EUV collector mirror 15 is obtained in advance. A specific method for obtaining the sputtering ratio will be described later.

  Then, the spatter amount (for example, indicating the film thickness of gold) represented by the detection signal output from the QCM (sputter amount detector 22) is expressed as a sputter ratio based on a difference in surface material and a sputter ratio based on a difference in installation position. The amount of sputtering of the multilayer film of the EUV collector mirror 15 is obtained by converting using

The control device 30 includes, for example, a personal computer, and determines the replacement timing of the EUV collector mirror 15 based on detection signals output from the EUV light detection unit 20, the ion detector 21, and the sputtering amount detector 22. Arithmetic processing for estimating or judging is performed. This arithmetic processing is controlled by, for example, a CPU that operates according to a program.
FIG. 1 shows the EUV light detector 20, the ion detector 21, and the spatter amount detector 22. When determining the replacement time of the EUV collector mirror 15, the EUV light detector 20, the ion detector 21, and the spatter amount detector 22 are shown. Any one of them may be provided.

  Such an EUV light source device determines the replacement timing of the EUV collector mirror 15 based on the energy of EUV light at the plasma emission point, the amount of ions generated from the plasma, or the amount of sputtering obtained using a sputtering amount detector. It is characterized by estimating or judging with high accuracy. Therefore, the principle that the mirror replacement time can be determined based on these amounts will be described with reference to FIGS.

  FIG. 2 is a schematic diagram showing a configuration of an apparatus used in an experiment conducted by the inventor of the present application. This apparatus removes an EUV collector mirror 15 (see FIG. 1) from a general EUV light source apparatus including a vacuum chamber 10 (including a window 17) to a target recovery apparatus 16, and an EUV light detection unit 20, an ion detector 21, In addition, a QCM 23 for measuring the amount of spatter is provided. The ion detector 21 and the sputter measurement QCM 23 are normally arranged at the position where the EUV collector mirror 15 is installed so as to be symmetrical with respect to the plasma.

  The inventor of the present application uses the apparatus shown in FIG. 2 to obtain EUV pulse energy (energy of EUV light radiated from plasma), ion amount, and sputtering obtained almost simultaneously every time one shot of laser light 3 is emitted. The amount of spatter on the sensor surface of the quantity measuring QCM 23 was measured. 3 to 5 show correlations obtained on the basis of these actually measured values.

  FIG. 3 shows the relationship between the thickness (nm) of the film formed on the sensor surface of the sputtering amount measuring QCM 23 and the total amount (integrated value) of EUV pulse energy. The EUV pulse energy was measured for two types of 0.3 mJ, 0.7 mJ, and 1.4 mJ. Here, since the film thickness and the amount of sputtering are in a linear relationship with a coefficient of minus 1, it can be said that FIG. 3 indirectly represents the relationship between the amount of sputtering and the total amount of EUV pulse energy.

  As shown in FIG. 3, since the film thickness decreases almost linearly as the total amount of EUV pulse energy increases, it can be seen that the amount of sputtering increases as the total amount of energy increases. This correlation does not depend on the magnitude of each EUV pulse energy (0.3 mJ, 0.7 mJ, and 1.4 mJ). Therefore, by utilizing this correlation, the sputter amount of the EUV collector mirror can be obtained from only the total amount regardless of the magnitude of each EUV pulse energy. Here, the EUV pulse energy may change depending on the requirements of the user, adjustments, etc. However, if the total amount of EUV pulse energy is known, the time to replace the EUV collector mirror reflecting the amount of spatter can be determined. It becomes possible to judge accurately.

  FIG. 4 shows the relationship between the thickness (nm) of the film formed on the sensor surface of the sputtering amount measuring QCM 23 and the total ion amount (integral value of the ion amount). The total amount of ions was measured for three types of EUV pulse energy of 0.3 mJ, 0.7 mJ, and 1.4 mJ. Here, since the film thickness and the sputtering amount are in a linear relationship with a coefficient of minus 1, it can be said that FIG. 4 indirectly represents the relationship between the sputtering amount and the total ion amount. In addition, the amount of ions is measured with one monovalent ion. Therefore, for example, when one divalent ion is detected, the ion amount = 2 is output.

  As shown in FIG. 4, the amount of sputtering does not depend on the magnitude of EUV pulse energy (three types: 0.3 mJ, 0.7 mJ, and 1.4 mJ) and is almost linear as the total amount of ions increases. (In FIG. 4, this is indicated by a decrease in film thickness). Therefore, by utilizing this correlation, the sputter amount of the EUV collector mirror can be obtained only from the total amount of ions regardless of the magnitude of each EUV pulse energy. It becomes possible to judge accurately.

  FIG. 5 shows the relationship between the amount of ions per pulse (number of ions, vertical axis) and EUV pulse energy (mJ, horizontal axis). As shown in FIG. 5, the amount of ions and EUV pulse energy show a very good correlation, and it can be seen that the amount of ions per pulse changes almost linearly as the EUV pulse energy changes. This confirms that the replacement time of the EUV collector mirror can be accurately determined by using any of the EUV pulse energy and the ion amount (see FIGS. 3 and 4).

Next, a method for acquiring information necessary for determining the replacement time of the EUV collector mirror will be described based on such a relationship (FIGS. 3 to 5).
In the EUV light source apparatus shown in FIG. 1, in order to measure the amount of sputtering of the EUV collector mirror 15, it is necessary to obtain in advance at least one of the following three correlations by actual measurement.
(1) Relationship between the total amount of EUV light energy detected by the EUV light detection unit 20 and the amount of sputtering of the EUV collector mirror 15 (total amount of EUV pulse energy versus amount of sputtering)
(2) Relationship between the total amount of ions detected by the ion detector 21 and the sputtering amount of the EUV collector mirror 15 (total ion amount versus sputtering amount)
(3) Relationship between the sputtering amount of the film on the sensor surface detected by the sputtering amount detector 22 and the sputtering amount of the EUV collector mirror 15 (sensor to mirror sputtering amount)

  FIG. 6 is a schematic diagram showing a configuration of an apparatus for actually measuring the three correlations (1) to (3). This apparatus removes an EUV collector mirror 15 (see FIG. 1) from a general EUV light source apparatus including a vacuum chamber 10 (including a window 17) to a target recovery apparatus 16, and replaces the EUV collector mirror 15 with an installation range. A plurality of EUV multilayer film samples 40 are arranged. In the EUV multilayer film sample 40, the same multilayer film as that formed on the EUV collector mirror 15 (for example, 300 Mo / Si multilayer films) is formed. The number of layers of the multilayer film may be a number that can measure the correlation. The reason for using such a sample is that it is not necessary to use a large and expensive EUV collector mirror in order to actually measure the amount of the sample.

In the apparatus shown in FIG. 6, EUV light is radiated by generating plasma 2, and the EUV pulse energy, ion amount, and spatter amount on the sensor surface of the sputter amount detector 22 at that time are detected, and the total amount is calculated. To do. On the other hand, the sputter amount of the plurality of EUV multilayer film samples 40 is measured. Regarding the amount of sputtering, after the generation of the plasma 2 is stopped, the EUV multilayer film sample 40 is taken out from the vacuum chamber 10, and AFM (atomic force microscope), SEM (scanning electron microscope), TEM (transmission electron microscope), etc. The measurement may be performed using a laser interferometer or the like while the EUV multilayer film sample 40 is installed in the vacuum chamber 10. Alternatively, other known measurement methods may be used.
The above correlations (1) to (3) are obtained on the basis of the actually measured values.

  FIG. 7 is a schematic diagram showing another configuration of an apparatus used for actually measuring the above three correlations (1) to (3). In this apparatus, instead of the plurality of EUV multilayer film samples 40 in the apparatus shown in FIG. 6, a plurality of correlation measurement QCMs 41 are arranged. By generating plasma 2 in such an apparatus, EUV light is emitted, and the EUV pulse energy, ion amount, spatter amount in the spatter amount detector 22 and spatter amount in the correlation measurement QCM 41 are detected, and Find the total amount. Further, the sputter amount in the QCM 41 for correlation measurement is determined based on the sputtering ratio of the film material (Au) on the sensor surface to the Mo / Si multilayer film (see Table 1 of the above-mentioned Anderson et al. Literature). Convert to quantity. Thereby, the correlations (1) to (3) are obtained.

  Here, as shown in FIGS. 6 and 7, the plurality of EUV multilayer film samples 40 and the correlation measurement QCMs 41 are used in order to grasp the spatial distribution of the sputtering amount in the EUV collector mirror 15. That is, by obtaining a correlation between the measurement values of the EUV multilayer film sample 40 and the like at a plurality of locations and the measurement values of the detection devices 20 to 22 in advance, the EUV collector mirror is based only on the measurement values of the detection devices 20 to 22. It is possible to obtain information regarding the amount of sputtering at a plurality of 15 locations. Thereby, for example, when the spatial distribution of the spatter amount in the EUV collector mirror 15 is not uniform, the repair is preferentially performed from the portion where the sputter amount of the EUV collector mirror 15 is large before the entire EUV collector mirror 15 is replaced. Or partially exchanged.

Here, such correlation characteristics vary depending on the type of laser oscillator 13 and the target material. For example, FIG. 8 shows the relationship between the total amount of EUV pulse energy and the sputtering amount when an Nd: YAG laser and a CO ₂ laser are used as the excitation laser. Therefore, it is desirable to acquire such a correlation in accordance with conditions such as equipment and a target material used when generating EUV light for exposure.

  Further, the arrangement of the EUV light detector 20, the ion detector 21, and the spatter amount detector 22 is not limited to the positions shown in FIGS. That is, as long as a measurement value that can obtain the above correlation can be obtained, it may be arranged at any position in the vacuum chamber 10. In that case, it is preferable to arrange | position those detection apparatuses 20-22 other than the optical path (incident optical path and reflected optical path) of EUV light condensed and reflected by the EUV collector mirror 15. FIG. Thereby, the influence on the EUV light used as the exposure light can be suppressed, so that it is possible to always measure without energy loss.

Next, data processing for determining the replacement time of the EUV collector mirror 15 in the EUV light source apparatus according to an embodiment of the present invention will be described with reference to FIGS. This data processing is performed in the control device 30 shown in FIG. As illustrated in FIG. 9, the control device 30 includes an A / D converter 31, a calculation unit 32, a determination unit 33, and a storage unit 34. The storage unit 34 includes the correlations (1) and / or (2) and / or (3) acquired in advance (that is, the total amount of EUV energy versus the amount of sputtering and / or the total amount of ions versus the amount of sputtering). And / or the sputtering amount of the sensor film versus the EUV collector mirror multilayer film), the thickness (nm) of the multilayer film corresponding to the number of layers (L _MAX ) of the multilayer film of the EUV collector mirror 15 in the initial state, and EUV The thickness (nm) of the multilayer film corresponding to the number of multilayer films (L _MIN ) that can secure the reflectance necessary for collecting and reflecting EUV light in the collector mirror 15 is stored. For example, the number of layers of the multilayer film in the initial state is 300, and the number of layers that can ensure the reflectance is at least 20 to 30.

(Embodiment 1) When data processing is performed based on a detection signal of EUV pulse energy By starting generation of EUV light in the EUV light source apparatus shown in FIG. 1, an EUV light detection unit according to the generation timing of plasma 2 From 20, a detection signal representing EUV pulse energy is output. This detection signal is converted into a digital signal by the A / D converter 31, whereby detection data representing EUV pulse energy E _P1 , E _P2 ,... E _Pi,. . These detection data are input to the calculation unit 32 and integrated. Thereby, the integrated value (total value) of EUV pulse energy E _TOTAL = E _P1 + E _P2 +... = ΣE _Pi (i = 1, 2,...) Is calculated. The total amount value E _TOTAL is calculated every time detection data is input, and is output to the determination unit 33.

On the other hand, the determination unit 33 has a thickness corresponding to the number of layers (L _MAX -L _MIN ) based on the correlation (1) (total EUV pulse energy amount versus sputtering amount) stored in the storage unit 34 in advance (that is, An energy value _ETH corresponding to (amount of spatter) is acquired. This energy value _ETH is set as a reference value for the replacement time. Alternatively, when the relationship between the sputtering amount of the EUV collector mirror 15 and the reflectance is obtained in advance, the determination unit 33 sets the energy value corresponding to the sputtering amount when the necessary reflectance is ensured at a minimum. The replacement time reference value E _TH may be used. Such a replacement time reference value _ETH is calculated every time the EUV collector mirror 15 is replaced with a new one.

Then, the determination unit 33 compares the EUV pulse energy total amount value E _TOTAL output from the calculation unit 32 with the replacement time reference value E _TH, and when E _TOTAL ≧ E _TH , the replacement time of the EUV collector mirror 15 is reached. Is output.

(Example 2) When data processing is performed based on the detection signal of ions By starting generation of EUV light in the EUV light source apparatus shown in FIG. 1, ions are generated from the ion detector 21 in accordance with the generation timing of the plasma 2. A detection signal representing the quantity is output. This detection signal is converted into a digital signal by the A / D converter 31 to sequentially generate detection data representing the ion amounts I _P1 , I _P2 ,..., I _Pi (i is the number of times of plasma generation). These detection data are input to the calculation unit 32 and integrated. Thereby, an integrated value (total value) of ions I _TOTAL = I _P1 + I _P2 +... = ΣI _Pi (i = 1, 2,...) Is calculated. The total amount value I _TOTAL is calculated every time detection data is input and is output to the determination unit 33.

On the other hand, the determination unit 33 sets the thickness (sputter amount) corresponding to the number of layers (L _MAX -L _MIN ) based on the correlation (2) (total ion amount vs. sputtering amount) stored in the storage unit 34 in advance. The corresponding ion amount I _TH is acquired. This ion amount I _TH is set as a reference value for the replacement time. Alternatively, when the relationship between the sputtering amount of the EUV collector mirror 15 and the reflectance is obtained in advance, the determination unit 33 sets the ion amount corresponding to the sputtering amount when the required reflectance is ensured at a minimum. The replacement time reference value I _TH may be used. Such replacement time reference value I _TH is calculated every time the EUV collector mirror 15 is replaced with a new one.

Then, the determination unit 33 compares the total ion amount value I _TOTAL output from the calculation unit 32 with the replacement time reference value I _TH, and represents the replacement time of the EUV collector mirror 15 when I _TOTAL ≧ I _TH. Outputs a judgment signal.

(Embodiment 3) When data processing is performed based on a detection signal of the amount of spatter By starting generation of EUV light in the EUV light source apparatus shown in FIG. To periodically output a detection signal indicating the film thickness of the sensor surface. This detection signal is converted into a digital signal by the A / D converter 31 and input to the calculation unit 32. The calculation unit 32 calculates a total film thickness change amount T _TOTAL that is a change amount with respect to the film thickness of the sensor in the initial state based on the input detection data. The total sensor film thickness change amount T _TOTAL is calculated every time detection data is input and is output to the determination unit 33.

On the other hand, the determination unit 33 has a thickness corresponding to the number of layers (L _MAX -L _MIN ) based on the correlation (3) (amount of sputtering of the sensor film versus the EUV collector mirror multilayer film) stored in the storage unit 34 in advance. The sensor film thickness change amount T _TH corresponding to the length (that is, the sputtering amount) is acquired. This sensor film thickness change amount _TTH is set as a reference value for the replacement time. Alternatively, when the relationship between the sputtering amount and the reflectance of the EUV collector mirror multilayer film is obtained in advance, the determination unit 33 determines whether the sensor film corresponds to the sputtering amount when the necessary reflectance is ensured at a minimum. The thickness change amount may be used as the replacement time reference value _TTH . Such a replacement time reference value _TTH is calculated every time the EUV collector mirror 15 is replaced with a new one.

Then, the determination unit 33 compares the total sensor film thickness change amount T _TOTAL output from the calculation unit 32 with the replacement time reference value T _TH and determines the replacement time of the EUV collector mirror 15 when T _TOTAL ≧ T _TH. A determination signal is output.

  Here, when the spatial distribution of the spatter amount in the EUV collector mirror 15 is obtained in advance, the determination unit 33 determines a plurality of locations in the EUV collector mirror 15 and repairs each of those locations. You may make it output the determination signal showing a time.

Above in Examples 1 to 3 described, since replacement time reference value E _TH and I _TH and T _TH is varies depending on various conditions, (type of the exposure apparatus) type and EUV light of the purpose of use of the multilayer film or the like Accordingly, it is preferable to obtain the correlations (1) to (3) and appropriately set their reference values.

  The present invention can be used for an extreme ultra violet (EUV) light source device used as a light source of an exposure machine.

  DESCRIPTION OF SYMBOLS 1,111 ... Target, 2, 112 ... Plasma, 3, 109 ... Laser light, 4, 110 ... EUV light, 10, 100 ... Vacuum chamber, 11, 101 ... Target production | generation apparatus, 12, 102 ... Injection nozzle, 13, DESCRIPTION OF SYMBOLS 103 ... Laser oscillator 14, 104 ... Condensing optical system, 15, 105 ... EUV collector mirror, 16, 106 ... Target collection device, 17, 107 ... Window, 18, 108 ... Derivation port, 20 ... EUV light detection part, DESCRIPTION OF SYMBOLS 21 ... Ion detector, 22 ... Spatter amount detector, 23 ... QCM for spatter amount measurement, 30 ... Control device, 31 ... A / D converter, 32 ... Calculation part, 33 ... Determination part, 34 ... Memory | storage part, 40 ... EUV multilayer film sample, 41 ... QCM for correlation measurement

Claims (4)

A laser that excites the target material by irradiating the target material supplied into the vacuum chamber with laser light to generate plasma, and collects and outputs extreme ultraviolet light emitted from the plasma by a condensing mirror Excited plasma type extreme ultraviolet light source device,
It has a sensor that is disposed in the vacuum chamber and has a film formed on its surface, and monitors changes in film thickness that occur when particles containing ions generated from plasma sputter the film formed on the sensor surface. A spatter amount detector that outputs a detection signal indicating a change in film thickness;
Based on the detection signal output from the sputtering amount detector, a calculation unit for calculating the amount of change in film thickness;
When the amount of change in the film thickness calculated by the calculation unit reaches a predetermined reference value, a determination unit that outputs a determination signal indicating the replacement time or repair time of the condenser mirror;
An extreme ultraviolet light source device comprising: Change in film thickness of the sensor surface calculated based on the film thickness of the multilayer film formed on the reflecting surface of the condenser mirror or the sputter amount in the multilayer film and the detection signal output from the sputter quantity detector A storage unit that stores the correlation obtained by performing measurement in advance.
The determination unit corresponds to a difference between an initial thickness of the multilayer film formed on the reflecting surface of the collector mirror and a thickness of the multilayer film that can ensure a reflectance of a predetermined value or more in the collector mirror. The change amount of the film thickness on the sensor surface is acquired based on the correlation stored in the storage unit, and the acquired change amount of the film thickness is set as the reference value.
The extreme ultraviolet light source device according to claim 1.   The extreme ultraviolet light source device according to claim 1, wherein the spatter amount detector is disposed in a region excluding an incident optical path and a reflected optical path to the condenser mirror.   The sensor having a correlation with the film thickness of the multilayer film formed on the reflection surface of the condenser mirror or the sputtering amount in the multilayer film, based on the detection signal output from the sputtering quantity detector. The extreme ultraviolet light source device according to claim 1, wherein the amount of change in the film thickness on the surface is calculated.

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