Abstract:
A spectrum measuring apparatus that includes an extinction member for decreasing a light intensity from an EUV light source, a spectrum member for extracting light with a desired wavelength band from the decreased intensity light and a detector for detecting a light intensity of the light with a desired wavelength band is disclosed. Then, a spectrum intensity distribution (spectrum) is obtained by (a) a plural opening is located in the extinction member, and the light from the EUV light source passes through the plural opening at the same time, or (b) the detector detects the light volume of the light with a desired wavelength band as thermal energy.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a spectrum measuring apparatus that measures spectrum intensity of wide wavelength of a vacuum ultraviolet region to an infrared region that irradiated from an EUV light source. 
   Conventionally, in photolithography process to manufacture fine semiconductor devices such as semiconductor memory and logic circuit, a reduction projection exposure that uses ultraviolet light is done. The minimum critical dimension transferred by the projection exposure is proportional to the wavelength of light used for transfer and inversely proportional to the numerical aperture (“NA”) of the projection optical system. Therefore, to transfer the fine circuit pattern, shorter ultraviolet light wavelengths have been proposed—from an ultra-high pressure mercury lamp (i-line with a wavelength of approximately 365 nm) to KrF excimer laser (with a wavelength of approximately 248 nm) and ArF excimer laser (with a wavelength of approximately 193 nm). 
   However, lithography using ultraviolet light has limitations when it comes to satisfying the rapidly promoted fine processing of a semiconductor device. Therefore, a reduction projection optical system using extreme ultraviolet (“EUV”) light with a wavelength of 10 to 15 nm shorter than that of the ultraviolet has been developed to efficiently transfer very fine circuit patterns of 100 nm or less.  FIG. 11  is a conceptual rendering of the exposure apparatus that uses the EUV light. 
   The EUV light source uses, for example, a light source of laser plasma (LPP) method or a light source of discharge plasma (DPP) method. 
   The EUV light source of LPP method irradiates a highly intensified pulse laser beam to a target material put in vacuum, thus generating high-temperature plasma for use as EUV light with a wavelength of about 13 nm emitted from this. The target material may use a metallic thin film, inert gas, and droplets, etc., and is supplied by a means such as a gas jet in the vacuum. The pulse laser preferably has high repetitive frequency, e.g., usually several kHz, for increased average intensity of the emitted EUV light from the target. 
   On the other hand, the EUV light source of DPP method flows a gas such as Xenon between electrodes, generates the plasma with the electrical discharge, and generates the EUV light. 
   When the EUV light used for the exposure, the EUV light is absorbed by using a usual metallic mirror and a lens made of quartz etc. A multilayer mirror that laminates 20 layers with a molybdenum (Mo) layer and a silicon (Si) layer is used for the EUV light. In general, the multilayer mirror is adjusted by changing the thickness of the each layer of the multilayer so that reflectivity to the EUV light with a wavelength of 13.5 nm is high, and the EUV light with other wavelengths are absorbed by the mirror. 
   An optical system for the EUV exposure apparatus is composed with several multilayer mirrors. Especially, the EUV light source of LPP method arranges a condenser mirror surrounding the emission point to efficiently use the EUV light emitted from the target, and to condense the generated EUV light to a predetermined light wavelength. 
   The light emitted from the target includes not only the EUV light with the specific wavelength used for the exposure from the EUV light source of laser plasma method but also the light with a wavelength band such as the EUV light, X-ray, ultraviolet light, visible light and infrared light. Thereby, the EUV light with a wavelength different than the specific wavelength and X-ray light that can not be reflected by the multilayer mirror are absorbed by the multilayer mirror, and causes the rise in heat of the mirror. Moreover, the ultraviolet light activates a residual gas in the vacuum, and accelerates a deposition of a contamination on the condenser mirror. The light of the ultraviolet region to the infrared region is reflected by the multilayer mirror that composes the optical system of the exposure apparatus, and reaches a wafer. The light of the ultraviolet region to the infrared region is absorbed by resist, and heat expands the wafer. As the result, there is a possibility of decreasing overlay accuracy during exposure. 
   Therefore, it is necessary to measure the wide band spectrum of the light emitted from the EUV light source, and to measure the light intensity of the light discharged in each wavelength region precisely, to design the exposure apparatus that uses the EUV light and exposure. 
   An apparatus that is described to  FIG. 12  is disclosed in Japanese Laid-Open Patent Application No. 2002-175980 (correspond with U.S. Patent Publication No. 2002/085286) about the measurement of the EUV light emitted from the EUV light source. In  FIG. 12 , the EUV light emitted from a condenser point  101  decreases the intensity of the light by an aperture stop  105 , and reflects with a multilayer mirror  102 . Moreover, the EUV light reaches a CCD array  104  through an EUV filter  103  that transmits only an EUV light of a target for the measurement and is measured. 
   Details of spectrum of the EUV light of a predetermined wavelength region can be measured by a grazing incidence spectrum system shown in  FIG. 13 . This method uses the multilayer mirror as the filter, e.g., two multilayer mirrors  201  and  202 . The system can measure the wavelength region of about 5 to 50 nm, and can measure detail spectrum shape because it adjusts a wavelength resolution (λ/Δλ) to 500 or more. 
   However, the above-mentioned measuring apparatuses comparatively measure only a part of the light emitted from the EUV light source for the wavelength region in the narrow range. Thereby, it is difficult to measure the entire wide band spectrum of the light emitted from the EUV light source, and to know the absolute intensity. As the result, the wavelength intensity distribution of entire beams including the infrared ray region emitted from the EUV light source necessary to design the exposure apparatus that uses the EUV light and exposure stability can not be obtained. 
   BRIEF SUMMARY OF THE INVENTION 
   Accordingly, it is an exemplary object of the present invention to provide a spectrum measuring apparatus that can obtain spectrum intensity distribution of light emitted from an EUV light source. 
   A spectrum measuring apparatus of one aspect of the present invention includes an extinction member for decreasing the intensity of the light emitting from an EUV light source, a spectrum member for selecting a light with a desired wavelength band from the decreased intensity light and a detector for detecting a light volume of the light with a desired wavelength band. Then, it characterizes in (a) a plural opening is located in the extinction member, and the light from the EUV light source passes through the plural opening at the same time, or (b) the detector detects the light volume of the light with a desired wavelength band as thermal energy. 
   Other objects and further features of the present invention will become readily apparent from the following description of the preferred embodiments with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view of a spectrum measuring apparatus of the first embodiment according to the present invention. 
       FIG. 2  is one example of arranging a pinhole array used for the spectrum measuring apparatus of the first embodiment according to the present invention. 
       FIG. 3  is one example of a pattern of the pinhole array used for the spectrum measuring apparatus of the first embodiment according to the present invention. 
       FIG. 4  is a schematic view of a state in a measurement process by the spectrum measuring apparatus of the first embodiment according to the present invention. 
       FIG. 5  is a graph that shown a light absorptance of a detector used for the spectrum measuring apparatus of the first embodiment according to the present invention. 
       FIG. 6  is a schematic view of a state in a measurement process by the spectrum measuring apparatus of the first embodiment according to the present invention. 
       FIG. 7  is a schematic view of a state in a measurement process by the spectrum measuring apparatus of the first embodiment according to the present invention. 
       FIG. 8  is a graph that shown a transmittance of a filter used for the spectrum measuring apparatus of the first embodiment according to the present invention. 
       FIG. 9  is a schematic view of a spectrum measuring apparatus of the second embodiment according to the present invention. 
       FIG. 10  is a graph that shown a transmittance of a filter used for the spectrum measuring apparatus of the second embodiment according to the present invention. 
       FIG. 11  is a conceptual rendering of an exposure apparatus that uses the EUV light. 
       FIG. 12  is one example of a conventional measuring system of an EUV light source. 
       FIG. 13  is an other example of a conventional measuring system of an EUV light source. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The First Embodiment 
   The instant embodiment explains a spectrum measuring apparatus that can obtain a wavelength intensity distribution of entire beams emitted from an EUV source and the measuring procedure that uses it. 
     FIG. 1  is a schematic view of measuring a light intensity of a laser plasma light source, that is one example of EUV light source, by the spectrum measuring apparatus according to the present invention. 
   In a measurement chamber  17  of the spectrum measuring apparatus, an incident beam  18  from an EUV light source that passes through an aperture  16  decreases in light intensity by an pinhole array  1  where a lot of pinholes are located, and after passing a filter  2  and filter  3  to select a wavelength of the measured beam, is incident in a light intensity detector  4 . The EUV light is partially absorbed by a gas molecule that exists in the measurement chamber  17 , and attenuates. Therefore, it is desirable to exhaust in the measurement chamber  17  to high vacuum to increase the measurement accuracy. 
   The pinhole array  1  has a function to adjust the almost all incidence beam in the measurement chamber  17  to suitable light intensity for the measurement.  FIG. 2  is shown that one example of the pinhole array  1 . The plural pinhole array  1  as shown in  FIG. 2  are housed in the measurement chamber  17  selectable, and can attenuate the incidence beam from the EUV light source to predetermined ratio as for example 1/10,  1 / 100 ,  1 / 1000 . Moreover, it is also possible to pass the all intensity incidence beam without attenuation. The pinhole array  1  is switched by moving the pinhole array  1  by a motor  5 . The attenuation factor with the pinhole array  1  switches according to the maximum output of the measured light source and kind of the light source (LPP method and DPP method etc.) used, and is adjusted to suitable light intensity for the measurement by the measuring apparatus as noted above. 
     FIG. 3  shows an example of an array pattern of the pinhole array  1 .  FIG. 3A  is a pattern of same diameter hole by the overall even pitch,  FIG. 3B  is a random pattern, and  FIG. 3C  is a pattern evenly arranged in a direction of the diameter in consideration of the shape of the condenser mirror. The pattern of these pinhole arrays are selected so that the light that passed the pinhole array  1  is not causing an unnecessary diffraction etc. and the beam never locally concentrates on the filter  2  and  3 , or the light intensity detector  4 . The numerical rate (e.g., a rate that the light passes through the array) is selected so that it is adjusted to suitable light intensity for the measurement by the measuring apparatus latter part.  FIG. 4  shows the state when the pinhole array  1  is not used. When the beam from the EUV light source has a low intensity, as shown in  FIG. 4 , it measures without attenuating the beam by the pinhole array  1 . 
   It is desirable to redirect the emitting light to the filter  2  and  3  or the detector  4  by considering the distance with the pinhole array  1  and the filter  2  and  3  or a receiving inspection plane of the pinhole array  1 . It is desirable that the diameter of the pinhole is larger than the measured wavelength because there is maximum wavelength of light that cannot pass through the pinhole array  1 . Therefore, it is desirable to have the pinhole diameter ten times larger or more than the wavelength. 
   For example, the detector  4  of the instant embodiment uses a calorie meter that detects the light intensity as thermal energy. When measuring the beam with a wavelength λ=10 μm near the upper bound of the detection wavelength of the calorie meter, if the distance L with the receiving inspection plane of the detector  4  is 40 mm, the shade off amount (e.g., amount of “shade off” or shadow) on a focus plane (detection plate) becomes 2.9 mm by using the pinhole array  1  (hole diameter d=φ0.14 mm), and it is enough to prevent that the beam locally concentrates on the light volume detector  4 . The pinhole diameter of φ0.14 mm does not interrupt the beam because the pinhole diameter is sufficiently larger than the measured wavelength λ=10 μm. 
   The filters  2  and  3  are used to combine one or two filters if necessary, and to pass only the beam with the measured wavelength band. It is effective to change a material and a thickness etc. of the filter to select the wavelength band of the passed beam. The material of the filter is selected from CaF 2  (fluorite), MgF 2  (magnesium fluoride), ZnSe (zinc selenide), Si, Thallium-Bromide Chloride and optical glass that contain a material that absorbs light below a specific wavelength region. 
   There is a mechanism to arrange the filters  2  and  3  in the measurement chamber  17 , and the filter that passes the desired wavelength band to be measured and the state that the filter is not used can be selected by the motor  5 . 
   After attenuating by the pinhole array  1  and the specific wavelength is cut out by the filter  2  and  3 , the light intensity of the incidence light are measured with the detector  4 .  FIG. 5  shows the absorptance of each wavelength of the calorie meter used by the instant embodiment. As shown in  FIG. 5 , the calorie meter can absorb light with the absorptance of 90% or more in the wide wavelength band, and measure the light intensity. A CCD and a photodiode etc. can be used for others as the detector. 
   The cooling apparatus to keep below a predetermined temperature is located in a part that light is irradiated from the EUV light source such as the aperture  16 , the pinhole array  1 , filter  2  and  3 , the detector  4  mentioned above. A chamber inner wall  19  is coated by a material that absorbs light easily to suppress a diffuse reflection of the light (especially, infrared light) that is reflected by the pinhole array  1 . If a reflection coefficient of the chamber inner wall is about 0.1 or less toward the measured light with all wavelength bands, the measuring error by the diffuse reflection is in an allowed range. 
   In  FIG. 1 , a structure of the EUV light that the spectrum is measured by the spectrum measuring apparatus of the instant embodiment according to the present invention is as follows. However, the spectrum measuring apparatus according to the present invention can be applied also to an EUV light source that has a structure different from the EUV light source shown in  FIG. 1 . 
   In the EUV light source shown in  FIG. 1 , a nozzle  8  that supplies a target  10  (for example, Xenon etc.) in an EUV light source chamber  14  is located, and the target  10  is supplied. The target  10  generates a plasma  7  with a pulse laser  13  that is emitted from a laser generation apparatus  12  and condenses on the target  10 , and radiates the beam including the EUV light. The radiated light includes, besides the EUV light used for the exposure, the light of wavelength band in large range such as the EUV light outside the band, X-ray, ultraviolet light, visible light, infrared light. The majority of the target  10  used to generate the plasma is collected by a target collection mechanism  9 , and taken out outside of the chamber. 
   The EUV light with wavelength used for the exposure that is radiated from the plasma  7  is condensed by a condenser mirror  11  of spheroid to improve the use efficiency. The condenser mirror  11  generally uses the multilayer mirror that has a silicon layer and molybdenum layer of a certain film thickness where the reflectivity becomes the maximum for EUV light of wavelength used for projection exposure are alternately formed by already-known method. 
   Therefore, the part of the light radiated from the plasma  7  is absorbed by the condenser mirror  11  composed of the above-mentioned multilayer mirror without reflecting, and the light measured by the spectrum measuring apparatus according to the present invention is the light that is reflected by the condenser mirror  11 . 
   In the EUV light source shown in  FIG. 1 , the condenser mirror  11  is composed of spheroid shape, makes the position in which the plasma  7  is generated the other focus, and condenses the reflection light in the condenser point  6 . The spectrum measuring apparatus according to the present invention can be applied also to the EUV light source, for example, that radiate a parallel light according to a structure different from the EUV light source shown in  FIG. 1 . 
   The EUV light source chamber  14  is connected with the measurement chamber  17  by a bellows  15 . Moreover, the aperture  16  forms a transmission part near the condenser point  6 . The aperture  16  is located for the purpose to reduce the inflow of the gas from the EUV light source chamber  14  to the measurement chamber  17 , because of it is desirable that the EUV light source chamber  14  is maintained about 10 Pa of pressure that is higher than the measurement chamber  17  of the spectrum measuring apparatus to reduce a pollution and a damage of the condenser mirror  11  by a dispersion material from the plasma  7 . 
   Thereinafter, a description will be given of spectrum measuring method by the spectrum measuring apparatus shown in  FIG. 1 . 
   First, all light volume of light from the EUV light source is measured.  FIG. 4  shows the state of the spectrum measuring apparatus when the all amount of the light from the EUV light source is measured. To measure the all amount of the light from the EUV light source, as shown in  FIG. 4 , the pinhole array  1  and the filter  2  and  3  are removed, and the light is detected by the detector  4 . 
   The detector  4  used by the instant embodiment is the calorie meter, has detection sensitivity shown in  FIG. 5 . In other words, the detector  4  has the sensitivity that can detect 95% or more in the band of wavelength 100 nm or less, about 100% in the EUV light with wavelength of 13.5 nm, 88% or more in the minimum part of the long-wavelength band, and about 93% in the average. Moreover, because the detector  4  has the sensitivity to wavelength of about 30 μm on the long-wavelength band side, an all light volume Wt that is almost all of the light radiated from the EUV light source is detected by the calorie meter. An absolute light intensity is obtained by correcting the detection result by using the absorptance to the wavelength of the calorie meter shown in  FIG. 5 . 
   In the instant embodiment, the pinhole array  1  is removed and the all light intensity Wt is measured. However, when the light intensity from the EUV light source is large and exceeds a capacity of the calorie meter, it may be measured by using the pinhole array  1  that has suitable attenuation factor. 
   Next, the pinhole array  1  is selected based on detected all light intensity Wt. to attenuate the light intensity so that the filter  2  and  3  used for later are not damaged.  FIG. 6  shows the state of the spectrum measuring apparatus when the pinhole array  1  that has an extinction rate of 1/100 is selected. It is desirable to measure the light intensity from the EUV light source without using the filter  2  and  3  to confirm the accurate attenuation factor of the selected pinhole array  1  as shown in  FIG. 6 . When the light intensity detected by the detector  4  via the pinhole array  1  decreases to the light intensity Wp 1  by measuring, shown in  FIG. 6 , the actual extinction rate of the pinhole array  1  can be obtained by Wp 1 /Wt. 
   Next, the light intensity is measured in each frequency band.  FIG. 7  shows the state that the pinhole array  1  that has the extinction rate of 1/100 and the one filter  2  that the absorption edge is an already-known filter insert in an optical path to measure the light intensity of the specific wavelength band. A filter a that shuts out light with the wavelength region of 390 nm or less is used as one example of the filter  2  in  FIG. 7 .  FIG. 8  shows absorption characteristics of the filter a and the filter b. The filter a has the transmittance only for the light with the wavelength region of 390 nm or more as shown in  FIG. 8 . For example, a general optical glass filter like the sharp cut filter made by SHIGMA KOKI CO., LTD. can be used as the filter a and filter b. 
   When irradiating the light from the EUV light source while shown in  FIG. 7 , the light intensity Wf 1 ′ to which the wavelength band that is attenuated by the pinhole array  1 , and cut out by the filter a is decreased. The light intensity Wf 1 ′ is the light intensity in the wavelength region of 390 nm or more, the light intensity Wf 1  of light with the wavelength region with 390 nm or more is obtained by considering the transmittance of the filter a in the region and the sensitivity of the detector  4 . 
   Next, in the filter a exchange with a filter b that shuts out the light below the wavelength region of 560 nm, and the similar measuring, a light intensity Wf 2 ′ is detected by the detector  4 . The light intensity Wf 2 ′ is the light intensity in the wavelength region of 560 nm or more, the light intensity Wf 2  of light with the wavelength region with 560 nm or more is obtained by considering the transmittance of the filter b in the region and the sensitivity of the detector  4 . Moreover, the subtraction of the light intensity Wf 1  and the light intensity Wf 2  becomes the light intensity Wf of 390 nm to 560 nm under the existence of the pinhole array  1 , and the absolute light intensity If 1  of the wavelength band of 390 nm to 560 nm that be reflected from the EUV light source is obtained by considering the extinction rate F of the pinhole array  1 . 
   As an example of other materials used, as the filter  2 , it is possible to use the filters of ZnSe (zinc selenide) or Si (silicon) of 5 mm thickness. In this case, ZnSe transmits the light with wavelength of 0.6 μm or more to 20 μm, and Si transmits the light with wavelength of 1.2 μm or more to 15 μm. The light with wavelength of 15 to 20 μm can not be substantially detected by the detector  4 . Thereby, the absolute light intensity of light with wavelength of 0.6 μm to 1.2 μm is obtained by using the above-mentioned filter. 
   As mentioned above, measuring the light intensity in each part of the spectrum distribution of light from the EUV light source becomes possible by switching to the filter that has the absorption range in the measured wavelength band. As the result, the spectrum distribution and absolute intensity of the entire emitting light can be decided by considering these. 
   The Second Embodiment 
     FIG. 9  shows a spectrum measuring apparatus of the second embodiment according to the present invention.  FIG. 9  shows the state to apply the spectrum measuring apparatus according to the present invention to the discharge method plasma light source (DPP) that is one method of EUV light source. The instant embodiment chiefly explains a point different from the first embodiment. 
   The discharge method plasma light source (DPP) generates the plasma by discharging the high density current pinch electrical discharge etc., and takes out the EUV light. Because the DDP method differs from the LLP method in construction, the condenser mirror cannot be arranged on the upstream side of a discharge electrode  21  (the plasma emission point is base, the opposite side of the side that the exposure apparatus and the measuring apparatus is attached). A grazing incidence mirror  22  is provided to condense the emitting light from the electrical discharge electrode  21  to the downstream side. Thereby, in the condenser point  6 , there expects to be a higher percentage of light elements present other than EUV light elements compared to the LPP method. 
   Therefore, when the spectrum measuring apparatus according to the present invention is applied to the EUV light source of the DPP method, it is desirable to cover the chamber inner wall  19  with the material that absorbs light easily to prevent the diffuse reflection of the light that is reflected by the pinhole array  1 . Moreover, it is also desirable to arrange an antireflection board  23  that coats similar to the chamber inner wall  19  to increase an area that absorbs the light. If the reflection coefficient is about 0.1 or less, these coatings do not harmfully influence the measurement in the wavelength band of the measured light. However, if the reflection coefficient is 0.05 or less, it is more desirable. 
   Thereinafter, a description will be given of spectrum measuring method by the spectrum measuring apparatus shown in  FIG. 9 .  FIG. 10  shows one example of the transmittance distribution of the spectrum filter that is used by the spectrum measuring apparatus shown in  FIG. 9 . 
   For example, when the filter a and filter b are composed of materials that have different absorption ranges, the spectrum measuring apparatus shown in  FIG. 9 , to similar the first embodiment, can measure the light intensity of a prescribed wavelength region from the difference of the light intensity that the detector  4  detects. 
   On the other hand, the instant embodiment explains the method of measuring the light intensity of a prescribed wavelength region by using the filter a and a filter c that are composed of the same material, and only thickness is different. 
   Generally, the transmittance decreases in proportion to the square of thickness when paying attention to the transmittance in the specific wavelength range of the filter composed of a homogeneous material. Therefore, for two different wavelengths, their transmittances will change differently with different filter thicknesses. Especially, in the vicinity of the absorption range of the material that composes the filter, measuring the light intensity of each detailed wavelength region becomes possible by using this. 
   Concretely, the filter a shown in  FIG. 10  has the transmittance of about 90% in 450 nm or more, but the transmittance decreases rapidly in 450 nm or less, becomes about 40% in 400 nm, and becomes substantially opaque in vicinity of 380 nm. On the other hand, when using the filter c that composed of the same material as the filter a and has twice the thickness as filter a, the transmittance of about 81% can be kept in 450 nm or more, and it becomes the transmittance of about 16% in 400 nm. When the thickness of the filter increases, using the phenomenon that the transmittance decreases especially greatly for certain wavelength can form the wavelength filter that has low transmittance. The wavelength filter by such the technique is effective to the wavelength region that the transmittance rapidly changes, and changing the thickness of the filter one by one and measuring can obtain a detailed spectrum. 
   As mentioned above, obtaining the absolute light intensity in each wavelength region according to the difference of the transmittance caused because the thickness of the filter that uses the material corresponding to the measured wavelength band is switched one by one becomes possible. 
   This application claims foreign priority benefits based on Japanese Patent Applications No. 2003-299649, filed on Aug. 25, 2003, which is hereby incorporated by reference herein in its entirety as if fully set forth herein.