JP3934347B2 - Sample contamination measuring method for electron beam inspection equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sample contamination measuring method for an electron beam inspection apparatus, and more particularly to a sample contamination measuring method for an electron beam inspection apparatus suitable for inspecting a semiconductor.
[0002]
[Prior art]
An electron beam inspection apparatus that scans an electron beam on a sample and measures and observes the size and shape of a pattern or contact hole formed on the sample from the obtained secondary electron image or reflected electron image is a semiconductor element. As miniaturization progresses, the role becomes more important.
[0003]
On the other hand, when observation is performed using an electron beam, it is known that contaminants adhere to the portion of the sample irradiated with the electron beam. In this regard, for example, as described in “Specimen Protection in the Electron Microscope, 19 (1982) p. 465, HEYWOOD JA, Pract Metallogr”, the cause of sample contamination is the adsorption to the sample. It is thought that this is due to the adsorption of hydrocarbon-based gas molecules and hydrocarbons in the residual gas of the device to the sample. In either case, the adsorbed gas is said to be solidified by receiving electron beam energy. ing. Thus, when contaminants adhere to the sample surface, it is impossible to capture an image of the true surface because the surface of the contaminants is observed on the outermost surface. In the case of an inspection apparatus for a semiconductor device, the purpose is dimension measurement and appearance inspection. Therefore, it is a serious problem that contaminants adhere and the dimensions and shape change during the inspection.
[0004]
Therefore, as a method for evaluating sample contamination in an electron beam inspection apparatus, for example, “Journal of Electron Microscopy, 16-1, (1981), p.2-10, Keiji Yada”, “Journal of Electron Microscopy, 19- 1, (1984), 58-60, Ikuo Kore-eda ”, an electron beam is applied to a fixed point on the sample surface, and the cylindrical or conical contaminants attached to the irradiated part A device that measures the diameter or height together with the electron beam irradiation time and measures the amount of contaminants is known.
[0005]
[Problems to be solved by the invention]
However, in the conventional method for evaluating sample contamination using an electron beam inspection apparatus, when measuring the amount of contaminants deposited, an electron beam is applied to a fixed point on the observation surface. Irradiation is performed while scanning the region of the surface to be observed, and the electron beam irradiation method is different, so that there is a problem that the amount of contaminants attached cannot be measured accurately.
[0006]
An object of the present invention is to provide a sample contamination measuring method of an electron beam inspection apparatus capable of quantitatively measuring the amount of contaminants adhering to the observation surface of the electron beam inspection apparatus.
[0008]
[Means for Solving the Problems]
( 1 ) In order to achieve the above object, the present invention irradiates a sample placed in a sample chamber with an electron beam from an electron gun in an electron gun chamber, detects secondary electrons generated from the sample, and Using an electron beam inspection device that measures the dimensions of the sample, the convex part or concave part provided on the surface of the sample coated with the lubricant is irradiated with an electron beam, and contaminants attached to the electron beam irradiation surface The lubricant is evaluated by measuring the amount of adhered contaminants from the changed convex or concave dimensions.
[0009]
( 2 ) To achieve the above object, the present invention irradiates a sample placed in a sample chamber with an electron beam from an electron gun in an electron gun chamber, detects secondary electrons generated from the sample, Using an electron beam inspection device that measures the dimensions of the sample, a material intended for use in the electron beam inspection device is placed in an arbitrary sample chamber that is not irradiated with the electron beam, and a convex provided on the surface of the sample. Irradiate the electron beam to the shape part or concave shape part, measure the adhesion amount of the contaminant from the dimension of the convex shape or concave shape changed by the contaminant adhering to the electron beam irradiation surface, and depending on the adhesion amount of the contaminant, The material is evaluated.
[0010]
(3) In any one of the above (1) or (2) , preferably, the amount of contaminated substances is measured periodically and the measured amount of adhering contaminants is displayed or recorded. .
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the sample contamination measuring method of the electron beam inspection apparatus according to the first embodiment of the present invention will be described with reference to FIGS.
First, the configuration of the electron beam inspection apparatus used in the sample contamination measuring method according to the present embodiment will be described with reference to FIG.
FIG. 1 is an overall configuration diagram showing the configuration of an electron beam inspection apparatus used in the sample contamination measuring method according to the first embodiment of the present invention.
[0012]
As shown in FIG. 1, in the electron beam inspection apparatus according to this embodiment, an electron gun chamber 1, a condenser lens chamber 2, an intermediate chamber 3, and a sample chamber 4 are arranged in the vertical direction. A preliminary exhaust chamber 25 is disposed adjacent to the sample chamber 4. The sample 16 is introduced into the sample chamber 4 in the vacuum atmosphere from the atmospheric atmosphere through the preliminary exhaust chamber 25.
[0013]
The electron gun chamber 1 is provided with an electron gun 7, an extraction electrode 8, an acceleration electrode 9, and a fixed aperture 10. A condenser lens 11 is provided in the condenser lens chamber 2. In the intermediate chamber 3, a deflection coil 12, an objective lens 13, and an objective lens fixed diaphragm 14 are provided. The sample chamber 4 is provided with an X stage 6 and a Y stage 6 ′, which are sample stages. A sample 16 is placed on the Y stage 6 ′. The sample stages 6 and 6 ′ are installed on the base 5. A sliding portion 15 of the guide mechanism is provided between the X stage 6 and the base 5 and between the Y stage 6 ′ and the X stage 6, and the X stage 6 and the Y stage 6 ′ are connected to the sliding portion 15. Moved by. Although illustration is omitted, when moving in the X direction and the Y direction, a motor installed outside the sample chamber is connected to a power transmission system such as a ball screw installed in the sample chamber and driven.
[0014]
Vacuum pumps 19 and 20 are connected to the electron gun chamber 1. A vacuum pump 21 is connected to the condenser lens chamber 2. In order to obtain a stable electron beam from the electron source 7, differential evacuation is performed by the vacuum pumps 19, 20, and 21, and the electron gun chamber 1 and the condenser lens chamber 2 are decompressed to a pressure of 10 ⁻⁷ Pa or less. A vacuum pump 22 is connected to the sample chamber 4 and is evacuated to 10 ⁻³ Pa or less.
[0015]
A reflected electron / secondary electron detector 23 for detecting secondary electrons or reflected electrons B2 from the surface of the sample 16 when the sample 16 is irradiated with the electron beam B1 from the electron gun 7 is attached to the intermediate chamber 3. ing. Note that the sample chamber 4 and the intermediate chamber 3 communicate with each other by an exhaust bypass 18.
[0016]
The transport mechanism 26 transports the sample 16 from the preliminary exhaust chamber 25 to the sample chamber 4. When the sample 16 is introduced into the sample chamber 4, the sample is introduced through the preliminary exhaust chamber 25. That is, the sample 16 is introduced with the preliminary exhaust chamber 25 being in the atmospheric state, and when the preliminary exhaust chamber 25 is evacuated and reaches a predetermined pressure, the gate valve 17 is opened and the sample 16 is carried into the sample chamber 4. Then, the gate valve 17 is closed.
[0017]
When observing the sample surface, the electron beam B1 emitted from the electron gun 7 is extracted by the voltage applied to the extraction electrode 8, and the extracted electron beam B1 is desired by the acceleration voltage applied to the acceleration electrode 9. Adjusted to the energy of Further, after passing through the fixed aperture 10, the electron beam B 1 is converged on the sample 16 by the condenser lens 11 and the objective lens 13. The converged electron beam B1 is scanned on the sample 16 by the deflection coil 12. The deflection control unit 40 varies the deflection current flowing through the deflection coil 12 and scans the sample 16 with the electron beam B1. At this time, secondary electrons and reflected electrons B2 are generated from the 16 surface of the sample, and these secondary electrons and reflected electrons B2 are detected by the reflected electron / secondary electron detector 23, and the sample image is displayed on the display unit 42. Can be displayed. In normal observation of the sample surface, a clear sample image can be obtained with only secondary electrons. However, if the sensitivity is low, in addition to the detected secondary electron information, By superimposing the images, a better sample image can be obtained. Further, the signal detected by the backscattered electron / secondary electron detector 23 measures the amount of contaminants attached by the control unit 44. Data such as the measured adhesion amount can be transmitted to a monitoring center 50 or the like at a remote location via the network NW.
[0018]
By the way, as already described, when the electron beam B1 is irradiated to the sample 16 installed in the sample chamber where many gas components mainly composed of hydrocarbon remain in the sample chamber 4, the hydrocarbon-based gas molecules become electrons. A phenomenon in which a substance mainly composed of carbon is gradually deposited on the surface of the sample 16 by receiving energy from the line occurs. The amount of deposition is very small, at most several nanometers to several tens of nanometers. However, since another substance is deposited on the surface that is actually desired to be observed, it is necessary for high-magnification observation more than tens of thousands The difference in shape becomes obvious. Therefore, it is important to provide a simple and quick evaluation method for quantitatively determining how much contaminants adhere to the observation surface.
[0019]
Next, the sample contamination measuring method according to the present embodiment will be described with reference to FIGS.
FIG. 2 and FIG. 3 are principle configuration diagrams for explaining the principle of the sample contamination measuring method according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view, and FIG. 3 is a plan view schematically showing a diagram observed as an electron microscope image.
[0020]
As shown in FIG. 2, a convex portion 28 is formed in advance on the surface of the sample 16. The convex portion 28 is a contaminant evaluation pattern that can be referred to as an inspection pattern or a dummy pattern. The width a0 of the convex portion 28 has a width substantially equal to the wiring pattern in the actual semiconductor device. For example, the width a0 of the convex portion 28 is 0.5 μm. The length of the convex portion 28 is longer than the width a0, and is a linear protrusion as shown in FIG. The convex portion 28 may be a convex portion having a straight planar shape, or may be a shape bent in an L shape. Further, the planar shape may be circular.
[0021]
2 and 3, a region C1 indicated by a one-dot chain line is a first visual field region. A region C2 indicated by a broken line is a second visual field region. In the first visual field region C1 and the second visual field region C2, an electron beam is irradiated, and the surface of the sample 16 and the convex portion 28 is scanned to obtain an image of an electron microscope.
[0022]
Here, the length of one side of the first visual field region C1 is n1, and the length of one side of the second visual field region C2 is n2. The length n1 of one side of the first visual field region C1 is made larger than the width a0 of the convex portion 28. For example, when the width a0 of the convex portion 28 is 0.5 μm, the length n1 of one side of the first visual field region C1 is 1.0 μm. At this time, the length n2 of one side of the second visual field region C2 is set to 2.0 μm. The length of the convex portion 28 only needs to be longer than the length n1 of one side of the first visual field region C1.
[0023]
First, the control unit 44 controls the deflection control unit 40 to set a region where the sample 16 is scanned by the electron beam B1 as a first visual field region C1. Then, in this first visual field region C1, observation is performed for a predetermined time, for example, about 10 minutes. In an electron microscope in which a large amount of a gas component mainly composed of hydrocarbon remains in the sample chamber 4, when the electron beam B1 is irradiated for a certain period of time, the irradiated surface, in this case, n1 × n1 first field region C1. Contaminant 29 mainly composed of carbon is deposited on the surface of the film in a film form as shown in FIG. Since the pollutant 29 is also deposited on the side surface of the convex portion 28, the width of the convex portion apparently increases to a width a4 and a convex shape. After a predetermined time elapses, the control unit 44 controls the deflection control unit 40 to set a region where the sample 16 is scanned by the electron beam B1 as the second visual field region C2. That is, the magnification of the visual field is lowered. As a result, as shown in FIG. 3, the portion where the pollutant 29 is attached and the line width is a4 and the convex portion 28 of the original line width a0 where no contaminant is attached are in the same field of view. It can be observed simultaneously in C2.
[0024]
Since the electron beam inspection apparatus generally has a measurement refusal function for measuring the distance between two points or the distance between two parallel lines, a portion where the line width is increased by the contaminant 29 and a portion where the original line width is a0. By measuring the distance between and the line width a1, the line width a1 increased due to the adhesion of the contaminant 29 can be measured. Further, even if the line width a4 of the portion where the line width is increased by the contaminant 29 and the line width a0 of the convex portion 28 are individually measured, the line width a1 (= (a4) increased by the adhesion of the contaminant 29 -A0) / 2) can be obtained by calculation. Further, if the width a0 of the convex portion 28 is a known one, for example, if it is measured in advance by an atomic force microscope (AFM (Atomic Force Microscopy)), the line width of the portion where the line width is increased by the contaminant 29 By measuring a4, the line width a1 (= (a4-a0) / 2) increased by the adhesion of the pollutant 29 can be obtained by calculation.
[0025]
Strictly speaking, a1 measured by this measurement method is not necessarily equal to a2 or a3, but is almost equal, and is a simple measurement method and can be an index for quantitative evaluation. The magnification at the time of evaluating the deposit amount of the contaminant 29 is preferably about 1/2 because the increase amount is difficult to measure if it is too low. The adhesion amount a0 of the pollutant 29 is about 1 nm when the pollutant is small, but it becomes several nm or more when the pollutant increases.
[0026]
As described above, sample contamination can be measured quantitatively, and the influence of sample contamination can be grasped quantitatively. In addition, the amount of contaminants can be measured easily and quickly. Further, such a sample contamination evaluation method can be used for inspection items and performance evaluation of an electron beam inspection apparatus.
[0027]
Here, the gas mainly composed of hydrocarbon that causes sample contamination may be brought into the sample chamber 4 by the sample 16 to be inspected. That is, it is conceivable that the gas adsorbed on the sample 16 is desorbed in the sample chamber 3 and becomes a hydrocarbon-based residual gas. In this case, the hydrocarbon-based residual gas gradually increases depending on the number of times of introduction of the sample, and accordingly, the amount of contaminant 29 deposited on the sample 16 per unit time also gradually increases depending on the number of times of introduction of the sample. Become.
[0028]
Therefore, the deposit evaluation method described above is periodically performed to display the amount of adhered contaminants measured on the display unit 42 of the electron beam inspection apparatus and to record the amount of adhesion in the control unit 44. As a result, the trend of increase in pollutants can be understood and used as a guide for maintenance time. Further, by transmitting the recording information of the amount of contaminants to the monitoring center 50 via the network NW or the like, it is possible to determine the maintenance time of the electron beam inspection apparatus even in a remote place.
[0029]
As described above, according to the present embodiment, it is possible to quantitatively measure the amount of contaminants attached to the observation surface of the electron beam inspection apparatus.
[0030]
Next, the sample contamination measuring method of the electron beam inspection apparatus according to the second embodiment of the present invention will be described with reference to FIGS.
The cause of the generation of residual gas mainly composed of hydrocarbon which causes sample contamination is the gas released from the inner wall of the sample chamber 4, stages 6 and 6 ', a power transmission mechanism such as a ball screw, a stage guide 15, and the like. In addition, there are other gases released from various components in the sample chamber, such as sensors and wiring for stage control. Further, the gas adsorbed on the sample may be desorbed and become a hydrocarbon-based residual gas in the sample chamber 4. As described above, since there are a wide variety of parts that generate residual gases mainly composed of hydrocarbons that cause sample contamination, how much each part or lubricant affects the generation of contaminants 29 on the sample. An evaluation method is required.
[0031]
In particular, an electron beam inspection apparatus used in a semiconductor manufacturing inspection apparatus has a fine processing shape (pattern or hole) whose inspection target is micron order or less, and a semiconductor wafer to be inspected has a diameter of 200 mm to 300 mm, for example. Since the diameter is increased, for example, the XY stages 6 and 6 ′ in the sample chamber 3 are required to be positioned very precisely in a vacuum atmosphere such as 10 ⁻² Pa or less. Lubricants such as vacuum lubricant and vacuum grease are indispensable for the guide mechanism 15 and the ball screw for driving when moving. In addition, parts made of a polymer compound are required for the stage drive system and the sliding portion. Among these oils and greases, there are some that evaporate the lubricant in a vacuum and easily generate hydrocarbon gas molecules in a vacuum, and also release the hydrocarbon gas from the polymer compound. Therefore, a method for evaluating the sample contamination of such an electron beam inspection apparatus and a method for evaluating the influence of the lubricant and parts used in the sample chamber on the sample contamination are very important, and the substance has little influence on the sample contamination. It is necessary to select.
[0032]
In the present embodiment, the amount of contamination of the lubricant is evaluated using the above-described method for measuring the amount of adhered contaminant. The lubricant to be evaluated is applied entirely on the surface of the sample 16. The convex portion 28 shown in FIG. 2 is formed in advance on the surface of the sample 16, and a lubricant is applied to the surface of the convex portion 28. In this state, the first visual field region C1 is irradiated with the electron beam B1 for a certain time. At the start of irradiation, the diluted lubricant is in a liquid state and is not observed as an electron microscope image. The residual gas in the sample chamber 3 repeatedly adsorbs and desorbs on the sample surface, but when adsorbed, it is considered that it solidifies upon receiving the energy of the electron beam. Therefore, if a lubricant to be evaluated is applied to the sample surface in advance, when it receives the energy of an electron beam, it will solidify and the contaminants 29 will adhere. After a certain period of time, the amount of contamination 29 (line width increase a1) is measured by the method described with reference to FIGS. 1 to 3 with the field of view as the second field region C2 of low magnification. By measuring the adhesion amount of the contaminant 29, it is possible to evaluate whether the lubricant has a composition that tends to solidify and become the contaminant 29, or a lubricant that has a composition that hardly forms the contaminant 29. it can. For example, when the adhesion amount is several tens nm, it can be said that the lubricant has a composition that tends to solidify and become the contaminant 29, and the adhesion amount is almost 0 nm, that is, an undetectable adhesion amount. If there is, it can be evaluated that the lubricant has a composition that hardly forms the contaminant 29.
[0033]
According to this embodiment, the lubricant can be selected by measuring the amount of contaminants generated from the lubricant used in the apparatus.
[0034]
Next, a sample contamination measuring method for an electron beam inspection apparatus according to the third embodiment of the present invention will be described with reference to FIG.
FIG. 4 is an overall configuration diagram showing the configuration of an electron beam inspection apparatus used in the sample contamination measuring method according to the third embodiment of the present invention. The same reference numerals as those in FIG. 1 indicate the same parts.
[0035]
In the present embodiment, another chamber 30 is provided so as to be connected to the sample chamber 4, and a component 31 to be evaluated such as a sensor, a wiring, and various polymer materials can be installed therein.
[0036]
As described above, there are various parts such as various sensors, sensor wirings, and polymer materials in addition to the lubricant that generate residual gas mainly composed of hydrocarbons that cause sample contamination. In this embodiment, it is possible to evaluate how much each component affects the generation of the contaminant 29 on the sample.
[0037]
A sample 31 having a convex shape 28 with a known dimension (width a0) provided on the surface of the sample is placed in the electron beam inspection apparatus after the component 31 to be evaluated is placed in the room 30 and the first field of view. The region C1 is irradiated with the electron beam B1 for a certain time. Next, the magnification is reduced to a low magnification, and the line width increase amount a1 due to the contaminant 29 is measured in the same manner as in the example shown in FIG.
[0038]
Gas is released from the component 31 installed in the room 30 connected to the sample chamber 4 and flows into the sample chamber 4. The determination of whether the gas released from the component 31 is easily solidified by receiving the energy of the electron beam can be easily evaluated by measuring the contaminant 29. Instead of providing another room 30 in the sample room 4, a place may be provided on the stage and parts may be installed.
[0039]
According to the present embodiment, to what extent various sensors, sensor wiring, polymer materials, and the like, which are components that generate residual gas mainly composed of hydrocarbons that cause sample contamination, generate contaminant 29 on the sample. It can be evaluated whether it has an impact.
[0040]
Next, a sample contamination measuring method for an electron beam inspection apparatus according to the fourth embodiment of the present invention will be described with reference to FIG.
FIG. 5 is a principle configuration diagram for explaining the principle of the sample contamination measuring method according to the fourth embodiment of the present invention. The same reference numerals as those in FIG. 2 indicate the same parts.
[0041]
The configuration of the electron beam inspection apparatus used in the sample contamination measuring method according to the present embodiment is the same as that shown in FIG. In the present embodiment, instead of the convex portion 28 shown in FIG. 2, a sample 16 ′ having a concave portion 32 of a known size is used to attach the contaminant 29 and the amount of deposition is evaluated. In this case, the concave inner width dimension a0 is narrowed by the deposit, and as a result, the dimension becomes (a0−a1 × 2). This dimensional change can be grasped quantitatively, and carbon deposits adhering to and depositing on the sample observation surface of the electron beam inspection apparatus described in the above embodiments can be evaluated. Also used for evaluation of carbon deposits caused by hydrocarbon gases released from lubricating oils and polymer materials used in equipment, and used for selection of lubricants and materials that have little effect on carbon deposit formation. Can do.
[0042]
Next, a sample contamination measuring method for an electron beam inspection apparatus according to the fifth embodiment of the present invention will be described with reference to FIG.
FIG. 6 is a principle configuration diagram for explaining the principle of the sample contamination measuring method according to the fifth embodiment of the present invention. The same reference numerals as those in FIG. 2 indicate the same parts.
[0043]
The configuration of the electron beam inspection apparatus used in the sample contamination measuring method according to the present embodiment is the same as that shown in FIG. Furthermore, in the present embodiment, an electron beam inspection apparatus that can observe a sample by tilting it is used as the electron beam inspection apparatus.
[0044]
The sample 16 is irradiated with an electron beam perpendicularly, and then the sample 16 is tilted, and the observation is performed at a reduced magnification so that the entire portion irradiated with the electron beam can be observed first. When the sample 16 is observed only from the vertical direction, only the dimension a1 is an object to be evaluated for the deposition amount of the contaminant 29. However, when the electron beam inspection apparatus capable of observing the sample with an inclination is used, the contaminant 29 is used. The actual dimensions a2 and a3 can be calculated by geometric calculation based on the inclination angle of the sample 16 and the dimensions a2 and a3 of the observation image. Therefore, the accumulated thickness of the contaminant 29 can be evaluated. In addition, as an angle which inclines at the time of observation, it shall be 45 degree | times, for example.
[0045]
According to the present embodiment, the thickness of each part of the contaminant can be accurately measured.
[0046]
【The invention's effect】
According to the present invention, it is possible to quantitatively measure the amount of contaminants attached to the observation surface of the electron beam inspection apparatus.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram showing a configuration of an electron beam inspection apparatus used in a sample contamination measuring method according to a first embodiment of the present invention.
FIG. 2 is a principle configuration diagram for explaining the principle of the sample contamination measuring method according to the first embodiment of the present invention.
FIG. 3 is a principle configuration diagram for explaining the principle of the sample contamination measuring method according to the first embodiment of the present invention;
FIG. 4 is an overall configuration diagram showing a configuration of an electron beam inspection apparatus used in a sample contamination measuring method according to a third embodiment of the present invention.
FIG. 5 is a principle configuration diagram for explaining the principle of a sample contamination measuring method according to a fourth embodiment of the present invention.
FIG. 6 is a principle configuration diagram for explaining the principle of a sample contamination measuring method according to a fifth embodiment of the present invention.
[Explanation of symbols]
4 ... Sample chamber 12 ... Deflection coil 16 ... Sample 23 ... Reflected electron / secondary electron detector 28 ... Convex shaped part 29 ... Contaminant 30 ... Room 31 ... Component 32 ... Concave shaped part 40 ... Deflection control part 42 ... Display part 44 ... Control unit

Claims (3)

Using an electron beam inspection apparatus that irradiates a sample placed in a sample chamber with an electron beam from an electron gun in an electron gun chamber, detects secondary electrons generated from the sample, and measures the size of the sample,
Contaminants from the convex or concave dimensions changed by contaminants irradiating the electron beam to the convex or concave portions provided on the surface of the sample coated with the lubricant A sample contamination measuring method, wherein the lubricant is evaluated by measuring the amount of adhesion. Using an electron beam inspection apparatus that irradiates a sample placed in a sample chamber with an electron beam from an electron gun in an electron gun chamber, detects secondary electrons generated from the sample, and measures the size of the sample,
A material intended for use in an electron beam inspection device is installed in any sample chamber that is not irradiated with an electron beam,
Irradiate a convex or concave part on the surface of the sample with an electron beam, and measure the amount of contaminants deposited from the convex or concave dimensions changed by the contaminants adhering to the electron beam irradiation surface. And a sample contamination measuring method, wherein the material is evaluated according to the amount of the adhered contaminants. In the sample contamination measuring method of the electron beam inspection apparatus according to claim 1 or 2,
A sample contamination measuring method characterized by periodically measuring the amount of contaminants adhered and displaying or recording the measured amount of contaminants adhered.

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