JP2009264772A - Flow evaluation apparatus and flow evaluation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flow evaluation apparatus which can evaluate the flow of a fluid around a mobile unit with high precision. <P>SOLUTION: The flow evaluation apparatus comprises: a tank 30 having a supply port, a discharge port, and a light-transmissive wall 33; a fluid circulation unit for allowing a fluid into which tracer particles are mixed to flow from the supply port to the discharge port; drive sections 37, 39 for moving a mobile test piece 36 within the fluid in the tank 30; illuminators 101 to 103 for making planar sheet light L incident on a measuring area within the tank 30 through the light-transmissive wall 33; an imaging unit 104 for imaging the tracer particles illuminated by the sheet light L; and an arithmetic section 107 for calculating the velocity of the fluid around the mobile test piece 36 by the particle image velocimetry on the basis of a plurality of pieces of imaged data imaged by the imaging unit 104 at predetermined time intervals. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a flow evaluation apparatus and a flow evaluation method for evaluating a flow of a fluid around a moving body.

  As a countermeasure against chemical contamination in a semiconductor manufacturing process, an exposure apparatus that employs an air conditioning system called downflow is known (see, for example, Patent Document 1). Downflow is an air conditioning system that blows out air from the top of the apparatus and exhausts it from the bottom of the apparatus, thereby keeping the space around the wafer mounted on the wafer stage in the exposure apparatus in a highly clean state. Can do.

JP 2004-63934 A

  In this type of exposure apparatus, there is a wafer stage that moves at a high speed immediately below the downflow, so that the downflow flow is disturbed when the wafer stage moves. A laser interferometer is generally used to measure the position of the wafer stage, but local refractive index changes due to air fluctuations in the laser beam optical path may occur due to disturbances in the downflow flow during stage movement. is there. Such a local refractive index change may cause fluctuations in the measurement value of the interferometer, which may impair the position measurement accuracy of the wafer stage.

  Therefore, in an exposure apparatus or the like, it is very important to evaluate the air flow accompanying the stage movement in advance and reflect the result in the apparatus design. However, there is a problem that it is very difficult to perform flow evaluation using an actual machine installed in a downflow environment.

The flow evaluation apparatus according to the invention of claim 1 is a flow evaluation apparatus for evaluating the flow of air around a moving test specimen, and a tank having a supply port, a discharge port and a light transmission wall, and tracer particles are mixed. Fluid circulation device that causes the fluid to flow from the supply port to the discharge port, a drive unit that moves the moving specimen within the fluid in the tank, and a planar sheet light that is incident on the measurement region in the tank through the light transmission wall An illuminating device, an imaging device that images tracer particles illuminated by sheet light, and a fluid around a moving specimen by a particle image velocimetry based on a plurality of imaging data captured by the imaging device at predetermined time intervals And an arithmetic unit for calculating the speed of the motor.
According to a second aspect of the present invention, in the flow evaluation device according to the first aspect, the illuminating device converts the light of the pulse light source into a planar sheet light and emits it, and drives the drive unit and emits light from the pulse light source. And a synchronization control unit that controls the imaging of the imaging apparatus synchronously.
According to a third aspect of the present invention, in the flow evaluation apparatus according to the first or second aspect, the moving test body is formed by simulating the stage of the exposure apparatus, and the fluid circulation device corresponds to the flow condition of the ambient air around the stage. It is made to flow under the flow conditions.
According to a fourth aspect of the present invention, there is provided a flow evaluation method for evaluating a flow of ambient air around a stage of an exposure apparatus, wherein a tracer is placed in a tank for storing a moving specimen formed by simulating the stage. The fluid mixed with particles is caused to flow under a flow condition corresponding to the flow condition of the ambient air around the stage, the fluid around the moving specimen is illuminated with a planar sheet light, and the tracer particles illuminated with the sheet light are predetermined. It is characterized in that a plurality of images are taken at time intervals and the flow of fluid around the moving specimen is measured by a particle image velocimetry.

  According to the present invention, it is possible to accurately measure the flow of the fluid around the moving specimen.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a flow evaluation apparatus according to the present invention. The flow evaluation device includes a pseudo downflow device 200 and a PIV measurement system 100. The flow evaluation apparatus shown in FIG. 1 performs flow evaluation of an exposure apparatus (stepper apparatus) arranged in the downflow space, and the pseudo downflow apparatus 200 simulates the wafer stage arranged in the downflow space. It is a device that reproduces automatically.

  FIG. 2 is a view showing a schematic configuration of the exposure apparatus. The exposure apparatus S includes an illumination system 13 that illuminates the reticle R with exposure light, a reticle stage 2 on which the reticle R is placed, a wafer stage 3 on which the wafer W is placed, and a pattern formed on the reticle R. A projection optical system 4 that projects and exposes the wafer W is provided. These components are accommodated in an exposure chamber 6 covered with a case 5. The exposure apparatus S is installed in a clean room.

  The reticle stage 2 is supported on a support base 7 and constitutes a two-dimensional stage that can move in directions (for example, XY directions) orthogonal to each other in a horizontal plane. The wafer stage 3 is supported on the base 8 and constitutes a two-dimensional stage movable in the XY directions. Each of the stages 2 and 3 is driven in the XY directions by a driving device such as a linear motor, for example.

  The XY direction position of reticle stage 2 and the XY direction position of wafer stage 3 are measured by laser interferometers 9a and 10a, respectively. The laser interferometers 9a and 10a irradiate a laser beam toward the movable mirrors 9b and 10b fixed on the respective stages 2 and 3, and the reflected light from the movable mirrors 9b and 10b and the reflected light from the reference surface. The positions of reticle stage 2 and wafer stage 3 are measured by interference. The stages 2 and 3 are driven based on the measurement result of the stage position, and the pattern formed on the reticle R is accurately projected and exposed at a predetermined position on the wafer W. The interferometers 9a and 10a and the movable mirrors 9b and 10b are provided for the X axis and the Y axis, respectively, but only one of them is shown here.

  The support frame 11 disposed above the wafer stage 3 is provided with a duct 12. From a plurality of outlets 12a formed on the lower surface of the duct 12, air of a predetermined temperature generated by an air conditioner (not shown) is blown out downward. This conditioned air is exhausted to the outside of the exposure chamber 6 through an exhaust port 12 b formed around the base 8. As a result, the periphery of the wafer W and the wafer stage 3 is a downflow space.

(Description of the pseudo down flow apparatus 200)
In the exposure apparatus as shown in FIG. 1, it is difficult to measure the turbulence of the air flow during the movement of the wafer stage using an actual apparatus. The air turbulence in the flow space is reproduced, and the flow is measured by the PIV measurement system 100.

  FIG. 3 is a diagram showing an example of the pseudo downflow device 200, (a) shows the overall configuration of the pseudo downflow device 200, and (b) is a view taken in the direction of arrow b in (a). The pseudo downflow apparatus 200 is configured as a circulating water tank having a duct 20 through which water circulates and a substantially rectangular parallelepiped water tank 30 provided in the middle of the duct 20. The duct 20 has a pair of upper and lower horizontal duct portions 21 and 22 extending in the horizontal direction, and a pair of vertical duct portions 23 and 24 erected at both ends of the horizontal duct portions 21 and 22. The parts 21 and 22 and the vertical duct parts 23 and 24 communicate with each other.

  A water supply port 31 and a drainage port 32 are opened at the same height on both side portions of the water tank 30, and the inside of the water tank communicates with the horizontal duct portion 22 through the water supply port 31 and the drainage port 32. The horizontal duct portion 22 is provided with an impeller 25 for circulating water. When the impeller 25 is driven, the water in the duct flows into the water tank 30 through the water supply port 31, flows in the water tank 30 from the right side to the left side in the figure, and flows out from the drain port 32 to the duct side. The rotation speed of the impeller 25 can be changed. By adjusting the rotation speed of the impeller 25, the flow velocity of the water flowing in the water tank can be adjusted. The water tank 30 is entirely formed of a transparent plate 33 such as glass or acrylic so that the state inside the water tank can be observed from the outside.

  A rectifier 34 is attached to the inner wall of the water tank 30 so as to face the drain port 32, and a pseudo floor 35 is fixed in the water tank via the rectifier 34. A test body 36 is provided on the surface of the simulated floor 35 that faces the water supply port 31 at substantially the same height as the water supply port 31. The test body 36 is supported by a strut 37 so as to be slidable on the surface of the simulated floor 35. The upper end portion of the strut 37 penetrates the upper surface of the water tank 30 and is connected to an actuator 39 provided on a support base 38 above the water tank. By driving the actuator 39, the test body 36 can move along the surface of the pseudo floor 35 in each direction (up / down / left / right and diagonal directions) indicated by arrows in FIG.

  4A and 4B are views showing the rectifier 34, in which FIG. 4A is a perspective view seen from the drain port 32 side, and FIG. 4B is a perspective view seen from the water supply port 31 side. The rectifying device 34 includes a cross plate 341 formed so as to intersect substantially in an X shape, and a base plate 342 fixed to one end surface of the cross plate 341, and the pseudo floor 35 is fixed to the other end surface of the cross plate 341. Has been. A drain port 32 is opened at the center of the base plate 342. As shown in FIG. 4B, both the base plate 342 and the pseudo floor 35 are substantially rectangular, but the vertical and horizontal lengths of the pseudo floor 35 are shorter than the vertical and horizontal lengths of the base plate 342. . Around the simulated floor 35, a running water recovery unit 343 is provided.

  FIG. 5 is a view showing the flow of water in the water tank 30. The water that has flowed into the water tank 30 flows substantially vertically toward the surface of the simulated floor 35 as indicated by the arrows in the figure, and then passes through the flowing water recovery unit 343 outside the simulated floor 35 to the back side of the simulated floor 35. It detours and flows out of the central drain port 32. As a result, the flow in the vicinity of the drainage port is rectified, the occurrence of drift due to the suction of the drainage port 32 can be prevented, and the periphery of the test body 36 can be made uniform.

  A pseudo downflow apparatus 200 shown in FIG. 3 is an apparatus that reproduces a downflow flow equivalent to that in the exposure apparatus, and is obtained by scaling down an actual apparatus. The water tank 30 corresponds to the exposure apparatus 100, the test body 36 corresponds to the wafer stage 3, and the pseudo floor 35 corresponds to the base 8. Further, the water supply port 31 corresponds to the outlet 12a, and the flowing water recovery unit 343 and the drain port 32 correspond to the exhaust port 12b.

  Comparing the flow conditions in the exposure apparatus and the water tank, the temperature-controlled air flows in the exposure apparatus, but the water flows in the water tank. For this reason, in order to evaluate the same flow field, it is necessary to make the Reynolds number Re (Re = Ud / ν), which is an index representing the flow state, substantially coincide. U is the representative speed, d is the representative length, and ν is the kinematic viscosity coefficient of the fluid. For example, the speed of the fluid in the water tank 30 is selected as the representative speed U, and the dimension of the specimen 36 is selected as the representative length d. . The ratio of the kinematic viscosity coefficient of water and the kinematic viscosity coefficient of air is about 1/15 at 20 ° C., for example, so the value of numerator = Ud is also about 1/15, and the test body 36 and the water tank 30 are downsized. can do. The flow rate of water, which is the representative speed U, can be adjusted by changing the rotation speed of the impeller 25.

  When the downflow flow is measured by the PIV measuring system 100, a tracer is mixed in order to visualize the flow of water in the water tank. It is preferable to use a tracer having a specific gravity close to that of water, such as polystyrene particles. Polyamide-based powders and fluorescent particles can also be used. After mixing the tracer, the impeller 25 is driven at a predetermined rotational speed to supply water into the water tank. The water that flows in through the water supply port 31 flows around the test body 36 and flows out from the drain port 32. Since the tracer moves along the fluid flow, by measuring the position of the tracer with the PIV measurement system 100, it is possible to measure a change in the fluid flow when the test body 36 is moved.

(Description of PIV measurement system)
FIG. 6 is a diagram for explaining the principle of PIV (Particle Image Velocimetry). PIV is a type of velocity measurement method for fluids such as water and air. As an example, as shown in FIG. 6, fine tracer particles 60 are mixed in a flow, and a sheet-like light L (hereinafter referred to as sheet light) by laser light or the like is mixed with the flow. Irradiate. The tracer particles 60 irradiated with the sheet light are imaged by a CCD camera or the like, and images at two consecutive times (time t0, t1) are acquired. Assuming that the tracer particle 60 in the flow space moves together with the local flow, the local flow velocity U in the flow space is obtained from the movement amount ΔX of the tracer particle 60 on the image and the time interval ΔT (= t1−t0) at two times. It can be obtained from equation (1). In Expression (1), α is an image conversion coefficient, and is given by α = β / M from the lateral magnification M of the imaging system and the unit conversion count β.
U = α · ΔX / ΔT (1)

  As shown in FIG. 1, the PIV measurement system 100 of this embodiment includes a laser light source 101, a sheet optical system 102, a reflection mirror 103, a camera 104, a synchronization device 105, a signal input / output unit 106, a control PC (personal computer). ) 107 and an analysis PC 108. When pulsed laser light is emitted from the laser light source 101, the laser light is converted into sheet light L by the sheet optical system 102. The sheet light L is reflected by the reflection mirror 103 and enters substantially vertically upward from the bottom surface of the water tank 30. At that time, the sheet light L is incident so that the surface of the sheet light L is substantially parallel to the flow and crosses the specimen 36. Note that the tilt angle of the reflection mirror 103 may be changed to change the incident angle of the sheet light L to perform measurement.

  The camera 104 images scattered light from tracer particles (not shown) mixed in the fluid. In this embodiment, a digital camera using a solid-state imaging device (CCD sensor, CMOS sensor, or the like) is used as the camera 104, and a plurality of images can be captured at a minute time interval (for example, every 1 millisecond interval). it can. In addition, when using a double pulse laser light source, it illuminates for 2 continuous time instants.

  Data of an image captured by the camera 104 is input to the signal input / output unit 106, sent to the analysis PC 108 via the signal input / output unit 106, and recorded on a recording medium of the PC 108. The tracer particle image is processed by the analysis PC 108, and the velocity distribution is obtained from the two-time image. The obtained velocity vector is corrected as a final instantaneous velocity distribution by removing an erroneous vector after post-processing. Note that a three-dimensional velocity vector can also be obtained by imaging from different directions using two cameras.

  The actuator 39 is composed of a stepping motor, and the moving speed can be easily controlled by the control PC 107. When an operation command for the actuator 39 is issued by the control PC 107, a pulse voltage (trigger signal) is input to the signal input / output unit 106, and the pulse voltage is used as a trigger to start photographing with the camera 104. In this way, by synchronizing the camera photographing and the movement of the test body 36, it is possible to measure in detail the change in flow associated with the movement. Since the laser light source 101 emits pulsed laser light, a synchronizer 105 such as a synchronizer is used to synchronize the emission of the sheet light L and the camera photographing. In FIG. 2, a pulse voltage (trigger signal) is input from the control PC 108 to the signal input / output unit 106. However, as indicated by a broken line, the trigger signal is directly input to the synchronization device 105, and the synchronization device 105 causes the laser light source to be input. 101 and the camera 104 may be synchronized.

  In the example shown in FIG. 1, since the pulsed light is used for the laser light, the light emission timing is synchronized with the photographing using the synchronization device 105, but the synchronization device 105 is necessary when using a laser light source that generates continuous light. Absent. Further, the analysis PC 107 and the control PC 108 may be configured by the same PC. Here, the digital image data of the camera 104 is taken into the analysis PC 107 and the flow velocity is obtained. However, in principle, the flow velocity can be obtained from the position of the tracer particles on the image taken by the film type high-speed camera. Is possible.

  As described above, in the flow evaluation apparatus according to the present embodiment, by applying the PIV measurement system to the pseudo downflow apparatus 200, the time from the movement to the stop as in the wafer stage is very short, and the high speed With respect to the test body 36 that moves, the flow change within a short time due to the movement can be evaluated with high accuracy.

  For example, in the case of a wafer stage of a stepper device, one shot of IC manufacturing is generally around 25 mm square, and the movement distance of 25 mm must be stopped in about 0.2 seconds. The speed in the meantime reaches 500 mm / s at the maximum, and if acceleration of 2G is required, the acceleration time to reach the maximum speed of 500 mm is about 0.026 seconds. In order to accurately measure such a change in flow within a short time, it is necessary to perform a plurality of measurements within the acceleration time. For example, when measurement is performed five times, a measurement resolution of at least about 200 Hz is required. Such measurement is possible with the PIV measurement described above.

  As described above, the position of the wafer stage is controlled based on the measurement result of the laser interferometer as described above. However, when the refractive index locally changes due to the fluctuation of the air in the beam optical path, the measurement value also changes. For example, when the fine resolution of the interferometer is 0.01 μm, the amount of fluctuation when a gas having a temperature difference slowly traverses the beam optical path may reach about ± 0.1 μm at worst. Since the fluctuation amount is 0.2 μm, it cannot be put into practical use as an apparatus for exposing a pattern having a line width of about 0.5 μm.

  Conventionally, it has been difficult to actually measure the air flow accompanying the movement of the wafer stage of the stepper device. However, as in this embodiment, by moving the test body 36 in the simulated downflow apparatus 200, the air flow around the wafer stage is simulated and the flow velocity distribution is measured by the PIV measurement system. It becomes possible to measure the actual flow change. By utilizing the measurement results obtained in this way for flow simulation during wafer stage design, it becomes possible to design with higher accuracy, and to the stage position measurement system due to flow disturbance due to wafer stage movement. The influence can be reduced.

  In addition to the structure shown in FIG. 2, a structure as shown in FIG. 7 may be adopted as the pseudo downflow apparatus 200 for reproducing the movement of the wafer stage. 7A and 7B show the overall configuration of the flow evaluation apparatus 200, where FIG. 7A is a front view and FIG. 7B is a view taken in the direction of arrow b in FIG. In addition, the same code | symbol is attached | subjected to the location same as FIG. 3, and it demonstrates centering on a different part below.

  In the apparatus shown in FIG. 7A, a water tank 30 is provided at the intersection of the horizontal duct portion 21 and the vertical duct portion 24. A water supply port 31 is opened at the center of the bottom surface of the water tank 30 so as to communicate with the vertical duct portion 24, and a drain port 32 is opened at the side surface of the water tank 30 so as to communicate with the horizontal duct portion 21. Inside the aquarium 30, a pseudo floor 35 is fixed and supported substantially horizontally from the inner wall surface of the aquarium 30 via a plurality of struts 41, and passes through a flowing water passage 42 between the struts 41 to move through the aquarium from below to above. And water is flowing. In FIG. 7A, the rectifier 34 is not provided downstream of the simulated floor 35, so that the suction from the drain port 32 does not affect the flow of water below the simulated floor 36 from the simulated floor 35. The length to the drain port 32 is set.

  As shown in FIG. 7B, a through hole 35a is opened at the center of the simulated floor 35, and the test body 36 can be slid along the bottom surface of the simulated floor 35 via a strut 37 penetrating the through hole 35a. It is supported. The upper end portion of the strut 37 passes through the support base 38 above the water tank 30 and is connected to the actuator 39. By driving the actuator 39, the test body 36 can be moved along the bottom surface of the pseudo floor 35 in each direction (front and rear, right and left directions and diagonal directions) indicated by arrows in FIG. Here, since the test body 36 is provided on the bottom surface of the simulated floor 35 and water is allowed to flow from the lower side to the upper side, the influence of the potential energy of water is reduced, and the downflow flow can be realized with high accuracy.

  In the above description, the pseudo downflow apparatus 200 is configured by taking the wafer stage of the stepper apparatus as an example, and the change in flow due to the movement of the test body 36 assuming the wafer stage is measured by the PIV measurement system 100. However, the flow velocity distribution measurement around the moving body using the pseudo downflow device 200 and the PIV measuring system 100 can be applied to various moving bodies. In that case, what is necessary is just to comprise the test body 36 etc. which are arrange | positioned in the water tank 30 according to an apparatus structure. For example, as shown in FIG. 8, only the test body 36 corresponding to the moving body may be provided in the water tank 30. Also in the case shown in FIG. 8, the test body 36 is configured to move in a plane perpendicular to the fluid, but is not necessarily limited to the vertical plane.

  In the present embodiment described above, since the wafer stage of the stepper device is assumed, the flow of the fluid is downflow. However, the present invention is not limited to downflow and can be applied. That is, according to the present embodiment, it is possible to accurately measure a change in flow when an object quickly moves in a fluid flowing in one direction, not limited to a downflow. In addition, although water is used as the fluid to circulate in the downflow device 200, it is not necessary to use water, and the type of fluid may be selected so that an equivalent flow state can be realized.

  In the above-described embodiment, the wafer stage of the stepper device has been described as an example, but the present invention can also be applied to the flow measurement of the ambient fluid around the reticle stage. Since the stepper apparatus performs reduction projection, the movement speed of the reticle stage is higher than that of the wafer stage, and may be, for example, four times the wafer stage at the highest speed. Therefore, although the required accuracy of the temperature air conditioning is higher in the wafer stage, the fluid around the reticle stage becomes more complicated. In addition, the present invention is not limited to the above embodiment as long as the characteristics of the present invention are not impaired.

It is a figure which shows one Embodiment of the flow evaluation apparatus by this invention. It is a figure which shows schematic structure of exposure apparatus. The pseudo down flow apparatus 200 is shown, (a) is a front view which shows the whole structure, (b) is a b arrow view of (a). It is a figure which shows the rectifier 34, (a) is the perspective view seen from the drain port 32 side, (b) is the perspective view seen from the water supply port 31 side. FIG. 3 is a diagram showing the flow of water in the water tank 30. It is a figure explaining the principle of PIV (Particle Image Velocimetry). It is a figure which shows the other example of the flow evaluation apparatus 200, (a) is a front view which shows the whole structure, (b) is a b arrow line view of (a). It is a figure which shows the flow evaluation apparatus 200 at the time of providing only the test body 36 corresponded to a moving body in the water tank 30. FIG.

Explanation of symbols

  3: Wafer stage, 20: Duct, 25: Impeller, 30: Water tank, 31: Water supply port, 32: Drainage port, 33: Transparent plate, 36: Specimen, 39: Actuator, 60: Tracer particle, 100: PIV measurement System: 101: Laser light source, 102: Sheet optical system, 103: Mirror, 104: Camera, 105: Synchronizer, 106: Signal input / output unit, 107: PC for control, 108: PC for analysis, 200: Pseudo down flow Apparatus, L: sheet light, S: exposure apparatus,

Claims (4)

A flow evaluation device for evaluating the flow of air around a moving specimen,
A tank having a supply port, a discharge port and a light transmission wall;
A fluid circulation device for flowing a fluid mixed with tracer particles from the supply port to the discharge port;
A drive unit for moving the movable specimen in the fluid of the tank;
Illumination device that makes planar sheet light incident on the measurement region in the tank through the light transmission wall;
An imaging device that images the tracer particles illuminated by the sheet light;
A flow evaluation unit, comprising: a calculation unit that calculates a velocity of a fluid around the moving specimen by a particle image flow velocity measurement method based on a plurality of pieces of imaging data imaged by the imaging device at predetermined time intervals. apparatus. The flow evaluation apparatus according to claim 1,
The illumination device converts the light from the pulsed light source into a planar sheet light and emits it,
A flow evaluation apparatus comprising: a synchronization control unit configured to synchronously control driving of the driving unit, light emission of the pulse light source, and imaging of the imaging device. In the flow evaluation apparatus according to claim 1 or 2,
The moving test body is formed by simulating a stage of an exposure apparatus, and the fluid circulation apparatus causes the fluid to flow under a flow condition corresponding to a flow condition of air around the stage. A flow evaluation method for evaluating a flow of air around a stage of an exposure apparatus,
In a tank containing a moving test body formed by simulating the stage, a fluid mixed with tracer particles is allowed to flow under a flow condition corresponding to the flow condition of the ambient air of the stage,
Illuminating the fluid around the moving specimen with a planar sheet light,
A flow evaluation method, wherein the tracer particles illuminated with the sheet light are imaged a plurality of times at predetermined time intervals, and the flow of fluid around the moving test specimen is measured by a particle image flow velocity measurement method.

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