Observation device

Abstract

To provide an observation device capable of accurately calculating the state of air flow using the Background Oriented Schlieren method even when an optical axis direction of a background image is positionally unstable.SOLUTION: An observation device 60 comprises a background image 61, an imaging part 63, a light wave modulation element 64 and a computer 50. The imaging part 63 images the background image 61 through an observation area S in which air flow is present. The light wave modulation element 64 is interposed between the observation area S and the imaging part 63. The light wave modulation element 64 uses light incident from the background image 62 through the observation area S to form a plurality of diffraction images each having different focal position by the imaging part 63. The computer calculates the state of air flow by the Background Oriented Schlieren method, using the plurality of diffraction images obtained by the imaging part 63.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an observation device for observing an air current. [Background technology]

[0002] Conventionally, there is known an apparatus for performing a cleaning process on a substrate such as a semiconductor wafer by supplying a processing liquid to the substrate. In this type of apparatus, even a slight change in airflow in the chamber can cause a deterioration in the quality of the product. For this reason, there is a demand for a technology that can observe the state of airflow in the chamber while performing a substrate cleaning process.

[0003] A known technique for observing airflow is, for example, the Background Oriented Schlieren (BOS) method. The Background Schlieren method is a method for calculating the state of airflow in an observation area by capturing a background image through the observation area where airflow is formed and measuring the distortion of the background image in the captured image.

[0004] A conventional apparatus using the background type Schlieren method is described in, for example, Patent Document 1. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2020-143917 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the background type Schlieren method, it is necessary to capture a background image by focusing on it. However, in a chamber in which a substrate is processed, there are steps and curved surfaces due to various structures. For this reason, in the chamber, it may not be possible to arrange the background image on a single plane. In addition, if the background image is arranged along the steps or curved surfaces in the chamber, it is difficult to capture the background image by focusing on all positions. For this reason, there is a problem that it is difficult to apply the background type Schlieren method.

[0007] The present invention has been developed in consideration of the above circumstances, and aims to provide an observation device that can accurately calculate the airflow state using the background Schlieren method, even if the position of the background image in the optical axis direction is not constant. [Means for solving the problem]

[0008] In order to solve the above problems, the first invention of the present application is an observation device for observing airflow, comprising: a background image; an imaging unit for capturing the background image through an observation area in which the airflow exists; an optical wave modulation element interposed between the observation area and the imaging unit; and a computer for calculating the state of the airflow by a background-type Schlieren method using the image acquired by the imaging unit, wherein the optical wave modulation element forms multiple diffraction images with different focal positions in the imaging unit due to light incident from the background image through the observation area.

[0009] A second aspect of the present invention is the observation device of the first aspect of the present invention, wherein the light wave modulation element is a diffraction grating having a plurality of grating patterns.

[0010] A third invention of the present application is the observation device of the second invention, wherein the multiple grating patterns are formed at positions displaced from coordinates at regular intervals in a plane perpendicular to the optical axis by a shift amount corresponding to the coordinates, and the focal positions of the multiple diffraction images change due to the displacement of the grating pattern.

[0011] A fourth aspect of the present invention is the observation device of the first aspect, wherein the light wave modulation element is a spatial light modulator capable of changing the grating pattern in response to an electric signal.

[0012] A fifth aspect of the present invention is an observation device according to any one of the first to fourth aspects, wherein a difference in focal positions of the multiple diffraction images is smaller than a depth of field of an imaging optical system of the imaging section.

[0013] A sixth invention of the present application is an observation device according to any one of the first to fifth inventions, wherein the computer creates an all-focused image by synthesizing the multiple diffraction images acquired by the imaging unit, and calculates the state of the airflow based on the all-focused image. Effect of the Invention

[0014] According to the first to sixth aspects of the present invention, even if the position of the background image in the optical axis direction is not constant, a plurality of diffraction images with different focal positions can be obtained by the light wave modulation element. Therefore, the state of the airflow can be calculated with high accuracy by the background type Schlieren method based on the obtained plurality of diffraction images.

[0015] In particular, according to the fourth aspect of the present invention, the grating pattern can be changed without replacing the light wave modulation element itself.

[0016] In particular, according to the fifth aspect of the present invention, a plurality of diffraction images can be used to continuously ensure positions in the optical axis direction where the light is substantially in focus.

[0017] In particular, according to the sixth aspect of the present invention, the state of the airflow can be calculated with high accuracy based on one omnifocal image. [Brief description of the drawings]

[0018] [Figure 1] 1 is a vertical sectional view of a substrate processing apparatus; [Diagram 2] 4 is a block diagram showing electrical connections between a control unit and each unit in the substrate processing apparatus. FIG. [Diagram 3]FIG. 2 is a perspective view of a light wave modulation element. [Figure 4] 1A and 1B are diagrams illustrating the principle of changing the focal position of a diffraction image. [Diagram 5] 1A and 1B are diagrams showing examples of a plurality of grating patterns of a light wave modulation element. [Figure 6] 1A and 1B are diagrams showing examples of a plurality of diffraction images formed on an imaging plane. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0020] <1. Overall configuration of substrate processing equipment> 1 is a vertical cross-sectional view of a substrate processing apparatus 1 equipped with an observation apparatus 60 according to one embodiment. The substrate processing apparatus 1 is an apparatus for supplying a processing liquid to a surface of a disk-shaped substrate W to clean the substrate W in a semiconductor wafer manufacturing process. As shown in FIG. 1, the substrate processing apparatus 1 includes a chamber 10, a substrate holding unit 20, a rotation mechanism 30, a processing liquid supply unit 40, and a computer 50.

[0021] The chamber 10 is a housing containing a processing space 11 for processing a substrate W. The chamber 10 has a sidewall 12 surrounding the sides of the processing space 11, a top plate portion 13 covering an upper portion of the processing space 11, and a bottom plate portion 14 covering a lower portion of the processing space 11. The substrate holder 20, the rotating mechanism 30, and the nozzle 45 of the processing liquid supply unit 40 are housed inside the chamber 10. A load / unload port for loading and unloading the substrate W into and from the chamber 10, and a shutter for opening and closing the load / unload port are provided in a part of the sidewall 12.

[0022] The substrate holding unit 20 is a mechanism for holding the substrate W horizontally (in a position in which the normal line faces the vertical direction) inside the chamber 10. As shown in FIG. 1, the substrate holding unit 20 has a disk-shaped spin base 21 and a plurality of chuck pins 22. The plurality of chuck pins 22 are provided on the outer periphery of the upper surface of the spin base 21. The substrate W is held by the plurality of chuck pins 22 with the processing surface on which a pattern is to be formed facing upward. Each chuck pin 22 contacts the lower surface and outer periphery end surface of the peripheral portion of the substrate W, and supports the substrate W at a position above the upper surface of the spin base 21 with a small gap therebetween.

[0023] The rotation mechanism 30 is a mechanism for rotating the substrate holding part 20. As shown in Fig. 1, the rotation mechanism 30 has a motor 31 and a support shaft 32. The support shaft 32 extends in the vertical direction, with its lower end connected to the motor 31 and its upper end fixed to the center of the lower surface of the spin base 21. When the motor 31 is driven, the support shaft 32 rotates about its axis 320. Then, together with the support shaft 32, the substrate holding part 20 and the substrate W held by the substrate holding part 20 also rotate about the axis 320.

[0024] The processing liquid supply unit 40 is a mechanism for supplying a processing liquid to the upper surface of the substrate W held by the substrate holding unit 20. The processing liquid supply unit 40 has a liquid supply source 41, a liquid supply pipe 42, a valve 43, a pump 44, and a nozzle 45. The liquid supply source 41 is a tank for storing the processing liquid before supply. Examples of the processing liquid that can be used include an SPM cleaning liquid (a mixture of sulfuric acid and hydrogen peroxide), an SC-1 cleaning liquid (a mixture of ammonia water, hydrogen peroxide, and pure water), an SC-2 cleaning liquid (a mixture of hydrochloric acid, hydrogen peroxide, and pure water), a DHF cleaning liquid (dilute hydrofluoric acid), and pure water (deionized water).

[0025] The liquid supply pipe 42 is a pipe that connects the liquid supply source 41 and the nozzle 45. The valve 43 and the pump 44 are provided on the path of the liquid supply pipe 42. The nozzle 45 is disposed facing the upper surface of the substrate W. When the valve 43 is opened and the pump 44 is operated, the processing liquid is supplied from the liquid supply source 41 through the liquid supply pipe 42 to the nozzle 45. Then, the processing liquid is discharged from the nozzle 45 toward the center of the upper surface of the substrate W.

[0026] The processing liquid discharged from the nozzle 45 onto the upper surface of the substrate W spreads outward from the center of the substrate W due to centrifugal force caused by the rotation of the substrate W. The processing liquid scattered outward from the substrate W is collected in a cup (not shown) and then discharged to the outside of the chamber 10.

[0027] The computer 50 is an information processing device for controlling the operation of each part of the substrate processing apparatus 1. Fig. 2 is a block diagram showing electrical connections between the computer 50 and each part in the substrate processing apparatus 1. As conceptually shown in Fig. 2, the computer 50 has a processor 51 such as a CPU, a memory 52 such as a RAM, and a storage unit 53 such as a hard disk drive.

[0028] An operation control program P1 and an air current observation program P2 are stored in the storage unit 53. The operation control program P1 is a computer program for controlling the operation of each unit of the substrate processing apparatus 1 in order to execute processing of the substrate W in the substrate processing apparatus 1. The air current observation program P2 is a computer program for observing the state of the air current in the chamber 10 based on an image obtained from an imaging unit 63 described later.

[0029] 2, the computer 50 is electrically connected to the chuck pin 22, the motor 31, the valve 43, and the pump 44 described above. The computer 50 controls the operation of each of the above-mentioned parts according to an operation control program P1 stored in the storage unit 53. This allows the cleaning process of the substrate W in the substrate processing apparatus 1 to proceed. The computer 50 is also electrically connected to an imaging unit 63 described later. The computer 50 performs an observation process of the airflow in the chamber 10 based on an image obtained from the imaging unit 63.

[0030] <2. Observation equipment> During the cleaning process of the substrate W, various air currents are generated in the chamber 10 due to the downflow of purified air, the discharge of the processing liquid, the evaporation of the processing liquid, the temperature change of the gas, etc. These air currents may affect the cleaning quality of the substrate W. Therefore, the substrate processing apparatus 1 is provided with an observation device 60 that observes the state of the air current in a predetermined observation area S in the chamber 10.

[0031] As shown in FIG. 1, the observation device 60 includes a background image 61, an objective lens 62, an imaging section 63, a light wave modulation element 64, and the computer 50 described above.

[0032] The background image 61 is an image arranged inside the chamber 10. The background image 61 may be a geometric repeating pattern such as dots or stripes, or may be a random pattern or design. The background image 61 is arranged on the surface of a structure inside the chamber 10. The surface on which the background image 61 is arranged intersects with the optical axis A of the observation device 60. However, in this embodiment, the position of the background image 61 in the optical axis direction is not constant. In the example of FIG. 1, the background image 61 is formed on three surfaces at different positions in the optical axis direction.

[0033] The objective lens 62 is a lens disposed on the optical axis A between the observation area S and the light wave modulation element 64. A transparent window 15 is provided on the side wall 12 of the chamber 10. Light incident on the objective lens 62 from the background image 61 through the observation area S and the window 15 is collected by the objective lens 62 and enters the light wave modulation element 64. In this embodiment, the objective lens 62 is disposed outside the chamber 10. However, the objective lens 62 may be disposed inside the chamber 10.

[0034] The imaging unit 63 is a unit that captures a background image 61. The imaging unit 63 is disposed outside the chamber 10. The imaging unit 63 captures a background image 61 in the chamber 10 via the observation area S, the window 15, and the light wave modulation element 64. As shown in FIG. 1, the imaging unit 63 has an imaging optical system 631 and an imaging sensor 632. The imaging optical system 631 includes one or more lenses. The imaging sensor 632 includes an imaging element such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor).

[0035] The imaging sensor 632 receives light incident from the background image 61 through the observation area S, the window 15, the objective lens 62, the light wave modulation element 64, and the imaging optical system 631. This allows multi-tone image data composed of multiple pixels to be obtained. The imaging sensor 632 also obtains multiple pieces of image data by repeatedly capturing images at short time intervals.

[0036] The light wave modulation element 64 is an optical element for forming a plurality of diffraction images 9 at the position of the imaging sensor 632 (hereinafter referred to as "imaging plane P"). The light wave modulation element 64 is disposed on the optical axis A between the objective lens 62 and the imaging section 63. In this embodiment, the light wave modulation element 64 is disposed outside the chamber 10. However, the light wave modulation element 64 may be disposed inside the chamber 10 together with the objective lens 62.

[0037] 3 is a perspective view of the light wave modulation element 64. The light wave modulation element 64 of this embodiment is a diffraction grating (DOE: Diffractive Optical Element). The light wave modulation element 64 is plate-shaped and disposed perpendicular to the optical axis A. As shown in FIG. 3, the light wave modulation element 64 has a plurality of grating patterns 641. The grating patterns 641 are light-transmitting portions formed in the light wave modulation element 64.

[0038] Light incident on the light wave modulation element 64 from the background image 61 via the observation area S, the window 15, and the objective lens 62 passes through a plurality of grating patterns 641. At that time, the incident light is split into zeroth-order diffracted light, first-order diffracted light, second-order diffracted light, m-th-order diffracted light (m is an integer) by diffraction at each of the grating patterns 641. As a result, a plurality of diffraction images 9 are formed on the imaging plane P. Each of the plurality of diffraction images 9 includes an image of the background image 61.

[0039] Here, when the angle θ of the diffracted light with respect to the optical axis A is small and can be regarded as sin θ≒cos θ, the following formula (1) holds.

[0040] λ=dx / ml (1)

[0041] The symbols in formula (1) represent the following: λ: wavelength of incident light d: Interval of the grating pattern 641 in the light wave modulation element 64 x: Interval of diffraction images 9 on the imaging plane P m: order of diffracted light l: distance along the optical axis from the light wave modulation element 64 to the imaging plane P

[0042] The multiple grating patterns 641 are two-dimensionally arranged in a plane perpendicular to the optical axis A. Therefore, the incident light is divided two-dimensionally by diffraction in the light wave modulation element 64. As a result, multiple diffraction images 9 arranged two-dimensionally vertically and horizontally are formed on the imaging plane P. For example, as shown in FIG. 3, nine diffraction images 9 are arranged in a matrix of three columns and three rows on the imaging plane P.

[0043] However, the multiple lattice patterns 641 of the light wave modulation element 64 are not arranged at regular intervals vertically and horizontally, but are arranged at distorted positions. That is, the multiple lattice patterns 641 are arranged at positions displaced by a shift amount according to each coordinate from the coordinates arranged vertically and horizontally at regular intervals in a plane perpendicular to the optical axis A. The focal positions of the multiple diffraction images 9 can be changed by displacing the lattice patterns 641. As a result, the multiple diffraction images 9 can be images with mutually different focal positions.

[0044] Fig. 4 is a diagram showing the principle of changing the focal position of the diffraction image 9. In Fig. 4, the wavefront aberration δφ(dz) is expressed by the following formula (2).

[0045]

number

[0046] The symbols in formula (2) represent the following: dz: Defocus amount (amount of deviation of the focal position in the optical axis direction) δφ(dz): Wavefront aberration n: refractive index k: wave number fobj: focal length of the objective lens (xp,yp): Coordinates of grid pattern 641

[0047] Therefore, the shift amount of the grating pattern 641 at the coordinates (xp, yp) corresponding to the wavefront aberration Δφ(dz) calculated by the formula (2) is expressed by the following formula (3).

[0048]

number

[0049] The symbols in formula (3) represent the following: N: Number of defocuses (3 for 3x3) δx(xp,yp): Displacement of the lattice pattern 641 in the x direction at (xp,yp) δy(xp,yp): Displacement of the lattice pattern 641 in the y direction at (xp,yp)

[0050] Fig. 5 is a diagram showing an example of a plurality of lattice patterns 641 of the light wave modulation element 64. The left diagram of Fig. 5 shows an example (comparative example) in which the plurality of lattice patterns 641 are not displaced. The right diagram of Fig. 5 shows an example (embodiment) in which the plurality of lattice patterns 641 are displaced by the above-mentioned calculation. As shown in the right diagram of Fig. 5, in this embodiment, the plurality of lattice patterns 641 are arranged at positions shifted by the distortion amounts δx and δy corresponding to each coordinate.

[0051] 5 is a shape that optimizes the light intensity of each diffraction image 9 when the number of diffraction images 9 is 3 rows x 3 columns. However, the shape of each grating pattern 641 may be determined appropriately depending on the number of diffraction images 9 used for observation.

[0052] The light wave modulation element 64 is disposed on the Fourier plane between the objective lens 62 on the optical axis A and the imaging optical system 631. As a result, a plurality of diffraction images 9 having different focal positions are formed on the imaging plane P. FIG. 6 is a diagram showing an example of a plurality of diffraction images 9 formed on the imaging plane P. In FIG. 6, the defocus amount of each diffraction image 9 is added. As shown in FIG. 6, each diffraction image 9 is an image of a background image 61 having a mutually different focal position. The imaging unit 63 captures a single image including such a plurality of diffraction images 9. The captured image obtained is input from the imaging unit 63 to the computer 50.

[0053] The computer 50 calculates the state of airflow in the observation region S by a background oriented Schlieren (BOS) method using the captured image input from the imaging unit 63. The background image 61 in this embodiment is not located at a constant position in the optical axis direction, but is formed on three planes located at different positions in the optical axis direction. Therefore, the computer 50 selects the diffraction image 9 that is most in focus for each position of the background image 61 from the multiple diffraction images 9 included in the captured image. Then, the computer 50 applies the background oriented Schlieren method to the selected diffraction image 9 to calculate the state of airflow at that position.

[0054] When an airflow is formed in the observation region S, the observation region S becomes a non-uniform field, and the light rays passing through the observation region S are displaced. This distorts the background image 61 in the diffraction image 9 captured by the imaging unit 63. The computer 50 measures the distortion of the background image 61 in the diffraction image 9. The computer 50 then calculates the state of the airflow in the observation region S based on the measured distortion of the background image 61. In particular, in this embodiment, the distortion of the background image 61 is measured using the diffraction image 9 that is most in focus for each position of the background image 61. This allows the state of the airflow to be calculated more accurately than when an unfocused image is used.

[0055] The computer 50 may create one all-focus image by combining a plurality of diffraction images 9. In this case, the computer 50 may, for example, calculate the sharpness of the plurality of diffraction images 9 for each coordinate, and adopt the pixel value of the diffraction image 9 with the highest sharpness for each coordinate. Then, the pixel values ​​of the adopted diffraction images 9 are combined to create one all-focus image. As a result, an all-focus image of the background image 61 in focus at all coordinates is obtained. The computer 50 may calculate the state of the airflow by applying the background-type Schlieren method to such an all-focus image.

[0056] As described above, in this observation device 60, by using the light wave modulation element 64, it is possible to obtain the diffraction images 9 of the background images 61 with different focal positions in one shooting. Therefore, even if the position of the background image 61 in the optical axis direction is not constant, the airflow state in the observation area S can be calculated with high accuracy by applying the background type Schlieren method using the multiple diffraction images 9.

[0057] At this time, it is desirable to make the difference in focal positions of the multiple diffraction images 9 (dz in FIG. 6) smaller than the depth of field of the imaging optical system 631 of the imaging section 63. In this way, it is possible to continuously ensure positions in the optical axis direction where the multiple diffraction images 9 are substantially in focus. Therefore, it is possible to obtain focused images at all positions near the background image 61 in the optical axis direction. This makes it possible to more accurately calculate the state of the airflow in the observation region S.

[0058] The computer 50 calculates the state of the airflow in the observation area S by the above method while performing the cleaning process of the substrate W. Then, the computer 50 monitors whether the calculated state of the airflow is within a predetermined allowable range. If the calculated state of the airflow is outside the allowable range, the computer 50 executes anomaly response control. The anomaly response control may be, for example, displaying a warning on a display unit such as a display, turning on a warning lamp, or sounding a warning sound. The anomaly response control may also be outputting information indicating an anomaly to an external terminal. The anomaly response control may also be stopping or limiting the cleaning process of the substrate W. This allows a user of the substrate processing apparatus 1 to recognize that the state of the airflow in the observation area S is outside the allowable range.

[0059] <3. Modifications> Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.

[0060] The diffraction grating used as the light wave modulation element 64 may be a phase modulation type diffraction grating or an amplitude modulation type diffraction grating. However, if an amplitude modulation type diffraction grating is used, and the diffraction image 9 by the zero-order light (for example, the central diffraction image 9 in Figs. 3 and 6) is too bright, it is preferable to use a phase modulation type diffraction grating. Furthermore, the diffraction grating in the present invention may be a CGH (Computer-Generated Hologram).

[0061] When a diffraction grating is used as the light wave modulation element 64 as in the above embodiment, it is necessary to replace the light wave modulation element 64 itself when it is desired to change the grating pattern 641. Therefore, a spatial light modulator (SLM: Spatial Light Modulator) such as a GLV (Grating Light Valve) (registered trademark) or a PLV (Planar Light Valve) may be used as the light wave modulation element 64. The spatial light modulator may be either a transmissive type or a reflective type. The spatial light modulator can change the grating pattern 641 according to an input electrical signal. Therefore, if a spatial light modulator is used as the light wave modulation element 64, the grating pattern 641 can be changed without replacing the light wave modulation element 64 itself.

[0062] In the above embodiment, the background image 61 is arranged on a surface having a step. However, the background image 61 may be arranged on a curved surface whose position in the optical axis direction is not constant. Also, in the above embodiment, the background image 61 is fixedly arranged on the surface of the structure in the chamber 10. However, the background image 61 may be realized by projecting light onto the surface of the structure in the chamber 10 from outside the chamber 10.

[0063] In the above embodiment, an apparatus for performing a cleaning process on a substrate W has been described. However, the apparatus in which the observation apparatus of the present invention is mounted may be an apparatus for performing a process other than a cleaning process. Furthermore, the apparatus in which the observation apparatus of the present invention is mounted may be an apparatus for performing a process on an object other than a substrate W.

[0064] However, in an apparatus that supplies a processing liquid to a substrate W for precision electronic components such as a semiconductor wafer, it is necessary to extremely precisely control the state of airflow within the chamber 10. For this reason, in an apparatus that supplies a processing liquid to the substrate W, it is particularly significant to install the observation device of the present invention.

[0065] The observation device of the present invention is not limited to a device to be mounted on a specific processing device, but may be a device for general use. The observation device may be one used outdoors. The observation device may be one in which a projector for projecting a background image 61, an objective lens 62, an imaging unit 63, and a light wave modulation element 64 are integrally configured.

[0066] Furthermore, the elements appearing in the above-described embodiments and modifications may be combined as appropriate or some of them may be deleted to the extent that no contradictions arise. [Explanation of symbols]

[0067] 1. Substrate Processing Equipment 9 Diffraction images 10. Chamber 15. Windows 20 Board holding part 30 Rotation mechanism 40 Processing liquid supply section 50 Computer 60 Observation Equipment 61 Background Images 62 Objective Lens 63 Imaging unit 64 Light Wave Modulation Element 631 Imaging Optical System 632 Image Sensor 641 Lattice Pattern A optical axis P imaging plane S Observation area W substrate

Claims

1. An observation device for observing an air flow, comprising: A background image and an imaging unit that captures the background image through an observation area in which the air flow exists; a light wave modulation element interposed between the observation area and the imaging unit; a computer that calculates the state of the airflow by a background type Schlieren method using the image acquired by the imaging unit; Equipped with The light wave modulation element forms a plurality of diffraction images having different focal positions in the imaging unit using light incident from the background image through the observation region.

2. The observation device according to claim 1, The optical wave modulation element is a diffraction grating having a plurality of grating patterns.

3. The observation device according to claim 2, the plurality of grating patterns are formed at positions displaced from coordinates at regular intervals in a plane perpendicular to an optical axis by a shift amount corresponding to the coordinates, An observation apparatus in which the focal positions of the multiple diffraction images change due to the displacement of the grating pattern.

4. The observation device according to claim 1, The light wave modulation element is a spatial light modulator capable of changing a grating pattern in response to an electrical signal.

5. The observation device according to any one of claims 1 to 4, an observation device, wherein a difference between focal positions of the plurality of diffraction images is smaller than a depth of field of an imaging optical system of the imaging unit.

6. The observation device according to any one of claims 1 to 4, The computer creates an all-focus image by synthesizing the multiple diffraction images acquired by the imaging unit, and calculates the state of the airflow based on the all-focus image.

Images