JPH0732117B2 - Focusing device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focusing device in a reduction projection exposure apparatus used for exposure transfer of a semiconductor or the like.

2. Description of the Related Art Recently, a reduction projection exposure apparatus (hereinafter referred to as a stepper) has been actively used for manufacturing DRAM, LSI, etc. as an apparatus for transferring a pattern drawn on a mask onto a wafer. . In this step, a focusing device for clearly projecting the reticle pattern on the wafer through the projection lens is incorporated. As this focusing device, for example,
It is known by the constitution described in JP-A-60-101540, the Japan Society for Precision Engineering, Precision Machinery (Ohm Co.), Japan Society for Precision Engineering, Research Meeting No. 89-03 and the like. Hereinafter, the focusing device in the conventional stepper will be described with reference to the drawings. FIG. 7 is a block diagram showing a focusing device in a conventional example.

In FIG. 7, 101 is a wafer, and 102 is a wafer stage for three-dimensionally moving the wafer 101, which is mainly moved in the vertical direction (Z-axis direction) in focusing adjustment. 103
Is a projection lens for projecting and exposing a pattern of a reticle (not shown) on the surface of the wafer 101, 104 is a light emitting element such as an LED,
Reference numeral 105 denotes a lens for making parallel light rays emitted from the light emitting element 104, and the light emitting element 104 is provided near the focal point of the lens 105. Reference numeral 106 denotes a light-sending slit, which is provided with a rectangular slit for passing a part of the parallel rays, and is provided so that the center of the rectangular slit serves as the optical axis. 107 is a lens for focusing the slit light emitted from the light-transmitting slit 106 on the surface of the wafer 101, and 1
08 is a lens for re-imaging the slit light reflected on the wafer 101, 109 is a vibrating mirror that vibrates in the circumferential direction about the optical axis, and 110 is a vibrating frequency f of the vibrating mirror 109.
Mirror driver driven by, 111 is a light-receiving slit having a rectangular slit opened at the center of the optical axis that is conjugate with the vibration center (non-vibration state) of the vibrating mirror 109, and 112 is the image forming point by the lens 108 as well. A light-receiving element provided at a position conjugate with the light-receiving slit 11 for converting light passing through the light-receiving slit 11 into an electric signal. Reference numeral 113 denotes a signal 114 from the light-receiving element 112.
A phase synchronization detection processing circuit for performing phase synchronization detection and smoothing with a sine wave signal with an oscillation frequency f of 09, 115 calculates a defocus amount from a signal 116 from the phase synchronization detection processing circuit 113, and according to it, the wafer A wafer stage control drive circuit for moving the stage 102 in the vertical direction (Z-axis direction).

The operation of the above configuration will be described below.

In FIG. 7, the reticle, projection lens 103, and wafer 1 are shown.
The reticle pattern is focused on the wafer 101 by the 01 optical system.
The state when they are fitted on each other is shown, and the distance between the projection lens 103 and the wafer 101 at this time is Z ₀ .

The light from the light emitting element 104 is collimated by the lens 105. Of this parallel light, light near the optical axis passes through the light-sending lift 106, and forms an image of the light-sending slit 106 directly below the center of the projection lens 103 and on the surface of the wafer 101 by the lens 107. This image is reflected on the wafer 101, passes through the lens 108, and is reflected by the vibrating mirror 109 driven by the mirror driver 110 at the vibration frequency f. As described above, the wafer 101 has the focal point Z.
Since it is located at = Z ₀ , this reflected light is
It vibrates with a constant amplitude A ₀ with the center of the slit in the light receiving slit 111 provided in front of 112, that is, the center of the optical axis as the center. Now, if the slit width of the light-transmitting slit 106 is L ₁ and the slit width of the light-receiving slit 111 is L ₂ , then L ₁ ≦ L ₂ ≦ A ₀
At this time, the electric signal 114 of the light receiving element 112 has a frequency 2 which is twice the vibration frequency f of the vibrating mirror 109 as indicated by V in FIG.
The signal is close to the sine wave of f. Then, as the wafer stage 102 is moved, the center of the image of the light-sending slit 106 projected on the light-receiving slit 111 moves, so that the eighth
The waveform changes from I to IX shown in the figure. Light receiving element 112
When the sine wave signal of the vibration frequency f from the mirror driver 110 is detected as a reference signal by the phase-locked detection processing circuit 113 and smoothed, the output signal 114 of the wafer 101
Is at the focal point Z = Z ₀ , the output signal 116 becomes zero. Then, as the wafer stage 102 is moved, an S-shaped characteristic as shown in FIG. 9 is obtained. Based on this characteristic, the wafer stage control drive circuit 115 uses the output signal 116 of the phase synchronous detection processing circuit 113 to detect the wafer at the present time.
The position Z of 101 is determined, and the difference from the focal point Z = Z ₀ (Z−Z ₀ )
Only the wafer stage 102 is moved. Focusing is performed in this manner.

In general, wafers are vapor-deposited in the process of manufacturing semiconductor devices,
The wafer is subjected to various process treatments such as resist coating and etching, and the surface state of the wafer, that is, the reflectance changes with each treatment. Further, even in the same process, the reflectance slightly differs for each wafer. Therefore, in the configuration of the conventional example as described above, even if the distance between the projection resist 103 and the wafer 101 is a constant value, the output of the light receiving element 112 is different for each process or for each wafer 101 due to the difference in reflectance. The amplitude changes. Therefore, in each of the waveforms of FIG. 8 obtained by changing the distance between the projection resist 103 and the wafer 101, the amplitude also changes according to the change in reflectance. Further, when this signal is subjected to phase synchronous detection processing, the vibrating mirror 109
Even if the frequency and vibration are the same, differences such as characteristics A and B occur as shown in FIG. 10 due to the difference in reflectance of the wafer 101. Therefore, it is necessary to move the wafer stage 102 for each wafer 101 and for each process step to obtain the characteristics shown in FIG. 9 and perform focusing according to the characteristics, which requires a lot of time. However, there is a problem that the improvement of the exposure efficiency is hindered.

The present invention is to solve the above problems of the prior art, and normalizes the output of the light receiving element of the focus detection optical system so that the output value after the phase-coherent detection process and the amount of movement of the wafer are The S-shaped characteristic that is the characteristic is a single characteristic that is not related to the reflectance, that is, the normalized characteristic, and
An object of the present invention is to provide a focusing device capable of efficiently performing a focusing operation in a short time without re-taking the characteristics for each process stage.

Means for Solving the Problems In order to achieve the above object, the present invention according to claim 1 includes: a focus detection light source; and a light-sending slit into which light emitted from the focus detection light source is incident. An imaging lens for focus detection that forms an image of light that has passed through the light-sending slit on an in-focus object, and light that has entered through the in-focus object while changing its reflection angle periodically. A focus detection optical system including a reflective vibrating mirror and a focus detection light receiving element that receives the light reflected by the vibrating mirror, a monitor detection light source, and light emitted from the monitor detection light source. Via a monitor detection imaging lens that forms an image on the focused object in an area including an area where the light emitted from the focus detection light source is imaged, and the focused object Detection optical system including a monitor light-receiving element that receives light that has been incident And division means for obtaining a ratio signal between the output signal from the focus detection light-receiving element and the output signal from the monitor detection light-receiving element, and a synchronous detection for phase-coherent detection using the ratio signal and the reference signal. And a means for detecting the focus state of the focused object.

Alternatively, as described in claim 2, for a similar focus detection optical system, a leveling detection light source, a pinhole into which light emitted from the leveling detection light source is incident, and the pinhole are passed. The collimator lens for irradiating the focused object with the focused light on the area including the area where the light emitted from the focus detection optical system is focused, and the focused object is incident through the focused object. Leveling detection optical system including a leveling light-receiving element having a plurality of light-receiving sections for receiving the received light, and leveling detection including an adding means for adding respective output signals corresponding to the plurality of light-receiving sections of the leveling light-receiving element. A circuit, division means for obtaining a ratio signal between the output signal from the focus detection light receiving element and the output signal from the adding means, and a synchronous detector for phase-coherent detection using the ratio signal and a reference signal. A focusing device that adds and.

Effect According to the present invention, therefore, the monitor detection optical system or the leveling detection optical system performs incident reflection at the same point as the incident reflection point on the wafer by the focus detection optical system, or the inclusion surface,
Set the ratio of the light-receiving element outputs of the focus detection optical system and the monitor detection optical system, or the ratio of the combined value of the outputs of the light-receiving elements of the focus detection optical system and the light-receiving elements of the leveling detection optical system. The output of the light receiving element of the focus detection optical system is normalized, and the normalized value is used as the reference signal with the frequency of the oscillating mirror of the focus detection optical system to perform phase-locked detection to perform focusing, thereby reflecting the wafer. Focus detection can be performed without depending on the change in the ratio.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

First, a first embodiment of the present invention will be described.

1 and 2 show a focusing device according to a first embodiment of the present invention. FIG. 1 is an overall configuration diagram and FIG. 2 is an explanatory diagram of an optical system.

Both FIG. 1 and FIG. 2 show the state when the reticle pattern and the wafer are in focus.

In FIGS. 1 and 2, 1 is a wafer, and 2 is a wafer stage for moving the wafer 3 three-dimensionally. In focusing adjustment, movement in the vertical direction (Z-axis direction) is mainly performed. To do. 3 is a projection lens for projecting and exposing a pattern of a reticle (not shown) on the surface of the wafer 1, 4 is a light emitting element such as an LED in the focus detection optical system, and 5 is point light emitted from the light emitting element 4. Is a lens for making
The light emitting element 4 is provided near the focal point of the lens 5. Reference numeral 6 denotes a light-sending slit, which is provided with a rectangular slit for passing a part of the parallel rays from the lens 5, and is provided so that the center of the rectangular slit serves as the optical axis. Reference numeral 7 denotes a lens, which is provided at a position where the light passing through the light-sending slit 6 is imaged on the surface P of the wafer 1 when the exposure focus is achieved. Reference numeral 8 is a lens for re-imaging the slit image reflected on the wafer 1, 9 is a vibrating mirror vibrating in the circumferential direction about the optical axis, and 10 is vibrating the vibrating mirror 9 at a frequency f and a constant amplitude. It is a driver and has a built-in oscillation circuit of frequency f. Reference numeral 11 denotes a light-receiving slit, which has an optical axis which is conjugate to the vibration mirror 9 when the vibration mirror 9 is at the vibration center, that is, when the vibration is stopped.
Reference numeral 12 is a light-receiving element for converting the light passing through the light-receiving slit 11 into an electric signal, which is provided near the position of the oscillating mirror 9 which is conjugate with the focal point of the lens 8. 13 is a monitor light-emitting element in the monitor detection optical system,
Reference numeral 14 denotes a lens, which is provided so as to image the light emitted from the monitor light emitting element 13 at the same point as the image forming point P on the wafer 1 of the focus detection optical system. Reference numeral 15 is a lens that connects the image formed by the lens 14 again on the optical axis of the monitor detection optical system, and 16 is a monitor light receiving element that receives the light that has passed through the lens 15 and converts it into an electrical signal. Is provided near the image forming point, that is, the focal point. Reference numeral 17 denotes an amplifier, which amplifies an electric signal of the light receiving element 12 of the focus detection optical system. Reference numeral 18 is an amplifier, which is a light receiving element for monitoring 16 of the monitor detection optical system.
Amplifies the electrical signal of. 19 is the output of amplifier 17 to amplifier 18
An analog divider that divides by the output of 20, a phase-locking detector that detects the output of the divider 19 by phase-locking, using 20 as the reference signal of the frequency signal of the driver 10, and 21 is a phase-locking detector.
20 is a reduction filter for smoothing the output signal of 20, and 22 is a wafer stage control circuit. The output signal of the filter 21 determines the amount of movement of the wafer stage 2 to the focal point, and outputs the movement signal. A wafer stage drive circuit 23 is a drive circuit for moving the wafer stage 2 based on a movement signal output from the wafer stage control circuit 22.

The operation of the above configuration will be described below.

The light emitted from the light emitting element 4 of the focus detection optical system is reflected by the lens 5
It becomes a parallel light. Of the parallel light, the light in the vicinity of the optical axis passes through the light-sending slit 6 and forms an image of the light-sending slit 6 at a point P directly below the center of the projection lens 3 by the lens 7 and on the surface of the wafer 1. . This slit image is reflected on the wafer 1 and passes through the lens 8 to form an image at the focal point of the lens 8 shown by the dotted line in FIG. 1, but the vibrating mirror 9 driven by the drive 10 at a frequency f and a constant amplitude. And is imaged at a point conjugate with the vibrating mirror 9. A light receiving element 12 is provided at this conjugate point, and a light receiving slit 11 is provided immediately before the light receiving element 12.
Further, since the wafer 1 is placed at the focal point Z = Z ₀ as described above, the light reflected by the mirror 9 has the center of the slit in the light receiving slit 11, that is, the optical axis as the center.
It vibrates with a constant amplitude. This constant width is A ₀ . The light passing through the light receiving slit 11 is received by the light receiving element 12, and the output signal of the light receiving element 12 is amplified by the amplifier 17.

On the other hand, the light emitted from the monitor light-emitting element 13 of the monitor detection optical system is imaged by the lens 14 at the image forming point P of the lens 7 of the focus detection optical system of the wafer 1. The light imaged at the point P is reflected by the wafer 1 and imaged by the lens 15. Then, this image-forming light is received by the monitor light-receiving element 16 provided near the focal point of the lens 15. The output of the monitor light receiving element 16 is amplified by the amplifier 18.

Now, when the vibrating mirror 9 is stopped at the center of vibration, the ratio of the output of the light receiving element 12 of the focus detection optical system and the output of the monitor light receiving element 16 of the monitor detection optical system becomes constant. Therefore,
By adjusting the amplifiers 17 and 18 so that the ratio becomes 1, the output of the divider 19 becomes 1. Further, since the focus detection optical system and the monitor detection optical system are reflected and reflected at the same point on the wafer 1, when the vibrating mirror 9 is stopped, the wafer stage 2 is moved in the horizontal direction (X and Y axis directions). The output of the divider 19 becomes 1 even when the wafer 1 is moved to the vertical direction (Z-axis direction) or when the wafer 1 having a different reflectance is used. Then, when the Z axis of the wafer stage 2 is moved to the focal point (this point is designated as Z ₀ ), and the oscillating mirror 9 is activated again, the image of the light transmitting slit 6 becomes the image of the light receiving slit 11.
It vibrates on the surface of with a width A ₀ with the center of the slit as the center. If the slit intervals of the light-transmitting slit 6 and the light-receiving slit 11 are L ₁ and L ₂ , respectively, when L ₁ ≤L ₂ ≤A ₀ , the divider
As the output of 19, as shown by V in FIG. 3, a normalized analog waveform having a maximum value of 1 and a frequency of 2f is obtained. And
By moving the Z axis of the wafer stage 2, the third
Normalized waveforms such as I-IX in the figure can be obtained. Further, since the focus detection optical system and the monitor detection optical system perform incident reflection at the same point, even if the reflectance differs for each wafer 1, the reflectance partially differs for the same wafer 1. However, the output signal of the divider 19 obtained when the wafer 1 is moved in the Z-axis direction is normalized by I to IX in FIG. 3 even if the reflectance differs for each process step. Waveform is obtained. Therefore, the output of the divider 19 is used as the signal input of the phase-locking detector 20, the frequency signal of the driver 10 is phase-locked as the reference signal, and the output is smoothed by the reduction filter 21, and its output is the wafer. According to the movement amount of 1 in the Z-axis direction, the maximum constant value V ₀ as shown in FIG. 4 is obtained, but an S-shaped characteristic is obtained. This characteristic is
Even if the reflectance at the point P on the wafer 1 is different, it is always the same.

Therefore, the S-shaped characteristic shown in FIG. 4 is stored in the wafer stage control circuit 22, and the output of the reduction filter 21 when it is not in focus is input to the wafer stage control circuit 22. The amount of movement of the wafer stage 2 up to the in-focus point is calculated by comparing with the S-shaped characteristic, and the amount of movement is output to the wafer stage drive circuit 23 to drive the wafer stage 2 or compared with the S-shaped characteristic. By driving the wafer stage 2 until the output of the reduction filter 21 becomes 0, the wafer 1 can be moved to the focal point.

Thus, according to this embodiment, the light receiving element 4, the light receiving element
Focus detection optical system including 12 and the like, monitor light emitting element 13,
The light-receiving element 12 of the focus detection optical system has the same incident / reflection point as that of the monitor detection optical system including the monitor light-receiving element 16 and the like.
Is amplified and the amplified output of the monitor light receiving element 16 is divided by a divider 19 for normalization, and the normalized value is phase-coherently detected with the vibration frequency of the vibration mirror 9 as a reference signal. Even if the reflectance of the wafer 1 is different, it is necessary to re-correct the S-shaped characteristic by detecting and smoothing the focus and detecting the in-focus point by the filter 20 and the reduction filter 21 and moving the wafer stage 2 to focus. Therefore, it is possible to immediately deal with a change in the reflectance of the wafer 1, and an efficient focusing device can be provided.

In this embodiment, the case where no slit is provided between the monitor light-emitting element 13 and the lens 14 and between the lens 15 and the monitor light-receiving element 16 has been described. Good.

Next, a second embodiment of the present invention will be described.

5 and 6 show a focusing device according to a second embodiment of the present invention, FIG. 5 is an overall configuration diagram, and FIG. 6 is an explanatory diagram of an optical system.

5 and 6 both show the state when the reticle pattern and the wafer are in focus.

In this embodiment, as for the focus detection optical system, as shown in FIG. 6, a reflection mirror 24 is inserted between the light transmitting slit 6 and the lens 7, and the optical axis is changed between the lens 8 and the vibrating mirror 9. The structure is the same as that of the first embodiment shown in FIG. 1 and FIG. 2 except that the plate 25 (which can be omitted) is inserted. The description is omitted.

The feature of this embodiment is that the leveling detection optical system has the monitor detection function in the first embodiment, and the optical axis of the leveling detection optical system is the same as the optical axis of the focus detection optical system. It is provided so as to intersect at the in-reflection point P of the focusing system. The leveling detection optical system will be described below. In FIGS. 5 and 6, reference numeral 26 denotes a light emitting element.
LED, 27 is a lens that images the light emitted from the LED 26, 28 is a pinhole provided near the focal point of the lens 27, 29 is a collimator lens that makes the light passing through the pinhole 28 parallel light,
30 is a condenser lens that collects parallel light, 31 is a four-division photodiode as a light-receiving element, the center point of the four divisions coincides with the optical axis, and is provided at the focal point of the condenser lens 30. Reference numeral 32 is an amplifier that amplifies each output of the four-division photodiode 31 equally, and 33 is an adder that adds the four signals amplified by the amplifier 32. Leveling is performed by the four-division photodiode 31, the amplifier 32, and the adder 33. The detection circuit 34 is configured, and the addition result of the adder 33 is output to the divider 19.

The operation of the above configuration will be described below.

The light emitted from the LED 26 is condensed by the lens 27. A part of the condensed light passes through the pinhole 28 and is collimated by the collimator lens 29. This parallel light is incident on the surface S on the wafer 1 centered on the entrance / reflection point P of the focus detection optical system and forms an enlarged image of the pinhole 28. The light reflected by the surface S on the wafer 1 passes through the condenser lens 30 and is pinhole on the four-division photodiode 31 provided at the focal point of the condenser lens 30.
Connect 28 statues. When the wafer 1 is not tilted and is placed horizontally, this pinhole image is connected to the center of the four-divided photodiode 31 and the four photodiodes 31 have the same output, but the wafer 1 is tilted. If so, the pinhole image deviates from the center of the four-divided photodiode 31, and the outputs of the four photodiodes become nonuniform. However, the total output of the four photodiodes remains unchanged. Therefore, for leveling detection, the values of {(A + B)-(C + D)} / (A + B + C + D) and {(A + D)-(B + C)} / (A + B + C + D) are calculated so that these values become zero. Then, the inclination of the wafer 1 is controlled.

Next, each photodiode output of the four-divided photodiode 31 is equally amplified by the amplifier 32, added by the adder 33, and added to 4
Adder as the total amount of light incident on the split photodiode 31
It is output from 33.

The entrance / reflection surface S of the wafer 1 of the leveling detection optical system includes an entrance / reflection point P of the focus detection optical system. Therefore,
The difference in the wafer 1 and the change in the reflectance at the incident / reflecting point P caused by each process step occur at the same ratio on the incident / reflective surface S as well. That is, the four-divided photodiode 31 has the same function as the monitor light-receiving element 16 in the first embodiment.

Therefore, in FIG. 5, it can be seen that the ratio of the output of the amplifier 17 and the output of the adder 33, that is, the output of the divider 19 does not depend on the difference in the reflectance of the wafer 1. In other words, the output of the divider 19 has a value normalized with respect to the reflectance.

Then, the output of the divider 19 is changed to the same as in the first embodiment.
Focusing can be detected by performing phase-coherent detection, and the wafer 1 can be moved to a focal point.

As described above, according to the present embodiment, by adopting the leveling detection optical system having the monitor detection function, the reflectance of the wafer 1 is normalized without newly providing the monitor detection optical system. A focused detection signal can be obtained.

In the above embodiment, the focus detection optical system and the level detection optical system use different optical axes, but the same optical axis can be used by using a method of mixing and separating light.

EFFECTS OF THE INVENTION As described above, according to the present invention, in addition to the focus detection optical system, monitor detection is performed at the same point as the incident / reflection point on the wafer by the focus detection optical system or at the inclusion surface. It is equipped with an optical system or leveling detection optical system, and the ratio of the output of the light receiving element of the focus detection optical system and the output of the light receiving element of the monitor detection optical system or the output of the plurality of light receiving parts of the light receiving element of the leveling detection optical system. The output of the light receiving element of the focus detection optical system is normalized by obtaining the added value, and the normalized value is phase-synchronized with the frequency of the vibration mirror of the focus detection optical system as a reference signal to perform focus detection. I have to. Therefore, the focusing operation can be performed quickly and efficiently without depending on the change in the reflectance of the wafer.

[Brief description of drawings]

1 and 2 show a focusing device according to a first embodiment of the present invention. FIG. 1 is an overall configuration diagram, FIG. 2 is an explanatory diagram of an optical system, and FIG. FIG. 4 is a waveform diagram showing the output signal of the division circuit in the focusing device in the embodiment, and FIG. 4 shows the output of the reduction filter circuit in the focusing device in the first embodiment and the amount of movement of the wafer in the Z-axis direction. FIG. 5 and FIG. 6 are characteristic diagrams showing the relationship, FIG. 5 and FIG. 6 show a focusing device in a second embodiment of the present invention, FIG. 5 is an overall configuration diagram, FIG. 6 is an explanatory diagram of an optical system, and FIG. FIG. 8 is an overall configuration diagram showing a focusing device of a conventional example, FIG. 8 is a waveform diagram showing an output signal of a light receiving element in the focusing device of the conventional example, and FIGS. It is a characteristic view which shows the relationship between the output of the phase-coherent detection processing circuit and the amount of movement of the wafer in the Z direction in the focusing device. 1 ... Wafer, 2 ... Wafer stage, 3 ... Projection lens, 4
... light emitting element, 5 ... lens, 6 ... light transmitting slit, 7 and 8 as lens, 9 ... vibrating mirror, 10 ... driver, 11 ... light receiving slit, 12 ... light receiving element, 13 ... monitor light receiving element, 14, 15 ...
Lens, 16 ... Monitor light receiving element, 17, 18 ... Amplifier, 19 ...
Divider, 20 ... Phase synchronous detection, 21 ... Reduction filter, 22 ... Wafer stage control circuit, 23 ... Wafer stage drive circuit, 26
... LED, 27 ... Lens, 28 ... Pinhole, 29 ... Collimator lens, 30 ... Condenser lens, 31 ... Quadrant photodiode, 32 ... Amplifier, 33 ... Adder, 34 ... Leveling detection circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-1-170022 (JP, A) JP-A-63-306626 (JP, A) JP-A-63-255917 (JP, A)

Claims (2)

[Claims] 1. A light source for focus detection, a light-sending slit into which light emitted from the light source for focus-detection enters, and light passing through the light-sending slit is imaged on a focused object. An imaging lens for focus detection, an oscillating mirror capable of reflecting light incident via the in-focus object while periodically changing its reflection angle, and a light reflected by the oscillating mirror. A focus detection optical system including a focus detection light receiving element, a monitor detection light source, and light emitted from the monitor detection light source, the light emitted from the focus detection light source is imaged. Monitor detection optics including a monitor detection imaging lens that forms an image on the focused object with respect to a region including a region, and a monitor light receiving element that receives light that has entered via the focused object System, output signals from the focus detection light receiving element and the monitor detection signal A division means for obtaining a ratio signal with the output signal from the optical element, and a synchronous detection means for performing phase-coherent detection using the ratio signal and a reference signal are provided, and the focus state of the focused object is detected. Focusing device. 2. A focus detection light source, a light-sending slit into which light emitted from the focus detection light source is incident, and light passing through the light-sending slit is imaged on a focused object. An imaging lens for focus detection, an oscillating mirror capable of reflecting light incident via the in-focus object while periodically changing its reflection angle, and a light reflected by the oscillating mirror. A focus detection optical system including a light receiving element for focus detection, a leveling detection light source, a pinhole into which light emitted from the leveling detection light source is incident, and light passing through the pinhole, A collimator lens that irradiates the focused object onto a region including a region where the light emitted from the focus detection optical system is imaged, and receives light that has entered via the focused object. A leveling light receiving element having a plurality of light receiving sections A leveling detection optical system, a leveling detection circuit including an addition means for adding respective output signals corresponding to a plurality of light receiving portions of the leveling light receiving element, an output signal from the focus detection light receiving element and the addition A division means for obtaining a ratio signal with the output signal from the means, and a synchronous detection means for performing phase-coherent detection using the ratio signal and a reference signal are provided, and a focus state of the focused object is detected. Focusing device.