KR101568980B1 - Automatic focus control apparatus and automatic focus control method using the same - Google Patents

Abstract

The present invention relates to an automatic focusing apparatus, and more particularly, to an automatic focusing apparatus which irradiates a subject with a plurality of laser light sources for outputting laser lights of different wavelengths and uses the light reflected from the irradiated light to perform a chromatic aberration An auto-focusing device using the optical system is provided. In the present invention, there is also proposed a technique of adjusting autofocus by filtering only one laser beam among a plurality of laser beams reflected and reflected from a subject, and applying a triangulation method using the beam intensity of the filtered laser beam.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an automatic focusing apparatus,

The present invention relates to an automatic focusing apparatus and an automatic focusing method, and more particularly, to an automatic focusing apparatus and an automatic focusing apparatus which can automatically adjust a focus using a chromatic aberration using two or more laser light sources, And an autofocus method.

In general, industrial microscopes are used for surface inspection of semiconductor wafers, circuit boards (PCBs), etc., including display panels such as LCDs and PDPs, and such industrial microscopes are equipped with automatic focusing devices that automatically adjust the focus.

In order to obtain a clear image in an optical system (microscope) for acquiring an image of a measurement object (object), the measurement object must be located at a predetermined focal distance of the objective lens. The focal length of the lens has a range that is regarded as focused, not a single position value, and is referred to as depth of field (D.O.F.).

Auto Focus refers to automatically focusing the subject so that the subject is within the depth of field of the lens at the focal length of the lens.

In the case of an inspection system using optical, which is widely used in flat panel displays or the semiconductor industry, when the depth of an objective lens used is low or when the flatness of a sample as a subject is poor or when floor vibrations are large, It is difficult to obtain images. To overcome these problems and obtain clear images, an autofocus system is needed.

The autofocusing system implements focus control through various methods, and dual photodetection and chromatic aberration are widely used.

The auto-focus adjustment method using the optical triangulation method is a method of detecting the reflected light after the light is irradiated to the object to be inspected, and the spot of the reflected light is detected to detect the focal plane of the objective lens. Brief description will be given. When the laser light source 10 is incident parallel to the optical axis of the objective lens 20 using a beam splitter 11, the light is refracted in the object direction z1, z2 and z3 from the objective lens 20 The light reflected from the object is reversely traveled toward the objective lens again. The object displacement? Z in the direction of the optical axis is converted into a displacement? P on the plane of the image sensor 31 provided in the first camera 41, and the focal position is obtained by converting the displacement.

In this process, the incident angle of the light refracted through the objective lens 20 and incident on the subject is proportional to the NA (Numerical Aperture) of the lens. For reference, NA is expressed as nsin? Using the maximum incident angle? That enters the lens aperture among the rays passing through the focus of the lens in a general optical lens. Where n is the index of refraction of the medium between the focal point and the lens, the symbol NA is the two letters of the English letter, and the value of NA indicates how large the light beam can be focused by the lens, As shown in FIG.

The disadvantage of the auto-focusing method using the optical triangulation is the low focus resolution. 2, the focus resolution is proportional to the NA of the objective lens 20, and the NA of the objective lens 20-1 shown in (a) is larger than the NA of the objective lens 20-2 shown in (b) . The smaller the NA of the objective lens 20 is, the smaller the laser position change amount? P formed on the image sensor in accordance with the height change? Z of the subject. That is, the relationship of? P1>? P2 is established. Therefore, the focus resolution according to the optical triangulation method has a limitation depending on the NA of the objective lens 20. [

Another method of auto focus adjustment is to use chromatic aberration. 3 is a configuration diagram of an auto-focus adjusting apparatus for explaining a chromatic aberration method. A white light source 13 is incident on the optical axis of the objective lens 20 through a first pinhole (or a spatial filter 15) using a beam splitter 11. Here, the pinhole 15 is generally called a slit, and is preferably configured to have a rectangular opening, and is mainly used for converting the shape of input light. The white light source incident on the objective lens 20 transmits the objective lens and has a different focal distance for each wavelength band. The light reflected from the object passes through the beam splitter 11 and is incident on the second pinhole 17. At this time, only the wavelength having the focal distance coinciding with the position of the subject passes through the second pinhole 17. As shown in Fig. 3, if the subject is located at the focal length of z2, only light having a wavelength of? 2 passes through the second pinhole 17. Fig. The light having passed through the second pinhole 17 is converted into parallel light by the condenser lens 19, enters the diffraction grating 23 or the prism, and is refracted at a different transmission angle for each wavelength. The light passing through the diffraction grating 23 is focused on the line sensor 33 after being condensed by the condenser lens 25 and has different pixel positions for respective wavelengths. Therefore, by analyzing the pixel position data of the line sensor 33, it is possible to know the distance from the objective lens 20 to the subject. By using this, the optical system can be controlled in the direction of the optical axis so that the subject is located at the focal length of the objective lens, It is controlled in the optical axis direction. Of course, an image sensor can be used instead of the line sensor 33. However, when an image sensor is used, it is preferable to use a line sensor because it needs to be separated again in units of lines.

However, a white light source such as a halogen or an LED is used for the automatic focusing method using the chromatic aberration. The white light source has low coherence, collimation and brightness compared with the laser. That is, in the case of a subject having a longer optical path or a higher transmittance because of better diffusion than a laser and a smaller energy density, the exposure time of the image sensor must be increased in order to acquire an image. This increases the focus adjustment time, which is not suitable for use in industry, and the increase in exposure time also increases the noise of the image sensor, which is disadvantageous in that the accuracy is lowered. Xenon lighting can be used to overcome low luminance, but Xenon lighting has problems with high unit cost and short lifetime (about 1,000 hr) that are not suitable for the industry.

Patent Document 1: Korean Patent Laid-Open No. 10-2011-0023992 (published on March 09, 2011) Patent Document 2: Korean Patent Laid-Open No. 10-2007-0078918 (published on Aug. 03, 2007)

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to solve the above-mentioned problems, The present invention provides an automatic focusing device and an automatic focusing method that automatically generate a chromatic aberration by using more than two lasers,

The object of the present invention is to provide an automatic focus adjusting apparatus which has an objective lens equipped with a beam splitter and which automatically focuses a focus formed on a subject placed at the lower end of the objective lens, A first beam splitter for combining the light emitted from the first pinhole and the first pinhole for outputting the light emitted from the two laser light sources as parallel light, A chromatic aberration lens for increasing the chromatic aberration of the laser beam output from the splitter and outputting the laser beam to the lens; a second pinhole for emitting the light output from the beam splitter provided in the objective lens as parallel light; A diffraction grating for diffracting light; and a line sensor for sensing light output from the diffraction grating, It can be achieved by the apparatus.

Preferably, the autofocusing apparatus outputs only light having a predetermined range of frequency from the output laser beam, after outputting the light reflected from the object after the light output from the chromatic aberration lens is irradiated on the subject, And an image sensor for converting electrical signals output from the band pass filter to an electrical signal.

It is still another object of the present invention to provide an automatic focusing method for automatically adjusting a distance to a subject by irradiating a plurality of laser beams to a subject, comprising: a first step of causing a plurality of laser beams having different wavelengths to enter a chromatic aberration lens; A second step of irradiating laser light emitted from a chromatic aberration lens to a subject, a third step of causing a laser light reflected from the subject to enter a pinhole, a fourth step of causing the laser light emitted from the pinhole to enter the diffraction grating, And a fifth step of sensing an intensity of each laser beam emitted from the diffraction grating at each wavelength of the laser beam.

Preferably, the automatic focusing method further includes a sixth step of performing band pass filtering for transmitting only a specific wavelength of the laser light reflected from the subject, and a seventh step of sensing the intensity value of the band-pass filtered laser light It is good to do.

Advantages of the automatic focusing device proposed by the present invention are as follows. By using two image sensors, the distance from the lens to the subject is analyzed by the optical triangulation method and the chromatic aberration method, respectively.

By using the chromatic aberration method, the optical triangulation method, in which the resolution decreased as NA of the lens decreased, was compensated. Therefore, the present invention can be applied to an optical system having a small NA such as a telecentric lens, and can be utilized in various inspection systems. In addition, the use of the laser light source can also reduce the exposure time of the image sensor, thereby increasing the focusing time.

Brief Description of the Drawings Fig. 1 is a configuration diagram of an auto-focus adjusting apparatus for explaining a triangulation method. Fig.
FIG. 2 is a view for explaining the accuracy of the automatic focusing device according to the NA value of the lens when using the phototriangular method; FIG.
3 is a configuration diagram of an automatic focusing device for explaining a chromatic aberration method.
4 is a configuration diagram of an automatic focusing device using chromatic aberration according to an embodiment of the present invention.
FIG. 5 is an explanatory view for explaining a method of analyzing a distance from a lens to a subject through a chromatic aberration using the automatic focusing device shown in FIG. 4;
6 is a configuration diagram of an automatic focusing device using a chromatic aberration and a photodetection method according to an embodiment of the present invention.
FIG. 7 is an explanatory view for explaining a method of analyzing the distance from a lens to a subject through a photo-trigonometric method using the automatic focusing device shown in FIG. 6;

In the following, preferred embodiments, advantages and features of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 4 is a block diagram of an automatic focusing apparatus using chromatic aberration according to an embodiment of the present invention. The automatic focusing apparatus using the chromatic aberration according to the present invention replaces a white light source used in a conventional chromatic aberration microscope by using two laser light sources 12 and 14 having different wavelengths. By replacing the white light source with a laser, it is possible to secure a high output light amount with respect to the volume of the light source. In addition, the use of a laser as a light source has many advantages in terms of coherence, collimation, and brightness. 4, the two laser light sources 12 and 14 having different wavelengths are used. However, as the number of laser light sources having different wavelengths is increased, the number of measured data increases, so that the accuracy can be improved. For convenience, an embodiment using two laser light sources as shown in FIG. 4 will be described.

The diffused light output from the two laser diodes 12 and 14 having different wavelengths lambda 1 and lambda 2 is output as parallel light through the first pinholes 15-1 and 15-2 through the condenser lens. The parallel light is incident on the chromatic aberration lens 18 through the first beam splitter 16-1 and 16-2 and the laser light having passed through the chromatic aberration lens 18 is incident on the beam splitter 16 of the objective lens 20, (11). The chromatic aberration lens 18 is a lens that outputs different refractive indices for different wavelengths. Of course, the first beam splitter 16-2 may be implemented as a fully reflective mirror in the optical principle, or may be implemented by a laser diode 14 and a second beam splitter 16-1 at a position extending between the chromatic aberration lens 18 and the first beam splitter 16-1. It is needless to say that the pinhole 15-2 may be omitted. The laser beam incident on the objective lens 20 passes through the objective lens 20 and has a different focal length for each wavelength band. The laser reflected from the objects z1 and z2 enters the second pinhole 17 through the beam splitter 11 and the second beam splitter 22 of the objective lens. The laser beam having passed through the second pinhole 17 is incident on the second image sensor 33 at different transmission angles for respective wavelengths due to the diffraction grating 23 or the prism. Here, reference numerals 32 and 34 denote a condenser lens.

FIG. 5 is an explanatory view illustrating a method of analyzing a distance from a lens to a subject through a chromatic aberration using the automatic focusing device shown in FIG. FIG. 5A shows a case where the subject is located at z1, FIG. 5B shows a case where the subject is located between z1 and z2, FIG. 5C shows a case where the subject is located at z2, Pixel position, and the vertical axis represents the amount of light. As shown in Fig. 5 (a), when the subject is at z1, the amount of light passing through the second pinhole 17 increases because? 1 is increased and? 1 is decreased. That is, the intensity of the laser obtained by the line sensor 33 is lambda 1 is bright and lambda 2 is dark. As shown in Figs. 5 (b) and 5 (c), as the subject moves from z1 to z2, the brightness of? 1 decreases and the brightness of? 2 increases. Therefore, the object displacement in the direction of the optical axis can be accurately discriminated from the laser brightness data acquired by the line sensor.

FIG. 6 is a configuration diagram of an automatic focusing device using a chromatic aberration and a photodetection method according to an embodiment of the present invention. As shown in FIG. 6, the automatic focus adjustment method of adding the optical trigonometry to the principle of the chromatic aberration includes the bandpass filter 43 and the first image sensor 31 in the method using the principle of the chromatic aberration described with reference to FIG. 4 and FIG. And has an added configuration. Only the method using the optical triangulation method will be briefly described in the configuration of FIG.

The diffused light output from the two laser diodes 12 and 14 having different wavelengths is generated as parallel light through the first pinholes 15-1 and 15-2 and through the condenser lens. The parallel light is incident on the chromatic aberration lens 18 through the first beam splitter 16-1 and 16-2 and the laser light having passed through the chromatic aberration lens 18 is incident on the beam splitter 16 of the objective lens 20, (11). In this configuration, the first beam splitter 16-2 does not need a selective transmission function according to the wavelength, so a fully reflective mirror may be used. The laser beam incident on the objective lens 20 passes through the objective lens and has a different focal distance for each wavelength band. Some of the laser beams reflected by the objects z1 and z2 are reflected by the beam splitter 11 of the objective lens and then incident on the second beam splitter 22 and the remaining beams are transmitted through the beam splitter 11 of the objective lens Passes through the band-pass filter 43, and forms an image on the image sensor 31. In the configuration of FIG. 6, when two laser light sources 12 and 14 having different wavelengths are used, only laser light of a single wavelength is required when using the triangulation method. Therefore, the laser light of the remaining wavelength is removed by using the band- So that only the laser light having a desired wavelength is incident on the image sensor 31.

FIG. 7 is an explanatory view illustrating a method of analyzing a distance from a lens to a subject through a photo-trigonometric method using the automatic focusing device shown in FIG. 7 (a) shows a case where the subject is located at z1, (b) shows a case where the subject is located at z2, the horizontal axis of each graph represents the pixel position, and the vertical axis represents the amount of light. When the subject is at z1 and at z2, the pixel position of the laser spot formed on the image sensor 31 is changed. Therefore, the object displacement in the direction of the optical axis can be determined as the pixel position data of the laser spot acquired by the image sensor 31.

The automatic focusing device is omitted from the description of the conventional automatic focusing device. However, the automatic focusing device includes a vertical movement actuator for moving the member for placing the inspection specimen such as the objective lens or the object up and down, and an output value output from the image sensor and / And a control operation unit for generating a control signal for adjusting the up-and-down moving actuator. 4, the control operation unit generates a control signal for controlling the up-and-down movement actuator by using the beam intensity values of the two laser light sources output from the line sensor 33. In the case of FIG. 6, The arithmetic operation unit generates (1) a control signal for controlling the up-and-down moving actuator by using a beam intensity value for each wavelength of the two laser light sources output from the line sensor 33, (2) A control signal for controlling the up-and-down movement actuator is generated using the beam intensity value of any one of the output laser light sources, or (3) the beam intensity of each of the two laser light sources output from the line sensor 33 intensity control signal for controlling the up-and-down movement actuator using both the intensity value of the laser light source and the intensity value of one of the laser light sources output from the image sensor 31. [

6 schematically shows an automatic focusing method for automatically adjusting the distance to a subject by irradiating a plurality of laser beams onto a subject according to the present invention. A second step of irradiating a laser beam emitted from a chromatic aberration lens onto a subject, a third step of causing a laser beam reflected from the subject to enter a pinhole, and a step of causing the laser beam emitted from the pinhole to enter a diffraction grating A fourth step and a fifth step of sensing the intensity of the laser beam emitted from the diffraction grating at each wavelength. The automatic focus adjustment method shown in FIG. 6 can be applied together with the optical triangulation method in addition to the chromatic aberration method, and is performed after the second step, and performs band pass filtering that transmits only a specific region of the laser light reflected from the subject, And a seventh step of sensing the intensity value of the band-pass filtered laser light, in addition to the optical triangulation method.

While the preferred embodiments of the present invention have been described and illustrated above using specific terms, such terms are used only for the purpose of clarifying the invention, and it is to be understood that the embodiments of the invention and the described terminology are intended to cover various modifications, It is obvious that various changes and changes can be made without departing from the scope of the present invention. Such modified embodiments should not be understood individually from the spirit and scope of the present invention, but should be regarded as being within the scope of the claims of the present invention.

10, 12, 14: laser light source 11: beam splitter
13: white light source 15, 15-1, 15-2: first pinhole
16-1, 16-2: first beam splitter 17: second pinhole
18: chromatic aberration lenses 19, 32, 34: condensing lens
20: objective lens 22: second beam splitter
23: diffraction grating 31: image sensor
33: line sensor 41: first camera
42: Second camera

Claims (8)

delete An automatic focus adjusting apparatus comprising an objective lens having a beam splitter and automatically focusing a focus on a subject placed at the lower end of the objective lens,
A plurality of laser light sources respectively outputting different wavelengths;
A first pinhole for emitting the light emitted from the plurality of laser light sources as parallel light,
A first beam splitter for combining and outputting light emitted from the first pinhole,
A chromatic aberration lens for increasing the chromatic aberration of laser light output from the first beam splitter and outputting the chromatic aberration to the lens;
A second pinhole for emitting the light output from the beam splitter provided in the objective lens as parallel light,
A diffraction grating for diffracting laser light emitted from the second pinhole;
A line sensor for sensing light output from the diffraction grating,
A band-pass filter for outputting light reflected from the object after the light output from the chromatic aberration lens is irradiated to the object and then band-pass only light having a frequency within a predetermined range from the output laser light;
And an image sensor for converting electrical signals output from the band-pass filter into electrical signals.
3. The method of claim 2,
A vertical movement actuator for vertically moving the objective lens or the object,
Further comprising a control operation unit for generating a control signal for controlling a moving direction of the up-and-down movement actuator by using intensity values of wavelengths of the plurality of laser light sources output from the line sensor, Device.
3. The method of claim 2,
Wherein the band-pass filter transmits only the wavelength of any one of the plurality of laser light sources.
5. The method of claim 4,
A vertical movement actuator for vertically moving the objective lens or the object,
Further comprising a control operation unit for generating a control signal for controlling a moving direction of the up-and-down movement actuator by using an intensity value of the one laser light source output from the image sensor.
3. The method of claim 2,
A vertical movement actuator for vertically moving the objective lens or the object,
A movement direction of the up-and-down movement actuator is controlled using an intensity value of each of the plurality of laser light sources output from the line sensor and an intensity value of the one laser light source output from the image sensor Further comprising a control arithmetic unit for generating a control signal.
delete An automatic focus adjustment method for automatically adjusting a distance from a subject by irradiating a subject with a plurality of laser beams,
A first step of causing a plurality of laser beams having different wavelengths to enter the chromatic aberration lens,
A second step of irradiating the subject with laser light emitted from the chromatic aberration lens,
A third step of causing the laser light reflected from the subject to enter the pinhole,
A fourth step of causing the laser beam emitted from the pinhole to enter the diffraction grating;
And a fifth step of sensing an intensity of each laser beam emitted from the diffraction grating by wavelength,
The step performed after the second step,
A sixth step of performing band pass filtering to transmit only a specific region of the laser light reflected from the subject,
And a seventh step of sensing intensity values of the band-pass filtered laser light.

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