JPH05187839A - Scanning optical inspecting device - Google Patents

Abstract

PURPOSE:To inexpensively perform high-speed scanning by providing a luminous flux separating means which separates reflected light from a specimen and one-dimensional CCD sensor array provided with an opening which is parallel to the slit-like shape of a second luminous flux of laser. CONSTITUTION:Reflected light separated by means of a 45 deg.-mirror 11 forms the image of a slit-like luminous flux 9 of laser on the focal surface of an image forming lens 12 afocally provided against an objective lens 7. The image is a slit-like image parallel to the luminous flux 9 and formed in the opening, namely, on the light receiving surface of a one-dimensional CCD 13 arranged on the focal surface of the luminous flux 9. A spring-up mirror 14 is provided between the lens 12 and CCD 13 and part of or, when required, all of the reflected light is taken out. The taken-out luminous flux forms the image of a specimen 8 at a position 15 equivalent to the CCD 13 and position adjustment can be performed by observing the image by enlarging the image through an eyepiece 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a confocal scanning type optical inspection apparatus.

[0002]

2. Description of the Related Art A confocal scanning microscope is superior in spatial resolution to a conventional optical microscope. In particular, because of its excellent depth resolution, it has been widely used for shape measurement and fluorescent image observation. In addition, due to the scanning type, observation and display of a two-dimensional distribution of optical interaction represented by an orbic (Optical Beam Induced Current) is also performed.

For application to shape measurement and the like, good throughput is required, and the beam scanning speed becomes a problem. Then, although a scanning speed as high as a TV rate is required, in the conventional method, an AOD (acousto-optic deflector)
A combination of the light beam deflection (X deflection) by the X-axis and the low-speed deflection (Y deflection) orthogonal to the X-deflection by the galvanometer is used. With other deflection methods, for example, a method that uses the rotation of a motor such as a polygon mirror in a copy machine or a hologram scanner in a POS, or a resonance type galvanometer, a scanning speed on the order of TV rate is easily realized at present. Can not.

[0004]

SUMMARY OF THE INVENTION Therefore, the present invention solves the above-mentioned drawbacks of the conventional scanning optical inspection apparatus, that is, the AOD "deflection limited by the band of the piezoelectric element". This is to solve the drawbacks of "small angle" and the astigmatic difference caused by the need to increase the beam diameter in order to increase the deflection efficiency ", and to solve the" expensive "drawback. Can be improved by cascading connection, but there arises a heterogeneous problem such as deviation of the deflection center from the entrance pupil or higher cost.
The astigmatic difference can be corrected by the axially displaced cylinder lens, but there is a problem in that the deflection speed cannot be changed and the scanning direction shift easily occurs due to the inclination of the lens axis. In view of the above problems, it is an object of the present invention to provide a confocal scanning type inspection apparatus that can realize high-speed scanning at low cost.

[0005]

In order to solve the above technical problems, the present invention provides a semiconductor laser, LD driving means for driving the LD, and the LD as a light source, and a laser from the light source. A light beam conversion optical system that converts a light beam into a first slit-shaped laser light beam, a scanning unit that scans the first slit-shaped laser light beam in a slit direction of the first slit-shaped laser light beam, and a scanning unit. Parallel beam of light is focused on the sample, the divergent beam from the scanning means is transferred as a parallel beam onto the sample, and the divergent beam of the first slit-shaped laser beam is orthogonal to the slit direction. 2, an objective lens for producing a slit-shaped light beam, the light beam conversion optical system, and a light beam separating means for separating reflected light from the sample, which is arranged between the scanning means, and a position equivalent to the sample, The light beam separating means One-dimensional CCD sensor array (hereinafter, referred to as CCD in the present specification) for receiving the reflected light from the sample separated by the above-mentioned method and having an opening parallel to the slit shape of the second slit laser beam. Provided is a scanning type optical inspection device including: Further, the LD drive means combines the direct current drive means, the frequency modulation high frequency drive means for sweeping the frequency in synchronization with the scanning of the scanning means, and the outputs from the direct current means and the frequency modulation frequency drive means. Therefore, it is preferable to provide a combining means for driving the LD. Further, it is preferable that the LD driving means includes a sawtooth wave driving means synchronized with the scanning of the scanning means.

[0006]

According to the scanning type optical inspection apparatus of the present invention, a sample is illuminated with a slit-shaped light beam, and the slit-shaped light beam is received by a one-dimensional CCD having an opening parallel to the slit-shaped light beam. With such a configuration, X scanning can be omitted, high-speed image acquisition can be performed, and in this case, correction of astigmatic difference is not necessary.

Further, in slit-shaped illumination using laser light, speckles may occur depending on the sample, and the S / N ratio of the image may deteriorate. The scanning optical inspection apparatus of the present invention uses an LD having a wider spectrum than a He-Ne laser which is normally used as a light source. Further, a high frequency drive is superposed on a direct current drive as an LD drive means, The S / N ratio can be improved by sweeping the high frequency, changing the oscillation frequency of the LD for a 1H period (referring to one horizontal scanning period in TV scanning), and averaging the speckles.
A D drive means is provided.

LD is another means for removing speckle.
Is driven by a ramp wave having a period of 1H period, and the fact that the oscillation wavelength of the LD changes with the change of the drive current value,
By changing the oscillation wavelength of the LD with a period of 1H,
By averaging the speckle effect, it is possible to provide the LD driving means capable of improving the S / N ratio.

Next, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

[0010]

1 is a block diagram showing the optical system of a scanning type optical inspection apparatus of the present invention. Reference numeral 1 is an LD, 2 is a laser beam, 3 is a collimator lens, 4 is a cylinder lens which is a light beam converting means, 11 is a light beam separating means, and 5
Is a polarizing mirror, 7 is an objective lens, and 8 is a sample. 6
Indicates the state of the first slit-shaped light beam formed on the polarization mirror, 9 indicates the state of the second slit-shaped light beam formed by the objective lens and applied to the sample, and 13 indicates the CCD.
Is. Further, 12 is an image forming lens, 14 is a half mirror or a flip-up mirror, 15 is an image forming position, 16 is an eyepiece lens, 17 is a half mirror or dichroic mirror, 1
Reference numeral 8 indicates a condenser lens, and 19 indicates a lamp.

The y component of the laser light flux from the LD becomes a light flux having a large divergence angle by using the end surface of the LD as a light source, and becomes a parallel beam (y-beam) having a prescribed width by the collimator lens 3. On the other hand, the x component from the LD is a light beam whose light source is a point a which enters about 4 μm from the end face to the inside of the LD, and becomes a beam (x beam) which can also be regarded as substantially parallel by the collimator lens 3. Furthermore, the x beam is a cylindrical lens 4 that has power only in the x direction.
Is condensed on the surface of the mirror 5 which gives y-deflection, and forms the first slit-shaped light flux 6 6. On the other hand, the y-beam remains parallel without being affected by the cylindrical lens 4. Therefore, on the deflecting mirror 5 surface, the first slit-shaped light beam 6 is obtained in the YZ plane.

This first slit-shaped light beam is reflected by the mirror 5 and transferred onto the sample 8 by the objective lens 7.
It becomes the second slit-shaped light beam 9. At this time, the parallel y beam is condensed to a spot diameter that can be obtained by NA (aperture diameter) regulated by the aperture diameter (Y beam diameter) of the objective lens, while the x beam is the objective lens. By arranging 7 and the cylindrical lens 4 in an afocal arrangement, parallel beams are formed. That is, the second slit-shaped light beam 9 is orthogonal to the first slit-shaped light beam 6.

The reflected light of the second light beam 9 from the sample 8 is collected again by the objective lens 7, but it becomes a concentrating system as a telecentric system using the deflection mirror 5 as an aperture. Light flux conversion optical system by lens 4, mirror 5 and motor 10
It is arranged between the deflecting means consisting of
By means of a 45-degree mirror 11 serving as a surface, this is paired with a half mirror or a quarter-wave plate (not shown), which serves as a deflecting beam splitter to be used and separates the reflected light from the illumination light beam. ..

The separated reflected light forms an image by the slit-shaped light beam 9 on its focal plane by the objective lens 7 and the imaging lens 12 disposed afocal. The image is a slit-shaped image parallel to the light flux 9, and is formed on the aperture (that is, the light receiving surface) of the one-dimensional CCD 13 arranged on the focal plane thereof. The sample 8 and the CCD 13 have a confocal arrangement, and stray light from outside the illumination point is removed. Further, each point on the slit-shaped light beam 9 and each pixel on the CCD 13 correspond to each other via the photographing magnification.

A half mirror or a mirror 14 capable of flipping up is arranged between the imaging lens 12 and the CCD 13 by a mechanism not shown, and a part of the reflected light is reflected through the mirror 14 or if necessary. It takes out all of the light. The extracted light flux forms a sample image at a position 15 equivalent to the CCD 13, and the image is passed through an eyepiece lens 16,
The magnified observation can be performed and the position can be adjusted.

Further, the light beam splitting means 11 and the imaging lens 12
A half mirror or dichroic mirror 17 is arranged between the two, and an image of the filament of the lamp 19 is formed on the surface of the deflecting mirror 5 through the mirror 17 and the condenser lens 18, thereby illuminating the specimen 8 by Koehler illumination. .. The mirror 14 and the mirror 17 using a mechanism not shown can be simultaneously put in and taken out from the optical path, and the specimen 8 can be illuminated and observed by the lamp 19 only at the time of observation.

The deflection mirror 5 is rotated by a pulsus motor or a galvanometer 10 having an x-axis as a rotation axis, and a slit light 9 is displaced on the sample 8. Generally, a Y scan is done. The reflected light flux from the slit light 9 at the displaced position is returned to the optical axis 2 by the mirror 5,
An image is formed on the surface of the fixed CCD 13.

The deflection mirror 5 is rotated stepwise by the motor 10, but during the step period (1H), CC
D13 integrates the incident light and is read out at high speed as a signal while moving to the next step. The signal is written in the memory as a digital signal by an electric circuit (not shown). The scanning is repeated over the Y scanning range to acquire a two-dimensional image of the sample. The signal is read from the memory according to the TV rate and displayed as an image on a CRT or the like. In slit scanning, the resolution in the slit direction becomes worse than in the direction perpendicular to the slit direction. In FIG. 1, x
Decomposition is worse than y-decomposition. Therefore, in the CRT, the memory is read so that the y-scan signal is placed on the horizontal raster having a higher resolution. In addition, measurement and processing are performed based on the acquired image, and the result is displayed in a superimposed manner.

Next, a means for removing the speckle effect of speckle that may occur when scanning a sample having a rough surface will be described with reference to FIGS. 2 and 3. In observation and measurement using an image, speckle becomes harmful noise, which causes deterioration of the S / N ratio of the image. In general, speckles are scattered light from different points on the specimen that gather at the same point on the observation surface, and the degree of interference changes depending on the relationship between the optical phases of the two. It is described as a random high-contrast light spot distribution.

When observing through a lens, the diameter of the spot is approximately λL / W (λ is the wavelength, L is the distance between the lens and the observation surface, and W is the aperture diameter of the lens).
And the diameter depends on the wavelength and the NA of the lens. In order to suppress the speckle effect, that is, the generation of spatially random signals and noises on the observation surface, a method of making the spot diameter smaller than the observation resolution, or a light source with a wide wavelength distribution ( That is, there is a method of using a light source with poor coherence. In the former case, they are averaged within the observed decomposed pixels.

In the latter method using a light source in which the wavelength is distributed over a wide range, the position where the spot appears and the spot diameter are distributed because the optical path length changes depending on the wavelength. The speckle effect is eliminated by averaging on the surface. The coherence length indicating the degree of coherence is about 15 μm in a light emitting diode (LED) without speckle effect, and is about 6 m in a He—Ne laser in which speckle is easily generated. In an LD, this distance is about 3 mm, and speckles are generated, but it can be said that it is a light source in which removal measures are easier to take than in a commonly used He-Ne laser. In applications requiring high brightness, LEDs are unsuitable and LDs are used, but in applications where speckle cannot be ignored, it is necessary to take measures to remove them.

In FIG. 2A, the LD driving means includes a DC driving means, a frequency modulation high frequency driving means for sweeping the frequency in synchronization with the scanning of the scanning means, the DC means and the frequency. FIG. 6 is a block diagram which is a unit including a combining unit that combines outputs from the modulation high frequency driving unit and thereby drives the LD. Also, FIG. 2B
FIG. 6 is a diagram for explaining the operation. LD (1)
Is a monitor photodiode (PD) 20, an IV conversion circuit 21 that converts the PD output into a voltage, and a filter 22 that receives the output thereof and removes the high-frequency components contained therein.
And a level setting circuit 23 for setting an average light output, and
It is driven at a constant DC light level by a DC drive circuit 24 which receives the signals 2 and 23 and drives the LD (1) by APC (automatic output control). Motor drive circuit 25
Via a synthesizing means 28 for synthesizing a high frequency obtained by sweeping the frequency from the frequency modulation high frequency driving means 27 for changing the frequency in response to the ramp wave from the ramp wave generating circuit 26 for generating the ramp wave in synchronization with the motor driving by Put it on. The synthesizing means 28 is a simple circuit as shown, in which the 24 side is connected to the inductor 34 and the 27 side is connected to the capacitor 35.

This system is an extension of the high frequency carrier modulation method used for mode locking. The oscillation mode is phase-modulated by the high frequency to become the multi-longitudinal mode and the oscillation frequency changes. 29 in FIG. 2B
Indicates the change in the superimposed frequency (f), and is 30
Indicates the motor drive timing, and the CCD 13 integrates the incident light during the T ₁ period (corresponding to 1H). Therefore, if the frequency applied during the T ₁ period is changed,
The laser oscillation frequency (wavelength) changes according to the applied frequency, and the spot position and the diameter thereof due to speckle change. The signal output of the CCD 13 is read during the T ₂ period shown in FIG. Also, during this T ₂ period, the motor 10
One step is driven in the Y direction, and scanning is performed with the slit light 9 to the next 1H position. Noise due to speckles is spatially averaged in the signal output of the CCD 13, and no noise is detected.

FIG. 3 is a diagram for explaining another speckle removing means. That (a) is a block of circuitry,
The (b) shows the LD drive current. During the T ₁ period, the drive voltage is changed between i _max and i _min centering on i ₀ by a sawtooth wave, and the wavelength is changed according to the drive current level. That is, the speckle noise is averaged by utilizing the fact that the refractive index changes depending on the carrier concentration and the laser oscillation wavelength changes. In synchronism with the motor drive from the motor drive circuit 25, the sawtooth wave drive means 32 produces a drive current indicated by the curve 33 in (b), and LD
(1) is driven. LD (1) is P
The D (2) output is IV-converted (21), integrated for the T ₁ period, and converted into a direct current. An integrating circuit 31 and a level setting circuit 23.
With, the operation is centered on the average output level corresponding to the set average current i ₀ .

As another means for removing speckle, a so-called SLD (super luminescent diode) whose oscillation wavelength band is close to that of an LED and whose brightness is close to that of an LD is used as a light source, or a prism or the like. It is possible to use a method of using an optical system in which a large number of light beams having an optical path difference are created by combining the internal reflection of the above, and these are superposed, and again made into one light beam.

[0026]

As described above, the following remarkable technical effects are obtained by the scanning type optical inspection device of the present invention. High-speed scanning can be omitted by using one of the XY scanning as the slit light, and the S / N ratio can be reduced by taking measures to suppress the speckle noise that may occur in the slit light scanning. It has become possible to provide a high-speed and low-cost confocal scanning optical inspection device with good quality.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an optical system of a scanning type optical inspection apparatus of the present invention.

FIG. 2A is a block diagram of an electric circuit showing an LD driving means before speckle noise removal according to the present invention,
(B) is an explanatory view for explaining the operation.

FIG. 3A is an electric circuit block diagram showing an LD driving means of a different system for speckle noise removal,
(B) is an explanatory view for explaining the operation.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Semiconductor laser (LD) 3 Collimator lens 4 Cylinder lens of light flux conversion means 5 Deflection mirror 6 First slit-shaped light flux 7 Objective lens 8 Specimen 9 Second slit-shaped light flux 13 CCD 24 DC drive means 27 Frequency modulation high frequency drive means 28 Synthesizing Means 32 Sawtooth Wave Driving Means

Claims (3)

[Claims] 1. A semiconductor laser (hereinafter, L in this specification)
(Referred to as D), LD driving means for driving the LD, the LD serving as a light source, and the laser light flux from the light source
Beam conversion optical system for converting into a slit-shaped laser beam, and the first slit-shaped laser beam in the slit direction.
Scanning means for scanning the slit-shaped laser light flux of, and a parallel beam from the scanning means is condensed on the sample, and a divergent beam from the scanning means is transferred onto the sample as a parallel beam, The first slit-shaped laser beam is arranged between the objective lens that forms a second slit-shaped beam in a direction orthogonal to the slit direction, the beam conversion optical system, and the scanning unit, and is reflected from the sample. A beam splitting means for splitting the light, and a slit shape of the second slit laser beam, which is at a position equivalent to the sample and receives reflected light from the sample split by the beam splitting means. One-dimensional CCD sensor array (hereinafter, in the present specification, C
(Hereinafter referred to as CD). 2. The LD driving means comprises a DC driving means,
The frequency modulation high frequency driving means for sweeping the frequency in synchronization with the scanning of the scanning means, the outputs from the direct current means and the frequency modulation frequency driving means are combined, and thereby, the combination for driving the LD. The scanning optical inspection apparatus according to claim 1, further comprising: 3. The scanning optical inspection apparatus according to claim 1, wherein the LD driving means is driven by a sawtooth wave pulse synchronized with the scanning of the scanning means.