JP2528870B2 - Imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention scans a sample with a light beam two-dimensionally to capture an image of the sample, to capture a fluorescent image of the sample, The present invention relates to an image pickup device for picking up an optical beam induced current (OBIC) image.

(Prior Art) A light beam focused in the form of a minute spot is two-dimensionally deflected by two deflecting means to scan a sample at high speed, and reflected light or transmitted light from the sample is detected by a photomultiplier. Have been put into practical use. Although this microscope imaging device has various advantages, it is difficult to deflect the light beam in the main scanning direction at a constant high speed,
The scanning speed may fluctuate. In such a case, when light emitted from the sample is received by the photomultiplier, image distortion occurs, and there is a disadvantage that the sample image cannot be accurately reproduced.

As a method of solving such a defect, the present applicant has disclosed in Japanese Patent Laid-Open No. Sho 61-80215 that a sample to be imaged is scanned with a light beam in the form of a minute spot in the main scanning direction and the sub scanning direction orthogonal thereto. , An imaging device that deflects reflected light or transmitted light from the sample in the sub-scanning direction and sequentially receives the linear image sensor to form an optical image of the sample. In this image pickup device, a light beam emitted from a light source is vibrated at a high speed in the main scanning direction by an acousto-optic element, and is deflected in the sub scanning direction by using a vibrating mirror, and the two-dimensionally deflected light beam is spotted by an objective lens. The light beam from the sample is sequentially received by a linear image sensor in which a large number of photoelectric conversion elements are linearly arranged in a direction corresponding to the main scanning direction through a vibrating mirror. The charge accumulated in each element is sequentially read at a predetermined read frequency to create a photoelectric output signal. As described above, if the linear image sensor receives the reflected light or the transmitted light from the sample and sequentially reads out the charges accumulated in each element of the linear image sensor, the main scanning speed of the light beam by the acousto-optic element is increased. The remarkable advantage that a clear image with no image distortion can be obtained even when the value fluctuates is achieved.

The imaging device described above is suitable for use in capturing images of semiconductor chips, wafers, and various biological samples, but captures fluorescence generated when a light beam is projected onto the biological sample to capture a fluorescent image. Or to capture an OBIC image by capturing a current induced when a semiconductor wafer or a chip is irradiated with a light beam.

(Problems to be Solved by the Invention) When the above-described image pickup device is used, for example, when the reflectance of the sample is extremely low, the S / N of the image signal is lowered, and there is a drawback that a sufficiently good image cannot be picked up. When used in the same way as a fluorescence microscope, the fluorescence induced by the incident beam on the living body is generally weak, so the S /
There is a drawback that the quality of an image reproduced when N is low is deteriorated.
Furthermore, when capturing an OBIC image, if the moving speed of the beam spot is fast, that is, if the scanning rate is high, a large OB
There is a drawback that the IC current cannot be obtained and the S / N of the OBIC signal decreases. Furthermore, when capturing OBIC images, the optical image and OB
In order to make a correspondence with the IC image, it is necessary to detect the position where the beam spot is irradiated, but when scanning at high speed, it becomes difficult to detect the beam position,
It has the drawback of low detection accuracy.

In order to eliminate such a defect, it is conceivable that the scanning rates of the first and second deflecting means and the linear image sensor are slowed down, but the driving circuit of the linear image sensor and the process connected to the subsequent stage of the linear image sensor. It is generally difficult to slow down the scanning rate of the vibrating mirror or the like that constitutes the circuit and the second deflecting means. For example, when a CCD array is used as a linear image sensor, the free-running frequency is set so that optimum operation is performed, so changing the frequency may deteriorate the operating characteristics. Further, the vibrating mirror which constitutes the second deflecting means is also designed so that adverse effects such as resonance do not appear at a predetermined frequency. Therefore, if the vibrating frequency is changed as it is, the characteristics deteriorate and proper scanning cannot be performed. Will end up.

As described above, the object of the present invention is not to change the scanning rate of the portion where the scanning rate is difficult to change, and to slow down the scanning rate of the portion where the scanning rate is easy to change and does not have an adverse effect. An object of the present invention is to provide an imaging device capable of obtaining an image signal with high / N.

(Means for Solving Problems) An image pickup apparatus according to the present invention includes a light source that emits a light beam, a first deflecting unit that deflects the light beam emitted from the light source in a main scanning direction, and the light beam. Second deflecting means for deflecting the light beam in the sub-scanning direction orthogonal to the main scanning direction, an objective lens for projecting the light beam two-dimensionally deflected by the first and second deflecting means onto the sample surface, A linear image having a plurality of light receiving elements arranged one-dimensionally in a direction corresponding to the main scanning direction and receiving light from a sample through the second deflecting means or the deflecting means operating in synchronization with the second deflecting means. A sensor and a scanning rate changing means for slowing the scanning rate of the first deflecting means by 1 / n (where n is a natural number greater than 1) compared to the scanning rates of the second deflecting means and the linear image sensor. , Recording the image signal read from the linear image sensor,
The recording means is adapted to capture an image signal for one screen by performing the operation over the field period.

(Operation) According to the above-described image pickup apparatus of the present invention, the scanning rate in the first deflecting unit, which can be configured by, for example, an acousto-optic deflecting element, is slowed down, but such a deflecting element considerably increases the deflection frequency. Even if it is changed, the characteristics are not deteriorated at all, and the second deflecting means and the linear image sensor are kept operating at the optimum scanning rate. Therefore, for example, even when imaging a sample having extremely low reflectance, the S / N ratio is reduced.
It is possible to obtain a high image signal. In the present invention, the equivalent sensitivity can be increased by n times by setting the scanning rate of the first deflecting means to 1 / n.

(Embodiment) FIG. 1 is a diagram showing a configuration of an example of an image pickup apparatus according to the present invention. The light beam emitted from the laser beam 1 is expanded by the expander 2 and converted into a parallel light beam by the collimator lens 3 and then incident on the acousto-optic element 4 which is the first deflecting element. The acousto-optic element 4 vibrates the light beam at high speed, and the light beam vibrates at high speed to scan the sample surface at high speed in the X direction (main scanning direction). The light beam deflected by the acousto-optic element 4 is a cylindrical lens 5
Is expanded in one direction into a circular light beam, and is incident on the condenser lens 6. The light beam condensed by the condenser lens 6 is changed in direction by the mirror 7, then passes through the half mirror 8 acting as a beam splitter, and is incident on the galvanometer mirror 9. The galvanometer mirror 9 is connected to the driving device 10 and deflects the light beam in the Y direction (sub scanning direction) orthogonal to the X direction of the sample. The light beam reflected by the galvanometer mirror 9 is focused by the objective lens 11 in the form of a minute spot and is incident on the sample 12. As a result, the sample 12 is scanned at a predetermined scanning frequency in the X and Y directions by the light beam in the form of a minute spot. In this example, the sample 12 is irradiated with a laser beam, and the light reflected from the sample 12 is captured to capture a sample image. The reflected light emitted from the sample 12 is condensed by the objective lens 11, is deflected in the sub-scanning direction by the galvanometer mirror 9, enters the half mirror 8, and the light reflected here is passed through a large number of light receiving elements in the main scanning direction. It is incident on the linear image sensor 14 arrayed in. When capturing a fluorescence image of a sample, a filter 13 that transmits fluorescence and cuts laser light may be inserted between the half mirror 8 and the linear image sensor 14.

The acousto-optic element 4 is driven by the drive circuit 15, and this drive method will be described later. In addition, the drive circuit 16 of the drive device 10 that swings the galvanometer mirror 9 drives the galvanometer mirror at 60 Hz (field frequency f _F ) when performing image signal processing according to the NTSC system. Furthermore, the drive circuit 17 of the linear image sensor 14 is 15.75 KHz.
Read the linear image sensor repeatedly at (line frequency f _H ). That is, the scanning rate of the galvanometer mirror 9 which is the second deflecting means and the linear image sensor 14
The scanning rate, which is the reading speed of the, is set to a standard value. In the present invention, the scanning rate in the acousto-optic element 4 constituting the first deflecting means has been described above, but is set to be 1 / n (n is a natural number larger than 1) slower than the standard scanning rate in the galvano mirror 9 and the linear image sensor 14. . It is preferable that a large number of scanning frequencies of the acousto-optic element 4 are prepared in the embodiment described later and a desired one can be selected from them, but this is not always an essential requirement. . Further, when the scanning rate in the first deflecting unit is slowed in this way, it may not be possible to capture the information of the entire screen by simply slowing it down. However, in the present invention, it is possible to extend over n fields of the standard system. By capturing the signal, the information of the full screen is captured. For this purpose, the pixels on the screen are not overlapped during the n field period. A scanning rate control circuit 18 is provided to perform such scanning, and thereby controls the drive circuit 15 for the acoustooptic device 4, the drive circuit 16 for the galvano mirror 9, and the drive circuit 17 for the linear image sensor 14. The image signal read from the linear image sensor 14 is amplified by the preamplifier 19 and then stored in the frame memory 20 for writing in synchronization with the standard scanning rate. As mentioned above,
By capturing the image signal over the n fields, the information of one entire screen can be stored in the frame memory 20. After the information of one screen is taken in this way, it is read and supplied to the image processing circuit 21 to be a television signal, which is reproduced on the monitor 22. Further, without providing the frame memory 20, the output signal of the preamplifier 19 is directly supplied to the image processing circuit 21, displayed on the monitor 22, and the image formed on the screen of this monitor is photographed by the photographic camera 23. You can also Therefore, the recording means of the present invention does not mean only a signal storage means such as a frame memory, but also includes an image recording means such as a camera. In the present invention, since the linear image sensor 14 is operated at a standard scanning rate, the frame memory 20, the image processing circuit 21, and the monitor 22 that process and reproduce the output signal thereof.
Can be operated at standard scan rates without any modification of these circuits.

Next, scanning in the first and second deflecting means and the linear image sensor will be described in detail.

Now, the scanning speed in the main scanning direction in the first deflecting means 4 is set to 1/2 (n = 2) of the standard scanning speed in the main scanning direction. In this case, the scanning line in the first field scans on the first scanning line up to half the length of the first scanning line, as shown in FIG. The line will be scanned. After that, the same shift will occur. Here, the movement in the sub-scanning direction is intermittently performed for convenience of description. Next, when shifting to the second field, the deflection signal to the first deflecting means is shifted by half the period, and the latter half portion on the first scanning line is scanned as shown in FIG. The first half of the scanning line is scanned, and the same scanning is performed thereafter. As a result, by scanning over two fields, the pixels on the entire screen are scanned once, and information of the entire screen can be obtained. Fig. 3A
3C to 3C show the deflection signal of the first deflection means, the deflection signal for main scanning in the standard method, and the deflection signal of the second deflection means in this example. In this example, the scanning period of the first deflecting means is set to 2T _{H, which} is twice the horizontal scanning period T _H of the standard system.

The method of shifting the deflection signal of the first deflecting means by half of the period for each field as in the above-mentioned embodiment is called a discontinuous method. Generally, the period of the deflection signal of the first deflecting means is set to the standard horizontal direction. When the period of the deflection signal is n times, each scanning line is divided into n. Therefore n
By capturing the image signal over the field, it is possible to obtain information on the entire screen. Generally, if the scanning speed of the first deflecting means is 1 / n, the equivalent sensitivity is n
It will be doubled.

4 and 5A to 5C are diagrams for explaining the principle of the method for continuously shifting the scanning phase of the first deflecting means,
This is the case when n = 2. In the case of this continuous method,
A certain relationship is required between the total number of scanning lines and the value n,
It is necessary that the total number of scanning lines is not a multiple of n, and that n is not a multiple of the total number of scanning lines. Therefore, when n = 2, the total number of scanning lines must be an odd number. In the first field, as shown by the solid line in FIG. 4, after scanning the first half of the first scanning line, the second half of the second scanning line is then scanned, and so on. The latter half of the scanning lines of are scanned one after another. Since the last scan line is odd,
The first half is scanned and then the second field is moved to the first
The latter half of the scan line is scanned. In the second field, the second half of the odd-numbered scan lines and the first half of the even-numbered scan lines are sequentially scanned, and the entire screen is scanned over the two fields. In FIG. 5, A is a deflection signal for the first deflection means, B is a horizontal deflection signal in the standard system,
C is a deflection signal for the second deflection means.

FIG. 6 shows an embodiment in which the scanning phase is shifted by the above-mentioned continuous method. In this example, the total number of scanning lines is 455, and n can be changed to 2,4,8,16,32 ... 4096. First, it is assumed that a deflection signal for the acousto-optic element, which is the first deflection means, is created using the clock pulse of 14.31818 MHz generated from the bit clock oscillator 31. A counter that counts this clock
32 and B counter 33 are arranged in series. In this example, these counters act as frequency dividers, and the frequency division ratios a and b are appropriately combined to generate a desired deflection signal. Therefore, a P-ROM 34 for setting the frequency division ratio a of the A counter 32 and a P-ROM 35 for setting the frequency division ratio b of the B counter 33 are provided. By selecting the addresses of these P-ROMs with the rotary switch 36, the frequency division ratios a and b can be set. B counter
The digital output signal 33 is supplied to the sweep D / A converter 37 to create a staircase-shaped analog sweep signal.
This sweep signal is supplied to one contact 39a of the changeover switch 39 via the amplifier 38. The other contact 3 of this switch 39
A standard type sweep signal generation circuit 40 is connected to 9b. The contact 39c is connected to the output terminal 41. In this example, since the frequency division ratio b in the B counter 33 is also changed, the amplitude of the sweep signal changes as it is. Therefore, the value set in the P-ROM 35 is also supplied to the amplitude adjusting D / A converter 42. The output of this converter is supplied to the sweep D / A converter 37 via the amplifier 43 so that a sweep signal having a predetermined maximum amplitude is always obtained. Further, when a circuit 44 for detecting whether or not the pixel information of the entire screen is stored in the frame memory, that is, whether or not scanning is performed over n fields is provided and it is detected that scanning over n fields is completed, Is indicated by the light emitting diode 45.

Frequency division ratio a, B counter in A counter 32 in this example
The relationship with the frequency division ratio b in 33 is shown in the following table. In this table, the number of pulses supplied to the B counter in one horizontal scanning period of the standard method, the sensitivity, and the amplitude adjustment D / A converter 42 are used for adjustment. The ratio of power amplitudes is also shown.

In this example, if the sensitivity is lower, the frequency division ratio of the A counter 32
Although 1 / a is made as small as possible and the division ratio 1 / b of the B counter 33 is changed to change the scanning rate, this reduces the step of the sweep signal to obtain a sweep signal that changes as smoothly as possible. I am allowed to do so. An amplifier 38 that amplifies the output of the sweep D / A converter 37 has an integrating action to smooth the output from the D / A converter 37. Further, when the scanning rate is to be remarkably slowed, the number of bits of the B counter 33 may be increased, but since the configuration of the B counter becomes very complicated, the A counter 32 is provided and a certain frequency division is performed here. I am trying to do it. Also, divide the division ratio of the A counter by 1/1 and the division ratio of the B counter by 1
By setting / 910, a sweep signal having a standard scanning rate can be obtained, but in this example, a standard method sweep signal generating circuit 40 is separately provided and a switch 39 can select the output of this circuit. As described above, in the present embodiment, the scanning rate of the first deflecting means can be changed over a very wide range, whereby the sensitivity can be remarkably increased.

The present invention is not limited to the above-described embodiments, but various modifications and changes can be made. For example, in the above-described embodiment, the reflected light from the sample is received, but the fluorescence from the sample can be received. Further, the sample may be irradiated with a light beam and the transmitted light may be received. In this case, it is necessary to allow the transmitted light to be incident on the linear image sensor via a galvano mirror provided on the incident side or a deflecting means that is driven in synchronization with the galvano mirror. It is also possible to obtain an OBIC image by detecting a current induced by irradiating a semiconductor wafer or chip with a laser beam. Further, in the above-described embodiment, the rate of slowing the scanning rate of the first deflecting unit is an integer (n is an integer), but the present invention is not limited to this, and n may be a natural number larger than 1. it can.

(Effects of the Invention) As described above, in the present invention, the second deflecting means including, for example, a galvanometer mirror and the linear image sensor are operated in accordance with a standard method, and the scanning rate of the first deflecting means including, for example, an acousto-optic device is set to a standard. The equivalent sensitivity can be increased by slowing down compared to the system. Therefore, it is possible to project an image of an object with extremely low reflectance and a fluorescent image in a good condition, and to obtain a good OBIC.
You can also get a statue. Further, since the scanning rates of the second deflecting unit and the linear image sensor are not changed, the structure is very simple and accurate scanning can be performed.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of an image pickup apparatus according to the present invention, and FIGS. 2A and 2B and FIGS. 3A, 3B and 3C show a method of discontinuously changing the scanning phase of the first deflecting means. FIGS. 4 and 5 A, B and C are diagrams for explaining a method of continuously changing the scanning phase, and FIG. 6 is an embodiment of the scanning rate control means of the image pickup apparatus of the present invention. 3 is a block diagram showing the configuration of FIG. DESCRIPTION OF SYMBOLS 1 ... Laser light source 4 ... Acousto-optic element (1st deflection means) 9 ... Galvano mirror (2nd deflection means) 11 ... Objective lens, 12 ... Sample 14 ... Linear image sensor 18 ... Scan rate control circuit 20 ... Frame memory, 21 … Image processing circuit 22… Monitor

Claims (3)

(57) [Claims] 1. A light source for emitting a light beam, a first deflecting unit for deflecting the light beam emitted from the light source in a main scanning direction, and a light beam for deflecting the light beam in a sub-scanning direction orthogonal to the main scanning direction. Second deflecting means, an objective lens for projecting the light beam two-dimensionally deflected by the first and second deflecting means onto a sample surface, and one-dimensionally in a direction corresponding to the main scanning direction. A linear image sensor having a plurality of light receiving elements arranged, and receiving light from a sample through the second deflecting means or the deflecting means operating in synchronization with the second deflecting means, and a scanning rate in the first deflecting means. Scanning rate changing means for slowing the scanning rate by 1 / n (where n is a natural number greater than 1) compared to the scanning rates in the second deflecting means and the linear image sensor, and reading from the linear image sensor. Imaging apparatus characterized by the recording of the image signal, comprising a recording means so as to capture the image signal for one screen by performing over a period of n fields. 2. The image pickup apparatus according to claim 1, wherein the recording means is constituted by a frame memory for storing image signals for at least one screen. 3. The image pickup apparatus according to claim 1, wherein the scanning rate changing means is configured so that the value of n can be arbitrarily selected from a plurality of integers.