JPS63278023A - Image pickup device - Google Patents

Abstract

PURPOSE:To detect a light beam induced current (OBIC) generated in a sample to form an OBIC image simultaneously with the optical image by deflecting the light beam emitted from a light source in the main scanning direction and the subscanning direction orthogonal to the main scanning direction and two- dimensionally scanning the sample with deflected light beams. CONSTITUTION:The light beam emitted from a laser light source 1 is deflected in X and Y directions by a first deflecting means 4 for deflection in the main scanning direction and a second deflecting means 8 for deflection in the subscanning direction and is projected toward a sample 11 having the photovoltaic effect. The OBIC current is induced in the sample by projecting the light beam, and this OBIC current is detected by an OBIC current detecting means, and the output signal is supplied to a picture signal input terminal of a monitor. Simultaneously, the reflected light or the transmitted light from the sample 11 is received line by line by a linear image sensor 14, and the photoelectric output signal is supplied to another picture signal input terminal of the monitor 13. Thus, the optical image of the sample and the OBIC image are displayed together on the monitor 13.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an imaging device, and particularly to an imaging device that can capture both an optical image and an optical beam induced current image (OBIC image) of a sample.

(Prior art) A light beam focused into a minute spot is deflected two-dimensionally by two deflecting means to scan the sample at high speed, and the reflected light or transmitted light from the sample is detected by a photomultiplier. A microscopic imaging device that creates optical images has 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, and the scanning speed may fluctuate. In such a case, if the light emitted from the sample is received by the photomultiplier, image distortion will occur, resulting in the drawback that the sample image cannot be accurately reproduced.

As a method to eliminate such drawbacks, the applicant proposed in Japanese Patent Application Laid-Open No. 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 in the sub-scanning direction orthogonal thereto. proposed an imaging device that creates an optical image of a sample by sequentially receiving reflected light or transmitted light from the sample using a linear image sensor. This imaging device vibrates a light beam emitted from a light source at high speed in the main scanning direction using an acousto-optic element, deflects it in the sub-scanning direction using a vibrating mirror, and focuses the deflected light beam on a minute spot using an objective lens. The light beam is projected onto the sample, and the light beam from the sample is sequentially received by a linear image sensor in which a large number of photoelectric conversion elements are arranged linearly in a direction corresponding to the main scanning direction, and the charges accumulated in each element are transferred in a predetermined sequence. The photoelectric output signal is configured to be read out sequentially at frequencies to create a photoelectric output signal. In this way, if the configuration is such that the linear image sensor receives reflected or 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 can be adjusted by the acousto-optic element. A significant advantage is achieved in that a clear image without image distortion can be obtained even when the values vary.

On the other hand, with the development of various integrated circuits, there is a strong demand for the development of a method for inspecting defects in integrated circuits formed on semiconductor substrates. As a method of inspecting the integrated circuit for defects, an optical image of the integrated circuit is displayed on a monitor using the imaging device,
There is a method of visually inspecting the displayed external image for defects. Furthermore, as another method, a defect inspection method that utilizes the photovoltaic effect of semiconductor materials has been proposed. This method utilizes the fact that when a light beam is projected toward a semiconductor substrate to be inspected, an optical beam induced current (OBIC current) is generated in the substrate, and the semiconductor substrate is placed on a two-dimensionally movable sample stage. At the same time, the light source is placed in a fixed position, and the sample stage is driven two-dimensionally to illuminate the sample with two light beams.
Scans dimensionally, detects the 0BIC current generated in the semiconductor substrate two-dimensionally, amplifies the detected 0BIC current to create an 0BIC image signal, and supplies this 0BIC image signal to a monitor to create an 0BIC image. configured to display. Further, in order to compare the displayed 0BIC image with an optical image, an external image of the semiconductor substrate is taken with a television camera, and defect inspection is performed by making the external image correspond to the 0BIC image.

(Problems to be Solved by the Invention) When detecting defects in a semiconductor substrate, it is more preferable to perform an inspection based on external information and internal information of the semiconductor substrate.
For example, an optical image of the external appearance obtained by an imaging device and 0BIC
By superimposing and displaying both images on the same screen, a correlation between external information and internal information can be obtained, and defect inspection can be performed with higher accuracy.

However, since the imaging device proposed by the applicant mentioned above can only capture an optical image of the semiconductor substrate, the 0BI
It was necessary to separately provide a C image photographing device and compare the 0BIC image and the optical image separately.

Therefore, there is a drawback that the scanning position of the light beam of the imaging device and the scanning position of the light beam of the 0BIC image capturing device do not correspond accurately.

On the other hand, in the conventional 0BIC image capture device, the light source is fixedly arranged and the sample stage is driven two-dimensionally to perform beam scanning, so a mechanical scanning device that can position with high precision is required, and the structure of the device is It also had the disadvantage of complicating the process. Furthermore,
In order to identify the location of the defective part that appears on the 0BIC image, it is necessary to take an external image with a TV camera, which makes the structure of the device even more complicated, and it is difficult to accurately match the 0BIC image and the external image taken with the TV camera. There were also drawbacks to not doing so.

Furthermore, acousto-optic elements are widely used as a means for main-scanning a light beam. However, it is difficult to manufacture an acousto-optic element with linear scanning characteristics, and many acousto-optic elements have nonlinear scanning characteristics. When a light beam is vibrated using an acousto-optic element having such nonlinear characteristics, the above-mentioned imaging device can reproduce a clear image without image distortion. Image distortion occurs depending on the scanning characteristics, and the optical image and 0B
This results in the inconvenience that the IC image is not accurately matched.

Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks, to be able to display both an optical image and an 0BIC image by scanning the same light beam, and to be able to display an optical image even if an acousto-optic element has a nonlinear scanning characteristic. The object of the present invention is to provide an imaging device that can accurately match the 0BIC image and the 0BIC image on a monitor.

(Means for Solving the Problems) An imaging device according to the present invention includes a light source that emits at least one light beam, and a first deflection unit that deflects the light beam emitted from the light source in the main scanning direction. , a second deflection means for deflecting the light beam in a sub-scanning direction perpendicular to the scanning direction by the first deflection means, and a light beam deflected by the first and second deflection means is focused on a minute spot and scanned. an objective lens for projecting onto a sample located on a surface; means for detecting a light beam induced current generated in the sample by irradiation with the light beam; and a plurality of light receiving elements arranged one-dimensionally in a direction corresponding to the main scanning direction. a linear image sensor that receives reflected light or transmitted light from a sample via the second deflection means or a deflection means that operates in synchronization with the second deflection means; a photoelectric output signal from the linear image sensor and the light beam; The apparatus is characterized in that it comprises an image reproducing means for receiving a signal output from the induced current detecting means and reproducing an optical image and a light beam induced current image of the sample which correspond to each other in position.

(Function) The light beam emitted from the light source is deflected in the X and Y directions by the first deflection means that deflects it in the main scanning direction and the second deflection means that deflects it in the sub-scanning direction, thereby producing a photovoltaic effect. Project it toward the sample. 0BI on the sample by light beam irradiation
C current is induced, this 0BIC current is detected by the 0BIC current detection means, and this output signal is supplied to the image signal input terminal of the monitor device. At the same time, a linear image sensor receives reflected or transmitted light from the sample line by line.
This photoelectric output signal is supplied to another image signal input terminal of the monitor. Then, each synchronization signal generated by the synchronization signal generation circuit is supplied to the first and second deflection means, the linear image sensor, and the monitor, respectively, to drive these means and devices in synchronization, respectively. As a result, the optical image of the sample and the 0BIC image can be displayed in a superimposed manner on the monitor.

Furthermore, when an acousto-optic element is used as the first deflection means for main scanning, means for correcting the nonlinear scanning characteristics of the acousto-optic element is provided. This correction method displays a 0BIC image without image distortion on the monitor by correcting the deflection signal for driving the acousto-optic element or the output signal from the 0BIC signal detection means in accordance with the nonlinear amount of the acousto-optic element. Therefore, the optical image and the OBIC image can be accurately displayed on the screen.

(Example) FIG. 1 is a diagram showing the configuration of an example of an imaging device according to the present invention. A light beam emitted from a laser light source 1 is made into an expanded light beam by an expander 2, made into a parallel light beam by a collimator lens 3, and then made incident on an acousto-optic element 4, which is a first deflection element.

This acousto-optic element 4 vibrates a 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) at a scanning frequency f+. The light beam deflected by the acousto-optic element 4 is expanded in one direction by the cylindrical lens 5 to form a circular light beam, and enters the condenser lens 6 . The light beam condensed by the condenser lens 6 passes through a half mirror 7 that acts as a beam splitter and enters a galvano mirror 8. This galvanometer mirror
8 is connected to a drive device 9 to deflect the light beam in the Y direction perpendicular to the X direction of the sample. The light beam reflected by the galvanometer mirror 8 is focused into a minute spot by an objective lens 10 and is incident on a sample 11 .

As a result, the sample 11 is scanned by the minute spot-shaped light beam in the X and Y directions at a predetermined scanning frequency. In this example, the sample 11 is an integrated circuit in which various electronic devices are formed on a semiconductor substrate.

When a light beam is incident on this semiconductor substrate, a light beam-induced current is generated due to the photovoltaic effect of the semiconductor material. Therefore, if an external circuit is formed by connecting lead wires to the lead terminals in each region of the semiconductor substrate, the external circuit can generate 0BI.
C current can be detected. That is, for example, if the substrate and the base region are connected and a light beam is projected onto the base region, the base current can be detected, and if the base region and the emitter region are connected and a light beam is projected onto the emitter region, the base-emitter current can be detected. can be detected. Then, the detected current is amplified by the amplifier 12 and inputted to the red terminal of the monitor 13 as an image signal. Note that various methods are known for forming this induced current, and an appropriate method can be adopted depending on the type of semiconductor material to be inspected, inspection items, etc.

On the other hand, the light beam reflected by the sample 11 returns to the objective lens 1.
The light is focused by 0, passes through the galvanometer mirror 8, is reflected by the half mirror 7, and enters the linear image sensor 14 in a state where it is focused into a minute spot.

This linear image sensor 14 is placed at the imaging position of the objective lens 10, and each element is arranged one-dimensionally in a direction corresponding to the X direction of the sample so as to receive the reflected light from the sample 11 line by line in the main scanning direction. The reflected light from the sample 11 is sequentially received by each element to perform photoelectric conversion, and the charges accumulated in each element are sequentially read out at a constant successive frequency. Since this linear image sensor 14 has a charge storage ability, there is always a 1=1 relationship between the pixels of the sample 11 and each light receiving element constituting the near image sensor 14, and the acousto-optic element 4 is used to control the main scanning direction. Even if the scanning speed becomes uneven, the amount of received light changes only slightly and image distortion does not occur.

Next, an image display method will be explained. A synchronization signal generation circuit 20 that generates a horizontal synchronization signal and a vertical synchronization signal is provided,
A horizontal synchronizing signal is supplied to the variable deflection circuit 21. The variable deflection circuit 21 creates a deflection signal based on the supplied horizontal synchronizing signal, and supplies this deflection signal to the AO drive circuit 22. The AO drive circuit 22 creates a drive signal for driving the acousto-optic element 4 based on the deflection signal, supplies this drive signal to the acousto-optic element 4, and drives the acousto-optic element at a predetermined scanning frequency. Also, C from the synchronization signal generation circuit 20
A horizontal synchronizing signal is supplied to the CD drive circuit 23 to create a drive signal for sequentially reading out the charges accumulated in each element of the linear image sensor 14, and the charge accumulated in each element is controlled by this drive signal. The generated charges are sequentially read out, and this photoelectric output signal is amplified by an amplifier 24 and supplied to the green terminal of the monitor 13 as an image signal. Further, a vertical synchronizing signal is supplied from the synchronizing signal generating circuit 20 to the driving circuit 25 to create a driving signal for the galvano mirror, and this driving signal is supplied to the driving device 9 to drive the galvano mirror 8 at a predetermined frequency.

Furthermore, a horizontal synchronization signal and a vertical synchronization signal are supplied to the monitor 13, and an OATC image signal and an image signal supplied from the linear image sensor are supplied to the monitor 13 for image display. With this configuration, the optical image of the semiconductor substrate is displayed in green and the 0BIC image is displayed in red on the monitor 13, so that the optical image and the 0BIC image are displayed superimposed on the same screen in a color-coded state. Ru.

On the other hand, the acousto-optic element 4 that performs main scanning with a light beam has a problem in that it is difficult to obtain linear characteristics due to manufacturing.

That is, for example, as shown in FIG. 2, there is a characteristic in which the scanning speed gradually becomes slower or faster as scanning progresses. If the scanning speed fluctuates in this way, image distortion will occur in the 0BIC image. On the other hand, since the linear image sensor always reads out the charges accumulated in each element at a constant speed, the optical image is not generated without image distortion, resulting in the problem that the 0BIC image does not correspond accurately to the optical image. It ends up.

This problem will be explained using FIG. 3. When an acousto-optic element having the scanning characteristics shown in FIG. 2 is driven by supplying a normal deflection signal shown in FIG. 3, the scanning position on the sample becomes as shown in FIG. 3C.

On the other hand, the position on the sample of the device signal constituted by the linear image sensor is shown in FIG. 3d. As a result, 0BI
A positional error shown in FIG. 3e occurs between the C image and the optical image. In order to eliminate the image mismatch between the optical image and the 0BIC image due to such fluctuations in the scanning speed of the acousto-optic element, this example provides means for correcting the image distortion of the 0BIC image. In this example, correction is added to the deflection signal for driving the acousto-optic element 4 to transform the 0BIC image into an optical image. That is, when the acousto-optic element 4 has the characteristics shown in FIG. to drive. As a result, the scanning position of the light beam on the sample becomes as shown in FIG. 4C, which coincides with the scanning position of the output signal from the linear image sensor 14.

FIG. 5 shows an example of a variable deflection circuit. A synchronizing signal is supplied to a function generator 30 , and the function generator 30 creates a function for correcting scanning speed fluctuations of the acousto-optic element 4 and supplies it to a voltage-controlled oscillator 31 . On the other hand, a reference deflection signal is supplied from the other input terminal of this voltage controlled oscillator, and the deflection signal shown in FIG. 4 is output based on the correction signal supplied from the function generator 3o. With this configuration, it is possible to create a deflection signal according to the characteristics of the acousto-optic element with a simple configuration.

FIG. 6 is a diagram showing the configuration of a modified example of the imaging bag/place according to the present invention. The same members as those used in FIG. 1 will be described with the same reference numerals. In this example, a deflection circuit 4o that generates a normal deflection signal shown in FIG.
1, and this variable timing circuit 41 corrects the image signal to make the 0BIC image match the optical image.

FIG. 7 shows the configuration of an example of the variable timing circuit 41,
FIG. 8 diagrammatically shows the operation. Upon arrival of the synchronization signal, a deflection signal shown in FIG. 8 is supplied to the acousto-optic element 4 via the AO drive circuit. At this time, a distorted image signal as shown in FIG. 8C is input to the shift register 5o.

On the other hand, the linear image sensor 14 outputs an undistorted image signal as shown in FIG. 8d.

Therefore, the function generator 51 generates a signal having an inverse characteristic corresponding to the amount of distortion of the 0BIC image signal with respect to the image signal from the linear image sensor 14 shown in FIG. The write signal shown in FIG. 8e is created by supplying the write signal. Then, under the control of this write signal, a 0BIC image signal is written into the shift register 50,
The written signal is supplied to the readout monitor 13 at a constant speed as shown in FIG. 8f. As a result, the variable timing circuit 41 outputs the signal shown in FIG.

The present invention is not limited to the embodiments described above, and various modifications are possible. For example, in the above embodiment, an example was explained in which an image of an integrated circuit fabricated on a semiconductor substrate was taken as a sample.
It can be used as

Furthermore, in the embodiment described above, the optical image and the 0BIC image are superimposed and displayed on the same screen, but the optical image and the 0BIC image are superimposed and displayed on the same screen.
Each BIC image can also be displayed and used individually.

Furthermore, in the embodiment described above, a color monitor device is used, and 0
The BIC image signal and the image signal from the linear image sensor are supplied to separate color terminals, and the image is displayed in different colors. For example, if the 0BIC image and the optical image are displayed with different brightnesses, a monochrome image can be displayed. A monitor can also be used.

Furthermore, a color optical image is created using three light sources of R, G, and B, and on the other hand, the output signal from the photoinduced current detection means is superimposed on each color image signal to add white to the color optical image. 0B
It is also possible to superimpose and reproduce an IC image.

Further, in the above-described embodiment, the configuration is such that the reflected optical image is reproduced by receiving the reflected light from the sample, but it is also possible to receive the transmitted light from the sample and reproduce the transmitted image.

(Effects of the Invention) As explained above, according to the present invention, the light beam emitted from the light source is deflected in the main scanning direction and the sub-scanning direction perpendicular to the main scanning direction, and the sample is scanned two-dimensionally by the deflected light beam. Since it has a scanning configuration, it is possible to form an optical image using reflected light or transmitted light from the sample, and at the same time, it is possible to form an optical image using the reflected light or transmitted light from the sample.
The BIC current can be detected and an 0BIC image can be formed simultaneously. As a result, both the optical image and the OBIC image of the sample can be displayed on the monitor using one imaging device.

Furthermore, since both the optical image and the 0BIC image are created using the same light beam, the optical image and the 0BIC image can be made to correspond accurately on the monitor.

Furthermore, the light flux from the sample is received by a linear image sensor, and the charges accumulated in each element are sequentially read out at a constant reading speed to create an image signal of an optical image. Since a means for correcting image distortion of an image is provided, an optical image and an OBIC image without image distortion can be created. As a result, even if the acousto-optic element has nonlinear characteristics, the 0BIC image and the optical image can be made to correspond to each other in position.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration of an example of the imaging device according to the present invention, Fig. 2 is a graph showing the characteristics of the acousto-optic element, and Fig. 3 is a diagram for explaining the image discrepancy between the optical image and the 0BIC image. 4 is a diagram for explaining the correction action, FIG. 5 is a circuit diagram showing the configuration of an example of a variable deflection circuit, and FIG. 6 is a diagram showing the configuration of a modified example of the imaging device of the present invention. FIG. 7 is a circuit diagram showing the configuration of an example of the variable timing circuit, and FIG. 8 is a diagram for explaining the correction action. 1... Laser light source 4... Acousto-optic element 8
... Galvanometer mirror 10 ... Objective lens 11 ...
Sample 13...Monitor 14...Linear image sensor 20...Synchronization circuit 21...Variable deflection circuit 40...Deflection circuit 41...Variable timing circuit Patent Applicant Lasertic Co., Ltd. Agent Patent Attorney Akira Sugimura Tsuba Patent Attorney Oki Sugimura
Figure 5 Figure 7

Claims (1)

[Claims] 1. A light source that emits at least one light beam, a first deflection means that deflects the light beam emitted from the light source in the main scanning direction, and a first deflection means that deflects the light beam. a second deflection means for deflecting in a sub-scanning direction perpendicular to the scanning direction; and an objective for converging the light beams deflected by the first and second deflection means into a minute spot and projecting the light beams onto a sample located on the scanning plane. It includes a lens, a means for detecting a light beam-induced current generated in the sample by irradiation with the light beam, and a plurality of light receiving elements arranged one-dimensionally in a direction corresponding to the main scanning direction, and detects light reflected from the sample. Or transmit the transmitted light to the second
A linear image sensor that receives light through a deflection means or a deflection means that operates in synchronization with the deflection means, and a linear image sensor that receives a photoelectric output signal from the linear image sensor and an output signal from the light beam induced current detection means to determine the relative position of the sample. An imaging device comprising an image reproducing means for reproducing an optical image and a light beam induced current image corresponding to the above. 2. Means for correcting the scanning speed of the first deflection means is provided so that the optical image of the sample and the light beam induced current image correspond to each other in position. The imaging device described in Section 1. 3. Means for correcting the output signal from the light beam induced current detection means is provided, and the optical image of the sample and the light beam induced current image are configured to correspond to each other in position. The imaging device according to scope 1.