JP2003004653A - Automatic ccd camera changeover system in scanning electron microscope with laser defect detecting function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the efficiency of an operation by constructing a system whose operation is not stopped frequently due to the operation of a safety device, by receiving strong scattered light from a comparatively large foreign substance or the like when a high-sensitivity CCD camera is operated in a scanning electron microscope equipped with the high-sensitivity CCD camera which performs a laser defect detection. SOLUTION: The automatic CCD camera changeover system in the scanning electron microscope equipped with a laser defect detecting function is used in the scanning electron microscope for wafer surface observation. The system is equipped with a laser optical system by which the position of a defect is irradiated with a laser from the oblique upper part, and an optical microscope which observes scattered light from the defect. The high-sensitivity CCD camera and a standard-type CCD camera are attached to the optical microscope, its optical axis is positioned on the basis of preliminarily measured defect position information, and the defect is observed by the standard CCD camera at the optical microscope. The standard CCD camera is changed over to the high-sensitivity CCD camera when the defect cannot be observed with the standard CCD camera and the defect is observed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching system between a standard CCD camera and a high-sensitivity CCD camera of an optical microscope provided in a scanning electron microscope used for controlling yield in a semiconductor manufacturing process.

[0002]

2. Description of the Related Art It is said that the main cause of defective products in the recent manufacture of ultra-highly integrated LSIs is minute foreign substances attached to a wafer. That is, the minute foreign matter becomes a contaminant and causes a disconnection or short circuit of the circuit pattern.
This has led to a decrease in reliability. With the miniaturization of circuit patterns, even minute foreign particles with a diameter of 0.1 μm are targeted. Therefore, it is the most important issue to improve the yield in the manufacture of ultra-high-integrated LSIs in order to quantitatively and accurately measure and analyze the actual condition such as the adhered state of minute foreign substances, to grasp and manage it.

At present, as a method for quantitatively and accurately measuring and analyzing the actual state of the adhered state of such minute foreign matter, FIG.
The particle inspection device as shown in FIG.
This apparatus uses a scanning electron microscope image, a high-sensitivity dark-field image obtained through the high-sensitivity CCD camera 4, and a dark-field image or bright-field image obtained by the CCD camera 5 as a CRT.
9 is a device that can be displayed. The scanning electron microscope 1 includes a lens barrel portion 11 and a secondary electron detector (SED) 12,
The secondary electrons that are deflected and scanned by the deflection means of the lens barrel 11 and emitted by the electron beam irradiated on the sample 6 are S
It is detected by the ED 12, and the detected information is imaged in correspondence with the beam irradiation position to obtain a scanning electron microscope image. The bright field image of illuminates the light spot from the light 8 onto the sample surface from above through the optical path, and is uniformly reflected when the sample surface is a mirror surface, and when there is a foreign substance, the light is emitted there. This is an image obtained by photographing the sample surface from above with the CCD camera 5 based on the scattering. The dark field image of the sample is based on the fact that the beam from the laser light source 7 is radiated onto the sample surface from diagonally above, and the sample surface is totally reflected when the sample surface is a mirror surface and the light is scattered there when there is a foreign matter. It is an image obtained by photographing the surface from above with a CCD camera 5. The high-sensitivity proposed field image is basically the same as the dark-field image, but is an image obtained through the high-sensitivity CCD camera 4 for observing smaller particles. Since the target is ultra-fine particles, the scattered light is weak, so a highly sensitive CCD
A (ICCD) camera is used.

In the conventional defect detection using this device, first, the presence of foreign matter is detected by a low-magnification bright-field image or dark-field image, and the number and distribution of the foreign matter are grasped. When obtaining a bright field image, the control box 11 is operated via the computer 10 to turn on the light 8 to illuminate a spot on the sample surface from above, and the CCD camera 5 captures a microscope image.
When capturing a dark field image, the control box 11 is operated via the computer 10 to cause the laser light source to emit light, irradiate the laser beam onto the sample surface from diagonally above, and the CCD camera 5 captures a microscope image. With respect to the foreign substances whose existence was confirmed by the initial inspection, the high-sensitivity CCD camera 4 showed a high-magnification dark-field image or a scanning electron microscope image to detect the foreign substances including fine foreign particles that could not be observed in the first inspection. The shape and size are observed and evaluated. The fine foreign particles can be observed at a high magnification after being located at a low magnification. Fine positional information that cannot be treated as positional information of the sample stage can also be treated as information on screen coordinates. Further, the composition of foreign particles of interest cannot be analyzed from a high-magnification optical image or a scanning electron microscope image of secondary electron detection, but this cannot be analyzed by secondary X-ray detection (ED
S) It can be analyzed by using an electron microscope having a function. By the way, when observing the laser scattered light with an optical microscope, the amount of the laser scattered light greatly differs depending on the size of the defect. This scattered light is imaged by a CCD camera, but a high-sensitivity CCD (Imag is set to have a high detection sensitivity in order to observe weak scattered light due to minute particles or the like.
The e intensifier CCD (ICCD) is designed to stop the operation by receiving a high scattered light from a relatively large foreign substance or the like, or by operating a safety device for high voltage protection when the stage is moved. Therefore, there is a problem that the work is interrupted each time and the work efficiency is deteriorated.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, namely, in a scanning electron microscope equipped with a high-sensitivity CCD camera for detecting a laser defect, a high-sensitivity CCD is used.
Improve the work efficiency by constructing a system that does not frequently stop the operation of the safety device by receiving strong scattered light from a relatively large foreign object when operating the camera. Especially.

[0006]

A CCD camera automatic switching system in a scanning electron microscope having a laser defect detection function according to the present invention is a laser optical system for irradiating a defect position with a laser obliquely from above and a scattered light from the defect. In a scanning electron microscope for observing wafer surfaces equipped with an optical microscope for observing, the high-sensitivity and standard-type CCD cameras are attached to the optical microscope, and the optical axis is positioned based on the defect position information measured in advance. A method of observing a defect with a standard CCD camera of a microscope and a step of observing the defect by switching to a high sensitivity CCD camera when the standard CCD camera could not observe the defect was adopted.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Scanning electron microscopes are used to detect and inspect minute foreign substances present on a flat sample surface such as a silicon wafer by using a scanning electron microscope equipped with a laser defect detection function. Prior to the above observation, when observing a dark field image of a minute foreign substance by laser irradiation with a high-sensitivity CCD camera and attempting to identify its position, the safety device is activated and the operation is immediately stopped, and the work is interrupted. The reason for this is that in the case of a high-sensitivity CCD camera, as described above, the detection sensitivity is set high, so that when strong light from a relatively large foreign object is received, the output signal becomes a high voltage, so the safety of high-voltage circuit protection is high. Due to the operation of the device. Therefore, the present invention provides the high-sensitivity CCD only when the diffuse reflection light is not received by the observation with the standard CCD camera in advance.
The idea is to make the camera work.
That is, even if the defect size is large, the high sensitivity CCD camera is operated after confirming that there is no relatively large foreign matter by observation with a standard CCD camera in which the output signal does not become high voltage. The output of the high-sensitivity CCD camera never becomes high voltage. Therefore, even if the high sensitivity CCD camera is used, the work is not interrupted and the work efficiency can be improved.

The operation of the CCD camera switching system in the scanning electron microscope having the laser defect detecting function of the present invention will be described with reference to FIG. First, (S
T1) The relative positional relationship between the optical axis of the optical microscope in the scanning electron microscope to be used and the electron optical axis of the scanning electron microscope is stored. (ST2) Subsequently, defect position information measured by another inspection device is stored. The above is the preparatory work. (ST3) An inspected sample such as a wafer is placed on the sample stage to prepare the environment in the chamber. In addition,
The above steps may be interchanged in order. (ST
4) Based on the previously stored defect position information, the drive mechanism of the sample stage (generally the x and y axis drive mechanism) is drive-controlled to position the defect of interest at the optical axis position of the optical microscope.
(ST5) First, a defect image is observed with a standard CCD camera. (ST6) It is determined whether or not a defect image can be seen in the observation image of the standard CCD camera. (ST7) When the defect image can be observed, the defect position information with respect to the reference position of the device is measured and stored on the image. (ST8) When the defect image cannot be observed, the defect is observed with the high sensitivity CCD camera. (ST9) Then, the defect position information with respect to the reference position of the apparatus is measured and stored on the observed image. (ST10)
Based on the position information measured in step 7 or 9, the drive mechanism (generally the x and y axis drive mechanism) of the sample stage is drive-controlled to position the defect of interest at the optical axis position of the scanning electron microscope. (ST11) Observation with a scanning electron microscope
Perform analysis. (ST12) Observation of all defects
When the analysis is not completed, the process is returned to step 4 and the work is repeated. When the observation / analysis is completed for all the defects, the series of work is completed.

[0009]

Further, the present invention realizes a system for automatically executing the above-mentioned CCD camera automatic switching method in micro defect inspection performed using a scanning electron microscope having a laser defect detection function, and also recognizes defects. Provide an automated system. As shown in FIG. 1, the system of the present invention is for observing a wafer surface including a laser optical system for irradiating a defect position with a laser beam from a laser light source 7 obliquely from above and an optical microscope 3 for observing scattered light from the defect. In the scanning electron microscope, the optical microscope 3 is provided with a high sensitivity CCD camera 4 and a standard type CCD camera 5, and the optical axis of the optical microscope is positioned based on defect position information measured in advance by another inspection device. It was equipped with the means to do. This means outputs a control signal to the x, y drive mechanism of the sample stage to operate the x, y drive mechanism of the sample stage based on the defect position information stored in the storage device as a function of the computer 10 to perform optical operation. The microscope 3 is positioned so that the defect of interest comes to the optical axis position of the microscope 3. In this state, the computer 10 is the standard CCD of the optical microscope.
Operate the camera to perform defect observation. The standard CCD camera that receives this starts operation and images the sample surface, but this image signal is transmitted to the computer 10, and C
It is transmitted to a display 9 such as RT and displayed as an image. Although it is possible to manually detect the presence or absence of laser scattered light from the defective portion on the display screen, it is preferable in the present invention that the computer 10 has a luminance signal above a threshold value in the image information from the standard CCD camera. Provide a function to detect By providing this function as the system, it is possible to automatically determine whether or not there is defect information in the image.

If a defect signal is recognized in the above step, the defect position is measured as position information with respect to the reference point of the system, and the position information is stored in the storage device of the computer 10. Subsequently, the defect is observed by the scanning electron microscope 1. However, since the optical axis of the optical microscope 3 and the optical axis of the electron microscope 1 are separated from each other by several tens of millimeters in position, the recognized defect of interest is detected as an electron. In order to observe with the microscope 1, the sample stage must be moved by that distance. The relative positional relationship between the two optical systems is a fixed value that is uniquely determined when the device is assembled, but this information is stored in the storage device of the computer 10 in advance. The position information with respect to the reference point of this system is measured and stored by the observation with the optical microscope, so that the control signal to be moved to the x, y drive mechanism of the sample stage is output from the stored information and the sample stage is output. The x and y drive mechanisms are operated to position the scanning electron microscope 1 so that the defect of interest comes to the electron optical axis position.

When there is no defect information in the image information from the standard CCD camera 5, the standard CCD camera 5 is stopped by a command from the computer 10, and the high sensitivity CCD camera 4 is operated instead. Then, the defect is observed by the high-sensitivity CCD camera 4, and the laser scattered light in this region has a low light quantity level.
In other words, since it has been confirmed that there are no major defects,
The dark-field image output signal from the high-sensitivity CCD camera 4 whose detection sensitivity is set high does not become high voltage. This image information is transmitted to the computer 10 and further transmitted to the display 9 for image display. From this observed image, the positional information with respect to the reference point of this system is measured and stored as in the above case. Further, since the relative position information of the optical axis of the optical microscope 3 and the optical axis of the electron microscope 1 is stored in the storage device, control to move to the x, y drive mechanism of the sample stage from these stored information. The operation of outputting a signal to operate the x, y drive mechanism of the sample stage to position the scanning electron microscope 1 so that the defect of interest comes to the electron optical axis position of the scanning electron microscope 1 is similar to the above case.

[0012]

The CCD camera automatic switching method in the scanning electron microscope having the laser defect detecting function of the present invention is as follows:
In the scanning electron microscope for observing the wafer surface, which is equipped with a laser optical system that irradiates a defect position with a laser obliquely from above and an optical microscope that observes scattered light from the defect, a high sensitivity and standard type CCD camera is used for the optical microscope. Mounting and positioning the optical axis based on previously measured defect position information to observe defects with a standard CCD camera of the optical microscope; and high sensitivity CCD when the defect observation cannot be observed with the standard CCD camera. Since the camera is switched to the step of observing defects, the output signal becomes high voltage when switching to the high-sensitivity CCD camera, and the work is not interrupted by operating the circuit protection layer device. ,
This type of inspection / analysis work can be made more efficient.

Further, the CCD camera automatic switching system in the scanning electron microscope having the laser defect detecting function of the present invention is a laser optical system for irradiating the defect position with a laser obliquely from above and an optical system for observing scattered light from the defect. A scanning electron microscope for observing a wafer surface equipped with a microscope, wherein the optical microscope is equipped with a high sensitivity CCD camera and a standard type CCD camera, and the optical axis of the optical microscope is positioned based on previously measured defect position information. Means and standard CC of optical microscope
A means for observing defects by operating the D camera, and the standard C
It is composed of means for detecting the presence or absence of defect information in the image information of the CD camera, and means for observing the defect by operating the high sensitivity CCD camera when the defect information cannot be detected by the detecting means. , CCD cameras can be automatically switched, and whether or not there is defect information in image information of a standard CCD camera is detected by detecting the presence or absence of a luminance signal above a threshold value in the image information. By providing the means, the workability and the time reduction can be promoted, and the efficiency can be further improved. Moreover, the system configuration does not require any special hardware to be added to the conventional device, and can be realized simply by providing software.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of a scanning electron microscope system having a laser defect detection function that realizes an autofocus system of the present invention.

FIG. 2 is a flow chart showing the operation of the present invention.

[Explanation of symbols]

1 Scanning Electron Microscope 7 Laser Light Source 11 Lens Barrel 8 Light 12 Secondary Electron Detector 9 CRT 3 Optical Microscope 10 Computer 4 High Sensitivity CCD Camera 15 Control Box 5 CCD Camera 6 Sample

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Claims (3)

[Claims] 1. A scanning electron microscope for observing a wafer surface, comprising a laser optical system for irradiating a defect position with a laser obliquely from above and an optical microscope for observing scattered light from the defect. Type CCD camera is attached, the optical axis is positioned based on the defect position information measured in advance, and the defect observation is performed by the standard CCD camera of the optical microscope; and when the defect observation cannot be observed by the standard CCD camera. Is a CCD in a scanning electron microscope having a laser defect detection function, characterized by switching to a high-sensitivity CCD camera and performing a step of observing defects.
Automatic camera switching method. 2. A scanning electron microscope for observing a wafer surface, comprising a laser optical system for irradiating a defect position with a laser obliquely from above and an optical microscope for observing scattered light from the defect, wherein the optical microscope has a high CCD for sensitivity and standard type
A means for positioning the optical axis of the optical microscope based on the defect position information measured in advance, and a means for observing the defect by operating a standard CCD camera of the optical microscope;
Laser defect comprising means for detecting the presence or absence of defect information in the image information of the standard CCD camera, and means for observing the defect by operating the high sensitivity CCD camera when the defect information cannot be detected by the detecting means. Automatic CCD camera switching system for scanning electron microscopes with detection function. 3. The means for detecting the presence / absence of defect information in the image information of the standard CCD camera is for detecting the presence / absence of a luminance signal above a threshold value in the image information of the standard CCD camera. Automatic CCD camera switching system for scanning electron microscopes.