JPH11250847A - Focusing charged particle beam device and inspection method using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always observe and work and object in the focused state by optically detecting the height in the optical axis direction of sample, adjusting the height of the sample, detecting secondary charged particles generating by scanning electron beams, and inspecting a secondary charged particle image. SOLUTION: Electron beams from an electron gun are focused with an object lens 2, then used to scan the surface of a sample. Secondary electrons generated on the surface of a sample wager 3 by irradiation of electron beams are detected with a secondary electron detector 5, and inputted as an image signal in an image input part 6. An optical height detector 11 detects the sample surface height without contacting the sample, and inputs detected results into a control computer 10. The control computer 10 varies the focal point position of an electronic optical system or a Z stage according to the sample surface height, and inputs an image signal. The image signal inputted is compared with a previously memorized non-defective pattern based on inspection position information detected with a position measuring part to judge a defect.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focused charged particle beam apparatus having a processing or observation function using charged particle beams such as electrons and ions, and an inspection method using the same. Related to methods and devices.

[0002]

2. Description of the Related Art As an apparatus using a charged particle beam, an automatic inspection system for inspecting and measuring a fine circuit pattern formed on a semiconductor wafer or the like will be described as an example. Defect inspection of fine circuit patterns formed on semiconductor wafers and the like is performed by comparing the pattern to be inspected with non-defective patterns and the same kind of pattern on the wafer to be inspected, and many apparatuses using optical microscope images have been put into practical use. ing. Similarly, when an electron microscope image is used, a defect inspection is performed by comparing pattern images. Also, in a length measuring device using a scanning electron microscope that measures the line width and hole diameter of a fine circuit pattern used for setting the manufacturing process conditions of a semiconductor device and for monitoring, etc., the length measurement is automated by image processing. Have been done.

[0003] As described above, when a comparative inspection for detecting a defect by comparing electron beam images of similar patterns or when a line width of a pattern is measured by processing an electron beam image, the obtained electron beam is used. The quality of the line image has a great influence on the reliability of the test results. The quality of the electron beam image is degraded due to image distortion caused by deflection or aberration of the electron optical system, or a decrease in resolution due to defocus. These deteriorations in image quality degrade the performance of comparative inspection and length measurement.

When the inspection is performed under the same conditions over the entire range when the height of the sample surface is not constant, the electron beam image changes depending on the inspection location as shown in FIG. If the inspection is performed by comparing the focused image a with the defocused images b and c, correct results cannot be obtained. Further, in these images, the width of the pattern changes and the result of edge detection of the image cannot be obtained stably, so that the line width and hole diameter of the pattern cannot be measured stably. Conventionally, electron microscope focusing has been performed by adjusting the control current of the objective lens while observing the electron beam image, but in addition to requiring a lot of time, the electron beam scans the sample surface many times. However, damage to the sample may also be a problem.

To solve such a problem, Japanese Patent Laid-Open Publication No.
In 5-258703, the control current of the objective lens optimal for the sample surface height is measured in advance at several points in the sample before the start of the inspection, and these data are interpolated during the inspection to adjust the focus of each point. Although the method is disclosed, it takes a lot of time to measure the optimal control current before the inspection, and the height of the sample surface may change during the inspection depending on the method of holding the wafer. is there.

Japanese Patent Application Laid-Open No. 63-254649 discloses a method for focusing a scanning electron microscope by using an optical height detecting means, but the optical system for detecting the height is vacuum. There is a problem that it is arranged in the apparatus and it is difficult to adjust its optical axis and the like.

Further, in the case of a processing apparatus using a convergent charged particle beam, focusing of the charged particle beam affects processing accuracy, and is a very important problem as in the case of an observation apparatus. Examples of the processing apparatus include an electron beam type semiconductor pattern exposure apparatus and an FIB circuit correction apparatus.

[0008]

In a scanning electron microscope, a method of measuring an optimum control current using an electron beam image requires a number of electron beam images to detect a focus position. The time required for focusing becomes long, and it is not suitable for short-time focusing. In addition, when performing inspection and length measurement automatically over a wide range, it is difficult to perform focusing at all points using such a method. It is necessary to devise a method such as estimating the height of the building. As an example, FIG. 1 shows an outline of an electron beam automatic inspection system for a semiconductor device to which the present invention is applied. In such an automatic inspection system,
A sample wafer, which is an object to be inspected, is moved by a stage with respect to the electron optical system to realize a wide range of inspection.

A semiconductor wafer as an object to be inspected in the middle of a manufacturing process is deformed due to a heat treatment or the like, and the amount of the deformation is a maximum of several hundred μm. However, it is very difficult to stably hold a sample in a vacuum sample chamber by a method that does not interfere with the electron optical system, and it is not possible to obtain the flatness by a vacuum chuck as in an optical inspection apparatus.

[0010] In addition, since the inspection is performed for a long time, the holding state of the sample is likely to change due to the principle of reciprocation of the stage, and the sample surface height may change from the previously measured state. .

For this reason, the height of the sample surface under inspection exceeds the depth of focus of the electron optical system (several μm at a magnification of 10,000, but the depth of focus required at the time of inspection depends on the inspection performance). Likely to change unstable. In the adjustment using electron beam images, it is necessary to acquire multiple electron beam images at each point with the stage stopped, and to adjust the focus continuously while detecting the height while moving the stage during inspection. It is impossible to do.

In the case where the focus adjustment using such an electron beam image is carried out in advance at several points on the sample surface before the start of the inspection, a lot of time is required for the calibration before the start of the inspection. With the increase in the diameter of, the decrease in throughput becomes a serious problem. Further, as the diameter increases, it is considered that the deformation of the wafer such as warpage increases, and the demand for the automatic focus becomes more severe. In addition, depending on the material of the sample, the state of charge on the surface changes when the electron beam is applied, which affects an electron beam image used for inspection.

For these reasons, it is difficult for the conventional method to secure sufficient performance in a long-term inspection by SEM. When it is difficult to hold the sample stably, it is desirable to detect the surface height of the observation range by the electron optical system immediately before acquiring an image during inspection. When the inspection is performed while the stage is continuously moved, it is necessary to detect the sample surface height continuously and at a high speed without obstructing the flow of the inspection. As described above, in order to continuously detect the height at the same time as the inspection, it is necessary to rapidly detect the height at or near the inspection position.

However, if an object such as an insulator or a magnetic material that changes the electric field or magnetic field in the vicinity is arranged in the vicinity of the observation region, the scanning of the electron beam is affected. Therefore, the sensor is arranged in the vicinity of the electron optical system. It is difficult. In addition, since the observation area is in the vacuum sample chamber, it must be possible to perform measurement in a vacuum. Also, because it is used in a vacuum sample chamber,
It is desirable that adjustment and maintenance are easy. The electron beam inspection apparatus has been described as an example, but the same applies to an observation / processing apparatus using other convergent charged particle beams such as ions. In addition, these problems are not limited to those for converging a charged particle beam to only one point, and are the same for an apparatus for imaging and projecting a shape such as an aperture or a mask. The particle beam device includes a device having these imaging type charged particle optical systems.

An object of the present invention is to provide a means for observing a charged particle optical system or detecting a height around a processing area at high speed without interference with the charged particle optical system and using the height detection result. In this way, it is possible to realize observation and processing of an object in an always focused state, and to construct a highly reliable apparatus and system.

[0016]

SUMMARY OF THE INVENTION The above-mentioned problem is caused by a height detector which does not interfere with a charged particle optical system and can detect the height of an object surface in an observation or processing area simultaneously with observation and processing. The present invention can be realized by a charged particle optical system capable of performing focus adjustment using height information and a system capable of performing processing and observation using the obtained charged particle beam image. In order to detect the height of the sample surface without interfering with the charged particle optical system, a height detector capable of detecting the height from a remote position is required. Also, in order not to affect the scanning of the charged particle beam, the method must be such that the effect on the electric and magnetic fields around the detection position does not change over time. Must be available.

In the present invention, such a height is obtained by using an optical height detection method in which light is projected obliquely to the height detection position and the height is detected using reflected light on the sample surface. Implement a detector.

That is, in the present invention, the focused charged particle beam apparatus comprises an electron beam source, an electron optical system means for converging an electron beam emitted from the electron beam source to a focal point, and a vacuum which is evacuated to a vacuum. Chamber means, and stage means inside the vacuum chamber means, on which a test object is placed and which can move in a plane,
By scanning and irradiating an electron beam focused by the electron optical system means on the inspection object mounted on the stage means, secondary charged electrons generated from the inspection object are detected, and an electron beam image of the sample surface is detected. Electron beam image observation means for observing the object, height detection means for optically detecting the height of the surface of the object to be inspected in an area irradiated by scanning the electron beam with the electron optical system means,
Control means for controlling the focus position of the electron beam by the electron optical system means and the relative position in the height direction of the object to be inspected using the result detected by the height detection means; and the focus position of the electron beam by the control means Detecting means for processing an electron beam image of a surface of a sample to be inspected observed by an electron beam image observing means in a state where a relative position in a height direction between the object and the object to be inspected is controlled and detecting a defect of the sample to be inspected And was configured.

Further, according to the present invention, an inspection method using a focused charged particle beam apparatus is described in which an object to be processed is set on a movable table inside the processing chamber, and the processing chamber in which the object is set is evacuated. The electron beam emitted from the electron beam source scans and irradiates the electron beam emitted from the electron beam source while moving the movable table inside the evacuated processing chamber. Optically detecting the height in the axial direction, adjusting the height in the optical axis direction of the inspection object based on the detected result,
Scanning and irradiating the electron beam emitted from the electron beam source while moving the movable table to the object whose height is adjusted, and scanning and irradiating the electron beam, the electron beam is generated from the object to be inspected. Secondary charged particles are detected to obtain a secondary charged current image of the surface of the inspection object, and the inspection sample is inspected based on the secondary charged current image.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As an example of an embodiment of the present invention,
An outline of an automatic inspection system using an electron beam image will be described with reference to FIG. The electron optical system shown in FIG. 1 can converge an electron beam emitted from an electron gun 1 by an objective lens 2 and scan the sample surface in an arbitrary order. A secondary electron signal 4 generated on the surface of the sample wafer 3 by irradiation with an electron beam is detected by a secondary electron detector 5 and input to an image input unit 6 as an image signal.

The wafer to be inspected can be moved by the XY stage 7 and the Z stage 8, and any position on the sample surface can be observed by the electron optical system by moving the stage. The irradiation of the electron beam and the image input synchronized with the stage movement are possible, and the movement of the stage is controlled by the control computer 10. The optical height detector 11 can detect the sample surface height near the position where the electron optical system observes at high speed without contact and without interfering with the electron optical system. The result is input to the control computer 10.

The control computer 10 changes the focal position or the Z stage of the electron optical system according to the sample surface height, and inputs an image signal. Based on the image signal input in focus and the inspection position information detected by the position measurement unit, the non-defective pattern stored in advance by the image processing unit 9 or a different place on the inspected wafer or a different wafer Defect judgment is performed by comparing with the same kind of pattern. In FIG. 1, 2
Although an example of the automatic inspection apparatus using the secondary electron image is shown, the means for observing the state of the sample surface may use an image of backscattered electrons, transmitted electrons, or the like in addition to the secondary electrons.

In the example shown in FIG. 1, a spot or slit-like light is projected on the surface of the sample, the specular reflection light is imaged, and the position of the image is detected (hereinafter, referred to as a light reflection position detection method). The height of the sample surface is detected. this is,
As shown in FIG. 3, a spot or slit-shaped light beam is applied to the sample surface from a predetermined incident angle θ to form an image on the sample surface, and the reflected light of the light beam on the sample surface is detected to detect the height of the sample surface. The change is converted into the movement amount of the light beam image, and the height of the sample surface is obtained by detecting the movement amount.

This height detecting device is not limited to the system shown in FIG. 1, but can be used in other observing and processing devices using convergent charged particle beams. In the following, the embodiment relating to the height detector will be described by taking as an example the case of an observation device using charged particle beams. However, the present invention is similarly applicable to the case of a processing device using these charged particle beams. At this time, it goes without saying that a reduction in image quality in the observation device results in a reduction in processing accuracy in the processing device. The charged particle beam device to which the present invention is applied is not limited to a device that converges a charged particle beam to only one point, but also includes a device that forms and projects a shape such as an aperture or a mask. The same effect can be obtained also in an apparatus having these imaging type charged particle optical systems. As an example of such a processing apparatus, there is an EB drawing apparatus using collective figure irradiation.

In this light reflection position detection method, the height of the observation area of the charged particle optical system is simultaneously detected without substantially interfering with the charged particle optical system because the height detection optical system does not use the position directly above the detection position. Can do things. By matching the height detection position of the height detector with the observation area of the charged particle optical system, the height of the object surface can be known during observation, and the height information is fed back to the charged particle optical system. In addition, observation can be performed using a charged particle beam that is always in focus.

The observation area by the desired charged particle optical system and the height detection position of the height detector do not necessarily have to completely coincide with each other. What is necessary is just to know the height of the surface. When the light reflection position detection method is used, the arrangement of the optical system components can be flexibly changed to some extent by the design of the optical system, and the arrangement can be made in consideration of interference with the charged particle optical system.

The arrangement of the height detector based on this light reflection position detection method is greatly restricted by the angle of incidence on the surface of the object.
In the light reflection position detection method, since the size of the incident angle affects the height detection performance, the incident angle cannot be determined only by the arrangement of components in the system. FIG. 4 shows the incident angle dependence of the surface reflectance of Si and a resist, which are typical materials used in the process of manufacturing a circuit pattern on a semiconductor wafer. The reflectivity on the sample surface increases as the incident angle increases, and the reflectivity difference between the materials decreases as the incident angle increases. This tendency is the same for other materials. The difference in reflectance between the materials results in uneven reflectance of the sample surface, which affects the distribution of the detected light amount. If a light amount distribution due to the sample surface pattern occurs in the detection slit image, a slit position detection error occurs, and the accuracy of height detection decreases.

In FIG. 3, the amount of movement of the light beam image can be detected by any means other than the position sensor shown in FIG. 3 as long as the irradiation position of the light beam can be detected by a linear image sensor or the like. In order to secure N, a sufficient amount of detected light is required. Independent of material and surface pattern,
In order to secure a stable amount of detected light, it is desirable to increase the incident angle. In addition, in this light reflection position detection method, the detection sensitivity increases in principle as the incident angle increases. By setting this incident angle to 60 degrees or more, the detected light amount is secured.

Next, an example of the embodiment relating to the arrangement of the optical components of the height detecting optical system will be described. In general, when an insulator is placed near a charged particle optical system, the charging of the insulator causes a change in the surrounding electric field, which affects the deflection of the charged particle beam and causes deterioration in image quality such as blur and distortion. .
It is difficult to correct the influence of such charging because it changes with time as the charging state changes.

In order to obtain a stable charged particle beam image, it is necessary to avoid placing an insulator such as a lens at a position facing the charged particle beam. Alternatively, the effect can be reduced by arranging a conductive film at a position sufficiently distant from the charged particle optical system, for example, by attaching a conductive film. The effects of these components such as lenses on the charged particle optical system vary depending on the specifications of the charged particle optical system, such as the field of view and the required accuracy and resolution. Such an influence can be avoided by determining a range that has an influence on the charged particle optical system based on the specification of the charged particle optical system and designing an optical path that does not require disposing components within the range.

The effect on the charged particle beam when the lens for the height detector is arranged around the charged particle optical system can be estimated by computer simulation, and the position where the lens can be arranged is determined as shown in FIG. After that, the optical system of the height detector may be designed in consideration of this. The distance between the lenses 16 and 17 facing the sample and the sample surface (imaging position) can be set to an appropriate value by selecting the focal length of the lens to be used.

In the above embodiment, the lens is disposed at a position where the charged particle optical system is not affected. However, if the distance between the lens facing the sample and the sample surface is further increased, as shown in FIG. It is also possible to take the components of the height detection optical system out of the vacuum sample chamber. A transparent window such as glass may be formed between the vacuum sample chamber 13 and the atmosphere. If the optical components of the height detection system can be arranged outside the sample chamber in this manner, adjustment and maintenance at the time of installation are easier than when the height detection optical system is arranged in a vacuum as shown in FIG. There are advantages.

As in the case of the previous embodiment, some or all of the components may be arranged outside the vacuum sample chamber depending on the form of the height detecting optical system. When part or all of the optical system is disposed outside the sample chamber as shown in FIG. 8, there is an outer wall that separates the sample chamber from the atmosphere in the middle of the optical path. Requires the entrance window to be made of a transparent material such as glass. At this time, FIG.
When the incident window is directly attached to the outer wall of the upper part of the sample chamber as shown in (2), when the incident light is projected at a high incident angle by the light reflection position detection method, the incident angle of the luminous flux to the incident window becomes large. Becomes very large.

FIG. 9 shows the incident angle dependence of the surface reflectance of a typical glass BK7 often used as an optical material. In some cases, the surface of the entrance window is treated with a conductive film or the like. Depending on the material used, the dependence on the incidence angle may vary slightly, but the tendency remains the same. Has a high reflectance on its surface, so that the loss of light quantity at the window is large.

As shown in FIG. 8, when the number of times of passing through the window increases, such as when the beam passes through the window twice at the time of incidence and after reflection on the sample surface, the loss further increases. Considering the distribution of the incident angle in the light beam (for example, in the case of NA 0.1, it is distributed in the range of ± 5.7 degrees). Must be avoided.

Therefore, as shown in FIG. 10, by arranging the entrance window 23 at an angle perpendicular to or close to the optical path of the height detecting optical system, it is possible to reduce the reflectance on the surface of the window, and to reduce the reflectance on the optical path. Can be reduced. In consideration of uneven light amount distribution in the light beam, it is desirable to arrange the windows in FIG. 9 so that the incident angle is 30 degrees or less where the reflectance hardly changes depending on the incident angle. In addition to the atmosphere and the vacuum sample chamber, if there is any member in the optical path of the height detection optical system and it is not possible to make a hole, an entrance window is also necessary. If the shape of the window does not affect the charged particle optical system, it is possible to prevent the loss of light amount by making the shape as close as possible to the optical path as much as possible.

Next, an embodiment of a method for reducing the influence of chromatic aberration due to dispersion of the refractive index of glass, which occurs when an entrance window is used, will be described. The optical path shifts when the light beam used for height detection passes through the glass window.
As shown in (2), the shift amount varies depending on the wavelength because of the dispersion of the refractive index of the glass. When the height of the sample surface is detected using white light, a height detection error occurs due to the aberration due to the color.

The shift amount of the optical path depends on the incident angle.
It is proportional to the thickness of the glass plate. As described in the previous embodiment, if the angle of incidence on the window glass can be reduced, this effect can be reduced. However, when the angle of incidence is large, it is particularly problematic (for example, when the angle of incidence is 70 degrees). , Material BK7, plate thickness 2mm
In the case of, the difference between the shift amounts of the optical paths of the wavelengths of 656.28 nm and 404.66 nm is 9 μm).

When white light is used, the effects of these chromatic aberrations change depending on the color of the object to be inspected, so that correction is difficult. Examples of the method for reducing the influence of the chromatic aberration include reducing the thickness of the glass plate of the entrance window and inserting an aberration correcting glass plate in the middle of the optical path. Since the shift amount of the optical path is proportional to the thickness of the glass plate, a glass plate having a thickness in which the influence of chromatic aberration does not matter may be used in consideration of the wavelength range to be used and a desired height detection accuracy.

The glass is not necessarily required to satisfy the required strength, and an optically transparent member such as a pellicle may be used. However, when strength is required such as an entrance window to a vacuum sample chamber, the glass plate cannot be made sufficiently thin. In such a case, a glass plate for correcting chromatic aberration may be inserted in the optical path.

As shown in FIG. 12, when the glass plate for correction is inserted in the same direction as the entrance window with respect to the imaging lens, the incident angle θ to the glass plate for correction with respect to the incident angle θ to the glass window. By disposing a correction glass plate having the same material and the same thickness as the window so as to be −θ, it is possible to cancel the difference in the shift amount of the optical path due to the wavelength.

When the lens is inserted on the opposite side of the imaging lens as shown in FIG. 13, the thickness is corrected in parallel with the entrance window using the same material as the window and in proportion to the magnification of the imaging lens. By disposing the glass plate for use, the difference in the shift amount of the optical path due to the wavelength can be similarly canceled.

In some cases, a flat plate electrode is arranged on the upper surface of the sample in parallel with the sample for the purpose of reducing the acceleration voltage of the charged particle beam irradiated on the sample. In such a case, it is necessary to make a hole or a window in the plate electrode in order to secure the optical path of the height detector. Since the shape of the plate electrode affects the electric field distribution near the sample, the shape of the window may affect the image quality of the charged particle beam image. An embodiment of a method for reducing the influence on a charged particle beam image when arranging holes or windows in such a flat electrode will be described below.

The effect on the charged particle optical system changes depending on the size and arrangement of the holes formed in the plate electrode. The extent to which the effect of the hole becomes a problem depends on the required performance of the charged particle optical system, but if the size of the hole is small, the effect may be negligible. Therefore, a method for reducing the size of the hole will be described.

When the angle of incidence on the object surface is increased, the shape of the optical path passing through a plane parallel to the object surface is changed as shown in FIG. 14 even when the NA of the optical path of the height detecting optical system is constant. growing. When the optical path crosses the middle of the plate electrode in this way, the shape of the passing hole becomes very large in the axial direction where the optical axis is projected onto the plate electrode. This is the NA of the optical system
This is particularly problematic when the distance between the flat plate and the object surface is large. The position of the plate electrode is determined by the specifications of the charged particle optical system and cannot be changed in general. Also, the NA cannot be made too small to obtain a sufficient amount of light. Therefore, a method for reducing the shape of the hole without reducing the overall light amount will be described below.

Normally, a light stop having a circular shape centered on the optical axis is used. The shape of the stop is defined by setting its major axis in the axial direction perpendicular to the optical axis and parallel to the object surface, and in the axial direction perpendicular to this axis and the optical axis. An elliptical or rectangular light stop having a short diameter is used. At this time, if the area of the ellipse or the rectangle is made the same as in the case of using the circular diaphragm, the total light amount used for height detection can be secured.

FIG. 15 shows the shape of an optical path passing over a flat plate electrode when a circular stop is used, and FIG. 16 shows a plan view of an optical path when an elliptical stop having substantially the same area as the stop of FIG. 15 is used. Is the shape of the optical path passing through. As can be seen from FIGS. 15 and 16, it can be seen that the shape of the hole on the plate electrode can be reduced. In this way, by changing the shape of the aperture as long as the performance of the height detector can be ensured, the size and shape of the hole can be changed, and the effect on the charged particle optical system can be reduced. .

If the size of the hole affects the charged particle optical system and desired performance cannot be obtained, further measures are required. Rather than simply making a hollow hole in a flat plate electrode, if a window is formed on the flat plate electrode using glass or the like with a conductive film to secure an optical path, the effect of an electric field on the periphery of an object can be reduced. . If the window is directly arranged in the hole in FIG. 14 as in FIG. 8, the loss of the light amount is large due to the reflection on the window surface as shown in the example of FIG. 8, and the uneven light amount distribution in the light beam occurs. Therefore, similarly to the example of FIG. 10, by changing the shape of the window so as to be perpendicular to the optical path or at an angle close to the optical path, it is possible to prevent loss of the light amount due to reflection on the window surface. FIG. 17 shows an example of the window shape in this case.

The holes and windows on the flat electrode in the above-mentioned example have a considerable influence on the potential distribution around the object. A method for arranging holes and windows to reduce this effect will be described below. The same is true for windows and holes,
The following description is made using windows.

In the observation or processing apparatus of the present invention,
The means for observing or processing the dimensions is usually either two-dimensional scanning by deflection of the convergent charged particle beam, or stage scanning by a combination of one-dimensional scanning by deflection of the charged particle beam and stage movement in a direction perpendicular to the direction. There are many. According to the present invention, when such a charged particle beam is scanned, a method of reducing the influence of the electric field change due to the window by arranging the windows in consideration of the deflection of the charged particle beam and the direction of the stage movement. suggest.

FIG. 18 shows an example in which windows are arranged circumferentially around the optical axis of the charged particle optical system. Since the position of the window is located away from the scanning range of the charged particle beam, if the window is arranged as shown in FIG. 18, the effect of the electric field change by the window is isotropic, and the charged particle optical system Is expected to be substantially uniform within the observation region of. Also, as shown in FIG. 19, substantially the same effect can be obtained by arranging the windows around the axis in the deflection direction and the stage movement direction.

In particular, in the case of stage scanning, by arranging the windows in parallel with the deflection direction as shown in FIG. 20, the distribution of the electric field within the deflection range can be kept constant.
If the electric field distribution is kept constant, the scanning position and the like can be corrected, and the image quality can be improved. The effects of the shapes and arrangements of these windows and holes may be examined in consideration of the specifications of the charged particle optical system, desired inspection performance, and the like, and an appropriate one may be selected.

Next, an embodiment of a method of adjusting the focus of a charged particle beam using the height detection result obtained by the height detector will be described.

The focal position of the charged particle beam is controlled by the current of the objective lens. Inputting the height of the surface of the object in the observation area of the charged particle optical system obtained by the height detector as input, and controlling the amount of current of this objective lens to perform observation with a charged particle beam image that is always in focus Can be. The control current amount of the objective lens with respect to the change in the object surface height is calibrated in advance by the charged particle optical system alone.

The offset and gain between the height detector and the charged particle optical system are also calibrated in advance. These calibration methods will be described in the following embodiments. If the charged particle optical system is not a telecentric system, a magnification error will occur in addition to the defocus due to the height fluctuation of the object surface, and this magnification error also uses the height fluctuation amount. Correction can be performed by feeding back to the deflection system, and a charged particle beam image can always be obtained at the same magnification.

If the observation or inspection device using the focused charged particle beam has a mechanism capable of moving the object in the Z-axis direction with sufficient accuracy and response speed to control the focal position,
Instead of feeding back the height detection result to the charged particle optical system, it is also possible to feed back to the target stage height.

When the feedback is made to the stage height, the object surface is always kept at a constant height with respect to the height detector and the charged particle optical system, so that the detection accuracy of the height detector is guaranteed. Range can be narrow. As a driving mechanism of the object stage, a mechanism by piezo can be considered as a mechanism capable of minute movement at high speed in a vacuum. In this case, since the height of the surface of the object is always kept constant with respect to the charged particle optical system, no magnification error occurs.

Next, an embodiment relating to a method for calibrating the control current and the focal position of the objective lens of the charged particle optical system will be described. When the relationship between the control current and the focal position is non-linear, it is necessary to correct the non-linearity. A method for evaluating the linearity and determining the correction value will be described. A calibration standard pattern 30 as shown in FIG. 21 is fixedly arranged on a stage holding an object as shown in FIG. The standard pattern for calibration is made of a conductive material so as not to be charged by the scanning of the charged particle beam. Further, it is desirable that the surface pattern is such that the height of each position can be determined.

If the stage for holding an object can be moved in a plane as in the inspection apparatus shown in FIG. 1, this standard pattern is moved to the observation area during calibration. Using this standard pattern, the control current of the objective lens at which the charged particle beam image is sharpest at each point is measured. At this time, the definition of the charged particle beam image is determined by visual observation or image processing. By this measurement, the relationship between the displacement of the object surface height and the optimal amount of control current of the objective lens can be obtained as shown in FIG. If the relationship between the displacement of the object surface height and the amount of control current of the objective lens is known, it is possible to obtain a focused charged particle beam image from information on the object surface height obtained by the height sensor. The optimum value of the objective lens control current can be found.

The standard pattern 30 shown in FIG. 21 has flat ends at both ends. Measurement is performed by a height sensor at these two points to determine a reference height. Calibration of current gain and offset is also possible. When the characteristics of the control current and the focus position are calibrated by the objective lens alone by another method, as shown in FIG. 24, the control current of the optical height detector and the objective lens in a standard pattern having one step is used. It is sufficient to calibrate the gain and the offset.

When the object holding stage has no moving mechanism, if the standard pattern is always arranged in the field of view of the charged particle optical system, calibration of the charged particle optical system alone can be performed. In addition, if the standard pattern is shaped so that it can be attached to the jig for holding the object, even if the stage for holding the object does not have a moving mechanism, the standard pattern will Observation can be performed in exchange for objects.

When the charged particle beam apparatus has a mechanism for moving an object in the height direction as shown in FIG. 25,
It is possible to calibrate the height detector and the objective lens control current by moving the Z stage, detecting the height, and evaluating the image, using only the normal pattern without steps, instead of the standard pattern shown in FIG. it can. If the Z stage has a moving mechanism, the Z stage can be used to adjust the focus. However, if the response speed of the stage is not fast enough to change the observation position, the stage should be fixed and the objective lens should be fixed. Focus adjustment can also be performed by the control current.

The calibration method of the charged particle optical system using the standard pattern shown in FIG. 21 is effective only in the case of an observation / inspection apparatus capable of observing the pattern on the surface of the standard pattern by the charged particle optical system. It is necessary to calibrate only the height detector using the standard pattern having a step shown in FIG. 24, and calibrate the relationship between the focal position of the charged particle optical system and the control current alone in advance. At this time, if the processing equipment has a mode to observe the charged particle beam image by changing the accelerating voltage of the convergent charged particle beam, etc., check the position detected by the height detector with the charged particle beam image. can do.

Next, a description will be given of an embodiment relating to the relationship between the height measurement position during the inspection and the observation position of the charged particle optical system and the correction of the focus. When the observation position of the charged particle optical system and the height detection position of the height sensor completely match, focus adjustment may be performed based on the detected height information. However, in the light reflection position detection method, a detection position shift occurs due to a change in the height of the target object surface as shown in FIG. Assuming the assumed maximum height change amount Zmax of the object surface and the incident angle θ of the height detection optical system, the maximum displacement Xmax is Zmax · tanθ. Assuming that the height variation of the object surface allowed from the depth of focus of the charged particle optical system and the required performance of the system is z0 and the assumed maximum gradient of the object surface is Δmax, as shown in FIG. Height detection error dz is Δmax × Xmax = Δmax
・ Zmax ・ tanθ There is no problem if the height detection error dz is smaller than z0, but if it is larger, it is necessary to obtain the height of the charged particle optical system at the optical axis.

In the inspection system of the present invention, since the inspection is continuously performed by moving the stage, the height information at each point can also be continuously obtained. Using these height detection results,
Focus adjustment can be performed by estimating and estimating the object surface height in the observation region of the charged particle optical system.
A description will be given of an embodiment of a focus adjustment method in a case where there is a positional shift between the height detection position and the observation region of the charged particle optical system as described above. In the following description, when performing a stage scan, the deflection direction of the charged particle optical system is made to coincide with the y-axis direction, and the stage is moved in the x direction to obtain a two-dimensional image.

First, an embodiment in which the moving directions of the x-axis and y-axis stages during inspection are always limited to one direction will be described. As shown in FIG. 27, when the x and y axis stage movements do not always reciprocate in only one direction,
As shown in a, if the height detector is arranged with an offset so that the height detection position is always ahead of the electron optical system observation position with respect to the stage movement direction, it can be obtained before the inspection starts. The height at a desired position can be obtained using the height information around the observation region to be obtained.

As shown in FIG. 27B, three points around the current inspection point are selected, a local plane determined by the three points is determined, and the height of the inspection point is estimated. At this time, the height can be stably estimated by interpolation by selecting three points so that the current inspection point is always located inside the triangle composed of three points. In this case, it is not possible to estimate the height of the stage scanning portion at the start of the inspection, but this can be obtained by performing a single scan in advance for height detection.

Next, a description will be given of an embodiment in which the movement direction of either the x or y axis stage is always limited to one direction, and the axis coincides with the projection direction of the height detecting optical system. As shown in FIG. 28, when the x-axis stage movement is always in only one direction and the projection direction of the height detection optical system is the x-axis direction, the displacement of the height detection due to the height change is in the x-axis direction. Therefore, if an offset is given in the x-axis direction as shown in FIG. 28A, the height can be obtained by one-dimensional interpolation using only the height information on one line. In this case, linear interpolation using two points or 3
The height of the inspection location may be obtained by spline interpolation using points. At the start of the inspection, the height detection value in the approach section until the stage reaches a constant speed may be used.

When the movement of the y-axis stage is always in only one direction and the projection direction of the height detecting optical system is in the y-axis direction as shown in FIG. Since this occurs only in the y-axis direction, if an offset is given in the y-axis direction as shown in FIG. 29a, the height of the inspection point is always stabilized by interpolation using the height detection value several lines before. Can be sought. When the stage reciprocates, such an offset cannot be given in one direction.

Although it is possible to make the optical axis of the electron optical system coincide with the height detection reference position and estimate the height of the inspection point from the obtained height detection value, it is not always possible to obtain the height by inspection. Therefore, there is some instability. If a movable mechanism is attached to the height detection optical system and the entire optical system is translated in parallel as shown in Fig. 27 to give an offset to the stage movement direction, inspection is always performed by interpolation in the same manner as in the previous embodiment. The height of the portion can be obtained stably. It is also possible to arrange a plurality of sets of height detectors so that the heights at several locations around the inspection location can be measured, and to use only those required according to the stage moving direction.

Next, an embodiment of an optical height detecting method for stably detecting the height without being affected by the state of the sample surface will be described. As shown in FIG. 3, when the height of the sample surface is detected by the light reflection position detection method, a detection position shift occurs, which causes a height detection error. In addition, as shown in FIG.
(The high-reflectance portion 36 and the low-reflectance portion 37), and when the slit light is projected on the boundary 38, the reflected light intensity distribution 34 of the detected slit light is affected. A detection error occurs. A method for reducing such a height detection error will be described below.

As shown in FIG. 32, two slit lights are projected on the sample surface from directions symmetric with respect to the normal to the sample surface, and the reflected light on the sample surface is detected. If these slit light detecting sensors are arranged as shown in FIG. 32, the light flux image moving direction due to the sample surface height is in the same direction, and the measurement error due to the sample surface pattern is in the opposite direction. Thus, the influence of the sample surface can be canceled. Further, when the slit light beam is projected from two directions as shown in FIG. 32, the detected position shift caused by the change in height will occur by the same amount in the opposite direction. Therefore, by averaging these, the detected position shift is eliminated. be able to.

FIG. 33 illustrates a method for reducing the influence of the pattern on the sample surface by using a plurality of narrow slits. The height detection error caused by the sample surface pattern shown in FIG. 31 increases in proportion to the width of the slit. Therefore, as shown in FIG. 33, a plurality of narrow slits are projected, and these are detected by a linear image sensor.
An error can be reduced by calculating and averaging the centers of gravity of the plurality of slit light beam images. As shown in FIG. 34, the error at the pattern boundary is reduced by reducing the slit width. In addition, since the slits other than the boundary are not affected by the pattern, by taking the average of these, errors at the boundary can be reduced. In addition, although the detected light amount is reduced by making the slit narrow, the S / N is improved by averaging a plurality of slit positions, and stable height detection can be performed.

[0074]

According to the present invention, the height of the observation position of the electron optical system is detected simultaneously with the inspection by the optical height detector,
An in-focus electron beam image can be obtained. In an electron beam type inspection apparatus, inspection performance and stability can be improved by always performing inspection using an electron beam image in the same focused state. Further, since the height can be detected simultaneously with the inspection, the inspection can be performed by continuously moving the stage, and the inspection time can be reduced. This is particularly effective for increasing the diameter of semiconductor wafers in the future. Similarly, the same effect can be obtained in an observation processing apparatus using a convergent charged particle beam. Further, by arranging the height detecting optical system outside the vacuum sample chamber, adjustment and maintenance are facilitated.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a configuration example of an automatic inspection system of the present invention.

FIG. 2 is a plan view showing an example of a defocused electron beam image.

FIG. 3 is a schematic sectional view of an optical system for explaining a principle of height detection.

FIG. 4 is a diagram showing a change in reflectance with respect to an incident angle for each material.

FIG. 5 is a schematic cross-sectional view of a sample chamber showing an example of a change in arrangement position of components of a height detection optical system.

FIG. 6 is a schematic cross-sectional view of the sample chamber when the height detection optical system is taken out of the sample chamber.

FIG. 7 is a schematic cross-sectional view of the sample chamber showing a case where the height detection optical system is arranged in the sample chamber.

FIG. 8 is a schematic sectional view of the sample chamber showing a case where an optical path window is arranged on the outer wall of the sample chamber.

FIG. 9 is a diagram showing a change in reflectance with respect to an incident angle of BK7.

FIG. 10 is a schematic cross-sectional view of the sample chamber showing a case where an optical path window is arranged on the outer wall of the sample chamber perpendicular to the optical path.

FIG. 11 is a schematic sectional view illustrating chromatic aberration caused by a glass window.

FIG. 12 is a schematic cross-sectional view illustrating a method of correcting chromatic aberration caused by a glass window by inserting a glass plate.

FIG. 13 is a schematic cross-sectional view illustrating a method for correcting chromatic aberration caused by a glass window by inserting a glass plate.

FIG. 14 is a schematic cross-sectional view showing a change in an optical path shape required for a plate electrode depending on an incident angle.

FIG. 15 is a schematic cross-sectional view showing a shape of an incident hole for a plate electrode when a light amount aperture is circular.

FIG. 16 is a schematic cross-sectional view showing the shape of a flat electrode entrance hole when the light amount aperture is elliptical.

FIG. 17 is a schematic sectional view showing an example of a plate electrode window perpendicular to the optical path.

FIG. 18 is a schematic plan view showing an arrangement example of an entrance window which is symmetric with respect to the optical axis of the electron optical system.

FIG. 19 is a schematic plan view showing an arrangement example of an entrance window which is symmetrical with an axis in a deflection direction.

FIG. 20 is a schematic plan view showing an arrangement example of an entrance window which is symmetrical with an axis in a deflection direction.

FIG. 21 is a perspective view of a calibration standard pattern having an inclined portion.

FIG. 22 is a schematic sectional view of an automatic inspection system in which standard patterns are arranged on an XY stage.

FIG. 23 is a diagram for explaining calibration of an objective lens control current and a sample surface height.

FIG. 24 is a perspective view of a standard pattern for calibration having one step.

FIG. 25 is a schematic sectional view of an automatic inspection system in which a standard pattern is arranged on a Z stage.

FIG. 26 is a diagram illustrating a relationship between a measurement position shift and a height detection error.

FIG. 27 is a schematic plan view of a sample surface for explaining a method of estimating an observation region height based on a continuous height detection value.

28A and 28B are a schematic cross-sectional view and a schematic plan view of a sample surface for explaining a method of estimating an observation region height based on a continuous height detection value.

FIG. 29 is a schematic plan view of a sample surface for explaining a method of estimating an observation region height based on a continuous height detection value.

FIG. 30 is a schematic cross-sectional view of the sample chamber for explaining a case where the height detection optical system can move in parallel with the electron optical system.

FIG. 31 is a schematic cross-sectional view of a sample for explaining a height detection error caused by uneven reflectance of the sample surface.

FIG. 32 is a schematic cross-sectional view of an optical system illustrating a case where height is detected by projecting a slit from two directions.

FIG. 33 is a diagram illustrating a height detection method using a plurality of slits.

[Explanation of symbols]

1. Electron gun 2. Objective lens 3. Sample wafer
DESCRIPTION OF SYMBOLS 4 ... Secondary electron 5 ... Secondary electron detector 6 ... Image input part 7 ... XY stage 8 ... Z stage 9 ... Image processing circuit 10 ... Control computer 11 ... Height detector 12 ... Position monitor length measuring device 1
3 vacuum sample chamber 14 light source 15 slit 16 first imaging lens 17 second imaging lens 18 position sensor
DESCRIPTION OF SYMBOLS 19 ... Imaging lens 20 ... Aberration correction glass plate 1 21 ... Aberration correction glass plate 2 22 ... Height detection optical system 23 ... Entrance window 24 ... Height detection optical system optical path 25 ... Plate electrode 26 ... Aperture is circular The entrance window for a flat plate electrode in the case of (2) ... The entrance window for a flat plate electrode in the case of an elliptical stop 28
... Dummy window 29 ... Detection position shift 30 ... Standard pattern 31 ... Gain offset adjustment standard pattern 32 ...
Sample surface 34 ... reflected light intensity distribution 35 ... measurement error 36 ... high reflectivity part 37 ... low reflectivity part 38 ... pattern boundary

Continuing on the front page (72) Inventor Hiroyuki Shinada 1-280 Higashi Koigabo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory of Hitachi, Ltd. (72) Inventor Taku Ninomiya 882 Ma, Hitachinaka-shi, Hitachinaka-shi, Ibaraki Measuring Instruments Business, Hitachi, Ltd. Inside

Claims (16)

[Claims] 1. An electron beam source, an electron optical system means for converging an electron beam emitted from the electron beam source to a focal point, a vacuum chamber means for evacuating the inside to a vacuum, and an inside of the vacuum chamber means. A stage means on which the object to be inspected is placed and movable in a plane; and the electron beam converged by the electron optical system means to scan and irradiate the object to be inspected mounted on the stage means. Electron beam image observation means for detecting secondary charge electrons generated from the inspection object and observing an electron beam image on the surface of the sample, and scanning and irradiating the electron beam with the electron optical system means. Height detecting means for optically detecting the height of the surface of the inspection object in a region, a focal position of the electron beam by the electron optical system means using the result detected by the height detection means, and the inspection object Control means for controlling the relative position in the height direction with respect to An electron beam image of the surface of the sample to be inspected, which is observed by the electron beam image observing unit, is processed in a state in which the focal position of the electron beam and the relative position in the height direction of the object to be inspected are controlled by the controller And a defect detecting means for detecting a defect of the sample to be inspected. 2. The height detecting means detects the height of the area while irradiating the inspection object with an electron beam by the electron optical system means, and based on the detected result, the control means controls the 2. The focusing apparatus according to claim 1, wherein a focus position of the electron beam and a relative position in a height direction of the inspection object are controlled while the inspection object is being irradiated with the electron beam by an electron optical system. Charged particle beam device. 3. A light beam projection unit for projecting a slit-shaped or spot-shaped light beam onto the inspection object, and a light beam projected by the light beam projection unit and reflected on the surface of the inspection object. And a height calculator for calculating the height of the electron beam in the focus direction of the inspection object based on positional information of the light beam received by the light receiver on the light receiver. The focused charged particle beam device according to claim 1, wherein: 4. The apparatus according to claim 3, wherein the light beam projection unit irradiates the surface of the inspection object from a direction inclined at least 60 degrees with respect to a normal direction of the surface of the inspection object. Focused charged particle beam equipment. 5. The apparatus according to claim 3, wherein the light receiving section receives the light beam reflected by the inspection object at an angle inclined by 60 degrees or more with respect to a normal direction of a surface of the inspection object. 3. The focused charged particle beam device according to item 1. 6. The light beam projection unit and the light receiving unit are arranged outside the vacuum chamber means, and the light beam projection unit is connected to the table via a first light transmission window provided in the vacuum chamber means. Irradiating the inspection object mounted on the means with a light beam, and the light receiving unit receives the light beam reflected by the inspection object through a second light transmission window provided in the vacuum chamber means. 4. The focused charged particle beam device according to claim 3, wherein: 7. The charged charged particle according to claim 6, wherein the first light transmission window includes an aberration correction member for correcting an aberration of the light beam transmitted through the first light transmission portion. Line equipment. 8. The focused charged particle beam apparatus according to claim 6, wherein said aberration correcting member is made of a member of the same quality as said first light transmitting portion. 9. The height detecting means includes two pairs of the light beam projecting unit and the light receiving unit, and the two pairs of light beam projecting unit and the light receiving unit are respectively set at a normal to the surface of the inspection object. The focused charged particle beam apparatus according to claim 3, wherein the focused charged particle beam apparatus is provided on an object. 10. The focused charged particle beam apparatus according to claim 1, wherein said electron optical system means is a telecentric optical system. 11. An object to be processed is set on a movable table inside the processing chamber, the processing chamber in which the object is set is evacuated to a vacuum, and the inside of the evacuated processing chamber is evacuated. While moving the movable table, the electron beam emitted from the electron beam source scans and optically detects the height in the optical axis direction of the electron beam source in the area of the object to be inspected and irradiated, The height of the inspection object in the optical axis direction is adjusted based on the detected result, and the electron beam is emitted from the electron beam source while moving the movable table to the inspection object whose height has been adjusted. Scanning and irradiating the electron beam, and detecting secondary charged particles generated from the inspected object by scanning and irradiating the electron beam to obtain a secondary charged current image of the surface of the inspected object. Inspecting the inspected sample based on the secondary charged current image. Inspection method using the particle beam device. 12. A height of an area of the object to be inspected, which is irradiated by scanning the electron beam, in an optical axis direction of the electron beam source is set to 60 degrees with respect to a normal direction of a surface of the object to be inspected. By irradiating light from the above inclined direction, light reflected on the surface of the inspection object is detected from a direction inclined by 60 degrees or more with respect to a normal direction of the surface of the inspection object, and the detected reflected light is detected. The inspection method using the focused charged particle beam device according to claim 11, wherein the detection is performed based on the information of: 13. A height of the electron beam source in a region of the inspection object irradiated with the electron beam scanned in the optical axis direction is known at least at two or more points. The focused charged particle beam according to claim 11, wherein the measurement is performed using a height detection optical system calibrated using a calibration standard pattern having an optically observable pattern having a step or an inclination. Inspection method using the device. 14. The position of the focal point of an electron beam emitted from an electron beam source is made of a material that is stable with respect to irradiation of a charged particle beam, and can be observed on the surface with a charged particle optical system at least at two or more positions The inspection method using the focused charged particle beam apparatus according to claim 11, wherein the calibration is performed using a calibration standard pattern having a pattern having a step or a slope whose height difference is known at a point. 15. A secondary overcurrent element image of the inspection object obtained by calibrating a focal position of an electron beam emitted from the electron beam source and irradiating the electron beam with the calibrated focal position. The inspection method using the focused charged particle beam apparatus according to claim 14, wherein the magnification of the particle is corrected. 16. The method according to claim 16, wherein a height of the electron beam source in an optical axis direction of an area of the inspection object irradiated with the electron beam scanned is continuously detected while moving the moving table. Based on the height information around the inspection point obtained by
The inspection method using the focused charged particle beam apparatus according to claim 11, wherein the height of the surface of the inspection object in a desired observation region is estimated, and the height is adjusted based on the estimated result. .