JPH11167893A - Scanning electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily carry out a work of transforming the coordinate data of a foreign matter sent out of a foreign substance inspecting apparatus into the coordinate of the scanning electron microscope. SOLUTION: The coordinate value of a foreign matter to be used for deriving a coordinate transformation expression is registered in a stage coordinate system which is not affected by coordinate transformation. It is made possible to optionally or automatically select a foreign matter to be used for deriving the coordinate transformation expression from the foreign matters whose coordinates are registered. The coordinate transformation expression is derived by using, for example, only a foreign matter 36 existing in a region 37 selected by a mouse from the foreign matter 35 whose coordinate values in the scanning electron microscope are registered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning electron microscope for observing a minute area on a sample, and more particularly to adapting coordinate data of an object to be observed on the sample measured by another inspection apparatus to its own coordinate system. The present invention relates to a scanning electron microscope which is used when observing an observation object.

[0002]

2. Description of the Related Art Scanning electron microscopes are used in many research and development fields to observe the fine structure of a sample. Scanning electron microscopy is an SEM (Scanni
ng Electron Microscope) image is displayed on the screen. This technique is also applied to observation of a fine structure of a semiconductor device. In recent years, semiconductor devices have been miniaturized, and semiconductor devices are currently manufactured with a pattern width of 0.5 μm or less. In such a semiconductor device, a fault may occur only when a foreign substance / defect of about 0.2 μm exists on a wafer on which a semiconductor pattern is formed. It is necessary to observe these foreign substances / defects with a scanning electron microscope in order to investigate the foreign substances / defects that caused the obstacle in detail.

With a scanning electron microscope, such fine foreign matter /
When observing a defect, it is usual to measure the position of the foreign matter / defect on the wafer in advance using another foreign matter / defect inspection device, etc., and to search for and observe the foreign matter / defect based on the coordinate data obtained by the measurement. It is. When observing a foreign substance / defect of about 0.2 μm with a scanning electron microscope, it is necessary to enlarge the foreign substance / defect by at least about 5,000 times and display it on a SEM image screen. However, since the range that can be observed at one time is limited due to the limitation of the screen size of the SEM image, if the coordinate data of the foreign substance / defect obtained from the foreign substance / defect inspection apparatus contains a large error, the foreign substance / defect is not detected. It may run off the SEM image screen. For example, when observing foreign matter / defects at a magnification of 5,000 using a scanning electron microscope having a SEM image display screen size of 200 mm × 200 mm, the range of the SEM image that can be observed at a time is only 40 μm × 40 μm. / ± 20μm for coordinate data from defect inspection equipment
When the above error is included, the foreign matter / defect is deviated from the SEM image display screen, and the foreign matter / defect cannot be found.

[0004] In order to reduce the coordinate error of the foreign matter / defect inspection apparatus, a method such as "Multiple scanning method for wafer particle analysis" has been proposed in Japanese Patent Application Laid-Open No. Hei 7-193109. Could not be obtained, and foreign matter / defects were observed when using a scanning electron microscope.
Often defects cannot be found.

[0005]

SUMMARY OF THE INVENTION Based on coordinate data from a foreign substance / defect inspection apparatus having a large coordinate error (hereinafter, simply referred to as a foreign substance inspection apparatus), a foreign substance / defect (hereinafter, referred to as foreign substance and defect) is matched by a scanning electron microscope. In order to observe such an object, it is necessary to perform coordinate conversion on the scanning electron microscope side so as to reduce the coordinate error, or to devise an observation method that is less affected by the coordinate error.

[0006] The factors of the coordinate error of the foreign matter inspection device depend on the operation principle of the device. For example, in order to express the coordinates of a foreign substance on a wafer, an XY coordinate system adapted to the outer shape of the wafer may be used. The definition of the origin of the XY coordinates and the inclination of the XY coordinate axis with respect to the wafer shape are determined by the foreign substance inspection device. May be slightly different. In such a case, for example, a coordinate shift between the scanning electron microscope and the foreign matter inspection device can be corrected using the following coordinate conversion formula [Equation 1]. In the formula, (x ₁ , y ₁ ) is the foreign matter coordinates measured by the foreign matter inspection device, (x ₂ , y ₂ ) is the foreign matter coordinates converted to fit the coordinate system of the scanning electron microscope, and (a, b) Is the coordinate origin error of the particle inspection device, θ is the XY of the particle inspection device
Indicates the tilt error of the coordinate axis.

[0007]

(Equation 1) If at least two foreign substances are measured for foreign substance coordinates by a foreign substance inspection apparatus and a scanning electron microscope, and these values are substituted into [Equation 1], a simultaneous equation obtained by solving the equations so that the residual error is minimized, , B and θ can be obtained. By using [Equation 1] in which the values of a, b and θ obtained in this way are substituted, it is possible to convert the coordinate value of the foreign matter measured by the foreign matter inspection device into a coordinate value suitable for the coordinate system of the scanning electron microscope. .

However, the cause of the coordinate error of the foreign matter inspection apparatus is not only the coordinate origin error (a, b) of the foreign matter inspection apparatus and the inclination error θ of the XY coordinate axes, but also various other factors. For example, coordinate dimensional accuracy (coordinate scale) If there is an error in [Equation 1]
It is not possible to perform appropriate coordinate correction for all foreign substances by using only the above. Of course, if a coordinate conversion formula capable of better correcting the error is known, the coordinate conversion formula may be used instead of [Equation 1]. For example, when it is known that there is an orthogonality error between the XY coordinate axes, a calculation formula that can correct the orthogonality may be used. However, when coordinate data from an unknown foreign matter inspection device whose error factors are not sufficiently understood is used, it may not be possible to prepare an appropriate coordinate conversion formula.

When a coordinate conversion formula is derived using only coordinate data of some foreign materials, the user needs to select a foreign material to be used for deriving the coordinate conversion formula. In some cases, coordinate data relating to the foreign matter may be sent, and it may not be possible to easily determine which foreign matter should be used to create the coordinate conversion formula. Also, when many foreign substances are selected, it may not be possible to determine which foreign substance has already been selected. Further, every time the observation position on the sample is changed by the scanning electron microscope, it is necessary to reselect a foreign substance used for deriving the coordinate transformation formula, and thus there is a problem that workability is poor.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and can easily perform the operation of converting coordinate data of a foreign substance sent from a foreign substance inspection apparatus into coordinates of a scanning electron microscope. Even if various error factors are included in the coordinate data from the foreign matter inspection device, the coordinate data from the foreign matter inspection device can be used to find fine foreign matter with a scanning electron microscope without complicating the coordinate correction calculation. It is an object of the present invention to provide a scanning electron microscope that can convert the data.

[0011]

In a scanning electron microscope for observing a semiconductor wafer, the wafer is moved by moving a wafer holder and a sample holding table called a wafer holder in a sample chamber of the scanning electron microscope. Equipped with a moving stage that changes the observation position. Scanning electron microscopes generally use two coordinate systems, a coordinate system based on the origin of movement of the moving stage (stage coordinate system) and a coordinate system based on the outer shape of the wafer (wafer coordinate system). It represents the position of the observation target. The stage coordinate system is a coordinate system unique to the scanning electron microscope used, and does not change even when the wafer is changed. However, since the coordinate system is unique to the device, the coordinate value cannot be shared with another device.

On the other hand, in the wafer coordinate system, even if the shape and position of the wafer are changed, the coordinate axes are defined according to the outer shape of the wafer. Therefore, if the same wafer is used with another apparatus, the coordinate values must be shared. Can be. However, as described above, since the origin and inclination of the coordinate axes of the coordinate system may be shifted depending on the device used, it is necessary to correct the coordinate error between the devices by some means.

Normally, when the coordinate transformation is performed, the result is reflected on the wafer coordinate system, and the coordinate axis itself of the wafer coordinate system changes. Therefore, the coordinate value of the foreign matter measured in the wafer coordinate system may be different before and after coordinate correction by coordinate conversion. If the scanning electron microscope has a means for registering (storing) the coordinate value of the foreign matter, even if a value obtained by measuring the coordinate value of the foreign matter in the wafer coordinate system is registered, if the coordinate transformation is executed later, the coordinate will be obtained. The value can be meaningless. In the present invention, in order to avoid such a problem, the registration of the coordinate value of the detected foreign substance is performed by registering the coordinate value measured in the stage coordinate system which does not change even by the coordinate conversion. .

Even if the coordinate data from the foreign matter inspection device contains an error whose factor is unknown and an appropriate coordinate conversion formula cannot be prepared, if the foreign matter is in a very narrow area, Even with simple coordinate conversion as shown in [Equation 1], the coordinates can be corrected to such an extent that a foreign substance can be found with a scanning electron microscope. Regarding the registration of the coordinate values of the foreign matter used in the calculation of the coordinate conversion formula, if the result of observing the foreign matter with the scanning electron microscope conforms to the preset condition, the scanning electron microscope of the foreign matter is automatically used. By registering the coordinate values in the coordinate system, the burden on the operator can be reduced. This feature
It is also effective when driving unmanned. As conditions to be set in advance for automatic registration of coordinate values, an image contrast, an abnormality in a semiconductor repetitive pattern, or the like can be used. That is, it is possible to set conditions such as registering only a foreign substance having an image contrast equal to or higher than a predetermined value, or preferentially registering an abnormality in a repetitive pattern. One condition is that a foreign substance having a coordinate error that is extremely large compared to the coordinate errors of other foreign substances is not used.

Further, based on the coordinate data from the particle inspection apparatus, the position of the particle on the wafer is displayed two-dimensionally on a display, and the coordinate value of these particles measured by a scanning electron microscope is displayed. It is convenient to provide a foreign substance position display means for displaying the registered foreign substance in a characteristic mark or color so that the user can see at a glance which coordinate value of the foreign substance is registered. Furthermore, on this position display means, a foreign substance used for deriving a coordinate conversion formula can be arbitrarily selected from the foreign substances whose coordinate values have been registered, and the selected foreign substance can be displayed in a characteristic mark or color. It is also convenient to provide means.

With such a function, the flexibility of the coordinate correction calculation can be increased. For example, if coordinate accuracy is required only in a certain area of the wafer, it is better to derive a coordinate conversion formula using the coordinate values of foreign substances located near the area,
The coordinate correction accuracy is higher. Based on the coordinate data from the foreign matter inspection device, all foreign matters are displayed in a list, and the foreign matter for which coordinate values are registered and the foreign matter used for deriving the coordinate conversion formula are marked with distinctive marks and colors. The same effect can be obtained by expressing.

In addition, due to the characteristics of the foreign substance inspection apparatus, when measuring the coordinates of a large foreign substance that does not conform to the foreign substance detection sensitivity of the foreign substance inspection apparatus, errors may increase. Therefore,
By automatically selecting the coordinates of the foreign matter to be used for deriving the coordinate conversion equation according to preset conditions, it is possible to improve the coordinate correction accuracy. For example, if the size of the foreign matter used for deriving the coordinate conversion formula is set according to the detection sensitivity of the foreign matter inspection device, based on the information on the size of the foreign matter brought together with the coordinate data from the foreign matter inspection device, Foreign matter having a large coordinate error in the foreign matter inspection device can be automatically removed.

Further, when the position on the wafer to be observed by the scanning electron microscope is changed, the coordinate conversion formula is automatically recalculated by using only the foreign matter present near the moved position. Even if the user does not reset the coordinate value of the foreign matter used for deriving the coordinate conversion formula every time the location is changed, the optimum coordinate correction for the moved position can be performed and the workability can be improved. . This feature
It is also effective when driving unmanned.

Further, even when a coordinate conversion formula is derived while including a foreign substance having an extremely large coordinate error as compared with other foreign substances, the coordinate correction accuracy is not improved. In such a case, if a foreign object having a coordinate error equal to or greater than the set value after the coordinate correction is removed and the coordinate conversion formula is derived again, the coordinate correction accuracy can be improved. If the coordinate conversion equation is automatically derived again, the user's labor can be saved. This function is also effective when driving unmanned.

That is, the present invention provides a stage which holds a sample and can be moved two-dimensionally in a stage coordinate system, means for converging and scanning an electron beam on the sample held on the stage, A detecting means for detecting secondary particles generated from the sample by irradiation, and a sample coordinate system (wafer coordinate system) fixed to the sample on the stage in a scanning electron microscope for forming a sample image using the output of the detecting means. ), And coordinate conversion means for converting coordinate values supplied from another device to indicate the position of the observation target on the sample into coordinate values in the sample coordinate system. The coordinate conversion means is a coordinate value registration means for registering the detected coordinate value of the observation object in the sample coordinate system, and a coordinate value supplied from another device and a coordinate value registration means for the observation object. Of detected coordinate values Wherein the the comprising a coordinate error calculation means for calculating an error, and a coordinate conversion formula setting means the error sets a coordinate conversion formula to minimize.

A second coordinate value registration means for registering a coordinate value of the object to be detected in the stage coordinate system is provided, and the coordinate value of the object to be detected detected by the scanning electron microscope is the coordinate value in the coordinate system of the sample. Also, it is preferable to register the detected coordinate value in the stage coordinate system. Since the coordinate values in the stage coordinate system are not affected by the coordinate transformation, the detected coordinate values of the observation target are also registered in the stage coordinate system. The observation target can be immediately found based on the coordinate values.

The scanning electron microscope according to the present invention includes coordinate registration condition setting means for setting conditions of the observation object to be registered in the coordinate value registration means, and the observation object in the sample coordinate system conforming to the coordinate registration conditions. It is possible to have a function of automatically registering the detected coordinate value in the coordinate value registration means. The apparatus further includes position display means for displaying a two-dimensional arrangement of the observation target on the sample based on the coordinate data supplied from another device, and the observation target having the detected coordinate values registered in the coordinate value registration means. And an observation object that has not been registered can be displayed on the position display means. Further, it is preferable that the apparatus further comprises means for selecting an observation target to be used by the coordinate error calculating means on the position display means, and has a function of distinguishing and displaying the selected observation target from others. The distinction on the display can be made with different shapes or different colors.

Alternatively, a list display means for displaying a list of observation objects based on coordinate data supplied from another device, an observation object whose detected coordinate values have been registered in the coordinate value registration means, and an observation object which has not been registered. It is possible to have a function of displaying the object and the object separately on the list display means. Further, it is possible to provide a means for selecting an observation object to be used by the coordinate error calculating means on the list display means, and to have a function of displaying the selected observation object separately from others. Also in this case, the distinction on the display can be made with a different shape or a different color.

The apparatus further comprises a coordinate error calculation condition setting means for setting conditions of the observation object used by the coordinate error calculation means. The apparatus may have a function of setting a coordinate conversion equation using detected coordinate values of the observation target object that meet the conditions set by the condition setting means.

The coordinate error calculation condition setting means has a function of setting the condition of the observation object used by the coordinate error calculation means in relation to the observation position on the sample. The apparatus may have a function of setting a coordinate conversion equation using a detected coordinate value of the observation target object that meets conditions related to the observation position on the moved sample set by the coordinate error calculation condition setting means.

Means for setting the permissible error of the detected coordinate value of the observation object used by the coordinate error calculating means and the coordinate value in the sample coordinate system transformed by the coordinate transforming means, and the observation object having an error exceeding the permissible error When an object is present, a function of removing the observation object and re-executing the error calculation by the coordinate error calculating means may be provided. According to the present invention, it is possible to register the coordinate value of a foreign substance measured in the stage coordinate system which is not affected by the coordinate conversion. Therefore, it is possible to register the effective coordinate value of the foreign substance even after performing the coordinate correction. it can. Further, based on the observation result by the scanning electron microscope, the coordinate value of the foreign substance in the coordinate system of the scanning electron microscope can be automatically registered. In addition, it is possible to distinguish the foreign matter whose coordinate values are registered from the layout drawing or the list, and further arrange the foreign matter used for deriving the coordinate conversion formula in a state where it is possible to determine which foreign matter has been selected. It can be arbitrarily selected from figures and lists. Also,
A foreign substance used for deriving a coordinate conversion equation can be automatically selected according to measurement conditions in the foreign substance inspection device. Further, it is possible to automatically select a foreign substance used for deriving a coordinate conversion equation in accordance with the movement of the observation position on the sample of the scanning electron microscope. In addition, it is possible to automatically remove a foreign substance having a large coordinate error and derive the coordinate conversion formula again.

With such a function, when observing a foreign substance or the like on a sample using the coordinate data from the foreign substance inspection apparatus, highly accurate coordinate correction is always performed without the user's time and effort. It is possible to always correct the coordinate error between the devices to an optimum state.

[0028]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing a configuration of an example of a scanning electron microscope according to the present invention. This scanning electron microscope includes an electron gun 1, an electron lens 2, a lens control circuit 9, a deflector 3, a deflection control circuit 10, a secondary particle detector 4, an analog / digital converter 11, an address control circuit 12, an image memory 13, It comprises a control means 14, a display 15, a computer 16, an image synthesizing means 17, a keyboard 18, a mouse 19 input means and the like.

The electron beam 7 emitted from the electron gun 1 is converged by the electron lens 2, scanned and deflected two-dimensionally by the deflector 3, and irradiates the sample 5. When the sample 5 is irradiated with the electron beam 7, secondary particles 8 such as reflected electrons and secondary electrons according to the shape and material of the sample are generated. The secondary particles 8 are detected and amplified by the secondary particle detector 4, and are converted into digital values by the analog / digital converter 11. The data converted into the digital value is stored in the image memory 13. Image memory 1 at this time
As address 3, the address control circuit 12 generates an address synchronized with the scanning signal of the electron beam. Further, the image memory 13 transfers the stored image data of the SEM image to the image synthesizing unit 17 as needed. The image combining means 17 combines the image data with the screen data in the display memory of the computer 16 and displays the combined data on the display 15 in real time.

A sample 5 observed by a scanning electron microscope is held by a sample stage 6. In addition, the moving stage 21
The position of the electron beam 7 with respect to the sample 5 can be changed by moving, tilting, or rotating the sample table 6 three-dimensionally in accordance with a control signal from the control device 14. The scanning electron microscope has an imaging optical system 50 and C
An optical imaging device including a CD camera 51 is also provided. The moving stage 2 is controlled by a control signal from the controller 14.
By positioning 1 below the optical imaging device, the sample (wafer) 5 can be imaged by the CCD camera 51. By processing the image signal obtained from the CCD camera 51 by the computer 16, the position (posture) of the sample 5 on the sample stage 6 can be detected.

FIG. 2 is a diagram showing the relationship between the wafer coordinate system and the stage coordinate system. The stage coordinate system is a coordinate system unique to the apparatus. In this example, the coordinate axes 41,
Reference numeral 42 is based on the movement origin O of the movement stage 21. The stage coordinate system is always constant irrespective of the position and shape of the wafer, and is not affected by the result of the coordinate conversion. However, since the coordinate system is unique to the apparatus, the coordinate values measured in the stage coordinate system cannot be shared with other apparatuses.

On the other hand, the wafer coordinate system is a coordinate system determined according to the shape of the wafer. As shown in FIG. 2, in this example, the X axis 43 of the wafer coordinate system is a straight line that is in contact with the extended line 33 of the wafer outer circumference circle and is parallel to the orientation flat 32.
The axis 44 is a straight line that is in contact with the wafer outline 31 and is perpendicular to the X axis 43. That is, a fixed coordinate axis can always be defined for the wafer regardless of the position of the wafer with respect to the moving stage. Therefore, even if different apparatuses use the same wafer, they can theoretically share the same coordinate value in the same wafer coordinate system. The orientation flat 32 is a notch for determining the direction of rotation of the wafer. The orientation flat 32 has a crescent shape in this figure, but may have a V-shaped notch called a V notch.

However, since the result of the coordinate conversion is reflected on the wafer coordinate system, for example, when the offset of the origin is corrected, the X axis 45 and the Y axis 46 of the wafer coordinate system are shown in FIG.
As shown in (1), the coordinate axes are as if the original wafer coordinate axes were moved in the X 'and Y' directions. Therefore, the coordinate value of the foreign matter 35 in the wafer coordinate system is (x ′,
y ′), but changes to (x ″, y ″) after the coordinate correction. On the other hand, the coordinate value of the foreign matter 35 in the stage coordinate system is (x, y) before and after the coordinate correction and is always constant.

According to the present invention, when registering the coordinate value of the detected foreign matter, the coordinate value (x ′, y ′) or (x ″, y ″) in the currently used wafer coordinate system is registered. In addition to the registration, the coordinate value (x, y) in the stage coordinate system which does not depend on the coordinate correction result, that is, the coordinate value effective after the coordinate correction can be registered. The function of registering (storing) the coordinate values of the foreign substance in the wafer coordinate system and the stage coordinate system can be implemented in the computer 16, for example, as software.

FIG. 3 is a flowchart for explaining a procedure for observing foreign matter on a wafer using a scanning electron microscope for semiconductors. Prior to the step shown in FIG. 3, the coordinate measurement of a foreign substance (or defect) on a wafer is performed using a foreign substance inspection device. At this time, the coordinate system indicating the position of the foreign matter is basically the same as the wafer coordinate system used in the scanning electron microscope. However, actually, there is generally a slight error between the coordinate system of the inspection apparatus and the coordinate system of the scanning electron microscope.

In step 11 of FIG. 3, the coordinate data of the foreign matter measured by the foreign matter inspection device is read into the scanning electron microscope. The coordinate data is passed from the foreign matter inspection device to the scanning electron microscope via a floppy disk or a network connection. Next, in step 12, the wafer subjected to the foreign substance measurement by the foreign substance inspection device is loaded into the scanning electron microscope.
Step 11 and step 12 may be reversed.

Next, in the rough alignment (outline alignment) in step 13, the coordinates of the outline point of the wafer held on the stage 21 of the scanning electron microscope in the stage coordinate system (X-O-Y) are measured. The position (posture) of the wafer with respect to the stage coordinate system is examined.
Specifically, as shown by a broken line in FIG. 1, the moving stage 21 holding the wafer is moved below the optical imaging device including the imaging optical system 50 and the CCD camera 51. Then, as shown in FIG. 4, five points on the wafer outline 31, that is, two points 61 on the orientation flat 32,
The coordinates in the stage coordinate system of 62 and three points 63 to 65 on the wafer outer circumference are measured. Based on these coordinate values, the X axis 43 of the wafer coordinate system is determined as a straight line that is in contact with the extended line 33 of the wafer outer circumference circle and that is parallel to the orientation flat 32.
And a Y axis 44 is defined as a straight line perpendicular to the X axis 43. Thus, a wafer coordinate system (X′-O′-Y ′) is defined.

Next, in step 14, several relatively large foreign substances, usually 5 to 10 foreign substances, are observed using the coordinate data (X1, Y1) from the foreign substance inspection apparatus, and the wafer coordinate system ( X'-O'-Y '), the coordinate values (X2, Y2) of the foreign matter, and the stage coordinate system (X-O-Y').
The coordinate value (X, Y) of the foreign substance measured in Y) is registered. At this time, if no foreign matter is found at the position indicated by the coordinate data from the foreign matter inspection device, the coordinate value measured in the vicinity of the foreign matter detected as the foreign matter indicated by the coordinate data is registered.

Then, the process proceeds to a step 15, wherein fine alignment (foreign matter alignment) using the coordinates of the foreign matter is performed.
In this fine alignment, the coordinate value (X2, Y2) of the foreign matter measured in the wafer coordinate system (X'-O'-Y ') of the scanning electron microscope in Step 14 and the coordinate value of the foreign matter obtained from the foreign matter inspection device By comparing (X1, Y1), a coordinate error between the devices is calculated. Then, for example, the constants (a, b) of the above [Equation 1] are set so that the coordinate error between the devices is minimized.
And θ are determined, and a coordinate conversion formula is created. Then, using the conversion formula, the coordinate values (X1, Y
1) is converted, and the coordinate values (X3, Y3) after the conversion are obtained. If the conversion formula is appropriate, (X3, Y3) ≒ (X2,
Y2), and using the coordinate values (X3, Y3) after conversion, foreign substances can be easily found on the scanning electron microscope wafer coordinate system (X'-O'-Y '). Further, as will be described later, even if the wafer coordinate system (X'-O'-Y ') of the scanning electron microscope itself is deformed in accordance with the coordinate value from the foreign matter inspection device, (X "-
O "-Y"), a similar effect can be obtained.

Step 15 is a coordinate error calculating means for calculating a coordinate error between the devices, a coordinate conversion formula setting means for determining a constant of the coordinate conversion formula and creating a coordinate conversion formula, and using the created coordinate conversion formula. This is realized by coordinate conversion means for converting the coordinate values from the foreign substance inspection device for use in a scanning electron microscope.
Each of these units can be realized in software in the computer 16, for example.

In the following step 16, foreign matter observation is performed.
At this time, if the wafer coordinate system is deformed, foreign matter is searched for on the newly defined wafer coordinate system (X "-O" -Y ") using the coordinate values from the foreign matter inspection apparatus, and the SEM image is obtained. In the case where the coordinate values have been converted, the wafer coordinate system (X′-O′-) defined in step 13 is used.
Y ′), the converted coordinate value (X
(3, Y3) to search for foreign matter, and observe the foreign matter with an SEM image.

Referring now to FIG. 5, the coordinate system (X "-O"-) of the wafer coordinate system (X'-O'-Y ') of the scanning electron microscope is adjusted to the coordinate value from the foreign matter inspection apparatus. A method of deforming the image as shown in FIG.
-OY) is the stage coordinate system of the scanning electron microscope, (X'-
O'-Y ') is the wafer coordinate system of the scanning electron microscope, (X "-
O "-Y") is the modified wafer coordinate system of the scanning electron microscope, (x, y) is the coordinate value in the stage coordinate system of the scanning electron microscope, and (x ', y') is the wafer coordinate of the scanning electron microscope. The coordinate values in the system, (x ", y") are the coordinate values from the inspection device.

The scanning electron microscope changes the observation position by moving the stage using the stage coordinate system (X-O-Y). For the sake of simplicity, if the coordinate error factors are only the origin offset (a, b) and the rotational direction error (θ),
Stage coordinate system (X-O-Y) and wafer coordinate system (X'-
The relationship between O′-Y ′) is as shown in FIG. 5, and the stage coordinate value (x, y) can be calculated from the wafer coordinate value (x ′, y ′) using the following [Equation 2]. .

[0044]

(Equation 2) The parameters (a, b, θ) defining the wafer coordinate system (X′-O′-Y ′) are matched with the foreign object coordinate values (x ″, y ″) from the inspection apparatus (a ′, b ′). , Θ ′), the stage coordinate value (x, y) of the foreign matter is calculated using the following [Equation 3].

[0045]

(Equation 3) As described above, by changing the definition parameters of the wafer coordinate system (X'-O'-Y ') with respect to the stage coordinate system (X-O-Y) and deforming the wafer coordinate system, the coordinate values from the inspection apparatus are obtained. (X ", y") can be used as it is as the wafer coordinate value of the scanning electron microscope.

The origin error has been considered as a factor of the coordinate error.
Coordinate transformation when only offset and rotation direction errors are included
And explained. However, various other coordinate errors
Even when factors are included, coordinate conversion between two
Can be. As an example, referring to FIG.
Factors include origin offset, rotation direction error, X axis and Y
The position when the dimensional accuracy error of the axis and the orthogonality error of the coordinate axis are included
The target conversion will be described. In FIG. 6, (X₁-O-
Y₁) Is the coordinate axis of the inspection device, (X _Two-O-Y_Two) Is dimensional accuracy
Coordinate axes after correction, (X_Three-O-Y_Three) Are coordinates after orthogonality correction
Axis, (X_Four-O-Y_Four) Are coordinate axes after rotation correction, and (X_Five-O'-
Y_Five) Is the coordinate axis of the scanning electron microscope, (x₁, Y₁) Inspection
Foreign object coordinates of the device, (x_Five, Y_Five) Indicates foreign matter in a scanning electron microscope
Coordinates, (c, d) is the origin offset between coordinate axes, α is
(X₁-O-Y₁) Coordinate orthogonality error, β is the angle between coordinate axes
Error, m is dimensional accuracy error of X-axis, n is dimensional accuracy error of Y-axis
Is the difference.

At this time, the foreign matter coordinates (x ₁ ,
The coordinate conversion formula for converting y ₁ ) into the foreign object coordinates (x ₅ , y ₅ ) of the scanning electron microscope is represented by the following [Equation 4]. When this coordinate conversion formula is used, six or more different foreign substances are selected and parameters c, d, α, and α are set so that the residual error between the coordinate value of the inspection apparatus and the coordinate value of the scanning electron microscope is minimized.
Determine β, m, and n.

[0048]

(Equation 4) As means for registering the coordinates of the foreign matter detected by the scanning electron microscope, in addition to the conventional method of aligning the cross cursor with the foreign matter on the image display screen and registering the coordinates of the intersection of the cross cursor as the coordinates of the foreign matter, It is possible to provide a function of automatically recognizing the position of a foreign object based on a difference in surrounding shape or a difference in contrast by using image processing, and automatically registering the coordinates of the foreign object.

As an actual application example, after observing a foreign substance, a predetermined repetitive shape of a normal semiconductor pattern registered in advance is compared with the observed image, and the shape, size, and center position of the foreign substance are determined. The coordinates of the foreign matter are calculated, and the calculated coordinate values are registered as the coordinate values of the foreign matter. Further, regarding a foreign substance on a flat wafer having no pattern, a change in contrast with the surroundings is recognized, and similarly, the coordinates of the foreign substance can be calculated from the shape, size, and center position of the foreign substance. With such a function, the coordinate values of the foreign matter can be automatically registered even during unmanned operation.
At this time, the coordinate values of the detected foreign matter and the coordinate values measured by the foreign matter inspection device are associated with each other based on the coordinate value from the foreign matter inspection device (or the coordinate value after error correction) on the sample. The position is moved, and the coordinate value of the foreign matter detected at the position closest to the position is used as the coordinate value of the foreign matter with a scanning electron microscope.

FIG. 7 is a diagram showing an example in which a foreign substance whose coordinate values are registered in a scanning electron microscope and a foreign substance whose registration is not registered are distinguished and displayed two-dimensionally on an operation screen of the scanning electron microscope. In this example, the display window 30 on the operation screen of the scanning electron microscope displays the outer shape 3 of the wafer as the observation sample.
1 and the position of the foreign matter 34 are shown. The position of the foreign substance 34 is
It is determined based on data measured by a foreign substance inspection device. In the figure, a foreign substance 35 indicated by a mark is a foreign substance in which the coordinate values measured by a scanning electron microscope are registered among the foreign substances 34. By using such a display method, it is possible to easily identify which foreign substance coordinate value is registered. In this example, the foreign matter whose coordinate values have been registered is distinguished from the foreign matter that is not, by marking different shapes (□ and +). However, if color display is possible, the two colors may be changed by changing the colors of both. .

FIG. 8 shows an example in which a foreign substance used for coordinate correction calculation, that is, derivation of a coordinate conversion formula is selected using a layout diagram of foreign substances. The selected foreign matter is indicated by a mark. In this example, a coordinate conversion formula is derived using only the foreign substance 36 in the area 37 selected by using the mouse 19 or the like among the foreign substances 35 whose coordinate values are registered in the scanning electron microscope. As described above, when the foreign matter used for deriving the coordinate conversion formula is limited and selected, a more accurate coordinate conversion formula can be derived for a certain region. In this example, the rectangular area 37 is selected, but it may be selected using an area surrounded by an arbitrary polygon or curve. Alternatively, a plurality of foreign substances may be individually selected by a mouse instruction instead of area selection.

FIG. 9 shows an example in which data on foreign matter obtained from the foreign matter inspection device is displayed in the form of a list. In this example, a foreign substance in which coordinate values measured by a scanning electron microscope are registered is marked with a circle 39 to distinguish it from a foreign substance whose coordinates are not registered. In addition, among the foreign substances whose coordinate values are registered, foreign substances used for deriving a coordinate conversion equation are further distinguished by a mark 40. The foreign substance used to derive the coordinate transformation formula can be freely selected by the user using this list, for example, by clicking the foreign substance selected from the circles in the “Register” section with the mouse in the “Select” section. You can choose. In this example, various foreign substances are distinguished by using characteristic marks. However, when color display is possible, the foreign substances may be distinguished by displaying the number and coordinate value of the foreign substances in a different color. Due to the characteristics of the foreign matter inspection device, a coordinate measurement error may increase when a foreign material having a size that does not match the measurement sensitivity of the device is observed. If a coordinate conversion formula is derived using the coordinate data of such a foreign substance having a large measurement error, the accuracy of the coordinate correction deteriorates. According to the present invention, a foreign substance whose coordinate value can be registered with a scanning electron microscope or a foreign substance which can be used for deriving a coordinate conversion formula is automatically determined according to the size and type of the foreign substance preset according to the measurement sensitivity of the foreign substance inspection apparatus. To be able to choose.

The foreign substance inspection apparatus provides data obtained by classifying the size and type of the foreign substance using numbers and symbols, together with the coordinate data of the detected foreign substance. It is convenient to use the classification data provided by the foreign substance inspection device when automatically registering the coordinates of the foreign substance with the scanning electron microscope or automatically selecting the foreign substance to be used for deriving the coordinate conversion formula. is there.

For example, when a foreign substance is detected by comparing a predetermined repetitive shape of a semiconductor pattern registered in advance with an observed image, and the coordinate value of the foreign substance is calculated and registered, the scanning electron microscope is used. A coordinate registration condition setting screen for the foreign matter is displayed on the operation screen, and the upper limit of the size of the foreign matter to be coordinate-registered and the kind of the foreign matter to be excluded (for example, the one located at the wafer edge, the spot-like thing) are indicated by a mouse or a keyboard. Can be specified using. The conditions can be set in the same manner even in the automatic selection of the foreign substance used for deriving the coordinate transformation formula. That is, the condition setting screen of the foreign substance used for deriving the coordinate transformation formula is displayed on the operation screen of the scanning electron microscope,
An upper limit of the size of a foreign substance to be taken in to derive a coordinate conversion formula and a type of a foreign substance to be excluded can be designated using a mouse or a keyboard.

FIG. 10 is an explanatory diagram showing a method of automatically selecting a foreign substance used for deriving a coordinate conversion equation in accordance with an image display area on a sample by a scanning electron microscope. Here, an example is shown in which a coordinate conversion formula is derived using only the foreign substance 36 in which coordinate values near the area 38 observed by the scanning electron microscope are registered. The region 38 observed by the scanning electron microscope changes when the sample 5 and the sample stage 6 are moved by the moving stage 21. In this example, the foreign matter 36 near the observation area 38 is automatically selected after the movement of the observation area (indicated by the mark ■), and a coordinate conversion formula is derived using only the foreign matter. At this time, the observation area 3
Adjusting the number of foreign substances used to derive the coordinate transformation formula by allowing the conditions such as the distance from 8 and the number of foreign substances to be selected to be set by displaying the condition setting screen on the operation screen of the scanning electron microscope can do. As the coordinate data of the foreign matter, for example, data that meets the conditions may be automatically selected from the list shown in FIG. 9 each time. With such a function, it is possible to save the trouble of reselecting a foreign substance to be used for the correction calculation for the seat each time the observation position with the scanning electron microscope is changed.

For a foreign substance having a large coordinate error, not only the accuracy of calculating the coordinate error is reduced, but also a large coordinate error may remain after the coordinate correction compared to other foreign substances. Therefore, in the present invention, an allowable error between the corrected coordinate value obtained by correcting the coordinate value of the foreign material supplied from the foreign material inspection device by coordinate conversion or the like and the foreign material coordinate value detected by the scanning electron microscope is set on the operation screen. I do. Then, after performing the coordinate correction calculation using the derived coordinate conversion formula, if there is a foreign substance exceeding the error range set in advance, the coordinate conversion formula is derived again by using data excluding the coordinate data of the foreign substance. To The condition set in advance may include not only the coordinate error but also the total number of foreign substances excluded from the calculation.

[0057]

According to the present invention, when observing a foreign substance or the like on a sample using the coordinate data from the foreign substance inspection apparatus, highly accurate coordinate correction is always performed without the user's time and effort. Thus, it is possible to provide a scanning electron microscope capable of always correcting a coordinate error between devices to an optimum state.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an example of a scanning electron microscope according to the present invention.

FIG. 2 is a diagram showing a relationship between a wafer coordinate system and a stage coordinate system.

FIG. 3 is a flowchart illustrating a procedure for observing foreign matter on a wafer using a scanning electron microscope for semiconductors.

FIG. 4 is an explanatory diagram showing a relationship between a wafer outer shape and a wafer coordinate system.

FIG. 5 is an explanatory diagram showing the relationship between a stage coordinate system, a wafer coordinate system, and a deformed wafer coordinate system.

FIG. 6 is a diagram illustrating coordinate conversion between two coordinate systems.

FIG. 7 is a diagram showing an example of an arrangement diagram of a foreign substance in which a foreign substance in which coordinate values are registered is distinguished from another foreign substance.

FIG. 8 is an explanatory diagram showing a state in which a foreign substance used for deriving a coordinate conversion formula is selected from a layout diagram of the foreign substance.

FIG. 9 is an explanatory diagram showing a state in which a foreign substance used for deriving a coordinate conversion formula is selected from a foreign substance list.

FIG. 10 is an explanatory diagram showing a state in which a foreign substance used for deriving a coordinate conversion formula is automatically selected according to an image display area on a sample by a scanning electron microscope.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electron gun, 2 ... Electron lens, 3 ... Deflector, 4 ... Secondary particle detector, 5 ... Sample, 6 ... Sample stage, 7 ... Electron beam, 8 ... Secondary particle, 9 ... Lens control circuit, 10 ... Deflection control circuit, 1
DESCRIPTION OF SYMBOLS 1 ... Analog / digital converter, 12 ... Address control circuit, 13 ... Image memory, 14 ... Control means, 15 ... Display, 16 ... Computer, 17 ... Image synthesis means, 1
8 keyboard, 19 mouse, 21 moving stage,
30 ... display window, 31 ... outside shape of wafer, 32 ...
Orientation flat, 33 ... Extension line of wafer outer circumference circle, 34 ... Foreign matter, 35 ... Foreign matter whose coordinate value is registered, 3
6: Foreign matter used for deriving a coordinate conversion formula; 37: Frame for selecting a foreign material; 38: SEM image display range; 39: Mark indicating a foreign matter for which coordinate values are registered; 40: Used for deriving a coordinate conversion formula Mark indicating foreign matter to be performed, 41... X of stage coordinate system
Axis, 42: Y axis of stage coordinate system, 43: X axis of wafer coordinate system before coordinate correction, 44: Y axis of wafer coordinate system before coordinate correction, 45: X of wafer coordinate system after coordinate correction
Axis, 46: Y axis of wafer coordinate system after coordinate correction, 50:
Imaging optical system, 51 ... CCD camera

Claims (10)

[Claims] 1. A stage movable two-dimensionally in a stage coordinate system defined by a stage in an apparatus for holding / moving a sample, and an electron beam converging and scanning the sample held on the stage. And a detecting means for detecting secondary particles generated from the sample by electron beam irradiation, and in a scanning electron microscope for forming a sample image using the output of the detecting means, the shape of the sample on the stage A sample coordinate system setting means for setting a sample coordinate system defined together; and a coordinate value supplied from another device for indicating a position of an observation target on the sample, the coordinate value in the sample coordinate system. Coordinate conversion means for converting the coordinate value of the observation object into the coordinate value of the observation object detected in the sample coordinate system; and the other device for the observation object. Or Coordinate error calculating means for calculating an error between the supplied coordinate value and the detected coordinate value registered in the coordinate value registering means, and a coordinate conversion equation setting for setting a coordinate conversion equation so as to minimize the error Scanning electron microscope comprising: 2. The scanning electron microscope according to claim 1, further comprising second coordinate value registration means for registering a coordinate value of the observation target object detected in the stage coordinate system. 3. A coordinate registration condition setting means for setting a condition of an observation object to be registered in the coordinate value registration means, wherein a detected coordinate value in the sample coordinate system of the observation object conforming to the coordinate registration condition is provided. 3. The scanning electron microscope according to claim 1, further comprising a function of automatically registering the coordinates in the coordinate value registration unit. 4. A position display means for displaying a two-dimensional arrangement of an observation target on the sample based on coordinate data supplied from the other device, wherein the coordinate value registration means stores detected coordinate values. 2. The scanning electron microscope according to claim 1, wherein the scanning electron microscope has a function of distinguishing and displaying an observation object in which the object is registered and an observation object in which the object is not registered on the position display means. 5. The apparatus according to claim 1, further comprising means for selecting an observation object to be used by said coordinate error calculating means on said position display means, and having a function of displaying the selected observation object separately from others. The scanning electron microscope according to claim 4. 6. A list display means for displaying a list of observation objects based on coordinate data supplied from said another device, and an observation object whose detected coordinate values have been registered in said coordinate value registration means are registered. 2. The scanning electron microscope according to claim 1, wherein the scanning electron microscope has a function of distinguishing and displaying an unobserved object on the list display means. 7. The apparatus according to claim 1, further comprising means for selecting an observation object to be used by the coordinate error calculation means on the list display means, and having a function of displaying the selected observation object separately from others. The scanning electron microscope according to claim 6. 8. A coordinate error calculation condition setting means for setting a condition of an observation object used by the coordinate error calculation means, wherein the coordinate conversion equation setting means includes a coordinate conversion equation 2. The scanning electron microscope according to claim 1, wherein the scanning electron microscope has a function of setting a coordinate conversion formula using a detected coordinate value of an observation target object that meets a condition set by the coordinate error calculation condition setting means. 9. The coordinate error calculation condition setting means has a function of setting conditions of an observation target used by the coordinate error calculation means in relation to an observation position on the sample, and moves the observation position on the sample. Then, there is provided a function of setting a coordinate conversion formula using a detected coordinate value of an observation target object that meets conditions related to the observation position on the moved sample set by the coordinate error calculation condition setting means. The scanning electron microscope according to claim 8, wherein: 10. A means for setting an allowable error between a detected coordinate value of an observation object used by said coordinate error calculating means and a coordinate value in said sample coordinate system converted by said coordinate converting means, and 2. The scanning electron microscope according to claim 1, further comprising a function of removing an observation object having an error exceeding the error and re-executing the error calculation by the coordinate error calculation means.