JPS62195840A - Scanning electron microscope - Google Patents

Abstract

PURPOSE:To simplify the view field finding work, by mark-displaying the observed positions through electron beam scanning depending on signals to display the inclination, movement, and the rotation angle of a sample, overlapping on the object view field image. CONSTITUTION:When a sample is inclined at an angle thetat by a push button on a scanning table 20, and the surface J of a wafer is apart at z from the the surface S, the positioning directly under the optical axis is moved in the -X direction at ztanthetat, and the rectangular mark displayed on the graphic display CRT 15 is shown at the position M. Then by handling the push button 20 to drive an X, Y movement mechanism 3, and moving the sample in the X, Y direction, the center coordinate of the rectangular mark M is moved depending on the signal operated in a movement arithmetic unit 18a, and as a result, the rectangular mark M displayed on the CRT 15 is moved to the position responding to the point A. Then, the surface of the point A of the wafer W arranged directly under the optical axis is scanned by the electron beam 6, and the image at the point A is displayed on a display CRT 12 to be observed. Therefore, the view field setting can be secured simply.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a scanning electron microscope, and more particularly, to a scanning electron microscope capable of displaying an actual observation position in a field of view to be observed.

[Prior Art] The scanning electronics 81 mirror has a sample device as shown in FIG. That is, a tilting mechanism 2 is attached to the side wall 1 of the sample chamber, and its tilting axis (J is fixed). 4 is placed, and the observation sample 5 is placed on the rotating mechanism 4.
It is attached via a boulder. Observation of IC wafers and the like has come to be carried out using such a sample load, but there are attachments such as detectors 1 to 1 in the sample chamber.
are arranged in various ways, so that the tilting mechanism can tilt only on one side. In such an apparatus, as shown in FIG. 6, an IC wafer W is set on a rotation mechanism F, and after scanning the electron beam 6 and observing the Δ portion of the exposure pattern of the wafer W, , when trying to observe part 8 by irradiating the electron beam 6 from the direction of arrow H,
It is necessary to first tilt the wafer W to observe part A, then rotate the wafer W by about 180 degrees, and then move part 8 directly below the optical axis C by moving it in X and Y directions.

“Problems to be Solved by the Invention” As described above, when rotation and tilt are added to the X and Y movements, it becomes extremely difficult to find the field of view of the position to be observed, and it is difficult to easily observe the target position. I can't.

The present invention solves these conventional drawbacks, and the sample is
To provide a scanning electron microscope that can display which part of the entire field of view the position under observation is in by electron beam scanning, not only when it is moved but also when rotated or tilted, thereby simplifying the work of searching the field of view. It is intended to.

[Means for Solving the Problems] Therefore, the present invention provides a sample tilting mechanism for tilting a sample, a sample moving mechanism, a sample rotation mechanism, and a means for two-dimensionally scanning an electron beam in a sample soil. , an apparatus comprising a display means for displaying an image of the sample based on a detection signal accompanying scanning of the electron beam, a display for graphically displaying a visual field image of the sample to be observed;
It is characterized by comprising means for superimposing and marking an observation position by electron beam scanning on the object visual field image based on signals representing the inclination angle θt, movement amounts lx, ly, and rotation angle θr of the sample. There is.

[Example] Embodiments of the present invention will be described in detail below based on the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention, and the same components as in FIG. 5 are given the same numbers. In the figure, 7 is an electron gun, 8 is a focusing lens for focusing the electron beam 6, and 9x and 9y are deflection coils. A sawtooth scanning signal is supplied from a scanning signal generation circuit 10 to the deflection coils 9x and 9y. 11X and 11V are amplifiers.

The scanning signal from the scanning signal generating circuit 10 is also supplied to the deflection device of the cathode ray tube 12 for image display, and the cathode ray tube 12 is scanned in synchronization with the electron beam 6. A secondary electron detector 13 is arranged to detect secondary electrons generated from the sample by irradiation with the electron beam 6. The output signal from the detector 13 is supplied via an amplifier 14 to an image display cathode ray tube 12 as a luminance signal. 16T and 16R are pulse motors for driving the tilting mechanism 2 and rotation mechanism 4, respectively, and 16X and 16Y are pulse motors for driving the X and Y moving mechanisms. These motors 16T, 16R,
16X, 16Y are motor drive circuits 17T, 17R, respectively.
It rotates by supplying drive pulses generated from 17X and 17Y. The generation of drive pulses in each of these drive circuits is controlled by control signals from the sieve control device 18. This control device 18 has a main calculation section 18C as well as a storage section 18m that stores pattern data and the like for graphically displaying the patterns of each type of wafer. Furthermore, the arithmetic and control unit 18 is X.

A parallel movement calculation unit 18a that calculates observation position coordinates after X and Y movement based on signals representing the X and Y movement amounts lx and ly by the Y movement mechanism 3; a tilt calculation unit 1st that calculates coordinates after tilting the sample; It has a rotation calculation section 18r and a correction calculation section 18b for calculating coordinates after rotation. Furthermore, as shown in FIG. 2(a), it is assumed that the tilt axis U is perpendicular to the plane of the paper, and the thickness of the sample deviates from the standard thickness. The position J of the sample surface is the eucentric position (plane) S of the sample inclination
Although it will be shifted by a certain distance Z from the storage unit 1
8m contains a table containing the relationship between the wafer type and the deviation MAz so that when the wafer type is input during the operation described later, the value of the deviation amount Z can be read out based on the information on the wafer type. C is memorized. Arithmetic control unit 18
'', ri control signals are sent to the graphic display cathode ray tube 15 via the graphic display signal generation circuit 19. 20 is in operation, 20 in operation
As shown in FIG. 3, there are buttons 20 t for changing the tilt angle of the sample, and buttons 20 a and 20 b for instructing movement of the sample in the X and Y directions.

20c, 20d, and a legitimate child 2Or for instructing the rotation of the sample. Historically, wafer molds selected as specimens have been manually manipulated.

In this configuration, the wafer W was selected as a sample, and the wafer W was tilted as shown in FIG.
The operation of the above-mentioned apparatus will be explained by taking as an example the case where part B of the sample is observed after observing part A of '81.

First, the operator sets the bar W by attaching it to a sample holder (not shown). Then, the type of the mounted wafer is input using the input device 20. In response to this input, the main calculation control section 18c reads out graphic display pattern information corresponding to this type of wafer from the storage section 18m based on the information on this type of wafer, and sends it to the graphic display signal generation circuit 19.

As a result, based on the signal from the circuit 19, as shown in FIG.
A wafer pattern P as shown in is displayed on the cathode ray tube 15. The display position of this pattern P is fixed with respect to the screen. Furthermore, since the main controller 18c sends information for graphically displaying a rectangular pattern representing the observation area to the circuit 19, a rectangular mark M is displayed on the cathode ray tube 15 superimposed on the wafer pattern P.

Furthermore, a part of the rectangular pattern M is displayed as a high-intensity bright line Ma in order to represent the start side of scanning by the electron beam. The position of this mark M is at the center of the wafer pattern as shown in FIG. 4(a) when the sample device is not driven at all. Therefore, using the 20th legitimate child 20t during scanning, the 6th
When the sample is tilted at an angle θ as shown in the figure, as shown in Figure 2 (
As shown in a), the surface J of the double bar W is 7 points from the Eusen 1-7 plane S of the sample inclination (if it is shifted, the position directly below the optical axis is only z tan θ [ −
Because it moves in the X direction, the rectangular mark displayed on the graphic display cathode ray tube 15 is M in FIG. 4(b).
It will be displayed in the position shown. Then, push button 20
a, 20b, 20c, and 20d to drive the X and Y mobile units 1M3, and move lx and lx in the X and Y directions, respectively.
ly (lV=o) When the sample is moved, the center coordinates of the rectangular mark M move to the following coordinates (x1, yi) based on the signal calculated by the movement calculation section 18a.

As a result, the rectangular mark M displayed on the cathode ray tube 15 moves to a position corresponding to section A in FIG. 6, as shown in FIG. 4(C). Therefore, a portion A of the wafer W placed directly below the optical axis is scanned by the electron beam 6, and an image of the portion A is displayed on the image display cathode ray tube 12 for observation. In addition, cathode ray tube 1
Although it is not actually displayed on the screen of 5, as shown in FIG. 4(a), the coordinate system 0-X, Vh<
This defines the display position of each mark. Next, observe the image of part B in Figure 6 and cover it! When the second child 2Or of the operation console 20 is then rotated, a control signal is sent from the central processing unit 18 to the motor drive circuit 17R, and as a result, the motor 16R rotates and the sample r15 rotates by an angle θr. At this time, the central processing unit 18 calculates the following equation (2) in the rotary wave sieve unit 18r of the central processing unit 18 based on the signal representing the angle θr instructed by the operating unit 20, and tilts the sample. Assuming that the displacement mZ of the wafer surface from the axis is O, coordinates (x2.y2) representing the center of the observation area after rotation are determined.

Further, the main calculation control section 18c reads out data representing the misaligned product 7 corresponding to this wafer stored in the storage section 18m based on the information representing the first part of the wafer W, and sends it to the correction calculation section 18b. The correction calculation unit 18b calculates the following equation (3) based on this data Z, and calculates the deviation Z.
The mark center position coordinates (x3, y3) representing the center of the observation area when the mark exists are calculated.

Note that the correction term (second term) in Equation (3) is such that the center of the observation area, which is moved in the X direction by =z tanθt due to the tilt, is caused by the rotation of the wafer W, as is clear from FIG. 2(b). Due to the accompanying rotation of x and y coordinates, z tanθt c
The X component osθr and the X component z tanθtsinθr
This indicates that it is distributed among the components. Based on the rectangle center coordinate values obtained in this manner, the central processing unit 18 moves the rectangle representing the observation area. the result,
A rectangular mark M representing the observation area position rotates on the display screen of the cathode ray tube for graphic display as shown by arrow N in FIG. 4(C). Therefore, further operation 2
If the legitimate child 2Or of 0 is rotated, the rectangular mark M moves to the position shown by M- in FIG. 4(C), so the operation of the legitimate child 2Or is stopped at this stage.

Further, buttons 20a, 20b, 20c, 2
By scanning 0d and moving the wafer W in the X and Y directions, the mark M moves to the position shown in FIG. 4 (d>).

Therefore, by scanning the electron beam 6 over the sample and displaying the sample image on the cathode ray tube 12, it is possible to observe the image obtained by irradiating the electron beam 6 onto the portion 13 of the wafer W from the direction of the arrow H. .

In this way, even if the sample is rotated or tilted as well as moved in the The target part of the sample can be observed using the

In the above embodiment, calculation of the coordinates of the center of the mark has been explained, but calculation of the coordinates of each point constituting the rectangular mark M is based on the fact that this point is the center coordinate (xl, yl)
If there is a deviation from α and β in the X and X directions, respectively,
×1+α, V1 instead of center coordinates (xl, yl)
It can be obtained by substituting +β. Since each point constituting the rectangular mark M is calculated and displayed in this way, it can always be displayed correctly regardless of the rotation of the bar W with the bright line Ma representing the scanning start side. It is possible to grasp not only which position of the sample the image displayed on the image display cathode ray tube is, but also which side the image was obtained from when scanning started.

In the above-described embodiment, the rectangular mark is displayed as a bright line, but when the graphic display is performed in color, the rectangular part is displayed in a different color from the square part. Also good. In that case, a part of the rectangular part may be displayed in a different color from other parts of the rectangle to represent the scanning start side.

Further, in the above-described embodiment, the deviation amount 2 is read out based on information representing the wafer type.
You may also manually press the keys directly.

Further, for simplicity, in FIG. 4, the mark indicating the observation area is always shown as a rectangle.

However, as this area actually deforms into a parallelogram other than a rectangle due to the inclination of the sample, etc., by observing the shape of this mark, it is possible to determine not only the actual position of the observation area but also the shape of the observation area. You can also know.

Furthermore, when the position of the sample in the optical axis direction is changed, the amount of excitation of the objective lens is usually changed in order to refocus the sample, but with this change in the amount of excitation, the amount of image rotation also changes. do. Therefore, the relationship between the excitation amount of the objective lens and the image rotation amount is investigated in advance and stored as a table in the storage device, and the image rotation amount is expressed from the table based on the signal representing the actual excitation current value of the objective lens. The mark M may be displayed at an accurate position by reading data and adding the amount of image rotation by the objective lens to the amount of image rotation by the sample rotation mechanism based on the read data.

[Effects of the Invention] As is clear from the above description, the apparatus based on the present invention can display the observation position of the sample not only when moving in the X and Y directions but also when the sample is tilted and rotated. It is also possible to set the field of view inside the cylinder.

Further, according to the apparatus of the above-described embodiment, even when the sample surface deviates from the eucentric position of the sample inclination, the observation position of the sample can be displayed correctly.

Furthermore, according to the apparatus of the series of embodiments, not only the observation position within the entire observation field is displayed, but also the scanning start side of the electron beam is displayed, so that the displayed image It is possible to know from which side the image was scanned.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an embodiment of the present invention, Fig. 2 is a diagram illustrating correction of the observation position when the sample surface deviates from the eucentric plane of the sample inclination, and Fig. 3 4 is a diagram for explaining the display during operation, FIG. 4 is a diagram for explaining a display example of the observation position in a cathode ray tube for graphic display, and FIG. FIG. 6 is a diagram for explaining an example of an observation region when observing a sample by rotating and tilting the sample. 1: Sample chamber side wall 2: Sample tilt mechanism 3: X, Y movement mechanism 4: Sample rotation mechanism 5: Sample 6: Electron beam 7: Electron gun 8: Focusing lens 9x, 9V: Deflection coil 10: Scanning signal generation circuit 12 :Cathode ray tube for image display 13:Secondary electron detector 15Cathode ray tube for Nigella hook display 16X, 1
6Y, 16R, 16T: Pulse motor 17X, 17Y,
17R, 17T: Drive circuit 18: Arithmetic control unit 19 Nigella quick display signal generation circuit 20: Operation console W: Wafer P: Wafer pattern

Claims (3)

[Claims] (1) A sample tilting mechanism for tilting the sample, a sample moving mechanism, a sample rotation mechanism, a means for two-dimensionally scanning an electron beam on the sample, and a detection signal based on the scanning of the electron beam. In the apparatus, the apparatus includes a display means for displaying an image of the sample, a display for graphically displaying a visual field image of the sample to be observed; 1. A scanning electron microscope characterized by comprising means for displaying a mark by superimposing an observation position by electron beam scanning on the object visual field image based on a signal representing the field of view of the object. (2) The sample tilting mechanism is a tilting mechanism for tilting the sample around a eucentric axis, and includes means for inputting information representing the amount of deviation z of the sample surface from the eucentric axis, and the mark display means The scanning electron microscope according to claim 1, wherein the observation position is displayed as a mark by correcting a display position shift based on the shift based on a signal representing the shift amount z. (3) The scanning electron microscope according to claim 1, wherein the mark includes a portion displaying information indicating the scanning start side of the electron beam at the observation position.