JPH027183B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a positioning device that automatically positions a predetermined pattern formed on a member to be measured, such as a pattern on a semiconductor wafer, to a fixed position on a scanning electron microscope.

[Technical background of the invention and its problems]

In the field of semiconductor devices, as the density of integrated circuits increases, there is a need for equipment that can measure fine patterns formed on the surface of semiconductor wafers at high speed and with high precision. Normally, to measure such fine patterns, measuring instruments that use optical means are widely used, such as micrometers that use an optical microscope, and electronic measuring instruments that combine an optical microscope and an industrial television. However, when the pattern size becomes sub-micron, it becomes difficult to measure using measuring instruments using these optical means due to the resolution.

Non-optical means, such as a measuring instrument that combines a scanning electron microscope with a monitor television, are capable of measuring even such fine patterns in terms of resolution. However, if the cultivation rate is increased in order to measure patterns with high accuracy, it takes time to find and position the desired pattern, which significantly reduces the efficiency of inspection and measurement. Therefore, a device for positioning a predetermined pattern at high speed and with high precision is required for a scanning electron microscope.

However, for this positioning, mechanical methods such as pressing an orientation flat formed on a semiconductor wafer against a reference pin have a large positioning error, and the conventional optical method using alignment marks Positioning by means requires a complicated device and a highly accurate and expensive stage on which the semiconductor wafer is mounted.

[Purpose of the invention]

The object of the present invention is to process image data of a member to be measured on which a predetermined pattern is formed, which is obtained from a scanning electron microscope, and to easily position the desired pattern with high precision.

[Summary of the invention]

A scanning electron microscope, an −
a stage control unit that controls the movement of the Y stage; a scan control unit that controls the electron beam to scan at a specified magnification; and a scan control unit that controls the electron beam to scan at a specified magnification, and reproduces an image signal sent from the scanning electron microscope to generate an image of the predetermined area. a display section that displays the image signal, a frame memory section that stores the image signal as image data, a reference pattern generation section that stores a plurality of reference patterns with different magnifications corresponding to a predetermined pattern of the member to be measured, and a frame memory section. Correlation calculation that calculates a correlation with a reference pattern at a magnification corresponding to the scanning magnification of the electron beam selected from a plurality of reference patterns stored in the memory, and calculates the coordinates of the predetermined pattern in the predetermined area from this correlation. scan command, scan control unit, frame memory unit, and reference pattern generation unit, respectively.
In addition to transmitting image data and a reference pattern calling command, the difference between the coordinates of the predetermined pattern calculated by the correlation calculation unit and the center coordinates of the display device that constitutes the display unit is calculated, and X is executed so that they match. - Consists of an arithmetic control unit that sends drive commands to move the Y stage to the stage control unit, and first performs rough positioning using low-magnification operation processing, and then performs high-magnification operation processing to precisely position a predetermined pattern. I decided to position it.

[Embodiments of the invention]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention in which a predetermined pattern formed on a semiconductor wafer is positioned will be described below with reference to the drawings.

As shown in FIG. 1, the positioning device of this example moves by positioning and mounting a scanning electron microscope 1 and a semiconductor wafer W, and positions the mounted semiconductor wafer W with respect to the scanning electron microscope 1. It has an X-Y stage 2 for positioning. The scanning electron microscope 1 focuses an electron beam 4 emitted from an electron gun 3 with an electron lens system 5, deflects it with a deflection system 6, and scans the semiconductor wafer W positioned at the fixed position, Secondary electrons 7 generated by this scanning are captured by a secondary electron detector 8. The secondary electrons 7 captured by the secondary electron detector 8 are
It is sent to the display section 9 and frame memory section 10 as an image signal.

The movement of the XY stage 2 is controlled by a signal sent from a stage control section 13 based on a drive command sent from an arithmetic control section 12 that includes a computer, memory, etc.
The deflection of the electron beam 4 is determined by the scan control unit 14 based on a scan command specifying the scanning width and scan angle of the electron beam 4 and a magnification command specifying the scanning magnification, which are also sent from the arithmetic control unit 12. controlled by

The display section 9 captures the image signal sent from the secondary electron detector 8 in synchronization with the scanning of the electron beam 4 by the signal sent from the scan control section 14, and displays a display device (not shown in this example). playback and display on the CRT screen. Further, the image signal sent to the frame memory section is binarized and then stored in the frame memory section 10 as image data.

Further, this positioning device may be a single or a plurality of reference patterns that store a plurality of reference patterns having the same shape as a predetermined pattern formed on the semiconductor wafer W, such as an alignment mark or a pattern whose dimensions are to be measured, and having different magnifications. Based on the reference pattern generator 15 consisting of one or more reference pattern memories A, B, C, etc. storing a plurality of reference patterns, and the arithmetic control section 12, the frame memory section 10 The reference pattern generation unit 15 uses the called image data.
It has a correlation calculation unit 16 that calculates the correlation with the reference pattern selected and called from among the reference patterns, and calculates the center address (x ₁ , y ₁ ) of the comparison area where the maximum correlation is obtained.

The calculation control unit 12 sends commands to the scan control unit 14, frame memory unit 10, and reference pattern generation unit 15 as described above, and also sends the address (x ₁ , y ₁ ) and the pre-memorized address of the center of the screen of the display cathode ray tube (x ₀ ,
_y0 ) to determine the amount of movement of the XY stage 2, and sends a drive command to the stage control section 13.

Next, a method of positioning the alignment marks formed on the semiconductor wafer W in a predetermined pattern so that the image of the alignment marks is placed in the center of the screen of the display cathode ray tube will be described.

First, the semiconductor wafer W is placed on the X-Y stage 13.
is positioned and mounted, and this semiconductor wafer W is fed into a fixed position with respect to the scanning electron microscope 1. This feeding is performed with constant accuracy by the stage control section based on a command sent from the arithmetic control section 12.

With respect to the semiconductor wafer W sent into this fixed position, the deflection system 6 of the scanning electron microscope 1 moves the electron gun The electron beam 4 emitted from the electron lens system 5 is deflected at a low magnification of several 100 to 1000 times to scan the predetermined area. Secondary electrons emitted from the semiconductor wafer W in accordance with this scanning are captured by the secondary electron detector 8 and sent to the display section 9 and the frame memory section 10 as an image signal. The display unit 9 reproduces this and displays the image of the predetermined area on the screen of the display cathode ray tube. Further, the frame memory unit 10 binarizes and stores it as image data.

Performing the deflection scanning of the electron beam 4 at a low magnification means that even if the semiconductor wafer W is fed with a relatively low constant precision as described above, the target alignment mark will not be included in the scanning area of the electron beam 4. Then, as shown in FIG. 2A, an alignment mark M is displayed on the screen 18 of the display cathode ray tube, and as schematically shown in FIG. 3, the image data stored in the frame memory section 10 is This means that it is also included in 20.

The image data 20 stored in the frame memory section 10 is called up by the correlation calculation section 16 based on a calling command sent from the calculation control section 12.
At the same time, based on a calling command sent from the calculation control section 12 to the reference pattern generation section 15, the calculation control section 12 sends the scan control section 1
The reference pattern of the magnification that corresponds to the magnification command sent to 4, that is, the scanning magnification of the electron beam 4 of the scanning electron microscope 1, is selected from a plurality of reference patterns stored in the reference pattern generator 15, and the correlation is It is called by the calculation unit 16.

The correlation calculation unit 16 first calculates these image data 2.
0 and the reference pattern, as shown in FIG.
is determined, and the entire surface of the image data 20 is scanned by shifting the comparison area 21 one pixel at a time in the horizontal and vertical directions, for example, as shown by arrows 22 and 23, and the image data and An AND operation is performed on pixels corresponding to the reference pattern, and the sum of pixels determined to be the same is determined. Figure 4 shows an example of this.
21c are different comparison areas, 24 are reference patterns, and 25a to 25c are comparison areas 21.
This is the result of an AND operation between a to 21c and the reference pattern 24, and the crosshatch portion 26 indicates pixels determined to be the same. Shown as 25a in this diagram
The comparison area 21a where the AND operation result was obtained had the highest number of pixels, 26, which were determined to be the same, indicating that the greatest correlation was obtained. The correlation calculation unit 16 then selects the comparison area 21a from which the maximum correlation has been obtained.
Find the center address (x ₁ , y ₁ ) of the comparison area 21a, that is, the center coordinates of the alignment mark M in the predetermined area scanned by the electron beam 4, and calculate the center address (x ₁ , y ₁ ) of the comparison area 21a. It is sent to the calculation control section 12.

The arithmetic control unit 12 calculates the difference between this address (x ₁ , y ₁ ) and the pre-stored address of the center of the screen 18 of the display cathode ray tube, that is, the center coordinates of the screen 18, Find the feed amount. Then, based on this feed amount, a drive command is sent to the stage control section 13, and the second
As shown in Figure B, the X-Y stage 2 is moved so that the center of the alignment mark M coincides with the center of the screen 18 of the display cathode ray tube.

Thereafter, the arithmetic control unit 12 sends a magnification command higher than the magnification to the scan control unit 14, and the scanning magnification of the electron beam 4 is increased to, for example, several thousand times, so that the center of the alignment mark M is displayed. A predetermined area of the semiconductor wafer W, which is positioned to coincide with the center of the screen 18 of the cathode ray tube, is scanned. As a result, on the screen 18 of the display cathode ray tube, as shown in FIG.
is displayed. This alignment mark M is on screen 18.
If it deviates from the center of the screen 18, the same process is performed again to move the X-Y stage 2 so that the center of the alignment mark M coincides with the center of the screen 18, as shown in FIG. In this case, the process is as follows:
Needless to say, a reference pattern with a magnification corresponding to the above-mentioned scanning magnification is called from the reference pattern generation section 15.

If the alignment mark M positioned at the center of the pixel 18 of the display cathode ray tube does not reach the predetermined size as described above, the scanning magnification of the electron beam 4 is increased again to further align the position mark M positioned at the center of the pixel 18 of the display cathode ray tube. The enlarged display mark M is displayed and the same process is performed to position it at the center of the screen 18.

In addition, when measuring the dimension of the alignment mark M positioned at the center of this screen 18, as shown in FIG. 5, the cursor 28 is placed on the measurement position and measured. In this case, in advance, cursor 2
If the address of 8 is stored in the arithmetic control unit 12, the command sent from the arithmetic control unit 12 will cause
The cursor 28 can be moved automatically.

Furthermore, if the distance from the alignment mark M to the pattern P to be measured is known as shown by x ₃ and y ₃ in Fig. 5, after detecting the position of the alignment mark M as described above, this Based on the drive command sent from the calculation control unit 12 based on the values of x ₃ and y ₃ ,
As shown in FIG. 6, it is also possible to measure by positioning the pattern P at the center of the screen 18 of the display cathode ray tube and placing the cursor 28 thereon.

When the positioning device is configured as described above, it is possible to first scan a predetermined area of the semiconductor wafer W at a low magnification to find the position of a predetermined pattern, and then use a high magnification to position the predetermined pattern at a predetermined position. Positioning of a pattern image enlarged to a required size and subsequent measurement of pattern dimensions can be easily performed in a short time. In addition, this type of positioning does not require a highly accurate and expensive X-Y stage, unlike conventional positioning using optical means, and the device can be assembled using low-cost mechanical components. .

〔Effect of the invention〕

The member to be measured, on which a predetermined pattern has been formed, is mounted on an X-Y stage, sent to a fixed position in a scanning electron microscope, first scans the predetermined area at low magnification to find the position of the predetermined pattern, and then Since the predetermined pattern is positioned at a predetermined position using a high magnification, the predetermined pattern enlarged to a required size can be easily positioned at a predetermined position with high precision.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a positioning device that is an embodiment of the present invention, and FIGS. 2A to 2D are screens of a cathode ray tube for display showing the order in which alignment marks formed on a semiconductor wafer are positioned. Figure 3 is a diagram for explaining the image data processing method, Figure 4 is a diagram for explaining the correlation between image measurement and reference patterns, and Figures 5 and 6 are diagrams for explaining the alignment marks and patterns, respectively. FIG. 3 is a diagram for explaining dimension measurement. DESCRIPTION OF SYMBOLS 1...Scanning electron microscope, 2...X-Y stage, 3...Musketball gun, 4...Electron beam, 5...Electron lens system, 6...Deflection system, 7...Secondary electron, 8
... Secondary electron detector, 9 ... Display section, 10 ... Frame memory section, 12 ... Arithmetic control section, 13 ...
Stage control section, 14...Scan control section, 15...Reference pattern generation section, 16
... Correlation calculation section, M ... Alignment mark, P ...
Pattern, W...semiconductor wafer.

Claims (1)

[Claims] 1. A scanning electron microscope that scans a predetermined region of a member to be measured on which a predetermined pattern is formed with an electron beam, and captures secondary electrons emitted from the region through this scanning and sends them out as an image signal; The member to be measured is mounted and moved in the X and Y directions, and the member to be measured is positioned relative to the scanning electron microscope so that the electron beam can scan a predetermined area of the member to be measured. Y stage and this X-
a stage control unit that controls movement of the Y stage; a scan control unit that controls scanning of the electron beam so that the electron beam scans at a designated magnification selected from a plurality of magnifications; and a display device based on the image signal. a display unit that reproduces and displays an image of the predetermined area; a frame memory unit that stores the image signal as image data; and a frame memory unit that stores a plurality of reference patterns with different magnifications corresponding to the predetermined pattern of the member to be measured. and a reference pattern having a magnification corresponding to a scanning magnification of the electron beam selected from the image data stored in the frame memory unit and a plurality of reference patterns stored in the reference pattern generation unit. a correlation calculation unit that obtains a correlation and calculates the coordinates of a predetermined pattern in the predetermined area from the correlation;
A scan command means for instructing the scan control section to scan the electron beam and the scanning magnification; and a scan command means for instructing the scan control section to scan the electron beam and the scanning magnification; calling command sending means for selecting a reference pattern corresponding to the scanning magnification of the electron beam and sending out a calling command to the correlation calculating section; coordinates of the predetermined pattern calculated by the correlation calculating section and center coordinates of the display device; positional deviation calculation means for calculating the difference between
A positioning device comprising: an arithmetic control section having a drive command sending means for sending a drive command for moving the Y stage to the stage control section.