JPH04149943A - Scanning electron microscope for pattern inspection - Google Patents

Abstract

PURPOSE:To simplify the inspection on success or failure by displaying two cursors specifying the width of a pattern to be inspected and a marker indicating the allowable range on a screen, and calculating the marker position based on the difference between both cursor positions and the allowable error. CONSTITUTION:A scanning signal is fed to a deflecting coil 4 from a scanning signal generating circuit, and the region containing a pattern to be inspected on a sample 3 is scanned by an electron beam. Generated secondary electrons are detected by a detector 6 and inputted to a cathode-ray tube 10 fed with the scanning signal from a circuit 5 via an amplifier 7 as an intensity signal, and the secondary electron image of the specific region of the sample 3 is displayed on the screen of the tube 10. The first and second cursors C1, C2 are displayed in superimposition on the pattern P of an inspection subject on the screen, the position signals are fed to an allowable line width calculating means 15 from counters 13, 14, the means 15 receives the error rate from a memory 16 and calculates the allowable line width, the line width signal is fed to a signal generation section 9, and the marker signal is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a scanning electron microscope for pattern inspection suitable as an inspection device in the manufacturing process of semiconductor integrated circuits.

(Prior Art) Scanning electron microscopes are increasingly being used as inspection devices in the manufacturing process of semiconductor integrated circuits. In particular, the width, length, etc. of a pattern formed on a wafer are one of the important inspection items in a scanning electron microscope. In order to facilitate such inspections, two parallel straight lines (cursors) are displayed superimposed on the observation image of the scanning electron microscope, and the width and position of the cursors are adjusted to match the measurement target. Conventionally, a function has been used in which the width and length corresponding to the cursor are displayed or printed according to the magnification of the scanning electron microscope image.

(Problem to be solved by the invention) By the way, when inspecting the width and length of a pattern, a tolerance is often set, and if the deviation of the measured value from the set value exceeds this tolerance, the inspection is performed. Target sample (
semiconductor integrated circuit) is determined to be rejected. When this inspection is performed using the functions of the scanning electron microscope described above, it is necessary to numerically determine whether the displayed inspection results fall within the allowable range. Therefore, the actual
In the invention described in No. 53, by clearly displaying the design line width and its tolerance range as three straight lines on the image, it is easy to judge whether the width of the object to be measured is within this range or not. This makes it easy to determine whether the test is pass or fail. This method is very simple and useful when the object to be inspected has a single width and the object is within the tolerance range. When holding, the design line width and tolerance must be entered again.
It has the disadvantage of being time consuming.

Further, the width and position of the cursor are often adjusted by switching one moving means and moving the left and right (or up and down) cursors, respectively. However, in the above invention, since the two cursors are the same type of line, it is not clear on the screen which cursor can be moved at the moment, and it is easy to make mistakes in operation.

The present invention has been made in view of these points, and its purpose is to realize an inspection scanning electron microscope that can easily perform pass/fail inspections even for different widths and lengths. be.

(Means for Solving the Problems) An inspection scanning electron microscope based on the present invention includes a focusing means for focusing an electron beam on a sample, and a focusing means for focusing an electron beam on a sample.
a scanning means for dimensionally scanning; a detector for detecting a signal generated based on irradiation of the sample with an electron beam;
A cathode ray tube to which a detection signal from the detector is supplied as a luminance signal, and a first and second cathode ray tube that determines the pattern range to be inspected.
a marker position calculation unit that automatically calculates an allowable width marker position based on the difference between the first and second cursor positions and an allowable error rate; 2, a cursor signal and a marker signal are generated based on the cursor position and the marker position, and a cursor and a marker based on these cursor signals and marker signals are displayed on the cathode ray tube based on the detection signal. The present invention is characterized by comprising means for superimposing and displaying the sample image on the sample image.

(Function) In the inspection scanning electron microscope based on the present invention, two cursors defining the width of the pattern to be inspected and a marker indicating the tolerance range are displayed on the screen, and the first and second cursors The marker position is automatically calculated based on the position difference and the allowable error rate.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an embodiment of the present invention, where 1 is an electron gun. An electron beam generated from the electron gun 1 is narrowly focused onto a sample 3 by an objective lens 2. The sample 3
The upper electron beam irradiation position is changed according to a signal supplied to the deflection coil 4. A scanning signal is supplied to the deflection coil 4 from a scanning signal generating circuit 5. The sample 3
The secondary electrons generated by the electron beam irradiation are 2
It is detected by the secondary electron detector 6. The signal detected by the detector 6 is amplified by an amplifier 7, and then
It is supplied to an adder 8. The adder 8 adds the detection signal from the amplifier 7 and the signal from the cursor marker signal generator 9, and supplies the added signal to the cathode ray tube 10 as a video luminance signal.

Reference numeral 11 denotes a cursor moving means such as a joystick, and by operating this cursor moving means, the cursor position is set from the first cursor position counter 13 to the second cursor position counter 14 via the switch 12. Based on the values stored in the first and second cursor position counters 13 and 14, the cursor marker signal creation section 9 creates a cursor signal. The values of the first and second position counters are also supplied to the allowable line width calculating means 15, and the allowable line width calculating means 15 stores the values of the first and second position counters and the error rate memory 16. An allowable line width is calculated from the set error rate, and the calculated value is supplied to the cursor marker signal generation section 9. The operation of the scanning electron microscope having such a configuration is as follows.

A scanning signal for two-dimensionally scanning a specific range on the sample 3 is supplied from the scanning signal generation circuit 5 to the deflection coil 4, and as a result, the area of the sample 3 including the pattern to be inspected is exposed to the electron beam. scanned. Secondary electrons generated based on the scanning of this electron beam are detected by a detector 6. This detection signal is amplified by an amplifier 7,
Since the brightness signal is supplied to the cathode ray tube 10 to which the scanning signal is supplied from the scanning signal generation circuit 5 via the adder 8, the secondary electrons in the specific area of the sample 3 are displayed on the screen of the cathode ray tube 10. A statue is displayed. FIG. 2 shows an example of the screen of the cathode ray tube 10, and P in the figure is a pattern to be inspected.

In inspecting whether the line width of the pattern P described above is within the permissible range, first and second cursors C1 and C2 are displayed on the screen of the cathode ray tube 10, superimposed on the pattern P. The positions of the cursors C1 and C2 on the screen are determined by the values set in the first and second position counters 13 and 14. To determine the position of the first cursor C1, switch the switch 12 as shown by the solid line and operate the cursor moving means 11 so that the first cursor C1 almost coincides with one end of the pattern P to be inspected. This is done by setting the value of the first cursor position counter. Further, to determine the position of the second cursor C2, switch the switch 12 as indicated by the dotted line, operate the cursor moving means 11, and move the second cursor C2 to the pattern to be inspected P.
This is done by setting the value of the second cursor position counter 15 so that it almost coincides with the other end of the cursor position counter 15.

2, the position of the end of the pattern to be inspected is set.

On the other hand, the error rate R of the width of the pattern is set in the error rate memory 16 described above. The error rate set in the memory 16 is supplied to the allowable line width calculation means 15. The allowable line width calculation means 15 is also supplied with position signals of the two cursors CL and C2 from the first and second cursor position counters 1.3.14, and the calculation means calculates the error rate and the cursor position. From this, calculate the allowable line width. The calculation means 15
The signal corresponding to the allowable line width determined by is supplied to the cursor marker signal creation section 9, where a marker signal is created. For example, as shown in FIG. 2, when displaying two markers M1 to M4 at each edge of a pattern on the screen of the cathode ray tube 10, the position of the cursor C1 is
, if the position of cursor C2 is X2, each marker M1~
The coordinates of M4 are as follows.

Ml-Xi-(X2-Xi)(R/2)M
2-Xi + (X2-Xi) (R/2)M3-
X2- (X2-Xi) (R/2)M4-X2
+ (X2-Xi) (R/2) Thus,
In the example of FIG. 2, markers M1 to M4 indicating allowable line widths are displayed around cursors C1 and C2 displayed at both ends of the pattern to be inspected P, and the operator can compare these markers with the pattern image. It is possible to check whether the pattern width is within the allowable range.

FIG. 3 shows an example in which the first cursor C1 is aligned with one end of the pattern to be inspected, and two markers Ml and M2 indicating the allowable line width are displayed for the second cursor C2. There is. Marker M1 in the example of FIG. The coordinates of M2 are as follows.

Ml =X2- (X2-Xi) ・RM2-X2
+ (X2-Xi) ・R Also, if the shape of the marker is clear on the cathode ray tube, then
It does not have to be a long straight line as shown in the figure, but may be line segments M1 to M6 as shown in FIG.

In the examples shown in FIGS. 2 to 4 above, the first cursor C1 is displayed as a solid line, and the second cursor is displayed as a dotted line, so that it is easy to determine which cursor to move. I can do it.

Although the present invention has been described above, the present invention is not limited to the embodiments described above. For example, although a secondary electron image is displayed, a backscattered electron image may also be displayed. Although the first and second cursors are displayed separately using solid lines and dotted lines, if color display is possible, the two types of cursors may be distinguished by changing their display colors.

(Effects of the Invention) As explained above, in the scanning electron microscope for pattern inspection based on the present invention, two cursors defining the width of the pattern to be inspected and a marker indicating the allowable range are displayed on the screen. However, the marker position is automatically calculated based on the difference between the first and second cursor positions and the allowable error rate, so even if there are several types of inspection line widths, you can simply change the cursor width. , it is possible to automatically display a marker indicating the allowable line width, and it is possible to easily determine whether a pattern is acceptable or not. Furthermore, since the two cursors are displayed in different shapes or colors, it is possible to prevent erroneous operations when moving the cursors.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a scanning electron microscope according to the present invention, and FIGS. 2 to 4 are diagrams showing examples of display screens of a cathode ray tube according to the present invention. 1...Electron gun 2...Objective lens 3...
Sample 4... Deflection coil 5... Scanning signal generation circuit 6... Detector 7... Amplifier 8... Adder 9... Cursor marker signal generation section 10... Cathode ray tube 11... Cursor moving means 12...Switch 13.14...Cursor position counter 15...Allowable line width calculation means 16...Error rate memory

Claims (1)

[Claims] a focusing means for focusing an electron beam on a sample; a scanning means for two-dimensionally scanning the electron beam on the sample; a detector for detecting a signal generated based on irradiation of the electron beam on the sample; a cathode ray tube to which a detection signal from the detector is supplied as a luminance signal; a position setting means for setting the positions of first and second cursors for determining a pattern range to be inspected; and position setting means for setting the positions of the first and second cursors. a marker position calculation unit that automatically calculates an allowable width marker position based on the difference between and means for generating a marker signal and displaying a cursor based on these cursor signals and marker signals and a marker superimposed on a sample image displayed on a cathode ray tube based on the detection signal. electronic microscope.