JPS60161514A - Measurement of length by electron beam scanning - Google Patents

Abstract

PURPOSE:To enhance the reproducibility of measurement, by selecting two scanning positions on the basis of the scanning position, which corresponds to the signal with predetermined intensity among signals obtained on the bais of electron beam scanning corresponding to an arc, and a cursor position and measuring the distance between both positions. CONSTITUTION:Electron beam generated from an electron gun 1 is condensed by a condensing lens 2 and performs the digital scanning of a material by the scanning signal from a digital scanning signal generation circuit 5 through a magnification setting circuit 6 and a deflection coil 4. The reflected electron thereof is detected by a detector 7 and the detection signal is sent to a cathod ray tube 10 to which the scanning signal is supplied from the circuit 5 through an amplifier 8 and an adder circuit 9. A mark and two cursor signals are also supplied to the cathod ray tube 10 from a mark and cursor position setting circuit 14 and a coincidence circuit. A computer 12 takes in the scanning signal corresponding to a mark M on the basis of the mark position signal from the circuit 14. The width of an object can be calculated with good reproducibility from the distance between points N1, N4 near to cursor positions M1-M2 in the scanning positions N1-N4 of data points D1-D4 on set levels I1, I2.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a length measurement method using electron beam scanning, and in particular,
This paper relates to a sub-length method using electron beam scanning that has excellent length measurement reproducibility.

[Prior art] LS1. In the manufacturing process of devices such as VLSIs, it is required to precisely measure the length and width of elements formed on semiconductor wafers. In order to measure the length of this minute element, a sub-length device using an electron beam has been developed. In this electron beam length measurement device, an electron beam is scanned two-dimensionally on a material to be sublengthened, for example, reflected electrons obtained based on the scanning are detected, and the detection signal is transmitted to a cathode ray synchronized with the scanning. tube to obtain a backscattered electron image of the material.

Furthermore, one marker and two cursors are displayed on the cathode ray tube, and the marker and cursor are moved to the part of the electron beam image where the length should be measured, so that the length of an arbitrary line width, etc. can be measured. There is. In the invention disclosed in JP-A-58-117404,
Basically, the length between the positions indicated by two cursors is measured. That is, in order to find the width of element 1 in the electron beam image of the material to be sublengthened shown in FIG.
The marker M is moved to the position where the length should be measured, and the length measurement range is further indicated with the two cursors + and 2. Second
Figure (a) shows a cross-sectional view of the element 1, and Figure 2 (1
)) indicates a reflected electron signal detected by scanning an electron beam across the element 1. For example, the position specified by the cursor with 1 is Pl, and the cursor is 2
If the specified position is P2, then the length Ll between the two points is measured based on the number of digital scanning steps from the position P1 to the position P2. In this length measurement method, two points to be measured can be directly selected depending on the position of the cursor on the cathode ray tube screen. When performing sublength measurement, the cursor is set manually, so the position of the cursor relative to the end of the sublength element differs slightly each time, and cursor setting errors have a non-negligible effect on length measurement accuracy. It turns out. Furthermore,
For example, in the case of moving the mark to position B in the image of FIG. 1 to measure the width of element 10, and in the case of moving the mark to position B and measuring the width of element 1, The position of A and B
Even if the width of the cord 1 is the same at the position , the measurement results will differ depending on the cursor settings. That is, the conventional method of directly specifying two points to be measured using a cursor has a problem in the reproducibility of length measurements.

[Object of the Invention] The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a sub-length method using an electron beam with excellent measurement reproducibility.

[Structure of the Invention] The submaster method based on the present invention is characterized by comprising the following steps.

(A) Digitally scanning an electron beam two-dimensionally on the material to be sublengthened; (B) Displaying a sample image on a display device based on information signals from the material obtained based on the scanning. (C) Displaying a linear marker and two cursors perpendicular to the marker along with the sample image; (D) Based on electron beam scanning on the material corresponding to the linear marker. a step of storing the information signal; ([) a step of confirming a scanning position at which a signal of a predetermined intensity was obtained among the stored information signals; (F) a step of displaying the cursor among the stored information signals; (G) from the positions confirmed in steps (E) and (F), confirming in step (E) based on a predetermined relationship; (H) determining the length between the two scan positions selected in step (G) based on the number of digital scans between the two scan positions; step.

[Example] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 3 shows an example of a length measuring device that implements the sub-length method of the present invention, and numeral 1 in the figure is an electron gun.

The electron beam generated from the electron gun 1 is focused onto a length-measuring material 3 by a focusing lens 2, and is deflected by a deflection coil 4. A digital scanning signal is supplied to the deflection coil 4 from a digital scanning signal generation circuit 5 via a magnification setting circuit 6, and as a result, a desired area of the material 3 is digitally scanned by the electron beam. Become. The reflected electrons generated from the material upon irradiation of the material with an electron beam are anti! )l is detected by the electron detector 7. After the detection signal is amplified by an amplifier 8,
The scanning signal is supplied as a brightness modulation signal to the cathode ray tube 10 to which the scanning signal is supplied from the scanning signal generation circuit 5 via the addition circuit 9. Further, the detection signal is sent to the A-D converter 11 by J,
After being converted into a digital signal, the computer 12
a memory 1 connected to the computer 12;
It is stored within 3. 14 is a mark and cursor position setting circuit, and this circuit 14 generates signals corresponding to the set mark and cursor positions. The position signal from the circuit 14 and the output signal of the scanning signal generation circuit 5 are -number circuit 15.
When the position signal and the scanning signal match, the minus number circuit 15 generates a pulse. -
The pulse signal of the several circuit 15 is supplied to the addition circuit 9 and added to the detection signal of the detector 7, so that the cathode ray tube 10
The marks and force lines will be displayed along with the backscattered electron image of the desired area of the material.

In the configuration as described above, the scanning signal shown in FIG. 4(a) is supplied from the digital scanning signal generating circuit 5 to the deflection coil 4. The electron beam is scanned in steps by the scanning signal, and the number of steps is, for example, 1024. It is also set to 1024 in the Y direction. The scanning signal is appropriately amplified by the magnification setting circuit 6, and as a result, a desired area on the material 3 is scanned by the electron beam.

Based on the irradiation of the material 3 with the electron beam, reflected electrons generated from the material are detected by the detector 7. The detection signal is sent to amplifier 8. Since the scanning signal is supplied from the scanning signal generation circuit 5 to the cathode ray tube 10 via the addition circuit 9, the cathode ray tube has a backscattered electron image of a desired area of the material as shown in FIG. Is displayed. The cathode ray tube 1
The magnification of the image on 0 can be changed by controlling the magnification setting circuit with commands from the computer 12. The cathode ray tube 10 includes a mark and cursor position setting circuit 14. - Mark and cursor signals are also supplied from the number circuit 15, and one specific example of the circuit 14.15 is described in detail in Japanese Patent Application No. 178386/1986. Based on the mark and cursor signal, the cathode ray tube screen displays a mark M in the X direction and two cursors + and 2 in the direction perpendicular to the mark, as shown in FIG. Ru. The positions of the mark and the cursor can be changed arbitrarily by operating the setting circuit 14, and the operator of the apparatus places the mark at the position to be measured while observing the image on the cathode ray tube. and set the cursor.

After setting the position to be measured, the computer 12 moves J3 to the position on the material corresponding to the mark M displayed on the screen of the cathode ray tube 10 based on the mark position signal from the mark and cursor position setting circuit 13. A reflected electron signal based on the X-direction scan is taken in via the AD converter 11. The captured signal is supplied to the memory 13 and stored therein, and the signal waveform based on the X-direction scanning is shown in FIG. 4(b). Note that this signal is formed by 1024 data points. The computer 12 selects among the stored signals:
The scanned position of the data point at a predetermined signal strength level of 11.12 is searched and stored. In the case of the signal shown in FIG. 4(b), data points D+, D2.0
3. The signal strength of 'D4 is at the corresponding level, and the scanning position corresponding to each data point (the number of digital scanning steps from the starting point No. of the X-direction scanning to the data point) N1°N2, N3, N4 is stored by the computer. Next, the computer 12 stores the set cursor positions M+ and M2 based on the mark and the cursor position signal from the cursor position setting circuit 14. The computer 12 selects the cursor position M1 . It is programmed to select the scan position closest to M2, and in FIG. 4, scan positions N1 and N4 are selected. The computer 12 is adapted to measure the width of the element 1 from the number of digital scanning steps between the selected scanning positions, ie (N1-N4). The computer 12 stores in advance a table containing the relationship between the magnification of the image displayed on the cathode ray tube 10 and the distance traveled by the electron beam on the material corresponding to one step of digital scanning at that magnification. , the width of the element 1 is determined by the distance of one step and the number of steps derived from this table.

[Effect] As detailed above, in the present invention, the scanning position when a signal of a predetermined intensity is obtained among the signals obtained based on linear electron beam scanning corresponding to the mark, and the cursor Since two scanning positions are selected based on the cursor position and the distance between the selected scanning positions is measured, the measurement results do not differ depending on the cursor setting position and the reproducibility of the measurement is improved. It will improve.

[Variations of the invention]

Note that the present invention is not limited to the embodiments described above, and can be modified in many ways. For example, the closest to the cursor position,
Although the scanning position of the data point at the set intensity level is selected, the scanning position of the second closest data point may be selected. Moreover, although the reflected electrons based on the irradiation of the material with an electron beam are detected, secondary electrons may also be detected. Furthermore, I tried to display the mark in the X direction, but 1. A mark may be displayed in the Y direction and a cursor in the X direction may be displayed to measure the length in the Y direction. Furthermore, the electron beam

[Brief Description of the Drawings] Figure 1 is a diagram showing the backscattered electron image of U 11 displayed on a cathode ray tube, a marker, and a cursor, Figure 2 is a diagram for explaining the conventional length measurement method, and Figure 3 is a diagram for explaining the conventional length measurement method. The figure shows an example of a sub-length device for carrying out the length measurement method based on the present invention, and FIG. 4 is a signal waveform diagram for explaining an embodiment of the present invention. Gun 2... Focusing lens 3... Length measurement material 4... Deflection coil 5... Digital scanning signal generation circuit 6... Magnification setting circuit 7... Backscattered electron detector 8... Amplifier 9...Addition circuit 10...Cathode ray tube 11...A-D converter 12...
・Computer 13...Memory 14...Mark and cursor position setting circuit 15...Concordance circuit Patent applicant JEOL Ltd. Representative 9 Fujio ゛Figure 3Figure 4(a) Figure 4( b)

Claims (1)

[Claims] A length measurement method involving electron beam scanning comprising the following steps: (A) digitally scanning the electron beam two-dimensionally on the material to be sublengthened; (B) (C) displaying a marker in a straight line and two cursors in a direction perpendicular to the marker along with the sample image; (D) storing an information signal based on electron beam scanning on the material corresponding to the linear marker; ([) among the stored information signals, a signal with a predetermined intensity was obtained; (F) Confirming the scan position corresponding to the vJf+1 portion where the cursor is displayed in the stored information signal; (G) Step (E) and step (, From the position identified by step (E), two of the scanning positions identified by step (E) are determined based on a predetermined relationship.
selecting a point; (]'') determining the length between the two points selected in step (G) based on the number of digital scans between the two points;