JPS6273105A - Length measurement device using charged particle beam - Google Patents

Abstract

PURPOSE:To perform the measurement of a length with good reproducibility, by dividing a signal with the coordinates, which impact the maximum and minimum values of the signal, as a boundary, selecting only the specific partial signal of the divided partial signals, and processing said signal. CONSTITUTION:A sample 4 is scanned by an electron beam EB. A signal from a detector 5 based on the scanning is fed to a CRT 9 through a combining circuit 20. Based on the signal from a cursor memory 14, a bright-up signal is sent to the CRT from a bright-up signal generator 16. When the start of the length measurement is instructed, the electron beam EB continuously scans a line corresponding to the cursor. The signal, which is obtained from the detector 5, is stored in a line memory 11. A CPU 17 reads the signal stored in the memory 11 and obtains the coordinates, which impart the maximum or minimum values of the signal. Then, with the coordinates as a boundary, the signal is divided, and operation is carried out based on the divided partial signal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention scans a sample using a charged particle beam, displays an image of the sample on a display device based on a detection signal obtained during scanning, and The present invention relates to a device for measuring the length of any part of interest in an image.

[Prior art] An area including the object to be measured is scanned with an electron beam, an image of the area including the object to be measured is displayed on a display device such as a cathode ray tube, and the object is measured while observing this image. This is done by specifying the part to be measured with a marker and measuring the length.

Now, let us consider a case where the width W of the mask M shown in FIG. 4-tree vertical cursor Cx1.Cx as shown in
2. Cx3. Both routes displaying Cx4 display one horizontal cursor Cy. Using such a device, while monitoring the positional relationship between the image of the mask M and each cursor,
As shown in FIG. 8(b), move the vertical cursor CX1. While moving CX2, move the vertical cursor Cx3. While moving Cx4, the horizontal cursor Cy is also moved to the vertical position where the length is to be measured. After each cursor movement like this, when you instruct the start of length measurement, the device moves the horizontal cursor C.
Vertical cursor CX1. The video signal indicated by A in FIG. 9(a) corresponding to the area sandwiched by Cx2 and the vertical cursor CX3 . The video signal indicated by 8 in FIG. 9(a) corresponding to the area sandwiched by CX4 is taken into a line memory or the like. Next, the horizontal scanning positions of both ends of the mask M are automatically determined based on these signals as described below. That is, first, the maximum value 1pa and the minimum value 1(I
a is determined, and then the horizontal scanning position X1 of a point that internally divides the maximum value and minimum value at a predetermined ratio is determined. As this ratio, 50% is often used because it is appropriate in many cases from the comparison with the image. For the signal B in Fig. 9(a), the maximum value tab and minimum value [qb are obtained by similar signal processing, and based on these values, the horizontal position coordinate x 2 of the similar internal division point It is determined as the coordinates corresponding to the other end of the mask M. Further, the length measurement value of the mask M is measured and displayed using the position data XI, X2 obtained in this manner and observation magnification information. In addition, Fig. 9 (d
) is a mask M to facilitate comparison with the object to be measured.
and each cursor.

[Problems to be Solved by the Invention] However, when the mask M is moved and its positional relationship with the secondary electron detector etc. changes, each of the cursors is moved to scan the same location on the object to be measured. Even though the signal is sampled, the video signal in FIG. 9(a) may change as shown in FIG. 9(b), for example. If we apply the same signal processing as above to such a signal, we get
Ipa, Iqa, Xl in FIG. 9(a),
Ipb, IQb.

The value of ×2 is Ipa=, Iqa-, X in Fig. 9(b)
1+, Ipb-, Iqb-, and X2-.

As is clear from comparing FIG. 9(b) with FIG. 9(a), the position of X2'' with respect to the position of ×2 is almost unchanged, but This is because the position that gives the maximum value 1pa' of signal portion A in Fig. 9(b) hardly changes compared to the case in Fig. 9(a). On the other hand, the minimum value za′
This is because the horizontal scanning position that gives It becomes W'. Furthermore, the signal may change as shown in FIG. 9(C) due to changes in the accelerating voltage of the electron beam. In such a case, two approximately the same minimum values occur for signal portion A, and two approximately same minimum values occur for signal portion B, resulting in the minimum value due to the influence of noise etc. As a result of selecting the positions indicated by Ua and Ub as points, the distance aw between the horizontal position coordinates ×1" and X2" may be measured.In this way, conventional methods In some cases, sexuality was impaired.

The present invention solves these conventional drawbacks and can measure the length of 811 with good reproducibility even when the position of the object to be measured is moved or the acceleration voltage of the charged particle beam irradiated to the object to be measured is changed. The purpose of the present invention is to provide a length measurement method using a charged particle beam that can perform the following steps.

[Means for Solving the Problems 1] In order to achieve such an object, the present invention scans a sample with a charged particle beam, and displays an image of the sample on a display device based on a detection signal obtained by 1q during the scanning. means for displaying, and means for selecting a specific area of the displayed image by displaying a marker on the sample image, the area being on an arbitrary linear or strip area and having an arbitrary width. a means which is a region, and a first means and a second means whose one is the maximum value and the other is the minimum value based on the video signal corresponding to the selected and specified region.
means for determining the scanning position on the linear or band-shaped area of a point that internally divides the pair of values by a predetermined ratio; Based on the scanning position data of two points such as
In a device designed to measure the length of a portion of interest in 4S, a specific partial molecule fa region is selected from among 211!1 partial regions divided based on the scanning position that gives the first value, and The method is characterized by comprising means for determining the internal division point within the partial area signal based on the first value and the second value existing within the partial area.

[Example] Hereinafter, embodiments will be described in detail based on the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention. In the figure, 1 is an electron gun, 2 is a focusing lens that focuses the electron beam EB from the electron gun 1, and 3 is an X (horizontal) and a Y ( 4 is a sample to be measured such as a mask. 5 is a secondary electron detector, 6 is a digital scanning signal generation circuit, 7 and 8 are scanning circuits that convert the scanning signals from the digital scanning signal generation circuit into analog signals and amplified them, 9 is a cathode ray tube, and 90 is a scanning coil. , 10 is an AD converter, 11 is a line memory, 12 is a memory controller 213 is a product, =
14 is a cursor memory, 15 is a cursor memory controller, 16 is a bright-up circuit that generates a bright-up signal based on a signal from the cursor memory 14, and 17 is a CPU.

18 is an operation console, 19 has a built-in memory for displaying data, etc.
A data display signal generation circuit generates a display signal for displaying measurement value data etc. on the cathode ray tube 9 based on the signal from PtJ 17, and 20 is a synthesis circuit whose output end is introduced into the grid 9G of the cathode ray tube 9. It is.

As shown in FIG. 2, the line memory 10 is connected to the -
It has 4096 addresses corresponding to the X-direction scan line, and each address has a depth of 8 bits. Furthermore, as shown in FIG.
It has 96 addresses.

Four horizontal cursors C parallel to the X direction on the screen of the cathode ray tube 9
xl, Cx2. Cx3. In order to display one horizontal cursor Cy parallel to Cx4 in the Y direction, 1 is stored in the corresponding address of the cursor memory 14. As shown in FIG. 4, the operation console 18 has the cursor C×1.
~． Cx4. To control the position of Cy on the screen, use the operation knobs Vxl, ~, Vx4. Vy is provided. or,
When dividing a signal corresponding to the entire area between the vertical cursors into signals corresponding to two partial areas, the operation console 18 performs the division using the scanning position that gives the maximum value of the entire area signal as a boundary. Selection buttons Kp and Kq are provided for instructing whether to perform division based on the minimum value or the minimum value. Furthermore, a button Ji for instructing which side of the divided partial area signal to select from among the two divided partial area signals;
Jo is provided. Furthermore, the console 18 is also equipped with a key (not shown) for instructing the number of times the video signal is integrated.

Next, the present invention will be explained in detail by taking as an example the case where the width W of the mask M shown in FIG. 8(a) is measured.

In the above-described configuration, pressing the button Kp on the operation console 18 instructs to divide the area using the horizontal scanning position that gives the maximum value as the boundary in this measurement, and
By pressing the button Jo, the user instructs to select a partial region located on the outside of such a pair of boundary points and to perform signal processing.

After this, when the apparatus is operated, a scanning signal is generated from the digital scanning signal generation circuit 6, the electron beam EB scans the sample 4 two-dimensionally, and the signal from the detector 5 accompanying this scanning is sent to the synthesis circuit. The luminance signal is supplied to the cathode ray tube 9 via 20 as a luminance signal. Therefore, the sample image is displayed on the cathode ray tube 9. At this time, since the scanning signal from the digital scanning signal generation circuit 6 is sent to the cursor memory controller 15, the cursor memory 14 is read out in synchronization with the two-dimensional scanning of the sample 4 by the electron beam EB.

The bright-up signal generation circuit 16 generates a bright-up signal based on the signal from the cursor memory 14,
The bright-up signal is sent to the cathode ray tube 9 via the synthesis circuit 2°.
5 superimposed on the sample image on the screen of the cathode ray tube 9.
Book cursor CX'l, ~.

CX4. cy is displayed. Therefore, the knobs VXl, . . . , VX4. When VVl and VV2 are operated, the cursor memory controller 15 is controlled based on a signal from the CPU 17, and the address for writing 1 in the cursor memory 14 is changed, so the cathode ray tube 9
The position of the cursor displayed on the screen moves. Such knobs Vxi, ~, Vx4. By operating vy, Figure 8 (
Each cursor CXI, Cx2. CX
3. CX4. (,' is moved. Now, move the cursor Cxl, Cx2. Cx3. Cx4 in the horizontal direction (×
The position or coordinates of direction) Hl, H2, )(3.

Let's call it H4. Therefore, when I instruct the start of the vice-master, the CPU
17 is sent to the digital scanning signal generation circuit 6, and the electron beam EB continuously scans the line corresponding to the horizontal cursor Cy of the mask M 10 times based on the X scanning signal shown in FIG. scan.

The signal received by the detector 5 during the first scan is sent to the AD converter 10 and converted into a digital signal, and then stored at an address corresponding to the coordinates of each pixel in the line memory 11. Almost the same detection signals are sent to the line memory 11 from the second and subsequent scans, but the line memory controller 12 receives the coordinates 1-11.82, !-13, HA from the CPU 17. The signal representing the area is being sent, and the signal in the area between the coordinates H1 and 112 and the digital signal in the area between the coordinates H3 and H4 are multiplied by f?40 by the multiplier 13, and this integrated signal is is stored in the line memory 11.

Now, if this stored signal is as shown in FIG. 5(b) corresponding to FIG. 9(a), CPU1
7 performs control according to the flow shown in FIG. 6 below. That is, first, as shown in step 21 in FIG. 6, by reading out the signal stored in the line memory 11 and comparing the values of each coordinate of this signal, the coordinates 1-11,
Find the coordinate Xpa where the signal A in the area sandwiched by H2 takes the maximum value [pa, and the coordinate m x qa where the signal A takes the minimum value ■qa. Next, the seat a that takes a large quantity value! Since the console 18 instructs to divide the signal A by Xpa, the CPU 17 calculates the coordinates
a, the signal portion shown in FIG. 5(b) is divided into an outer area signal AO indicated by a solid line and an inner area signal Ai indicated by a dotted line in the figure.
Divide into. Next, since the operating vehicle 18 instructs to select the outer area signal, the CPU 17 selects the outer area signal AO as shown in step 23 in the figure. Next, the CPU 17 determines the minimum value of the outer area signal AO as shown at 24 in the figure based on the video signal stored in the line memory 11. ia foqa (= I
Find aa).

Then, as shown in 25 in the same figure, the coordinates of a point that internally divides the maximum value 1pa and the minimum value 1aloqa into, for example, 50% x 1
seek. The CPU 17 performs similar processing on the signal B in FIG. 5(b), and calculates the maximum value + pb and the outer minimum value 1.
Find coordinates x 2 based on oab.

Finally, the width W is lengthened based on the difference between these two coordinates and observation magnification information, and this value is displayed on the cathode ray tube 9.

Therefore, it is assumed that after moving the length-measuring object, each cursor is moved and then length measurement is started in order to measure the same part of the length-measuring object. As a result, the signal shown in FIG. 5(C) corresponding to FIG. 8(b) is stored in the line memory 11.
9, the CPU 17 sequentially performs the processing as shown in FIG. 6. Therefore, the solid line in FIG. The outer part AO' shown and the inner part A shown by the dotted line
Divide into i-. The outer partial signal AQ' is selected, the minimum value 1 oba' of the partial signal AO- is determined, and the coordinate x 1' that divides the maximum value 1 pa' and the minimum value 1 oqa- into 50% is determined. Similarly, by processing the signal portion B' in Fig. 5(C), the coordinates of the point that divides the maximum value [pb- and the minimum value oqb- into 50% are obtained, and the width W is calculated based on these coordinates. The length is measured and the sub-length value is displayed on the cathode F2 tube 9.

Now, if you compare the coordinate x1 in Figure 5(b) and the coordinate The previously measured coordinate X1 is discarded, and the coordinate X1' outside the point that takes the maximum value is automatically selected as in the previous measurement. The subsequent length measurement value hardly changes, and the reproducibility of length measurement can be improved.

Note that the embodiment described above is only one embodiment of the present invention, and many other modifications are possible.

For example, in the above-mentioned embodiment, a case was explained in which the deviation of the measured length value due to the movement of the object to be measured was dealt with. The present invention can also be applied to deal with deviations in long values.

Furthermore, in the embodiment described above, the coordinates H1°1'2
Although the signal corresponding to the area sandwiched by , etc. is divided at the coordinates where the maximum value is taken, it may be divided at the coordinates where the minimum value is taken. Moreover, in the above-mentioned embodiment,
Of the partial signals generated by the division, the outer signal is selected for processing, but in some cases it may be preferable to select the inner signal for processing.
An inside signal may be selected.

Further, in the above-described embodiment, when selecting a partial signal, the selection is made from the viewpoint of the inside and the outside, but the selection may be made from the viewpoint of the right side, the left side, etc., for example.

Furthermore, in the above-described embodiment, when a region is divided according to the maximum value or the minimum value, each of the partial region signals generated by the division has a point at which its slope is maximum. Of these, the present invention can be similarly applied to the case where the maximum slope point included in a specific partial area signal is selected.

Furthermore, in the above-described embodiment, the signals in the area corresponding to two line segments on the horizontal position line are sampled in the line memory, but the signals in the area corresponding to the two line segments on the horizontal position line are sampled in the line memory. The present invention is similarly applicable to the case where length measurement is performed based on the average value of the signal. Further, the direction of the line is not limited to the horizontal direction, and may be oriented in any direction.

Furthermore, the markers for indicating the length measurement position are not limited to those in the embodiment, and for example, frame-shaped markers Ul and lJ2 whose positions are variable as shown in FIG. 7 may be used.

[Effects of the Invention] P As is clear from the above description, according to the present invention, a signal corresponding to the designated area is sampled, and this signal is processed to obtain the coordinates corresponding to the end of the object to be measured. In this case, the signal is divided into two partial signals using the coordinates giving the maximum or minimum value of the signal as a boundary, and only a specific partial signal from among the divided partial signals is selected and processed. Therefore, length measurement can be performed with good reproducibility regardless of movement of the object to be measured or changes in the accelerating voltage of the irradiated charged particle beam.

[Brief explanation of drawings]

Figure 1 is a diagram showing an embodiment of the present invention, Figure 2 is a diagram explaining a line memory, Figure 3 is a diagram explaining a cursor memory, and Figure 4 is a diagram explaining an operating wheel. 5 is a signal waveform diagram for explaining the operation of the device shown in FIG. 1, FIG. 6 is a flowchart for explaining the present invention in detail, and FIG. A diagram for explaining one embodiment. Figure 8 is a diagram for explaining an example of the display of the object to be measured using a cathode ray tube and instructions using a cursor for the length measurement part. Figure 9 is a diagram for explaining the shortcomings of the conventional device. FIG. 3 is a signal waveform diagram for 1: Electron gun EB: Electron beam 2: Focusing lens 3: & i-directed cocoil 4: Sample
5: Detector 6: Digital scanning signal generation circuit 7.8: Scanning circuit 9: Cathode ray tube 10: AD converter 11 Line memory 12.15
:Memory controller 14:Cursor memory 16:Bright-up circuit 17:CPU 18:Operation console 19:Data signal generation circuit 20:Synthesis circuit M:Mask SL, S2:Cross marker Cxl, ~, Cx4. GV: Cursor input ≦G1) fNri Figure 2 Figure 7 Figure 9

Claims (1)

[Claims] means for scanning a sample with a charged particle beam and displaying a sample image on a display device based on a detection signal obtained with the scanning;
means for selecting a specific region of the displayed image by displaying a marker on the sample image, the region being on an arbitrary linear or band-like region and having an arbitrary width; , means for determining first and second values, one of which is a maximum value and the other a minimum value, based on the video signal corresponding to the selected and designated area; and a means for determining a predetermined ratio between the pair of values. means for determining the scanning position on the linear or band-shaped area of points internally divided by , and a means for determining the scanning position of points internally divided by In this apparatus, a specific partial area is selected from two divided partial areas based on a scanning position that gives a first value, and the first value and the part are measured. A length measuring device using a charged particle beam, comprising means for determining the internal division point within the partial region signal based on a second value existing within the region.