JPS6316683B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for measuring the length between two desired points in a sample image using a scanning electron microscope, and in particular, to an apparatus for measuring the length between two desired points in a sample image, and in particular, to
Regarding circuit patterns such as LSI or super LSI,
The present invention relates to a device suitable for measuring the line width, distance between lines, pitch between lines, etc.

In general, it is important to accurately measure and know the value of the line width etc. on circuit patterns formed on semiconductor wafers in order to reduce the incidence of defective products and produce large quantities of products with high reliability. It is considered important.

Furthermore, it is important to accurately measure and know the values of the line widths and the like on the circuit pattern in order to realize high-quality LSIs and ultra-LSUs with high integration density.

Incidentally, as the integration of circuits progresses, it has become common to observe circuit patterns using a scanning electron microscope.

Conventionally, as a means of measuring the length between two desired points in a circuit pattern using a scanning electron microscope, the circuit pattern image projected on a cathode ray tube is photographed with a camera, and the obtained photographic image is used. Only the primitive means of measuring the length between the two points has been used, which poses the problem of not only requiring a lot of effort but also making it difficult to measure accurately.

Furthermore, in the conventional measurement method using an optical microscope, markers b and b' are placed at the ends c and c of the line to be measured, respectively, on the image a of the circuit pattern as shown in FIG. 1a. ’, the first
The video signal d shown in Figure b is obtained, and the video signal d is compared with a fixed threshold value e to create a line width signal f and determine the line width g. ing.

Therefore, it is conceivable to simply apply this measurement method using an optical microscope to the measurement method using a scanning electron microscope, but with such a method, the wafer cross-sectional pattern is Since the wire 1a on the wire 1a is irradiated with the electron beam 2 and the secondary electron detector 3 collects the secondary electrons, the signal level 4 is different at the ends 1b and 1b' of the wire 1a, and the
A problem arises in that the signal level varies depending on the position of the secondary electron detector 3, the direction in which it scans, the incident angle of the beam on the sample, etc., and this causes the problem that the line width etc. cannot be measured accurately.

The present invention aims to solve these problems by simply moving the marker to both ends of the sample image between the two points you want to measure while looking at the cathode ray tube screen of the scanning electron microscope. An object of the present invention is to provide a length measuring device using a scanning electron microscope that can accurately, quickly and universally measure the length between gaps.

For this reason, the length measuring device of the present invention is a scanning device having a sample chamber for storing a sample, a detector attached to the sample chamber, and a cathode ray tube that receives a video signal from the detector and projects an image of the sample. a marker generation circuit that is equipped with a type electron microscope and outputs electric signals for generating first and second markers that can be superposed on each part corresponding to an edge between two points in the image of the sample;
From each maximum value and each minimum value of the video signal in the range where the first and second markers overlap, first and second threads are determined suitable for each portion corresponding to the end between the two points. A threshold value setter that determines the threshold value sets the threshold value, and compares the signal corresponding to the first threshold value from the threshold value setter with the video signal from the detector to determine the same image. a first binarization circuit that binarizes a signal and outputs a first binarized signal; a signal corresponding to the second threshold value from the threshold value setter; and a signal from the detector. a second binarization circuit that compares the video signal with the video signal and outputs a second binarized signal; and a second binarization circuit that determines one end between the two points from the first binarized signal; a calculation means for measuring the length between the two points by determining the other end between the two points from the digitized signal; and a calculation means for measuring the length between the two points from the calculation means; The present invention is characterized in that a display means for displaying the value of the length between points is provided.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A length measuring device using a scanning electron microscope as an embodiment of the present invention will be described below with reference to the drawings.

The attached drawings show the above-mentioned length measuring device, and FIG. 3 is its overall configuration diagram, FIG. 4 is its electric circuit diagram, FIG. 5 is an electric circuit diagram showing its main parts, and FIGS. 6 a to 6.
f, Figures 7a-f, Figures 8a-g and Figure 9a
~f are their respective electrical signal diagrams, Figure 10a,
b is a schematic diagram to explain the state in which the length between the two points is measured, FIG. 11 is a front view showing the arrangement of the display means, and FIG. 12 is the threshold value. FIG. 3 is a schematic diagram for explaining the relationship between scanning lines at the time of setting and scanning lines at the time of length measurement.

As shown in FIG. 3, in a scanning electron microscope, sawtooth wave generators 5 and 6 for horizontal and vertical scanning are used.
are connected via deflection circuits 7 and 8 to deflection coils 10 and 11 as deflection members for horizontal and vertical scanning of a cathode ray tube (CRT) 9 for projecting sample images, and via magnification switching circuits 12 and 13, lens barrel
It is connected to deflection coils 15 and 16 as horizontal and vertical scanning deflection members disposed within the CM and scanning the electron beam 14.

Therefore, the sawtooth wave from the generator 5 is sent to the deflection coil 1 by changing the amplitude appropriately by the magnification switching circuit 12.
5, where a horizontal scanning of the electron beam 14 takes place, while the sawtooth wave, synchronized with the sawtooth wave fed to this deflection coil 15, is fed to the coil 10 of the cathode ray tube 9. Here, the electron beam inside the cathode ray tube 9 is scanned in the horizontal direction in synchronization with the electron beam 14. As a result, the generator 5, the deflection coils 10, 1
5. The deflection circuit 7 and the magnification switching circuit 12 constitute a horizontal scanning system HS.

The sawtooth wave from the generator 6 and the sawtooth wave synchronized therewith are also generated by the horizontal scanning system described above.
In almost the same way as in the case of HS, the deflection coil 16,
11, where the electron beam 14 in the lens barrel CM and the electron beam in the cathode ray tube 9 are scanned in the vertical direction. As a result, the generator 6, the deflection coils 11 and 16, the deflection circuit 8, and the magnification switching circuit 13 constitute a vertical scanning system VS.

In addition, the reference numeral 17 in FIG. 3 indicates a condenser lens, and the reference numeral 18 indicates an objective lens.

In addition, a sample chamber 19 is formed at the bottom of the lens barrel CM, and on the sample stage 20 inside the sample chamber 19,
A semiconductor wafer 21 as a sample on which a circuit pattern of a VLSI or the like is formed is placed.

The sample chamber 19 is equipped with a detector 22 that detects secondary electrons, reflected electrons, sample current, etc. generated when the semiconductor wafer 21 is irradiated with the electron beam 14. The detection signal from the preamplifier 23 and main amplifier 24
The signal is amplified and supplied to the cathode or grid of the cathode ray tube 9. As a result, the screen 9a of the cathode ray tube 9 [FIG. 10b,
11 and FIGS. 12a and 12b], an image of the circuit pattern on the semiconductor wafer 21 is projected by brightness modulation.

By the way, a marker generation circuit 25 is provided, and as shown in FIG. 4, this marker generation circuit 25 includes first and second marker generators 26 and 27 and a schematic length measurement marker generator 28. .

First and second marker generation signals M1 and M2 are sent from the threshold value determination circuit 29 to the first and second marker generators 26 and 27 [Figs.
(see Figures c and d)].
And these first and second marker generators 26, 2
Marker signals are generated at 7, and these marker signals are supplied to the cathode or grid of the cathode ray tube 9 via the main amplifier 24.

As a result, the desired two points in the lateral (horizontal) direction of the circuit pattern image on the cathode ray tube screen 9a are obtained.
When measuring the length l between points, first and second markers MK1 and MK2 are placed so as to respectively indicate the circuit pattern ends 59a and 59a' (see FIG. 10b) between the two points to be measured. 10b] can be displayed on the screen 9a by brightness modulation.

This threshold value determining circuit 29 includes:
First and second measurement range setters 30 and 31, maximum value detection circuits 32 and 33, and minimum value detection circuit 3
4, 35 and first and second threshold value setters 36, 37 are provided, and each signal is controlled by each panel setting value from an operation panel section 38. , operation panel section 38
In FIG. 4, the variable resistors 39 to 46 included in the threshold value determining circuit 29 are depicted as being included in the threshold value determining circuit 29.

First, in FIGS. 4 and 5, the sawtooth wave generator 5 for horizontal scanning of the scanning electron microscope 47 generates a sawtooth wave EH for horizontal scanning (see each a in FIGS. 6 to 8). It is added to the measurement range setters 30 and 31.

The first measurement range setter 30 is a first marker MK.
A variable resistor 39 that determines the vertical position of the screen 9a in order to determine the range (position and size) of
is connected to a variable resistor 40 that determines the horizontal position, and further connected to a variable resistor 41 that determines the vertical width of the marker and a variable resistor 42 that determines the horizontal width of the marker. from the resistance value and the sawtooth wave EH for horizontal scanning.
A detection period signal A1 (here, the same as M1) [see each c in FIGS. It is designed to be supplied to the input terminal.

The maximum value detection circuit 32 inputs the video signal Aa from the preamplifier 23 (see b, d, e in FIGS. 6 and 7, b in FIG. 8, and a in FIG. 10) to other input terminals, and
For each scan, this video signal Aa is compared with the signal A1 indicating the first detection period from the first range setter 30, and as shown in FIG. 5, the brightest level within the first detection period is determined. The maximum level value B1 (see FIG. 6d) is detected by the maximum value detector 32a, stored, and held by the hold circuit 32b for use in determining the threshold value for the next scan.

The minimum value detection circuit 34 receives and compares the signals A1 and Aa from the maximum value detection circuit 32, and as shown in FIG. e) is detected by the minimum value detector 34a, stored, and held by the hold circuit 34b for use in determining the threshold value for the next scan.

The signals Ba and Bb held by these hold circuits 32b and 34b (see FIG. 6f) are sent to the first threshold value setter 36, and the maximum value (signal Ba) and minimum value (signal Bb) are sent to the first threshold value setter 36. 100% difference between
A value corresponding to 60% of the value obtained when so signal B1, B2
It is designed to be output at the next scan after it is obtained.

This percentage (60%) is determined by a variable resistor 45, and can be adjusted to any appropriate value other than 60% using the operation panel section 38.

The determination of the second threshold value is performed in substantially the same manner as the determination of the first threshold value, and the second measurement range setter 31 determines the range (position and size) of the first marker MK2. In order to determine
A variable resistor 39 that determines the vertical position of the screen 9a and a variable resistor 43 that determines the horizontal position
are connected to the variable resistors 41 and 44.
are connected, and a second detection period signal A2 is obtained from these resistance values and the sawtooth wave EH for horizontal scanning.
(Here, it is the same as M2.) [See Figures 7c and 8d] is generated, and this signal A
2 is a maximum value detection circuit 33 and a minimum value detection circuit 3
5 to each one input terminal.

The maximum value detection circuit 33 inputs the video signal Aa from the preamplifier 23 (see each b in FIGS. 6 to 8) to the other input terminal, and outputs this video signal Aa from the second range setter 31 for each scan. The maximum level value C1 (see FIG. 7d) within the second detection period is detected by the maximum value detector 33a in the same way as shown in FIG. , and held by the hold circuit 33b for use in determining the threshold value for the next scan.

The minimum value detection circuit 35 receives and compares the signals A2 and Aa from the maximum value detection circuit 33, and as shown in FIG. 5, the minimum level value C within the second detection period is determined.
2 (see FIG. 7e) is detected by the minimum value detector 35a, stored, and held by the hold circuit 35b for use in determining the threshold value for the next scan.

The signals Ca and Cb held by these hold circuits 33b and 35b (see FIG. 7f) are sent to the second threshold value setter 37, and the maximum value (signal When the difference between Ca) and the minimum value (signal Cb) is taken as 100%, the value corresponding to 60% is obtained as the output signal Cc [see Figure 7 f, Figure 8 b]. signal
Cc is designed to be output as a second hold value at the time of the next scan after obtaining the signals C1 and C2, as will be described later.

This percentage (60%) is determined by a variable resistor 46, and in conjunction with the variable resistor 45, it can be adjusted to an appropriate value other than 60% by the operation panel section 38.

Further, the percentage determined by the variable resistor 46 may be determined separately from the variable resistor 45. In this case, the threshold values for the rising and falling portions of the signal Aa will be different, and the percentage determined by the variable resistor 46 will be different. 45 and 46 as shown in FIG. 2a and b, depending on the position of the detector 3, the
The characteristics occurring at level 4 of secondary electrons can be more appropriately corrected.

Now, these first and second threshold value signals Bc and Cc are output from the circuit pattern length measurement circuit 48 as outputs from the threshold value determination circuit 29.
It is now being supplied to

This circuit pattern length measurement circuit 48 is composed of a comparator 49 as a first binarization circuit, a comparator 50 as a second binarization circuit, and a pulse generation circuit 51.

As shown in FIG. 8, the comparator 49 outputs the first threshold value signal Bc and the video signal Aa.
When the video signal Aa is larger than the signal Bc, and when the first detection period signal A1 is on, the length measurement start signal D as the first binarized signal [see Fig. 8e] ] is now output.
This signal D is supplied to one input terminal of the pulse generating circuit 51.

The comparator 50 compares the second threshold value signal Cc and the video signal Aa, and compares the second threshold value signal Cc with the video signal Aa.
When the video signal Aa is larger and the second detection period signal A2 is on, the length measurement end signal E [see Fig. 8 f] is output as the second binarized signal. This signal E is supplied to the other input terminal of the pulse generating circuit 51.

The pulse generating circuit 51 inputs the length measurement start signal D and the length measurement end signal E, and uses the rise of the length measurement start signal D as the rise of the output signal F [see FIGS. 8g and 9b], and , the falling edge of the length measurement end signal E is taken as the falling edge of the output signal F, and this output signal F is used as a measurement period signal.
The signal is supplied to an arithmetic circuit 52 as an arithmetic means.

The arithmetic circuit 52 is a circuit that calculates the length between two points of a circuit pattern based on the clock pulse G (see FIG. 9a) generated from the clock generation circuit 53. It's getting old.

The clock pulse G is supplied to one input terminal of the counter 54, and the measurement period signal F from the circuit pattern length measurement circuit 48 is similarly supplied to the other input terminal of the counter 54. There is.

The counter 54 receives this signal F [see FIG. 9b]
is input, clock pulses G are counted and output, and this output signal H
The latch circuit 5 uses [see Fig. 9c] as a length measurement signal.
5.

The latch circuit 55 stores and holds this length measurement signal H, and outputs the held length measurement signal H' (see FIG. 9c).
H' is supplied to one input terminal of the averaging circuit 56.

The averaging circuit 56 receives the length measurement signal H' and also receives the measurement range signal I from the first measurement range setting device 30 (see FIG. 9d), and generates an averaged length measurement signal J [see FIG. e], and this signal J is sent as the output of the arithmetic circuit to a count display 57 as a display means.

This count value display 57 displays the averaged measured value (this value) based on the averaged length measurement signal J using the digital display 58a on the operation panel 38a provided in the main body 58 of the device as shown in FIG. 16, 33 in the example)
Display.

Here, the signals H, H', and J are treated as count values.

Note that as this count value display 57, a liquid crystal display element, a light emitting diode, or a Nixie tube is used.

With this configuration, when measuring the length of the line width, use
As shown in FIG. 1, the centers of the first and second markers MK1 and MK2 are positioned at both ends 59a and 59a' of the line width l to be measured in the circuit pattern image 59 projected on the cathode ray tube screen 9a, respectively. Then, the adjustment knobs 60a, 60b, and 60c on the operation panel section 38 are operated.

At this time, adjust the adjustment knobs 60a, 60b, 60c.
are for adjusting the variable resistors 39, 40, 43, respectively, and the l on the CRT screen 9a.
The lengths corresponding to the respective parts 1, l2, and l3 (see FIG. 11) are adjusted.

In addition, the parts l4, l4, and l5 in FIG. 11 are adjusted by variable resistors 42, 44, and 41, and these adjustment knobs are provided separately from the operation panel 38a so that they can be adjusted. ing.

Further, an adjustment knob 60d for setting a threshold value is provided, and the variable resistors 45 and 46 are adjusted together or separately to set the maximum and minimum values in order to determine the first and second threshold values. The threshold value between the two is set as a percentage.

By operating in this way, the first and second markers MK1 and MK2 will be located at the positions shown in FIG. As shown in Figure a, the ends 59a and 59a' of the wiring 59 can be accurately captured, and the length of the portion L of the signal Aa corresponding to the length l between the two points to be measured can be more accurately determined. It can be measured.

At this time, markers MK1 and MK2 are joined on the screen 9a of the cathode ray tube 9, making it look like one.
It can also be used like a marker, and
Markers MK1 and MK2 may be slightly overlapped to form a single marker with high brightness in the center, and in these cases, the functions are almost the same as those displayed as two markers.

Also, the length l on the actual circuit pattern and the signal
The correspondence between Aa and portion L can be easily achieved by adjusting the clock pulse G, etc.

Note that the averaging circuit 56 may be removed and the count may be displayed by sampling.

Furthermore, in addition to measuring the line width of a circuit pattern, it is also possible to measure the distance between lines and the pitch between lines, and in those cases, the comparator 4
9, 50, when the signal Aa is smaller than the threshold values Bc, Cc, and
When the signals A1 and A2 are being input, they are output from another terminal, and the output signals D',
By combining E' with the original output signals D and E, it is possible to selectively measure the distance between lines and the pitch between lines.

Note that to measure the length in the vertical direction, the video signal is sampled at points with equal distances in the horizontal direction for each horizontal scan, and the sampled video signal is
This can be easily done by sequentially supplying the AD converter, memory, and DA converter.
Video signal stored in memory that you want to measure in the vertical direction
If the value of Aa is converted to DA at once, the length can be measured using almost the same measurement method as the horizontal length measurement. In addition, diagonal measurements can also be performed by shifting the sampled point sequence in this vertical length measurement.

By the way, the relationship between the scanning line when setting the threshold value and the scanning line when measuring the length is as shown in FIG.
1a, 61b and scanning lines 62a, 62b for length measurement
As shown in each f in Figs. 6 and 7, the threshold value is used at the next scan after setting the threshold value to adjust the level. It is beginning to contribute to comparisons.

In addition, as shown by reference numeral 63 in FIG. 12b, by appropriately adjusting the sawtooth wave for vertical scanning of the scanning line, the same circuit pattern surface can be scanned twice, and the first time is a threshold. Hold value Bc,
Even if you set Cc and measure the length the second time,
Almost the same effect can be obtained as by alternately setting and measuring the length each time.

Further, hold circuits 32b, 33b, 34
If the hold signals supplied to b and 35b are adjusted appropriately, for example during horizontal blanking, maximum and minimum value detection can be performed during each scan,
At the same time, using the maximum values B1, C1 and minimum values B2, C2 from the previous scan, these B1, B2,
Threshold value created from C1 and C2
The length can be measured by comparing Bc, Cc and the video signal Aa for each scan.

Further, the video signal Aa is configured to be supplied to the detectors 32a, 33a, 34a, and 35a via a delay circuit, and the delay time of this delay circuit is determined by the signal Aa.
By setting the threshold value to be the same as or larger than the larger of the on-state time widths of 1 and A2, the threshold value can be compared with the video signal during the same scan that created the threshold value, making it more accurate. It is possible to measure length. In this case, the signals A1,
Hold circuits 32b and 33 for the falling edge of A2
It is set to be the hold signal of b, 34b, and 35b.

By the way, the length l between the two points currently being measured is displayed on the cathode ray tube screen 5a by brightness modulation.
A model length measurement marker generator 28 is provided which displays a model marker MMK (see FIG. 10b) equal to .

This model length measurement marker generator 28 receives the signal F from the pulse generation circuit 51 and generates a model length measurement marker MMK on the cathode ray tube screen 9a. In order to display the length l, as shown in FIG. 10b, by sending one or several length measurement pulses F within the length measurement range to the main amplifier The markers MK1 and MK2 can be displayed with different widths in the vertical direction, or with their brightness changed so that they can be clearly distinguished from the first and second markers MK1 and MK2. The signal F′ [see Figure 9 f] is sent to the main amplifier 2.
4 to the cathode ray tube 9, and as a result, on the cathode ray tube screen 9a, a schematic marker MMK of the same length is placed between two predetermined points to be measured as shown in FIG. 10b. The image of the circuit pattern and the first and second markers MK1 and MK2, which are present in a superimposed manner at the end between the two points, are superimposed and displayed.

By changing the connection state of the variable resistors 45 and 46, as the first marker MK1 moves on the cathode ray tube screen 9a, the second marker MK
2 can also be moved.

Furthermore, the means of the present invention can also be applied to length measurements of various minute patterns.

As described in detail above, the measuring device using the scanning electron microscope of the present invention has the advantage that it can automatically, accurately and quickly measure the length between two points to be measured on a sample image. Unlike conventional measurement methods using fixed threshold values (see Figure 1), this method has the advantage of being able to perform accurate and universal length measurements regardless of differences in the voltage bias or amplitude level of the video signal during observation. .

[Brief explanation of the drawing]

Figures 1 and 2 show conventional circuit pattern length measuring means. Figures 2a and 2b are both schematic diagrams for explaining the state in which length is measured using a scanning electron microscope, and Figures 3 to 12 are scanning electron microscopes as an embodiment of the present invention. This shows a length measuring device using an electron microscope. Figure 3 is its overall configuration diagram, Figure 4 is its electric circuit diagram, Figure 5 is an electric circuit diagram showing its main parts, and Figures 6 a to f. , Figures 7a-f, 8th
Figures a to g and Figures 9 a to f are each electrical signal diagram, and Figures 10 a and b are schematic diagrams for explaining the state in which the length between the two points is measured, FIG. 11 is a front view showing the arrangement of the display means, and FIG. 12 is a schematic diagram for explaining the relationship between the scanning line when setting the threshold value and the scanning line when measuring the length. DESCRIPTION OF SYMBOLS 1...Wafer cross-sectional pattern, 1a...Wiring of circuit pattern, 1b, 1b'...End of circuit pattern, 2...Electron beam, 3...Secondary electron detector, 4...
...Signal level, 5,6...Sawtooth wave generator,7,
8... Deflection circuit, 9... Braun tube, 9a... Braun tube screen, 10, 11... Deflection coil, 12, 13... Magnification switching circuit, 14... Electron beam, 15, 16... Deflection coil, 17... ...Condenser lens, 18...Objective lens, 19...
sample chamber, 20... sample stage, 21... semiconductor wafer as sample, 22... detector, 23... preamplifier, 24... main amplifier, 25... marker generation circuit, 26, 27... first, Second marker generator, 28... Model length measurement marker generator, 29... Threshold value determination circuit, 30, 31... First and second measurement range setter, 32, 33... Maximum value detection Circuit, 32a, 33a... Maximum value detector,
34, 35... Minimum value detection circuit, 34a, 35a
...minimum value detector, 32b, 33b, 34b, 3
5b...Hold circuit, 36, 37...First and second threshold value setter, 38...Operation panel section, 38a...Operation panel, 39-46...
...Resistance, 47... Conventional scanning electron microscope, 48
... Circuit pattern length measuring circuit, 49, 50 ... Comparator as first and second binarization circuit, 5
DESCRIPTION OF SYMBOLS 1...Pulse generation circuit, 52...Arithmetic circuit as arithmetic means, 53...Clock generation circuit, 54...
...Counter, 55...Latch circuit, 56...Averaging circuit, 57...Count value display as display means, 58...Device main body, 58a...Digital display, 59...Circuit pattern image, 60a, 60
b, 60c, 60d...adjustment knob, 61a,
61b, 62a, 62b, 63...scanning line, CM
... Lens barrel, MK1, MK2 ... First and second markers, MMK ... Model length measurement marker, HS ... Horizontal direction scanning system, VS ... Vertical direction scanning system.

Claims (1)

[Claims] 1 A scanning electron microscope is equipped with a sample chamber for storing a sample, a detector attached to the sample chamber, and a cathode ray tube that receives a video signal from the detector and projects an image of the sample. 2 in
a marker generation circuit that outputs electrical signals for generating each of the first and second markers that can be superimposed on each portion corresponding to the end between the points; a threshold value setter that determines first and second threshold values suitable for each portion corresponding to the edge between the two points from each maximum value and each minimum value of the video signal; Comparing the signal corresponding to the first threshold value from the threshold value setter with the video signal from the detector and outputting a first binarized signal obtained by binarizing the video signal. A first binarization circuit compares the signal corresponding to the second threshold value from the threshold value setter with the video signal from the detector to generate a second binarization signal. a second binarization circuit that outputs the above, and determines one end between the two points from the first binarization signal and determines the other end between the two points from the second binarization signal. Calculating means for measuring the length between two points, and display means for receiving a signal corresponding to the length between the two points from the calculating means and displaying the value of the length between the two points. A length measuring device using a scanning electron microscope, characterized by: