JPS63124353A - Pattern detecting device - Google Patents

Abstract

PURPOSE:To enable the full contrast detection of an image of scanning transmission electron beams by selecting outputs of respective photoelectric conversion elements synchronously with the scanning on a scintillator and detecting a fine pattern on a sample by the use of these selective outputs. CONSTITUTION:When scanning transmission electron beams 1b for a sample 5 are scanned on a scintillator 10, diameters of luminous spots formed on respective scanning positions are made smaller than sizes of respective elements of a corresponding photodiode array 15. When a period of repetitive scanning on the scintillator 10 is set longer than afterglow time on the respective scanning positions, outputs of respective elements of the diode array 15, which detects only light spots formed by the use of scanning operations performed synchronously with the scanning on the scintillator 10 at the respective scanning positions so that no aftergrow effect is brought at the adjacent scanning positions and present scanning positions, can be selectively outputted. Hence, a fine pattern on this sample 5 can be detected with high speed and high resolution and without the afterglow effects on the scintillator 10.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pattern detection device for detecting patterns on a sample using a scanning transmission electron microscope, and particularly for detecting a scanning transmission electron image of a sample having a fine pattern. The present invention relates to a pattern detection device suitable for high-speed detection.

[Conventional technology]

A configuration diagram of a conventional pattern detection apparatus using a scanning transmission electron microscope is illustrated in FIG. In FIG. 4, 1 is an electron gun, 2 is a converging lens, 6 is a deflection coil, 4 is an objective lens,
5 is a sample, 6 is a scanning circuit.

7 is an electron beam detector, 8 is an amplifier, and 9 is a cathode ray tube (CRT).
). Note that the path through which the electron beam passes is kept in a vacuum by a vacuum container. With this configuration, electrons (a) 1a generated from the electron gun 1 are directed onto the sample 5 by the converging lens 2 and the objective lens 4 #i! 1. The electrons (rays) 1a are focused into a minute spot having a diameter of about nm, and the minute spot of the electrons (rays) 1a is scanned over the sample 5 by a deflection coil 3 driven by a scanning circuit 6. The electrons (rays) 1b transmitted through the sample 5 covering this fine pattern are incident on the electron beam detector 7 and converted into an electric signal 7a, and this electric signal 7a is amplified by the amplifier 8 and the signal is used to perform the above-mentioned scanning. By performing brightness modulation of the CBr4 deflected by the circuit 6, a scanning transmission electron image of the sample 5 is displayed on the CBr4.

FIG. 5 is a configuration diagram illustrating the conventional electron beam detector 7 of FIG. 4, which is a combination of a scintillator and a photoelectron amplification tube. In FIG. 5, 10 is a scintillator, 11 is a fluorescent material, 12 is a photomultiplier, 13 is a photocathode, and 14 is a photomultiplier. With this configuration, the scanning transmitted electrons 1b incident on the electron beam detector 7 (scanning transmitted electrons 1b that are incident on the scintillator 10t) excites the fluorescent material 11 coated on the surface of the scintillator 10 and generate photons 10a. 10a hits the photocathode 16 of the photoelectron field multiplier g12 to generate photoelectrons 13a, and the photoelectrons 13a are multiplied by the photoelectron amplifier 14 to output an electric signal 78. At this time, the photoelectrons 10a applied to the scintillator 10 described above are Fluorescent material 11
The electron (ray) 1b still emits light, but then the electron (ray) 1b
(line) Even if the irradiation of 1b is stopped, it continues to emit light for a certain period of time, and this afterglow decreases with time. Therefore, if the afterglow time is long, the pattern of the sample 5 having a pattern including minute parts cannot be detected correctly.

FIG. 6 is a perspective view illustrating the sample 5 having the fine pattern (gl, small isolated pattern) 15 shown in FIG.

In FIG. 6, 50 is a minute isolated pattern.

The sample 5 in FIG. 6 consists of a substrate made of a material (such as polyimide or silicon nitride) that transmits electrons (rays) 1a, and its minute isolated pattern 50 is made of a material that does not transmit electrons (rays) 1a (such as Au). and Ta).

At this time, consider the case of detecting a scanning transmission electron image when electrons (line) Ia are scanned in the direction of the arrow along the broken line, and the spot diameter of the scanning electron (line) 1a is the size of the minute isolated pattern 50. shall be sufficiently small compared to .

FIG. 7 shows a sample 5 having the minute isolated pattern 50 shown in FIG.
FIG. 3 is an explanatory diagram illustrating a temporal change in the number of electrons incident on the scintillator 10 of the IE:iM excess electron 1b.

In FIG. 7, the horizontal axis represents the scanning time, and the vertical axis represents the number of scanning transmitted electrons 1b per unit time that enter the scintillator 10. The time t in FIG. 7 is the time during which the fine isolated pattern 15 that does not pass through the electron (lfi ray 3-1a) is scanned.

FIG. 8 illustrates a temporal change in the amount of light emitted from the scintillator 10 depending on the number of electrons incident on the scintillator 10 in FIG.
FIG. 6 is an explanatory diagram of a case where the scanning speed is relatively slow so that the afterglow time T of the fluorescent material 11 of the scintillator 10 satisfies the condition that it is sufficiently smaller than the scanning time t on the minute isolated pattern 50. In FIG. 8, T is the afterglow time of the scintillator 10. When the scanning speed in FIG. 8 is relatively slow and Tit is used, the minute isolated pattern 50 on the sample 5 can be detected with sufficient contrast.

FIG. 9 illustrates a temporal change in the amount of light emitted from the scintillator 10 depending on the number of electrons incident on the scintillator 10 in FIG. 7,
FIG. 4 is an explanatory diagram of a case where the scanning speed is relatively fast so that the afterglow time T of the fluorescent material 11 of the scintillator 10 is longer than the scanning time t on the minute isolated pattern 15. Since the scanning speed in FIG. 9 is relatively fast, in the case of Tit, the minute isolated pattern 15 on the sample 5 cannot be detected with sufficient contrast. Note that FIG. 9 is illustrated on a scale such that the afterglow time T becomes relatively long.

Regarding conventional scanning transmission electron microscopes, for example, see the book edited by the Japan Society for the Promotion of Science [Microbeam Analysis J (1
984), pp. 199-206. Regarding the conventional electron beam detector using a scintillator and a photomultiplier tube, please refer to [Microbeam Analysis J (1984), pp. 149 to 15].
Discussed on page 6.

[Problems to be Solved by the Invention] The above-mentioned conventional technology does not take into consideration the influence of the afterglow time of the fluorescent material of the scintillator of the pattern detection device using a scanning transmission electron microscope, When detecting a scanning transmission electron image by scanning an electron beam, patterns in microscopic areas cannot be detected with sufficient contrast. There has been a problem in that it is not possible to detect fine pattern defects that occur in the mask used at high speed.The purpose of the present invention is to detect fine pattern defects on a sample even if the electron beam is scanned at high speed, without depending on the afterglow time of the fluorescent material of the scintillator. An object of the present invention is to provide a pattern detection device capable of detecting a scanning transmission electron image of a pattern with sufficient contrast.

[Means for solving problems]

The above purpose is a method for scanning a scintillator with an electron beam that has passed through a sample having a fine pattern. A pattern detection device comprising a photoelectric conversion element and a means for selectively outputting the output of each element of the photoelectric conversion element in synchronization with scanning on the scintillator, and detecting a fine pattern on a sample based on the selected output. This is achieved by

[Effect]

In the above-mentioned pattern detection device, the scanning transmission electron beam of the sample is scanned on the scintillator so that the emission spot diameter at each scanning position is smaller than the size of each element of the corresponding photoelectric conversion element, and the electron beam is scanned repeatedly on the scintillator. If the scanning period is set longer than the afterglow time at each scanning position,
Photoelectric conversion element 0 which detected only the light emitting spot due to scanning without the influence of afterglow at each scan position and at the scan position in synchronization with the scan on the scintillator] Selects and outputs the output of each element. As a result, fine patterns on the sample can be detected at high speed and with high resolution without being affected by the afterglow of the scintillator.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 5.

FIG. 1 is a block diagram showing an embodiment of a pattern detection device according to the present invention. In Figure 1, 1 is an electron gun (charged particle source), 2 is a converging lens (convergent coil), 6 is a deflection coil, 4 is an objective lens, 5 is a sample, 6 is a scanning circuit, 8 is an amplifier, and 9 is a cathode ray. tube (CRT), 1o is a scintillator of an electron beam detector, 15 is a one-dimensional photodiode play (non-storage type image + 78 one-dimensional sensor), 16 is a multiplexer, 17 is a deflection coil, 18 is a scanning circuit (scanning drive circuit), 19 is a D/A converter, 20 is a counter, 21 is a clock pulse oscillator, and 22 is a sample and hold circuit.

Note that the passage paths of the electron beams 1a, 1b, etc. are kept in a vacuum through which electrons can pass by a vacuum container (not shown).

With this configuration, the electron beam 1a generated from the electron gun 1 is focused onto the sample 5 by the converging lens 2 and the objective lens 4 into a minute spot with a diameter of several nanometers, and at the same time, the electron beam 1a is focused by the scanning circuit B. The sample 5 is scanned two-dimensionally by the driven deflection coil 3. Note that the acceleration voltage of the electron gun 1 is a voltage sufficient to pass through the sample 5 having a fine pattern. Here, the clock pulse oscillator 21 generates a clock pulse with a cycle shorter than the time □ resolution to required for detecting the scanning transmission electron image of the sample 5, and the counter 20 is a binary counter that counts the number of pulses of the clock pulse oscillator 20. After counting up to the number of elements in the photodiode array 15 of the electron beam detector, it is reset and counting is repeated again. The output of the counter 20 is input to the input of the A/D converter 19 together with the control input of the multiplexer 16.

FIG. 2 is an input/output characteristic diagram of the D/A converter 19 shown in FIG. In FIG. 2, the horizontal axis is the input from the counter 20, and the vertical axis is the analog output, which is a stepped signal as shown. The output signal of the A converter 19 is input to the scanning circuit (scanning drive circuit) 18, and by driving the deflection coil 17 with the output of the scanning circuit 18, the scanning transmitted electrons transmitted through the sample 5 are transmitted. 1b is scanned onto a scintillator 10 of an electron beam detector. When this scanning electron (ray) 1b is incident on the scintillator 10, photons IQa are generated from the scintillator 10, and the amount of light is reflected in the photon of the non-storage type image sensor having multiple elements arranged below the scintillator 10 (in the figure). It is detected by the diode array 15 and converted into an electric signal 15a, and the electric signal 15a from each element is selected and outputted by the multiplexer 16.

FIG. 3 is a block diagram of the main parts of the electron beam detector shown in FIG. 1. In Figure 3, 26.24 is photodiode array 1
5 elements. The spot diameter of the electron i1b on the scintillator 1o in 3rd (2) (Fig. 1) is set to be less than or equal to the size of each element 26°24 of the photodiode array 15. The scintillator 1o detects only the light of the photon 10a generated by the incidence of the scanning electron 1b, and the adjacent niremen) 23
The photodiode array 15 is placed close to the bottom of the scintillator 10 so as not to detect the afterglow of the scintillator 10 directly above (24). The element arrangement direction of this photodiode array 15 is the scintillator 10.
This is the same as the scanning direction (arrow direction) of the electron beam 1b by the deflection coil 17 described above, and the scanning width of the electron beam 1b is equal to the length of the photodiode array 15. In this way, during the holding time of each step of the stepped signal of the output of the D/A converter 19 shown in FIG. 23 (24), etc., and receives light from the scanning electron beam 1b synchronized with the progress of the steps of the step-like signal) 23 (24)
4) etc. are sequentially replaced, and the scintillator 1o reaches the corresponding position of the element at the end of the photodiode array 15.
When the electron beam 1b is scanned at the top, it returns to the corresponding position of the element at the other end and repeats the scanning. At this time, the multiplexer 15 selects the output of the element at the position indicated by the value of the counter 20, but the scanning of the electron beam 1b is also controlled by the counter 2o.
The multiplexer 15 always outputs an electrical signal 15a such as 23, 24 at the corresponding position of the scintillator 1o where the electron beam 1b is incident.
is selected and output to the sample and hold circuit 22. Sample-and-hold circuit 22 Samples the electric signal 15a% from the output of the multiplexer 16 when the electron beam 1b is on the scintillator 1o directly above the center of each element (23, 24, etc.) The value is held during the period of time when the element 23 (24) or other corresponding position on the scintillator is moved by scanning.

The output of the sample-and-hold circuit 22 is amplified to an appropriate signal by the amplifier 8 to perform brightness modulation of the CRT 9. As a result, a scanning transmission electron image of the sample 5 having a fine pattern is displayed on the CR, T9. Is displayed.

In this way, the scanning transmitted electrons 1b of the sample 5 in FIG. By scanning the scintillator 10 completely independently, for example, when the electron beam 1b is at the position indicated by the broken line in FIG.
The light enters the element 23 of the photodiode array 15 directly below and is converted into an electric signal 15a. At this time, the multiplexer 16 selects and outputs the electric signal 15a output from the element 23, and then the electron beam 1b When the scanning moves to the position shown by the solid line, the light of the photon 10a enters the next element 24 and is converted into an electric signal 15a, and at this time, the multiplexer 16
By selectively outputting the electrical signal 15a output from the scintillators 1o, 12, and 12, the electron beam 1b moves to the solid line position EC, and the element 23 of the BU moves the afterglow to the scintillator 1o, 12, and the afterglow during the afterglow time T. However, at this time, the multiplexer 16 selects and outputs only the electrical signal 15a of the output of the next element 24, so the electrical signal 15a of the afterglow component of the scintillator 1o is not output as the output of the multiplexer 16. . Therefore, if the scanning period of the electron beam 1b on the scintillator 1o by the deflection coil 17 is set to be longer than the afterglow time T of the fluorescent material of the scintillator 1o above the elements of the 7-otodiode array 15, the electron beams on the scintillator 1o By switching the selection elements of the multiplexer 16 one after another in synchronization with the movement of the line 1b, it is possible to always detect the pattern of the sample 5 by electron beam detection without being affected by the afterglow of the scintillator 10.

In the above embodiment, the photodiode array 16 was placed immediately after (directly below) the scintillator 1o, but using an optical fiber image guide, one end of the photodiode array 16 was placed immediately after the scintillator 1o, and the other end of the photodiode array 16 was placed directly behind the scintillator 1o. By arranging it directly in front of the photodiode array 15, the light generated by the photons 10a of the scintillator 1o may be guided to the photodiode array 15 through the image guide. In this case, if the other end of the image guide is divided into individual guides, a large image sensor such as a photomultiplier tube can be used instead of the photodiode array 15. In addition, if the other end of the optical fiber image guide is placed outside the vacuum container, a detector such as an image sensor after the scintillator 10 can be placed outside the vacuum, thereby reducing the effects of gas generation from the detector and wiring. This helps keep the electron beam path in a clean vacuum state.

〔Effect of the invention〕

According to the present invention, it is possible to detect fine patterns at high resolution and at high speed without being affected by the afterglow time of a scintillator that detects a scanning transmission electron image.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a pattern detection device according to the present invention, FIG. 2 is an input/output characteristic diagram of the D/A converter shown in FIG. 1, and FIG. 6 is a diagram of the electron beam detector shown in FIG. Main part configuration diagram,
FIG. 4 is a configuration diagram showing an example of a conventional pattern detection device;
Figure 5 is a configuration diagram of the electron beam detector in Figure 4, and Figure 6 is the configuration diagram of the electron beam detector in Figure 4.
Figure 7 is a perspective view of the sample with the fine pattern shown in Figure 4.
A time change diagram of electrons incident on the scintillator corresponding to Figure 6 in the figure,
FIG. 8 is a graph showing how the amount of light emitted by the scintillator changes over time during low-speed scanning, corresponding to FIG. 7 of FIG. 4, and FIG. 1... Electron gun 2... Converging lens. 3... Deflection coil, 4... Objective lens 5...
・Sample 6...Scanning circuit. 8...Amplifier 9...CRT. 10...Scintillator. 15...Photodiode array (non-storage type image sensor). 16...Multiplexer, 17... Deflection coil. 18...Scanning circuit (scanning drive circuit). 19...D/A converter, 20...Counter. 21... Clock pulse oscillator. 1st figure foot 2 figure small 3 Roshima 4M "・he, Masa J, 11; mouth t et al figure

Claims (1)

[Claims] 1. An electron beam source, means for focusing the electron beam on a sample in the form of a spot, means for scanning the spot-like electron beam on the sample, and an electron beam transmitted through the sample. means for scanning a scintillator, a multi-element non-storage type photoelectric conversion element that receives light emitted from the scintillator, and selectively outputting the output of each element of the photoelectric conversion element in synchronization with the scanning on the scintillator. A pattern detection device comprising means for detecting a pattern on a sample. 2. The pattern detection device according to claim 1, wherein the photoelectric conversion element receives light emitted from the scintillator through an image guide.