JPS60143642A - Stroboscopic electron beam device - Google Patents

Abstract

PURPOSE:To enable to control the generation timing of electron beam pulse (EB pulse) with higher precision by a method wherein a high-precision delay circuit for EB pulse generation timing correction is provided and the correction amount of a delay circuit is decided by comparing a previously already-known voltage waveform for the EB pulse with the voltage waveform observed by a stroboscope in the high-precision delay circuit. CONSTITUTION:A pulse gate 2, which is used for making EB pulse generate, a proper sample 3, which is used for seeking after correction data on electron beam pulse generation timing, and a secondary electron detector 5 are disposed in the enterior of a stroboscopic electron beam optical system-mirror cylinder 1. The pulse gate 2 is driven by a deflecting voltage signal 24, which is made to generate in a pulse gate driver 11, whereto a delay circuit 9 and a high-precision delay circuit 10 have been connected in a cascade. A delay set value is decided in the delay circuit 9 by a delay amount appointed signal 27 which is sent from a control circuit 12, while a high-precision delay set value is decided in the high- precision delay circuit 10 by a high-precision delay amount appointed signal 28 which is sent from the control circuit 12 and a high-precision delay operation is performed to the output signal of the delay circuit 9.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical field of the invention The present invention relates to an electron beam device for analyzing detailed operations of ICs or LSIs, and particularly to an electron beam device for precisely controlling the generation timing of electron beam pulses. This invention relates to a strobe electron beam device.

(2) Background of the Technology In recent years, strobe electron beam devices have been attracting attention as a means for analyzing the precise operation of ICs, LSIs (hereinafter referred to as samples), and the like.

When an electron beam is irradiated to a specific point on the surface of a sample during operation, secondary electrons are emitted into space, but the amount of secondary electrons detected depends on the potential of the sample at the point irradiated with the electron beam. It changes depending on.

Based on this principle, a scanning electron microscope equipped with a strobe observation means is used to observe changes in potential on the surface of a sample. Since the sample repeats the same operation at a certain period, a short pulsed electron beam (hereinafter referred to as EB pulse) is scanned and irradiated two-dimensionally over the entire sample at a specific timing synchronized with the period. By detecting the electronic signal, it is possible to observe the voltage distribution of the movement of the sample at a certain moment (image mode). In addition, by irradiating the BB pulse to a specific part of the sample with the above-mentioned timing slightly shifted and detecting the secondary electron signal, the operation during the - period is observed with a slight shift. It is possible to observe temporal changes in voltage (waveform mode).

In the above observation, in order to achieve high temporal resolution, a highly accurate control device that can irradiate an EB pulse with a short pulse width at an accurate generation timing is required.

(3) Conventional technology and problems In the conventional strobe electron beam device, there was no technology to efficiently measure the generation timing of the above-mentioned EB pulse, so there was a limit to the accuracy of its control, and there was an error in the generation timing of the EB pulse. The above detected secondary electron signal (
There was a problem in that an error occurred in the strobe observation voltage waveform (hereinafter referred to as the strobe observation voltage waveform).

(4) Purpose of the Invention In order to eliminate the above-mentioned problems, the present invention includes a high-precision delay circuit for correcting the EB pulse generation timing.

E
It is an object of the present invention to provide a strobe electron beam device that can control the generation timing of B pulses with high precision.

(5) The structure and purpose of the invention is to provide a means for measuring the relationship between the sample applied voltage value and the amount of secondary electron signal, and a means for measuring the relationship between the sample applied voltage value and the amount of secondary electron signal, and based on the measurement result, the secondary electron signal for a predetermined voltage waveform applied to the sample. means for calculating a correction amount by comparing the calculation result with a strobe observation secondary electron waveform when the predetermined voltage waveform is applied to the sample; This is achieved by providing a strobe electron beam device characterized by comprising means for correcting pulse generation timing.

(6) Examples of the invention Embodiments of the present invention will be described in detail below.

FIG. 1 is an overall configuration diagram of a strobe electron beam device according to the present invention. 1 is a strobe electron beam optical system lens barrel, and a pulse gate 2 for generating a BB pulse therein. Suitable sample for collecting correction data for electron beam pulse generation timing 3. and a secondary electron detector 5 are arranged.

Sample 3 is control surface 1i! Selectively via the changeover switch 14 by the function generator 4 controlled by the function generator voltage value designation signal 31 from &12 or the DC power supply 13 controlled by the DC power supply voltage value designation signal 32 from the control circuit 12 Driven. Further, the pulse gate 2 is driven by a deflection voltage signal 24 generated in a pulse gate driver 11 to which a delay circuit 9 and a high precision delay circuit 10 are connected in cascade. The delay circuit 9 has a delay setting value determined by the delay amount designation signal 27 from the control circuit 12, and transmits the clock 21 from the function generator 4 to the frequency division circuit 8, which is controlled by the frequency division ratio designation signal 23 from the control circuit 12. A delay operation is performed on the frequency-divided clock 22.

Further, the high-precision delay circuit 10 has a high-precision delay setting value determined by the high-precision delay amount designation signal 28 from the control circuit 12, and performs a high-5-precision delay operation on the output signal of the delay circuit 9. In addition, the pulse gate driver 11
is controlled by driver control signals 30 from control circuit 12. On the other hand, a secondary electron detector 5 amplified by an amplifier 6
The secondary electronic signal 25 from 2 is sampled by the sampling circuit 7 controlled by the strobe signal 29 from the high precision delay circuit 10 and is converted into a digital secondary electronic signal 26.
The signal is given to the control circuit 12 as a signal.

FIG. 2 shows the delay circuit 9. High precision delay circuit 10. FIG. 3 is an internal configuration diagram of the control circuit 12 regarding the sampling circuit 7 and the sampling circuit 7. FIG. The delay amount designation signal 27 that specifies the delay setting value of the delay circuit 9 is generated by the delay amount setting circuit 33, and from the delay amount setting circuit 33, a correction signal that stores the correction secondary electronic signal amount as a digital value is generated. Secondary electronic signal amount table 3
4, an address signal 39 corresponding to the designated delay setting value is applied.

On the other hand, the digital secondary electronic signal 26 which is the output of the sampling circuit 7 is input to the comparison circuit 35, and in the comparison circuit 35, the digital secondary electronic signal 6-26 and the correction from the correction secondary electronic signal amount table 34 are input. A comparison with the secondary electron signal 40 is performed. The output of the comparison circuit 25 is given to a high-precision position setting delay circuit 36, and the output of the high-precision delay amount setting circuit 36 is connected to the input of the high-precision delay circuit 10 via a switch 38. Connected to input. The output of the delay correction amount table is also connected to the input of the high precision delay circuit 10 via the switch 38. Atlus designation of each correction value in the delay correction amount table 37 is performed by the address designation signal 39.

Next, the delay amount correction operation in the strobe electron beam device having the above configuration will be explained.

First, connect the selector switch 14 to the terminal T2 side.

A constant DC voltage is applied to the sample 3 from the DC power supply 13 in accordance with the DC power supply voltage value designation signal 32 from the control circuit 12 .

Then, the secondary electron signal is detected from the secondary electron detector 5 via the amplifier 6 and the sampling circuit 7 at appropriate sampling intervals. In this case, the relationship between the DC voltage (2) and the detected secondary electron signal amount S is as shown in FIG. From this diagram, a voltage section (Vl, V2) in which the DC voltage V versus the secondary electron signal amount S changes linearly is extracted. In general, Vl and ■2
The potential difference between them is on the order of several volts. Next, selector switch 14
is connected to the terminal TI side, and the voltage V! is input from the control circuit 12 via the function generator voltage value designation signal 31. and V2 to the function generator 4, the function generator 4 generates a sawtooth voltage waveform with a constant period T [seconds] as shown in FIG. 4 that changes between the voltage levels (Vl, V2), and Apply. Although this period T (seconds) can be set appropriately, a case will be described below as an example in which T is made to match the delay time width to be corrected. First, the relationship between each time period (hereinafter referred to as delay setting value d [seconds]) obtained by dividing one cycle T [seconds] of the sawtooth voltage waveform into n equal parts and the amount of secondary electron signal S is shown in Fig. 3. By doing this, each point (d+, 5ad) (d2, 5a2) (d3, 5a3) on the broken line shown in FIG.
) ... (dn, 5an), the calculated values Sa+ to San are stored in addresses A1 to An of the correction secondary electronic signal amount table 34. On the other hand, for the sawtooth voltage waveform generated by the function generator 4 as shown in FIG.
Specify the frequency division ratio as 1 and set the frequency division ratio to 1 at time t+, t2. t3.・・・
・Create a frequency-divided clock 22 that is generated every time (Fig. 4). Next, a fixed delay setting value d [seconds] (Fig. 4) is set in the delay amount setting circuit 33, and the clock 22 is delayed in accordance with this setting value in the delay circuit 9, and an EB pulse is generated by the pulse gate 2. Irradiate sample 3. As a result, the secondary electron signal detected from the secondary electron detector 5 is synchronously encoded in the sampling circuit 7 using the strobe signal 29, so that each point A+ is detected.

A2. A3. ...Digital 2 in (Figure 4)
A second electronic signal 26 is obtained. These signal values are the same as long as the delay setting value d [seconds] is constant. Furthermore, the relationship between the delay setting value d (seconds) and the secondary electron signal amount S should ideally match the point corresponding to phase 9 on the broken line in FIG. That is, in FIG. 5, for example, if the delay setting value is set to d3 [seconds], the amount of secondary electron signal obtained from the secondary electron detector 5 via the amplifier No. 63 sampling circuit 7, that is, the strobe observation waveform value becomes Sa3. It should be. However, in reality, there is a delay error in the delay circuit 9.

Even if the delay setting value is set to d3 (seconds), the strobe observed waveform value will not be a point on the broken line in FIG. address A3 of the correction secondary electron signal amount table 34 is specified by the address signal 39, and the comparison circuit 35 compares the ideal secondary electron signal waveform value Sa3 stored there with the strobe observation waveform. The high-precision delay amount setting circuit 36 sets a high-precision delay setting value for correction that is proportional to the difference, and supplies it to the high-precision delay circuit 10 as a high-precision delay amount designation signal 28 (at this time, the selector switch 38 is connected to the terminal (connected to the T3 side).As a result, a delay for correction by the high-precision delay circuit 10 is added to the delay in the delay circuit 9, and the BB pulse is emitted at the corrected generation timing. Repeat until Sa3 and the strobe observation waveform match, and then set the high-precision delay setting value set by the high-precision delay amount setting circuit 36 as the delay setting value d3.
The delay correction amount Δd3 [seconds] (FIG. 5) is stored in the address A3 of the delay correction amount table 37 designated by the address signal 39. By performing the above operation for each delay setting value d1 to dn (seconds) set by the delay amount setting circuit 33, di to d
d1 to Δdn [seconds] can be added to the delay correction amount for n (seconds), and these are stored in addresses A1 to An of the delay correction amount table 37.

As a result, each strobe observed waveform value S on the solid line in FIG.
b+, Sb2. Sb3. ...Sbn is the ideal value Sad, Sa2 . . . on the broken line. Sa3.・--8an, and the respective delay correction amounts for this are Δd1, Δd2. Δd3
．． ...Δdn (seconds).

By the above operation, any delay setting value d1 to dn (seconds)
Since the correction values Δd1 to Δdn (seconds) have been obtained, the first step is to perform strobe observation on the sample for actual operation analysis.To do this, first set the changeover switch 14 to terminal T.
Connect to the I side.

A clock pulse is applied to the sample 3 by the function generator 4. Then, the delay setting value corresponding to the occurrence timing to be observed is set to d1 in the delay amount setting circuit 33.
Delay circuit 9 by selecting from ~dn [seconds]
The delay amount designation signal 27 is given to the delay amount setting circuit 33, and the address signal 39 corresponding to the delay setting value is given to the delay correction amount table 37, so that the corresponding delay correction amount is specified as a high precision delay amount. It is given to the high-precision delay circuit 10 as a signal 28 (at this time, the changeover switch 3
8 is connected to the terminal T4 side). As a result, the sample 3 is irradiated with the EB pulse at an accurate generation timing corresponding to the delay setting value.

An accurate strobe waveform can be obtained by plotting the digital secondary electronic signal 26 obtained by changing the delay amount by one operation period against the delay time.

In this embodiment, a sawtooth voltage waveform was used as the correction voltage waveform, but other waveforms may be used as long as the relationship between the delay setting value d (seconds) and the secondary electron signal amount S is correlated. They can also be used as Funkshi Sun Generator 4.
(Fig. 1).

(7) Effects of the Invention According to the present invention, it is possible to efficiently correct errors in the generation timing of EB pulses for strobe observation of a sample, and it is possible to perform sample motion analysis with high precision.

[Brief explanation of the drawing]

Fig. 1 is an overall block diagram of the strobe electron beam device according to the present invention, Fig. 2 is a specific block diagram of the EB pulse generation timing correction section according to the present invention, and Fig. 3 is a diagram showing the DC voltage V applied to the sample versus the secondary 4 is an explanatory diagram of the sawtooth voltage waveform applied to the sample. FIG. 5 is a diagram showing the relationship between the amount of electronic signal S and the delay setting value d versus the amount of secondary electron signal S for explaining the correction of the EB pulse generation timing. It is a relationship diagram. 1... Strobe electron beam optical system lens barrel 13- 3... Sample 4... Function generator 5... Secondary electron detector 7... Sampling circuit 8... Frequency dividing circuit 9...・Delay circuit 10... High precision delay circuit 11... Pulse gate driver 12... Control circuit 13... DC power supply 14.38... Changeover switch 20... Sample input voltage 21... Clock 27...Delay amount designation signal 28...High precision delay amount designation signal 29...Strobe signal 33...Delay amount designation circuit 34...Secondary electronic signal amount table for correction 35...Comparison circuit 37 ...Delay correction amount table = 14- Figure 3 S Figure 4 ■ Figure 5

Claims (1)

[Claims] means for measuring the relationship between the sample applied voltage value and the amount of secondary electron signal; means for calculating the amount of secondary electron signal for a predetermined voltage waveform applied to the sample based on this measurement result; It is characterized by comprising means for calculating a correction amount by comparing the strobe observed secondary electron waveform when a voltage waveform is applied, and means for correcting the generation timing of the electron beam pulse based on the correction amount. A strobe electron beam device.