JPS5999731A - Measuring device for potential distribution of electronic device - Google Patents

Abstract

PURPOSE:To measure potential distribution accurately by normalizing potential contrast informations obtained from detecting secondary electronic signals and correcting the effect of a partial field-effect. CONSTITUTION:A switch 10 is turned ON to S1, a sample 4 is driven 7, pulse beams are irradiated in designated phase between 0 and 2, secondary electrons are detected 8, and A/D converted 9, and Imax and Imin at the position of the picture element are detected 11 by a command from a computer 20 and memorized. Said operation is repeated at every picture element. The switch S is turned ON to S2, phase obtaining a potential contrast image is designated, beams are irradiated selectively, the secondary electronic detecting signals are memorized 12, the potential contrast informations Imes are acquired through repetition about all picture elements, picture element informations P=(Imes-Imin)/(Imax-Imin) are computed 14, and binary-coded 15, and black and white potential contrast images are displayed 16. According to the method, the variation of the level and amplitude of the secondary electronic signals can be prevented by a partial electric field by adjacent electrode potential in the vicinity of a measuring position, and potential and its distribution can be measured accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in a potential distribution measuring device for an electronic device using an electron beam for non-contact measurement of the potential distribution of an electronic device such as a semiconductor device.

[Technical background of the invention and its problems]

Recently, research and development has been carried out on a Seiko potential distribution measuring device that measures the potential of the sample surface without contact by irradiating an electron beam onto a semiconductor sample such as an IC or LSI and detecting the secondary electrons emitted from the sample. has been done. This device applies the following two principles. In other words, when a gust-shaped electron beam is irradiated onto a semiconductor sample in an operating state to which a drive signal has been applied, in synchronization with the drive signal, 2 electrons are emitted from the sample.
From the second electron signal, information about the sample potential at the phase in which the crusoidal electron beam is irradiated is routinely obtained. Furthermore, when a high potential region is irradiated with an electron beam, the amount of detected secondary d-son signals is small, and conversely, when a low potential region is irradiated with an electron beam, the amount of detected secondary electron signals is large.

Therefore, in the above-mentioned apparatus, the 1st drive No. 46 is applied to the sample, the pulsed electron beam is irradiated onto the sample only in a fixed phase of the sample movement, and the irradiation position is set by the deflection of the electron beam. By changing the voltage two-dimensionally, a potential contrast image can be obtained. The potential distribution on the sample surface at any given time can be observed from this potential contrast image, and the state of signal transmission can also be observed by changing the phase of the potential contrast image one after another. Therefore, it is extremely effective for observing high-speed operation of semiconductor testing.

However, this type of device has the following problems. In other words, the detected secondary electron signal detected when the sample surface is irradiated with an electron beam is strongly influenced by the potential and arrangement of surrounding electrodes (regions with potential on the sample surface), so-called local electric field effects. . Then, the level and amplitude of the detected secondary electron signal vary. For example, in a sample with the configuration shown in FIG. 1(a), when comparing the amount of secondary electrons detected when an electron beam is irradiated at points A and B of the same type of element, it is found that The effect is as shown in Figure 2. In other words, since the secondary electrons emitted from point A are more strongly influenced by the attractive electric field by the 5 ■ distribution C than the secondary electrons emitted from point B, both the amplitude and the level at point A are smaller than those at point B. is measured.

As described above, the level, amplitude, etc. of the detected secondary electron signal vary in each pixel due to differences in local electric field effects, and even points with the same potential may have different potential contrast images.

For example, if the binarization threshold is set as Q as shown in Fig. 2, at time t, point A is judged to be O (high potential) and point B is judged to be 1 (low potential), but in the conventional technology, the binary value is In order to perform a chromatic display, the threshold value is set to be the same for all pixels, or the shunted secondary electron detection signal is inputted uncorrected as a brightness modulation signal to a CRT display to display a potential contrast image. For this reason, conventional potential contrast images can only be used to roughly measure the amount of potential or potential distribution.

[Purpose of the invention]

An object of the present invention is to be able to prevent fluctuations in the level and amplitude of a detected secondary electronic signal due to local field effects;
An object of the present invention is to provide an electric potential measuring device capable of accurately measuring electric potential and measuring electric potential distribution.

[Summary of the invention]

The gist of the present invention is to normalize potential contrast data obtained from detected secondary electron signals and correct the influence of local electric field effects seen in potential contrast images.

That is, the present invention provides means for applying a driving signal to an electronic device and scanning a pulsed electron beam over the electronic device, and means for detecting secondary electrons emitted from the electronic device to obtain potential contrast data. and a means for displaying a potential contrast image according to a change in the surface potential of the electronic device based on this data, wherein the electronic device corresponds to each pixel of the potential contrast image. A drive signal is immediately applied to the electronic device so as to sequentially set a different potential state for each planar position (2π change in a circuit that operates periodically). The maximum value and minimum value of the secondary electron signal detected by irradiating the electron beam at each position of the electronic device corresponding to The potential contrast image is displayed based on the converted data.

〔Effect of the invention〕

According to the present invention, since the potential contrast arter is normalized, it is possible to correct the influence of local field effects based on the surrounding electrode potential at the measurement location. 1, etc., to eliminate the measurement error of 4th place based on the fluctuation of force i,,.

Wear. Therefore, the obtained potential cannot accurately shift the potential distribution of the electronic device, thus improving the measurement accuracy of the potential distribution.

I can understand it.

[Embodiments of the invention]

FIG. 3 is a 1-schematic diagram showing an embodiment of the present invention. In the figure, numeral 1 is an electron gun, and the emitted electron beam is directed to a deflection coil for scanning the beam.

j4@- is placed on the semiconductor sample 4 which is a child device.

A logic circuit is formed to The deflection plate 2 is for converting the electron beam into pulses. It is driven by □. The deflection coil 3 is used to control the irradiation position of the 'seiko beam' which is irradiated in a pattern on the sample 4 at each pixel position. Next, it is something that fundamentally changes.') 1 (1ni
It is driven by the rotation driver 6. Sample 4 includes a juice calculator,
The drive signal from the drive signal generator 7 controlled by the drive signal generator 7 is applied and placed in the operating state. In addition, the driver 5 and the drive signal generator 7 are synchronized with each other, and only when the drive and image signals from the drive signal generator 7 reach a specific phase state. , Ch3. The collar driver 5 is activated and the sample 4 is irradiated with a pulsed beam.

・Secondary electrons emitted from sample 4 due to the irradiation of the Gurus beam are detected as 2 ignites! The digital data converted by the VD converter 9 is sent to the A/D converter 9 through the switch 10. 1' is supplied to the image meter 12.The peak detector 11 detects the maximum and minimum values of the input digital signal, and these values are stored in the peak system meter ν13. The contrast image memory 12 sequentially stores the input digital data to obtain the potential contrast data, and this data is sent to the normal i processing section 14.

The normalization processing unit 14 normalizes the potential contrast arter based on the maximum value and minimum value stored in the peak hold memory 13, and the normalized data is
The data is supplied to the value conversion processing section 15. The binarization processing unit 15 converts the normalized data into 2 at a threshold level R.
The data is converted into a value, and this binary data is supplied to an indicator 16 made of, for example, a CRT display.

Then, the above-mentioned two-digit data is displayed on the optical indicator 16 as one image of black and white "potential contrast." The operation of the apparatus configured as described above will be explained.

First, the switch 10 is switched to the Sl side, and then the irradiation position of the pulse beam is fixed to one pixel by the deflection coil 3 and the deflection dryer 6. In this state, a continuous pulse-like or sinusoidal drive signal from the drive signal generator 7 is applied to the sample 4, and the sample 4 is irradiated with a pulsed beam at the specified phase of this applied signal. The phase of pulse beam irradiation is sequentially changed within the range of 0 to 2π, and in this interval phase, the secondary electrons emitted from the sample 4 during pulse beam irradiation are detected by the fourth-order LD detector 8, and the A/ /D converter 9 and switch 10
is sent to the peak detector 11 via. At the time when the phase of irradiating the pulse beam changes by 2π, the detected secondary forceps signal at that pixel position is divided into one period, and the maximum value 1 max and minimum value I ''min of this period are determined by the computer 20. It is detected by the ♂-ri detector 1□1 according to the command.Then,
These maximum value Imax and minimum value Irn1n are written into the peak hold memory 13.

Next, the irradiation position of the pulse beam is changed by one pixel using the deflection coil 3 and the deflection 1 and the cutter 6. The same process as above is performed, i.e., the □ phase is applied to the sample 4 with respect to the symbol ■. Detection 2 during this time by converting to □2π
Maximum value Imax and lowest value I m4' n of the next electronic signal
A process of determining and writing it into the peak hold memory 13 is performed. Further, the above process is repeated until it is completed for the 'pot□' pixel or all designated pixels. As a result, the maximum value I ma of detected secondary electrons in each phase is stored in the peak hold memory 13 for each pixel.
x and the minimum one shift lm1n are respectively stored.

Next, the switch 10 is switched from the S side to the 82 side. When a phase for obtaining a potential contrast image is specified, the beam chopping deflection plate 2 and the chopper driver 5 irradiate the sample 4 with a pulsed beam only at this phase.

At this time, the secondary electrons emitted from the sample 4 are detected by the secondary electron detector 8, converted into digital data Imes (potential contrast data) by the A//D converter 9, and then sent via the switch lθ. The contrast image is written into the contrast image memory 12. When the above processing is completed for one pixel, the deflection coil 3 and the deflection driver 6 change the irradiation position of the sipulse beam by one pixel, and the same processing as above is performed. Further, the above process is repeated until it is completed for all pixels or all specified pixels.

Potential contrast 1-data I for all pixels or all specified pixels is stored in the contrast image memory 12.
When mes is written, the normalization processing unit 14 normalizes the potential contrast data Imes as follows. First, ε contrast data Imes is read out from the contrast image memory 12, and at the same time, the maximum value 1max and minimum value lm1n are read out from the peak hold memory 13 corresponding to the same pixel position as the data Imes. is normalization processing unit 1
Sent to 4. The normalization processing unit 14 calculates P-(Imes-lm1n)/(Imax-Im
The pixel data P normalized by the formula: in)-(1) is obtained.

In addition, in the case of a pixel with a constant potential, for example, if l Imax - lm1n l(α for a given α, then P = (Imes - lm1n' ) / (Imax'
-lm1n')---Pixel data P normalized by the formula (2) is obtained.

The pixel data P thus normalized is then processed by the binarization processing unit 15.
sent to. In the binarization processing unit 15, for example, when displaying a potential contrast image divided into a black high potential area and a white low potential area, the threshold level R=0.
5 ToL.

Each pixel data P is binarized under the following conditions. And 2
The converted data is displayed on the display 16 as a black and white potential contrast image.

In this way, in this device, the control 2nd image memory 1
The potential contrast arter Imes written in 2 is
The data Im written in the peak hold memory 12
Based on the maximum value ynax and the minimum value lm1n corresponding to the pixel position of es, normalization is performed by the calculation shown in the first equation. Therefore, the detected secondary electron signals shown in FIG. 2 have the same level and amplitude.

In other words, the influence of the local electric field based on the adjacent electrode potential near the measurement point is corrected, and the potential contrast image displayed on the display 16 accurately represents the potential and potential distribution of the sample 4. Therefore, the sample potential and potential distribution can be measured accurately. Further, data Imax and lm1n need only be written once for each pixel to the peak hold memory 13, and even if the potential contrast data Imea is measured with a different phase, the same data Imax and lm1n can be used as they are. be able to. Therefore, after data has been stored in the peak hold memory 13, the data Imes can be quickly normalized regardless of the phase of the potential contrast data Imes.

Note that the present invention is not limited to the embodiments described above. For example, the normalization process of the potential contrast data Imes by the normalization processing unit is not limited to the first equation, but is performed using the maximum value Imax and the minimum value lm1.
Any method may be used as long as the potential contrast data Imes is normalized by arithmetic processing based on n. In addition, when displaying the normalized image data P, this data P is binarized in the embodiment, but it is not limited to simple binarization processing, but is in a transient state between high potential and low potential due to an external command. Gradation may be applied under various conditions to enable identification of objects. For example, gradation may be performed under the following conditions. Further, the display device is not limited to a black and white CRT display, but may of course be one capable of displaying color. In addition, in the above-described embodiment, secondary electrons are detected by irradiating the electron beam in pulses to each pixel with a specific phase of the sample drive signal, but unlike television scanning, the electron beam is continuously applied to the sample. Alternatively, a potential contrast image may be obtained by irradiating and scanning. In addition, various modifications can be made without departing from the gist of the present invention.

[Brief explanation of drawings]

Figures 1 and 2 are for explaining the effects of local electric field effects, and Figure 1 is a plan view showing an example of arrangement of elements and wiring;
FIG. 2 is a schematic diagram showing a detected secondary electron signal waveform, and FIG. 3 is a schematic diagram showing an embodiment of the present invention. 1... Electron gun, 2... Deflection plate for beam chop, 3
... Deflection coil for beam scanning, 4... Semiconductor sample,
5... Chopper driver, 6... Deflection dryer,
7... Drive signal generator, 8... Secondary electron detector, 9
... h/e converter, 10... switch, 1 no...
Peak detector, 12... Contrast image memory, 13... Peak hold memory, 14... Normalization processing section, 15... Binarization processing section, 16... Display device,
20... Calculator.

Claims (2)

[Claims] (1) While applying a drive signal to the electronic device, an electron beam is moved on the electronic device, a secondary electron signal emitted from the electronic device is detected, a potential contrast arter is obtained, and this data is Base: In a potential distribution measuring device for an electronic device that displays a potential contrast image according to a change in the potential of the electronic device t, a potential state that sequentially differs for each position of the electronic device corresponding to each pixel of the potential contrast image is determined. means for applying a drive signal to the electronic device so as to set the electric potential to the electronic device;
Illuminates each child device with an electron beam. means for storing the maximum value and minimum value of the secondary electron signal detected by the radiation; and means for normalizing the potential contrast arter based on the stored maximum value and minimum value; 1. A potential distribution measuring device for an electronic device, characterized in that the potential contrast image is displayed based on converted data. (2) The normalization means is configured to set the stored maximum value to Im
ax, maximum/''-value is l1nin, and the potential contrast data is Imes, P=(Imeg-Irn1n)/(Imax-
Find the normalized pixel data P using the formula
A potential distribution measuring device for an electronic device according to claim 1 dC, characterized in that: