JPS61126752A - Deflection electric power supply for scanning electron microscope - Google Patents

Abstract

PURPOSE:To minimize electron ray damage by preventing any overcharge of a scanning electron microscope by performing scanning while gradually moving scanning lines by varying the d.c. level of the deflection signal. CONSTITUTION:Similar to a usual SEM, electrons on a CRT10 are deflected in X-direction by using a current amplifier 14 to convert sawtooth waves produced from an X-direction scanning signal generator 13 into X-direction deflection current (IX) and then feeding it to a deflecting coil 5. The electrons are deflected in Y-direction, for example, by using a D/A converter 15 of eight bit to produce step-like sawtooth waves and then, in order to adjust the number of interlaced scanning lines to seven, outputs of an octal notation counter 17 for the lower three bits and outputs of 32-notation counter 18 for the upper five bits are entered into the D/A converter 15. The blanking signal from the X-direction scanning signal generator 13 is used as a clock signal for the 32-notation counter 18. And, the carry signal for the 32-notation counter 18 is used as a clock signal for the octal notation counter 17.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention is directed to a scanning electron microscope! (hereinafter referred to as SEM), especially for observing or photographing samples with low conductivity without vapor deposition. SEM suitable for lifting and photographing samples that are prone to deformation due to the heat of ion beam irradiation
Regarding.

[Background of the invention]

In recent years, attempts have been made to use SEM to detect semiconductors and other materials without vapor deposition, but such samples have low conductivity and the charge-up phenomenon that occurs when the irradiated charge builds up on the sample surface causes an abnormal contrast in the observed image. For this reason, in the past, the charge applied to the sample was reduced by lowering the accelerating voltage or increasing the convergent lens current for observation. However, even with these methods, the charge-up phenomenon described above cannot be completely eliminated, and lowering the accelerating voltage or reducing the sample current will lower the SZX ratio of the image and deteriorate the image quality. There was a drawback.

Recently, SEM has been increasingly used to study organic materials, but when these samples are irradiated with electron beams for a long time, the problem arises that the samples become deformed due to the heat generated by the electron beam irradiation. are doing.

As a countermeasure for this, it is necessary to perform observation by lowering the accelerating voltage or reducing the sample current as described above, which similarly causes the problem of deterioration of image quality.

In addition, these problems are particularly serious when taking photographs that are scanned at a slower speed than in the normal iI festival state.

[Purpose of the invention]

The purpose of the present invention is to detect or photograph samples with low conductivity such as semiconductors without vapor deposition and without charge-up phenomenon, and to detect samples such as organic materials while minimizing electron beam damage. To provide a SEM suitable for

[Summary of the invention]

In the present invention, if the scanning line is deflected at a period longer than the time required for the charge accumulated on the sample surface due to electron beam irradiation to discharge, and at a period longer than the time required for the heat generated by the electron beam irradiation to dissipate, a charge-up phenomenon occurs. Electron beam damage is
Since it is possible to minimize the number of images, an arbitrary number of intermittent scans are performed in the vertical direction of the SEM, and one screen is constructed while sequentially moving.

[Embodiments of the invention] FIG. 1 is a block diagram of an embodiment of the invention.

An electron beam 3 generated by an electron gun 1 is accelerated by a high voltage 2 and narrowed by a converging lens 4. After that, the sample 7 is deflected two-dimensionally by the deflection coil 5, and the sample 7 is deflected by the objective lens.
Secondary electrons 8 generated from the sample and focused upward are detected by a secondary electron detector 9 and converted into an electrical signal. This signal is a CRTI beam deflected synchronously with the electron beam 3 on the sample 7.
It is sent to O to obtain an SEM image. Now, on the CRTIO, let the horizontal direction be the same and the vertical direction be Y. For deflection in the X direction, as in a normal SEM, a sawtooth wave generated by an X direction scanning signal generator 13 is converted into a current by a current amplifier 14, and an X direction deflection current Ix is caused to flow through the deflection coil 5 for deflection. The Y direction is
The configuration is such that a stepped sawtooth wave is generated by the D/A converter 15, and in order to set the number of scanning lines in the Y direction to 256, an 8-bit D/A converter is adopted.

The input reference voltage to the D/A converter 15 is assumed to be the output vy of the reference voltage generator 16.

Then, in order to make the number of skipped scanning lines 7, the lower 3
The bits are the output of the octal counter 17, and the upper 5 bits are 3
The output of the binary counter 18 is connected to the D/A converter 1.
Input as data to 5. X direction scanning signal generator 1
The blanking signal from 3 is input as a clock signal to the 32-decimal counter 18, and the carry signal of the 32-decimal counter 18 is input as a clock signal to the 8-decimal counter 17.

The Y-direction scanning signal generated by the above configuration, that is, D/A
The voltage waveform of the output part A of the converter 15 is as shown in FIG. 2. The one-step sawtooth wave gradually increases its DC level and completes one scan in the Y direction when the octal counter is reset. When this state is observed using the scanning line on the CRTIO, it becomes as shown in FIG. That is, the scanning line starting from the part ■ repeats scanning while skipping seven scanning lines, and the instantaneous scanning line of the 0th order reaches the 0th part by skipping the position by one line and scans the 0th part. While repeating this operation, the entire scanning surface is scanned to form one screen.

According to this embodiment, the scanning period in the X direction from the part ■ to the part 0 is 32 times that of a normal SEM. In a normal SEM, the charge irradiated at the part ■ is converted into an electric current to the sample stage 12, which is at ground potential. Discharge: The irradiation charge due to 0 parts is accumulated before discharge.

This is repeated and a charge-up phenomenon occurs, but according to this embodiment.

The accumulated charge due to scanning in the part (■) will be discharged by the time the next part 0 is scanned, and no charge-up phenomenon will occur. Similarly, the heat generated in the part (■) due to electron beam irradiation will be Heat is dissipated by the time the 0 part is scanned, and the temperature rise on the sample surface can be minimized.

In this example, the number of scanning lines is 256 and the number of skips is 7, but if you make it possible to select the counter and arbitrarily select the number of jumps, you can select the most suitable scan for the sample. You can choose.

〔Effect of the invention〕

1. According to the present invention, the charge-up phenomenon can be minimized when observing or photographing a sample with low conductivity such as a semiconductor. Furthermore, when inspecting or photographing a sample that is easily deformed by heat generated by electron beam irradiation, the sample surface temperature rise can be minimized, and the electron beam damage can be minimized.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the embodiment, FIG. 2 is a vertical deflection signal waveform diagram, and FIG. 3 is a scanning line diagram on a CRT according to the embodiment. DESCRIPTION OF SYMBOLS 1... Electron gun, 2... High voltage power supply, 3... Electron beam, 4... Converging lens, 5... Deflection coil, 6...
objective lens. 7... Sample, 8... Secondary electron, 9... Secondary electron detector, 10... CRT, 11... Current amplifier, 12
...Sample stand. 13...Horizontal scanning signal generator, 14...Current amplifier, 15...8-bit D/A converter, 16...
・Reference voltage generator, 17...octal counter, 18...
・32-decimal counter.

Claims (1)

[Claims] 1. In the deflection power supply of a scanning electron microscope that scans an electron beam over a sample in two-dimensional directions and deflects the electron beam with a step-like sawtooth wave current on at least one side, the step height of the deflection signal is determined. Deflection of a scanning electron microscope characterized by having a function of performing intermittent scanning that can be set arbitrarily, and a function of configuring a scanning surface while sequentially moving the scanning line by sequentially changing the DC level of the deflection signal. power supply.