JPH04337234A - Scanning electron microscope - Google Patents

Abstract

PURPOSE:To find the distribution state such as the potential, fine magnetic field, and fine electric field of a fine region on the surface of a sample by providing an energy spectrograph between the sample and a secondary electron detector. CONSTITUTION:When an electron beam 1 is radiated to a sample 6, secondary electrons 2 are emitted. When a spectral grid 3 is provided between the sample 6 and a secondary electron detector 9 and the output voltage of a bias power source 5 is changed by a regulator 4 to analyze the energy of the secondary electrons 2, the output current of the detector 9 becomes a curve 10. An electrode 7 biased to the positive voltage by a power source 8 unifies the extraction of the secondary electrons 2 and the electric field distribution to serve as a buffer. The distribution state such as the potential, fine magnetic field, and fine electric field of a fine region on the surface of the sample 6 can be easily found.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to a scanning electron microscope.
This invention relates to a method of forming images by detecting the energy possessed by secondary electrons in order to expand its functionality.

0002

[Prior Art] In a scanning electron microscope, images are formed by detecting changes in the number of secondary electrons emitted as information media, such as irregularities on the surface of a sample, surface potential, local electric fields, magnetic fields, etc. It is impossible to detect changes in secondary electron energy. However, energy spectroscopy of secondary electrons has been put into practical use with an electron beam tester, and the
There are many reports including 5th study meeting materials PP60-65.

0003

However, in the prior art described above, image interpretation is difficult because the secondary electron emission efficiency depends on the unevenness of the sample, the work function of the sample surface, the surface potential, the electric field or magnetic field near the sample, etc. There are many cases where this is difficult. Furthermore, it is not suitable for measuring surface potential, magnetization strength, etc. On the other hand, technologies such as electron beam testers that can measure the sample surface potential have been put into practical use, but images are formed using changes in the number of secondary electrons emitted as information media rather than changes in the energy of secondary electrons. There is.

An object of the present invention is to add a function to a scanning electron microscope to form an image by detecting changes in secondary electron energy, and to provide a new means of observation using surface potential images, minute magnetic field images, etc. .

[0005]

[Means for solving the problem] The above purpose is to make the upper and lower limit levels of the secondary electron signal constant when changing the voltage of the energy spectrometer installed between the sample and the secondary electron detector. After signal processing, it is possible to detect the energy width and energy difference of secondary electrons by setting a threshold value and comparing the signals by reading the spectral grid voltage. This is achieved by performing image formation.

[0006]

[Operation] The energy-separated secondary electron signal is digitized by changing the analysis grid voltage of the energy spectrometer installed between the sample and the secondary electron detector, and the upper and lower limit levels of the signal are detected by computer processing. Then, the bias voltage of the secondary electron detector is controlled so that the upper and lower limit levels are constant. This makes it possible to quantify the signal, and by reading the analysis grid voltage, it is possible to know the energy width of the secondary electrons and the energy difference between the secondary electron signals when an appropriate threshold is set.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the principle of the present invention. Secondary electrons 2 are emitted by irradiating the sample 6 with the electron beam 1, and the number of emitted secondary electrons depends on the unevenness of the sample surface, work function, surface potential, and the like. On the other hand, since the energy possessed by secondary electrons is affected by the surface potential and local electric and magnetic fields, detecting this provides useful information that cannot be obtained from ordinary SEM images. To perform energy separation of secondary electrons,
When a spectroscopic grid 3 is provided between the sample and the secondary electron detector and the output voltage of the bias power supply 5 is varied by the regulator 4, the output current of the secondary electron detector changes as shown by a curve 10. In addition, when the surface potential of the sample changes, for example, curve 1
It changes like 1. Further, the electrode 7 biased to a positive voltage by the power source 8 functions as a buffer for extracting secondary electrons and making the electric field distribution uniform.

FIG. 2 shows an embodiment of the present invention, in which secondary electrons 2 generated in the irradiation area of the electron beam 1 focused by the objective lens 13 on the surface of the sample 6 are energy-separated by a spectroscopic grid 3. Secondary electron detector 9
Detected in The secondary electronic signal is digitized by the D/A converter 14 and stored in the memory 15. For level correction, the upper and lower limits of the signal are detected in the correction circuit 18 and compared with a reference, and the bias voltage of the secondary electron detector 9 is controlled via the D/A converter 17 so as not to cause a deviation.

[0009] The spectroscopic grid also includes a signal generation circuit 1.
A signal obtained by controlling the power supply 28 via the D/A converter 17 is added to the output of the power supply 9. After the secondary electronic signals stored in the memory 15 are read out, the signal processing circuit 16 sets a threshold value, compares the signals, and the like. Thereafter, the arithmetic circuit 20 calculates the energy width, the difference, etc., and the signal is converted into an analog signal by the D/A converter 17, which drives the video amplifier 24 and excites the grid of the CRT 26. Furthermore, by switching the switch 22, inputting the video signal to the CRT deflection amplifier 23, amplifying it, and applying it to the deflection coil 25, a Y-modulated image can be obtained. On the other hand, the scanning signal generated by the scanning signal generator 21 is amplified by the amplifier 27 and supplied to the deflection coil 12, thereby scanning the electron beam 1 two-dimensionally in the X-Y direction.

FIG. 3 is for explaining a method of detecting the energy width and difference of secondary electrons. In the left diagram, the upper and lower limit levels of signals 10 and 11 do not match, but after correction, they are processed as shown in the right diagram, so the energy difference D can be calculated by setting a threshold 31. Further, the energy width W can be obtained by providing the threshold values 29 and 30.

FIG. 4 shows the timing of the X and Y scanning signals, the spectral grid signal and the video signal. The X scanning signal 32 and the Y scanning signal 33 are for scanning the electron beam two-dimensionally in the X-Y direction. The period of the spectral grid signal is shorter than that of the
is output, that is, one pixel is formed for each period of the spectral grid signal.

0012

[Effects of the Invention] According to the present invention, since the energy width and difference of secondary electrons can be visualized as an information medium, it is possible to easily know the distribution state of electric potential, minute magnetic field, minute electric field, etc. in minute areas on the sample surface. Can be done.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the principle of the present invention.

FIG. 2 is a diagram showing the configuration of an apparatus according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram of a method of calculating energy width and difference.

FIG. 4 is a diagram for explaining the timing of various signals.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Electron beam, 2... Secondary electron, 3... Spectroscopic grid, 4... Voltage regulator, 5... Power supply, 6... Sample, 7... Extraction and buffer electrode, 8... Power supply, 10 and 11... Secondary electron signal, 12
... Deflection coil, 13... Objective lens, 14... A/D converter, 15... Memory, 16... Signal processing circuit, 17... D/A converter, 18... Level correction circuit, 19... Analysis grid signal generator, 20 ...Arithmetic circuit, 21...Scanning signal generator, 22
...Switch, 23...Deflection amplifier, 24...Video amplifier, 2
5...CRT deflection coil, 26...CRT, 27...deflection amplifier, 28...spectral grid control power supply, 29-31...threshold value,
32...X scanning signal, 33...Y scanning signal, 34...spectral grid signal, 35...video signal, D...energy difference, W...energy width.

Claims (2)

[Claims] 1. A scanning electron microscope characterized by detecting the energy width, energy difference, etc. of a secondary electron signal, and converting this information into a brightness modulation signal or the like to form an image. 2. A scanning electron microscope characterized by having a function of automatically adjusting an upper limit level and a lower limit level of an energy-separated secondary electron signal to arbitrary constant values set in advance.