JPS5887744A - Strobo scanning electron microscope - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is applicable to a scanning electron microscope 11K1. D. Particularly related to a microscope capable of observing the waveform of the sample surface potential by detecting reflected electrons out of the electrons emitted from the sample surface.Generally, when an electron beam is irradiated onto a sample whose surface has a potential. It is known that the energy distribution of secondary electrons emitted from the sample surface changes under the influence of the sample surface potential. Therefore, it is possible to detect the sample surface potential without mechanical contact by using the electron beam as a glove. When an electron beam is used as a glove, (a) it can be narrowed down to a probe with a diameter of 1 μm or less, making it possible to measure minute areas; and (b) the beam position can be precisely controlled from the outside, making it easy to perform arbitrary measurements. It has features such as being able to measure the voltage at a location. Taking advantage of this feature, a scanning electron microscope (sm) has been realized that detects the sample surface potential with an electronic glove and displays the detection results.

By using this so-called S, we can observe the internal operation of LSIs (Large-Scale Integrated Circuits), which are becoming increasingly miniaturized.

This is very effective as it allows analysis of LSI operation or failure analysis. On the other hand, IC-? L
In a synchronous phenomenon such as an electric signal propagating inside an SI element, potential changes occur regularly and repeatedly each time. Therefore, even if the potential changes are at a high speed of several hundred kHz or more, the output signal obtained when repeatedly irradiating the Dalsumiko beam only at a certain phase corresponds to the potential at this phase. The beam is stopped at a desired point on the sample surface, and the phase difference between the sample excitation and the /4 Luss electron beam is electrically changed, and the phase amount is displayed on the horizontal axis of the display.
By inputting the secondary electron signal amount on the vertical axis, the voltage waveform at a desired point can be displayed on the display.

In this way, a conventional metro scanning electron microscope is a scanning electron microscope that adds a base pulse generation function to the surface potential detection function of a conventional SEM and applies sampling technology. In other words, the Stro & SEM includes a SEM that has a beam irradiation section that irradiates a sample surface with a 7-pulse electron beam, and an SEM control section that synchronizes the beam irradiation of the beam irradiation section with sample excitation. and the above S
It is equipped with a secondary electron detector that detects the secondary electrons emitted from the sample and a display that displays the output of the secondary electron detector. .

By the way, when the surface of a solid sample is irradiated with an electron beam, various types of electrons are emitted from the surface, but conventionally, measurements have been performed focusing on secondary electrons. Secondary electrons have a very low energy of about several eV and are easily influenced by the surface potential. In other words, if there is a potential on the surface, the energy shifts by that amount, so it is sufficient to measure the amount of energy.This measurement principle is not limited to secondary electrons, but for secondary electrons, energy is originally Since it is small, the influence of the shift amount is large and measurement is easy.

However, the measurement method using secondary electrons has several problems. Secondary electrons have a very low energy of several eV, so if another potential exists near the measurement point, the secondary electron emission efficiency will be affected by the lateral electric field generated there. changes, resulting in poor measurement accuracy. Furthermore, in order to efficiently collect low-energy secondary electron signals, it is necessary to bias the secondary electron detector to a positive potential and use an extraction electric field to extract the secondary electrons, and this electric field affects the trajectory of the secondary electrons. give. These problems are caused by the low energy of secondary electrons.

The present invention has been made in view of the above circumstances, and focuses on the characteristics of backscattered electrons among the electrons emitted from the sample surface, and detects the backscattered electrons by utilizing the characteristics of the backscattered electrons. The object of the present invention is to provide a Stroh I scanning electron microscope that is not easily affected by the effects of irradiation, does not require an extraction electric field, and has good measurement accuracy and reproducibility.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

Figure 1 shows the energy distribution of electrons emitted from the surface of a solid sample when the surface of the sample is irradiated with an electron beam.In addition to secondary electrons, there are Ohnoe electrons and backscattered electrons.
Backscattered electrons are incident electrons that are re-emitted as they are after some energy loss occurs due to scattering with sample solid atoms. If the peak energy of reflected electrons is E1 and the energy of incident electrons is Eo, it is approximately E/E0-0.9. Figure 2 is E. ” shows the energy distribution at 100 aV, and the energy peak E of the reflected electrons is approximately 9
0 @V, the energy peak of secondary electrons is approximately 10 eV
It is.

@ In the Stro/8EM shown in Figure 3, 3o is SEM
1. Main body, No. 3 is a solid sample (for example, LSI) placed in the main body 30; ? ,? A beam generator 34 is a beam pulse generator that is controlled by the pulse from the pulse generator 33 and generates a beam pulse. The 4-lux generator 33 has a control function that synchronizes sample excitation and irradiation with the Norsum beam in order to set the desired phase relationship between the beam 9-lux and the potential change on the surface of the sample. . Reference numeral 35 denotes a backscattered electron detector provided within the main body 30 to detect backscattered electrons emitted from the surface of the sample, and is installed, for example, around the exit port for incident electrons. Reference numeral 36 denotes an amplifier for amplifying the output from the detector 35 and supplying the amplified output to a video display (not shown) such as a CRT.

In the Stroz sEM with the above configuration, No! A backscattered electron detector 35 detects the backscattered electrons emitted from the sample surface when the sample surface is irradiated with a laser electron beam, and the waveform of the sample surface potential is measured by displaying the detection results visually. .

In this case, as described above, the energy of the reflected electrons is sufficiently higher than the energy of the secondary electrons, and is hardly affected by the lateral electric field, so that no extraction electric field is required. Therefore, the measurement accuracy is not affected by the positional relationship between the backscattered electron detector 35 and the sample 31.

Further, unlike the conventional secondary electron detector, the backscattered electron detector 35 can be attached around the exit port of the incident electrons as described above. As a result, the positional relationship between the sample 31, the backscattered electron detector 35, and the incident electron beam is uniquely fixed, resulting in good measurement reproducibility.

As described above, according to the present invention, it is possible to perform measurements using a scanning electron microscope with good measurement accuracy and reproducibility.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the energy distribution of emitted electrons when the surface of a solid sample is irradiated with an electron beam, Figure 1g2 is a diagram showing the energy distribution of emitted electrons when the incident electron energy dfg in Figure 1 is 100 @V, FIG. 3 is a configuration explanatory diagram showing an embodiment of a Strogo scanning electron microscope according to the present invention. 30...SFJ/i main body, 31...sample, 33-...
Arm lux generator, 34... Beam 9 lus generator, 3
5... Backscattered electron detector.

Claims (1)

[Claims] a scanning electron microscope having a beam irradiation section for irradiating a sample surface with a Kz4 Luss electron beam; a control section that synchronizes the Nonolus electron beam irradiation of the beam irradiation section with sample excitation; and a control section within the scanning electron microscope. 1. A scanning electron microscope comprising a backscattered electron detector for detecting backscattered electrons emitted from a sample irradiated with a Noyals electron beam.