JPS6114552A - Scanning type auger electron analyzing instrument - Google Patents

Abstract

PURPOSE:To eliminate the influence of secondary electrons by making a scan within a small range based upon specific energy as a center and detecting transmitted electrons, differentiating its detected signal and detecting an Auger electron, and subtracting the differential value of the detection signal corresponding to a discharge electron from a sample surface. CONSTITUTION:An electron beam B scans on the surface of a sample 3 and an energy analyzer 4 selects electron energy emitted from the sample 3; and only specific energy E0 determined by the voltage obtained by superposing a voltage with voltage width delta and a frequency omega upon the potential difference between electrodes U1 and U2, i.e. constant voltage U applied from an electric power circuit 10 is passed and detected by a detector D1 and a lock-in amplifier 5 extracts a component of frequency omega. Further, the output N of a detector D1 is as shown by an equation, where N(U) is a function of the voltage U, and thus the component of frequency omega is extracted to obtain a signal proportional to dN/dU. Further, the output of a secondary electron detector D2 is passed through a variable gain amplifier 6 and differentiated by a differentiating circuit 7, and then subtracted from the output of an amplifier 5 by a subtracting circuit 8, thereby displaying the result on a CRT9.

Description

Detailed Description of the Invention A. Industrial Application Field The present invention scans a sample surface with an electron beam, detects Auger electrons emitted from the sample surface, and uses the detection signal to detect CR.
The present invention relates to an Auger electron analyzer that performs TCRT display screen modulation to display an image of the element distribution on the sample surface, the bonding state of atoms of sample constituent elements, etc.

2. Prior Art When the energy of electrons emitted from a sample surface is analyzed when the sample surface is irradiated with an electron beam, the relationship between the detected amount of emitted electrons and the energy is as shown in FIG. Most of these emitted electrons are secondary electrons emitted from the sample, and Auger electrons give a small peak p on top of the background of the secondary electrons. In this way, Auger electrons are very small in quantity compared to secondary electrons, so even if we simply analyze the energy of the electrons emitted from the sample and detect only the electrons with energy Eo in Figure 2, it will not work. It is not possible to know the amount of Auger electrons by Therefore, normally an energy analyzer performs an energy scan in a minute range Δ around energy E, differentiates the electron detection signal at that time, and uses the differentiated signal to scan the CRT.
The brightness of the display surface is modulated. In other words, the background of secondary electrons has a gentle slope in the range of energy Δ, so the value of its differential signal is close to O, whereas the peak of Auger electrons shows sharp rises and falls. Therefore, the differential signal takes a large value. In this way, the background due to secondary electrons can be removed and only Auger electrons can be detected. However, if secondary electrons and Auger electrons are discriminated by such a method, the following problem arises. Since the secondary electron emission efficiency of the sample surface is generally not uniform, when the sample surface is scanned with an electron beam, the secondary electron detection signal fluctuates over time. This fluctuation can be seen in the energy width Δ around the energy Eo in Figure 2.
It also appears in secondary electrons in the range of Since information on changes is also included, CRT noise becomes a noise in the Auger electron distribution image, interfering with the observation of the Auger electron image.

C. Problems to be Solved by the Invention The present invention aims to eliminate the above-mentioned influence of secondary electrons in conventional Auger electron analyzers.

2. Means to solve the problem An energy analyzer scans a small range of energy around a predetermined energy to detect transmitted electrons, differentiates the detection signal to detect Auger electrons, and separately By detecting the electrons that can be emitted from the surface, differentiating the detection signal, multiplying the differential signal by an appropriate coefficient, and subtracting it from the Auger electron detection signal, the secondary electrons contained in the Auger electron detection signal are calculated. It removes the influence.

E. Effect In Fig. 3, A indicates the Auger electron detection output. That is, A is a rectified and smoothed differential signal of an electron detection signal that has passed through an energy analyzer that performs energy scanning in a predetermined energy range. B in the figure is a detection signal obtained by separately detecting electrons emitted from the sample surface. Although this detection signal includes Auger electrons, it is mostly a detection signal of secondary electrons themselves. This is a result of differentiating the signal Cl-1'B in the figure, and corresponds to the S part in the signal A.

In other words, the S part of the A signal was not an Auger electron, but a signal at the boundary between regions where the radiation efficiency of secondary electrons differed on the sample surface. The third step is to multiply the signal of B by an appropriate coefficient and adjust the amplification degree of the signal of pB appropriately.
This is the result of subtraction from the signal of A, in which the S part of the signal of A is removed, and a signal of only Auger electrons is obtained.

Embodiment FIG. 1 shows an embodiment of the present invention. 1 is an electron gun, and 2 is an electron optical system that focuses an electron beam B onto the surface of the sample 3, and scans the sample surface with the electron beam in response to a signal from a scan control circuit (not shown). 4 is an energy analyzer that selects the energy of the electrons emitted from the surface of the sample 3 and sends them to the electrode U.
The specific energy EO determined by the potential difference between l and U2
The electrons that have passed through the energy analyzer 3 are detected by the detector D1. The output of the detector DI is input to the lock-in amplifier 5. The lock-in amplifier 5 extracts the frequency ω component from the input signal, and the voltage applied between the two electrodes of the energy analyzer 4 includes a constant voltage U and a voltage width 6 frequency ω superimposed on the voltage applied between the two electrodes of the energy analyzer 4. voltage is applied. At this time, detector D1
The component of frequency ω in the output of is proportional to dN/dE.

That is, the output N of the detector D1 is a function of the interelectrode voltage U of the energy analyzer 4, and if this is set as N(U), then N(U+δ
)-N(TJ)+, δ-a sinωt, the above equation becomes N(U+δ
) = N(U) 10-,,-a sln ω Therefore, if we extract the component of frequency ω from N(U+δ), we get aN/a
Since there is a linear relationship between the interelectrode voltage U and the energy E of the transmitted electrons, the output of the lock-in amplifier 5 corresponds to the signal shown in FIG. 3A. D2 is a secondary electron detector, the output of which is input to a variable gain amplifier 6, whose output corresponds to the signal shown in FIG. 3B. This signal is differentiated by the differentiating circuit 7 and then input to the subtracting circuit 8 , which subtracts the output of the differentiating circuit 7 from the output of the lock-in amplifier 5 .

This subtraction result corresponds to the third diagram, and this signal is appropriately amplified and applied to the CRT 9 as a luminance signal.

Effects According to the present invention, the influence of secondary electrons, which was not removed conventionally, is removed, and a clear Auger electron image without ghosts or noise can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an apparatus according to an embodiment of the present invention, FIG. 2 is a graph showing the energy distribution of electrons emitted from a sample, and FIG. 3 is a graph explaining the operation of the apparatus of the present invention. . 1... Electron gun, 2... Electron optical system, B... Electron beam, DI, D2... Electron detector. Agent Patent Attorney Kosuke 111'

Claims (1)

[Claims] An energy analyzer scans energy in a small range around a predetermined energy to detect transmitted electrons, and the detection signal is differentiated to detect Auger electrons, and electrons emitted from the sample surface are detected. The detection signal is differentiated and subtracted from the Auger electron detection signal to remove the influence of secondary electrons included in the Auger electron detection signal, and the output of the subtraction circuit is C
A scanning Auger electronic analyzer characterized by displaying information using RT.