JPH0265045A - Electron beam scanning type analyzing device - Google Patents

Abstract

PURPOSE:To eliminate the relative oscillation of a sample and an objective lens by adding the output signal of a relative displacement detecting means for detecting the relative displacement of a sample and electron optics systems to the signal for the deflection of an electron beam. CONSTITUTION:A relative oscillation detecting means 5 for detecting the relative oscillation is provided between electron optics systems 1, 2, 4 and a sample S, and the relative oscillation detecting signal detected by the relative oscillation detecting means 5 is added to the electron beam deflecting signal. Since the electron beam E is deflected by the quantity fitting for the oscillation of the sample S, adding to the original deflection for scanning, the relative displacement between the sample S and the electron optics systems 1, 2, 4 can be 0. Thereby, the influence caused by the relative oscillation between the sample S and the electron optics systems 1, 2, 4 can be electrically eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a relative vibration canceling mechanism for an EPM or a scanning electron microscope.

(Prior Art) Scanning microscopes such as EPMA allow viewing at a magnification of tens of thousands to hundreds of thousands of times. Therefore, even the slightest vibration is magnified to that magnification, which affects the displayed image9.
These vibrations are relative vibrations between the sample and the electron lens,
Sources of vibration include the motor of a cooling device that cools an electronic lens in the device, and vibrations coming from an external source such as the floor. Conventional countermeasures have been to hold the sample through an elastic body (rubber, spring air, etc.) so that the vibrations transmitted to the sample are absorbed by the elastic body, and to connect the sample to the electron optical system. For example, by pressing a rigid rod protruding from the sample against the electron lens yoke, the sample and the electron optical system are radically coupled to eliminate relative vibration between the two. However, in the former case, it is impossible to completely absorb and insulate vibrations, and in the latter case, there is no completely rigid body, and when moving the sample stage relative to the electron optical system, it is impossible to completely absorb and insulate vibrations. The sample stage must be lowered, making operation difficult.

(Problems to be Solved by the Invention) The present invention aims to provide a vibration isolation method based on a principle different from the above-mentioned mechanical structure method. The purpose is to electrically eliminate the effects of

(Means for Solving the Problem) In a scanning electron microscope, a relative displacement detection means for detecting relative displacement between a sample and an electron optical system is provided, and an output signal of the relative displacement detection means is used as an electron beam deflection signal. I added it.

(Function) The present invention eliminates the influence of vibration by causing the electron beam to follow the vibrational displacement of the specimen instead of suppressing the relative vibration of the electron optical system of the specimen.

In the scanning electron microscope, a relative vibration detection means for detecting relative vibration between the electron optical system and the sample is provided, and a relative vibration detection signal detected by the relative vibration detection means is converted into an electron beam deflection signal. When added, the electron beam is deflected by an amount corresponding to the vibration of the sample in addition to the original scanning deflection, so that the relative displacement between the sample and the electron optical system can be set to O.

As mentioned above, there are limits to vibration isolation using mechanical structural methods alone, but by stacking these methods with different principles, it is possible to increase the vibration isolation effect compared to a single method. .

(Example) FIG. 1 shows an example of the present invention.
D is a sample, and D is an electron gun that emits an electron beam E. 1 is a scanning coil that scans the electron beam E in the X and Y directions; 2 is an objective lens; 3 is a sample stage; 4 is a light source fixed to the objective lens 2 and irradiates the semiconductor device detection element 5 with a light beam. The semiconductor device detection element 5 is composed of four divided photodetection elements 5A to 5D as shown in FIG. 3, and is fixed to the sample stage 3. 50 is an arithmetic circuit that calculates the signal intensity [5A +5
C] and the signal strength [5B+5D], which is the sum of the detection outputs of photodetecting elements 5B and 5D. It is measured by the ratio (or difference) of [5C+5D]. 6 are adder circuits 6A, 6A' and scanning signal oscillators 6B, 6B.
This is a scanning coil control section that has capacitors 6C and 6C'' and variable resistors 6R and 6R, and controls the deflection of the electron beam on the X and Y axes. A signal as shown in FIG. 3B is generated so that the electron beam scans the measurement area S, and the DC component is cut off from the X-direction displacement signal from the arithmetic circuit 50 using a capacitor 6C, as shown in FIG. 3A. Take out a signal with only the relative vibration component, and adjust the signal strength with a variable resistor R so that the magnitude of the deflection of the electron beam is the same as the relative vibration,
The above-mentioned scanning signal generator 6B and variable resistor 6R are connected to the adder circuit 6A.
The two signals from the sample are added to form a superimposed signal of the above two signals as shown in Figure 3C, and this scanning signal controls the scanning coil 1 to deflect the electron beam in accordance with the vibration of the sample . 7 is a secondary electron detector that detects secondary electrons emitted from the sample S excited by the electron beam E; 8 is an amplifier that amplifies the output signal of the secondary electron detector 7; 9 is a signal from the amplifier 8; This is a CRT that displays

The adjustment operation of the variable resistors 6R and 6R' for eliminating the influence of relative vibration between the sample and the electron optical system will be described. Stop scanning with the electron beam, irradiate one point on the sample, and use the secondary electron detection signal at that time as the Y-axis signal of the CRT.
When the X-axis of T is swept in synchronization with the cycle of the motor drive, which is the vibration source of the device, a single waveform is drawn on the CRT. This is because the irradiation point of the electron beam moves due to the relative vibration of the sample, causing the secondary electron emissivity to fluctuate. X in this)
When only the vibrational displacement signal is taken out from the directional displacement detection signal through the capacitor 6C, the vibrational displacement signal is applied to the X-direction deflection coil through the variable resistor 6R, and the displacement signal strength is adjusted by the variable resistor 6R, the electron beam moves in the same manner as the vibrational displacement. When the X-direction displacement of the electron beam and the X-direction displacement of the sample completely match, the waveform on the CRT becomes minimum. If the minimum point is not found, it is considered that the direction of displacement of the sample and the direction of deflection of the electron beam are opposite, so the polarity of the displacement signal may be changed and applied to the deflection coil. After this adjustment, the amplitude of the waveform on the CRT can be set to O by making a similar adjustment in the Y-axis direction. Drive stage 3 to a predetermined position, and light II
The light beam from 4 is detected by a semiconductor device detection element 5.

As shown in Figure 2, the detection signal is a signal in which a DC component and an AC component representing relative vibration are added, so the DC component is cut off with a capacitor 6C or 6C'' and the AC component representing relative vibration is added. The intensity of the extracted signal is adjusted using a resistor 6R, etc., and then sent to a scanning signal generator 6B using an adding circuit 6A etc.
The displacement signal and the X- and Y-axis scanning signals are added together to form a scanning signal (Fig. 3C), which is sent to the scanning coil 1 to scan the electron beam E. control. By this scanning control, the electron beam E is displaced according to the relative displacement of the sample S, so the relative displacement between the objective lens 2 and the sample S is eliminated, and the secondary electron detector 7
However, various other methods can be considered for measuring the relative displacement between the objective lens 2 and the sample stage 3. FIG. 5 shows an embodiment using a position detection diode (PSD). In the figure, 5 is a PSD, which is a semiconductor pn junction element, and an electric current f! 5X is attached, electrodes 5Y are attached to both edges in the Y direction on the bottom surface, and a light beam K from a light source 4 attached to the objective lens 2 is irradiated perpendicularly to the pn junction surface on the top surface of the element. There is. The electrode 5X corresponds to the irradiation position of this light beam.

Since the voltage of the displacement detection signal in the X direction and the Y direction obtained from 5Y fluctuates, the relative displacement can be extracted as a voltage signal. By using this signal to control the electron beam in the same manner as in the first embodiment, the shake of the image projected on the CRT 9 is eliminated.

If high sensitivity is required, it is also possible to use the method shown in FIG. The principle of this method is shown in Figure 7.
When light is projected onto two precision plane-parallel plates 53 with high reflectance and low transmittance, the light incident between the plane-parallel plates 53 is reflected many times (almost an infinite number of times) between the plane-parallel plates 53. , only the light strengthened by interference is transmitted. That is, if the wavelength is λ and the distance between the parallel plane plates 53 is d, then only light with a wavelength that satisfies (1) is transmitted, and is transmitted many times. Because it is reflective,
The transmittance is extremely sensitive to changes in the spacing of the parallel plane plates. The method shown in FIG. 6 uses this principle, and uses semiconductor laser light of a specific wavelength as a light source, and connects one of the Y-direction parallel flat plates 53 and the X-direction parallel flat plate 54 to the light sources 41 in each direction. .42 is fixed to the objective lens of the electron optical system, and the other is fixed to the sample stage, the intensity of the transmitted light will vary depending on the variation of the distance d between both plane plates. Fluctuations in the transmitted light are measured by photodetecting elements 51 and 52 fixed to the sample stage. The measured detection signal shows the maximum intensity at d, which satisfies the equation (1), and the signal intensity decreases as the signal deviates from this point, resulting in a signal as shown in FIG. 8A. Here, if the stage position is set to the position shown by cio, the rate of change in light intensity with respect to a change in stage position becomes extremely large. Such a position exists when the stage is moved by a half wavelength of light, so the stage position as described above can be set within a range where the optical axis of the electron optical system is near the center of the III detection area of the sample. When the interval between the parallel plane plates is set near dO in FIG. 8A, the detection sensitivity of the displacement signal intensity to displacement is maximized, and when displacement is detected in this state, a detection signal as shown in FIG. 8B is obtained. This detection signal is input to the scanning coil control section 6 in FIG.
The variable resistors 6R and 6R' are adjusted using the same adjustment method as described above so that the fluctuation of the secondary electron detection signal becomes zero.

Furthermore, there is also a method of using a piezoelectric element to detect the relative displacement between the sample and the electron optical system.

(Effects of the Invention) Regarding vibration isolation and damping, when there is a limit to using a single principle alone, it is necessary to adopt another principle or to use both principles overlappingly. In such a case, the present invention is significant in that it provides a means based on a principle different from conventional mechanical structural means, and thereby,
Relative vibration between the sample and objective lens has been eliminated to a high degree, making it possible to further improve resolution.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a detection signal diagram obtained by a semiconductor device detection element, FIG. 3 is a signal diagram in the scanning coil control section, and FIG. 4 is a semiconductor device detection element 5. FIG. 5 is a diagram showing the configuration of the second embodiment of the position detection device, and FIG. 6 is a diagram showing the third embodiment of the position detection device.
FIG. 7 is a side sectional view of the parallel plane plate used in FIG. 6, and FIG. 8 is an explanatory diagram of the detection operation of the displacement signal obtained by the apparatus shown in FIG. 6. S...sample, E...electron beam, K...light, D...
・Electron gun 1...scanning coil, 2...objective lens, 3
. . . Sample stage, 4 . . Light source, 5 .・
...Scanning signal generator, 6R, 6R'...Variable resistor, 6
C, 6C'... Capacitor, 7... Secondary electron detector, 8... Amplifier, 9-... CRT.

Claims (1)

[Claims] An electron beam scanning type, characterized in that a relative displacement detection means for detecting a relative displacement between a sample and an electron optical system is provided, and an output signal of the relative displacement detection means is added to a polarization signal of an electron beam. Analysis equipment.