JPH0321002Y2 - - Google Patents

Description

[Detailed description of the invention] A. Field of industrial application It is common practice to detect secondary electrons emitted from a sample surface using an X-ray microanalyzer to form an enlarged image of the sample surface. Secondary electrons mainly provide information about the shape of the sample surface. There is a need for a method of obtaining a high magnification of the distribution of the chemical composition of a sample using an X-ray microanalyzer, and the present invention corresponds to such a method.

B. Prior Art When a sample is irradiated with an accelerated electron beam, secondary electrons and reflected electrons are emitted from the sample. The difference between secondary electrons and backscattered electrons is the difference in kinetic energy; secondary electrons have low energy, and backscattered electrons are high-energy components of the electrons emitted from the sample. The electrons incident on the sample are scattered by atoms constituting the sample inside the sample (although this is an extremely shallow region), and a portion of the electrons escapes from the sample surface. In this case, atoms with larger atomic numbers scatter electrons better and the energy loss at that time is smaller, so the amount of reflected electrons increases. Therefore, the amount of backscattered electrons contains information about the elemental distribution near the sample surface, and an image of the elemental distribution can be obtained. For the purpose of elemental analysis, a method of spectroscopy of X-rays emitted from a sample is also used, but the measurement takes time, so the backscattered electron method is attractive because it can obtain images of elemental distribution in a relatively short time. It's a method. However, backscattered electrons have directionality, and the direction in which backscattered electrons are strongly detected differs depending on the inclination of the sample surface at the sample irradiation point of the electron beam and the electron beam. It is necessary to arrange multiple backscattered electron detection means using photomultiplier tubes and semiconductor elements with current amplification functions around the sample, and to perform calculations such as averaging the output of each detector, making the equipment complex and expensive. becomes.

Considering the balance of charges when a sample is irradiated with an electron beam, the current obtained by subtracting the current due to secondary electrons and reflected electrons from the incident electron beam current flows from the sample to the ground (the device body) as the sample current. become. Quantitatively, there are more reflected electrons than secondary electrons, and in particular, secondary electrons are almost constant regardless of atomic number (see Figure 3), so if the incident electron beam current is constant, reflected electrons and In a reciprocal relationship with the sample current, the sample current also includes information on the elemental composition of the sample. Therefore, it is possible to form an image of the elemental composition of the sample using the sample current, and in this case, there is no need to use multiple backscattered electron detection means, and there is an advantage that the device configuration is simple and inexpensive. However, as a practical matter, a detector with a current amplification effect cannot be used as in the case of backscattered electrons, and the signal level is low because the current signal is directly handled.
For this reason, when attempting to obtain a high magnification image, the response speed was low and the S/N ratio was reduced, making it impossible to obtain a high magnification image.

C. Problems to be Solved by the Invention The present invention attempts to obtain a high-magnification image of the composition distribution of a sample relatively quickly with an inexpensive device configuration.

D. Means for solving the problems In view of the above-mentioned background situation, the present invention aims to enable an inexpensive device structure by using the sample current as an information source, and to reduce the influence of external noise due to low signal levels. By improving the S/N ratio and reducing the input capacitance of the sample current amplifier, the response speed is low due to the low signal level and is affected by the capacitance of each part of the circuit. A sample current amplifier is built into the sample holder, eliminating the increase in input capacitance of the amplifier due to the extension of the signal line, increasing response speed, and lowering the impedance of the output line to the same level as the ground line, allowing a differential amplifier to be used in the next stage. The S/N ratio is improved by canceling out external noise.

E. Embodiment FIG. 1 shows an embodiment of the present invention. 1 is the sample, and 2 is the main body of the sample holder. The sample 1 is adapted to be housed in a container 3 of insulating material which is fitted and secured to the sample holder 2. This container 3
A conductive film is formed on the inner surface. A substrate 4 of a sample current amplifier for converting a sample current into a voltage signal is fixedly mounted on the bottom surface of the sample holder main body 2 via an insulating spacer 6. 7 is a screw for fixing the container 3 to the sample holder 2, and the screw 5 passing through the bottom of the container 3 presses the substrate 4 of the sample current amplifier against the spacer 6 to fix the same substrate, The conductive film on the inner surface of the container 3 and the input terminal of the sample current amplifier are electrically connected. 8 is a screw for fixing the sample 1 to the container 3. S is the power supply line of the sample current amplifier, P is the signal output line of the same amplifier, and E is also the ground line.

FIG. 2 shows an example of a sample current amplifier. A is a high gain amplifier using a commercially available FET input operational amplifier, and the non-inverting terminal is the ground connected to the sample holder body. The sample current is input to the inverting terminal of amplifier A. The sample current flows through the negative feedback resistor Rf of amplifier A, and the voltage drop due to the sample current at Rf becomes a signal output. A value of about 1 MΩ is used as the resistance Rf, and the sample current of 1 pA is converted to 1 μV, and the sample current changes between 0 and 400 pA at an acceleration voltage of the irradiated electron beam of 30 KV and an irradiated electron beam current of about 400 pA, with an average of 200 pA. Therefore, the average output voltage of amplifier A is about 0.2 mV, and subsequent signal amplification is easy. Output signal line P and ground line E are connected to the two input terminals of the next-stage differential amplifier, but amplifier A is a constant-voltage power supply when viewed from the next-stage amplifier, and output signal line P is of the same level as the ground line. The impedance is low, and noise that enters both lines in the same mode is canceled out by this second stage differential amplifier.

F. Effect When using the sample holder of the present invention, since the sample current amplifier for impedance conversion is built into the sample holder, there is no lead wire to lead the sample current to the amplifier, and there is no static electricity between the sample and the amplifier. The capacitance is extremely small, so even though the signal level is low, the response speed does not decrease, making it easy to obtain high magnification. This is because the input capacitance of the amplifier becomes smaller, and the response speed of the amplifier decreases due to the negative feedback resistance.
This is because it is limited only by the stray capacitance of Rf.

Additionally, since an amplifier for impedance conversion is built into the sample holder and outputs the sample current signal to the video signal amplification circuit, external common-mode noise components that mix between the low-impedance signal line and the ground line are eliminated from the By using a differential amplifier as the signal amplification circuit, it is canceled out, and the video signal has a low S/N despite the low signal level of the original sample current.
It can be amplified relatively well.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal side view of a sample holder according to an embodiment of the present invention, Fig. 2 is a circuit diagram of a sample current amplifier in the same embodiment, and Fig. 3 shows the interrelationships among reflected electrons, secondary electrons, and sample current. This is a graph showing.

Claims (1)

[Scope of utility model registration request] A sample container having a conductive surface that insulates the sample and the holder body and conducts the sample current on the surface in contact with the sample is fixed to the sample holder body, a sample current amplifier is attached to the sample holder body, and a signal input to the amplifier is performed. A sample holder for an electron beam analysis device in which a terminal and a conductive surface of the sample container are connected.