JPH0715809B2 - Coincidence electron microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] When an electron penetrates a sample, an electron microscope is provided with an X-ray detector for detecting X-rays emitted from the sample and a wave height detector for discriminating the energy level of the X-ray. At the position where the specific atom collides with a specific atom, emits characteristic X-rays, receives energy loss, and then enters the image plane, the specific atom emits X
The lines were identified by the timing detected by the X-ray detector and the wave height detector, and the distribution of any specific element present in the sample was converted into image information with a high S / N and made observable.

TECHNICAL FIELD The present invention relates to a coincidence electron microscope capable of observing a distribution state of an arbitrary element in a sample by imaging.

[Conventional technology]

As a method of analyzing the elements contained in the sample, there is a method of irradiating the sample with an electron beam and examining the energy loss of the electrons inelastically scattered by the atoms in the sample.

This method utilizes the fact that the energy of the inelastically scattered electron, which collides with an atom at a constant energy as shown in FIG. 6, undergoes energy loss of a value peculiar to the element of the atom. Is.

Furthermore, the same method can be used to make the distribution image of the specific element in the sample observable. Specifically, an apparatus in which an electron spectroscope (energy analyzer or energy filter) is inserted in the electron optical system of a scanning or ordinary electron microscope is used.

When a scanning electron microscope is used, scattered electrons may be detected at each scanning position of the electron beam, and the element may be identified from the energy level thereof. In this case, the electron beam should be narrowed down to irradiate the sample. Therefore, the damage of the sample becomes large. When using a normal transmission electron microscope,
Since it is necessary to generate a distribution image of the specific element on the image plane, there are many technically difficult problems. Conventionally known devices using a normal type electron microscope include the Casinging-Henry type and the Ω (omega) type depending on the structure of the electron spectrometer, but there are very few examples.

[Problems to be Solved by the Invention]

A conventional device capable of observing an element distribution image using an electron microscope and an electron spectroscope has a structure in which an electron spectroscope is inserted in the electron optical system of the electron microscope, so that the structure is complicated and the cost is considerably high. There was a problem.

Moreover, since an electron spectroscope is inserted in the electron optical system of the electron microscope, aberrations and distortions increase, and a high-resolution element distribution image cannot be obtained.

Furthermore, the loss energy spectrum of scattered electrons is
As shown in the figure, the image quality of the obtained element distribution image was unsatisfactory because the S / N was quite poor and the element discrimination was low.

INDUSTRIAL APPLICABILITY The present invention utilizes the basic structure of a conventional electron microscope as it is to reduce irradiation damage to a sample with a high-quality element distribution image at a low cost without degrading the high-resolution performance. The purpose is to provide a means of obtaining.

[Means for Solving the Problems]

The present invention identifies an element from the level of X-rays emitted from a certain atom in a sample by irradiation electrons, while identifying the position of the electron-emitting atom by a position detector on the image plane. However, the position of the specific element in the sample is known from the position of the atom identified by the position detector at the time of detecting the X-ray. That is, as shown in FIG. 6, in an electron microscope, the characteristic X-rays emitted when electrons are scattered by the atoms in the sample are detected, and the energy that reaches the image plane at the same time as this is detected. Detecting lost electrons by coincidence method, identifying their incident position, and utilizing the correlation between X-ray level and element type, identifying any element and creating its element distribution image Is.

FIG. 1 is a principle diagram of the present invention. In the figure, 1 is a non-scanning electron beam column of the electron microscope main body, in which electrons generated by an electron gun are accelerated by a high-voltage electric field and focused by an electron lens for focusing to cover the entire sample surface. An electron beam with a diameter to cover the sample is generated, the sample surface is irradiated, the X-rays emitted from the sample are detected by the X-ray detector, and the sample image due to the scattered electrons transmitted is magnified by the electron lens for image formation. , It has a structure to project on the image plane (fluorescent screen).

2 is a sample to be analyzed.

Reference numeral 3 denotes a high-speed incident position detector provided on the image plane, which is the X, Y of electrons emitted from the sample 2 and incident on the image plane.
Detect the position. In this case, the higher the detection speed, the higher the rate at which electrons that are randomly incident on the time axis can be detected. That is, the time resolution of detection is improved.

4 is the incident position of the electron detected by the incident position detector 3 X,
It is a coordinate data converter that converts Y coordinate data.

Reference numeral 5 is a shift register that delays coordinate data by a predetermined time.

Reference numeral 6 is a gate for extracting only necessary coordinate data.

An X-ray detector 7 detects X-rays emitted from the sample 2.

Reference numeral 8 denotes a wave height detector that identifies only the pulse wave height corresponding to the value of the element designated in advance among the X-ray pulses detected by the X-ray detector 7. 6 is opened, and at that time, coordinate data of only the electrons incident on the incident position detector 3 are taken out in synchronization with the X-ray pulse having the specific wave height.

Reference numeral 10 denotes an image data buffer corresponding to the screen, and display information indicating the presence of the element is sequentially accumulated at the address indicated by the coordinate data of the incident electron corresponding to the X-ray pulse of the specific element detected by the wave height detector 8. .

Reference numeral 11 is a display control unit that performs image display control of the element distribution image based on the display information accumulated in the image data buffer 10.

12 is a CRT on which an element distribution image is displayed.

[Action]

The operation based on the configuration of the present invention shown in FIG. 1 will be described below. 2. FIG. 2 is a time chart showing the explanation of the operation of the present invention.

In Fig. 1, when a sample 2 in an electron beam column 1 is irradiated with an electron beam, the electrons collide with some atom in the sample with a certain probability, causing an energy loss in the electrons and causing inelastic scattering. X-rays are emitted.

Among the scattered electrons, those that are directed toward the image plane pass through the trajectory determined by the electron lens for image formation, and reach the position corresponding to the sample on the image plane, as in the case of the conventional transmission electron microscope. The incident position is detected by the incident position detector 3, and the incident position is detected. The position is converted into coordinate data by the coordinate data converter 4 and further input to the shift register 5 to be delayed by a predetermined amount.

On the other hand, the simultaneously emitted X-rays are detected by the X-ray detector 7, and the wave height of the output X-ray pulse is identified by the wave height detector 8. Only when the X-ray pulse has a predetermined wave height. The specific wave height pulse whose wave height has been selected is output to the gate 6.

FIG. 2 shows an example of an X-ray pulse, in which the wave height changes according to the types of elements α, β, γ. FIG. 2 shows an example of pulse height-selected specific pulse heights, when the element β is designated.

At this time, the coordinate data shifted out of the shift register 5 indicates the incident position of the electron corresponding to the X-ray detected by the wave height detector 8.

In this way, in the gate 6, the coordinate data as shown in FIG. 2 is extracted, and when the atom of the designated element exists in the sample, the image data buffer 10 is sequentially read by the coordinate data of the position. It is accessed and image data of element distribution image is created. As described above, the collision of atoms in the sample with the electrons of the electron beam occurs stochastically, so the element distribution image shown in the image data formed in the image data buffer 10 is initially vague. Yes, it will show a clear shape over time. Therefore, when the number of atoms of the designated element is small or when the time resolution of the detection by the incident position detector is low, it takes a longer time to obtain sufficient image data.

〔Example〕

 FIG. 3 shows the configuration of one embodiment of the present invention.

In the figure, 1 is a non-scanning electron beam column, 2 is a sample, and 3
Is an incident position detector, 4 is a coordinate data converter, 5 is a shift register, 6 is a gate, 7 is an X-ray detector, 8 is a wave height detector, 9 is a gate pulse generator, 10 is an image data buffer, and 13 is an image data buffer. An element distribution image in the sample (phage (gene)), 14 is a transmission image of the sample fluorescently displayed on the image plane. Elements common to those in FIG. 1 are designated by the same reference numerals, and the description made with respect to FIG. 1 also applies to FIG.

The incident position detector 3 is a detector for particles such as two-dimensional electrons or photons, and various conventionally known ones such as a photo-resistive surface type detector, an interline type CCD camera or a counterhodoscope are used. it can.

FIG. 4 shows the structure of a photo resistance surface type detector which is an example of the incident position detector. Photoresistors (photoconductive materials) such as CdS and CdSe
The layer 15 is provided on the metal plate 16, and the resistor film 17 is further provided on the photo-resistor layer 15, and X is formed at each end of the resistor film 17.
Attach electrodes XA, XB and Y electrodes YA, YB (YA, YB in the figure)
Is omitted). An appropriate voltage is applied to the resistor film 17 of the metal plate 16 via a resistor.

The incident position detector 3 is attached in contact with the phosphor layer on the image plane of the electron beam column 1, and when an electron is incident on any of the phosphor layers to cause light emission, a photoresistor layer in contact with the phosphor layer. The resistance value of the portion 15 decreases, and the pulse propagates on the resistor film 17 toward the X and Y electrodes XA, XB, YA, and YB while being attenuated. Therefore, the amplitude of the pulse reaching the electrode increases when light emission occurs at a position closer to the electrode, and the amplitude of the pulse reaching the electrode decreases as light emission occurs at a position farther than the electrode. Therefore, for the X coordinate, take the pair of electrodes XA and XB, and for the Y coordinate take the pair of electrodes YA and YB.
By taking the ratio of the amplitudes of the pulses reaching the electrodes of each pair respectively for X and Y, the light emitting position, that is, the electron incident position can be obtained.

In this way, the electrons emitted randomly from the sample 2 in the electron beam column 1 temporally and spatially and incident on the phosphor layer on the image plane are sequentially detected by the incident position detector 3. To be detected. The detected incident position of each electron is converted into, for example, X-coordinate data and Y-coordinate data of 1-byte length by the coordinate data converter 4 of FIG.

The shift register 5 gives a delay corresponding to the product of the clock cycle and the number of stages of the shift register 5 to each coordinate data of X and Y. This delay amount is provided to compensate for the timing difference between the gate pulse and the coordinate data based on the pulse height-selected specific pulse pulse. If the timing of the gate pulse is earlier than the coordinate data, Instead of providing the shift register 5, it is necessary to provide an appropriate delay circuit before the gate pulse generator 9.

The pulse height selected specific pulse pulse output from the pulse detector 8 is converted into a gate pulse having an appropriate pulse width by the gate pulse generator 9 and applied to the gate 6.

The image data buffer 10 has a memory capacity corresponding to, for example, if the number of dots on the CRT screen is 1024 × 1024. However, since each dot has brightness information, 1-byte data can be set. Therefore, the memory capacity is 1024 x 1024 x 1 byte (1 Mbyte).

The X and Y coordinate data output from the gate 6 becomes the address of the image data buffer 10 as it is, and the luminance information is written at the address. The brightness information of each address is first cleared to 0, and then +1 is updated every time the address is accessed. That is, the brightness information of each address is represented by the number of times of access to that address. As described above, an atom of a specified element distributed in the sample is irradiated with the electron beam and collides with the electron with a certain probability to cause inelastic scattering of the electron and emission of X-ray. Here, the scattered electrons are incident position detector 3
An address indicating the position of the colliding atom on the sample surface is generated and input to the gate 6. On the other hand, the emitted X-rays are detected by the X-ray detector 7 and further identified by the wave height detector 8 as the designated element. Therefore, the address input to the gate 6 at that time is the image data buffer. Sent to 10 for access.

Therefore, as each atom of the designated element distributed in the sample stochastically collides with the electron in the electron beam, the address in the image data buffer 10 corresponding to the position of the colliding atom is accessed, Since the brightness information stored at that address is updated by 1, the brightness information indicating the concentration distribution of the atoms of the designated element in the sample is obtained at each address of the image data buffer 10 after an appropriate time has elapsed. Therefore, the CRT can display an element distribution image whose brightness changes according to the element concentration.

Furthermore, the data length of each address of the image data buffer 10 is set to multiple bytes, the brightness information and color attribute information of multiple types of elements can be stored, and multiple element distributions can be displayed in multiple colors with different colors for each element. Is.

FIG. 5 shows a display example of such an element distribution image. As shown in the figure, Fe-image, Hg-image, and C-image can be observed individually or in an arbitrary multiplex.

〔The invention's effect〕

According to the present invention, only the energy loss electrons that coincide with the X-ray detection time are extracted and used as a signal, so that the S / N is significantly improved and an element distribution image with good image quality can be obtained.

In addition, since the S / N is good, it is effective for observation using extremely weak electron beam intensity such as high resolution electron microscope. Similarly, a sufficiently good image can be obtained even with weak electron beam intensity. It is possible to reduce the degree to which the electron beam is damaged by the electron beam.

Also, because it does not require an electron spectrometer like the conventional method,
There is an advantage that a normal high resolution electron microscope can be used as it is, which is also advantageous in terms of cost.

[Brief description of drawings]

1 is a principle diagram of the present invention, FIG. 2 is a time chart showing the operation of the present invention, FIG. 3 is a configuration diagram of one embodiment of the present invention,
FIG. 4 is an explanatory view showing an example of an incident position detector, FIG. 5 is an explanatory view showing a display example of element distribution, FIG. 6 is an explanatory view of inelastic scattering of electrons, and FIG. 7 is a loss of scattered electrons. It is explanatory drawing of an energy spectrum. In Fig. 1: 1: Electron beam column 2: Sample 3: Incident position detector 4: Coordinate data converter 5: Shift register 6: Gate 7: X-ray detector 8: Wave height detector 10: Image data buffer 11: Display Controller 12: CRT

Claims (1)

[Claims] 1. A non-scanning electron beam column for enlarging and projecting an image of energy-loss electrons transmitted through the sample by irradiating the sample with an electron beam, and electrons on the image plane of the electron beam column. The incident position detector that detects the incident position at high speed, the X-ray detector that detects the X-rays emitted from the sample in the electron beam column, and the X-ray pulse output from the X-ray detector are specified. The pulse height detector that discriminates the X-ray pulse of the pulse height corresponding to a specific element, and the incident position data output from the incident position detector are gate-selected by the pulse height selected specific pulse height pulse output from the pulse height detector. It is equipped with a gate circuit and an image data buffer that stores gate-selected incident position data. It is possible to take out and observe only the image data of the specified element in the sample. Coincidence type electron microscope to be.