JP2852054B2 - Spin-polarized scanning electron microscope - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a spin-polarized scanning electron microscope suitable for a case where the number of electrons emitted from a sample changes largely within an observation region.

[Conventional technology]

Conventionally, as described in JP-A-54-48478,
2. Description of the Related Art A spin-polarized scanning electron microscope that discriminates a signal intensity immediately before being introduced into a display device and changes a scanning speed of the display device according to an output signal thereof is known. However, since the signal intensity immediately before the display device is not related to the noise of the image, the noise cannot be controlled by the conventional method as described above. In addition, the conventional method did not give enough consideration to quantitative control.

[Problems to be Solved by the Invention] The present invention can quantitatively control the noise of an image signal for each pixel even in the case of a spin-polarized scanning electron microscope where the intensity of the image signal is irrelevant to the image quality, and can reduce the The purpose of the present invention is to provide a device capable of obtaining an image signal.

[Means for solving the problem]

In order to achieve the above object, according to the present invention, an image signal is formed from a spin detection unit including an electron beam irradiation unit, an electron beam deflection unit, and a plurality of electron detectors, and a plurality of signals output from the detection unit. An electron detector disposed in a spin detector in a spin-polarized scanning electron microscope including a means for calculating a spin polarization degree and a display means for visualizing the image signal in synchronization with the electron beam deflection means. And a control means for outputting a control command to the electron beam deflecting means in accordance with an output signal from the electron detector and a preset value.

Alternatively, the above object can be achieved by providing a means for varying the electron beam intensity according to the output signal from the electron detector and a preset value.

[Action]

The noise (statistical error) of the image signal can be theoretically calculated from the fluctuation of the number of electrons incident on two electron detectors arranged in the spin detector. Now, assuming that the numbers of electrons incident on the electron detector are N1 and N2, the statistical error Δp is given by the following equation.

(S is a device-specific definition) If Δp is set in advance for each pixel, 2
The sum of the number of electrons to be incident on one electron detector is determined by equation (2).

The ^{N1 + N2 = 1 / S 2} / Δp 2 ... (2) electron beam irradiation on one point on the sample. When the number of electrons incident on the electron detector by the control means becomes larger than the equation (2), a command to move the electron beam by one pixel to the electron beam deflecting means is output to the beam deflector, and the spin polarization Is calculated and output to the display means. By performing the same processing for each pixel, the beam irradiation time per pixel is variable, and an image can be obtained in real time with a statistical error specified for each pixel.

One point of the sample is irradiated with an electron beam. The sum of the number of electrons incident on the two electron detectors at a preset time is compared with the set value determined by the equation (2). If the sum is smaller than the set value, the beam intensity is calculated according to a predetermined arithmetic expression. Means to increase the beam intensity. The above series of processing is repeated until the sum of the number of electrons becomes equal to or greater than the set value. However, the number of electrons incident on the electric detector is integrated during the above processing. If the value exceeds the set value, a command to move the beam position on the sample by one pixel is output to the beam deflector. Further calculate the spin polarization,
It is output to the display means. By repeating the above processing, an image can be obtained in real time with a statistical error designated for each pixel.

〔Example〕

Hereinafter, the present invention will be described with reference to FIG. This scanning electron microscope uses the spin polarization of secondary electrons to image magnetization information of a sample.

The primary electron beam 2 emitted from the electron gun 1 enters the sample 5 via the deflector 3. At that time, the secondary electrons 6 emitted from the sample 5 are guided into the spin detector 7. The spin polarization is detected as the asymmetry of the number of scattered electrons incident on two electron detectors in the spin detector. At this time, the number of electrons incident on each electron detector is converted into an electric pulse. Is output from the spin detector.

The signal processing device 10 is roughly divided into a processing unit A, a processing unit B, an image / display memory, and an absorption current image / display memory. First, the processing unit A issues an initial setting (counter clear) instruction for the counters 8 and 9. Then, a count start instruction is output. The counters 8 and 9 count each pulse train output from the spin detector for Δt time, and output the count values N1 and N2 to the signal processing device 10. After that, each counter also returns Δ
The t time count is started and integrated with the previous count value. The counters 8 and 9 repeat this integration / output operation until a count stop instruction is issued from the processing section A in the signal processing device 10.

The processing unit A compares the sum of N1 and N2 with the set value obtained from the equation (2) by using a high-speed arithmetic unit inside itself. If the sum is equal to or larger than the set value, the output of the counters 8 and 9 is waited. Where N1, N2
Is performed within Δt time. After the counter outputs the count values N1 and N2, the processing unit A takes in N1 and N2 again and compares them with the established values. The processing unit A repeats the above processing from the capture of the count value to the comparison, and when the sum reaches the set value or more, transfers the count values N1 and N2 to the processing unit B, and from the processing unit A to the scanning circuit 4. An instruction to deflect the primary electron beam 2 by one pixel on the sample is output. The scanning circuit 4 receives the command and operates the deflector 3. At the same time, the processing unit A initializes the counters 8 and 9 (clears the counters) and starts counting the time Δt. The processing unit A repeats the above processing.

Next, the processing unit B calculates the spin polarization degree p = (N1−N2) / (N1 + N2) / S from the transferred N1 and N2 using the internal high-speed arithmetic unit, and stores it in the image memory and the display memory. I do. The storage location at this time corresponds to the primary electron beam irradiation position on the sample. The calculation from the calculation of the spin polarization to the storage in the memory is performed within the time Δt.
The processing unit B repeats the above processing.

The sample absorption current amplified by the amplifier 12 is
Is converted into a digital signal and input to the processing section B.
Then, it is stored in the image / display memory for the absorption current for each pixel in the same manner as the spin polarization.

The TV 11 visualizes the data in the display memory by luminance modulation, and displays a magnetic domain image (spin polarization image) and an absorption current image in one screen. At this time, the contents of the display memory are always read out and displayed on the TV 11.

As a result, a magnetic domain image in which a statistical error is specified for each pixel can be obtained in real time. In addition, since the TV 11 is used, for example, even if it takes a long time to display one pixel, the already displayed pixel does not disappear. Since the data is stored in the memory as numerical values, various types of image processing can be performed on the obtained images.

The reason why the image memory and the display memory are provided here is that the image memory is used as a data storage memory and the display memory is used as a dedicated memory of the TV 11. The bit length of data per pixel in the image memory is determined by the accuracy of the spin polarization, and the bit length of data per pixel in the display memory is determined by the gradation display capability of one pixel of the TV 11. They generally differ in bit length.

Although the present embodiment displays only one direction component of the spin polarization vector, the present invention can be extended to display independent two-direction or three-direction components. In the case of the three-direction component display, the spin detector can detect three components,
Another two sets of counter and image / display memory are prepared. Then, the same processing as described above may be performed on each component.

In this case, an image of a component in an arbitrary direction of the spin polarization vector can be reconstructed from the data stored in the memory after the observation.

In the above embodiment, the primary electron beam irradiation time is controlled for each pixel, but the primary electron beam irradiation time and the primary electron beam intensity can be varied by adding a control circuit 14 as shown in FIG. And the statistical error can be controlled. In the case of a field emission type electron gun, the primary electron beam intensity can be controlled by controlling the voltage V between the chip and the anode, which is the electron beam irradiated portion in the electron gun 1. The relationship between the sum N of the number of electrons detected by each detector during the Δt time and the voltage V must be checked in advance with the spin detector. It is assumed that the relationship is as shown in the following equation.

V = f (N) (3) First, the processing unit A outputs the voltage Vo from the control circuit 14 so as to obtain an appropriate primary electron beam irradiation intensity, and fixes the primary electron beam at an appropriate irradiation position. I do. Next, after the counters 8 and 9 are initialized, counting is started. Each counter outputs a count value at time intervals of Δt while continuing integration until it is initialized. From the first output from the counter, the processing unit A calculates the total N of the respective counts necessary to make the statistical error of the spin polarization degree equal to or greater than the set value.
It is obtained by the following equation using 1, N2.

N = N1 '+ N2'-(N1 + N2) (4) Here, N1 '+ N2' is the sum of the number of electrons obtained from the equation (2) when ΔP is a set value of the statistical error. If N is positive, equation (3) is corrected as follows.

V = f (N) + Vo-f (N1 + N2) (5) Using N of the expression (4), V is calculated from the expression (5), and the voltage V is output from the control circuit 14. Further, from the second counter output to the output of the voltage V from the calculation of N in the same manner as above. Thereafter, the same processing is repeated until N becomes smaller than O. When N becomes smaller than O, the processing unit A causes the control circuit 14 to output the voltage Vo. After outputting to the scanning circuit 4 a command to deflect the primary electron beam 2 by one pixel on the sample, the counter is initialized and counting is started. Next, N1 and N2 are transferred to the processing unit B. The processing unit A repeats the above processing. Otherwise, the same processing as in the first embodiment is performed.

〔effect〕

According to the present invention, since noise of an image can be set in advance for each pixel, an image having an image quality desired by a user can be obtained in the shortest time.

[Brief description of the drawings]

1 and 2 are block diagrams of the basic configuration of a spin-polarized scanning electron microscope according to an embodiment of the present invention. 1 ... electron gun, 2 ... primary electron beam, 3 ... deflector, 4 ...
... Scanning circuit, 5 ... Sample, 6 ... Secondary electron, 7 ... Spin detector, 8 ... Counter I, 9 ... Counter II, 10 ...
... Signal processing device, 11 ... TV, 12 ... Amplifier, 13 ... AD converter, 14 ... Control circuit.

Continuation of the front page (56) References JP-A-60-177539 (JP, A) JP-A-62-255616 (JP, A) JP-A-54-48478 (JP, A) JP-A-57-143251 (JP) , A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H01J 37/28 H01J 37/22 H01J 37/147 H01J 37/04

Claims (2)

(57) [Claims] An electron beam irradiating means for generating an electron beam; an electron beam deflecting means for deflecting the electron beam;
A spin detecting unit including a plurality of electron detectors for detecting secondary electrons, a unit for calculating a spin polarization degree serving as an image signal from a plurality of signals output from the spin detecting unit, and the electron beam deflecting unit; A display device for synchronously visualizing the image signal, wherein the electron beam is applied to a predetermined position on the sample, and the sample is incident on the plurality of electron detectors. An electron beam control means for outputting a command to move the electron beam to another predetermined position on the sample to the electron beam deflecting means when the intensity of the secondary electrons reaches a predetermined value. A spin-polarized scanning electron microscope, wherein a statistical error of an image signal with respect to the predetermined position on the sample is set to a predetermined value. 2. An electron beam irradiating means for generating an electron beam; an electron beam deflecting means for deflecting the electron beam;
A spin detecting unit including a plurality of electron detectors for detecting secondary electrons, a unit for calculating a spin polarization degree serving as an image signal from a plurality of signals output from the spin detecting unit, and the electron beam deflecting unit; A display device for synchronously visualizing the image signal, wherein the electron beam is applied to a predetermined position on the sample, and the sample is incident on the plurality of electron detectors. Controlling the intensity of the electron beam so that the intensity of the secondary electrons becomes a predetermined value;
When the intensity of secondary electrons from the sample incident on the plurality of electron detectors reaches a predetermined value, a command to move the electron beam to another predetermined position on the sample is output to the electron beam deflecting means. A spin-polarized scanning electron microscope, comprising electron beam control means, wherein a statistical error of an image signal with respect to the predetermined position on a sample irradiated with an electron beam is set to a predetermined value.