SU1088089A1 - Method and device for producing secondary-emission image - Google Patents

Abstract

1. A method of obtaining a secondary emission image, including irradiating an object with a scanning beam, storing signals of secondary particles, deploying a beam of an electron beam tube of a video monitor device simultaneously with reading luminance modulation signals from the memory, characterized in that in order to increase the resolution of images in secondary particles , in the process of scanning, the beam is periodically stopped, and the irradiation is carried out by pulses in each of the beam stopping periods. 2. A method according to claim 1, characterized in that the storage of the signals of the secondary particles is carried out simultaneously with the reading from the memory. --- / 3. Method according to paragraphs. 1 and 2, which is based on the fact that the signals of secondary particles are memorized during the entire time of each beam stopping period. 4. Method according to paragraphs. 1-3, characterized in that the reading from the memory is made with an increased frequency in relation to the memorization frequency. 5. A device for obtaining a secondary emission image comprising a source of primary beam, a deflecting system, an object holder and an imaging circuit including serially connected (Listed analyzer and secondary particle receiver, image frame memory block with register, digital-to-analog converter , the output of which is connected to the modulating electrode of the cathode-ray tube, as well as the master oscillator, the control unit of the diverting system, the sweep generator of the electron-beam tube, 00 and the block The primary beam, characterized by the fact that it is equipped with an integrator, a frequency divider, a write control unit and a read control unit, in which the integrator is switched on by the receiver, particles and the frame memory block, the output of the master oscillator is connected to the input of the frequency divider and the first input of the control unit by coupling, the output of the frequency divider is connected to the block

Description

interrupt the primary beam, the control unit of the deflecting system, implemented in the form of a step voltage generator, the sweep generator of the electron-beam tube, with the inputs of the integrator and the recording control unit, the output of which is connected to the second input of the frame's memory control unit, block output

read control is connected to the second input of the frame memory block.

6. The device according to claim 5, in which it is provided with an adder, the inputs of which are connected to the output of the block of frame memory and the output of the integrator, and its output is connected to the third input of the block of frame memory.

The invention relates to a technique for producing a secondary emission image of the surface of solids and can be used in the analysis of microscopic objects. A known method for producing a secondary emission image, during which an object is scanned with an irradiating beam of primary particles, such as electrodes, simultaneously measures the current of secondary particles dislodged by the primary beam from the object (electrons, X-rays, etc.). Synchronously with the movement of the primary beam, a beam of a cathode ray tube (CRT) is swept, the brightness of which is modulated by a signal of detected secondary particles, as a result of which a secondary emission image of the object appears on the screen. The object is irradiated with the primary beam continuously for the entire time of scanning the primary beam necessary to form one frame of the image, after which the irradiation is interrupted. The image is recorded by photographing from a CRT screen l,. The disadvantage of the method lies in the need for photographic registration, which requires up-to-date photographic materials and includes a long process of their processing. The closest to. The technical essence is a method of obtaining a secondary emission image, including irradiating an object with a scanning beam, storing sigals of secondary particles, deploying a CRT beam of a video control device simultaneously with reading the 2J modulation signals from the memory, the device corresponding to the primary beam, a deflecting system (OS), an object holder and an imaging circuit including a series-connected analyzer and a secondary particle receiver, a block image frame memory with a register, a digital-to-analog converter (D / A converter), the output of which is connected to a CRT modulating electrode, and also a master oscillator, an OS control unit, a CRT scan generator and a primary beam interrupt block 2J. A disadvantage of the known method and device is that when registering an image in the secondary ions dislodged from the object by the primary beam, the resolution is low. One of the reasons for the low resolution is the considerable scatter of heavy secondary ions in time from the sample to the ion receiver, which is about. As a result, as the primary beam continuously moves across the object's surface, the correlation between the coordinates of the point from which the ion was knocked out and the point in time at which the ion was recorded is violated. Therefore, the image of each point of the object is blurred into an elongated spot with a characteristic size D D - rC- + DO, where N is the number of lines in the image} L is the length of the line on the object's surface; о - time variation of the secondary ion flight JT - total single scan time of the objectJ DO - beam diameter of the primary particles on the object's surface Another reason for the low resolution is the difficulty in accurately focusing the primary beam on the object's surface, due to the small D the intensity of the primary beam is small and, therefore, the current of the secondary ions is small. As a result, the single scan time has to be made very long, and the larger, the smaller the primary beam diameter. Since, in the known method, the image appears on the CRT screen only after the object is scanned once and disappears from the screen when a new scan starts, the long intervals between individual frames the images practically deprive the operator of the possibility of precise focusing of the primary beam, i.e. achieve high resolution. A disadvantage of the known method is also the difficulty of correctly choosing the current strength of the primary beam when registering an image in the secondary ions. This is due to the fact that, depending on the properties of the object, the emission coefficient of the secondary ions can vary within wide limits (approximately by three orders of magnitude). Therefore, in order to correctly select the current intensity of the primary beam, it is necessary to carry out several preliminary image recordings with different values of the primary beam current, which leads to an increase in the time for choosing the correct recording mode. In addition, during a long scan, the surface of an object can be destroyed by an intense primary beam already at the stage of selecting the image recording mode. The aim of the invention is to improve the resolution of the image in the secondary particles, as well as to reduce the time of image acquisition. This goal is achieved in that, according to the method of obtaining a secondary emission image, including irradiating an object with a scanning beam, storing signals of secondary particles, deploying a CRT beam of a video control device simultaneously with reading luminance modulation signals, the scanning process periodically stops the beam, and the irradiation is carried out by pulses in each of the periods of stopping the beam. The storage of the signals of the secondary particles is carried out simultaneously with the reading from the memory. The storage of the signals of the secondary particles takes place during the entire time of each period of the beam stopping. Reading from memory was made with. povipenoy frequency relative to the frequency of memorization. This goal is also achieved by the fact that a device for implementing a method of obtaining a secondary emission image, comprising a primary beam source, a deflecting system, an object holder and an imaging circuit including a serially connected analyzer and a secondary particle receiver, an image frame memory block with a register, The DAC, the output of which is connected to the modulating electrode of the CRT, as well as the master oscillator, the OS control unit, the CRT scan generator, and the pre-beam interrupt block, are equipped with The generator, the frequency divider, the write control unit and the read control unit, the integrator is connected between the secondary particle receiver and the frame memory, the output of the generator is connected to the input of the frequency divider and the first input of the read control unit, the output of the frequency divider is connected to the breaker unit primary beam, OS control unit, made in the form of a step voltage generator, a CRT sweep generator, with inputs of an integrator and a recording control unit, the output of which is connected to the second the input of the read control block and the first input of the frame memory block, the output of the read control block is connected to the second input of the frame memory block. The device is equipped with an adder, to the inputs of which the output of the frame's memory block and the integrator's output are connected, and its output is connected to the third input of the frame's memory block. FIG. 1 shows a block diagram of the device, FIG. 2 shows timing diagrams explaining the operations of the method. A device for obtaining a secondary emission image containing the source 1 of the primary beam, the deflecting plates 2 and 3 forming the deflecting system (OS), the object 4, the analyzer 5 of the secondary particles and the receiver 6 of the secondary particles, the block 7 interrupting the primary beam, the block OS control, including a generator of 8 and 9 step voltage, driving generator 10, frequency divider 11 and additional frequency divider 12 included in the OS control unit, integrator 13 (for example, digital counter) adder 14, frame memory block 15 , register 1 block 17 y the integrator, the read control block 18 from the frame memory 15, the write control block 19, the D / A converter 20, the output of which is connected to the modulating electrode of the CRT 21, and the EL sweep generator 22 The essence of the method and the operation of the device are as follows. In the initial state of the device, the contents of all the cells of the memory block 15 are zero. An example of obtaining a secondary emission image of an object area 4 with dimensions of 150 X 150 μm with a primary ion beam diameter of Dg 0.3 μm with a maximum achieved current density of the primary beam of 30 mA / cm is considered. With these parameters, the primary current of the beam is 1.4-10 ions / s. In this case, the maximum possible intensity of the current of the secondary ions knocked out from the object 4 and passed through the analyzer 5 to the receiver 6 is 1.4-10 ions / s, i.e. three orders of magnitude lower than the intensity of the primary beam. The image is recorded as follows. The master oscillator 10 generates a pulse train with a frequency of 50 MHz, shown in diagram 23 (FIG. 2). These pulses enter the frequency divider 11, which produces pulses (division factor 850) at a frequency of 58.8 kHz (diagram 24). The pulse duration (diagram 24) is 7 10 sec. Intervals between pulses. The scan generator 22 enters. The CRT, pulses (diagram 24) trigger the scan of the CRT 21. Figure 23 shows the time variation of the line voltage 3: spin of the tube. In addition, during the pulse produced by the frequency divider (diagram 24), the pulses (diagram 23) of the master oscillator 10 are sent to the read control block 18, which with the frequency of the oscillator pulses (chart 23) reads sequentially from the cells of the memory block 15. The read numbers through the register 16 are fed to the DAC 20, the output voltage of which modulates the brightness of the beam of the tube 21. During time, 500 numbers are read from block 15 corresponding to one line of the image. When the next pulse appears (diagram 24), block 18 causes the next 500 numbers to be read, corresponding to the next image line, and so on, until all 2.5 and 10 numbers corresponding to one full frame of the image are read in block 15. Simultaneously with the processes of reading information from memory 15 and imaging, the following processes occur, leading to writing information about object 4 to block 15. The pulses (diagram 24) from the output of frequency divider 11 go to block 7 of the primary beam interruption, which at the leading edge of the incoming pulse interrupts the primary beam of source 1, and again switches on the primary beam with a delay less than the trailing edge of this pulse. Diagram 26 shows the pulse shape of the current of the primary beam, having a duration of about 710 s and separated by intervals of more than 10 s. At the moment of irradiation pulse termination, an 8-step voltage generator, also triggered by a frequency divider pulse (diagram 24), changes the output voltage applied to the horizontal deflection of plate 2 (diagram 27) in steps. Thus, at the moment the irradiation beam acts on the object 4, the voltage on the plates 2 is constant, i.e. the beam is fixed and acts on one point of the surface of the object. The object is moved to the neighboring point in the gap between the irradiation pulses. The secondary ions, knocked out by a pulse of a fixed irradiating beam from this point of the object 4, pass through the analyzer 5 and are recorded by the receiver 6 in the form of individual pulses. Since the secondary ions have a significant scatter in the kinetic energy, the secondary ion pulses can appear not only during the action of the irradiation pulse (Figure 26), but also for some time after its termination, and this delay can be reached. Therefore, the integrator 13 counts (integrates) pulses from receiver 6 over a period of time that exceeds the duration of the irradiation pulse by approximately. The length of the integration time interval is determined by the interval between pulses (diagram 28) generated by the integrator control unit 17 with pulses entering it ( diagram 24) and the 13-to-zero integrator installing. Immediately before the pulse 28 arrives at the integrator 13, the latter contains the number of registered secondary ions, therefore, the pulses generated by the recording control block 19 (chart 29) preceding the pulses in chart 28 produce the following operations: with their leading edges. tom pulses on. diagram 29, the read control block 18 is activated and the previously recorded number from the cell with the number corresponding to the number of the irradiated point of object 4 is read from block 15 to register 16. In the adder 14, this number is summed with the number in the integrator 13, and the sum enters at the information input of block 15, at the time of the trailing edge of the pulse (chart 29), the sum is written into block 15 in the cell with the same number, i.e. All information about the same point of the object 4 always falls into the cell of block 15 with the same number. Since, in the initial state, all the cells of the memory block 15 contain zeros, the first scan simply memorizes the numbers from the integrator 13, but all subsequent repeated scans lead to the accumulation of information by summing it over the points. The process of recording points on the block 15 of memory is repeated at a frequency of 58.8 kHz for all 500 points of one line of the image. After the end of the scanning of the line, the additional divider 12 of the frequency absorbs the pulse, under the action of which the generator 9 of the step voltage changes the voltage on the plates 3, which leads to the next scan. a row of the surface of the object 4, until in block 15 all 2,510 cells are filled, which corresponds to the full frame of the image. After the scanning of one frame is completed, the next scan starts automatically with the accumulation of information in block 15. The accumulation of information can be stopped by the operator, who can continuously observe the image on the screen of the tube 21 directly during the sample scan, for example, by deflecting the primary beam from the sample or manually setting integrator 13 to zero. In this example, the total recording time of one frame of the image is about 2.5 Ux 1, i.e. about 4 st. In this case, at the maximum possible current of the primary beam with a diameter of 0.3 µm from each point of the surface, approximately one secondary ion is detected. Due to the fact that information is read directly in the process of scanning a sample at a much higher frequency than the frequency of writing, the image is displayed on the screen almost instantly with a delay of no more than 10 s. after that, get the information in memory block 15. The transition from scanning one frame to scanning the next frame is accompanied by the accumulation of information by increasing the image contrast, but without any interruption in the display of the image on the screen. The proposed method has several advantages over the known. By recording the image by points by periodically stopping the primary beam during the interruption of the irradiation, it is possible to completely eliminate the spreading of the image of the point organically inherent in the known method under similar recording conditions. those. N 500; L. 150 microns, TD and Dp 0.3 microns; T 4 s, the resolution of the known method is 0.5 µm, whereas the resolution proposed only depends on 0.3 µm. Due to the continuous output of information on the screen directly during the recording of the image, the time for selecting the recording mode is reduced to the limit. Since the image begins to appear on the screen simultaneously with the start of the object scan and does not disappear from the screen the rest of the time, but only increases its contrast, the operator has the opportunity immediately after the start of the scan to begin operations to select the mode without waiting for the frame scan. All changes made by the operator in the recording mode are immediately reflected in the continuously observed image on the screen. The selection of the primary beam current is extremely simplified, since the recording is kept at the maximum possible (for a given) current, but for a minimum time. If the emission coefficient of secondary ions is large, then the necessary image contrast will be obtained in the very first scan. If the coefficient is small, then on average less than 1 ion will be recorded per one point of the object during a single scan. Then, due to the accumulation of information during repeated scans, the necessary contrast will be obtained without changing the current of the primary beam by increasing the total recording time, which is determined visually by the operator. Due to the continuous visual control of the image in the proposed method and device, it becomes possible to stop the recording process at any time, i.e. prevent excessive destruction of the object by the irradiation beam.

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Claims (6)

1. A method of obtaining a secondary emission image, including irradiating the object with a scanning * beam, remembering the signals are secondary! particles, expanding the beam of the cathode ray tube of the video monitoring device simultaneously with reading the brightness modulation signals from the memory, characterized in that, in order to increase the resolution of the images in the secondary particles, the beam is periodically stopped during scanning, and irradiation is performed by pulses in each of the periods of beam stop . 2. The method according to claim 1, characterized in that the storage of signals of the secondary particles is carried out simultaneously with reading from memory. 3. The method according to PP. 1 and 2, which includes the fact that the memorization of the signals of the secondary particles is carried out during the entire time of each period of stopping the beam. 4. The method according to PP. 1-3, resulting in the fact that reading from the memory is performed with an increased frequency at _{0 with} respect to the memory frequency. 5. A device for obtaining a secondary emission image containing a source of a primary beam, a deflecting system, an object holder and an image forming circuit, p including a analyzer and a receiver of secondary particles connected in series, an image frame memory block with a register, a digital-to-analog converter, the output of which is connected with a modulating electrode of the cathode ray tube, as well as a master oscillator, a control unit for the deflecting system, a sweep generator of the cathode ray tube, and an interrupt unit primary beam, characterized in that, in order to increase the resolution in the secondary particles and reduce the time of image acquisition, it is equipped with an integrator, a frequency divider, a recording control unit and a read control unit, the integrator being connected between the secondary particle receiver and the frame memory unit, the output of the master oscillator is connected to the input of the frequency divider and the first input of the readout control unit, the output of the frequency divider is connected to the block of interruption of the primary beam, the control unit a biasing system made in the form of a step voltage generator, a cathode ray generator, with inputs of an integrator and a recording control unit, the output of which is connected to the second input of the read control unit and the first input of the frame memory unit, the output of the read control unit is connected to the second input of the memory unit frame. 6. The device according to claim 5, wherein the device is equipped with an adder, to the inputs of which the output of the frame memory unit and the output of the integrator are connected, and its output is connected to the third input of the frame memory unit.