Deflection detection system, deflection detection method, and scanning electron microscope

Abstract

The invention belongs to the field of scanning electron detection imaging, and relates to a deflection detection system, a deflection detection method and a scanning electron microscop.A Wien filter is arranged in an electron lens cone and adopts alternating signal excitation to generate a deflection electric field and a deflection magnetic field which are perpendicular to each other; electric field force and magnetic field force which are opposite to each other are generated on a descending main electron beam, and electric field force and magnetic field force which are in the same direction are generated on an ascending secondary electron to form off-axis resultant force; the alternating excitation signal of the Wien filter is configured to be synchronous with the raster scanning signal of the deflector, and the frequency and the phase maintain a specific relationship, so that the excitation signal is enhanced when the main electron beam scans towards the line / frame center, and the excitation signal is weakened when the main electron beam scans towards the line / frame edge. The problem that signal electrons near the optical axis miss the detector is solved, the requirement for the coverage of the detector is lowered, the contradiction between the sampling frequency and the view field is solved, the image signal-to-noise ratio is improved, and the imaging rate or the detection rate is increased.

Description

Technical Field

[0001] The invention belongs to the field of scanning electron detection imaging, and in particular relates to a deflection detection system, a deflection detection method and a scanning electron microscope. Background Art

[0002] Electron beam imaging equipment used for detection or measurement in industry or laboratories, such as critical dimension measurement microscopes (CDSEMs) and electron beam defect detection equipment, usually need to work in a low energy state to reduce sample damage or charge accumulation; at the same time, resolution must be taken into account, and the working distance must be reduced. To achieve this goal, a rejection field lens design is often used. The problem with this design is that most of the secondary electrons representing the morphology and / or backscattered electrons reflecting the material properties (hereinafter collectively referred to as signal electrons) generated by scanning the sample are accelerated into the lens barrel, and a detector needs to be designed in the lens barrel to collect as many signal electrons entering the lens barrel as possible, which is called the in-lens detector solution. This is different from a traditional electron microscope, in which the detector can be set between the objective lens and the sample, or at the position of the optical axis.

[0003] The detector in the lens tube is usually a ring detector, whose central hole is coaxial with the optical axis to facilitate the passage of the main electron beam, but the central hole will inevitably miss some signal electrons. Figure 1 As shown, the main electron beam 1001 emitted from the electron source 101 is focused on the surface of the sample 1010 through the condenser 102 and the rejection field objective lens 108. When the main electron beam 1001 passes through the deflector 106, a raster scanning signal 200 is applied, wherein the line scanning signal 201 and the frame scanning signal 202 are used to scan the ABCD area on the sample surface (O is the center), please refer to Figure 2 , the corresponding position will excite secondary electrons 1002 and be reversely accelerated and converged, falling on the surface of the annular detector 107, the corresponding position is A'B'C'D', O' is the center of the A'B'C'D' area. Usually, signal electrons that pass through the center hole of the detector cannot be detected. Figure 1 Figure 1 shows the trajectory envelopes 1002O and 1002C of secondary electrons excited at the center position 1010O and the corner position 1010C of the sample scanning area reaching the detector surface. The secondary electron trajectory envelope 1002O will diverge in the detector plane, and the degree of divergence depends on the conditions of the rejection field objective. In general, the secondary electron trajectory envelope 1002O still has different proportions of secondary electrons passing through the central hole of the detector; while a large part of the electrons from the far-axis part of the imaging scanning area will be collected by the detector, as shown in the secondary electron trajectory envelope 1002C, and the central part of the image is relatively dark, or presents a black hole effect.

[0004] The industry uses Wien filters to solve this problem. As is known, Wien filters usually include a pair of coaxial electric deflectors and a pair of magnetic deflectors. The electric deflectors and magnetic deflectors are usually arranged orthogonally, and are excited with DC voltage and current respectively, thereby generating orthogonal electric fields and magnetic fields on the cross section perpendicular to the axis. Charged particles passing along the axis will be affected by radial electromagnetic forces. Depending on the mass, speed (including velocity and direction), charge, etc. of the charged particles, the electromagnetic forces on the charged particles, including the deflection distance and direction, will be different. For electrons, the mass and charge are determined, and the deflection force is only related to the speed and direction; the role of the Wien filter in the electron microscope is to filter electrons of different energies and directions of motion, or to deflect them to different degrees. The reason why Wien filters are used in the field of electron microscopy is mainly to use them to treat the downward main electron beam and the upward signal electrons differently to achieve selective deflection.

[0005] For details, see Figure 3 , a Wien filter 105 is arranged between the deflector 106 and the objective lens 108; the Wien filter is not associated with the deflector, and a pair of electric deflectors and a pair of magnetic deflectors thereon are respectively applied with a constant voltage excitation signal 301 and a current excitation signal 302, generating a constant electric field and a magnetic field that are orthogonal to each other in space, and the ratio and polarity of the constant voltage excitation signal 301 and the current excitation signal 302 can be appropriately selected to just meet the following requirements: the electric field force and the magnetic field force on the downward main electron beam cancel each other out, and the trajectory is almost unaffected. Figure 1 The main electron beam trajectory 1001 and Figure 2 The electron beam trajectory 1001 in the image is almost unchanged; the electric field and magnetic field on the upward secondary electrons are superimposed in the same direction, causing the trajectory to deflect to one side of the axis. Figure 3 1002C and 1002O in Figure 1 The electron trajectory envelopes of the 1002C and 1002O signals in the figure both originate from the sample positions 1001C and 1001O, but the landing points when they reach the detector are completely different. Figure 3 The scheme helps to reduce the signal loss in the center of the image; however, this scheme has the following problems in practice:

[0006] 1. Limited field of view: Without the use of Wien filter, the annular detector can cover the entire imaging area ABCD scanned by the main electron beam. After using the Wien filter, only the detector surface on the off-axis side receives signal electrons from the entire imaging area, resulting in the imaging field of view must be reduced, otherwise part of the signal electrons will fall outside the detector, such as Figure 4 shown.

[0007] 2. Limited detector bandwidth: To ensure that the field of view is not lost, the detector area needs to be increased. Increasing the detector area will inevitably increase the equivalent capacitance of the detector, resulting in a decrease in frequency response. The sampling clock of the imaging signal must be reduced, which becomes one of the main factors restricting the speed of industrial detection equipment. Summary of the invention

[0008] The present invention provides a deflection detection system to solve the problem of limited field of view and limited detector bandwidth when using a Wien filter to deflect uplink signal electrons off-axis in the existing deflection detection system. The reason why it is called a deflection detection system is that it is different from the traditional DC drive Wien filter method, but dynamically links the excitation of the Wien filter and the excitation of the deflection, excites the Wien filter in an AC manner, and more effectively utilizes the detector to overcome the limitations of the field of view and frequency response.

[0009] Deflection detection system, reference Figure 5 , comprising at least one set of deflectors, at least one Wien filter and at least one detector;

[0010] The deflector may be an electric deflector or a magnetic deflector, to which an alternating line scanning signal and a frame scanning signal are applied to realize raster scanning of a main electron beam on a specific area of ​​the sample surface;

[0011] The Wien filter comprises a group of electric deflectors and a group of magnetic deflectors, which are respectively excited by an alternating voltage signal and a current signal to generate a deflection electric field and a deflection magnetic field which are perpendicular to each other; the alternating voltage signal and the current signal which excite the Wien filter are synchronous and in phase, and the amplitude (including polarity) ratio between them is fixed and adjustable; the generated deflection electric field and deflection magnetic field meet the following basic requirements: they generate electric field forces and magnetic field forces in opposite directions to the downward main electron beam, and generate electric field forces and magnetic field forces in the same direction to the upward signal electrons;

[0012] The alternating excitation signal of the Wien filter is also synchronized with the line or frame scanning signal of the deflector and maintains a fixed phase relationship; the phase relationship satisfies that during the scanning stage when the main electron beam approaches the central axis (image center), that is, during the weakening stage of the line or frame grating scanning signal, the excitation signal of the Wien filter is enhanced; during the scanning stage when the main electron beam deviates from the central axis (image center), that is, during the strengthening stage of the line or frame grating scanning signal, the excitation signal of the Wien filter is weakened.

[0013] Preferably, for a given main electron beam energy and direction of movement, the relative strengths of the alternating voltage excitation signal and the current excitation signal of the Wien filter exist in a specific ratio, so that the electromagnetic resultant force applied to the main electron beam passing through is zero, that is, the so-called direct axis condition of the Wien filter is satisfied. This is the requirement for an ideal Wien filter. In practice, for a non-ideal Wien filter, it can also be implemented in accordance with the net deflection force applied to the main electron beam passing along the axis being close to zero or the net deflection distance achieved being zero;

[0014] Furthermore, the absolute intensities of the alternating voltage excitation signal and current excitation signal of the Wien filter are adjustable in linkage while maintaining the set ratio, so as to adjust the off-axis deflection force or distance of the signal electrons passing through.

[0015] The grating scanning signal includes a line scanning signal and a frame scanning signal, and the excitation signal is an associated signal with the line scanning signal and / or the frame scanning signal, and the associated signal satisfies: the frequency of the excitation signal applied by the Wien filter maintains a preset multiple relationship with the frequency of the grating scanning signal, and the phase maintains a preset offset value, so that the zero value of the excitation signal corresponds to the peak value of the grating scanning signal, and the peak value of the excitation signal corresponds to the zero value of the grating scanning signal.

[0016] Optionally, the frequency of the excitation signal is n times or 1 / (2n) times the frequency of the grating scanning signal; if it is n times the frequency, it means that the zero value point of the grating scanning signal corresponds to at least the peak value of one periodic signal in the n-times frequency excitation signal; if it is 1 / (2n) times the frequency, it means that one period of the excitation signal covers 2n row scanning or frame scanning periods of the grating scanning signal, then the peak value of the excitation signal is required to correspond to at least the zero value of one periodic signal in the 2n scanning signal periods.

[0017] Preferably, n=1, that is, the frequency of the excitation signal is the same frequency or half frequency of the grating scanning signal; the phase of the excitation signal is offset by ±180° relative to the grating scanning signal, thereby ensuring that the zero value of each grating scanning signal corresponds to a peak value (maximum or minimum) of the excitation signal.

[0018] Optionally, the excitation signal is a composite of a first signal and a second signal, the first signal is associated with a row scanning signal, and the second signal is associated with a frame scanning signal.

[0019] Optionally, the waveform of the excitation signal is the same as the waveform of the grating scanning signal; or the waveform of the excitation signal is different from the waveform of the grating scanning signal; the excitation signal is any one of a sawtooth wave, a triangle wave, and a sine wave, or a combination of at least two waveforms.

[0020] Optionally, the excitation signal is a unipolar alternating signal, or the excitation signal is a bipolar alternating signal.

[0021] Furthermore, a DC bias signal is superimposed on the unipolar alternating signal or the bipolar alternating signal.

[0022] The present application also provides a deflection detection method of a deflection detection system, wherein a control device provided in the deflection detection system controls the main electron beam to converge on the sample surface after passing through the objective lens to excite signal electrons;

[0023] The deflection detection system is communicatively connected with a control device, which controls the main electron beam to scan a specific surface area of ​​the sample to be imaged in a raster form on the sample surface, and at the same time controls the excited reverse-accelerated signal electrons to be deflected and concentrated in a specific area or position of the selected detector; the signal electrons in the entire imaging scanning area can avoid the central hole of the detector surface without going beyond the boundary of the detector.

[0024] The control method includes controlling the deflector to output line scanning and frame scanning signals of specific waveform and frequency, applying a deflection force to the main electron beam, and scanning a set area on the sample surface;

[0025] The control method also includes controlling the Wien filter to output an excitation signal with a specific intensity that is synchronized with the grating scanning signal and maintains a fixed phase difference, so that the excitation signal is enhanced to a peak value when the main electron beam is at the center of the scanning field of view, and the excitation signal is weakened to near zero at the edge of the field of view; the intensity of the output excitation signal determines the distance from the signal electron to the deflected off-axis.

[0026] Preferably, the intensity of the excitation signal is adjusted according to the landing area to be controlled, thereby changing the deflection off-axis distance of the signal electrons.

[0027] Another object of the present application is to provide a scanning electron microscope, comprising an electron source, a condenser, an aperture, an objective lens, the above-mentioned deflection detection system, a sample stage, and an imaging amplifier and a display device;

[0028] The electron source generates electrons which are accelerated to form a main electron beam; the condenser collimates the main electron beam and limits the current through a coaxial aperture below to obtain a desired beam size; the objective lens is located between the aperture and the sample, and focuses the passing main electron beam on the sample surface so as to excite signal electrons (including secondary electrons and backscattered electrons) on the sample surface; the sample is located on a sample stage, to which a negative voltage can be applied, which decelerates the main electron beam and accelerates the signal electrons in reverse; the deflector of the deflection detection system realizes raster scanning of the main electron beam in a set area on the sample surface; by applying an appropriate alternating excitation signal to the Wien filter, the downward main electron beam is hardly affected, and the upward signal electrons are dynamically deflected off-axis, so that the signal electrons in the scanning area are gathered in a specific effective area in the detector outside the axis without being missed; finally, the imaging amplifier amplifies the signal captured by the detector and transmits it to a display device, or digitally stores it in a storage medium to obtain a sample morphology image.

[0029] The beneficial effects of the present invention are:

[0030] The present invention proposes an improved excitation method for the detector scheme in the lens barrel of a conventional electron microscope equipped with a Wien filter, which overcomes the problem of low secondary electron collection rate on the axis; at the same time, the excitation mode of the Wien filter is changed from the conventional DC steady-state excitation to a dynamic excitation synchronized with the electron beam scanning signal, and the scanning signal and the Wien filter excitation signal maintain a fixed phase difference, so that when the electron beam is in the center of the scanning field of view, the Wien filter excitation reaches the strongest and has the strongest deflection effect on the signal electrons; while when imaging at the edge of the field of view, the Wien filter excitation is the weakest (even reduced to zero), and the deflection of the signal electrons is the weakest or there is no deflection. This scheme reduces the coverage requirements for the detector, and at the same time solves the problem of signal electrons near the optical axis missing the detector. Therefore, even for the design of an electron microscope with large field of view and high throughput application requirements, a smaller detector can still be adopted, which solves the contradiction between the sampling frequency and the field of view, and plays an important role in improving the image signal-to-noise ratio, the imaging rate or the detection rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0032] Figure 1 It is a schematic diagram of the trajectory envelope of secondary electrons emitted from the image center and the image edge when no Wien filter is provided in the lens barrel used for electron detection in the prior art;

[0033] Figure 2 yes Figure 1 Schematic diagram of the relationship between the corresponding scanning area on the sample side and the secondary electron landing area on the detector side;

[0034] Figure 3 It is a schematic diagram of the trajectory envelope of secondary electrons emitted from the image center and the image edge when a Wien filter is set in the lens barrel;

[0035] Figure 4 yes Figure 3 Schematic diagram of secondary electrons emitted from the scanning area at the sample end being deflected by the Wien filter and mapped to the off-axis side of the detector;

[0036] Figure 5 is a schematic diagram of mapping secondary electrons to a detector in Example 1 of the present application;

[0037] Figure 6 It is a schematic diagram of the corresponding relationship between the excitation signal waveform and the grating scanning signal waveform of Example 1 of the present application;

[0038] Figure 7 is a schematic diagram of mapping secondary electrons to a detector in Example 2 of the present application;

[0039] Figure 8 It is a schematic diagram of the corresponding relationship between the excitation signal waveform and the grating scanning signal waveform of Example 2 of the present application;

[0040] Fig. 9 is a schematic diagram of mapping secondary electrons to a detector in Example 3 of the present application;

[0041] Fig.10 Schematic diagram of the corresponding relationship between the excitation signal waveform and the grating scanning signal waveform of Example 3 of the present application;

[0042] Fig.11 is a schematic diagram of mapping secondary electrons to a detector in Example 4 of the present application;

[0043] Fig.12 It is a schematic diagram of the corresponding relationship between the excitation signal waveform and the grating scanning signal waveform of Example 4 of the present application;

[0044] Fig.13 is a schematic diagram of mapping secondary electrons to a detector in Example 5 of the present application;

[0045] Fig.14 It is a schematic diagram of the corresponding relationship between the excitation signal waveform and the grating scanning signal waveform of Example 5 of the present application;

[0046] Fig.15 is a schematic diagram of mapping secondary electrons to a detector in Example 6 of the present application;

[0047] Fig.16 Schematic diagram of the corresponding relationship between the excitation signal waveform and the grating scanning signal waveform of Example 6 of the present application;

[0048] Fig.17 is a schematic diagram of mapping secondary electrons to a detector in Example 7 of the present application;

[0049] Fig.18 Schematic diagram of the corresponding relationship between the excitation signal waveform and the grating scanning signal waveform of Example 7 of the present application;

[0050] Fig.19 is a schematic diagram of mapping secondary electrons to a detector in Example 8 of the present application;

[0051] Fig. 20 It is a schematic diagram of the corresponding relationship between the excitation signal waveform and the grating scanning signal waveform of Example 8 of the present application;

[0052] Fig.21 It is a schematic diagram of the internal modules of the electron microscope of the present application. DETAILED DESCRIPTION

[0053] The deflection detection system disclosed in the present invention is an in-tube detection system equipped with a Wien filter. The present invention also discloses an electron microscope including the system, such as Fig.21 shown.

[0054] Specifically, the deflection detection system 567 includes a detector 107, a deflector 106, and a Wien filter 105 from top to bottom. The main electron beam 1001 emitted from the electron source passes through the deflector 106; the deflector 106 is in communication with the deflection controller 200, and under the action of the line scanning signal 201 and the frame scanning signal 202, the generated deflection field deflects the main electron beam, and forms a raster scan in a set area on the surface of the scanning sample 1010, such as the ABCD area, with O being the center of the scanning area. The main electron beam 1001 also passes through the objective lens 108, and the objective lens 108 and the sample 1010 together form a rejection field objective lens (because the sample 1010 is biased by a negative pressure), focusing the incident main electron beam 1001 on the sample surface and generating secondary electrons 1002; the rejection field objective lens reversely accelerates the secondary electrons 1002 from the sample surface into the objective lens 108. The detector 107 is located above the deflector 106 and receives the reverse accelerated secondary electrons 1002 from the sample surface. The Wien filter 105 is coaxially arranged with the main electron beam 1001. The Wien filter 105 is located between the deflector 106 and the objective lens 108. The Wien filter 105 is driven by the controller 300 to output an alternating voltage excitation signal 301 and a current excitation signal 302, generating a mutually perpendicular deflection electric field E and a deflection magnetic field B (ExB), and their directions satisfy: the deflection electric field and the deflection magnetic field generate opposite electric field forces and magnetic field forces on the downward main electron beam 1001, and generate the same electric field forces and magnetic field forces on the upward secondary electrons, thereby forming an off-axis combined force. The intensities of the voltage excitation signal 301 and the current excitation signal 302 satisfy: when the main electron beam 1001 passes through the generated ExB field region along the optical axis, the electric field force and the electromagnetic force cancel each other out at any position on the axis, which is the ideal direct-axis condition of the Wien filter; or the net deflection displacement of the main electron beam 1001 on the imaging surface after passing through the ExB field region is zero or close to zero, which is the non-ideal direct-axis condition of the Wien filter.

[0055] Under the action of the Wien filter, a reference trajectory of the secondary electron 1002 arriving at the detector is as follows Figure 3 shown.

[0056] One feature disclosed in the present invention is that the excitation signal of the Wien filter 105 is an alternating signal, and two groups are output by the Wien filter controller 300. The alternating voltage excitation signal 301 (divided into positive and negative paths) acts on the electric deflector (501 / 502); the alternating current excitation signal 302 (divided into positive and negative paths) acts on the magnetic deflector (503 / 504). The alternating current excitation signal 302 and the voltage excitation signal 301 are themselves synchronized and in phase. During the effective imaging detection period, the current excitation signal 302 and the voltage excitation signal 301 should also maintain a set ratio, so that the main electron beam meets the ideal direct axis condition of the Wien filter, or at least meets the non-ideal direct axis condition, so as to reduce the influence of the Wien filter on the main electron beam during the dynamic adjustment process.

[0057] Another feature disclosed by the present invention is that the alternating excitation signal of the Wien filter 105 is not independent, and it must be associated with the line scan signal 201 or the frame scan signal 202 output by the deflector controller 200. The association requires that a specific relationship be satisfied in frequency and phase. The main purpose is: during the effective imaging scan (invalid scanning stages such as retrace and nonlinear intervals are not limited), the minimum amplitude value of the excitation signal waveform of the Wien filter corresponds to the peak value of the grating scan signal waveform, and the peak value of the excitation signal waveform corresponds to the minimum amplitude value of the grating scan signal waveform. When the excitation signal is not set with a DC bias, its minimum amplitude value is zero, and when the excitation signal is set with a DC bias, the minimum amplitude value is the DC bias value.

[0058] According to the correlation between the signals of the deflector controller 200 and the Wien filter controller 300, the frequency of the excitation signal output by the Wien filter controller 300 is n times or 1 / (2n) times the frequency of the row scanning signal 201 or the frame scanning signal 202 output by the deflector controller 200, where n is an arbitrary integer; at the same time, in terms of phase, within a complete cycle of the excitation signal including the grating scanning signal and the Wien filter, there is at least one time point when the zero value of the grating scanning signal corresponds to the peak value of the Wien excitation signal.

[0059] When n=1, the frequency of the excitation signal and the frequency of the line scanning signal or frame scanning signal of the grating scanning satisfy the same frequency or half frequency relationship; the phase of the excitation signal and the phase of the line scanning signal or frame scanning signal of the grating scanning maintain an offset of ±180°; specifically: when the main electron beam scans toward the center of the line / frame, the excitation signal is enhanced, and the excitation signal is strongest when it reaches the center of the line / frame, while the excitation signal is weakened when scanning toward the edge of the line / frame, and the excitation signal is weakest when it reaches the edge of the line / frame, and even weakened to zero.

[0060] The various embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. In the following description of the accompanying drawings, the same reference numerals refer to the same components. Generally, only the differences about the various embodiments are described. Each example is provided by way of explanation of the present invention and is not meant to limit the present invention.

[0061] Example 1

[0062] Please refer to Figure 5 and Figure 6 The Wien filter controller 300 controls the excitation signal source to generate a waveform such as Figure 6The voltage excitation signal 301 and the current excitation signal 302 shown are associated with the waveform of the line scan signal 201 of the deflector controller 200. The correlation characteristics are the same period and a phase difference of 180° or -180°. The amplitudes of the voltage excitation signal 301 and the current excitation signal 302 maintain a set ratio in the imaging stage, and the direct axis condition or basically satisfy the direct axis condition for the main electron beam. When the line scan signal 201 is the strongest, that is, at the two ends of a line scan cycle, the landing point of the secondary electrons on the detector originally falls on both sides away from the center hole, and the Wien filter does not need to provide a large deflection force. Therefore, the voltage excitation signal 301 and the current excitation signal 302 of the Wien filter are the smallest at this time. When passing through the line scan center, that is, when the line scan signal is close to zero, the excitation of the Wien filter reaches or approaches the strongest in any primary direction, so that the secondary electrons avoid the center hole of the detector and are detected completely or nearly completely on either side of the detector.

[0063] Specifically in this embodiment, when scanning the first half of the first line AB, the excitation of the Wien filter gradually increases, and when scanning through the center point of the line, the excitation signal reaches or approaches a certain polarity direction, and the secondary electrons on this half are detected on the right side of the detector; when scanning the second half of the first line AB, due to the characteristics of the sawtooth wave, the voltage excitation signal 301 and the current excitation signal 302 of the Wien filter are switched to another polarity direction, and gradually weaken from the peak value, so the deflection force on the secondary electrons also turns to another direction and drops to the minimum at point B. The secondary electrons excited by the second half of the scan of the line are detected on the left side of the detector surface. The above process is repeated for each subsequent line, and under the action of the frame scanning signal, the position of each line will be translated toward the center line by line, and the landing point of the secondary electrons excited by each line on the detector surface is stretched in the direction corresponding to the frame scan to form a strip shape, such as Figure 5 Therefore, the secondary electrons of each frame image (ABCD area) will be detected by clustering in two rectangular areas A'B'C'D' with the first half of the line and the second half of the line as boundaries, and a gap area will be formed between the two rectangular areas, avoiding the central hole of the detector.

[0064] Example 2

[0065] In the implementation example 1, the reverse polarity jump of the Wien filter excitation signal at the scanning center is difficult in practice and can be further optimized.

[0066] Please refer to Figure 7 and Figure 8 The voltage excitation signal 301 and the current excitation signal 302 of this embodiment are still associated with the line scanning waveform 201 of the deflector controller 200, but the sawtooth wave of the excitation waveform is changed to a triangle wave, and the signal period is doubled (the frequency is halved), as shown in FIG. Figure 8As shown. During the first row AB scanning, the voltage excitation and current excitation of the Wien filter both complete a linear increase and decrease in polarity direction, for example, first increase in the positive direction, and the excitation signal reaches a positive peak at the center point of the first row AB, and is ready to turn to the reverse direction and linearly weaken. At this time, the deflection force is the strongest, and the secondary electrons generated by the row scanning excitation are all deflected and fall on the rear side of the central hole of the detector; then the scan enters the second row, at which time the voltage excitation signal 301 and the current excitation signal 302 of the Wien filter have entered the anti-phase cycle, and the direction of the deflection force on the secondary electrons points to the front side of the central hole. Accordingly, the secondary electrons generated by the second row scanning excitation fall on the opposite side of the secondary electrons generated by the first row excitation (the front side of the central hole) on the detector surface. Repeat the above scanning process until the last row CD scan is completed.

[0067] Generally speaking, in this embodiment, the secondary electrons generated by the sample excitation during the scanning of the odd and even rows are deflected in opposite directions by the Wien filter, and fall on opposite sides of the center hole on the detector surface. Considering the effect of frame scanning, each row of emitted secondary electrons will be affected by frame scanning signals of different intensities, and the landing points on the detector will be stretched in the direction corresponding to the frame scanning to form a strip shape. Therefore, the field of view ABCD area on the sample surface will fall on both sides of the center hole of the detector surface alternately according to the rule of odd and even rows, such as Figure 7 As shown, odd-numbered rows of secondary electrons represented by AB fall on the back side of the central hole of the detector to form A'B', and even-numbered rows of secondary electrons represented by CD fall on the front side of the central hole of the detector to form C'D'. The gap between these two areas is adjusted by the excitation signal intensity of the Wien filter to avoid the central hole of the detector. The aggregation of two areas divided by the center on the detector surface is due to the fact that the excitation signal is a bipolar signal.

[0068] Example 3

[0069] Please refer to Fig. 9 and Fig.10 In this embodiment, the bipolar triangle wave in Embodiment 2 is changed into a unipolar triangle wave. The unipolarity can be negative or positive. Therefore, the period of the Wien filter excitation signal is the same as the period of the line scanning signal. The phase difference is still maintained at 180°. The excitation signal of the Wien filter is the strongest when the line deflection signal is the strongest, and the excitation signal of the Wien filter is the weakest when the line deflection signal is the weakest. However, the polarity is not reversed during the entire dynamic excitation process.

[0070] Fig. 9 The figure shows the landing area of ​​secondary electrons on the detector surface when the excitation signal is positive. Since the excitation signal is unipolar, all the secondary electrons generated by the sample scanning area ABCD fall on the right side of the detector center hole to form A'B'C'D'. Similarly, the frame scanning signal makes the landing points of secondary electrons distributed in a strip area.

[0071] Example 4

[0072] In the aforementioned embodiments, the excitation signal of the Wien filter follows the line scanning signal, or has the same frequency or half the frequency as the line scanning signal. However, since the line scanning signal frequency is usually higher, it is more difficult for the excitation signal to follow its changes. Therefore, the excitation signal waveform of the Wien filter can follow the changes of the frame scanning signal with a lower frequency.

[0073] Please refer to Fig.11 and Fig.12 In this embodiment, based on the first embodiment, the excitation signal of the Wien filter follows the frame scanning signal, and the excitation signal waveform is a sawtooth wave, and the phase difference with the frame scanning signal is 180°. The frame deflection is strongest at the head and tail ends of the frame, at which time the Wien filter basically does not work and the excitation signal is the smallest; the frame deflection is weakest at the center line of the image, the excitation signal of the Wien filter is the strongest, and the deflection force on the secondary electrons is also the strongest.

[0074] During the linear change of the first half frame scanning signal from the negative peak starting point to the zero point, the excitation signal of the Wien filter increases linearly from the zero point to the positive peak direction. The secondary electrons from the first half frame area are subjected to the deflection force in a specific direction and fall on one side (e.g., the rear side) of the center hole of the detector surface. After the scan reaches the center position of the frame scan, the second half frame scanning signal continues to increase linearly from the zero point, while the excitation signal of the Wien filter jumps to the reverse negative peak due to the retracement characteristics of the sawtooth wave, and then the reverse signal intensity decreases line by line. When it reaches the other edge of the frame scan area, the excitation signal of the Wien filter reaches zero value or the minimum amplitude value. In the second half frame stage, the excitation signal of the Wien filter is reversed, so that the secondary electrons in the corresponding area fall on the other side (e.g., the front side) of the center hole on the detector. Therefore, the secondary electrons excited by the frame scan area ABCD use the first half frame and the second half frame as the dividing line, covering the A'B'C'D' area of ​​the detector surface in a strip shape, avoiding the center hole of the detector.

[0075] The disadvantage of this embodiment is the same as that of the first embodiment, that is, the sawtooth wave of the excitation signal has a polarity jump in the effective scanning phase, and the following optimization can be made:

[0076] Example 5

[0077] In order to avoid the polarity jump of the sawtooth wave of the excitation signal in Example 4, the present embodiment adopts a unipolar triangle wave as the excitation signal, and each frame scanning process corresponds to a cycle of the triangle wave. The excitation signal variation of the first half frame area scanning increases linearly from the zero point to the positive peak value, and during the second half frame area scanning process, the excitation signal of the Wien filter does not jump to the reverse negative peak value, but weakens from the positive peak value line by line, and when reaching the other edge of the frame scanning area, the excitation signal reaches zero value or the minimum amplitude value.

[0078] like Fig.13 and Fig.14 As shown, the secondary electrons excited at different times in the scanning area ABCD of each frame will be deflected by the constant direction of the Wien filter, avoid the center hole of the detector, and cluster in strips on the same side A'B'C'D' of the center hole of the detector.

[0079] Example 6

[0080] This embodiment is an improvement on the embodiment 5. In this embodiment, every two frames are regarded as a scanning cycle, and the secondary electrons in each scanning cycle are excited by a bipolar triangle wave signal.

[0081] like Fig.15 and Fig.16 As shown, due to the bipolar excitation signal, the secondary electrons excited to be emitted from the ABCD area during the scanning period of the first frame 2021 and the secondary electrons excited to be emitted during the scanning period of the second frame 2022 will be affected by the deflection force of the Wien filter in different deflection directions, and will skip the part of the central hole of the detector, and will be clustered in the shape of strips in the A'B'C'D' area on both sides of the central hole of the detector; generally speaking, the secondary electrons produced by odd frames and even frames will be alternately clustered on the opposite sides of the central hole of the detector.

[0082] Example 7

[0083] In this embodiment, the excitation signal waveform of the Wien filter is changed from a linearly changing sawtooth wave or triangle wave to a sine wave or cosine wave. Fig.18 The corresponding secondary electron signal clustering diagram on the detector surface is shown in Fig.17 Similar to Example 6, the secondary electrons produced in the odd-numbered frames and the even-numbered frames are alternately clustered on opposite sides of the central hole of the detector.

[0084] Example 8

[0085] In this embodiment, based on the superposition principle of electromagnetic fields, a line scanning signal waveform with a phase shift of 180° and a frame scanning signal waveform with a phase shift of 180° are excited, and the excitations are synchronously superimposed and applied to the Wien filter.

[0086] Fig.19 and Fig. 20 An embodiment of this combination is given, in which the excitation signal of the Wien filter adopts a composite positive-spin waveform, which is synchronously misaligned with the line scanning signal and the frame scanning signal. This embodiment is a composite superposition of embodiment 3 (but preferably adopts a waveform of a single-polarity positive-spin waveform) and embodiment 5 (but preferably adopts a single-polarity positive-spin waveform), and the effect is that the secondary electrons excited by the scanning area ABCD are deflected by the Wien filter to a small range in a certain direction of the central hole, further enabling a small detector to meet the imaging detection of a large field of view.

[0087] In the above-mentioned embodiments, the excitation signal strength of the Wien filter determines the deflection off-axis distance of the secondary electrons, and the excitation strength is optimized and adjusted according to the required landing area.

[0088] The deflection detection systems of the above-mentioned embodiments all include a control device for controlling each device to operate according to a set program. The control device interacts with each device through signals and controls the operation of each device based on control instructions.

[0089] The deflection detection method of the present application comprises the following steps:

[0090] The control device controls the primary electron beam 1001 to converge through the objective lens 108 and then focus on the surface of the sample 1010 to excite the secondary electrons 1002;

[0091] The deflector controller 200 controls the deflector 106 to apply a raster scanning signal, i.e., a line scanning signal 201 and a frame scanning signal 202, to the main electron beam 1001 to scan a set area on the sample surface, such as the ABCD area;

[0092] The Wien filter controller 300 controls the excitation signal of the Wien filter 105, namely the voltage excitation signal 301 and the current excitation signal 302, which mainly include waveform and intensity, so that the excitation signal satisfies the straight axis condition or the collimated axis condition for the main electron beam 1001; and forms a deflection force in a certain direction for the upward secondary electrons.

[0093] The deflector controller 200 and the Wien filter controller 300 are also interrelated. The Wien excitation signal of the Wien filter controller 300 is synchronized with the raster scanning signal of the deflector controller 200, and the frequency and phase maintain a specific relationship, which requires that: when the line scan or frame scan of the main electron beam 1001 reaches the vicinity of the central axis position, the excitation signal should be enhanced to a peak value; and at the edge position of the line scan / frame scan, the excitation signal is weakened to a minimum, for example, to a zero value;

[0094] The secondary electrons 1002 excited in the scanning area are reversely accelerated and mapped onto the detector 107 to form an off-axis imaging area A'B'C'D'. The alternating excitation signal of the Wien filter causes the off-axis imaging area to be divided or shifted on the receiving surface of the detector, avoiding the central hole of the detector surface, so that the central part will not present a black hole effect; all signal electrons fall on the detector surface, meeting the conditions for large field of view imaging detection.

[0095] The present application also discloses a scanning electron microscope, see Fig.21 , including an electron source 101, a focusing lens 102, an aperture 104, an objective lens 108, and the deflection detection system 567 (105, 106, 107) of the above-mentioned embodiments, and also including an imaging amplifier and a display or storage device (not shown in the figure) and the like.

[0096] The electron beam emitted by the electron source 101 is accelerated to form a high-energy main electron beam 1001;

[0097] The focusing lens 102 is coaxially arranged below the electron source 101 to collimate the main electron beam 1001 and to limit the current through the coaxial aperture 104 below to intercept the required beam current size;

[0098] The deflection detection system 567, including a Wien filter 105, a deflector 106, and a detector 107, is located between the focusing lens 102 and the sample 1010. The deflector 106 realizes raster scanning of the main electron beam 1001 in the ABCD area on the sample surface and excites secondary electrons 1002. The Wien filter 105 deflects and maps the reversely accelerated secondary electrons 1002 to one side of the center hole on the detector 107 (or both sides, see the embodiment) to form an off-axis imaging area A'B'C'D'.

[0099] The imaging amplifier amplifies the signal of the off-axis imaging area A'B'C'D' and transmits it to a display device for display, or stores it in a storage medium for subsequent processing.

[0100] The present invention is described in most cases using secondary electrons as an example, but is also applicable to backscattered electrons. In addition, it can also be applied to detect secondary and / or backscattered charged particles in the form of electrons, ions or other signals to obtain a specimen image. The "sample" referred to herein includes but is not limited to semiconductor wafers, semiconductor workpieces and other workpieces, such as storage disks, etc.

[0101] The directional characteristic words such as "left" and "right" in the above content are only used to indicate a rough relative position relationship, and do not limit the relevant structures in the embodiments of the present application.

[0102] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A deflection detection system, comprising at least one group of deflectors, at least one Wien filter and at least one detector; the deflectors are applied with alternating line scanning signals and frame scanning signals to realize raster scanning of a main electron beam on a specific area of ​​a sample surface; the Wien filter comprises a group of electric deflectors and a group of magnetic deflectors, which meet the design requirements of the Wien filter, and are respectively excited by alternating voltage signals and current signals to generate mutually perpendicular deflection electric fields and deflection magnetic fields on a cross section perpendicular to the optical axis; the alternating voltage signal and current signal that excite the Wien filter are synchronous and in phase, and the amplitude ratio and polarity between them are adjustable, and under the set main electron beam energy condition, the generated deflection electric field and deflection magnetic field meet the following requirements: generating mutually opposite electric field forces and magnetic field forces for the downward main electron beam, and generating the same electric field forces and magnetic field forces for the upward secondary electrons and / or backscattered electrons; characterized in that: The alternating excitation signal of the Wien filter is also synchronized with the line scanning signal or the frame scanning signal of the deflector and maintains a fixed phase relationship; the phase relationship satisfies that during the scanning stage when the main electron beam approaches the central axis, that is, during the weakening stage of the line scanning signal or the frame scanning signal, the excitation signal of the Wien filter is enhanced; during the scanning stage when the main electron beam deviates from the central axis, that is, during the strengthening stage of the line scanning signal or the frame scanning signal, the excitation signal of the Wien filter is weakened.

2. The deflection detection system according to claim 1, characterized in that: The relative strength of the alternating voltage excitation signal and the current excitation signal of the Wien filter is maintained at a set ratio during the imaging scanning stage, so that the net deflection force applied to the main electron beam passing axially near the central axis is zero or close to zero; the absolute strength of the amplitude of the voltage excitation signal and the current excitation signal is adjustable in linkage to adjust the off-axis deflection force or distance of the secondary electrons and / or backscattered electrons passing through; The excitation signal of the Wien filter and the line scanning signal or frame scanning signal of the deflector are associated signals, and the associated signals satisfy: the frequency of the excitation signal applied by the Wien filter maintains a preset multiple relationship with the frequency of the line scanning signal or the frame scanning signal, and the phase maintains a preset offset, so that the minimum amplitude value of the excitation signal waveform corresponds to the peak value of the grating scanning signal waveform, and the peak value of the excitation signal waveform corresponds to the minimum amplitude value of the grating scanning signal waveform.

3. The deflection detection system according to claim 2, characterized in that: The frequency of the excitation signal is n times or 1 / (2n) the frequency of the row scanning signal or frame scanning signal of the grating scanning, where n is an arbitrary integer; within a complete cycle of the excitation signal including the grating scanning signal and the Wien filter, there is at least one time point when the excitation signal and the grating scanning signal meet the requirements of the associated signal.

4. The deflection detection system according to claim 3, characterized in that: The frequency of the excitation signal and the frequency of the line scanning signal or frame scanning signal of the grating scan satisfy the same frequency or half frequency relationship; the phase of the excitation signal and the phase of the line scanning signal or frame scanning signal of the grating scan maintain an offset of ±180°; within each signal cycle, the grating scanning signal and the excitation signal both meet the requirements of the associated signal.

5. The deflection detection system according to claim 2, characterized in that: The excitation signal of the Wien filter is composed of two signals superimposed and compounded, and the two signals are respectively associated with the line scanning signal and the frame scanning signal.

6. The deflection detection system according to claim 1, characterized in that: The waveform of the excitation signal is the same as that of the grating scanning signal; or the waveform of the excitation signal is different from that of the grating scanning signal; the excitation signal is any one of a sawtooth wave, a triangle wave, and a sine wave, or a combination of at least two waveforms.

7. The deflection detection system according to claim 1, characterized in that: The excitation signal is a unipolar alternating signal, or the excitation signal is a bipolar alternating signal; the unipolar alternating signal or the bipolar alternating signal can be obtained by superimposing a DC bias signal on a symmetrical alternating signal.

8. The deflection detection method of the deflection detection system according to any one of claims 1 to 7, characterized in that: The deflection detection system is in communication with the control device, and the control device controls the main electron beam to scan the preset surface area of ​​the sample to be imaged in a raster form on the sample surface, and at the same time controls the excited reverse accelerated secondary electrons and / or backscattered electrons to be deflected and gathered in a specific area or position of the selected detector; the signal electrons in the entire imaging scanning area avoid the central hole of the detector surface, but do not go beyond the boundary of the detector; The control method comprises: Control the deflector to output a line scan signal and a frame scan signal of a set waveform and frequency, apply a deflection force to the main electron beam, and scan a set area on the sample surface; The Wien filter is controlled to output an excitation signal that is synchronized with the grating scanning signal and maintains a fixed phase difference, so that the excitation signal is enhanced to a peak value when the main electron beam is at the center of the scanning field of view, and the excitation signal is weakened to near zero at the edge of the field of view.

9. The deflection detection method according to claim 8, characterized in that: The intensity of the excitation signal is adjusted according to the required landing area of ​​the signal electron, and the off-axis deflection distance of the secondary electrons and / or backscattered electrons is changed.

10. A scanning electron microscope, characterized in that: The device comprises an electron source, a condenser, an aperture, an objective lens, a deflection detection system as claimed in any one of claims 1 to 7, a sample stage, an imaging amplifier and a display device; the electron source generates electrons which are accelerated to form a main electron beam; the condenser collimates the main electron beam and limits the current through the coaxial aperture below to obtain the required beam current size; The objective lens is located between the aperture and the sample, and focuses the passing main electron beam on the sample surface so as to excite secondary electrons and / or backscattered electrons on the sample surface; the sample is located on a sample stage, to which a negative voltage can be applied, which decelerates the main electron beam while accelerating the secondary electrons and / or backscattered electrons; the Wien filter of the deflection detection system has almost no effect on the downward main electron beam by applying an appropriate alternating excitation signal, and realizes dynamic off-axis deflection of the upward secondary electrons and / or backscattered electrons, so that the secondary electrons and / or backscattered electrons in the scanning area are all gathered in the effective area of ​​the detector outside the axis; the imaging amplifier amplifies the signal captured by the detector and transmits it to a display device, or digitally stores it in a storage medium to obtain a sample morphology image.

Images