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

Abstract

The present application belongs to the field of scanning electron detection imaging, and relates to a deflection detection system, a deflection detection method and a scanning electron microscope. A Wien filter is arranged in the electron lens barrel of the present application. The Wien filter is excited by an alternating signal to generate a deflection electric field and a deflection magnetic field which are perpendicular to each other. The electric field force and the magnetic field force generated by the Wien filter are opposite to the main electron beam going downward, and the electric field force and the magnetic field force generated by the Wien filter are the same as the secondary electron going upward, so as to form an off-axis resultant force. The alternating excitation signal of the Wien filter is configured to be synchronous with the grating scanning signal of the deflector, and the frequency and the phase are maintained in a specific relationship. When the main electron beam scans to the center of the row / frame, the excitation signal is enhanced, and when the main electron beam scans to the edge of the row / frame, the excitation signal is weakened. The present application solves the problem that the signal electrons near the optical axis miss the detector, reduces the coverage requirement of the detector, solves the contradiction between the sampling frequency and the field of view, improves the signal-to-noise ratio of the image, and improves the imaging rate or the detection rate.

Description

Technical Field

[0001] This invention belongs to the field of scanning electron detection imaging, and specifically relates to deflection detection systems, deflection detection methods, and scanning electron microscopes. Background Technology

[0002] Electron beam imaging equipment used for detection or measurement in industry or laboratories, such as critical dimension microscopy (CDSEM) and electron beam defect detection equipment, typically needs to operate at low energy levels to reduce sample damage or charge accumulation; simultaneously, to maintain resolution, the working distance must be minimized. To achieve this, a repulsive field lens design is often employed. This design introduces the problem that most of the secondary electrons representing the morphology and / or backscattered electrons reflecting material properties (hereinafter collectively referred to as signal electrons) generated during sample scanning are accelerated into the microscope tube. Therefore, a detector needs to be designed inside the microscope tube to collect as many signal electrons as possible; this is known as an in-tube detector scheme. This differs from traditional electron microscopes, where the detector can be placed either between the objective lens and the sample or along the optical axis.

[0003] The detector inside the microscope tube is often a ring detector, with its central aperture coaxial with the optical axis to facilitate the passage of the main electron beam. However, the central aperture 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 by the condenser lens 102 and the repulsion field objective lens 108. When the main electron beam 1001 passes through the deflector 106, a grating scan signal 200 is applied, including a line scan signal 201 and a frame scan signal 202, to achieve scanning of the ABCD region on the sample surface (with O as its center). Please refer to [reference needed]. Figure 2 At the corresponding location, secondary electrons 1002 are excited and accelerated in the opposite direction, converging and falling onto the surface of the ring detector 107, corresponding to positions A'B'C'D', where O' is the center of region A'B'C'D'. Signal electrons that normally pass through the central aperture of the detector will not be detected. Figure 1 The diagram shows the trajectory envelopes 1002O and 1002C of secondary electrons excited at the center position 1010O and corner position 1010C of the sample scanning area as they reach the detector surface. The secondary electron trajectory envelope 1002O diverges within the detector plane, and the degree of divergence depends on the conditions of the repulsive field objective. Generally, a certain proportion of secondary electrons still pass through the detector's central aperture in the secondary electron trajectory envelope 1002O. However, a large portion of the electrons from the far-axis portion of the imaging scanning area are collected by the detector, as shown in the secondary electron trajectory envelope 1002C. This results in a darker central area of ​​the image, or a black hole effect.

[0004] The industry uses Wien filters to solve this problem. As is known, a Wien filter typically comprises a pair of coaxial electric deflectors and a pair of magnetic deflectors, usually arranged orthogonally. These deflectors are excited by DC voltage and current, respectively, thereby generating orthogonal electric and magnetic fields in a cross-section perpendicular to the axis. Charged particles passing along the axis experience radial electromagnetic forces. Depending on the mass, velocity (including speed and direction), and charge of the charged particle, the electromagnetic force experienced by the particle, including the deflection distance and direction, will vary. For electrons, whose mass and charge are fixed, the deflection force depends only on their velocity and direction. The role of Wien filters in electron microscopy is to filter electrons with different energies and directions of motion, or to deflect them to different degrees. The main reason for using Wien filters in electron microscopy is their ability to selectively deflect the descending main electron beam and the ascending signal electrons.

[0005] For details, see Figure 3 A Wien filter 105 is disposed between the deflector 106 and the objective lens 108. The Wien filter is not associated with the deflector; a constant voltage excitation signal 301 and a current excitation signal 302 are applied to a pair of electric deflectors and a pair of magnetic deflectors on it, respectively, generating constant, mutually orthogonal electric and magnetic fields in space. The ratio and polarity of the constant voltage excitation signal 301 and the current excitation signal 302 can be appropriately selected to precisely meet the following requirement: the electric and magnetic forces acting on the descending 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 remains almost unchanged; the electric and magnetic forces acting on the upward-moving secondary electrons are superimposed in the same direction, causing the trajectory to deflect to one side of the axis. For example... Figure 3 1002C and 1002O in Figure 1 The electron trajectory envelopes of the 1002C and 1002O signals both originate from sample positions 1001C and 1001O, but their landing points at the detector are completely different. Clearly... Figure 3 This approach helps reduce signal loss at the image center; however, it has the following problems in practice:

[0006] 1. Limited Field of View: Without a Wien filter, the ring detector can cover the entire imaging area ABCD scanned by the main electron beam. However, with a Wien filter, only the detector surface on the off-axis side receives signal electrons from the entire imaging area. This necessitates a reduction in the imaging field of view; otherwise, some signal electrons will fall outside the detector, such as... Figure 4 As shown.

[0007] 2. Limited detector bandwidth: To ensure no loss of field of view, the detector area needs to be increased. However, increasing the detector area inevitably increases the detector's equivalent capacitance, leading to a decrease in frequency response. The sampling clock of the imaging signal must be reduced, which is one of the main factors restricting the speed of industrial inspection equipment. Summary of the Invention

[0008] This invention provides a deflection detection system to address the limitations of field of view and detector bandwidth in existing deflection detection systems that use Wien filters to deflect upward-moving signal electrons off-axis. It is called a deflection detection system because, unlike traditional DC-driven Wien filters, it dynamically correlates the excitation of the Wien filter with the excitation of the deflection, exciting the Wien filter in an AC manner. This more effectively utilizes the detector and overcomes the limitations of field of view and frequency response.

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

[0010] The deflector can be an electric deflector or a magnetic deflector, on which alternating line scanning signals and frame scanning signals are applied to achieve grating scanning of the main electron beam in a specific area of ​​the sample surface.

[0011] The Wien filter comprises a set of electric deflectors and a set of magnetic deflectors, which are excited by alternating voltage and current signals, respectively, to generate mutually perpendicular deflecting electric and magnetic fields. The alternating voltage and current signals that excite the Wien filter are synchronous and in phase, and their amplitude (including polarity) ratio is fixed and adjustable. The generated deflecting electric and magnetic fields meet the following basic requirements: they generate opposing electric and magnetic forces on the downward main electron beam, and in the same direction on the upward signal electrons.

[0012] The alternating excitation signal of the Wien filter is synchronized with the line or frame scanning signal of the deflector and maintains a fixed phase relationship. The phase relationship satisfies the following conditions: during the scanning phase of the main electron beam approaching the central axis (image center), that is, during the weakening phase of the line or frame raster scanning signal, the excitation signal of the Wien filter is enhanced; during the scanning phase of the main electron beam away from the central axis (image center), that is, during the enhancement phase of the line or frame raster scanning signal, the excitation signal of the Wien filter is weakened.

[0013] Preferably, for a given energy and direction of motion of the main electron beam, the relative intensities of the alternating voltage excitation signal and current excitation signal of the Wien filter exist in a specific ratio such that the electromagnetic resultant force exerted on the passing main electron beam is zero, thus satisfying the so-called direct-axis condition of the Wien filter. This is the requirement for an ideal Wien filter. In practice, for non-ideal Wien filters, it can also be implemented such that the net deflection force exerted on the main electron beam traveling along the axis is close to zero or the net deflection distance is zero.

[0014] Furthermore, the absolute strengths of the alternating voltage excitation signal and current excitation signal of the Wien filter are adjustable in conjunction with each other while maintaining the set ratio, in order 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. The excitation signal is associated with the line scanning signal and / or the frame scanning signal. The associated signal satisfies the following: 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 an n-fold or 1 / (2n)-fold of the grating scan signal; if it is an n-fold, it means that the zero point of the grating scan signal corresponds to at least the peak value of one period signal in the n-fold excitation signal; if it is a 1 / (2n)-fold, it means that one period of the excitation signal covers 2n line scan or frame scan periods of the grating scan signal, then the peak value of the excitation signal is required to correspond to at least the zero value of one period signal in one of the 2n scan 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, which ensures 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 superposition of signal one and signal two, where signal one is associated with the line scan signal and signal two is associated with the frame scan 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 or a combination of at least two waveforms of sawtooth wave, triangular wave, and sine wave.

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

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

[0022] This application also provides a deflection detection method for a deflection detection system, wherein the control device inside the deflection detection system controls the main electron beam to be focused on the sample surface after passing through the objective lens to excite signal electrons.

[0023] The deflection detection system is communicatively connected to the control device. The control device controls the main electron beam to scan a specific surface area of ​​the sample to be imaged in a grating pattern. At the same time, it can control 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 a deflector to output line scanning and frame scanning signals of specific waveforms and frequencies, applying a deflection force to the main electron beam, and scanning a set area on the sample surface.

[0025] The control method further 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, such 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 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 excitation signal strength is adjusted according to the landing area to be controlled, thereby changing the off-axis deflection distance of the signal electrons.

[0027] Another objective of this application is to provide a scanning electron microscope, including an electron source, a condenser lens, an aperture, an objective lens, the aforementioned deflection detection system, a sample stage, an imaging amplifier, and a display device, etc.

[0028] The electron source generates electrons and accelerates them to form a main electron beam; the condenser lens collimates the main electron beam and limits the current through a coaxial aperture below to obtain the desired beam current; the objective lens is located between the aperture and the sample, focusing the passing main electron beam onto the sample surface to excite signal electrons (including secondary electrons and backscattered electrons) on the sample surface; the sample is located on the sample stage, on which a negative voltage can be applied to decelerate the main electron beam while simultaneously accelerating the signal electrons in the opposite direction; the deflector of the deflection detection system enables grating 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 almost unaffected, while the upward signal electrons are dynamically deflected off-axis, so that the signal electrons in the scanning area are concentrated in a specific effective area within the off-axis detector without being missed; finally, the imaging amplifier amplifies the signal captured by the detector and transmits it to a display device or digitizes it in a storage medium to obtain a sample morphology image.

[0029] The beneficial effects of this invention are as follows:

[0030] This invention proposes an improved excitation method for the in-tube detector scheme of traditional electron microscopes equipped with Wien filters, overcoming the problem of low on-axis secondary electron collection rate. Simultaneously, the excitation mode of the Wien filter is changed from the traditional DC steady-state excitation to dynamic excitation synchronized with the electron beam scanning signal. The scanning signal and the Wien filter excitation signal maintain a fixed phase difference, ensuring that the Wien filter excitation is strongest when the electron beam is at the center of the scanning field of view, exerting the strongest deflection effect on the signal electrons; while at the edge of the field of view, the Wien filter excitation is weakest (even reduced to zero), with the weakest or no deflection of the signal electrons. This scheme reduces the coverage requirements of the detector while solving the problem of signal electrons missing the detector near the optical axis. Therefore, even for electron microscope designs requiring large field of view and high throughput, a smaller detector can still be adopted, resolving the contradiction between sampling frequency and field of view. This plays an important role in improving image signal-to-noise ratio and increasing imaging or detection speed. Attached Figure Description

[0031] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0032] Figure 1 This is a schematic diagram of the secondary electron trajectory envelope emitted from the image center and image edge when no Wien filter is set inside the microscope tube used for electronic detection in the prior art;

[0033] Figure 2 yes Figure 1 A schematic diagram showing the relationship between the corresponding sample end scanning area and the detector end secondary electron landing area;

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

[0035] Figure 4 yes Figure 3 A schematic diagram showing secondary electrons emitted from the sample end scanning region being deflected by the Wien filter and mapped onto the off-axis side of the detector.

[0036] Figure 5 This is a schematic diagram of secondary electron mapping onto the detector in Embodiment 1 of this application;

[0037] Figure 6 This is a schematic diagram showing the correspondence between the excitation signal waveform and the grating scanning signal waveform in Embodiment 1 of this application;

[0038] Figure 7 This is a schematic diagram of secondary electron mapping onto the detector in Embodiment 2 of this application;

[0039] Figure 8 This is a schematic diagram showing the correspondence between the excitation signal waveform and the grating scanning signal waveform in Embodiment 2 of this application;

[0040] Figure 9 This is a schematic diagram of secondary electron mapping onto the detector in Embodiment 3 of this application;

[0041] Figure 10 This is a schematic diagram showing the correspondence between the excitation signal waveform and the grating scanning signal waveform in Embodiment 3 of this application;

[0042] Figure 11 This is a schematic diagram of secondary electron mapping onto the detector in Embodiment 4 of this application;

[0043] Figure 12 This is a schematic diagram showing the correspondence between the excitation signal waveform and the grating scanning signal waveform in Embodiment 4 of this application;

[0044] Figure 13 This is a schematic diagram of secondary electron mapping onto the detector in Embodiment 5 of this application;

[0045] Figure 14 This is a schematic diagram showing the correspondence between the excitation signal waveform and the grating scanning signal waveform in Embodiment 5 of this application;

[0046] Figure 15 This is a schematic diagram of secondary electron mapping onto the detector in Embodiment 6 of this application;

[0047] Figure 16 This is a schematic diagram showing the correspondence between the excitation signal waveform and the grating scanning signal waveform in Embodiment 6 of this application;

[0048] Figure 17 This is a schematic diagram of secondary electron mapping onto the detector in Embodiment 7 of this application;

[0049] Figure 18 This is a schematic diagram showing the correspondence between the excitation signal waveform and the grating scanning signal waveform in Embodiment 7 of this application;

[0050] Figure 19 This is a schematic diagram of secondary electron mapping onto the detector in Embodiment 8 of this application;

[0051] Figure 20 This is a schematic diagram showing the correspondence between the excitation signal waveform and the grating scanning signal waveform in Embodiment 8 of this application;

[0052] Figure 21 This is a schematic diagram of the internal modules of the electron microscope of this application. Detailed Implementation

[0053] The deflection detection system disclosed in this invention is an in-tube detection system equipped with a Wien filter. This invention also discloses an electron microscope incorporating the aforementioned system, such as... Figure 21 As shown.

[0054] Specifically, the deflection detection system 567 includes, from top to bottom, a detector 107, a deflector 106, and a Wien filter 105. The main electron beam 1001 emitted from the electron source passes through the deflector 106; the deflector 106 is communicatively connected to the deflection controller 200. Under the action of the line scan signal 201 and the frame scan signal 202, the generated deflection field deflects the main electron beam, forming a raster scan in a designated area on the surface of the scanning sample 1010, such as the ABCD region, with O being the center of the scan area. The main electron beam 1001 also passes through the objective lens 108. The objective lens 108 and the sample 1010 together form a repulsive field objective lens (because the sample 1010 is subjected to a negative pressure bias), focusing the incident main electron beam 1001 onto the sample surface and generating secondary electrons 1002; the repulsive field objective lens then accelerates the secondary electrons 1002 from the sample surface back into the objective lens 108. Detector 107 is located above deflector 106 and receives secondary electrons 1002 that are accelerated in the opposite direction from the sample surface. Wien filter 105 is coaxially arranged with the main electron beam 1001 and is located between deflector 106 and objective lens 108. Wien filter 105 is driven by controller 300 to output alternating voltage excitation signal 301 and current excitation signal 302, generating mutually perpendicular deflection electric field E and deflection magnetic field B (ExB). Their directions satisfy the following: the deflection electric field and deflection magnetic field generate opposite electric and magnetic forces on the downward main electron beam 1001, and generate electric and magnetic forces in the same direction on the upward secondary electrons, thus forming an off-axis resultant force. The intensity of the voltage excitation signal 301 and the current excitation signal 302 satisfies the following conditions: when the main electron beam 1001 passes through the generated ExB field region along the optical axis, the electric field force and 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 plane 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 influence of the Wien filter, the secondary electron 1002 reaches a reference trajectory of the detector as follows: Figure 3 As shown.

[0056] A key feature of this invention is that the excitation signal for the Wien filter 105 is an alternating signal, output by the Wien filter controller 300 in two sets: an alternating voltage excitation signal 301 (with positive and negative paths) acts on the electric deflectors (501 / 502); and an alternating current excitation signal 302 (with positive and negative paths) acts on the magnetic deflectors (503 / 504). The alternating current excitation signal 302 and voltage excitation signal 301 are synchronous and in phase. During effective imaging detection, the current excitation signal 302 and voltage excitation signal 301 must maintain a set ratio to ensure that the main electron beam meets the ideal direct-axis condition of the Wien filter, or at least the non-ideal direct-axis condition, thereby reducing the impact of the Wien filter on the main electron beam during dynamic adjustment.

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

[0058] Based on 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 an n-fold or 1 / (2n)-fold of the line scan signal 201 or frame scan signal 202 output by the deflector controller 200, where n is any integer; at the same time, in terms of phase, within a complete cycle of the excitation signal containing the grating scan signal and the Wien filter, there is at least one time point where the zero value of the grating scan 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 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°; specifically, the excitation signal is enhanced when the main electron beam scans towards the center of the line / frame, and the excitation signal is strongest when it reaches the center of the line / frame, while the excitation signal is weakened when scanning towards the edge of the line / frame, and the excitation signal is weakest when it reaches the edge of the line / frame, or even weakened to zero.

[0060] The various embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In the following description of the drawings, the same reference numerals refer to the same components. Generally, only differences with respect to the various embodiments are described. Each example is provided by way of explanation and is not intended to limit the 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 waveforms such as... Figure 6The voltage excitation signal 301 and current excitation signal 302 shown are correlated with the waveform of the line scan signal 201 of the deflector controller 200. The correlation is characterized by the same period and a phase difference of 180° or -180°. The amplitudes of the voltage excitation signal 301 and current excitation signal 302 maintain a set ratio during the imaging stage, satisfying or essentially satisfying the direct-axis condition for the main electron beam. When the line scan signal 201 is strongest, i.e., at the two ends of a line scan cycle, the secondary electrons' landing points on the detector are already far from the central aperture, and the Wien filter does not need to provide a large deflection force. Therefore, the voltage excitation signal 301 and current excitation signal 302 of the Wien filter are at their minimum at this time. When passing the center of the line scan, i.e., when the line scan signal is close to zero, the excitation of the Wien filter reaches or approaches its strongest in any arbitrary direction, causing the secondary electrons to avoid the central aperture of the detector and be detected entirely or nearly entirely on either side of the detector.

[0063] Specifically, in this embodiment, when scanning the first half of the first row AB, the excitation of the Wien filter gradually increases. When the scan passes the center point of the row, the excitation signal reaches or approaches its strongest point in a certain polarity direction, and the secondary electrons in this half are detected on the right side of the detector. When scanning the second half of the first row AB, due to the characteristics of the sawtooth wave, the voltage excitation signal 301 and the current excitation signal 302 of the Wien filter switch to the other polarity direction and gradually weaken from the peak value. Therefore, the deflection force on the secondary electrons also shifts to the other direction and reaches its minimum at point B. The secondary electrons excited in the second half of the row are detected on the left side of the detector surface. The above process is repeated for each subsequent row. Under the action of the frame scan signal, the position of each row will shift towards the center one row at a time. The landing point of the secondary electrons excited in each row on the detector surface is stretched in the direction corresponding to the frame scan, forming a strip shape, such as... Figure 5 As shown. Therefore, the secondary electrons in each frame of the image (Area ABCD) will be detected by clustering in two rectangular regions, A'B'C'D', with the first and second halves of the row as boundaries, respectively, and a gap region will be formed between the two rectangular regions, thus avoiding the central aperture of the detector.

[0064] Example 2

[0065] Implementing the Wien filter excitation signal with a reverse polarity jump at the scan center in example 1 is quite difficult in practice and can be further optimized.

[0066] Please refer to Figure 7 and Figure 8 In this embodiment, the voltage excitation signal 301 and the current excitation signal 302 are still associated with the row scan waveform 201 of the deflector controller 200, but the sawtooth wave of the excitation waveform is changed to a triangular wave, and the signal period is doubled (the frequency is halved), such as Figure 8As shown. During the first row AB scan, the voltage and current excitation of the Wien filter both undergo a linear increase and decrease in polarity. For example, it first increases in the positive direction, reaching a positive peak at the center point of the first row AB, and then prepares to turn in the opposite direction and weaken linearly. At this time, the deflection force is strongest, and the secondary electrons generated by the row scan excitation are all deflected and fall behind the central aperture of the detector. Then, the scan enters the second row. At this time, the voltage excitation signal 301 and the current excitation signal 302 of the Wien filter have entered the inverse phase period. The direction of the deflection force on the secondary electrons points to the front of the central aperture. Correspondingly, the secondary electrons generated by the second row scan excitation fall on the opposite side of the secondary electrons generated by the first row excitation (the front of the central aperture) on the detector surface. The above scanning process is repeated until the last row CD scan is completed.

[0067] Generally, in this embodiment, the secondary electrons generated by the sample excitation during the odd-numbered and even-numbered scans are deflected in opposite ways by the Wien filter, landing on opposite sides of the central aperture on the detector surface. Considering the effect of frame scanning, the secondary electrons emitted from each row are affected by frame scanning signals of varying intensities, causing their landing points on the detector to be stretched into stripes in the direction corresponding to the frame scan. Therefore, the ABCD region of the sample surface field of view will alternately fall on both sides of the central aperture of the detector surface according to the odd-even row pattern, as shown below. Figure 7 As shown, the odd-numbered rows of secondary electrons, represented by AB, fall behind the central aperture of the detector to form A'B', while the even-numbered rows of secondary electrons, represented by CD, fall in front of the central aperture of the detector to form C'D'. The gap between these two regions is adjusted by the intensity of the excitation signal from the Wien filter to avoid the central aperture of the detector. The aggregation of the two regions on the detector surface, divided by the center, is due to the fact that the excitation signal is a bipolar signal.

[0068] Example 3

[0069] Please refer to Figure 9 and Figure 10 In this embodiment, the bipolar triangular wave in embodiment 2 is replaced with a unipolar triangular 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 horizontal scanning signal, and the phase difference is still maintained at 180°. The excitation signal of the Wien filter is strongest when the horizontal deflection signal is strongest and weakest when the horizontal deflection signal is weakest. However, the polarity does not reverse during the entire dynamic excitation process.

[0070] Figure 9 The diagram 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 excitation in 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 causes the landing points of the secondary electrons to be distributed in a strip-shaped area.

[0071] Example 4

[0072] In the foregoing embodiments, the excitation signal of the Wien filter follows the line scan signal, or is at the same frequency or half the frequency of the line scan signal. However, since the frequency of the line scan signal is usually high, it is difficult for the excitation signal to follow its changes. Therefore, the waveform of the excitation signal of the Wien filter can follow the changes of the frame scan signal with a lower frequency.

[0073] Please refer to Figure 11 and Figure 12 In this embodiment, based on Embodiment 1, the Wien filter excitation signal follows the frame scan signal. The excitation signal waveform is a sawtooth wave with a phase difference of 180° from the frame scan signal. Frame deflection is strongest at the beginning and end of the frame, at which point the Wien filter has virtually no effect and the excitation signal is minimal. Frame deflection is weakest in the center line of the image, the excitation signal of the Wien filter is strongest, and the deflection force on secondary electrons is also strongest.

[0074] During the linear transition of the first half-frame scan signal from a negative peak to zero, the excitation signal of the Wien filter increases linearly from zero to a positive peak. Secondary electrons from the first half-frame region are deflected by a specific force and fall on one side (e.g., the rear side) of the detector's central aperture. After reaching the center of the frame scan, the second half-frame scan signal continues to linearly increase from zero, while the excitation signal of the Wien filter jumps to a negative peak due to the sawtooth wave's retracement characteristics. The reverse signal strength then gradually weakens, reaching zero or its minimum amplitude when it reaches the other edge of the frame scan region. In the second half-frame stage, the excitation signal of the Wien filter is out of phase, causing the secondary electrons in the corresponding region to land on the other side of the central aperture (e.g., the front side). Therefore, the secondary electrons excited in the frame scan region ABCD form strips covering the A'B'C'D' regions of the detector surface, separated by the first and second half-frames, thus avoiding the detector's central aperture.

[0075] The disadvantage of this embodiment is the same as that of embodiment 1, namely, the sawtooth wave of the excitation signal has a polarity jump during the effective scanning phase. The following optimizations can be made:

[0076] Example 5

[0077] In this embodiment, to avoid the polarity jump of the sawtooth wave in the excitation signal in Embodiment 4, a unipolar triangular wave is used for the excitation signal, and each frame scanning process corresponds to one cycle of the triangular wave. During the scanning of the first half of the frame, the excitation signal increases linearly from zero to the positive peak value. During the scanning of the second half of the frame, the excitation signal of the Wien filter does not jump to the opposite negative peak value, but gradually weakens from the positive peak value. When it reaches the other edge of the frame scanning area, the excitation signal reaches zero or the minimum amplitude value.

[0078] like Figure 13 and Figure 14 As shown, the secondary electrons excited at different times within the scanning area ABCD of each frame are deflected by the Wien filter in a constant direction, avoiding the part of the detector's central aperture, and clustering in strips on the same side A'B'C'D' of the detector's central aperture.

[0079] Example 6

[0080] This embodiment is an improvement on 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 triangular wave signal.

[0081] like Figure 15 and Figure 16 As shown, due to the bipolar excitation signal, the secondary electrons emitted from the ABCD region during the first frame 2021 scan and the secondary electrons emitted during the second frame 2022 scan will be deflected by the Wien filter in different directions. They will all skip the central aperture of the detector and cluster in strips on both sides of the central aperture of the detector in regions A'B'C'D'. Generally speaking, the secondary electrons produced in odd-numbered frames and even-numbered frames will alternately cluster on opposite sides of the central aperture of the detector.

[0082] Example 7

[0083] In this embodiment, the excitation signal waveform of the Wien filter is changed from a linearly varying sawtooth or triangular wave to a sine or cosine wave. A schematic diagram of one such waveform change is shown below. Figure 18 As shown, the corresponding secondary electron signal clustering diagram on the detector surface is as follows: Figure 17 As shown. Similar to Example 6, the secondary electrons produced in odd-numbered and even-numbered frames will alternately cluster on opposite sides of the detector's central aperture.

[0084] Example 8

[0085] In this embodiment, based on the principle of electromagnetic field superposition, the excitation of the line scan signal waveform with a phase shift of 180° and the excitation of the frame scan signal waveform with a phase shift of 180° are synchronously superimposed on the Wien filter.

[0086] Figure 19 and Figure 20 An embodiment of this combination is given, in which the excitation signal of the Wien filter adopts a composite sine wave, which is synchronously misaligned with the line scan signal and the frame scan signal. This embodiment combines and superimposes Embodiment 3 (but preferably uses a unipolar sine wave) and Embodiment 5 (but preferably uses a unipolar sine wave). The effect is that the secondary electrons excited in 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 requirements of a large field of view.

[0087] In the above embodiments, the excitation signal strength of the Wien filter determines the off-axis deflection 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 embodiments all include a control device that controls each device to operate according to a set program, and the device interacts with each device via signals and controls the operation of each device based on control commands.

[0089] The deflection detection method of this application includes the following steps:

[0090] The control device controls the main electron beam 1001 to be focused on the surface of the sample 1010 after passing through the objective lens 108, thereby exciting the secondary electrons 1002.

[0091] The deflector controller 200 controls the deflector 106 to apply a grating scanning signal, namely the line scanning signal 201 and the 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 signals 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 signals satisfy the direct axis condition or the quasi-direct axis condition for the main electron beam 1001; and form a deflection force in a certain direction for the upward secondary electrons.

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

[0094] The secondary electrons 1002 excited in the scanning area are accelerated in the opposite direction and mapped onto the detector 107 to form off-axis imaging regions A'B'C'D'. The alternating excitation signal of the Wien filter causes the off-axis imaging region to be divided or shifted on the receiving surface of the detector, avoiding the central hole of the detector surface. Therefore, the central part will not present a black hole effect. All signal electrons fall on the detector surface, which satisfies the large field of view imaging detection conditions.

[0095] This application also discloses a scanning electron microscope, see [link to document]. Figure 21 It includes an electronic source 101, a condenser lens 102, an aperture 104, an objective lens 108, and a deflection detection system 567 (105, 106, 107) of each of the above embodiments, as well as an imaging amplifier and a display or storage device (not shown in the figure).

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

[0097] A condenser lens 102 is coaxially positioned below the electron source 101 to collimate the main electron beam 1001; and the current is limited by a coaxial aperture 104 below it to select the desired beam size.

[0098] The deflection detection system 567 includes a Wien filter 105, a deflector 106, and a detector 107, located between the condenser lens 102 and the sample 1010. The deflector 106 enables the main electron beam 1001 to perform grating scanning on the sample surface ABCD region and excite secondary electrons 1002. The Wien filter 105 deflects and maps the reverse-accelerated secondary electrons 1002 onto one side (or both sides, see embodiment) of the central hole on the detector 107, forming an off-axis imaging region A'B'C'D'.

[0099] The imaging amplifier amplifies the signals from the off-axis imaging regions A'B'C'D' and transmits them to a display device for display or stores them in a storage medium for subsequent processing.

[0100] This invention is primarily described using secondary electrons as an example, but it is also applicable to backscattered electrons. It can also be applied to the detection of charged particles that are secondary and / or backscattered, such as electrons, ions, or other signal forms, to obtain specimen images. The term "sample" as used herein includes, but is not limited to, semiconductor wafers, semiconductor components, and other components such as storage disks.

[0101] The directional terms such as "left" and "right" in the above content are only used to indicate a general relative positional relationship, and are not intended to limit the relevant structures in the embodiments of this application.

[0102] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A deflection detection system comprising at least one set of deflectors, at least one Wien filter, and at least one detector; wherein alternating line scan signals and frame scan signals are applied to the deflectors to achieve grating scanning of the main electron beam in a specific area of ​​the sample surface; the Wien filter comprises one set of electric deflectors and one set of magnetic deflectors, meeting the design requirements of the Wien filter, and is excited by alternating voltage and current signals respectively, generating mutually perpendicular deflection electric and magnetic fields on a cross section perpendicular to the optical axis; the alternating voltage and current signals exciting the Wien filter are synchronized and in phase, with adjustable amplitude ratios and polarities, and under a set main electron beam energy condition, the generated deflection electric and magnetic fields satisfy the following requirements: generating mutually opposite electric and magnetic forces on the downward main electron beam, and generating electric and magnetic forces in the same direction on the upward secondary electrons and / or backscattered electrons; characterized in that: The alternating excitation signal of the Wien filter is synchronized with the line scan signal or frame scan signal of the deflector and maintains a fixed phase relationship. The phase relationship satisfies the following conditions: during the scanning phase when the main electron beam approaches the central axis, that is, during the weakening phase of the line scan signal or frame scan signal, the excitation signal of the Wien filter is enhanced; during the scanning phase when the main electron beam moves away from the central axis, that is, during the enhancement phase of the line scan signal or frame scan signal, the excitation signal of the Wien filter is weakened.

2. The deflection detection system according to claim 1, characterized in that, The relative intensity of the alternating voltage excitation signal and current excitation signal of the Wien filter is maintained at a set ratio during the imaging scanning phase, so that the net deflection force exerted on the main electron beam passing along the central axis is zero or close to zero; the absolute intensity of the amplitude of the voltage excitation signal and the current excitation signal can be adjusted in linkage to adjust the off-axis deflection force or distance on the passing secondary electrons and / or backscattered electrons. The excitation signal of the Wien filter is associated with the line scan signal or frame scan signal of the deflector. The associated signal satisfies the following: the frequency of the excitation signal applied by the Wien filter maintains a preset multiple relationship with the frequency of the line scan signal or frame scan 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 raster scan signal waveform, and the peak value of the excitation signal waveform corresponds to the minimum amplitude value of the raster scan signal waveform.

3. The deflection detection system according to claim 2, characterized in that, The frequency of the excitation signal is an n-fold or 1 / (2n) frequency of the line scan signal or frame scan signal of the grating scan, where n is any integer; within a complete cycle of the excitation signal containing the grating scan signal and the Wien filter, at least at one point in time, the excitation signal and the grating scan signal satisfy the requirements of the associated signal.

4. The deflection detection system according to claim 3, characterized in that, The frequency of the excitation signal is in the same frequency or half frequency relationship with the frequency of the row scan signal or frame scan signal of the grating scan; the phase of the excitation signal is offset from the phase of the row scan signal or frame scan signal of the grating scan by ±180°; in each signal period, both the grating scan signal and the excitation signal 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 a superposition of two signals, which are associated with the line scan signal and the frame scan signal, respectively.

6. The deflection detection system according to claim 1, characterized in that: 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 or a combination of at least two waveforms of sawtooth wave, triangular wave, and sine wave.

7. The deflection detection system according to claim 1, characterized in that: The excitation signal is a unipolar alternating signal or 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 communicatively connected to the control device, which controls the main electron beam to scan the preset surface area of ​​the sample to be imaged in a grating pattern, while controlling the excited reverse-accelerated secondary electrons and / or backscattered 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 avoid the central hole of the detector surface, but do not go beyond the boundary of the detector. The control method includes: The deflector is controlled to output line scan signals and frame scan signals with set waveforms and frequencies, which apply 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 the peak value when the main electron beam is at the center of the scanning field of view, and 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 desired landing area of ​​the signal electrons, thereby changing the off-axis deflection distance of the secondary electrons and / or backscattered electrons.

10. A scanning electron microscope, characterized in that: The system includes an electron source, a condenser lens, an aperture, an objective lens, a deflection detection system as described in any one of claims 1 to 7, a sample stage, and an imaging amplifier and a display device; the electron source generates electrons and accelerates them to form a main electron beam; the condenser lens collimates the main electron beam and limits the current through a coaxial aperture below to obtain the desired beam current; The objective lens, positioned between the aperture and the sample, focuses the passing main electron beam onto the sample surface to excite secondary electrons and / or backscattered electrons. The sample, located on the sample stage, can be subjected to a negative voltage, which decelerates the main electron beam while accelerating the secondary electrons and / or backscattered electrons. The Wien filter of the deflection detection system, by applying an appropriate alternating excitation signal, has almost no effect on the downward-moving main electron beam, while dynamically deflecting the upward-moving secondary electrons and / or backscattered electrons off-axis, ensuring that the secondary electrons and / or backscattered electrons in the scanning area are concentrated within the effective region of the off-axis detector. The imaging amplifier amplifies the signal captured by the detector and transmits it to a display device or digitizes it for storage, obtaining an image of the sample morphology.

Images