Scanning electron microscope and wafer surface topography image imaging method

Abstract

The invention discloses a scanning electron microscope and a wafer surface topography imaging method, which are applied to the technical field of integrated circuits. The detector scans the corresponding pixel points in the signal acquisition time periods corresponding to the pixel points on the wafer sample, continuously acquires electronic signals and outputs voltage signals, and the voltage signals output by the detector can be acquired at a certain frequency through the waveform generator. Due to the signal trailing phenomenon of the detector, the deflection signal is sent to the electron beam shielding assembly through the processor in the scheme, so that the electron beam shielding assembly shields the electron beam in the target time period. The target time period is the time period after the preset time length in the signal acquisition time period, so that the electron beam is deflected in the time period, the influence of the signal of the previous pixel point on the current pixel point can be avoided, the accuracy of the acquired signal is ensured, and more real morphological characteristics of the wafer can be obtained.

Description

Technical Field

[0001] The present application belongs to the field of integrated circuit technology, and in particular relates to a scanning electron microscope and a wafer surface topography imaging method. Background Art

[0002] Scanning electron microscopes are used in yield detection in the semiconductor industry. By hitting the surface of the wafer with an electron beam, electronic signals such as secondary electrons (SE) and backscattered electrons (BSE) are generated. In actual applications, the detector will collect the SE and BSE of each pixel on the wafer sample in turn. For each pixel, during its signal collection period, the detector will continuously collect electronic signals and output voltage signals. The waveform generator collects the voltage signal output by the detector at a fixed frequency. The voltage signal can reflect the contrast of each pixel, so imaging can be performed based on the voltage signal to reflect the morphology and electrical defects of the wafer surface.

[0003] However, the detector signal is not instantaneous and has a long tail. Therefore, the voltage signal of the previous pixel will affect the voltage signal of the current pixel, which will cause the signal of each pixel to be inaccurate, and the generated image cannot accurately reflect the surface morphology of the wafer. Summary of the invention

[0004] The embodiments of the present application provide a scanning electron microscope and a wafer surface morphology imaging method, which can accurately reflect the surface morphology of the wafer.

[0005] In one aspect, an embodiment of the present application provides a scanning electron microscope, comprising:

[0006] A waveform generator, used for collecting voltage signals of corresponding pixel points multiple times during a signal collection period corresponding to each pixel point on the wafer sample; the voltage signal is determined based on the collected electronic signal, and the electronic signal is obtained by the electron beam of the scanning electron microscope hitting the wafer sample;

[0007] An electron beam shielding component, used for shielding the electron beam hitting the wafer sample within a target time period when a shielding signal is received; the target time period is a time period after a preset time length in the signal acquisition time period;

[0008] a processor, connected to the electron beam shielding assembly, and configured to send the shielding signal to the electron beam shielding assembly;

[0009] The processor is also connected to the waveform generator for acquiring the voltage signal collected by the waveform generator and generating a grayscale image of the wafer sample based on the voltage signal.

[0010] In another aspect, the electron beam shielding assembly includes an electron beam deflection assembly;

[0011] The electron beam deflection component is used to deviate the electron beam from the wafer sample within the target time period.

[0012] On the other hand, the electron beam shielding assembly further includes: a baffle disposed in the lens barrel of the scanning electron microscope;

[0013] The baffle is used to shield the electron beam after being deflected by the electron beam deflection component.

[0014] On the other hand, the detector of the scanning electron microscope is arranged closer to the wafer sample stage of the scanning electron microscope than the electron beam shielding component.

[0015] On the other hand, the present application also provides a wafer surface topography imaging method, which is applied to the above-mentioned scanning electron microscope, and the method comprises:

[0016] The waveform generator collects voltage signals of corresponding pixel points multiple times during the signal collection period corresponding to each pixel point on the wafer sample; the voltage signal is determined based on the collected electronic signal, and the electronic signal is generated by the electron beam of the scanning electron microscope hitting the wafer sample;

[0017] sending a shielding signal to the electron beam shielding assembly via a processor;

[0018] In response to the shielding signal, the electron beam hitting the wafer sample is shielded within a target time period by the electron beam shielding component; the target time period is a time period after a preset time length in the signal acquisition time period;

[0019] The voltage signal collected by the waveform generator is acquired by the processor, and a grayscale image of the wafer sample is generated based on the voltage signal.

[0020] On the other hand, before collecting voltage signals of corresponding pixel points multiple times during the signal collection period corresponding to each pixel point on the wafer sample by the waveform generator, the method further includes:

[0021] Acquire multiple test voltage signals corresponding to each pixel point through the waveform generator;

[0022] The target time period is determined by the processor based on the test voltage signal.

[0023] On the other hand, determining the target time period based on the test voltage signal by the processor includes:

[0024] generating a corresponding waveform image based on the test voltage signal by the processor;

[0025] The target time period is determined by the processor based on the waveform image.

[0026] On the other hand, determining the target time period based on the test voltage signal by the processor includes:

[0027] generating, by the processor, a grayscale image of the test sample based on the test voltage signal;

[0028] The target time period is determined by the processor based on image parameters of the grayscale image.

[0029] On the other hand, before collecting voltage signals of corresponding pixel points multiple times during the signal collection period corresponding to each pixel point on the wafer sample by the waveform generator, the method further includes:

[0030] Acquiring the signal acquisition frequency of the waveform generator by the processor;

[0031] The signal acquisition period is determined by the processor based on the signal acquisition frequency.

[0032] On the other hand, after determining the duration of the signal acquisition period based on the signal acquisition frequency, the method further includes:

[0033] The target time period is determined by the processor based on the signal acquisition frequency and the signal acquisition time period.

[0034] A scanning electron microscope provided in an embodiment of the present application has a detector that scans the corresponding pixel points on the wafer sample during the signal collection period corresponding to each pixel point, and continuously collects electronic signals and outputs voltage signals, and the voltage signal output by the detector can be collected at a certain frequency by a waveform generator. Since the signal of the detector is not instantaneous and there is a tailing phenomenon, the signal of the previous pixel point will affect the signal of the next pixel point; therefore, this solution sends a deflection signal to the electron beam shielding component through the processor, so that the electron beam shielding component shields the electron beam during the target period. Since the target period is the period after the preset duration in the signal collection period, the electron beam is deflected during this period, which can avoid the signal of the previous pixel point from affecting the current pixel point, thereby ensuring the accuracy of the collected signal, and thus being able to obtain more realistic morphological features of the wafer. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solution of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0036] Figure 1 It is a schematic diagram of the working principle of a scanning electron microscope in a traditional scheme;

[0037] Figure 2 A schematic diagram of a waveform generated by a waveform generator in a traditional solution;

[0038] Figure 3 Schematic diagram of the normalized response signal of the detector in the traditional scheme;

[0039] Figure 4 This is a schematic diagram of the response voltage of the detector in the traditional scheme when it continuously detects for 20ns;

[0040] Figure 5 Schematic diagram of the input voltage of the detector under continuous signal in the traditional scheme;

[0041] Figure 6 It is a schematic diagram of the surface contrast ratio for four given pixels in the traditional scheme;

[0042] Figure 7 This is a schematic diagram of the voltage signal output by the detector when the signal acquisition period of each pixel point is 5ns in the traditional solution;

[0043] Figure 8 This is a schematic diagram of the voltage signal output by the detector when the signal acquisition period of each pixel point is 40ns in the traditional solution;

[0044] Fig. 9 This is a schematic diagram of the voltage signal output by the detector when the signal acquisition period of each pixel point is 80ns in the traditional solution;

[0045] Fig.10 A schematic diagram of the structure of a scanning electron microscope provided by an embodiment of the present application is shown;

[0046] Fig.11 A schematic diagram showing the operation of an electrode plate provided by an embodiment of the present application is shown;

[0047] Fig.12 A schematic diagram showing the installation position of a baffle provided in one embodiment of the present application is shown;

[0048] Fig.13 A schematic diagram of a detector response signal with a signal acquisition period of 40ns is provided for an embodiment of the present application;

[0049] Fig.14A schematic diagram of the output signal of a detector with a signal acquisition period of 40ns is provided for an embodiment of the present application;

[0050] Fig.15 A schematic diagram of a detector response signal with a signal acquisition period of 20ns is provided for an embodiment of the present application;

[0051] Fig.16 A schematic flow chart of a wafer surface topography imaging method provided in one embodiment of the present application is shown. DETAILED DESCRIPTION

[0052] The features and exemplary embodiments of various aspects of the present application will be described in detail below. In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, rather than to limit the present application. For those skilled in the art, the present application can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present application by illustrating the examples of the present application.

[0053] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "include..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0054] The processing of semiconductor wafers is very complicated, involving multiple procedures, and it is necessary to constantly monitor the electrical properties, dimensions, and defects of the wafers. The commonly used method is to obtain images of the surface of the wafer sample through a scanning electron microscope, and then analyze the surface characteristics of the wafer sample.

[0055] When a scanning electron microscope is imaging the wafer surface morphology, electrons of a certain energy are sequentially hit on each pixel on the wafer surface, thereby generating SE and BSE, etc. The detector of the scanning electron microscope collects the SE and BSE of each pixel, and the contrast of each pixel can be calculated to generate a grayscale image, thereby reflecting the morphology and electrical defects of the wafer surface.

[0056] During the imaging process, the scanning electron microscope uses a waveform generator to control the deflector to scan, and then uses the detector to collect signals. Since the pulse period of the detector is long, the signal output of the signal collected by the previous pixel will affect the signal of the current pixel, which in turn affects the contrast of the wafer surface morphology, resulting in the inability to truly restore the surface features of the wafer sample. The specific reasons are analyzed as follows:

[0057] When a scanning electron microscope is imaging, a scanning signal is generated by a waveform generator, then amplified by an amplifier, and finally the voltage signal is added to the deflector in the electron microscope barrel to form an electron beam to bombard the surface of the wafer sample.

[0058] Under the action of the electric field or magnetic field of the deflector, the electron beam scans a rectangle (corresponding to a pixel) on the wafer surface. Each pixel will generate SE and BSE. The wafer sample includes multiple pixels. The waveform generator controls the deflector to move between the pixels and scans each pixel in turn.

[0059] Figure 1 Figure 1 is a schematic diagram of the working principle of a scanning electron microscope in a traditional scheme. Figure 1 As shown, the figure includes an electron beam 101, a wafer sample 102, electrons 103, a deflector 104, a detector 105, a preamplifier 106, a main amplifier 107, and a waveform generator 108. The electron beam 101 bombards the surface of the wafer sample 102 under the action of the deflector 104, generating electrons 103, namely SE and BSE. Subsequently, these electrons 103 are collected by the detector 105 under the action of the electromagnetic field. After the detector 105 collects the electronic signal, it outputs a corresponding voltage signal. The voltage signal output by the detector 105 is amplified by the preamplifier 106 and the main amplifier 107, and then the voltage signal is collected by the waveform generator 108. The waveform generator collects the voltage signal at a fixed frequency. For each pixel, multiple voltage signals are usually collected, and finally these voltage signals are processed by software to form a grayscale image.

[0060] Figure 2 Figure 1 is a schematic diagram of the waveform generated by the waveform generator in the traditional solution. Figure 2 As shown, the waveform generated by the waveform generator is sawtooth-shaped. Currently, a DC source is used in scanning electron microscopes. Under the action of the waveform generator, the electron beam 101 will generate a continuous signal output when it moves between two pixel points. Since the signal of the detector 105 is not instantaneous, there is a long tail.

[0061] Figure 3 Schematic diagram of the normalized response signal of the detector in the conventional solution. The response time of the detector 105 to receive the signal is related to its own pulse period, such as Figure 3As shown, the pulse period of the currently commonly used PN junction detector 105 is about 40ns. Taking this as an example, assuming that the signal acquisition frequency of the waveform generator is 200MHz, the corresponding signal acquisition time interval is 5ns. However, the response time of the detector 105 to receive the signal is as long as 40ns, so during the scanning period, the signal collected by the detection should be the superposition of all signals.

[0062] Figure 4 This is a schematic diagram of the response voltage of the detector in the traditional scheme when it continuously detects for 20ns. Figure 4 As shown, taking a duration of 20 ns as an example, within the 20 ns period, the voltage signal is continuously detected by the detector 105 and a response voltage is generated. Figure 5 This is a schematic diagram of the detector input voltage under a continuous signal in the traditional scheme. Figure 5 As shown, the voltage signal output by the detector 105 is the sum of all signals within the time period. The longer the duration, the greater the voltage output.

[0063] Figure 6 FIG. 1 is a schematic diagram of the surface contrast ratio for four given pixel points in a conventional solution. For the wafer sample 102, its surface morphology is represented by a contrast signal, such as Figure 6 As shown, in order from left to right, the actual surface contrast ratio of the four pixels is 1:1:2:1.

[0064] The detector 105 is used to scan the above four pixels in sequence and output corresponding voltage signals. Figure 7 Schematic diagram of the voltage signal output by the detector 105 when the signal acquisition period of each pixel point is 5ns in the traditional solution. Figure 7 As shown, the waveform generator collects the voltage signal output by the detector 105. Assuming that the waveform generator collects signals from the above four pixel points in sequence at the highest frequency (set to 200MHz), that is, collecting voltage signals every 5ns, the signal collection time points of the four pixel points are 5ns, 10ns, 15ns, and 20ns respectively. The corresponding values ​​are 1.47, 6.17, 10.54, and 14.68 respectively (the unit of voltage data in this application is mV).

[0065] Normalized with the second pixel as the standard, the contrast ratio of the four pixels is: 0.238:1:1.708:2.379. This is not the same as the actual ratio, and cannot truly display the morphology of the wafer sample 102. This is because the response time of the detector 105 is relatively long, so that the following pixels are affected by the previous pixels. Considering the small amount of data collected, usually, in order to ensure the accuracy of the results, the duration of the signal acquisition period of each pixel can be increased to 40ns, that is, multiple voltage signals will be collected for each pixel, and their average value is calculated to characterize the contrast of the pixel.

[0066] Figure 8 Schematic diagram of the voltage signal output by the detector when the signal acquisition period of each pixel point is 40ns in the traditional solution. Figure 8 As shown in the figure, assuming that the waveform generator still collects signals at the highest frequency (set to 200MHz), for each pixel, 8 voltage signals (5ns, 10ns, 15ns...35ns, 40ns) will be collected, and then the average value of each voltage signal will be calculated. The contrast values ​​of the four pixels are 8.45, 10.24, 18.68, and 12.03 respectively. Normalized in the same way as above, the ratio of the four pixels is 0.825:1:1.824:1.175.

[0067] Although increasing the number of voltage signals at each pixel can roughly reflect the fluctuations of the surface morphology of the wafer sample 102, it still cannot accurately reflect the proportional relationship of the morphology. In addition, due to the increase in the time interval between each pixel, the acquisition time of each picture will also be lengthened. Taking a 1K*1K picture as an example, the acquisition time corresponding to a 5ns time interval is about 5.24ms. After the time interval increases, the acquisition time of a photo increases to 42.94ms. The duration has increased by 7 times.

[0068] Fig. 9 Schematic diagram of the voltage signal output by the detector when the signal acquisition period of each pixel point is 80ns in the traditional solution. Fig. 9 As shown in the figure, when the time interval increases to 80ns, the contrast values ​​corresponding to the four pixels are: 9.34, 10.237, 19.58, 11.13, and the ratio is 0.912:1:1.913:1.087. Compared with 40ns, it is closer to the real pixel ratio, but the acquisition time will increase to 85.88ms. It can be seen that in this way, reflecting more realistic morphological features comes at the cost of time.

[0069] In summary, since the detector signal is not instantaneous and has a long tail, if the signal collected by the detector is directly used for imaging, the accuracy of the final image will be poor. Although increasing the signal collection period of each pixel point can improve the accuracy of the voltage value to a certain extent, this method not only has little effect, but also increases the collection time, which will seriously affect the detection efficiency in the semiconductor field.

[0070] After analyzing the working principle of the detector, the present application found that when it collects signals from each pixel point in turn, the signal of the current pixel point is mainly affected by the second half of the signal of the previous pixel point. Therefore, in order to avoid mutual influence between the signals of each pixel point, the present application designs a solution to eliminate the influencing part of the signal of each pixel point. Specifically, this solution proposes to shield the electron beam 101 of the scanning electron microscope in the second half of the signal collection period of each pixel point, so that it cannot bombard the wafer sample 102 during this period of time, thereby eliminating the influence on the signal of the next pixel point, and finally improving the accuracy of the imaging result.

[0071] Based on this, the embodiment of the present application provides a scanning electron microscope and a wafer surface topography imaging method. The scanning electron microscope provided by the embodiment of the present application is first introduced below. Fig.10 A schematic structural diagram of a scanning electron microscope provided in one embodiment of the present application is shown.

[0072] like Fig.10 As shown, the scanning electron microscope 110 includes:

[0073] The waveform generator 108 is used to collect voltage signals for each pixel point on the wafer sample 102 for multiple times during the signal collection period corresponding to each pixel point; the voltage signal is determined based on the collected electronic signal, and the electronic signal is obtained by the electron beam 101 of the scanning electron microscope 110 hitting the wafer sample 102;

[0074] The electron beam shielding component 109 is used to shield the electron beam 101 hitting the wafer sample 102 within a target period when a shielding signal is received; the target period is a period after a preset time length in the signal acquisition period;

[0075] The processor 111 is connected to the electron beam shielding component 109 and is used to send a shielding signal to the electron beam shielding component 109;

[0076] The processor 111 is also connected to the waveform generator 108 for acquiring the voltage signal collected by the waveform generator 108 and generating a grayscale image of the wafer sample 102 based on the voltage signal.

[0077] The detector 105 of the scanning electron microscope 110 sequentially collects the SE and BSE of each pixel on the wafer sample 102. For each pixel, during its signal collection period, the detector 105 continuously collects electronic signals and outputs voltage signals. The waveform generator 108 collects the voltage signal output by the detector 105 at a fixed frequency.

[0078] The waveform generator 108 is connected to the detector 105. In order to collect more signals and achieve a higher signal-to-noise ratio, the detector 105 usually scans each pixel for a longer time. The waveform generator 108 collects voltage signals from each pixel multiple times in the signal collection period corresponding to each pixel.

[0079] As an optional implementation, assuming that the signal acquisition frequency of the waveform generator 108 is 200 MHz, the signal acquisition period corresponding to each pixel point can be set to an integer multiple of 5 ns. The waveform generator 108 performs multiple voltage signal acquisitions on the pixel point within the signal acquisition period corresponding to each pixel point to obtain multiple voltage signals.

[0080] It can be seen from the above analysis that the signal of the previous pixel mainly affects the signal of the first half of the current pixel. Therefore, in the target time period after the preset time length in the signal acquisition period, the electron beam 101 hitting the wafer sample 102 is shielded. In practical applications, the length of the preset time length and the target time period is not limited and can be divided according to needs. As an optional implementation, the target time period is usually the last time period in the signal acquisition period. In addition, for different pixels, the signal acquisition period length is the same, so the preset time length and target time period of the same length can be used.

[0081] As an optional implementation, when the signal of the previous pixel point has a greater impact on the signal of the current pixel point, a longer target period can be set to shield the electron beam 101 for a longer time, thereby better eliminating the influence between the signals of each pixel point. When the signal of the previous pixel point has a smaller impact on the signal of the current pixel point, a shorter target period can be set to shield the electron beam 101 for a shorter time, thereby acquiring more voltage signals.

[0082] In practical applications, the specific elements used in the electron beam shielding assembly 109 and the position in the lens barrel are not limited. As an optional implementation, an electron beam offset assembly, such as an electrode plate, may be used, and the electron beam offset assembly may be set at a position farther from the sample stage than the detector 105. In other embodiments, the electron beam shielding assembly 109 may also be a combination of an electron beam offset assembly and a baffle, and the baffle is used to shield the electron beam 101 after being offset by the electron beam offset assembly.

[0083] A scanning electron microscope provided in an embodiment of the present application has a detector that scans the corresponding pixel points on the wafer sample during the signal collection period corresponding to each pixel point, and continuously collects electronic signals and outputs voltage signals, and the voltage signal output by the detector can be collected at a certain frequency by a waveform generator. Since the signal of the detector is not instantaneous and there is a tailing phenomenon, the signal of the previous pixel point will affect the signal of the next pixel point; therefore, this solution sends a deflection signal to the electron beam shielding component through the processor, so that the electron beam shielding component shields the electron beam during the target period. Since the target period is the period after the preset duration in the signal collection period, the electron beam is deflected during this period, which can avoid the signal of the previous pixel point from affecting the current pixel point, thereby ensuring the accuracy of the collected signal, and thus being able to obtain more realistic morphological features of the wafer.

[0084] In the above-mentioned embodiment, it is mentioned that the electron beam shielding component 109 may specifically include an electron beam deflection component, such as an electrode plate, through which the electron beam 101 can be deflected away from the wafer sample 102 within a target period of time.

[0085] Fig.11 FIG. 2 shows a schematic diagram of the working state of an electrode plate provided by an embodiment of the present application. Fig.11 As shown, in order to eliminate the tailing effect of the detector 105, the present application sets an electrode plate 112 in the barrel of the scanning electron microscope 110, specifically including a positive electrode plate and a negative electrode plate, and the two are symmetrically arranged based on the axis of the barrel. By releasing a voltage between the positive electrode plate and the negative electrode plate, the electron beam 101 of the scanning electron microscope 110 can be deflected. The electrode plate 112 deflects the electron beam 101 in the barrel so that the electron beam 101 deviates from the wafer sample 102 within the target time period in the signal acquisition period. Among them, the electron beam 101 normally bombards the pixel points of the wafer sample 102 within the preset time period in the front of the signal acquisition period.

[0086] In this implementation, the deflection of the electron beam 101 is achieved through an electron beam offset component. For example, a simple structural element such as an electrode plate 112 can offset the electron beam 101 so that it cannot bombard the wafer sample 102 during the target time period, thereby isolating the electron beam 101 and preventing the signal of the previous pixel from affecting the current pixel.

[0087] The above embodiment mentioned that by offsetting the electron beam 101 in the lens barrel through the electron beam offset component, the electron beam 101 can be deviated from the wafer sample 102 within the target time period. However, only offsetting the electron beam 101 cannot completely isolate the electron beam 101 from the wafer sample 102. If the isolation effect between the electron beam 101 and the wafer sample 102 is not good, the signals of each pixel point will still have a certain mutual influence. Therefore, as an optional embodiment, the electron beam shielding component 109 can also include a baffle, which is arranged in the lens barrel of the scanning electron microscope 110.

[0088] Fig.12 FIG. 1 shows a schematic diagram of the installation position of a baffle provided by an embodiment of the present application. Fig.12 As shown, a baffle 113 is disposed in the lens barrel of the scanning electron microscope 110. The baffle 113 is disposed closer to the wafer sample 102 of the scanning electron microscope 110 than the electron beam offset component (i.e., the electrode plate 112); and is used to shield the electron beam 101 deflected by the electron beam offset component. In the embodiment of the present application, by disposing the baffle 113 in the lens barrel of the scanning electron microscope 110, the isolation between the electron beam 101 and the wafer sample 102 can be better achieved, thereby better eliminating the influence between the signals of each pixel point.

[0089] The above embodiment does not limit the positional relationship between the detector 105 and the electron beam shielding assembly 109, and the two are respectively located at different positions in the lens barrel of the scanning electron microscope 110. Since the detector 105 needs to receive the electron signal returned from the surface of the wafer sample 102, if the electron beam shielding assembly 109 is set between the detector 105 and the sample stage, it may cause the detector 105 to be unable to normally receive the electron signal generated on the surface of the wafer sample 102 when the electron beam 101 bombards the surface of the wafer sample 102. Therefore, as an optional embodiment, the detector 105 is set closer to the wafer sample 102 stage direction than the electron beam shielding assembly 109. For details, please refer to Fig.12 .

[0090] In this implementation, the detector 105 is disposed closer to the wafer sample 102 of the scanning electron microscope 110 than the electron beam shielding assembly 109, so as to prevent the electron beam shielding assembly 109 from affecting the normal scanning electronic signal of the detector 105.

[0091] Here is a specific example to illustrate the solution proposed in this application. Assuming that the signal acquisition period of each pixel point is 40ns, the waveform generator 108 controls the deflector 104 to move between 4 pixel points. If the electron beam 101 is always hitting the surface of the wafer sample 102 during this time, the detector 105 will continuously receive the electronic signal, resulting in the tailing phenomenon.

[0092] In this embodiment, the electron beam shielding component 109 is introduced to deflect the electron beam 101 within the target time period of each signal acquisition period. Assuming that the first pixel point is scanned from 0ns, and the target time period is the last 20ns of the signal acquisition period, the electron beam shielding component 109 will shield the electron beam 101 in the time periods of 20ns to 40ns, 60ns to 80ns, 100ns to 120ns and 140ns to 160ns.

[0093] Fig.13 A schematic diagram of the response signal of the detector when the signal acquisition period is 40ns is provided for the embodiment of the present application. Fig.13 As shown, during the target period in the signal acquisition period, the detector 105 has no response signal. Fig.14 A schematic diagram of the output signal of the detector when the signal acquisition period is 40ns is provided for the embodiment of the present application. Fig.14 It can be seen from the waveform image shown that after the electrode plate 112 deflects the electron beam 101 within the target time period of each signal acquisition period, the output voltage signal of the detector 105 can well reflect the original morphological contrast of the wafer sample 102.

[0094] If the waveform generator 108 collects a voltage signal every 5 ns, 8 data points will be obtained; in practical applications, the corresponding calculation method can be selected according to actual needs to obtain the contrast corresponding to the pixel point based on these data points. As some feasible implementation methods, the 8 data points can be averaged to obtain the contrasts of: 5.11, 5.12, 10.23, 5.13, and the contrast ratio is 0.998:1:1.999:1.001. If the first 4 points are discarded, the contrasts obtained are 1.775, 1.775, 3.55, 1.775, and the contrast ratio obtained is 1:1:2:1; accurate restoration is achieved. If only the maximum value is counted, it will be 9.98, 9.98, 19.96, 9.98, and the contrast ratio is 1:1:2:1. Regardless of the maximum value or the first 4 points are discarded. The original contrast ratio of the sample can be accurately restored. It can be seen that the introduction of the electrode plate 112 is beneficial to the reflection of contrast characteristics.

[0095] This embodiment shortens the length of the signal acquisition period. Assuming that the signal acquisition period of each pixel point is 20ns, the target period is the last 10ns of the signal acquisition period, and the waveform generator 108 still acquires a voltage signal every 5ns. Fig.15 A schematic diagram of the response signal of the detector when the signal acquisition period is 20ns is provided for the embodiment of the present application. Fig.15As shown, in the target period of the signal acquisition period, the detector 105 has no response signal. At this time, each pixel corresponds to 4 data points. The 4 data points are averaged to obtain contrasts of: 4.76, 5.12, 9.88, 5.47, and the contrast ratio is 0.93:1:1.93:1.07. If the first two points are discarded, the contrasts obtained are 2.85, 2.86, 5.72, 2.89, and the contrast ratio is 0.995:1:1.995:1.005. If only the maximum value is counted, it will be 7.59, 7.64, 15.23, 7.68, and the contrast ratio is 0.993:1:1.993:1.005. It can be seen that this scheme can restore the original contrast ratio of the sample more accurately, and the acquisition time is shortened by half compared with the previous one.

[0096] In order to solve the above technical problems, an embodiment of the present application further provides a wafer surface topography imaging method, which is applied to the scanning electron microscope 110 provided in the above embodiment. Fig.16 FIG. 1 is a flow chart of a wafer surface topography imaging method provided by an embodiment of the present application. Fig.16 As shown, the method comprises the following steps:

[0097] S1601: Using a waveform generator, collect voltage signals of corresponding pixel points multiple times during a signal collection period corresponding to each pixel point on a wafer sample.

[0098] The voltage signal is determined based on the collected electronic signal, and the electronic signal is generated by the electron beam 101 of the scanning electron microscope 110 hitting the wafer sample 102. As described above, the electron beam 101 of the scanning electron microscope 110 hits the wafer sample 102 to generate SE and BSE, and the detector 105 will collect the SE and BSE of each pixel on the wafer sample 102 in sequence. For each pixel, during its signal collection period, the detector 105 will continuously collect electronic signals and output voltage signals. The waveform generator 108 will collect the voltage signal output by the detector 105 at a fixed frequency.

[0099] S1602: Send a shielding signal to the electron beam shielding component through the processor.

[0100] S1603: In response to the shielding signal, the electron beam shielding component shields the electron beam hitting the wafer sample within the target time period.

[0101] The target period is the period after the preset time length in the signal acquisition period. The processor 111 is connected to the electron beam shielding assembly 109. In the target period when the electron beam 101 needs to be shielded, a shielding signal can be sent to the electron beam shielding assembly 109 through the processor 111. Then, the electron beam shielding assembly 109 will shield the electron beam 101 of the scanning electron microscope 110 in response to the shielding signal, so as to shield the electron beam 101 hitting the wafer sample 102 during the target period.

[0102] S1604: The processor obtains the voltage signal collected by the waveform generator, and generates a grayscale image of the wafer sample based on the voltage signal.

[0103] Finally, the processor 111 can obtain the contrast corresponding to each pixel based on the collected voltage signal, and further generate a grayscale image based on the obtained pixel contrast.

[0104] The wafer surface morphology imaging method provided in the embodiment of the present application corresponds to the scanning electron microscope provided above, so the two have the same embodiments and beneficial effects, which will not be repeated here.

[0105] In practical applications, if the signal of the previous pixel has a different effect on the signal of the current pixel, the duration of shielding the electron beam 101 also needs to be adjusted accordingly. This is because if the shielding time of the electron beam 101 is insufficient, the signal of the previous pixel will still affect the signal of the current pixel, resulting in inaccurate final results. If the shielding time of the electron beam 101 is too long, the number of voltage signals used for calculation may be too small, which may also result in inaccurate final results. If the duration of the signal acquisition period of each pixel is increased, the overall detection time will be longer.

[0106] Therefore, when the signal of the previous pixel point has a greater impact on the signal of the current pixel point, a longer target period can be set, that is, the shielding time of the electron beam 101 is longer. When the signal of the previous pixel point has a smaller impact on the signal of the current pixel point, a shorter target period can be set, that is, the deflection time of the electron beam 101 is shorter. In practical applications, it is necessary to accurately determine the target period in each signal acquisition period.

[0107] In actual applications, due to production process limitations, when different detectors 105 are scanning, the signal of the previous pixel has different effects on the signal of the current pixel. When the same detector 105 scans different wafer samples, the difference can be ignored. Therefore, before the first use of the scanning electron microscope 110 for detection, the corresponding target time period can be determined in advance, and the set parameters, that is, the fixed target time period, can be directly used in the subsequent detection of different wafer samples.

[0108] As an optional implementation, before collecting the voltage signal, the waveform generator 108 may collect multiple test voltage signals corresponding to each pixel point on the test sample; and then the processor 111 may determine the target time period based on the test voltage signal.

[0109] In this implementation, before the detector 105 is used for scanning for the first time, an accurate target time period is determined through a wafer sample for testing, thereby ensuring the accuracy of imaging by the scanning electron microscope 110 .

[0110] The present application does not limit how to determine the target time period based on the test voltage signal. In actual applications, the user generally judges the degree of signal influence between each pixel point based on experience, and then determines the number of voltage signals that need to be discarded, that is, determines the target time period in each signal acquisition period.

[0111] As a feasible implementation, the processor 111 may generate a corresponding waveform image based on the test voltage signal, and then determine the target time period based on the waveform image.

[0112] Here, a feasible method is provided, which can display a waveform image to the user, and the user can determine the degree of signal influence between each pixel point under the detector 105 based on experience according to the waveform image, and then determine the target time period. In addition, in addition to judging the degree of signal influence between each pixel point based on the user's experience, the processor 111 can also automatically determine the target time period based on the waveform image, avoiding the possibility of erroneous operation or misjudgment caused by artificial division.

[0113] In this implementation, by generating a waveform image of the test voltage signal, the time period in which the impact occurs can be quickly and accurately determined. The user can analyze the waveform image based on experience and quickly and accurately determine the time period in which the impact occurs, and then determine the target time period.

[0114] In practical applications, in addition to analyzing the waveform image of the test voltage signal, the grayscale image generated by the test voltage signal can also be analyzed. As a feasible implementation, the processor 111 can generate a grayscale image of the test sample based on the test voltage signal; then the target time period is determined based on the image parameters of the grayscale image. The image parameters may include image quality, resolution, signal-to-noise ratio, and sharpness, etc. Based on these image parameters, the degree of signal influence between each pixel can be determined, and then the target time period can be accurately determined.

[0115] Similarly, as a feasible implementation, a grayscale image can be displayed to the user, and the user can determine the signal influence degree between each pixel under the detector 105 based on the grayscale image based on experience, and then determine the target time period. In addition, in addition to the user's experience judgment, the processor 111 can also automatically determine the target time period based on the waveform image, avoiding the possible misoperation or misjudgment caused by artificial division.

[0116] In this implementation, a grayscale image of the test sample is generated based on the test voltage signal, and the degree of influence of the previous pixel on the current pixel can be accurately determined according to the image parameters of the grayscale image, thereby accurately determining the target time period.

[0117] In practical applications, the duration of the signal acquisition period for each pixel point needs to be set reasonably. If the duration of the signal acquisition period is too long, the time consumption of the entire detection process will increase; if the duration of the signal acquisition period is too short, it may not be possible to obtain sufficient voltage signals, affecting the accuracy of the final imaging results.

[0118] Therefore, before obtaining the multiple voltage signals of each pixel on the wafer sample 102 collected by the waveform generator 108 through the detector 105, the specific duration of the signal collection period of each pixel can be determined. As a feasible implementation method, the signal collection frequency of the waveform generator 108 can be obtained, and then the duration of the signal collection period can be determined based on the signal collection frequency. For example, assuming that the signal collection frequency of the waveform generator 108 is 200MHz, that is, the voltage signal is collected every 5ns, then the signal collection period can be set to an integer multiple of 5ns, such as 20ns, 40ns or 60ns.

[0119] In practical applications, different numbers of sampled signals can be obtained in the same time period for different signal acquisition frequencies of the detector 105. Therefore, the length of the signal acquisition period can be determined based on the signal acquisition frequency, thereby reducing the acquisition time while ensuring that a sufficient number of signals are collected.

[0120] As an optional implementation, the target time period can be determined based on the signal acquisition frequency and the signal acquisition time period. Because after the duration of the signal acquisition time period is determined based on the signal acquisition frequency, the duration of the detector 105 scanning each pixel point is determined, and the time interval for the waveform generator 108 to collect voltage signals can be known through the signal acquisition frequency. On the premise of determining the degree of influence between each pixel point, based on this information, the target time period can be accurately determined.

[0121] In this implementation, the frequency of signal acquisition of the detector 105 can be used to determine how often the detector 105 acquires a voltage signal, and based on the length of the signal acquisition period, it can be determined how many times the detector 105 acquires a signal within a signal acquisition period. The number of signals corresponding to each pixel can be used to determine how many sampling points need to be shielded, and thus the target period can be accurately determined.

[0122] It should be clear that the present application is not limited to the specific configuration and processing described above and shown in the figures. For the sake of simplicity, a detailed description of the known method is omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present application is not limited to the specific steps described and shown, and those skilled in the art can make various changes, modifications and additions, or change the order between the steps after understanding the spirit of the present application.

[0123] The steps shown in the flow chart above can be realized by hardware, software, firmware or their combination. When implemented in hardware, it can be, for example, electronic circuit, ASIC, suitable firmware, plug-in, function card, etc. When implemented in software, the elements of the present application are programs or code segments used to perform the required tasks. Programs or code segments can be stored in machine-readable media, or transmitted on a transmission medium or communication link by a data signal carried in a carrier wave. "Machine-readable media" can include any medium capable of storing or transmitting information. Examples of machine-readable media include electronic circuits, semiconductor memory devices, ROM, flash memory, erasable ROM (Erasable ROM, EROM), floppy disks, compact disc read-only memory (Compact Disc Read-Only Memory, CD-ROM), optical discs, hard disks, optical fiber media, radio frequency (Radio Frequency, RF) links, etc. Code segments can be downloaded via computer networks such as the Internet, intranets, etc.

[0124] It should also be noted that the exemplary embodiments mentioned in this application describe some methods or systems based on a series of steps or devices. However, this application is not limited to the order of the above steps, that is, the steps can be performed in the order mentioned in the embodiment, or in a different order from the embodiment, or several steps can be performed simultaneously.

[0125] Aspects of the present disclosure are described above with reference to a flow chart and / or block diagram of a scanning electron microscope and a wafer surface topography image imaging method according to an embodiment of the present disclosure. It should be understood that each box in the flow chart and / or block diagram and the combination of each box in the flow chart and / or block diagram can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device to produce a machine so that these instructions executed by the processor of the computer or other programmable data processing device enable the implementation of the function / action specified in one or more boxes of the flow chart and / or block diagram. Such a processor can be, but is not limited to, a general-purpose processor, a special-purpose processor, a special application processor, or a field programmable logic circuit. It can also be understood that each box in the block diagram and / or flow chart and the combination of boxes in the block diagram and / or flow chart can also be implemented by dedicated hardware that performs a specified function or action, or can be implemented by a combination of dedicated hardware and computer instructions.

[0126] The above contents are only specific implementation methods of the present application. Those skilled in the art can clearly understand that for the convenience and simplicity of description, the specific working processes of the systems, modules and units described above can refer to the corresponding processes in the aforementioned method embodiments, and will not be repeated here. It should be understood that the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application.

Claims

1. A scanning electron microscope, characterized in that include: A waveform generator is used to collect voltage signals of corresponding pixel points multiple times during a signal collection period corresponding to each pixel point on the wafer sample; The voltage signal is determined based on a collected electronic signal, where the electronic signal is generated by an electron beam of the scanning electron microscope hitting the wafer sample; An electron beam shielding component, used for shielding the electron beam hitting the wafer sample within a target time period when a shielding signal is received; The target time period is a time period after a preset time length in the signal acquisition time period; a processor, connected to the electron beam shielding assembly, and configured to send the shielding signal to the electron beam shielding assembly; The processor is also connected to the waveform generator for acquiring the voltage signal collected by the waveform generator and generating a grayscale image of the wafer sample based on the voltage signal.

2. The scanning electron microscope according to claim 1, characterized in that The electron beam shielding assembly includes an electron beam deflection assembly; The electron beam deflection component is used to deviate the electron beam from the wafer sample within the target time period.

3. The scanning electron microscope according to claim 2, characterized in that The electron beam shielding assembly further includes: a baffle, disposed in the lens barrel of the scanning electron microscope; The baffle is used to shield the electron beam after being deflected by the electron beam deflection component.

4. The scanning electron microscope according to any one of claims 1 to 3, characterized in that The detector of the scanning electron microscope is arranged closer to the wafer sample stage of the scanning electron microscope than the electron beam shielding component.

5. A wafer surface topography imaging method, characterized in that: Applied to the scanning electron microscope according to any one of claims 1 to 4, the method comprising: The waveform generator collects voltage signals of corresponding pixel points multiple times during the signal collection period corresponding to each pixel point on the wafer sample; the voltage signal is determined based on the collected electronic signal, and the electronic signal is generated by the electron beam of the scanning electron microscope hitting the wafer sample; sending a shielding signal to the electron beam shielding assembly via a processor; In response to the shielding signal, the electron beam hitting the wafer sample is shielded within a target time period by the electron beam shielding component; the target time period is a time period after a preset time length in the signal acquisition time period; The voltage signal collected by the waveform generator is acquired by the processor, and a grayscale image of the wafer sample is generated based on the voltage signal.

6. The wafer surface topography imaging method according to claim 5, characterized in that: Before collecting voltage signals of corresponding pixel points multiple times during a signal collection period corresponding to each pixel point on the wafer sample by a waveform generator, the method further includes: Acquire multiple test voltage signals corresponding to each pixel point through the waveform generator; The target time period is determined by the processor based on the test voltage signal.

7. The wafer surface topography imaging method according to claim 6, characterized in that: Determining the target time period based on the test voltage signal by the processor includes: generating a corresponding waveform image based on the test voltage signal by the processor; The target time period is determined by the processor based on the waveform image.

8. The wafer surface topography imaging method according to claim 6, characterized in that: Determining the target time period based on the test voltage signal by the processor includes: generating, by the processor, a grayscale image of the test sample based on the test voltage signal; The target time period is determined by the processor based on image parameters of the grayscale image.

9. The wafer surface topography imaging method according to any one of claims 5 to 8, characterized in that: Before collecting voltage signals of corresponding pixel points multiple times during a signal collection period corresponding to each pixel point on the wafer sample by a waveform generator, the method further includes: Acquiring the signal acquisition frequency of the waveform generator by the processor; The signal acquisition period is determined by the processor based on the signal acquisition frequency.

10. The wafer surface topography imaging method according to claim 9, characterized in that: After determining the duration of the signal acquisition period based on the signal acquisition frequency, the method further includes: The target time period is determined by the processor based on the signal acquisition frequency and the signal acquisition time period.

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