CN110579340A - Method for judging magnification of transmission electron microscope and method for calibrating magnification of transmission electron microscope - Google Patents
Method for judging magnification of transmission electron microscope and method for calibrating magnification of transmission electron microscope Download PDFInfo
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- CN110579340A CN110579340A CN201910875100.1A CN201910875100A CN110579340A CN 110579340 A CN110579340 A CN 110579340A CN 201910875100 A CN201910875100 A CN 201910875100A CN 110579340 A CN110579340 A CN 110579340A
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Abstract
The invention relates to a method for judging the magnification of a transmission electron microscope, which comprises the following steps: providing a monocrystalline silicon sample; calibrating a first magnification of the transmission electron microscope, wherein the first magnification is larger than the resolution ratio of the monocrystalline silicon lattice; forming a plurality of small holes on the monocrystalline silicon sample, and measuring the hole spacing of at least two of the small holes under the first magnification, and recording the hole spacing as a first hole spacing; measuring the hole spacing of at least two of the plurality of small holes in each magnification under a plurality of magnifications smaller than the first magnification, and recording as a second hole spacing; calculating first accuracy of magnification corresponding to the second hole spacing according to the first hole spacing and the second hole spacing; and comparing the first accuracy with a first threshold, and judging that the magnification corresponding to the first accuracy meets the requirement when the first accuracy is smaller than the first threshold.
Description
Technical Field
The invention mainly relates to the field of semiconductor testing, in particular to a method for judging the magnification of a transmission electron microscope and a method for calibrating the magnification of the transmission electron microscope.
background
A Transmission Electron Microscope (TEM) is an instrument widely used for testing semiconductor structures, and is referred to as "Transmission Electron Microscope". In the using process of the transmission electron microscope, the nominal magnification of the transmission electron microscope can generate certain deviation under the influence of sample quality, accelerating voltage and current stability. Therefore, the magnification of the transmission electron microscope needs to be regularly evaluated and calibrated.
The magnification of a transmission electron microscope is usually calibrated by a standard method, that is, under high magnification, the graphene layer interplanar spacing (0.344nm), the (111) interplanar spacing of Pt nanoparticles or the (111) plane of single crystal Si are used for calibration; under medium and low multiplying power (less than 20 ten thousand times), the carbon film grating is used as a standard sample, and the line spacing of the grating is used as a scale to calibrate different multiplying power. The calibration result of this method depends on the dimensional error of the standard sample (the difference between the designed value and the actual value of the grating line spacing), and the magnification error of the TEM can be controlled within +/-5% (the difference between the measured value and the reference value is divided by the reference value).
Disclosure of Invention
The invention aims to provide a method for judging and calibrating the magnification of a transmission electron microscope.
the invention provides a method for judging the magnification of a transmission electron microscope, which is used for solving the technical problem and comprises the following steps: providing a monocrystalline silicon sample; calibrating a first magnification of the transmission electron microscope, wherein the first magnification is larger than the resolution ratio of the monocrystalline silicon lattice; forming a plurality of small holes on the monocrystalline silicon sample, and measuring the hole spacing of at least two of the small holes under the first magnification, and recording the hole spacing as a first hole spacing; measuring the hole spacing of at least two of the plurality of small holes in each magnification under a plurality of magnifications smaller than the first magnification, and recording as a second hole spacing; calculating first accuracy of magnification corresponding to the second hole spacing according to the first hole spacing and the second hole spacing; and comparing the first accuracy with a first threshold, and judging that the magnification corresponding to the first accuracy meets the requirement when the first accuracy is smaller than the first threshold.
In an embodiment of the invention, the step of calibrating the first magnification of the transmission electron microscope includes: collecting a transmission electron microscope image of the monocrystalline silicon sample at the first magnification; carrying out Fourier transform on the transmission electron microscope image to obtain a corresponding diffraction pattern; measuring the surface spacing of the monocrystalline silicon reference surface in the diffraction pattern, and recording as a surface spacing measured value; calculating second accuracy of the first magnification according to the measured value of the surface distance of the monocrystalline silicon reference surface and the theoretical value of the surface distance; comparing the second accuracy to a second threshold, calibrating the first magnification when the second accuracy is greater than the second threshold.
In an embodiment of the invention, the plurality of magnifications smaller than the first magnification include a first magnification range and a second magnification range, the second hole pitch is selected in the first magnification range, and the fourth hole pitch is selected in the second magnification range, wherein the first magnification range is larger than the second magnification range, and the second hole pitch is smaller than the fourth hole pitch.
in one embodiment of the invention, a focused electron beam is used to form a plurality of apertures in the single crystal silicon sample.
In an embodiment of the present invention, the small holes are circular holes, and a distance between centers of the circular holes is recorded as a first hole pitch.
In an embodiment of the present invention, two small holes are formed on the single crystal silicon sample, and the hole distance between the two small holes is measured under the first magnification and is recorded as a first hole distance.
in an embodiment of the present invention, at least three small holes are formed in the single crystal silicon sample, the hole pitch between every two small holes is measured at the first magnification, and the average value of the calculated hole pitches is recorded as a first hole pitch.
In an embodiment of the present invention, a formula for calculating the first accuracy of the magnification corresponding to the second hole pitch is as follows: (%) becoming equal to d/d0-1, where α represents a first accuracy, d0Denotes a first hole pitch and d denotes a second hole pitch.
The invention also provides a method for calibrating the magnification of a transmission electron microscope to solve the technical problem, which comprises the following steps: providing a monocrystalline silicon sample; calibrating a first magnification of the transmission electron microscope, wherein the first magnification is larger than the resolution ratio of the monocrystalline silicon lattice; forming a plurality of small holes on the monocrystalline silicon sample, and measuring the hole spacing of at least two of the small holes under the first magnification, and recording the hole spacing as a first hole spacing; measuring the hole spacing of at least two of the plurality of small holes in each magnification under a plurality of magnifications smaller than the first magnification, and recording as a second hole spacing; calculating first accuracy of magnification corresponding to the second hole spacing according to the first hole spacing and the second hole spacing; the first accuracy is compared to a first threshold and the magnification is calibrated when the first accuracy is greater than the first threshold.
In an embodiment of the present invention, the step of calibrating the magnification when the first accuracy is greater than the first threshold value includes: and adjusting the size of the pixel point with the magnification.
compared with the prior art, the invention forms a plurality of small holes on the monocrystalline silicon sample, measures the hole spacing between the small holes under the calibrated high multiplying power, and compares the hole spacing with the hole spacing between the same small holes measured under the medium and low multiplying power by taking the hole spacing as a reference value, thereby judging and calibrating the precision of the medium and low multiplying power and ensuring that the error of each multiplying power is less than 1 percent. According to the judging and calibrating method, the magnification of the transmission electron microscope can be quickly and accurately calibrated without purchasing a standard sample; under the medium-low multiplying power, the distance between the Si/SiGe alloy boundaries is measured by measuring the hole spacing instead of a standard method, so that the precision of the measurement result is greatly improved, and the calibration result is more reliable.
Drawings
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below, wherein:
FIG. 1A is a TEM image of a carbon film grating standard;
FIG. 1B is a TEM image of a multi-layer Si/SiGe alloy layer standard;
FIG. 2 is a flowchart illustrating a method for evaluating a magnification of a transmission electron microscope according to an embodiment of the invention;
FIG. 3A is a transmission electron microscope image of a single crystal silicon lattice;
FIG. 3B is a diffraction pattern obtained by Fourier transform of FIG. 3A;
FIG. 3C is a schematic diagram of measuring the (111) interplanar spacing of single crystal silicon on the [01-1] ribbon axis;
FIG. 4 is a schematic view of a single crystal silicon sample with a plurality of small holes formed therein according to a method for evaluating transmission electron microscope magnification according to an embodiment of the present invention;
FIG. 5 is an enlarged schematic view of a pinhole formed in a single-crystal silicon sample in a method for evaluating transmission electron microscope magnification according to an embodiment of the present invention;
Fig. 6 is an exemplary flowchart of a method for calibrating transmission electron microscope magnification according to an embodiment of the present invention.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described herein, and thus the present invention is not limited to the specific embodiments disclosed below.
As used in this application and the appended claims, the terms "a," "an," "the," and/or "the" are not intended to be inclusive in the singular, but rather are intended to be inclusive in the plural unless the context clearly dictates otherwise. In general, the terms "comprises" and "comprising" merely indicate that steps and elements are included which are explicitly identified, that the steps and elements do not form an exclusive list, and that a method or apparatus may include other steps or elements.
In describing the embodiments of the present invention in detail, the cross-sectional views illustrating the structure of the device are not enlarged partially in a general scale for convenience of illustration, and the schematic drawings are only examples, which should not limit the scope of the present invention. In addition, the three-dimensional dimensions of length, width and depth should be included in the actual fabrication.
for convenience in description, spatial relational terms such as "below," "beneath," "below," "under," "over," "upper," and the like may be used herein to describe one element or feature's relationship to another element or feature as illustrated in the figures. It will be understood that these terms of spatial relationship are intended to encompass other orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary words "below" and "beneath" can encompass both an orientation of up and down. The device may have other orientations (rotated 90 degrees or at other orientations) and the spatial relationship descriptors used herein should be interpreted accordingly. Further, it will also be understood that when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present.
In the context of this application, a structure described as having a first feature "on" a second feature may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features are formed in between the first and second features, such that the first and second features may not be in direct contact.
Flow charts are used herein to illustrate the operations performed by methods according to embodiments of the present invention. It should be understood that the preceding operations are not necessarily performed in the exact order in which they are performed. Rather, various steps may be processed in reverse order or simultaneously. Meanwhile, other operations are added to or removed from these processes.
Figure 1A is a TEM image of a carbon film grating standard. Referring to fig. 1A, a carbon film grating sample has a plurality of grating lines, and the distance a between adjacent grating lines is used as a scale to calibrate different magnifications of a transmission electron microscope. However, the actual value of the grating line pitch may be different from the design value, resulting in some error in the calibrated magnification.
FIG. 1B is a TEM image of a multi-layer Si/SiGe alloy layer standard. The Si/SiGe alloy layer standard sample is a standard sample commonly used for magnification calibration of a transmission electron microscope at present. The staggered five-layer Si can be grown by adopting Molecular Beam Epitaxy (MBE) technology0.81Ge0.19Alloy layer and four Si single crystal layers, and the thickness of these single crystal silicon layers is determined according to the number of atomic layers contained therein. Referring to FIG. 1B, a first region 120 of the sample 110 is enlarged, and it can be seen that the enlarged first region 120 includes five layers of Si0.81Ge0.19An alloy layer 121 and four Si single crystal layers 122. A second region 130 of the first region 120 is enlarged, and the enlarged second region 130 is seen to include three layers of Si0.81Ge0.19an alloy layer 121 and two Si single crystal layers 122. As can be seen from the enlarged view of the second region 130, at high magnification, Si0.81Ge0.19The interface between the alloy layer 121 and the Si single crystal layer 122 is not clear, it is difficult to determine the position of the boundary when actually measuring the layer thickness, which leads to inaccurate thickness measurement, and measurement errors due to limitations of image resolution at low magnification. In addition, the influence of defocusing on the interface position cannot be ignored, so that the magnification error of the TEM can be only controlled within +/-4% by using the Si/SiGe alloy layer standard sample for calibration.
According to fig. 1A and 1B, the TEM's requirement for accurate measurement (less than ± 1% magnification error) cannot be met by calibrating the transmission electron microscope's magnification using the standard method based on the above.
currently, high-magnification calibration is mainly performed using the (111) plane of single crystal Si, and Si is used0.81Ge0.19And calibrating the thicknesses of the alloy layer and the Si single crystal layer at a medium and low multiplying power. Typical TEM's have a magnification range of 2000-. In the embodiment of the present invention, the magnification that can distinguish the single crystal silicon unit cell is defined as the single crystal silicon cell resolution, and the magnification that is smaller than the single crystal silicon cell resolution is referred to as the medium-low magnification,The magnification greater than the resolution of the single crystal silicon lattice is called high magnification.
In a preferred embodiment of the present invention, the single crystal silicon has a lattice resolution of 190000 times. Accordingly, the medium and low magnification ranges from 2000-190000 times, and the high magnification ranges from 190000-1050000 times.
fig. 2 is an exemplary flowchart of a method for evaluating a transmission electron microscope magnification according to an embodiment of the present invention. Referring to fig. 2, the evaluation method includes the steps of:
Step 210, a monocrystalline silicon sample is provided.
In this step, a single crystal silicon sample with a thickness of about 60-80nm may be prepared using Focused Ion Beam (FIB) technology.
And step 220, calibrating a first magnification of the transmission electron microscope, wherein the first magnification is larger than the lattice resolution of the monocrystalline silicon.
In some embodiments, the first magnification may range from 190000-. Therefore, the first magnification belongs to the high magnification range of the transmission electron microscope.
In these embodiments, the step of calibrating the first magnification of the transmission electron microscope may include the steps of:
Step 221, acquiring a transmission electron microscope image of the monocrystalline silicon sample at the first magnification.
First, the magnification of the transmission electron microscope is set to a first magnification M1. The monocrystalline silicon sample provided in step 210 is placed in the irradiation field of a transmission electron microscope, and the monocrystalline silicon sample is imaged under the first magnification M1, and the obtained transmission electron microscope image is shown in fig. 3A. Fig. 3A shows a part of a transmission electron micrograph of a single-crystal silicon sample, in which white bright spots arranged in a matrix are crystal lattices 301 in the single-crystal silicon sample. Since the first magnification M1 is larger than the resolution of the single crystal silicon lattice, the crystal lattice 301 in the single crystal silicon sample can be clearly resolved in the transmission electron microscope image.
step 222, performing fourier transform on the transmission electron microscope image to obtain a corresponding diffraction pattern.
In this step, fourier transform is performed on the transmission electron microscope image obtained in step 221, and a corresponding diffraction pattern can be obtained, as shown in fig. 3B. In FIG. 3B, the Fourier transformed diffraction pattern may include a plurality of facets, such as (11-1), (1-11), and (200).
And step 223, measuring the interplanar spacing of the monocrystalline silicon reference surface in the diffraction pattern, and recording as an interplanar spacing measured value.
In this step, the interplanar pitch b of the (111) plane of the single crystal silicon in the diffraction pattern is accurately measured and is referred to as an interplanar pitch measured value b, as shown in fig. 3C.
And 224, calculating a second accuracy of the first magnification according to the measured value of the surface distance of the monocrystalline silicon reference surface and the theoretical value of the surface distance.
Single crystal silicon in [01-1]]Standard face spacing b of (111) faces on tape spool00.3136nm, the standard interplanar spacing b0As a theoretical value of the interplanar spacing. The measured value b of the interplanar spacing and the theoretical value b of the interplanar spacing obtained in step 223 are calculated according to the following equations0The second accuracy β to obtain the first magnification M1 is calculated:
β(％)＝b/b0-1
The second accuracy β obtained is a percentage.
step 225, compare the second accuracy to a second threshold and calibrate the first magnification when the second accuracy is greater than the second threshold.
In some embodiments, the second threshold is set to 1%. When the second accuracy β is greater than the second threshold value by 1%, indicating that the first magnification M1 does not meet the requirement, the true value of the first magnification M1 needs to be adjusted according to the calculated second accuracy β, that is, the magnification is calibrated; otherwise, no adjustment is needed.
the high magnification of the transmission electron microscope includes a certain range. The first magnification M1 for calibrating the transmission electron microscope may be a plurality of first magnifications of the transmission electron microscope within a high magnification range, and the transmission electron microscope image of the single-crystal silicon sample is acquired at the plurality of first magnifications and analyzed. The plurality of first magnifications may be selected sequentially from large to small within a range of 190000-.
In the calibration step, for the same first magnification M1, an average of the measured values of the inter-plane distance of a plurality of times (for example, 10 times) can be taken as the measured value b of the inter-plane distance of the first magnification M1, and used to calculate the second accuracy β corresponding to the first magnification M1.
The present invention does not specifically limit the step size of the first magnification from large to small. It is understood that the smaller the adjustment step size is, the larger the number of high-resolution TEM photographs of the single-crystal silicon sample taken within the range of the first magnification is; the larger the adjustment step size is, the smaller the number of high-resolution TEM photographs of the single-crystal silicon sample taken or within the range of the first magnification is.
In other embodiments, the first magnification may be adjusted from small to large.
In the present invention, the adjustment of the first magnification may be of an equal step size or of an unequal step size.
And 230, forming a plurality of small holes on the monocrystalline silicon sample, and measuring the hole spacing of at least two of the small holes under a first magnification, and recording as a first hole spacing.
The step 220 and the corresponding step 221-225 calibrate the first magnification, i.e. the high magnification, of the transmission electron microscope. The secondary step 230-260 mainly involves evaluating the medium and low magnification of the transmission electron microscope, i.e. the second magnification M2 which is smaller than the first magnification M1.
the medium and low magnification of the transmission electron microscope is usually 190000 times, and the crystal lattice image of the monocrystalline silicon cannot be obtained at the medium and low magnification, so that the medium and low magnification cannot be calibrated by using the crystal lattice, and only the characteristic pattern with larger size can be calibrated. One embodiment of a plurality of small holes, i.e., larger sized characteristic patterns, formed in step 230.
Fig. 4 is a schematic view of a single crystal silicon sample on which a plurality of small holes are formed in a transmission electron microscope magnification evaluation method according to an embodiment of the present invention. Referring to fig. 4, in this step, a plurality of small holes, for example, small holes 401, 402, 403, 404 are formed in a single-crystal silicon sample 400. The present invention does not limit the shape of the single crystal silicon sample 400, and does not limit the shape and number of the small holes. Fig. 4 may represent a portion of a single crystal silicon sample 400. The plurality of small holes may be of the same shape or of different shapes. Such as circular, square, triangular, etc.
In this step, the hole pitch d of at least two of the plurality of holes is measured at a first magnification M1 and is denoted as a first hole pitch0。
In some embodiments, as shown in fig. 4, the plurality of small holes are circular holes, and the distance between the centers of the circular holes is recorded as the first hole pitch d0. When the plurality of small holes are of other shapes, the skilled person can define himself the way in which the hole spacing is determined.
Fig. 5 is an enlarged schematic view of the small holes formed in the single-crystal silicon sample in the method for evaluating the magnification of a transmission electron microscope according to an embodiment of the present invention. Referring to fig. 5, it can be seen that the small hole 501 formed in the single crystal silicon sample 500 is enlarged, and the small hole 501 has a circular shape and a diameter of about 3 nm.
The present invention does not limit the method of forming the small hole in the single-crystal silicon sample. In some embodiments, a focused electron beam may be used to form the plurality of apertures.
in the embodiment shown in fig. 5, the monocrystalline silicon sample 500 has a thickness of about 80nm and can be prepared using FIB techniques. Irradiation of the single crystal silicon sample 500 with a high energy focused electron beam (200keV, gun lens 3 in STEM mode) produced a plurality of circular holes of about 3nm in diameter. The spacing and orientation of the circular holes can be freely designed according to the multiplying power visual field range of the transmission electron microscope which needs to be judged and/or calibrated.
In some embodiments, two apertures are formed in a single crystal silicon sample, and the aperture spacing of the two apertures is measured at a first magnification M1 and is noted as a first aperture spacing d0。
In other embodiments, as shown in FIG. 4, a single crystal silicon sample is formed withAt least three small holes, measuring the hole spacing between every two small holes under the first magnification M1, and calculating the average value of the hole spacing to be recorded as the first hole spacing d0。
In this step, the first hole pitch d measured at the first magnification M10Can be used as a reference value for comparing with the hole spacing measured at medium and low multiplying power.
In some embodiments, the first hole spacing d is measured at 190000 times the first magnification M10As a reference value, the second accuracy beta corresponding to the reference value is less than +/-0.3%, and the requirement on the multiplying power accuracy can be met.
and 240, measuring the hole distance of at least two small holes in the plurality of small holes in each magnification under a plurality of magnifications smaller than the first magnification, and recording as a second hole distance.
let second magnification M2< first magnification M1. In this step, the magnification of the transmission electron microscope is adjusted from the first magnification M1 to a value smaller than the first magnification. In some embodiments, the magnification may be gradually decreased in a high-to-low order, i.e., adjusted to a higher magnification of the plurality of second magnifications M2. In the process of adjusting the magnification, an adjustment mode with equal step length or an adjustment mode with unequal step length can be adopted.
In this step, the hole pitch of two of the plurality of small holes is measured at a plurality of second magnifications M2 and is denoted as a second hole pitch d.
In some embodiments, the hole spacing of at least two of the plurality of holes is measured at a second plurality of magnifications M2, denoted as second hole spacing d.
In other embodiments, the hole spacing between each two of the apertures is measured at a plurality of second magnifications M2, and the average of the hole spacings is calculated and recorded as the second hole spacing d.
And 250, calculating first accuracy of the magnification corresponding to the second hole interval according to the first hole interval and the second hole interval.
In some embodiments, the first accuracy α may be calculated according to the following formula:
∝(％)＝d/d0-1
Wherein α represents a first accuracy, d0Denotes a first hole pitch and d denotes a second hole pitch.
Step 260, comparing the first accuracy with a first threshold, and judging that the magnification corresponding to the first accuracy meets the requirement when the first accuracy is smaller than the first threshold.
In some embodiments, the first threshold is set to 1%. Thus, in this step, when the first accuracy α is less than the first threshold value 1%, according to the evaluation method of the present invention, it can be evaluated that the second magnification M2 meets the requirement.
In some embodiments, the magnification of the transmission electron microscope may be adjusted according to the evaluation result of the step 260. If the result of the evaluation is that a certain second magnification M2 is not satisfactory, the true value of the second magnification M2 may be adjusted according to the calculated first accuracy α, otherwise no adjustment is required.
It is considered that when the magnification is low, the center of the pinhole is not well recognized due to the large pixel size of the transmission electron microscope image, thereby affecting the accuracy of measurement. In this case, the pattern of the more distant holes may be redesigned several times apart, and the steps 230-260 may be repeated. Specifically, when the current magnification is lower, the small holes may be designed to have a longer distance therebetween in step 230, and then step 240 and step 260 may be performed. Thus, errors due to the deviation of the center positions of the pinholes can be reduced.
In some embodiments, the plurality of magnifications less than the first magnification M1 may include a first magnification range R1 and a second magnification range R2. In these embodiments, in step 240, a second hole spacing d may be selected within the first range of magnifications R12and a fourth hole spacing d is selected in a second magnification range R24. Wherein the first magnification range R1 is larger than the second magnification range R2, and the second hole spacing d2Is less than fourth hole spacing d4。
In these embodiments, the method is equivalent to transmission electron microscopyThe medium and low magnification range of (2) is refined. For the part with lower magnification, namely the second magnification M2 in the second magnification range R2, the fourth hole pitch d between the small holes formed on the monocrystalline silicon4the second hole pitch d is larger than that in the first magnification range R12And the second magnification M2 in the middle and low magnification range is judged in a segmented manner, so that the judgment result is more accurate.
Tables I to III show the results of measurement and evaluation at different magnifications according to the method for evaluating the magnification of the transmission electron microscope of the invention. Wherein table one shows the measurement and evaluation results when the magnification is within the range of the first magnification M1. In table i, the left-most column represents the magnification set by the transmission electron microscope, and the magnifications decrease from top to bottom. The first magnification M1 in table one is 1050k times at the maximum and 190k times at the minimum. According to step 220 and the related step 221-225, the measured value b of the interplanar spacing of the reference plane of the monocrystalline silicon can be measured and obtained under different magnifications within the high magnification range. The "mean value of the inter-planar distances" in the second column from left to right in table one means the average value of the measured values b of the inter-planar distances obtained after ten measurements. The "standard deviation of area spacing (nm)" in the third column from left to right in table one is the standard deviation of area spacing calculated from the ten measurements at that magnification, in nanometers (nm). "3 σ (nm)" and "3 σ (%)" in table one are 3 σ values and corresponding percentage values, respectively, corresponding to the ten measurements, characterizing the accuracy of the measurement results, with smaller values being more accurate. The mean value of the interplanar spacing under each magnification and the standard interplanar spacing b0A second accuracy, β, was obtained as the rightmost column in table one, for comparison at 0.3136 nm. As can be seen from table one, in the high magnification range, the second accuracy obtained under a plurality of different magnifications is less than 1% of the second threshold, and the evaluation result shows that these magnifications satisfy the requirements.
Watch 1
| Magnification factor | Mean value of interplanar spacing | standard deviation of interplanar spacing (nm) | 3σ(nm) | 3σ(％) | Second degree of accuracy |
| 1050k | 0.3116 | 0.0002 | 0.0006 | 0.19％ | -0.64％ |
| 820k | 0.3114 | 0.0002 | 0.0006 | 0.19％ | -0.69％ |
| 650k | 0.3129 | 0.0000 | 0 | 0.00％ | -0.22％ |
| 630k | 0.3129 | 0.0000 | 0 | 0.00％ | -0.22％ |
| 500k | 0.3107 | 0.0000 | 0 | 0.00％ | -0.92％ |
| 390k | 0.3124 | 0.0000 | 0 | 0.00％ | -0.38％ |
| 310k | 0.3139 | 0.0004 | 0.0012 | 0.38％ | 0.10％ |
| 245k | 0.3126 | 0.0001 | 0.0003 | 0.10％ | -0.33％ |
| 190k | 0.3129 | 0 0000 | 0 | 0.00％ | -0.02％ |
Table two shows the measurement and evaluation results when the magnification is within the first magnification range R1 that is smaller than the first magnification M1. As shown in Table two, in this first magnification range R1, the magnification of the transmission electron microscope was gradually reduced from 190k to 94k, and a second hole pitch d on the single-crystal silicon sample was measured corresponding to each magnification2. The "average hole spacing" in the second column from left to right in Table two refers to the second hole spacing d obtained after ten measurements2Average value of (a). The "Standard deviation of hole spacing (nm)" in the third column from left to right in Table two is the second hole spacing d calculated from the ten measurements at the rod magnification2Standard deviation in nanometers (nm). "3 σ (nm)" and "3 σ (%)" in table two are 3 σ values and corresponding percentage values, respectively, corresponding to the ten measurements, and characterize the accuracy of the measurement results, with smaller values indicating higher accuracy. The first row under the table in the second table represents the value measured at 190k magnification. The average hole pitch is used as the reference hole pitch, i.e. the first hole pitch d0Second hole spacing d measured at other magnifications less than 190k2a distance d from the first hole0a comparison is made. The comparison method may be according to the following formula:
∝(％)＝d2/d0-1
Where α represents the first accuracy. As can be seen from table two, in the first magnification range R1 in the middle and low magnification range, the absolute values of the first accuracy α obtained at a plurality of different magnifications are all less than the first threshold value of 1%, and the evaluation result indicates that these magnifications satisfy the requirements.
Watch two
| magnification factor | Mean value of pore spacing | standard deviation of hole spacing (nm) | 3σ(nm) | 3σ(％) | First degree of accuracy |
| 190k | 336.54 | 0.2162 | 0.65 | 0.19％ | 0.00％ |
| 150k | 335.50 | 0.2216 | 0.66 | 0.20％ | -0.31％ |
| 120k | 334.97 | 0.1138 | 0.34 | 0.10％ | -0.47％ |
| 94k | 337.35 | 0.4444 | 1.33 | 0.40％ | 0.24％ |
Table three shows the measurement and evaluation results when the magnification is within the second magnification range R2 smaller than the first magnification M1. As shown in Table three, in this second magnification range R2, the magnification of the transmission electron microscope was gradually reduced from 94k to 8.6k, and the fourth hole pitch d on the single-crystal silicon sample was measured corresponding to each magnification4. The "average hole spacing" in the second column from left to right in Table III refers to the fourth hole spacing d obtained after ten measurements4Average value of (a). "Standard deviation of hole spacing (nm)" in the third column from left to right in Table III is a fourth hole spacing d calculated from ten measurements at rod magnification4standard deviation in nanometers (nm). "3 σ (nm)" and "3 σ (%)" in table three are 3 σ values and corresponding percentage values corresponding to the ten measurements, respectively, and characterize the accuracy of the measurement results, with smaller values indicating higher accuracy. The first row under the head in table three is the value measured at 94k magnification. The average hole pitch is taken as the reference hole pitch, i.e. the third hole pitch d3Fourth hole spacing d measured at other magnifications less than 94k4a distance d from the third hole3A comparison is made. The comparison method may be according to the following formula:
∝(％)＝d4/d3-1
Where α represents the first accuracy. As can be seen from table two, in the second magnification range R2 in the middle and low magnification range, the absolute values of the first accuracy α obtained at a plurality of different magnifications are all less than 1% of the first threshold, and the evaluation result shows that these magnifications satisfy the requirements.
Watch III
The results of ten measurements are exemplarily used to obtain the average value in the above embodiments, and the number of the measurements is not limited in the present application.
It is understood that in some embodiments, the middle and low magnification range smaller than the first magnification M1 may be further subdivided, for example, the middle and low magnification range is divided into a plurality of magnification ranges greater than 2, and different hole pitches are selected in the plurality of magnification ranges respectively.
Fig. 6 is an exemplary flowchart of a method for calibrating transmission electron microscope magnification according to an embodiment of the present invention. Referring to fig. 6, the method for calibrating the magnification of a transmission electron microscope of this embodiment includes the following steps:
Step 610, a monocrystalline silicon sample is provided.
And step 620, calibrating a first magnification of the transmission electron microscope, wherein the first magnification is larger than the lattice resolution of the monocrystalline silicon.
Step 630, forming a plurality of small holes on the monocrystalline silicon sample, and measuring the hole distance between at least two of the plurality of small holes under a first magnification, and recording as a first hole distance.
And step 640, measuring the hole distance of at least two of the plurality of small holes in each magnification under a plurality of magnifications smaller than the first magnification, and recording as a second hole distance.
And 650, calculating a first accuracy of the magnification corresponding to the second hole pitch according to the first hole pitch and the second hole pitch.
Steps 610 through 650 are the same as steps 210 through 250 shown in fig. 2. The description of steps 210 to 250 in this specification also applies to steps 610 to 650.
Step 660 compares the first accuracy to a first threshold, and calibrates the magnification when the first accuracy is greater than the first threshold.
The method of comparing the first accuracy to the first threshold in step 660 is the same as in step 260. The difference is that after the comparison result is obtained, step 260 evaluates whether the corresponding magnification is satisfactory according to the comparison result, and step 660 calibrates the magnification when the first accuracy is greater than the first threshold.
In some embodiments, the step of calibrating the magnification in step 660 comprises: and adjusting the size of the pixel point with the magnification.
it can be understood that the calibration method according to the present embodiment can also judge whether the magnification meets the requirement.
The results of tables one to three in the foregoing of the present invention are also obtained after the respective magnifications are calibrated by the calibration method of the present embodiment. It can be seen that, after calibration, the precision (3 σ) of the measurement result is less than 0.5% in both the high-magnification range (table one) and the medium-low-magnification range (tables two and three), and the absolute value of the deviation (the first accuracy and the second accuracy) is less than 1%, which meets the requirement of the transmission electron microscope on the magnification precision.
According to the judging and calibrating method, the magnification of the transmission electron microscope can be quickly and accurately calibrated without purchasing a standard sample; under the medium-low multiplying power, the distance between the Si/SiGe alloy boundaries is measured by measuring the hole spacing instead of a standard method, so that the precision of the measurement result is greatly improved, and the calibration result is more reliable.
Although the present invention has been described with reference to the present specific embodiments, it will be appreciated by those skilled in the art that the above embodiments are merely illustrative of the present invention, and various equivalent changes and substitutions may be made without departing from the spirit of the invention, and therefore, it is intended that all changes and modifications to the above embodiments within the spirit and scope of the present invention be covered by the appended claims.
Claims (10)
1. A method for judging the magnification of a transmission electron microscope comprises the following steps:
providing a monocrystalline silicon sample;
Calibrating a first magnification of the transmission electron microscope, wherein the first magnification is larger than the resolution ratio of the monocrystalline silicon lattice;
forming a plurality of small holes on the monocrystalline silicon sample, and measuring the hole spacing of at least two of the small holes under the first magnification, and recording the hole spacing as a first hole spacing;
Measuring the hole spacing of at least two of the plurality of small holes in each magnification under a plurality of magnifications smaller than the first magnification, and recording as a second hole spacing;
Calculating first accuracy of magnification corresponding to the second hole spacing according to the first hole spacing and the second hole spacing;
and comparing the first accuracy with a first threshold, and judging that the magnification corresponding to the first accuracy meets the requirement when the first accuracy is smaller than the first threshold.
2. The evaluation method according to claim 1, wherein the step of calibrating the first magnification of the transmission electron microscope comprises:
Collecting a transmission electron microscope image of the monocrystalline silicon sample at the first magnification;
carrying out Fourier transform on the transmission electron microscope image to obtain a corresponding diffraction pattern;
Measuring the surface spacing of the monocrystalline silicon reference surface in the diffraction pattern, and recording as a surface spacing measured value;
Calculating second accuracy of the first magnification according to the measured value of the surface distance of the monocrystalline silicon reference surface and the theoretical value of the surface distance;
Comparing the second accuracy to a second threshold, calibrating the first magnification when the second accuracy is greater than the second threshold.
3. The method of claim 1, wherein the plurality of magnifications less than the first magnification includes a first magnification range and a second magnification range, the second hole pitch being selected within the first magnification range, and a fourth hole pitch being selected within the second magnification range, wherein the first magnification range is greater than the second magnification range, and the second hole pitch is less than the fourth hole pitch.
4. The method of evaluating according to claim 1, wherein a plurality of small holes on the single-crystal silicon sample are formed using a focused electron beam.
5. The method of claim 1, wherein the plurality of small holes are circular holes, and the distance between the centers of the circular holes is recorded as a first hole pitch.
6. the method of evaluating according to claim 1, wherein two small holes are formed on the single-crystal silicon sample, and a hole pitch of the two small holes is measured at the first magnification and is denoted as a first hole pitch.
7. The evaluation method according to claim 1, wherein at least three small holes are formed in the single-crystal silicon sample, the hole pitch between every two small holes is measured at the first magnification, and the average of the hole pitches is calculated and is taken as the first hole pitch.
8. The evaluation method according to claim 1, wherein the formula for calculating the first accuracy of the magnification corresponding to the second hole pitch is:
∝(％)＝d/d0-1
Wherein α represents a first accuracy, d0Denotes a first hole pitch and d denotes a second hole pitch.
9. A method for calibrating the magnification of a transmission electron microscope comprises the following steps:
Providing a monocrystalline silicon sample;
Calibrating a first magnification of the transmission electron microscope, wherein the first magnification is larger than the resolution ratio of the monocrystalline silicon lattice;
forming a plurality of small holes on the monocrystalline silicon sample, and measuring the hole spacing of at least two of the small holes under the first magnification, and recording the hole spacing as a first hole spacing;
Measuring the hole spacing of at least two of the plurality of small holes in each magnification under a plurality of magnifications smaller than the first magnification, and recording as a second hole spacing;
Calculating first accuracy of magnification corresponding to the second hole spacing according to the first hole spacing and the second hole spacing;
The first accuracy is compared to a first threshold and the magnification is calibrated when the first accuracy is greater than the first threshold.
10. The calibration method according to claim 9, wherein the step of calibrating the magnification when the first accuracy is greater than a first threshold comprises: and adjusting the size of the pixel point with the magnification.
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