CN117405624A - Terahertz near-field imaging system measurement method with precision superior to 10 nanometers - Google Patents

Terahertz near-field imaging system measurement method with precision superior to 10 nanometers Download PDF

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CN117405624A
CN117405624A CN202311403878.5A CN202311403878A CN117405624A CN 117405624 A CN117405624 A CN 117405624A CN 202311403878 A CN202311403878 A CN 202311403878A CN 117405624 A CN117405624 A CN 117405624A
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imaging
terahertz
scanning
nanometers
point
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CN117405624B (en
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张文丙
彭承尧
江凤婷
余振春
崔洪波
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Institute of Energy of Hefei Comprehensive National Science Center
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    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3581Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation

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Abstract

The terahertz near field imaging system measuring method with the precision being better than 10 nanometers utilizes terahertz wave penetrating imaging in terahertz near field imaging, terahertz waves can penetrate the inside and feed back to the outside for receiving imaging after point-by-point scanning, the problem that the probe tip imaging limits the imaging precision of the system in terahertz near field imaging is solved, a fixed scanning range is selected according to the principle of terahertz wave point-by-point scanning imaging, the number of scanning points is increased, and the measuring method with the precision being better than 10 nanometers can be obtained. The problem that imaging accuracy depends on probe tip accuracy is solved. The method has the characteristic of simple process, and can be popularized and applied to the 10-nanometer semiconductor process.

Description

Terahertz near-field imaging system measurement method with precision superior to 10 nanometers
Technical Field
A measurement method of a terahertz near-field imaging system with precision superior to 10 nanometers belongs to the field of terahertz near-field imaging, and particularly relates to measurement of the precision of the terahertz near-field imaging system.
Background
The terahertz near-field imaging system is based on an atomic force microscope system, terahertz waves with certain power are coupled on the tip of an atomic force probe and enter the interior of a sample to be detected, and the high-resolution imaging function of the surface and the interior of the sample to be detected is realized simultaneously by utilizing the penetrability of the terahertz waves and the diffractiveness of the tip of the atomic force probe. The imaging accuracy of terahertz near-field imaging systems is generally nano-scale accuracy, in particular tens of nanometers accuracy, often depending on the radius of curvature of the tip of the probe tip, otherwise the imaging pattern may be distorted. For example, the radius of curvature of the probe tip is 40 nanometers, the imaging accuracy is typically 40 nanometers, and as the tip is used, the wearing radius of curvature of the tip becomes 50 nanometers, and the imaging accuracy is 50 nanometers. The fabrication of atomic force microscope probe tips is complicated, and if the radius of curvature of the tip is too small, the tip will wear due to the forces acting between the tip and the sample during use. In theory, the curvature radius of the probe tip can be very small, and the probe tip can be completely realized by breaking through 40 nanometers, but the method has very high requirements on the manufacturing process, the cost and the use condition, and is not beneficial to popularization and use. The curvature radius of the probe tip is 40 nanometers generally, so that the precision of the terahertz near-field imaging system is difficult to break through 40 nanometers.
With the development of technology, for example, the process of a semiconductor chip breaks through to 11 nanometers or even 7 nanometers, a measurement means is needed to achieve the accuracy better than 10 nanometers, a scanning electron microscope is one of the choices, but the scanning electron microscope needs to vacuumize and plate a conductive film when in use, so that the performance of a sample to be measured is affected. The terahertz near-field imaging system can directly image in an atmospheric environment without treatment, does not need special treatment, but needs to optimize a measurement method, improves the measurement precision to be better than 10 nanometers precision, and meets the requirement of semiconductor process development.
Disclosure of Invention
The method aims at solving the problem that imaging precision of the terahertz near-field system depends on the probe tip precision of the atomic force microscope and is difficult to break through the imaging precision of 40 nanometers. According to the terahertz near-field imaging system, the terahertz wave penetrability characteristic is utilized, the number of scanning points is increased in a fixed scanning range according to the principle of terahertz near-field imaging point-by-point scanning imaging, the accuracy of the imaging system is improved, and the terahertz near-field imaging system can be better than 10 nanometers.
The method is characterized in that the method adopts the characteristic of penetrability of terahertz waves in a terahertz near-field imaging system, adopts a mode of maintaining precision and resolution by point-by-point scanning imaging, increases the number of scanning points to improve the precision, adopts terahertz wave imaging in terahertz near-field imaging, and can penetrate a sample to be detected and feed back to be received for imaging after point-by-point scanning, so that the problem that the imaging precision depends on the probe tip precision of an atomic force microscope is solved. According to the principle of terahertz wave point-by-point scanning imaging, a fixed scanning range is selected, the number of scanning points is increased, and a measuring method with the accuracy being better than that of a measuring method with the accuracy of more than 10 nanometers can be obtained.
The invention provides a terahertz near-field imaging system measurement method with the precision being better than 10 nanometers, which comprises the following steps:
selecting a probe with a curvature radius of 40 nanometers;
step two, utilizing a terahertz near-field imaging system to scan and image point by point, and setting scanning parameters;
and thirdly, after point-by-point scanning, the terahertz wave penetrates through the sample to be detected and is fed back to the receiving device for imaging, wherein an imaging image is an internal imaging image.
Further, the terahertz source power of the terahertz system is at least 50 milliwatts or more.
Further, the method for setting the scan parameters in the second step is that the scan range is a nanometers, the number of scan points is n, the value of the number of scan points n can be increased under the condition that the scan range a is fixed, or the value of the scan range a can be reduced under the condition that the number of scan points n is fixed, and a/n is set to be less than 10 nanometers in the internal imaging diagram.
Specifically, the measuring method of the terahertz near-field imaging system with the precision being better than 10 nanometers utilizes the principle of point-by-point scanning imaging of the terahertz near-field imaging system and the characteristic of the penetrability of terahertz waves, and the point-by-point scanning imaging keeps the precision and the resolution of the imaging system. The terahertz wave penetrability of the needle point gets rid of the precision error of the curvature radius of the needle point, the terahertz wave penetrability imaging in terahertz near-field imaging is utilized, the terahertz wave can penetrate the inside and feed back to the outside for receiving imaging after point-by-point scanning, and the problem that the imaging precision of a probe needle point imaging limiting system in terahertz near-field imaging is solved. According to the problem that the imaging precision is limited by the size of the probe tip structure in terahertz wave point-by-point imaging, the number of scanning points is theoretically increased, and the precision of an imaging system can be infinitely improved. In consideration of the point-by-point scanning motor precision, signal transmission time delay and the like, the number of scanning points is properly increased in a certain scanning range, and the imaging precision can be improved from 40 nanometers to 10 nanometers in the current terahertz near-field imaging system.
The invention has the following beneficial effects:
the invention has the advantages of simple process (compared with an electron microscope), low cost (the cost is greatly reduced compared with a 10 nanometer precision probe by utilizing a 40 nanometer precision probe), simple operation and popularization and application to the 10 nanometer semiconductor process.
Drawings
FIG. 1 is a schematic view of a needle tip terahertz wave entering the interior of a sample;
FIG. 2 is a schematic diagram of scan points within a scan range;
fig. 3 is an image precision chart of the measurement method.
Wherein in fig. 1: 1 is a probe, 2 is a sample to be measured, 3 is a direction in which terahertz waves enter, and 4 is a return direction of the terahertz waves after entering the sample.
Detailed Description
The invention will be further described with reference to the drawings and examples.
According to the terahertz near-field imaging system measuring method with the precision being better than 10 nanometers, the terahertz wave penetrating imaging in terahertz near-field imaging can penetrate the inside and feed back to the outside for receiving imaging after point-by-point scanning by utilizing the principle of point-by-point scanning imaging of the terahertz near-field imaging system and the characteristic of terahertz wave penetrability, and the problem that the imaging precision of a probe tip imaging limiting system in terahertz near-field imaging is solved. In a certain scanning range, the number of scanning points is increased, and the precision of the imaging system can be improved. In the current terahertz near-field imaging system, a probe with the diameter of 40 nanometers can be used, so that the imaging precision is improved from 40 nanometers to 10 nanometers.
Terahertz penetrability, terahertz near-field imaging system couple terahertz wave of certain power at the tip of atomic force probe, and when near-field imaging is at the work, as shown in fig. 1, terahertz wave propagates in probe 1 tip below sample 2 direction that awaits measuring, i.e. terahertz wave gets into direction 3, as shown in fig. 1. The terahertz source power in the terahertz near-field imaging system is strong enough and is at least 50 milliwatts, and the terahertz wave energy at the probe is small due to the fact that the power is too small, and the sample to be detected is difficult to penetrate. After the terahertz wave penetrates through the sample to be detected, part of the terahertz wave propagates towards the probe, namely, the terahertz wave returns to the direction 4 after entering the sample, as shown in fig. 1, at the moment, the terahertz wave carries certain sample information to be detected, and the terahertz wave and near-field information carried by the probe are jointly transmitted to an imaging system, so that surface and interior imaging can be simultaneously carried out. The signal of the terahertz wave mainly appears in the internal imaging.
The imaging of the terahertz near-field imaging system is characterized in that the imaging of the terahertz near-field imaging system is realized by utilizing the characteristic of point-by-point scanning, as shown in fig. 2, the scanning range is square, the scanning point number is the total point number of a line of scanning completion, and the scanning point number is the same as the scanning line number. In terahertz near-field imaging, the probe is imaged as a surface image, for example, the number of scanning points is too large, the distance between two adjacent points is smaller than the radius of curvature of the probe, the surface image is distorted, and a real image cannot be obtained. Imaging of terahertz wave penetration is free from the limitation of the structural size of the probe, and the internal image is free from distortion.
The scanning setting, when scanning, setting scanning parameters, such as a nanometer scanning range and n scanning points, can increase the value of the scanning point n when the scanning range a is fixed, or reduce the value of the scanning range a when the scanning point n is fixed. The surface imaging map setting of terahertz near-field imaging is to ensure that a/n is greater than 40 nanometers (radius of curvature of probe). In the internal imaging diagram, a/n is set to be smaller than 10 nanometers, so that the imaging precision in the internal imaging diagram is ensured to be better than 10 nanometers by utilizing the point-by-point scanning and the terahertz penetrability.
Test example as shown in fig. 3, an internal imaging of a silicon-based sample was performed, a/n=1.965, and a section line measurement was taken in the internal imaging graph, where the distance between two marked points with peaks was 3.93 nm, which was already superior to 10 nm accuracy. There are also peaks in the graph that are less than the two marked points apart, with an accuracy better than 3.93 nanometers.
According to the measuring method of the terahertz near-field imaging system with the precision being better than 10 nanometers, the principle of point-by-point scanning imaging of the terahertz near-field imaging system and the characteristic of terahertz wave penetrability are utilized, and the imaging precision being better than 10 nanometers is realized by utilizing a probe with the precision being 40 nanometers in an imaging diagram in near-field imaging by setting scanning parameters. The invention has the advantages of simple process (compared with an electron microscope), low cost (the cost is greatly reduced compared with a 10 nanometer precision probe by utilizing a 40 nanometer precision probe), and simple operation, and can be popularized and applied to the 10 nanometer semiconductor process.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.

Claims (3)

1. The terahertz near field imaging system measurement method with the precision being better than 10 nanometers is characterized by comprising the following steps of:
selecting a probe with a curvature radius of 40 nanometers;
step two, utilizing a terahertz near-field imaging system to scan and image a sample to be detected point by point, and setting scanning parameters;
and thirdly, after point-by-point scanning, the terahertz wave penetrates through the sample to be detected and is fed back to the receiving device for imaging, wherein an imaging image is an internal imaging image.
2. The method of claim 1, wherein the terahertz source power of the terahertz near-field imaging system is at least 50 milliwatts.
3. The method according to claim 1, wherein the scanning parameters are set in the second step by a scanning range of a nanometers and a number of scanning points of n, and the value of the scanning point number n is increased in the case that the scanning range a is fixed, or the value of the scanning range a is decreased in the case that the scanning point number n is fixed, and a/n is set to be less than 10 nanometers in the internal imaging map.
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