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

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

A measurement method for terahertz near-field imaging system with an accuracy better than 10 nanometers

Technical field

A terahertz near-field imaging system measurement method with an accuracy better than 10 nanometers belongs to the field of terahertz near-field system imaging and specifically involves the accuracy measurement of terahertz near-field systems.

Background technique

The terahertz near-field imaging system is based on the atomic force microscope system. A terahertz wave of a certain power is coupled to the tip of the atomic force probe into the interior of the sample to be measured. The penetrating property of the terahertz wave and the diffraction property of the atomic force probe tip are used to treat the The high-resolution imaging function is realized simultaneously on the surface and inside of the measured sample. The imaging accuracy of a terahertz near-field imaging system is generally nanometer-level, specifically tens of nanometers, and often depends on the radius of curvature of the tip of the probe tip, otherwise the imaging pattern will be distorted. For example, if the radius of curvature of the probe tip is 40 nanometers, the imaging accuracy is generally 40 nanometers. As the tip is used, the tip wears and the radius of curvature becomes 50 nanometers, then the imaging accuracy is 50 nanometers. The production of the atomic force microscope probe tip is relatively complicated. If the tip curvature radius is too small, the force acting between the tip and the sample during use will cause tip wear. Theoretically, the radius of curvature of the probe tip can be very small, and a breakthrough of 40 nanometers is completely achievable. However, it places high requirements on the manufacturing process, cost, and usage conditions, which is not conducive to popularization and use. Generally, the radius of curvature of the probe tip is 40 nanometers, making it difficult for the accuracy of the terahertz near-field imaging system to exceed 40 nanometers.

With the development of science and technology, such as the breakthrough of semiconductor chip technology to 11 nanometers or even 7 nanometers, a measurement method is needed to achieve an accuracy better than 10 nanometers. Scanning electron microscope is one of the options, but scanning electron microscope requires extraction when used. Vacuum and conductive film plating affect the performance of the sample to be tested. The terahertz near-field imaging system can directly perform imaging in the atmospheric environment without special processing, but it needs to optimize the measurement method and improve the measurement accuracy to better than 10 nanometers to meet the needs of semiconductor process development.

Contents of the invention

In order to solve the problem that the imaging accuracy of the terahertz near-field system relies on the accuracy of the atomic force microscope probe tip, it is difficult to break through the imaging accuracy of 40 nanometers. This invention utilizes the penetrability characteristics of terahertz waves in the terahertz near-field imaging system, and based on the principle of point-by-point scanning of terahertz near-field imaging, increases the number of scanning points within a fixed scanning range and improves the accuracy of the imaging system. Can be better than 10 nanometers.

The content of the present invention is to utilize the penetrating characteristics of terahertz waves in the terahertz near-field imaging system, adopt a point-by-point scanning imaging method to maintain accuracy and resolution, increase the number of scanning points to improve accuracy, and utilize the terahertz near-field imaging system to maintain accuracy and resolution. Terahertz wave imaging, after point-by-point scanning, the internal terahertz wave can penetrate the sample to be measured and be fed back to the receiver for imaging, eliminating the problem of imaging accuracy that relies on the probe tip accuracy of the atomic force microscope. According to the principle of point-by-point scanning imaging of terahertz waves, by selecting a fixed scanning range and increasing the number of scanning points, a measurement method with an accuracy better than 10 nanometers can be obtained.

The present invention provides a terahertz near-field imaging system measurement method with an accuracy better than 10 nanometers, which includes the following steps:

Step 1: Select a probe with a curvature radius of 40 nanometers;

Step 2: Use the terahertz near-field imaging system to scan point by point and set the scanning parameters;

Step 3: After point-by-point scanning, the terahertz wave penetrates the sample to be tested and is fed back to the receiver for imaging. The imaging picture is the internal imaging picture.

Furthermore, the terahertz source power of the terahertz system is at least 50 milliwatts.

Furthermore, the method of setting the scanning parameters in step 2 is as follows: the scanning range is a nanometer and the number of scanning points is n. When the scanning range a is fixed, the value of the scanning point n can be increased, or when the scanning point number n is fixed , reduce the value of the scanning range a, and set a/n to less than 10 nanometers in the internal imaging map.

Specifically, a measurement method for a terahertz near-field imaging system with an accuracy better than 10 nanometers uses the principle of point-by-point scanning imaging of the terahertz near-field imaging system and the characteristics of the penetrability of terahertz waves. The point-by-point scanning imaging maintains the imaging system accuracy and resolution. The terahertz wave penetrability of the tip gets rid of the precision error caused by the tip curvature radius. The terahertz wave penetration imaging in terahertz near-field imaging is used. After point-by-point scanning, the terahertz wave can penetrate the interior and be fed back to the outside for reception and imaging. The problem of probe tip imaging in terahertz near-field imaging limits the imaging accuracy of the system. According to the point-by-point imaging of terahertz waves, there is no problem that the size of the probe tip structure limits the imaging accuracy. In theory, increasing the number of scanning points can infinitely improve the accuracy of the imaging system. Taking into account the point-by-point scanning motor accuracy, signal transmission time delay, etc., within a certain scanning range, appropriately increasing the number of scanning points can improve the imaging accuracy from 40 nanometers to 10 nanometers in the current terahertz near-field imaging system.

The invention has the following beneficial effects:

The advantages of the patented invention are simple process (compared to electron microscopy), low cost (using a 40-nanometer precision probe, the cost is much lower than a 10-nanometer precision probe), simple operation, and can be applied to 10-nanometer semiconductor processes In process.

Description of the drawings

Figure 1 is a schematic diagram of the needle tip terahertz wave entering the interior of the sample;

Figure 2 is a schematic diagram of scanning points within the scanning range;

Figure 3 is a chart of imaging accuracy using this measurement method.

In Figure 1: 1 is the probe, 2 is the sample to be measured, 3 is the direction in which the terahertz wave enters, and 4 is the return direction of the terahertz wave after entering the sample.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and examples.

A measurement method for a terahertz near-field imaging system with an accuracy better than 10 nanometers. It uses the principle of point-by-point scanning imaging of the terahertz near-field imaging system and the characteristics of the terahertz wave penetration. In terahertz near-field imaging, the terahertz wave penetrates Transparent imaging, after point-by-point scanning, the terahertz wave can penetrate the interior and be fed back to the outside for reception and imaging, getting rid of the problem of probe tip imaging in terahertz near-field imaging that limits the imaging accuracy of the system. Within a certain scanning range, increasing the number of scanning points can improve the accuracy of the imaging system. In current terahertz near-field imaging systems, 40-nanometer probes can be used to increase imaging accuracy from 40 nanometers to 10 nanometers.

Terahertz penetration, the terahertz near-field imaging system couples a certain power of terahertz waves at the tip of the atomic force probe. When working in the near-field imaging, as shown in Figure 1, the terahertz wave waits downward at the tip of probe 1. The measured sample propagates in direction 2, which is the direction 3 where the terahertz wave enters, as shown in Figure 1. The power of the terahertz source in the terahertz near-field imaging system must be strong enough, at least 50 milliwatts. If the power is too small, the energy of the terahertz wave at the probe will be small, making it difficult to penetrate the sample to be measured. After the terahertz wave penetrates the sample to be measured, part of the terahertz wave propagates toward the probe, that is, the terahertz wave returns in the direction 4 after entering the sample, as shown in Figure 1. At this time, the terahertz wave carries a certain amount of radiation to be measured. The measured sample information and the near-field information carried by the probe are jointly transmitted to the imaging system, which can perform surface and internal imaging at the same time. The signal of terahertz wave is mainly manifested in internal imaging.

Point-by-point scanning imaging. The imaging characteristic of the terahertz near-field imaging system is the use of point-by-point scanning characteristics. As shown in Figure 2, the scanning range is square, the number of scanning points is the total number of points when scanning a line, the number of points scanned and the number of scanned lines. same. In terahertz near-field imaging, the imaging of the probe is a surface image. If there are too many scanning points and the distance between two adjacent points is less than the radius of curvature of the probe, the surface image will be distorted and the real image will not be obtained. Since there is no restriction on the size of the probe structure in the imaging of terahertz wave penetration, there is no distortion in the internal image.

Scan setting, when scanning, set the scanning parameters, such as the scanning range is a nanometer and the number of scanning points is n. When the scanning range a is fixed, the value of the scanning point n can be increased, or when the scanning point n is fixed Next, reduce the value of scan range a. The surface imaging map setting for terahertz near-field imaging must ensure that a/n is greater than 40 nanometers (radius of curvature of the probe). In the internal imaging map, set a/n to less than 10 nanometers, so that point-by-point scanning and the penetration of terahertz are used to ensure that the imaging accuracy in the internal imaging map is better than 10 nanometers.

As an example of the test, as shown in Figure 3, internal imaging of a silicon-based sample was performed, a/n = 1.965, and cross-section line measurements were taken in the internal imaging diagram. The distance between the two marked points with sharp peaks was 3.93 nanometers, which is already better than 10nm accuracy. There are also sharp peaks smaller than the distance between the two labeled points in the figure, and their accuracy is better than 3.93 nanometers.

A measurement method for a terahertz near-field imaging system with an accuracy better than 10 nanometers. It uses the principle of point-by-point scanning imaging of the terahertz near-field imaging system and the characteristics of the penetrability of terahertz waves. By setting the scanning parameters, inside the near-field imaging In the imaging picture, a 40-nanometer probe is used to achieve imaging accuracy better than 10 nanometers. The patented invention has the advantages of simple process (compared to an electron microscope), low cost (using a 40-nanometer precision probe, the cost is much lower than a 10-nanometer precision probe), and simple operation, and can be applied to 10-nanometer semiconductor processes. In process.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements, etc., made within the spirit and principles of the present invention, All should be included in the protection scope of the present 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.